1 /*
2 * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.hpp"
52 #include "memory/referencePolicy.hpp"
53 #include "memory/resourceArea.hpp"
54 #include "oops/oop.inline.hpp"
55 #include "prims/jvmtiExport.hpp"
56 #include "runtime/globals_extension.hpp"
57 #include "runtime/handles.inline.hpp"
58 #include "runtime/java.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "services/memoryService.hpp"
61 #include "services/runtimeService.hpp"
62
63 // statics
64 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
65 bool CMSCollector::_full_gc_requested = false;
66
67 //////////////////////////////////////////////////////////////////
68 // In support of CMS/VM thread synchronization
69 //////////////////////////////////////////////////////////////////
70 // We split use of the CGC_lock into 2 "levels".
71 // The low-level locking is of the usual CGC_lock monitor. We introduce
72 // a higher level "token" (hereafter "CMS token") built on top of the
73 // low level monitor (hereafter "CGC lock").
74 // The token-passing protocol gives priority to the VM thread. The
75 // CMS-lock doesn't provide any fairness guarantees, but clients
76 // should ensure that it is only held for very short, bounded
77 // durations.
78 //
79 // When either of the CMS thread or the VM thread is involved in
80 // collection operations during which it does not want the other
81 // thread to interfere, it obtains the CMS token.
82 //
83 // If either thread tries to get the token while the other has
84 // it, that thread waits. However, if the VM thread and CMS thread
85 // both want the token, then the VM thread gets priority while the
86 // CMS thread waits. This ensures, for instance, that the "concurrent"
87 // phases of the CMS thread's work do not block out the VM thread
88 // for long periods of time as the CMS thread continues to hog
89 // the token. (See bug 4616232).
90 //
91 // The baton-passing functions are, however, controlled by the
92 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
93 // and here the low-level CMS lock, not the high level token,
94 // ensures mutual exclusion.
95 //
96 // Two important conditions that we have to satisfy:
97 // 1. if a thread does a low-level wait on the CMS lock, then it
98 // relinquishes the CMS token if it were holding that token
99 // when it acquired the low-level CMS lock.
100 // 2. any low-level notifications on the low-level lock
101 // should only be sent when a thread has relinquished the token.
102 //
103 // In the absence of either property, we'd have potential deadlock.
104 //
105 // We protect each of the CMS (concurrent and sequential) phases
106 // with the CMS _token_, not the CMS _lock_.
107 //
108 // The only code protected by CMS lock is the token acquisition code
109 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
110 // baton-passing code.
111 //
112 // Unfortunately, i couldn't come up with a good abstraction to factor and
113 // hide the naked CGC_lock manipulation in the baton-passing code
114 // further below. That's something we should try to do. Also, the proof
115 // of correctness of this 2-level locking scheme is far from obvious,
116 // and potentially quite slippery. We have an uneasy supsicion, for instance,
117 // that there may be a theoretical possibility of delay/starvation in the
118 // low-level lock/wait/notify scheme used for the baton-passing because of
119 // potential intereference with the priority scheme embodied in the
120 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
121 // invocation further below and marked with "XXX 20011219YSR".
122 // Indeed, as we note elsewhere, this may become yet more slippery
123 // in the presence of multiple CMS and/or multiple VM threads. XXX
124
125 class CMSTokenSync: public StackObj {
126 private:
127 bool _is_cms_thread;
128 public:
129 CMSTokenSync(bool is_cms_thread):
130 _is_cms_thread(is_cms_thread) {
131 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
132 "Incorrect argument to constructor");
133 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
134 }
135
136 ~CMSTokenSync() {
137 assert(_is_cms_thread ?
138 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
139 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
140 "Incorrect state");
141 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
142 }
143 };
144
145 // Convenience class that does a CMSTokenSync, and then acquires
146 // upto three locks.
147 class CMSTokenSyncWithLocks: public CMSTokenSync {
148 private:
149 // Note: locks are acquired in textual declaration order
150 // and released in the opposite order
151 MutexLockerEx _locker1, _locker2, _locker3;
152 public:
153 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
154 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
155 CMSTokenSync(is_cms_thread),
156 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
157 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
158 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
159 { }
160 };
161
162
163 // Wrapper class to temporarily disable icms during a foreground cms collection.
164 class ICMSDisabler: public StackObj {
165 public:
166 // The ctor disables icms and wakes up the thread so it notices the change;
167 // the dtor re-enables icms. Note that the CMSCollector methods will check
168 // CMSIncrementalMode.
169 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
170 ~ICMSDisabler() { CMSCollector::enable_icms(); }
171 };
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size, int level,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, level, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _debug_collection_type(Concurrent_collection_type)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 if (_cmsSpace == NULL) {
216 vm_exit_during_initialization(
217 "CompactibleFreeListSpace allocation failure");
218 }
219 _cmsSpace->_gen = this;
220
221 _gc_stats = new CMSGCStats();
222
223 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
224 // offsets match. The ability to tell free chunks from objects
225 // depends on this property.
226 debug_only(
227 FreeChunk* junk = NULL;
228 assert(UseCompressedOops ||
229 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
230 "Offset of FreeChunk::_prev within FreeChunk must match"
231 " that of OopDesc::_klass within OopDesc");
232 )
233 if (CollectedHeap::use_parallel_gc_threads()) {
234 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
235 _par_gc_thread_states =
236 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
237 if (_par_gc_thread_states == NULL) {
238 vm_exit_during_initialization("Could not allocate par gc structs");
239 }
240 for (uint i = 0; i < ParallelGCThreads; i++) {
241 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
242 if (_par_gc_thread_states[i] == NULL) {
243 vm_exit_during_initialization("Could not allocate par gc structs");
244 }
245 }
246 } else {
247 _par_gc_thread_states = NULL;
248 }
249 _incremental_collection_failed = false;
250 // The "dilatation_factor" is the expansion that can occur on
251 // account of the fact that the minimum object size in the CMS
252 // generation may be larger than that in, say, a contiguous young
253 // generation.
254 // Ideally, in the calculation below, we'd compute the dilatation
255 // factor as: MinChunkSize/(promoting_gen's min object size)
256 // Since we do not have such a general query interface for the
257 // promoting generation, we'll instead just use the mimimum
258 // object size (which today is a header's worth of space);
259 // note that all arithmetic is in units of HeapWords.
