1 /*
   2  * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/classLoaderData.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "code/codeCache.hpp"
  30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
  31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
  32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
  33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
  34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
  35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
  36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
  37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
  38 #include "gc_implementation/parNew/parNewGeneration.hpp"
  39 #include "gc_implementation/shared/collectorCounters.hpp"
  40 #include "gc_implementation/shared/isGCActiveMark.hpp"
  41 #include "gc_interface/collectedHeap.inline.hpp"
  42 #include "memory/cardTableRS.hpp"
  43 #include "memory/collectorPolicy.hpp"
  44 #include "memory/gcLocker.inline.hpp"
  45 #include "memory/genCollectedHeap.hpp"
  46 #include "memory/genMarkSweep.hpp"
  47 #include "memory/genOopClosures.inline.hpp"
  48 #include "memory/iterator.hpp"
  49 #include "memory/referencePolicy.hpp"
  50 #include "memory/resourceArea.hpp"
  51 #include "oops/oop.inline.hpp"
  52 #include "prims/jvmtiExport.hpp"
  53 #include "runtime/globals_extension.hpp"
  54 #include "runtime/handles.inline.hpp"
  55 #include "runtime/java.hpp"
  56 #include "runtime/vmThread.hpp"
  57 #include "services/memoryService.hpp"
  58 #include "services/runtimeService.hpp"
  59 
  60 // statics
  61 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
  62 bool          CMSCollector::_full_gc_requested          = false;
  63 
  64 //////////////////////////////////////////////////////////////////
  65 // In support of CMS/VM thread synchronization
  66 //////////////////////////////////////////////////////////////////
  67 // We split use of the CGC_lock into 2 "levels".
  68 // The low-level locking is of the usual CGC_lock monitor. We introduce
  69 // a higher level "token" (hereafter "CMS token") built on top of the
  70 // low level monitor (hereafter "CGC lock").
  71 // The token-passing protocol gives priority to the VM thread. The
  72 // CMS-lock doesn't provide any fairness guarantees, but clients
  73 // should ensure that it is only held for very short, bounded
  74 // durations.
  75 //
  76 // When either of the CMS thread or the VM thread is involved in
  77 // collection operations during which it does not want the other
  78 // thread to interfere, it obtains the CMS token.
  79 //
  80 // If either thread tries to get the token while the other has
  81 // it, that thread waits. However, if the VM thread and CMS thread
  82 // both want the token, then the VM thread gets priority while the
  83 // CMS thread waits. This ensures, for instance, that the "concurrent"
  84 // phases of the CMS thread's work do not block out the VM thread
  85 // for long periods of time as the CMS thread continues to hog
  86 // the token. (See bug 4616232).
  87 //
  88 // The baton-passing functions are, however, controlled by the
  89 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
  90 // and here the low-level CMS lock, not the high level token,
  91 // ensures mutual exclusion.
  92 //
  93 // Two important conditions that we have to satisfy:
  94 // 1. if a thread does a low-level wait on the CMS lock, then it
  95 //    relinquishes the CMS token if it were holding that token
  96 //    when it acquired the low-level CMS lock.
  97 // 2. any low-level notifications on the low-level lock
  98 //    should only be sent when a thread has relinquished the token.
  99 //
 100 // In the absence of either property, we'd have potential deadlock.
 101 //
 102 // We protect each of the CMS (concurrent and sequential) phases
 103 // with the CMS _token_, not the CMS _lock_.
 104 //
 105 // The only code protected by CMS lock is the token acquisition code
 106 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
 107 // baton-passing code.
 108 //
 109 // Unfortunately, i couldn't come up with a good abstraction to factor and
 110 // hide the naked CGC_lock manipulation in the baton-passing code
 111 // further below. That's something we should try to do. Also, the proof
 112 // of correctness of this 2-level locking scheme is far from obvious,
 113 // and potentially quite slippery. We have an uneasy supsicion, for instance,
 114 // that there may be a theoretical possibility of delay/starvation in the
 115 // low-level lock/wait/notify scheme used for the baton-passing because of
 116 // potential intereference with the priority scheme embodied in the
 117 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
 118 // invocation further below and marked with "XXX 20011219YSR".
 119 // Indeed, as we note elsewhere, this may become yet more slippery
 120 // in the presence of multiple CMS and/or multiple VM threads. XXX
 121 
 122 class CMSTokenSync: public StackObj {
 123  private:
 124   bool _is_cms_thread;
 125  public:
 126   CMSTokenSync(bool is_cms_thread):
 127     _is_cms_thread(is_cms_thread) {
 128     assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
 129            "Incorrect argument to constructor");
 130     ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
 131   }
 132 
 133   ~CMSTokenSync() {
 134     assert(_is_cms_thread ?
 135              ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
 136              ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
 137           "Incorrect state");
 138     ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
 139   }
 140 };
 141 
 142 // Convenience class that does a CMSTokenSync, and then acquires
 143 // upto three locks.
 144 class CMSTokenSyncWithLocks: public CMSTokenSync {
 145  private:
 146   // Note: locks are acquired in textual declaration order
 147   // and released in the opposite order
 148   MutexLockerEx _locker1, _locker2, _locker3;
 149  public:
 150   CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
 151                         Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
 152     CMSTokenSync(is_cms_thread),
 153     _locker1(mutex1, Mutex::_no_safepoint_check_flag),
 154     _locker2(mutex2, Mutex::_no_safepoint_check_flag),
 155     _locker3(mutex3, Mutex::_no_safepoint_check_flag)
 156   { }
 157 };
 158 
 159 
 160 // Wrapper class to temporarily disable icms during a foreground cms collection.
 161 class ICMSDisabler: public StackObj {
 162  public:
 163   // The ctor disables icms and wakes up the thread so it notices the change;
 164   // the dtor re-enables icms.  Note that the CMSCollector methods will check
 165   // CMSIncrementalMode.
 166   ICMSDisabler()  { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
 167   ~ICMSDisabler() { CMSCollector::enable_icms(); }
 168 };
 169 
 170 //////////////////////////////////////////////////////////////////
 171 //  Concurrent Mark-Sweep Generation /////////////////////////////
 172 //////////////////////////////////////////////////////////////////
 173 
 174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
 175 
 176 // This struct contains per-thread things necessary to support parallel
 177 // young-gen collection.
 178 class CMSParGCThreadState: public CHeapObj<mtGC> {
 179  public:
 180   CFLS_LAB lab;
 181   PromotionInfo promo;
 182 
 183   // Constructor.
 184   CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
 185     promo.setSpace(cfls);
 186   }
 187 };
 188 
 189 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
 190      ReservedSpace rs, size_t initial_byte_size, int level,
 191      CardTableRS* ct, bool use_adaptive_freelists,
 192      FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
 193   CardGeneration(rs, initial_byte_size, level, ct),
 194   _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
 195   _debug_collection_type(Concurrent_collection_type)
 196 {
 197   HeapWord* bottom = (HeapWord*) _virtual_space.low();
 198   HeapWord* end    = (HeapWord*) _virtual_space.high();
 199 
 200   _direct_allocated_words = 0;
 201   NOT_PRODUCT(
 202     _numObjectsPromoted = 0;
 203     _numWordsPromoted = 0;
 204     _numObjectsAllocated = 0;
 205     _numWordsAllocated = 0;
 206   )
 207 
 208   _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
 209                                            use_adaptive_freelists,
 210                                            dictionaryChoice);
 211   NOT_PRODUCT(debug_cms_space = _cmsSpace;)
 212   if (_cmsSpace == NULL) {
 213     vm_exit_during_initialization(
 214       "CompactibleFreeListSpace allocation failure");
 215   }
 216   _cmsSpace->_gen = this;
 217 
 218   _gc_stats = new CMSGCStats();
 219 
 220   // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
 221   // offsets match. The ability to tell free chunks from objects
 222   // depends on this property.
 223   debug_only(
 224     FreeChunk* junk = NULL;
 225     assert(UseCompressedOops ||
 226            junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
 227            "Offset of FreeChunk::_prev within FreeChunk must match"
 228            "  that of OopDesc::_klass within OopDesc");
 229   )
 230   if (CollectedHeap::use_parallel_gc_threads()) {
 231     typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
 232     _par_gc_thread_states =
 233       NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
 234     if (_par_gc_thread_states == NULL) {
 235       vm_exit_during_initialization("Could not allocate par gc structs");
 236     }
 237     for (uint i = 0; i < ParallelGCThreads; i++) {
 238       _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
 239       if (_par_gc_thread_states[i] == NULL) {
 240         vm_exit_during_initialization("Could not allocate par gc structs");
 241       }
 242     }
 243   } else {
 244     _par_gc_thread_states = NULL;
 245   }
 246   _incremental_collection_failed = false;
 247   // The "dilatation_factor" is the expansion that can occur on
 248   // account of the fact that the minimum object size in the CMS
 249   // generation may be larger than that in, say, a contiguous young
 250   //  generation.
 251   // Ideally, in the calculation below, we'd compute the dilatation
 252   // factor as: MinChunkSize/(promoting_gen's min object size)
 253   // Since we do not have such a general query interface for the
 254   // promoting generation, we'll instead just use the mimimum
 255   // object size (which today is a header's worth of space);
 256   // note that all arithmetic is in units of HeapWords.
 257   assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
 258   assert(_dilatation_factor >= 1.0, "from previous assert");
 259 }
 260 
 261 
 262 // The field "_initiating_occupancy" represents the occupancy percentage
 263 // at which we trigger a new collection cycle.  Unless explicitly specified
 264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
 265 // is calculated by:
 266 //
 267 //   Let "f" be MinHeapFreeRatio in
 268 //
 269 //    _intiating_occupancy = 100-f +
 270 //                           f * (CMSTriggerRatio/100)
 271 //   where CMSTriggerRatio is the argument "tr" below.
 272 //
 273 // That is, if we assume the heap is at its desired maximum occupancy at the
 274 // end of a collection, we let CMSTriggerRatio of the (purported) free
 275 // space be allocated before initiating a new collection cycle.
 276 //
 277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
 278   assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
 279   if (io >= 0) {
 280     _initiating_occupancy = (double)io / 100.0;
 281   } else {
 282     _initiating_occupancy = ((100 - MinHeapFreeRatio) +
 283                              (double)(tr * MinHeapFreeRatio) / 100.0)
 284                             / 100.0;
 285   }
 286 }
 287 
 288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
 289   assert(collector() != NULL, "no collector");
 290   collector()->ref_processor_init();
 291 }
 292 
 293 void CMSCollector::ref_processor_init() {
 294   if (_ref_processor == NULL) {
 295     // Allocate and initialize a reference processor
 296     _ref_processor =
 297       new ReferenceProcessor(_span,                               // span
 298                              (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
 299                              (int) ParallelGCThreads,             // mt processing degree
 300                              _cmsGen->refs_discovery_is_mt(),     // mt discovery
 301                              (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
 302                              _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
 303                              &_is_alive_closure,                  // closure for liveness info
 304                              false);                              // next field updates do not need write barrier
 305     // Initialize the _ref_processor field of CMSGen
 306     _cmsGen->set_ref_processor(_ref_processor);
 307 
 308   }
 309 }
 310 
 311 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
 312   GenCollectedHeap* gch = GenCollectedHeap::heap();
 313   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
 314     "Wrong type of heap");
 315   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
 316     gch->gen_policy()->size_policy();
 317   assert(sp->is_gc_cms_adaptive_size_policy(),
 318     "Wrong type of size policy");
 319   return sp;
 320 }
 321 
 322 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
 323   CMSGCAdaptivePolicyCounters* results =
 324     (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
 325   assert(
 326     results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
 327     "Wrong gc policy counter kind");
 328   return results;
 329 }
 330 
 331 
 332 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
 333 
 334   const char* gen_name = "old";
 335 
 336   // Generation Counters - generation 1, 1 subspace
 337   _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
 338 
 339   _space_counters = new GSpaceCounters(gen_name, 0,
 340                                        _virtual_space.reserved_size(),
 341                                        this, _gen_counters);
 342 }
 343 
 344 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
 345   _cms_gen(cms_gen)
 346 {
 347   assert(alpha <= 100, "bad value");
 348   _saved_alpha = alpha;
 349 
 350   // Initialize the alphas to the bootstrap value of 100.
 351   _gc0_alpha = _cms_alpha = 100;
 352 
 353   _cms_begin_time.update();
 354   _cms_end_time.update();
 355 
 356   _gc0_duration = 0.0;
 357   _gc0_period = 0.0;
 358   _gc0_promoted = 0;
 359 
 360   _cms_duration = 0.0;
 361   _cms_period = 0.0;
 362   _cms_allocated = 0;
 363 
 364   _cms_used_at_gc0_begin = 0;
 365   _cms_used_at_gc0_end = 0;
 366   _allow_duty_cycle_reduction = false;
 367   _valid_bits = 0;
 368   _icms_duty_cycle = CMSIncrementalDutyCycle;
 369 }
 370 
 371 double CMSStats::cms_free_adjustment_factor(size_t free) const {
 372   // TBD: CR 6909490
 373   return 1.0;
 374 }
 375 
 376 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
 377 }
 378 
 379 // If promotion failure handling is on use
 380 // the padded average size of the promotion for each
 381 // young generation collection.
 382 double CMSStats::time_until_cms_gen_full() const {
 383   size_t cms_free = _cms_gen->cmsSpace()->free();
 384   GenCollectedHeap* gch = GenCollectedHeap::heap();
 385   size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
 386                                    (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
 387   if (cms_free > expected_promotion) {
 388     // Start a cms collection if there isn't enough space to promote
 389     // for the next minor collection.  Use the padded average as
 390     // a safety factor.
 391     cms_free -= expected_promotion;
 392 
 393     // Adjust by the safety factor.
 394     double cms_free_dbl = (double)cms_free;
 395     double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
 396     // Apply a further correction factor which tries to adjust
 397     // for recent occurance of concurrent mode failures.
 398     cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
 399     cms_free_dbl = cms_free_dbl * cms_adjustment;
 400 
 401     if (PrintGCDetails && Verbose) {
 402       gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
 403         SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
 404         cms_free, expected_promotion);
 405       gclog_or_tty->print_cr("  cms_free_dbl %f cms_consumption_rate %f",
 406         cms_free_dbl, cms_consumption_rate() + 1.0);
 407     }
 408     // Add 1 in case the consumption rate goes to zero.
 409     return cms_free_dbl / (cms_consumption_rate() + 1.0);
 410   }
 411   return 0.0;
 412 }
 413 
 414 // Compare the duration of the cms collection to the
 415 // time remaining before the cms generation is empty.
 416 // Note that the time from the start of the cms collection
 417 // to the start of the cms sweep (less than the total
 418 // duration of the cms collection) can be used.  This
 419 // has been tried and some applications experienced
 420 // promotion failures early in execution.  This was
 421 // possibly because the averages were not accurate
 422 // enough at the beginning.
 423 double CMSStats::time_until_cms_start() const {
 424   // We add "gc0_period" to the "work" calculation
 425   // below because this query is done (mostly) at the
 426   // end of a scavenge, so we need to conservatively
 427   // account for that much possible delay
 428   // in the query so as to avoid concurrent mode failures
 429   // due to starting the collection just a wee bit too
 430   // late.
 431   double work = cms_duration() + gc0_period();
 432   double deadline = time_until_cms_gen_full();
 433   // If a concurrent mode failure occurred recently, we want to be
 434   // more conservative and halve our expected time_until_cms_gen_full()
 435   if (work > deadline) {
 436     if (Verbose && PrintGCDetails) {
 437       gclog_or_tty->print(
 438         " CMSCollector: collect because of anticipated promotion "
 439         "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
 440         gc0_period(), time_until_cms_gen_full());
 441     }
 442     return 0.0;
 443   }
 444   return work - deadline;
 445 }
 446 
 447 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
 448 // amount of change to prevent wild oscillation.
 449 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
 450                                               unsigned int new_duty_cycle) {
 451   assert(old_duty_cycle <= 100, "bad input value");
 452   assert(new_duty_cycle <= 100, "bad input value");
 453 
 454   // Note:  use subtraction with caution since it may underflow (values are
 455   // unsigned).  Addition is safe since we're in the range 0-100.
 456   unsigned int damped_duty_cycle = new_duty_cycle;
 457   if (new_duty_cycle < old_duty_cycle) {
 458     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
 459     if (new_duty_cycle + largest_delta < old_duty_cycle) {
 460       damped_duty_cycle = old_duty_cycle - largest_delta;
 461     }
 462   } else if (new_duty_cycle > old_duty_cycle) {
 463     const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
 464     if (new_duty_cycle > old_duty_cycle + largest_delta) {
 465       damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
 466     }
 467   }
 468   assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
 469 
 470   if (CMSTraceIncrementalPacing) {
 471     gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
 472                            old_duty_cycle, new_duty_cycle, damped_duty_cycle);
 473   }
 474   return damped_duty_cycle;
 475 }
 476 
 477 unsigned int CMSStats::icms_update_duty_cycle_impl() {
 478   assert(CMSIncrementalPacing && valid(),
 479          "should be handled in icms_update_duty_cycle()");
 480 
 481   double cms_time_so_far = cms_timer().seconds();
 482   double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
 483   double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
 484 
 485   // Avoid division by 0.
 486   double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
 487   double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
 488 
 489   unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
 490   if (new_duty_cycle > _icms_duty_cycle) {
 491     // Avoid very small duty cycles (1 or 2); 0 is allowed.
 492     if (new_duty_cycle > 2) {
 493       _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
 494                                                 new_duty_cycle);
 495     }
 496   } else if (_allow_duty_cycle_reduction) {
 497     // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
 498     new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
 499     // Respect the minimum duty cycle.
 500     unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
 501     _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
 502   }
 503 
 504   if (PrintGCDetails || CMSTraceIncrementalPacing) {
 505     gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
 506   }
 507 
 508   _allow_duty_cycle_reduction = false;
 509   return _icms_duty_cycle;
 510 }
 511 
 512 #ifndef PRODUCT
 513 void CMSStats::print_on(outputStream *st) const {
 514   st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
 515   st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
 516                gc0_duration(), gc0_period(), gc0_promoted());
 517   st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
 518             cms_duration(), cms_duration_per_mb(),
 519             cms_period(), cms_allocated());
 520   st->print(",cms_since_beg=%g,cms_since_end=%g",
 521             cms_time_since_begin(), cms_time_since_end());
 522   st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
 523             _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
 524   if (CMSIncrementalMode) {
 525     st->print(",dc=%d", icms_duty_cycle());
 526   }
 527 
 528   if (valid()) {
 529     st->print(",promo_rate=%g,cms_alloc_rate=%g",
 530               promotion_rate(), cms_allocation_rate());
 531     st->print(",cms_consumption_rate=%g,time_until_full=%g",
 532               cms_consumption_rate(), time_until_cms_gen_full());
 533   }
 534   st->print(" ");
 535 }
 536 #endif // #ifndef PRODUCT
 537 
 538 CMSCollector::CollectorState CMSCollector::_collectorState =
 539                              CMSCollector::Idling;
 540 bool CMSCollector::_foregroundGCIsActive = false;
 541 bool CMSCollector::_foregroundGCShouldWait = false;
 542 
 543 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
 544                            CardTableRS*                   ct,
 545                            ConcurrentMarkSweepPolicy*     cp):
 546   _cmsGen(cmsGen),
 547   _ct(ct),
 548   _ref_processor(NULL),    // will be set later
 549   _conc_workers(NULL),     // may be set later
 550   _abort_preclean(false),
 551   _start_sampling(false),
 552   _between_prologue_and_epilogue(false),
 553   _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
 554   _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
 555                  -1 /* lock-free */, "No_lock" /* dummy */),
 556   _modUnionClosure(&_modUnionTable),
 557   _modUnionClosurePar(&_modUnionTable),
 558   // Adjust my span to cover old (cms) gen
 559   _span(cmsGen->reserved()),
 560   // Construct the is_alive_closure with _span & markBitMap
 561   _is_alive_closure(_span, &_markBitMap),
 562   _restart_addr(NULL),
 563   _overflow_list(NULL),
 564   _stats(cmsGen),
 565   _eden_chunk_array(NULL),     // may be set in ctor body
 566   _eden_chunk_capacity(0),     // -- ditto --
 567   _eden_chunk_index(0),        // -- ditto --
 568   _survivor_plab_array(NULL),  // -- ditto --
 569   _survivor_chunk_array(NULL), // -- ditto --
 570   _survivor_chunk_capacity(0), // -- ditto --
 571   _survivor_chunk_index(0),    // -- ditto --
 572   _ser_pmc_preclean_ovflw(0),
 573   _ser_kac_preclean_ovflw(0),
 574   _ser_pmc_remark_ovflw(0),
 575   _par_pmc_remark_ovflw(0),
 576   _ser_kac_ovflw(0),
 577   _par_kac_ovflw(0),
 578 #ifndef PRODUCT
 579   _num_par_pushes(0),
 580 #endif
 581   _collection_count_start(0),
 582   _verifying(false),
 583   _icms_start_limit(NULL),
 584   _icms_stop_limit(NULL),
 585   _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
 586   _completed_initialization(false),
 587   _collector_policy(cp),
 588   _should_unload_classes(false),
 589   _concurrent_cycles_since_last_unload(0),
 590   _roots_scanning_options(0),
 591   _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
 592   _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
 593 {
 594   if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
 595     ExplicitGCInvokesConcurrent = true;
 596   }
 597   // Now expand the span and allocate the collection support structures
 598   // (MUT, marking bit map etc.) to cover both generations subject to
 599   // collection.
 600 
 601   // For use by dirty card to oop closures.
 602   _cmsGen->cmsSpace()->set_collector(this);
 603 
 604   // Allocate MUT and marking bit map
 605   {
 606     MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
 607     if (!_markBitMap.allocate(_span)) {
 608       warning("Failed to allocate CMS Bit Map");
 609       return;
 610     }
 611     assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
 612   }
 613   {
 614     _modUnionTable.allocate(_span);
 615     assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
 616   }
 617 
 618   if (!_markStack.allocate(MarkStackSize)) {
 619     warning("Failed to allocate CMS Marking Stack");
 620     return;
 621   }
 622 
 623   // Support for multi-threaded concurrent phases
 624   if (CMSConcurrentMTEnabled) {
 625     if (FLAG_IS_DEFAULT(ConcGCThreads)) {
 626       // just for now
 627       FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
 628     }
 629     if (ConcGCThreads > 1) {
 630       _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
 631                                  ConcGCThreads, true);
 632       if (_conc_workers == NULL) {
 633         warning("GC/CMS: _conc_workers allocation failure: "
 634               "forcing -CMSConcurrentMTEnabled");
 635         CMSConcurrentMTEnabled = false;
 636       } else {
 637         _conc_workers->initialize_workers();
 638       }
 639     } else {
 640       CMSConcurrentMTEnabled = false;
 641     }
 642   }
 643   if (!CMSConcurrentMTEnabled) {
 644     ConcGCThreads = 0;
 645   } else {
 646     // Turn off CMSCleanOnEnter optimization temporarily for
 647     // the MT case where it's not fixed yet; see 6178663.
 648     CMSCleanOnEnter = false;
 649   }
 650   assert((_conc_workers != NULL) == (ConcGCThreads > 1),
 651          "Inconsistency");
 652 
 653   // Parallel task queues; these are shared for the
 654   // concurrent and stop-world phases of CMS, but
 655   // are not shared with parallel scavenge (ParNew).
 656   {
 657     uint i;
 658     uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
 659 
 660     if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
 661          || ParallelRefProcEnabled)
 662         && num_queues > 0) {
 663       _task_queues = new OopTaskQueueSet(num_queues);
 664       if (_task_queues == NULL) {
 665         warning("task_queues allocation failure.");
 666         return;
 667       }
 668       _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
 669       if (_hash_seed == NULL) {
 670         warning("_hash_seed array allocation failure");
 671         return;
 672       }
 673 
 674       typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
 675       for (i = 0; i < num_queues; i++) {
 676         PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
 677         if (q == NULL) {
 678           warning("work_queue allocation failure.");
 679           return;
 680         }
 681         _task_queues->register_queue(i, q);
 682       }
 683       for (i = 0; i < num_queues; i++) {
 684         _task_queues->queue(i)->initialize();
 685         _hash_seed[i] = 17;  // copied from ParNew
 686       }
 687     }
 688   }
 689 
 690   _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
 691 
 692   // Clip CMSBootstrapOccupancy between 0 and 100.
 693   _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
 694                          /(double)100;
 695 
 696   _full_gcs_since_conc_gc = 0;
 697 
 698   // Now tell CMS generations the identity of their collector
 699   ConcurrentMarkSweepGeneration::set_collector(this);
 700 
 701   // Create & start a CMS thread for this CMS collector
 702   _cmsThread = ConcurrentMarkSweepThread::start(this);
 703   assert(cmsThread() != NULL, "CMS Thread should have been created");
 704   assert(cmsThread()->collector() == this,
 705          "CMS Thread should refer to this gen");
 706   assert(CGC_lock != NULL, "Where's the CGC_lock?");
 707 
 708   // Support for parallelizing young gen rescan
 709   GenCollectedHeap* gch = GenCollectedHeap::heap();
 710   _young_gen = gch->prev_gen(_cmsGen);
 711   if (gch->supports_inline_contig_alloc()) {
 712     _top_addr = gch->top_addr();
 713     _end_addr = gch->end_addr();
 714     assert(_young_gen != NULL, "no _young_gen");
 715     _eden_chunk_index = 0;
 716     _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
 717     _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
 718     if (_eden_chunk_array == NULL) {
 719       _eden_chunk_capacity = 0;
 720       warning("GC/CMS: _eden_chunk_array allocation failure");
 721     }
 722   }
 723   assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
 724 
 725   // Support for parallelizing survivor space rescan
 726   if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
 727     const size_t max_plab_samples =
 728       ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
 729 
 730     _survivor_plab_array  = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
 731     _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
 732     _cursor               = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
 733     if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
 734         || _cursor == NULL) {
 735       warning("Failed to allocate survivor plab/chunk array");
 736       if (_survivor_plab_array  != NULL) {
 737         FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 738         _survivor_plab_array = NULL;
 739       }
 740       if (_survivor_chunk_array != NULL) {
 741         FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 742         _survivor_chunk_array = NULL;
 743       }
 744       if (_cursor != NULL) {
 745         FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
 746         _cursor = NULL;
 747       }
 748     } else {
 749       _survivor_chunk_capacity = 2*max_plab_samples;
 750       for (uint i = 0; i < ParallelGCThreads; i++) {
 751         HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
 752         if (vec == NULL) {
 753           warning("Failed to allocate survivor plab array");
 754           for (int j = i; j > 0; j--) {
 755             FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
 756           }
 757           FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
 758           FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
 759           _survivor_plab_array = NULL;
 760           _survivor_chunk_array = NULL;
 761           _survivor_chunk_capacity = 0;
 762           break;
 763         } else {
 764           ChunkArray* cur =
 765             ::new (&_survivor_plab_array[i]) ChunkArray(vec,
 766                                                         max_plab_samples);
 767           assert(cur->end() == 0, "Should be 0");
 768           assert(cur->array() == vec, "Should be vec");
 769           assert(cur->capacity() == max_plab_samples, "Error");
 770         }
 771       }
 772     }
 773   }
 774   assert(   (   _survivor_plab_array  != NULL
 775              && _survivor_chunk_array != NULL)
 776          || (   _survivor_chunk_capacity == 0
 777              && _survivor_chunk_index == 0),
 778          "Error");
 779 
 780   // Choose what strong roots should be scanned depending on verification options
 781   if (!CMSClassUnloadingEnabled) {
 782     // If class unloading is disabled we want to include all classes into the root set.
 783     add_root_scanning_option(SharedHeap::SO_AllClasses);
 784   } else {
 785     add_root_scanning_option(SharedHeap::SO_SystemClasses);
 786   }
 787 
 788   NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
 789   _gc_counters = new CollectorCounters("CMS", 1);
 790   _completed_initialization = true;
 791   _inter_sweep_timer.start();  // start of time
 792 #ifdef SPARC
 793   // Issue a stern warning, but allow use for experimentation and debugging.
 794   if (VM_Version::is_sun4v() && UseMemSetInBOT) {
 795     assert(!FLAG_IS_DEFAULT(UseMemSetInBOT), "Error");
 796     warning("Experimental flag -XX:+UseMemSetInBOT is known to cause instability"
 797             " on sun4v; please understand that you are using at your own risk!");
 798   }
 799 #endif
 800 }
 801 
 802 const char* ConcurrentMarkSweepGeneration::name() const {
 803   return "concurrent mark-sweep generation";
 804 }
 805 void ConcurrentMarkSweepGeneration::update_counters() {
 806   if (UsePerfData) {
 807     _space_counters->update_all();
 808     _gen_counters->update_all();
 809   }
 810 }
 811 
 812 // this is an optimized version of update_counters(). it takes the
 813 // used value as a parameter rather than computing it.
 814 //
 815 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
 816   if (UsePerfData) {
 817     _space_counters->update_used(used);
 818     _space_counters->update_capacity();
 819     _gen_counters->update_all();
 820   }
 821 }
 822 
 823 void ConcurrentMarkSweepGeneration::print() const {
 824   Generation::print();
 825   cmsSpace()->print();
 826 }
 827 
 828 #ifndef PRODUCT
 829 void ConcurrentMarkSweepGeneration::print_statistics() {
 830   cmsSpace()->printFLCensus(0);
 831 }
 832 #endif
 833 
 834 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
 835   GenCollectedHeap* gch = GenCollectedHeap::heap();
 836   if (PrintGCDetails) {
 837     if (Verbose) {
 838       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
 839         level(), short_name(), s, used(), capacity());
 840     } else {
 841       gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
 842         level(), short_name(), s, used() / K, capacity() / K);
 843     }
 844   }
 845   if (Verbose) {
 846     gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
 847               gch->used(), gch->capacity());
 848   } else {
 849     gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
 850               gch->used() / K, gch->capacity() / K);
 851   }
 852 }
 853 
 854 size_t
 855 ConcurrentMarkSweepGeneration::contiguous_available() const {
 856   // dld proposes an improvement in precision here. If the committed
 857   // part of the space ends in a free block we should add that to
 858   // uncommitted size in the calculation below. Will make this
 859   // change later, staying with the approximation below for the
 860   // time being. -- ysr.
 861   return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
 862 }
 863 
 864 size_t
 865 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
 866   return _cmsSpace->max_alloc_in_words() * HeapWordSize;
 867 }
 868 
 869 size_t ConcurrentMarkSweepGeneration::max_available() const {
 870   return free() + _virtual_space.uncommitted_size();
 871 }
 872 
 873 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
 874   size_t available = max_available();
 875   size_t av_promo  = (size_t)gc_stats()->avg_promoted()->padded_average();
 876   bool   res = (available >= av_promo) || (available >= max_promotion_in_bytes);
 877   if (Verbose && PrintGCDetails) {
 878     gclog_or_tty->print_cr(
 879       "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
 880       "max_promo("SIZE_FORMAT")",
 881       res? "":" not", available, res? ">=":"<",
 882       av_promo, max_promotion_in_bytes);
 883   }
 884   return res;
 885 }
 886 
 887 // At a promotion failure dump information on block layout in heap
 888 // (cms old generation).
 889 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
 890   if (CMSDumpAtPromotionFailure) {
 891     cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
 892   }
 893 }
 894 
 895 CompactibleSpace*
 896 ConcurrentMarkSweepGeneration::first_compaction_space() const {
 897   return _cmsSpace;
 898 }
 899 
 900 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
 901   // Clear the promotion information.  These pointers can be adjusted
 902   // along with all the other pointers into the heap but
 903   // compaction is expected to be a rare event with
 904   // a heap using cms so don't do it without seeing the need.
 905   if (CollectedHeap::use_parallel_gc_threads()) {
 906     for (uint i = 0; i < ParallelGCThreads; i++) {
 907       _par_gc_thread_states[i]->promo.reset();
 908     }
 909   }
 910 }
 911 
 912 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
 913   blk->do_space(_cmsSpace);
 914 }
 915 
 916 void ConcurrentMarkSweepGeneration::compute_new_size() {
 917   assert_locked_or_safepoint(Heap_lock);
 918 
 919   // If incremental collection failed, we just want to expand
 920   // to the limit.
 921   if (incremental_collection_failed()) {
 922     clear_incremental_collection_failed();
 923     grow_to_reserved();
 924     return;
 925   }
 926 
 927   size_t expand_bytes = 0;
 928   double free_percentage = ((double) free()) / capacity();
 929   double desired_free_percentage = (double) MinHeapFreeRatio / 100;
 930   double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
 931 
 932   // compute expansion delta needed for reaching desired free percentage
 933   if (free_percentage < desired_free_percentage) {
 934     size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 935     assert(desired_capacity >= capacity(), "invalid expansion size");
 936     expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
 937   }
 938   if (expand_bytes > 0) {
 939     if (PrintGCDetails && Verbose) {
 940       size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
 941       gclog_or_tty->print_cr("\nFrom compute_new_size: ");
 942       gclog_or_tty->print_cr("  Free fraction %f", free_percentage);
 943       gclog_or_tty->print_cr("  Desired free fraction %f",
 944         desired_free_percentage);
 945       gclog_or_tty->print_cr("  Maximum free fraction %f",
 946         maximum_free_percentage);
 947       gclog_or_tty->print_cr("  Capactiy "SIZE_FORMAT, capacity()/1000);
 948       gclog_or_tty->print_cr("  Desired capacity "SIZE_FORMAT,
 949         desired_capacity/1000);
 950       int prev_level = level() - 1;
 951       if (prev_level >= 0) {
 952         size_t prev_size = 0;
 953         GenCollectedHeap* gch = GenCollectedHeap::heap();
 954         Generation* prev_gen = gch->_gens[prev_level];
 955         prev_size = prev_gen->capacity();
 956           gclog_or_tty->print_cr("  Younger gen size "SIZE_FORMAT,
 957                                  prev_size/1000);
 958       }
 959       gclog_or_tty->print_cr("  unsafe_max_alloc_nogc "SIZE_FORMAT,
 960         unsafe_max_alloc_nogc()/1000);
 961       gclog_or_tty->print_cr("  contiguous available "SIZE_FORMAT,
 962         contiguous_available()/1000);
 963       gclog_or_tty->print_cr("  Expand by "SIZE_FORMAT" (bytes)",
 964         expand_bytes);
 965     }
 966     // safe if expansion fails
 967     expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
 968     if (PrintGCDetails && Verbose) {
 969       gclog_or_tty->print_cr("  Expanded free fraction %f",
 970         ((double) free()) / capacity());
 971     }
 972   }
 973 }
 974 
 975 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
 976   return cmsSpace()->freelistLock();
 977 }
 978 
 979 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
 980                                                   bool   tlab) {
 981   CMSSynchronousYieldRequest yr;
 982   MutexLockerEx x(freelistLock(),
 983                   Mutex::_no_safepoint_check_flag);
 984   return have_lock_and_allocate(size, tlab);
 985 }
 986 
 987 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
 988                                                   bool   tlab /* ignored */) {
 989   assert_lock_strong(freelistLock());
 990   size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
 991   HeapWord* res = cmsSpace()->allocate(adjustedSize);
 992   // Allocate the object live (grey) if the background collector has
 993   // started marking. This is necessary because the marker may
 994   // have passed this address and consequently this object will
 995   // not otherwise be greyed and would be incorrectly swept up.
 996   // Note that if this object contains references, the writing
 997   // of those references will dirty the card containing this object
 998   // allowing the object to be blackened (and its references scanned)
 999   // either during a preclean phase or at the final checkpoint.
1000   if (res != NULL) {
1001     // We may block here with an uninitialized object with
1002     // its mark-bit or P-bits not yet set. Such objects need
1003     // to be safely navigable by block_start().
1004     assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1005     assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1006     collector()->direct_allocated(res, adjustedSize);
1007     _direct_allocated_words += adjustedSize;
1008     // allocation counters
1009     NOT_PRODUCT(
1010       _numObjectsAllocated++;
1011       _numWordsAllocated += (int)adjustedSize;
1012     )
1013   }
1014   return res;
1015 }
1016 
1017 // In the case of direct allocation by mutators in a generation that
1018 // is being concurrently collected, the object must be allocated
1019 // live (grey) if the background collector has started marking.
1020 // This is necessary because the marker may
1021 // have passed this address and consequently this object will
1022 // not otherwise be greyed and would be incorrectly swept up.
1023 // Note that if this object contains references, the writing
1024 // of those references will dirty the card containing this object
1025 // allowing the object to be blackened (and its references scanned)
1026 // either during a preclean phase or at the final checkpoint.
1027 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1028   assert(_markBitMap.covers(start, size), "Out of bounds");
1029   if (_collectorState >= Marking) {
1030     MutexLockerEx y(_markBitMap.lock(),
1031                     Mutex::_no_safepoint_check_flag);
1032     // [see comments preceding SweepClosure::do_blk() below for details]
1033     //
1034     // Can the P-bits be deleted now?  JJJ
1035     //
1036     // 1. need to mark the object as live so it isn't collected
1037     // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1038     // 3. need to mark the end of the object so marking, precleaning or sweeping
1039     //    can skip over uninitialized or unparsable objects. An allocated
1040     //    object is considered uninitialized for our purposes as long as
1041     //    its klass word is NULL.  All old gen objects are parsable
1042     //    as soon as they are initialized.)
1043     _markBitMap.mark(start);          // object is live
1044     _markBitMap.mark(start + 1);      // object is potentially uninitialized?
1045     _markBitMap.mark(start + size - 1);
1046                                       // mark end of object
1047   }
1048   // check that oop looks uninitialized
1049   assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1050 }
1051 
1052 void CMSCollector::promoted(bool par, HeapWord* start,
1053                             bool is_obj_array, size_t obj_size) {
1054   assert(_markBitMap.covers(start), "Out of bounds");
1055   // See comment in direct_allocated() about when objects should
1056   // be allocated live.
1057   if (_collectorState >= Marking) {
1058     // we already hold the marking bit map lock, taken in
1059     // the prologue
1060     if (par) {
1061       _markBitMap.par_mark(start);
1062     } else {
1063       _markBitMap.mark(start);
1064     }
1065     // We don't need to mark the object as uninitialized (as
1066     // in direct_allocated above) because this is being done with the
1067     // world stopped and the object will be initialized by the
1068     // time the marking, precleaning or sweeping get to look at it.
1069     // But see the code for copying objects into the CMS generation,
1070     // where we need to ensure that concurrent readers of the
1071     // block offset table are able to safely navigate a block that
1072     // is in flux from being free to being allocated (and in
1073     // transition while being copied into) and subsequently
1074     // becoming a bona-fide object when the copy/promotion is complete.
1075     assert(SafepointSynchronize::is_at_safepoint(),
1076            "expect promotion only at safepoints");
1077 
1078     if (_collectorState < Sweeping) {
1079       // Mark the appropriate cards in the modUnionTable, so that
1080       // this object gets scanned before the sweep. If this is
1081       // not done, CMS generation references in the object might
1082       // not get marked.
1083       // For the case of arrays, which are otherwise precisely
1084       // marked, we need to dirty the entire array, not just its head.
1085       if (is_obj_array) {
1086         // The [par_]mark_range() method expects mr.end() below to
1087         // be aligned to the granularity of a bit's representation
1088         // in the heap. In the case of the MUT below, that's a
1089         // card size.
1090         MemRegion mr(start,
1091                      (HeapWord*)round_to((intptr_t)(start + obj_size),
1092                         CardTableModRefBS::card_size /* bytes */));
1093         if (par) {
1094           _modUnionTable.par_mark_range(mr);
1095         } else {
1096           _modUnionTable.mark_range(mr);
1097         }
1098       } else {  // not an obj array; we can just mark the head
1099         if (par) {
1100           _modUnionTable.par_mark(start);
1101         } else {
1102           _modUnionTable.mark(start);
1103         }
1104       }
1105     }
1106   }
1107 }
1108 
1109 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1110 {
1111   size_t delta = pointer_delta(addr, space->bottom());
1112   return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1113 }
1114 
1115 void CMSCollector::icms_update_allocation_limits()
1116 {
1117   Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1118   EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1119 
1120   const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1121   if (CMSTraceIncrementalPacing) {
1122     stats().print();
1123   }
1124 
1125   assert(duty_cycle <= 100, "invalid duty cycle");
1126   if (duty_cycle != 0) {
1127     // The duty_cycle is a percentage between 0 and 100; convert to words and
1128     // then compute the offset from the endpoints of the space.
1129     size_t free_words = eden->free() / HeapWordSize;
1130     double free_words_dbl = (double)free_words;
1131     size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1132     size_t offset_words = (free_words - duty_cycle_words) / 2;
1133 
1134     _icms_start_limit = eden->top() + offset_words;
1135     _icms_stop_limit = eden->end() - offset_words;
1136 
1137     // The limits may be adjusted (shifted to the right) by
1138     // CMSIncrementalOffset, to allow the application more mutator time after a
1139     // young gen gc (when all mutators were stopped) and before CMS starts and
1140     // takes away one or more cpus.
1141     if (CMSIncrementalOffset != 0) {
1142       double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1143       size_t adjustment = (size_t)adjustment_dbl;
1144       HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1145       if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1146         _icms_start_limit += adjustment;
1147         _icms_stop_limit = tmp_stop;
1148       }
1149     }
1150   }
1151   if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1152     _icms_start_limit = _icms_stop_limit = eden->end();
1153   }
1154 
1155   // Install the new start limit.
1156   eden->set_soft_end(_icms_start_limit);
1157 
1158   if (CMSTraceIncrementalMode) {
1159     gclog_or_tty->print(" icms alloc limits:  "
1160                            PTR_FORMAT "," PTR_FORMAT
1161                            " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1162                            _icms_start_limit, _icms_stop_limit,
1163                            percent_of_space(eden, _icms_start_limit),
1164                            percent_of_space(eden, _icms_stop_limit));
1165     if (Verbose) {
1166       gclog_or_tty->print("eden:  ");
1167       eden->print_on(gclog_or_tty);
1168     }
1169   }
1170 }
1171 
1172 // Any changes here should try to maintain the invariant
1173 // that if this method is called with _icms_start_limit
1174 // and _icms_stop_limit both NULL, then it should return NULL
1175 // and not notify the icms thread.
1176 HeapWord*
1177 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1178                                        size_t word_size)
1179 {
1180   // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1181   // nop.
