1 /* 2 * Copyright (c) 2001, 2013, 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/gcTimer.hpp" 41 #include "gc_implementation/shared/gcTrace.hpp" 42 #include "gc_implementation/shared/gcTraceTime.hpp" 43 #include "gc_implementation/shared/isGCActiveMark.hpp" 44 #include "gc_interface/collectedHeap.inline.hpp" 45 #include "memory/allocation.hpp" 46 #include "memory/cardTableRS.hpp" 47 #include "memory/collectorPolicy.hpp" 48 #include "memory/gcLocker.inline.hpp" 49 #include "memory/genCollectedHeap.hpp" 50 #include "memory/genMarkSweep.hpp" 51 #include "memory/genOopClosures.inline.hpp" 52 #include "memory/iterator.hpp" 53 #include "memory/referencePolicy.hpp" 54 #include "memory/resourceArea.hpp" 55 #include "memory/tenuredGeneration.hpp" 56 #include "oops/oop.inline.hpp" 57 #include "prims/jvmtiExport.hpp" 58 #include "runtime/globals_extension.hpp" 59 #include "runtime/handles.inline.hpp" 60 #include "runtime/java.hpp" 61 #include "runtime/vmThread.hpp" 62 #include "services/memoryService.hpp" 63 #include "services/runtimeService.hpp" 64 65 // statics 66 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; 67 bool CMSCollector::_full_gc_requested = false; 68 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc; 69 70 ////////////////////////////////////////////////////////////////// 71 // In support of CMS/VM thread synchronization 72 ////////////////////////////////////////////////////////////////// 73 // We split use of the CGC_lock into 2 "levels". 74 // The low-level locking is of the usual CGC_lock monitor. We introduce 75 // a higher level "token" (hereafter "CMS token") built on top of the 76 // low level monitor (hereafter "CGC lock"). 77 // The token-passing protocol gives priority to the VM thread. The 78 // CMS-lock doesn't provide any fairness guarantees, but clients 79 // should ensure that it is only held for very short, bounded 80 // durations. 81 // 82 // When either of the CMS thread or the VM thread is involved in 83 // collection operations during which it does not want the other 84 // thread to interfere, it obtains the CMS token. 85 // 86 // If either thread tries to get the token while the other has 87 // it, that thread waits. However, if the VM thread and CMS thread 88 // both want the token, then the VM thread gets priority while the 89 // CMS thread waits. This ensures, for instance, that the "concurrent" 90 // phases of the CMS thread's work do not block out the VM thread 91 // for long periods of time as the CMS thread continues to hog 92 // the token. (See bug 4616232). 93 // 94 // The baton-passing functions are, however, controlled by the 95 // flags _foregroundGCShouldWait and _foregroundGCIsActive, 96 // and here the low-level CMS lock, not the high level token, 97 // ensures mutual exclusion. 98 // 99 // Two important conditions that we have to satisfy: 100 // 1. if a thread does a low-level wait on the CMS lock, then it 101 // relinquishes the CMS token if it were holding that token 102 // when it acquired the low-level CMS lock. 103 // 2. any low-level notifications on the low-level lock 104 // should only be sent when a thread has relinquished the token. 105 // 106 // In the absence of either property, we'd have potential deadlock. 107 // 108 // We protect each of the CMS (concurrent and sequential) phases 109 // with the CMS _token_, not the CMS _lock_. 110 // 111 // The only code protected by CMS lock is the token acquisition code 112 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the 113 // baton-passing code. 114 // 115 // Unfortunately, i couldn't come up with a good abstraction to factor and 116 // hide the naked CGC_lock manipulation in the baton-passing code 117 // further below. That's something we should try to do. Also, the proof 118 // of correctness of this 2-level locking scheme is far from obvious, 119 // and potentially quite slippery. We have an uneasy supsicion, for instance, 120 // that there may be a theoretical possibility of delay/starvation in the 121 // low-level lock/wait/notify scheme used for the baton-passing because of 122 // potential intereference with the priority scheme embodied in the 123 // CMS-token-passing protocol. See related comments at a CGC_lock->wait() 124 // invocation further below and marked with "XXX 20011219YSR". 125 // Indeed, as we note elsewhere, this may become yet more slippery 126 // in the presence of multiple CMS and/or multiple VM threads. XXX 127 128 class CMSTokenSync: public StackObj { 129 private: 130 bool _is_cms_thread; 131 public: 132 CMSTokenSync(bool is_cms_thread): 133 _is_cms_thread(is_cms_thread) { 134 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), 135 "Incorrect argument to constructor"); 136 ConcurrentMarkSweepThread::synchronize(_is_cms_thread); 137 } 138 139 ~CMSTokenSync() { 140 assert(_is_cms_thread ? 141 ConcurrentMarkSweepThread::cms_thread_has_cms_token() : 142 ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 143 "Incorrect state"); 144 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); 145 } 146 }; 147 148 // Convenience class that does a CMSTokenSync, and then acquires 149 // upto three locks. 150 class CMSTokenSyncWithLocks: public CMSTokenSync { 151 private: 152 // Note: locks are acquired in textual declaration order 153 // and released in the opposite order 154 MutexLockerEx _locker1, _locker2, _locker3; 155 public: 156 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, 157 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): 158 CMSTokenSync(is_cms_thread), 159 _locker1(mutex1, Mutex::_no_safepoint_check_flag), 160 _locker2(mutex2, Mutex::_no_safepoint_check_flag), 161 _locker3(mutex3, Mutex::_no_safepoint_check_flag) 162 { } 163 }; 164 165 166 // Wrapper class to temporarily disable icms during a foreground cms collection. 167 class ICMSDisabler: public StackObj { 168 public: 169 // The ctor disables icms and wakes up the thread so it notices the change; 170 // the dtor re-enables icms. Note that the CMSCollector methods will check 171 // CMSIncrementalMode. 172 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); } 173 ~ICMSDisabler() { CMSCollector::enable_icms(); } 174 }; 175 176 ////////////////////////////////////////////////////////////////// 177 // Concurrent Mark-Sweep Generation ///////////////////////////// 178 ////////////////////////////////////////////////////////////////// 179 180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) 181 182 // This struct contains per-thread things necessary to support parallel 183 // young-gen collection. 184 class CMSParGCThreadState: public CHeapObj<mtGC> { 185 public: 186 CFLS_LAB lab; 187 PromotionInfo promo; 188 189 // Constructor. 190 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { 191 promo.setSpace(cfls); 192 } 193 }; 194 195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( 196 ReservedSpace rs, size_t initial_byte_size, int level, 197 CardTableRS* ct, bool use_adaptive_freelists, 198 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) : 199 CardGeneration(rs, initial_byte_size, level, ct), 200 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))), 201 _debug_collection_type(Concurrent_collection_type), 202 _did_compact(false) 203 { 204 HeapWord* bottom = (HeapWord*) _virtual_space.low(); 205 HeapWord* end = (HeapWord*) _virtual_space.high(); 206 207 _direct_allocated_words = 0; 208 NOT_PRODUCT( 209 _numObjectsPromoted = 0; 210 _numWordsPromoted = 0; 211 _numObjectsAllocated = 0; 212 _numWordsAllocated = 0; 213 ) 214 215 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end), 216 use_adaptive_freelists, 217 dictionaryChoice); 218 NOT_PRODUCT(debug_cms_space = _cmsSpace;) 219 if (_cmsSpace == NULL) { 220 vm_exit_during_initialization( 221 "CompactibleFreeListSpace allocation failure"); 222 } 223 _cmsSpace->_gen = this; 224 225 _gc_stats = new CMSGCStats(); 226 227 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass 228 // offsets match. The ability to tell free chunks from objects 229 // depends on this property. 230 debug_only( 231 FreeChunk* junk = NULL; 232 assert(UseCompressedKlassPointers || 233 junk->prev_addr() == (void*)(oop(junk)->klass_addr()), 234 "Offset of FreeChunk::_prev within FreeChunk must match" 235 " that of OopDesc::_klass within OopDesc"); 236 ) 237 if (CollectedHeap::use_parallel_gc_threads()) { 238 typedef CMSParGCThreadState* CMSParGCThreadStatePtr; 239 _par_gc_thread_states = 240 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC); 241 if (_par_gc_thread_states == NULL) { 242 vm_exit_during_initialization("Could not allocate par gc structs"); 243 } 244 for (uint i = 0; i < ParallelGCThreads; i++) { 245 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); 246 if (_par_gc_thread_states[i] == NULL) { 247 vm_exit_during_initialization("Could not allocate par gc structs"); 248 } 249 } 250 } else { 251 _par_gc_thread_states = NULL; 252 } 253 _incremental_collection_failed = false; 254 // The "dilatation_factor" is the expansion that can occur on 255 // account of the fact that the minimum object size in the CMS 256 // generation may be larger than that in, say, a contiguous young 257 // generation. 258 // Ideally, in the calculation below, we'd compute the dilatation 259 // factor as: MinChunkSize/(promoting_gen's min object size) 260 // Since we do not have such a general query interface for the 261 // promoting generation, we'll instead just use the mimimum 262 // object size (which today is a header's worth of space); 263 // note that all arithmetic is in units of HeapWords. 264 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking"); 265 assert(_dilatation_factor >= 1.0, "from previous assert"); 266 } 267 268 269 // The field "_initiating_occupancy" represents the occupancy percentage 270 // at which we trigger a new collection cycle. Unless explicitly specified 271 // via CMSInitiatingOccupancyFraction (argument "io" below), it 272 // is calculated by: 273 // 274 // Let "f" be MinHeapFreeRatio in 275 // 276 // _intiating_occupancy = 100-f + 277 // f * (CMSTriggerRatio/100) 278 // where CMSTriggerRatio is the argument "tr" below. 279 // 280 // That is, if we assume the heap is at its desired maximum occupancy at the 281 // end of a collection, we let CMSTriggerRatio of the (purported) free 282 // space be allocated before initiating a new collection cycle. 283 // 284 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) { 285 assert(io <= 100 && tr <= 100, "Check the arguments"); 286 if (io >= 0) { 287 _initiating_occupancy = (double)io / 100.0; 288 } else { 289 _initiating_occupancy = ((100 - MinHeapFreeRatio) + 290 (double)(tr * MinHeapFreeRatio) / 100.0) 291 / 100.0; 292 } 293 } 294 295 void ConcurrentMarkSweepGeneration::ref_processor_init() { 296 assert(collector() != NULL, "no collector"); 297 collector()->ref_processor_init(); 298 } 299 300 void CMSCollector::ref_processor_init() { 301 if (_ref_processor == NULL) { 302 // Allocate and initialize a reference processor 303 _ref_processor = 304 new ReferenceProcessor(_span, // span 305 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing 306 (int) ParallelGCThreads, // mt processing degree 307 _cmsGen->refs_discovery_is_mt(), // mt discovery 308 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree 309 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic 310 &_is_alive_closure, // closure for liveness info 311 false); // next field updates do not need write barrier 312 // Initialize the _ref_processor field of CMSGen 313 _cmsGen->set_ref_processor(_ref_processor); 314 315 } 316 } 317 318 CMSAdaptiveSizePolicy* CMSCollector::size_policy() { 319 GenCollectedHeap* gch = GenCollectedHeap::heap(); 320 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 321 "Wrong type of heap"); 322 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) 323 gch->gen_policy()->size_policy(); 324 assert(sp->is_gc_cms_adaptive_size_policy(), 325 "Wrong type of size policy"); 326 return sp; 327 } 328 329 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() { 330 CMSGCAdaptivePolicyCounters* results = 331 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters(); 332 assert( 333 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, 334 "Wrong gc policy counter kind"); 335 return results; 336 } 337 338 339 void ConcurrentMarkSweepGeneration::initialize_performance_counters() { 340 341 const char* gen_name = "old"; 342 343 // Generation Counters - generation 1, 1 subspace 344 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space); 345 346 _space_counters = new GSpaceCounters(gen_name, 0, 347 _virtual_space.reserved_size(), 348 this, _gen_counters); 349 } 350 351 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): 352 _cms_gen(cms_gen) 353 { 354 assert(alpha <= 100, "bad value"); 355 _saved_alpha = alpha; 356 357 // Initialize the alphas to the bootstrap value of 100. 358 _gc0_alpha = _cms_alpha = 100; 359 360 _cms_begin_time.update(); 361 _cms_end_time.update(); 362 363 _gc0_duration = 0.0; 364 _gc0_period = 0.0; 365 _gc0_promoted = 0; 366 367 _cms_duration = 0.0; 368 _cms_period = 0.0; 369 _cms_allocated = 0; 370 371 _cms_used_at_gc0_begin = 0; 372 _cms_used_at_gc0_end = 0; 373 _allow_duty_cycle_reduction = false; 374 _valid_bits = 0; 375 _icms_duty_cycle = CMSIncrementalDutyCycle; 376 } 377 378 double CMSStats::cms_free_adjustment_factor(size_t free) const { 379 // TBD: CR 6909490 380 return 1.0; 381 } 382 383 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) { 384 } 385 386 // If promotion failure handling is on use 387 // the padded average size of the promotion for each 388 // young generation collection. 389 double CMSStats::time_until_cms_gen_full() const { 390 size_t cms_free = _cms_gen->cmsSpace()->free(); 391 GenCollectedHeap* gch = GenCollectedHeap::heap(); 392 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(), 393 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average()); 394 if (cms_free > expected_promotion) { 395 // Start a cms collection if there isn't enough space to promote 396 // for the next minor collection. Use the padded average as 397 // a safety factor. 398 cms_free -= expected_promotion; 399 400 // Adjust by the safety factor. 401 double cms_free_dbl = (double)cms_free; 402 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0; 403 // Apply a further correction factor which tries to adjust 404 // for recent occurance of concurrent mode failures. 405 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free); 406 cms_free_dbl = cms_free_dbl * cms_adjustment; 407 408 if (PrintGCDetails && Verbose) { 409 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free " 410 SIZE_FORMAT " expected_promotion " SIZE_FORMAT, 411 cms_free, expected_promotion); 412 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f", 413 cms_free_dbl, cms_consumption_rate() + 1.0); 414 } 415 // Add 1 in case the consumption rate goes to zero. 416 return cms_free_dbl / (cms_consumption_rate() + 1.0); 417 } 418 return 0.0; 419 } 420 421 // Compare the duration of the cms collection to the 422 // time remaining before the cms generation is empty. 423 // Note that the time from the start of the cms collection 424 // to the start of the cms sweep (less than the total 425 // duration of the cms collection) can be used. This 426 // has been tried and some applications experienced 427 // promotion failures early in execution. This was 428 // possibly because the averages were not accurate 429 // enough at the beginning. 430 double CMSStats::time_until_cms_start() const { 431 // We add "gc0_period" to the "work" calculation 432 // below because this query is done (mostly) at the 433 // end of a scavenge, so we need to conservatively 434 // account for that much possible delay 435 // in the query so as to avoid concurrent mode failures 436 // due to starting the collection just a wee bit too 437 // late. 438 double work = cms_duration() + gc0_period(); 439 double deadline = time_until_cms_gen_full(); 440 // If a concurrent mode failure occurred recently, we want to be 441 // more conservative and halve our expected time_until_cms_gen_full() 442 if (work > deadline) { 443 if (Verbose && PrintGCDetails) { 444 gclog_or_tty->print( 445 " CMSCollector: collect because of anticipated promotion " 446 "before full %3.7f + %3.7f > %3.7f ", cms_duration(), 447 gc0_period(), time_until_cms_gen_full()); 448 } 449 return 0.0; 450 } 451 return work - deadline; 452 } 453 454 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the 455 // amount of change to prevent wild oscillation. 456 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle, 457 unsigned int new_duty_cycle) { 458 assert(old_duty_cycle <= 100, "bad input value"); 459 assert(new_duty_cycle <= 100, "bad input value"); 460 461 // Note: use subtraction with caution since it may underflow (values are 462 // unsigned). Addition is safe since we're in the range 0-100. 463 unsigned int damped_duty_cycle = new_duty_cycle; 464 if (new_duty_cycle < old_duty_cycle) { 465 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U); 466 if (new_duty_cycle + largest_delta < old_duty_cycle) { 467 damped_duty_cycle = old_duty_cycle - largest_delta; 468 } 469 } else if (new_duty_cycle > old_duty_cycle) { 470 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U); 471 if (new_duty_cycle > old_duty_cycle + largest_delta) { 472 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U); 473 } 474 } 475 assert(damped_duty_cycle <= 100, "invalid duty cycle computed"); 476 477 if (CMSTraceIncrementalPacing) { 478 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ", 479 old_duty_cycle, new_duty_cycle, damped_duty_cycle); 480 } 481 return damped_duty_cycle; 482 } 483 484 unsigned int CMSStats::icms_update_duty_cycle_impl() { 485 assert(CMSIncrementalPacing && valid(), 486 "should be handled in icms_update_duty_cycle()"); 487 488 double cms_time_so_far = cms_timer().seconds(); 489 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M; 490 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far); 491 492 // Avoid division by 0. 493 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01); 494 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full; 495 496 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U); 497 if (new_duty_cycle > _icms_duty_cycle) { 498 // Avoid very small duty cycles (1 or 2); 0 is allowed. 499 if (new_duty_cycle > 2) { 500 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, 501 new_duty_cycle); 502 } 503 } else if (_allow_duty_cycle_reduction) { 504 // The duty cycle is reduced only once per cms cycle (see record_cms_end()). 505 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle); 506 // Respect the minimum duty cycle. 507 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin; 508 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle); 509 } 510 511 if (PrintGCDetails || CMSTraceIncrementalPacing) { 512 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle); 513 } 514 515 _allow_duty_cycle_reduction = false; 516 return _icms_duty_cycle; 517 } 518 519 #ifndef PRODUCT 520 void CMSStats::print_on(outputStream *st) const { 521 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); 522 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, 523 gc0_duration(), gc0_period(), gc0_promoted()); 524 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, 525 cms_duration(), cms_duration_per_mb(), 526 cms_period(), cms_allocated()); 527 st->print(",cms_since_beg=%g,cms_since_end=%g", 528 cms_time_since_begin(), cms_time_since_end()); 529 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, 530 _cms_used_at_gc0_begin, _cms_used_at_gc0_end); 531 if (CMSIncrementalMode) { 532 st->print(",dc=%d", icms_duty_cycle()); 533 } 534 535 if (valid()) { 536 st->print(",promo_rate=%g,cms_alloc_rate=%g", 537 promotion_rate(), cms_allocation_rate()); 538 st->print(",cms_consumption_rate=%g,time_until_full=%g", 539 cms_consumption_rate(), time_until_cms_gen_full()); 540 } 541 st->print(" "); 542 } 543 #endif // #ifndef PRODUCT 544 545 CMSCollector::CollectorState CMSCollector::_collectorState = 546 CMSCollector::Idling; 547 bool CMSCollector::_foregroundGCIsActive = false; 548 bool CMSCollector::_foregroundGCShouldWait = false; 549 550 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, 551 CardTableRS* ct, 552 ConcurrentMarkSweepPolicy* cp): 553 _cmsGen(cmsGen), 554 _ct(ct), 555 _ref_processor(NULL), // will be set later 556 _conc_workers(NULL), // may be set later 557 _abort_preclean(false), 558 _start_sampling(false), 559 _between_prologue_and_epilogue(false), 560 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), 561 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), 562 -1 /* lock-free */, "No_lock" /* dummy */), 563 _modUnionClosure(&_modUnionTable), 564 _modUnionClosurePar(&_modUnionTable), 565 // Adjust my span to cover old (cms) gen 566 _span(cmsGen->reserved()), 567 // Construct the is_alive_closure with _span & markBitMap 568 _is_alive_closure(_span, &_markBitMap), 569 _restart_addr(NULL), 570 _overflow_list(NULL), 571 _stats(cmsGen), 572 _eden_chunk_array(NULL), // may be set in ctor body 573 _eden_chunk_capacity(0), // -- ditto -- 574 _eden_chunk_index(0), // -- ditto -- 575 _survivor_plab_array(NULL), // -- ditto -- 576 _survivor_chunk_array(NULL), // -- ditto -- 577 _survivor_chunk_capacity(0), // -- ditto -- 578 _survivor_chunk_index(0), // -- ditto -- 579 _ser_pmc_preclean_ovflw(0), 580 _ser_kac_preclean_ovflw(0), 581 _ser_pmc_remark_ovflw(0), 582 _par_pmc_remark_ovflw(0), 583 _ser_kac_ovflw(0), 584 _par_kac_ovflw(0), 585 #ifndef PRODUCT 586 _num_par_pushes(0), 587 #endif 588 _collection_count_start(0), 589 _verifying(false), 590 _icms_start_limit(NULL), 591 _icms_stop_limit(NULL), 592 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), 593 _completed_initialization(false), 594 _collector_policy(cp), 595 _should_unload_classes(false), 596 _concurrent_cycles_since_last_unload(0), 597 _roots_scanning_options(0), 598 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 599 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding), 600 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()), 601 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()), 602 _cms_start_registered(false) 603 { 604 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) { 605 ExplicitGCInvokesConcurrent = true; 606 } 607 // Now expand the span and allocate the collection support structures 608 // (MUT, marking bit map etc.) to cover both generations subject to 609 // collection. 610 611 // For use by dirty card to oop closures. 612 _cmsGen->cmsSpace()->set_collector(this); 613 614 // Allocate MUT and marking bit map 615 { 616 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); 617 if (!_markBitMap.allocate(_span)) { 618 warning("Failed to allocate CMS Bit Map"); 619 return; 620 } 621 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); 622 } 623 { 624 _modUnionTable.allocate(_span); 625 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); 626 } 627 628 if (!_markStack.allocate(MarkStackSize)) { 629 warning("Failed to allocate CMS Marking Stack"); 630 return; 631 } 632 633 // Support for multi-threaded concurrent phases 634 if (CMSConcurrentMTEnabled) { 635 if (FLAG_IS_DEFAULT(ConcGCThreads)) { 636 // just for now 637 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4); 638 } 639 if (ConcGCThreads > 1) { 640 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads", 641 ConcGCThreads, true); 642 if (_conc_workers == NULL) { 643 warning("GC/CMS: _conc_workers allocation failure: " 644 "forcing -CMSConcurrentMTEnabled"); 645 CMSConcurrentMTEnabled = false; 646 } else { 647 _conc_workers->initialize_workers(); 648 } 649 } else { 650 CMSConcurrentMTEnabled = false; 651 } 652 } 653 if (!CMSConcurrentMTEnabled) { 654 ConcGCThreads = 0; 655 } else { 656 // Turn off CMSCleanOnEnter optimization temporarily for 657 // the MT case where it's not fixed yet; see 6178663. 658 CMSCleanOnEnter = false; 659 } 660 assert((_conc_workers != NULL) == (ConcGCThreads > 1), 661 "Inconsistency"); 662 663 // Parallel task queues; these are shared for the 664 // concurrent and stop-world phases of CMS, but 665 // are not shared with parallel scavenge (ParNew). 666 { 667 uint i; 668 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads); 669 670 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled 671 || ParallelRefProcEnabled) 672 && num_queues > 0) { 673 _task_queues = new OopTaskQueueSet(num_queues); 674 if (_task_queues == NULL) { 675 warning("task_queues allocation failure."); 676 return; 677 } 678 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC); 679 if (_hash_seed == NULL) { 680 warning("_hash_seed array allocation failure"); 681 return; 682 } 683 684 typedef Padded<OopTaskQueue> PaddedOopTaskQueue; 685 for (i = 0; i < num_queues; i++) { 686 PaddedOopTaskQueue *q = new PaddedOopTaskQueue(); 687 if (q == NULL) { 688 warning("work_queue allocation failure."); 689 return; 690 } 691 _task_queues->register_queue(i, q); 692 } 693 for (i = 0; i < num_queues; i++) { 694 _task_queues->queue(i)->initialize(); 695 _hash_seed[i] = 17; // copied from ParNew 696 } 697 } 698 } 699 700 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio); 701 702 // Clip CMSBootstrapOccupancy between 0 and 100. 703 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100; 704 705 _full_gcs_since_conc_gc = 0; 706 707 // Now tell CMS generations the identity of their collector 708 ConcurrentMarkSweepGeneration::set_collector(this); 709 710 // Create & start a CMS thread for this CMS collector 711 _cmsThread = ConcurrentMarkSweepThread::start(this); 712 assert(cmsThread() != NULL, "CMS Thread should have been created"); 713 assert(cmsThread()->collector() == this, 714 "CMS Thread should refer to this gen"); 715 assert(CGC_lock != NULL, "Where's the CGC_lock?"); 716 717 // Support for parallelizing young gen rescan 718 GenCollectedHeap* gch = GenCollectedHeap::heap(); 719 _young_gen = gch->prev_gen(_cmsGen); 720 if (gch->supports_inline_contig_alloc()) { 721 _top_addr = gch->top_addr(); 722 _end_addr = gch->end_addr(); 723 assert(_young_gen != NULL, "no _young_gen"); 724 _eden_chunk_index = 0; 725 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain; 726 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC); 727 if (_eden_chunk_array == NULL) { 728 _eden_chunk_capacity = 0; 729 warning("GC/CMS: _eden_chunk_array allocation failure"); 730 } 731 } 732 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error"); 733 734 // Support for parallelizing survivor space rescan 735 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) { 736 const size_t max_plab_samples = 737 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize; 738 739 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC); 740 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC); 741 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC); 742 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL 743 || _cursor == NULL) { 744 warning("Failed to allocate survivor plab/chunk array"); 745 if (_survivor_plab_array != NULL) { 746 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC); 747 _survivor_plab_array = NULL; 748 } 749 if (_survivor_chunk_array != NULL) { 750 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC); 751 _survivor_chunk_array = NULL; 752 } 753 if (_cursor != NULL) { 754 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC); 755 _cursor = NULL; 756 } 757 } else { 758 _survivor_chunk_capacity = 2*max_plab_samples; 759 for (uint i = 0; i < ParallelGCThreads; i++) { 760 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC); 761 if (vec == NULL) { 762 warning("Failed to allocate survivor plab array"); 763 for (int j = i; j > 0; j--) { 764 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC); 765 } 766 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC); 767 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC); 768 _survivor_plab_array = NULL; 769 _survivor_chunk_array = NULL; 770 _survivor_chunk_capacity = 0; 771 break; 772 } else { 773 ChunkArray* cur = 774 ::new (&_survivor_plab_array[i]) ChunkArray(vec, 775 max_plab_samples); 776 assert(cur->end() == 0, "Should be 0"); 777 assert(cur->array() == vec, "Should be vec"); 778 assert(cur->capacity() == max_plab_samples, "Error"); 779 } 780 } 781 } 782 } 783 assert( ( _survivor_plab_array != NULL 784 && _survivor_chunk_array != NULL) 785 || ( _survivor_chunk_capacity == 0 786 && _survivor_chunk_index == 0), 787 "Error"); 788 789 // Choose what strong roots should be scanned depending on verification options 790 if (!CMSClassUnloadingEnabled) { 791 // If class unloading is disabled we want to include all classes into the root set. 792 add_root_scanning_option(SharedHeap::SO_AllClasses); 793 } else { 794 add_root_scanning_option(SharedHeap::SO_SystemClasses); 795 } 796 797 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) 798 _gc_counters = new CollectorCounters("CMS", 1); 799 _completed_initialization = true; 800 _inter_sweep_timer.start(); // start of time 801 } 802 803 const char* ConcurrentMarkSweepGeneration::name() const { 804 return "concurrent mark-sweep generation"; 805 } 806 void ConcurrentMarkSweepGeneration::update_counters() { 807 if (UsePerfData) { 808 _space_counters->update_all(); 809 _gen_counters->update_all(); 810 } 811 } 812 813 // this is an optimized version of update_counters(). it takes the 814 // used value as a parameter rather than computing it. 815 // 816 void ConcurrentMarkSweepGeneration::update_counters(size_t used) { 817 if (UsePerfData) { 818 _space_counters->update_used(used); 819 _space_counters->update_capacity(); 820 _gen_counters->update_all(); 821 } 822 } 823 824 void ConcurrentMarkSweepGeneration::print() const { 825 Generation::print(); 826 cmsSpace()->print(); 827 } 828 829 #ifndef PRODUCT 830 void ConcurrentMarkSweepGeneration::print_statistics() { 831 cmsSpace()->printFLCensus(0); 832 } 833 #endif 834 835 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) { 836 GenCollectedHeap* gch = GenCollectedHeap::heap(); 837 if (PrintGCDetails) { 838 if (Verbose) { 839 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]", 840 level(), short_name(), s, used(), capacity()); 841 } else { 842 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]", 843 level(), short_name(), s, used() / K, capacity() / K); 844 } 845 } 846 if (Verbose) { 847 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")", 848 gch->used(), gch->capacity()); 849 } else { 850 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)", 851 gch->used() / K, gch->capacity() / K); 852 } 853 } 854 855 size_t 856 ConcurrentMarkSweepGeneration::contiguous_available() const { 857 // dld proposes an improvement in precision here. If the committed 858 // part of the space ends in a free block we should add that to 859 // uncommitted size in the calculation below. Will make this 860 // change later, staying with the approximation below for the 861 // time being. -- ysr. 862 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); 863 } 864 865 size_t 866 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { 867 return _cmsSpace->max_alloc_in_words() * HeapWordSize; 868 } 869 870 size_t ConcurrentMarkSweepGeneration::max_available() const { 871 return free() + _virtual_space.uncommitted_size(); 872 } 873 874 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const { 875 size_t available = max_available(); 876 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average(); 877 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes); 878 if (Verbose && PrintGCDetails) { 879 gclog_or_tty->print_cr( 880 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT")," 881 "max_promo("SIZE_FORMAT")", 882 res? "":" not", available, res? ">=":"<", 883 av_promo, max_promotion_in_bytes); 884 } 885 return res; 886 } 887 888 // At a promotion failure dump information on block layout in heap 889 // (cms old generation). 890 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() { 891 if (CMSDumpAtPromotionFailure) { 892 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty); 893 } 894 } 895 896 CompactibleSpace* 897 ConcurrentMarkSweepGeneration::first_compaction_space() const { 898 return _cmsSpace; 899 } 900 901 void ConcurrentMarkSweepGeneration::reset_after_compaction() { 902 // Clear the promotion information. These pointers can be adjusted 903 // along with all the other pointers into the heap but 904 // compaction is expected to be a rare event with 905 // a heap using cms so don't do it without seeing the need. 906 if (CollectedHeap::use_parallel_gc_threads()) { 907 for (uint i = 0; i < ParallelGCThreads; i++) { 908 _par_gc_thread_states[i]->promo.reset(); 909 } 910 } 911 } 912 913 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) { 914 blk->do_space(_cmsSpace); 915 } 916 917 void ConcurrentMarkSweepGeneration::compute_new_size() { 918 assert_locked_or_safepoint(Heap_lock); 919 920 // If incremental collection failed, we just want to expand 921 // to the limit. 922 if (incremental_collection_failed()) { 923 clear_incremental_collection_failed(); 924 grow_to_reserved(); 925 return; 926 } 927 928 // The heap has been compacted but not reset yet. 929 // Any metric such as free() or used() will be incorrect. 930 931 CardGeneration::compute_new_size(); 932 933 // Reset again after a possible resizing 934 if (did_compact()) { 935 cmsSpace()->reset_after_compaction(); 936 } 937 } 938 939 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() { 940 assert_locked_or_safepoint(Heap_lock); 941 942 // If incremental collection failed, we just want to expand 943 // to the limit. 944 if (incremental_collection_failed()) { 945 clear_incremental_collection_failed(); 946 grow_to_reserved(); 947 return; 948 } 949 950 double free_percentage = ((double) free()) / capacity(); 951 double desired_free_percentage = (double) MinHeapFreeRatio / 100; 952 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; 953 954 // compute expansion delta needed for reaching desired free percentage 955 if (free_percentage < desired_free_percentage) { 956 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 957 assert(desired_capacity >= capacity(), "invalid expansion size"); 958 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); 959 if (PrintGCDetails && Verbose) { 960 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 961 gclog_or_tty->print_cr("\nFrom compute_new_size: "); 962 gclog_or_tty->print_cr(" Free fraction %f", free_percentage); 963 gclog_or_tty->print_cr(" Desired free fraction %f", 964 desired_free_percentage); 965 gclog_or_tty->print_cr(" Maximum free fraction %f", 966 maximum_free_percentage); 967 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000); 968 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, 969 desired_capacity/1000); 970 int prev_level = level() - 1; 971 if (prev_level >= 0) { 972 size_t prev_size = 0; 973 GenCollectedHeap* gch = GenCollectedHeap::heap(); 974 Generation* prev_gen = gch->_gens[prev_level]; 975 prev_size = prev_gen->capacity(); 976 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT, 977 prev_size/1000); 978 } 979 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, 980 unsafe_max_alloc_nogc()/1000); 981 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, 982 contiguous_available()/1000); 983 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", 984 expand_bytes); 985 } 986 // safe if expansion fails 987 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); 988 if (PrintGCDetails && Verbose) { 989 gclog_or_tty->print_cr(" Expanded free fraction %f", 990 ((double) free()) / capacity()); 991 } 992 } else { 993 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); 994 assert(desired_capacity <= capacity(), "invalid expansion size"); 995 size_t shrink_bytes = capacity() - desired_capacity; 996 // Don't shrink unless the delta is greater than the minimum shrink we want 997 if (shrink_bytes >= MinHeapDeltaBytes) { 998 shrink_free_list_by(shrink_bytes); 999 } 1000 } 1001 } 1002 1003 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { 1004 return cmsSpace()->freelistLock(); 1005 } 1006 1007 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, 1008 bool tlab) { 1009 CMSSynchronousYieldRequest yr; 1010 MutexLockerEx x(freelistLock(), 1011 Mutex::_no_safepoint_check_flag); 1012 return have_lock_and_allocate(size, tlab); 1013 } 1014 1015 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, 1016 bool tlab /* ignored */) { 1017 assert_lock_strong(freelistLock()); 1018 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); 1019 HeapWord* res = cmsSpace()->allocate(adjustedSize); 1020 // Allocate the object live (grey) if the background collector has 1021 // started marking. This is necessary because the marker may 1022 // have passed this address and consequently this object will 1023 // not otherwise be greyed and would be incorrectly swept up. 1024 // Note that if this object contains references, the writing 1025 // of those references will dirty the card containing this object 1026 // allowing the object to be blackened (and its references scanned) 1027 // either during a preclean phase or at the final checkpoint. 1028 if (res != NULL) { 1029 // We may block here with an uninitialized object with 1030 // its mark-bit or P-bits not yet set. Such objects need 1031 // to be safely navigable by block_start(). 1032 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here."); 1033 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size"); 1034 collector()->direct_allocated(res, adjustedSize); 1035 _direct_allocated_words += adjustedSize; 1036 // allocation counters 1037 NOT_PRODUCT( 1038 _numObjectsAllocated++; 1039 _numWordsAllocated += (int)adjustedSize; 1040 ) 1041 } 1042 return res; 1043 } 1044 1045 // In the case of direct allocation by mutators in a generation that 1046 // is being concurrently collected, the object must be allocated 1047 // live (grey) if the background collector has started marking. 1048 // This is necessary because the marker may 1049 // have passed this address and consequently this object will 1050 // not otherwise be greyed and would be incorrectly swept up. 1051 // Note that if this object contains references, the writing 1052 // of those references will dirty the card containing this object 1053 // allowing the object to be blackened (and its references scanned) 1054 // either during a preclean phase or at the final checkpoint. 1055 void CMSCollector::direct_allocated(HeapWord* start, size_t size) { 1056 assert(_markBitMap.covers(start, size), "Out of bounds"); 1057 if (_collectorState >= Marking) { 1058 MutexLockerEx y(_markBitMap.lock(), 1059 Mutex::_no_safepoint_check_flag); 1060 // [see comments preceding SweepClosure::do_blk() below for details] 1061 // 1062 // Can the P-bits be deleted now? JJJ 1063 // 1064 // 1. need to mark the object as live so it isn't collected 1065 // 2. need to mark the 2nd bit to indicate the object may be uninitialized 1066 // 3. need to mark the end of the object so marking, precleaning or sweeping 1067 // can skip over uninitialized or unparsable objects. An allocated 1068 // object is considered uninitialized for our purposes as long as 1069 // its klass word is NULL. All old gen objects are parsable 1070 // as soon as they are initialized.) 1071 _markBitMap.mark(start); // object is live 1072 _markBitMap.mark(start + 1); // object is potentially uninitialized? 1073 _markBitMap.mark(start + size - 1); 1074 // mark end of object 1075 } 1076 // check that oop looks uninitialized 1077 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL"); 1078 } 1079 1080 void CMSCollector::promoted(bool par, HeapWord* start, 1081 bool is_obj_array, size_t obj_size) { 1082 assert(_markBitMap.covers(start), "Out of bounds"); 1083 // See comment in direct_allocated() about when objects should 1084 // be allocated live. 1085 if (_collectorState >= Marking) { 1086 // we already hold the marking bit map lock, taken in 1087 // the prologue 1088 if (par) { 1089 _markBitMap.par_mark(start); 1090 } else { 1091 _markBitMap.mark(start); 1092 } 1093 // We don't need to mark the object as uninitialized (as 1094 // in direct_allocated above) because this is being done with the 1095 // world stopped and the object will be initialized by the 1096 // time the marking, precleaning or sweeping get to look at it. 1097 // But see the code for copying objects into the CMS generation, 1098 // where we need to ensure that concurrent readers of the 1099 // block offset table are able to safely navigate a block that 1100 // is in flux from being free to being allocated (and in 1101 // transition while being copied into) and subsequently 1102 // becoming a bona-fide object when the copy/promotion is complete. 1103 assert(SafepointSynchronize::is_at_safepoint(), 1104 "expect promotion only at safepoints"); 1105 1106 if (_collectorState < Sweeping) { 1107 // Mark the appropriate cards in the modUnionTable, so that 1108 // this object gets scanned before the sweep. If this is 1109 // not done, CMS generation references in the object might 1110 // not get marked. 1111 // For the case of arrays, which are otherwise precisely 1112 // marked, we need to dirty the entire array, not just its head. 1113 if (is_obj_array) { 1114 // The [par_]mark_range() method expects mr.end() below to 1115 // be aligned to the granularity of a bit's representation 1116 // in the heap. In the case of the MUT below, that's a 1117 // card size. 1118 MemRegion mr(start, 1119 (HeapWord*)round_to((intptr_t)(start + obj_size), 1120 CardTableModRefBS::card_size /* bytes */)); 1121 if (par) { 1122 _modUnionTable.par_mark_range(mr); 1123 } else { 1124 _modUnionTable.mark_range(mr); 1125 } 1126 } else { // not an obj array; we can just mark the head 1127 if (par) { 1128 _modUnionTable.par_mark(start); 1129 } else { 1130 _modUnionTable.mark(start); 1131 } 1132 } 1133 } 1134 } 1135 } 1136 1137 static inline size_t percent_of_space(Space* space, HeapWord* addr) 1138 { 1139 size_t delta = pointer_delta(addr, space->bottom()); 1140 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize)); 1141 } 1142 1143 void CMSCollector::icms_update_allocation_limits() 1144 { 1145 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0); 1146 EdenSpace* eden = gen0->as_DefNewGeneration()->eden(); 1147 1148 const unsigned int duty_cycle = stats().icms_update_duty_cycle(); 1149 if (CMSTraceIncrementalPacing) { 1150 stats().print(); 1151 } 1152 1153 assert(duty_cycle <= 100, "invalid duty cycle"); 1154 if (duty_cycle != 0) { 1155 // The duty_cycle is a percentage between 0 and 100; convert to words and 1156 // then compute the offset from the endpoints of the space. 1157 size_t free_words = eden->free() / HeapWordSize; 1158 double free_words_dbl = (double)free_words; 1159 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0); 1160 size_t offset_words = (free_words - duty_cycle_words) / 2; 1161 1162 _icms_start_limit = eden->top() + offset_words; 1163 _icms_stop_limit = eden->end() - offset_words; 1164 1165 // The limits may be adjusted (shifted to the right) by 1166 // CMSIncrementalOffset, to allow the application more mutator time after a 1167 // young gen gc (when all mutators were stopped) and before CMS starts and 1168 // takes away one or more cpus. 1169 if (CMSIncrementalOffset != 0) { 1170 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0; 1171 size_t adjustment = (size_t)adjustment_dbl; 1172 HeapWord* tmp_stop = _icms_stop_limit + adjustment; 1173 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) { 1174 _icms_start_limit += adjustment; 1175 _icms_stop_limit = tmp_stop; 1176 } 1177 } 1178 } 1179 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) { 1180 _icms_start_limit = _icms_stop_limit = eden->end(); 1181 } 1182 1183 // Install the new start limit. 1184 eden->set_soft_end(_icms_start_limit); 1185 1186 if (CMSTraceIncrementalMode) { 1187 gclog_or_tty->print(" icms alloc limits: " 1188 PTR_FORMAT "," PTR_FORMAT 1189 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ", 1190 _icms_start_limit, _icms_stop_limit, 1191 percent_of_space(eden, _icms_start_limit), 1192 percent_of_space(eden, _icms_stop_limit)); 1193 if (Verbose) { 1194 gclog_or_tty->print("eden: "); 1195 eden->print_on(gclog_or_tty); 1196 } 1197 } 1198 } 1199 1200 // Any changes here should try to maintain the invariant 1201 // that if this method is called with _icms_start_limit 1202 // and _icms_stop_limit both NULL, then it should return NULL 1203 // and not notify the icms thread. 1204 HeapWord* 1205 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top, 1206 size_t word_size) 1207 { 1208 // A start_limit equal to end() means the duty cycle is 0, so treat that as a 1209 // nop. 1210 if (CMSIncrementalMode && _icms_start_limit != space->end()) { 1211 if (top <= _icms_start_limit) { 1212 if (CMSTraceIncrementalMode) { 1213 space->print_on(gclog_or_tty); 1214 gclog_or_tty->stamp(); 1215 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT 1216 ", new limit=" PTR_FORMAT 1217 " (" SIZE_FORMAT "%%)", 1218 top, _icms_stop_limit, 1219 percent_of_space(space, _icms_stop_limit)); 1220 } 1221 ConcurrentMarkSweepThread::start_icms(); 1222 assert(top < _icms_stop_limit, "Tautology"); 1223 if (word_size < pointer_delta(_icms_stop_limit, top)) { 1224 return _icms_stop_limit; 1225 } 1226 1227 // The allocation will cross both the _start and _stop limits, so do the 1228 // stop notification also and return end(). 