260 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
261 assert(_dilatation_factor >= 1.0, "from previous assert");
262 }
263
264
265 // The field "_initiating_occupancy" represents the occupancy percentage
266 // at which we trigger a new collection cycle. Unless explicitly specified
267 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
268 // is calculated by:
269 //
270 // Let "f" be MinHeapFreeRatio in
271 //
272 // _intiating_occupancy = 100-f +
273 // f * (CMSTrigger[Perm]Ratio/100)
274 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
275 //
276 // That is, if we assume the heap is at its desired maximum occupancy at the
277 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
278 // space be allocated before initiating a new collection cycle.
279 //
280 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
281 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
282 if (io >= 0) {
283 _initiating_occupancy = (double)io / 100.0;
284 } else {
285 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
286 (double)(tr * MinHeapFreeRatio) / 100.0)
287 / 100.0;
288 }
289 }
290
291 void ConcurrentMarkSweepGeneration::ref_processor_init() {
292 assert(collector() != NULL, "no collector");
293 collector()->ref_processor_init();
294 }
295
296 void CMSCollector::ref_processor_init() {
297 if (_ref_processor == NULL) {
298 // Allocate and initialize a reference processor
299 _ref_processor =
300 new ReferenceProcessor(_span, // span
301 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
302 (int) ParallelGCThreads, // mt processing degree
303 _cmsGen->refs_discovery_is_mt(), // mt discovery
304 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
305 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
306 &_is_alive_closure, // closure for liveness info
307 false); // next field updates do not need write barrier
308 // Initialize the _ref_processor field of CMSGen
309 _cmsGen->set_ref_processor(_ref_processor);
310
311 // Allocate a dummy ref processor for perm gen.
312 ReferenceProcessor* rp2 = new ReferenceProcessor();
313 if (rp2 == NULL) {
314 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
315 }
316 _permGen->set_ref_processor(rp2);
317 }
318 }
319
320 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
321 GenCollectedHeap* gch = GenCollectedHeap::heap();
322 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
323 "Wrong type of heap");
324 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
325 gch->gen_policy()->size_policy();
326 assert(sp->is_gc_cms_adaptive_size_policy(),
327 "Wrong type of size policy");
328 return sp;
329 }
330
331 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
332 CMSGCAdaptivePolicyCounters* results =
333 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
334 assert(
335 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
336 "Wrong gc policy counter kind");
337 return results;
338 }
339
340
341 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
342
343 const char* gen_name = "old";
344
345 // Generation Counters - generation 1, 1 subspace
346 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
347
348 _space_counters = new GSpaceCounters(gen_name, 0,
349 _virtual_space.reserved_size(),
350 this, _gen_counters);
351 }
352
353 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
354 _cms_gen(cms_gen)
355 {
356 assert(alpha <= 100, "bad value");
357 _saved_alpha = alpha;
358
359 // Initialize the alphas to the bootstrap value of 100.
360 _gc0_alpha = _cms_alpha = 100;
361
362 _cms_begin_time.update();
363 _cms_end_time.update();
364
365 _gc0_duration = 0.0;
366 _gc0_period = 0.0;
367 _gc0_promoted = 0;
368
369 _cms_duration = 0.0;
370 _cms_period = 0.0;
371 _cms_allocated = 0;
372
373 _cms_used_at_gc0_begin = 0;
374 _cms_used_at_gc0_end = 0;
375 _allow_duty_cycle_reduction = false;
376 _valid_bits = 0;
377 _icms_duty_cycle = CMSIncrementalDutyCycle;
378 }
379
380 double CMSStats::cms_free_adjustment_factor(size_t free) const {
381 // TBD: CR 6909490
382 return 1.0;
383 }
384
385 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
386 }
387
388 // If promotion failure handling is on use
389 // the padded average size of the promotion for each
390 // young generation collection.
391 double CMSStats::time_until_cms_gen_full() const {
392 size_t cms_free = _cms_gen->cmsSpace()->free();
393 GenCollectedHeap* gch = GenCollectedHeap::heap();
394 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
395 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
396 if (cms_free > expected_promotion) {
397 // Start a cms collection if there isn't enough space to promote
398 // for the next minor collection. Use the padded average as
399 // a safety factor.
400 cms_free -= expected_promotion;
401
402 // Adjust by the safety factor.
403 double cms_free_dbl = (double)cms_free;
404 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
405 // Apply a further correction factor which tries to adjust
406 // for recent occurance of concurrent mode failures.
407 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
408 cms_free_dbl = cms_free_dbl * cms_adjustment;
409
410 if (PrintGCDetails && Verbose) {
411 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
412 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
413 cms_free, expected_promotion);
414 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
415 cms_free_dbl, cms_consumption_rate() + 1.0);
416 }
417 // Add 1 in case the consumption rate goes to zero.
418 return cms_free_dbl / (cms_consumption_rate() + 1.0);
419 }
420 return 0.0;
421 }
422
423 // Compare the duration of the cms collection to the
424 // time remaining before the cms generation is empty.
425 // Note that the time from the start of the cms collection
426 // to the start of the cms sweep (less than the total
427 // duration of the cms collection) can be used. This
428 // has been tried and some applications experienced
429 // promotion failures early in execution. This was
430 // possibly because the averages were not accurate
431 // enough at the beginning.
432 double CMSStats::time_until_cms_start() const {
433 // We add "gc0_period" to the "work" calculation
434 // below because this query is done (mostly) at the
435 // end of a scavenge, so we need to conservatively
436 // account for that much possible delay
437 // in the query so as to avoid concurrent mode failures
438 // due to starting the collection just a wee bit too
439 // late.
440 double work = cms_duration() + gc0_period();
441 double deadline = time_until_cms_gen_full();
442 // If a concurrent mode failure occurred recently, we want to be
443 // more conservative and halve our expected time_until_cms_gen_full()
444 if (work > deadline) {
445 if (Verbose && PrintGCDetails) {
446 gclog_or_tty->print(
447 " CMSCollector: collect because of anticipated promotion "
448 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
449 gc0_period(), time_until_cms_gen_full());
450 }
451 return 0.0;
452 }
453 return work - deadline;
454 }
455
456 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
457 // amount of change to prevent wild oscillation.
458 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
459 unsigned int new_duty_cycle) {
460 assert(old_duty_cycle <= 100, "bad input value");
461 assert(new_duty_cycle <= 100, "bad input value");
462
463 // Note: use subtraction with caution since it may underflow (values are
464 // unsigned). Addition is safe since we're in the range 0-100.