1182   if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1183     if (top <= _icms_start_limit) {
1184       if (CMSTraceIncrementalMode) {
1185         space->print_on(gclog_or_tty);
1186         gclog_or_tty->stamp();
1187         gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1188                                ", new limit=" PTR_FORMAT
1189                                " (" SIZE_FORMAT "%%)",
1190                                top, _icms_stop_limit,
1191                                percent_of_space(space, _icms_stop_limit));
1192       }
1193       ConcurrentMarkSweepThread::start_icms();
1194       assert(top < _icms_stop_limit, "Tautology");
1195       if (word_size < pointer_delta(_icms_stop_limit, top)) {
1196         return _icms_stop_limit;
1197       }
1198 
1199       // The allocation will cross both the _start and _stop limits, so do the
1200       // stop notification also and return end().
1201       if (CMSTraceIncrementalMode) {
1202         space->print_on(gclog_or_tty);
1203         gclog_or_tty->stamp();
1204         gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1205                                ", new limit=" PTR_FORMAT
1206                                " (" SIZE_FORMAT "%%)",
1207                                top, space->end(),
1208                                percent_of_space(space, space->end()));
1209       }
1210       ConcurrentMarkSweepThread::stop_icms();
1211       return space->end();
1212     }
1213 
1214     if (top <= _icms_stop_limit) {
1215       if (CMSTraceIncrementalMode) {
1216         space->print_on(gclog_or_tty);
1217         gclog_or_tty->stamp();
1218         gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1219                                ", new limit=" PTR_FORMAT
1220                                " (" SIZE_FORMAT "%%)",
1221                                top, space->end(),
1222                                percent_of_space(space, space->end()));
1223       }
1224       ConcurrentMarkSweepThread::stop_icms();
1225       return space->end();
1226     }
1227 
1228     if (CMSTraceIncrementalMode) {
1229       space->print_on(gclog_or_tty);
1230       gclog_or_tty->stamp();
1231       gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1232                              ", new limit=" PTR_FORMAT,
1233                              top, NULL);
1234     }
1235   }
1236 
1237   return NULL;
1238 }
1239 
1240 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1241   assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1242   // allocate, copy and if necessary update promoinfo --
1243   // delegate to underlying space.
1244   assert_lock_strong(freelistLock());
1245 
1246 #ifndef PRODUCT
1247   if (Universe::heap()->promotion_should_fail()) {
1248     return NULL;
1249   }
1250 #endif  // #ifndef PRODUCT
1251 
1252   oop res = _cmsSpace->promote(obj, obj_size);
1253   if (res == NULL) {
1254     // expand and retry
1255     size_t s = _cmsSpace->expansionSpaceRequired(obj_size);  // HeapWords
1256     expand(s*HeapWordSize, MinHeapDeltaBytes,
1257       CMSExpansionCause::_satisfy_promotion);
1258     // Since there's currently no next generation, we don't try to promote
1259     // into a more senior generation.
1260     assert(next_gen() == NULL, "assumption, based upon which no attempt "
1261                                "is made to pass on a possibly failing "
1262                                "promotion to next generation");
1263     res = _cmsSpace->promote(obj, obj_size);
1264   }
1265   if (res != NULL) {
1266     // See comment in allocate() about when objects should
1267     // be allocated live.
1268     assert(obj->is_oop(), "Will dereference klass pointer below");
1269     collector()->promoted(false,           // Not parallel
1270                           (HeapWord*)res, obj->is_objArray(), obj_size);
1271     // promotion counters
1272     NOT_PRODUCT(
1273       _numObjectsPromoted++;
1274       _numWordsPromoted +=
1275         (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1276     )
1277   }
1278   return res;
1279 }
1280 
1281 
1282 HeapWord*
1283 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1284                                              HeapWord* top,
1285                                              size_t word_sz)
1286 {
1287   return collector()->allocation_limit_reached(space, top, word_sz);
1288 }
1289 
1290 // IMPORTANT: Notes on object size recognition in CMS.
1291 // ---------------------------------------------------
1292 // A block of storage in the CMS generation is always in
1293 // one of three states. A free block (FREE), an allocated
1294 // object (OBJECT) whose size() method reports the correct size,
1295 // and an intermediate state (TRANSIENT) in which its size cannot
1296 // be accurately determined.
1297 // STATE IDENTIFICATION:   (32 bit and 64 bit w/o COOPS)
1298 // -----------------------------------------------------
1299 // FREE:      klass_word & 1 == 1; mark_word holds block size
1300 //
1301 // OBJECT:    klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1302 //            obj->size() computes correct size
1303 //
1304 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1305 //
1306 // STATE IDENTIFICATION: (64 bit+COOPS)
1307 // ------------------------------------
1308 // FREE:      mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1309 //
1310 // OBJECT:    klass_word installed; klass_word != 0;
1311 //            obj->size() computes correct size
1312 //
1313 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1314 //
1315 //
1316 // STATE TRANSITION DIAGRAM
1317 //
1318 //        mut / parnew                     mut  /  parnew
1319 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1320 //  ^                                                                   |
1321 //  |------------------------ DEAD <------------------------------------|
1322 //         sweep                            mut
1323 //
1324 // While a block is in TRANSIENT state its size cannot be determined
1325 // so readers will either need to come back later or stall until
1326 // the size can be determined. Note that for the case of direct
1327 // allocation, P-bits, when available, may be used to determine the
1328 // size of an object that may not yet have been initialized.
1329 
1330 // Things to support parallel young-gen collection.
1331 oop
1332 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1333                                            oop old, markOop m,
1334                                            size_t word_sz) {
1335 #ifndef PRODUCT
1336   if (Universe::heap()->promotion_should_fail()) {
1337     return NULL;
1338   }
1339 #endif  // #ifndef PRODUCT
1340 
1341   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1342   PromotionInfo* promoInfo = &ps->promo;
1343   // if we are tracking promotions, then first ensure space for
1344   // promotion (including spooling space for saving header if necessary).
1345   // then allocate and copy, then track promoted info if needed.
1346   // When tracking (see PromotionInfo::track()), the mark word may
1347   // be displaced and in this case restoration of the mark word
1348   // occurs in the (oop_since_save_marks_)iterate phase.
1349   if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1350     // Out of space for allocating spooling buffers;
1351     // try expanding and allocating spooling buffers.
1352     if (!expand_and_ensure_spooling_space(promoInfo)) {
1353       return NULL;
1354     }
1355   }
1356   assert(promoInfo->has_spooling_space(), "Control point invariant");
1357   const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1358   HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1359   if (obj_ptr == NULL) {
1360      obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1361      if (obj_ptr == NULL) {
1362        return NULL;
1363      }
1364   }
1365   oop obj = oop(obj_ptr);
1366   OrderAccess::storestore();
1367   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1368   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1369   // IMPORTANT: See note on object initialization for CMS above.
1370   // Otherwise, copy the object.  Here we must be careful to insert the
1371   // klass pointer last, since this marks the block as an allocated object.
1372   // Except with compressed oops it's the mark word.
1373   HeapWord* old_ptr = (HeapWord*)old;
1374   // Restore the mark word copied above.
1375   obj->set_mark(m);
1376   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1377   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1378   OrderAccess::storestore();
1379 
1380   if (UseCompressedKlassPointers) {
1381     // Copy gap missed by (aligned) header size calculation below
1382     obj->set_klass_gap(old->klass_gap());
1383   }
1384   if (word_sz > (size_t)oopDesc::header_size()) {
1385     Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1386                                  obj_ptr + oopDesc::header_size(),
1387                                  word_sz - oopDesc::header_size());
1388   }
1389 
1390   // Now we can track the promoted object, if necessary.  We take care
1391   // to delay the transition from uninitialized to full object
1392   // (i.e., insertion of klass pointer) until after, so that it
1393   // atomically becomes a promoted object.
1394   if (promoInfo->tracking()) {
1395     promoInfo->track((PromotedObject*)obj, old->klass());
1396   }
1397   assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1398   assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1399   assert(old->is_oop(), "Will use and dereference old klass ptr below");
1400 
1401   // Finally, install the klass pointer (this should be volatile).
1402   OrderAccess::storestore();
1403   obj->set_klass(old->klass());
1404   // We should now be able to calculate the right size for this object
1405   assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1406 
1407   collector()->promoted(true,          // parallel
1408                         obj_ptr, old->is_objArray(), word_sz);
1409 
1410   NOT_PRODUCT(
1411     Atomic::inc_ptr(&_numObjectsPromoted);
1412     Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1413   )
1414 
1415   return obj;
1416 }
1417 
1418 void
1419 ConcurrentMarkSweepGeneration::
1420 par_promote_alloc_undo(int thread_num,
1421                        HeapWord* obj, size_t word_sz) {
1422   // CMS does not support promotion undo.
1423   ShouldNotReachHere();
1424 }
1425 
1426 void
1427 ConcurrentMarkSweepGeneration::
1428 par_promote_alloc_done(int thread_num) {
1429   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1430   ps->lab.retire(thread_num);
1431 }
1432 
1433 void
1434 ConcurrentMarkSweepGeneration::
1435 par_oop_since_save_marks_iterate_done(int thread_num) {
1436   CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1437   ParScanWithoutBarrierClosure* dummy_cl = NULL;
1438   ps->promo.promoted_oops_iterate_nv(dummy_cl);
1439 }
1440 
1441 bool ConcurrentMarkSweepGeneration::should_collect(bool   full,
1442                                                    size_t size,
1443                                                    bool   tlab)
1444 {
1445   // We allow a STW collection only if a full
1446   // collection was requested.
1447   return full || should_allocate(size, tlab); // FIX ME !!!
1448   // This and promotion failure handling are connected at the
1449   // hip and should be fixed by untying them.
1450 }
1451 
1452 bool CMSCollector::shouldConcurrentCollect() {
1453   if (_full_gc_requested) {
1454     if (Verbose && PrintGCDetails) {
1455       gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1456                              " gc request (or gc_locker)");
1457     }
1458     return true;
1459   }
1460 
1461   // For debugging purposes, change the type of collection.
1462   // If the rotation is not on the concurrent collection
1463   // type, don't start a concurrent collection.
1464   NOT_PRODUCT(
1465     if (RotateCMSCollectionTypes &&
1466         (_cmsGen->debug_collection_type() !=
1467           ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1468       assert(_cmsGen->debug_collection_type() !=
1469         ConcurrentMarkSweepGeneration::Unknown_collection_type,
1470         "Bad cms collection type");
1471       return false;
1472     }
1473   )
1474 
1475   FreelistLocker x(this);
1476   // ------------------------------------------------------------------
1477   // Print out lots of information which affects the initiation of
1478   // a collection.
1479   if (PrintCMSInitiationStatistics && stats().valid()) {
1480     gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1481     gclog_or_tty->stamp();
1482     gclog_or_tty->print_cr("");
1483     stats().print_on(gclog_or_tty);
1484     gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1485       stats().time_until_cms_gen_full());
1486     gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1487     gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1488                            _cmsGen->contiguous_available());
1489     gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1490     gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1491     gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1492     gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1493     gclog_or_tty->print_cr("metadata initialized %d",
1494       MetaspaceGC::should_concurrent_collect());
1495   }
1496   // ------------------------------------------------------------------
1497 
1498   // If the estimated time to complete a cms collection (cms_duration())
1499   // is less than the estimated time remaining until the cms generation
1500   // is full, start a collection.
1501   if (!UseCMSInitiatingOccupancyOnly) {
1502     if (stats().valid()) {
1503       if (stats().time_until_cms_start() == 0.0) {
1504         return true;
1505       }
1506     } else {
1507       // We want to conservatively collect somewhat early in order
1508       // to try and "bootstrap" our CMS/promotion statistics;
1509       // this branch will not fire after the first successful CMS
1510       // collection because the stats should then be valid.
1511       if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1512         if (Verbose && PrintGCDetails) {
1513           gclog_or_tty->print_cr(
1514             " CMSCollector: collect for bootstrapping statistics:"
1515             " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1516             _bootstrap_occupancy);
1517         }
1518         return true;
1519       }
1520     }
1521   }
1522 
1523   // Otherwise, we start a collection cycle if
1524   // old gen want a collection cycle started. Each may use
1525   // an appropriate criterion for making this decision.
1526   // XXX We need to make sure that the gen expansion
1527   // criterion dovetails well with this. XXX NEED TO FIX THIS
1528   if (_cmsGen->should_concurrent_collect()) {
1529     if (Verbose && PrintGCDetails) {
1530       gclog_or_tty->print_cr("CMS old gen initiated");
1531     }
1532     return true;
1533   }
1534 
1535   // We start a collection if we believe an incremental collection may fail;
1536   // this is not likely to be productive in practice because it's probably too
1537   // late anyway.
1538   GenCollectedHeap* gch = GenCollectedHeap::heap();
1539   assert(gch->collector_policy()->is_two_generation_policy(),
1540          "You may want to check the correctness of the following");
1541   if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1542     if (Verbose && PrintGCDetails) {
1543       gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1544     }
1545     return true;
1546   }
1547 
1548   if (MetaspaceGC::should_concurrent_collect()) {
1549       if (Verbose && PrintGCDetails) {
1550       gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1551       }
1552       return true;
1553     }
1554 
1555   return false;
1556 }
1557 
1558 // Clear _expansion_cause fields of constituent generations
1559 void CMSCollector::clear_expansion_cause() {
1560   _cmsGen->clear_expansion_cause();
1561 }
1562 
1563 // We should be conservative in starting a collection cycle.  To
1564 // start too eagerly runs the risk of collecting too often in the
1565 // extreme.  To collect too rarely falls back on full collections,
1566 // which works, even if not optimum in terms of concurrent work.
1567 // As a work around for too eagerly collecting, use the flag
1568 // UseCMSInitiatingOccupancyOnly.  This also has the advantage of
1569 // giving the user an easily understandable way of controlling the
1570 // collections.
1571 // We want to start a new collection cycle if any of the following
1572 // conditions hold:
1573 // . our current occupancy exceeds the configured initiating occupancy
1574 //   for this generation, or
1575 // . we recently needed to expand this space and have not, since that
1576 //   expansion, done a collection of this generation, or
1577 // . the underlying space believes that it may be a good idea to initiate
1578 //   a concurrent collection (this may be based on criteria such as the
1579 //   following: the space uses linear allocation and linear allocation is
1580 //   going to fail, or there is believed to be excessive fragmentation in
1581 //   the generation, etc... or ...
1582 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1583 //   the case of the old generation; see CR 6543076):
1584 //   we may be approaching a point at which allocation requests may fail because
1585 //   we will be out of sufficient free space given allocation rate estimates.]
1586 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1587 
1588   assert_lock_strong(freelistLock());
1589   if (occupancy() > initiating_occupancy()) {
1590     if (PrintGCDetails && Verbose) {
1591       gclog_or_tty->print(" %s: collect because of occupancy %f / %f  ",
1592         short_name(), occupancy(), initiating_occupancy());
1593     }
1594     return true;
1595   }
1596   if (UseCMSInitiatingOccupancyOnly) {
1597     return false;
1598   }
1599   if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1600     if (PrintGCDetails && Verbose) {
1601       gclog_or_tty->print(" %s: collect because expanded for allocation ",
1602         short_name());
1603     }
1604     return true;
1605   }
1606   if (_cmsSpace->should_concurrent_collect()) {
1607     if (PrintGCDetails && Verbose) {
1608       gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1609         short_name());
1610     }
1611     return true;
1612   }
1613   return false;
1614 }
1615 
1616 void ConcurrentMarkSweepGeneration::collect(bool   full,
1617                                             bool   clear_all_soft_refs,
1618                                             size_t size,
1619                                             bool   tlab)
1620 {
1621   collector()->collect(full, clear_all_soft_refs, size, tlab);
1622 }
1623 
1624 void CMSCollector::collect(bool   full,
1625                            bool   clear_all_soft_refs,
1626                            size_t size,
1627                            bool   tlab)
1628 {
1629   if (!UseCMSCollectionPassing && _collectorState > Idling) {
1630     // For debugging purposes skip the collection if the state
1631     // is not currently idle
1632     if (TraceCMSState) {
1633       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1634         Thread::current(), full, _collectorState);
1635     }
1636     return;
1637   }
1638 
1639   // The following "if" branch is present for defensive reasons.
1640   // In the current uses of this interface, it can be replaced with:
1641   // assert(!GC_locker.is_active(), "Can't be called otherwise");
1642   // But I am not placing that assert here to allow future
1643   // generality in invoking this interface.
1644   if (GC_locker::is_active()) {
1645     // A consistency test for GC_locker
1646     assert(GC_locker::needs_gc(), "Should have been set already");
1647     // Skip this foreground collection, instead
1648     // expanding the heap if necessary.
1649     // Need the free list locks for the call to free() in compute_new_size()
1650     compute_new_size();
1651     return;
1652   }
1653   acquire_control_and_collect(full, clear_all_soft_refs);
1654   _full_gcs_since_conc_gc++;
1655 
1656 }
1657 
1658 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1659   GenCollectedHeap* gch = GenCollectedHeap::heap();
1660   unsigned int gc_count = gch->total_full_collections();
1661   if (gc_count == full_gc_count) {
1662     MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1663     _full_gc_requested = true;
1664     CGC_lock->notify();   // nudge CMS thread
1665   } else {
1666     assert(gc_count > full_gc_count, "Error: causal loop");
1667   }
1668 }
1669 
1670 
1671 // The foreground and background collectors need to coordinate in order
1672 // to make sure that they do not mutually interfere with CMS collections.
1673 // When a background collection is active,
1674 // the foreground collector may need to take over (preempt) and
1675 // synchronously complete an ongoing collection. Depending on the
1676 // frequency of the background collections and the heap usage
1677 // of the application, this preemption can be seldom or frequent.
1678 // There are only certain
1679 // points in the background collection that the "collection-baton"
1680 // can be passed to the foreground collector.
1681 //
1682 // The foreground collector will wait for the baton before
1683 // starting any part of the collection.  The foreground collector
1684 // will only wait at one location.
1685 //
1686 // The background collector will yield the baton before starting a new
1687 // phase of the collection (e.g., before initial marking, marking from roots,
1688 // precleaning, final re-mark, sweep etc.)  This is normally done at the head
1689 // of the loop which switches the phases. The background collector does some
1690 // of the phases (initial mark, final re-mark) with the world stopped.
1691 // Because of locking involved in stopping the world,
1692 // the foreground collector should not block waiting for the background
1693 // collector when it is doing a stop-the-world phase.  The background
1694 // collector will yield the baton at an additional point just before
1695 // it enters a stop-the-world phase.  Once the world is stopped, the
1696 // background collector checks the phase of the collection.  If the
1697 // phase has not changed, it proceeds with the collection.  If the
1698 // phase has changed, it skips that phase of the collection.  See
1699 // the comments on the use of the Heap_lock in collect_in_background().
1700 //
1701 // Variable used in baton passing.
1702 //   _foregroundGCIsActive - Set to true by the foreground collector when
1703 //      it wants the baton.  The foreground clears it when it has finished
1704 //      the collection.
1705 //   _foregroundGCShouldWait - Set to true by the background collector
1706 //        when it is running.  The foreground collector waits while
1707 //      _foregroundGCShouldWait is true.
1708 //  CGC_lock - monitor used to protect access to the above variables
1709 //      and to notify the foreground and background collectors.
1710 //  _collectorState - current state of the CMS collection.
1711 //
1712 // The foreground collector
1713 //   acquires the CGC_lock
1714 //   sets _foregroundGCIsActive
1715 //   waits on the CGC_lock for _foregroundGCShouldWait to be false
1716 //     various locks acquired in preparation for the collection
1717 //     are released so as not to block the background collector
1718 //     that is in the midst of a collection
1719 //   proceeds with the collection
1720 //   clears _foregroundGCIsActive
1721 //   returns
1722 //
1723 // The background collector in a loop iterating on the phases of the
1724 //      collection
1725 //   acquires the CGC_lock
1726 //   sets _foregroundGCShouldWait
1727 //   if _foregroundGCIsActive is set
1728 //     clears _foregroundGCShouldWait, notifies _CGC_lock
1729 //     waits on _CGC_lock for _foregroundGCIsActive to become false
1730 //     and exits the loop.
1731 //   otherwise
1732 //     proceed with that phase of the collection
1733 //     if the phase is a stop-the-world phase,
1734 //       yield the baton once more just before enqueueing
1735 //       the stop-world CMS operation (executed by the VM thread).
1736 //   returns after all phases of the collection are done
1737 //
1738 
1739 void CMSCollector::acquire_control_and_collect(bool full,
1740         bool clear_all_soft_refs) {
1741   assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1742   assert(!Thread::current()->is_ConcurrentGC_thread(),
1743          "shouldn't try to acquire control from self!");
1744 
1745   // Start the protocol for acquiring control of the
1746   // collection from the background collector (aka CMS thread).
1747   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1748          "VM thread should have CMS token");
1749   // Remember the possibly interrupted state of an ongoing
1750   // concurrent collection
1751   CollectorState first_state = _collectorState;
1752 
1753   // Signal to a possibly ongoing concurrent collection that
1754   // we want to do a foreground collection.
1755   _foregroundGCIsActive = true;
1756 
1757   // Disable incremental mode during a foreground collection.
1758   ICMSDisabler icms_disabler;
1759 
1760   // release locks and wait for a notify from the background collector
1761   // releasing the locks in only necessary for phases which
1762   // do yields to improve the granularity of the collection.
1763   assert_lock_strong(bitMapLock());
1764   // We need to lock the Free list lock for the space that we are
1765   // currently collecting.
1766   assert(haveFreelistLocks(), "Must be holding free list locks");
1767   bitMapLock()->unlock();
1768   releaseFreelistLocks();
1769   {
1770     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1771     if (_foregroundGCShouldWait) {
1772       // We are going to be waiting for action for the CMS thread;
1773       // it had better not be gone (for instance at shutdown)!
1774       assert(ConcurrentMarkSweepThread::cmst() != NULL,
1775              "CMS thread must be running");
1776       // Wait here until the background collector gives us the go-ahead
1777       ConcurrentMarkSweepThread::clear_CMS_flag(
1778         ConcurrentMarkSweepThread::CMS_vm_has_token);  // release token
1779       // Get a possibly blocked CMS thread going:
1780       //   Note that we set _foregroundGCIsActive true above,
1781       //   without protection of the CGC_lock.
1782       CGC_lock->notify();
1783       assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1784              "Possible deadlock");
1785       while (_foregroundGCShouldWait) {
1786         // wait for notification
1787         CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1788         // Possibility of delay/starvation here, since CMS token does
1789         // not know to give priority to VM thread? Actually, i think
1790         // there wouldn't be any delay/starvation, but the proof of
1791         // that "fact" (?) appears non-trivial. XXX 20011219YSR
1792       }
1793       ConcurrentMarkSweepThread::set_CMS_flag(
1794         ConcurrentMarkSweepThread::CMS_vm_has_token);
1795     }
1796   }
1797   // The CMS_token is already held.  Get back the other locks.
1798   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1799          "VM thread should have CMS token");
1800   getFreelistLocks();
1801   bitMapLock()->lock_without_safepoint_check();
1802   if (TraceCMSState) {
1803     gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1804       INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1805     gclog_or_tty->print_cr("    gets control with state %d", _collectorState);
1806   }
1807 
1808   // Check if we need to do a compaction, or if not, whether
1809   // we need to start the mark-sweep from scratch.
1810   bool should_compact    = false;
1811   bool should_start_over = false;
1812   decide_foreground_collection_type(clear_all_soft_refs,
1813     &should_compact, &should_start_over);
1814 
1815 NOT_PRODUCT(
1816   if (RotateCMSCollectionTypes) {
1817     if (_cmsGen->debug_collection_type() ==
1818         ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1819       should_compact = true;
1820     } else if (_cmsGen->debug_collection_type() ==
1821                ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1822       should_compact = false;
1823     }
1824   }
1825 )
1826 
1827   if (PrintGCDetails && first_state > Idling) {
1828     GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1829     if (GCCause::is_user_requested_gc(cause) ||
1830         GCCause::is_serviceability_requested_gc(cause)) {
1831       gclog_or_tty->print(" (concurrent mode interrupted)");
1832     } else {
1833       gclog_or_tty->print(" (concurrent mode failure)");
1834     }
1835   }
1836 
1837   if (should_compact) {
1838     // If the collection is being acquired from the background
1839     // collector, there may be references on the discovered
1840     // references lists that have NULL referents (being those
1841     // that were concurrently cleared by a mutator) or
1842     // that are no longer active (having been enqueued concurrently
1843     // by the mutator).
1844     // Scrub the list of those references because Mark-Sweep-Compact
1845     // code assumes referents are not NULL and that all discovered
1846     // Reference objects are active.
1847     ref_processor()->clean_up_discovered_references();
1848 
1849     do_compaction_work(clear_all_soft_refs);
1850 
1851     // Has the GC time limit been exceeded?
1852     DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1853     size_t max_eden_size = young_gen->max_capacity() -
1854                            young_gen->to()->capacity() -
1855                            young_gen->from()->capacity();
1856     GenCollectedHeap* gch = GenCollectedHeap::heap();
1857     GCCause::Cause gc_cause = gch->gc_cause();
1858     size_policy()->check_gc_overhead_limit(_young_gen->used(),
1859                                            young_gen->eden()->used(),
1860                                            _cmsGen->max_capacity(),
1861                                            max_eden_size,
1862                                            full,
1863                                            gc_cause,
1864                                            gch->collector_policy());
1865   } else {
1866     do_mark_sweep_work(clear_all_soft_refs, first_state,
1867       should_start_over);
1868   }
1869   // Reset the expansion cause, now that we just completed
1870   // a collection cycle.
1871   clear_expansion_cause();
1872   _foregroundGCIsActive = false;
1873   return;
1874 }
1875 
1876 // Resize the tenured generation
1877 // after obtaining the free list locks for the
1878 // two generations.
1879 void CMSCollector::compute_new_size() {
1880   assert_locked_or_safepoint(Heap_lock);
1881   FreelistLocker z(this);
1882   MetaspaceGC::compute_new_size();
1883   _cmsGen->compute_new_size();
1884 }
1885 
1886 // A work method used by foreground collection to determine
1887 // what type of collection (compacting or not, continuing or fresh)
1888 // it should do.
1889 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1890 // and CMSCompactWhenClearAllSoftRefs the default in the future
1891 // and do away with the flags after a suitable period.
1892 void CMSCollector::decide_foreground_collection_type(
1893   bool clear_all_soft_refs, bool* should_compact,
1894   bool* should_start_over) {
1895   // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1896   // flag is set, and we have either requested a System.gc() or
1897   // the number of full gc's since the last concurrent cycle
1898   // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1899   // or if an incremental collection has failed
1900   GenCollectedHeap* gch = GenCollectedHeap::heap();
1901   assert(gch->collector_policy()->is_two_generation_policy(),
1902          "You may want to check the correctness of the following");
1903   // Inform cms gen if this was due to partial collection failing.
1904   // The CMS gen may use this fact to determine its expansion policy.
1905   if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1906     assert(!_cmsGen->incremental_collection_failed(),
1907            "Should have been noticed, reacted to and cleared");
1908     _cmsGen->set_incremental_collection_failed();
1909   }
1910   *should_compact =
1911     UseCMSCompactAtFullCollection &&
1912     ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1913      GCCause::is_user_requested_gc(gch->gc_cause()) ||
1914      gch->incremental_collection_will_fail(true /* consult_young */));
1915   *should_start_over = false;
1916   if (clear_all_soft_refs && !*should_compact) {
1917     // We are about to do a last ditch collection attempt
1918     // so it would normally make sense to do a compaction
1919     // to reclaim as much space as possible.
1920     if (CMSCompactWhenClearAllSoftRefs) {
1921       // Default: The rationale is that in this case either
1922       // we are past the final marking phase, in which case
1923       // we'd have to start over, or so little has been done
1924       // that there's little point in saving that work. Compaction
1925       // appears to be the sensible choice in either case.
1926       *should_compact = true;
1927     } else {
1928       // We have been asked to clear all soft refs, but not to
1929       // compact. Make sure that we aren't past the final checkpoint
1930       // phase, for that is where we process soft refs. If we are already
1931       // past that phase, we'll need to redo the refs discovery phase and
1932       // if necessary clear soft refs that weren't previously
1933       // cleared. We do so by remembering the phase in which
1934       // we came in, and if we are past the refs processing
1935       // phase, we'll choose to just redo the mark-sweep
1936       // collection from scratch.
1937       if (_collectorState > FinalMarking) {
1938         // We are past the refs processing phase;
1939         // start over and do a fresh synchronous CMS cycle
1940         _collectorState = Resetting; // skip to reset to start new cycle
1941         reset(false /* == !asynch */);
1942         *should_start_over = true;
1943       } // else we can continue a possibly ongoing current cycle
1944     }
1945   }
1946 }
1947 
1948 // A work method used by the foreground collector to do
1949 // a mark-sweep-compact.
1950 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1951   GenCollectedHeap* gch = GenCollectedHeap::heap();
1952   TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1953   if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1954     gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1955       "collections passed to foreground collector", _full_gcs_since_conc_gc);
1956   }
1957 
1958   // Sample collection interval time and reset for collection pause.
1959   if (UseAdaptiveSizePolicy) {
1960     size_policy()->msc_collection_begin();
1961   }
1962 
1963   // Temporarily widen the span of the weak reference processing to
1964   // the entire heap.
1965   MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1966   ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1967   // Temporarily, clear the "is_alive_non_header" field of the
1968   // reference processor.
1969   ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1970   // Temporarily make reference _processing_ single threaded (non-MT).
1971   ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1972   // Temporarily make refs discovery atomic
1973   ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1974   // Temporarily make reference _discovery_ single threaded (non-MT)
1975   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1976 
1977   ref_processor()->set_enqueuing_is_done(false);
1978   ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1979   ref_processor()->setup_policy(clear_all_soft_refs);
1980   // If an asynchronous collection finishes, the _modUnionTable is
1981   // all clear.  If we are assuming the collection from an asynchronous
1982   // collection, clear the _modUnionTable.
1983   assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1984     "_modUnionTable should be clear if the baton was not passed");
1985   _modUnionTable.clear_all();
1986   assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1987     "mod union for klasses should be clear if the baton was passed");
1988   _ct->klass_rem_set()->clear_mod_union();
1989 
1990   // We must adjust the allocation statistics being maintained
1991   // in the free list space. We do so by reading and clearing
1992   // the sweep timer and updating the block flux rate estimates below.
1993   assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1994   if (_inter_sweep_timer.is_active()) {
1995     _inter_sweep_timer.stop();
1996     // Note that we do not use this sample to update the _inter_sweep_estimate.
1997     _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1998                                             _inter_sweep_estimate.padded_average(),
1999                                             _intra_sweep_estimate.padded_average());
2000   }
2001 
2002   GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2003     ref_processor(), clear_all_soft_refs);
2004   #ifdef ASSERT
2005     CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2006     size_t free_size = cms_space->free();
2007     assert(free_size ==
2008            pointer_delta(cms_space->end(), cms_space->compaction_top())
2009            * HeapWordSize,
2010       "All the free space should be compacted into one chunk at top");
2011     assert(cms_space->dictionary()->total_chunk_size(
2012                                       debug_only(cms_space->freelistLock())) == 0 ||
2013            cms_space->totalSizeInIndexedFreeLists() == 0,
2014       "All the free space should be in a single chunk");
2015     size_t num = cms_space->totalCount();
2016     assert((free_size == 0 && num == 0) ||
2017            (free_size > 0  && (num == 1 || num == 2)),
2018          "There should be at most 2 free chunks after compaction");
2019   #endif // ASSERT
2020   _collectorState = Resetting;
2021   assert(_restart_addr == NULL,
2022          "Should have been NULL'd before baton was passed");
2023   reset(false /* == !asynch */);
2024   _cmsGen->reset_after_compaction();
2025   _concurrent_cycles_since_last_unload = 0;
2026 
2027   // Clear any data recorded in the PLAB chunk arrays.
2028   if (_survivor_plab_array != NULL) {
2029     reset_survivor_plab_arrays();
2030   }
2031 
2032   // Adjust the per-size allocation stats for the next epoch.
2033   _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2034   // Restart the "inter sweep timer" for the next epoch.
2035   _inter_sweep_timer.reset();
2036   _inter_sweep_timer.start();
2037 
2038   // Sample collection pause time and reset for collection interval.
2039   if (UseAdaptiveSizePolicy) {
2040     size_policy()->msc_collection_end(gch->gc_cause());
2041   }
2042 
2043   // For a mark-sweep-compact, compute_new_size() will be called
2044   // in the heap's do_collection() method.
2045 }
2046 
2047 // A work method used by the foreground collector to do
2048 // a mark-sweep, after taking over from a possibly on-going
2049 // concurrent mark-sweep collection.
2050 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2051   CollectorState first_state, bool should_start_over) {
2052   if (PrintGC && Verbose) {
2053     gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2054       "collector with count %d",
2055       _full_gcs_since_conc_gc);
2056   }
2057   switch (_collectorState) {
2058     case Idling:
2059       if (first_state == Idling || should_start_over) {
2060         // The background GC was not active, or should
2061         // restarted from scratch;  start the cycle.
2062         _collectorState = InitialMarking;
2063       }
2064       // If first_state was not Idling, then a background GC
2065       // was in progress and has now finished.  No need to do it
2066       // again.  Leave the state as Idling.
2067       break;
2068     case Precleaning:
2069       // In the foreground case don't do the precleaning since
2070       // it is not done concurrently and there is extra work
2071       // required.
2072       _collectorState = FinalMarking;
2073   }
2074   if (PrintGCDetails &&
2075       (_collectorState > Idling ||
2076        !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2077     gclog_or_tty->print(" (concurrent mode failure)");
2078   }
2079   collect_in_foreground(clear_all_soft_refs);
2080 
2081   // For a mark-sweep, compute_new_size() will be called
2082   // in the heap's do_collection() method.
2083 }
2084 
2085 
2086 void CMSCollector::getFreelistLocks() const {
2087   // Get locks for all free lists in all generations that this
2088   // collector is responsible for
2089   _cmsGen->freelistLock()->lock_without_safepoint_check();
2090 }
2091 
2092 void CMSCollector::releaseFreelistLocks() const {
2093   // Release locks for all free lists in all generations that this
2094   // collector is responsible for
2095   _cmsGen->freelistLock()->unlock();
2096 }
2097 
2098 bool CMSCollector::haveFreelistLocks() const {
2099   // Check locks for all free lists in all generations that this
2100   // collector is responsible for
2101   assert_lock_strong(_cmsGen->freelistLock());
2102   PRODUCT_ONLY(ShouldNotReachHere());
2103   return true;
2104 }
2105 
2106 // A utility class that is used by the CMS collector to
2107 // temporarily "release" the foreground collector from its
2108 // usual obligation to wait for the background collector to
2109 // complete an ongoing phase before proceeding.
2110 class ReleaseForegroundGC: public StackObj {
2111  private:
2112   CMSCollector* _c;
2113  public:
2114   ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2115     assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2116     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2117     // allow a potentially blocked foreground collector to proceed
2118     _c->_foregroundGCShouldWait = false;
2119     if (_c->_foregroundGCIsActive) {
2120       CGC_lock->notify();
2121     }
2122     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2123            "Possible deadlock");
2124   }
2125 
2126   ~ReleaseForegroundGC() {
2127     assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2128     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2129     _c->_foregroundGCShouldWait = true;
2130   }
2131 };
2132 
2133 // There are separate collect_in_background and collect_in_foreground because of
2134 // the different locking requirements of the background collector and the
2135 // foreground collector.  There was originally an attempt to share
2136 // one "collect" method between the background collector and the foreground
2137 // collector but the if-then-else required made it cleaner to have
2138 // separate methods.
2139 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2140   assert(Thread::current()->is_ConcurrentGC_thread(),
2141     "A CMS asynchronous collection is only allowed on a CMS thread.");
2142 
2143   GenCollectedHeap* gch = GenCollectedHeap::heap();
2144   {
2145     bool safepoint_check = Mutex::_no_safepoint_check_flag;
2146     MutexLockerEx hl(Heap_lock, safepoint_check);
2147     FreelistLocker fll(this);
2148     MutexLockerEx x(CGC_lock, safepoint_check);
2149     if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2150       // The foreground collector is active or we're
2151       // not using asynchronous collections.  Skip this
2152       // background collection.
2153       assert(!_foregroundGCShouldWait, "Should be clear");
2154       return;
2155     } else {
2156       assert(_collectorState == Idling, "Should be idling before start.");
2157       _collectorState = InitialMarking;
2158       // Reset the expansion cause, now that we are about to begin
2159       // a new cycle.
2160       clear_expansion_cause();
2161 
2162       // Clear the MetaspaceGC flag since a concurrent collection
2163       // is starting but also clear it after the collection.
2164       MetaspaceGC::set_should_concurrent_collect(false);
2165     }
2166     // Decide if we want to enable class unloading as part of the
2167     // ensuing concurrent GC cycle.
2168     update_should_unload_classes();
2169     _full_gc_requested = false;           // acks all outstanding full gc requests
2170     // Signal that we are about to start a collection
2171     gch->increment_total_full_collections();  // ... starting a collection cycle
2172     _collection_count_start = gch->total_full_collections();
2173   }
2174 
2175   // Used for PrintGC
2176   size_t prev_used;
2177   if (PrintGC && Verbose) {
2178     prev_used = _cmsGen->used(); // XXXPERM
2179   }
2180 
2181   // The change of the collection state is normally done at this level;
2182   // the exceptions are phases that are executed while the world is
2183   // stopped.  For those phases the change of state is done while the
2184   // world is stopped.  For baton passing purposes this allows the
2185   // background collector to finish the phase and change state atomically.
2186   // The foreground collector cannot wait on a phase that is done
2187   // while the world is stopped because the foreground collector already
2188   // has the world stopped and would deadlock.
2189   while (_collectorState != Idling) {
2190     if (TraceCMSState) {
2191       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2192         Thread::current(), _collectorState);
2193     }
2194     // The foreground collector
2195     //   holds the Heap_lock throughout its collection.
2196     //   holds the CMS token (but not the lock)
2197     //     except while it is waiting for the background collector to yield.
2198     //
2199     // The foreground collector should be blocked (not for long)
2200     //   if the background collector is about to start a phase
2201     //   executed with world stopped.  If the background
2202     //   collector has already started such a phase, the
2203     //   foreground collector is blocked waiting for the
2204     //   Heap_lock.  The stop-world phases (InitialMarking and FinalMarking)
2205     //   are executed in the VM thread.
2206     //
2207     // The locking order is
2208     //   PendingListLock (PLL)  -- if applicable (FinalMarking)
2209     //   Heap_lock  (both this & PLL locked in VM_CMS_Operation::prologue())
2210     //   CMS token  (claimed in
2211     //                stop_world_and_do() -->
2212     //                  safepoint_synchronize() -->
2213     //                    CMSThread::synchronize())
2214 
2215     {
2216       // Check if the FG collector wants us to yield.
2217       CMSTokenSync x(true); // is cms thread
2218       if (waitForForegroundGC()) {
2219         // We yielded to a foreground GC, nothing more to be
2220         // done this round.
2221         assert(_foregroundGCShouldWait == false, "We set it to false in "
2222                "waitForForegroundGC()");
2223         if (TraceCMSState) {
2224           gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2225             " exiting collection CMS state %d",
2226             Thread::current(), _collectorState);
2227         }
2228         return;
2229       } else {
2230         // The background collector can run but check to see if the
2231         // foreground collector has done a collection while the
2232         // background collector was waiting to get the CGC_lock
2233         // above.  If yes, break so that _foregroundGCShouldWait
2234         // is cleared before returning.
2235         if (_collectorState == Idling) {
2236           break;
2237         }
2238       }
2239     }
2240 
2241     assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2242       "should be waiting");
2243 
2244     switch (_collectorState) {
2245       case InitialMarking:
2246         {
2247           ReleaseForegroundGC x(this);
2248           stats().record_cms_begin();
2249 
2250           VM_CMS_Initial_Mark initial_mark_op(this);
2251           VMThread::execute(&initial_mark_op);
2252         }
2253         // The collector state may be any legal state at this point
2254         // since the background collector may have yielded to the
2255         // foreground collector.
2256         break;
2257       case Marking:
2258         // initial marking in checkpointRootsInitialWork has been completed
2259         if (markFromRoots(true)) { // we were successful
2260           assert(_collectorState == Precleaning, "Collector state should "
2261             "have changed");
2262         } else {
2263           assert(_foregroundGCIsActive, "Internal state inconsistency");
2264         }
2265         break;
2266       case Precleaning:
2267         if (UseAdaptiveSizePolicy) {
2268           size_policy()->concurrent_precleaning_begin();
2269         }
2270         // marking from roots in markFromRoots has been completed
2271         preclean();
2272         if (UseAdaptiveSizePolicy) {
2273           size_policy()->concurrent_precleaning_end();
2274         }
2275         assert(_collectorState == AbortablePreclean ||
2276                _collectorState == FinalMarking,
2277                "Collector state should have changed");
2278         break;
2279       case AbortablePreclean:
2280         if (UseAdaptiveSizePolicy) {
2281         size_policy()->concurrent_phases_resume();
2282         }
2283         abortable_preclean();
2284         if (UseAdaptiveSizePolicy) {
2285           size_policy()->concurrent_precleaning_end();
2286         }
2287         assert(_collectorState == FinalMarking, "Collector state should "
2288           "have changed");
2289         break;
2290       case FinalMarking:
2291         {
2292           ReleaseForegroundGC x(this);
2293 
2294           VM_CMS_Final_Remark final_remark_op(this);
2295           VMThread::execute(&final_remark_op);
2296         }
2297         assert(_foregroundGCShouldWait, "block post-condition");
2298         break;
2299       case Sweeping:
2300         if (UseAdaptiveSizePolicy) {
2301           size_policy()->concurrent_sweeping_begin();
2302         }
2303         // final marking in checkpointRootsFinal has been completed
2304         sweep(true);
2305         assert(_collectorState == Resizing, "Collector state change "
2306           "to Resizing must be done under the free_list_lock");
2307         _full_gcs_since_conc_gc = 0;
2308 
2309         // Stop the timers for adaptive size policy for the concurrent phases
2310         if (UseAdaptiveSizePolicy) {
2311           size_policy()->concurrent_sweeping_end();
2312           size_policy()->concurrent_phases_end(gch->gc_cause(),
2313                                              gch->prev_gen(_cmsGen)->capacity(),
2314                                              _cmsGen->free());
2315         }
2316 
2317       case Resizing: {
2318         // Sweeping has been completed...
2319         // At this point the background collection has completed.
2320         // Don't move the call to compute_new_size() down
2321         // into code that might be executed if the background
2322         // collection was preempted.