1229 if (CMSTraceIncrementalMode) { 1230 space->print_on(gclog_or_tty); 1231 gclog_or_tty->stamp(); 1232 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT 1233 ", new limit=" PTR_FORMAT 1234 " (" SIZE_FORMAT "%%)", 1235 top, space->end(), 1236 percent_of_space(space, space->end())); 1237 } 1238 ConcurrentMarkSweepThread::stop_icms(); 1239 return space->end(); 1240 } 1241 1242 if (top <= _icms_stop_limit) { 1243 if (CMSTraceIncrementalMode) { 1244 space->print_on(gclog_or_tty); 1245 gclog_or_tty->stamp(); 1246 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT 1247 ", new limit=" PTR_FORMAT 1248 " (" SIZE_FORMAT "%%)", 1249 top, space->end(), 1250 percent_of_space(space, space->end())); 1251 } 1252 ConcurrentMarkSweepThread::stop_icms(); 1253 return space->end(); 1254 } 1255 1256 if (CMSTraceIncrementalMode) { 1257 space->print_on(gclog_or_tty); 1258 gclog_or_tty->stamp(); 1259 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT 1260 ", new limit=" PTR_FORMAT, 1261 top, NULL); 1262 } 1263 } 1264 1265 return NULL; 1266 } 1267 1268 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) { 1269 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); 1270 // allocate, copy and if necessary update promoinfo -- 1271 // delegate to underlying space. 1272 assert_lock_strong(freelistLock()); 1273 1274 #ifndef PRODUCT 1275 if (Universe::heap()->promotion_should_fail()) { 1276 return NULL; 1277 } 1278 #endif // #ifndef PRODUCT 1279 1280 oop res = _cmsSpace->promote(obj, obj_size); 1281 if (res == NULL) { 1282 // expand and retry 1283 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords 1284 expand(s*HeapWordSize, MinHeapDeltaBytes, 1285 CMSExpansionCause::_satisfy_promotion); 1286 // Since there's currently no next generation, we don't try to promote 1287 // into a more senior generation. 1288 assert(next_gen() == NULL, "assumption, based upon which no attempt " 1289 "is made to pass on a possibly failing " 1290 "promotion to next generation"); 1291 res = _cmsSpace->promote(obj, obj_size); 1292 } 1293 if (res != NULL) { 1294 // See comment in allocate() about when objects should 1295 // be allocated live. 1296 assert(obj->is_oop(), "Will dereference klass pointer below"); 1297 collector()->promoted(false, // Not parallel 1298 (HeapWord*)res, obj->is_objArray(), obj_size); 1299 // promotion counters 1300 NOT_PRODUCT( 1301 _numObjectsPromoted++; 1302 _numWordsPromoted += 1303 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); 1304 ) 1305 } 1306 return res; 1307 } 1308 1309 1310 HeapWord* 1311 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space, 1312 HeapWord* top, 1313 size_t word_sz) 1314 { 1315 return collector()->allocation_limit_reached(space, top, word_sz); 1316 } 1317 1318 // IMPORTANT: Notes on object size recognition in CMS. 1319 // --------------------------------------------------- 1320 // A block of storage in the CMS generation is always in 1321 // one of three states. A free block (FREE), an allocated 1322 // object (OBJECT) whose size() method reports the correct size, 1323 // and an intermediate state (TRANSIENT) in which its size cannot 1324 // be accurately determined. 1325 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS) 1326 // ----------------------------------------------------- 1327 // FREE: klass_word & 1 == 1; mark_word holds block size 1328 // 1329 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0; 1330 // obj->size() computes correct size 1331 // 1332 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 1333 // 1334 // STATE IDENTIFICATION: (64 bit+COOPS) 1335 // ------------------------------------ 1336 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size 1337 // 1338 // OBJECT: klass_word installed; klass_word != 0; 1339 // obj->size() computes correct size 1340 // 1341 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT 1342 // 1343 // 1344 // STATE TRANSITION DIAGRAM 1345 // 1346 // mut / parnew mut / parnew 1347 // FREE --------------------> TRANSIENT ---------------------> OBJECT --| 1348 // ^ | 1349 // |------------------------ DEAD <------------------------------------| 1350 // sweep mut 1351 // 1352 // While a block is in TRANSIENT state its size cannot be determined 1353 // so readers will either need to come back later or stall until 1354 // the size can be determined. Note that for the case of direct 1355 // allocation, P-bits, when available, may be used to determine the 1356 // size of an object that may not yet have been initialized. 1357 1358 // Things to support parallel young-gen collection. 1359 oop 1360 ConcurrentMarkSweepGeneration::par_promote(int thread_num, 1361 oop old, markOop m, 1362 size_t word_sz) { 1363 #ifndef PRODUCT 1364 if (Universe::heap()->promotion_should_fail()) { 1365 return NULL; 1366 } 1367 #endif // #ifndef PRODUCT 1368 1369 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1370 PromotionInfo* promoInfo = &ps->promo; 1371 // if we are tracking promotions, then first ensure space for 1372 // promotion (including spooling space for saving header if necessary). 1373 // then allocate and copy, then track promoted info if needed. 1374 // When tracking (see PromotionInfo::track()), the mark word may 1375 // be displaced and in this case restoration of the mark word 1376 // occurs in the (oop_since_save_marks_)iterate phase. 1377 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { 1378 // Out of space for allocating spooling buffers; 1379 // try expanding and allocating spooling buffers. 1380 if (!expand_and_ensure_spooling_space(promoInfo)) { 1381 return NULL; 1382 } 1383 } 1384 assert(promoInfo->has_spooling_space(), "Control point invariant"); 1385 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz); 1386 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz); 1387 if (obj_ptr == NULL) { 1388 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz); 1389 if (obj_ptr == NULL) { 1390 return NULL; 1391 } 1392 } 1393 oop obj = oop(obj_ptr); 1394 OrderAccess::storestore(); 1395 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1396 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1397 // IMPORTANT: See note on object initialization for CMS above. 1398 // Otherwise, copy the object. Here we must be careful to insert the 1399 // klass pointer last, since this marks the block as an allocated object. 1400 // Except with compressed oops it's the mark word. 1401 HeapWord* old_ptr = (HeapWord*)old; 1402 // Restore the mark word copied above. 1403 obj->set_mark(m); 1404 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1405 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1406 OrderAccess::storestore(); 1407 1408 if (UseCompressedKlassPointers) { 1409 // Copy gap missed by (aligned) header size calculation below 1410 obj->set_klass_gap(old->klass_gap()); 1411 } 1412 if (word_sz > (size_t)oopDesc::header_size()) { 1413 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), 1414 obj_ptr + oopDesc::header_size(), 1415 word_sz - oopDesc::header_size()); 1416 } 1417 1418 // Now we can track the promoted object, if necessary. We take care 1419 // to delay the transition from uninitialized to full object 1420 // (i.e., insertion of klass pointer) until after, so that it 1421 // atomically becomes a promoted object. 1422 if (promoInfo->tracking()) { 1423 promoInfo->track((PromotedObject*)obj, old->klass()); 1424 } 1425 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here."); 1426 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size"); 1427 assert(old->is_oop(), "Will use and dereference old klass ptr below"); 1428 1429 // Finally, install the klass pointer (this should be volatile). 1430 OrderAccess::storestore(); 1431 obj->set_klass(old->klass()); 1432 // We should now be able to calculate the right size for this object 1433 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object"); 1434 1435 collector()->promoted(true, // parallel 1436 obj_ptr, old->is_objArray(), word_sz); 1437 1438 NOT_PRODUCT( 1439 Atomic::inc_ptr(&_numObjectsPromoted); 1440 Atomic::add_ptr(alloc_sz, &_numWordsPromoted); 1441 ) 1442 1443 return obj; 1444 } 1445 1446 void 1447 ConcurrentMarkSweepGeneration:: 1448 par_promote_alloc_undo(int thread_num, 1449 HeapWord* obj, size_t word_sz) { 1450 // CMS does not support promotion undo. 1451 ShouldNotReachHere(); 1452 } 1453 1454 void 1455 ConcurrentMarkSweepGeneration:: 1456 par_promote_alloc_done(int thread_num) { 1457 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1458 ps->lab.retire(thread_num); 1459 } 1460 1461 void 1462 ConcurrentMarkSweepGeneration:: 1463 par_oop_since_save_marks_iterate_done(int thread_num) { 1464 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; 1465 ParScanWithoutBarrierClosure* dummy_cl = NULL; 1466 ps->promo.promoted_oops_iterate_nv(dummy_cl); 1467 } 1468 1469 bool ConcurrentMarkSweepGeneration::should_collect(bool full, 1470 size_t size, 1471 bool tlab) 1472 { 1473 // We allow a STW collection only if a full 1474 // collection was requested. 1475 return full || should_allocate(size, tlab); // FIX ME !!! 1476 // This and promotion failure handling are connected at the 1477 // hip and should be fixed by untying them. 1478 } 1479 1480 bool CMSCollector::shouldConcurrentCollect() { 1481 if (_full_gc_requested) { 1482 if (Verbose && PrintGCDetails) { 1483 gclog_or_tty->print_cr("CMSCollector: collect because of explicit " 1484 " gc request (or gc_locker)"); 1485 } 1486 return true; 1487 } 1488 1489 // For debugging purposes, change the type of collection. 1490 // If the rotation is not on the concurrent collection 1491 // type, don't start a concurrent collection. 1492 NOT_PRODUCT( 1493 if (RotateCMSCollectionTypes && 1494 (_cmsGen->debug_collection_type() != 1495 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) { 1496 assert(_cmsGen->debug_collection_type() != 1497 ConcurrentMarkSweepGeneration::Unknown_collection_type, 1498 "Bad cms collection type"); 1499 return false; 1500 } 1501 ) 1502 1503 FreelistLocker x(this); 1504 // ------------------------------------------------------------------ 1505 // Print out lots of information which affects the initiation of 1506 // a collection. 1507 if (PrintCMSInitiationStatistics && stats().valid()) { 1508 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: "); 1509 gclog_or_tty->stamp(); 1510 gclog_or_tty->print_cr(""); 1511 stats().print_on(gclog_or_tty); 1512 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f", 1513 stats().time_until_cms_gen_full()); 1514 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free()); 1515 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT, 1516 _cmsGen->contiguous_available()); 1517 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate()); 1518 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate()); 1519 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy()); 1520 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy()); 1521 gclog_or_tty->print_cr("metadata initialized %d", 1522 MetaspaceGC::should_concurrent_collect()); 1523 } 1524 // ------------------------------------------------------------------ 1525 1526 // If the estimated time to complete a cms collection (cms_duration()) 1527 // is less than the estimated time remaining until the cms generation 1528 // is full, start a collection. 1529 if (!UseCMSInitiatingOccupancyOnly) { 1530 if (stats().valid()) { 1531 if (stats().time_until_cms_start() == 0.0) { 1532 return true; 1533 } 1534 } else { 1535 // We want to conservatively collect somewhat early in order 1536 // to try and "bootstrap" our CMS/promotion statistics; 1537 // this branch will not fire after the first successful CMS 1538 // collection because the stats should then be valid. 1539 if (_cmsGen->occupancy() >= _bootstrap_occupancy) { 1540 if (Verbose && PrintGCDetails) { 1541 gclog_or_tty->print_cr( 1542 " CMSCollector: collect for bootstrapping statistics:" 1543 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(), 1544 _bootstrap_occupancy); 1545 } 1546 return true; 1547 } 1548 } 1549 } 1550 1551 // Otherwise, we start a collection cycle if 1552 // old gen want a collection cycle started. Each may use 1553 // an appropriate criterion for making this decision. 1554 // XXX We need to make sure that the gen expansion 1555 // criterion dovetails well with this. XXX NEED TO FIX THIS 1556 if (_cmsGen->should_concurrent_collect()) { 1557 if (Verbose && PrintGCDetails) { 1558 gclog_or_tty->print_cr("CMS old gen initiated"); 1559 } 1560 return true; 1561 } 1562 1563 // We start a collection if we believe an incremental collection may fail; 1564 // this is not likely to be productive in practice because it's probably too 1565 // late anyway. 1566 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1567 assert(gch->collector_policy()->is_two_generation_policy(), 1568 "You may want to check the correctness of the following"); 1569 if (gch->incremental_collection_will_fail(true /* consult_young */)) { 1570 if (Verbose && PrintGCDetails) { 1571 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail "); 1572 } 1573 return true; 1574 } 1575 1576 if (MetaspaceGC::should_concurrent_collect()) { 1577 if (Verbose && PrintGCDetails) { 1578 gclog_or_tty->print("CMSCollector: collect for metadata allocation "); 1579 } 1580 return true; 1581 } 1582 1583 return false; 1584 } 1585 1586 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); } 1587 1588 // Clear _expansion_cause fields of constituent generations 1589 void CMSCollector::clear_expansion_cause() { 1590 _cmsGen->clear_expansion_cause(); 1591 } 1592 1593 // We should be conservative in starting a collection cycle. To 1594 // start too eagerly runs the risk of collecting too often in the 1595 // extreme. To collect too rarely falls back on full collections, 1596 // which works, even if not optimum in terms of concurrent work. 1597 // As a work around for too eagerly collecting, use the flag 1598 // UseCMSInitiatingOccupancyOnly. This also has the advantage of 1599 // giving the user an easily understandable way of controlling the 1600 // collections. 1601 // We want to start a new collection cycle if any of the following 1602 // conditions hold: 1603 // . our current occupancy exceeds the configured initiating occupancy 1604 // for this generation, or 1605 // . we recently needed to expand this space and have not, since that 1606 // expansion, done a collection of this generation, or 1607 // . the underlying space believes that it may be a good idea to initiate 1608 // a concurrent collection (this may be based on criteria such as the 1609 // following: the space uses linear allocation and linear allocation is 1610 // going to fail, or there is believed to be excessive fragmentation in 1611 // the generation, etc... or ... 1612 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for 1613 // the case of the old generation; see CR 6543076): 1614 // we may be approaching a point at which allocation requests may fail because 1615 // we will be out of sufficient free space given allocation rate estimates.] 1616 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const { 1617 1618 assert_lock_strong(freelistLock()); 1619 if (occupancy() > initiating_occupancy()) { 1620 if (PrintGCDetails && Verbose) { 1621 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ", 1622 short_name(), occupancy(), initiating_occupancy()); 1623 } 1624 return true; 1625 } 1626 if (UseCMSInitiatingOccupancyOnly) { 1627 return false; 1628 } 1629 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { 1630 if (PrintGCDetails && Verbose) { 1631 gclog_or_tty->print(" %s: collect because expanded for allocation ", 1632 short_name()); 1633 } 1634 return true; 1635 } 1636 if (_cmsSpace->should_concurrent_collect()) { 1637 if (PrintGCDetails && Verbose) { 1638 gclog_or_tty->print(" %s: collect because cmsSpace says so ", 1639 short_name()); 1640 } 1641 return true; 1642 } 1643 return false; 1644 } 1645 1646 void ConcurrentMarkSweepGeneration::collect(bool full, 1647 bool clear_all_soft_refs, 1648 size_t size, 1649 bool tlab) 1650 { 1651 collector()->collect(full, clear_all_soft_refs, size, tlab); 1652 } 1653 1654 void CMSCollector::collect(bool full, 1655 bool clear_all_soft_refs, 1656 size_t size, 1657 bool tlab) 1658 { 1659 if (!UseCMSCollectionPassing && _collectorState > Idling) { 1660 // For debugging purposes skip the collection if the state 1661 // is not currently idle 1662 if (TraceCMSState) { 1663 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d", 1664 Thread::current(), full, _collectorState); 1665 } 1666 return; 1667 } 1668 1669 // The following "if" branch is present for defensive reasons. 1670 // In the current uses of this interface, it can be replaced with: 1671 // assert(!GC_locker.is_active(), "Can't be called otherwise"); 1672 // But I am not placing that assert here to allow future 1673 // generality in invoking this interface. 1674 if (GC_locker::is_active()) { 1675 // A consistency test for GC_locker 1676 assert(GC_locker::needs_gc(), "Should have been set already"); 1677 // Skip this foreground collection, instead 1678 // expanding the heap if necessary. 1679 // Need the free list locks for the call to free() in compute_new_size() 1680 compute_new_size(); 1681 return; 1682 } 1683 acquire_control_and_collect(full, clear_all_soft_refs); 1684 _full_gcs_since_conc_gc++; 1685 } 1686 1687 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) { 1688 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1689 unsigned int gc_count = gch->total_full_collections(); 1690 if (gc_count == full_gc_count) { 1691 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag); 1692 _full_gc_requested = true; 1693 _full_gc_cause = cause; 1694 CGC_lock->notify(); // nudge CMS thread 1695 } else { 1696 assert(gc_count > full_gc_count, "Error: causal loop"); 1697 } 1698 } 1699 1700 bool CMSCollector::is_external_interruption() { 1701 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause(); 1702 return GCCause::is_user_requested_gc(cause) || 1703 GCCause::is_serviceability_requested_gc(cause); 1704 } 1705 1706 void CMSCollector::report_concurrent_mode_interruption() { 1707 if (is_external_interruption()) { 1708 if (PrintGCDetails) { 1709 gclog_or_tty->print(" (concurrent mode interrupted)"); 1710 } 1711 } else { 1712 if (PrintGCDetails) { 1713 gclog_or_tty->print(" (concurrent mode failure)"); 1714 } 1715 _gc_tracer_cm->report_concurrent_mode_failure(); 1716 } 1717 } 1718 1719 1720 // The foreground and background collectors need to coordinate in order 1721 // to make sure that they do not mutually interfere with CMS collections. 1722 // When a background collection is active, 1723 // the foreground collector may need to take over (preempt) and 1724 // synchronously complete an ongoing collection. Depending on the 1725 // frequency of the background collections and the heap usage 1726 // of the application, this preemption can be seldom or frequent. 1727 // There are only certain 1728 // points in the background collection that the "collection-baton" 1729 // can be passed to the foreground collector. 1730 // 1731 // The foreground collector will wait for the baton before 1732 // starting any part of the collection. The foreground collector 1733 // will only wait at one location. 1734 // 1735 // The background collector will yield the baton before starting a new 1736 // phase of the collection (e.g., before initial marking, marking from roots, 1737 // precleaning, final re-mark, sweep etc.) This is normally done at the head 1738 // of the loop which switches the phases. The background collector does some 1739 // of the phases (initial mark, final re-mark) with the world stopped. 1740 // Because of locking involved in stopping the world, 1741 // the foreground collector should not block waiting for the background 1742 // collector when it is doing a stop-the-world phase. The background 1743 // collector will yield the baton at an additional point just before 1744 // it enters a stop-the-world phase. Once the world is stopped, the 1745 // background collector checks the phase of the collection. If the 1746 // phase has not changed, it proceeds with the collection. If the 1747 // phase has changed, it skips that phase of the collection. See 1748 // the comments on the use of the Heap_lock in collect_in_background(). 1749 // 1750 // Variable used in baton passing. 1751 // _foregroundGCIsActive - Set to true by the foreground collector when 1752 // it wants the baton. The foreground clears it when it has finished 1753 // the collection. 1754 // _foregroundGCShouldWait - Set to true by the background collector 1755 // when it is running. The foreground collector waits while 1756 // _foregroundGCShouldWait is true. 1757 // CGC_lock - monitor used to protect access to the above variables 1758 // and to notify the foreground and background collectors. 1759 // _collectorState - current state of the CMS collection. 1760 // 1761 // The foreground collector 1762 // acquires the CGC_lock 1763 // sets _foregroundGCIsActive 1764 // waits on the CGC_lock for _foregroundGCShouldWait to be false 1765 // various locks acquired in preparation for the collection 1766 // are released so as not to block the background collector 1767 // that is in the midst of a collection 1768 // proceeds with the collection 1769 // clears _foregroundGCIsActive 1770 // returns 1771 // 1772 // The background collector in a loop iterating on the phases of the 1773 // collection 1774 // acquires the CGC_lock 1775 // sets _foregroundGCShouldWait 1776 // if _foregroundGCIsActive is set 1777 // clears _foregroundGCShouldWait, notifies _CGC_lock 1778 // waits on _CGC_lock for _foregroundGCIsActive to become false 1779 // and exits the loop. 1780 // otherwise 1781 // proceed with that phase of the collection 1782 // if the phase is a stop-the-world phase, 1783 // yield the baton once more just before enqueueing 1784 // the stop-world CMS operation (executed by the VM thread). 1785 // returns after all phases of the collection are done 1786 // 1787 1788 void CMSCollector::acquire_control_and_collect(bool full, 1789 bool clear_all_soft_refs) { 1790 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); 1791 assert(!Thread::current()->is_ConcurrentGC_thread(), 1792 "shouldn't try to acquire control from self!"); 1793 1794 // Start the protocol for acquiring control of the 1795 // collection from the background collector (aka CMS thread). 1796 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1797 "VM thread should have CMS token"); 1798 // Remember the possibly interrupted state of an ongoing 1799 // concurrent collection 1800 CollectorState first_state = _collectorState; 1801 1802 // Signal to a possibly ongoing concurrent collection that 1803 // we want to do a foreground collection. 1804 _foregroundGCIsActive = true; 1805 1806 // Disable incremental mode during a foreground collection. 1807 ICMSDisabler icms_disabler; 1808 1809 // release locks and wait for a notify from the background collector 1810 // releasing the locks in only necessary for phases which 1811 // do yields to improve the granularity of the collection. 1812 assert_lock_strong(bitMapLock()); 1813 // We need to lock the Free list lock for the space that we are 1814 // currently collecting. 1815 assert(haveFreelistLocks(), "Must be holding free list locks"); 1816 bitMapLock()->unlock(); 1817 releaseFreelistLocks(); 1818 { 1819 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 1820 if (_foregroundGCShouldWait) { 1821 // We are going to be waiting for action for the CMS thread; 1822 // it had better not be gone (for instance at shutdown)! 1823 assert(ConcurrentMarkSweepThread::cmst() != NULL, 1824 "CMS thread must be running"); 1825 // Wait here until the background collector gives us the go-ahead 1826 ConcurrentMarkSweepThread::clear_CMS_flag( 1827 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token 1828 // Get a possibly blocked CMS thread going: 1829 // Note that we set _foregroundGCIsActive true above, 1830 // without protection of the CGC_lock. 1831 CGC_lock->notify(); 1832 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), 1833 "Possible deadlock"); 1834 while (_foregroundGCShouldWait) { 1835 // wait for notification 1836 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 1837 // Possibility of delay/starvation here, since CMS token does 1838 // not know to give priority to VM thread? Actually, i think 1839 // there wouldn't be any delay/starvation, but the proof of 1840 // that "fact" (?) appears non-trivial. XXX 20011219YSR 1841 } 1842 ConcurrentMarkSweepThread::set_CMS_flag( 1843 ConcurrentMarkSweepThread::CMS_vm_has_token); 1844 } 1845 } 1846 // The CMS_token is already held. Get back the other locks. 1847 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 1848 "VM thread should have CMS token"); 1849 getFreelistLocks(); 1850 bitMapLock()->lock_without_safepoint_check(); 1851 if (TraceCMSState) { 1852 gclog_or_tty->print_cr("CMS foreground collector has asked for control " 1853 INTPTR_FORMAT " with first state %d", Thread::current(), first_state); 1854 gclog_or_tty->print_cr(" gets control with state %d", _collectorState); 1855 } 1856 1857 // Check if we need to do a compaction, or if not, whether 1858 // we need to start the mark-sweep from scratch. 1859 bool should_compact = false; 1860 bool should_start_over = false; 1861 decide_foreground_collection_type(clear_all_soft_refs, 1862 &should_compact, &should_start_over); 1863 1864 NOT_PRODUCT( 1865 if (RotateCMSCollectionTypes) { 1866 if (_cmsGen->debug_collection_type() == 1867 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) { 1868 should_compact = true; 1869 } else if (_cmsGen->debug_collection_type() == 1870 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) { 1871 should_compact = false; 1872 } 1873 } 1874 ) 1875 1876 if (first_state > Idling) { 1877 report_concurrent_mode_interruption(); 1878 } 1879 1880 set_did_compact(should_compact); 1881 if (should_compact) { 1882 // If the collection is being acquired from the background 1883 // collector, there may be references on the discovered 1884 // references lists that have NULL referents (being those 1885 // that were concurrently cleared by a mutator) or 1886 // that are no longer active (having been enqueued concurrently 1887 // by the mutator). 1888 // Scrub the list of those references because Mark-Sweep-Compact 1889 // code assumes referents are not NULL and that all discovered 1890 // Reference objects are active. 1891 ref_processor()->clean_up_discovered_references(); 1892 1893 if (first_state > Idling) { 1894 save_heap_summary(); 1895 } 1896 1897 do_compaction_work(clear_all_soft_refs); 1898 1899 // Has the GC time limit been exceeded? 1900 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration(); 1901 size_t max_eden_size = young_gen->max_capacity() - 1902 young_gen->to()->capacity() - 1903 young_gen->from()->capacity(); 1904 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1905 GCCause::Cause gc_cause = gch->gc_cause(); 1906 size_policy()->check_gc_overhead_limit(_young_gen->used(), 1907 young_gen->eden()->used(), 1908 _cmsGen->max_capacity(), 1909 max_eden_size, 1910 full, 1911 gc_cause, 1912 gch->collector_policy()); 1913 } else { 1914 do_mark_sweep_work(clear_all_soft_refs, first_state, 1915 should_start_over); 1916 } 1917 // Reset the expansion cause, now that we just completed 1918 // a collection cycle. 1919 clear_expansion_cause(); 1920 _foregroundGCIsActive = false; 1921 return; 1922 } 1923 1924 // Resize the tenured generation 1925 // after obtaining the free list locks for the 1926 // two generations. 1927 void CMSCollector::compute_new_size() { 1928 assert_locked_or_safepoint(Heap_lock); 1929 FreelistLocker z(this); 1930 MetaspaceGC::compute_new_size(); 1931 _cmsGen->compute_new_size_free_list(); 1932 } 1933 1934 // A work method used by foreground collection to determine 1935 // what type of collection (compacting or not, continuing or fresh) 1936 // it should do. 1937 // NOTE: the intent is to make UseCMSCompactAtFullCollection 1938 // and CMSCompactWhenClearAllSoftRefs the default in the future 1939 // and do away with the flags after a suitable period. 1940 void CMSCollector::decide_foreground_collection_type( 1941 bool clear_all_soft_refs, bool* should_compact, 1942 bool* should_start_over) { 1943 // Normally, we'll compact only if the UseCMSCompactAtFullCollection 1944 // flag is set, and we have either requested a System.gc() or 1945 // the number of full gc's since the last concurrent cycle 1946 // has exceeded the threshold set by CMSFullGCsBeforeCompaction, 1947 // or if an incremental collection has failed 1948 GenCollectedHeap* gch = GenCollectedHeap::heap(); 1949 assert(gch->collector_policy()->is_two_generation_policy(), 1950 "You may want to check the correctness of the following"); 1951 // Inform cms gen if this was due to partial collection failing. 1952 // The CMS gen may use this fact to determine its expansion policy. 1953 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) { 1954 assert(!_cmsGen->incremental_collection_failed(), 1955 "Should have been noticed, reacted to and cleared"); 1956 _cmsGen->set_incremental_collection_failed(); 1957 } 1958 *should_compact = 1959 UseCMSCompactAtFullCollection && 1960 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) || 1961 GCCause::is_user_requested_gc(gch->gc_cause()) || 1962 gch->incremental_collection_will_fail(true /* consult_young */)); 1963 *should_start_over = false; 1964 if (clear_all_soft_refs && !*should_compact) { 1965 // We are about to do a last ditch collection attempt 1966 // so it would normally make sense to do a compaction 1967 // to reclaim as much space as possible. 1968 if (CMSCompactWhenClearAllSoftRefs) { 1969 // Default: The rationale is that in this case either 1970 // we are past the final marking phase, in which case 1971 // we'd have to start over, or so little has been done 1972 // that there's little point in saving that work. Compaction 1973 // appears to be the sensible choice in either case. 1974 *should_compact = true; 1975 } else { 1976 // We have been asked to clear all soft refs, but not to 1977 // compact. Make sure that we aren't past the final checkpoint 1978 // phase, for that is where we process soft refs. If we are already 1979 // past that phase, we'll need to redo the refs discovery phase and 1980 // if necessary clear soft refs that weren't previously 1981 // cleared. We do so by remembering the phase in which 1982 // we came in, and if we are past the refs processing 1983 // phase, we'll choose to just redo the mark-sweep 1984 // collection from scratch. 1985 if (_collectorState > FinalMarking) { 1986 // We are past the refs processing phase; 1987 // start over and do a fresh synchronous CMS cycle 1988 _collectorState = Resetting; // skip to reset to start new cycle 1989 reset(false /* == !asynch */); 1990 *should_start_over = true; 1991 } // else we can continue a possibly ongoing current cycle 1992 } 1993 } 1994 } 1995 1996 // A work method used by the foreground collector to do 1997 // a mark-sweep-compact. 1998 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { 1999 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2000 2001 STWGCTimer* gc_timer = GenMarkSweep::gc_timer(); 2002 gc_timer->register_gc_start(os::elapsed_counter()); 2003 2004 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer(); 2005 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start()); 2006 2007 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL); 2008 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) { 2009 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d " 2010 "collections passed to foreground collector", _full_gcs_since_conc_gc); 2011 } 2012 2013 // Sample collection interval time and reset for collection pause. 2014 if (UseAdaptiveSizePolicy) { 2015 size_policy()->msc_collection_begin(); 2016 } 2017 2018 // Temporarily widen the span of the weak reference processing to 2019 // the entire heap. 2020 MemRegion new_span(GenCollectedHeap::heap()->reserved_region()); 2021 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span); 2022 // Temporarily, clear the "is_alive_non_header" field of the 2023 // reference processor. 2024 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL); 2025 // Temporarily make reference _processing_ single threaded (non-MT). 2026 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false); 2027 // Temporarily make refs discovery atomic 2028 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true); 2029 // Temporarily make reference _discovery_ single threaded (non-MT) 2030 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 2031 2032 ref_processor()->set_enqueuing_is_done(false); 2033 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/); 2034 ref_processor()->setup_policy(clear_all_soft_refs); 2035 // If an asynchronous collection finishes, the _modUnionTable is 2036 // all clear. If we are assuming the collection from an asynchronous 2037 // collection, clear the _modUnionTable. 2038 assert(_collectorState != Idling || _modUnionTable.isAllClear(), 2039 "_modUnionTable should be clear if the baton was not passed"); 2040 _modUnionTable.clear_all(); 2041 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(), 2042 "mod union for klasses should be clear if the baton was passed"); 2043 _ct->klass_rem_set()->clear_mod_union(); 2044 2045 // We must adjust the allocation statistics being maintained 2046 // in the free list space. We do so by reading and clearing 2047 // the sweep timer and updating the block flux rate estimates below. 2048 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive"); 2049 if (_inter_sweep_timer.is_active()) { 2050 _inter_sweep_timer.stop(); 2051 // Note that we do not use this sample to update the _inter_sweep_estimate. 2052 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 2053 _inter_sweep_estimate.padded_average(), 2054 _intra_sweep_estimate.padded_average()); 2055 } 2056 2057 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(), 2058 ref_processor(), clear_all_soft_refs); 2059 #ifdef ASSERT 2060 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 2061 size_t free_size = cms_space->free(); 2062 assert(free_size == 2063 pointer_delta(cms_space->end(), cms_space->compaction_top()) 2064 * HeapWordSize, 2065 "All the free space should be compacted into one chunk at top"); 2066 assert(cms_space->dictionary()->total_chunk_size( 2067 debug_only(cms_space->freelistLock())) == 0 || 2068 cms_space->totalSizeInIndexedFreeLists() == 0, 2069 "All the free space should be in a single chunk"); 2070 size_t num = cms_space->totalCount(); 2071 assert((free_size == 0 && num == 0) || 2072 (free_size > 0 && (num == 1 || num == 2)), 2073 "There should be at most 2 free chunks after compaction"); 2074 #endif // ASSERT 2075 _collectorState = Resetting; 2076 assert(_restart_addr == NULL, 2077 "Should have been NULL'd before baton was passed"); 2078 reset(false /* == !asynch */); 2079 _cmsGen->reset_after_compaction(); 2080 _concurrent_cycles_since_last_unload = 0; 2081 2082 // Clear any data recorded in the PLAB chunk arrays. 2083 if (_survivor_plab_array != NULL) { 2084 reset_survivor_plab_arrays(); 2085 } 2086 2087 // Adjust the per-size allocation stats for the next epoch. 2088 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */); 2089 // Restart the "inter sweep timer" for the next epoch. 2090 _inter_sweep_timer.reset(); 2091 _inter_sweep_timer.start(); 2092 2093 // Sample collection pause time and reset for collection interval. 2094 if (UseAdaptiveSizePolicy) { 2095 size_policy()->msc_collection_end(gch->gc_cause()); 2096 } 2097 2098 gc_timer->register_gc_end(os::elapsed_counter()); 2099 2100 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions()); 2101 2102 // For a mark-sweep-compact, compute_new_size() will be called 2103 // in the heap's do_collection() method. 2104 } 2105 2106 // A work method used by the foreground collector to do 2107 // a mark-sweep, after taking over from a possibly on-going 2108 // concurrent mark-sweep collection. 2109 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs, 2110 CollectorState first_state, bool should_start_over) { 2111 if (PrintGC && Verbose) { 2112 gclog_or_tty->print_cr("Pass concurrent collection to foreground " 2113 "collector with count %d", 2114 _full_gcs_since_conc_gc); 2115 } 2116 switch (_collectorState) { 2117 case Idling: 2118 if (first_state == Idling || should_start_over) { 2119 // The background GC was not active, or should 2120 // restarted from scratch; start the cycle. 2121 _collectorState = InitialMarking; 2122 } 2123 // If first_state was not Idling, then a background GC 2124 // was in progress and has now finished. No need to do it 2125 // again. Leave the state as Idling. 2126 break; 2127 case Precleaning: 2128 // In the foreground case don't do the precleaning since 2129 // it is not done concurrently and there is extra work 2130 // required. 2131 _collectorState = FinalMarking; 2132 } 2133 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause()); 2134 2135 // For a mark-sweep, compute_new_size() will be called 2136 // in the heap's do_collection() method. 2137 } 2138 2139 2140 void CMSCollector::getFreelistLocks() const { 2141 // Get locks for all free lists in all generations that this 2142 // collector is responsible for 2143 _cmsGen->freelistLock()->lock_without_safepoint_check(); 2144 } 2145 2146 void CMSCollector::releaseFreelistLocks() const { 2147 // Release locks for all free lists in all generations that this 2148 // collector is responsible for 2149 _cmsGen->freelistLock()->unlock(); 2150 } 2151 2152 bool CMSCollector::haveFreelistLocks() const { 2153 // Check locks for all free lists in all generations that this 2154 // collector is responsible for 2155 assert_lock_strong(_cmsGen->freelistLock()); 2156 PRODUCT_ONLY(ShouldNotReachHere()); 2157 return true; 2158 } 2159 2160 // A utility class that is used by the CMS collector to 2161 // temporarily "release" the foreground collector from its 2162 // usual obligation to wait for the background collector to 2163 // complete an ongoing phase before proceeding. 2164 class ReleaseForegroundGC: public StackObj { 2165 private: 2166 CMSCollector* _c; 2167 public: 2168 ReleaseForegroundGC(CMSCollector* c) : _c(c) { 2169 assert(_c->_foregroundGCShouldWait, "Else should not need to call"); 2170 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 2171 // allow a potentially blocked foreground collector to proceed 2172 _c->_foregroundGCShouldWait = false; 2173 if (_c->_foregroundGCIsActive) { 2174 CGC_lock->notify(); 2175 } 2176 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 2177 "Possible deadlock"); 2178 } 2179 2180 ~ReleaseForegroundGC() { 2181 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); 2182 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 2183 _c->_foregroundGCShouldWait = true; 2184 } 2185 }; 2186 2187 // There are separate collect_in_background and collect_in_foreground because of 2188 // the different locking requirements of the background collector and the 2189 // foreground collector. There was originally an attempt to share 2190 // one "collect" method between the background collector and the foreground 2191 // collector but the if-then-else required made it cleaner to have 2192 // separate methods. 2193 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) { 2194 assert(Thread::current()->is_ConcurrentGC_thread(), 2195 "A CMS asynchronous collection is only allowed on a CMS thread."); 2196 2197 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2198 { 2199 bool safepoint_check = Mutex::_no_safepoint_check_flag; 2200 MutexLockerEx hl(Heap_lock, safepoint_check); 2201 FreelistLocker fll(this); 2202 MutexLockerEx x(CGC_lock, safepoint_check); 2203 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) { 2204 // The foreground collector is active or we're 2205 // not using asynchronous collections. Skip this 2206 // background collection. 2207 assert(!_foregroundGCShouldWait, "Should be clear"); 2208 return; 2209 } else { 2210 assert(_collectorState == Idling, "Should be idling before start."); 2211 _collectorState = InitialMarking; 2212 register_gc_start(cause); 2213 // Reset the expansion cause, now that we are about to begin 2214 // a new cycle. 2215 clear_expansion_cause(); 2216 2217 // Clear the MetaspaceGC flag since a concurrent collection 2218 // is starting but also clear it after the collection. 2219 MetaspaceGC::set_should_concurrent_collect(false); 2220 } 2221 // Decide if we want to enable class unloading as part of the 2222 // ensuing concurrent GC cycle. 2223 update_should_unload_classes(); 2224 _full_gc_requested = false; // acks all outstanding full gc requests 2225 _full_gc_cause = GCCause::_no_gc; 2226 // Signal that we are about to start a collection 2227 gch->increment_total_full_collections(); // ... starting a collection cycle 2228 _collection_count_start = gch->total_full_collections(); 2229 } 2230 2231 // Used for PrintGC 2232 size_t prev_used; 2233 if (PrintGC && Verbose) { 2234 prev_used = _cmsGen->used(); // XXXPERM 2235 } 2236 2237 // The change of the collection state is normally done at this level; 2238 // the exceptions are phases that are executed while the world is 2239 // stopped. For those phases the change of state is done while the 2240 // world is stopped. For baton passing purposes this allows the 2241 // background collector to finish the phase and change state atomically. 2242 // The foreground collector cannot wait on a phase that is done 2243 // while the world is stopped because the foreground collector already 2244 // has the world stopped and would deadlock. 2245 while (_collectorState != Idling) { 2246 if (TraceCMSState) { 2247 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", 2248 Thread::current(), _collectorState); 2249 } 2250 // The foreground collector 2251 // holds the Heap_lock throughout its collection. 2252 // holds the CMS token (but not the lock) 2253 // except while it is waiting for the background collector to yield. 2254 // 2255 // The foreground collector should be blocked (not for long) 2256 // if the background collector is about to start a phase 2257 // executed with world stopped. If the background 2258 // collector has already started such a phase, the 2259 // foreground collector is blocked waiting for the 2260 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) 2261 // are executed in the VM thread. 2262 // 2263 // The locking order is 2264 // PendingListLock (PLL) -- if applicable (FinalMarking) 2265 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) 2266 // CMS token (claimed in 2267 // stop_world_and_do() --> 2268 // safepoint_synchronize() --> 2269 // CMSThread::synchronize()) 2270 2271 { 2272 // Check if the FG collector wants us to yield. 2273 CMSTokenSync x(true); // is cms thread 2274 if (waitForForegroundGC()) { 2275 // We yielded to a foreground GC, nothing more to be 2276 // done this round. 2277 assert(_foregroundGCShouldWait == false, "We set it to false in " 2278 "waitForForegroundGC()"); 2279 if (TraceCMSState) { 2280 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT 2281 " exiting collection CMS state %d", 2282 Thread::current(), _collectorState); 2283 } 2284 return; 2285 } else { 2286 // The background collector can run but check to see if the 2287 // foreground collector has done a collection while the 2288 // background collector was waiting to get the CGC_lock 2289 // above. If yes, break so that _foregroundGCShouldWait 2290 // is cleared before returning. 2291 if (_collectorState == Idling) { 2292 break; 2293 } 2294 } 2295 } 2296 2297 assert(_foregroundGCShouldWait, "Foreground collector, if active, " 2298 "should be waiting"); 2299 2300 switch (_collectorState) { 2301 case InitialMarking: 2302 { 2303 ReleaseForegroundGC x(this); 2304 stats().record_cms_begin(); 2305 VM_CMS_Initial_Mark initial_mark_op(this); 2306 VMThread::execute(&initial_mark_op); 2307 } 2308 // The collector state may be any legal state at this point 2309 // since the background collector may have yielded to the 2310 // foreground collector. 2311 break; 2312 case Marking: 2313 // initial marking in checkpointRootsInitialWork has been completed 2314 if (markFromRoots(true)) { // we were successful 2315 assert(_collectorState == Precleaning, "Collector state should " 2316 "have changed"); 2317 } else { 2318 assert(_foregroundGCIsActive, "Internal state inconsistency"); 2319 } 2320 break; 2321 case Precleaning: 2322 if (UseAdaptiveSizePolicy) { 2323 size_policy()->concurrent_precleaning_begin(); 2324 } 2325 // marking from roots in markFromRoots has been completed 2326 preclean(); 2327 if (UseAdaptiveSizePolicy) { 2328 size_policy()->concurrent_precleaning_end(); 2329 } 2330 assert(_collectorState == AbortablePreclean || 2331 _collectorState == FinalMarking, 2332 "Collector state should have changed"); 2333 break; 2334 case AbortablePreclean: 2335 if (UseAdaptiveSizePolicy) { 2336 size_policy()->concurrent_phases_resume(); 2337 } 2338 abortable_preclean(); 2339 if (UseAdaptiveSizePolicy) { 2340 size_policy()->concurrent_precleaning_end(); 2341 } 2342 assert(_collectorState == FinalMarking, "Collector state should " 2343 "have changed"); 2344 break; 2345 case FinalMarking: 2346 { 2347 ReleaseForegroundGC x(this); 2348 2349 VM_CMS_Final_Remark final_remark_op(this); 2350 VMThread::execute(&final_remark_op); 2351 } 2352 assert(_foregroundGCShouldWait, "block post-condition"); 2353 break; 2354 case Sweeping: 2355 if (UseAdaptiveSizePolicy) { 2356 size_policy()->concurrent_sweeping_begin(); 2357 } 2358 // final marking in checkpointRootsFinal has been completed 2359 sweep(true); 2360 assert(_collectorState == Resizing, "Collector state change " 2361 "to Resizing must be done under the free_list_lock"); 2362 _full_gcs_since_conc_gc = 0; 2363 2364 // Stop the timers for adaptive size policy for the concurrent phases 2365 if (UseAdaptiveSizePolicy) { 2366 size_policy()->concurrent_sweeping_end(); 2367 size_policy()->concurrent_phases_end(gch->gc_cause(), 2368 gch->prev_gen(_cmsGen)->capacity(), 2369 _cmsGen->free()); 2370 } 2371 2372 case Resizing: { 2373 // Sweeping has been completed... 