465 unsigned int damped_duty_cycle = new_duty_cycle;
466 if (new_duty_cycle < old_duty_cycle) {
467 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
468 if (new_duty_cycle + largest_delta < old_duty_cycle) {
469 damped_duty_cycle = old_duty_cycle - largest_delta;
470 }
471 } else if (new_duty_cycle > old_duty_cycle) {
472 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
473 if (new_duty_cycle > old_duty_cycle + largest_delta) {
474 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
475 }
476 }
477 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
478
479 if (CMSTraceIncrementalPacing) {
480 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
481 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
482 }
483 return damped_duty_cycle;
484 }
485
486 unsigned int CMSStats::icms_update_duty_cycle_impl() {
487 assert(CMSIncrementalPacing && valid(),
488 "should be handled in icms_update_duty_cycle()");
489
490 double cms_time_so_far = cms_timer().seconds();
491 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
492 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
493
494 // Avoid division by 0.
495 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
496 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
497
498 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
499 if (new_duty_cycle > _icms_duty_cycle) {
500 // Avoid very small duty cycles (1 or 2); 0 is allowed.
501 if (new_duty_cycle > 2) {
502 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
503 new_duty_cycle);
504 }
505 } else if (_allow_duty_cycle_reduction) {
506 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
507 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
508 // Respect the minimum duty cycle.
509 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
510 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
511 }
512
513 if (PrintGCDetails || CMSTraceIncrementalPacing) {
514 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
515 }
516
517 _allow_duty_cycle_reduction = false;
518 return _icms_duty_cycle;
519 }
520
521 #ifndef PRODUCT
522 void CMSStats::print_on(outputStream *st) const {
523 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
524 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
525 gc0_duration(), gc0_period(), gc0_promoted());
526 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
527 cms_duration(), cms_duration_per_mb(),
528 cms_period(), cms_allocated());
529 st->print(",cms_since_beg=%g,cms_since_end=%g",
530 cms_time_since_begin(), cms_time_since_end());
531 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
532 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
533 if (CMSIncrementalMode) {
534 st->print(",dc=%d", icms_duty_cycle());
535 }
536
537 if (valid()) {
538 st->print(",promo_rate=%g,cms_alloc_rate=%g",
539 promotion_rate(), cms_allocation_rate());
540 st->print(",cms_consumption_rate=%g,time_until_full=%g",
541 cms_consumption_rate(), time_until_cms_gen_full());
542 }
543 st->print(" ");
544 }
545 #endif // #ifndef PRODUCT
546
547 CMSCollector::CollectorState CMSCollector::_collectorState =
548 CMSCollector::Idling;
549 bool CMSCollector::_foregroundGCIsActive = false;
550 bool CMSCollector::_foregroundGCShouldWait = false;
551
552 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
553 ConcurrentMarkSweepGeneration* permGen,
554 CardTableRS* ct,
555 ConcurrentMarkSweepPolicy* cp):
556 _cmsGen(cmsGen),
557 _permGen(permGen),
558 _ct(ct),
559 _ref_processor(NULL), // will be set later
560 _conc_workers(NULL), // may be set later
561 _abort_preclean(false),
562 _start_sampling(false),
563 _between_prologue_and_epilogue(false),
564 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
565 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
566 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
567 -1 /* lock-free */, "No_lock" /* dummy */),
568 _modUnionClosure(&_modUnionTable),
569 _modUnionClosurePar(&_modUnionTable),
570 // Adjust my span to cover old (cms) gen and perm gen
571 _span(cmsGen->reserved()._union(permGen->reserved())),
572 // Construct the is_alive_closure with _span & markBitMap
573 _is_alive_closure(_span, &_markBitMap),
574 _restart_addr(NULL),
575 _overflow_list(NULL),
576 _stats(cmsGen),
577 _eden_chunk_array(NULL), // may be set in ctor body
578 _eden_chunk_capacity(0), // -- ditto --
579 _eden_chunk_index(0), // -- ditto --
580 _survivor_plab_array(NULL), // -- ditto --
581 _survivor_chunk_array(NULL), // -- ditto --
582 _survivor_chunk_capacity(0), // -- ditto --
583 _survivor_chunk_index(0), // -- ditto --
584 _ser_pmc_preclean_ovflw(0),
585 _ser_kac_preclean_ovflw(0),
586 _ser_pmc_remark_ovflw(0),
587 _par_pmc_remark_ovflw(0),
588 _ser_kac_ovflw(0),
589 _par_kac_ovflw(0),
590 #ifndef PRODUCT
591 _num_par_pushes(0),
592 #endif
593 _collection_count_start(0),
594 _verifying(false),
595 _icms_start_limit(NULL),
596 _icms_stop_limit(NULL),
597 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
598 _completed_initialization(false),
599 _collector_policy(cp),
600 _should_unload_classes(false),
601 _concurrent_cycles_since_last_unload(0),
602 _roots_scanning_options(0),
603 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
604 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
605 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
606 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
607 _cms_start_registered(false)
608 {
609 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
610 ExplicitGCInvokesConcurrent = true;
611 }
612 // Now expand the span and allocate the collection support structures
613 // (MUT, marking bit map etc.) to cover both generations subject to
614 // collection.
615
616 // First check that _permGen is adjacent to _cmsGen and above it.
617 assert( _cmsGen->reserved().word_size() > 0
618 && _permGen->reserved().word_size() > 0,
619 "generations should not be of zero size");
620 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
621 "_cmsGen and _permGen should not overlap");
622 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
623 "_cmsGen->end() different from _permGen->start()");
624
625 // For use by dirty card to oop closures.
626 _cmsGen->cmsSpace()->set_collector(this);
627 _permGen->cmsSpace()->set_collector(this);
628
629 // Allocate MUT and marking bit map
630 {
631 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
632 if (!_markBitMap.allocate(_span)) {
633 warning("Failed to allocate CMS Bit Map");
634 return;
635 }
636 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
637 }
638 {
639 _modUnionTable.allocate(_span);
640 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
641 }
642
643 if (!_markStack.allocate(MarkStackSize)) {
644 warning("Failed to allocate CMS Marking Stack");
645 return;
646 }
647 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
648 warning("Failed to allocate CMS Revisit Stack");
649 return;
650 }
651
652 // Support for multi-threaded concurrent phases
653 if (CMSConcurrentMTEnabled) {
654 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
655 // just for now
656 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
657 }
658 if (ConcGCThreads > 1) {
659 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
660 ConcGCThreads, true);
661 if (_conc_workers == NULL) {
662 warning("GC/CMS: _conc_workers allocation failure: "
663 "forcing -CMSConcurrentMTEnabled");
664 CMSConcurrentMTEnabled = false;
665 } else {
666 _conc_workers->initialize_workers();
667 }
668 } else {
669 CMSConcurrentMTEnabled = false;
670 }
671 }
672 if (!CMSConcurrentMTEnabled) {
673 ConcGCThreads = 0;
674 } else {
675 // Turn off CMSCleanOnEnter optimization temporarily for
676 // the MT case where it's not fixed yet; see 6178663.