2323         {
2324           ReleaseForegroundGC x(this);   // unblock FG collection
2325           MutexLockerEx       y(Heap_lock, Mutex::_no_safepoint_check_flag);
2326           CMSTokenSync        z(true);   // not strictly needed.
2327           if (_collectorState == Resizing) {
2328             compute_new_size();
2329             _collectorState = Resetting;
2330           } else {
2331             assert(_collectorState == Idling, "The state should only change"
2332                    " because the foreground collector has finished the collection");
2333           }
2334         }
2335         break;
2336       }
2337       case Resetting:
2338         // CMS heap resizing has been completed
2339         reset(true);
2340         assert(_collectorState == Idling, "Collector state should "
2341           "have changed");
2342 
2343         MetaspaceGC::set_should_concurrent_collect(false);
2344 
2345         stats().record_cms_end();
2346         // Don't move the concurrent_phases_end() and compute_new_size()
2347         // calls to here because a preempted background collection
2348         // has it's state set to "Resetting".
2349         break;
2350       case Idling:
2351       default:
2352         ShouldNotReachHere();
2353         break;
2354     }
2355     if (TraceCMSState) {
2356       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2357         Thread::current(), _collectorState);
2358     }
2359     assert(_foregroundGCShouldWait, "block post-condition");
2360   }
2361 
2362   // Should this be in gc_epilogue?
2363   collector_policy()->counters()->update_counters();
2364 
2365   {
2366     // Clear _foregroundGCShouldWait and, in the event that the
2367     // foreground collector is waiting, notify it, before
2368     // returning.
2369     MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2370     _foregroundGCShouldWait = false;
2371     if (_foregroundGCIsActive) {
2372       CGC_lock->notify();
2373     }
2374     assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2375            "Possible deadlock");
2376   }
2377   if (TraceCMSState) {
2378     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2379       " exiting collection CMS state %d",
2380       Thread::current(), _collectorState);
2381   }
2382   if (PrintGC && Verbose) {
2383     _cmsGen->print_heap_change(prev_used);
2384   }
2385 }
2386 
2387 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2388   assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2389          "Foreground collector should be waiting, not executing");
2390   assert(Thread::current()->is_VM_thread(), "A foreground collection"
2391     "may only be done by the VM Thread with the world stopped");
2392   assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2393          "VM thread should have CMS token");
2394 
2395   NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2396     true, gclog_or_tty);)
2397   if (UseAdaptiveSizePolicy) {
2398     size_policy()->ms_collection_begin();
2399   }
2400   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2401 
2402   HandleMark hm;  // Discard invalid handles created during verification
2403 
2404   if (VerifyBeforeGC &&
2405       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2406     Universe::verify(true);
2407   }
2408 
2409   // Snapshot the soft reference policy to be used in this collection cycle.
2410   ref_processor()->setup_policy(clear_all_soft_refs);
2411 
2412   bool init_mark_was_synchronous = false; // until proven otherwise
2413   while (_collectorState != Idling) {
2414     if (TraceCMSState) {
2415       gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2416         Thread::current(), _collectorState);
2417     }
2418     switch (_collectorState) {
2419       case InitialMarking:
2420         init_mark_was_synchronous = true;  // fact to be exploited in re-mark
2421         checkpointRootsInitial(false);
2422         assert(_collectorState == Marking, "Collector state should have changed"
2423           " within checkpointRootsInitial()");
2424         break;
2425       case Marking:
2426         // initial marking in checkpointRootsInitialWork has been completed
2427         if (VerifyDuringGC &&
2428             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2429           gclog_or_tty->print("Verify before initial mark: ");
2430           Universe::verify(true);
2431         }
2432         {
2433           bool res = markFromRoots(false);
2434           assert(res && _collectorState == FinalMarking, "Collector state should "
2435             "have changed");
2436           break;
2437         }
2438       case FinalMarking:
2439         if (VerifyDuringGC &&
2440             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2441           gclog_or_tty->print("Verify before re-mark: ");
2442           Universe::verify(true);
2443         }
2444         checkpointRootsFinal(false, clear_all_soft_refs,
2445                              init_mark_was_synchronous);
2446         assert(_collectorState == Sweeping, "Collector state should not "
2447           "have changed within checkpointRootsFinal()");
2448         break;
2449       case Sweeping:
2450         // final marking in checkpointRootsFinal has been completed
2451         if (VerifyDuringGC &&
2452             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2453           gclog_or_tty->print("Verify before sweep: ");
2454           Universe::verify(true);
2455         }
2456         sweep(false);
2457         assert(_collectorState == Resizing, "Incorrect state");
2458         break;
2459       case Resizing: {
2460         // Sweeping has been completed; the actual resize in this case
2461         // is done separately; nothing to be done in this state.
2462         _collectorState = Resetting;
2463         break;
2464       }
2465       case Resetting:
2466         // The heap has been resized.
2467         if (VerifyDuringGC &&
2468             GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2469           gclog_or_tty->print("Verify before reset: ");
2470           Universe::verify(true);
2471         }
2472         reset(false);
2473         assert(_collectorState == Idling, "Collector state should "
2474           "have changed");
2475         break;
2476       case Precleaning:
2477       case AbortablePreclean:
2478         // Elide the preclean phase
2479         _collectorState = FinalMarking;
2480         break;
2481       default:
2482         ShouldNotReachHere();
2483     }
2484     if (TraceCMSState) {
2485       gclog_or_tty->print_cr("  Thread " INTPTR_FORMAT " done - next CMS state %d",
2486         Thread::current(), _collectorState);
2487     }
2488   }
2489 
2490   if (UseAdaptiveSizePolicy) {
2491     GenCollectedHeap* gch = GenCollectedHeap::heap();
2492     size_policy()->ms_collection_end(gch->gc_cause());
2493   }
2494 
2495   if (VerifyAfterGC &&
2496       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2497     Universe::verify(true);
2498   }
2499   if (TraceCMSState) {
2500     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2501       " exiting collection CMS state %d",
2502       Thread::current(), _collectorState);
2503   }
2504 }
2505 
2506 bool CMSCollector::waitForForegroundGC() {
2507   bool res = false;
2508   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2509          "CMS thread should have CMS token");
2510   // Block the foreground collector until the
2511   // background collectors decides whether to
2512   // yield.
2513   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2514   _foregroundGCShouldWait = true;
2515   if (_foregroundGCIsActive) {
2516     // The background collector yields to the
2517     // foreground collector and returns a value
2518     // indicating that it has yielded.  The foreground
2519     // collector can proceed.
2520     res = true;
2521     _foregroundGCShouldWait = false;
2522     ConcurrentMarkSweepThread::clear_CMS_flag(
2523       ConcurrentMarkSweepThread::CMS_cms_has_token);
2524     ConcurrentMarkSweepThread::set_CMS_flag(
2525       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2526     // Get a possibly blocked foreground thread going
2527     CGC_lock->notify();
2528     if (TraceCMSState) {
2529       gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2530         Thread::current(), _collectorState);
2531     }
2532     while (_foregroundGCIsActive) {
2533       CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2534     }
2535     ConcurrentMarkSweepThread::set_CMS_flag(
2536       ConcurrentMarkSweepThread::CMS_cms_has_token);
2537     ConcurrentMarkSweepThread::clear_CMS_flag(
2538       ConcurrentMarkSweepThread::CMS_cms_wants_token);
2539   }
2540   if (TraceCMSState) {
2541     gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2542       Thread::current(), _collectorState);
2543   }
2544   return res;
2545 }
2546 
2547 // Because of the need to lock the free lists and other structures in
2548 // the collector, common to all the generations that the collector is
2549 // collecting, we need the gc_prologues of individual CMS generations
2550 // delegate to their collector. It may have been simpler had the
2551 // current infrastructure allowed one to call a prologue on a
2552 // collector. In the absence of that we have the generation's
2553 // prologue delegate to the collector, which delegates back
2554 // some "local" work to a worker method in the individual generations
2555 // that it's responsible for collecting, while itself doing any
2556 // work common to all generations it's responsible for. A similar
2557 // comment applies to the  gc_epilogue()'s.
2558 // The role of the varaible _between_prologue_and_epilogue is to
2559 // enforce the invocation protocol.
2560 void CMSCollector::gc_prologue(bool full) {
2561   // Call gc_prologue_work() for the CMSGen
2562   // we are responsible for.
2563 
2564   // The following locking discipline assumes that we are only called
2565   // when the world is stopped.
2566   assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2567 
2568   // The CMSCollector prologue must call the gc_prologues for the
2569   // "generations" that it's responsible
2570   // for.
2571 
2572   assert(   Thread::current()->is_VM_thread()
2573          || (   CMSScavengeBeforeRemark
2574              && Thread::current()->is_ConcurrentGC_thread()),
2575          "Incorrect thread type for prologue execution");
2576 
2577   if (_between_prologue_and_epilogue) {
2578     // We have already been invoked; this is a gc_prologue delegation
2579     // from yet another CMS generation that we are responsible for, just
2580     // ignore it since all relevant work has already been done.
2581     return;
2582   }
2583 
2584   // set a bit saying prologue has been called; cleared in epilogue
2585   _between_prologue_and_epilogue = true;
2586   // Claim locks for common data structures, then call gc_prologue_work()
2587   // for each CMSGen.
2588 
2589   getFreelistLocks();   // gets free list locks on constituent spaces
2590   bitMapLock()->lock_without_safepoint_check();
2591 
2592   // Should call gc_prologue_work() for all cms gens we are responsible for
2593   bool duringMarking =    _collectorState >= Marking
2594                          && _collectorState < Sweeping;
2595 
2596   // The young collections clear the modified oops state, which tells if
2597   // there are any modified oops in the class. The remark phase also needs
2598   // that information. Tell the young collection to save the union of all
2599   // modified klasses.
2600   if (duringMarking) {
2601     _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2602   }
2603 
2604   bool registerClosure = duringMarking;
2605 
2606   ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2607                                                &_modUnionClosurePar
2608                                                : &_modUnionClosure;
2609   _cmsGen->gc_prologue_work(full, registerClosure, muc);
2610 
2611   if (!full) {
2612     stats().record_gc0_begin();
2613   }
2614 }
2615 
2616 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2617   // Delegate to CMScollector which knows how to coordinate between
2618   // this and any other CMS generations that it is responsible for
2619   // collecting.
2620   collector()->gc_prologue(full);
2621 }
2622 
2623 // This is a "private" interface for use by this generation's CMSCollector.
2624 // Not to be called directly by any other entity (for instance,
2625 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2626 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2627   bool registerClosure, ModUnionClosure* modUnionClosure) {
2628   assert(!incremental_collection_failed(), "Shouldn't be set yet");
2629   assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2630     "Should be NULL");
2631   if (registerClosure) {
2632     cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2633   }
2634   cmsSpace()->gc_prologue();
2635   // Clear stat counters
2636   NOT_PRODUCT(
2637     assert(_numObjectsPromoted == 0, "check");
2638     assert(_numWordsPromoted   == 0, "check");
2639     if (Verbose && PrintGC) {
2640       gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2641                           SIZE_FORMAT" bytes concurrently",
2642       _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2643     }
2644     _numObjectsAllocated = 0;
2645     _numWordsAllocated   = 0;
2646   )
2647 }
2648 
2649 void CMSCollector::gc_epilogue(bool full) {
2650   // The following locking discipline assumes that we are only called
2651   // when the world is stopped.
2652   assert(SafepointSynchronize::is_at_safepoint(),
2653          "world is stopped assumption");
2654 
2655   // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2656   // if linear allocation blocks need to be appropriately marked to allow the
2657   // the blocks to be parsable. We also check here whether we need to nudge the
2658   // CMS collector thread to start a new cycle (if it's not already active).
2659   assert(   Thread::current()->is_VM_thread()
2660          || (   CMSScavengeBeforeRemark
2661              && Thread::current()->is_ConcurrentGC_thread()),
2662          "Incorrect thread type for epilogue execution");
2663 
2664   if (!_between_prologue_and_epilogue) {
2665     // We have already been invoked; this is a gc_epilogue delegation
2666     // from yet another CMS generation that we are responsible for, just
2667     // ignore it since all relevant work has already been done.
2668     return;
2669   }
2670   assert(haveFreelistLocks(), "must have freelist locks");
2671   assert_lock_strong(bitMapLock());
2672 
2673   _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2674 
2675   _cmsGen->gc_epilogue_work(full);
2676 
2677   if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2678     // in case sampling was not already enabled, enable it
2679     _start_sampling = true;
2680   }
2681   // reset _eden_chunk_array so sampling starts afresh
2682   _eden_chunk_index = 0;
2683 
2684   size_t cms_used   = _cmsGen->cmsSpace()->used();
2685 
2686   // update performance counters - this uses a special version of
2687   // update_counters() that allows the utilization to be passed as a
2688   // parameter, avoiding multiple calls to used().
2689   //
2690   _cmsGen->update_counters(cms_used);
2691 
2692   if (CMSIncrementalMode) {
2693     icms_update_allocation_limits();
2694   }
2695 
2696   bitMapLock()->unlock();
2697   releaseFreelistLocks();
2698 
2699   if (!CleanChunkPoolAsync) {
2700     Chunk::clean_chunk_pool();
2701   }
2702 
2703   _between_prologue_and_epilogue = false;  // ready for next cycle
2704 }
2705 
2706 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2707   collector()->gc_epilogue(full);
2708 
2709   // Also reset promotion tracking in par gc thread states.
2710   if (CollectedHeap::use_parallel_gc_threads()) {
2711     for (uint i = 0; i < ParallelGCThreads; i++) {
2712       _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2713     }
2714   }
2715 }
2716 
2717 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2718   assert(!incremental_collection_failed(), "Should have been cleared");
2719   cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2720   cmsSpace()->gc_epilogue();
2721     // Print stat counters
2722   NOT_PRODUCT(
2723     assert(_numObjectsAllocated == 0, "check");
2724     assert(_numWordsAllocated == 0, "check");
2725     if (Verbose && PrintGC) {
2726       gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2727                           SIZE_FORMAT" bytes",
2728                  _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2729     }
2730     _numObjectsPromoted = 0;
2731     _numWordsPromoted   = 0;
2732   )
2733 
2734   if (PrintGC && Verbose) {
2735     // Call down the chain in contiguous_available needs the freelistLock
2736     // so print this out before releasing the freeListLock.
2737     gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2738                         contiguous_available());
2739   }
2740 }
2741 
2742 #ifndef PRODUCT
2743 bool CMSCollector::have_cms_token() {
2744   Thread* thr = Thread::current();
2745   if (thr->is_VM_thread()) {
2746     return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2747   } else if (thr->is_ConcurrentGC_thread()) {
2748     return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2749   } else if (thr->is_GC_task_thread()) {
2750     return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2751            ParGCRareEvent_lock->owned_by_self();
2752   }
2753   return false;
2754 }
2755 #endif
2756 
2757 // Check reachability of the given heap address in CMS generation,
2758 // treating all other generations as roots.
2759 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2760   // We could "guarantee" below, rather than assert, but i'll
2761   // leave these as "asserts" so that an adventurous debugger
2762   // could try this in the product build provided some subset of
2763   // the conditions were met, provided they were intersted in the
2764   // results and knew that the computation below wouldn't interfere
2765   // with other concurrent computations mutating the structures
2766   // being read or written.
2767   assert(SafepointSynchronize::is_at_safepoint(),
2768          "Else mutations in object graph will make answer suspect");
2769   assert(have_cms_token(), "Should hold cms token");
2770   assert(haveFreelistLocks(), "must hold free list locks");
2771   assert_lock_strong(bitMapLock());
2772 
2773   // Clear the marking bit map array before starting, but, just
2774   // for kicks, first report if the given address is already marked
2775   gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2776                 _markBitMap.isMarked(addr) ? "" : " not");
2777 
2778   if (verify_after_remark()) {
2779     MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2780     bool result = verification_mark_bm()->isMarked(addr);
2781     gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2782                            result ? "IS" : "is NOT");
2783     return result;
2784   } else {
2785     gclog_or_tty->print_cr("Could not compute result");
2786     return false;
2787   }
2788 }
2789 
2790 ////////////////////////////////////////////////////////
2791 // CMS Verification Support
2792 ////////////////////////////////////////////////////////
2793 // Following the remark phase, the following invariant
2794 // should hold -- each object in the CMS heap which is
2795 // marked in markBitMap() should be marked in the verification_mark_bm().
2796 
2797 class VerifyMarkedClosure: public BitMapClosure {
2798   CMSBitMap* _marks;
2799   bool       _failed;
2800 
2801  public:
2802   VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2803 
2804   bool do_bit(size_t offset) {
2805     HeapWord* addr = _marks->offsetToHeapWord(offset);
2806     if (!_marks->isMarked(addr)) {
2807       oop(addr)->print_on(gclog_or_tty);
2808       gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2809       _failed = true;
2810     }
2811     return true;
2812   }
2813 
2814   bool failed() { return _failed; }
2815 };
2816 
2817 bool CMSCollector::verify_after_remark() {
2818   gclog_or_tty->print(" [Verifying CMS Marking... ");
2819   MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2820   static bool init = false;
2821 
2822   assert(SafepointSynchronize::is_at_safepoint(),
2823          "Else mutations in object graph will make answer suspect");
2824   assert(have_cms_token(),
2825          "Else there may be mutual interference in use of "
2826          " verification data structures");
2827   assert(_collectorState > Marking && _collectorState <= Sweeping,
2828          "Else marking info checked here may be obsolete");
2829   assert(haveFreelistLocks(), "must hold free list locks");
2830   assert_lock_strong(bitMapLock());
2831 
2832 
2833   // Allocate marking bit map if not already allocated
2834   if (!init) { // first time
2835     if (!verification_mark_bm()->allocate(_span)) {
2836       return false;
2837     }
2838     init = true;
2839   }
2840 
2841   assert(verification_mark_stack()->isEmpty(), "Should be empty");
2842 
2843   // Turn off refs discovery -- so we will be tracing through refs.
2844   // This is as intended, because by this time
2845   // GC must already have cleared any refs that need to be cleared,
2846   // and traced those that need to be marked; moreover,
2847   // the marking done here is not going to intefere in any
2848   // way with the marking information used by GC.
2849   NoRefDiscovery no_discovery(ref_processor());
2850 
2851   COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2852 
2853   // Clear any marks from a previous round
2854   verification_mark_bm()->clear_all();
2855   assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2856   verify_work_stacks_empty();
2857 
2858   GenCollectedHeap* gch = GenCollectedHeap::heap();
2859   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
2860   // Update the saved marks which may affect the root scans.
2861   gch->save_marks();
2862 
2863   if (CMSRemarkVerifyVariant == 1) {
2864     // In this first variant of verification, we complete
2865     // all marking, then check if the new marks-verctor is
2866     // a subset of the CMS marks-vector.
2867     verify_after_remark_work_1();
2868   } else if (CMSRemarkVerifyVariant == 2) {
2869     // In this second variant of verification, we flag an error
2870     // (i.e. an object reachable in the new marks-vector not reachable
2871     // in the CMS marks-vector) immediately, also indicating the
2872     // identify of an object (A) that references the unmarked object (B) --
2873     // presumably, a mutation to A failed to be picked up by preclean/remark?
2874     verify_after_remark_work_2();
2875   } else {
2876     warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2877             CMSRemarkVerifyVariant);
2878   }
2879   gclog_or_tty->print(" done] ");
2880   return true;
2881 }
2882 
2883 void CMSCollector::verify_after_remark_work_1() {
2884   ResourceMark rm;
2885   HandleMark  hm;
2886   GenCollectedHeap* gch = GenCollectedHeap::heap();
2887 
2888   // Get a clear set of claim bits for the strong roots processing to work with.
2889   ClassLoaderDataGraph::clear_claimed_marks();
2890 
2891   // Mark from roots one level into CMS
2892   MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2893   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2894 
2895   gch->gen_process_strong_roots(_cmsGen->level(),
2896                                 true,   // younger gens are roots
2897                                 true,   // activate StrongRootsScope
2898                                 false,  // not scavenging
2899                                 SharedHeap::ScanningOption(roots_scanning_options()),
2900                                 &notOlder,
2901                                 true,   // walk code active on stacks
2902                                 NULL,
2903                                 NULL); // SSS: Provide correct closure
2904 
2905   // Now mark from the roots
2906   MarkFromRootsClosure markFromRootsClosure(this, _span,
2907     verification_mark_bm(), verification_mark_stack(),
2908     false /* don't yield */, true /* verifying */);
2909   assert(_restart_addr == NULL, "Expected pre-condition");
2910   verification_mark_bm()->iterate(&markFromRootsClosure);
2911   while (_restart_addr != NULL) {
2912     // Deal with stack overflow: by restarting at the indicated
2913     // address.
2914     HeapWord* ra = _restart_addr;
2915     markFromRootsClosure.reset(ra);
2916     _restart_addr = NULL;
2917     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2918   }
2919   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2920   verify_work_stacks_empty();
2921 
2922   // Marking completed -- now verify that each bit marked in
2923   // verification_mark_bm() is also marked in markBitMap(); flag all
2924   // errors by printing corresponding objects.
2925   VerifyMarkedClosure vcl(markBitMap());
2926   verification_mark_bm()->iterate(&vcl);
2927   if (vcl.failed()) {
2928     gclog_or_tty->print("Verification failed");
2929     Universe::heap()->print_on(gclog_or_tty);
2930     fatal("CMS: failed marking verification after remark");
2931   }
2932 }
2933 
2934 class VerifyKlassOopsKlassClosure : public KlassClosure {
2935   class VerifyKlassOopsClosure : public OopClosure {
2936     CMSBitMap* _bitmap;
2937    public:
2938     VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2939     void do_oop(oop* p)       { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2940     void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2941   } _oop_closure;
2942  public:
2943   VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2944   void do_klass(Klass* k) {
2945     k->oops_do(&_oop_closure);
2946   }
2947 };
2948 
2949 void CMSCollector::verify_after_remark_work_2() {
2950   ResourceMark rm;
2951   HandleMark  hm;
2952   GenCollectedHeap* gch = GenCollectedHeap::heap();
2953 
2954   // Get a clear set of claim bits for the strong roots processing to work with.
2955   ClassLoaderDataGraph::clear_claimed_marks();
2956 
2957   // Mark from roots one level into CMS
2958   MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2959                                      markBitMap());
2960   CMKlassClosure klass_closure(&notOlder);
2961 
2962   gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2963   gch->gen_process_strong_roots(_cmsGen->level(),
2964                                 true,   // younger gens are roots
2965                                 true,   // activate StrongRootsScope
2966                                 false,  // not scavenging
2967                                 SharedHeap::ScanningOption(roots_scanning_options()),
2968                                 &notOlder,
2969                                 true,   // walk code active on stacks
2970                                 NULL,
2971                                 &klass_closure);
2972 
2973   // Now mark from the roots
2974   MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2975     verification_mark_bm(), markBitMap(), verification_mark_stack());
2976   assert(_restart_addr == NULL, "Expected pre-condition");
2977   verification_mark_bm()->iterate(&markFromRootsClosure);
2978   while (_restart_addr != NULL) {
2979     // Deal with stack overflow: by restarting at the indicated
2980     // address.
2981     HeapWord* ra = _restart_addr;
2982     markFromRootsClosure.reset(ra);
2983     _restart_addr = NULL;
2984     verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2985   }
2986   assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2987   verify_work_stacks_empty();
2988 
2989   VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2990   ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2991 
2992   // Marking completed -- now verify that each bit marked in
2993   // verification_mark_bm() is also marked in markBitMap(); flag all
2994   // errors by printing corresponding objects.
2995   VerifyMarkedClosure vcl(markBitMap());
2996   verification_mark_bm()->iterate(&vcl);
2997   assert(!vcl.failed(), "Else verification above should not have succeeded");
2998 }
2999 
3000 void ConcurrentMarkSweepGeneration::save_marks() {
3001   // delegate to CMS space
3002   cmsSpace()->save_marks();
3003   for (uint i = 0; i < ParallelGCThreads; i++) {
3004     _par_gc_thread_states[i]->promo.startTrackingPromotions();
3005   }
3006 }
3007 
3008 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3009   return cmsSpace()->no_allocs_since_save_marks();
3010 }
3011 
3012 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix)    \
3013                                                                 \
3014 void ConcurrentMarkSweepGeneration::                            \
3015 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) {   \
3016   cl->set_generation(this);                                     \
3017   cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl);      \
3018   cl->reset_generation();                                       \
3019   save_marks();                                                 \
3020 }
3021 
3022 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3023 
3024 void
3025 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3026 {
3027   // Not currently implemented; need to do the following. -- ysr.
3028   // dld -- I think that is used for some sort of allocation profiler.  So it
3029   // really means the objects allocated by the mutator since the last
3030   // GC.  We could potentially implement this cheaply by recording only
3031   // the direct allocations in a side data structure.
3032   //
3033   // I think we probably ought not to be required to support these
3034   // iterations at any arbitrary point; I think there ought to be some
3035   // call to enable/disable allocation profiling in a generation/space,
3036   // and the iterator ought to return the objects allocated in the
3037   // gen/space since the enable call, or the last iterator call (which
3038   // will probably be at a GC.)  That way, for gens like CM&S that would
3039   // require some extra data structure to support this, we only pay the
3040   // cost when it's in use...
3041   cmsSpace()->object_iterate_since_last_GC(blk);
3042 }
3043 
3044 void
3045 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3046   cl->set_generation(this);
3047   younger_refs_in_space_iterate(_cmsSpace, cl);
3048   cl->reset_generation();
3049 }
3050 
3051 void
3052 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3053   if (freelistLock()->owned_by_self()) {
3054     Generation::oop_iterate(mr, cl);
3055   } else {
3056     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3057     Generation::oop_iterate(mr, cl);
3058   }
3059 }
3060 
3061 void
3062 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3063   if (freelistLock()->owned_by_self()) {
3064     Generation::oop_iterate(cl);
3065   } else {
3066     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3067     Generation::oop_iterate(cl);
3068   }
3069 }
3070 
3071 void
3072 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3073   if (freelistLock()->owned_by_self()) {
3074     Generation::object_iterate(cl);
3075   } else {
3076     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3077     Generation::object_iterate(cl);
3078   }
3079 }
3080 
3081 void
3082 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3083   if (freelistLock()->owned_by_self()) {
3084     Generation::safe_object_iterate(cl);
3085   } else {
3086     MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3087     Generation::safe_object_iterate(cl);
3088   }
3089 }
3090 
3091 void
3092 ConcurrentMarkSweepGeneration::post_compact() {
3093 }
3094 
3095 void
3096 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3097   // Fix the linear allocation blocks to look like free blocks.
3098 
3099   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3100   // are not called when the heap is verified during universe initialization and
3101   // at vm shutdown.
3102   if (freelistLock()->owned_by_self()) {
3103     cmsSpace()->prepare_for_verify();
3104   } else {
3105     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3106     cmsSpace()->prepare_for_verify();
3107   }
3108 }
3109 
3110 void
3111 ConcurrentMarkSweepGeneration::verify() {
3112   // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3113   // are not called when the heap is verified during universe initialization and
3114   // at vm shutdown.
3115   if (freelistLock()->owned_by_self()) {
3116     cmsSpace()->verify();
3117   } else {
3118     MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3119     cmsSpace()->verify();
3120   }
3121 }
3122 
3123 void CMSCollector::verify() {
3124   _cmsGen->verify();
3125 }
3126 
3127 #ifndef PRODUCT
3128 bool CMSCollector::overflow_list_is_empty() const {
3129   assert(_num_par_pushes >= 0, "Inconsistency");
3130   if (_overflow_list == NULL) {
3131     assert(_num_par_pushes == 0, "Inconsistency");
3132   }
3133   return _overflow_list == NULL;
3134 }
3135 
3136 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3137 // merely consolidate assertion checks that appear to occur together frequently.
3138 void CMSCollector::verify_work_stacks_empty() const {
3139   assert(_markStack.isEmpty(), "Marking stack should be empty");
3140   assert(overflow_list_is_empty(), "Overflow list should be empty");
3141 }
3142 
3143 void CMSCollector::verify_overflow_empty() const {
3144   assert(overflow_list_is_empty(), "Overflow list should be empty");
3145   assert(no_preserved_marks(), "No preserved marks");
3146 }
3147 #endif // PRODUCT
3148 
3149 // Decide if we want to enable class unloading as part of the
3150 // ensuing concurrent GC cycle. We will collect and
3151 // unload classes if it's the case that:
3152 // (1) an explicit gc request has been made and the flag
3153 //     ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3154 // (2) (a) class unloading is enabled at the command line, and
3155 //     (b) old gen is getting really full
3156 // NOTE: Provided there is no change in the state of the heap between
3157 // calls to this method, it should have idempotent results. Moreover,
3158 // its results should be monotonically increasing (i.e. going from 0 to 1,
3159 // but not 1 to 0) between successive calls between which the heap was
3160 // not collected. For the implementation below, it must thus rely on
3161 // the property that concurrent_cycles_since_last_unload()
3162 // will not decrease unless a collection cycle happened and that
3163 // _cmsGen->is_too_full() are
3164 // themselves also monotonic in that sense. See check_monotonicity()
3165 // below.
3166 void CMSCollector::update_should_unload_classes() {
3167   _should_unload_classes = false;
3168   // Condition 1 above
3169   if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3170     _should_unload_classes = true;
3171   } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3172     // Disjuncts 2.b.(i,ii,iii) above
3173     _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3174                               CMSClassUnloadingMaxInterval)
3175                            || _cmsGen->is_too_full();
3176   }
3177 }
3178 
3179 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3180   bool res = should_concurrent_collect();
3181   res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3182   return res;
3183 }
3184 
3185 void CMSCollector::setup_cms_unloading_and_verification_state() {
3186   const  bool should_verify =   VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3187                              || VerifyBeforeExit;
3188   const  int  rso           =   SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3189 
3190   if (should_unload_classes()) {   // Should unload classes this cycle
3191     remove_root_scanning_option(rso);  // Shrink the root set appropriately
3192     set_verifying(should_verify);    // Set verification state for this cycle
3193     return;                            // Nothing else needs to be done at this time
3194   }
3195 
3196   // Not unloading classes this cycle
3197   assert(!should_unload_classes(), "Inconsitency!");
3198   if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3199     // Include symbols, strings and code cache elements to prevent their resurrection.
3200     add_root_scanning_option(rso);
3201     set_verifying(true);
3202   } else if (verifying() && !should_verify) {
3203     // We were verifying, but some verification flags got disabled.
3204     set_verifying(false);
3205     // Exclude symbols, strings and code cache elements from root scanning to
3206     // reduce IM and RM pauses.
3207     remove_root_scanning_option(rso);
3208   }
3209 }
3210 
3211 
3212 #ifndef PRODUCT
3213 HeapWord* CMSCollector::block_start(const void* p) const {
3214   const HeapWord* addr = (HeapWord*)p;
3215   if (_span.contains(p)) {
3216     if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3217       return _cmsGen->cmsSpace()->block_start(p);
3218     }
3219   }
3220   return NULL;
3221 }
3222 #endif
3223 
3224 HeapWord*
3225 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3226                                                    bool   tlab,
3227                                                    bool   parallel) {
3228   CMSSynchronousYieldRequest yr;
3229   assert(!tlab, "Can't deal with TLAB allocation");
3230   MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3231   expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3232     CMSExpansionCause::_satisfy_allocation);
3233   if (GCExpandToAllocateDelayMillis > 0) {
3234     os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3235   }
3236   return have_lock_and_allocate(word_size, tlab);
3237 }
3238 
3239 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3240 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3241 // to CardGeneration and share it...
3242 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3243   return CardGeneration::expand(bytes, expand_bytes);
3244 }
3245 
3246 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3247   CMSExpansionCause::Cause cause)
3248 {
3249 
3250   bool success = expand(bytes, expand_bytes);
3251 
3252   // remember why we expanded; this information is used
3253   // by shouldConcurrentCollect() when making decisions on whether to start
3254   // a new CMS cycle.
3255   if (success) {
3256     set_expansion_cause(cause);
3257     if (PrintGCDetails && Verbose) {
3258       gclog_or_tty->print_cr("Expanded CMS gen for %s",
3259         CMSExpansionCause::to_string(cause));
3260     }
3261   }
3262 }
3263 
3264 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3265   HeapWord* res = NULL;
3266   MutexLocker x(ParGCRareEvent_lock);
3267   while (true) {
3268     // Expansion by some other thread might make alloc OK now:
3269     res = ps->lab.alloc(word_sz);
3270     if (res != NULL) return res;
3271     // If there's not enough expansion space available, give up.
3272     if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3273       return NULL;
3274     }
3275     // Otherwise, we try expansion.
3276     expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3277       CMSExpansionCause::_allocate_par_lab);
3278     // Now go around the loop and try alloc again;
3279     // A competing par_promote might beat us to the expansion space,
3280     // so we may go around the loop again if promotion fails agaion.
3281     if (GCExpandToAllocateDelayMillis > 0) {
3282       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3283     }
3284   }
3285 }
3286 
3287 
3288 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3289   PromotionInfo* promo) {
3290   MutexLocker x(ParGCRareEvent_lock);
3291   size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3292   while (true) {
3293     // Expansion by some other thread might make alloc OK now:
3294     if (promo->ensure_spooling_space()) {
3295       assert(promo->has_spooling_space(),
3296              "Post-condition of successful ensure_spooling_space()");
3297       return true;
3298     }
3299     // If there's not enough expansion space available, give up.
3300     if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3301       return false;
3302     }
3303     // Otherwise, we try expansion.
3304     expand(refill_size_bytes, MinHeapDeltaBytes,
3305       CMSExpansionCause::_allocate_par_spooling_space);
3306     // Now go around the loop and try alloc again;
3307     // A competing allocation might beat us to the expansion space,
3308     // so we may go around the loop again if allocation fails again.
3309     if (GCExpandToAllocateDelayMillis > 0) {
3310       os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3311     }
3312   }
3313 }
3314 
3315 
3316 
3317 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3318   assert_locked_or_safepoint(Heap_lock);
3319   size_t size = ReservedSpace::page_align_size_down(bytes);
3320   if (size > 0) {
3321     shrink_by(size);
3322   }
3323 }
3324 
3325 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3326   assert_locked_or_safepoint(Heap_lock);
3327   bool result = _virtual_space.expand_by(bytes);
3328   if (result) {
3329     HeapWord* old_end = _cmsSpace->end();
3330     size_t new_word_size =
3331       heap_word_size(_virtual_space.committed_size());
3332     MemRegion mr(_cmsSpace->bottom(), new_word_size);
3333     _bts->resize(new_word_size);  // resize the block offset shared array
3334     Universe::heap()->barrier_set()->resize_covered_region(mr);
3335     // Hmmmm... why doesn't CFLS::set_end verify locking?
3336     // This is quite ugly; FIX ME XXX
3337     _cmsSpace->assert_locked(freelistLock());
3338     _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3339 
3340     // update the space and generation capacity counters
3341     if (UsePerfData) {
3342       _space_counters->update_capacity();
3343       _gen_counters->update_all();
3344     }
3345 
3346     if (Verbose && PrintGC) {
3347       size_t new_mem_size = _virtual_space.committed_size();
3348       size_t old_mem_size = new_mem_size - bytes;
3349       gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3350                     name(), old_mem_size/K, bytes/K, new_mem_size/K);
3351     }
3352   }
3353   return result;
3354 }
3355 
3356 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3357   assert_locked_or_safepoint(Heap_lock);
3358   bool success = true;
3359   const size_t remaining_bytes = _virtual_space.uncommitted_size();
3360   if (remaining_bytes > 0) {
3361     success = grow_by(remaining_bytes);
3362     DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3363   }
3364   return success;
3365 }
3366 
3367 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3368   assert_locked_or_safepoint(Heap_lock);
3369   assert_lock_strong(freelistLock());
3370   // XXX Fix when compaction is implemented.
3371   warning("Shrinking of CMS not yet implemented");
3372   return;
3373 }
3374 
3375 
3376 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3377 // phases.
3378 class CMSPhaseAccounting: public StackObj {
3379  public:
3380   CMSPhaseAccounting(CMSCollector *collector,
3381                      const char *phase,
3382                      bool print_cr = true);
3383   ~CMSPhaseAccounting();
3384 
3385  private:
3386   CMSCollector *_collector;
3387   const char *_phase;
3388   elapsedTimer _wallclock;
3389   bool _print_cr;
3390 
3391  public:
3392   // Not MT-safe; so do not pass around these StackObj's
3393   // where they may be accessed by other threads.
3394   jlong wallclock_millis() {
3395     assert(_wallclock.is_active(), "Wall clock should not stop");
3396     _wallclock.stop();  // to record time
3397     jlong ret = _wallclock.milliseconds();
3398     _wallclock.start(); // restart
3399     return ret;
3400   }
3401 };
3402 
3403 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3404                                        const char *phase,
3405                                        bool print_cr) :
3406   _collector(collector), _phase(phase), _print_cr(print_cr) {
3407 
3408   if (PrintCMSStatistics != 0) {
3409     _collector->resetYields();
3410   }
3411   if (PrintGCDetails && PrintGCTimeStamps) {
3412     gclog_or_tty->date_stamp(PrintGCDateStamps);
3413     gclog_or_tty->stamp();
3414     gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3415       _collector->cmsGen()->short_name(), _phase);
3416   }
3417   _collector->resetTimer();
3418   _wallclock.start();
3419   _collector->startTimer();
3420 }
3421 
3422 CMSPhaseAccounting::~CMSPhaseAccounting() {
3423   assert(_wallclock.is_active(), "Wall clock should not have stopped");
3424   _collector->stopTimer();
3425   _wallclock.stop();
3426   if (PrintGCDetails) {
3427     gclog_or_tty->date_stamp(PrintGCDateStamps);
3428     gclog_or_tty->stamp(PrintGCTimeStamps);
3429     gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3430                  _collector->cmsGen()->short_name(),
3431                  _phase, _collector->timerValue(), _wallclock.seconds());
3432     if (_print_cr) {
3433       gclog_or_tty->print_cr("");
3434     }
3435     if (PrintCMSStatistics != 0) {
3436       gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3437                     _collector->yields());
3438     }
3439   }
3440 }
3441 
3442 // CMS work
3443 
3444 // Checkpoint the roots into this generation from outside
3445 // this generation. [Note this initial checkpoint need only
3446 // be approximate -- we'll do a catch up phase subsequently.]
3447 void CMSCollector::checkpointRootsInitial(bool asynch) {
3448   assert(_collectorState == InitialMarking, "Wrong collector state");
3449   check_correct_thread_executing();
3450   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3451 
3452   ReferenceProcessor* rp = ref_processor();
3453   SpecializationStats::clear();
3454   assert(_restart_addr == NULL, "Control point invariant");
3455   if (asynch) {
3456     // acquire locks for subsequent manipulations
3457     MutexLockerEx x(bitMapLock(),
3458                     Mutex::_no_safepoint_check_flag);
3459     checkpointRootsInitialWork(asynch);
3460     // enable ("weak") refs discovery
3461     rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3462     _collectorState = Marking;
3463   } else {
3464     // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3465     // which recognizes if we are a CMS generation, and doesn't try to turn on
3466     // discovery; verify that they aren't meddling.
3467     assert(!rp->discovery_is_atomic(),
3468            "incorrect setting of discovery predicate");
3469     assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3470            "ref discovery for this generation kind");
3471     // already have locks
3472     checkpointRootsInitialWork(asynch);
3473     // now enable ("weak") refs discovery
3474     rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3475     _collectorState = Marking;
3476   }
3477   SpecializationStats::print();
3478 }
3479 
3480 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3481   assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3482   assert(_collectorState == InitialMarking, "just checking");
3483 
3484   // If there has not been a GC[n-1] since last GC[n] cycle completed,
3485   // precede our marking with a collection of all
3486   // younger generations to keep floating garbage to a minimum.
3487   // XXX: we won't do this for now -- it's an optimization to be done later.
3488 
3489   // already have locks
3490   assert_lock_strong(bitMapLock());
3491   assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3492 
3493   // Setup the verification and class unloading state for this
3494   // CMS collection cycle.
3495   setup_cms_unloading_and_verification_state();
3496 
3497   NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3498     PrintGCDetails && Verbose, true, gclog_or_tty);)
3499   if (UseAdaptiveSizePolicy) {
3500     size_policy()->checkpoint_roots_initial_begin();
3501   }
3502 
3503   // Reset all the PLAB chunk arrays if necessary.
3504   if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3505     reset_survivor_plab_arrays();
3506   }
3507 
3508   ResourceMark rm;
3509   HandleMark  hm;
3510 
3511   FalseClosure falseClosure;
3512   // In the case of a synchronous collection, we will elide the
3513   // remark step, so it's important to catch all the nmethod oops
3514   // in this step.
3515   // The final 'true' flag to gen_process_strong_roots will ensure this.
3516   // If 'async' is true, we can relax the nmethod tracing.
3517   MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3518   GenCollectedHeap* gch = GenCollectedHeap::heap();
3519 
3520   verify_work_stacks_empty();
3521   verify_overflow_empty();
3522 
3523   gch->ensure_parsability(false);  // fill TLABs, but no need to retire them
3524   // Update the saved marks which may affect the root scans.
3525   gch->save_marks();
3526 
3527   // weak reference processing has not started yet.
3528   ref_processor()->set_enqueuing_is_done(false);
3529 
3530   // Need to remember all newly created CLDs,
3531   // so that we can guarantee that the remark finds them.
3532   ClassLoaderDataGraph::remember_new_clds(true);
3533 
3534   // Whenever a CLD is found, it will be claimed before proceeding to mark
3535   // the klasses. The claimed marks need to be cleared before marking starts.
3536   ClassLoaderDataGraph::clear_claimed_marks();
3537 
3538   CMKlassClosure klass_closure(&notOlder);
3539   {
3540     COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3541     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3542     gch->gen_process_strong_roots(_cmsGen->level(),
3543                                   true,   // younger gens are roots
3544                                   true,   // activate StrongRootsScope
3545                                   false,  // not scavenging
3546                                   SharedHeap::ScanningOption(roots_scanning_options()),
3547                                   &notOlder,
3548                                   true,   // walk all of code cache if (so & SO_CodeCache)
3549                                   NULL,
3550                                   &klass_closure);
3551   }
3552 
3553   // Clear mod-union table; it will be dirtied in the prologue of
3554   // CMS generation per each younger generation collection.
3555 
3556   assert(_modUnionTable.isAllClear(),
3557        "Was cleared in most recent final checkpoint phase"
3558        " or no bits are set in the gc_prologue before the start of the next "
3559        "subsequent marking phase.");
3560 
3561   assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3562 
3563   // Save the end of the used_region of the constituent generations
3564   // to be used to limit the extent of sweep in each generation.