2374 // At this point the background collection has completed. 2375 // Don't move the call to compute_new_size() down 2376 // into code that might be executed if the background 2377 // collection was preempted. 2378 { 2379 ReleaseForegroundGC x(this); // unblock FG collection 2380 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag); 2381 CMSTokenSync z(true); // not strictly needed. 2382 if (_collectorState == Resizing) { 2383 compute_new_size(); 2384 save_heap_summary(); 2385 _collectorState = Resetting; 2386 } else { 2387 assert(_collectorState == Idling, "The state should only change" 2388 " because the foreground collector has finished the collection"); 2389 } 2390 } 2391 break; 2392 } 2393 case Resetting: 2394 // CMS heap resizing has been completed 2395 reset(true); 2396 assert(_collectorState == Idling, "Collector state should " 2397 "have changed"); 2398 2399 MetaspaceGC::set_should_concurrent_collect(false); 2400 2401 stats().record_cms_end(); 2402 // Don't move the concurrent_phases_end() and compute_new_size() 2403 // calls to here because a preempted background collection 2404 // has it's state set to "Resetting". 2405 break; 2406 case Idling: 2407 default: 2408 ShouldNotReachHere(); 2409 break; 2410 } 2411 if (TraceCMSState) { 2412 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", 2413 Thread::current(), _collectorState); 2414 } 2415 assert(_foregroundGCShouldWait, "block post-condition"); 2416 } 2417 2418 // Should this be in gc_epilogue? 2419 collector_policy()->counters()->update_counters(); 2420 2421 { 2422 // Clear _foregroundGCShouldWait and, in the event that the 2423 // foreground collector is waiting, notify it, before 2424 // returning. 2425 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 2426 _foregroundGCShouldWait = false; 2427 if (_foregroundGCIsActive) { 2428 CGC_lock->notify(); 2429 } 2430 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 2431 "Possible deadlock"); 2432 } 2433 if (TraceCMSState) { 2434 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT 2435 " exiting collection CMS state %d", 2436 Thread::current(), _collectorState); 2437 } 2438 if (PrintGC && Verbose) { 2439 _cmsGen->print_heap_change(prev_used); 2440 } 2441 } 2442 2443 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) { 2444 if (!_cms_start_registered) { 2445 register_gc_start(cause); 2446 } 2447 } 2448 2449 void CMSCollector::register_gc_start(GCCause::Cause cause) { 2450 _cms_start_registered = true; 2451 _gc_timer_cm->register_gc_start(os::elapsed_counter()); 2452 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start()); 2453 } 2454 2455 void CMSCollector::register_gc_end() { 2456 if (_cms_start_registered) { 2457 report_heap_summary(GCWhen::AfterGC); 2458 2459 _gc_timer_cm->register_gc_end(os::elapsed_counter()); 2460 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions()); 2461 _cms_start_registered = false; 2462 } 2463 } 2464 2465 void CMSCollector::save_heap_summary() { 2466 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2467 _last_heap_summary = gch->create_heap_summary(); 2468 _last_metaspace_summary = gch->create_metaspace_summary(); 2469 } 2470 2471 void CMSCollector::report_heap_summary(GCWhen::Type when) { 2472 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_metaspace_summary); 2473 } 2474 2475 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) { 2476 assert(_foregroundGCIsActive && !_foregroundGCShouldWait, 2477 "Foreground collector should be waiting, not executing"); 2478 assert(Thread::current()->is_VM_thread(), "A foreground collection" 2479 "may only be done by the VM Thread with the world stopped"); 2480 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), 2481 "VM thread should have CMS token"); 2482 2483 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose, 2484 true, NULL);) 2485 if (UseAdaptiveSizePolicy) { 2486 size_policy()->ms_collection_begin(); 2487 } 2488 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); 2489 2490 HandleMark hm; // Discard invalid handles created during verification 2491 2492 if (VerifyBeforeGC && 2493 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2494 Universe::verify(); 2495 } 2496 2497 // Snapshot the soft reference policy to be used in this collection cycle. 2498 ref_processor()->setup_policy(clear_all_soft_refs); 2499 2500 bool init_mark_was_synchronous = false; // until proven otherwise 2501 while (_collectorState != Idling) { 2502 if (TraceCMSState) { 2503 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", 2504 Thread::current(), _collectorState); 2505 } 2506 switch (_collectorState) { 2507 case InitialMarking: 2508 register_foreground_gc_start(cause); 2509 init_mark_was_synchronous = true; // fact to be exploited in re-mark 2510 checkpointRootsInitial(false); 2511 assert(_collectorState == Marking, "Collector state should have changed" 2512 " within checkpointRootsInitial()"); 2513 break; 2514 case Marking: 2515 // initial marking in checkpointRootsInitialWork has been completed 2516 if (VerifyDuringGC && 2517 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2518 Universe::verify("Verify before initial mark: "); 2519 } 2520 { 2521 bool res = markFromRoots(false); 2522 assert(res && _collectorState == FinalMarking, "Collector state should " 2523 "have changed"); 2524 break; 2525 } 2526 case FinalMarking: 2527 if (VerifyDuringGC && 2528 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2529 Universe::verify("Verify before re-mark: "); 2530 } 2531 checkpointRootsFinal(false, clear_all_soft_refs, 2532 init_mark_was_synchronous); 2533 assert(_collectorState == Sweeping, "Collector state should not " 2534 "have changed within checkpointRootsFinal()"); 2535 break; 2536 case Sweeping: 2537 // final marking in checkpointRootsFinal has been completed 2538 if (VerifyDuringGC && 2539 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2540 Universe::verify("Verify before sweep: "); 2541 } 2542 sweep(false); 2543 assert(_collectorState == Resizing, "Incorrect state"); 2544 break; 2545 case Resizing: { 2546 // Sweeping has been completed; the actual resize in this case 2547 // is done separately; nothing to be done in this state. 2548 _collectorState = Resetting; 2549 break; 2550 } 2551 case Resetting: 2552 // The heap has been resized. 2553 if (VerifyDuringGC && 2554 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2555 Universe::verify("Verify before reset: "); 2556 } 2557 save_heap_summary(); 2558 reset(false); 2559 assert(_collectorState == Idling, "Collector state should " 2560 "have changed"); 2561 break; 2562 case Precleaning: 2563 case AbortablePreclean: 2564 // Elide the preclean phase 2565 _collectorState = FinalMarking; 2566 break; 2567 default: 2568 ShouldNotReachHere(); 2569 } 2570 if (TraceCMSState) { 2571 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", 2572 Thread::current(), _collectorState); 2573 } 2574 } 2575 2576 if (UseAdaptiveSizePolicy) { 2577 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2578 size_policy()->ms_collection_end(gch->gc_cause()); 2579 } 2580 2581 if (VerifyAfterGC && 2582 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 2583 Universe::verify(); 2584 } 2585 if (TraceCMSState) { 2586 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT 2587 " exiting collection CMS state %d", 2588 Thread::current(), _collectorState); 2589 } 2590 } 2591 2592 bool CMSCollector::waitForForegroundGC() { 2593 bool res = false; 2594 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 2595 "CMS thread should have CMS token"); 2596 // Block the foreground collector until the 2597 // background collectors decides whether to 2598 // yield. 2599 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 2600 _foregroundGCShouldWait = true; 2601 if (_foregroundGCIsActive) { 2602 // The background collector yields to the 2603 // foreground collector and returns a value 2604 // indicating that it has yielded. The foreground 2605 // collector can proceed. 2606 res = true; 2607 _foregroundGCShouldWait = false; 2608 ConcurrentMarkSweepThread::clear_CMS_flag( 2609 ConcurrentMarkSweepThread::CMS_cms_has_token); 2610 ConcurrentMarkSweepThread::set_CMS_flag( 2611 ConcurrentMarkSweepThread::CMS_cms_wants_token); 2612 // Get a possibly blocked foreground thread going 2613 CGC_lock->notify(); 2614 if (TraceCMSState) { 2615 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", 2616 Thread::current(), _collectorState); 2617 } 2618 while (_foregroundGCIsActive) { 2619 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 2620 } 2621 ConcurrentMarkSweepThread::set_CMS_flag( 2622 ConcurrentMarkSweepThread::CMS_cms_has_token); 2623 ConcurrentMarkSweepThread::clear_CMS_flag( 2624 ConcurrentMarkSweepThread::CMS_cms_wants_token); 2625 } 2626 if (TraceCMSState) { 2627 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", 2628 Thread::current(), _collectorState); 2629 } 2630 return res; 2631 } 2632 2633 // Because of the need to lock the free lists and other structures in 2634 // the collector, common to all the generations that the collector is 2635 // collecting, we need the gc_prologues of individual CMS generations 2636 // delegate to their collector. It may have been simpler had the 2637 // current infrastructure allowed one to call a prologue on a 2638 // collector. In the absence of that we have the generation's 2639 // prologue delegate to the collector, which delegates back 2640 // some "local" work to a worker method in the individual generations 2641 // that it's responsible for collecting, while itself doing any 2642 // work common to all generations it's responsible for. A similar 2643 // comment applies to the gc_epilogue()'s. 2644 // The role of the varaible _between_prologue_and_epilogue is to 2645 // enforce the invocation protocol. 2646 void CMSCollector::gc_prologue(bool full) { 2647 // Call gc_prologue_work() for the CMSGen 2648 // we are responsible for. 2649 2650 // The following locking discipline assumes that we are only called 2651 // when the world is stopped. 2652 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); 2653 2654 // The CMSCollector prologue must call the gc_prologues for the 2655 // "generations" that it's responsible 2656 // for. 2657 2658 assert( Thread::current()->is_VM_thread() 2659 || ( CMSScavengeBeforeRemark 2660 && Thread::current()->is_ConcurrentGC_thread()), 2661 "Incorrect thread type for prologue execution"); 2662 2663 if (_between_prologue_and_epilogue) { 2664 // We have already been invoked; this is a gc_prologue delegation 2665 // from yet another CMS generation that we are responsible for, just 2666 // ignore it since all relevant work has already been done. 2667 return; 2668 } 2669 2670 // set a bit saying prologue has been called; cleared in epilogue 2671 _between_prologue_and_epilogue = true; 2672 // Claim locks for common data structures, then call gc_prologue_work() 2673 // for each CMSGen. 2674 2675 getFreelistLocks(); // gets free list locks on constituent spaces 2676 bitMapLock()->lock_without_safepoint_check(); 2677 2678 // Should call gc_prologue_work() for all cms gens we are responsible for 2679 bool duringMarking = _collectorState >= Marking 2680 && _collectorState < Sweeping; 2681 2682 // The young collections clear the modified oops state, which tells if 2683 // there are any modified oops in the class. The remark phase also needs 2684 // that information. Tell the young collection to save the union of all 2685 // modified klasses. 2686 if (duringMarking) { 2687 _ct->klass_rem_set()->set_accumulate_modified_oops(true); 2688 } 2689 2690 bool registerClosure = duringMarking; 2691 2692 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ? 2693 &_modUnionClosurePar 2694 : &_modUnionClosure; 2695 _cmsGen->gc_prologue_work(full, registerClosure, muc); 2696 2697 if (!full) { 2698 stats().record_gc0_begin(); 2699 } 2700 } 2701 2702 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { 2703 2704 _capacity_at_prologue = capacity(); 2705 _used_at_prologue = used(); 2706 2707 // Delegate to CMScollector which knows how to coordinate between 2708 // this and any other CMS generations that it is responsible for 2709 // collecting. 2710 collector()->gc_prologue(full); 2711 } 2712 2713 // This is a "private" interface for use by this generation's CMSCollector. 2714 // Not to be called directly by any other entity (for instance, 2715 // GenCollectedHeap, which calls the "public" gc_prologue method above). 2716 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, 2717 bool registerClosure, ModUnionClosure* modUnionClosure) { 2718 assert(!incremental_collection_failed(), "Shouldn't be set yet"); 2719 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, 2720 "Should be NULL"); 2721 if (registerClosure) { 2722 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); 2723 } 2724 cmsSpace()->gc_prologue(); 2725 // Clear stat counters 2726 NOT_PRODUCT( 2727 assert(_numObjectsPromoted == 0, "check"); 2728 assert(_numWordsPromoted == 0, "check"); 2729 if (Verbose && PrintGC) { 2730 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, " 2731 SIZE_FORMAT" bytes concurrently", 2732 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); 2733 } 2734 _numObjectsAllocated = 0; 2735 _numWordsAllocated = 0; 2736 ) 2737 } 2738 2739 void CMSCollector::gc_epilogue(bool full) { 2740 // The following locking discipline assumes that we are only called 2741 // when the world is stopped. 2742 assert(SafepointSynchronize::is_at_safepoint(), 2743 "world is stopped assumption"); 2744 2745 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks 2746 // if linear allocation blocks need to be appropriately marked to allow the 2747 // the blocks to be parsable. We also check here whether we need to nudge the 2748 // CMS collector thread to start a new cycle (if it's not already active). 2749 assert( Thread::current()->is_VM_thread() 2750 || ( CMSScavengeBeforeRemark 2751 && Thread::current()->is_ConcurrentGC_thread()), 2752 "Incorrect thread type for epilogue execution"); 2753 2754 if (!_between_prologue_and_epilogue) { 2755 // We have already been invoked; this is a gc_epilogue delegation 2756 // from yet another CMS generation that we are responsible for, just 2757 // ignore it since all relevant work has already been done. 2758 return; 2759 } 2760 assert(haveFreelistLocks(), "must have freelist locks"); 2761 assert_lock_strong(bitMapLock()); 2762 2763 _ct->klass_rem_set()->set_accumulate_modified_oops(false); 2764 2765 _cmsGen->gc_epilogue_work(full); 2766 2767 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { 2768 // in case sampling was not already enabled, enable it 2769 _start_sampling = true; 2770 } 2771 // reset _eden_chunk_array so sampling starts afresh 2772 _eden_chunk_index = 0; 2773 2774 size_t cms_used = _cmsGen->cmsSpace()->used(); 2775 2776 // update performance counters - this uses a special version of 2777 // update_counters() that allows the utilization to be passed as a 2778 // parameter, avoiding multiple calls to used(). 2779 // 2780 _cmsGen->update_counters(cms_used); 2781 2782 if (CMSIncrementalMode) { 2783 icms_update_allocation_limits(); 2784 } 2785 2786 bitMapLock()->unlock(); 2787 releaseFreelistLocks(); 2788 2789 if (!CleanChunkPoolAsync) { 2790 Chunk::clean_chunk_pool(); 2791 } 2792 2793 set_did_compact(false); 2794 _between_prologue_and_epilogue = false; // ready for next cycle 2795 } 2796 2797 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { 2798 collector()->gc_epilogue(full); 2799 2800 // Also reset promotion tracking in par gc thread states. 2801 if (CollectedHeap::use_parallel_gc_threads()) { 2802 for (uint i = 0; i < ParallelGCThreads; i++) { 2803 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i); 2804 } 2805 } 2806 } 2807 2808 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { 2809 assert(!incremental_collection_failed(), "Should have been cleared"); 2810 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); 2811 cmsSpace()->gc_epilogue(); 2812 // Print stat counters 2813 NOT_PRODUCT( 2814 assert(_numObjectsAllocated == 0, "check"); 2815 assert(_numWordsAllocated == 0, "check"); 2816 if (Verbose && PrintGC) { 2817 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, " 2818 SIZE_FORMAT" bytes", 2819 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); 2820 } 2821 _numObjectsPromoted = 0; 2822 _numWordsPromoted = 0; 2823 ) 2824 2825 if (PrintGC && Verbose) { 2826 // Call down the chain in contiguous_available needs the freelistLock 2827 // so print this out before releasing the freeListLock. 2828 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ", 2829 contiguous_available()); 2830 } 2831 } 2832 2833 #ifndef PRODUCT 2834 bool CMSCollector::have_cms_token() { 2835 Thread* thr = Thread::current(); 2836 if (thr->is_VM_thread()) { 2837 return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); 2838 } else if (thr->is_ConcurrentGC_thread()) { 2839 return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); 2840 } else if (thr->is_GC_task_thread()) { 2841 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && 2842 ParGCRareEvent_lock->owned_by_self(); 2843 } 2844 return false; 2845 } 2846 #endif 2847 2848 // Check reachability of the given heap address in CMS generation, 2849 // treating all other generations as roots. 2850 bool CMSCollector::is_cms_reachable(HeapWord* addr) { 2851 // We could "guarantee" below, rather than assert, but i'll 2852 // leave these as "asserts" so that an adventurous debugger 2853 // could try this in the product build provided some subset of 2854 // the conditions were met, provided they were intersted in the 2855 // results and knew that the computation below wouldn't interfere 2856 // with other concurrent computations mutating the structures 2857 // being read or written. 2858 assert(SafepointSynchronize::is_at_safepoint(), 2859 "Else mutations in object graph will make answer suspect"); 2860 assert(have_cms_token(), "Should hold cms token"); 2861 assert(haveFreelistLocks(), "must hold free list locks"); 2862 assert_lock_strong(bitMapLock()); 2863 2864 // Clear the marking bit map array before starting, but, just 2865 // for kicks, first report if the given address is already marked 2866 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr, 2867 _markBitMap.isMarked(addr) ? "" : " not"); 2868 2869 if (verify_after_remark()) { 2870 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2871 bool result = verification_mark_bm()->isMarked(addr); 2872 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr, 2873 result ? "IS" : "is NOT"); 2874 return result; 2875 } else { 2876 gclog_or_tty->print_cr("Could not compute result"); 2877 return false; 2878 } 2879 } 2880 2881 2882 void 2883 CMSCollector::print_on_error(outputStream* st) { 2884 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector; 2885 if (collector != NULL) { 2886 CMSBitMap* bitmap = &collector->_markBitMap; 2887 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap); 2888 bitmap->print_on_error(st, " Bits: "); 2889 2890 st->cr(); 2891 2892 CMSBitMap* mut_bitmap = &collector->_modUnionTable; 2893 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap); 2894 mut_bitmap->print_on_error(st, " Bits: "); 2895 } 2896 } 2897 2898 //////////////////////////////////////////////////////// 2899 // CMS Verification Support 2900 //////////////////////////////////////////////////////// 2901 // Following the remark phase, the following invariant 2902 // should hold -- each object in the CMS heap which is 2903 // marked in markBitMap() should be marked in the verification_mark_bm(). 2904 2905 class VerifyMarkedClosure: public BitMapClosure { 2906 CMSBitMap* _marks; 2907 bool _failed; 2908 2909 public: 2910 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} 2911 2912 bool do_bit(size_t offset) { 2913 HeapWord* addr = _marks->offsetToHeapWord(offset); 2914 if (!_marks->isMarked(addr)) { 2915 oop(addr)->print_on(gclog_or_tty); 2916 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); 2917 _failed = true; 2918 } 2919 return true; 2920 } 2921 2922 bool failed() { return _failed; } 2923 }; 2924 2925 bool CMSCollector::verify_after_remark(bool silent) { 2926 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... "); 2927 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); 2928 static bool init = false; 2929 2930 assert(SafepointSynchronize::is_at_safepoint(), 2931 "Else mutations in object graph will make answer suspect"); 2932 assert(have_cms_token(), 2933 "Else there may be mutual interference in use of " 2934 " verification data structures"); 2935 assert(_collectorState > Marking && _collectorState <= Sweeping, 2936 "Else marking info checked here may be obsolete"); 2937 assert(haveFreelistLocks(), "must hold free list locks"); 2938 assert_lock_strong(bitMapLock()); 2939 2940 2941 // Allocate marking bit map if not already allocated 2942 if (!init) { // first time 2943 if (!verification_mark_bm()->allocate(_span)) { 2944 return false; 2945 } 2946 init = true; 2947 } 2948 2949 assert(verification_mark_stack()->isEmpty(), "Should be empty"); 2950 2951 // Turn off refs discovery -- so we will be tracing through refs. 2952 // This is as intended, because by this time 2953 // GC must already have cleared any refs that need to be cleared, 2954 // and traced those that need to be marked; moreover, 2955 // the marking done here is not going to intefere in any 2956 // way with the marking information used by GC. 2957 NoRefDiscovery no_discovery(ref_processor()); 2958 2959 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) 2960 2961 // Clear any marks from a previous round 2962 verification_mark_bm()->clear_all(); 2963 assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); 2964 verify_work_stacks_empty(); 2965 2966 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2967 gch->ensure_parsability(false); // fill TLABs, but no need to retire them 2968 // Update the saved marks which may affect the root scans. 2969 gch->save_marks(); 2970 2971 if (CMSRemarkVerifyVariant == 1) { 2972 // In this first variant of verification, we complete 2973 // all marking, then check if the new marks-verctor is 2974 // a subset of the CMS marks-vector. 2975 verify_after_remark_work_1(); 2976 } else if (CMSRemarkVerifyVariant == 2) { 2977 // In this second variant of verification, we flag an error 2978 // (i.e. an object reachable in the new marks-vector not reachable 2979 // in the CMS marks-vector) immediately, also indicating the 2980 // identify of an object (A) that references the unmarked object (B) -- 2981 // presumably, a mutation to A failed to be picked up by preclean/remark? 2982 verify_after_remark_work_2(); 2983 } else { 2984 warning("Unrecognized value %d for CMSRemarkVerifyVariant", 2985 CMSRemarkVerifyVariant); 2986 } 2987 if (!silent) gclog_or_tty->print(" done] "); 2988 return true; 2989 } 2990 2991 void CMSCollector::verify_after_remark_work_1() { 2992 ResourceMark rm; 2993 HandleMark hm; 2994 GenCollectedHeap* gch = GenCollectedHeap::heap(); 2995 2996 // Get a clear set of claim bits for the strong roots processing to work with. 2997 ClassLoaderDataGraph::clear_claimed_marks(); 2998 2999 // Mark from roots one level into CMS 3000 MarkRefsIntoClosure notOlder(_span, verification_mark_bm()); 3001 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 3002 3003 gch->gen_process_strong_roots(_cmsGen->level(), 3004 true, // younger gens are roots 3005 true, // activate StrongRootsScope 3006 false, // not scavenging 3007 SharedHeap::ScanningOption(roots_scanning_options()), 3008 ¬Older, 3009 true, // walk code active on stacks 3010 NULL, 3011 NULL); // SSS: Provide correct closure 3012 3013 // Now mark from the roots 3014 MarkFromRootsClosure markFromRootsClosure(this, _span, 3015 verification_mark_bm(), verification_mark_stack(), 3016 false /* don't yield */, true /* verifying */); 3017 assert(_restart_addr == NULL, "Expected pre-condition"); 3018 verification_mark_bm()->iterate(&markFromRootsClosure); 3019 while (_restart_addr != NULL) { 3020 // Deal with stack overflow: by restarting at the indicated 3021 // address. 3022 HeapWord* ra = _restart_addr; 3023 markFromRootsClosure.reset(ra); 3024 _restart_addr = NULL; 3025 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 3026 } 3027 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 3028 verify_work_stacks_empty(); 3029 3030 // Marking completed -- now verify that each bit marked in 3031 // verification_mark_bm() is also marked in markBitMap(); flag all 3032 // errors by printing corresponding objects. 3033 VerifyMarkedClosure vcl(markBitMap()); 3034 verification_mark_bm()->iterate(&vcl); 3035 if (vcl.failed()) { 3036 gclog_or_tty->print("Verification failed"); 3037 Universe::heap()->print_on(gclog_or_tty); 3038 fatal("CMS: failed marking verification after remark"); 3039 } 3040 } 3041 3042 class VerifyKlassOopsKlassClosure : public KlassClosure { 3043 class VerifyKlassOopsClosure : public OopClosure { 3044 CMSBitMap* _bitmap; 3045 public: 3046 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { } 3047 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); } 3048 void do_oop(narrowOop* p) { ShouldNotReachHere(); } 3049 } _oop_closure; 3050 public: 3051 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {} 3052 void do_klass(Klass* k) { 3053 k->oops_do(&_oop_closure); 3054 } 3055 }; 3056 3057 void CMSCollector::verify_after_remark_work_2() { 3058 ResourceMark rm; 3059 HandleMark hm; 3060 GenCollectedHeap* gch = GenCollectedHeap::heap(); 3061 3062 // Get a clear set of claim bits for the strong roots processing to work with. 3063 ClassLoaderDataGraph::clear_claimed_marks(); 3064 3065 // Mark from roots one level into CMS 3066 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), 3067 markBitMap()); 3068 CMKlassClosure klass_closure(¬Older); 3069 3070 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 3071 gch->gen_process_strong_roots(_cmsGen->level(), 3072 true, // younger gens are roots 3073 true, // activate StrongRootsScope 3074 false, // not scavenging 3075 SharedHeap::ScanningOption(roots_scanning_options()), 3076 ¬Older, 3077 true, // walk code active on stacks 3078 NULL, 3079 &klass_closure); 3080 3081 // Now mark from the roots 3082 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, 3083 verification_mark_bm(), markBitMap(), verification_mark_stack()); 3084 assert(_restart_addr == NULL, "Expected pre-condition"); 3085 verification_mark_bm()->iterate(&markFromRootsClosure); 3086 while (_restart_addr != NULL) { 3087 // Deal with stack overflow: by restarting at the indicated 3088 // address. 3089 HeapWord* ra = _restart_addr; 3090 markFromRootsClosure.reset(ra); 3091 _restart_addr = NULL; 3092 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); 3093 } 3094 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); 3095 verify_work_stacks_empty(); 3096 3097 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm()); 3098 ClassLoaderDataGraph::classes_do(&verify_klass_oops); 3099 3100 // Marking completed -- now verify that each bit marked in 3101 // verification_mark_bm() is also marked in markBitMap(); flag all 3102 // errors by printing corresponding objects. 3103 VerifyMarkedClosure vcl(markBitMap()); 3104 verification_mark_bm()->iterate(&vcl); 3105 assert(!vcl.failed(), "Else verification above should not have succeeded"); 3106 } 3107 3108 void ConcurrentMarkSweepGeneration::save_marks() { 3109 // delegate to CMS space 3110 cmsSpace()->save_marks(); 3111 for (uint i = 0; i < ParallelGCThreads; i++) { 3112 _par_gc_thread_states[i]->promo.startTrackingPromotions(); 3113 } 3114 } 3115 3116 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { 3117 return cmsSpace()->no_allocs_since_save_marks(); 3118 } 3119 3120 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ 3121 \ 3122 void ConcurrentMarkSweepGeneration:: \ 3123 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ 3124 cl->set_generation(this); \ 3125 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ 3126 cl->reset_generation(); \ 3127 save_marks(); \ 3128 } 3129 3130 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) 3131 3132 void 3133 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk) 3134 { 3135 // Not currently implemented; need to do the following. -- ysr. 3136 // dld -- I think that is used for some sort of allocation profiler. So it 3137 // really means the objects allocated by the mutator since the last 3138 // GC. We could potentially implement this cheaply by recording only 3139 // the direct allocations in a side data structure. 3140 // 3141 // I think we probably ought not to be required to support these 3142 // iterations at any arbitrary point; I think there ought to be some 3143 // call to enable/disable allocation profiling in a generation/space, 3144 // and the iterator ought to return the objects allocated in the 3145 // gen/space since the enable call, or the last iterator call (which 3146 // will probably be at a GC.) That way, for gens like CM&S that would 3147 // require some extra data structure to support this, we only pay the 3148 // cost when it's in use... 3149 cmsSpace()->object_iterate_since_last_GC(blk); 3150 } 3151 3152 void 3153 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) { 3154 cl->set_generation(this); 3155 younger_refs_in_space_iterate(_cmsSpace, cl); 3156 cl->reset_generation(); 3157 } 3158 3159 void 3160 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) { 3161 if (freelistLock()->owned_by_self()) { 3162 Generation::oop_iterate(mr, cl); 3163 } else { 3164 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 3165 Generation::oop_iterate(mr, cl); 3166 } 3167 } 3168 3169 void 3170 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) { 3171 if (freelistLock()->owned_by_self()) { 3172 Generation::oop_iterate(cl); 3173 } else { 3174 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 3175 Generation::oop_iterate(cl); 3176 } 3177 } 3178 3179 void 3180 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { 3181 if (freelistLock()->owned_by_self()) { 3182 Generation::object_iterate(cl); 3183 } else { 3184 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 3185 Generation::object_iterate(cl); 3186 } 3187 } 3188 3189 void 3190 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) { 3191 if (freelistLock()->owned_by_self()) { 3192 Generation::safe_object_iterate(cl); 3193 } else { 3194 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 3195 Generation::safe_object_iterate(cl); 3196 } 3197 } 3198 3199 void 3200 ConcurrentMarkSweepGeneration::post_compact() { 3201 } 3202 3203 void 3204 ConcurrentMarkSweepGeneration::prepare_for_verify() { 3205 // Fix the linear allocation blocks to look like free blocks. 3206 3207 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 3208 // are not called when the heap is verified during universe initialization and 3209 // at vm shutdown. 3210 if (freelistLock()->owned_by_self()) { 3211 cmsSpace()->prepare_for_verify(); 3212 } else { 3213 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 3214 cmsSpace()->prepare_for_verify(); 3215 } 3216 } 3217 3218 void 3219 ConcurrentMarkSweepGeneration::verify() { 3220 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those 3221 // are not called when the heap is verified during universe initialization and 3222 // at vm shutdown. 3223 if (freelistLock()->owned_by_self()) { 3224 cmsSpace()->verify(); 3225 } else { 3226 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); 3227 cmsSpace()->verify(); 3228 } 3229 } 3230 3231 void CMSCollector::verify() { 3232 _cmsGen->verify(); 3233 } 3234 3235 #ifndef PRODUCT 3236 bool CMSCollector::overflow_list_is_empty() const { 3237 assert(_num_par_pushes >= 0, "Inconsistency"); 3238 if (_overflow_list == NULL) { 3239 assert(_num_par_pushes == 0, "Inconsistency"); 3240 } 3241 return _overflow_list == NULL; 3242 } 3243 3244 // The methods verify_work_stacks_empty() and verify_overflow_empty() 3245 // merely consolidate assertion checks that appear to occur together frequently. 3246 void CMSCollector::verify_work_stacks_empty() const { 3247 assert(_markStack.isEmpty(), "Marking stack should be empty"); 3248 assert(overflow_list_is_empty(), "Overflow list should be empty"); 3249 } 3250 3251 void CMSCollector::verify_overflow_empty() const { 3252 assert(overflow_list_is_empty(), "Overflow list should be empty"); 3253 assert(no_preserved_marks(), "No preserved marks"); 3254 } 3255 #endif // PRODUCT 3256 3257 // Decide if we want to enable class unloading as part of the 3258 // ensuing concurrent GC cycle. We will collect and 3259 // unload classes if it's the case that: 3260 // (1) an explicit gc request has been made and the flag 3261 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR 3262 // (2) (a) class unloading is enabled at the command line, and 3263 // (b) old gen is getting really full 3264 // NOTE: Provided there is no change in the state of the heap between 3265 // calls to this method, it should have idempotent results. Moreover, 3266 // its results should be monotonically increasing (i.e. going from 0 to 1, 3267 // but not 1 to 0) between successive calls between which the heap was 3268 // not collected. For the implementation below, it must thus rely on 3269 // the property that concurrent_cycles_since_last_unload() 3270 // will not decrease unless a collection cycle happened and that 3271 // _cmsGen->is_too_full() are 3272 // themselves also monotonic in that sense. See check_monotonicity() 3273 // below. 3274 void CMSCollector::update_should_unload_classes() { 3275 _should_unload_classes = false; 3276 // Condition 1 above 3277 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) { 3278 _should_unload_classes = true; 3279 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above 3280 // Disjuncts 2.b.(i,ii,iii) above 3281 _should_unload_classes = (concurrent_cycles_since_last_unload() >= 3282 CMSClassUnloadingMaxInterval) 3283 || _cmsGen->is_too_full(); 3284 } 3285 } 3286 3287 bool ConcurrentMarkSweepGeneration::is_too_full() const { 3288 bool res = should_concurrent_collect(); 3289 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0); 3290 return res; 3291 } 3292 3293 void CMSCollector::setup_cms_unloading_and_verification_state() { 3294 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC 3295 || VerifyBeforeExit; 3296 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache; 3297 3298 if (should_unload_classes()) { // Should unload classes this cycle 3299 remove_root_scanning_option(rso); // Shrink the root set appropriately 3300 set_verifying(should_verify); // Set verification state for this cycle 3301 return; // Nothing else needs to be done at this time 3302 } 3303 3304 // Not unloading classes this cycle 3305 assert(!should_unload_classes(), "Inconsitency!"); 3306 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) { 3307 // Include symbols, strings and code cache elements to prevent their resurrection. 3308 add_root_scanning_option(rso); 3309 set_verifying(true); 3310 } else if (verifying() && !should_verify) { 3311 // We were verifying, but some verification flags got disabled. 3312 set_verifying(false); 3313 // Exclude symbols, strings and code cache elements from root scanning to 3314 // reduce IM and RM pauses. 3315 remove_root_scanning_option(rso); 3316 } 3317 } 3318 3319 3320 #ifndef PRODUCT 3321 HeapWord* CMSCollector::block_start(const void* p) const { 3322 const HeapWord* addr = (HeapWord*)p; 3323 if (_span.contains(p)) { 3324 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { 3325 return _cmsGen->cmsSpace()->block_start(p); 3326 } 3327 } 3328 return NULL; 3329 } 3330 #endif 3331 3332 HeapWord* 3333 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, 3334 bool tlab, 3335 bool parallel) { 3336 CMSSynchronousYieldRequest yr; 3337 assert(!tlab, "Can't deal with TLAB allocation"); 3338 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); 3339 expand(word_size*HeapWordSize, MinHeapDeltaBytes, 3340 CMSExpansionCause::_satisfy_allocation); 3341 if (GCExpandToAllocateDelayMillis > 0) { 3342 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 3343 } 3344 return have_lock_and_allocate(word_size, tlab); 3345 } 3346 3347 // YSR: All of this generation expansion/shrinking stuff is an exact copy of 3348 // OneContigSpaceCardGeneration, which makes me wonder if we should move this 3349 // to CardGeneration and share it... 3350 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) { 3351 return CardGeneration::expand(bytes, expand_bytes); 3352 } 3353 3354 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes, 3355 CMSExpansionCause::Cause cause) 3356 { 3357 3358 bool success = expand(bytes, expand_bytes); 3359 3360 // remember why we expanded; this information is used 3361 // by shouldConcurrentCollect() when making decisions on whether to start 3362 // a new CMS cycle. 3363 if (success) { 3364 set_expansion_cause(cause); 3365 if (PrintGCDetails && Verbose) { 3366 gclog_or_tty->print_cr("Expanded CMS gen for %s", 3367 CMSExpansionCause::to_string(cause)); 3368 } 3369 } 3370 } 3371 3372 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { 3373 HeapWord* res = NULL; 3374 MutexLocker x(ParGCRareEvent_lock); 3375 while (true) { 3376 // Expansion by some other thread might make alloc OK now: 3377 res = ps->lab.alloc(word_sz); 3378 if (res != NULL) return res; 3379 // If there's not enough expansion space available, give up. 3380 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { 3381 return NULL; 3382 } 3383 // Otherwise, we try expansion. 3384 expand(word_sz*HeapWordSize, MinHeapDeltaBytes, 3385 CMSExpansionCause::_allocate_par_lab); 3386 // Now go around the loop and try alloc again; 3387 // A competing par_promote might beat us to the expansion space, 3388 // so we may go around the loop again if promotion fails agaion. 3389 if (GCExpandToAllocateDelayMillis > 0) { 3390 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 3391 } 3392 } 3393 } 3394 3395 3396 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( 3397 PromotionInfo* promo) { 3398 MutexLocker x(ParGCRareEvent_lock); 3399 size_t refill_size_bytes = promo->refillSize() * HeapWordSize; 3400 while (true) { 3401 // Expansion by some other thread might make alloc OK now: 3402 if (promo->ensure_spooling_space()) { 3403 assert(promo->has_spooling_space(), 3404 "Post-condition of successful ensure_spooling_space()"); 3405 return true; 3406 } 3407 // If there's not enough expansion space available, give up. 3408 if (_virtual_space.uncommitted_size() < refill_size_bytes) { 3409 return false; 3410 } 3411 // Otherwise, we try expansion. 3412 expand(refill_size_bytes, MinHeapDeltaBytes, 3413 CMSExpansionCause::_allocate_par_spooling_space); 3414 // Now go around the loop and try alloc again; 3415 // A competing allocation might beat us to the expansion space, 3416 // so we may go around the loop again if allocation fails again. 3417 if (GCExpandToAllocateDelayMillis > 0) { 3418 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); 3419 } 3420 } 3421 } 3422 3423 3424 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) { 3425 assert_locked_or_safepoint(ExpandHeap_lock); 3426 // Shrink committed space 3427 _virtual_space.shrink_by(bytes); 3428 // Shrink space; this also shrinks the space's BOT 3429 _cmsSpace->set_end((HeapWord*) _virtual_space.high()); 3430 size_t new_word_size = heap_word_size(_cmsSpace->capacity()); 3431 // Shrink the shared block offset array 3432 _bts->resize(new_word_size); 3433 MemRegion mr(_cmsSpace->bottom(), new_word_size); 3434 // Shrink the card table 3435 Universe::heap()->barrier_set()->resize_covered_region(mr); 3436 3437 if (Verbose && PrintGC) { 3438 size_t new_mem_size = _virtual_space.committed_size(); 3439 size_t old_mem_size = new_mem_size + bytes; 3440 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K", 3441 name(), old_mem_size/K, new_mem_size/K); 3442 } 3443 } 3444 3445 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { 3446 assert_locked_or_safepoint(Heap_lock); 3447 size_t size = ReservedSpace::page_align_size_down(bytes); 3448 if (size > 0) { 3449 shrink_by(size); 3450 } 3451 } 3452 3453 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) { 3454 assert_locked_or_safepoint(Heap_lock); 3455 bool result = _virtual_space.expand_by(bytes); 3456 if (result) { 3457 size_t new_word_size = 3458 heap_word_size(_virtual_space.committed_size()); 3459 MemRegion mr(_cmsSpace->bottom(), new_word_size); 3460 _bts->resize(new_word_size); // resize the block offset shared array 3461 Universe::heap()->barrier_set()->resize_covered_region(mr); 3462 // Hmmmm... why doesn't CFLS::set_end verify locking? 3463 // This is quite ugly; FIX ME XXX 3464 _cmsSpace->assert_locked(freelistLock()); 3465 _cmsSpace->set_end((HeapWord*)_virtual_space.high()); 3466 3467 // update the space and generation capacity counters 3468 if (UsePerfData) { 3469 _space_counters->update_capacity(); 3470 _gen_counters->update_all(); 3471 } 3472 3473 if (Verbose && PrintGC) { 3474 size_t new_mem_size = _virtual_space.committed_size(); 3475 size_t old_mem_size = new_mem_size - bytes; 3476 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K", 3477 name(), old_mem_size/K, bytes/K, new_mem_size/K); 3478 } 3479 } 3480 return result; 3481 } 3482 3483 bool ConcurrentMarkSweepGeneration::grow_to_reserved() { 3484 assert_locked_or_safepoint(Heap_lock); 3485 bool success = true; 3486 const size_t remaining_bytes = _virtual_space.uncommitted_size(); 3487 if (remaining_bytes > 0) { 3488 success = grow_by(remaining_bytes); 3489 DEBUG_ONLY(if (!success) warning("grow to reserved failed");) 3490 } 3491 return success; 3492 } 3493 3494 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) { 3495 assert_locked_or_safepoint(Heap_lock); 3496 assert_lock_strong(freelistLock()); 3497 if (PrintGCDetails && Verbose) { 3498 warning("Shrinking of CMS not yet implemented"); 3499 } 3500 return; 3501 } 3502 3503 3504 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent 3505 // phases. 3506 class CMSPhaseAccounting: public StackObj { 3507 public: 3508 CMSPhaseAccounting(CMSCollector *collector, 3509 const char *phase, 3510 bool print_cr = true); 3511 ~CMSPhaseAccounting(); 3512 3513 private: 3514 CMSCollector *_collector; 3515 const char *_phase; 3516 elapsedTimer _wallclock; 3517 bool _print_cr; 3518 3519 public: 3520 // Not MT-safe; so do not pass around these StackObj's 3521 // where they may be accessed by other threads. 3522 jlong wallclock_millis() { 3523 assert(_wallclock.is_active(), "Wall clock should not stop"); 3524 _wallclock.stop(); // to record time 3525 jlong ret = _wallclock.milliseconds(); 3526 _wallclock.start(); // restart 3527 return ret; 3528 } 3529 }; 3530 3531 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, 3532 const char *phase, 3533 bool print_cr) : 3534 _collector(collector), _phase(phase), _print_cr(print_cr) { 3535 3536 if (PrintCMSStatistics != 0) { 3537 _collector->resetYields(); 3538 } 3539 if (PrintGCDetails) { 3540 gclog_or_tty->date_stamp(PrintGCDateStamps); 3541 gclog_or_tty->stamp(PrintGCTimeStamps); 3542 gclog_or_tty->print_cr("[%s-concurrent-%s-start]", 3543 _collector->cmsGen()->short_name(), _phase); 3544 } 3545 _collector->resetTimer(); 3546 _wallclock.start(); 3547 _collector->startTimer(); 3548 } 3549 3550 CMSPhaseAccounting::~CMSPhaseAccounting() { 3551 assert(_wallclock.is_active(), "Wall clock should not have stopped"); 3552 _collector->stopTimer(); 3553 _wallclock.stop(); 3554 if (PrintGCDetails) { 3555 gclog_or_tty->date_stamp(PrintGCDateStamps); 3556 gclog_or_tty->stamp(PrintGCTimeStamps); 3557 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]", 3558 _collector->cmsGen()->short_name(), 3559 _phase, _collector->timerValue(), _wallclock.seconds()); 3560 if (_print_cr) { 3561 gclog_or_tty->print_cr(""); 3562 } 3563 if (PrintCMSStatistics != 0) { 3564 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase, 3565 _collector->yields()); 3566 } 3567 } 3568 } 3569 3570 // CMS work 3571 3572 // Checkpoint the roots into this generation from outside 3573 // this generation. [Note this initial checkpoint need only 3574 // be approximate -- we'll do a catch up phase subsequently.] 3575 void CMSCollector::checkpointRootsInitial(bool asynch) { 3576 assert(_collectorState == InitialMarking, "Wrong collector state"); 3577 check_correct_thread_executing(); 3578 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 3579 3580 save_heap_summary(); 3581 report_heap_summary(GCWhen::BeforeGC); 3582 3583 ReferenceProcessor* rp = ref_processor(); 3584 SpecializationStats::clear(); 3585 assert(_restart_addr == NULL, "Control point invariant"); 3586 if (asynch) { 3587 // acquire locks for subsequent manipulations 3588 MutexLockerEx x(bitMapLock(), 3589 Mutex::_no_safepoint_check_flag); 3590 checkpointRootsInitialWork(asynch); 3591 // enable ("weak") refs discovery 3592 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/); 3593 _collectorState = Marking; 3594 } else { 3595 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection 3596 // which recognizes if we are a CMS generation, and doesn't try to turn on 3597 // discovery; verify that they aren't meddling. 