677 CMSCleanOnEnter = false;
678 }
679 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
680 "Inconsistency");
681
682 // Parallel task queues; these are shared for the
683 // concurrent and stop-world phases of CMS, but
684 // are not shared with parallel scavenge (ParNew).
685 {
686 uint i;
687 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
688
689 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
690 || ParallelRefProcEnabled)
691 && num_queues > 0) {
692 _task_queues = new OopTaskQueueSet(num_queues);
693 if (_task_queues == NULL) {
694 warning("task_queues allocation failure.");
695 return;
696 }
697 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
698 if (_hash_seed == NULL) {
699 warning("_hash_seed array allocation failure");
700 return;
701 }
702
703 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
704 for (i = 0; i < num_queues; i++) {
705 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
706 if (q == NULL) {
707 warning("work_queue allocation failure.");
708 return;
709 }
710 _task_queues->register_queue(i, q);
711 }
712 for (i = 0; i < num_queues; i++) {
713 _task_queues->queue(i)->initialize();
714 _hash_seed[i] = 17; // copied from ParNew
715 }
716 }
717 }
718
719 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
720 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
721
722 // Clip CMSBootstrapOccupancy between 0 and 100.
723 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
724 /(double)100;
725
726 _full_gcs_since_conc_gc = 0;
727
728 // Now tell CMS generations the identity of their collector
729 ConcurrentMarkSweepGeneration::set_collector(this);
730
731 // Create & start a CMS thread for this CMS collector
732 _cmsThread = ConcurrentMarkSweepThread::start(this);
733 assert(cmsThread() != NULL, "CMS Thread should have been created");
734 assert(cmsThread()->collector() == this,
735 "CMS Thread should refer to this gen");
736 assert(CGC_lock != NULL, "Where's the CGC_lock?");
737
738 // Support for parallelizing young gen rescan
739 GenCollectedHeap* gch = GenCollectedHeap::heap();
740 _young_gen = gch->prev_gen(_cmsGen);
741 if (gch->supports_inline_contig_alloc()) {
742 _top_addr = gch->top_addr();
743 _end_addr = gch->end_addr();
744 assert(_young_gen != NULL, "no _young_gen");
745 _eden_chunk_index = 0;
746 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
747 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
748 if (_eden_chunk_array == NULL) {
749 _eden_chunk_capacity = 0;
750 warning("GC/CMS: _eden_chunk_array allocation failure");
751 }
752 }
753 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
754
755 // Support for parallelizing survivor space rescan
756 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
757 const size_t max_plab_samples =
758 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
759
760 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
761 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
762 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
763 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
764 || _cursor == NULL) {
765 warning("Failed to allocate survivor plab/chunk array");
766 if (_survivor_plab_array != NULL) {
767 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
768 _survivor_plab_array = NULL;
769 }
770 if (_survivor_chunk_array != NULL) {
771 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
772 _survivor_chunk_array = NULL;
773 }
774 if (_cursor != NULL) {
775 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
776 _cursor = NULL;
777 }
778 } else {
779 _survivor_chunk_capacity = 2*max_plab_samples;
780 for (uint i = 0; i < ParallelGCThreads; i++) {
781 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
782 if (vec == NULL) {
783 warning("Failed to allocate survivor plab array");
784 for (int j = i; j > 0; j--) {
785 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
786 }
787 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
788 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
789 _survivor_plab_array = NULL;
790 _survivor_chunk_array = NULL;
791 _survivor_chunk_capacity = 0;
792 break;
793 } else {
794 ChunkArray* cur =
795 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
796 max_plab_samples);
797 assert(cur->end() == 0, "Should be 0");
798 assert(cur->array() == vec, "Should be vec");
799 assert(cur->capacity() == max_plab_samples, "Error");
800 }
801 }
802 }
803 }
804 assert( ( _survivor_plab_array != NULL
805 && _survivor_chunk_array != NULL)
806 || ( _survivor_chunk_capacity == 0
807 && _survivor_chunk_index == 0),
808 "Error");
809
810 // Choose what strong roots should be scanned depending on verification options
811 // and perm gen collection mode.
812 if (!CMSClassUnloadingEnabled) {
813 // If class unloading is disabled we want to include all classes into the root set.
814 add_root_scanning_option(SharedHeap::SO_AllClasses);
815 } else {
816 add_root_scanning_option(SharedHeap::SO_SystemClasses);
817 }
818
819 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
820 _gc_counters = new CollectorCounters("CMS", 1);
821 _completed_initialization = true;
822 _inter_sweep_timer.start(); // start of time
823 }
824
825 const char* ConcurrentMarkSweepGeneration::name() const {
826 return "concurrent mark-sweep generation";
827 }
828 void ConcurrentMarkSweepGeneration::update_counters() {
829 if (UsePerfData) {
830 _space_counters->update_all();
831 _gen_counters->update_all();
832 }
833 }
834
835 // this is an optimized version of update_counters(). it takes the
836 // used value as a parameter rather than computing it.
837 //
838 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
839 if (UsePerfData) {
840 _space_counters->update_used(used);
841 _space_counters->update_capacity();
842 _gen_counters->update_all();
843 }
844 }
845
846 void ConcurrentMarkSweepGeneration::print() const {
847 Generation::print();
848 cmsSpace()->print();
849 }
850
851 #ifndef PRODUCT
852 void ConcurrentMarkSweepGeneration::print_statistics() {
853 cmsSpace()->printFLCensus(0);
854 }
855 #endif
856
857 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
858 GenCollectedHeap* gch = GenCollectedHeap::heap();
859 if (PrintGCDetails) {
860 if (Verbose) {
861 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
862 level(), short_name(), s, used(), capacity());
863 } else {
864 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
865 level(), short_name(), s, used() / K, capacity() / K);
866 }
867 }
868 if (Verbose) {
869 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
870 gch->used(), gch->capacity());
871 } else {
872 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
873 gch->used() / K, gch->capacity() / K);
874 }
875 }
876
877 size_t
878 ConcurrentMarkSweepGeneration::contiguous_available() const {
879 // dld proposes an improvement in precision here. If the committed
880 // part of the space ends in a free block we should add that to
881 // uncommitted size in the calculation below. Will make this
882 // change later, staying with the approximation below for the
883 // time being. -- ysr.