3565   save_sweep_limits();
3566   if (UseAdaptiveSizePolicy) {
3567     size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3568   }
3569   verify_overflow_empty();
3570 }
3571 
3572 bool CMSCollector::markFromRoots(bool asynch) {
3573   // we might be tempted to assert that:
3574   // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3575   //        "inconsistent argument?");
3576   // However that wouldn't be right, because it's possible that
3577   // a safepoint is indeed in progress as a younger generation
3578   // stop-the-world GC happens even as we mark in this generation.
3579   assert(_collectorState == Marking, "inconsistent state?");
3580   check_correct_thread_executing();
3581   verify_overflow_empty();
3582 
3583   bool res;
3584   if (asynch) {
3585 
3586     // Start the timers for adaptive size policy for the concurrent phases
3587     // Do it here so that the foreground MS can use the concurrent
3588     // timer since a foreground MS might has the sweep done concurrently
3589     // or STW.
3590     if (UseAdaptiveSizePolicy) {
3591       size_policy()->concurrent_marking_begin();
3592     }
3593 
3594     // Weak ref discovery note: We may be discovering weak
3595     // refs in this generation concurrent (but interleaved) with
3596     // weak ref discovery by a younger generation collector.
3597 
3598     CMSTokenSyncWithLocks ts(true, bitMapLock());
3599     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3600     CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3601     res = markFromRootsWork(asynch);
3602     if (res) {
3603       _collectorState = Precleaning;
3604     } else { // We failed and a foreground collection wants to take over
3605       assert(_foregroundGCIsActive, "internal state inconsistency");
3606       assert(_restart_addr == NULL,  "foreground will restart from scratch");
3607       if (PrintGCDetails) {
3608         gclog_or_tty->print_cr("bailing out to foreground collection");
3609       }
3610     }
3611     if (UseAdaptiveSizePolicy) {
3612       size_policy()->concurrent_marking_end();
3613     }
3614   } else {
3615     assert(SafepointSynchronize::is_at_safepoint(),
3616            "inconsistent with asynch == false");
3617     if (UseAdaptiveSizePolicy) {
3618       size_policy()->ms_collection_marking_begin();
3619     }
3620     // already have locks
3621     res = markFromRootsWork(asynch);
3622     _collectorState = FinalMarking;
3623     if (UseAdaptiveSizePolicy) {
3624       GenCollectedHeap* gch = GenCollectedHeap::heap();
3625       size_policy()->ms_collection_marking_end(gch->gc_cause());
3626     }
3627   }
3628   verify_overflow_empty();
3629   return res;
3630 }
3631 
3632 bool CMSCollector::markFromRootsWork(bool asynch) {
3633   // iterate over marked bits in bit map, doing a full scan and mark
3634   // from these roots using the following algorithm:
3635   // . if oop is to the right of the current scan pointer,
3636   //   mark corresponding bit (we'll process it later)
3637   // . else (oop is to left of current scan pointer)
3638   //   push oop on marking stack
3639   // . drain the marking stack
3640 
3641   // Note that when we do a marking step we need to hold the
3642   // bit map lock -- recall that direct allocation (by mutators)
3643   // and promotion (by younger generation collectors) is also
3644   // marking the bit map. [the so-called allocate live policy.]
3645   // Because the implementation of bit map marking is not
3646   // robust wrt simultaneous marking of bits in the same word,
3647   // we need to make sure that there is no such interference
3648   // between concurrent such updates.
3649 
3650   // already have locks
3651   assert_lock_strong(bitMapLock());
3652 
3653   verify_work_stacks_empty();
3654   verify_overflow_empty();
3655   bool result = false;
3656   if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3657     result = do_marking_mt(asynch);
3658   } else {
3659     result = do_marking_st(asynch);
3660   }
3661   return result;
3662 }
3663 
3664 // Forward decl
3665 class CMSConcMarkingTask;
3666 
3667 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3668   CMSCollector*       _collector;
3669   CMSConcMarkingTask* _task;
3670  public:
3671   virtual void yield();
3672 
3673   // "n_threads" is the number of threads to be terminated.
3674   // "queue_set" is a set of work queues of other threads.
3675   // "collector" is the CMS collector associated with this task terminator.
3676   // "yield" indicates whether we need the gang as a whole to yield.
3677   CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3678     ParallelTaskTerminator(n_threads, queue_set),
3679     _collector(collector) { }
3680 
3681   void set_task(CMSConcMarkingTask* task) {
3682     _task = task;
3683   }
3684 };
3685 
3686 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3687   CMSConcMarkingTask* _task;
3688  public:
3689   bool should_exit_termination();
3690   void set_task(CMSConcMarkingTask* task) {
3691     _task = task;
3692   }
3693 };
3694 
3695 // MT Concurrent Marking Task
3696 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3697   CMSCollector* _collector;
3698   int           _n_workers;                  // requested/desired # workers
3699   bool          _asynch;
3700   bool          _result;
3701   CompactibleFreeListSpace*  _cms_space;
3702   char          _pad_front[64];   // padding to ...
3703   HeapWord*     _global_finger;   // ... avoid sharing cache line
3704   char          _pad_back[64];
3705   HeapWord*     _restart_addr;
3706 
3707   //  Exposed here for yielding support
3708   Mutex* const _bit_map_lock;
3709 
3710   // The per thread work queues, available here for stealing
3711   OopTaskQueueSet*  _task_queues;
3712 
3713   // Termination (and yielding) support
3714   CMSConcMarkingTerminator _term;
3715   CMSConcMarkingTerminatorTerminator _term_term;
3716 
3717  public:
3718   CMSConcMarkingTask(CMSCollector* collector,
3719                  CompactibleFreeListSpace* cms_space,
3720                  bool asynch,
3721                  YieldingFlexibleWorkGang* workers,
3722                  OopTaskQueueSet* task_queues):
3723     YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3724     _collector(collector),
3725     _cms_space(cms_space),
3726     _asynch(asynch), _n_workers(0), _result(true),
3727     _task_queues(task_queues),
3728     _term(_n_workers, task_queues, _collector),
3729     _bit_map_lock(collector->bitMapLock())
3730   {
3731     _requested_size = _n_workers;
3732     _term.set_task(this);
3733     _term_term.set_task(this);
3734     _restart_addr = _global_finger = _cms_space->bottom();
3735   }
3736 
3737 
3738   OopTaskQueueSet* task_queues()  { return _task_queues; }
3739 
3740   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3741 
3742   HeapWord** global_finger_addr() { return &_global_finger; }
3743 
3744   CMSConcMarkingTerminator* terminator() { return &_term; }
3745 
3746   virtual void set_for_termination(int active_workers) {
3747     terminator()->reset_for_reuse(active_workers);
3748   }
3749 
3750   void work(uint worker_id);
3751   bool should_yield() {
3752     return    ConcurrentMarkSweepThread::should_yield()
3753            && !_collector->foregroundGCIsActive()
3754            && _asynch;
3755   }
3756 
3757   virtual void coordinator_yield();  // stuff done by coordinator
3758   bool result() { return _result; }
3759 
3760   void reset(HeapWord* ra) {
3761     assert(_global_finger >= _cms_space->end(),  "Postcondition of ::work(i)");
3762     _restart_addr = _global_finger = ra;
3763     _term.reset_for_reuse();
3764   }
3765 
3766   static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3767                                            OopTaskQueue* work_q);
3768 
3769  private:
3770   void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3771   void do_work_steal(int i);
3772   void bump_global_finger(HeapWord* f);
3773 };
3774 
3775 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3776   assert(_task != NULL, "Error");
3777   return _task->yielding();
3778   // Note that we do not need the disjunct || _task->should_yield() above
3779   // because we want terminating threads to yield only if the task
3780   // is already in the midst of yielding, which happens only after at least one
3781   // thread has yielded.
3782 }
3783 
3784 void CMSConcMarkingTerminator::yield() {
3785   if (_task->should_yield()) {
3786     _task->yield();
3787   } else {
3788     ParallelTaskTerminator::yield();
3789   }
3790 }
3791 
3792 ////////////////////////////////////////////////////////////////
3793 // Concurrent Marking Algorithm Sketch
3794 ////////////////////////////////////////////////////////////////
3795 // Until all tasks exhausted (both spaces):
3796 // -- claim next available chunk
3797 // -- bump global finger via CAS
3798 // -- find first object that starts in this chunk
3799 //    and start scanning bitmap from that position
3800 // -- scan marked objects for oops
3801 // -- CAS-mark target, and if successful:
3802 //    . if target oop is above global finger (volatile read)
3803 //      nothing to do
3804 //    . if target oop is in chunk and above local finger
3805 //        then nothing to do
3806 //    . else push on work-queue
3807 // -- Deal with possible overflow issues:
3808 //    . local work-queue overflow causes stuff to be pushed on
3809 //      global (common) overflow queue
3810 //    . always first empty local work queue
3811 //    . then get a batch of oops from global work queue if any
3812 //    . then do work stealing
3813 // -- When all tasks claimed (both spaces)
3814 //    and local work queue empty,
3815 //    then in a loop do:
3816 //    . check global overflow stack; steal a batch of oops and trace
3817 //    . try to steal from other threads oif GOS is empty
3818 //    . if neither is available, offer termination
3819 // -- Terminate and return result
3820 //
3821 void CMSConcMarkingTask::work(uint worker_id) {
3822   elapsedTimer _timer;
3823   ResourceMark rm;
3824   HandleMark hm;
3825 
3826   DEBUG_ONLY(_collector->verify_overflow_empty();)
3827 
3828   // Before we begin work, our work queue should be empty
3829   assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3830   // Scan the bitmap covering _cms_space, tracing through grey objects.
3831   _timer.start();
3832   do_scan_and_mark(worker_id, _cms_space);
3833   _timer.stop();
3834   if (PrintCMSStatistics != 0) {
3835     gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3836       worker_id, _timer.seconds());
3837       // XXX: need xxx/xxx type of notation, two timers
3838   }
3839 
3840   // ... do work stealing
3841   _timer.reset();
3842   _timer.start();
3843   do_work_steal(worker_id);
3844   _timer.stop();
3845   if (PrintCMSStatistics != 0) {
3846     gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3847       worker_id, _timer.seconds());
3848       // XXX: need xxx/xxx type of notation, two timers
3849   }
3850   assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3851   assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3852   // Note that under the current task protocol, the
3853   // following assertion is true even of the spaces
3854   // expanded since the completion of the concurrent
3855   // marking. XXX This will likely change under a strict
3856   // ABORT semantics.
3857   // After perm removal the comparison was changed to
3858   // greater than or equal to from strictly greater than.
3859   // Before perm removal the highest address sweep would
3860   // have been at the end of perm gen but now is at the
3861   // end of the tenured gen.
3862   assert(_global_finger >=  _cms_space->end(),
3863          "All tasks have been completed");
3864   DEBUG_ONLY(_collector->verify_overflow_empty();)
3865 }
3866 
3867 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3868   HeapWord* read = _global_finger;
3869   HeapWord* cur  = read;
3870   while (f > read) {
3871     cur = read;
3872     read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3873     if (cur == read) {
3874       // our cas succeeded
3875       assert(_global_finger >= f, "protocol consistency");
3876       break;
3877     }
3878   }
3879 }
3880 
3881 // This is really inefficient, and should be redone by
3882 // using (not yet available) block-read and -write interfaces to the
3883 // stack and the work_queue. XXX FIX ME !!!
3884 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3885                                                       OopTaskQueue* work_q) {
3886   // Fast lock-free check
3887   if (ovflw_stk->length() == 0) {
3888     return false;
3889   }
3890   assert(work_q->size() == 0, "Shouldn't steal");
3891   MutexLockerEx ml(ovflw_stk->par_lock(),
3892                    Mutex::_no_safepoint_check_flag);
3893   // Grab up to 1/4 the size of the work queue
3894   size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3895                     (size_t)ParGCDesiredObjsFromOverflowList);
3896   num = MIN2(num, ovflw_stk->length());
3897   for (int i = (int) num; i > 0; i--) {
3898     oop cur = ovflw_stk->pop();
3899     assert(cur != NULL, "Counted wrong?");
3900     work_q->push(cur);
3901   }
3902   return num > 0;
3903 }
3904 
3905 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3906   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3907   int n_tasks = pst->n_tasks();
3908   // We allow that there may be no tasks to do here because
3909   // we are restarting after a stack overflow.
3910   assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3911   uint nth_task = 0;
3912 
3913   HeapWord* aligned_start = sp->bottom();
3914   if (sp->used_region().contains(_restart_addr)) {
3915     // Align down to a card boundary for the start of 0th task
3916     // for this space.
3917     aligned_start =
3918       (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3919                                  CardTableModRefBS::card_size);
3920   }
3921 
3922   size_t chunk_size = sp->marking_task_size();
3923   while (!pst->is_task_claimed(/* reference */ nth_task)) {
3924     // Having claimed the nth task in this space,
3925     // compute the chunk that it corresponds to:
3926     MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3927                                aligned_start + (nth_task+1)*chunk_size);
3928     // Try and bump the global finger via a CAS;
3929     // note that we need to do the global finger bump
3930     // _before_ taking the intersection below, because
3931     // the task corresponding to that region will be
3932     // deemed done even if the used_region() expands
3933     // because of allocation -- as it almost certainly will
3934     // during start-up while the threads yield in the
3935     // closure below.
3936     HeapWord* finger = span.end();
3937     bump_global_finger(finger);   // atomically
3938     // There are null tasks here corresponding to chunks
3939     // beyond the "top" address of the space.
3940     span = span.intersection(sp->used_region());
3941     if (!span.is_empty()) {  // Non-null task
3942       HeapWord* prev_obj;
3943       assert(!span.contains(_restart_addr) || nth_task == 0,
3944              "Inconsistency");
3945       if (nth_task == 0) {
3946         // For the 0th task, we'll not need to compute a block_start.
3947         if (span.contains(_restart_addr)) {
3948           // In the case of a restart because of stack overflow,
3949           // we might additionally skip a chunk prefix.
3950           prev_obj = _restart_addr;
3951         } else {
3952           prev_obj = span.start();
3953         }
3954       } else {
3955         // We want to skip the first object because
3956         // the protocol is to scan any object in its entirety
3957         // that _starts_ in this span; a fortiori, any
3958         // object starting in an earlier span is scanned
3959         // as part of an earlier claimed task.
3960         // Below we use the "careful" version of block_start
3961         // so we do not try to navigate uninitialized objects.
3962         prev_obj = sp->block_start_careful(span.start());
3963         // Below we use a variant of block_size that uses the
3964         // Printezis bits to avoid waiting for allocated
3965         // objects to become initialized/parsable.
3966         while (prev_obj < span.start()) {
3967           size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3968           if (sz > 0) {
3969             prev_obj += sz;
3970           } else {
3971             // In this case we may end up doing a bit of redundant
3972             // scanning, but that appears unavoidable, short of
3973             // locking the free list locks; see bug 6324141.
3974             break;
3975           }
3976         }
3977       }
3978       if (prev_obj < span.end()) {
3979         MemRegion my_span = MemRegion(prev_obj, span.end());
3980         // Do the marking work within a non-empty span --
3981         // the last argument to the constructor indicates whether the
3982         // iteration should be incremental with periodic yields.
3983         Par_MarkFromRootsClosure cl(this, _collector, my_span,
3984                                     &_collector->_markBitMap,
3985                                     work_queue(i),
3986                                     &_collector->_markStack,
3987                                     _asynch);
3988         _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3989       } // else nothing to do for this task
3990     }   // else nothing to do for this task
3991   }
3992   // We'd be tempted to assert here that since there are no
3993   // more tasks left to claim in this space, the global_finger
3994   // must exceed space->top() and a fortiori space->end(). However,
3995   // that would not quite be correct because the bumping of
3996   // global_finger occurs strictly after the claiming of a task,
3997   // so by the time we reach here the global finger may not yet
3998   // have been bumped up by the thread that claimed the last
3999   // task.
4000   pst->all_tasks_completed();
4001 }
4002 
4003 class Par_ConcMarkingClosure: public CMSOopClosure {
4004  private:
4005   CMSCollector* _collector;
4006   CMSConcMarkingTask* _task;
4007   MemRegion     _span;
4008   CMSBitMap*    _bit_map;
4009   CMSMarkStack* _overflow_stack;
4010   OopTaskQueue* _work_queue;
4011  protected:
4012   DO_OOP_WORK_DEFN
4013  public:
4014   Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4015                          CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4016     CMSOopClosure(collector->ref_processor()),
4017     _collector(collector),
4018     _task(task),
4019     _span(collector->_span),
4020     _work_queue(work_queue),
4021     _bit_map(bit_map),
4022     _overflow_stack(overflow_stack)
4023   { }
4024   virtual void do_oop(oop* p);
4025   virtual void do_oop(narrowOop* p);
4026 
4027   void trim_queue(size_t max);
4028   void handle_stack_overflow(HeapWord* lost);
4029   void do_yield_check() {
4030     if (_task->should_yield()) {
4031       _task->yield();
4032     }
4033   }
4034 };
4035 
4036 // Grey object scanning during work stealing phase --
4037 // the salient assumption here is that any references
4038 // that are in these stolen objects being scanned must
4039 // already have been initialized (else they would not have
4040 // been published), so we do not need to check for
4041 // uninitialized objects before pushing here.
4042 void Par_ConcMarkingClosure::do_oop(oop obj) {
4043   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4044   HeapWord* addr = (HeapWord*)obj;
4045   // Check if oop points into the CMS generation
4046   // and is not marked
4047   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4048     // a white object ...
4049     // If we manage to "claim" the object, by being the
4050     // first thread to mark it, then we push it on our
4051     // marking stack
4052     if (_bit_map->par_mark(addr)) {     // ... now grey
4053       // push on work queue (grey set)
4054       bool simulate_overflow = false;
4055       NOT_PRODUCT(
4056         if (CMSMarkStackOverflowALot &&
4057             _collector->simulate_overflow()) {
4058           // simulate a stack overflow
4059           simulate_overflow = true;
4060         }
4061       )
4062       if (simulate_overflow ||
4063           !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4064         // stack overflow
4065         if (PrintCMSStatistics != 0) {
4066           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4067                                  SIZE_FORMAT, _overflow_stack->capacity());
4068         }
4069         // We cannot assert that the overflow stack is full because
4070         // it may have been emptied since.
4071         assert(simulate_overflow ||
4072                _work_queue->size() == _work_queue->max_elems(),
4073               "Else push should have succeeded");
4074         handle_stack_overflow(addr);
4075       }
4076     } // Else, some other thread got there first
4077     do_yield_check();
4078   }
4079 }
4080 
4081 void Par_ConcMarkingClosure::do_oop(oop* p)       { Par_ConcMarkingClosure::do_oop_work(p); }
4082 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4083 
4084 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4085   while (_work_queue->size() > max) {
4086     oop new_oop;
4087     if (_work_queue->pop_local(new_oop)) {
4088       assert(new_oop->is_oop(), "Should be an oop");
4089       assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4090       assert(_span.contains((HeapWord*)new_oop), "Not in span");
4091       new_oop->oop_iterate(this);  // do_oop() above
4092       do_yield_check();
4093     }
4094   }
4095 }
4096 
4097 // Upon stack overflow, we discard (part of) the stack,
4098 // remembering the least address amongst those discarded
4099 // in CMSCollector's _restart_address.
4100 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4101   // We need to do this under a mutex to prevent other
4102   // workers from interfering with the work done below.
4103   MutexLockerEx ml(_overflow_stack->par_lock(),
4104                    Mutex::_no_safepoint_check_flag);
4105   // Remember the least grey address discarded
4106   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4107   _collector->lower_restart_addr(ra);
4108   _overflow_stack->reset();  // discard stack contents
4109   _overflow_stack->expand(); // expand the stack if possible
4110 }
4111 
4112 
4113 void CMSConcMarkingTask::do_work_steal(int i) {
4114   OopTaskQueue* work_q = work_queue(i);
4115   oop obj_to_scan;
4116   CMSBitMap* bm = &(_collector->_markBitMap);
4117   CMSMarkStack* ovflw = &(_collector->_markStack);
4118   int* seed = _collector->hash_seed(i);
4119   Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4120   while (true) {
4121     cl.trim_queue(0);
4122     assert(work_q->size() == 0, "Should have been emptied above");
4123     if (get_work_from_overflow_stack(ovflw, work_q)) {
4124       // Can't assert below because the work obtained from the
4125       // overflow stack may already have been stolen from us.
4126       // assert(work_q->size() > 0, "Work from overflow stack");
4127       continue;
4128     } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4129       assert(obj_to_scan->is_oop(), "Should be an oop");
4130       assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4131       obj_to_scan->oop_iterate(&cl);
4132     } else if (terminator()->offer_termination(&_term_term)) {
4133       assert(work_q->size() == 0, "Impossible!");
4134       break;
4135     } else if (yielding() || should_yield()) {
4136       yield();
4137     }
4138   }
4139 }
4140 
4141 // This is run by the CMS (coordinator) thread.
4142 void CMSConcMarkingTask::coordinator_yield() {
4143   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4144          "CMS thread should hold CMS token");
4145   // First give up the locks, then yield, then re-lock
4146   // We should probably use a constructor/destructor idiom to
4147   // do this unlock/lock or modify the MutexUnlocker class to
4148   // serve our purpose. XXX
4149   assert_lock_strong(_bit_map_lock);
4150   _bit_map_lock->unlock();
4151   ConcurrentMarkSweepThread::desynchronize(true);
4152   ConcurrentMarkSweepThread::acknowledge_yield_request();
4153   _collector->stopTimer();
4154   if (PrintCMSStatistics != 0) {
4155     _collector->incrementYields();
4156   }
4157   _collector->icms_wait();
4158 
4159   // It is possible for whichever thread initiated the yield request
4160   // not to get a chance to wake up and take the bitmap lock between
4161   // this thread releasing it and reacquiring it. So, while the
4162   // should_yield() flag is on, let's sleep for a bit to give the
4163   // other thread a chance to wake up. The limit imposed on the number
4164   // of iterations is defensive, to avoid any unforseen circumstances
4165   // putting us into an infinite loop. Since it's always been this
4166   // (coordinator_yield()) method that was observed to cause the
4167   // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4168   // which is by default non-zero. For the other seven methods that
4169   // also perform the yield operation, as are using a different
4170   // parameter (CMSYieldSleepCount) which is by default zero. This way we
4171   // can enable the sleeping for those methods too, if necessary.
4172   // See 6442774.
4173   //
4174   // We really need to reconsider the synchronization between the GC
4175   // thread and the yield-requesting threads in the future and we
4176   // should really use wait/notify, which is the recommended
4177   // way of doing this type of interaction. Additionally, we should
4178   // consolidate the eight methods that do the yield operation and they
4179   // are almost identical into one for better maintenability and
4180   // readability. See 6445193.
4181   //
4182   // Tony 2006.06.29
4183   for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4184                    ConcurrentMarkSweepThread::should_yield() &&
4185                    !CMSCollector::foregroundGCIsActive(); ++i) {
4186     os::sleep(Thread::current(), 1, false);
4187     ConcurrentMarkSweepThread::acknowledge_yield_request();
4188   }
4189 
4190   ConcurrentMarkSweepThread::synchronize(true);
4191   _bit_map_lock->lock_without_safepoint_check();
4192   _collector->startTimer();
4193 }
4194 
4195 bool CMSCollector::do_marking_mt(bool asynch) {
4196   assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4197   int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4198                                        conc_workers()->total_workers(),
4199                                        conc_workers()->active_workers(),
4200                                        Threads::number_of_non_daemon_threads());
4201   conc_workers()->set_active_workers(num_workers);
4202 
4203   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
4204 
4205   CMSConcMarkingTask tsk(this,
4206                          cms_space,
4207                          asynch,
4208                          conc_workers(),
4209                          task_queues());
4210 
4211   // Since the actual number of workers we get may be different
4212   // from the number we requested above, do we need to do anything different
4213   // below? In particular, may be we need to subclass the SequantialSubTasksDone
4214   // class?? XXX
4215   cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4216 
4217   // Refs discovery is already non-atomic.
4218   assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4219   assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4220   conc_workers()->start_task(&tsk);
4221   while (tsk.yielded()) {
4222     tsk.coordinator_yield();
4223     conc_workers()->continue_task(&tsk);
4224   }
4225   // If the task was aborted, _restart_addr will be non-NULL
4226   assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4227   while (_restart_addr != NULL) {
4228     // XXX For now we do not make use of ABORTED state and have not
4229     // yet implemented the right abort semantics (even in the original
4230     // single-threaded CMS case). That needs some more investigation
4231     // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4232     assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4233     // If _restart_addr is non-NULL, a marking stack overflow
4234     // occurred; we need to do a fresh marking iteration from the
4235     // indicated restart address.
4236     if (_foregroundGCIsActive && asynch) {
4237       // We may be running into repeated stack overflows, having
4238       // reached the limit of the stack size, while making very
4239       // slow forward progress. It may be best to bail out and
4240       // let the foreground collector do its job.
4241       // Clear _restart_addr, so that foreground GC
4242       // works from scratch. This avoids the headache of
4243       // a "rescan" which would otherwise be needed because
4244       // of the dirty mod union table & card table.
4245       _restart_addr = NULL;
4246       return false;
4247     }
4248     // Adjust the task to restart from _restart_addr
4249     tsk.reset(_restart_addr);
4250     cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4251                   _restart_addr);
4252     _restart_addr = NULL;
4253     // Get the workers going again
4254     conc_workers()->start_task(&tsk);
4255     while (tsk.yielded()) {
4256       tsk.coordinator_yield();
4257       conc_workers()->continue_task(&tsk);
4258     }
4259   }
4260   assert(tsk.completed(), "Inconsistency");
4261   assert(tsk.result() == true, "Inconsistency");
4262   return true;
4263 }
4264 
4265 bool CMSCollector::do_marking_st(bool asynch) {
4266   ResourceMark rm;
4267   HandleMark   hm;
4268 
4269   // Temporarily make refs discovery single threaded (non-MT)
4270   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4271   MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4272     &_markStack, CMSYield && asynch);
4273   // the last argument to iterate indicates whether the iteration
4274   // should be incremental with periodic yields.
4275   _markBitMap.iterate(&markFromRootsClosure);
4276   // If _restart_addr is non-NULL, a marking stack overflow
4277   // occurred; we need to do a fresh iteration from the
4278   // indicated restart address.
4279   while (_restart_addr != NULL) {
4280     if (_foregroundGCIsActive && asynch) {
4281       // We may be running into repeated stack overflows, having
4282       // reached the limit of the stack size, while making very
4283       // slow forward progress. It may be best to bail out and
4284       // let the foreground collector do its job.
4285       // Clear _restart_addr, so that foreground GC
4286       // works from scratch. This avoids the headache of
4287       // a "rescan" which would otherwise be needed because
4288       // of the dirty mod union table & card table.
4289       _restart_addr = NULL;
4290       return false;  // indicating failure to complete marking
4291     }
4292     // Deal with stack overflow:
4293     // we restart marking from _restart_addr
4294     HeapWord* ra = _restart_addr;
4295     markFromRootsClosure.reset(ra);
4296     _restart_addr = NULL;
4297     _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4298   }
4299   return true;
4300 }
4301 
4302 void CMSCollector::preclean() {
4303   check_correct_thread_executing();
4304   assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4305   verify_work_stacks_empty();
4306   verify_overflow_empty();
4307   _abort_preclean = false;
4308   if (CMSPrecleaningEnabled) {
4309     _eden_chunk_index = 0;
4310     size_t used = get_eden_used();
4311     size_t capacity = get_eden_capacity();
4312     // Don't start sampling unless we will get sufficiently
4313     // many samples.
4314     if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4315                 * CMSScheduleRemarkEdenPenetration)) {
4316       _start_sampling = true;
4317     } else {
4318       _start_sampling = false;
4319     }
4320     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4321     CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4322     preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4323   }
4324   CMSTokenSync x(true); // is cms thread
4325   if (CMSPrecleaningEnabled) {
4326     sample_eden();
4327     _collectorState = AbortablePreclean;
4328   } else {
4329     _collectorState = FinalMarking;
4330   }
4331   verify_work_stacks_empty();
4332   verify_overflow_empty();
4333 }
4334 
4335 // Try and schedule the remark such that young gen
4336 // occupancy is CMSScheduleRemarkEdenPenetration %.
4337 void CMSCollector::abortable_preclean() {
4338   check_correct_thread_executing();
4339   assert(CMSPrecleaningEnabled,  "Inconsistent control state");
4340   assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4341 
4342   // If Eden's current occupancy is below this threshold,
4343   // immediately schedule the remark; else preclean
4344   // past the next scavenge in an effort to
4345   // schedule the pause as described avove. By choosing
4346   // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4347   // we will never do an actual abortable preclean cycle.
4348   if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4349     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4350     CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4351     // We need more smarts in the abortable preclean
4352     // loop below to deal with cases where allocation
4353     // in young gen is very very slow, and our precleaning
4354     // is running a losing race against a horde of
4355     // mutators intent on flooding us with CMS updates
4356     // (dirty cards).
4357     // One, admittedly dumb, strategy is to give up
4358     // after a certain number of abortable precleaning loops
4359     // or after a certain maximum time. We want to make
4360     // this smarter in the next iteration.
4361     // XXX FIX ME!!! YSR
4362     size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4363     while (!(should_abort_preclean() ||
4364              ConcurrentMarkSweepThread::should_terminate())) {
4365       workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4366       cumworkdone += workdone;
4367       loops++;
4368       // Voluntarily terminate abortable preclean phase if we have
4369       // been at it for too long.
4370       if ((CMSMaxAbortablePrecleanLoops != 0) &&
4371           loops >= CMSMaxAbortablePrecleanLoops) {
4372         if (PrintGCDetails) {
4373           gclog_or_tty->print(" CMS: abort preclean due to loops ");
4374         }
4375         break;
4376       }
4377       if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4378         if (PrintGCDetails) {
4379           gclog_or_tty->print(" CMS: abort preclean due to time ");
4380         }
4381         break;
4382       }
4383       // If we are doing little work each iteration, we should
4384       // take a short break.
4385       if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4386         // Sleep for some time, waiting for work to accumulate
4387         stopTimer();
4388         cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4389         startTimer();
4390         waited++;
4391       }
4392     }
4393     if (PrintCMSStatistics > 0) {
4394       gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4395                           loops, waited, cumworkdone);
4396     }
4397   }
4398   CMSTokenSync x(true); // is cms thread
4399   if (_collectorState != Idling) {
4400     assert(_collectorState == AbortablePreclean,
4401            "Spontaneous state transition?");
4402     _collectorState = FinalMarking;
4403   } // Else, a foreground collection completed this CMS cycle.
4404   return;
4405 }
4406 
4407 // Respond to an Eden sampling opportunity
4408 void CMSCollector::sample_eden() {
4409   // Make sure a young gc cannot sneak in between our
4410   // reading and recording of a sample.
4411   assert(Thread::current()->is_ConcurrentGC_thread(),
4412          "Only the cms thread may collect Eden samples");
4413   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4414          "Should collect samples while holding CMS token");
4415   if (!_start_sampling) {
4416     return;
4417   }
4418   if (_eden_chunk_array) {
4419     if (_eden_chunk_index < _eden_chunk_capacity) {
4420       _eden_chunk_array[_eden_chunk_index] = *_top_addr;   // take sample
4421       assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4422              "Unexpected state of Eden");
4423       // We'd like to check that what we just sampled is an oop-start address;
4424       // however, we cannot do that here since the object may not yet have been
4425       // initialized. So we'll instead do the check when we _use_ this sample
4426       // later.
4427       if (_eden_chunk_index == 0 ||
4428           (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4429                          _eden_chunk_array[_eden_chunk_index-1])
4430            >= CMSSamplingGrain)) {
4431         _eden_chunk_index++;  // commit sample
4432       }
4433     }
4434   }
4435   if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4436     size_t used = get_eden_used();
4437     size_t capacity = get_eden_capacity();
4438     assert(used <= capacity, "Unexpected state of Eden");
4439     if (used >  (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4440       _abort_preclean = true;
4441     }
4442   }
4443 }
4444 
4445 
4446 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4447   assert(_collectorState == Precleaning ||
4448          _collectorState == AbortablePreclean, "incorrect state");
4449   ResourceMark rm;
4450   HandleMark   hm;
4451 
4452   // Precleaning is currently not MT but the reference processor
4453   // may be set for MT.  Disable it temporarily here.
4454   ReferenceProcessor* rp = ref_processor();
4455   ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4456 
4457   // Do one pass of scrubbing the discovered reference lists
4458   // to remove any reference objects with strongly-reachable
4459   // referents.
4460   if (clean_refs) {
4461     CMSPrecleanRefsYieldClosure yield_cl(this);
4462     assert(rp->span().equals(_span), "Spans should be equal");
4463     CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4464                                    &_markStack, true /* preclean */);
4465     CMSDrainMarkingStackClosure complete_trace(this,
4466                                    _span, &_markBitMap, &_markStack,
4467                                    &keep_alive, true /* preclean */);
4468 
4469     // We don't want this step to interfere with a young
4470     // collection because we don't want to take CPU
4471     // or memory bandwidth away from the young GC threads
4472     // (which may be as many as there are CPUs).
4473     // Note that we don't need to protect ourselves from
4474     // interference with mutators because they can't
4475     // manipulate the discovered reference lists nor affect
4476     // the computed reachability of the referents, the
4477     // only properties manipulated by the precleaning
4478     // of these reference lists.
4479     stopTimer();
4480     CMSTokenSyncWithLocks x(true /* is cms thread */,
4481                             bitMapLock());
4482     startTimer();
4483     sample_eden();
4484 
4485     // The following will yield to allow foreground
4486     // collection to proceed promptly. XXX YSR:
4487     // The code in this method may need further
4488     // tweaking for better performance and some restructuring
4489     // for cleaner interfaces.
4490     rp->preclean_discovered_references(
4491           rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4492   }
4493 
4494   if (clean_survivor) {  // preclean the active survivor space(s)
4495     assert(_young_gen->kind() == Generation::DefNew ||
4496            _young_gen->kind() == Generation::ParNew ||
4497            _young_gen->kind() == Generation::ASParNew,
4498          "incorrect type for cast");
4499     DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4500     PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4501                              &_markBitMap, &_modUnionTable,
4502                              &_markStack, true /* precleaning phase */);
4503     stopTimer();
4504     CMSTokenSyncWithLocks ts(true /* is cms thread */,
4505                              bitMapLock());
4506     startTimer();
4507     unsigned int before_count =
4508       GenCollectedHeap::heap()->total_collections();
4509     SurvivorSpacePrecleanClosure
4510       sss_cl(this, _span, &_markBitMap, &_markStack,
4511              &pam_cl, before_count, CMSYield);
4512     dng->from()->object_iterate_careful(&sss_cl);
4513     dng->to()->object_iterate_careful(&sss_cl);
4514   }
4515   MarkRefsIntoAndScanClosure
4516     mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4517              &_markStack, this, CMSYield,
4518              true /* precleaning phase */);
4519   // CAUTION: The following closure has persistent state that may need to
4520   // be reset upon a decrease in the sequence of addresses it
4521   // processes.
4522   ScanMarkedObjectsAgainCarefullyClosure
4523     smoac_cl(this, _span,
4524       &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4525 
4526   // Preclean dirty cards in ModUnionTable and CardTable using
4527   // appropriate convergence criterion;
4528   // repeat CMSPrecleanIter times unless we find that
4529   // we are losing.
4530   assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4531   assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4532          "Bad convergence multiplier");
4533   assert(CMSPrecleanThreshold >= 100,
4534          "Unreasonably low CMSPrecleanThreshold");
4535 
4536   size_t numIter, cumNumCards, lastNumCards, curNumCards;
4537   for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4538        numIter < CMSPrecleanIter;
4539        numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4540     curNumCards  = preclean_mod_union_table(_cmsGen, &smoac_cl);
4541     if (Verbose && PrintGCDetails) {
4542       gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4543     }
4544     // Either there are very few dirty cards, so re-mark
4545     // pause will be small anyway, or our pre-cleaning isn't
4546     // that much faster than the rate at which cards are being
4547     // dirtied, so we might as well stop and re-mark since
4548     // precleaning won't improve our re-mark time by much.
4549     if (curNumCards <= CMSPrecleanThreshold ||
4550         (numIter > 0 &&
4551          (curNumCards * CMSPrecleanDenominator >
4552          lastNumCards * CMSPrecleanNumerator))) {
4553       numIter++;
4554       cumNumCards += curNumCards;
4555       break;
4556     }
4557   }
4558 
4559   preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4560 
4561   curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4562   cumNumCards += curNumCards;
4563   if (PrintGCDetails && PrintCMSStatistics != 0) {
4564     gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4565                   curNumCards, cumNumCards, numIter);
4566   }
4567   return cumNumCards;   // as a measure of useful work done
4568 }
4569 
4570 // PRECLEANING NOTES:
4571 // Precleaning involves:
4572 // . reading the bits of the modUnionTable and clearing the set bits.
4573 // . For the cards corresponding to the set bits, we scan the
4574 //   objects on those cards. This means we need the free_list_lock
4575 //   so that we can safely iterate over the CMS space when scanning
4576 //   for oops.
4577 // . When we scan the objects, we'll be both reading and setting
4578 //   marks in the marking bit map, so we'll need the marking bit map.
4579 // . For protecting _collector_state transitions, we take the CGC_lock.
4580 //   Note that any races in the reading of of card table entries by the
4581 //   CMS thread on the one hand and the clearing of those entries by the
4582 //   VM thread or the setting of those entries by the mutator threads on the
4583 //   other are quite benign. However, for efficiency it makes sense to keep
4584 //   the VM thread from racing with the CMS thread while the latter is
4585 //   dirty card info to the modUnionTable. We therefore also use the
4586 //   CGC_lock to protect the reading of the card table and the mod union
4587 //   table by the CM thread.
4588 // . We run concurrently with mutator updates, so scanning
4589 //   needs to be done carefully  -- we should not try to scan
4590 //   potentially uninitialized objects.
4591 //
4592 // Locking strategy: While holding the CGC_lock, we scan over and
4593 // reset a maximal dirty range of the mod union / card tables, then lock
4594 // the free_list_lock and bitmap lock to do a full marking, then
4595 // release these locks; and repeat the cycle. This allows for a
4596 // certain amount of fairness in the sharing of these locks between
4597 // the CMS collector on the one hand, and the VM thread and the
4598 // mutators on the other.
4599 
4600 // NOTE: preclean_mod_union_table() and preclean_card_table()
4601 // further below are largely identical; if you need to modify
4602 // one of these methods, please check the other method too.
4603 
4604 size_t CMSCollector::preclean_mod_union_table(
4605   ConcurrentMarkSweepGeneration* gen,
4606   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4607   verify_work_stacks_empty();
4608   verify_overflow_empty();
4609 
4610   // strategy: starting with the first card, accumulate contiguous
4611   // ranges of dirty cards; clear these cards, then scan the region
4612   // covered by these cards.
4613 
4614   // Since all of the MUT is committed ahead, we can just use
4615   // that, in case the generations expand while we are precleaning.
4616   // It might also be fine to just use the committed part of the
4617   // generation, but we might potentially miss cards when the
4618   // generation is rapidly expanding while we are in the midst
4619   // of precleaning.
4620   HeapWord* startAddr = gen->reserved().start();
4621   HeapWord* endAddr   = gen->reserved().end();
4622 
4623   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4624 
4625   size_t numDirtyCards, cumNumDirtyCards;
4626   HeapWord *nextAddr, *lastAddr;
4627   for (cumNumDirtyCards = numDirtyCards = 0,
4628        nextAddr = lastAddr = startAddr;
4629        nextAddr < endAddr;
4630        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4631 
4632     ResourceMark rm;
4633     HandleMark   hm;
4634 
4635     MemRegion dirtyRegion;
4636     {
4637       stopTimer();
4638       // Potential yield point
4639       CMSTokenSync ts(true);
4640       startTimer();
4641       sample_eden();
4642       // Get dirty region starting at nextOffset (inclusive),
4643       // simultaneously clearing it.
4644       dirtyRegion =
4645         _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4646       assert(dirtyRegion.start() >= nextAddr,
4647              "returned region inconsistent?");
4648     }
4649     // Remember where the next search should begin.
4650     // The returned region (if non-empty) is a right open interval,
4651     // so lastOffset is obtained from the right end of that
4652     // interval.
4653     lastAddr = dirtyRegion.end();
4654     // Should do something more transparent and less hacky XXX
4655     numDirtyCards =
4656       _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4657 
4658     // We'll scan the cards in the dirty region (with periodic
4659     // yields for foreground GC as needed).
4660     if (!dirtyRegion.is_empty()) {
4661       assert(numDirtyCards > 0, "consistency check");
4662       HeapWord* stop_point = NULL;
4663       stopTimer();
4664       // Potential yield point
4665       CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4666                                bitMapLock());
4667       startTimer();
4668       {
4669         verify_work_stacks_empty();
4670         verify_overflow_empty();
4671         sample_eden();
4672         stop_point =
4673           gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4674       }
4675       if (stop_point != NULL) {
4676         // The careful iteration stopped early either because it found an
4677         // uninitialized object, or because we were in the midst of an
4678         // "abortable preclean", which should now be aborted. Redirty
4679         // the bits corresponding to the partially-scanned or unscanned
4680         // cards. We'll either restart at the next block boundary or
4681         // abort the preclean.
4682         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4683                "Should only be AbortablePreclean.");
4684         _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4685         if (should_abort_preclean()) {
4686           break; // out of preclean loop
4687         } else {
4688           // Compute the next address at which preclean should pick up;
4689           // might need bitMapLock in order to read P-bits.
4690           lastAddr = next_card_start_after_block(stop_point);
4691         }
4692       }
4693     } else {
4694       assert(lastAddr == endAddr, "consistency check");
4695       assert(numDirtyCards == 0, "consistency check");
4696       break;
4697     }
4698   }
4699   verify_work_stacks_empty();
4700   verify_overflow_empty();
4701   return cumNumDirtyCards;
4702 }
4703 
4704 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4705 // below are largely identical; if you need to modify
4706 // one of these methods, please check the other method too.
4707 
4708 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4709   ScanMarkedObjectsAgainCarefullyClosure* cl) {
4710   // strategy: it's similar to precleamModUnionTable above, in that
4711   // we accumulate contiguous ranges of dirty cards, mark these cards
4712   // precleaned, then scan the region covered by these cards.