3598 assert(!rp->discovery_is_atomic(), 3599 "incorrect setting of discovery predicate"); 3600 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control " 3601 "ref discovery for this generation kind"); 3602 // already have locks 3603 checkpointRootsInitialWork(asynch); 3604 // now enable ("weak") refs discovery 3605 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/); 3606 _collectorState = Marking; 3607 } 3608 SpecializationStats::print(); 3609 } 3610 3611 void CMSCollector::checkpointRootsInitialWork(bool asynch) { 3612 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); 3613 assert(_collectorState == InitialMarking, "just checking"); 3614 3615 // If there has not been a GC[n-1] since last GC[n] cycle completed, 3616 // precede our marking with a collection of all 3617 // younger generations to keep floating garbage to a minimum. 3618 // XXX: we won't do this for now -- it's an optimization to be done later. 3619 3620 // already have locks 3621 assert_lock_strong(bitMapLock()); 3622 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); 3623 3624 // Setup the verification and class unloading state for this 3625 // CMS collection cycle. 3626 setup_cms_unloading_and_verification_state(); 3627 3628 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork", 3629 PrintGCDetails && Verbose, true, _gc_timer_cm);) 3630 if (UseAdaptiveSizePolicy) { 3631 size_policy()->checkpoint_roots_initial_begin(); 3632 } 3633 3634 // Reset all the PLAB chunk arrays if necessary. 3635 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { 3636 reset_survivor_plab_arrays(); 3637 } 3638 3639 ResourceMark rm; 3640 HandleMark hm; 3641 3642 FalseClosure falseClosure; 3643 // In the case of a synchronous collection, we will elide the 3644 // remark step, so it's important to catch all the nmethod oops 3645 // in this step. 3646 // The final 'true' flag to gen_process_strong_roots will ensure this. 3647 // If 'async' is true, we can relax the nmethod tracing. 3648 MarkRefsIntoClosure notOlder(_span, &_markBitMap); 3649 GenCollectedHeap* gch = GenCollectedHeap::heap(); 3650 3651 verify_work_stacks_empty(); 3652 verify_overflow_empty(); 3653 3654 gch->ensure_parsability(false); // fill TLABs, but no need to retire them 3655 // Update the saved marks which may affect the root scans. 3656 gch->save_marks(); 3657 3658 // weak reference processing has not started yet. 3659 ref_processor()->set_enqueuing_is_done(false); 3660 3661 // Need to remember all newly created CLDs, 3662 // so that we can guarantee that the remark finds them. 3663 ClassLoaderDataGraph::remember_new_clds(true); 3664 3665 // Whenever a CLD is found, it will be claimed before proceeding to mark 3666 // the klasses. The claimed marks need to be cleared before marking starts. 3667 ClassLoaderDataGraph::clear_claimed_marks(); 3668 3669 CMKlassClosure klass_closure(¬Older); 3670 { 3671 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) 3672 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 3673 gch->gen_process_strong_roots(_cmsGen->level(), 3674 true, // younger gens are roots 3675 true, // activate StrongRootsScope 3676 false, // not scavenging 3677 SharedHeap::ScanningOption(roots_scanning_options()), 3678 ¬Older, 3679 true, // walk all of code cache if (so & SO_CodeCache) 3680 NULL, 3681 &klass_closure); 3682 } 3683 3684 // Clear mod-union table; it will be dirtied in the prologue of 3685 // CMS generation per each younger generation collection. 3686 3687 assert(_modUnionTable.isAllClear(), 3688 "Was cleared in most recent final checkpoint phase" 3689 " or no bits are set in the gc_prologue before the start of the next " 3690 "subsequent marking phase."); 3691 3692 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be"); 3693 3694 // Save the end of the used_region of the constituent generations 3695 // to be used to limit the extent of sweep in each generation. 3696 save_sweep_limits(); 3697 if (UseAdaptiveSizePolicy) { 3698 size_policy()->checkpoint_roots_initial_end(gch->gc_cause()); 3699 } 3700 verify_overflow_empty(); 3701 } 3702 3703 bool CMSCollector::markFromRoots(bool asynch) { 3704 // we might be tempted to assert that: 3705 // assert(asynch == !SafepointSynchronize::is_at_safepoint(), 3706 // "inconsistent argument?"); 3707 // However that wouldn't be right, because it's possible that 3708 // a safepoint is indeed in progress as a younger generation 3709 // stop-the-world GC happens even as we mark in this generation. 3710 assert(_collectorState == Marking, "inconsistent state?"); 3711 check_correct_thread_executing(); 3712 verify_overflow_empty(); 3713 3714 bool res; 3715 if (asynch) { 3716 3717 // Start the timers for adaptive size policy for the concurrent phases 3718 // Do it here so that the foreground MS can use the concurrent 3719 // timer since a foreground MS might has the sweep done concurrently 3720 // or STW. 3721 if (UseAdaptiveSizePolicy) { 3722 size_policy()->concurrent_marking_begin(); 3723 } 3724 3725 // Weak ref discovery note: We may be discovering weak 3726 // refs in this generation concurrent (but interleaved) with 3727 // weak ref discovery by a younger generation collector. 3728 3729 CMSTokenSyncWithLocks ts(true, bitMapLock()); 3730 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 3731 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails); 3732 res = markFromRootsWork(asynch); 3733 if (res) { 3734 _collectorState = Precleaning; 3735 } else { // We failed and a foreground collection wants to take over 3736 assert(_foregroundGCIsActive, "internal state inconsistency"); 3737 assert(_restart_addr == NULL, "foreground will restart from scratch"); 3738 if (PrintGCDetails) { 3739 gclog_or_tty->print_cr("bailing out to foreground collection"); 3740 } 3741 } 3742 if (UseAdaptiveSizePolicy) { 3743 size_policy()->concurrent_marking_end(); 3744 } 3745 } else { 3746 assert(SafepointSynchronize::is_at_safepoint(), 3747 "inconsistent with asynch == false"); 3748 if (UseAdaptiveSizePolicy) { 3749 size_policy()->ms_collection_marking_begin(); 3750 } 3751 // already have locks 3752 res = markFromRootsWork(asynch); 3753 _collectorState = FinalMarking; 3754 if (UseAdaptiveSizePolicy) { 3755 GenCollectedHeap* gch = GenCollectedHeap::heap(); 3756 size_policy()->ms_collection_marking_end(gch->gc_cause()); 3757 } 3758 } 3759 verify_overflow_empty(); 3760 return res; 3761 } 3762 3763 bool CMSCollector::markFromRootsWork(bool asynch) { 3764 // iterate over marked bits in bit map, doing a full scan and mark 3765 // from these roots using the following algorithm: 3766 // . if oop is to the right of the current scan pointer, 3767 // mark corresponding bit (we'll process it later) 3768 // . else (oop is to left of current scan pointer) 3769 // push oop on marking stack 3770 // . drain the marking stack 3771 3772 // Note that when we do a marking step we need to hold the 3773 // bit map lock -- recall that direct allocation (by mutators) 3774 // and promotion (by younger generation collectors) is also 3775 // marking the bit map. [the so-called allocate live policy.] 3776 // Because the implementation of bit map marking is not 3777 // robust wrt simultaneous marking of bits in the same word, 3778 // we need to make sure that there is no such interference 3779 // between concurrent such updates. 3780 3781 // already have locks 3782 assert_lock_strong(bitMapLock()); 3783 3784 verify_work_stacks_empty(); 3785 verify_overflow_empty(); 3786 bool result = false; 3787 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) { 3788 result = do_marking_mt(asynch); 3789 } else { 3790 result = do_marking_st(asynch); 3791 } 3792 return result; 3793 } 3794 3795 // Forward decl 3796 class CMSConcMarkingTask; 3797 3798 class CMSConcMarkingTerminator: public ParallelTaskTerminator { 3799 CMSCollector* _collector; 3800 CMSConcMarkingTask* _task; 3801 public: 3802 virtual void yield(); 3803 3804 // "n_threads" is the number of threads to be terminated. 3805 // "queue_set" is a set of work queues of other threads. 3806 // "collector" is the CMS collector associated with this task terminator. 3807 // "yield" indicates whether we need the gang as a whole to yield. 3808 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) : 3809 ParallelTaskTerminator(n_threads, queue_set), 3810 _collector(collector) { } 3811 3812 void set_task(CMSConcMarkingTask* task) { 3813 _task = task; 3814 } 3815 }; 3816 3817 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator { 3818 CMSConcMarkingTask* _task; 3819 public: 3820 bool should_exit_termination(); 3821 void set_task(CMSConcMarkingTask* task) { 3822 _task = task; 3823 } 3824 }; 3825 3826 // MT Concurrent Marking Task 3827 class CMSConcMarkingTask: public YieldingFlexibleGangTask { 3828 CMSCollector* _collector; 3829 int _n_workers; // requested/desired # workers 3830 bool _asynch; 3831 bool _result; 3832 CompactibleFreeListSpace* _cms_space; 3833 char _pad_front[64]; // padding to ... 3834 HeapWord* _global_finger; // ... avoid sharing cache line 3835 char _pad_back[64]; 3836 HeapWord* _restart_addr; 3837 3838 // Exposed here for yielding support 3839 Mutex* const _bit_map_lock; 3840 3841 // The per thread work queues, available here for stealing 3842 OopTaskQueueSet* _task_queues; 3843 3844 // Termination (and yielding) support 3845 CMSConcMarkingTerminator _term; 3846 CMSConcMarkingTerminatorTerminator _term_term; 3847 3848 public: 3849 CMSConcMarkingTask(CMSCollector* collector, 3850 CompactibleFreeListSpace* cms_space, 3851 bool asynch, 3852 YieldingFlexibleWorkGang* workers, 3853 OopTaskQueueSet* task_queues): 3854 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), 3855 _collector(collector), 3856 _cms_space(cms_space), 3857 _asynch(asynch), _n_workers(0), _result(true), 3858 _task_queues(task_queues), 3859 _term(_n_workers, task_queues, _collector), 3860 _bit_map_lock(collector->bitMapLock()) 3861 { 3862 _requested_size = _n_workers; 3863 _term.set_task(this); 3864 _term_term.set_task(this); 3865 _restart_addr = _global_finger = _cms_space->bottom(); 3866 } 3867 3868 3869 OopTaskQueueSet* task_queues() { return _task_queues; } 3870 3871 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 3872 3873 HeapWord** global_finger_addr() { return &_global_finger; } 3874 3875 CMSConcMarkingTerminator* terminator() { return &_term; } 3876 3877 virtual void set_for_termination(int active_workers) { 3878 terminator()->reset_for_reuse(active_workers); 3879 } 3880 3881 void work(uint worker_id); 3882 bool should_yield() { 3883 return ConcurrentMarkSweepThread::should_yield() 3884 && !_collector->foregroundGCIsActive() 3885 && _asynch; 3886 } 3887 3888 virtual void coordinator_yield(); // stuff done by coordinator 3889 bool result() { return _result; } 3890 3891 void reset(HeapWord* ra) { 3892 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)"); 3893 _restart_addr = _global_finger = ra; 3894 _term.reset_for_reuse(); 3895 } 3896 3897 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 3898 OopTaskQueue* work_q); 3899 3900 private: 3901 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); 3902 void do_work_steal(int i); 3903 void bump_global_finger(HeapWord* f); 3904 }; 3905 3906 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() { 3907 assert(_task != NULL, "Error"); 3908 return _task->yielding(); 3909 // Note that we do not need the disjunct || _task->should_yield() above 3910 // because we want terminating threads to yield only if the task 3911 // is already in the midst of yielding, which happens only after at least one 3912 // thread has yielded. 3913 } 3914 3915 void CMSConcMarkingTerminator::yield() { 3916 if (_task->should_yield()) { 3917 _task->yield(); 3918 } else { 3919 ParallelTaskTerminator::yield(); 3920 } 3921 } 3922 3923 //////////////////////////////////////////////////////////////// 3924 // Concurrent Marking Algorithm Sketch 3925 //////////////////////////////////////////////////////////////// 3926 // Until all tasks exhausted (both spaces): 3927 // -- claim next available chunk 3928 // -- bump global finger via CAS 3929 // -- find first object that starts in this chunk 3930 // and start scanning bitmap from that position 3931 // -- scan marked objects for oops 3932 // -- CAS-mark target, and if successful: 3933 // . if target oop is above global finger (volatile read) 3934 // nothing to do 3935 // . if target oop is in chunk and above local finger 3936 // then nothing to do 3937 // . else push on work-queue 3938 // -- Deal with possible overflow issues: 3939 // . local work-queue overflow causes stuff to be pushed on 3940 // global (common) overflow queue 3941 // . always first empty local work queue 3942 // . then get a batch of oops from global work queue if any 3943 // . then do work stealing 3944 // -- When all tasks claimed (both spaces) 3945 // and local work queue empty, 3946 // then in a loop do: 3947 // . check global overflow stack; steal a batch of oops and trace 3948 // . try to steal from other threads oif GOS is empty 3949 // . if neither is available, offer termination 3950 // -- Terminate and return result 3951 // 3952 void CMSConcMarkingTask::work(uint worker_id) { 3953 elapsedTimer _timer; 3954 ResourceMark rm; 3955 HandleMark hm; 3956 3957 DEBUG_ONLY(_collector->verify_overflow_empty();) 3958 3959 // Before we begin work, our work queue should be empty 3960 assert(work_queue(worker_id)->size() == 0, "Expected to be empty"); 3961 // Scan the bitmap covering _cms_space, tracing through grey objects. 3962 _timer.start(); 3963 do_scan_and_mark(worker_id, _cms_space); 3964 _timer.stop(); 3965 if (PrintCMSStatistics != 0) { 3966 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec", 3967 worker_id, _timer.seconds()); 3968 // XXX: need xxx/xxx type of notation, two timers 3969 } 3970 3971 // ... do work stealing 3972 _timer.reset(); 3973 _timer.start(); 3974 do_work_steal(worker_id); 3975 _timer.stop(); 3976 if (PrintCMSStatistics != 0) { 3977 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec", 3978 worker_id, _timer.seconds()); 3979 // XXX: need xxx/xxx type of notation, two timers 3980 } 3981 assert(_collector->_markStack.isEmpty(), "Should have been emptied"); 3982 assert(work_queue(worker_id)->size() == 0, "Should have been emptied"); 3983 // Note that under the current task protocol, the 3984 // following assertion is true even of the spaces 3985 // expanded since the completion of the concurrent 3986 // marking. XXX This will likely change under a strict 3987 // ABORT semantics. 3988 // After perm removal the comparison was changed to 3989 // greater than or equal to from strictly greater than. 3990 // Before perm removal the highest address sweep would 3991 // have been at the end of perm gen but now is at the 3992 // end of the tenured gen. 3993 assert(_global_finger >= _cms_space->end(), 3994 "All tasks have been completed"); 3995 DEBUG_ONLY(_collector->verify_overflow_empty();) 3996 } 3997 3998 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { 3999 HeapWord* read = _global_finger; 4000 HeapWord* cur = read; 4001 while (f > read) { 4002 cur = read; 4003 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur); 4004 if (cur == read) { 4005 // our cas succeeded 4006 assert(_global_finger >= f, "protocol consistency"); 4007 break; 4008 } 4009 } 4010 } 4011 4012 // This is really inefficient, and should be redone by 4013 // using (not yet available) block-read and -write interfaces to the 4014 // stack and the work_queue. XXX FIX ME !!! 4015 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, 4016 OopTaskQueue* work_q) { 4017 // Fast lock-free check 4018 if (ovflw_stk->length() == 0) { 4019 return false; 4020 } 4021 assert(work_q->size() == 0, "Shouldn't steal"); 4022 MutexLockerEx ml(ovflw_stk->par_lock(), 4023 Mutex::_no_safepoint_check_flag); 4024 // Grab up to 1/4 the size of the work queue 4025 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 4026 (size_t)ParGCDesiredObjsFromOverflowList); 4027 num = MIN2(num, ovflw_stk->length()); 4028 for (int i = (int) num; i > 0; i--) { 4029 oop cur = ovflw_stk->pop(); 4030 assert(cur != NULL, "Counted wrong?"); 4031 work_q->push(cur); 4032 } 4033 return num > 0; 4034 } 4035 4036 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { 4037 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 4038 int n_tasks = pst->n_tasks(); 4039 // We allow that there may be no tasks to do here because 4040 // we are restarting after a stack overflow. 4041 assert(pst->valid() || n_tasks == 0, "Uninitialized use?"); 4042 uint nth_task = 0; 4043 4044 HeapWord* aligned_start = sp->bottom(); 4045 if (sp->used_region().contains(_restart_addr)) { 4046 // Align down to a card boundary for the start of 0th task 4047 // for this space. 4048 aligned_start = 4049 (HeapWord*)align_size_down((uintptr_t)_restart_addr, 4050 CardTableModRefBS::card_size); 4051 } 4052 4053 size_t chunk_size = sp->marking_task_size(); 4054 while (!pst->is_task_claimed(/* reference */ nth_task)) { 4055 // Having claimed the nth task in this space, 4056 // compute the chunk that it corresponds to: 4057 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size, 4058 aligned_start + (nth_task+1)*chunk_size); 4059 // Try and bump the global finger via a CAS; 4060 // note that we need to do the global finger bump 4061 // _before_ taking the intersection below, because 4062 // the task corresponding to that region will be 4063 // deemed done even if the used_region() expands 4064 // because of allocation -- as it almost certainly will 4065 // during start-up while the threads yield in the 4066 // closure below. 4067 HeapWord* finger = span.end(); 4068 bump_global_finger(finger); // atomically 4069 // There are null tasks here corresponding to chunks 4070 // beyond the "top" address of the space. 4071 span = span.intersection(sp->used_region()); 4072 if (!span.is_empty()) { // Non-null task 4073 HeapWord* prev_obj; 4074 assert(!span.contains(_restart_addr) || nth_task == 0, 4075 "Inconsistency"); 4076 if (nth_task == 0) { 4077 // For the 0th task, we'll not need to compute a block_start. 4078 if (span.contains(_restart_addr)) { 4079 // In the case of a restart because of stack overflow, 4080 // we might additionally skip a chunk prefix. 4081 prev_obj = _restart_addr; 4082 } else { 4083 prev_obj = span.start(); 4084 } 4085 } else { 4086 // We want to skip the first object because 4087 // the protocol is to scan any object in its entirety 4088 // that _starts_ in this span; a fortiori, any 4089 // object starting in an earlier span is scanned 4090 // as part of an earlier claimed task. 4091 // Below we use the "careful" version of block_start 4092 // so we do not try to navigate uninitialized objects. 4093 prev_obj = sp->block_start_careful(span.start()); 4094 // Below we use a variant of block_size that uses the 4095 // Printezis bits to avoid waiting for allocated 4096 // objects to become initialized/parsable. 4097 while (prev_obj < span.start()) { 4098 size_t sz = sp->block_size_no_stall(prev_obj, _collector); 4099 if (sz > 0) { 4100 prev_obj += sz; 4101 } else { 4102 // In this case we may end up doing a bit of redundant 4103 // scanning, but that appears unavoidable, short of 4104 // locking the free list locks; see bug 6324141. 4105 break; 4106 } 4107 } 4108 } 4109 if (prev_obj < span.end()) { 4110 MemRegion my_span = MemRegion(prev_obj, span.end()); 4111 // Do the marking work within a non-empty span -- 4112 // the last argument to the constructor indicates whether the 4113 // iteration should be incremental with periodic yields. 4114 Par_MarkFromRootsClosure cl(this, _collector, my_span, 4115 &_collector->_markBitMap, 4116 work_queue(i), 4117 &_collector->_markStack, 4118 _asynch); 4119 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); 4120 } // else nothing to do for this task 4121 } // else nothing to do for this task 4122 } 4123 // We'd be tempted to assert here that since there are no 4124 // more tasks left to claim in this space, the global_finger 4125 // must exceed space->top() and a fortiori space->end(). However, 4126 // that would not quite be correct because the bumping of 4127 // global_finger occurs strictly after the claiming of a task, 4128 // so by the time we reach here the global finger may not yet 4129 // have been bumped up by the thread that claimed the last 4130 // task. 4131 pst->all_tasks_completed(); 4132 } 4133 4134 class Par_ConcMarkingClosure: public CMSOopClosure { 4135 private: 4136 CMSCollector* _collector; 4137 CMSConcMarkingTask* _task; 4138 MemRegion _span; 4139 CMSBitMap* _bit_map; 4140 CMSMarkStack* _overflow_stack; 4141 OopTaskQueue* _work_queue; 4142 protected: 4143 DO_OOP_WORK_DEFN 4144 public: 4145 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue, 4146 CMSBitMap* bit_map, CMSMarkStack* overflow_stack): 4147 CMSOopClosure(collector->ref_processor()), 4148 _collector(collector), 4149 _task(task), 4150 _span(collector->_span), 4151 _work_queue(work_queue), 4152 _bit_map(bit_map), 4153 _overflow_stack(overflow_stack) 4154 { } 4155 virtual void do_oop(oop* p); 4156 virtual void do_oop(narrowOop* p); 4157 4158 void trim_queue(size_t max); 4159 void handle_stack_overflow(HeapWord* lost); 4160 void do_yield_check() { 4161 if (_task->should_yield()) { 4162 _task->yield(); 4163 } 4164 } 4165 }; 4166 4167 // Grey object scanning during work stealing phase -- 4168 // the salient assumption here is that any references 4169 // that are in these stolen objects being scanned must 4170 // already have been initialized (else they would not have 4171 // been published), so we do not need to check for 4172 // uninitialized objects before pushing here. 4173 void Par_ConcMarkingClosure::do_oop(oop obj) { 4174 assert(obj->is_oop_or_null(true), "expected an oop or NULL"); 4175 HeapWord* addr = (HeapWord*)obj; 4176 // Check if oop points into the CMS generation 4177 // and is not marked 4178 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 4179 // a white object ... 4180 // If we manage to "claim" the object, by being the 4181 // first thread to mark it, then we push it on our 4182 // marking stack 4183 if (_bit_map->par_mark(addr)) { // ... now grey 4184 // push on work queue (grey set) 4185 bool simulate_overflow = false; 4186 NOT_PRODUCT( 4187 if (CMSMarkStackOverflowALot && 4188 _collector->simulate_overflow()) { 4189 // simulate a stack overflow 4190 simulate_overflow = true; 4191 } 4192 ) 4193 if (simulate_overflow || 4194 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 4195 // stack overflow 4196 if (PrintCMSStatistics != 0) { 4197 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " 4198 SIZE_FORMAT, _overflow_stack->capacity()); 4199 } 4200 // We cannot assert that the overflow stack is full because 4201 // it may have been emptied since. 4202 assert(simulate_overflow || 4203 _work_queue->size() == _work_queue->max_elems(), 4204 "Else push should have succeeded"); 4205 handle_stack_overflow(addr); 4206 } 4207 } // Else, some other thread got there first 4208 do_yield_check(); 4209 } 4210 } 4211 4212 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); } 4213 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); } 4214 4215 void Par_ConcMarkingClosure::trim_queue(size_t max) { 4216 while (_work_queue->size() > max) { 4217 oop new_oop; 4218 if (_work_queue->pop_local(new_oop)) { 4219 assert(new_oop->is_oop(), "Should be an oop"); 4220 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); 4221 assert(_span.contains((HeapWord*)new_oop), "Not in span"); 4222 new_oop->oop_iterate(this); // do_oop() above 4223 do_yield_check(); 4224 } 4225 } 4226 } 4227 4228 // Upon stack overflow, we discard (part of) the stack, 4229 // remembering the least address amongst those discarded 4230 // in CMSCollector's _restart_address. 4231 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { 4232 // We need to do this under a mutex to prevent other 4233 // workers from interfering with the work done below. 4234 MutexLockerEx ml(_overflow_stack->par_lock(), 4235 Mutex::_no_safepoint_check_flag); 4236 // Remember the least grey address discarded 4237 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 4238 _collector->lower_restart_addr(ra); 4239 _overflow_stack->reset(); // discard stack contents 4240 _overflow_stack->expand(); // expand the stack if possible 4241 } 4242 4243 4244 void CMSConcMarkingTask::do_work_steal(int i) { 4245 OopTaskQueue* work_q = work_queue(i); 4246 oop obj_to_scan; 4247 CMSBitMap* bm = &(_collector->_markBitMap); 4248 CMSMarkStack* ovflw = &(_collector->_markStack); 4249 int* seed = _collector->hash_seed(i); 4250 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw); 4251 while (true) { 4252 cl.trim_queue(0); 4253 assert(work_q->size() == 0, "Should have been emptied above"); 4254 if (get_work_from_overflow_stack(ovflw, work_q)) { 4255 // Can't assert below because the work obtained from the 4256 // overflow stack may already have been stolen from us. 4257 // assert(work_q->size() > 0, "Work from overflow stack"); 4258 continue; 4259 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 4260 assert(obj_to_scan->is_oop(), "Should be an oop"); 4261 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); 4262 obj_to_scan->oop_iterate(&cl); 4263 } else if (terminator()->offer_termination(&_term_term)) { 4264 assert(work_q->size() == 0, "Impossible!"); 4265 break; 4266 } else if (yielding() || should_yield()) { 4267 yield(); 4268 } 4269 } 4270 } 4271 4272 // This is run by the CMS (coordinator) thread. 4273 void CMSConcMarkingTask::coordinator_yield() { 4274 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 4275 "CMS thread should hold CMS token"); 4276 // First give up the locks, then yield, then re-lock 4277 // We should probably use a constructor/destructor idiom to 4278 // do this unlock/lock or modify the MutexUnlocker class to 4279 // serve our purpose. XXX 4280 assert_lock_strong(_bit_map_lock); 4281 _bit_map_lock->unlock(); 4282 ConcurrentMarkSweepThread::desynchronize(true); 4283 ConcurrentMarkSweepThread::acknowledge_yield_request(); 4284 _collector->stopTimer(); 4285 if (PrintCMSStatistics != 0) { 4286 _collector->incrementYields(); 4287 } 4288 _collector->icms_wait(); 4289 4290 // It is possible for whichever thread initiated the yield request 4291 // not to get a chance to wake up and take the bitmap lock between 4292 // this thread releasing it and reacquiring it. So, while the 4293 // should_yield() flag is on, let's sleep for a bit to give the 4294 // other thread a chance to wake up. The limit imposed on the number 4295 // of iterations is defensive, to avoid any unforseen circumstances 4296 // putting us into an infinite loop. Since it's always been this 4297 // (coordinator_yield()) method that was observed to cause the 4298 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) 4299 // which is by default non-zero. For the other seven methods that 4300 // also perform the yield operation, as are using a different 4301 // parameter (CMSYieldSleepCount) which is by default zero. This way we 4302 // can enable the sleeping for those methods too, if necessary. 4303 // See 6442774. 4304 // 4305 // We really need to reconsider the synchronization between the GC 4306 // thread and the yield-requesting threads in the future and we 4307 // should really use wait/notify, which is the recommended 4308 // way of doing this type of interaction. Additionally, we should 4309 // consolidate the eight methods that do the yield operation and they 4310 // are almost identical into one for better maintenability and 4311 // readability. See 6445193. 4312 // 4313 // Tony 2006.06.29 4314 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && 4315 ConcurrentMarkSweepThread::should_yield() && 4316 !CMSCollector::foregroundGCIsActive(); ++i) { 4317 os::sleep(Thread::current(), 1, false); 4318 ConcurrentMarkSweepThread::acknowledge_yield_request(); 4319 } 4320 4321 ConcurrentMarkSweepThread::synchronize(true); 4322 _bit_map_lock->lock_without_safepoint_check(); 4323 _collector->startTimer(); 4324 } 4325 4326 bool CMSCollector::do_marking_mt(bool asynch) { 4327 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition"); 4328 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers( 4329 conc_workers()->total_workers(), 4330 conc_workers()->active_workers(), 4331 Threads::number_of_non_daemon_threads()); 4332 conc_workers()->set_active_workers(num_workers); 4333 4334 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 4335 4336 CMSConcMarkingTask tsk(this, 4337 cms_space, 4338 asynch, 4339 conc_workers(), 4340 task_queues()); 4341 4342 // Since the actual number of workers we get may be different 4343 // from the number we requested above, do we need to do anything different 4344 // below? In particular, may be we need to subclass the SequantialSubTasksDone 4345 // class?? XXX 4346 cms_space ->initialize_sequential_subtasks_for_marking(num_workers); 4347 4348 // Refs discovery is already non-atomic. 4349 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); 4350 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT"); 4351 conc_workers()->start_task(&tsk); 4352 while (tsk.yielded()) { 4353 tsk.coordinator_yield(); 4354 conc_workers()->continue_task(&tsk); 4355 } 4356 // If the task was aborted, _restart_addr will be non-NULL 4357 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); 4358 while (_restart_addr != NULL) { 4359 // XXX For now we do not make use of ABORTED state and have not 4360 // yet implemented the right abort semantics (even in the original 4361 // single-threaded CMS case). That needs some more investigation 4362 // and is deferred for now; see CR# TBF. 07252005YSR. XXX 4363 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); 4364 // If _restart_addr is non-NULL, a marking stack overflow 4365 // occurred; we need to do a fresh marking iteration from the 4366 // indicated restart address. 4367 if (_foregroundGCIsActive && asynch) { 4368 // We may be running into repeated stack overflows, having 4369 // reached the limit of the stack size, while making very 4370 // slow forward progress. It may be best to bail out and 4371 // let the foreground collector do its job. 4372 // Clear _restart_addr, so that foreground GC 4373 // works from scratch. This avoids the headache of 4374 // a "rescan" which would otherwise be needed because 4375 // of the dirty mod union table & card table. 4376 _restart_addr = NULL; 4377 return false; 4378 } 4379 // Adjust the task to restart from _restart_addr 4380 tsk.reset(_restart_addr); 4381 cms_space ->initialize_sequential_subtasks_for_marking(num_workers, 4382 _restart_addr); 4383 _restart_addr = NULL; 4384 // Get the workers going again 4385 conc_workers()->start_task(&tsk); 4386 while (tsk.yielded()) { 4387 tsk.coordinator_yield(); 4388 conc_workers()->continue_task(&tsk); 4389 } 4390 } 4391 assert(tsk.completed(), "Inconsistency"); 4392 assert(tsk.result() == true, "Inconsistency"); 4393 return true; 4394 } 4395 4396 bool CMSCollector::do_marking_st(bool asynch) { 4397 ResourceMark rm; 4398 HandleMark hm; 4399 4400 // Temporarily make refs discovery single threaded (non-MT) 4401 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false); 4402 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, 4403 &_markStack, CMSYield && asynch); 4404 // the last argument to iterate indicates whether the iteration 4405 // should be incremental with periodic yields. 4406 _markBitMap.iterate(&markFromRootsClosure); 4407 // If _restart_addr is non-NULL, a marking stack overflow 4408 // occurred; we need to do a fresh iteration from the 4409 // indicated restart address. 4410 while (_restart_addr != NULL) { 4411 if (_foregroundGCIsActive && asynch) { 4412 // We may be running into repeated stack overflows, having 4413 // reached the limit of the stack size, while making very 4414 // slow forward progress. It may be best to bail out and 4415 // let the foreground collector do its job. 4416 // Clear _restart_addr, so that foreground GC 4417 // works from scratch. This avoids the headache of 4418 // a "rescan" which would otherwise be needed because 4419 // of the dirty mod union table & card table. 4420 _restart_addr = NULL; 4421 return false; // indicating failure to complete marking 4422 } 4423 // Deal with stack overflow: 4424 // we restart marking from _restart_addr 4425 HeapWord* ra = _restart_addr; 4426 markFromRootsClosure.reset(ra); 4427 _restart_addr = NULL; 4428 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); 4429 } 4430 return true; 4431 } 4432 4433 void CMSCollector::preclean() { 4434 check_correct_thread_executing(); 4435 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); 4436 verify_work_stacks_empty(); 4437 verify_overflow_empty(); 4438 _abort_preclean = false; 4439 if (CMSPrecleaningEnabled) { 4440 _eden_chunk_index = 0; 4441 size_t used = get_eden_used(); 4442 size_t capacity = get_eden_capacity(); 4443 // Don't start sampling unless we will get sufficiently 4444 // many samples. 4445 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100) 4446 * CMSScheduleRemarkEdenPenetration)) { 4447 _start_sampling = true; 4448 } else { 4449 _start_sampling = false; 4450 } 4451 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 4452 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails); 4453 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); 4454 } 4455 CMSTokenSync x(true); // is cms thread 4456 if (CMSPrecleaningEnabled) { 4457 sample_eden(); 4458 _collectorState = AbortablePreclean; 4459 } else { 4460 _collectorState = FinalMarking; 4461 } 4462 verify_work_stacks_empty(); 4463 verify_overflow_empty(); 4464 } 4465 4466 // Try and schedule the remark such that young gen 4467 // occupancy is CMSScheduleRemarkEdenPenetration %. 4468 void CMSCollector::abortable_preclean() { 4469 check_correct_thread_executing(); 4470 assert(CMSPrecleaningEnabled, "Inconsistent control state"); 4471 assert(_collectorState == AbortablePreclean, "Inconsistent control state"); 4472 4473 // If Eden's current occupancy is below this threshold, 4474 // immediately schedule the remark; else preclean 4475 // past the next scavenge in an effort to 4476 // schedule the pause as described avove. By choosing 4477 // CMSScheduleRemarkEdenSizeThreshold >= max eden size 4478 // we will never do an actual abortable preclean cycle. 4479 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { 4480 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 4481 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails); 4482 // We need more smarts in the abortable preclean 4483 // loop below to deal with cases where allocation 4484 // in young gen is very very slow, and our precleaning 4485 // is running a losing race against a horde of 4486 // mutators intent on flooding us with CMS updates 4487 // (dirty cards). 4488 // One, admittedly dumb, strategy is to give up 4489 // after a certain number of abortable precleaning loops 4490 // or after a certain maximum time. We want to make 4491 // this smarter in the next iteration. 4492 // XXX FIX ME!!! YSR 4493 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; 4494 while (!(should_abort_preclean() || 4495 ConcurrentMarkSweepThread::should_terminate())) { 4496 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); 4497 cumworkdone += workdone; 4498 loops++; 4499 // Voluntarily terminate abortable preclean phase if we have 4500 // been at it for too long. 4501 if ((CMSMaxAbortablePrecleanLoops != 0) && 4502 loops >= CMSMaxAbortablePrecleanLoops) { 4503 if (PrintGCDetails) { 4504 gclog_or_tty->print(" CMS: abort preclean due to loops "); 4505 } 4506 break; 4507 } 4508 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { 4509 if (PrintGCDetails) { 4510 gclog_or_tty->print(" CMS: abort preclean due to time "); 4511 } 4512 break; 4513 } 4514 // If we are doing little work each iteration, we should 4515 // take a short break. 4516 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { 4517 // Sleep for some time, waiting for work to accumulate 4518 stopTimer(); 4519 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); 4520 startTimer(); 4521 waited++; 4522 } 4523 } 4524 if (PrintCMSStatistics > 0) { 4525 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ", 4526 loops, waited, cumworkdone); 4527 } 4528 } 4529 CMSTokenSync x(true); // is cms thread 4530 if (_collectorState != Idling) { 4531 assert(_collectorState == AbortablePreclean, 4532 "Spontaneous state transition?"); 4533 _collectorState = FinalMarking; 4534 } // Else, a foreground collection completed this CMS cycle. 4535 return; 4536 } 4537 4538 // Respond to an Eden sampling opportunity 4539 void CMSCollector::sample_eden() { 4540 // Make sure a young gc cannot sneak in between our 4541 // reading and recording of a sample. 4542 assert(Thread::current()->is_ConcurrentGC_thread(), 4543 "Only the cms thread may collect Eden samples"); 4544 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 4545 "Should collect samples while holding CMS token"); 4546 if (!_start_sampling) { 4547 return; 4548 } 4549 if (_eden_chunk_array) { 4550 if (_eden_chunk_index < _eden_chunk_capacity) { 4551 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample 4552 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, 4553 "Unexpected state of Eden"); 4554 // We'd like to check that what we just sampled is an oop-start address; 4555 // however, we cannot do that here since the object may not yet have been 4556 // initialized. So we'll instead do the check when we _use_ this sample 4557 // later. 4558 if (_eden_chunk_index == 0 || 4559 (pointer_delta(_eden_chunk_array[_eden_chunk_index], 4560 _eden_chunk_array[_eden_chunk_index-1]) 4561 >= CMSSamplingGrain)) { 4562 _eden_chunk_index++; // commit sample 4563 } 4564 } 4565 } 4566 if ((_collectorState == AbortablePreclean) && !_abort_preclean) { 4567 size_t used = get_eden_used(); 4568 size_t capacity = get_eden_capacity(); 4569 assert(used <= capacity, "Unexpected state of Eden"); 4570 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { 4571 _abort_preclean = true; 4572 } 4573 } 4574 } 4575 4576 4577 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { 4578 assert(_collectorState == Precleaning || 4579 _collectorState == AbortablePreclean, "incorrect state"); 4580 ResourceMark rm; 4581 HandleMark hm; 4582 4583 // Precleaning is currently not MT but the reference processor 4584 // may be set for MT. Disable it temporarily here. 4585 ReferenceProcessor* rp = ref_processor(); 4586 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false); 4587 4588 // Do one pass of scrubbing the discovered reference lists 4589 // to remove any reference objects with strongly-reachable 4590 // referents. 4591 if (clean_refs) { 4592 CMSPrecleanRefsYieldClosure yield_cl(this); 4593 assert(rp->span().equals(_span), "Spans should be equal"); 4594 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, 4595 &_markStack, true /* preclean */); 4596 CMSDrainMarkingStackClosure complete_trace(this, 4597 _span, &_markBitMap, &_markStack, 4598 &keep_alive, true /* preclean */); 4599 4600 // We don't want this step to interfere with a young 4601 // collection because we don't want to take CPU 4602 // or memory bandwidth away from the young GC threads 4603 // (which may be as many as there are CPUs). 4604 // Note that we don't need to protect ourselves from 4605 // interference with mutators because they can't 4606 // manipulate the discovered reference lists nor affect 4607 // the computed reachability of the referents, the 4608 // only properties manipulated by the precleaning 4609 // of these reference lists. 4610 stopTimer(); 4611 CMSTokenSyncWithLocks x(true /* is cms thread */, 4612 bitMapLock()); 4613 startTimer(); 4614 sample_eden(); 4615 4616 // The following will yield to allow foreground 4617 // collection to proceed promptly. XXX YSR: 4618 // The code in this method may need further 4619 // tweaking for better performance and some restructuring 4620 // for cleaner interfaces. 4621 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases 4622 rp->preclean_discovered_references( 4623 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl, 4624 gc_timer); 4625 } 4626 4627 if (clean_survivor) { // preclean the active survivor space(s) 4628 assert(_young_gen->kind() == Generation::DefNew || 4629 _young_gen->kind() == Generation::ParNew || 4630 _young_gen->kind() == Generation::ASParNew, 4631 "incorrect type for cast"); 4632 DefNewGeneration* dng = (DefNewGeneration*)_young_gen; 4633 PushAndMarkClosure pam_cl(this, _span, ref_processor(), 4634 &_markBitMap, &_modUnionTable, 4635 &_markStack, true /* precleaning phase */); 4636 stopTimer(); 4637 CMSTokenSyncWithLocks ts(true /* is cms thread */, 4638 bitMapLock()); 4639 startTimer(); 4640 unsigned int before_count = 4641 GenCollectedHeap::heap()->total_collections(); 4642 SurvivorSpacePrecleanClosure 4643 sss_cl(this, _span, &_markBitMap, &_markStack, 4644 &pam_cl, before_count, CMSYield); 4645 dng->from()->object_iterate_careful(&sss_cl); 4646 dng->to()->object_iterate_careful(&sss_cl); 4647 } 4648 MarkRefsIntoAndScanClosure 4649 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, 4650 &_markStack, this, CMSYield, 4651 true /* precleaning phase */); 4652 // CAUTION: The following closure has persistent state that may need to 4653 // be reset upon a decrease in the sequence of addresses it 4654 // processes. 4655 ScanMarkedObjectsAgainCarefullyClosure 4656 smoac_cl(this, _span, 4657 &_markBitMap, &_markStack, &mrias_cl, CMSYield); 4658 4659 // Preclean dirty cards in ModUnionTable and CardTable using 4660 // appropriate convergence criterion; 4661 // repeat CMSPrecleanIter times unless we find that 4662 // we are losing. 4663 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); 4664 assert(CMSPrecleanNumerator < CMSPrecleanDenominator, 4665 "Bad convergence multiplier"); 4666 assert(CMSPrecleanThreshold >= 100, 4667 "Unreasonably low CMSPrecleanThreshold"); 4668 4669 size_t numIter, cumNumCards, lastNumCards, curNumCards; 4670 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; 4671 numIter < CMSPrecleanIter; 4672 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { 4673 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); 4674 if (Verbose && PrintGCDetails) { 4675 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards); 4676 } 4677 // Either there are very few dirty cards, so re-mark 4678 // pause will be small anyway, or our pre-cleaning isn't 4679 // that much faster than the rate at which cards are being 4680 // dirtied, so we might as well stop and re-mark since 4681 // precleaning won't improve our re-mark time by much. 4682 if (curNumCards <= CMSPrecleanThreshold || 4683 (numIter > 0 && 4684 (curNumCards * CMSPrecleanDenominator > 4685 lastNumCards * CMSPrecleanNumerator))) { 4686 numIter++; 4687 cumNumCards += curNumCards; 4688 break; 4689 } 4690 } 4691 4692 preclean_klasses(&mrias_cl, _cmsGen->freelistLock()); 4693 4694 curNumCards = preclean_card_table(_cmsGen, &smoac_cl); 4695 cumNumCards += curNumCards; 4696 if (PrintGCDetails && PrintCMSStatistics != 0) { 4697 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)", 4698 curNumCards, cumNumCards, numIter); 4699 } 4700 return cumNumCards; // as a measure of useful work done 4701 } 4702 4703 // PRECLEANING NOTES: 4704 // Precleaning involves: 4705 // . reading the bits of the modUnionTable and clearing the set bits. 4706 // . For the cards corresponding to the set bits, we scan the 4707 // objects on those cards. This means we need the free_list_lock 4708 // so that we can safely iterate over the CMS space when scanning 4709 // for oops. 4710 // . When we scan the objects, we'll be both reading and setting 4711 // marks in the marking bit map, so we'll need the marking bit map. 4712 // . For protecting _collector_state transitions, we take the CGC_lock. 4713 // Note that any races in the reading of of card table entries by the 4714 // CMS thread on the one hand and the clearing of those entries by the 4715 // VM thread or the setting of those entries by the mutator threads on the 4716 // other are quite benign. However, for efficiency it makes sense to keep 4717 // the VM thread from racing with the CMS thread while the latter is 4718 // dirty card info to the modUnionTable. We therefore also use the 4719 // CGC_lock to protect the reading of the card table and the mod union 4720 // table by the CM thread. 4721 // . We run concurrently with mutator updates, so scanning 4722 // needs to be done carefully -- we should not try to scan 4723 // potentially uninitialized objects. 4724 // 4725 // Locking strategy: While holding the CGC_lock, we scan over and 4726 // reset a maximal dirty range of the mod union / card tables, then lock 4727 // the free_list_lock and bitmap lock to do a full marking, then 4728 // release these locks; and repeat the cycle. This allows for a 4729 // certain amount of fairness in the sharing of these locks between 4730 // the CMS collector on the one hand, and the VM thread and the 4731 // mutators on the other. 4732 4733 // NOTE: preclean_mod_union_table() and preclean_card_table() 4734 // further below are largely identical; if you need to modify 4735 // one of these methods, please check the other method too. 4736 4737 size_t CMSCollector::preclean_mod_union_table( 4738 ConcurrentMarkSweepGeneration* gen, 4739 ScanMarkedObjectsAgainCarefullyClosure* cl) { 4740 verify_work_stacks_empty(); 4741 verify_overflow_empty(); 4742 4743 // strategy: starting with the first card, accumulate contiguous 4744 // ranges of dirty cards; clear these cards, then scan the region 4745 // covered by these cards. 4746 4747 // Since all of the MUT is committed ahead, we can just use 4748 // that, in case the generations expand while we are precleaning. 