884 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
885 }
886
887 size_t
888 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
889 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
890 }
891
892 size_t ConcurrentMarkSweepGeneration::max_available() const {
893 return free() + _virtual_space.uncommitted_size();
894 }
895
896 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
897 size_t available = max_available();
898 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
899 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
900 if (Verbose && PrintGCDetails) {
901 gclog_or_tty->print_cr(
902 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
903 "max_promo("SIZE_FORMAT")",
904 res? "":" not", available, res? ">=":"<",
905 av_promo, max_promotion_in_bytes);
906 }
907 return res;
908 }
909
910 // At a promotion failure dump information on block layout in heap
911 // (cms old generation).
912 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
913 if (CMSDumpAtPromotionFailure) {
914 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
915 }
916 }
917
918 CompactibleSpace*
919 ConcurrentMarkSweepGeneration::first_compaction_space() const {
920 return _cmsSpace;
921 }
922
923 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
924 // Clear the promotion information. These pointers can be adjusted
925 // along with all the other pointers into the heap but
926 // compaction is expected to be a rare event with
927 // a heap using cms so don't do it without seeing the need.
928 if (CollectedHeap::use_parallel_gc_threads()) {
929 for (uint i = 0; i < ParallelGCThreads; i++) {
930 _par_gc_thread_states[i]->promo.reset();
931 }
932 }
933 }
934
935 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
936 blk->do_space(_cmsSpace);
937 }
938
939 void ConcurrentMarkSweepGeneration::compute_new_size() {
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 size_t expand_bytes = 0;
951 double free_percentage = ((double) free()) / capacity();
952 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
953 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
954
955 // compute expansion delta needed for reaching desired free percentage
956 if (free_percentage < desired_free_percentage) {
957 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
958 assert(desired_capacity >= capacity(), "invalid expansion size");
959 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
960 }
961 if (expand_bytes > 0) {
962 if (PrintGCDetails && Verbose) {
963 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
964 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
965 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
966 gclog_or_tty->print_cr(" Desired free fraction %f",
967 desired_free_percentage);
968 gclog_or_tty->print_cr(" Maximum free fraction %f",
969 maximum_free_percentage);
970 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
971 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
972 desired_capacity/1000);
973 int prev_level = level() - 1;
974 if (prev_level >= 0) {
975 size_t prev_size = 0;
976 GenCollectedHeap* gch = GenCollectedHeap::heap();
977 Generation* prev_gen = gch->_gens[prev_level];
978 prev_size = prev_gen->capacity();
979 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
980 prev_size/1000);
981 }
982 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
983 unsafe_max_alloc_nogc()/1000);
984 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
985 contiguous_available()/1000);
986 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
987 expand_bytes);
988 }
989 // safe if expansion fails
990 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
991 if (PrintGCDetails && Verbose) {
992 gclog_or_tty->print_cr(" Expanded free fraction %f",
993 ((double) free()) / capacity());
994 }
995 }
996 }
997
998 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
999 return cmsSpace()->freelistLock();
1000 }
1001
1002 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1003 bool tlab) {
1004 CMSSynchronousYieldRequest yr;
1005 MutexLockerEx x(freelistLock(),
1006 Mutex::_no_safepoint_check_flag);
1007 return have_lock_and_allocate(size, tlab);
1008 }
1009
1010 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1011 bool tlab /* ignored */) {
1012 assert_lock_strong(freelistLock());
1013 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1014 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1015 // Allocate the object live (grey) if the background collector has
1016 // started marking. This is necessary because the marker may
1017 // have passed this address and consequently this object will
1018 // not otherwise be greyed and would be incorrectly swept up.
1019 // Note that if this object contains references, the writing
1020 // of those references will dirty the card containing this object
1021 // allowing the object to be blackened (and its references scanned)
1022 // either during a preclean phase or at the final checkpoint.
1023 if (res != NULL) {
1024 // We may block here with an uninitialized object with
1025 // its mark-bit or P-bits not yet set. Such objects need
1026 // to be safely navigable by block_start().
1027 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1028 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1029 collector()->direct_allocated(res, adjustedSize);
1030 _direct_allocated_words += adjustedSize;
1031 // allocation counters
1032 NOT_PRODUCT(
1033 _numObjectsAllocated++;
1034 _numWordsAllocated += (int)adjustedSize;
1035 )
1036 }
1037 return res;
1038 }
1039
1040 // In the case of direct allocation by mutators in a generation that
1041 // is being concurrently collected, the object must be allocated
1042 // live (grey) if the background collector has started marking.
1043 // This is necessary because the marker may
1044 // have passed this address and consequently this object will
1045 // not otherwise be greyed and would be incorrectly swept up.
1046 // Note that if this object contains references, the writing
1047 // of those references will dirty the card containing this object
1048 // allowing the object to be blackened (and its references scanned)
1049 // either during a preclean phase or at the final checkpoint.
1050 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1051 assert(_markBitMap.covers(start, size), "Out of bounds");
1052 if (_collectorState >= Marking) {
1053 MutexLockerEx y(_markBitMap.lock(),
1054 Mutex::_no_safepoint_check_flag);
1055 // [see comments preceding SweepClosure::do_blk() below for details]
1056 // 1. need to mark the object as live so it isn't collected
1057 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1058 // 3. need to mark the end of the object so marking, precleaning or sweeping
1059 // can skip over uninitialized or unparsable objects. An allocated
1060 // object is considered uninitialized for our purposes as long as
1061 // its klass word is NULL. (Unparsable objects are those which are
1062 // initialized in the sense just described, but whose sizes can still
1063 // not be correctly determined. Note that the class of unparsable objects
1064 // can only occur in the perm gen. All old gen objects are parsable
1065 // as soon as they are initialized.)
1066 _markBitMap.mark(start); // object is live
1067 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1068 _markBitMap.mark(start + size - 1);
1069 // mark end of object
1070 }
1071 // check that oop looks uninitialized
1072 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1073 }
1074
1075 void CMSCollector::promoted(bool par, HeapWord* start,
1076 bool is_obj_array, size_t obj_size) {
1077 assert(_markBitMap.covers(start), "Out of bounds");
1078 // See comment in direct_allocated() about when objects should
1079 // be allocated live.