4713   HeapWord* endAddr   = (HeapWord*)(gen->_virtual_space.high());
4714   HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4715 
4716   cl->setFreelistLock(gen->freelistLock());   // needed for yielding
4717 
4718   size_t numDirtyCards, cumNumDirtyCards;
4719   HeapWord *lastAddr, *nextAddr;
4720 
4721   for (cumNumDirtyCards = numDirtyCards = 0,
4722        nextAddr = lastAddr = startAddr;
4723        nextAddr < endAddr;
4724        nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4725 
4726     ResourceMark rm;
4727     HandleMark   hm;
4728 
4729     MemRegion dirtyRegion;
4730     {
4731       // See comments in "Precleaning notes" above on why we
4732       // do this locking. XXX Could the locking overheads be
4733       // too high when dirty cards are sparse? [I don't think so.]
4734       stopTimer();
4735       CMSTokenSync x(true); // is cms thread
4736       startTimer();
4737       sample_eden();
4738       // Get and clear dirty region from card table
4739       dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4740                                     MemRegion(nextAddr, endAddr),
4741                                     true,
4742                                     CardTableModRefBS::precleaned_card_val());
4743 
4744       assert(dirtyRegion.start() >= nextAddr,
4745              "returned region inconsistent?");
4746     }
4747     lastAddr = dirtyRegion.end();
4748     numDirtyCards =
4749       dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4750 
4751     if (!dirtyRegion.is_empty()) {
4752       stopTimer();
4753       CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4754       startTimer();
4755       sample_eden();
4756       verify_work_stacks_empty();
4757       verify_overflow_empty();
4758       HeapWord* stop_point =
4759         gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4760       if (stop_point != NULL) {
4761         assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4762                "Should only be AbortablePreclean.");
4763         _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4764         if (should_abort_preclean()) {
4765           break; // out of preclean loop
4766         } else {
4767           // Compute the next address at which preclean should pick up.
4768           lastAddr = next_card_start_after_block(stop_point);
4769         }
4770       }
4771     } else {
4772       break;
4773     }
4774   }
4775   verify_work_stacks_empty();
4776   verify_overflow_empty();
4777   return cumNumDirtyCards;
4778 }
4779 
4780 class PrecleanKlassClosure : public KlassClosure {
4781   CMKlassClosure _cm_klass_closure;
4782  public:
4783   PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4784   void do_klass(Klass* k) {
4785     if (k->has_accumulated_modified_oops()) {
4786       k->clear_accumulated_modified_oops();
4787 
4788       _cm_klass_closure.do_klass(k);
4789     }
4790   }
4791 };
4792 
4793 // The freelist lock is needed to prevent asserts, is it really needed?
4794 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4795 
4796   cl->set_freelistLock(freelistLock);
4797 
4798   CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4799 
4800   // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4801   // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4802   PrecleanKlassClosure preclean_klass_closure(cl);
4803   ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4804 
4805   verify_work_stacks_empty();
4806   verify_overflow_empty();
4807 }
4808 
4809 void CMSCollector::checkpointRootsFinal(bool asynch,
4810   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4811   assert(_collectorState == FinalMarking, "incorrect state transition?");
4812   check_correct_thread_executing();
4813   // world is stopped at this checkpoint
4814   assert(SafepointSynchronize::is_at_safepoint(),
4815          "world should be stopped");
4816   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4817 
4818   verify_work_stacks_empty();
4819   verify_overflow_empty();
4820 
4821   SpecializationStats::clear();
4822   if (PrintGCDetails) {
4823     gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4824                         _young_gen->used() / K,
4825                         _young_gen->capacity() / K);
4826   }
4827   if (asynch) {
4828     if (CMSScavengeBeforeRemark) {
4829       GenCollectedHeap* gch = GenCollectedHeap::heap();
4830       // Temporarily set flag to false, GCH->do_collection will
4831       // expect it to be false and set to true
4832       FlagSetting fl(gch->_is_gc_active, false);
4833       NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4834         PrintGCDetails && Verbose, true, gclog_or_tty);)
4835       int level = _cmsGen->level() - 1;
4836       if (level >= 0) {
4837         gch->do_collection(true,        // full (i.e. force, see below)
4838                            false,       // !clear_all_soft_refs
4839                            0,           // size
4840                            false,       // is_tlab
4841                            level        // max_level
4842                           );
4843       }
4844     }
4845     FreelistLocker x(this);
4846     MutexLockerEx y(bitMapLock(),
4847                     Mutex::_no_safepoint_check_flag);
4848     assert(!init_mark_was_synchronous, "but that's impossible!");
4849     checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4850   } else {
4851     // already have all the locks
4852     checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4853                              init_mark_was_synchronous);
4854   }
4855   verify_work_stacks_empty();
4856   verify_overflow_empty();
4857   SpecializationStats::print();
4858 }
4859 
4860 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4861   bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4862 
4863   NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4864 
4865   assert(haveFreelistLocks(), "must have free list locks");
4866   assert_lock_strong(bitMapLock());
4867 
4868   if (UseAdaptiveSizePolicy) {
4869     size_policy()->checkpoint_roots_final_begin();
4870   }
4871 
4872   ResourceMark rm;
4873   HandleMark   hm;
4874 
4875   GenCollectedHeap* gch = GenCollectedHeap::heap();
4876 
4877   if (should_unload_classes()) {
4878     CodeCache::gc_prologue();
4879   }
4880   assert(haveFreelistLocks(), "must have free list locks");
4881   assert_lock_strong(bitMapLock());
4882 
4883   if (!init_mark_was_synchronous) {
4884     // We might assume that we need not fill TLAB's when
4885     // CMSScavengeBeforeRemark is set, because we may have just done
4886     // a scavenge which would have filled all TLAB's -- and besides
4887     // Eden would be empty. This however may not always be the case --
4888     // for instance although we asked for a scavenge, it may not have
4889     // happened because of a JNI critical section. We probably need
4890     // a policy for deciding whether we can in that case wait until
4891     // the critical section releases and then do the remark following
4892     // the scavenge, and skip it here. In the absence of that policy,
4893     // or of an indication of whether the scavenge did indeed occur,
4894     // we cannot rely on TLAB's having been filled and must do
4895     // so here just in case a scavenge did not happen.
4896     gch->ensure_parsability(false);  // fill TLAB's, but no need to retire them
4897     // Update the saved marks which may affect the root scans.
4898     gch->save_marks();
4899 
4900     {
4901       COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4902 
4903       // Note on the role of the mod union table:
4904       // Since the marker in "markFromRoots" marks concurrently with
4905       // mutators, it is possible for some reachable objects not to have been
4906       // scanned. For instance, an only reference to an object A was
4907       // placed in object B after the marker scanned B. Unless B is rescanned,
4908       // A would be collected. Such updates to references in marked objects
4909       // are detected via the mod union table which is the set of all cards
4910       // dirtied since the first checkpoint in this GC cycle and prior to
4911       // the most recent young generation GC, minus those cleaned up by the
4912       // concurrent precleaning.
4913       if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4914         TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4915         do_remark_parallel();
4916       } else {
4917         TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4918                     gclog_or_tty);
4919         do_remark_non_parallel();
4920       }
4921     }
4922   } else {
4923     assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4924     // The initial mark was stop-world, so there's no rescanning to
4925     // do; go straight on to the next step below.
4926   }
4927   verify_work_stacks_empty();
4928   verify_overflow_empty();
4929 
4930   {
4931     NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4932     refProcessingWork(asynch, clear_all_soft_refs);
4933   }
4934   verify_work_stacks_empty();
4935   verify_overflow_empty();
4936 
4937   if (should_unload_classes()) {
4938     CodeCache::gc_epilogue();
4939   }
4940   JvmtiExport::gc_epilogue();
4941 
4942   // If we encountered any (marking stack / work queue) overflow
4943   // events during the current CMS cycle, take appropriate
4944   // remedial measures, where possible, so as to try and avoid
4945   // recurrence of that condition.
4946   assert(_markStack.isEmpty(), "No grey objects");
4947   size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4948                      _ser_kac_ovflw        + _ser_kac_preclean_ovflw;
4949   if (ser_ovflw > 0) {
4950     if (PrintCMSStatistics != 0) {
4951       gclog_or_tty->print_cr("Marking stack overflow (benign) "
4952         "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4953         ", kac_preclean="SIZE_FORMAT")",
4954         _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4955         _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4956     }
4957     _markStack.expand();
4958     _ser_pmc_remark_ovflw = 0;
4959     _ser_pmc_preclean_ovflw = 0;
4960     _ser_kac_preclean_ovflw = 0;
4961     _ser_kac_ovflw = 0;
4962   }
4963   if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4964     if (PrintCMSStatistics != 0) {
4965       gclog_or_tty->print_cr("Work queue overflow (benign) "
4966         "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4967         _par_pmc_remark_ovflw, _par_kac_ovflw);
4968     }
4969     _par_pmc_remark_ovflw = 0;
4970     _par_kac_ovflw = 0;
4971   }
4972   if (PrintCMSStatistics != 0) {
4973      if (_markStack._hit_limit > 0) {
4974        gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4975                               _markStack._hit_limit);
4976      }
4977      if (_markStack._failed_double > 0) {
4978        gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4979                               " current capacity "SIZE_FORMAT,
4980                               _markStack._failed_double,
4981                               _markStack.capacity());
4982      }
4983   }
4984   _markStack._hit_limit = 0;
4985   _markStack._failed_double = 0;
4986 
4987   if ((VerifyAfterGC || VerifyDuringGC) &&
4988       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4989     verify_after_remark();
4990   }
4991 
4992   // Change under the freelistLocks.
4993   _collectorState = Sweeping;
4994   // Call isAllClear() under bitMapLock
4995   assert(_modUnionTable.isAllClear(),
4996       "Should be clear by end of the final marking");
4997   assert(_ct->klass_rem_set()->mod_union_is_clear(),
4998       "Should be clear by end of the final marking");
4999   if (UseAdaptiveSizePolicy) {
5000     size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5001   }
5002 }
5003 
5004 // Parallel remark task
5005 class CMSParRemarkTask: public AbstractGangTask {
5006   CMSCollector* _collector;
5007   int           _n_workers;
5008   CompactibleFreeListSpace* _cms_space;
5009 
5010   // The per-thread work queues, available here for stealing.
5011   OopTaskQueueSet*       _task_queues;
5012   ParallelTaskTerminator _term;
5013 
5014  public:
5015   // A value of 0 passed to n_workers will cause the number of
5016   // workers to be taken from the active workers in the work gang.
5017   CMSParRemarkTask(CMSCollector* collector,
5018                    CompactibleFreeListSpace* cms_space,
5019                    int n_workers, FlexibleWorkGang* workers,
5020                    OopTaskQueueSet* task_queues):
5021     AbstractGangTask("Rescan roots and grey objects in parallel"),
5022     _collector(collector),
5023     _cms_space(cms_space),
5024     _n_workers(n_workers),
5025     _task_queues(task_queues),
5026     _term(n_workers, task_queues) { }
5027 
5028   OopTaskQueueSet* task_queues() { return _task_queues; }
5029 
5030   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5031 
5032   ParallelTaskTerminator* terminator() { return &_term; }
5033   int n_workers() { return _n_workers; }
5034 
5035   void work(uint worker_id);
5036 
5037  private:
5038   // Work method in support of parallel rescan ... of young gen spaces
5039   void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5040                              ContiguousSpace* space,
5041                              HeapWord** chunk_array, size_t chunk_top);
5042 
5043   // ... of  dirty cards in old space
5044   void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5045                                   Par_MarkRefsIntoAndScanClosure* cl);
5046 
5047   // ... work stealing for the above
5048   void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5049 };
5050 
5051 class RemarkKlassClosure : public KlassClosure {
5052   CMKlassClosure _cm_klass_closure;
5053  public:
5054   RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5055   void do_klass(Klass* k) {
5056     // Check if we have modified any oops in the Klass during the concurrent marking.
5057     if (k->has_accumulated_modified_oops()) {
5058       k->clear_accumulated_modified_oops();
5059 
5060       // We could have transfered the current modified marks to the accumulated marks,
5061       // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5062     } else if (k->has_modified_oops()) {
5063       // Don't clear anything, this info is needed by the next young collection.
5064     } else {
5065       // No modified oops in the Klass.
5066       return;
5067     }
5068 
5069     // The klass has modified fields, need to scan the klass.
5070     _cm_klass_closure.do_klass(k);
5071   }
5072 };
5073 
5074 // work_queue(i) is passed to the closure
5075 // Par_MarkRefsIntoAndScanClosure.  The "i" parameter
5076 // also is passed to do_dirty_card_rescan_tasks() and to
5077 // do_work_steal() to select the i-th task_queue.
5078 
5079 void CMSParRemarkTask::work(uint worker_id) {
5080   elapsedTimer _timer;
5081   ResourceMark rm;
5082   HandleMark   hm;
5083 
5084   // ---------- rescan from roots --------------
5085   _timer.start();
5086   GenCollectedHeap* gch = GenCollectedHeap::heap();
5087   Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5088     _collector->_span, _collector->ref_processor(),
5089     &(_collector->_markBitMap),
5090     work_queue(worker_id));
5091 
5092   // Rescan young gen roots first since these are likely
5093   // coarsely partitioned and may, on that account, constitute
5094   // the critical path; thus, it's best to start off that
5095   // work first.
5096   // ---------- young gen roots --------------
5097   {
5098     DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5099     EdenSpace* eden_space = dng->eden();
5100     ContiguousSpace* from_space = dng->from();
5101     ContiguousSpace* to_space   = dng->to();
5102 
5103     HeapWord** eca = _collector->_eden_chunk_array;
5104     size_t     ect = _collector->_eden_chunk_index;
5105     HeapWord** sca = _collector->_survivor_chunk_array;
5106     size_t     sct = _collector->_survivor_chunk_index;
5107 
5108     assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5109     assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5110 
5111     do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5112     do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5113     do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5114 
5115     _timer.stop();
5116     if (PrintCMSStatistics != 0) {
5117       gclog_or_tty->print_cr(
5118         "Finished young gen rescan work in %dth thread: %3.3f sec",
5119         worker_id, _timer.seconds());
5120     }
5121   }
5122 
5123   // ---------- remaining roots --------------
5124   _timer.reset();
5125   _timer.start();
5126   gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5127                                 false,     // yg was scanned above
5128                                 false,     // this is parallel code
5129                                 false,     // not scavenging
5130                                 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5131                                 &par_mrias_cl,
5132                                 true,   // walk all of code cache if (so & SO_CodeCache)
5133                                 NULL,
5134                                 NULL);     // The dirty klasses will be handled below
5135   assert(_collector->should_unload_classes()
5136          || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5137          "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5138   _timer.stop();
5139   if (PrintCMSStatistics != 0) {
5140     gclog_or_tty->print_cr(
5141       "Finished remaining root rescan work in %dth thread: %3.3f sec",
5142       worker_id, _timer.seconds());
5143   }
5144 
5145   // ---------- unhandled CLD scanning ----------
5146   if (worker_id == 0) { // Single threaded at the moment.
5147     _timer.reset();
5148     _timer.start();
5149 
5150     // Scan all new class loader data objects and new dependencies that were
5151     // introduced during concurrent marking.
5152     ResourceMark rm;
5153     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5154     for (int i = 0; i < array->length(); i++) {
5155       par_mrias_cl.do_class_loader_data(array->at(i));
5156     }
5157 
5158     // We don't need to keep track of new CLDs anymore.
5159     ClassLoaderDataGraph::remember_new_clds(false);
5160 
5161     _timer.stop();
5162     if (PrintCMSStatistics != 0) {
5163       gclog_or_tty->print_cr(
5164           "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5165           worker_id, _timer.seconds());
5166     }
5167   }
5168 
5169   // ---------- dirty klass scanning ----------
5170   if (worker_id == 0) { // Single threaded at the moment.
5171     _timer.reset();
5172     _timer.start();
5173 
5174     // Scan all classes that was dirtied during the concurrent marking phase.
5175     RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5176     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5177 
5178     _timer.stop();
5179     if (PrintCMSStatistics != 0) {
5180       gclog_or_tty->print_cr(
5181           "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5182           worker_id, _timer.seconds());
5183     }
5184   }
5185 
5186   // We might have added oops to ClassLoaderData::_handles during the
5187   // concurrent marking phase. These oops point to newly allocated objects
5188   // that are guaranteed to be kept alive. Either by the direct allocation
5189   // code, or when the young collector processes the strong roots. Hence,
5190   // we don't have to revisit the _handles block during the remark phase.
5191 
5192   // ---------- rescan dirty cards ------------
5193   _timer.reset();
5194   _timer.start();
5195 
5196   // Do the rescan tasks for each of the two spaces
5197   // (cms_space) in turn.
5198   // "worker_id" is passed to select the task_queue for "worker_id"
5199   do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5200   _timer.stop();
5201   if (PrintCMSStatistics != 0) {
5202     gclog_or_tty->print_cr(
5203       "Finished dirty card rescan work in %dth thread: %3.3f sec",
5204       worker_id, _timer.seconds());
5205   }
5206 
5207   // ---------- steal work from other threads ...
5208   // ---------- ... and drain overflow list.
5209   _timer.reset();
5210   _timer.start();
5211   do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5212   _timer.stop();
5213   if (PrintCMSStatistics != 0) {
5214     gclog_or_tty->print_cr(
5215       "Finished work stealing in %dth thread: %3.3f sec",
5216       worker_id, _timer.seconds());
5217   }
5218 }
5219 
5220 // Note that parameter "i" is not used.
5221 void
5222 CMSParRemarkTask::do_young_space_rescan(int i,
5223   Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5224   HeapWord** chunk_array, size_t chunk_top) {
5225   // Until all tasks completed:
5226   // . claim an unclaimed task
5227   // . compute region boundaries corresponding to task claimed
5228   //   using chunk_array
5229   // . par_oop_iterate(cl) over that region
5230 
5231   ResourceMark rm;
5232   HandleMark   hm;
5233 
5234   SequentialSubTasksDone* pst = space->par_seq_tasks();
5235   assert(pst->valid(), "Uninitialized use?");
5236 
5237   uint nth_task = 0;
5238   uint n_tasks  = pst->n_tasks();
5239 
5240   HeapWord *start, *end;
5241   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5242     // We claimed task # nth_task; compute its boundaries.
5243     if (chunk_top == 0) {  // no samples were taken
5244       assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5245       start = space->bottom();
5246       end   = space->top();
5247     } else if (nth_task == 0) {
5248       start = space->bottom();
5249       end   = chunk_array[nth_task];
5250     } else if (nth_task < (uint)chunk_top) {
5251       assert(nth_task >= 1, "Control point invariant");
5252       start = chunk_array[nth_task - 1];
5253       end   = chunk_array[nth_task];
5254     } else {
5255       assert(nth_task == (uint)chunk_top, "Control point invariant");
5256       start = chunk_array[chunk_top - 1];
5257       end   = space->top();
5258     }
5259     MemRegion mr(start, end);
5260     // Verify that mr is in space
5261     assert(mr.is_empty() || space->used_region().contains(mr),
5262            "Should be in space");
5263     // Verify that "start" is an object boundary
5264     assert(mr.is_empty() || oop(mr.start())->is_oop(),
5265            "Should be an oop");
5266     space->par_oop_iterate(mr, cl);
5267   }
5268   pst->all_tasks_completed();
5269 }
5270 
5271 void
5272 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5273   CompactibleFreeListSpace* sp, int i,
5274   Par_MarkRefsIntoAndScanClosure* cl) {
5275   // Until all tasks completed:
5276   // . claim an unclaimed task
5277   // . compute region boundaries corresponding to task claimed
5278   // . transfer dirty bits ct->mut for that region
5279   // . apply rescanclosure to dirty mut bits for that region
5280 
5281   ResourceMark rm;
5282   HandleMark   hm;
5283 
5284   OopTaskQueue* work_q = work_queue(i);
5285   ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5286   // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5287   // CAUTION: This closure has state that persists across calls to
5288   // the work method dirty_range_iterate_clear() in that it has
5289   // imbedded in it a (subtype of) UpwardsObjectClosure. The
5290   // use of that state in the imbedded UpwardsObjectClosure instance
5291   // assumes that the cards are always iterated (even if in parallel
5292   // by several threads) in monotonically increasing order per each
5293   // thread. This is true of the implementation below which picks
5294   // card ranges (chunks) in monotonically increasing order globally
5295   // and, a-fortiori, in monotonically increasing order per thread
5296   // (the latter order being a subsequence of the former).
5297   // If the work code below is ever reorganized into a more chaotic
5298   // work-partitioning form than the current "sequential tasks"
5299   // paradigm, the use of that persistent state will have to be
5300   // revisited and modified appropriately. See also related
5301   // bug 4756801 work on which should examine this code to make
5302   // sure that the changes there do not run counter to the
5303   // assumptions made here and necessary for correctness and
5304   // efficiency. Note also that this code might yield inefficient
5305   // behaviour in the case of very large objects that span one or
5306   // more work chunks. Such objects would potentially be scanned
5307   // several times redundantly. Work on 4756801 should try and
5308   // address that performance anomaly if at all possible. XXX
5309   MemRegion  full_span  = _collector->_span;
5310   CMSBitMap* bm    = &(_collector->_markBitMap);     // shared
5311   MarkFromDirtyCardsClosure
5312     greyRescanClosure(_collector, full_span, // entire span of interest
5313                       sp, bm, work_q, cl);
5314 
5315   SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5316   assert(pst->valid(), "Uninitialized use?");
5317   uint nth_task = 0;
5318   const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5319   MemRegion span = sp->used_region();
5320   HeapWord* start_addr = span.start();
5321   HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5322                                            alignment);
5323   const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5324   assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5325          start_addr, "Check alignment");
5326   assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5327          chunk_size, "Check alignment");
5328 
5329   while (!pst->is_task_claimed(/* reference */ nth_task)) {
5330     // Having claimed the nth_task, compute corresponding mem-region,
5331     // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5332     // The alignment restriction ensures that we do not need any
5333     // synchronization with other gang-workers while setting or
5334     // clearing bits in thus chunk of the MUT.
5335     MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5336                                     start_addr + (nth_task+1)*chunk_size);
5337     // The last chunk's end might be way beyond end of the
5338     // used region. In that case pull back appropriately.
5339     if (this_span.end() > end_addr) {
5340       this_span.set_end(end_addr);
5341       assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5342     }
5343     // Iterate over the dirty cards covering this chunk, marking them
5344     // precleaned, and setting the corresponding bits in the mod union
5345     // table. Since we have been careful to partition at Card and MUT-word
5346     // boundaries no synchronization is needed between parallel threads.
5347     _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5348                                                  &modUnionClosure);
5349 
5350     // Having transferred these marks into the modUnionTable,
5351     // rescan the marked objects on the dirty cards in the modUnionTable.
5352     // Even if this is at a synchronous collection, the initial marking
5353     // may have been done during an asynchronous collection so there
5354     // may be dirty bits in the mod-union table.
5355     _collector->_modUnionTable.dirty_range_iterate_clear(
5356                   this_span, &greyRescanClosure);
5357     _collector->_modUnionTable.verifyNoOneBitsInRange(
5358                                  this_span.start(),
5359                                  this_span.end());
5360   }
5361   pst->all_tasks_completed();  // declare that i am done
5362 }
5363 
5364 // . see if we can share work_queues with ParNew? XXX
5365 void
5366 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5367                                 int* seed) {
5368   OopTaskQueue* work_q = work_queue(i);
5369   NOT_PRODUCT(int num_steals = 0;)
5370   oop obj_to_scan;
5371   CMSBitMap* bm = &(_collector->_markBitMap);
5372 
5373   while (true) {
5374     // Completely finish any left over work from (an) earlier round(s)
5375     cl->trim_queue(0);
5376     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5377                                          (size_t)ParGCDesiredObjsFromOverflowList);
5378     // Now check if there's any work in the overflow list
5379     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5380     // only affects the number of attempts made to get work from the
5381     // overflow list and does not affect the number of workers.  Just
5382     // pass ParallelGCThreads so this behavior is unchanged.
5383     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5384                                                 work_q,
5385                                                 ParallelGCThreads)) {
5386       // found something in global overflow list;
5387       // not yet ready to go stealing work from others.
5388       // We'd like to assert(work_q->size() != 0, ...)
5389       // because we just took work from the overflow list,
5390       // but of course we can't since all of that could have
5391       // been already stolen from us.
5392       // "He giveth and He taketh away."
5393       continue;
5394     }
5395     // Verify that we have no work before we resort to stealing
5396     assert(work_q->size() == 0, "Have work, shouldn't steal");
5397     // Try to steal from other queues that have work
5398     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5399       NOT_PRODUCT(num_steals++;)
5400       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5401       assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5402       // Do scanning work
5403       obj_to_scan->oop_iterate(cl);
5404       // Loop around, finish this work, and try to steal some more
5405     } else if (terminator()->offer_termination()) {
5406         break;  // nirvana from the infinite cycle
5407     }
5408   }
5409   NOT_PRODUCT(
5410     if (PrintCMSStatistics != 0) {
5411       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5412     }
5413   )
5414   assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5415          "Else our work is not yet done");
5416 }
5417 
5418 // Return a thread-local PLAB recording array, as appropriate.
5419 void* CMSCollector::get_data_recorder(int thr_num) {
5420   if (_survivor_plab_array != NULL &&
5421       (CMSPLABRecordAlways ||
5422        (_collectorState > Marking && _collectorState < FinalMarking))) {
5423     assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5424     ChunkArray* ca = &_survivor_plab_array[thr_num];
5425     ca->reset();   // clear it so that fresh data is recorded
5426     return (void*) ca;
5427   } else {
5428     return NULL;
5429   }
5430 }
5431 
5432 // Reset all the thread-local PLAB recording arrays
5433 void CMSCollector::reset_survivor_plab_arrays() {
5434   for (uint i = 0; i < ParallelGCThreads; i++) {
5435     _survivor_plab_array[i].reset();
5436   }
5437 }
5438 
5439 // Merge the per-thread plab arrays into the global survivor chunk
5440 // array which will provide the partitioning of the survivor space
5441 // for CMS rescan.
5442 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5443                                               int no_of_gc_threads) {
5444   assert(_survivor_plab_array  != NULL, "Error");
5445   assert(_survivor_chunk_array != NULL, "Error");
5446   assert(_collectorState == FinalMarking, "Error");
5447   for (int j = 0; j < no_of_gc_threads; j++) {
5448     _cursor[j] = 0;
5449   }
5450   HeapWord* top = surv->top();
5451   size_t i;
5452   for (i = 0; i < _survivor_chunk_capacity; i++) {  // all sca entries
5453     HeapWord* min_val = top;          // Higher than any PLAB address
5454     uint      min_tid = 0;            // position of min_val this round
5455     for (int j = 0; j < no_of_gc_threads; j++) {
5456       ChunkArray* cur_sca = &_survivor_plab_array[j];
5457       if (_cursor[j] == cur_sca->end()) {
5458         continue;
5459       }
5460       assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5461       HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5462       assert(surv->used_region().contains(cur_val), "Out of bounds value");
5463       if (cur_val < min_val) {
5464         min_tid = j;
5465         min_val = cur_val;
5466       } else {
5467         assert(cur_val < top, "All recorded addresses should be less");
5468       }
5469     }
5470     // At this point min_val and min_tid are respectively
5471     // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5472     // and the thread (j) that witnesses that address.
5473     // We record this address in the _survivor_chunk_array[i]
5474     // and increment _cursor[min_tid] prior to the next round i.
5475     if (min_val == top) {
5476       break;
5477     }
5478     _survivor_chunk_array[i] = min_val;
5479     _cursor[min_tid]++;
5480   }
5481   // We are all done; record the size of the _survivor_chunk_array
5482   _survivor_chunk_index = i; // exclusive: [0, i)
5483   if (PrintCMSStatistics > 0) {
5484     gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5485   }
5486   // Verify that we used up all the recorded entries
5487   #ifdef ASSERT
5488     size_t total = 0;
5489     for (int j = 0; j < no_of_gc_threads; j++) {
5490       assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5491       total += _cursor[j];
5492     }
5493     assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5494     // Check that the merged array is in sorted order
5495     if (total > 0) {
5496       for (size_t i = 0; i < total - 1; i++) {
5497         if (PrintCMSStatistics > 0) {
5498           gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5499                               i, _survivor_chunk_array[i]);
5500         }
5501         assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5502                "Not sorted");
5503       }
5504     }
5505   #endif // ASSERT
5506 }
5507 
5508 // Set up the space's par_seq_tasks structure for work claiming
5509 // for parallel rescan of young gen.
5510 // See ParRescanTask where this is currently used.
5511 void
5512 CMSCollector::
5513 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5514   assert(n_threads > 0, "Unexpected n_threads argument");
5515   DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5516 
5517   // Eden space
5518   {
5519     SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5520     assert(!pst->valid(), "Clobbering existing data?");
5521     // Each valid entry in [0, _eden_chunk_index) represents a task.
5522     size_t n_tasks = _eden_chunk_index + 1;
5523     assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5524     // Sets the condition for completion of the subtask (how many threads
5525     // need to finish in order to be done).
5526     pst->set_n_threads(n_threads);
5527     pst->set_n_tasks((int)n_tasks);
5528   }
5529 
5530   // Merge the survivor plab arrays into _survivor_chunk_array
5531   if (_survivor_plab_array != NULL) {
5532     merge_survivor_plab_arrays(dng->from(), n_threads);
5533   } else {
5534     assert(_survivor_chunk_index == 0, "Error");
5535   }
5536 
5537   // To space
5538   {
5539     SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5540     assert(!pst->valid(), "Clobbering existing data?");
5541     // Sets the condition for completion of the subtask (how many threads
5542     // need to finish in order to be done).
5543     pst->set_n_threads(n_threads);
5544     pst->set_n_tasks(1);
5545     assert(pst->valid(), "Error");
5546   }
5547 
5548   // From space
5549   {
5550     SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5551     assert(!pst->valid(), "Clobbering existing data?");
5552     size_t n_tasks = _survivor_chunk_index + 1;
5553     assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5554     // Sets the condition for completion of the subtask (how many threads
5555     // need to finish in order to be done).
5556     pst->set_n_threads(n_threads);
5557     pst->set_n_tasks((int)n_tasks);
5558     assert(pst->valid(), "Error");
5559   }
5560 }
5561 
5562 // Parallel version of remark
5563 void CMSCollector::do_remark_parallel() {
5564   GenCollectedHeap* gch = GenCollectedHeap::heap();
5565   FlexibleWorkGang* workers = gch->workers();
5566   assert(workers != NULL, "Need parallel worker threads.");
5567   // Choose to use the number of GC workers most recently set
5568   // into "active_workers".  If active_workers is not set, set it
5569   // to ParallelGCThreads.
5570   int n_workers = workers->active_workers();
5571   if (n_workers == 0) {
5572     assert(n_workers > 0, "Should have been set during scavenge");
5573     n_workers = ParallelGCThreads;
5574     workers->set_active_workers(n_workers);
5575   }
5576   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();
5577 
5578   CMSParRemarkTask tsk(this,
5579     cms_space,
5580     n_workers, workers, task_queues());
5581 
5582   // Set up for parallel process_strong_roots work.
5583   gch->set_par_threads(n_workers);
5584   // We won't be iterating over the cards in the card table updating
5585   // the younger_gen cards, so we shouldn't call the following else
5586   // the verification code as well as subsequent younger_refs_iterate
5587   // code would get confused. XXX
5588   // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5589 
5590   // The young gen rescan work will not be done as part of
5591   // process_strong_roots (which currently doesn't knw how to
5592   // parallelize such a scan), but rather will be broken up into
5593   // a set of parallel tasks (via the sampling that the [abortable]
5594   // preclean phase did of EdenSpace, plus the [two] tasks of
5595   // scanning the [two] survivor spaces. Further fine-grain
5596   // parallelization of the scanning of the survivor spaces
5597   // themselves, and of precleaning of the younger gen itself
5598   // is deferred to the future.
5599   initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5600 
5601   // The dirty card rescan work is broken up into a "sequence"
5602   // of parallel tasks (per constituent space) that are dynamically
5603   // claimed by the parallel threads.
5604   cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5605 
5606   // It turns out that even when we're using 1 thread, doing the work in a
5607   // separate thread causes wide variance in run times.  We can't help this
5608   // in the multi-threaded case, but we special-case n=1 here to get
5609   // repeatable measurements of the 1-thread overhead of the parallel code.
5610   if (n_workers > 1) {
5611     // Make refs discovery MT-safe, if it isn't already: it may not
5612     // necessarily be so, since it's possible that we are doing
5613     // ST marking.
5614     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5615     GenCollectedHeap::StrongRootsScope srs(gch);
5616     workers->run_task(&tsk);
5617   } else {
5618     ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5619     GenCollectedHeap::StrongRootsScope srs(gch);
5620     tsk.work(0);
5621   }
5622 
5623   gch->set_par_threads(0);  // 0 ==> non-parallel.
5624   // restore, single-threaded for now, any preserved marks
5625   // as a result of work_q overflow
5626   restore_preserved_marks_if_any();
5627 }
5628 
5629 // Non-parallel version of remark
5630 void CMSCollector::do_remark_non_parallel() {
5631   ResourceMark rm;
5632   HandleMark   hm;
5633   GenCollectedHeap* gch = GenCollectedHeap::heap();
5634   ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5635 
5636   MarkRefsIntoAndScanClosure
5637     mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5638              &_markStack, this,
5639              false /* should_yield */, false /* not precleaning */);
5640   MarkFromDirtyCardsClosure
5641     markFromDirtyCardsClosure(this, _span,
5642                               NULL,  // space is set further below
5643                               &_markBitMap, &_markStack, &mrias_cl);
5644   {
5645     TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5646     // Iterate over the dirty cards, setting the corresponding bits in the
5647     // mod union table.
5648     {
5649       ModUnionClosure modUnionClosure(&_modUnionTable);
5650       _ct->ct_bs()->dirty_card_iterate(
5651                       _cmsGen->used_region(),
5652                       &modUnionClosure);
5653     }
5654     // Having transferred these marks into the modUnionTable, we just need
5655     // to rescan the marked objects on the dirty cards in the modUnionTable.
5656     // The initial marking may have been done during an asynchronous
5657     // collection so there may be dirty bits in the mod-union table.
5658     const int alignment =
5659       CardTableModRefBS::card_size * BitsPerWord;
5660     {
5661       // ... First handle dirty cards in CMS gen
5662       markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5663       MemRegion ur = _cmsGen->used_region();
5664       HeapWord* lb = ur.start();
5665       HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5666       MemRegion cms_span(lb, ub);
5667       _modUnionTable.dirty_range_iterate_clear(cms_span,
5668                                                &markFromDirtyCardsClosure);
5669       verify_work_stacks_empty();
5670       if (PrintCMSStatistics != 0) {
5671         gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5672           markFromDirtyCardsClosure.num_dirty_cards());
5673       }
5674     }
5675   }
5676   if (VerifyDuringGC &&
5677       GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5678     HandleMark hm;  // Discard invalid handles created during verification
5679     Universe::verify(true);
5680   }
5681   {
5682     TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5683 
5684     verify_work_stacks_empty();
5685 
5686     gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5687     GenCollectedHeap::StrongRootsScope srs(gch);
5688     gch->gen_process_strong_roots(_cmsGen->level(),
5689                                   true,  // younger gens as roots
5690                                   false, // use the local StrongRootsScope
5691                                   false, // not scavenging
5692                                   SharedHeap::ScanningOption(roots_scanning_options()),
5693                                   &mrias_cl,
5694                                   true,   // walk code active on stacks
5695                                   NULL,
5696                                   NULL);  // The dirty klasses will be handled below
5697 
5698     assert(should_unload_classes()
5699            || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5700            "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5701   }
5702 
5703   {
5704     TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5705 
5706     verify_work_stacks_empty();
5707 
5708     // Scan all class loader data objects that might have been introduced
5709     // during concurrent marking.
5710     ResourceMark rm;
5711     GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5712     for (int i = 0; i < array->length(); i++) {
5713       mrias_cl.do_class_loader_data(array->at(i));
5714     }
5715 
5716     // We don't need to keep track of new CLDs anymore.
5717     ClassLoaderDataGraph::remember_new_clds(false);
5718 
5719     verify_work_stacks_empty();
5720   }
5721 
5722   {
5723     TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5724 
5725     verify_work_stacks_empty();
5726 
5727     RemarkKlassClosure remark_klass_closure(&mrias_cl);
5728     ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5729 
5730     verify_work_stacks_empty();
5731   }
5732 
5733   // We might have added oops to ClassLoaderData::_handles during the
5734   // concurrent marking phase. These oops point to newly allocated objects
5735   // that are guaranteed to be kept alive. Either by the direct allocation
5736   // code, or when the young collector processes the strong roots. Hence,
5737   // we don't have to revisit the _handles block during the remark phase.
5738 
5739   verify_work_stacks_empty();
5740   // Restore evacuated mark words, if any, used for overflow list links
5741   if (!CMSOverflowEarlyRestoration) {
5742     restore_preserved_marks_if_any();
5743   }
5744   verify_overflow_empty();
5745 }
5746 
5747 ////////////////////////////////////////////////////////
5748 // Parallel Reference Processing Task Proxy Class
5749 ////////////////////////////////////////////////////////
5750 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5751   typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5752   CMSCollector*          _collector;
5753   CMSBitMap*             _mark_bit_map;
5754   const MemRegion        _span;
5755   ProcessTask&           _task;
5756 
5757 public:
5758   CMSRefProcTaskProxy(ProcessTask&     task,
5759                       CMSCollector*    collector,
5760                       const MemRegion& span,
5761                       CMSBitMap*       mark_bit_map,
5762                       AbstractWorkGang* workers,
5763                       OopTaskQueueSet* task_queues):
5764     // XXX Should superclass AGTWOQ also know about AWG since it knows
5765     // about the task_queues used by the AWG? Then it could initialize
5766     // the terminator() object. See 6984287. The set_for_termination()
5767     // below is a temporary band-aid for the regression in 6984287.
5768     AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5769       task_queues),
5770     _task(task),
5771     _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5772   {
5773     assert(_collector->_span.equals(_span) && !_span.is_empty(),
5774            "Inconsistency in _span");
5775     set_for_termination(workers->active_workers());
5776   }
5777 
5778   OopTaskQueueSet* task_queues() { return queues(); }
5779 
5780   OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5781 
5782   void do_work_steal(int i,
5783                      CMSParDrainMarkingStackClosure* drain,
5784                      CMSParKeepAliveClosure* keep_alive,
5785                      int* seed);
5786 
5787   virtual void work(uint worker_id);
5788 };
5789 
5790 void CMSRefProcTaskProxy::work(uint worker_id) {
5791   assert(_collector->_span.equals(_span), "Inconsistency in _span");
5792   CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5793                                         _mark_bit_map,
5794                                         work_queue(worker_id));
5795   CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5796                                                  _mark_bit_map,
5797                                                  work_queue(worker_id));
5798   CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5799   _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5800   if (_task.marks_oops_alive()) {
5801     do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5802                   _collector->hash_seed(worker_id));
5803   }
5804   assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5805   assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5806 }
5807 
5808 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5809   typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5810   EnqueueTask& _task;
5811 
5812 public:
5813   CMSRefEnqueueTaskProxy(EnqueueTask& task)
5814     : AbstractGangTask("Enqueue reference objects in parallel"),
5815       _task(task)
5816   { }
5817 
5818   virtual void work(uint worker_id)
5819   {
5820     _task.work(worker_id);
5821   }
5822 };
5823 
5824 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5825   MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5826    _span(span),
5827    _bit_map(bit_map),
5828    _work_queue(work_queue),
5829    _mark_and_push(collector, span, bit_map, work_queue),
5830    _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5831                         (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5832 { }
5833 
5834 // . see if we can share work_queues with ParNew? XXX
5835 void CMSRefProcTaskProxy::do_work_steal(int i,
5836   CMSParDrainMarkingStackClosure* drain,
5837   CMSParKeepAliveClosure* keep_alive,
5838   int* seed) {
5839   OopTaskQueue* work_q = work_queue(i);
5840   NOT_PRODUCT(int num_steals = 0;)
5841   oop obj_to_scan;
5842 
5843   while (true) {
5844     // Completely finish any left over work from (an) earlier round(s)
5845     drain->trim_queue(0);
5846     size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5847                                          (size_t)ParGCDesiredObjsFromOverflowList);
5848     // Now check if there's any work in the overflow list
5849     // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5850     // only affects the number of attempts made to get work from the
5851     // overflow list and does not affect the number of workers.  Just
5852     // pass ParallelGCThreads so this behavior is unchanged.
5853     if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5854                                                 work_q,
5855                                                 ParallelGCThreads)) {
5856       // Found something in global overflow list;
5857       // not yet ready to go stealing work from others.
5858       // We'd like to assert(work_q->size() != 0, ...)
5859       // because we just took work from the overflow list,
5860       // but of course we can't, since all of that might have
5861       // been already stolen from us.
5862       continue;
5863     }
5864     // Verify that we have no work before we resort to stealing
5865     assert(work_q->size() == 0, "Have work, shouldn't steal");
5866     // Try to steal from other queues that have work
5867     if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5868       NOT_PRODUCT(num_steals++;)
5869       assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5870       assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5871       // Do scanning work
5872       obj_to_scan->oop_iterate(keep_alive);
5873       // Loop around, finish this work, and try to steal some more
5874     } else if (terminator()->offer_termination()) {
5875       break;  // nirvana from the infinite cycle
5876     }
5877   }
5878   NOT_PRODUCT(
5879     if (PrintCMSStatistics != 0) {
5880       gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5881     }
5882   )
5883 }
5884 
5885 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5886 {
5887   GenCollectedHeap* gch = GenCollectedHeap::heap();
5888   FlexibleWorkGang* workers = gch->workers();
5889   assert(workers != NULL, "Need parallel worker threads.");
5890   CMSRefProcTaskProxy rp_task(task, &_collector,
5891                               _collector.ref_processor()->span(),
5892                               _collector.markBitMap(),
5893                               workers, _collector.task_queues());
5894   workers->run_task(&rp_task);
5895 }
5896 
5897 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5898 {
5899 
5900   GenCollectedHeap* gch = GenCollectedHeap::heap();
5901   FlexibleWorkGang* workers = gch->workers();
5902   assert(workers != NULL, "Need parallel worker threads.");
5903   CMSRefEnqueueTaskProxy enq_task(task);
5904   workers->run_task(&enq_task);
5905 }
5906 
5907 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5908 
5909   ResourceMark rm;
5910   HandleMark   hm;
5911 
5912   ReferenceProcessor* rp = ref_processor();
5913   assert(rp->span().equals(_span), "Spans should be equal");
5914   assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5915   // Process weak references.