4749 // It might also be fine to just use the committed part of the 4750 // generation, but we might potentially miss cards when the 4751 // generation is rapidly expanding while we are in the midst 4752 // of precleaning. 4753 HeapWord* startAddr = gen->reserved().start(); 4754 HeapWord* endAddr = gen->reserved().end(); 4755 4756 cl->setFreelistLock(gen->freelistLock()); // needed for yielding 4757 4758 size_t numDirtyCards, cumNumDirtyCards; 4759 HeapWord *nextAddr, *lastAddr; 4760 for (cumNumDirtyCards = numDirtyCards = 0, 4761 nextAddr = lastAddr = startAddr; 4762 nextAddr < endAddr; 4763 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 4764 4765 ResourceMark rm; 4766 HandleMark hm; 4767 4768 MemRegion dirtyRegion; 4769 { 4770 stopTimer(); 4771 // Potential yield point 4772 CMSTokenSync ts(true); 4773 startTimer(); 4774 sample_eden(); 4775 // Get dirty region starting at nextOffset (inclusive), 4776 // simultaneously clearing it. 4777 dirtyRegion = 4778 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); 4779 assert(dirtyRegion.start() >= nextAddr, 4780 "returned region inconsistent?"); 4781 } 4782 // Remember where the next search should begin. 4783 // The returned region (if non-empty) is a right open interval, 4784 // so lastOffset is obtained from the right end of that 4785 // interval. 4786 lastAddr = dirtyRegion.end(); 4787 // Should do something more transparent and less hacky XXX 4788 numDirtyCards = 4789 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); 4790 4791 // We'll scan the cards in the dirty region (with periodic 4792 // yields for foreground GC as needed). 4793 if (!dirtyRegion.is_empty()) { 4794 assert(numDirtyCards > 0, "consistency check"); 4795 HeapWord* stop_point = NULL; 4796 stopTimer(); 4797 // Potential yield point 4798 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), 4799 bitMapLock()); 4800 startTimer(); 4801 { 4802 verify_work_stacks_empty(); 4803 verify_overflow_empty(); 4804 sample_eden(); 4805 stop_point = 4806 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 4807 } 4808 if (stop_point != NULL) { 4809 // The careful iteration stopped early either because it found an 4810 // uninitialized object, or because we were in the midst of an 4811 // "abortable preclean", which should now be aborted. Redirty 4812 // the bits corresponding to the partially-scanned or unscanned 4813 // cards. We'll either restart at the next block boundary or 4814 // abort the preclean. 4815 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 4816 "Should only be AbortablePreclean."); 4817 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); 4818 if (should_abort_preclean()) { 4819 break; // out of preclean loop 4820 } else { 4821 // Compute the next address at which preclean should pick up; 4822 // might need bitMapLock in order to read P-bits. 4823 lastAddr = next_card_start_after_block(stop_point); 4824 } 4825 } 4826 } else { 4827 assert(lastAddr == endAddr, "consistency check"); 4828 assert(numDirtyCards == 0, "consistency check"); 4829 break; 4830 } 4831 } 4832 verify_work_stacks_empty(); 4833 verify_overflow_empty(); 4834 return cumNumDirtyCards; 4835 } 4836 4837 // NOTE: preclean_mod_union_table() above and preclean_card_table() 4838 // below are largely identical; if you need to modify 4839 // one of these methods, please check the other method too. 4840 4841 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen, 4842 ScanMarkedObjectsAgainCarefullyClosure* cl) { 4843 // strategy: it's similar to precleamModUnionTable above, in that 4844 // we accumulate contiguous ranges of dirty cards, mark these cards 4845 // precleaned, then scan the region covered by these cards. 4846 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high()); 4847 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low()); 4848 4849 cl->setFreelistLock(gen->freelistLock()); // needed for yielding 4850 4851 size_t numDirtyCards, cumNumDirtyCards; 4852 HeapWord *lastAddr, *nextAddr; 4853 4854 for (cumNumDirtyCards = numDirtyCards = 0, 4855 nextAddr = lastAddr = startAddr; 4856 nextAddr < endAddr; 4857 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { 4858 4859 ResourceMark rm; 4860 HandleMark hm; 4861 4862 MemRegion dirtyRegion; 4863 { 4864 // See comments in "Precleaning notes" above on why we 4865 // do this locking. XXX Could the locking overheads be 4866 // too high when dirty cards are sparse? [I don't think so.] 4867 stopTimer(); 4868 CMSTokenSync x(true); // is cms thread 4869 startTimer(); 4870 sample_eden(); 4871 // Get and clear dirty region from card table 4872 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset( 4873 MemRegion(nextAddr, endAddr), 4874 true, 4875 CardTableModRefBS::precleaned_card_val()); 4876 4877 assert(dirtyRegion.start() >= nextAddr, 4878 "returned region inconsistent?"); 4879 } 4880 lastAddr = dirtyRegion.end(); 4881 numDirtyCards = 4882 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words; 4883 4884 if (!dirtyRegion.is_empty()) { 4885 stopTimer(); 4886 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock()); 4887 startTimer(); 4888 sample_eden(); 4889 verify_work_stacks_empty(); 4890 verify_overflow_empty(); 4891 HeapWord* stop_point = 4892 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); 4893 if (stop_point != NULL) { 4894 assert((_collectorState == AbortablePreclean && should_abort_preclean()), 4895 "Should only be AbortablePreclean."); 4896 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end())); 4897 if (should_abort_preclean()) { 4898 break; // out of preclean loop 4899 } else { 4900 // Compute the next address at which preclean should pick up. 4901 lastAddr = next_card_start_after_block(stop_point); 4902 } 4903 } 4904 } else { 4905 break; 4906 } 4907 } 4908 verify_work_stacks_empty(); 4909 verify_overflow_empty(); 4910 return cumNumDirtyCards; 4911 } 4912 4913 class PrecleanKlassClosure : public KlassClosure { 4914 CMKlassClosure _cm_klass_closure; 4915 public: 4916 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} 4917 void do_klass(Klass* k) { 4918 if (k->has_accumulated_modified_oops()) { 4919 k->clear_accumulated_modified_oops(); 4920 4921 _cm_klass_closure.do_klass(k); 4922 } 4923 } 4924 }; 4925 4926 // The freelist lock is needed to prevent asserts, is it really needed? 4927 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) { 4928 4929 cl->set_freelistLock(freelistLock); 4930 4931 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock()); 4932 4933 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean? 4934 // SSS: We should probably check if precleaning should be aborted, at suitable intervals? 4935 PrecleanKlassClosure preclean_klass_closure(cl); 4936 ClassLoaderDataGraph::classes_do(&preclean_klass_closure); 4937 4938 verify_work_stacks_empty(); 4939 verify_overflow_empty(); 4940 } 4941 4942 void CMSCollector::checkpointRootsFinal(bool asynch, 4943 bool clear_all_soft_refs, bool init_mark_was_synchronous) { 4944 assert(_collectorState == FinalMarking, "incorrect state transition?"); 4945 check_correct_thread_executing(); 4946 // world is stopped at this checkpoint 4947 assert(SafepointSynchronize::is_at_safepoint(), 4948 "world should be stopped"); 4949 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 4950 4951 verify_work_stacks_empty(); 4952 verify_overflow_empty(); 4953 4954 SpecializationStats::clear(); 4955 if (PrintGCDetails) { 4956 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]", 4957 _young_gen->used() / K, 4958 _young_gen->capacity() / K); 4959 } 4960 if (asynch) { 4961 if (CMSScavengeBeforeRemark) { 4962 GenCollectedHeap* gch = GenCollectedHeap::heap(); 4963 // Temporarily set flag to false, GCH->do_collection will 4964 // expect it to be false and set to true 4965 FlagSetting fl(gch->_is_gc_active, false); 4966 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark", 4967 PrintGCDetails && Verbose, true, _gc_timer_cm);) 4968 int level = _cmsGen->level() - 1; 4969 if (level >= 0) { 4970 gch->do_collection(true, // full (i.e. force, see below) 4971 false, // !clear_all_soft_refs 4972 0, // size 4973 false, // is_tlab 4974 level // max_level 4975 ); 4976 } 4977 } 4978 FreelistLocker x(this); 4979 MutexLockerEx y(bitMapLock(), 4980 Mutex::_no_safepoint_check_flag); 4981 assert(!init_mark_was_synchronous, "but that's impossible!"); 4982 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false); 4983 } else { 4984 // already have all the locks 4985 checkpointRootsFinalWork(asynch, clear_all_soft_refs, 4986 init_mark_was_synchronous); 4987 } 4988 verify_work_stacks_empty(); 4989 verify_overflow_empty(); 4990 SpecializationStats::print(); 4991 } 4992 4993 void CMSCollector::checkpointRootsFinalWork(bool asynch, 4994 bool clear_all_soft_refs, bool init_mark_was_synchronous) { 4995 4996 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);) 4997 4998 assert(haveFreelistLocks(), "must have free list locks"); 4999 assert_lock_strong(bitMapLock()); 5000 5001 if (UseAdaptiveSizePolicy) { 5002 size_policy()->checkpoint_roots_final_begin(); 5003 } 5004 5005 ResourceMark rm; 5006 HandleMark hm; 5007 5008 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5009 5010 if (should_unload_classes()) { 5011 CodeCache::gc_prologue(); 5012 } 5013 assert(haveFreelistLocks(), "must have free list locks"); 5014 assert_lock_strong(bitMapLock()); 5015 5016 if (!init_mark_was_synchronous) { 5017 // We might assume that we need not fill TLAB's when 5018 // CMSScavengeBeforeRemark is set, because we may have just done 5019 // a scavenge which would have filled all TLAB's -- and besides 5020 // Eden would be empty. This however may not always be the case -- 5021 // for instance although we asked for a scavenge, it may not have 5022 // happened because of a JNI critical section. We probably need 5023 // a policy for deciding whether we can in that case wait until 5024 // the critical section releases and then do the remark following 5025 // the scavenge, and skip it here. In the absence of that policy, 5026 // or of an indication of whether the scavenge did indeed occur, 5027 // we cannot rely on TLAB's having been filled and must do 5028 // so here just in case a scavenge did not happen. 5029 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them 5030 // Update the saved marks which may affect the root scans. 5031 gch->save_marks(); 5032 5033 { 5034 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) 5035 5036 // Note on the role of the mod union table: 5037 // Since the marker in "markFromRoots" marks concurrently with 5038 // mutators, it is possible for some reachable objects not to have been 5039 // scanned. For instance, an only reference to an object A was 5040 // placed in object B after the marker scanned B. Unless B is rescanned, 5041 // A would be collected. Such updates to references in marked objects 5042 // are detected via the mod union table which is the set of all cards 5043 // dirtied since the first checkpoint in this GC cycle and prior to 5044 // the most recent young generation GC, minus those cleaned up by the 5045 // concurrent precleaning. 5046 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) { 5047 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm); 5048 do_remark_parallel(); 5049 } else { 5050 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, 5051 _gc_timer_cm); 5052 do_remark_non_parallel(); 5053 } 5054 } 5055 } else { 5056 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode"); 5057 // The initial mark was stop-world, so there's no rescanning to 5058 // do; go straight on to the next step below. 5059 } 5060 verify_work_stacks_empty(); 5061 verify_overflow_empty(); 5062 5063 { 5064 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);) 5065 refProcessingWork(asynch, clear_all_soft_refs); 5066 } 5067 verify_work_stacks_empty(); 5068 verify_overflow_empty(); 5069 5070 if (should_unload_classes()) { 5071 CodeCache::gc_epilogue(); 5072 } 5073 JvmtiExport::gc_epilogue(); 5074 5075 // If we encountered any (marking stack / work queue) overflow 5076 // events during the current CMS cycle, take appropriate 5077 // remedial measures, where possible, so as to try and avoid 5078 // recurrence of that condition. 5079 assert(_markStack.isEmpty(), "No grey objects"); 5080 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + 5081 _ser_kac_ovflw + _ser_kac_preclean_ovflw; 5082 if (ser_ovflw > 0) { 5083 if (PrintCMSStatistics != 0) { 5084 gclog_or_tty->print_cr("Marking stack overflow (benign) " 5085 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT 5086 ", kac_preclean="SIZE_FORMAT")", 5087 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, 5088 _ser_kac_ovflw, _ser_kac_preclean_ovflw); 5089 } 5090 _markStack.expand(); 5091 _ser_pmc_remark_ovflw = 0; 5092 _ser_pmc_preclean_ovflw = 0; 5093 _ser_kac_preclean_ovflw = 0; 5094 _ser_kac_ovflw = 0; 5095 } 5096 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { 5097 if (PrintCMSStatistics != 0) { 5098 gclog_or_tty->print_cr("Work queue overflow (benign) " 5099 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")", 5100 _par_pmc_remark_ovflw, _par_kac_ovflw); 5101 } 5102 _par_pmc_remark_ovflw = 0; 5103 _par_kac_ovflw = 0; 5104 } 5105 if (PrintCMSStatistics != 0) { 5106 if (_markStack._hit_limit > 0) { 5107 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")", 5108 _markStack._hit_limit); 5109 } 5110 if (_markStack._failed_double > 0) { 5111 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT")," 5112 " current capacity "SIZE_FORMAT, 5113 _markStack._failed_double, 5114 _markStack.capacity()); 5115 } 5116 } 5117 _markStack._hit_limit = 0; 5118 _markStack._failed_double = 0; 5119 5120 if ((VerifyAfterGC || VerifyDuringGC) && 5121 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 5122 verify_after_remark(); 5123 } 5124 5125 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure); 5126 5127 // Change under the freelistLocks. 5128 _collectorState = Sweeping; 5129 // Call isAllClear() under bitMapLock 5130 assert(_modUnionTable.isAllClear(), 5131 "Should be clear by end of the final marking"); 5132 assert(_ct->klass_rem_set()->mod_union_is_clear(), 5133 "Should be clear by end of the final marking"); 5134 if (UseAdaptiveSizePolicy) { 5135 size_policy()->checkpoint_roots_final_end(gch->gc_cause()); 5136 } 5137 } 5138 5139 // Parallel remark task 5140 class CMSParRemarkTask: public AbstractGangTask { 5141 CMSCollector* _collector; 5142 int _n_workers; 5143 CompactibleFreeListSpace* _cms_space; 5144 5145 // The per-thread work queues, available here for stealing. 5146 OopTaskQueueSet* _task_queues; 5147 ParallelTaskTerminator _term; 5148 5149 public: 5150 // A value of 0 passed to n_workers will cause the number of 5151 // workers to be taken from the active workers in the work gang. 5152 CMSParRemarkTask(CMSCollector* collector, 5153 CompactibleFreeListSpace* cms_space, 5154 int n_workers, FlexibleWorkGang* workers, 5155 OopTaskQueueSet* task_queues): 5156 AbstractGangTask("Rescan roots and grey objects in parallel"), 5157 _collector(collector), 5158 _cms_space(cms_space), 5159 _n_workers(n_workers), 5160 _task_queues(task_queues), 5161 _term(n_workers, task_queues) { } 5162 5163 OopTaskQueueSet* task_queues() { return _task_queues; } 5164 5165 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 5166 5167 ParallelTaskTerminator* terminator() { return &_term; } 5168 int n_workers() { return _n_workers; } 5169 5170 void work(uint worker_id); 5171 5172 private: 5173 // Work method in support of parallel rescan ... of young gen spaces 5174 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl, 5175 ContiguousSpace* space, 5176 HeapWord** chunk_array, size_t chunk_top); 5177 5178 // ... of dirty cards in old space 5179 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, 5180 Par_MarkRefsIntoAndScanClosure* cl); 5181 5182 // ... work stealing for the above 5183 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed); 5184 }; 5185 5186 class RemarkKlassClosure : public KlassClosure { 5187 CMKlassClosure _cm_klass_closure; 5188 public: 5189 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {} 5190 void do_klass(Klass* k) { 5191 // Check if we have modified any oops in the Klass during the concurrent marking. 5192 if (k->has_accumulated_modified_oops()) { 5193 k->clear_accumulated_modified_oops(); 5194 5195 // We could have transfered the current modified marks to the accumulated marks, 5196 // like we do with the Card Table to Mod Union Table. But it's not really necessary. 5197 } else if (k->has_modified_oops()) { 5198 // Don't clear anything, this info is needed by the next young collection. 5199 } else { 5200 // No modified oops in the Klass. 5201 return; 5202 } 5203 5204 // The klass has modified fields, need to scan the klass. 5205 _cm_klass_closure.do_klass(k); 5206 } 5207 }; 5208 5209 // work_queue(i) is passed to the closure 5210 // Par_MarkRefsIntoAndScanClosure. The "i" parameter 5211 // also is passed to do_dirty_card_rescan_tasks() and to 5212 // do_work_steal() to select the i-th task_queue. 5213 5214 void CMSParRemarkTask::work(uint worker_id) { 5215 elapsedTimer _timer; 5216 ResourceMark rm; 5217 HandleMark hm; 5218 5219 // ---------- rescan from roots -------------- 5220 _timer.start(); 5221 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5222 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector, 5223 _collector->_span, _collector->ref_processor(), 5224 &(_collector->_markBitMap), 5225 work_queue(worker_id)); 5226 5227 // Rescan young gen roots first since these are likely 5228 // coarsely partitioned and may, on that account, constitute 5229 // the critical path; thus, it's best to start off that 5230 // work first. 5231 // ---------- young gen roots -------------- 5232 { 5233 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration(); 5234 EdenSpace* eden_space = dng->eden(); 5235 ContiguousSpace* from_space = dng->from(); 5236 ContiguousSpace* to_space = dng->to(); 5237 5238 HeapWord** eca = _collector->_eden_chunk_array; 5239 size_t ect = _collector->_eden_chunk_index; 5240 HeapWord** sca = _collector->_survivor_chunk_array; 5241 size_t sct = _collector->_survivor_chunk_index; 5242 5243 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); 5244 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); 5245 5246 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0); 5247 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct); 5248 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect); 5249 5250 _timer.stop(); 5251 if (PrintCMSStatistics != 0) { 5252 gclog_or_tty->print_cr( 5253 "Finished young gen rescan work in %dth thread: %3.3f sec", 5254 worker_id, _timer.seconds()); 5255 } 5256 } 5257 5258 // ---------- remaining roots -------------- 5259 _timer.reset(); 5260 _timer.start(); 5261 gch->gen_process_strong_roots(_collector->_cmsGen->level(), 5262 false, // yg was scanned above 5263 false, // this is parallel code 5264 false, // not scavenging 5265 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), 5266 &par_mrias_cl, 5267 true, // walk all of code cache if (so & SO_CodeCache) 5268 NULL, 5269 NULL); // The dirty klasses will be handled below 5270 assert(_collector->should_unload_classes() 5271 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache), 5272 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 5273 _timer.stop(); 5274 if (PrintCMSStatistics != 0) { 5275 gclog_or_tty->print_cr( 5276 "Finished remaining root rescan work in %dth thread: %3.3f sec", 5277 worker_id, _timer.seconds()); 5278 } 5279 5280 // ---------- unhandled CLD scanning ---------- 5281 if (worker_id == 0) { // Single threaded at the moment. 5282 _timer.reset(); 5283 _timer.start(); 5284 5285 // Scan all new class loader data objects and new dependencies that were 5286 // introduced during concurrent marking. 5287 ResourceMark rm; 5288 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 5289 for (int i = 0; i < array->length(); i++) { 5290 par_mrias_cl.do_class_loader_data(array->at(i)); 5291 } 5292 5293 // We don't need to keep track of new CLDs anymore. 5294 ClassLoaderDataGraph::remember_new_clds(false); 5295 5296 _timer.stop(); 5297 if (PrintCMSStatistics != 0) { 5298 gclog_or_tty->print_cr( 5299 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec", 5300 worker_id, _timer.seconds()); 5301 } 5302 } 5303 5304 // ---------- dirty klass scanning ---------- 5305 if (worker_id == 0) { // Single threaded at the moment. 5306 _timer.reset(); 5307 _timer.start(); 5308 5309 // Scan all classes that was dirtied during the concurrent marking phase. 5310 RemarkKlassClosure remark_klass_closure(&par_mrias_cl); 5311 ClassLoaderDataGraph::classes_do(&remark_klass_closure); 5312 5313 _timer.stop(); 5314 if (PrintCMSStatistics != 0) { 5315 gclog_or_tty->print_cr( 5316 "Finished dirty klass scanning work in %dth thread: %3.3f sec", 5317 worker_id, _timer.seconds()); 5318 } 5319 } 5320 5321 // We might have added oops to ClassLoaderData::_handles during the 5322 // concurrent marking phase. These oops point to newly allocated objects 5323 // that are guaranteed to be kept alive. Either by the direct allocation 5324 // code, or when the young collector processes the strong roots. Hence, 5325 // we don't have to revisit the _handles block during the remark phase. 5326 5327 // ---------- rescan dirty cards ------------ 5328 _timer.reset(); 5329 _timer.start(); 5330 5331 // Do the rescan tasks for each of the two spaces 5332 // (cms_space) in turn. 5333 // "worker_id" is passed to select the task_queue for "worker_id" 5334 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl); 5335 _timer.stop(); 5336 if (PrintCMSStatistics != 0) { 5337 gclog_or_tty->print_cr( 5338 "Finished dirty card rescan work in %dth thread: %3.3f sec", 5339 worker_id, _timer.seconds()); 5340 } 5341 5342 // ---------- steal work from other threads ... 5343 // ---------- ... and drain overflow list. 5344 _timer.reset(); 5345 _timer.start(); 5346 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id)); 5347 _timer.stop(); 5348 if (PrintCMSStatistics != 0) { 5349 gclog_or_tty->print_cr( 5350 "Finished work stealing in %dth thread: %3.3f sec", 5351 worker_id, _timer.seconds()); 5352 } 5353 } 5354 5355 // Note that parameter "i" is not used. 5356 void 5357 CMSParRemarkTask::do_young_space_rescan(int i, 5358 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space, 5359 HeapWord** chunk_array, size_t chunk_top) { 5360 // Until all tasks completed: 5361 // . claim an unclaimed task 5362 // . compute region boundaries corresponding to task claimed 5363 // using chunk_array 5364 // . par_oop_iterate(cl) over that region 5365 5366 ResourceMark rm; 5367 HandleMark hm; 5368 5369 SequentialSubTasksDone* pst = space->par_seq_tasks(); 5370 assert(pst->valid(), "Uninitialized use?"); 5371 5372 uint nth_task = 0; 5373 uint n_tasks = pst->n_tasks(); 5374 5375 HeapWord *start, *end; 5376 while (!pst->is_task_claimed(/* reference */ nth_task)) { 5377 // We claimed task # nth_task; compute its boundaries. 5378 if (chunk_top == 0) { // no samples were taken 5379 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task"); 5380 start = space->bottom(); 5381 end = space->top(); 5382 } else if (nth_task == 0) { 5383 start = space->bottom(); 5384 end = chunk_array[nth_task]; 5385 } else if (nth_task < (uint)chunk_top) { 5386 assert(nth_task >= 1, "Control point invariant"); 5387 start = chunk_array[nth_task - 1]; 5388 end = chunk_array[nth_task]; 5389 } else { 5390 assert(nth_task == (uint)chunk_top, "Control point invariant"); 5391 start = chunk_array[chunk_top - 1]; 5392 end = space->top(); 5393 } 5394 MemRegion mr(start, end); 5395 // Verify that mr is in space 5396 assert(mr.is_empty() || space->used_region().contains(mr), 5397 "Should be in space"); 5398 // Verify that "start" is an object boundary 5399 assert(mr.is_empty() || oop(mr.start())->is_oop(), 5400 "Should be an oop"); 5401 space->par_oop_iterate(mr, cl); 5402 } 5403 pst->all_tasks_completed(); 5404 } 5405 5406 void 5407 CMSParRemarkTask::do_dirty_card_rescan_tasks( 5408 CompactibleFreeListSpace* sp, int i, 5409 Par_MarkRefsIntoAndScanClosure* cl) { 5410 // Until all tasks completed: 5411 // . claim an unclaimed task 5412 // . compute region boundaries corresponding to task claimed 5413 // . transfer dirty bits ct->mut for that region 5414 // . apply rescanclosure to dirty mut bits for that region 5415 5416 ResourceMark rm; 5417 HandleMark hm; 5418 5419 OopTaskQueue* work_q = work_queue(i); 5420 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); 5421 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! 5422 // CAUTION: This closure has state that persists across calls to 5423 // the work method dirty_range_iterate_clear() in that it has 5424 // imbedded in it a (subtype of) UpwardsObjectClosure. The 5425 // use of that state in the imbedded UpwardsObjectClosure instance 5426 // assumes that the cards are always iterated (even if in parallel 5427 // by several threads) in monotonically increasing order per each 5428 // thread. This is true of the implementation below which picks 5429 // card ranges (chunks) in monotonically increasing order globally 5430 // and, a-fortiori, in monotonically increasing order per thread 5431 // (the latter order being a subsequence of the former). 5432 // If the work code below is ever reorganized into a more chaotic 5433 // work-partitioning form than the current "sequential tasks" 5434 // paradigm, the use of that persistent state will have to be 5435 // revisited and modified appropriately. See also related 5436 // bug 4756801 work on which should examine this code to make 5437 // sure that the changes there do not run counter to the 5438 // assumptions made here and necessary for correctness and 5439 // efficiency. Note also that this code might yield inefficient 5440 // behaviour in the case of very large objects that span one or 5441 // more work chunks. Such objects would potentially be scanned 5442 // several times redundantly. Work on 4756801 should try and 5443 // address that performance anomaly if at all possible. XXX 5444 MemRegion full_span = _collector->_span; 5445 CMSBitMap* bm = &(_collector->_markBitMap); // shared 5446 MarkFromDirtyCardsClosure 5447 greyRescanClosure(_collector, full_span, // entire span of interest 5448 sp, bm, work_q, cl); 5449 5450 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); 5451 assert(pst->valid(), "Uninitialized use?"); 5452 uint nth_task = 0; 5453 const int alignment = CardTableModRefBS::card_size * BitsPerWord; 5454 MemRegion span = sp->used_region(); 5455 HeapWord* start_addr = span.start(); 5456 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(), 5457 alignment); 5458 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units 5459 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) == 5460 start_addr, "Check alignment"); 5461 assert((size_t)round_to((intptr_t)chunk_size, alignment) == 5462 chunk_size, "Check alignment"); 5463 5464 while (!pst->is_task_claimed(/* reference */ nth_task)) { 5465 // Having claimed the nth_task, compute corresponding mem-region, 5466 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary). 5467 // The alignment restriction ensures that we do not need any 5468 // synchronization with other gang-workers while setting or 5469 // clearing bits in thus chunk of the MUT. 5470 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, 5471 start_addr + (nth_task+1)*chunk_size); 5472 // The last chunk's end might be way beyond end of the 5473 // used region. In that case pull back appropriately. 5474 if (this_span.end() > end_addr) { 5475 this_span.set_end(end_addr); 5476 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); 5477 } 5478 // Iterate over the dirty cards covering this chunk, marking them 5479 // precleaned, and setting the corresponding bits in the mod union 5480 // table. Since we have been careful to partition at Card and MUT-word 5481 // boundaries no synchronization is needed between parallel threads. 5482 _collector->_ct->ct_bs()->dirty_card_iterate(this_span, 5483 &modUnionClosure); 5484 5485 // Having transferred these marks into the modUnionTable, 5486 // rescan the marked objects on the dirty cards in the modUnionTable. 5487 // Even if this is at a synchronous collection, the initial marking 5488 // may have been done during an asynchronous collection so there 5489 // may be dirty bits in the mod-union table. 5490 _collector->_modUnionTable.dirty_range_iterate_clear( 5491 this_span, &greyRescanClosure); 5492 _collector->_modUnionTable.verifyNoOneBitsInRange( 5493 this_span.start(), 5494 this_span.end()); 5495 } 5496 pst->all_tasks_completed(); // declare that i am done 5497 } 5498 5499 // . see if we can share work_queues with ParNew? XXX 5500 void 5501 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, 5502 int* seed) { 5503 OopTaskQueue* work_q = work_queue(i); 5504 NOT_PRODUCT(int num_steals = 0;) 5505 oop obj_to_scan; 5506 CMSBitMap* bm = &(_collector->_markBitMap); 5507 5508 while (true) { 5509 // Completely finish any left over work from (an) earlier round(s) 5510 cl->trim_queue(0); 5511 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 5512 (size_t)ParGCDesiredObjsFromOverflowList); 5513 // Now check if there's any work in the overflow list 5514 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 5515 // only affects the number of attempts made to get work from the 5516 // overflow list and does not affect the number of workers. Just 5517 // pass ParallelGCThreads so this behavior is unchanged. 5518 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 5519 work_q, 5520 ParallelGCThreads)) { 5521 // found something in global overflow list; 5522 // not yet ready to go stealing work from others. 5523 // We'd like to assert(work_q->size() != 0, ...) 5524 // because we just took work from the overflow list, 5525 // but of course we can't since all of that could have 5526 // been already stolen from us. 5527 // "He giveth and He taketh away." 5528 continue; 5529 } 5530 // Verify that we have no work before we resort to stealing 5531 assert(work_q->size() == 0, "Have work, shouldn't steal"); 5532 // Try to steal from other queues that have work 5533 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 5534 NOT_PRODUCT(num_steals++;) 5535 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); 5536 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 5537 // Do scanning work 5538 obj_to_scan->oop_iterate(cl); 5539 // Loop around, finish this work, and try to steal some more 5540 } else if (terminator()->offer_termination()) { 5541 break; // nirvana from the infinite cycle 5542 } 5543 } 5544 NOT_PRODUCT( 5545 if (PrintCMSStatistics != 0) { 5546 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); 5547 } 5548 ) 5549 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), 5550 "Else our work is not yet done"); 5551 } 5552 5553 // Return a thread-local PLAB recording array, as appropriate. 5554 void* CMSCollector::get_data_recorder(int thr_num) { 5555 if (_survivor_plab_array != NULL && 5556 (CMSPLABRecordAlways || 5557 (_collectorState > Marking && _collectorState < FinalMarking))) { 5558 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); 5559 ChunkArray* ca = &_survivor_plab_array[thr_num]; 5560 ca->reset(); // clear it so that fresh data is recorded 5561 return (void*) ca; 5562 } else { 5563 return NULL; 5564 } 5565 } 5566 5567 // Reset all the thread-local PLAB recording arrays 5568 void CMSCollector::reset_survivor_plab_arrays() { 5569 for (uint i = 0; i < ParallelGCThreads; i++) { 5570 _survivor_plab_array[i].reset(); 5571 } 5572 } 5573 5574 // Merge the per-thread plab arrays into the global survivor chunk 5575 // array which will provide the partitioning of the survivor space 5576 // for CMS rescan. 5577 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv, 5578 int no_of_gc_threads) { 5579 assert(_survivor_plab_array != NULL, "Error"); 5580 assert(_survivor_chunk_array != NULL, "Error"); 5581 assert(_collectorState == FinalMarking, "Error"); 5582 for (int j = 0; j < no_of_gc_threads; j++) { 5583 _cursor[j] = 0; 5584 } 5585 HeapWord* top = surv->top(); 5586 size_t i; 5587 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries 5588 HeapWord* min_val = top; // Higher than any PLAB address 5589 uint min_tid = 0; // position of min_val this round 5590 for (int j = 0; j < no_of_gc_threads; j++) { 5591 ChunkArray* cur_sca = &_survivor_plab_array[j]; 5592 if (_cursor[j] == cur_sca->end()) { 5593 continue; 5594 } 5595 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); 5596 HeapWord* cur_val = cur_sca->nth(_cursor[j]); 5597 assert(surv->used_region().contains(cur_val), "Out of bounds value"); 5598 if (cur_val < min_val) { 5599 min_tid = j; 5600 min_val = cur_val; 5601 } else { 5602 assert(cur_val < top, "All recorded addresses should be less"); 5603 } 5604 } 5605 // At this point min_val and min_tid are respectively 5606 // the least address in _survivor_plab_array[j]->nth(_cursor[j]) 5607 // and the thread (j) that witnesses that address. 5608 // We record this address in the _survivor_chunk_array[i] 5609 // and increment _cursor[min_tid] prior to the next round i. 5610 if (min_val == top) { 5611 break; 5612 } 5613 _survivor_chunk_array[i] = min_val; 5614 _cursor[min_tid]++; 5615 } 5616 // We are all done; record the size of the _survivor_chunk_array 5617 _survivor_chunk_index = i; // exclusive: [0, i) 5618 if (PrintCMSStatistics > 0) { 5619 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i); 5620 } 5621 // Verify that we used up all the recorded entries 5622 #ifdef ASSERT 5623 size_t total = 0; 5624 for (int j = 0; j < no_of_gc_threads; j++) { 5625 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); 5626 total += _cursor[j]; 5627 } 5628 assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); 5629 // Check that the merged array is in sorted order 5630 if (total > 0) { 5631 for (size_t i = 0; i < total - 1; i++) { 5632 if (PrintCMSStatistics > 0) { 5633 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", 5634 i, _survivor_chunk_array[i]); 5635 } 5636 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], 5637 "Not sorted"); 5638 } 5639 } 5640 #endif // ASSERT 5641 } 5642 5643 // Set up the space's par_seq_tasks structure for work claiming 5644 // for parallel rescan of young gen. 5645 // See ParRescanTask where this is currently used. 5646 void 5647 CMSCollector:: 5648 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { 5649 assert(n_threads > 0, "Unexpected n_threads argument"); 5650 DefNewGeneration* dng = (DefNewGeneration*)_young_gen; 5651 5652 // Eden space 5653 { 5654 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks(); 5655 assert(!pst->valid(), "Clobbering existing data?"); 5656 // Each valid entry in [0, _eden_chunk_index) represents a task. 5657 size_t n_tasks = _eden_chunk_index + 1; 5658 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); 5659 // Sets the condition for completion of the subtask (how many threads 5660 // need to finish in order to be done). 5661 pst->set_n_threads(n_threads); 5662 pst->set_n_tasks((int)n_tasks); 5663 } 5664 5665 // Merge the survivor plab arrays into _survivor_chunk_array 5666 if (_survivor_plab_array != NULL) { 5667 merge_survivor_plab_arrays(dng->from(), n_threads); 5668 } else { 5669 assert(_survivor_chunk_index == 0, "Error"); 5670 } 5671 5672 // To space 5673 { 5674 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks(); 5675 assert(!pst->valid(), "Clobbering existing data?"); 5676 // Sets the condition for completion of the subtask (how many threads 5677 // need to finish in order to be done). 5678 pst->set_n_threads(n_threads); 5679 pst->set_n_tasks(1); 5680 assert(pst->valid(), "Error"); 5681 } 5682 5683 // From space 5684 { 5685 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks(); 5686 assert(!pst->valid(), "Clobbering existing data?"); 5687 size_t n_tasks = _survivor_chunk_index + 1; 5688 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); 5689 // Sets the condition for completion of the subtask (how many threads 5690 // need to finish in order to be done). 5691 pst->set_n_threads(n_threads); 5692 pst->set_n_tasks((int)n_tasks); 5693 assert(pst->valid(), "Error"); 5694 } 5695 } 5696 5697 // Parallel version of remark 5698 void CMSCollector::do_remark_parallel() { 5699 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5700 FlexibleWorkGang* workers = gch->workers(); 5701 assert(workers != NULL, "Need parallel worker threads."); 5702 // Choose to use the number of GC workers most recently set 5703 // into "active_workers". If active_workers is not set, set it 5704 // to ParallelGCThreads. 5705 int n_workers = workers->active_workers(); 5706 if (n_workers == 0) { 5707 assert(n_workers > 0, "Should have been set during scavenge"); 5708 n_workers = ParallelGCThreads; 5709 workers->set_active_workers(n_workers); 5710 } 5711 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); 5712 5713 CMSParRemarkTask tsk(this, 5714 cms_space, 5715 n_workers, workers, task_queues()); 5716 5717 // Set up for parallel process_strong_roots work. 5718 gch->set_par_threads(n_workers); 5719 // We won't be iterating over the cards in the card table updating 5720 // the younger_gen cards, so we shouldn't call the following else 5721 // the verification code as well as subsequent younger_refs_iterate 5722 // code would get confused. XXX 5723 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel 5724 5725 // The young gen rescan work will not be done as part of 5726 // process_strong_roots (which currently doesn't knw how to 5727 // parallelize such a scan), but rather will be broken up into 5728 // a set of parallel tasks (via the sampling that the [abortable] 5729 // preclean phase did of EdenSpace, plus the [two] tasks of 5730 // scanning the [two] survivor spaces. Further fine-grain 5731 // parallelization of the scanning of the survivor spaces 5732 // themselves, and of precleaning of the younger gen itself 5733 // is deferred to the future. 5734 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); 5735 5736 // The dirty card rescan work is broken up into a "sequence" 5737 // of parallel tasks (per constituent space) that are dynamically 5738 // claimed by the parallel threads. 5739 cms_space->initialize_sequential_subtasks_for_rescan(n_workers); 5740 5741 // It turns out that even when we're using 1 thread, doing the work in a 5742 // separate thread causes wide variance in run times. We can't help this 5743 // in the multi-threaded case, but we special-case n=1 here to get 5744 // repeatable measurements of the 1-thread overhead of the parallel code. 5745 if (n_workers > 1) { 5746 // Make refs discovery MT-safe, if it isn't already: it may not 5747 // necessarily be so, since it's possible that we are doing 5748 // ST marking. 5749 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true); 5750 GenCollectedHeap::StrongRootsScope srs(gch); 5751 workers->run_task(&tsk); 5752 } else { 5753 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 5754 GenCollectedHeap::StrongRootsScope srs(gch); 5755 tsk.work(0); 5756 } 5757 5758 gch->set_par_threads(0); // 0 ==> non-parallel. 5759 // restore, single-threaded for now, any preserved marks 5760 // as a result of work_q overflow 5761 restore_preserved_marks_if_any(); 5762 } 5763 5764 // Non-parallel version of remark 5765 void CMSCollector::do_remark_non_parallel() { 5766 ResourceMark rm; 5767 HandleMark hm; 5768 GenCollectedHeap* gch = GenCollectedHeap::heap(); 5769 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false); 5770 5771 MarkRefsIntoAndScanClosure 5772 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */, 5773 &_markStack, this, 5774 false /* should_yield */, false /* not precleaning */); 5775 MarkFromDirtyCardsClosure 5776 markFromDirtyCardsClosure(this, _span, 5777 NULL, // space is set further below 5778 &_markBitMap, &_markStack, &mrias_cl); 5779 { 5780 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm); 5781 // Iterate over the dirty cards, setting the corresponding bits in the 5782 // mod union table. 5783 { 5784 ModUnionClosure modUnionClosure(&_modUnionTable); 5785 _ct->ct_bs()->dirty_card_iterate( 5786 _cmsGen->used_region(), 5787 &modUnionClosure); 5788 } 5789 // Having transferred these marks into the modUnionTable, we just need 5790 // to rescan the marked objects on the dirty cards in the modUnionTable. 5791 // The initial marking may have been done during an asynchronous 5792 // collection so there may be dirty bits in the mod-union table. 5793 const int alignment = 5794 CardTableModRefBS::card_size * BitsPerWord; 5795 { 5796 // ... First handle dirty cards in CMS gen 5797 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); 5798 MemRegion ur = _cmsGen->used_region(); 5799 HeapWord* lb = ur.start(); 5800 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); 5801 MemRegion cms_span(lb, ub); 5802 _modUnionTable.dirty_range_iterate_clear(cms_span, 5803 &markFromDirtyCardsClosure); 5804 verify_work_stacks_empty(); 5805 if (PrintCMSStatistics != 0) { 5806 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ", 5807 markFromDirtyCardsClosure.num_dirty_cards()); 5808 } 5809 } 5810 } 5811 if (VerifyDuringGC && 5812 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { 5813 HandleMark hm; // Discard invalid handles created during verification 5814 Universe::verify(); 5815 } 5816 { 5817 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm); 5818 5819 verify_work_stacks_empty(); 5820 5821 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. 5822 GenCollectedHeap::StrongRootsScope srs(gch); 5823 gch->gen_process_strong_roots(_cmsGen->level(), 5824 true, // younger gens as roots 5825 false, // use the local StrongRootsScope 5826 false, // not scavenging 5827 SharedHeap::ScanningOption(roots_scanning_options()), 5828 &mrias_cl, 5829 true, // walk code active on stacks 5830 NULL, 5831 NULL); // The dirty klasses will be handled below 5832 5833 assert(should_unload_classes() 5834 || (roots_scanning_options() & SharedHeap::SO_CodeCache), 5835 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops"); 5836 } 5837 5838 { 5839 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm); 5840 5841 verify_work_stacks_empty(); 5842 5843 // Scan all class loader data objects that might have been introduced 5844 // during concurrent marking. 5845 ResourceMark rm; 5846 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds(); 5847 for (int i = 0; i < array->length(); i++) { 5848 mrias_cl.do_class_loader_data(array->at(i)); 5849 } 5850 5851 // We don't need to keep track of new CLDs anymore. 5852 ClassLoaderDataGraph::remember_new_clds(false); 5853 5854 verify_work_stacks_empty(); 5855 } 5856 5857 { 5858 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm); 5859 5860 verify_work_stacks_empty(); 5861 5862 RemarkKlassClosure remark_klass_closure(&mrias_cl); 5863 ClassLoaderDataGraph::classes_do(&remark_klass_closure); 5864 5865 verify_work_stacks_empty(); 5866 } 5867 5868 // We might have added oops to ClassLoaderData::_handles during the 5869 // concurrent marking phase. These oops point to newly allocated objects 5870 // that are guaranteed to be kept alive. Either by the direct allocation 5871 // code, or when the young collector processes the strong roots. Hence, 5872 // we don't have to revisit the _handles block during the remark phase. 5873 5874 verify_work_stacks_empty(); 5875 // Restore evacuated mark words, if any, used for overflow list links 5876 if (!CMSOverflowEarlyRestoration) { 5877 restore_preserved_marks_if_any(); 5878 } 5879 verify_overflow_empty(); 5880 } 5881 5882 //////////////////////////////////////////////////////// 5883 // Parallel Reference Processing Task Proxy Class 5884 //////////////////////////////////////////////////////// 5885 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues { 5886 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; 5887 CMSCollector* _collector; 5888 CMSBitMap* _mark_bit_map; 5889 const MemRegion _span; 5890 ProcessTask& _task; 5891 5892 public: 5893 CMSRefProcTaskProxy(ProcessTask& task, 5894 CMSCollector* collector, 5895 const MemRegion& span, 5896 CMSBitMap* mark_bit_map, 5897 AbstractWorkGang* workers, 5898 OopTaskQueueSet* task_queues): 5899 // XXX Should superclass AGTWOQ also know about AWG since it knows 5900 // about the task_queues used by the AWG? Then it could initialize 5901 // the terminator() object. See 6984287. The set_for_termination() 5902 // below is a temporary band-aid for the regression in 6984287. 5903 AbstractGangTaskWOopQueues("Process referents by policy in parallel", 5904 task_queues), 5905 _task(task), 5906 _collector(collector), _span(span), _mark_bit_map(mark_bit_map) 5907 { 5908 assert(_collector->_span.equals(_span) && !