1080 if (_collectorState >= Marking) {
1081 // we already hold the marking bit map lock, taken in
1082 // the prologue
1083 if (par) {
1084 _markBitMap.par_mark(start);
1085 } else {
1086 _markBitMap.mark(start);
1087 }
1088 // We don't need to mark the object as uninitialized (as
1089 // in direct_allocated above) because this is being done with the
1090 // world stopped and the object will be initialized by the
1091 // time the marking, precleaning or sweeping get to look at it.
1092 // But see the code for copying objects into the CMS generation,
1093 // where we need to ensure that concurrent readers of the
1094 // block offset table are able to safely navigate a block that
1095 // is in flux from being free to being allocated (and in
1096 // transition while being copied into) and subsequently
1097 // becoming a bona-fide object when the copy/promotion is complete.
1098 assert(SafepointSynchronize::is_at_safepoint(),
1099 "expect promotion only at safepoints");
1100
1101 if (_collectorState < Sweeping) {
1102 // Mark the appropriate cards in the modUnionTable, so that
1103 // this object gets scanned before the sweep. If this is
1104 // not done, CMS generation references in the object might
1105 // not get marked.
1106 // For the case of arrays, which are otherwise precisely
1107 // marked, we need to dirty the entire array, not just its head.
1108 if (is_obj_array) {
1109 // The [par_]mark_range() method expects mr.end() below to
1110 // be aligned to the granularity of a bit's representation
1111 // in the heap. In the case of the MUT below, that's a
1112 // card size.
1113 MemRegion mr(start,
1114 (HeapWord*)round_to((intptr_t)(start + obj_size),
1115 CardTableModRefBS::card_size /* bytes */));
1116 if (par) {
1117 _modUnionTable.par_mark_range(mr);
1118 } else {
1119 _modUnionTable.mark_range(mr);
1120 }
1121 } else { // not an obj array; we can just mark the head
1122 if (par) {
1123 _modUnionTable.par_mark(start);
1124 } else {
1125 _modUnionTable.mark(start);
1126 }
1127 }
1128 }
1129 }
1130 }
1131
1132 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1133 {
1134 size_t delta = pointer_delta(addr, space->bottom());
1135 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1136 }
1137
1138 void CMSCollector::icms_update_allocation_limits()
1139 {
1140 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1141 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1142
1143 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1144 if (CMSTraceIncrementalPacing) {
1145 stats().print();
1146 }
1147
1148 assert(duty_cycle <= 100, "invalid duty cycle");
1149 if (duty_cycle != 0) {
1150 // The duty_cycle is a percentage between 0 and 100; convert to words and
1151 // then compute the offset from the endpoints of the space.
1152 size_t free_words = eden->free() / HeapWordSize;
1153 double free_words_dbl = (double)free_words;
1154 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1155 size_t offset_words = (free_words - duty_cycle_words) / 2;
1156
1157 _icms_start_limit = eden->top() + offset_words;
1158 _icms_stop_limit = eden->end() - offset_words;
1159
1160 // The limits may be adjusted (shifted to the right) by
1161 // CMSIncrementalOffset, to allow the application more mutator time after a
1162 // young gen gc (when all mutators were stopped) and before CMS starts and
1163 // takes away one or more cpus.
1164 if (CMSIncrementalOffset != 0) {
1165 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1166 size_t adjustment = (size_t)adjustment_dbl;
1167 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1168 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1169 _icms_start_limit += adjustment;
1170 _icms_stop_limit = tmp_stop;
1171 }
1172 }
1173 }
1174 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1175 _icms_start_limit = _icms_stop_limit = eden->end();
1176 }
1177
1178 // Install the new start limit.
1179 eden->set_soft_end(_icms_start_limit);
1180
1181 if (CMSTraceIncrementalMode) {
1182 gclog_or_tty->print(" icms alloc limits: "
1183 PTR_FORMAT "," PTR_FORMAT
1184 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1185 _icms_start_limit, _icms_stop_limit,
1186 percent_of_space(eden, _icms_start_limit),
1187 percent_of_space(eden, _icms_stop_limit));
1188 if (Verbose) {
1189 gclog_or_tty->print("eden: ");
1190 eden->print_on(gclog_or_tty);
1191 }
1192 }
1193 }
1194
1195 // Any changes here should try to maintain the invariant
1196 // that if this method is called with _icms_start_limit
1197 // and _icms_stop_limit both NULL, then it should return NULL
1198 // and not notify the icms thread.
1199 HeapWord*
1200 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1201 size_t word_size)
1202 {
1203 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1204 // nop.
1205 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1206 if (top <= _icms_start_limit) {
1207 if (CMSTraceIncrementalMode) {
1208 space->print_on(gclog_or_tty);
1209 gclog_or_tty->stamp();
1210 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1211 ", new limit=" PTR_FORMAT
1212 " (" SIZE_FORMAT "%%)",
1213 top, _icms_stop_limit,
1214 percent_of_space(space, _icms_stop_limit));
1215 }
1216 ConcurrentMarkSweepThread::start_icms();
1217 assert(top < _icms_stop_limit, "Tautology");
1218 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1219 return _icms_stop_limit;
1220 }
1221
1222 // The allocation will cross both the _start and _stop limits, so do the
1223 // stop notification also and return end().
1224 if (CMSTraceIncrementalMode) {
1225 space->print_on(gclog_or_tty);
1226 gclog_or_tty->stamp();
1227 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1228 ", new limit=" PTR_FORMAT
1229 " (" SIZE_FORMAT "%%)",
1230 top, space->end(),
1231 percent_of_space(space, space->end()));
1232 }
1233 ConcurrentMarkSweepThread::stop_icms();
1234 return space->end();
1235 }
1236
1237 if (top <= _icms_stop_limit) {
1238 if (CMSTraceIncrementalMode) {
1239 space->print_on(gclog_or_tty);
1240 gclog_or_tty->stamp();
1241 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1242 ", new limit=" PTR_FORMAT
1243 " (" SIZE_FORMAT "%%)",
1244 top, space->end(),
1245 percent_of_space(space, space->end()));
1246 }
1247 ConcurrentMarkSweepThread::stop_icms();
1248 return space->end();
1249 }
1250
1251 if (CMSTraceIncrementalMode) {
1252 space->print_on(gclog_or_tty);
1253 gclog_or_tty->stamp();
1254 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1255 ", new limit=" PTR_FORMAT,
1256 top, NULL);
1257 }
1258 }
1259
1260 return NULL;
1261 }
1262
1263 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1264 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1265 // allocate, copy and if necessary update promoinfo --
1266 // delegate to underlying space.