5916   rp->setup_policy(clear_all_soft_refs);
5917   verify_work_stacks_empty();
5918 
5919   CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5920                                           &_markStack, false /* !preclean */);
5921   CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5922                                 _span, &_markBitMap, &_markStack,
5923                                 &cmsKeepAliveClosure, false /* !preclean */);
5924   {
5925     TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5926     if (rp->processing_is_mt()) {
5927       // Set the degree of MT here.  If the discovery is done MT, there
5928       // may have been a different number of threads doing the discovery
5929       // and a different number of discovered lists may have Ref objects.
5930       // That is OK as long as the Reference lists are balanced (see
5931       // balance_all_queues() and balance_queues()).
5932       GenCollectedHeap* gch = GenCollectedHeap::heap();
5933       int active_workers = ParallelGCThreads;
5934       FlexibleWorkGang* workers = gch->workers();
5935       if (workers != NULL) {
5936         active_workers = workers->active_workers();
5937         // The expectation is that active_workers will have already
5938         // been set to a reasonable value.  If it has not been set,
5939         // investigate.
5940         assert(active_workers > 0, "Should have been set during scavenge");
5941       }
5942       rp->set_active_mt_degree(active_workers);
5943       CMSRefProcTaskExecutor task_executor(*this);
5944       rp->process_discovered_references(&_is_alive_closure,
5945                                         &cmsKeepAliveClosure,
5946                                         &cmsDrainMarkingStackClosure,
5947                                         &task_executor);
5948     } else {
5949       rp->process_discovered_references(&_is_alive_closure,
5950                                         &cmsKeepAliveClosure,
5951                                         &cmsDrainMarkingStackClosure,
5952                                         NULL);
5953     }
5954     verify_work_stacks_empty();
5955   }
5956 
5957   if (should_unload_classes()) {
5958     {
5959       TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5960 
5961       // Follow SystemDictionary roots and unload classes
5962       bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5963 
5964       // Follow CodeCache roots and unload any methods marked for unloading
5965       CodeCache::do_unloading(&_is_alive_closure,
5966                               &cmsKeepAliveClosure,
5967                               purged_class);
5968 
5969       cmsDrainMarkingStackClosure.do_void();
5970       verify_work_stacks_empty();
5971 
5972       // Update subklass/sibling/implementor links in KlassKlass descendants
5973       Klass::clean_weak_klass_links(&_is_alive_closure);
5974       // Nothing should have been pushed onto the working stacks.
5975       verify_work_stacks_empty();
5976     }
5977 
5978     {
5979       TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
5980       // Clean up unreferenced symbols in symbol table.
5981       SymbolTable::unlink();
5982     }
5983   }
5984 
5985   // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
5986   // Need to check if we really scanned the StringTable.
5987   if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
5988     TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
5989     // Now clean up stale oops in StringTable
5990     StringTable::unlink(&_is_alive_closure);
5991   }
5992 
5993   verify_work_stacks_empty();
5994   // Restore any preserved marks as a result of mark stack or
5995   // work queue overflow
5996   restore_preserved_marks_if_any();  // done single-threaded for now
5997 
5998   rp->set_enqueuing_is_done(true);
5999   if (rp->processing_is_mt()) {
6000     rp->balance_all_queues();
6001     CMSRefProcTaskExecutor task_executor(*this);
6002     rp->enqueue_discovered_references(&task_executor);
6003   } else {
6004     rp->enqueue_discovered_references(NULL);
6005   }
6006   rp->verify_no_references_recorded();
6007   assert(!rp->discovery_enabled(), "should have been disabled");
6008 }
6009 
6010 #ifndef PRODUCT
6011 void CMSCollector::check_correct_thread_executing() {
6012   Thread* t = Thread::current();
6013   // Only the VM thread or the CMS thread should be here.
6014   assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6015          "Unexpected thread type");
6016   // If this is the vm thread, the foreground process
6017   // should not be waiting.  Note that _foregroundGCIsActive is
6018   // true while the foreground collector is waiting.
6019   if (_foregroundGCShouldWait) {
6020     // We cannot be the VM thread
6021     assert(t->is_ConcurrentGC_thread(),
6022            "Should be CMS thread");
6023   } else {
6024     // We can be the CMS thread only if we are in a stop-world
6025     // phase of CMS collection.
6026     if (t->is_ConcurrentGC_thread()) {
6027       assert(_collectorState == InitialMarking ||
6028              _collectorState == FinalMarking,
6029              "Should be a stop-world phase");
6030       // The CMS thread should be holding the CMS_token.
6031       assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6032              "Potential interference with concurrently "
6033              "executing VM thread");
6034     }
6035   }
6036 }
6037 #endif
6038 
6039 void CMSCollector::sweep(bool asynch) {
6040   assert(_collectorState == Sweeping, "just checking");
6041   check_correct_thread_executing();
6042   verify_work_stacks_empty();
6043   verify_overflow_empty();
6044   increment_sweep_count();
6045   TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6046 
6047   _inter_sweep_timer.stop();
6048   _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6049   size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6050 
6051   assert(!_intra_sweep_timer.is_active(), "Should not be active");
6052   _intra_sweep_timer.reset();
6053   _intra_sweep_timer.start();
6054   if (asynch) {
6055     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6056     CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6057     // First sweep the old gen
6058     {
6059       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6060                                bitMapLock());
6061       sweepWork(_cmsGen, asynch);
6062     }
6063 
6064     // Update Universe::_heap_*_at_gc figures.
6065     // We need all the free list locks to make the abstract state
6066     // transition from Sweeping to Resetting. See detailed note
6067     // further below.
6068     {
6069       CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6070       // Update heap occupancy information which is used as
6071       // input to soft ref clearing policy at the next gc.
6072       Universe::update_heap_info_at_gc();
6073       _collectorState = Resizing;
6074     }
6075   } else {
6076     // already have needed locks
6077     sweepWork(_cmsGen,  asynch);
6078     // Update heap occupancy information which is used as
6079     // input to soft ref clearing policy at the next gc.
6080     Universe::update_heap_info_at_gc();
6081     _collectorState = Resizing;
6082   }
6083   verify_work_stacks_empty();
6084   verify_overflow_empty();
6085 
6086   _intra_sweep_timer.stop();
6087   _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6088 
6089   _inter_sweep_timer.reset();
6090   _inter_sweep_timer.start();
6091 
6092   // We need to use a monotonically non-deccreasing time in ms
6093   // or we will see time-warp warnings and os::javaTimeMillis()
6094   // does not guarantee monotonicity.
6095   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6096   update_time_of_last_gc(now);
6097 
6098   // NOTE on abstract state transitions:
6099   // Mutators allocate-live and/or mark the mod-union table dirty
6100   // based on the state of the collection.  The former is done in
6101   // the interval [Marking, Sweeping] and the latter in the interval
6102   // [Marking, Sweeping).  Thus the transitions into the Marking state
6103   // and out of the Sweeping state must be synchronously visible
6104   // globally to the mutators.
6105   // The transition into the Marking state happens with the world
6106   // stopped so the mutators will globally see it.  Sweeping is
6107   // done asynchronously by the background collector so the transition
6108   // from the Sweeping state to the Resizing state must be done
6109   // under the freelistLock (as is the check for whether to
6110   // allocate-live and whether to dirty the mod-union table).
6111   assert(_collectorState == Resizing, "Change of collector state to"
6112     " Resizing must be done under the freelistLocks (plural)");
6113 
6114   // Now that sweeping has been completed, we clear
6115   // the incremental_collection_failed flag,
6116   // thus inviting a younger gen collection to promote into
6117   // this generation. If such a promotion may still fail,
6118   // the flag will be set again when a young collection is
6119   // attempted.
6120   GenCollectedHeap* gch = GenCollectedHeap::heap();
6121   gch->clear_incremental_collection_failed();  // Worth retrying as fresh space may have been freed up
6122   gch->update_full_collections_completed(_collection_count_start);
6123 }
6124 
6125 // FIX ME!!! Looks like this belongs in CFLSpace, with
6126 // CMSGen merely delegating to it.
6127 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6128   double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6129   HeapWord*  minAddr        = _cmsSpace->bottom();
6130   HeapWord*  largestAddr    =
6131     (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6132   if (largestAddr == NULL) {
6133     // The dictionary appears to be empty.  In this case
6134     // try to coalesce at the end of the heap.
6135     largestAddr = _cmsSpace->end();
6136   }
6137   size_t largestOffset     = pointer_delta(largestAddr, minAddr);
6138   size_t nearLargestOffset =
6139     (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6140   if (PrintFLSStatistics != 0) {
6141     gclog_or_tty->print_cr(
6142       "CMS: Large Block: " PTR_FORMAT ";"
6143       " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6144       largestAddr,
6145       _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6146   }
6147   _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6148 }
6149 
6150 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6151   return addr >= _cmsSpace->nearLargestChunk();
6152 }
6153 
6154 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6155   return _cmsSpace->find_chunk_at_end();
6156 }
6157 
6158 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6159                                                     bool full) {
6160   // The next lower level has been collected.  Gather any statistics
6161   // that are of interest at this point.
6162   if (!full && (current_level + 1) == level()) {
6163     // Gather statistics on the young generation collection.
6164     collector()->stats().record_gc0_end(used());
6165   }
6166 }
6167 
6168 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6169   GenCollectedHeap* gch = GenCollectedHeap::heap();
6170   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6171     "Wrong type of heap");
6172   CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6173     gch->gen_policy()->size_policy();
6174   assert(sp->is_gc_cms_adaptive_size_policy(),
6175     "Wrong type of size policy");
6176   return sp;
6177 }
6178 
6179 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6180   if (PrintGCDetails && Verbose) {
6181     gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6182   }
6183   _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6184   _debug_collection_type =
6185     (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6186   if (PrintGCDetails && Verbose) {
6187     gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6188   }
6189 }
6190 
6191 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6192   bool asynch) {
6193   // We iterate over the space(s) underlying this generation,
6194   // checking the mark bit map to see if the bits corresponding
6195   // to specific blocks are marked or not. Blocks that are
6196   // marked are live and are not swept up. All remaining blocks
6197   // are swept up, with coalescing on-the-fly as we sweep up
6198   // contiguous free and/or garbage blocks:
6199   // We need to ensure that the sweeper synchronizes with allocators
6200   // and stop-the-world collectors. In particular, the following
6201   // locks are used:
6202   // . CMS token: if this is held, a stop the world collection cannot occur
6203   // . freelistLock: if this is held no allocation can occur from this
6204   //                 generation by another thread
6205   // . bitMapLock: if this is held, no other thread can access or update
6206   //
6207 
6208   // Note that we need to hold the freelistLock if we use
6209   // block iterate below; else the iterator might go awry if
6210   // a mutator (or promotion) causes block contents to change
6211   // (for instance if the allocator divvies up a block).
6212   // If we hold the free list lock, for all practical purposes
6213   // young generation GC's can't occur (they'll usually need to
6214   // promote), so we might as well prevent all young generation
6215   // GC's while we do a sweeping step. For the same reason, we might
6216   // as well take the bit map lock for the entire duration
6217 
6218   // check that we hold the requisite locks
6219   assert(have_cms_token(), "Should hold cms token");
6220   assert(   (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6221          || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6222         "Should possess CMS token to sweep");
6223   assert_lock_strong(gen->freelistLock());
6224   assert_lock_strong(bitMapLock());
6225 
6226   assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6227   assert(_intra_sweep_timer.is_active(),  "Was switched on  in an outer context");
6228   gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6229                                       _inter_sweep_estimate.padded_average(),
6230                                       _intra_sweep_estimate.padded_average());
6231   gen->setNearLargestChunk();
6232 
6233   {
6234     SweepClosure sweepClosure(this, gen, &_markBitMap,
6235                             CMSYield && asynch);
6236     gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6237     // We need to free-up/coalesce garbage/blocks from a
6238     // co-terminal free run. This is done in the SweepClosure
6239     // destructor; so, do not remove this scope, else the
6240     // end-of-sweep-census below will be off by a little bit.
6241   }
6242   gen->cmsSpace()->sweep_completed();
6243   gen->cmsSpace()->endSweepFLCensus(sweep_count());
6244   if (should_unload_classes()) {                // unloaded classes this cycle,
6245     _concurrent_cycles_since_last_unload = 0;   // ... reset count
6246   } else {                                      // did not unload classes,
6247     _concurrent_cycles_since_last_unload++;     // ... increment count
6248   }
6249 }
6250 
6251 // Reset CMS data structures (for now just the marking bit map)
6252 // preparatory for the next cycle.
6253 void CMSCollector::reset(bool asynch) {
6254   GenCollectedHeap* gch = GenCollectedHeap::heap();
6255   CMSAdaptiveSizePolicy* sp = size_policy();
6256   AdaptiveSizePolicyOutput(sp, gch->total_collections());
6257   if (asynch) {
6258     CMSTokenSyncWithLocks ts(true, bitMapLock());
6259 
6260     // If the state is not "Resetting", the foreground  thread
6261     // has done a collection and the resetting.
6262     if (_collectorState != Resetting) {
6263       assert(_collectorState == Idling, "The state should only change"
6264         " because the foreground collector has finished the collection");
6265       return;
6266     }
6267 
6268     // Clear the mark bitmap (no grey objects to start with)
6269     // for the next cycle.
6270     TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6271     CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6272 
6273     HeapWord* curAddr = _markBitMap.startWord();
6274     while (curAddr < _markBitMap.endWord()) {
6275       size_t remaining  = pointer_delta(_markBitMap.endWord(), curAddr);
6276       MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6277       _markBitMap.clear_large_range(chunk);
6278       if (ConcurrentMarkSweepThread::should_yield() &&
6279           !foregroundGCIsActive() &&
6280           CMSYield) {
6281         assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6282                "CMS thread should hold CMS token");
6283         assert_lock_strong(bitMapLock());
6284         bitMapLock()->unlock();
6285         ConcurrentMarkSweepThread::desynchronize(true);
6286         ConcurrentMarkSweepThread::acknowledge_yield_request();
6287         stopTimer();
6288         if (PrintCMSStatistics != 0) {
6289           incrementYields();
6290         }
6291         icms_wait();
6292 
6293         // See the comment in coordinator_yield()
6294         for (unsigned i = 0; i < CMSYieldSleepCount &&
6295                          ConcurrentMarkSweepThread::should_yield() &&
6296                          !CMSCollector::foregroundGCIsActive(); ++i) {
6297           os::sleep(Thread::current(), 1, false);
6298           ConcurrentMarkSweepThread::acknowledge_yield_request();
6299         }
6300 
6301         ConcurrentMarkSweepThread::synchronize(true);
6302         bitMapLock()->lock_without_safepoint_check();
6303         startTimer();
6304       }
6305       curAddr = chunk.end();
6306     }
6307     // A successful mostly concurrent collection has been done.
6308     // Because only the full (i.e., concurrent mode failure) collections
6309     // are being measured for gc overhead limits, clean the "near" flag
6310     // and count.
6311     sp->reset_gc_overhead_limit_count();
6312     _collectorState = Idling;
6313   } else {
6314     // already have the lock
6315     assert(_collectorState == Resetting, "just checking");
6316     assert_lock_strong(bitMapLock());
6317     _markBitMap.clear_all();
6318     _collectorState = Idling;
6319   }
6320 
6321   // Stop incremental mode after a cycle completes, so that any future cycles
6322   // are triggered by allocation.
6323   stop_icms();
6324 
6325   NOT_PRODUCT(
6326     if (RotateCMSCollectionTypes) {
6327       _cmsGen->rotate_debug_collection_type();
6328     }
6329   )
6330 }
6331 
6332 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6333   gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6334   TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6335   TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6336   TraceCollectorStats tcs(counters());
6337 
6338   switch (op) {
6339     case CMS_op_checkpointRootsInitial: {
6340       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6341       checkpointRootsInitial(true);       // asynch
6342       if (PrintGC) {
6343         _cmsGen->printOccupancy("initial-mark");
6344       }
6345       break;
6346     }
6347     case CMS_op_checkpointRootsFinal: {
6348       SvcGCMarker sgcm(SvcGCMarker::OTHER);
6349       checkpointRootsFinal(true,    // asynch
6350                            false,   // !clear_all_soft_refs
6351                            false);  // !init_mark_was_synchronous
6352       if (PrintGC) {
6353         _cmsGen->printOccupancy("remark");
6354       }
6355       break;
6356     }
6357     default:
6358       fatal("No such CMS_op");
6359   }
6360 }
6361 
6362 #ifndef PRODUCT
6363 size_t const CMSCollector::skip_header_HeapWords() {
6364   return FreeChunk::header_size();
6365 }
6366 
6367 // Try and collect here conditions that should hold when
6368 // CMS thread is exiting. The idea is that the foreground GC
6369 // thread should not be blocked if it wants to terminate
6370 // the CMS thread and yet continue to run the VM for a while
6371 // after that.
6372 void CMSCollector::verify_ok_to_terminate() const {
6373   assert(Thread::current()->is_ConcurrentGC_thread(),
6374          "should be called by CMS thread");
6375   assert(!_foregroundGCShouldWait, "should be false");
6376   // We could check here that all the various low-level locks
6377   // are not held by the CMS thread, but that is overkill; see
6378   // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6379   // is checked.
6380 }
6381 #endif
6382 
6383 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6384    assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6385           "missing Printezis mark?");
6386   HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6387   size_t size = pointer_delta(nextOneAddr + 1, addr);
6388   assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6389          "alignment problem");
6390   assert(size >= 3, "Necessary for Printezis marks to work");
6391   return size;
6392 }
6393 
6394 // A variant of the above (block_size_using_printezis_bits()) except
6395 // that we return 0 if the P-bits are not yet set.
6396 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6397   if (_markBitMap.isMarked(addr + 1)) {
6398     assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6399     HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6400     size_t size = pointer_delta(nextOneAddr + 1, addr);
6401     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6402            "alignment problem");
6403     assert(size >= 3, "Necessary for Printezis marks to work");
6404     return size;
6405   }
6406   return 0;
6407 }
6408 
6409 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6410   size_t sz = 0;
6411   oop p = (oop)addr;
6412   if (p->klass_or_null() != NULL) {
6413     sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6414   } else {
6415     sz = block_size_using_printezis_bits(addr);
6416   }
6417   assert(sz > 0, "size must be nonzero");
6418   HeapWord* next_block = addr + sz;
6419   HeapWord* next_card  = (HeapWord*)round_to((uintptr_t)next_block,
6420                                              CardTableModRefBS::card_size);
6421   assert(round_down((uintptr_t)addr,      CardTableModRefBS::card_size) <
6422          round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6423          "must be different cards");
6424   return next_card;
6425 }
6426 
6427 
6428 // CMS Bit Map Wrapper /////////////////////////////////////////
6429 
6430 // Construct a CMS bit map infrastructure, but don't create the
6431 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6432 // further below.
6433 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6434   _bm(),
6435   _shifter(shifter),
6436   _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6437 {
6438   _bmStartWord = 0;
6439   _bmWordSize  = 0;
6440 }
6441 
6442 bool CMSBitMap::allocate(MemRegion mr) {
6443   _bmStartWord = mr.start();
6444   _bmWordSize  = mr.word_size();
6445   ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6446                      (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6447   if (!brs.is_reserved()) {
6448     warning("CMS bit map allocation failure");
6449     return false;
6450   }
6451   // For now we'll just commit all of the bit map up fromt.
6452   // Later on we'll try to be more parsimonious with swap.
6453   if (!_virtual_space.initialize(brs, brs.size())) {
6454     warning("CMS bit map backing store failure");
6455     return false;
6456   }
6457   assert(_virtual_space.committed_size() == brs.size(),
6458          "didn't reserve backing store for all of CMS bit map?");
6459   _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6460   assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6461          _bmWordSize, "inconsistency in bit map sizing");
6462   _bm.set_size(_bmWordSize >> _shifter);
6463 
6464   // bm.clear(); // can we rely on getting zero'd memory? verify below
6465   assert(isAllClear(),
6466          "Expected zero'd memory from ReservedSpace constructor");
6467   assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6468          "consistency check");
6469   return true;
6470 }
6471 
6472 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6473   HeapWord *next_addr, *end_addr, *last_addr;
6474   assert_locked();
6475   assert(covers(mr), "out-of-range error");
6476   // XXX assert that start and end are appropriately aligned
6477   for (next_addr = mr.start(), end_addr = mr.end();
6478        next_addr < end_addr; next_addr = last_addr) {
6479     MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6480     last_addr = dirty_region.end();
6481     if (!dirty_region.is_empty()) {
6482       cl->do_MemRegion(dirty_region);
6483     } else {
6484       assert(last_addr == end_addr, "program logic");
6485       return;
6486     }
6487   }
6488 }
6489 
6490 #ifndef PRODUCT
6491 void CMSBitMap::assert_locked() const {
6492   CMSLockVerifier::assert_locked(lock());
6493 }
6494 
6495 bool CMSBitMap::covers(MemRegion mr) const {
6496   // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6497   assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6498          "size inconsistency");
6499   return (mr.start() >= _bmStartWord) &&
6500          (mr.end()   <= endWord());
6501 }
6502 
6503 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6504     return (start >= _bmStartWord && (start + size) <= endWord());
6505 }
6506 
6507 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6508   // verify that there are no 1 bits in the interval [left, right)
6509   FalseBitMapClosure falseBitMapClosure;
6510   iterate(&falseBitMapClosure, left, right);
6511 }
6512 
6513 void CMSBitMap::region_invariant(MemRegion mr)
6514 {
6515   assert_locked();
6516   // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6517   assert(!mr.is_empty(), "unexpected empty region");
6518   assert(covers(mr), "mr should be covered by bit map");
6519   // convert address range into offset range
6520   size_t start_ofs = heapWordToOffset(mr.start());
6521   // Make sure that end() is appropriately aligned
6522   assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6523                         (1 << (_shifter+LogHeapWordSize))),
6524          "Misaligned mr.end()");
6525   size_t end_ofs   = heapWordToOffset(mr.end());
6526   assert(end_ofs > start_ofs, "Should mark at least one bit");
6527 }
6528 
6529 #endif
6530 
6531 bool CMSMarkStack::allocate(size_t size) {
6532   // allocate a stack of the requisite depth
6533   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6534                    size * sizeof(oop)));
6535   if (!rs.is_reserved()) {
6536     warning("CMSMarkStack allocation failure");
6537     return false;
6538   }
6539   if (!_virtual_space.initialize(rs, rs.size())) {
6540     warning("CMSMarkStack backing store failure");
6541     return false;
6542   }
6543   assert(_virtual_space.committed_size() == rs.size(),
6544          "didn't reserve backing store for all of CMS stack?");
6545   _base = (oop*)(_virtual_space.low());
6546   _index = 0;
6547   _capacity = size;
6548   NOT_PRODUCT(_max_depth = 0);
6549   return true;
6550 }
6551 
6552 // XXX FIX ME !!! In the MT case we come in here holding a
6553 // leaf lock. For printing we need to take a further lock
6554 // which has lower rank. We need to recallibrate the two
6555 // lock-ranks involved in order to be able to rpint the
6556 // messages below. (Or defer the printing to the caller.
6557 // For now we take the expedient path of just disabling the
6558 // messages for the problematic case.)
6559 void CMSMarkStack::expand() {
6560   assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6561   if (_capacity == MarkStackSizeMax) {
6562     if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6563       // We print a warning message only once per CMS cycle.
6564       gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6565     }
6566     return;
6567   }
6568   // Double capacity if possible
6569   size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6570   // Do not give up existing stack until we have managed to
6571   // get the double capacity that we desired.
6572   ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6573                    new_capacity * sizeof(oop)));
6574   if (rs.is_reserved()) {
6575     // Release the backing store associated with old stack
6576     _virtual_space.release();
6577     // Reinitialize virtual space for new stack
6578     if (!_virtual_space.initialize(rs, rs.size())) {
6579       fatal("Not enough swap for expanded marking stack");
6580     }
6581     _base = (oop*)(_virtual_space.low());
6582     _index = 0;
6583     _capacity = new_capacity;
6584   } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6585     // Failed to double capacity, continue;
6586     // we print a detail message only once per CMS cycle.
6587     gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6588             SIZE_FORMAT"K",
6589             _capacity / K, new_capacity / K);
6590   }
6591 }
6592 
6593 
6594 // Closures
6595 // XXX: there seems to be a lot of code  duplication here;
6596 // should refactor and consolidate common code.
6597 
6598 // This closure is used to mark refs into the CMS generation in
6599 // the CMS bit map. Called at the first checkpoint. This closure
6600 // assumes that we do not need to re-mark dirty cards; if the CMS
6601 // generation on which this is used is not an oldest
6602 // generation then this will lose younger_gen cards!
6603 
6604 MarkRefsIntoClosure::MarkRefsIntoClosure(
6605   MemRegion span, CMSBitMap* bitMap):
6606     _span(span),
6607     _bitMap(bitMap)
6608 {
6609     assert(_ref_processor == NULL, "deliberately left NULL");
6610     assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6611 }
6612 
6613 void MarkRefsIntoClosure::do_oop(oop obj) {
6614   // if p points into _span, then mark corresponding bit in _markBitMap
6615   assert(obj->is_oop(), "expected an oop");
6616   HeapWord* addr = (HeapWord*)obj;
6617   if (_span.contains(addr)) {
6618     // this should be made more efficient
6619     _bitMap->mark(addr);
6620   }
6621 }
6622 
6623 void MarkRefsIntoClosure::do_oop(oop* p)       { MarkRefsIntoClosure::do_oop_work(p); }
6624 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6625 
6626 // A variant of the above, used for CMS marking verification.
6627 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6628   MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6629     _span(span),
6630     _verification_bm(verification_bm),
6631     _cms_bm(cms_bm)
6632 {
6633     assert(_ref_processor == NULL, "deliberately left NULL");
6634     assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6635 }
6636 
6637 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6638   // if p points into _span, then mark corresponding bit in _markBitMap
6639   assert(obj->is_oop(), "expected an oop");
6640   HeapWord* addr = (HeapWord*)obj;
6641   if (_span.contains(addr)) {
6642     _verification_bm->mark(addr);
6643     if (!_cms_bm->isMarked(addr)) {
6644       oop(addr)->print();
6645       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6646       fatal("... aborting");
6647     }
6648   }
6649 }
6650 
6651 void MarkRefsIntoVerifyClosure::do_oop(oop* p)       { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6652 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6653 
6654 //////////////////////////////////////////////////
6655 // MarkRefsIntoAndScanClosure
6656 //////////////////////////////////////////////////
6657 
6658 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6659                                                        ReferenceProcessor* rp,
6660                                                        CMSBitMap* bit_map,
6661                                                        CMSBitMap* mod_union_table,
6662                                                        CMSMarkStack*  mark_stack,
6663                                                        CMSCollector* collector,
6664                                                        bool should_yield,
6665                                                        bool concurrent_precleaning):
6666   _collector(collector),
6667   _span(span),
6668   _bit_map(bit_map),
6669   _mark_stack(mark_stack),
6670   _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6671                       mark_stack, concurrent_precleaning),
6672   _yield(should_yield),
6673   _concurrent_precleaning(concurrent_precleaning),
6674   _freelistLock(NULL)
6675 {
6676   _ref_processor = rp;
6677   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6678 }
6679 
6680 // This closure is used to mark refs into the CMS generation at the
6681 // second (final) checkpoint, and to scan and transitively follow
6682 // the unmarked oops. It is also used during the concurrent precleaning
6683 // phase while scanning objects on dirty cards in the CMS generation.
6684 // The marks are made in the marking bit map and the marking stack is
6685 // used for keeping the (newly) grey objects during the scan.
6686 // The parallel version (Par_...) appears further below.
6687 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6688   if (obj != NULL) {
6689     assert(obj->is_oop(), "expected an oop");
6690     HeapWord* addr = (HeapWord*)obj;
6691     assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6692     assert(_collector->overflow_list_is_empty(),
6693            "overflow list should be empty");
6694     if (_span.contains(addr) &&
6695         !_bit_map->isMarked(addr)) {
6696       // mark bit map (object is now grey)
6697       _bit_map->mark(addr);
6698       // push on marking stack (stack should be empty), and drain the
6699       // stack by applying this closure to the oops in the oops popped
6700       // from the stack (i.e. blacken the grey objects)
6701       bool res = _mark_stack->push(obj);
6702       assert(res, "Should have space to push on empty stack");
6703       do {
6704         oop new_oop = _mark_stack->pop();
6705         assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6706         assert(_bit_map->isMarked((HeapWord*)new_oop),
6707                "only grey objects on this stack");
6708         // iterate over the oops in this oop, marking and pushing
6709         // the ones in CMS heap (i.e. in _span).
6710         new_oop->oop_iterate(&_pushAndMarkClosure);
6711         // check if it's time to yield
6712         do_yield_check();
6713       } while (!_mark_stack->isEmpty() ||
6714                (!_concurrent_precleaning && take_from_overflow_list()));
6715         // if marking stack is empty, and we are not doing this
6716         // during precleaning, then check the overflow list
6717     }
6718     assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6719     assert(_collector->overflow_list_is_empty(),
6720            "overflow list was drained above");
6721     // We could restore evacuated mark words, if any, used for
6722     // overflow list links here because the overflow list is
6723     // provably empty here. That would reduce the maximum
6724     // size requirements for preserved_{oop,mark}_stack.
6725     // But we'll just postpone it until we are all done
6726     // so we can just stream through.
6727     if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6728       _collector->restore_preserved_marks_if_any();
6729       assert(_collector->no_preserved_marks(), "No preserved marks");
6730     }
6731     assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6732            "All preserved marks should have been restored above");
6733   }
6734 }
6735 
6736 void MarkRefsIntoAndScanClosure::do_oop(oop* p)       { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6737 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6738 
6739 void MarkRefsIntoAndScanClosure::do_yield_work() {
6740   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6741          "CMS thread should hold CMS token");
6742   assert_lock_strong(_freelistLock);
6743   assert_lock_strong(_bit_map->lock());
6744   // relinquish the free_list_lock and bitMaplock()
6745   _bit_map->lock()->unlock();
6746   _freelistLock->unlock();
6747   ConcurrentMarkSweepThread::desynchronize(true);
6748   ConcurrentMarkSweepThread::acknowledge_yield_request();
6749   _collector->stopTimer();
6750   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6751   if (PrintCMSStatistics != 0) {
6752     _collector->incrementYields();
6753   }
6754   _collector->icms_wait();
6755 
6756   // See the comment in coordinator_yield()
6757   for (unsigned i = 0;
6758        i < CMSYieldSleepCount &&
6759        ConcurrentMarkSweepThread::should_yield() &&
6760        !CMSCollector::foregroundGCIsActive();
6761        ++i) {
6762     os::sleep(Thread::current(), 1, false);
6763     ConcurrentMarkSweepThread::acknowledge_yield_request();
6764   }
6765 
6766   ConcurrentMarkSweepThread::synchronize(true);
6767   _freelistLock->lock_without_safepoint_check();
6768   _bit_map->lock()->lock_without_safepoint_check();
6769   _collector->startTimer();
6770 }
6771 
6772 ///////////////////////////////////////////////////////////
6773 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6774 //                                 MarkRefsIntoAndScanClosure
6775 ///////////////////////////////////////////////////////////
6776 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6777   CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6778   CMSBitMap* bit_map, OopTaskQueue* work_queue):
6779   _span(span),
6780   _bit_map(bit_map),
6781   _work_queue(work_queue),
6782   _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6783                        (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6784   _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6785 {
6786   _ref_processor = rp;
6787   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6788 }
6789 
6790 // This closure is used to mark refs into the CMS generation at the
6791 // second (final) checkpoint, and to scan and transitively follow
6792 // the unmarked oops. The marks are made in the marking bit map and
6793 // the work_queue is used for keeping the (newly) grey objects during
6794 // the scan phase whence they are also available for stealing by parallel
6795 // threads. Since the marking bit map is shared, updates are
6796 // synchronized (via CAS).
6797 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6798   if (obj != NULL) {
6799     // Ignore mark word because this could be an already marked oop
6800     // that may be chained at the end of the overflow list.
6801     assert(obj->is_oop(true), "expected an oop");
6802     HeapWord* addr = (HeapWord*)obj;
6803     if (_span.contains(addr) &&
6804         !_bit_map->isMarked(addr)) {
6805       // mark bit map (object will become grey):
6806       // It is possible for several threads to be
6807       // trying to "claim" this object concurrently;
6808       // the unique thread that succeeds in marking the
6809       // object first will do the subsequent push on
6810       // to the work queue (or overflow list).
6811       if (_bit_map->par_mark(addr)) {
6812         // push on work_queue (which may not be empty), and trim the
6813         // queue to an appropriate length by applying this closure to
6814         // the oops in the oops popped from the stack (i.e. blacken the
6815         // grey objects)
6816         bool res = _work_queue->push(obj);
6817         assert(res, "Low water mark should be less than capacity?");
6818         trim_queue(_low_water_mark);
6819       } // Else, another thread claimed the object
6820     }
6821   }
6822 }
6823 
6824 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p)       { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6825 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6826 
6827 // This closure is used to rescan the marked objects on the dirty cards
6828 // in the mod union table and the card table proper.
6829 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6830   oop p, MemRegion mr) {
6831 
6832   size_t size = 0;
6833   HeapWord* addr = (HeapWord*)p;
6834   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6835   assert(_span.contains(addr), "we are scanning the CMS generation");
6836   // check if it's time to yield
6837   if (do_yield_check()) {
6838     // We yielded for some foreground stop-world work,
6839     // and we have been asked to abort this ongoing preclean cycle.
6840     return 0;
6841   }
6842   if (_bitMap->isMarked(addr)) {
6843     // it's marked; is it potentially uninitialized?
6844     if (p->klass_or_null() != NULL) {
6845         // an initialized object; ignore mark word in verification below
6846         // since we are running concurrent with mutators
6847         assert(p->is_oop(true), "should be an oop");
6848         if (p->is_objArray()) {
6849           // objArrays are precisely marked; restrict scanning
6850           // to dirty cards only.
6851           size = CompactibleFreeListSpace::adjustObjectSize(
6852                    p->oop_iterate(_scanningClosure, mr));
6853         } else {
6854           // A non-array may have been imprecisely marked; we need
6855           // to scan object in its entirety.
6856           size = CompactibleFreeListSpace::adjustObjectSize(
6857                    p->oop_iterate(_scanningClosure));
6858         }
6859         #ifdef DEBUG
6860           size_t direct_size =
6861             CompactibleFreeListSpace::adjustObjectSize(p->size());
6862           assert(size == direct_size, "Inconsistency in size");
6863           assert(size >= 3, "Necessary for Printezis marks to work");
6864           if (!_bitMap->isMarked(addr+1)) {
6865             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6866           } else {
6867             _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6868             assert(_bitMap->isMarked(addr+size-1),
6869                    "inconsistent Printezis mark");
6870           }
6871         #endif // DEBUG
6872     } else {
6873       // an unitialized object
6874       assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6875       HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6876       size = pointer_delta(nextOneAddr + 1, addr);
6877       assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6878              "alignment problem");
6879       // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6880       // will dirty the card when the klass pointer is installed in the
6881       // object (signalling the completion of initialization).
6882     }
6883   } else {
6884     // Either a not yet marked object or an uninitialized object
6885     if (p->klass_or_null() == NULL) {
6886       // An uninitialized object, skip to the next card, since
6887       // we may not be able to read its P-bits yet.
6888       assert(size == 0, "Initial value");
6889     } else {
6890       // An object not (yet) reached by marking: we merely need to
6891       // compute its size so as to go look at the next block.
6892       assert(p->is_oop(true), "should be an oop");
6893       size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6894     }
6895   }
6896   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6897   return size;
6898 }
6899 
6900 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6901   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6902          "CMS thread should hold CMS token");
6903   assert_lock_strong(_freelistLock);
6904   assert_lock_strong(_bitMap->lock());
6905   // relinquish the free_list_lock and bitMaplock()
6906   _bitMap->lock()->unlock();
6907   _freelistLock->unlock();
6908   ConcurrentMarkSweepThread::desynchronize(true);
6909   ConcurrentMarkSweepThread::acknowledge_yield_request();
6910   _collector->stopTimer();
6911   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6912   if (PrintCMSStatistics != 0) {
6913     _collector->incrementYields();
6914   }
6915   _collector->icms_wait();
6916 
6917   // See the comment in coordinator_yield()
6918   for (unsigned i = 0; i < CMSYieldSleepCount &&
6919                    ConcurrentMarkSweepThread::should_yield() &&
6920                    !CMSCollector::foregroundGCIsActive(); ++i) {
6921     os::sleep(Thread::current(), 1, false);
6922     ConcurrentMarkSweepThread::acknowledge_yield_request();
6923   }
6924 
6925   ConcurrentMarkSweepThread::synchronize(true);
6926   _freelistLock->lock_without_safepoint_check();
6927   _bitMap->lock()->lock_without_safepoint_check();
6928   _collector->startTimer();
6929 }
6930 
6931 
6932 //////////////////////////////////////////////////////////////////
6933 // SurvivorSpacePrecleanClosure
6934 //////////////////////////////////////////////////////////////////
6935 // This (single-threaded) closure is used to preclean the oops in
6936 // the survivor spaces.
6937 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6938 
6939   HeapWord* addr = (HeapWord*)p;
6940   DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6941   assert(!_span.contains(addr), "we are scanning the survivor spaces");
6942   assert(p->klass_or_null() != NULL, "object should be initializd");
6943   // an initialized object; ignore mark word in verification below
6944   // since we are running concurrent with mutators
6945   assert(p->is_oop(true), "should be an oop");
6946   // Note that we do not yield while we iterate over
6947   // the interior oops of p, pushing the relevant ones
6948   // on our marking stack.
6949   size_t size = p->oop_iterate(_scanning_closure);
6950   do_yield_check();
6951   // Observe that below, we do not abandon the preclean
6952   // phase as soon as we should; rather we empty the
6953   // marking stack before returning. This is to satisfy
6954   // some existing assertions. In general, it may be a
6955   // good idea to abort immediately and complete the marking
6956   // from the grey objects at a later time.
6957   while (!_mark_stack->isEmpty()) {
6958     oop new_oop = _mark_stack->pop();
6959     assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6960     assert(_bit_map->isMarked((HeapWord*)new_oop),
6961            "only grey objects on this stack");
6962     // iterate over the oops in this oop, marking and pushing
6963     // the ones in CMS heap (i.e. in _span).
6964     new_oop->oop_iterate(_scanning_closure);
6965     // check if it's time to yield
6966     do_yield_check();
6967   }
6968   unsigned int after_count =
6969     GenCollectedHeap::heap()->total_collections();
6970   bool abort = (_before_count != after_count) ||
6971                _collector->should_abort_preclean();
6972   return abort ? 0 : size;
6973 }
6974 
6975 void SurvivorSpacePrecleanClosure::do_yield_work() {
6976   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6977          "CMS thread should hold CMS token");
6978   assert_lock_strong(_bit_map->lock());
6979   // Relinquish the bit map lock
6980   _bit_map->lock()->unlock();
6981   ConcurrentMarkSweepThread::desynchronize(true);
6982   ConcurrentMarkSweepThread::acknowledge_yield_request();
6983   _collector->stopTimer();
6984   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6985   if (PrintCMSStatistics != 0) {
6986     _collector->incrementYields();
6987   }
6988   _collector->icms_wait();
6989 
6990   // See the comment in coordinator_yield()
6991   for (unsigned i = 0; i < CMSYieldSleepCount &&
6992                        ConcurrentMarkSweepThread::should_yield() &&
6993                        !CMSCollector::foregroundGCIsActive(); ++i) {
6994     os::sleep(Thread::current(), 1, false);
6995     ConcurrentMarkSweepThread::acknowledge_yield_request();
6996   }
6997 
6998   ConcurrentMarkSweepThread::synchronize(true);
6999   _bit_map->lock()->lock_without_safepoint_check();
7000   _collector->startTimer();
7001 }
7002 
7003 // This closure is used to rescan the marked objects on the dirty cards
7004 // in the mod union table and the card table proper. In the parallel
7005 // case, although the bitMap is shared, we do a single read so the
7006 // isMarked() query is "safe".
7007 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7008   // Ignore mark word because we are running concurrent with mutators
7009   assert(p->is_oop_or_null(true), "expected an oop or null");
7010   HeapWord* addr = (HeapWord*)p;
7011   assert(_span.contains(addr), "we are scanning the CMS generation");
7012   bool is_obj_array = false;
7013   #ifdef DEBUG
7014     if (!_parallel) {
7015       assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7016       assert(_collector->overflow_list_is_empty(),
7017              "overflow list should be empty");
7018 
7019     }
7020   #endif // DEBUG
7021   if (_bit_map->isMarked(addr)) {
7022     // Obj arrays are precisely marked, non-arrays are not;
7023     // so we scan objArrays precisely and non-arrays in their
7024     // entirety.
7025     if (p->is_objArray()) {
7026       is_obj_array = true;
7027       if (_parallel) {
7028         p->oop_iterate(_par_scan_closure, mr);
7029       } else {
7030         p->oop_iterate(_scan_closure, mr);
7031       }
7032     } else {
7033       if (_parallel) {
7034         p->oop_iterate(_par_scan_closure);
7035       } else {
7036         p->oop_iterate(_scan_closure);
7037       }
7038     }
7039   }
7040   #ifdef DEBUG
7041     if (!_parallel) {
7042       assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7043       assert(_collector->overflow_list_is_empty(),
7044              "overflow list should be empty");
7045 
7046     }
7047   #endif // DEBUG
7048   return is_obj_array;
7049 }
7050 
7051 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7052                         MemRegion span,
7053                         CMSBitMap* bitMap, CMSMarkStack*  markStack,
7054                         bool should_yield, bool verifying):
7055   _collector(collector),
7056   _span(span),
7057   _bitMap(bitMap),
7058   _mut(&collector->_modUnionTable),
7059   _markStack(markStack),
7060   _yield(should_yield),
7061   _skipBits(0)
7062 {
7063   assert(_markStack->isEmpty(), "stack should be empty");
7064   _finger = _bitMap->startWord();
7065   _threshold = _finger;
7066   assert(_collector->_restart_addr == NULL, "Sanity check");
7067   assert(_span.contains(_finger), "Out of bounds _finger?");
7068   DEBUG_ONLY(_verifying = verifying;)
7069 }
7070 
7071 void MarkFromRootsClosure::reset(HeapWord* addr) {
7072   assert(_markStack->isEmpty(), "would cause duplicates on stack");
7073   assert(_span.contains(addr), "Out of bounds _finger?");
7074   _finger = addr;
7075   _threshold = (HeapWord*)round_to(
7076                  (intptr_t)_finger, CardTableModRefBS::card_size);
7077 }
7078 
7079 // Should revisit to see if this should be restructured for
7080 // greater efficiency.