_span.is_empty(), 5909 "Inconsistency in _span"); 5910 set_for_termination(workers->active_workers()); 5911 } 5912 5913 OopTaskQueueSet* task_queues() { return queues(); } 5914 5915 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } 5916 5917 void do_work_steal(int i, 5918 CMSParDrainMarkingStackClosure* drain, 5919 CMSParKeepAliveClosure* keep_alive, 5920 int* seed); 5921 5922 virtual void work(uint worker_id); 5923 }; 5924 5925 void CMSRefProcTaskProxy::work(uint worker_id) { 5926 assert(_collector->_span.equals(_span), "Inconsistency in _span"); 5927 CMSParKeepAliveClosure par_keep_alive(_collector, _span, 5928 _mark_bit_map, 5929 work_queue(worker_id)); 5930 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, 5931 _mark_bit_map, 5932 work_queue(worker_id)); 5933 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map); 5934 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack); 5935 if (_task.marks_oops_alive()) { 5936 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive, 5937 _collector->hash_seed(worker_id)); 5938 } 5939 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty"); 5940 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); 5941 } 5942 5943 class CMSRefEnqueueTaskProxy: public AbstractGangTask { 5944 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; 5945 EnqueueTask& _task; 5946 5947 public: 5948 CMSRefEnqueueTaskProxy(EnqueueTask& task) 5949 : AbstractGangTask("Enqueue reference objects in parallel"), 5950 _task(task) 5951 { } 5952 5953 virtual void work(uint worker_id) 5954 { 5955 _task.work(worker_id); 5956 } 5957 }; 5958 5959 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, 5960 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): 5961 _span(span), 5962 _bit_map(bit_map), 5963 _work_queue(work_queue), 5964 _mark_and_push(collector, span, bit_map, work_queue), 5965 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), 5966 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))) 5967 { } 5968 5969 // . see if we can share work_queues with ParNew? XXX 5970 void CMSRefProcTaskProxy::do_work_steal(int i, 5971 CMSParDrainMarkingStackClosure* drain, 5972 CMSParKeepAliveClosure* keep_alive, 5973 int* seed) { 5974 OopTaskQueue* work_q = work_queue(i); 5975 NOT_PRODUCT(int num_steals = 0;) 5976 oop obj_to_scan; 5977 5978 while (true) { 5979 // Completely finish any left over work from (an) earlier round(s) 5980 drain->trim_queue(0); 5981 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4, 5982 (size_t)ParGCDesiredObjsFromOverflowList); 5983 // Now check if there's any work in the overflow list 5984 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads, 5985 // only affects the number of attempts made to get work from the 5986 // overflow list and does not affect the number of workers. Just 5987 // pass ParallelGCThreads so this behavior is unchanged. 5988 if (_collector->par_take_from_overflow_list(num_from_overflow_list, 5989 work_q, 5990 ParallelGCThreads)) { 5991 // Found something in global overflow list; 5992 // not yet ready to go stealing work from others. 5993 // We'd like to assert(work_q->size() != 0, ...) 5994 // because we just took work from the overflow list, 5995 // but of course we can't, since all of that might have 5996 // been already stolen from us. 5997 continue; 5998 } 5999 // Verify that we have no work before we resort to stealing 6000 assert(work_q->size() == 0, "Have work, shouldn't steal"); 6001 // Try to steal from other queues that have work 6002 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { 6003 NOT_PRODUCT(num_steals++;) 6004 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); 6005 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); 6006 // Do scanning work 6007 obj_to_scan->oop_iterate(keep_alive); 6008 // Loop around, finish this work, and try to steal some more 6009 } else if (terminator()->offer_termination()) { 6010 break; // nirvana from the infinite cycle 6011 } 6012 } 6013 NOT_PRODUCT( 6014 if (PrintCMSStatistics != 0) { 6015 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); 6016 } 6017 ) 6018 } 6019 6020 void CMSRefProcTaskExecutor::execute(ProcessTask& task) 6021 { 6022 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6023 FlexibleWorkGang* workers = gch->workers(); 6024 assert(workers != NULL, "Need parallel worker threads."); 6025 CMSRefProcTaskProxy rp_task(task, &_collector, 6026 _collector.ref_processor()->span(), 6027 _collector.markBitMap(), 6028 workers, _collector.task_queues()); 6029 workers->run_task(&rp_task); 6030 } 6031 6032 void CMSRefProcTaskExecutor::execute(EnqueueTask& task) 6033 { 6034 6035 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6036 FlexibleWorkGang* workers = gch->workers(); 6037 assert(workers != NULL, "Need parallel worker threads."); 6038 CMSRefEnqueueTaskProxy enq_task(task); 6039 workers->run_task(&enq_task); 6040 } 6041 6042 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) { 6043 6044 ResourceMark rm; 6045 HandleMark hm; 6046 6047 ReferenceProcessor* rp = ref_processor(); 6048 assert(rp->span().equals(_span), "Spans should be equal"); 6049 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete"); 6050 // Process weak references. 6051 rp->setup_policy(clear_all_soft_refs); 6052 verify_work_stacks_empty(); 6053 6054 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, 6055 &_markStack, false /* !preclean */); 6056 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, 6057 _span, &_markBitMap, &_markStack, 6058 &cmsKeepAliveClosure, false /* !preclean */); 6059 { 6060 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm); 6061 6062 ReferenceProcessorStats stats; 6063 if (rp->processing_is_mt()) { 6064 // Set the degree of MT here. If the discovery is done MT, there 6065 // may have been a different number of threads doing the discovery 6066 // and a different number of discovered lists may have Ref objects. 6067 // That is OK as long as the Reference lists are balanced (see 6068 // balance_all_queues() and balance_queues()). 6069 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6070 int active_workers = ParallelGCThreads; 6071 FlexibleWorkGang* workers = gch->workers(); 6072 if (workers != NULL) { 6073 active_workers = workers->active_workers(); 6074 // The expectation is that active_workers will have already 6075 // been set to a reasonable value. If it has not been set, 6076 // investigate. 6077 assert(active_workers > 0, "Should have been set during scavenge"); 6078 } 6079 rp->set_active_mt_degree(active_workers); 6080 CMSRefProcTaskExecutor task_executor(*this); 6081 stats = rp->process_discovered_references(&_is_alive_closure, 6082 &cmsKeepAliveClosure, 6083 &cmsDrainMarkingStackClosure, 6084 &task_executor, 6085 _gc_timer_cm); 6086 } else { 6087 stats = rp->process_discovered_references(&_is_alive_closure, 6088 &cmsKeepAliveClosure, 6089 &cmsDrainMarkingStackClosure, 6090 NULL, 6091 _gc_timer_cm); 6092 } 6093 _gc_tracer_cm->report_gc_reference_stats(stats); 6094 6095 } 6096 6097 // This is the point where the entire marking should have completed. 6098 verify_work_stacks_empty(); 6099 6100 if (should_unload_classes()) { 6101 { 6102 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm); 6103 6104 // Unload classes and purge the SystemDictionary. 6105 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); 6106 6107 // Unload nmethods. 6108 CodeCache::do_unloading(&_is_alive_closure, purged_class); 6109 6110 // Prune dead klasses from subklass/sibling/implementor lists. 6111 Klass::clean_weak_klass_links(&_is_alive_closure); 6112 } 6113 6114 { 6115 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm); 6116 // Clean up unreferenced symbols in symbol table. 6117 SymbolTable::unlink(); 6118 } 6119 } 6120 6121 // CMS doesn't use the StringTable as hard roots when class unloading is turned off. 6122 // Need to check if we really scanned the StringTable. 6123 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) { 6124 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm); 6125 // Delete entries for dead interned strings. 6126 StringTable::unlink(&_is_alive_closure); 6127 } 6128 6129 // Restore any preserved marks as a result of mark stack or 6130 // work queue overflow 6131 restore_preserved_marks_if_any(); // done single-threaded for now 6132 6133 rp->set_enqueuing_is_done(true); 6134 if (rp->processing_is_mt()) { 6135 rp->balance_all_queues(); 6136 CMSRefProcTaskExecutor task_executor(*this); 6137 rp->enqueue_discovered_references(&task_executor); 6138 } else { 6139 rp->enqueue_discovered_references(NULL); 6140 } 6141 rp->verify_no_references_recorded(); 6142 assert(!rp->discovery_enabled(), "should have been disabled"); 6143 } 6144 6145 #ifndef PRODUCT 6146 void CMSCollector::check_correct_thread_executing() { 6147 Thread* t = Thread::current(); 6148 // Only the VM thread or the CMS thread should be here. 6149 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), 6150 "Unexpected thread type"); 6151 // If this is the vm thread, the foreground process 6152 // should not be waiting. Note that _foregroundGCIsActive is 6153 // true while the foreground collector is waiting. 6154 if (_foregroundGCShouldWait) { 6155 // We cannot be the VM thread 6156 assert(t->is_ConcurrentGC_thread(), 6157 "Should be CMS thread"); 6158 } else { 6159 // We can be the CMS thread only if we are in a stop-world 6160 // phase of CMS collection. 6161 if (t->is_ConcurrentGC_thread()) { 6162 assert(_collectorState == InitialMarking || 6163 _collectorState == FinalMarking, 6164 "Should be a stop-world phase"); 6165 // The CMS thread should be holding the CMS_token. 6166 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6167 "Potential interference with concurrently " 6168 "executing VM thread"); 6169 } 6170 } 6171 } 6172 #endif 6173 6174 void CMSCollector::sweep(bool asynch) { 6175 assert(_collectorState == Sweeping, "just checking"); 6176 check_correct_thread_executing(); 6177 verify_work_stacks_empty(); 6178 verify_overflow_empty(); 6179 increment_sweep_count(); 6180 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause()); 6181 6182 _inter_sweep_timer.stop(); 6183 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds()); 6184 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free()); 6185 6186 assert(!_intra_sweep_timer.is_active(), "Should not be active"); 6187 _intra_sweep_timer.reset(); 6188 _intra_sweep_timer.start(); 6189 if (asynch) { 6190 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 6191 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails); 6192 // First sweep the old gen 6193 { 6194 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), 6195 bitMapLock()); 6196 sweepWork(_cmsGen, asynch); 6197 } 6198 6199 // Update Universe::_heap_*_at_gc figures. 6200 // We need all the free list locks to make the abstract state 6201 // transition from Sweeping to Resetting. See detailed note 6202 // further below. 6203 { 6204 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock()); 6205 // Update heap occupancy information which is used as 6206 // input to soft ref clearing policy at the next gc. 6207 Universe::update_heap_info_at_gc(); 6208 _collectorState = Resizing; 6209 } 6210 } else { 6211 // already have needed locks 6212 sweepWork(_cmsGen, asynch); 6213 // Update heap occupancy information which is used as 6214 // input to soft ref clearing policy at the next gc. 6215 Universe::update_heap_info_at_gc(); 6216 _collectorState = Resizing; 6217 } 6218 verify_work_stacks_empty(); 6219 verify_overflow_empty(); 6220 6221 if (should_unload_classes()) { 6222 ClassLoaderDataGraph::purge(); 6223 } 6224 6225 _intra_sweep_timer.stop(); 6226 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds()); 6227 6228 _inter_sweep_timer.reset(); 6229 _inter_sweep_timer.start(); 6230 6231 // We need to use a monotonically non-deccreasing time in ms 6232 // or we will see time-warp warnings and os::javaTimeMillis() 6233 // does not guarantee monotonicity. 6234 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC; 6235 update_time_of_last_gc(now); 6236 6237 // NOTE on abstract state transitions: 6238 // Mutators allocate-live and/or mark the mod-union table dirty 6239 // based on the state of the collection. The former is done in 6240 // the interval [Marking, Sweeping] and the latter in the interval 6241 // [Marking, Sweeping). Thus the transitions into the Marking state 6242 // and out of the Sweeping state must be synchronously visible 6243 // globally to the mutators. 6244 // The transition into the Marking state happens with the world 6245 // stopped so the mutators will globally see it. Sweeping is 6246 // done asynchronously by the background collector so the transition 6247 // from the Sweeping state to the Resizing state must be done 6248 // under the freelistLock (as is the check for whether to 6249 // allocate-live and whether to dirty the mod-union table). 6250 assert(_collectorState == Resizing, "Change of collector state to" 6251 " Resizing must be done under the freelistLocks (plural)"); 6252 6253 // Now that sweeping has been completed, we clear 6254 // the incremental_collection_failed flag, 6255 // thus inviting a younger gen collection to promote into 6256 // this generation. If such a promotion may still fail, 6257 // the flag will be set again when a young collection is 6258 // attempted. 6259 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6260 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up 6261 gch->update_full_collections_completed(_collection_count_start); 6262 } 6263 6264 // FIX ME!!! Looks like this belongs in CFLSpace, with 6265 // CMSGen merely delegating to it. 6266 void ConcurrentMarkSweepGeneration::setNearLargestChunk() { 6267 double nearLargestPercent = FLSLargestBlockCoalesceProximity; 6268 HeapWord* minAddr = _cmsSpace->bottom(); 6269 HeapWord* largestAddr = 6270 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict(); 6271 if (largestAddr == NULL) { 6272 // The dictionary appears to be empty. In this case 6273 // try to coalesce at the end of the heap. 6274 largestAddr = _cmsSpace->end(); 6275 } 6276 size_t largestOffset = pointer_delta(largestAddr, minAddr); 6277 size_t nearLargestOffset = 6278 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; 6279 if (PrintFLSStatistics != 0) { 6280 gclog_or_tty->print_cr( 6281 "CMS: Large Block: " PTR_FORMAT ";" 6282 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT, 6283 largestAddr, 6284 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset); 6285 } 6286 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); 6287 } 6288 6289 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { 6290 return addr >= _cmsSpace->nearLargestChunk(); 6291 } 6292 6293 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { 6294 return _cmsSpace->find_chunk_at_end(); 6295 } 6296 6297 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level, 6298 bool full) { 6299 // The next lower level has been collected. Gather any statistics 6300 // that are of interest at this point. 6301 if (!full && (current_level + 1) == level()) { 6302 // Gather statistics on the young generation collection. 6303 collector()->stats().record_gc0_end(used()); 6304 } 6305 } 6306 6307 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() { 6308 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6309 assert(gch->kind() == CollectedHeap::GenCollectedHeap, 6310 "Wrong type of heap"); 6311 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) 6312 gch->gen_policy()->size_policy(); 6313 assert(sp->is_gc_cms_adaptive_size_policy(), 6314 "Wrong type of size policy"); 6315 return sp; 6316 } 6317 6318 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() { 6319 if (PrintGCDetails && Verbose) { 6320 gclog_or_tty->print("Rotate from %d ", _debug_collection_type); 6321 } 6322 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1); 6323 _debug_collection_type = 6324 (CollectionTypes) (_debug_collection_type % Unknown_collection_type); 6325 if (PrintGCDetails && Verbose) { 6326 gclog_or_tty->print_cr("to %d ", _debug_collection_type); 6327 } 6328 } 6329 6330 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen, 6331 bool asynch) { 6332 // We iterate over the space(s) underlying this generation, 6333 // checking the mark bit map to see if the bits corresponding 6334 // to specific blocks are marked or not. Blocks that are 6335 // marked are live and are not swept up. All remaining blocks 6336 // are swept up, with coalescing on-the-fly as we sweep up 6337 // contiguous free and/or garbage blocks: 6338 // We need to ensure that the sweeper synchronizes with allocators 6339 // and stop-the-world collectors. In particular, the following 6340 // locks are used: 6341 // . CMS token: if this is held, a stop the world collection cannot occur 6342 // . freelistLock: if this is held no allocation can occur from this 6343 // generation by another thread 6344 // . bitMapLock: if this is held, no other thread can access or update 6345 // 6346 6347 // Note that we need to hold the freelistLock if we use 6348 // block iterate below; else the iterator might go awry if 6349 // a mutator (or promotion) causes block contents to change 6350 // (for instance if the allocator divvies up a block). 6351 // If we hold the free list lock, for all practical purposes 6352 // young generation GC's can't occur (they'll usually need to 6353 // promote), so we might as well prevent all young generation 6354 // GC's while we do a sweeping step. For the same reason, we might 6355 // as well take the bit map lock for the entire duration 6356 6357 // check that we hold the requisite locks 6358 assert(have_cms_token(), "Should hold cms token"); 6359 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token()) 6360 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()), 6361 "Should possess CMS token to sweep"); 6362 assert_lock_strong(gen->freelistLock()); 6363 assert_lock_strong(bitMapLock()); 6364 6365 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context"); 6366 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context"); 6367 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()), 6368 _inter_sweep_estimate.padded_average(), 6369 _intra_sweep_estimate.padded_average()); 6370 gen->setNearLargestChunk(); 6371 6372 { 6373 SweepClosure sweepClosure(this, gen, &_markBitMap, 6374 CMSYield && asynch); 6375 gen->cmsSpace()->blk_iterate_careful(&sweepClosure); 6376 // We need to free-up/coalesce garbage/blocks from a 6377 // co-terminal free run. This is done in the SweepClosure 6378 // destructor; so, do not remove this scope, else the 6379 // end-of-sweep-census below will be off by a little bit. 6380 } 6381 gen->cmsSpace()->sweep_completed(); 6382 gen->cmsSpace()->endSweepFLCensus(sweep_count()); 6383 if (should_unload_classes()) { // unloaded classes this cycle, 6384 _concurrent_cycles_since_last_unload = 0; // ... reset count 6385 } else { // did not unload classes, 6386 _concurrent_cycles_since_last_unload++; // ... increment count 6387 } 6388 } 6389 6390 // Reset CMS data structures (for now just the marking bit map) 6391 // preparatory for the next cycle. 6392 void CMSCollector::reset(bool asynch) { 6393 GenCollectedHeap* gch = GenCollectedHeap::heap(); 6394 CMSAdaptiveSizePolicy* sp = size_policy(); 6395 AdaptiveSizePolicyOutput(sp, gch->total_collections()); 6396 if (asynch) { 6397 CMSTokenSyncWithLocks ts(true, bitMapLock()); 6398 6399 // If the state is not "Resetting", the foreground thread 6400 // has done a collection and the resetting. 6401 if (_collectorState != Resetting) { 6402 assert(_collectorState == Idling, "The state should only change" 6403 " because the foreground collector has finished the collection"); 6404 return; 6405 } 6406 6407 // Clear the mark bitmap (no grey objects to start with) 6408 // for the next cycle. 6409 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 6410 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails); 6411 6412 HeapWord* curAddr = _markBitMap.startWord(); 6413 while (curAddr < _markBitMap.endWord()) { 6414 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); 6415 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); 6416 _markBitMap.clear_large_range(chunk); 6417 if (ConcurrentMarkSweepThread::should_yield() && 6418 !foregroundGCIsActive() && 6419 CMSYield) { 6420 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6421 "CMS thread should hold CMS token"); 6422 assert_lock_strong(bitMapLock()); 6423 bitMapLock()->unlock(); 6424 ConcurrentMarkSweepThread::desynchronize(true); 6425 ConcurrentMarkSweepThread::acknowledge_yield_request(); 6426 stopTimer(); 6427 if (PrintCMSStatistics != 0) { 6428 incrementYields(); 6429 } 6430 icms_wait(); 6431 6432 // See the comment in coordinator_yield() 6433 for (unsigned i = 0; i < CMSYieldSleepCount && 6434 ConcurrentMarkSweepThread::should_yield() && 6435 !CMSCollector::foregroundGCIsActive(); ++i) { 6436 os::sleep(Thread::current(), 1, false); 6437 ConcurrentMarkSweepThread::acknowledge_yield_request(); 6438 } 6439 6440 ConcurrentMarkSweepThread::synchronize(true); 6441 bitMapLock()->lock_without_safepoint_check(); 6442 startTimer(); 6443 } 6444 curAddr = chunk.end(); 6445 } 6446 // A successful mostly concurrent collection has been done. 6447 // Because only the full (i.e., concurrent mode failure) collections 6448 // are being measured for gc overhead limits, clean the "near" flag 6449 // and count. 6450 sp->reset_gc_overhead_limit_count(); 6451 _collectorState = Idling; 6452 } else { 6453 // already have the lock 6454 assert(_collectorState == Resetting, "just checking"); 6455 assert_lock_strong(bitMapLock()); 6456 _markBitMap.clear_all(); 6457 _collectorState = Idling; 6458 } 6459 6460 // Stop incremental mode after a cycle completes, so that any future cycles 6461 // are triggered by allocation. 6462 stop_icms(); 6463 6464 NOT_PRODUCT( 6465 if (RotateCMSCollectionTypes) { 6466 _cmsGen->rotate_debug_collection_type(); 6467 } 6468 ) 6469 6470 register_gc_end(); 6471 } 6472 6473 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) { 6474 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); 6475 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); 6476 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL); 6477 TraceCollectorStats tcs(counters()); 6478 6479 switch (op) { 6480 case CMS_op_checkpointRootsInitial: { 6481 SvcGCMarker sgcm(SvcGCMarker::OTHER); 6482 checkpointRootsInitial(true); // asynch 6483 if (PrintGC) { 6484 _cmsGen->printOccupancy("initial-mark"); 6485 } 6486 break; 6487 } 6488 case CMS_op_checkpointRootsFinal: { 6489 SvcGCMarker sgcm(SvcGCMarker::OTHER); 6490 checkpointRootsFinal(true, // asynch 6491 false, // !clear_all_soft_refs 6492 false); // !init_mark_was_synchronous 6493 if (PrintGC) { 6494 _cmsGen->printOccupancy("remark"); 6495 } 6496 break; 6497 } 6498 default: 6499 fatal("No such CMS_op"); 6500 } 6501 } 6502 6503 #ifndef PRODUCT 6504 size_t const CMSCollector::skip_header_HeapWords() { 6505 return FreeChunk::header_size(); 6506 } 6507 6508 // Try and collect here conditions that should hold when 6509 // CMS thread is exiting. The idea is that the foreground GC 6510 // thread should not be blocked if it wants to terminate 6511 // the CMS thread and yet continue to run the VM for a while 6512 // after that. 6513 void CMSCollector::verify_ok_to_terminate() const { 6514 assert(Thread::current()->is_ConcurrentGC_thread(), 6515 "should be called by CMS thread"); 6516 assert(!_foregroundGCShouldWait, "should be false"); 6517 // We could check here that all the various low-level locks 6518 // are not held by the CMS thread, but that is overkill; see 6519 // also CMSThread::verify_ok_to_terminate() where the CGC_lock 6520 // is checked. 6521 } 6522 #endif 6523 6524 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { 6525 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), 6526 "missing Printezis mark?"); 6527 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 6528 size_t size = pointer_delta(nextOneAddr + 1, addr); 6529 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 6530 "alignment problem"); 6531 assert(size >= 3, "Necessary for Printezis marks to work"); 6532 return size; 6533 } 6534 6535 // A variant of the above (block_size_using_printezis_bits()) except 6536 // that we return 0 if the P-bits are not yet set. 6537 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { 6538 if (_markBitMap.isMarked(addr + 1)) { 6539 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects"); 6540 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); 6541 size_t size = pointer_delta(nextOneAddr + 1, addr); 6542 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 6543 "alignment problem"); 6544 assert(size >= 3, "Necessary for Printezis marks to work"); 6545 return size; 6546 } 6547 return 0; 6548 } 6549 6550 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { 6551 size_t sz = 0; 6552 oop p = (oop)addr; 6553 if (p->klass_or_null() != NULL) { 6554 sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); 6555 } else { 6556 sz = block_size_using_printezis_bits(addr); 6557 } 6558 assert(sz > 0, "size must be nonzero"); 6559 HeapWord* next_block = addr + sz; 6560 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block, 6561 CardTableModRefBS::card_size); 6562 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) < 6563 round_down((uintptr_t)next_card, CardTableModRefBS::card_size), 6564 "must be different cards"); 6565 return next_card; 6566 } 6567 6568 6569 // CMS Bit Map Wrapper ///////////////////////////////////////// 6570 6571 // Construct a CMS bit map infrastructure, but don't create the 6572 // bit vector itself. That is done by a separate call CMSBitMap::allocate() 6573 // further below. 6574 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): 6575 _bm(), 6576 _shifter(shifter), 6577 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL) 6578 { 6579 _bmStartWord = 0; 6580 _bmWordSize = 0; 6581 } 6582 6583 bool CMSBitMap::allocate(MemRegion mr) { 6584 _bmStartWord = mr.start(); 6585 _bmWordSize = mr.word_size(); 6586 ReservedSpace brs(ReservedSpace::allocation_align_size_up( 6587 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); 6588 if (!brs.is_reserved()) { 6589 warning("CMS bit map allocation failure"); 6590 return false; 6591 } 6592 // For now we'll just commit all of the bit map up fromt. 6593 // Later on we'll try to be more parsimonious with swap. 6594 if (!_virtual_space.initialize(brs, brs.size())) { 6595 warning("CMS bit map backing store failure"); 6596 return false; 6597 } 6598 assert(_virtual_space.committed_size() == brs.size(), 6599 "didn't reserve backing store for all of CMS bit map?"); 6600 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low()); 6601 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= 6602 _bmWordSize, "inconsistency in bit map sizing"); 6603 _bm.set_size(_bmWordSize >> _shifter); 6604 6605 // bm.clear(); // can we rely on getting zero'd memory? verify below 6606 assert(isAllClear(), 6607 "Expected zero'd memory from ReservedSpace constructor"); 6608 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), 6609 "consistency check"); 6610 return true; 6611 } 6612 6613 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { 6614 HeapWord *next_addr, *end_addr, *last_addr; 6615 assert_locked(); 6616 assert(covers(mr), "out-of-range error"); 6617 // XXX assert that start and end are appropriately aligned 6618 for (next_addr = mr.start(), end_addr = mr.end(); 6619 next_addr < end_addr; next_addr = last_addr) { 6620 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); 6621 last_addr = dirty_region.end(); 6622 if (!dirty_region.is_empty()) { 6623 cl->do_MemRegion(dirty_region); 6624 } else { 6625 assert(last_addr == end_addr, "program logic"); 6626 return; 6627 } 6628 } 6629 } 6630 6631 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const { 6632 _bm.print_on_error(st, prefix); 6633 } 6634 6635 #ifndef PRODUCT 6636 void CMSBitMap::assert_locked() const { 6637 CMSLockVerifier::assert_locked(lock()); 6638 } 6639 6640 bool CMSBitMap::covers(MemRegion mr) const { 6641 // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); 6642 assert((size_t)_bm.size() == (_bmWordSize >> _shifter), 6643 "size inconsistency"); 6644 return (mr.start() >= _bmStartWord) && 6645 (mr.end() <= endWord()); 6646 } 6647 6648 bool CMSBitMap::covers(HeapWord* start, size_t size) const { 6649 return (start >= _bmStartWord && (start + size) <= endWord()); 6650 } 6651 6652 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { 6653 // verify that there are no 1 bits in the interval [left, right) 6654 FalseBitMapClosure falseBitMapClosure; 6655 iterate(&falseBitMapClosure, left, right); 6656 } 6657 6658 void CMSBitMap::region_invariant(MemRegion mr) 6659 { 6660 assert_locked(); 6661 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); 6662 assert(!mr.is_empty(), "unexpected empty region"); 6663 assert(covers(mr), "mr should be covered by bit map"); 6664 // convert address range into offset range 6665 size_t start_ofs = heapWordToOffset(mr.start()); 6666 // Make sure that end() is appropriately aligned 6667 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(), 6668 (1 << (_shifter+LogHeapWordSize))), 6669 "Misaligned mr.end()"); 6670 size_t end_ofs = heapWordToOffset(mr.end()); 6671 assert(end_ofs > start_ofs, "Should mark at least one bit"); 6672 } 6673 6674 #endif 6675 6676 bool CMSMarkStack::allocate(size_t size) { 6677 // allocate a stack of the requisite depth 6678 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 6679 size * sizeof(oop))); 6680 if (!rs.is_reserved()) { 6681 warning("CMSMarkStack allocation failure"); 6682 return false; 6683 } 6684 if (!_virtual_space.initialize(rs, rs.size())) { 6685 warning("CMSMarkStack backing store failure"); 6686 return false; 6687 } 6688 assert(_virtual_space.committed_size() == rs.size(), 6689 "didn't reserve backing store for all of CMS stack?"); 6690 _base = (oop*)(_virtual_space.low()); 6691 _index = 0; 6692 _capacity = size; 6693 NOT_PRODUCT(_max_depth = 0); 6694 return true; 6695 } 6696 6697 // XXX FIX ME !!! In the MT case we come in here holding a 6698 // leaf lock. For printing we need to take a further lock 6699 // which has lower rank. We need to recallibrate the two 6700 // lock-ranks involved in order to be able to rpint the 6701 // messages below. (Or defer the printing to the caller. 6702 // For now we take the expedient path of just disabling the 6703 // messages for the problematic case.) 6704 void CMSMarkStack::expand() { 6705 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted"); 6706 if (_capacity == MarkStackSizeMax) { 6707 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { 6708 // We print a warning message only once per CMS cycle. 6709 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit"); 6710 } 6711 return; 6712 } 6713 // Double capacity if possible 6714 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax); 6715 // Do not give up existing stack until we have managed to 6716 // get the double capacity that we desired. 6717 ReservedSpace rs(ReservedSpace::allocation_align_size_up( 6718 new_capacity * sizeof(oop))); 6719 if (rs.is_reserved()) { 6720 // Release the backing store associated with old stack 6721 _virtual_space.release(); 6722 // Reinitialize virtual space for new stack 6723 if (!_virtual_space.initialize(rs, rs.size())) { 6724 fatal("Not enough swap for expanded marking stack"); 6725 } 6726 _base = (oop*)(_virtual_space.low()); 6727 _index = 0; 6728 _capacity = new_capacity; 6729 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { 6730 // Failed to double capacity, continue; 6731 // we print a detail message only once per CMS cycle. 6732 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to " 6733 SIZE_FORMAT"K", 6734 _capacity / K, new_capacity / K); 6735 } 6736 } 6737 6738 6739 // Closures 6740 // XXX: there seems to be a lot of code duplication here; 6741 // should refactor and consolidate common code. 6742 6743 // This closure is used to mark refs into the CMS generation in 6744 // the CMS bit map. Called at the first checkpoint. This closure 6745 // assumes that we do not need to re-mark dirty cards; if the CMS 6746 // generation on which this is used is not an oldest 6747 // generation then this will lose younger_gen cards! 6748 6749 MarkRefsIntoClosure::MarkRefsIntoClosure( 6750 MemRegion span, CMSBitMap* bitMap): 6751 _span(span), 6752 _bitMap(bitMap) 6753 { 6754 assert(_ref_processor == NULL, "deliberately left NULL"); 6755 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); 6756 } 6757 6758 void MarkRefsIntoClosure::do_oop(oop obj) { 6759 // if p points into _span, then mark corresponding bit in _markBitMap 6760 assert(obj->is_oop(), "expected an oop"); 6761 HeapWord* addr = (HeapWord*)obj; 6762 if (_span.contains(addr)) { 6763 // this should be made more efficient 6764 _bitMap->mark(addr); 6765 } 6766 } 6767 6768 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); } 6769 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); } 6770 6771 // A variant of the above, used for CMS marking verification. 6772 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( 6773 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm): 6774 _span(span), 6775 _verification_bm(verification_bm), 6776 _cms_bm(cms_bm) 6777 { 6778 assert(_ref_processor == NULL, "deliberately left NULL"); 6779 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); 6780 } 6781 6782 void MarkRefsIntoVerifyClosure::do_oop(oop obj) { 6783 // if p points into _span, then mark corresponding bit in _markBitMap 6784 assert(obj->is_oop(), "expected an oop"); 6785 HeapWord* addr = (HeapWord*)obj; 6786 if (_span.contains(addr)) { 6787 _verification_bm->mark(addr); 6788 if (!_cms_bm->isMarked(addr)) { 6789 oop(addr)->print(); 6790 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr); 6791 fatal("... aborting"); 6792 } 6793 } 6794 } 6795 6796 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 6797 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); } 6798 6799 ////////////////////////////////////////////////// 6800 // MarkRefsIntoAndScanClosure 6801 ////////////////////////////////////////////////// 6802 6803 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, 6804 ReferenceProcessor* rp, 6805 CMSBitMap* bit_map, 6806 CMSBitMap* mod_union_table, 6807 CMSMarkStack* mark_stack, 6808 CMSCollector* collector, 6809 bool should_yield, 6810 bool concurrent_precleaning): 6811 _collector(collector), 6812 _span(span), 6813 _bit_map(bit_map), 6814 _mark_stack(mark_stack), 6815 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table, 6816 mark_stack, concurrent_precleaning), 6817 _yield(should_yield), 6818 _concurrent_precleaning(concurrent_precleaning), 6819 _freelistLock(NULL) 6820 { 6821 _ref_processor = rp; 6822 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); 6823 } 6824 6825 // This closure is used to mark refs into the CMS generation at the 6826 // second (final) checkpoint, and to scan and transitively follow 6827 // the unmarked oops. It is also used during the concurrent precleaning 6828 // phase while scanning objects on dirty cards in the CMS generation. 6829 // The marks are made in the marking bit map and the marking stack is 6830 // used for keeping the (newly) grey objects during the scan. 6831 // The parallel version (Par_...) appears further below. 6832 void MarkRefsIntoAndScanClosure::do_oop(oop obj) { 6833 if (obj != NULL) { 6834 assert(obj->is_oop(), "expected an oop"); 6835 HeapWord* addr = (HeapWord*)obj; 6836 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 6837 assert(_collector->overflow_list_is_empty(), 6838 "overflow list should be empty"); 6839 if (_span.contains(addr) && 6840 !_bit_map->isMarked(addr)) { 6841 // mark bit map (object is now grey) 6842 _bit_map->mark(addr); 6843 // push on marking stack (stack should be empty), and drain the 6844 // stack by applying this closure to the oops in the oops popped 6845 // from the stack (i.e. blacken the grey objects) 6846 bool res = _mark_stack->push(obj); 6847 assert(res, "Should have space to push on empty stack"); 6848 do { 6849 oop new_oop = _mark_stack->pop(); 6850 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 6851 assert(_bit_map->isMarked((HeapWord*)new_oop), 6852 "only grey objects on this stack"); 6853 // iterate over the oops in this oop, marking and pushing 6854 // the ones in CMS heap (i.e. in _span). 6855 new_oop->oop_iterate(&_pushAndMarkClosure); 6856 // check if it's time to yield 6857 do_yield_check(); 6858 } while (!_mark_stack->isEmpty() || 6859 (!_concurrent_precleaning && take_from_overflow_list())); 6860 // if marking stack is empty, and we are not doing this 6861 // during precleaning, then check the overflow list 6862 } 6863 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 6864 assert(_collector->overflow_list_is_empty(), 6865 "overflow list was drained above"); 6866 // We could restore evacuated mark words, if any, used for 6867 // overflow list links here because the overflow list is 6868 // provably empty here. That would reduce the maximum 6869 // size requirements for preserved_{oop,mark}_stack. 6870 // But we'll just postpone it until we are all done 6871 // so we can just stream through. 6872 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) { 6873 _collector->restore_preserved_marks_if_any(); 6874 assert(_collector->no_preserved_marks(), "No preserved marks"); 6875 } 6876 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(), 6877 "All preserved marks should have been restored above"); 6878 } 6879 } 6880 6881 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 6882 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); } 6883 6884 void MarkRefsIntoAndScanClosure::do_yield_work() { 6885 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 6886 "CMS thread should hold CMS token"); 6887 assert_lock_strong(_freelistLock); 6888 assert_lock_strong(_bit_map->lock()); 6889 // relinquish the free_list_lock and bitMaplock() 6890 _bit_map->lock()->unlock(); 6891 _freelistLock->unlock(); 6892 ConcurrentMarkSweepThread::desynchronize(true); 6893 ConcurrentMarkSweepThread::acknowledge_yield_request(); 6894 _collector->stopTimer(); 6895 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 6896 if (PrintCMSStatistics != 0) { 6897 _collector->incrementYields(); 6898 } 6899 _collector->icms_wait(); 6900 6901 // See the comment in coordinator_yield() 6902 for (unsigned i = 0; 6903 i < CMSYieldSleepCount && 6904 ConcurrentMarkSweepThread::should_yield() && 6905 !CMSCollector::foregroundGCIsActive(); 6906 ++i) { 6907 os::sleep(Thread::current(), 1, false); 6908 ConcurrentMarkSweepThread::acknowledge_yield_request(); 6909 } 6910 6911 ConcurrentMarkSweepThread::synchronize(true); 6912 _freelistLock->lock_without_safepoint_check(); 6913 _bit_map->lock()->lock_without_safepoint_check(); 6914 _collector->startTimer(); 6915 } 6916 6917 /////////////////////////////////////////////////////////// 6918 // Par_MarkRefsIntoAndScanClosure: a parallel version of 6919 // MarkRefsIntoAndScanClosure 6920 /////////////////////////////////////////////////////////// 6921 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure( 6922 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp, 6923 CMSBitMap* bit_map, OopTaskQueue* work_queue): 6924 _span(span), 6925 _bit_map(bit_map), 6926 _work_queue(work_queue), 6927 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), 6928 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))), 6929 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue) 6930 { 6931 _ref_processor = rp; 6932 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); 6933 } 6934 6935 // This closure is used to mark refs into the CMS generation at the 6936 // second (final) checkpoint, and to scan and transitively follow 6937 // the unmarked oops. The marks are made in the marking bit map and 6938 // the work_queue is used for keeping the (newly) grey objects during 6939 // the scan phase whence they are also available for stealing by parallel 6940 // threads. Since the marking bit map is shared, updates are 6941 // synchronized (via CAS). 6942 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) { 6943 if (obj != NULL) { 6944 // Ignore mark word because this could be an already marked oop 6945 // that may be chained at the end of the overflow list. 6946 assert(obj->is_oop(true), "expected an oop"); 6947 HeapWord* addr = (HeapWord*)obj; 6948 if (_span.contains(addr) && 6949 !_bit_map->isMarked(addr)) { 6950 // mark bit map (object will become grey): 6951 // It is possible for several threads to be 6952 // trying to "claim" this object concurrently; 6953 // the unique thread that succeeds in marking the 6954 // object first will do the subsequent push on 6955 // to the work queue (or overflow list). 6956 if (_bit_map->par_mark(addr)) { 6957 // push on work_queue (which may not be empty), and trim the 6958 // queue to an appropriate length by applying this closure to 6959 // the oops in the oops popped from the stack (i.e. blacken the 6960 // grey objects) 6961 bool res = _work_queue->push(obj); 6962 assert(res, "Low water mark should be less than capacity?"); 6963 trim_queue(_low_water_mark); 6964 } // Else, another thread claimed the object 6965 } 6966 } 6967 } 6968 6969 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } 6970 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); } 6971 6972 // This closure is used to rescan the marked objects on the dirty cards 6973 // in the mod union table and the card table proper. 6974 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( 6975 oop p, MemRegion mr) { 6976 6977 size_t size = 0; 6978 HeapWord* addr = (HeapWord*)p; 6979 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 6980 assert(_span.contains(addr), "we are scanning the CMS generation"); 6981 // check if it's time to yield 6982 if (do_yield_check()) { 6983 // We yielded for some foreground stop-world work, 6984 // and we have been asked to abort this ongoing preclean cycle. 6985 return 0; 6986 } 6987 if (_bitMap->isMarked(addr)) { 6988 // it's marked; is it potentially uninitialized? 6989 if (p->klass_or_null() != NULL) { 6990 // an initialized object; ignore mark word in verification below 6991 // since we are running concurrent with mutators 6992 assert(p->is_oop(true), "should be an oop"); 6993 if (p->is_objArray()) { 6994 // objArrays are precisely marked; restrict scanning 6995 // to dirty cards only. 6996 size = CompactibleFreeListSpace::adjustObjectSize( 6997 p->oop_iterate(_scanningClosure, mr)); 6998 } else { 6999 // A non-array may have been imprecisely marked; we need 7000 // to scan object in its entirety. 7001 size = CompactibleFreeListSpace::adjustObjectSize( 7002 p->oop_iterate(_scanningClosure)); 7003 } 7004 #ifdef ASSERT 7005 size_t direct_size = 7006 CompactibleFreeListSpace::adjustObjectSize(p->size()); 7007 assert(size == direct_size, "Inconsistency in size"); 7008 assert(size >= 3, "Necessary for Printezis marks to work"); 7009 if (!_bitMap->isMarked(addr+1)) { 7010 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size); 7011 } else { 7012 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1); 7013 assert(_bitMap->isMarked(addr+size-1), 7014 "inconsistent Printezis mark"); 7015 } 7016 #endif // ASSERT 7017 } else { 7018 // an unitialized object 7019 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); 7020 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 7021 size = pointer_delta(nextOneAddr + 1, addr); 7022 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 7023 "alignment problem"); 7024 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() 7025 // will dirty the card when the klass pointer is installed in the 7026 // object (signalling the completion of initialization). 7027 } 7028 } else { 7029 // Either a not yet marked object or an uninitialized object 7030 if (p->klass_or_null() == NULL) { 7031 // An uninitialized object, skip to the next card, since 7032 // we may not be able to read its P-bits yet. 7033 assert(size == 0, "Initial value"); 7034 } else { 7035 // An object not (yet) reached by marking: we merely need to 7036 // compute its size so as to go look at the next block. 7037 assert(p->is_oop(true), "should be an oop"); 7038 size = CompactibleFreeListSpace::adjustObjectSize(p->size()); 7039 } 7040 } 7041 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 7042 return size; 7043 } 7044 7045 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { 7046 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7047 "CMS thread should hold CMS token"); 7048 assert_lock_strong(_freelistLock); 7049 assert_lock_strong(_bitMap->lock()); 7050 // relinquish the free_list_lock and bitMaplock() 7051 _bitMap->lock()->unlock(); 7052 _freelistLock->unlock(); 7053 ConcurrentMarkSweepThread::desynchronize(true); 7054 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7055 _collector->stopTimer(); 7056 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 7057 if (PrintCMSStatistics != 0) { 7058 _collector->incrementYields(); 7059 } 7060 _collector->icms_wait(); 7061 7062 // See the comment in coordinator_yield() 7063 for (unsigned i = 0; i < CMSYieldSleepCount && 7064 ConcurrentMarkSweepThread::should_yield() && 7065 !CMSCollector::foregroundGCIsActive(); ++i) { 7066 os::sleep(Thread::current(), 1, false); 7067 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7068 } 7069 7070 ConcurrentMarkSweepThread::synchronize(true); 7071 _freelistLock->lock_without_safepoint_check(); 7072 _bitMap->lock()->lock_without_safepoint_check(); 7073 _collector->startTimer(); 7074 } 7075 7076 7077 ////////////////////////////////////////////////////////////////// 7078 // SurvivorSpacePrecleanClosure 7079 ////////////////////////////////////////////////////////////////// 7080 // This (single-threaded) closure is used to preclean the oops in 7081 // the survivor spaces. 7082 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { 7083 7084 HeapWord* addr = (HeapWord*)p; 7085 DEBUG_ONLY(_collector->verify_work_stacks_empty();) 7086 assert(!_span.contains(addr), "we are scanning the survivor spaces"); 7087 assert(p->klass_or_null() != NULL, "object should be initializd"); 7088 // an initialized object; ignore mark word in verification below 7089 // since we are running concurrent with mutators 7090 assert(p->is_oop(true), "should be an oop"); 7091 // Note that we do not yield while we iterate over 7092 // the interior oops of p, pushing the relevant ones 7093 // on our marking stack. 