1267 assert_lock_strong(freelistLock());
1268
1269 #ifndef PRODUCT
1270 if (Universe::heap()->promotion_should_fail()) {
1271 return NULL;
1272 }
1273 #endif // #ifndef PRODUCT
1274
1275 oop res = _cmsSpace->promote(obj, obj_size);
1276 if (res == NULL) {
1277 // expand and retry
1278 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1279 expand(s*HeapWordSize, MinHeapDeltaBytes,
1280 CMSExpansionCause::_satisfy_promotion);
1281 // Since there's currently no next generation, we don't try to promote
1282 // into a more senior generation.
1283 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1284 "is made to pass on a possibly failing "
1285 "promotion to next generation");
1286 res = _cmsSpace->promote(obj, obj_size);
1287 }
1288 if (res != NULL) {
1289 // See comment in allocate() about when objects should
1290 // be allocated live.
1291 assert(obj->is_oop(), "Will dereference klass pointer below");
1292 collector()->promoted(false, // Not parallel
1293 (HeapWord*)res, obj->is_objArray(), obj_size);
1294 // promotion counters
1295 NOT_PRODUCT(
1296 _numObjectsPromoted++;
1297 _numWordsPromoted +=
1298 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1299 )
1300 }
1301 return res;
1302 }
1303
1304
1305 HeapWord*
1306 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1307 HeapWord* top,
1308 size_t word_sz)
1309 {
1310 return collector()->allocation_limit_reached(space, top, word_sz);
1311 }
1312
1313 // IMPORTANT: Notes on object size recognition in CMS.
1314 // ---------------------------------------------------
1315 // A block of storage in the CMS generation is always in
1316 // one of three states. A free block (FREE), an allocated
1317 // object (OBJECT) whose size() method reports the correct size,
1318 // and an intermediate state (TRANSIENT) in which its size cannot
1319 // be accurately determined.
1320 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1321 // -----------------------------------------------------
1322 // FREE: klass_word & 1 == 1; mark_word holds block size
1323 //
1324 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1325 // obj->size() computes correct size
1326 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1327 //
1328 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1329 //
1330 // STATE IDENTIFICATION: (64 bit+COOPS)
1331 // ------------------------------------
1332 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1333 //
1334 // OBJECT: klass_word installed; klass_word != 0;
1335 // obj->size() computes correct size
1336 // [Perm Gen comment above continues to hold]
1337 //
1338 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1339 //
1340 //
1341 // STATE TRANSITION DIAGRAM
1342 //
1343 // mut / parnew mut / parnew
1344 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1345 // ^ |
1346 // |------------------------ DEAD <------------------------------------|
1347 // sweep mut
1348 //
1349 // While a block is in TRANSIENT state its size cannot be determined
1350 // so readers will either need to come back later or stall until
1351 // the size can be determined. Note that for the case of direct
1352 // allocation, P-bits, when available, may be used to determine the
1353 // size of an object that may not yet have been initialized.
1354
1355 // Things to support parallel young-gen collection.
1356 oop
1357 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1358 oop old, markOop m,
1359 size_t word_sz) {
1360 #ifndef PRODUCT
1361 if (Universe::heap()->promotion_should_fail()) {
1362 return NULL;
1363 }
1364 #endif // #ifndef PRODUCT
1365
1366 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1367 PromotionInfo* promoInfo = &ps->promo;
1368 // if we are tracking promotions, then first ensure space for
1369 // promotion (including spooling space for saving header if necessary).
1370 // then allocate and copy, then track promoted info if needed.
1371 // When tracking (see PromotionInfo::track()), the mark word may
1372 // be displaced and in this case restoration of the mark word
1373 // occurs in the (oop_since_save_marks_)iterate phase.
1374 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1375 // Out of space for allocating spooling buffers;
1376 // try expanding and allocating spooling buffers.
1377 if (!expand_and_ensure_spooling_space(promoInfo)) {
1378 return NULL;
1379 }
1380 }
1381 assert(promoInfo->has_spooling_space(), "Control point invariant");
1382 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1383 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1384 if (obj_ptr == NULL) {
1385 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1386 if (obj_ptr == NULL) {
1387 return NULL;
1388 }
1389 }
1390 oop obj = oop(obj_ptr);
1391 OrderAccess::storestore();
1392 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1393 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1394 // IMPORTANT: See note on object initialization for CMS above.
1395 // Otherwise, copy the object. Here we must be careful to insert the
1396 // klass pointer last, since this marks the block as an allocated object.
1397 // Except with compressed oops it's the mark word.
1398 HeapWord* old_ptr = (HeapWord*)old;
1399 // Restore the mark word copied above.
1400 obj->set_mark(m);
1401 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1402 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1403 OrderAccess::storestore();
1404
1405 if (UseCompressedOops) {
1406 // Copy gap missed by (aligned) header size calculation below
1407 obj->set_klass_gap(old->klass_gap());
1408 }
1409 if (word_sz > (size_t)oopDesc::header_size()) {
1410 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1411 obj_ptr + oopDesc::header_size(),
1412 word_sz - oopDesc::header_size());
1413 }
1414
1415 // Now we can track the promoted object, if necessary. We take care
1416 // to delay the transition from uninitialized to full object
1417 // (i.e., insertion of klass pointer) until after, so that it
1418 // atomically becomes a promoted object.
1419 if (promoInfo->tracking()) {
1420 promoInfo->track((PromotedObject*)obj, old->klass());
1421 }
1422 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1423 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1424 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1425
1426 // Finally, install the klass pointer (this should be volatile).
1427 OrderAccess::storestore();
1428 obj->set_klass(old->klass());
1429 // We should now be able to calculate the right size for this object
1430 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1431
1432 collector()->promoted(true, // parallel
1433 obj_ptr, old->is_objArray(), word_sz);
1434
1435 NOT_PRODUCT(
1436 Atomic::inc_ptr(&_numObjectsPromoted);
1437 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1438 )
1439
1440 return obj;
1441 }
1442
1443 void
1444 ConcurrentMarkSweepGeneration::
1445 par_promote_alloc_undo(int thread_num,
1446 HeapWord* obj, size_t word_sz) {
1447 // CMS does not support promotion undo.