7081 bool MarkFromRootsClosure::do_bit(size_t offset) {
7082   if (_skipBits > 0) {
7083     _skipBits--;
7084     return true;
7085   }
7086   // convert offset into a HeapWord*
7087   HeapWord* addr = _bitMap->startWord() + offset;
7088   assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7089          "address out of range");
7090   assert(_bitMap->isMarked(addr), "tautology");
7091   if (_bitMap->isMarked(addr+1)) {
7092     // this is an allocated but not yet initialized object
7093     assert(_skipBits == 0, "tautology");
7094     _skipBits = 2;  // skip next two marked bits ("Printezis-marks")
7095     oop p = oop(addr);
7096     if (p->klass_or_null() == NULL) {
7097       DEBUG_ONLY(if (!_verifying) {)
7098         // We re-dirty the cards on which this object lies and increase
7099         // the _threshold so that we'll come back to scan this object
7100         // during the preclean or remark phase. (CMSCleanOnEnter)
7101         if (CMSCleanOnEnter) {
7102           size_t sz = _collector->block_size_using_printezis_bits(addr);
7103           HeapWord* end_card_addr   = (HeapWord*)round_to(
7104                                          (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7105           MemRegion redirty_range = MemRegion(addr, end_card_addr);
7106           assert(!redirty_range.is_empty(), "Arithmetical tautology");
7107           // Bump _threshold to end_card_addr; note that
7108           // _threshold cannot possibly exceed end_card_addr, anyhow.
7109           // This prevents future clearing of the card as the scan proceeds
7110           // to the right.
7111           assert(_threshold <= end_card_addr,
7112                  "Because we are just scanning into this object");
7113           if (_threshold < end_card_addr) {
7114             _threshold = end_card_addr;
7115           }
7116           if (p->klass_or_null() != NULL) {
7117             // Redirty the range of cards...
7118             _mut->mark_range(redirty_range);
7119           } // ...else the setting of klass will dirty the card anyway.
7120         }
7121       DEBUG_ONLY(})
7122       return true;
7123     }
7124   }
7125   scanOopsInOop(addr);
7126   return true;
7127 }
7128 
7129 // We take a break if we've been at this for a while,
7130 // so as to avoid monopolizing the locks involved.
7131 void MarkFromRootsClosure::do_yield_work() {
7132   // First give up the locks, then yield, then re-lock
7133   // We should probably use a constructor/destructor idiom to
7134   // do this unlock/lock or modify the MutexUnlocker class to
7135   // serve our purpose. XXX
7136   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7137          "CMS thread should hold CMS token");
7138   assert_lock_strong(_bitMap->lock());
7139   _bitMap->lock()->unlock();
7140   ConcurrentMarkSweepThread::desynchronize(true);
7141   ConcurrentMarkSweepThread::acknowledge_yield_request();
7142   _collector->stopTimer();
7143   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7144   if (PrintCMSStatistics != 0) {
7145     _collector->incrementYields();
7146   }
7147   _collector->icms_wait();
7148 
7149   // See the comment in coordinator_yield()
7150   for (unsigned i = 0; i < CMSYieldSleepCount &&
7151                        ConcurrentMarkSweepThread::should_yield() &&
7152                        !CMSCollector::foregroundGCIsActive(); ++i) {
7153     os::sleep(Thread::current(), 1, false);
7154     ConcurrentMarkSweepThread::acknowledge_yield_request();
7155   }
7156 
7157   ConcurrentMarkSweepThread::synchronize(true);
7158   _bitMap->lock()->lock_without_safepoint_check();
7159   _collector->startTimer();
7160 }
7161 
7162 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7163   assert(_bitMap->isMarked(ptr), "expected bit to be set");
7164   assert(_markStack->isEmpty(),
7165          "should drain stack to limit stack usage");
7166   // convert ptr to an oop preparatory to scanning
7167   oop obj = oop(ptr);
7168   // Ignore mark word in verification below, since we
7169   // may be running concurrent with mutators.
7170   assert(obj->is_oop(true), "should be an oop");
7171   assert(_finger <= ptr, "_finger runneth ahead");
7172   // advance the finger to right end of this object
7173   _finger = ptr + obj->size();
7174   assert(_finger > ptr, "we just incremented it above");
7175   // On large heaps, it may take us some time to get through
7176   // the marking phase (especially if running iCMS). During
7177   // this time it's possible that a lot of mutations have
7178   // accumulated in the card table and the mod union table --
7179   // these mutation records are redundant until we have
7180   // actually traced into the corresponding card.
7181   // Here, we check whether advancing the finger would make
7182   // us cross into a new card, and if so clear corresponding
7183   // cards in the MUT (preclean them in the card-table in the
7184   // future).
7185 
7186   DEBUG_ONLY(if (!_verifying) {)
7187     // The clean-on-enter optimization is disabled by default,
7188     // until we fix 6178663.
7189     if (CMSCleanOnEnter && (_finger > _threshold)) {
7190       // [_threshold, _finger) represents the interval
7191       // of cards to be cleared  in MUT (or precleaned in card table).
7192       // The set of cards to be cleared is all those that overlap
7193       // with the interval [_threshold, _finger); note that
7194       // _threshold is always kept card-aligned but _finger isn't
7195       // always card-aligned.
7196       HeapWord* old_threshold = _threshold;
7197       assert(old_threshold == (HeapWord*)round_to(
7198               (intptr_t)old_threshold, CardTableModRefBS::card_size),
7199              "_threshold should always be card-aligned");
7200       _threshold = (HeapWord*)round_to(
7201                      (intptr_t)_finger, CardTableModRefBS::card_size);
7202       MemRegion mr(old_threshold, _threshold);
7203       assert(!mr.is_empty(), "Control point invariant");
7204       assert(_span.contains(mr), "Should clear within span");
7205       _mut->clear_range(mr);
7206     }
7207   DEBUG_ONLY(})
7208   // Note: the finger doesn't advance while we drain
7209   // the stack below.
7210   PushOrMarkClosure pushOrMarkClosure(_collector,
7211                                       _span, _bitMap, _markStack,
7212                                       _finger, this);
7213   bool res = _markStack->push(obj);
7214   assert(res, "Empty non-zero size stack should have space for single push");
7215   while (!_markStack->isEmpty()) {
7216     oop new_oop = _markStack->pop();
7217     // Skip verifying header mark word below because we are
7218     // running concurrent with mutators.
7219     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7220     // now scan this oop's oops
7221     new_oop->oop_iterate(&pushOrMarkClosure);
7222     do_yield_check();
7223   }
7224   assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7225 }
7226 
7227 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7228                        CMSCollector* collector, MemRegion span,
7229                        CMSBitMap* bit_map,
7230                        OopTaskQueue* work_queue,
7231                        CMSMarkStack*  overflow_stack,
7232                        bool should_yield):
7233   _collector(collector),
7234   _whole_span(collector->_span),
7235   _span(span),
7236   _bit_map(bit_map),
7237   _mut(&collector->_modUnionTable),
7238   _work_queue(work_queue),
7239   _overflow_stack(overflow_stack),
7240   _yield(should_yield),
7241   _skip_bits(0),
7242   _task(task)
7243 {
7244   assert(_work_queue->size() == 0, "work_queue should be empty");
7245   _finger = span.start();
7246   _threshold = _finger;     // XXX Defer clear-on-enter optimization for now
7247   assert(_span.contains(_finger), "Out of bounds _finger?");
7248 }
7249 
7250 // Should revisit to see if this should be restructured for
7251 // greater efficiency.
7252 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7253   if (_skip_bits > 0) {
7254     _skip_bits--;
7255     return true;
7256   }
7257   // convert offset into a HeapWord*
7258   HeapWord* addr = _bit_map->startWord() + offset;
7259   assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7260          "address out of range");
7261   assert(_bit_map->isMarked(addr), "tautology");
7262   if (_bit_map->isMarked(addr+1)) {
7263     // this is an allocated object that might not yet be initialized
7264     assert(_skip_bits == 0, "tautology");
7265     _skip_bits = 2;  // skip next two marked bits ("Printezis-marks")
7266     oop p = oop(addr);
7267     if (p->klass_or_null() == NULL) {
7268       // in the case of Clean-on-Enter optimization, redirty card
7269       // and avoid clearing card by increasing  the threshold.
7270       return true;
7271     }
7272   }
7273   scan_oops_in_oop(addr);
7274   return true;
7275 }
7276 
7277 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7278   assert(_bit_map->isMarked(ptr), "expected bit to be set");
7279   // Should we assert that our work queue is empty or
7280   // below some drain limit?
7281   assert(_work_queue->size() == 0,
7282          "should drain stack to limit stack usage");
7283   // convert ptr to an oop preparatory to scanning
7284   oop obj = oop(ptr);
7285   // Ignore mark word in verification below, since we
7286   // may be running concurrent with mutators.
7287   assert(obj->is_oop(true), "should be an oop");
7288   assert(_finger <= ptr, "_finger runneth ahead");
7289   // advance the finger to right end of this object
7290   _finger = ptr + obj->size();
7291   assert(_finger > ptr, "we just incremented it above");
7292   // On large heaps, it may take us some time to get through
7293   // the marking phase (especially if running iCMS). During
7294   // this time it's possible that a lot of mutations have
7295   // accumulated in the card table and the mod union table --
7296   // these mutation records are redundant until we have
7297   // actually traced into the corresponding card.
7298   // Here, we check whether advancing the finger would make
7299   // us cross into a new card, and if so clear corresponding
7300   // cards in the MUT (preclean them in the card-table in the
7301   // future).
7302 
7303   // The clean-on-enter optimization is disabled by default,
7304   // until we fix 6178663.
7305   if (CMSCleanOnEnter && (_finger > _threshold)) {
7306     // [_threshold, _finger) represents the interval
7307     // of cards to be cleared  in MUT (or precleaned in card table).
7308     // The set of cards to be cleared is all those that overlap
7309     // with the interval [_threshold, _finger); note that
7310     // _threshold is always kept card-aligned but _finger isn't
7311     // always card-aligned.
7312     HeapWord* old_threshold = _threshold;
7313     assert(old_threshold == (HeapWord*)round_to(
7314             (intptr_t)old_threshold, CardTableModRefBS::card_size),
7315            "_threshold should always be card-aligned");
7316     _threshold = (HeapWord*)round_to(
7317                    (intptr_t)_finger, CardTableModRefBS::card_size);
7318     MemRegion mr(old_threshold, _threshold);
7319     assert(!mr.is_empty(), "Control point invariant");
7320     assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7321     _mut->clear_range(mr);
7322   }
7323 
7324   // Note: the local finger doesn't advance while we drain
7325   // the stack below, but the global finger sure can and will.
7326   HeapWord** gfa = _task->global_finger_addr();
7327   Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7328                                       _span, _bit_map,
7329                                       _work_queue,
7330                                       _overflow_stack,
7331                                       _finger,
7332                                       gfa, this);
7333   bool res = _work_queue->push(obj);   // overflow could occur here
7334   assert(res, "Will hold once we use workqueues");
7335   while (true) {
7336     oop new_oop;
7337     if (!_work_queue->pop_local(new_oop)) {
7338       // We emptied our work_queue; check if there's stuff that can
7339       // be gotten from the overflow stack.
7340       if (CMSConcMarkingTask::get_work_from_overflow_stack(
7341             _overflow_stack, _work_queue)) {
7342         do_yield_check();
7343         continue;
7344       } else {  // done
7345         break;
7346       }
7347     }
7348     // Skip verifying header mark word below because we are
7349     // running concurrent with mutators.
7350     assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7351     // now scan this oop's oops
7352     new_oop->oop_iterate(&pushOrMarkClosure);
7353     do_yield_check();
7354   }
7355   assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7356 }
7357 
7358 // Yield in response to a request from VM Thread or
7359 // from mutators.
7360 void Par_MarkFromRootsClosure::do_yield_work() {
7361   assert(_task != NULL, "sanity");
7362   _task->yield();
7363 }
7364 
7365 // A variant of the above used for verifying CMS marking work.
7366 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7367                         MemRegion span,
7368                         CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7369                         CMSMarkStack*  mark_stack):
7370   _collector(collector),
7371   _span(span),
7372   _verification_bm(verification_bm),
7373   _cms_bm(cms_bm),
7374   _mark_stack(mark_stack),
7375   _pam_verify_closure(collector, span, verification_bm, cms_bm,
7376                       mark_stack)
7377 {
7378   assert(_mark_stack->isEmpty(), "stack should be empty");
7379   _finger = _verification_bm->startWord();
7380   assert(_collector->_restart_addr == NULL, "Sanity check");
7381   assert(_span.contains(_finger), "Out of bounds _finger?");
7382 }
7383 
7384 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7385   assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7386   assert(_span.contains(addr), "Out of bounds _finger?");
7387   _finger = addr;
7388 }
7389 
7390 // Should revisit to see if this should be restructured for
7391 // greater efficiency.
7392 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7393   // convert offset into a HeapWord*
7394   HeapWord* addr = _verification_bm->startWord() + offset;
7395   assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7396          "address out of range");
7397   assert(_verification_bm->isMarked(addr), "tautology");
7398   assert(_cms_bm->isMarked(addr), "tautology");
7399 
7400   assert(_mark_stack->isEmpty(),
7401          "should drain stack to limit stack usage");
7402   // convert addr to an oop preparatory to scanning
7403   oop obj = oop(addr);
7404   assert(obj->is_oop(), "should be an oop");
7405   assert(_finger <= addr, "_finger runneth ahead");
7406   // advance the finger to right end of this object
7407   _finger = addr + obj->size();
7408   assert(_finger > addr, "we just incremented it above");
7409   // Note: the finger doesn't advance while we drain
7410   // the stack below.
7411   bool res = _mark_stack->push(obj);
7412   assert(res, "Empty non-zero size stack should have space for single push");
7413   while (!_mark_stack->isEmpty()) {
7414     oop new_oop = _mark_stack->pop();
7415     assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7416     // now scan this oop's oops
7417     new_oop->oop_iterate(&_pam_verify_closure);
7418   }
7419   assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7420   return true;
7421 }
7422 
7423 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7424   CMSCollector* collector, MemRegion span,
7425   CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7426   CMSMarkStack*  mark_stack):
7427   CMSOopClosure(collector->ref_processor()),
7428   _collector(collector),
7429   _span(span),
7430   _verification_bm(verification_bm),
7431   _cms_bm(cms_bm),
7432   _mark_stack(mark_stack)
7433 { }
7434 
7435 void PushAndMarkVerifyClosure::do_oop(oop* p)       { PushAndMarkVerifyClosure::do_oop_work(p); }
7436 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7437 
7438 // Upon stack overflow, we discard (part of) the stack,
7439 // remembering the least address amongst those discarded
7440 // in CMSCollector's _restart_address.
7441 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7442   // Remember the least grey address discarded
7443   HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7444   _collector->lower_restart_addr(ra);
7445   _mark_stack->reset();  // discard stack contents
7446   _mark_stack->expand(); // expand the stack if possible
7447 }
7448 
7449 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7450   assert(obj->is_oop_or_null(), "expected an oop or NULL");
7451   HeapWord* addr = (HeapWord*)obj;
7452   if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7453     // Oop lies in _span and isn't yet grey or black
7454     _verification_bm->mark(addr);            // now grey
7455     if (!_cms_bm->isMarked(addr)) {
7456       oop(addr)->print();
7457       gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7458                              addr);
7459       fatal("... aborting");
7460     }
7461 
7462     if (!_mark_stack->push(obj)) { // stack overflow
7463       if (PrintCMSStatistics != 0) {
7464         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7465                                SIZE_FORMAT, _mark_stack->capacity());
7466       }
7467       assert(_mark_stack->isFull(), "Else push should have succeeded");
7468       handle_stack_overflow(addr);
7469     }
7470     // anything including and to the right of _finger
7471     // will be scanned as we iterate over the remainder of the
7472     // bit map
7473   }
7474 }
7475 
7476 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7477                      MemRegion span,
7478                      CMSBitMap* bitMap, CMSMarkStack*  markStack,
7479                      HeapWord* finger, MarkFromRootsClosure* parent) :
7480   CMSOopClosure(collector->ref_processor()),
7481   _collector(collector),
7482   _span(span),
7483   _bitMap(bitMap),
7484   _markStack(markStack),
7485   _finger(finger),
7486   _parent(parent)
7487 { }
7488 
7489 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7490                      MemRegion span,
7491                      CMSBitMap* bit_map,
7492                      OopTaskQueue* work_queue,
7493                      CMSMarkStack*  overflow_stack,
7494                      HeapWord* finger,
7495                      HeapWord** global_finger_addr,
7496                      Par_MarkFromRootsClosure* parent) :
7497   CMSOopClosure(collector->ref_processor()),
7498   _collector(collector),
7499   _whole_span(collector->_span),
7500   _span(span),
7501   _bit_map(bit_map),
7502   _work_queue(work_queue),
7503   _overflow_stack(overflow_stack),
7504   _finger(finger),
7505   _global_finger_addr(global_finger_addr),
7506   _parent(parent)
7507 { }
7508 
7509 // Assumes thread-safe access by callers, who are
7510 // responsible for mutual exclusion.
7511 void CMSCollector::lower_restart_addr(HeapWord* low) {
7512   assert(_span.contains(low), "Out of bounds addr");
7513   if (_restart_addr == NULL) {
7514     _restart_addr = low;
7515   } else {
7516     _restart_addr = MIN2(_restart_addr, low);
7517   }
7518 }
7519 
7520 // Upon stack overflow, we discard (part of) the stack,
7521 // remembering the least address amongst those discarded
7522 // in CMSCollector's _restart_address.
7523 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7524   // Remember the least grey address discarded
7525   HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7526   _collector->lower_restart_addr(ra);
7527   _markStack->reset();  // discard stack contents
7528   _markStack->expand(); // expand the stack if possible
7529 }
7530 
7531 // Upon stack overflow, we discard (part of) the stack,
7532 // remembering the least address amongst those discarded
7533 // in CMSCollector's _restart_address.
7534 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7535   // We need to do this under a mutex to prevent other
7536   // workers from interfering with the work done below.
7537   MutexLockerEx ml(_overflow_stack->par_lock(),
7538                    Mutex::_no_safepoint_check_flag);
7539   // Remember the least grey address discarded
7540   HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7541   _collector->lower_restart_addr(ra);
7542   _overflow_stack->reset();  // discard stack contents
7543   _overflow_stack->expand(); // expand the stack if possible
7544 }
7545 
7546 void CMKlassClosure::do_klass(Klass* k) {
7547   assert(_oop_closure != NULL, "Not initialized?");
7548   k->oops_do(_oop_closure);
7549 }
7550 
7551 void PushOrMarkClosure::do_oop(oop obj) {
7552   // Ignore mark word because we are running concurrent with mutators.
7553   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7554   HeapWord* addr = (HeapWord*)obj;
7555   if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7556     // Oop lies in _span and isn't yet grey or black
7557     _bitMap->mark(addr);            // now grey
7558     if (addr < _finger) {
7559       // the bit map iteration has already either passed, or
7560       // sampled, this bit in the bit map; we'll need to
7561       // use the marking stack to scan this oop's oops.
7562       bool simulate_overflow = false;
7563       NOT_PRODUCT(
7564         if (CMSMarkStackOverflowALot &&
7565             _collector->simulate_overflow()) {
7566           // simulate a stack overflow
7567           simulate_overflow = true;
7568         }
7569       )
7570       if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7571         if (PrintCMSStatistics != 0) {
7572           gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7573                                  SIZE_FORMAT, _markStack->capacity());
7574         }
7575         assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7576         handle_stack_overflow(addr);
7577       }
7578     }
7579     // anything including and to the right of _finger
7580     // will be scanned as we iterate over the remainder of the
7581     // bit map
7582     do_yield_check();
7583   }
7584 }
7585 
7586 void PushOrMarkClosure::do_oop(oop* p)       { PushOrMarkClosure::do_oop_work(p); }
7587 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7588 
7589 void Par_PushOrMarkClosure::do_oop(oop obj) {
7590   // Ignore mark word because we are running concurrent with mutators.
7591   assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7592   HeapWord* addr = (HeapWord*)obj;
7593   if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7594     // Oop lies in _span and isn't yet grey or black
7595     // We read the global_finger (volatile read) strictly after marking oop
7596     bool res = _bit_map->par_mark(addr);    // now grey
7597     volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7598     // Should we push this marked oop on our stack?
7599     // -- if someone else marked it, nothing to do
7600     // -- if target oop is above global finger nothing to do
7601     // -- if target oop is in chunk and above local finger
7602     //      then nothing to do
7603     // -- else push on work queue
7604     if (   !res       // someone else marked it, they will deal with it
7605         || (addr >= *gfa)  // will be scanned in a later task
7606         || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7607       return;
7608     }
7609     // the bit map iteration has already either passed, or
7610     // sampled, this bit in the bit map; we'll need to
7611     // use the marking stack to scan this oop's oops.
7612     bool simulate_overflow = false;
7613     NOT_PRODUCT(
7614       if (CMSMarkStackOverflowALot &&
7615           _collector->simulate_overflow()) {
7616         // simulate a stack overflow
7617         simulate_overflow = true;
7618       }
7619     )
7620     if (simulate_overflow ||
7621         !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7622       // stack overflow
7623       if (PrintCMSStatistics != 0) {
7624         gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7625                                SIZE_FORMAT, _overflow_stack->capacity());
7626       }
7627       // We cannot assert that the overflow stack is full because
7628       // it may have been emptied since.
7629       assert(simulate_overflow ||
7630              _work_queue->size() == _work_queue->max_elems(),
7631             "Else push should have succeeded");
7632       handle_stack_overflow(addr);
7633     }
7634     do_yield_check();
7635   }
7636 }
7637 
7638 void Par_PushOrMarkClosure::do_oop(oop* p)       { Par_PushOrMarkClosure::do_oop_work(p); }
7639 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7640 
7641 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7642                                        MemRegion span,
7643                                        ReferenceProcessor* rp,
7644                                        CMSBitMap* bit_map,
7645                                        CMSBitMap* mod_union_table,
7646                                        CMSMarkStack*  mark_stack,
7647                                        bool           concurrent_precleaning):
7648   CMSOopClosure(rp),
7649   _collector(collector),
7650   _span(span),
7651   _bit_map(bit_map),
7652   _mod_union_table(mod_union_table),
7653   _mark_stack(mark_stack),
7654   _concurrent_precleaning(concurrent_precleaning)
7655 {
7656   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7657 }
7658 
7659 // Grey object rescan during pre-cleaning and second checkpoint phases --
7660 // the non-parallel version (the parallel version appears further below.)
7661 void PushAndMarkClosure::do_oop(oop obj) {
7662   // Ignore mark word verification. If during concurrent precleaning,
7663   // the object monitor may be locked. If during the checkpoint
7664   // phases, the object may already have been reached by a  different
7665   // path and may be at the end of the global overflow list (so
7666   // the mark word may be NULL).
7667   assert(obj->is_oop_or_null(true /* ignore mark word */),
7668          "expected an oop or NULL");
7669   HeapWord* addr = (HeapWord*)obj;
7670   // Check if oop points into the CMS generation
7671   // and is not marked
7672   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7673     // a white object ...
7674     _bit_map->mark(addr);         // ... now grey
7675     // push on the marking stack (grey set)
7676     bool simulate_overflow = false;
7677     NOT_PRODUCT(
7678       if (CMSMarkStackOverflowALot &&
7679           _collector->simulate_overflow()) {
7680         // simulate a stack overflow
7681         simulate_overflow = true;
7682       }
7683     )
7684     if (simulate_overflow || !_mark_stack->push(obj)) {
7685       if (_concurrent_precleaning) {
7686          // During precleaning we can just dirty the appropriate card(s)
7687          // in the mod union table, thus ensuring that the object remains
7688          // in the grey set  and continue. In the case of object arrays
7689          // we need to dirty all of the cards that the object spans,
7690          // since the rescan of object arrays will be limited to the
7691          // dirty cards.
7692          // Note that no one can be intefering with us in this action
7693          // of dirtying the mod union table, so no locking or atomics
7694          // are required.
7695          if (obj->is_objArray()) {
7696            size_t sz = obj->size();
7697            HeapWord* end_card_addr = (HeapWord*)round_to(
7698                                         (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7699            MemRegion redirty_range = MemRegion(addr, end_card_addr);
7700            assert(!redirty_range.is_empty(), "Arithmetical tautology");
7701            _mod_union_table->mark_range(redirty_range);
7702          } else {
7703            _mod_union_table->mark(addr);
7704          }
7705          _collector->_ser_pmc_preclean_ovflw++;
7706       } else {
7707          // During the remark phase, we need to remember this oop
7708          // in the overflow list.
7709          _collector->push_on_overflow_list(obj);
7710          _collector->_ser_pmc_remark_ovflw++;
7711       }
7712     }
7713   }
7714 }
7715 
7716 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7717                                                MemRegion span,
7718                                                ReferenceProcessor* rp,
7719                                                CMSBitMap* bit_map,
7720                                                OopTaskQueue* work_queue):
7721   CMSOopClosure(rp),
7722   _collector(collector),
7723   _span(span),
7724   _bit_map(bit_map),
7725   _work_queue(work_queue)
7726 {
7727   assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7728 }
7729 
7730 void PushAndMarkClosure::do_oop(oop* p)       { PushAndMarkClosure::do_oop_work(p); }
7731 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7732 
7733 // Grey object rescan during second checkpoint phase --
7734 // the parallel version.
7735 void Par_PushAndMarkClosure::do_oop(oop obj) {
7736   // In the assert below, we ignore the mark word because
7737   // this oop may point to an already visited object that is
7738   // on the overflow stack (in which case the mark word has
7739   // been hijacked for chaining into the overflow stack --
7740   // if this is the last object in the overflow stack then
7741   // its mark word will be NULL). Because this object may
7742   // have been subsequently popped off the global overflow
7743   // stack, and the mark word possibly restored to the prototypical
7744   // value, by the time we get to examined this failing assert in
7745   // the debugger, is_oop_or_null(false) may subsequently start
7746   // to hold.
7747   assert(obj->is_oop_or_null(true),
7748          "expected an oop or NULL");
7749   HeapWord* addr = (HeapWord*)obj;
7750   // Check if oop points into the CMS generation
7751   // and is not marked
7752   if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7753     // a white object ...
7754     // If we manage to "claim" the object, by being the
7755     // first thread to mark it, then we push it on our
7756     // marking stack
7757     if (_bit_map->par_mark(addr)) {     // ... now grey
7758       // push on work queue (grey set)
7759       bool simulate_overflow = false;
7760       NOT_PRODUCT(
7761         if (CMSMarkStackOverflowALot &&
7762             _collector->par_simulate_overflow()) {
7763           // simulate a stack overflow
7764           simulate_overflow = true;
7765         }
7766       )
7767       if (simulate_overflow || !_work_queue->push(obj)) {
7768         _collector->par_push_on_overflow_list(obj);
7769         _collector->_par_pmc_remark_ovflw++; //  imprecise OK: no need to CAS
7770       }
7771     } // Else, some other thread got there first
7772   }
7773 }
7774 
7775 void Par_PushAndMarkClosure::do_oop(oop* p)       { Par_PushAndMarkClosure::do_oop_work(p); }
7776 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7777 
7778 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7779   Mutex* bml = _collector->bitMapLock();
7780   assert_lock_strong(bml);
7781   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7782          "CMS thread should hold CMS token");
7783 
7784   bml->unlock();
7785   ConcurrentMarkSweepThread::desynchronize(true);
7786 
7787   ConcurrentMarkSweepThread::acknowledge_yield_request();
7788 
7789   _collector->stopTimer();
7790   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7791   if (PrintCMSStatistics != 0) {
7792     _collector->incrementYields();
7793   }
7794   _collector->icms_wait();
7795 
7796   // See the comment in coordinator_yield()
7797   for (unsigned i = 0; i < CMSYieldSleepCount &&
7798                        ConcurrentMarkSweepThread::should_yield() &&
7799                        !CMSCollector::foregroundGCIsActive(); ++i) {
7800     os::sleep(Thread::current(), 1, false);
7801     ConcurrentMarkSweepThread::acknowledge_yield_request();
7802   }
7803 
7804   ConcurrentMarkSweepThread::synchronize(true);
7805   bml->lock();
7806 
7807   _collector->startTimer();
7808 }
7809 
7810 bool CMSPrecleanRefsYieldClosure::should_return() {
7811   if (ConcurrentMarkSweepThread::should_yield()) {
7812     do_yield_work();
7813   }
7814   return _collector->foregroundGCIsActive();
7815 }
7816 
7817 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7818   assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7819          "mr should be aligned to start at a card boundary");
7820   // We'd like to assert:
7821   // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7822   //        "mr should be a range of cards");
7823   // However, that would be too strong in one case -- the last
7824   // partition ends at _unallocated_block which, in general, can be
7825   // an arbitrary boundary, not necessarily card aligned.
7826   if (PrintCMSStatistics != 0) {
7827     _num_dirty_cards +=
7828          mr.word_size()/CardTableModRefBS::card_size_in_words;
7829   }
7830   _space->object_iterate_mem(mr, &_scan_cl);
7831 }
7832 
7833 SweepClosure::SweepClosure(CMSCollector* collector,
7834                            ConcurrentMarkSweepGeneration* g,
7835                            CMSBitMap* bitMap, bool should_yield) :
7836   _collector(collector),
7837   _g(g),
7838   _sp(g->cmsSpace()),
7839   _limit(_sp->sweep_limit()),
7840   _freelistLock(_sp->freelistLock()),
7841   _bitMap(bitMap),
7842   _yield(should_yield),
7843   _inFreeRange(false),           // No free range at beginning of sweep
7844   _freeRangeInFreeLists(false),  // No free range at beginning of sweep
7845   _lastFreeRangeCoalesced(false),
7846   _freeFinger(g->used_region().start())
7847 {
7848   NOT_PRODUCT(
7849     _numObjectsFreed = 0;
7850     _numWordsFreed   = 0;
7851     _numObjectsLive = 0;
7852     _numWordsLive = 0;
7853     _numObjectsAlreadyFree = 0;
7854     _numWordsAlreadyFree = 0;
7855     _last_fc = NULL;
7856 
7857     _sp->initializeIndexedFreeListArrayReturnedBytes();
7858     _sp->dictionary()->initialize_dict_returned_bytes();
7859   )
7860   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7861          "sweep _limit out of bounds");
7862   if (CMSTraceSweeper) {
7863     gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7864                         _limit);
7865   }
7866 }
7867 
7868 void SweepClosure::print_on(outputStream* st) const {
7869   tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7870                 _sp->bottom(), _sp->end());
7871   tty->print_cr("_limit = " PTR_FORMAT, _limit);
7872   tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7873   NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7874   tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7875                 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7876 }
7877 
7878 #ifndef PRODUCT
7879 // Assertion checking only:  no useful work in product mode --
7880 // however, if any of the flags below become product flags,
7881 // you may need to review this code to see if it needs to be
7882 // enabled in product mode.
7883 SweepClosure::~SweepClosure() {
7884   assert_lock_strong(_freelistLock);
7885   assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7886          "sweep _limit out of bounds");
7887   if (inFreeRange()) {
7888     warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7889     print();
7890     ShouldNotReachHere();
7891   }
7892   if (Verbose && PrintGC) {
7893     gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7894                         _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7895     gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects,  "
7896                            SIZE_FORMAT" bytes  "
7897       "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7898       _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7899       _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7900     size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7901                         * sizeof(HeapWord);
7902     gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7903 
7904     if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7905       size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7906       size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7907       size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7908       gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7909       gclog_or_tty->print("   Indexed List Returned "SIZE_FORMAT" bytes",
7910         indexListReturnedBytes);
7911       gclog_or_tty->print_cr("        Dictionary Returned "SIZE_FORMAT" bytes",
7912         dict_returned_bytes);
7913     }
7914   }
7915   if (CMSTraceSweeper) {
7916     gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7917                            _limit);
7918   }
7919 }
7920 #endif  // PRODUCT
7921 
7922 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7923     bool freeRangeInFreeLists) {
7924   if (CMSTraceSweeper) {
7925     gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7926                freeFinger, freeRangeInFreeLists);
7927   }
7928   assert(!inFreeRange(), "Trampling existing free range");
7929   set_inFreeRange(true);
7930   set_lastFreeRangeCoalesced(false);
7931 
7932   set_freeFinger(freeFinger);
7933   set_freeRangeInFreeLists(freeRangeInFreeLists);
7934   if (CMSTestInFreeList) {
7935     if (freeRangeInFreeLists) {
7936       FreeChunk* fc = (FreeChunk*) freeFinger;
7937       assert(fc->is_free(), "A chunk on the free list should be free.");
7938       assert(fc->size() > 0, "Free range should have a size");
7939       assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7940     }
7941   }
7942 }
7943 
7944 // Note that the sweeper runs concurrently with mutators. Thus,
7945 // it is possible for direct allocation in this generation to happen
7946 // in the middle of the sweep. Note that the sweeper also coalesces
7947 // contiguous free blocks. Thus, unless the sweeper and the allocator
7948 // synchronize appropriately freshly allocated blocks may get swept up.
7949 // This is accomplished by the sweeper locking the free lists while
7950 // it is sweeping. Thus blocks that are determined to be free are
7951 // indeed free. There is however one additional complication:
7952 // blocks that have been allocated since the final checkpoint and
7953 // mark, will not have been marked and so would be treated as
7954 // unreachable and swept up. To prevent this, the allocator marks
7955 // the bit map when allocating during the sweep phase. This leads,
7956 // however, to a further complication -- objects may have been allocated
7957 // but not yet initialized -- in the sense that the header isn't yet
7958 // installed. The sweeper can not then determine the size of the block
7959 // in order to skip over it. To deal with this case, we use a technique
7960 // (due to Printezis) to encode such uninitialized block sizes in the
7961 // bit map. Since the bit map uses a bit per every HeapWord, but the
7962 // CMS generation has a minimum object size of 3 HeapWords, it follows
7963 // that "normal marks" won't be adjacent in the bit map (there will
7964 // always be at least two 0 bits between successive 1 bits). We make use
7965 // of these "unused" bits to represent uninitialized blocks -- the bit
7966 // corresponding to the start of the uninitialized object and the next
7967 // bit are both set. Finally, a 1 bit marks the end of the object that
7968 // started with the two consecutive 1 bits to indicate its potentially
7969 // uninitialized state.
7970 
7971 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7972   FreeChunk* fc = (FreeChunk*)addr;
7973   size_t res;
7974 
7975   // Check if we are done sweeping. Below we check "addr >= _limit" rather
7976   // than "addr == _limit" because although _limit was a block boundary when
7977   // we started the sweep, it may no longer be one because heap expansion
7978   // may have caused us to coalesce the block ending at the address _limit
7979   // with a newly expanded chunk (this happens when _limit was set to the
7980   // previous _end of the space), so we may have stepped past _limit:
7981   // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7982   if (addr >= _limit) { // we have swept up to or past the limit: finish up
7983     assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7984            "sweep _limit out of bounds");
7985     assert(addr < _sp->end(), "addr out of bounds");
7986     // Flush any free range we might be holding as a single
7987     // coalesced chunk to the appropriate free list.
7988     if (inFreeRange()) {
7989       assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7990              err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
7991       flush_cur_free_chunk(freeFinger(),
7992                            pointer_delta(addr, freeFinger()));
7993       if (CMSTraceSweeper) {
7994         gclog_or_tty->print("Sweep: last chunk: ");
7995         gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
7996                    "[coalesced:"SIZE_FORMAT"]\n",
7997                    freeFinger(), pointer_delta(addr, freeFinger()),
7998                    lastFreeRangeCoalesced());
7999       }
8000     }
8001 
8002     // help the iterator loop finish
8003     return pointer_delta(_sp->end(), addr);
8004   }
8005 
8006   assert(addr < _limit, "sweep invariant");
8007   // check if we should yield
8008   do_yield_check(addr);
8009   if (fc->is_free()) {
8010     // Chunk that is already free
8011     res = fc->size();
8012     do_already_free_chunk(fc);
8013     debug_only(_sp->verifyFreeLists());
8014     // If we flush the chunk at hand in lookahead_and_flush()
8015     // and it's coalesced with a preceding chunk, then the
8016     // process of "mangling" the payload of the coalesced block
8017     // will cause erasure of the size information from the
8018     // (erstwhile) header of all the coalesced blocks but the
8019     // first, so the first disjunct in the assert will not hold
8020     // in that specific case (in which case the second disjunct
8021     // will hold).
8022     assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8023            "Otherwise the size info doesn't change at this step");
8024     NOT_PRODUCT(
8025       _numObjectsAlreadyFree++;
8026       _numWordsAlreadyFree += res;
8027     )
8028     NOT_PRODUCT(_last_fc = fc;)
8029   } else if (!_bitMap->isMarked(addr)) {
8030     // Chunk is fresh garbage
8031     res = do_garbage_chunk(fc);
8032     debug_only(_sp->verifyFreeLists());
8033     NOT_PRODUCT(
8034       _numObjectsFreed++;
8035       _numWordsFreed += res;
8036     )
8037   } else {
8038     // Chunk that is alive.
8039     res = do_live_chunk(fc);
8040     debug_only(_sp->verifyFreeLists());
8041     NOT_PRODUCT(
8042         _numObjectsLive++;
8043         _numWordsLive += res;
8044     )
8045   }
8046   return res;
8047 }
8048 
8049 // For the smart allocation, record following
8050 //  split deaths - a free chunk is removed from its free list because
8051 //      it is being split into two or more chunks.
8052 //  split birth - a free chunk is being added to its free list because
8053 //      a larger free chunk has been split and resulted in this free chunk.
8054 //  coal death - a free chunk is being removed from its free list because
8055 //      it is being coalesced into a large free chunk.
8056 //  coal birth - a free chunk is being added to its free list because
8057 //      it was created when two or more free chunks where coalesced into
8058 //      this free chunk.
8059 //
8060 // These statistics are used to determine the desired number of free
8061 // chunks of a given size.  The desired number is chosen to be relative
8062 // to the end of a CMS sweep.  The desired number at the end of a sweep
8063 // is the
8064 //      count-at-end-of-previous-sweep (an amount that was enough)
8065 //              - count-at-beginning-of-current-sweep  (the excess)
8066 //              + split-births  (gains in this size during interval)
8067 //              - split-deaths  (demands on this size during interval)
8068 // where the interval is from the end of one sweep to the end of the
8069 // next.
8070 //
8071 // When sweeping the sweeper maintains an accumulated chunk which is
8072 // the chunk that is made up of chunks that have been coalesced.  That
8073 // will be termed the left-hand chunk.  A new chunk of garbage that
8074 // is being considered for coalescing will be referred to as the
8075 // right-hand chunk.
8076 //
8077 // When making a decision on whether to coalesce a right-hand chunk with
8078 // the current left-hand chunk, the current count vs. the desired count
8079 // of the left-hand chunk is considered.  Also if the right-hand chunk
8080 // is near the large chunk at the end of the heap (see
8081 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8082 // left-hand chunk is coalesced.
8083 //
8084 // When making a decision about whether to split a chunk, the desired count
8085 // vs. the current count of the candidate to be split is also considered.
8086 // If the candidate is underpopulated (currently fewer chunks than desired)
8087 // a chunk of an overpopulated (currently more chunks than desired) size may
8088 // be chosen.  The "hint" associated with a free list, if non-null, points
8089 // to a free list which may be overpopulated.
8090 //
8091 
8092 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8093   const size_t size = fc->size();
8094   // Chunks that cannot be coalesced are not in the
8095   // free lists.
8096   if (CMSTestInFreeList && !fc->cantCoalesce()) {
8097     assert(_sp->verify_chunk_in_free_list(fc),
8098       "free chunk should be in free lists");
8099   }
8100   // a chunk that is already free, should not have been
8101   // marked in the bit map
8102   HeapWord* const addr = (HeapWord*) fc;
8103   assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8104   // Verify that the bit map has no bits marked between
8105   // addr and purported end of this block.
8106   _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8107 
8108   // Some chunks cannot be coalesced under any circumstances.
8109   // See the definition of cantCoalesce().
8110   if (!fc->cantCoalesce()) {
8111     // This chunk can potentially be coalesced.
8112     if (_sp->adaptive_freelists()) {
8113       // All the work is done in
8114       do_post_free_or_garbage_chunk(fc, size);
8115     } else {  // Not adaptive free lists
8116       // this is a free chunk that can potentially be coalesced by the sweeper;
8117       if (!inFreeRange()) {
8118         // if the next chunk is a free block that can't be coalesced
8119         // it doesn't make sense to remove this chunk from the free lists
8120         FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8121         assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8122         if ((HeapWord*)nextChunk < _sp->end() &&     // There is another free chunk to the right ...
8123             nextChunk->is_free()               &&     // ... which is free...
8124             nextChunk->cantCoalesce()) {             // ... but can't be coalesced
8125           // nothing to do
8126         } else {
8127           // Potentially the start of a new free range:
8128           // Don't eagerly remove it from the free lists.
8129           // No need to remove it if it will just be put
8130           // back again.  (Also from a pragmatic point of view
8131           // if it is a free block in a region that is beyond
8132           // any allocated blocks, an assertion will fail)
8133           // Remember the start of a free run.
8134           initialize_free_range(addr, true);
8135           // end - can coalesce with next chunk
8136         }
8137       } else {
8138         // the midst of a free range, we are coalescing
8139         print_free_block_coalesced(fc);
8140         if (CMSTraceSweeper) {
8141           gclog_or_tty->print("  -- pick up free block 0x%x (%d)\n", fc, size);
8142         }
8143         // remove it from the free lists
8144         _sp->removeFreeChunkFromFreeLists(fc);
8145         set_lastFreeRangeCoalesced(true);
8146         // If the chunk is being coalesced and the current free range is
8147         // in the free lists, remove the current free range so that it
8148         // will be returned to the free lists in its entirety - all
8149         // the coalesced pieces included.