7094 size_t size = p->oop_iterate(_scanning_closure); 7095 do_yield_check(); 7096 // Observe that below, we do not abandon the preclean 7097 // phase as soon as we should; rather we empty the 7098 // marking stack before returning. This is to satisfy 7099 // some existing assertions. In general, it may be a 7100 // good idea to abort immediately and complete the marking 7101 // from the grey objects at a later time. 7102 while (!_mark_stack->isEmpty()) { 7103 oop new_oop = _mark_stack->pop(); 7104 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 7105 assert(_bit_map->isMarked((HeapWord*)new_oop), 7106 "only grey objects on this stack"); 7107 // iterate over the oops in this oop, marking and pushing 7108 // the ones in CMS heap (i.e. in _span). 7109 new_oop->oop_iterate(_scanning_closure); 7110 // check if it's time to yield 7111 do_yield_check(); 7112 } 7113 unsigned int after_count = 7114 GenCollectedHeap::heap()->total_collections(); 7115 bool abort = (_before_count != after_count) || 7116 _collector->should_abort_preclean(); 7117 return abort ? 0 : size; 7118 } 7119 7120 void SurvivorSpacePrecleanClosure::do_yield_work() { 7121 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7122 "CMS thread should hold CMS token"); 7123 assert_lock_strong(_bit_map->lock()); 7124 // Relinquish the bit map lock 7125 _bit_map->lock()->unlock(); 7126 ConcurrentMarkSweepThread::desynchronize(true); 7127 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7128 _collector->stopTimer(); 7129 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 7130 if (PrintCMSStatistics != 0) { 7131 _collector->incrementYields(); 7132 } 7133 _collector->icms_wait(); 7134 7135 // See the comment in coordinator_yield() 7136 for (unsigned i = 0; i < CMSYieldSleepCount && 7137 ConcurrentMarkSweepThread::should_yield() && 7138 !CMSCollector::foregroundGCIsActive(); ++i) { 7139 os::sleep(Thread::current(), 1, false); 7140 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7141 } 7142 7143 ConcurrentMarkSweepThread::synchronize(true); 7144 _bit_map->lock()->lock_without_safepoint_check(); 7145 _collector->startTimer(); 7146 } 7147 7148 // This closure is used to rescan the marked objects on the dirty cards 7149 // in the mod union table and the card table proper. In the parallel 7150 // case, although the bitMap is shared, we do a single read so the 7151 // isMarked() query is "safe". 7152 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { 7153 // Ignore mark word because we are running concurrent with mutators 7154 assert(p->is_oop_or_null(true), "expected an oop or null"); 7155 HeapWord* addr = (HeapWord*)p; 7156 assert(_span.contains(addr), "we are scanning the CMS generation"); 7157 bool is_obj_array = false; 7158 #ifdef ASSERT 7159 if (!_parallel) { 7160 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); 7161 assert(_collector->overflow_list_is_empty(), 7162 "overflow list should be empty"); 7163 7164 } 7165 #endif // ASSERT 7166 if (_bit_map->isMarked(addr)) { 7167 // Obj arrays are precisely marked, non-arrays are not; 7168 // so we scan objArrays precisely and non-arrays in their 7169 // entirety. 7170 if (p->is_objArray()) { 7171 is_obj_array = true; 7172 if (_parallel) { 7173 p->oop_iterate(_par_scan_closure, mr); 7174 } else { 7175 p->oop_iterate(_scan_closure, mr); 7176 } 7177 } else { 7178 if (_parallel) { 7179 p->oop_iterate(_par_scan_closure); 7180 } else { 7181 p->oop_iterate(_scan_closure); 7182 } 7183 } 7184 } 7185 #ifdef ASSERT 7186 if (!_parallel) { 7187 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); 7188 assert(_collector->overflow_list_is_empty(), 7189 "overflow list should be empty"); 7190 7191 } 7192 #endif // ASSERT 7193 return is_obj_array; 7194 } 7195 7196 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, 7197 MemRegion span, 7198 CMSBitMap* bitMap, CMSMarkStack* markStack, 7199 bool should_yield, bool verifying): 7200 _collector(collector), 7201 _span(span), 7202 _bitMap(bitMap), 7203 _mut(&collector->_modUnionTable), 7204 _markStack(markStack), 7205 _yield(should_yield), 7206 _skipBits(0) 7207 { 7208 assert(_markStack->isEmpty(), "stack should be empty"); 7209 _finger = _bitMap->startWord(); 7210 _threshold = _finger; 7211 assert(_collector->_restart_addr == NULL, "Sanity check"); 7212 assert(_span.contains(_finger), "Out of bounds _finger?"); 7213 DEBUG_ONLY(_verifying = verifying;) 7214 } 7215 7216 void MarkFromRootsClosure::reset(HeapWord* addr) { 7217 assert(_markStack->isEmpty(), "would cause duplicates on stack"); 7218 assert(_span.contains(addr), "Out of bounds _finger?"); 7219 _finger = addr; 7220 _threshold = (HeapWord*)round_to( 7221 (intptr_t)_finger, CardTableModRefBS::card_size); 7222 } 7223 7224 // Should revisit to see if this should be restructured for 7225 // greater efficiency. 7226 bool MarkFromRootsClosure::do_bit(size_t offset) { 7227 if (_skipBits > 0) { 7228 _skipBits--; 7229 return true; 7230 } 7231 // convert offset into a HeapWord* 7232 HeapWord* addr = _bitMap->startWord() + offset; 7233 assert(_bitMap->endWord() && addr < _bitMap->endWord(), 7234 "address out of range"); 7235 assert(_bitMap->isMarked(addr), "tautology"); 7236 if (_bitMap->isMarked(addr+1)) { 7237 // this is an allocated but not yet initialized object 7238 assert(_skipBits == 0, "tautology"); 7239 _skipBits = 2; // skip next two marked bits ("Printezis-marks") 7240 oop p = oop(addr); 7241 if (p->klass_or_null() == NULL) { 7242 DEBUG_ONLY(if (!_verifying) {) 7243 // We re-dirty the cards on which this object lies and increase 7244 // the _threshold so that we'll come back to scan this object 7245 // during the preclean or remark phase. (CMSCleanOnEnter) 7246 if (CMSCleanOnEnter) { 7247 size_t sz = _collector->block_size_using_printezis_bits(addr); 7248 HeapWord* end_card_addr = (HeapWord*)round_to( 7249 (intptr_t)(addr+sz), CardTableModRefBS::card_size); 7250 MemRegion redirty_range = MemRegion(addr, end_card_addr); 7251 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 7252 // Bump _threshold to end_card_addr; note that 7253 // _threshold cannot possibly exceed end_card_addr, anyhow. 7254 // This prevents future clearing of the card as the scan proceeds 7255 // to the right. 7256 assert(_threshold <= end_card_addr, 7257 "Because we are just scanning into this object"); 7258 if (_threshold < end_card_addr) { 7259 _threshold = end_card_addr; 7260 } 7261 if (p->klass_or_null() != NULL) { 7262 // Redirty the range of cards... 7263 _mut->mark_range(redirty_range); 7264 } // ...else the setting of klass will dirty the card anyway. 7265 } 7266 DEBUG_ONLY(}) 7267 return true; 7268 } 7269 } 7270 scanOopsInOop(addr); 7271 return true; 7272 } 7273 7274 // We take a break if we've been at this for a while, 7275 // so as to avoid monopolizing the locks involved. 7276 void MarkFromRootsClosure::do_yield_work() { 7277 // First give up the locks, then yield, then re-lock 7278 // We should probably use a constructor/destructor idiom to 7279 // do this unlock/lock or modify the MutexUnlocker class to 7280 // serve our purpose. XXX 7281 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7282 "CMS thread should hold CMS token"); 7283 assert_lock_strong(_bitMap->lock()); 7284 _bitMap->lock()->unlock(); 7285 ConcurrentMarkSweepThread::desynchronize(true); 7286 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7287 _collector->stopTimer(); 7288 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 7289 if (PrintCMSStatistics != 0) { 7290 _collector->incrementYields(); 7291 } 7292 _collector->icms_wait(); 7293 7294 // See the comment in coordinator_yield() 7295 for (unsigned i = 0; i < CMSYieldSleepCount && 7296 ConcurrentMarkSweepThread::should_yield() && 7297 !CMSCollector::foregroundGCIsActive(); ++i) { 7298 os::sleep(Thread::current(), 1, false); 7299 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7300 } 7301 7302 ConcurrentMarkSweepThread::synchronize(true); 7303 _bitMap->lock()->lock_without_safepoint_check(); 7304 _collector->startTimer(); 7305 } 7306 7307 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { 7308 assert(_bitMap->isMarked(ptr), "expected bit to be set"); 7309 assert(_markStack->isEmpty(), 7310 "should drain stack to limit stack usage"); 7311 // convert ptr to an oop preparatory to scanning 7312 oop obj = oop(ptr); 7313 // Ignore mark word in verification below, since we 7314 // may be running concurrent with mutators. 7315 assert(obj->is_oop(true), "should be an oop"); 7316 assert(_finger <= ptr, "_finger runneth ahead"); 7317 // advance the finger to right end of this object 7318 _finger = ptr + obj->size(); 7319 assert(_finger > ptr, "we just incremented it above"); 7320 // On large heaps, it may take us some time to get through 7321 // the marking phase (especially if running iCMS). During 7322 // this time it's possible that a lot of mutations have 7323 // accumulated in the card table and the mod union table -- 7324 // these mutation records are redundant until we have 7325 // actually traced into the corresponding card. 7326 // Here, we check whether advancing the finger would make 7327 // us cross into a new card, and if so clear corresponding 7328 // cards in the MUT (preclean them in the card-table in the 7329 // future). 7330 7331 DEBUG_ONLY(if (!_verifying) {) 7332 // The clean-on-enter optimization is disabled by default, 7333 // until we fix 6178663. 7334 if (CMSCleanOnEnter && (_finger > _threshold)) { 7335 // [_threshold, _finger) represents the interval 7336 // of cards to be cleared in MUT (or precleaned in card table). 7337 // The set of cards to be cleared is all those that overlap 7338 // with the interval [_threshold, _finger); note that 7339 // _threshold is always kept card-aligned but _finger isn't 7340 // always card-aligned. 7341 HeapWord* old_threshold = _threshold; 7342 assert(old_threshold == (HeapWord*)round_to( 7343 (intptr_t)old_threshold, CardTableModRefBS::card_size), 7344 "_threshold should always be card-aligned"); 7345 _threshold = (HeapWord*)round_to( 7346 (intptr_t)_finger, CardTableModRefBS::card_size); 7347 MemRegion mr(old_threshold, _threshold); 7348 assert(!mr.is_empty(), "Control point invariant"); 7349 assert(_span.contains(mr), "Should clear within span"); 7350 _mut->clear_range(mr); 7351 } 7352 DEBUG_ONLY(}) 7353 // Note: the finger doesn't advance while we drain 7354 // the stack below. 7355 PushOrMarkClosure pushOrMarkClosure(_collector, 7356 _span, _bitMap, _markStack, 7357 _finger, this); 7358 bool res = _markStack->push(obj); 7359 assert(res, "Empty non-zero size stack should have space for single push"); 7360 while (!_markStack->isEmpty()) { 7361 oop new_oop = _markStack->pop(); 7362 // Skip verifying header mark word below because we are 7363 // running concurrent with mutators. 7364 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); 7365 // now scan this oop's oops 7366 new_oop->oop_iterate(&pushOrMarkClosure); 7367 do_yield_check(); 7368 } 7369 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); 7370 } 7371 7372 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task, 7373 CMSCollector* collector, MemRegion span, 7374 CMSBitMap* bit_map, 7375 OopTaskQueue* work_queue, 7376 CMSMarkStack* overflow_stack, 7377 bool should_yield): 7378 _collector(collector), 7379 _whole_span(collector->_span), 7380 _span(span), 7381 _bit_map(bit_map), 7382 _mut(&collector->_modUnionTable), 7383 _work_queue(work_queue), 7384 _overflow_stack(overflow_stack), 7385 _yield(should_yield), 7386 _skip_bits(0), 7387 _task(task) 7388 { 7389 assert(_work_queue->size() == 0, "work_queue should be empty"); 7390 _finger = span.start(); 7391 _threshold = _finger; // XXX Defer clear-on-enter optimization for now 7392 assert(_span.contains(_finger), "Out of bounds _finger?"); 7393 } 7394 7395 // Should revisit to see if this should be restructured for 7396 // greater efficiency. 7397 bool Par_MarkFromRootsClosure::do_bit(size_t offset) { 7398 if (_skip_bits > 0) { 7399 _skip_bits--; 7400 return true; 7401 } 7402 // convert offset into a HeapWord* 7403 HeapWord* addr = _bit_map->startWord() + offset; 7404 assert(_bit_map->endWord() && addr < _bit_map->endWord(), 7405 "address out of range"); 7406 assert(_bit_map->isMarked(addr), "tautology"); 7407 if (_bit_map->isMarked(addr+1)) { 7408 // this is an allocated object that might not yet be initialized 7409 assert(_skip_bits == 0, "tautology"); 7410 _skip_bits = 2; // skip next two marked bits ("Printezis-marks") 7411 oop p = oop(addr); 7412 if (p->klass_or_null() == NULL) { 7413 // in the case of Clean-on-Enter optimization, redirty card 7414 // and avoid clearing card by increasing the threshold. 7415 return true; 7416 } 7417 } 7418 scan_oops_in_oop(addr); 7419 return true; 7420 } 7421 7422 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { 7423 assert(_bit_map->isMarked(ptr), "expected bit to be set"); 7424 // Should we assert that our work queue is empty or 7425 // below some drain limit? 7426 assert(_work_queue->size() == 0, 7427 "should drain stack to limit stack usage"); 7428 // convert ptr to an oop preparatory to scanning 7429 oop obj = oop(ptr); 7430 // Ignore mark word in verification below, since we 7431 // may be running concurrent with mutators. 7432 assert(obj->is_oop(true), "should be an oop"); 7433 assert(_finger <= ptr, "_finger runneth ahead"); 7434 // advance the finger to right end of this object 7435 _finger = ptr + obj->size(); 7436 assert(_finger > ptr, "we just incremented it above"); 7437 // On large heaps, it may take us some time to get through 7438 // the marking phase (especially if running iCMS). During 7439 // this time it's possible that a lot of mutations have 7440 // accumulated in the card table and the mod union table -- 7441 // these mutation records are redundant until we have 7442 // actually traced into the corresponding card. 7443 // Here, we check whether advancing the finger would make 7444 // us cross into a new card, and if so clear corresponding 7445 // cards in the MUT (preclean them in the card-table in the 7446 // future). 7447 7448 // The clean-on-enter optimization is disabled by default, 7449 // until we fix 6178663. 7450 if (CMSCleanOnEnter && (_finger > _threshold)) { 7451 // [_threshold, _finger) represents the interval 7452 // of cards to be cleared in MUT (or precleaned in card table). 7453 // The set of cards to be cleared is all those that overlap 7454 // with the interval [_threshold, _finger); note that 7455 // _threshold is always kept card-aligned but _finger isn't 7456 // always card-aligned. 7457 HeapWord* old_threshold = _threshold; 7458 assert(old_threshold == (HeapWord*)round_to( 7459 (intptr_t)old_threshold, CardTableModRefBS::card_size), 7460 "_threshold should always be card-aligned"); 7461 _threshold = (HeapWord*)round_to( 7462 (intptr_t)_finger, CardTableModRefBS::card_size); 7463 MemRegion mr(old_threshold, _threshold); 7464 assert(!mr.is_empty(), "Control point invariant"); 7465 assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? 7466 _mut->clear_range(mr); 7467 } 7468 7469 // Note: the local finger doesn't advance while we drain 7470 // the stack below, but the global finger sure can and will. 7471 HeapWord** gfa = _task->global_finger_addr(); 7472 Par_PushOrMarkClosure pushOrMarkClosure(_collector, 7473 _span, _bit_map, 7474 _work_queue, 7475 _overflow_stack, 7476 _finger, 7477 gfa, this); 7478 bool res = _work_queue->push(obj); // overflow could occur here 7479 assert(res, "Will hold once we use workqueues"); 7480 while (true) { 7481 oop new_oop; 7482 if (!_work_queue->pop_local(new_oop)) { 7483 // We emptied our work_queue; check if there's stuff that can 7484 // be gotten from the overflow stack. 7485 if (CMSConcMarkingTask::get_work_from_overflow_stack( 7486 _overflow_stack, _work_queue)) { 7487 do_yield_check(); 7488 continue; 7489 } else { // done 7490 break; 7491 } 7492 } 7493 // Skip verifying header mark word below because we are 7494 // running concurrent with mutators. 7495 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); 7496 // now scan this oop's oops 7497 new_oop->oop_iterate(&pushOrMarkClosure); 7498 do_yield_check(); 7499 } 7500 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); 7501 } 7502 7503 // Yield in response to a request from VM Thread or 7504 // from mutators. 7505 void Par_MarkFromRootsClosure::do_yield_work() { 7506 assert(_task != NULL, "sanity"); 7507 _task->yield(); 7508 } 7509 7510 // A variant of the above used for verifying CMS marking work. 7511 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, 7512 MemRegion span, 7513 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 7514 CMSMarkStack* mark_stack): 7515 _collector(collector), 7516 _span(span), 7517 _verification_bm(verification_bm), 7518 _cms_bm(cms_bm), 7519 _mark_stack(mark_stack), 7520 _pam_verify_closure(collector, span, verification_bm, cms_bm, 7521 mark_stack) 7522 { 7523 assert(_mark_stack->isEmpty(), "stack should be empty"); 7524 _finger = _verification_bm->startWord(); 7525 assert(_collector->_restart_addr == NULL, "Sanity check"); 7526 assert(_span.contains(_finger), "Out of bounds _finger?"); 7527 } 7528 7529 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { 7530 assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); 7531 assert(_span.contains(addr), "Out of bounds _finger?"); 7532 _finger = addr; 7533 } 7534 7535 // Should revisit to see if this should be restructured for 7536 // greater efficiency. 7537 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) { 7538 // convert offset into a HeapWord* 7539 HeapWord* addr = _verification_bm->startWord() + offset; 7540 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), 7541 "address out of range"); 7542 assert(_verification_bm->isMarked(addr), "tautology"); 7543 assert(_cms_bm->isMarked(addr), "tautology"); 7544 7545 assert(_mark_stack->isEmpty(), 7546 "should drain stack to limit stack usage"); 7547 // convert addr to an oop preparatory to scanning 7548 oop obj = oop(addr); 7549 assert(obj->is_oop(), "should be an oop"); 7550 assert(_finger <= addr, "_finger runneth ahead"); 7551 // advance the finger to right end of this object 7552 _finger = addr + obj->size(); 7553 assert(_finger > addr, "we just incremented it above"); 7554 // Note: the finger doesn't advance while we drain 7555 // the stack below. 7556 bool res = _mark_stack->push(obj); 7557 assert(res, "Empty non-zero size stack should have space for single push"); 7558 while (!_mark_stack->isEmpty()) { 7559 oop new_oop = _mark_stack->pop(); 7560 assert(new_oop->is_oop(), "Oops! expected to pop an oop"); 7561 // now scan this oop's oops 7562 new_oop->oop_iterate(&_pam_verify_closure); 7563 } 7564 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); 7565 return true; 7566 } 7567 7568 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( 7569 CMSCollector* collector, MemRegion span, 7570 CMSBitMap* verification_bm, CMSBitMap* cms_bm, 7571 CMSMarkStack* mark_stack): 7572 CMSOopClosure(collector->ref_processor()), 7573 _collector(collector), 7574 _span(span), 7575 _verification_bm(verification_bm), 7576 _cms_bm(cms_bm), 7577 _mark_stack(mark_stack) 7578 { } 7579 7580 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 7581 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); } 7582 7583 // Upon stack overflow, we discard (part of) the stack, 7584 // remembering the least address amongst those discarded 7585 // in CMSCollector's _restart_address. 7586 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { 7587 // Remember the least grey address discarded 7588 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); 7589 _collector->lower_restart_addr(ra); 7590 _mark_stack->reset(); // discard stack contents 7591 _mark_stack->expand(); // expand the stack if possible 7592 } 7593 7594 void PushAndMarkVerifyClosure::do_oop(oop obj) { 7595 assert(obj->is_oop_or_null(), "expected an oop or NULL"); 7596 HeapWord* addr = (HeapWord*)obj; 7597 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { 7598 // Oop lies in _span and isn't yet grey or black 7599 _verification_bm->mark(addr); // now grey 7600 if (!_cms_bm->isMarked(addr)) { 7601 oop(addr)->print(); 7602 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", 7603 addr); 7604 fatal("... aborting"); 7605 } 7606 7607 if (!_mark_stack->push(obj)) { // stack overflow 7608 if (PrintCMSStatistics != 0) { 7609 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " 7610 SIZE_FORMAT, _mark_stack->capacity()); 7611 } 7612 assert(_mark_stack->isFull(), "Else push should have succeeded"); 7613 handle_stack_overflow(addr); 7614 } 7615 // anything including and to the right of _finger 7616 // will be scanned as we iterate over the remainder of the 7617 // bit map 7618 } 7619 } 7620 7621 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, 7622 MemRegion span, 7623 CMSBitMap* bitMap, CMSMarkStack* markStack, 7624 HeapWord* finger, MarkFromRootsClosure* parent) : 7625 CMSOopClosure(collector->ref_processor()), 7626 _collector(collector), 7627 _span(span), 7628 _bitMap(bitMap), 7629 _markStack(markStack), 7630 _finger(finger), 7631 _parent(parent) 7632 { } 7633 7634 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector, 7635 MemRegion span, 7636 CMSBitMap* bit_map, 7637 OopTaskQueue* work_queue, 7638 CMSMarkStack* overflow_stack, 7639 HeapWord* finger, 7640 HeapWord** global_finger_addr, 7641 Par_MarkFromRootsClosure* parent) : 7642 CMSOopClosure(collector->ref_processor()), 7643 _collector(collector), 7644 _whole_span(collector->_span), 7645 _span(span), 7646 _bit_map(bit_map), 7647 _work_queue(work_queue), 7648 _overflow_stack(overflow_stack), 7649 _finger(finger), 7650 _global_finger_addr(global_finger_addr), 7651 _parent(parent) 7652 { } 7653 7654 // Assumes thread-safe access by callers, who are 7655 // responsible for mutual exclusion. 7656 void CMSCollector::lower_restart_addr(HeapWord* low) { 7657 assert(_span.contains(low), "Out of bounds addr"); 7658 if (_restart_addr == NULL) { 7659 _restart_addr = low; 7660 } else { 7661 _restart_addr = MIN2(_restart_addr, low); 7662 } 7663 } 7664 7665 // Upon stack overflow, we discard (part of) the stack, 7666 // remembering the least address amongst those discarded 7667 // in CMSCollector's _restart_address. 7668 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 7669 // Remember the least grey address discarded 7670 HeapWord* ra = (HeapWord*)_markStack->least_value(lost); 7671 _collector->lower_restart_addr(ra); 7672 _markStack->reset(); // discard stack contents 7673 _markStack->expand(); // expand the stack if possible 7674 } 7675 7676 // Upon stack overflow, we discard (part of) the stack, 7677 // remembering the least address amongst those discarded 7678 // in CMSCollector's _restart_address. 7679 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { 7680 // We need to do this under a mutex to prevent other 7681 // workers from interfering with the work done below. 7682 MutexLockerEx ml(_overflow_stack->par_lock(), 7683 Mutex::_no_safepoint_check_flag); 7684 // Remember the least grey address discarded 7685 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); 7686 _collector->lower_restart_addr(ra); 7687 _overflow_stack->reset(); // discard stack contents 7688 _overflow_stack->expand(); // expand the stack if possible 7689 } 7690 7691 void CMKlassClosure::do_klass(Klass* k) { 7692 assert(_oop_closure != NULL, "Not initialized?"); 7693 k->oops_do(_oop_closure); 7694 } 7695 7696 void PushOrMarkClosure::do_oop(oop obj) { 7697 // Ignore mark word because we are running concurrent with mutators. 7698 assert(obj->is_oop_or_null(true), "expected an oop or NULL"); 7699 HeapWord* addr = (HeapWord*)obj; 7700 if (_span.contains(addr) && !_bitMap->isMarked(addr)) { 7701 // Oop lies in _span and isn't yet grey or black 7702 _bitMap->mark(addr); // now grey 7703 if (addr < _finger) { 7704 // the bit map iteration has already either passed, or 7705 // sampled, this bit in the bit map; we'll need to 7706 // use the marking stack to scan this oop's oops. 7707 bool simulate_overflow = false; 7708 NOT_PRODUCT( 7709 if (CMSMarkStackOverflowALot && 7710 _collector->simulate_overflow()) { 7711 // simulate a stack overflow 7712 simulate_overflow = true; 7713 } 7714 ) 7715 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow 7716 if (PrintCMSStatistics != 0) { 7717 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " 7718 SIZE_FORMAT, _markStack->capacity()); 7719 } 7720 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); 7721 handle_stack_overflow(addr); 7722 } 7723 } 7724 // anything including and to the right of _finger 7725 // will be scanned as we iterate over the remainder of the 7726 // bit map 7727 do_yield_check(); 7728 } 7729 } 7730 7731 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); } 7732 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); } 7733 7734 void Par_PushOrMarkClosure::do_oop(oop obj) { 7735 // Ignore mark word because we are running concurrent with mutators. 7736 assert(obj->is_oop_or_null(true), "expected an oop or NULL"); 7737 HeapWord* addr = (HeapWord*)obj; 7738 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { 7739 // Oop lies in _span and isn't yet grey or black 7740 // We read the global_finger (volatile read) strictly after marking oop 7741 bool res = _bit_map->par_mark(addr); // now grey 7742 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; 7743 // Should we push this marked oop on our stack? 7744 // -- if someone else marked it, nothing to do 7745 // -- if target oop is above global finger nothing to do 7746 // -- if target oop is in chunk and above local finger 7747 // then nothing to do 7748 // -- else push on work queue 7749 if ( !res // someone else marked it, they will deal with it 7750 || (addr >= *gfa) // will be scanned in a later task 7751 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk 7752 return; 7753 } 7754 // the bit map iteration has already either passed, or 7755 // sampled, this bit in the bit map; we'll need to 7756 // use the marking stack to scan this oop's oops. 7757 bool simulate_overflow = false; 7758 NOT_PRODUCT( 7759 if (CMSMarkStackOverflowALot && 7760 _collector->simulate_overflow()) { 7761 // simulate a stack overflow 7762 simulate_overflow = true; 7763 } 7764 ) 7765 if (simulate_overflow || 7766 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) { 7767 // stack overflow 7768 if (PrintCMSStatistics != 0) { 7769 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " 7770 SIZE_FORMAT, _overflow_stack->capacity()); 7771 } 7772 // We cannot assert that the overflow stack is full because 7773 // it may have been emptied since. 7774 assert(simulate_overflow || 7775 _work_queue->size() == _work_queue->max_elems(), 7776 "Else push should have succeeded"); 7777 handle_stack_overflow(addr); 7778 } 7779 do_yield_check(); 7780 } 7781 } 7782 7783 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); } 7784 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); } 7785 7786 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, 7787 MemRegion span, 7788 ReferenceProcessor* rp, 7789 CMSBitMap* bit_map, 7790 CMSBitMap* mod_union_table, 7791 CMSMarkStack* mark_stack, 7792 bool concurrent_precleaning): 7793 CMSOopClosure(rp), 7794 _collector(collector), 7795 _span(span), 7796 _bit_map(bit_map), 7797 _mod_union_table(mod_union_table), 7798 _mark_stack(mark_stack), 7799 _concurrent_precleaning(concurrent_precleaning) 7800 { 7801 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); 7802 } 7803 7804 // Grey object rescan during pre-cleaning and second checkpoint phases -- 7805 // the non-parallel version (the parallel version appears further below.) 7806 void PushAndMarkClosure::do_oop(oop obj) { 7807 // Ignore mark word verification. If during concurrent precleaning, 7808 // the object monitor may be locked. If during the checkpoint 7809 // phases, the object may already have been reached by a different 7810 // path and may be at the end of the global overflow list (so 7811 // the mark word may be NULL). 7812 assert(obj->is_oop_or_null(true /* ignore mark word */), 7813 "expected an oop or NULL"); 7814 HeapWord* addr = (HeapWord*)obj; 7815 // Check if oop points into the CMS generation 7816 // and is not marked 7817 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 7818 // a white object ... 7819 _bit_map->mark(addr); // ... now grey 7820 // push on the marking stack (grey set) 7821 bool simulate_overflow = false; 7822 NOT_PRODUCT( 7823 if (CMSMarkStackOverflowALot && 7824 _collector->simulate_overflow()) { 7825 // simulate a stack overflow 7826 simulate_overflow = true; 7827 } 7828 ) 7829 if (simulate_overflow || !_mark_stack->push(obj)) { 7830 if (_concurrent_precleaning) { 7831 // During precleaning we can just dirty the appropriate card(s) 7832 // in the mod union table, thus ensuring that the object remains 7833 // in the grey set and continue. In the case of object arrays 7834 // we need to dirty all of the cards that the object spans, 7835 // since the rescan of object arrays will be limited to the 7836 // dirty cards. 7837 // Note that no one can be intefering with us in this action 7838 // of dirtying the mod union table, so no locking or atomics 7839 // are required. 7840 if (obj->is_objArray()) { 7841 size_t sz = obj->size(); 7842 HeapWord* end_card_addr = (HeapWord*)round_to( 7843 (intptr_t)(addr+sz), CardTableModRefBS::card_size); 7844 MemRegion redirty_range = MemRegion(addr, end_card_addr); 7845 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 7846 _mod_union_table->mark_range(redirty_range); 7847 } else { 7848 _mod_union_table->mark(addr); 7849 } 7850 _collector->_ser_pmc_preclean_ovflw++; 7851 } else { 7852 // During the remark phase, we need to remember this oop 7853 // in the overflow list. 7854 _collector->push_on_overflow_list(obj); 7855 _collector->_ser_pmc_remark_ovflw++; 7856 } 7857 } 7858 } 7859 } 7860 7861 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector, 7862 MemRegion span, 7863 ReferenceProcessor* rp, 7864 CMSBitMap* bit_map, 7865 OopTaskQueue* work_queue): 7866 CMSOopClosure(rp), 7867 _collector(collector), 7868 _span(span), 7869 _bit_map(bit_map), 7870 _work_queue(work_queue) 7871 { 7872 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); 7873 } 7874 7875 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); } 7876 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); } 7877 7878 // Grey object rescan during second checkpoint phase -- 7879 // the parallel version. 7880 void Par_PushAndMarkClosure::do_oop(oop obj) { 7881 // In the assert below, we ignore the mark word because 7882 // this oop may point to an already visited object that is 7883 // on the overflow stack (in which case the mark word has 7884 // been hijacked for chaining into the overflow stack -- 7885 // if this is the last object in the overflow stack then 7886 // its mark word will be NULL). Because this object may 7887 // have been subsequently popped off the global overflow 7888 // stack, and the mark word possibly restored to the prototypical 7889 // value, by the time we get to examined this failing assert in 7890 // the debugger, is_oop_or_null(false) may subsequently start 7891 // to hold. 7892 assert(obj->is_oop_or_null(true), 7893 "expected an oop or NULL"); 7894 HeapWord* addr = (HeapWord*)obj; 7895 // Check if oop points into the CMS generation 7896 // and is not marked 7897 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { 7898 // a white object ... 7899 // If we manage to "claim" the object, by being the 7900 // first thread to mark it, then we push it on our 7901 // marking stack 7902 if (_bit_map->par_mark(addr)) { // ... now grey 7903 // push on work queue (grey set) 7904 bool simulate_overflow = false; 7905 NOT_PRODUCT( 7906 if (CMSMarkStackOverflowALot && 7907 _collector->par_simulate_overflow()) { 7908 // simulate a stack overflow 7909 simulate_overflow = true; 7910 } 7911 ) 7912 if (simulate_overflow || !_work_queue->push(obj)) { 7913 _collector->par_push_on_overflow_list(obj); 7914 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS 7915 } 7916 } // Else, some other thread got there first 7917 } 7918 } 7919 7920 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); } 7921 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); } 7922 7923 void CMSPrecleanRefsYieldClosure::do_yield_work() { 7924 Mutex* bml = _collector->bitMapLock(); 7925 assert_lock_strong(bml); 7926 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 7927 "CMS thread should hold CMS token"); 7928 7929 bml->unlock(); 7930 ConcurrentMarkSweepThread::desynchronize(true); 7931 7932 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7933 7934 _collector->stopTimer(); 7935 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 7936 if (PrintCMSStatistics != 0) { 7937 _collector->incrementYields(); 7938 } 7939 _collector->icms_wait(); 7940 7941 // See the comment in coordinator_yield() 7942 for (unsigned i = 0; i < CMSYieldSleepCount && 7943 ConcurrentMarkSweepThread::should_yield() && 7944 !CMSCollector::foregroundGCIsActive(); ++i) { 7945 os::sleep(Thread::current(), 1, false); 7946 ConcurrentMarkSweepThread::acknowledge_yield_request(); 7947 } 7948 7949 ConcurrentMarkSweepThread::synchronize(true); 7950 bml->lock(); 7951 7952 _collector->startTimer(); 7953 } 7954 7955 bool CMSPrecleanRefsYieldClosure::should_return() { 7956 if (ConcurrentMarkSweepThread::should_yield()) { 7957 do_yield_work(); 7958 } 7959 return _collector->foregroundGCIsActive(); 7960 } 7961 7962 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { 7963 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0, 7964 "mr should be aligned to start at a card boundary"); 7965 // We'd like to assert: 7966 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0, 7967 // "mr should be a range of cards"); 7968 // However, that would be too strong in one case -- the last 7969 // partition ends at _unallocated_block which, in general, can be 7970 // an arbitrary boundary, not necessarily card aligned. 7971 if (PrintCMSStatistics != 0) { 7972 _num_dirty_cards += 7973 mr.word_size()/CardTableModRefBS::card_size_in_words; 7974 } 7975 _space->object_iterate_mem(mr, &_scan_cl); 7976 } 7977 7978 SweepClosure::SweepClosure(CMSCollector* collector, 7979 ConcurrentMarkSweepGeneration* g, 7980 CMSBitMap* bitMap, bool should_yield) : 7981 _collector(collector), 7982 _g(g), 7983 _sp(g->cmsSpace()), 7984 _limit(_sp->sweep_limit()), 7985 _freelistLock(_sp->freelistLock()), 7986 _bitMap(bitMap), 7987 _yield(should_yield), 7988 _inFreeRange(false), // No free range at beginning of sweep 7989 _freeRangeInFreeLists(false), // No free range at beginning of sweep 7990 _lastFreeRangeCoalesced(false), 7991 _freeFinger(g->used_region().start()) 7992 { 7993 NOT_PRODUCT( 7994 _numObjectsFreed = 0; 7995 _numWordsFreed = 0; 7996 _numObjectsLive = 0; 7997 _numWordsLive = 0; 7998 _numObjectsAlreadyFree = 0; 7999 _numWordsAlreadyFree = 0; 8000 _last_fc = NULL; 8001 8002 _sp->initializeIndexedFreeListArrayReturnedBytes(); 8003 _sp->dictionary()->initialize_dict_returned_bytes(); 8004 ) 8005 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 8006 "sweep _limit out of bounds"); 8007 if (CMSTraceSweeper) { 8008 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT, 8009 _limit); 8010 } 8011 } 8012 8013 void SweepClosure::print_on(outputStream* st) const { 8014 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")", 8015 _sp->bottom(), _sp->end()); 8016 tty->print_cr("_limit = " PTR_FORMAT, _limit); 8017 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger); 8018 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);) 8019 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d", 8020 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced); 8021 } 8022 8023 #ifndef PRODUCT 8024 // Assertion checking only: no useful work in product mode -- 8025 // however, if any of the flags below become product flags, 8026 // you may need to review this code to see if it needs to be 8027 // enabled in product mode. 8028 SweepClosure::~SweepClosure() { 8029 assert_lock_strong(_freelistLock); 8030 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 8031 "sweep _limit out of bounds"); 8032 if (inFreeRange()) { 8033 warning("inFreeRange() should have been reset; dumping state of SweepClosure"); 8034 print(); 8035 ShouldNotReachHere(); 8036 } 8037 if (Verbose && PrintGC) { 8038 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes", 8039 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); 8040 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, " 8041 SIZE_FORMAT" bytes " 8042 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes", 8043 _numObjectsLive, _numWordsLive*sizeof(HeapWord), 8044 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); 8045 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) 8046 * sizeof(HeapWord); 8047 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes); 8048 8049 if (PrintCMSStatistics && CMSVerifyReturnedBytes) { 8050 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); 8051 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes(); 8052 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes; 8053 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes); 8054 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes", 8055 indexListReturnedBytes); 8056 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes", 8057 dict_returned_bytes); 8058 } 8059 } 8060 if (CMSTraceSweeper) { 8061 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================", 8062 _limit); 8063 } 8064 } 8065 #endif // PRODUCT 8066 8067 void SweepClosure::initialize_free_range(HeapWord* freeFinger, 8068 bool freeRangeInFreeLists) { 8069 if (CMSTraceSweeper) { 8070 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n", 8071 freeFinger, freeRangeInFreeLists); 8072 } 8073 assert(!inFreeRange(), "Trampling existing free range"); 8074 set_inFreeRange(true); 8075 set_lastFreeRangeCoalesced(false); 8076 8077 set_freeFinger(freeFinger); 8078 set_freeRangeInFreeLists(freeRangeInFreeLists); 8079 if (CMSTestInFreeList) { 8080 if (freeRangeInFreeLists) { 8081 FreeChunk* fc = (FreeChunk*) freeFinger; 8082 assert(fc->is_free(), "A chunk on the free list should be free."); 8083 assert(fc->size() > 0, "Free range should have a size"); 8084 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists"); 8085 } 8086 } 8087 } 8088 8089 // Note that the sweeper runs concurrently with mutators. Thus, 8090 // it is possible for direct allocation in this generation to happen 8091 // in the middle of the sweep. Note that the sweeper also coalesces 8092 // contiguous free blocks. Thus, unless the sweeper and the allocator 8093 // synchronize appropriately freshly allocated blocks may get swept up. 8094 // This is accomplished by the sweeper locking the free lists while 8095 // it is sweeping. Thus blocks that are determined to be free are 8096 // indeed free. There is however one additional complication: 8097 // blocks that have been allocated since the final checkpoint and 8098 // mark, will not have been marked and so would be treated as 8099 // unreachable and swept up. To prevent this, the allocator marks 8100 // the bit map when allocating during the sweep phase. This leads, 8101 // however, to a further complication -- objects may have been allocated 8102 // but not yet initialized -- in the sense that the header isn't yet 8103 // installed. The sweeper can not then determine the size of the block 8104 // in order to skip over it. To deal with this case, we use a technique 8105 // (due to Printezis) to encode such uninitialized block sizes in the 8106 // bit map. Since the bit map uses a bit per every HeapWord, but the 8107 // CMS generation has a minimum object size of 3 HeapWords, it follows 8108 // that "normal marks" won't be adjacent in the bit map (there will 8109 // always be at least two 0 bits between successive 1 bits). We make use 8110 // of these "unused" bits to represent uninitialized blocks -- the bit 8111 // corresponding to the start of the uninitialized object and the next 8112 // bit are both set. Finally, a 1 bit marks the end of the object that 8113 // started with the two consecutive 1 bits to indicate its potentially 8114 // uninitialized state. 8115 8116 size_t SweepClosure::do_blk_careful(HeapWord* addr) { 8117 FreeChunk* fc = (FreeChunk*)addr; 8118 size_t res; 8119 8120 // Check if we are done sweeping. Below we check "addr >= _limit" rather 8121 // than "addr == _limit" because although _limit was a block boundary when 8122 // we started the sweep, it may no longer be one because heap expansion 8123 // may have caused us to coalesce the block ending at the address _limit 8124 // with a newly expanded chunk (this happens when _limit was set to the 8125 // previous _end of the space), so we may have stepped past _limit: 8126 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740. 8127 if (addr >= _limit) { // we have swept up to or past the limit: finish up 8128 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), 8129 "sweep _limit out of bounds"); 8130 assert(addr < _sp->end(), "addr out of bounds"); 8131 // Flush any free range we might be holding as a single 8132 // coalesced chunk to the appropriate free list. 8133 if (inFreeRange()) { 8134 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit, 8135 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger())); 8136 flush_cur_free_chunk(freeFinger(), 8137 pointer_delta(addr, freeFinger())); 8138 if (CMSTraceSweeper) { 8139 gclog_or_tty->print("Sweep: last chunk: "); 8140 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") " 8141 "[coalesced:"SIZE_FORMAT"]\n", 8142 freeFinger(), pointer_delta(addr, freeFinger()), 8143 lastFreeRangeCoalesced()); 8144 } 8145 } 8146 8147 // help the iterator loop finish 8148 return pointer_delta(_sp->end(), addr); 8149 } 8150 8151 assert(addr < _limit, "sweep invariant"); 8152 // check if we should yield 8153 do_yield_check(addr); 8154 if (fc->is_free()) { 8155 // Chunk that is already free 8156 res = fc->size(); 8157 do_already_free_chunk(fc); 8158 debug_only(_sp->verifyFreeLists()); 8159 // If we flush the chunk at hand in lookahead_and_flush() 8160 // and it's coalesced with a preceding chunk, then the 8161 // process of "mangling" the payload of the coalesced block 8162 // will cause erasure of the size information from the 8163 // (erstwhile) header of all the coalesced blocks but the 8164 // first, so the first disjunct in the assert will not hold 8165 // in that specific case (in which case the second disjunct 8166 // will hold). 8167 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit, 8168 "Otherwise the size info doesn't change at this step"); 8169 NOT_PRODUCT( 8170 _numObjectsAlreadyFree++; 8171 _numWordsAlreadyFree += res; 8172 ) 8173 NOT_PRODUCT(_last_fc = fc;) 8174 } else if (!_bitMap->isMarked(addr)) { 8175 // Chunk is fresh garbage 8176 res = do_garbage_chunk(fc); 8177 debug_only(_sp->verifyFreeLists()); 8178 NOT_PRODUCT( 8179 _numObjectsFreed++; 8180 _numWordsFreed += res; 8181 ) 8182 } else { 8183 // Chunk that is alive. 8184 res = do_live_chunk(fc); 8185 debug_only(_sp->verifyFreeLists()); 8186 NOT_PRODUCT( 8187 _numObjectsLive++; 8188 _numWordsLive += res; 8189 ) 8190 } 8191 return res; 8192 } 8193 8194 // For the smart allocation, record following 8195 // split deaths - a free chunk is removed from its free list because 8196 // it is being split into two or more chunks. 8197 // split birth - a free chunk is being added to its free list because 8198 // a larger free chunk has been split and resulted in this free chunk. 8199 // coal death - a free chunk is being removed from its free list because 8200 // it is being coalesced into a large free chunk. 8201 // coal birth - a free chunk is being added to its free list because 8202 // it was created when two or more free chunks where coalesced into 8203 // this free chunk. 8204 // 8205 // These statistics are used to determine the desired number of free 8206 // chunks of a given size. The desired number is chosen to be relative 8207 // to the end of a CMS sweep. The desired number at the end of a sweep 8208 // is the 8209 // count-at-end-of-previous-sweep (an amount that was enough) 8210 // - count-at-beginning-of-current-sweep (the excess) 8211 // + split-births (gains in this size during interval) 8212 // - split-deaths (demands on this size during interval) 8213 // where the interval is from the end of one sweep to the end of the 8214 // next. 8215 // 8216 // When sweeping the sweeper maintains an accumulated chunk which is 8217 // the chunk that is made up of chunks that have been coalesced. That 8218 // will be termed the left-hand chunk. A new chunk of garbage that 8219 // is being considered for coalescing will be referred to as the 8220 // right-hand chunk. 8221 // 8222 // When making a decision on whether to coalesce a right-hand chunk with 8223 // the current left-hand chunk, the current count vs. the desired count 8224 // of the left-hand chunk is considered. Also if the right-hand chunk 8225 // is near the large chunk at the end of the heap (see 8226 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the 8227 // left-hand chunk is coalesced. 8228 // 8229 // When making a decision about whether to split a chunk, the desired count 8230 // vs. the current count of the candidate to be split is also considered. 8231 // If the candidate is underpopulated (currently fewer chunks than desired) 8232 // a chunk of an overpopulated (currently more chunks than desired) size may 8233 // be chosen. The "hint" associated with a free list, if non-null, points 8234 // to a free list which may be overpopulated. 8235 // 8236 8237 void SweepClosure::do_already_free_chunk(FreeChunk* fc) { 8238 const size_t size = fc->size(); 8239 // Chunks that cannot be coalesced are not in the 8240 // free lists. 8241 if (CMSTestInFreeList && !fc->cantCoalesce()) { 8242 assert(_sp->verify_chunk_in_free_list(fc), 8243 "free chunk should be in free lists"); 8244 } 8245 // a chunk that is already free, should not have been 8246 // marked in the bit map 8247 HeapWord* const addr = (HeapWord*) fc; 8248 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); 8249 // Verify that the bit map has no bits marked between 8250 // addr and purported end of this block. 8251 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 8252 8253 // Some chunks cannot be coalesced under any circumstances. 8254 // See the definition of cantCoalesce(). 8255 if (!fc->cantCoalesce()) { 8256 // This chunk can potentially be coalesced. 8257 if (_sp->adaptive_freelists()) { 8258 // All the work is done in 8259 do_post_free_or_garbage_chunk(fc, size); 8260 } else { // Not adaptive free lists 8261 // this is a free chunk that can potentially be coalesced by the sweeper; 8262 if (!inFreeRange()) { 8263 // if the next chunk is a free block that can't be coalesced 8264 // it doesn't make sense to remove this chunk from the free lists 8265 FreeChunk* nextChunk = (FreeChunk*)(addr + size); 8266 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?"); 8267 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ... 8268 nextChunk->is_free() && // ... which is free... 8269 nextChunk->cantCoalesce()) { // ... but can't be coalesced 8270 // nothing to do 8271 } else { 8272 // Potentially the start of a new free range: 8273 // Don't eagerly remove it from the free lists. 8274 // No need to remove it if it will just be put 8275 // back again. (Also from a pragmatic point of view 8276 // if it is a free block in a region that is beyond 8277 // any allocated blocks, an assertion will fail) 8278 // Remember the start of a free run. 8279 initialize_free_range(addr, true); 8280 // end - can coalesce with next chunk 8281 } 8282 } else { 8283 // the midst of a free range, we are coalescing 8284 print_free_block_coalesced(fc); 8285 if (CMSTraceSweeper) { 8286 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size); 8287 } 8288 // remove it from the free lists 8289 _sp->removeFreeChunkFromFreeLists(fc); 8290 set_lastFreeRangeCoalesced(true); 8291 // If the chunk is being coalesced and the current free range is 8292 // in the free lists, remove the current free range so that it 8293 // will be returned to the free lists in its entirety - all 8294 // the coalesced pieces included. 8295 if (freeRangeInFreeLists()) { 8296 FreeChunk* ffc = (FreeChunk*) freeFinger(); 8297 assert(ffc->size() == pointer_delta(addr, freeFinger()), 8298 "Size of free range is inconsistent with chunk size."); 8299 if (CMSTestInFreeList) { 8300 assert(_sp->verify_chunk_in_free_list(ffc), 8301 "free range is not in free lists"); 8302 } 8303 _sp->removeFreeChunkFromFreeLists(ffc); 8304 set_freeRangeInFreeLists(false); 8305 } 8306 } 8307 } 8308 // Note that if the chunk is not coalescable (the else arm 8309 // below), we unconditionally flush, without needing to do 8310 // a "lookahead," as we do below. 8311 if (inFreeRange()) lookahead_and_flush(fc, size); 8312 } else { 8313 // Code path common to both original and adaptive free lists. 8314 8315 // cant coalesce with previous block; this should be treated 8316 // as the end of a free run if any 8317 if (inFreeRange()) { 8318 // we kicked some butt; time to pick up the garbage 8319 assert(freeFinger() < addr, "freeFinger points too high"); 8320 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 8321 } 8322 // else, nothing to do, just continue 8323 } 8324 } 8325 8326 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) { 8327 // This is a chunk of garbage. It is not in any free list. 8328 // Add it to a free list or let it possibly be coalesced into 8329 // a larger chunk. 8330 HeapWord* const addr = (HeapWord*) fc; 8331 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 8332 8333 if (_sp->adaptive_freelists()) { 8334 // Verify that the bit map has no bits marked between 8335 // addr and purported end of just dead object. 8336 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 8337 8338 do_post_free_or_garbage_chunk(fc, size); 8339 } else { 8340 if (!inFreeRange()) { 8341 // start of a new free range 8342 assert(size > 0, "A free range should have a size"); 8343 initialize_free_range(addr, false); 8344 } else { 8345 // this will be swept up when we hit the end of the 8346 // free range 8347 if (CMSTraceSweeper) { 8348 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size); 8349 } 8350 // If the chunk is being coalesced and the current free range is 8351 // in the free lists, remove the current free range so that it 8352 // will be returned to the free lists in its entirety - all 8353 // the coalesced pieces included. 8354 if (freeRangeInFreeLists()) { 8355 FreeChunk* ffc = (FreeChunk*)freeFinger(); 8356 assert(ffc->size() == pointer_delta(addr, freeFinger()), 8357 "Size of free range is inconsistent with chunk size."); 8358 if (CMSTestInFreeList) { 8359 assert(_sp->verify_chunk_in_free_list(ffc), 8360 "free range is not in free lists"); 8361 } 8362 _sp->removeFreeChunkFromFreeLists(ffc); 8363 set_freeRangeInFreeLists(false); 8364 } 8365 set_lastFreeRangeCoalesced(true); 8366 } 8367 // this will be swept up when we hit the end of the free range 8368 8369 // Verify that the bit map has no bits marked between 8370 // addr and purported end of just dead object. 8371 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); 8372 } 8373 assert(_limit >= addr + size, 8374 "A freshly garbage chunk can't possibly straddle over _limit"); 8375 if (inFreeRange()) lookahead_and_flush(fc, size); 8376 return size; 8377 } 8378 8379 size_t SweepClosure::do_live_chunk(FreeChunk* fc) { 8380 HeapWord* addr = (HeapWord*) fc; 8381 // The sweeper has just found a live object. Return any accumulated 8382 // left hand chunk to the free lists. 8383 if (inFreeRange()) { 8384 assert(freeFinger() < addr, "freeFinger points too high"); 8385 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 8386 } 8387 8388 // This object is live: we'd normally expect this to be 8389 // an oop, and like to assert the following: 8390 // assert(oop(addr)->is_oop(), "live block should be an oop"); 8391 // However, as we commented above, this may be an object whose 8392 // header hasn't yet been initialized. 8393 size_t size; 8394 assert(_bitMap->isMarked(addr), "Tautology for this control point"); 8395 if (_bitMap->isMarked(addr + 1)) { 8396 // Determine the size from the bit map, rather than trying to 8397 // compute it from the object header. 8398 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); 8399 size = pointer_delta(nextOneAddr + 1, addr); 8400 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), 8401 "alignment problem"); 8402 8403 #ifdef ASSERT 8404 if (oop(addr)->klass_or_null() != NULL) { 8405 // Ignore mark word because we are running concurrent with mutators 8406 assert(oop(addr)->is_oop(true), "live block should be an oop"); 8407 assert(size == 8408 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), 8409 "P-mark and computed size do not agree"); 8410 } 8411 #endif 8412 8413 } else { 8414 // This should be an initialized object that's alive. 8415 assert(oop(addr)->klass_or_null() != NULL, 8416 "Should be an initialized object"); 8417 // Ignore mark word because we are running concurrent with mutators 8418 assert(oop(addr)->is_oop(true), "live block should be an oop"); 8419 // Verify that the bit map has no bits marked between 8420 // addr and purported end of this block. 8421 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); 8422 assert(size >= 3, "Necessary for Printezis marks to work"); 8423 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); 8424 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) 8425 } 8426 return size; 8427 } 8428 8429 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc, 8430 size_t chunkSize) { 8431 // do_post_free_or_garbage_chunk() should only be called in the case 8432 // of the adaptive free list allocator. 8433 const bool fcInFreeLists = fc->is_free(); 8434 assert(_sp->adaptive_freelists(), "Should only be used in this case."); 8435 assert((HeapWord*)fc <= _limit, "sweep invariant"); 8436 if (CMSTestInFreeList && fcInFreeLists) { 8437 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists"); 8438 } 8439 8440 if (CMSTraceSweeper) { 8441 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize); 8442 } 8443 8444 HeapWord* const fc_addr = (HeapWord*) fc; 8445 8446 bool coalesce; 8447 const size_t left = pointer_delta(fc_addr, freeFinger()); 8448 const size_t right = chunkSize; 8449 switch (FLSCoalescePolicy) { 8450 // numeric value forms a coalition aggressiveness metric 8451 case 0: { // never coalesce 8452 coalesce = false; 8453 break; 8454 } 8455 case 1: { // coalesce if left & right chunks on overpopulated lists 8456 coalesce = _sp->coalOverPopulated(left) && 8457 _sp->coalOverPopulated(right); 8458 break; 8459 } 8460 case 2: { // coalesce if left chunk on overpopulated list (default) 8461 coalesce = _sp->coalOverPopulated(left); 8462 break; 8463 } 8464 case 3: { // coalesce if left OR right chunk on overpopulated list 8465 coalesce = _sp->coalOverPopulated(left) || 8466 _sp->coalOverPopulated(right); 8467 break; 8468 } 8469 case 4: { // always coalesce 8470 coalesce = true; 8471 break; 8472 } 8473 default: 8474 ShouldNotReachHere(); 8475 } 8476 8477 // Should the current free range be coalesced? 8478 // If the chunk is in a free range and either we decided to coalesce above 8479 // or the chunk is near the large block at the end of the heap 8480 // (isNearLargestChunk() returns true), then coalesce this chunk. 8481 const bool doCoalesce = inFreeRange() 8482 && (coalesce || _g->isNearLargestChunk(fc_addr)); 8483 if (doCoalesce) { 8484 // Coalesce the current free range on the left with the new 8485 // chunk on the right. If either is on a free list, 8486 // it must be removed from the list and stashed in the closure. 8487 if (freeRangeInFreeLists()) { 8488 FreeChunk* const ffc = (FreeChunk*)freeFinger(); 8489 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()), 8490 "Size of free range is inconsistent with chunk size."); 8491 if (CMSTestInFreeList) { 8492 assert(_sp->verify_chunk_in_free_list(ffc), 8493 "Chunk is not in free lists"); 8494 } 8495 _sp->coalDeath(ffc->size()); 8496 _sp->removeFreeChunkFromFreeLists(ffc); 8497 set_freeRangeInFreeLists(false); 8498 } 8499 if (fcInFreeLists) { 8500 _sp->coalDeath(chunkSize); 8501 assert(fc->size() == chunkSize, 8502 "The chunk has the wrong size or is not in the free lists"); 8503 _sp->removeFreeChunkFromFreeLists(fc); 8504 } 8505 set_lastFreeRangeCoalesced(true); 8506 print_free_block_coalesced(fc); 8507 } else { // not in a free range and/or should not coalesce 8508 // Return the current free range and start a new one. 8509 if (inFreeRange()) { 8510 // In a free range but cannot coalesce with the right hand chunk. 8511 // Put the current free range into the free lists. 8512 flush_cur_free_chunk(freeFinger(), 8513 pointer_delta(fc_addr, freeFinger())); 8514 } 8515 // Set up for new free range. Pass along whether the right hand 8516 // chunk is in the free lists. 8517 initialize_free_range((HeapWord*)fc, fcInFreeLists); 8518 } 8519 } 8520 8521 // Lookahead flush: 8522 // If we are tracking a free range, and this is the last chunk that 8523 // we'll look at because its end crosses past _limit, we'll preemptively 8524 // flush it along with any free range we may be holding on to. Note that 8525 // this can be the case only for an already free or freshly garbage 8526 // chunk. If this block is an object, it can never straddle 8527 // over _limit. The "straddling" occurs when _limit is set at 8528 // the previous end of the space when this cycle started, and 8529 // a subsequent heap expansion caused the previously co-terminal 8530 // free block to be coalesced with the newly expanded portion, 8531 // thus rendering _limit a non-block-boundary making it dangerous 8532 // for the sweeper to step over and examine. 8533 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) { 8534 assert(inFreeRange(), "Should only be called if currently in a free range."); 8535 HeapWord* const eob = ((HeapWord*)fc) + chunk_size; 8536 assert(_sp->used_region().contains(eob - 1), 8537 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")" 8538 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")", 8539 _limit, _sp->bottom(), _sp->end(), fc, chunk_size)); 8540 if (eob >= _limit) { 8541 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit"); 8542 if (CMSTraceSweeper) { 8543 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block " 8544 "[" PTR_FORMAT "," PTR_FORMAT ") in space " 8545 "[" PTR_FORMAT "," PTR_FORMAT ")", 8546 _limit, fc, eob, _sp->bottom(), _sp->end()); 8547 } 8548 // Return the storage we are tracking back into the free lists. 8549 if (CMSTraceSweeper) { 8550 gclog_or_tty->print_cr("Flushing ... "); 8551 } 8552 assert(freeFinger() < eob, "Error"); 8553 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger())); 8554 } 8555 } 8556 8557 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) { 8558 assert(inFreeRange(), "Should only be called if currently in a free range."); 8559 assert(size > 0, 8560 "A zero sized chunk cannot be added to the free lists."); 8561 if (!freeRangeInFreeLists()) { 8562 if (CMSTestInFreeList) { 8563 FreeChunk* fc = (FreeChunk*) chunk; 8564 fc->set_size(size); 8565 assert(!_sp->verify_chunk_in_free_list(fc), 8566 "chunk should not be in free lists yet"); 8567 } 8568 if (CMSTraceSweeper) { 8569 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists", 8570 chunk, size); 8571 } 8572 // A new free range is going to be starting. The current 8573 // free range has not been added to the free lists yet or 8574 // was removed so add it back. 8575 // If the current free range was coalesced, then the death 8576 // of the free range was recorded. Record a birth now. 8577 if (lastFreeRangeCoalesced()) { 8578 _sp->coalBirth(size); 8579 } 8580 _sp->addChunkAndRepairOffsetTable(chunk, size, 8581 lastFreeRangeCoalesced()); 8582 } else if (CMSTraceSweeper) { 8583 gclog_or_tty->print_cr("Already in free list: nothing to flush"); 8584 } 8585 set_inFreeRange(false); 8586 set_freeRangeInFreeLists(false); 8587 } 8588 8589 // We take a break if we've been at this for a while, 8590 // so as to avoid monopolizing the locks involved. 8591 void SweepClosure::do_yield_work(HeapWord* addr) { 8592 // Return current free chunk being used for coalescing (if any) 8593 // to the appropriate freelist. After yielding, the next 8594 // free block encountered will start a coalescing range of 8595 // free blocks. If the next free block is adjacent to the 8596 // chunk just flushed, they will need to wait for the next 8597 // sweep to be coalesced. 8598 if (inFreeRange()) { 8599 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger())); 8600 } 8601 8602 // First give up the locks, then yield, then re-lock. 8603 // We should probably use a constructor/destructor idiom to 8604 // do this unlock/lock or modify the MutexUnlocker class to 8605 // serve our purpose. XXX 8606 assert_lock_strong(_bitMap->lock()); 8607 assert_lock_strong(_freelistLock); 8608 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), 8609 "CMS thread should hold CMS token"); 8610 _bitMap->lock()->unlock(); 8611 _freelistLock->unlock(); 8612 ConcurrentMarkSweepThread::desynchronize(true); 8613 ConcurrentMarkSweepThread::acknowledge_yield_request(); 8614 _collector->stopTimer(); 8615 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); 8616 if (PrintCMSStatistics != 0) { 8617 _collector->incrementYields(); 8618 } 8619 _collector->icms_wait(); 8620 8621 // See the comment in coordinator_yield() 8622 for (unsigned i = 0; i < CMSYieldSleepCount && 8623 ConcurrentMarkSweepThread::should_yield() && 8624 !CMSCollector::foregroundGCIsActive(); ++i) { 8625 os::sleep(Thread::current(), 1, false); 8626 ConcurrentMarkSweepThread::acknowledge_yield_request(); 8627 } 8628 8629 ConcurrentMarkSweepThread::synchronize(true); 8630 _freelistLock->lock(); 8631 _bitMap->lock()->lock_without_safepoint_check(); 8632 _collector->startTimer(); 8633 } 8634 8635 #ifndef PRODUCT 8636 // This is actually very useful in a product build if it can 8637 // be called from the debugger. Compile it into the product 8638 // as needed. 8639 bool debug_verify_chunk_in_free_list(FreeChunk* fc) { 8640 return debug_cms_space->verify_chunk_in_free_list(fc); 8641 } 8642 #endif 8643 8644 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const { 8645 if (CMSTraceSweeper) { 8646 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")", 8647 fc, fc->size()); 8648 } 8649 } 8650 8651 // CMSIsAliveClosure 8652 bool CMSIsAliveClosure::do_object_b(oop obj) { 8653 HeapWord* addr = (HeapWord*)obj; 8654 return addr != NULL && 8655 (!_span.contains(addr) || _bit_map->isMarked(addr)); 8656 } 8657 8658 8659 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector, 8660 MemRegion span, 8661 CMSBitMap* bit_map, CMSMarkStack* mark_stack, 8662 bool cpc): 8663 _collector(collector), 8664 _span(span), 8665 _bit_map(bit_map), 8666 _mark_stack(mark_stack), 8667 _concurrent_precleaning(cpc) { 8668 assert(!_span.is_empty(), "Empty span could spell trouble"); 8669 } 8670 8671 8672 // CMSKeepAliveClosure: the serial version 8673 void CMSKeepAliveClosure::do_oop(oop obj) { 8674 HeapWord* addr = (HeapWord*)obj; 8675 if (_span.contains(addr) && 8676 !_bit_map->isMarked(addr)) { 8677 _bit_map->mark(addr); 8678 bool simulate_overflow = false; 8679 NOT_PRODUCT( 8680 if (CMSMarkStackOverflowALot && 8681 _collector->simulate_overflow()) { 8682 // simulate a stack overflow 8683 simulate_overflow = true; 8684 } 8685 ) 8686 if (simulate_overflow || !_mark_stack->push(obj)) { 8687 if (_concurrent_precleaning) { 8688 // We dirty the overflown object and let the remark 8689 // phase deal with it. 8690 assert(_collector->overflow_list_is_empty(), "Error"); 8691 // In the case of object arrays, we need to dirty all of 8692 // the cards that the object spans. No locking or atomics 8693 // are needed since no one else can be mutating the mod union 8694 // table. 8695 if (obj->is_objArray()) { 8696 size_t sz = obj->size(); 8697 HeapWord* end_card_addr = 8698 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size); 8699 MemRegion redirty_range = MemRegion(addr, end_card_addr); 8700 assert(!redirty_range.is_empty(), "Arithmetical tautology"); 8701 _collector->_modUnionTable.mark_range(redirty_range); 8702 } else { 8703 _collector->_modUnionTable.mark(addr); 8704 } 8705 _collector->_ser_kac_preclean_ovflw++; 8706 } else { 8707 _collector->push_on_overflow_list(obj); 8708 _collector->_ser_kac_ovflw++; 8709 } 8710 } 8711 } 8712 } 8713 8714 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); } 8715 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); } 8716 8717 // CMSParKeepAliveClosure: a parallel version of the above. 8718 // The work queues are private to each closure (thread), 8719 // but (may be) available for stealing by other threads. 8720 void CMSParKeepAliveClosure::do_oop(oop obj) { 8721 HeapWord* addr = (HeapWord*)obj; 8722 if (_span.contains(addr) && 8723 !_bit_map->isMarked(addr)) { 8724 // In general, during recursive tracing, several threads 8725 // may be concurrently getting here; the first one to 8726 // "tag" it, claims it. 8727 if (_bit_map->par_mark(addr)) { 8728 bool res = _work_queue->push(obj); 8729 assert(res, "Low water mark should be much less than capacity"); 8730 // Do a recursive trim in the hope that this will keep 8731 // stack usage lower, but leave some oops for potential stealers 8732 trim_queue(_low_water_mark); 8733 } // Else, another thread got there first 8734 } 8735 } 8736 8737 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 8738 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); } 8739 8740 void CMSParKeepAliveClosure::trim_queue(uint max) { 8741 while (_work_queue->size() > max) { 8742 oop new_oop; 8743 if (_work_queue->pop_local(new_oop)) { 8744 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); 8745 assert(_bit_map->isMarked((HeapWord*)new_oop), 8746 "no white objects on this stack!"); 8747 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 8748 // iterate over the oops in this oop, marking and pushing 8749 // the ones in CMS heap (i.e. in _span). 8750 new_oop->oop_iterate(&_mark_and_push); 8751 } 8752 } 8753 } 8754 8755 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure( 8756 CMSCollector* collector, 8757 MemRegion span, CMSBitMap* bit_map, 8758 OopTaskQueue* work_queue): 8759 _collector(collector), 8760 _span(span), 8761 _bit_map(bit_map), 8762 _work_queue(work_queue) { } 8763 8764 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) { 8765 HeapWord* addr = (HeapWord*)obj; 8766 if (_span.contains(addr) && 8767 !_bit_map->isMarked(addr)) { 8768 if (_bit_map->par_mark(addr)) { 8769 bool simulate_overflow = false; 8770 NOT_PRODUCT( 8771 if (CMSMarkStackOverflowALot && 8772 _collector->par_simulate_overflow()) { 8773 // simulate a stack overflow 8774 simulate_overflow = true; 8775 } 8776 ) 8777 if (simulate_overflow || !_work_queue->push(obj)) { 8778 _collector->par_push_on_overflow_list(obj); 8779 _collector->_par_kac_ovflw++; 8780 } 8781 } // Else another thread got there already 8782 } 8783 } 8784 8785 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 8786 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); } 8787 8788 ////////////////////////////////////////////////////////////////// 8789 // CMSExpansionCause ///////////////////////////// 8790 ////////////////////////////////////////////////////////////////// 8791 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { 8792 switch (cause) { 8793 case _no_expansion: 8794 return "No expansion"; 8795 case _satisfy_free_ratio: 8796 return "Free ratio"; 8797 case _satisfy_promotion: 8798 return "Satisfy promotion"; 8799 case _satisfy_allocation: 8800 return "allocation"; 8801 case _allocate_par_lab: 8802 return "Par LAB"; 8803 case _allocate_par_spooling_space: 8804 return "Par Spooling Space"; 8805 case _adaptive_size_policy: 8806 return "Ergonomics"; 8807 default: 8808 return "unknown"; 8809 } 8810 } 8811 8812 void CMSDrainMarkingStackClosure::do_void() { 8813 // the max number to take from overflow list at a time 8814 const size_t num = _mark_stack->capacity()/4; 8815 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(), 8816 "Overflow list should be NULL during concurrent phases"); 8817 while (!_mark_stack->isEmpty() || 8818 // if stack is empty, check the overflow list 8819 _collector->take_from_overflow_list(num, _mark_stack)) { 8820 oop obj = _mark_stack->pop(); 8821 HeapWord* addr = (HeapWord*)obj; 8822 assert(_span.contains(addr), "Should be within span"); 8823 assert(_bit_map->isMarked(addr), "Should be marked"); 8824 assert(obj->is_oop(), "Should be an oop"); 8825 obj->oop_iterate(_keep_alive); 8826 } 8827 } 8828 8829 void CMSParDrainMarkingStackClosure::do_void() { 8830 // drain queue 8831 trim_queue(0); 8832 } 8833 8834 // Trim our work_queue so its length is below max at return 8835 void CMSParDrainMarkingStackClosure::trim_queue(uint max) { 8836 while (_work_queue->size() > max) { 8837 oop new_oop; 8838 if (_work_queue->pop_local(new_oop)) { 8839 assert(new_oop->is_oop(), "Expected an oop"); 8840 assert(_bit_map->isMarked((HeapWord*)new_oop), 8841 "no white objects on this stack!"); 8842 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); 8843 // iterate over the oops in this oop, marking and pushing 8844 // the ones in CMS heap (i.e. in _span). 8845 new_oop->oop_iterate(&_mark_and_push); 8846 } 8847 } 8848 } 8849 8850 //////////////////////////////////////////////////////////////////// 8851 // Support for Marking Stack Overflow list handling and related code 8852 //////////////////////////////////////////////////////////////////// 8853 // Much of the following code is similar in shape and spirit to the 8854 // code used in ParNewGC. We should try and share that code 8855 // as much as possible in the future. 8856 8857 #ifndef PRODUCT 8858 // Debugging support for CMSStackOverflowALot 8859 8860 // It's OK to call this multi-threaded; the worst thing 8861 // that can happen is that we'll get a bunch of closely 8862 // spaced simulated oveflows, but that's OK, in fact 8863 // probably good as it would exercise the overflow code 8864 // under contention. 8865 bool CMSCollector::simulate_overflow() { 8866 if (_overflow_counter-- <= 0) { // just being defensive 8867 _overflow_counter = CMSMarkStackOverflowInterval; 8868 return true; 8869 } else { 8870 return false; 8871 } 8872 } 8873 8874 bool CMSCollector::par_simulate_overflow() { 8875 return simulate_overflow(); 8876 } 8877 #endif 8878 8879 // Single-threaded 8880 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { 8881 assert(stack->isEmpty(), "Expected precondition"); 8882 assert(stack->capacity() > num, "Shouldn't bite more than can chew"); 8883 size_t i = num; 8884 oop cur = _overflow_list; 8885 const markOop proto = markOopDesc::prototype(); 8886 NOT_PRODUCT(ssize_t n = 0;) 8887 for (oop next; i > 0 && cur != NULL; cur = next, i--) { 8888 next = oop(cur->mark()); 8889 cur->set_mark(proto); // until proven otherwise 8890 assert(cur->is_oop(), "Should be an oop"); 8891 bool res = stack->push(cur); 8892 assert(res, "Bit off more than can chew?"); 8893 NOT_PRODUCT(n++;) 8894 } 8895 _overflow_list = cur; 8896 #ifndef PRODUCT 8897 assert(_num_par_pushes >= n, "Too many pops?"); 8898 _num_par_pushes -=n; 8899 #endif 8900 return !stack->isEmpty(); 8901 } 8902 8903 #define BUSY (oop(0x1aff1aff)) 8904 // (MT-safe) Get a prefix of at most "num" from the list. 8905 // The overflow list is chained through the mark word of 8906 // each object in the list. We fetch the entire list, 8907 // break off a prefix of the right size and return the 8908 // remainder. If other threads try to take objects from 8909 // the overflow list at that time, they will wait for 8910 // some time to see if data becomes available. If (and 8911 // only if) another thread places one or more object(s) 8912 // on the global list before we have returned the suffix 8913 // to the global list, we will walk down our local list 8914 // to find its end and append the global list to 8915 // our suffix before returning it. This suffix walk can 8916 // prove to be expensive (quadratic in the amount of traffic) 8917 // when there are many objects in the overflow list and 8918 // there is much producer-consumer contention on the list. 8919 // *NOTE*: The overflow list manipulation code here and 8920 // in ParNewGeneration:: are very similar in shape, 8921 // except that in the ParNew case we use the old (from/eden) 8922 // copy of the object to thread the list via its klass word. 8923 // Because of the common code, if you make any changes in 8924 // the code below, please check the ParNew version to see if 8925 // similar changes might be needed. 8926 // CR 6797058 has been filed to consolidate the common code. 8927 bool CMSCollector::par_take_from_overflow_list(size_t num, 8928 OopTaskQueue* work_q, 8929 int no_of_gc_threads) { 8930 assert(work_q->size() == 0, "First empty local work queue"); 8931 assert(num < work_q->max_elems(), "Can't bite more than we can chew"); 8932 if (_overflow_list == NULL) { 8933 return false; 8934 } 8935 // Grab the entire list; we'll put back a suffix 8936 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list); 8937 Thread* tid = Thread::current(); 8938 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was 8939 // set to ParallelGCThreads. 8940 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads; 8941 size_t sleep_time_millis = MAX2((size_t)1, num/100); 8942 // If the list is busy, we spin for a short while, 8943 // sleeping between attempts to get the list. 8944 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) { 8945 os::sleep(tid, sleep_time_millis, false); 8946 if (_overflow_list == NULL) { 8947 // Nothing left to take 8948 return false; 8949 } else if (_overflow_list != BUSY) { 8950 // Try and grab the prefix 8951 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list); 8952 } 8953 } 8954 // If the list was found to be empty, or we spun long 8955 // enough, we give up and return empty-handed. If we leave 8956 // the list in the BUSY state below, it must be the case that 8957 // some other thread holds the overflow list and will set it 8958 // to a non-BUSY state in the future. 8959 if (prefix == NULL || prefix == BUSY) { 8960 // Nothing to take or waited long enough 8961 if (prefix == NULL) { 8962 // Write back the NULL in case we overwrote it with BUSY above 8963 // and it is still the same value. 8964 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 8965 } 8966 return false; 8967 } 8968 assert(prefix != NULL && prefix != BUSY, "Error"); 8969 size_t i = num; 8970 oop cur = prefix; 8971 // Walk down the first "num" objects, unless we reach the end. 8972 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--); 8973 if (cur->mark() == NULL) { 8974 // We have "num" or fewer elements in the list, so there 8975 // is nothing to return to the global list. 8976 // Write back the NULL in lieu of the BUSY we wrote 8977 // above, if it is still the same value. 8978 if (_overflow_list == BUSY) { 8979 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY); 8980 } 8981 } else { 8982 // Chop off the suffix and rerturn it to the global list. 8983 assert(cur->mark() != BUSY, "Error"); 8984 oop suffix_head = cur->mark(); // suffix will be put back on global list 8985 cur->set_mark(NULL); // break off suffix 8986 // It's possible that the list is still in the empty(busy) state 8987 // we left it in a short while ago; in that case we may be 8988 // able to place back the suffix without incurring the cost 8989 // of a walk down the list. 8990 oop observed_overflow_list = _overflow_list; 8991 oop cur_overflow_list = observed_overflow_list; 8992 bool attached = false; 8993 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) { 8994 observed_overflow_list = 8995 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); 8996 if (cur_overflow_list == observed_overflow_list) { 8997 attached = true; 8998 break; 8999 } else cur_overflow_list = observed_overflow_list; 9000 } 9001 if (!attached) { 9002 // Too bad, someone else sneaked in (at least) an element; we'll need 9003 // to do a splice. Find tail of suffix so we can prepend suffix to global 9004 // list. 9005 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark())); 9006 oop suffix_tail = cur; 9007 assert(suffix_tail != NULL && suffix_tail->mark() == NULL, 9008 "Tautology"); 9009 observed_overflow_list = _overflow_list; 9010 do { 9011 cur_overflow_list = observed_overflow_list; 9012 if (cur_overflow_list != BUSY) { 9013 // Do the splice ... 9014 suffix_tail->set_mark(markOop(cur_overflow_list)); 9015 } else { // cur_overflow_list == BUSY 9016 suffix_tail->set_mark(NULL); 9017 } 9018 // ... and try to place spliced list back on overflow_list ... 9019 observed_overflow_list = 9020 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list); 9021 } while (cur_overflow_list != observed_overflow_list); 9022 // ... until we have succeeded in doing so. 9023 } 9024 } 9025 9026 // Push the prefix elements on work_q 9027 assert(prefix != NULL, "control point invariant"); 9028 const markOop proto = markOopDesc::prototype(); 9029 oop next; 9030 NOT_PRODUCT(ssize_t n = 0;) 9031 for (cur = prefix; cur != NULL; cur = next) { 9032 next = oop(cur->mark()); 9033 cur->set_mark(proto); // until proven otherwise 9034 assert(cur->is_oop(), "Should be an oop"); 9035 bool res = work_q->push(cur); 9036 assert(res, "Bit off more than we can chew?"); 9037 NOT_PRODUCT(n++;) 9038 } 9039 #ifndef PRODUCT 9040 assert(_num_par_pushes >= n, "Too many pops?"); 9041 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); 9042 #endif 9043 return true; 9044 } 9045 9046 // Single-threaded 9047 void CMSCollector::push_on_overflow_list(oop p) { 9048 NOT_PRODUCT(_num_par_pushes++;) 9049 assert(p->is_oop(), "Not an oop"); 9050 preserve_mark_if_necessary(p); 9051 p->set_mark((markOop)_overflow_list); 9052 _overflow_list = p; 9053 } 9054 9055 // Multi-threaded; use CAS to prepend to overflow list 9056 void CMSCollector::par_push_on_overflow_list(oop p) { 9057 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);) 9058 assert(p->is_oop(), "Not an oop"); 9059 par_preserve_mark_if_necessary(p); 9060 oop observed_overflow_list = _overflow_list; 9061 oop cur_overflow_list; 9062 do { 9063 cur_overflow_list = observed_overflow_list; 9064 if (cur_overflow_list != BUSY) { 9065 p->set_mark(markOop(cur_overflow_list)); 9066 } else { 9067 p->set_mark(NULL); 9068 } 9069 observed_overflow_list = 9070 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list); 9071 } while (cur_overflow_list != observed_overflow_list); 9072 } 9073 #undef BUSY 9074 9075 // Single threaded 9076 // General Note on GrowableArray: pushes may silently fail 9077 // because we are (temporarily) out of C-heap for expanding 9078 // the stack. The problem is quite ubiquitous and affects 9079 // a lot of code in the JVM. The prudent thing for GrowableArray 9080 // to do (for now) is to exit with an error. However, that may 9081 // be too draconian in some cases because the caller may be 9082 // able to recover without much harm. For such cases, we 9083 // should probably introduce a "soft_push" method which returns 9084 // an indication of success or failure with the assumption that 9085 // the caller may be able to recover from a failure; code in 9086 // the VM can then be changed, incrementally, to deal with such 9087 // failures where possible, thus, incrementally hardening the VM 9088 // in such low resource situations. 9089 void CMSCollector::preserve_mark_work(oop p, markOop m) { 9090 _preserved_oop_stack.push(p); 9091 _preserved_mark_stack.push(m); 9092 assert(m == p->mark(), "Mark word changed"); 9093 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 9094 "bijection"); 9095 } 9096 9097 // Single threaded 9098 void CMSCollector::preserve_mark_if_necessary(oop p) { 9099 markOop m = p->mark(); 9100 if (m->must_be_preserved(p)) { 9101 preserve_mark_work(p, m); 9102 } 9103 } 9104 9105 void CMSCollector::par_preserve_mark_if_necessary(oop p) { 9106 markOop m = p->mark(); 9107 if (m->must_be_preserved(p)) { 9108 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); 9109 // Even though we read the mark word without holding 9110 // the lock, we are assured that it will not change 9111 // because we "own" this oop, so no other thread can 9112 // be trying to push it on the overflow list; see 9113 // the assertion in preserve_mark_work() that checks 9114 // that m == p->mark(). 9115 preserve_mark_work(p, m); 9116 } 9117 } 9118 9119 // We should be able to do this multi-threaded, 9120 // a chunk of stack being a task (this is 9121 // correct because each oop only ever appears 9122 // once in the overflow list. However, it's 9123 // not very easy to completely overlap this with 9124 // other operations, so will generally not be done 9125 // until all work's been completed. Because we 9126 // expect the preserved oop stack (set) to be small, 9127 // it's probably fine to do this single-threaded. 9128 // We can explore cleverer concurrent/overlapped/parallel 9129 // processing of preserved marks if we feel the 9130 // need for this in the future. Stack overflow should 9131 // be so rare in practice and, when it happens, its 9132 // effect on performance so great that this will 9133 // likely just be in the noise anyway. 9134 void CMSCollector::restore_preserved_marks_if_any() { 9135 assert(SafepointSynchronize::is_at_safepoint(), 9136 "world should be stopped"); 9137 assert(Thread::current()->is_ConcurrentGC_thread() || 9138 Thread::current()->is_VM_thread(), 9139 "should be single-threaded"); 9140 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(), 9141 "bijection"); 9142 9143 while (!_preserved_oop_stack.is_empty()) { 9144 oop p = _preserved_oop_stack.pop(); 9145 assert(p->is_oop(), "Should be an oop"); 9146 assert(_span.contains(p), "oop should be in _span"); 9147 assert(p->mark() == markOopDesc::prototype(), 9148 "Set when taken from overflow list"); 9149 markOop m = _preserved_mark_stack.pop(); 9150 p->set_mark(m); 9151 } 9152 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(), 9153 "stacks were cleared above"); 9154 } 9155 9156 #ifndef PRODUCT 9157 bool CMSCollector::no_preserved_marks() const { 9158 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(); 9159 } 9160 #endif 9161 9162 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const 9163 { 9164 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); 9165 CMSAdaptiveSizePolicy* size_policy = 9166 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy(); 9167 assert(size_policy->is_gc_cms_adaptive_size_policy(), 9168 "Wrong type for size policy"); 9169 return size_policy; 9170 } 9171 9172 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size, 9173 size_t desired_promo_size) { 9174 if (cur_promo_size < desired_promo_size) { 9175 size_t expand_bytes = desired_promo_size - cur_promo_size; 9176 if (PrintAdaptiveSizePolicy && Verbose) { 9177 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " 9178 "Expanding tenured generation by " SIZE_FORMAT " (bytes)", 9179 expand_bytes); 9180 } 9181 expand(expand_bytes, 9182 MinHeapDeltaBytes, 9183 CMSExpansionCause::_adaptive_size_policy); 9184 } else if (desired_promo_size < cur_promo_size) { 9185 size_t shrink_bytes = cur_promo_size - desired_promo_size; 9186 if (PrintAdaptiveSizePolicy && Verbose) { 9187 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " 9188 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)", 9189 shrink_bytes); 9190 } 9191 shrink(shrink_bytes); 9192 } 9193 } 9194 9195 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() { 9196 GenCollectedHeap* gch = GenCollectedHeap::heap(); 9197 CMSGCAdaptivePolicyCounters* counters = 9198 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters(); 9199 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, 9200 "Wrong kind of counters"); 9201 return counters; 9202 } 9203 9204 9205 void ASConcurrentMarkSweepGeneration::update_counters() { 9206 if (UsePerfData) { 9207 _space_counters->update_all(); 9208 _gen_counters->update_all(); 9209 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); 9210 GenCollectedHeap* gch = GenCollectedHeap::heap(); 9211 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); 9212 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, 9213 "Wrong gc statistics type"); 9214 counters->update_counters(gc_stats_l); 9215 } 9216 } 9217 9218 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) { 9219 if (UsePerfData) { 9220 _space_counters->update_used(used); 9221 _space_counters->update_capacity(); 9222 _gen_counters->update_all(); 9223 9224 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); 9225 GenCollectedHeap* gch = GenCollectedHeap::heap(); 9226 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); 9227 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, 9228 "Wrong gc statistics type"); 9229 counters->update_counters(gc_stats_l); 9230 } 9231 } 9232 9233 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) { 9234 assert_locked_or_safepoint(Heap_lock); 9235 assert_lock_strong(freelistLock()); 9236 HeapWord* old_end = _cmsSpace->end(); 9237 HeapWord* unallocated_start = _cmsSpace->unallocated_block(); 9238 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start"); 9239 FreeChunk* chunk_at_end = find_chunk_at_end(); 9240 if (chunk_at_end == NULL) { 9241 // No room to shrink 9242 if (PrintGCDetails && Verbose) { 9243 gclog_or_tty->print_cr("No room to shrink: old_end " 9244 PTR_FORMAT " unallocated_start " PTR_FORMAT 9245 " chunk_at_end " PTR_FORMAT, 9246 old_end, unallocated_start, chunk_at_end); 9247 } 9248 return; 9249 } else { 9250 9251 // Find the chunk at the end of the space and determine 9252 // how much it can be shrunk. 9253 size_t shrinkable_size_in_bytes = chunk_at_end->size(); 9254 size_t aligned_shrinkable_size_in_bytes = 9255 align_size_down(shrinkable_size_in_bytes, os::vm_page_size()); 9256 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(), 9257 "Inconsistent chunk at end of space"); 9258 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes); 9259 size_t word_size_before = heap_word_size(_virtual_space.committed_size()); 9260 9261 // Shrink the underlying space 9262 _virtual_space.shrink_by(bytes); 9263 if (PrintGCDetails && Verbose) { 9264 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:" 9265 " desired_bytes " SIZE_FORMAT 9266 " shrinkable_size_in_bytes " SIZE_FORMAT 9267 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT 9268 " bytes " SIZE_FORMAT, 9269 desired_bytes, shrinkable_size_in_bytes, 9270 aligned_shrinkable_size_in_bytes, bytes); 9271 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT 9272 " unallocated_start " SIZE_FORMAT, 9273 old_end, unallocated_start); 9274 } 9275 9276 // If the space did shrink (shrinking is not guaranteed), 9277 // shrink the chunk at the end by the appropriate amount. 9278 if (((HeapWord*)_virtual_space.high()) < old_end) { 9279 size_t new_word_size = 9280 heap_word_size(_virtual_space.committed_size()); 9281 9282 // Have to remove the chunk from the dictionary because it is changing 9283 // size and might be someplace elsewhere in the dictionary. 9284 9285 // Get the chunk at end, shrink it, and put it 9286 // back. 9287 _cmsSpace->removeChunkFromDictionary(chunk_at_end); 9288 size_t word_size_change = word_size_before - new_word_size; 9289 size_t chunk_at_end_old_size = chunk_at_end->size(); 9290 assert(chunk_at_end_old_size >= word_size_change, 9291 "Shrink is too large"); 9292 chunk_at_end->set_size(chunk_at_end_old_size - 9293 word_size_change); 9294 _cmsSpace->freed((HeapWord*) chunk_at_end->end(), 9295 word_size_change); 9296 9297 _cmsSpace->returnChunkToDictionary(chunk_at_end); 9298 9299 MemRegion mr(_cmsSpace->bottom(), new_word_size); 9300 _bts->resize(new_word_size); // resize the block offset shared array 9301 Universe::heap()->barrier_set()->resize_covered_region(mr); 9302 _cmsSpace->assert_locked(); 9303 _cmsSpace->set_end((HeapWord*)_virtual_space.high()); 9304 9305 NOT_PRODUCT(_cmsSpace->dictionary()->verify()); 9306 9307 // update the space and generation capacity counters 9308 if (UsePerfData) { 9309 _space_counters->update_capacity(); 9310 _gen_counters->update_all(); 9311 } 9312 9313 if (Verbose && PrintGCDetails) { 9314 size_t new_mem_size = _virtual_space.committed_size(); 9315 size_t old_mem_size = new_mem_size + bytes; 9316 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K", 9317 name(), old_mem_size/K, bytes/K, new_mem_size/K); 9318 } 9319 } 9320 9321 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(), 9322 "Inconsistency at end of space"); 9323 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(), 9324 "Shrinking is inconsistent"); 9325 return; 9326 } 9327 } 9328 9329 // Transfer some number of overflown objects to usual marking 9330 // stack. Return true if some objects were transferred. 9331 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { 9332 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4, 9333 (size_t)ParGCDesiredObjsFromOverflowList); 9334 9335 bool res = _collector->take_from_overflow_list(num, _mark_stack); 9336 assert(_collector->overflow_list_is_empty() || res, 9337 "If list is not empty, we should have taken something"); 9338 assert(!res || !_mark_stack->isEmpty(), 9339 "If we took something, it should now be on our stack"); 9340 return res; 9341 } 9342 9343 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { 9344 size_t res = _sp->block_size_no_stall(addr, _collector); 9345 if (_sp->block_is_obj(addr)) { 9346 if (_live_bit_map->isMarked(addr)) { 9347 // It can't have been dead in a previous cycle 9348 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); 9349 } else { 9350 _dead_bit_map->mark(addr); // mark the dead object 9351 } 9352 } 9353 // Could be 0, if the block size could not be computed without stalling. 9354 return res; 9355 } 9356 9357 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() { 9358 9359 switch (phase) { 9360 case CMSCollector::InitialMarking: 9361 initialize(true /* fullGC */ , 9362 cause /* cause of the GC */, 9363 true /* recordGCBeginTime */, 9364 true /* recordPreGCUsage */, 9365 false /* recordPeakUsage */, 9366 false /* recordPostGCusage */, 9367 true /* recordAccumulatedGCTime */, 9368 false /* recordGCEndTime */, 9369 false /* countCollection */ ); 9370 break; 9371 9372 case CMSCollector::FinalMarking: 9373 initialize(true /* fullGC */ , 9374 cause /* cause of the GC */, 9375 false /* recordGCBeginTime */, 9376 false /* recordPreGCUsage */, 9377 false /* recordPeakUsage */, 9378 false /* recordPostGCusage */, 9379 true /* recordAccumulatedGCTime */, 9380 false /* recordGCEndTime */, 9381 false /* countCollection */ ); 9382 break; 9383 9384 case CMSCollector::Sweeping: 9385 initialize(true /* fullGC */ , 9386 cause /* cause of the GC */, 9387 false /* recordGCBeginTime */, 9388 false /* recordPreGCUsage */, 9389 true /* recordPeakUsage */, 9390 true /* recordPostGCusage */, 9391 false /* recordAccumulatedGCTime */, 9392 true /* recordGCEndTime */, 9393 true /* countCollection */ ); 9394 break; 9395 9396 default: 9397 ShouldNotReachHere(); 9398 } 9399 } 9400 --- EOF ---