8150         if (freeRangeInFreeLists()) {
8151           FreeChunk* ffc = (FreeChunk*) freeFinger();
8152           assert(ffc->size() == pointer_delta(addr, freeFinger()),
8153             "Size of free range is inconsistent with chunk size.");
8154           if (CMSTestInFreeList) {
8155             assert(_sp->verify_chunk_in_free_list(ffc),
8156               "free range is not in free lists");
8157           }
8158           _sp->removeFreeChunkFromFreeLists(ffc);
8159           set_freeRangeInFreeLists(false);
8160         }
8161       }
8162     }
8163     // Note that if the chunk is not coalescable (the else arm
8164     // below), we unconditionally flush, without needing to do
8165     // a "lookahead," as we do below.
8166     if (inFreeRange()) lookahead_and_flush(fc, size);
8167   } else {
8168     // Code path common to both original and adaptive free lists.
8169 
8170     // cant coalesce with previous block; this should be treated
8171     // as the end of a free run if any
8172     if (inFreeRange()) {
8173       // we kicked some butt; time to pick up the garbage
8174       assert(freeFinger() < addr, "freeFinger points too high");
8175       flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8176     }
8177     // else, nothing to do, just continue
8178   }
8179 }
8180 
8181 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8182   // This is a chunk of garbage.  It is not in any free list.
8183   // Add it to a free list or let it possibly be coalesced into
8184   // a larger chunk.
8185   HeapWord* const addr = (HeapWord*) fc;
8186   const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8187 
8188   if (_sp->adaptive_freelists()) {
8189     // Verify that the bit map has no bits marked between
8190     // addr and purported end of just dead object.
8191     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8192 
8193     do_post_free_or_garbage_chunk(fc, size);
8194   } else {
8195     if (!inFreeRange()) {
8196       // start of a new free range
8197       assert(size > 0, "A free range should have a size");
8198       initialize_free_range(addr, false);
8199     } else {
8200       // this will be swept up when we hit the end of the
8201       // free range
8202       if (CMSTraceSweeper) {
8203         gclog_or_tty->print("  -- pick up garbage 0x%x (%d) \n", fc, size);
8204       }
8205       // If the chunk is being coalesced and the current free range is
8206       // in the free lists, remove the current free range so that it
8207       // will be returned to the free lists in its entirety - all
8208       // the coalesced pieces included.
8209       if (freeRangeInFreeLists()) {
8210         FreeChunk* ffc = (FreeChunk*)freeFinger();
8211         assert(ffc->size() == pointer_delta(addr, freeFinger()),
8212           "Size of free range is inconsistent with chunk size.");
8213         if (CMSTestInFreeList) {
8214           assert(_sp->verify_chunk_in_free_list(ffc),
8215             "free range is not in free lists");
8216         }
8217         _sp->removeFreeChunkFromFreeLists(ffc);
8218         set_freeRangeInFreeLists(false);
8219       }
8220       set_lastFreeRangeCoalesced(true);
8221     }
8222     // this will be swept up when we hit the end of the free range
8223 
8224     // Verify that the bit map has no bits marked between
8225     // addr and purported end of just dead object.
8226     _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8227   }
8228   assert(_limit >= addr + size,
8229          "A freshly garbage chunk can't possibly straddle over _limit");
8230   if (inFreeRange()) lookahead_and_flush(fc, size);
8231   return size;
8232 }
8233 
8234 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8235   HeapWord* addr = (HeapWord*) fc;
8236   // The sweeper has just found a live object. Return any accumulated
8237   // left hand chunk to the free lists.
8238   if (inFreeRange()) {
8239     assert(freeFinger() < addr, "freeFinger points too high");
8240     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8241   }
8242 
8243   // This object is live: we'd normally expect this to be
8244   // an oop, and like to assert the following:
8245   // assert(oop(addr)->is_oop(), "live block should be an oop");
8246   // However, as we commented above, this may be an object whose
8247   // header hasn't yet been initialized.
8248   size_t size;
8249   assert(_bitMap->isMarked(addr), "Tautology for this control point");
8250   if (_bitMap->isMarked(addr + 1)) {
8251     // Determine the size from the bit map, rather than trying to
8252     // compute it from the object header.
8253     HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8254     size = pointer_delta(nextOneAddr + 1, addr);
8255     assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8256            "alignment problem");
8257 
8258 #ifdef DEBUG
8259       if (oop(addr)->klass_or_null() != NULL) {
8260         // Ignore mark word because we are running concurrent with mutators
8261         assert(oop(addr)->is_oop(true), "live block should be an oop");
8262         assert(size ==
8263                CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8264                "P-mark and computed size do not agree");
8265       }
8266 #endif
8267 
8268   } else {
8269     // This should be an initialized object that's alive.
8270     assert(oop(addr)->klass_or_null() != NULL,
8271            "Should be an initialized object");
8272     // Ignore mark word because we are running concurrent with mutators
8273     assert(oop(addr)->is_oop(true), "live block should be an oop");
8274     // Verify that the bit map has no bits marked between
8275     // addr and purported end of this block.
8276     size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8277     assert(size >= 3, "Necessary for Printezis marks to work");
8278     assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8279     DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8280   }
8281   return size;
8282 }
8283 
8284 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8285                                                  size_t chunkSize) {
8286   // do_post_free_or_garbage_chunk() should only be called in the case
8287   // of the adaptive free list allocator.
8288   const bool fcInFreeLists = fc->is_free();
8289   assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8290   assert((HeapWord*)fc <= _limit, "sweep invariant");
8291   if (CMSTestInFreeList && fcInFreeLists) {
8292     assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8293   }
8294 
8295   if (CMSTraceSweeper) {
8296     gclog_or_tty->print_cr("  -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8297   }
8298 
8299   HeapWord* const fc_addr = (HeapWord*) fc;
8300 
8301   bool coalesce;
8302   const size_t left  = pointer_delta(fc_addr, freeFinger());
8303   const size_t right = chunkSize;
8304   switch (FLSCoalescePolicy) {
8305     // numeric value forms a coalition aggressiveness metric
8306     case 0:  { // never coalesce
8307       coalesce = false;
8308       break;
8309     }
8310     case 1: { // coalesce if left & right chunks on overpopulated lists
8311       coalesce = _sp->coalOverPopulated(left) &&
8312                  _sp->coalOverPopulated(right);
8313       break;
8314     }
8315     case 2: { // coalesce if left chunk on overpopulated list (default)
8316       coalesce = _sp->coalOverPopulated(left);
8317       break;
8318     }
8319     case 3: { // coalesce if left OR right chunk on overpopulated list
8320       coalesce = _sp->coalOverPopulated(left) ||
8321                  _sp->coalOverPopulated(right);
8322       break;
8323     }
8324     case 4: { // always coalesce
8325       coalesce = true;
8326       break;
8327     }
8328     default:
8329      ShouldNotReachHere();
8330   }
8331 
8332   // Should the current free range be coalesced?
8333   // If the chunk is in a free range and either we decided to coalesce above
8334   // or the chunk is near the large block at the end of the heap
8335   // (isNearLargestChunk() returns true), then coalesce this chunk.
8336   const bool doCoalesce = inFreeRange()
8337                           && (coalesce || _g->isNearLargestChunk(fc_addr));
8338   if (doCoalesce) {
8339     // Coalesce the current free range on the left with the new
8340     // chunk on the right.  If either is on a free list,
8341     // it must be removed from the list and stashed in the closure.
8342     if (freeRangeInFreeLists()) {
8343       FreeChunk* const ffc = (FreeChunk*)freeFinger();
8344       assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8345         "Size of free range is inconsistent with chunk size.");
8346       if (CMSTestInFreeList) {
8347         assert(_sp->verify_chunk_in_free_list(ffc),
8348           "Chunk is not in free lists");
8349       }
8350       _sp->coalDeath(ffc->size());
8351       _sp->removeFreeChunkFromFreeLists(ffc);
8352       set_freeRangeInFreeLists(false);
8353     }
8354     if (fcInFreeLists) {
8355       _sp->coalDeath(chunkSize);
8356       assert(fc->size() == chunkSize,
8357         "The chunk has the wrong size or is not in the free lists");
8358       _sp->removeFreeChunkFromFreeLists(fc);
8359     }
8360     set_lastFreeRangeCoalesced(true);
8361     print_free_block_coalesced(fc);
8362   } else {  // not in a free range and/or should not coalesce
8363     // Return the current free range and start a new one.
8364     if (inFreeRange()) {
8365       // In a free range but cannot coalesce with the right hand chunk.
8366       // Put the current free range into the free lists.
8367       flush_cur_free_chunk(freeFinger(),
8368                            pointer_delta(fc_addr, freeFinger()));
8369     }
8370     // Set up for new free range.  Pass along whether the right hand
8371     // chunk is in the free lists.
8372     initialize_free_range((HeapWord*)fc, fcInFreeLists);
8373   }
8374 }
8375 
8376 // Lookahead flush:
8377 // If we are tracking a free range, and this is the last chunk that
8378 // we'll look at because its end crosses past _limit, we'll preemptively
8379 // flush it along with any free range we may be holding on to. Note that
8380 // this can be the case only for an already free or freshly garbage
8381 // chunk. If this block is an object, it can never straddle
8382 // over _limit. The "straddling" occurs when _limit is set at
8383 // the previous end of the space when this cycle started, and
8384 // a subsequent heap expansion caused the previously co-terminal
8385 // free block to be coalesced with the newly expanded portion,
8386 // thus rendering _limit a non-block-boundary making it dangerous
8387 // for the sweeper to step over and examine.
8388 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8389   assert(inFreeRange(), "Should only be called if currently in a free range.");
8390   HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8391   assert(_sp->used_region().contains(eob - 1),
8392          err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8393                  " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8394                  _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8395   if (eob >= _limit) {
8396     assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8397     if (CMSTraceSweeper) {
8398       gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8399                              "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8400                              "[" PTR_FORMAT "," PTR_FORMAT ")",
8401                              _limit, fc, eob, _sp->bottom(), _sp->end());
8402     }
8403     // Return the storage we are tracking back into the free lists.
8404     if (CMSTraceSweeper) {
8405       gclog_or_tty->print_cr("Flushing ... ");
8406     }
8407     assert(freeFinger() < eob, "Error");
8408     flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8409   }
8410 }
8411 
8412 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8413   assert(inFreeRange(), "Should only be called if currently in a free range.");
8414   assert(size > 0,
8415     "A zero sized chunk cannot be added to the free lists.");
8416   if (!freeRangeInFreeLists()) {
8417     if (CMSTestInFreeList) {
8418       FreeChunk* fc = (FreeChunk*) chunk;
8419       fc->set_size(size);
8420       assert(!_sp->verify_chunk_in_free_list(fc),
8421         "chunk should not be in free lists yet");
8422     }
8423     if (CMSTraceSweeper) {
8424       gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8425                     chunk, size);
8426     }
8427     // A new free range is going to be starting.  The current
8428     // free range has not been added to the free lists yet or
8429     // was removed so add it back.
8430     // If the current free range was coalesced, then the death
8431     // of the free range was recorded.  Record a birth now.
8432     if (lastFreeRangeCoalesced()) {
8433       _sp->coalBirth(size);
8434     }
8435     _sp->addChunkAndRepairOffsetTable(chunk, size,
8436             lastFreeRangeCoalesced());
8437   } else if (CMSTraceSweeper) {
8438     gclog_or_tty->print_cr("Already in free list: nothing to flush");
8439   }
8440   set_inFreeRange(false);
8441   set_freeRangeInFreeLists(false);
8442 }
8443 
8444 // We take a break if we've been at this for a while,
8445 // so as to avoid monopolizing the locks involved.
8446 void SweepClosure::do_yield_work(HeapWord* addr) {
8447   // Return current free chunk being used for coalescing (if any)
8448   // to the appropriate freelist.  After yielding, the next
8449   // free block encountered will start a coalescing range of
8450   // free blocks.  If the next free block is adjacent to the
8451   // chunk just flushed, they will need to wait for the next
8452   // sweep to be coalesced.
8453   if (inFreeRange()) {
8454     flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8455   }
8456 
8457   // First give up the locks, then yield, then re-lock.
8458   // We should probably use a constructor/destructor idiom to
8459   // do this unlock/lock or modify the MutexUnlocker class to
8460   // serve our purpose. XXX
8461   assert_lock_strong(_bitMap->lock());
8462   assert_lock_strong(_freelistLock);
8463   assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8464          "CMS thread should hold CMS token");
8465   _bitMap->lock()->unlock();
8466   _freelistLock->unlock();
8467   ConcurrentMarkSweepThread::desynchronize(true);
8468   ConcurrentMarkSweepThread::acknowledge_yield_request();
8469   _collector->stopTimer();
8470   GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8471   if (PrintCMSStatistics != 0) {
8472     _collector->incrementYields();
8473   }
8474   _collector->icms_wait();
8475 
8476   // See the comment in coordinator_yield()
8477   for (unsigned i = 0; i < CMSYieldSleepCount &&
8478                        ConcurrentMarkSweepThread::should_yield() &&
8479                        !CMSCollector::foregroundGCIsActive(); ++i) {
8480     os::sleep(Thread::current(), 1, false);
8481     ConcurrentMarkSweepThread::acknowledge_yield_request();
8482   }
8483 
8484   ConcurrentMarkSweepThread::synchronize(true);
8485   _freelistLock->lock();
8486   _bitMap->lock()->lock_without_safepoint_check();
8487   _collector->startTimer();
8488 }
8489 
8490 #ifndef PRODUCT
8491 // This is actually very useful in a product build if it can
8492 // be called from the debugger.  Compile it into the product
8493 // as needed.
8494 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8495   return debug_cms_space->verify_chunk_in_free_list(fc);
8496 }
8497 #endif
8498 
8499 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8500   if (CMSTraceSweeper) {
8501     gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8502                            fc, fc->size());
8503   }
8504 }
8505 
8506 // CMSIsAliveClosure
8507 bool CMSIsAliveClosure::do_object_b(oop obj) {
8508   HeapWord* addr = (HeapWord*)obj;
8509   return addr != NULL &&
8510          (!_span.contains(addr) || _bit_map->isMarked(addr));
8511 }
8512 
8513 
8514 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8515                       MemRegion span,
8516                       CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8517                       bool cpc):
8518   _collector(collector),
8519   _span(span),
8520   _bit_map(bit_map),
8521   _mark_stack(mark_stack),
8522   _concurrent_precleaning(cpc) {
8523   assert(!_span.is_empty(), "Empty span could spell trouble");
8524 }
8525 
8526 
8527 // CMSKeepAliveClosure: the serial version
8528 void CMSKeepAliveClosure::do_oop(oop obj) {
8529   HeapWord* addr = (HeapWord*)obj;
8530   if (_span.contains(addr) &&
8531       !_bit_map->isMarked(addr)) {
8532     _bit_map->mark(addr);
8533     bool simulate_overflow = false;
8534     NOT_PRODUCT(
8535       if (CMSMarkStackOverflowALot &&
8536           _collector->simulate_overflow()) {
8537         // simulate a stack overflow
8538         simulate_overflow = true;
8539       }
8540     )
8541     if (simulate_overflow || !_mark_stack->push(obj)) {
8542       if (_concurrent_precleaning) {
8543         // We dirty the overflown object and let the remark
8544         // phase deal with it.
8545         assert(_collector->overflow_list_is_empty(), "Error");
8546         // In the case of object arrays, we need to dirty all of
8547         // the cards that the object spans. No locking or atomics
8548         // are needed since no one else can be mutating the mod union
8549         // table.
8550         if (obj->is_objArray()) {
8551           size_t sz = obj->size();
8552           HeapWord* end_card_addr =
8553             (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8554           MemRegion redirty_range = MemRegion(addr, end_card_addr);
8555           assert(!redirty_range.is_empty(), "Arithmetical tautology");
8556           _collector->_modUnionTable.mark_range(redirty_range);
8557         } else {
8558           _collector->_modUnionTable.mark(addr);
8559         }
8560         _collector->_ser_kac_preclean_ovflw++;
8561       } else {
8562         _collector->push_on_overflow_list(obj);
8563         _collector->_ser_kac_ovflw++;
8564       }
8565     }
8566   }
8567 }
8568 
8569 void CMSKeepAliveClosure::do_oop(oop* p)       { CMSKeepAliveClosure::do_oop_work(p); }
8570 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8571 
8572 // CMSParKeepAliveClosure: a parallel version of the above.
8573 // The work queues are private to each closure (thread),
8574 // but (may be) available for stealing by other threads.
8575 void CMSParKeepAliveClosure::do_oop(oop obj) {
8576   HeapWord* addr = (HeapWord*)obj;
8577   if (_span.contains(addr) &&
8578       !_bit_map->isMarked(addr)) {
8579     // In general, during recursive tracing, several threads
8580     // may be concurrently getting here; the first one to
8581     // "tag" it, claims it.
8582     if (_bit_map->par_mark(addr)) {
8583       bool res = _work_queue->push(obj);
8584       assert(res, "Low water mark should be much less than capacity");
8585       // Do a recursive trim in the hope that this will keep
8586       // stack usage lower, but leave some oops for potential stealers
8587       trim_queue(_low_water_mark);
8588     } // Else, another thread got there first
8589   }
8590 }
8591 
8592 void CMSParKeepAliveClosure::do_oop(oop* p)       { CMSParKeepAliveClosure::do_oop_work(p); }
8593 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8594 
8595 void CMSParKeepAliveClosure::trim_queue(uint max) {
8596   while (_work_queue->size() > max) {
8597     oop new_oop;
8598     if (_work_queue->pop_local(new_oop)) {
8599       assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8600       assert(_bit_map->isMarked((HeapWord*)new_oop),
8601              "no white objects on this stack!");
8602       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8603       // iterate over the oops in this oop, marking and pushing
8604       // the ones in CMS heap (i.e. in _span).
8605       new_oop->oop_iterate(&_mark_and_push);
8606     }
8607   }
8608 }
8609 
8610 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8611                                 CMSCollector* collector,
8612                                 MemRegion span, CMSBitMap* bit_map,
8613                                 OopTaskQueue* work_queue):
8614   _collector(collector),
8615   _span(span),
8616   _bit_map(bit_map),
8617   _work_queue(work_queue) { }
8618 
8619 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8620   HeapWord* addr = (HeapWord*)obj;
8621   if (_span.contains(addr) &&
8622       !_bit_map->isMarked(addr)) {
8623     if (_bit_map->par_mark(addr)) {
8624       bool simulate_overflow = false;
8625       NOT_PRODUCT(
8626         if (CMSMarkStackOverflowALot &&
8627             _collector->par_simulate_overflow()) {
8628           // simulate a stack overflow
8629           simulate_overflow = true;
8630         }
8631       )
8632       if (simulate_overflow || !_work_queue->push(obj)) {
8633         _collector->par_push_on_overflow_list(obj);
8634         _collector->_par_kac_ovflw++;
8635       }
8636     } // Else another thread got there already
8637   }
8638 }
8639 
8640 void CMSInnerParMarkAndPushClosure::do_oop(oop* p)       { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8641 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8642 
8643 //////////////////////////////////////////////////////////////////
8644 //  CMSExpansionCause                /////////////////////////////
8645 //////////////////////////////////////////////////////////////////
8646 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8647   switch (cause) {
8648     case _no_expansion:
8649       return "No expansion";
8650     case _satisfy_free_ratio:
8651       return "Free ratio";
8652     case _satisfy_promotion:
8653       return "Satisfy promotion";
8654     case _satisfy_allocation:
8655       return "allocation";
8656     case _allocate_par_lab:
8657       return "Par LAB";
8658     case _allocate_par_spooling_space:
8659       return "Par Spooling Space";
8660     case _adaptive_size_policy:
8661       return "Ergonomics";
8662     default:
8663       return "unknown";
8664   }
8665 }
8666 
8667 void CMSDrainMarkingStackClosure::do_void() {
8668   // the max number to take from overflow list at a time
8669   const size_t num = _mark_stack->capacity()/4;
8670   assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8671          "Overflow list should be NULL during concurrent phases");
8672   while (!_mark_stack->isEmpty() ||
8673          // if stack is empty, check the overflow list
8674          _collector->take_from_overflow_list(num, _mark_stack)) {
8675     oop obj = _mark_stack->pop();
8676     HeapWord* addr = (HeapWord*)obj;
8677     assert(_span.contains(addr), "Should be within span");
8678     assert(_bit_map->isMarked(addr), "Should be marked");
8679     assert(obj->is_oop(), "Should be an oop");
8680     obj->oop_iterate(_keep_alive);
8681   }
8682 }
8683 
8684 void CMSParDrainMarkingStackClosure::do_void() {
8685   // drain queue
8686   trim_queue(0);
8687 }
8688 
8689 // Trim our work_queue so its length is below max at return
8690 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8691   while (_work_queue->size() > max) {
8692     oop new_oop;
8693     if (_work_queue->pop_local(new_oop)) {
8694       assert(new_oop->is_oop(), "Expected an oop");
8695       assert(_bit_map->isMarked((HeapWord*)new_oop),
8696              "no white objects on this stack!");
8697       assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8698       // iterate over the oops in this oop, marking and pushing
8699       // the ones in CMS heap (i.e. in _span).
8700       new_oop->oop_iterate(&_mark_and_push);
8701     }
8702   }
8703 }
8704 
8705 ////////////////////////////////////////////////////////////////////
8706 // Support for Marking Stack Overflow list handling and related code
8707 ////////////////////////////////////////////////////////////////////
8708 // Much of the following code is similar in shape and spirit to the
8709 // code used in ParNewGC. We should try and share that code
8710 // as much as possible in the future.
8711 
8712 #ifndef PRODUCT
8713 // Debugging support for CMSStackOverflowALot
8714 
8715 // It's OK to call this multi-threaded;  the worst thing
8716 // that can happen is that we'll get a bunch of closely
8717 // spaced simulated oveflows, but that's OK, in fact
8718 // probably good as it would exercise the overflow code
8719 // under contention.
8720 bool CMSCollector::simulate_overflow() {
8721   if (_overflow_counter-- <= 0) { // just being defensive
8722     _overflow_counter = CMSMarkStackOverflowInterval;
8723     return true;
8724   } else {
8725     return false;
8726   }
8727 }
8728 
8729 bool CMSCollector::par_simulate_overflow() {
8730   return simulate_overflow();
8731 }
8732 #endif
8733 
8734 // Single-threaded
8735 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8736   assert(stack->isEmpty(), "Expected precondition");
8737   assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8738   size_t i = num;
8739   oop  cur = _overflow_list;
8740   const markOop proto = markOopDesc::prototype();
8741   NOT_PRODUCT(ssize_t n = 0;)
8742   for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8743     next = oop(cur->mark());
8744     cur->set_mark(proto);   // until proven otherwise
8745     assert(cur->is_oop(), "Should be an oop");
8746     bool res = stack->push(cur);
8747     assert(res, "Bit off more than can chew?");
8748     NOT_PRODUCT(n++;)
8749   }
8750   _overflow_list = cur;
8751 #ifndef PRODUCT
8752   assert(_num_par_pushes >= n, "Too many pops?");
8753   _num_par_pushes -=n;
8754 #endif
8755   return !stack->isEmpty();
8756 }
8757 
8758 #define BUSY  (oop(0x1aff1aff))
8759 // (MT-safe) Get a prefix of at most "num" from the list.
8760 // The overflow list is chained through the mark word of
8761 // each object in the list. We fetch the entire list,
8762 // break off a prefix of the right size and return the
8763 // remainder. If other threads try to take objects from
8764 // the overflow list at that time, they will wait for
8765 // some time to see if data becomes available. If (and
8766 // only if) another thread places one or more object(s)
8767 // on the global list before we have returned the suffix
8768 // to the global list, we will walk down our local list
8769 // to find its end and append the global list to
8770 // our suffix before returning it. This suffix walk can
8771 // prove to be expensive (quadratic in the amount of traffic)
8772 // when there are many objects in the overflow list and
8773 // there is much producer-consumer contention on the list.
8774 // *NOTE*: The overflow list manipulation code here and
8775 // in ParNewGeneration:: are very similar in shape,
8776 // except that in the ParNew case we use the old (from/eden)
8777 // copy of the object to thread the list via its klass word.
8778 // Because of the common code, if you make any changes in
8779 // the code below, please check the ParNew version to see if
8780 // similar changes might be needed.
8781 // CR 6797058 has been filed to consolidate the common code.
8782 bool CMSCollector::par_take_from_overflow_list(size_t num,
8783                                                OopTaskQueue* work_q,
8784                                                int no_of_gc_threads) {
8785   assert(work_q->size() == 0, "First empty local work queue");
8786   assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8787   if (_overflow_list == NULL) {
8788     return false;
8789   }
8790   // Grab the entire list; we'll put back a suffix
8791   oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8792   Thread* tid = Thread::current();
8793   // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8794   // set to ParallelGCThreads.
8795   size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8796   size_t sleep_time_millis = MAX2((size_t)1, num/100);
8797   // If the list is busy, we spin for a short while,
8798   // sleeping between attempts to get the list.
8799   for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8800     os::sleep(tid, sleep_time_millis, false);
8801     if (_overflow_list == NULL) {
8802       // Nothing left to take
8803       return false;
8804     } else if (_overflow_list != BUSY) {
8805       // Try and grab the prefix
8806       prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8807     }
8808   }
8809   // If the list was found to be empty, or we spun long
8810   // enough, we give up and return empty-handed. If we leave
8811   // the list in the BUSY state below, it must be the case that
8812   // some other thread holds the overflow list and will set it
8813   // to a non-BUSY state in the future.
8814   if (prefix == NULL || prefix == BUSY) {
8815      // Nothing to take or waited long enough
8816      if (prefix == NULL) {
8817        // Write back the NULL in case we overwrote it with BUSY above
8818        // and it is still the same value.
8819        (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8820      }
8821      return false;
8822   }
8823   assert(prefix != NULL && prefix != BUSY, "Error");
8824   size_t i = num;
8825   oop cur = prefix;
8826   // Walk down the first "num" objects, unless we reach the end.
8827   for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8828   if (cur->mark() == NULL) {
8829     // We have "num" or fewer elements in the list, so there
8830     // is nothing to return to the global list.
8831     // Write back the NULL in lieu of the BUSY we wrote
8832     // above, if it is still the same value.
8833     if (_overflow_list == BUSY) {
8834       (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8835     }
8836   } else {
8837     // Chop off the suffix and rerturn it to the global list.
8838     assert(cur->mark() != BUSY, "Error");
8839     oop suffix_head = cur->mark(); // suffix will be put back on global list
8840     cur->set_mark(NULL);           // break off suffix
8841     // It's possible that the list is still in the empty(busy) state
8842     // we left it in a short while ago; in that case we may be
8843     // able to place back the suffix without incurring the cost
8844     // of a walk down the list.
8845     oop observed_overflow_list = _overflow_list;
8846     oop cur_overflow_list = observed_overflow_list;
8847     bool attached = false;
8848     while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8849       observed_overflow_list =
8850         (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8851       if (cur_overflow_list == observed_overflow_list) {
8852         attached = true;
8853         break;
8854       } else cur_overflow_list = observed_overflow_list;
8855     }
8856     if (!attached) {
8857       // Too bad, someone else sneaked in (at least) an element; we'll need
8858       // to do a splice. Find tail of suffix so we can prepend suffix to global
8859       // list.
8860       for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8861       oop suffix_tail = cur;
8862       assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8863              "Tautology");
8864       observed_overflow_list = _overflow_list;
8865       do {
8866         cur_overflow_list = observed_overflow_list;
8867         if (cur_overflow_list != BUSY) {
8868           // Do the splice ...
8869           suffix_tail->set_mark(markOop(cur_overflow_list));
8870         } else { // cur_overflow_list == BUSY
8871           suffix_tail->set_mark(NULL);
8872         }
8873         // ... and try to place spliced list back on overflow_list ...
8874         observed_overflow_list =
8875           (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8876       } while (cur_overflow_list != observed_overflow_list);
8877       // ... until we have succeeded in doing so.
8878     }
8879   }
8880 
8881   // Push the prefix elements on work_q
8882   assert(prefix != NULL, "control point invariant");
8883   const markOop proto = markOopDesc::prototype();
8884   oop next;
8885   NOT_PRODUCT(ssize_t n = 0;)
8886   for (cur = prefix; cur != NULL; cur = next) {
8887     next = oop(cur->mark());
8888     cur->set_mark(proto);   // until proven otherwise
8889     assert(cur->is_oop(), "Should be an oop");
8890     bool res = work_q->push(cur);
8891     assert(res, "Bit off more than we can chew?");
8892     NOT_PRODUCT(n++;)
8893   }
8894 #ifndef PRODUCT
8895   assert(_num_par_pushes >= n, "Too many pops?");
8896   Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8897 #endif
8898   return true;
8899 }
8900 
8901 // Single-threaded
8902 void CMSCollector::push_on_overflow_list(oop p) {
8903   NOT_PRODUCT(_num_par_pushes++;)
8904   assert(p->is_oop(), "Not an oop");
8905   preserve_mark_if_necessary(p);
8906   p->set_mark((markOop)_overflow_list);
8907   _overflow_list = p;
8908 }
8909 
8910 // Multi-threaded; use CAS to prepend to overflow list
8911 void CMSCollector::par_push_on_overflow_list(oop p) {
8912   NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8913   assert(p->is_oop(), "Not an oop");
8914   par_preserve_mark_if_necessary(p);
8915   oop observed_overflow_list = _overflow_list;
8916   oop cur_overflow_list;
8917   do {
8918     cur_overflow_list = observed_overflow_list;
8919     if (cur_overflow_list != BUSY) {
8920       p->set_mark(markOop(cur_overflow_list));
8921     } else {
8922       p->set_mark(NULL);
8923     }
8924     observed_overflow_list =
8925       (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8926   } while (cur_overflow_list != observed_overflow_list);
8927 }
8928 #undef BUSY
8929 
8930 // Single threaded
8931 // General Note on GrowableArray: pushes may silently fail
8932 // because we are (temporarily) out of C-heap for expanding
8933 // the stack. The problem is quite ubiquitous and affects
8934 // a lot of code in the JVM. The prudent thing for GrowableArray
8935 // to do (for now) is to exit with an error. However, that may
8936 // be too draconian in some cases because the caller may be
8937 // able to recover without much harm. For such cases, we
8938 // should probably introduce a "soft_push" method which returns
8939 // an indication of success or failure with the assumption that
8940 // the caller may be able to recover from a failure; code in
8941 // the VM can then be changed, incrementally, to deal with such
8942 // failures where possible, thus, incrementally hardening the VM
8943 // in such low resource situations.
8944 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8945   _preserved_oop_stack.push(p);
8946   _preserved_mark_stack.push(m);
8947   assert(m == p->mark(), "Mark word changed");
8948   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8949          "bijection");
8950 }
8951 
8952 // Single threaded
8953 void CMSCollector::preserve_mark_if_necessary(oop p) {
8954   markOop m = p->mark();
8955   if (m->must_be_preserved(p)) {
8956     preserve_mark_work(p, m);
8957   }
8958 }
8959 
8960 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8961   markOop m = p->mark();
8962   if (m->must_be_preserved(p)) {
8963     MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8964     // Even though we read the mark word without holding
8965     // the lock, we are assured that it will not change
8966     // because we "own" this oop, so no other thread can
8967     // be trying to push it on the overflow list; see
8968     // the assertion in preserve_mark_work() that checks
8969     // that m == p->mark().
8970     preserve_mark_work(p, m);
8971   }
8972 }
8973 
8974 // We should be able to do this multi-threaded,
8975 // a chunk of stack being a task (this is
8976 // correct because each oop only ever appears
8977 // once in the overflow list. However, it's
8978 // not very easy to completely overlap this with
8979 // other operations, so will generally not be done
8980 // until all work's been completed. Because we
8981 // expect the preserved oop stack (set) to be small,
8982 // it's probably fine to do this single-threaded.
8983 // We can explore cleverer concurrent/overlapped/parallel
8984 // processing of preserved marks if we feel the
8985 // need for this in the future. Stack overflow should
8986 // be so rare in practice and, when it happens, its
8987 // effect on performance so great that this will
8988 // likely just be in the noise anyway.
8989 void CMSCollector::restore_preserved_marks_if_any() {
8990   assert(SafepointSynchronize::is_at_safepoint(),
8991          "world should be stopped");
8992   assert(Thread::current()->is_ConcurrentGC_thread() ||
8993          Thread::current()->is_VM_thread(),
8994          "should be single-threaded");
8995   assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8996          "bijection");
8997 
8998   while (!_preserved_oop_stack.is_empty()) {
8999     oop p = _preserved_oop_stack.pop();
9000     assert(p->is_oop(), "Should be an oop");
9001     assert(_span.contains(p), "oop should be in _span");
9002     assert(p->mark() == markOopDesc::prototype(),
9003            "Set when taken from overflow list");
9004     markOop m = _preserved_mark_stack.pop();
9005     p->set_mark(m);
9006   }
9007   assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9008          "stacks were cleared above");
9009 }
9010 
9011 #ifndef PRODUCT
9012 bool CMSCollector::no_preserved_marks() const {
9013   return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9014 }
9015 #endif
9016 
9017 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9018 {
9019   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9020   CMSAdaptiveSizePolicy* size_policy =
9021     (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9022   assert(size_policy->is_gc_cms_adaptive_size_policy(),
9023     "Wrong type for size policy");
9024   return size_policy;
9025 }
9026 
9027 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9028                                            size_t desired_promo_size) {
9029   if (cur_promo_size < desired_promo_size) {
9030     size_t expand_bytes = desired_promo_size - cur_promo_size;
9031     if (PrintAdaptiveSizePolicy && Verbose) {
9032       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9033         "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9034         expand_bytes);
9035     }
9036     expand(expand_bytes,
9037            MinHeapDeltaBytes,
9038            CMSExpansionCause::_adaptive_size_policy);
9039   } else if (desired_promo_size < cur_promo_size) {
9040     size_t shrink_bytes = cur_promo_size - desired_promo_size;
9041     if (PrintAdaptiveSizePolicy && Verbose) {
9042       gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9043         "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9044         shrink_bytes);
9045     }
9046     shrink(shrink_bytes);
9047   }
9048 }
9049 
9050 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9051   GenCollectedHeap* gch = GenCollectedHeap::heap();
9052   CMSGCAdaptivePolicyCounters* counters =
9053     (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9054   assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9055     "Wrong kind of counters");
9056   return counters;
9057 }
9058 
9059 
9060 void ASConcurrentMarkSweepGeneration::update_counters() {
9061   if (UsePerfData) {
9062     _space_counters->update_all();
9063     _gen_counters->update_all();
9064     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9065     GenCollectedHeap* gch = GenCollectedHeap::heap();
9066     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9067     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9068       "Wrong gc statistics type");
9069     counters->update_counters(gc_stats_l);
9070   }
9071 }
9072 
9073 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9074   if (UsePerfData) {
9075     _space_counters->update_used(used);
9076     _space_counters->update_capacity();
9077     _gen_counters->update_all();
9078 
9079     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9080     GenCollectedHeap* gch = GenCollectedHeap::heap();
9081     CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9082     assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9083       "Wrong gc statistics type");
9084     counters->update_counters(gc_stats_l);
9085   }
9086 }
9087 
9088 // The desired expansion delta is computed so that:
9089 // . desired free percentage or greater is used
9090 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9091   assert_locked_or_safepoint(Heap_lock);
9092 
9093   GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9094 
9095   // If incremental collection failed, we just want to expand
9096   // to the limit.
9097   if (incremental_collection_failed()) {
9098     clear_incremental_collection_failed();
9099     grow_to_reserved();
9100     return;
9101   }
9102 
9103   assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9104 
9105   assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9106     "Wrong type of heap");
9107   int prev_level = level() - 1;
9108   assert(prev_level >= 0, "The cms generation is the lowest generation");
9109   Generation* prev_gen = gch->get_gen(prev_level);
9110   assert(prev_gen->kind() == Generation::ASParNew,
9111     "Wrong type of young generation");
9112   ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9113   size_t cur_eden = younger_gen->eden()->capacity();
9114   CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9115   size_t cur_promo = free();
9116   size_policy->compute_tenured_generation_free_space(cur_promo,
9117                                                        max_available(),
9118                                                        cur_eden);
9119   resize(cur_promo, size_policy->promo_size());
9120 
9121   // Record the new size of the space in the cms generation
9122   // that is available for promotions.  This is temporary.
9123   // It should be the desired promo size.
9124   size_policy->avg_cms_promo()->sample(free());
9125   size_policy->avg_old_live()->sample(used());
9126 
9127   if (UsePerfData) {
9128     CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9129     counters->update_cms_capacity_counter(capacity());
9130   }
9131 }
9132 
9133 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9134   assert_locked_or_safepoint(Heap_lock);
9135   assert_lock_strong(freelistLock());
9136   HeapWord* old_end = _cmsSpace->end();
9137   HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9138   assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9139   FreeChunk* chunk_at_end = find_chunk_at_end();
9140   if (chunk_at_end == NULL) {
9141     // No room to shrink
9142     if (PrintGCDetails && Verbose) {
9143       gclog_or_tty->print_cr("No room to shrink: old_end  "
9144         PTR_FORMAT "  unallocated_start  " PTR_FORMAT
9145         " chunk_at_end  " PTR_FORMAT,
9146         old_end, unallocated_start, chunk_at_end);
9147     }
9148     return;
9149   } else {
9150 
9151     // Find the chunk at the end of the space and determine
9152     // how much it can be shrunk.
9153     size_t shrinkable_size_in_bytes = chunk_at_end->size();
9154     size_t aligned_shrinkable_size_in_bytes =
9155       align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9156     assert(unallocated_start <= chunk_at_end->end(),
9157       "Inconsistent chunk at end of space");
9158     size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9159     size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9160 
9161     // Shrink the underlying space
9162     _virtual_space.shrink_by(bytes);
9163     if (PrintGCDetails && Verbose) {
9164       gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9165         " desired_bytes " SIZE_FORMAT
9166         " shrinkable_size_in_bytes " SIZE_FORMAT
9167         " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9168         "  bytes  " SIZE_FORMAT,
9169         desired_bytes, shrinkable_size_in_bytes,
9170         aligned_shrinkable_size_in_bytes, bytes);
9171       gclog_or_tty->print_cr("          old_end  " SIZE_FORMAT
9172         "  unallocated_start  " SIZE_FORMAT,
9173         old_end, unallocated_start);
9174     }
9175 
9176     // If the space did shrink (shrinking is not guaranteed),
9177     // shrink the chunk at the end by the appropriate amount.
9178     if (((HeapWord*)_virtual_space.high()) < old_end) {
9179       size_t new_word_size =
9180         heap_word_size(_virtual_space.committed_size());
9181 
9182       // Have to remove the chunk from the dictionary because it is changing
9183       // size and might be someplace elsewhere in the dictionary.
9184 
9185       // Get the chunk at end, shrink it, and put it
9186       // back.
9187       _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9188       size_t word_size_change = word_size_before - new_word_size;
9189       size_t chunk_at_end_old_size = chunk_at_end->size();
9190       assert(chunk_at_end_old_size >= word_size_change,
9191         "Shrink is too large");
9192       chunk_at_end->set_size(chunk_at_end_old_size -
9193                           word_size_change);
9194       _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9195         word_size_change);
9196 
9197       _cmsSpace->returnChunkToDictionary(chunk_at_end);
9198 
9199       MemRegion mr(_cmsSpace->bottom(), new_word_size);
9200       _bts->resize(new_word_size);  // resize the block offset shared array
9201       Universe::heap()->barrier_set()->resize_covered_region(mr);
9202       _cmsSpace->assert_locked();
9203       _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9204 
9205       NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9206 
9207       // update the space and generation capacity counters
9208       if (UsePerfData) {
9209         _space_counters->update_capacity();
9210         _gen_counters->update_all();
9211       }
9212 
9213       if (Verbose && PrintGCDetails) {
9214         size_t new_mem_size = _virtual_space.committed_size();
9215         size_t old_mem_size = new_mem_size + bytes;
9216         gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9217                       name(), old_mem_size/K, bytes/K, new_mem_size/K);
9218       }
9219     }
9220 
9221     assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9222       "Inconsistency at end of space");
9223     assert(chunk_at_end->end() == _cmsSpace->end(),
9224       "Shrinking is inconsistent");
9225     return;
9226   }
9227 }
9228 
9229 // Transfer some number of overflown objects to usual marking
9230 // stack. Return true if some objects were transferred.
9231 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9232   size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9233                     (size_t)ParGCDesiredObjsFromOverflowList);
9234 
9235   bool res = _collector->take_from_overflow_list(num, _mark_stack);
9236   assert(_collector->overflow_list_is_empty() || res,
9237          "If list is not empty, we should have taken something");
9238   assert(!res || !_mark_stack->isEmpty(),
9239          "If we took something, it should now be on our stack");
9240   return res;
9241 }
9242 
9243 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9244   size_t res = _sp->block_size_no_stall(addr, _collector);
9245   if (_sp->block_is_obj(addr)) {
9246     if (_live_bit_map->isMarked(addr)) {
9247       // It can't have been dead in a previous cycle
9248       guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9249     } else {
9250       _dead_bit_map->mark(addr);      // mark the dead object
9251     }
9252   }
9253   // Could be 0, if the block size could not be computed without stalling.
9254   return res;
9255 }
9256 
9257 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9258 
9259   switch (phase) {
9260     case CMSCollector::InitialMarking:
9261       initialize(true  /* fullGC */ ,
9262                  cause /* cause of the GC */,
9263                  true  /* recordGCBeginTime */,
9264                  true  /* recordPreGCUsage */,
9265                  false /* recordPeakUsage */,
9266                  false /* recordPostGCusage */,
9267                  true  /* recordAccumulatedGCTime */,
9268                  false /* recordGCEndTime */,
9269                  false /* countCollection */  );
9270       break;
9271 
9272     case CMSCollector::FinalMarking:
9273       initialize(true  /* fullGC */ ,
9274                  cause /* cause of the GC */,
9275                  false /* recordGCBeginTime */,
9276                  false /* recordPreGCUsage */,
9277                  false /* recordPeakUsage */,
9278                  false /* recordPostGCusage */,
9279                  true  /* recordAccumulatedGCTime */,
9280                  false /* recordGCEndTime */,
9281                  false /* countCollection */  );
9282       break;
9283 
9284     case CMSCollector::Sweeping:
9285       initialize(true  /* fullGC */ ,
9286                  cause /* cause of the GC */,
9287                  false /* recordGCBeginTime */,
9288                  false /* recordPreGCUsage */,
9289                  true  /* recordPeakUsage */,
9290                  true  /* recordPostGCusage */,
9291                  false /* recordAccumulatedGCTime */,
9292                  true  /* recordGCEndTime */,
9293                  true  /* countCollection */  );
9294       break;
9295 
9296     default:
9297       ShouldNotReachHere();
9298   }
9299 }
9300