1448 ShouldNotReachHere();
1449 }
1450
1451 void
1452 ConcurrentMarkSweepGeneration::
1453 par_promote_alloc_done(int thread_num) {
1454 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1455 ps->lab.retire(thread_num);
1456 }
1457
1458 void
1459 ConcurrentMarkSweepGeneration::
1460 par_oop_since_save_marks_iterate_done(int thread_num) {
1461 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1462 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1463 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1464 }
1465
1466 // XXXPERM
1467 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1468 size_t size,
1469 bool tlab)
1470 {
1471 // We allow a STW collection only if a full
1472 // collection was requested.
1473 return full || should_allocate(size, tlab); // FIX ME !!!
1474 // This and promotion failure handling are connected at the
1475 // hip and should be fixed by untying them.
1476 }
1477
1478 bool CMSCollector::shouldConcurrentCollect() {
1479 if (_full_gc_requested) {
1480 if (Verbose && PrintGCDetails) {
1481 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1482 " gc request (or gc_locker)");
1483 }
1484 return true;
1485 }
1486
1487 // For debugging purposes, change the type of collection.
1488 // If the rotation is not on the concurrent collection
1489 // type, don't start a concurrent collection.
1490 NOT_PRODUCT(
1491 if (RotateCMSCollectionTypes &&
1492 (_cmsGen->debug_collection_type() !=
1493 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1494 assert(_cmsGen->debug_collection_type() !=
1495 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1496 "Bad cms collection type");
1497 return false;
1498 }
1499 )
1500
1501 FreelistLocker x(this);
1502 // ------------------------------------------------------------------
1503 // Print out lots of information which affects the initiation of
1504 // a collection.
1505 if (PrintCMSInitiationStatistics && stats().valid()) {
1506 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1507 gclog_or_tty->stamp();
1508 gclog_or_tty->print_cr("");
1509 stats().print_on(gclog_or_tty);
1510 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1511 stats().time_until_cms_gen_full());
1512 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1513 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1514 _cmsGen->contiguous_available());
1515 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1516 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1517 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1518 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1519 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1520 }
1521 // ------------------------------------------------------------------
1522
1523 // If the estimated time to complete a cms collection (cms_duration())
1524 // is less than the estimated time remaining until the cms generation
1525 // is full, start a collection.
1526 if (!UseCMSInitiatingOccupancyOnly) {
1527 if (stats().valid()) {
1528 if (stats().time_until_cms_start() == 0.0) {
1529 return true;
1530 }
1531 } else {
1532 // We want to conservatively collect somewhat early in order
1533 // to try and "bootstrap" our CMS/promotion statistics;
1534 // this branch will not fire after the first successful CMS
1535 // collection because the stats should then be valid.
1536 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1537 if (Verbose && PrintGCDetails) {
1538 gclog_or_tty->print_cr(
1539 " CMSCollector: collect for bootstrapping statistics:"
1540 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1541 _bootstrap_occupancy);
1542 }
1543 return true;
1544 }
1545 }
1546 }
1547
1548 // Otherwise, we start a collection cycle if either the perm gen or
1549 // old gen want a collection cycle started. Each may use
1550 // an appropriate criterion for making this decision.
1551 // XXX We need to make sure that the gen expansion
1552 // criterion dovetails well with this. XXX NEED TO FIX THIS
1553 if (_cmsGen->should_concurrent_collect()) {
1554 if (Verbose && PrintGCDetails) {
1555 gclog_or_tty->print_cr("CMS old gen initiated");
1556 }
1557 return true;
1558 }
1559
1560 // We start a collection if we believe an incremental collection may fail;
1561 // this is not likely to be productive in practice because it's probably too
1562 // late anyway.
1563 GenCollectedHeap* gch = GenCollectedHeap::heap();
1564 assert(gch->collector_policy()->is_two_generation_policy(),
1565 "You may want to check the correctness of the following");
1566 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1567 if (Verbose && PrintGCDetails) {
1568 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1569 }
1570 return true;
1571 }
1572
1573 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1574 bool res = update_should_unload_classes();
1575 if (res) {
1576 if (Verbose && PrintGCDetails) {
1577 gclog_or_tty->print_cr("CMS perm gen initiated");
1578 }
1579 return true;
1580 }
1581 }
1582 return false;
1583 }
1584
1585 // Clear _expansion_cause fields of constituent generations
1586 void CMSCollector::clear_expansion_cause() {
1587 _cmsGen->clear_expansion_cause();
1588 _permGen->clear_expansion_cause();
1589 }
1590
1591 // We should be conservative in starting a collection cycle. To
1592 // start too eagerly runs the risk of collecting too often in the
1593 // extreme. To collect too rarely falls back on full collections,
1594 // which works, even if not optimum in terms of concurrent work.
1595 // As a work around for too eagerly collecting, use the flag
1596 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1597 // giving the user an easily understandable way of controlling the
1598 // collections.
1599 // We want to start a new collection cycle if any of the following
1600 // conditions hold:
1601 // . our current occupancy exceeds the configured initiating occupancy
1602 // for this generation, or
1603 // . we recently needed to expand this space and have not, since that
1604 // expansion, done a collection of this generation, or
1605 // . the underlying space believes that it may be a good idea to initiate
1606 // a concurrent collection (this may be based on criteria such as the
1607 // following: the space uses linear allocation and linear allocation is
1608 // going to fail, or there is believed to be excessive fragmentation in
1609 // the generation, etc... or ...
1610 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1611 // the case of the old generation, not the perm generation; see CR 6543076):
1612 // we may be approaching a point at which allocation requests may fail because
1613 // we will be out of sufficient free space given allocation rate estimates.]
1614 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1615
1616 assert_lock_strong(freelistLock());
1617 if (occupancy() > initiating_occupancy()) {
1618 if (PrintGCDetails && Verbose) {
1619 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1620 short_name(), occupancy(), initiating_occupancy());
1621 }
1622 return true;
1623 }
1624 if (UseCMSInitiatingOccupancyOnly) {
1625 return false;
1626 }
1627 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1628 if (PrintGCDetails && Verbose) {
1629 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1630 short_name());
1631 }
1632 return true;
1633 }
1634 if (_cmsSpace->should_concurrent_collect()) {
1635 if (PrintGCDetails && Verbose) {
1636 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1637 short_name());
1638 }
1639 return true;
1640 }
1641 return false;
1642 }
1643
1644 void ConcurrentMarkSweepGeneration::collect(bool full,
1645 bool clear_all_soft_refs,
1646 size_t size,
1647 bool tlab)
1648 {
1649 collector()->collect(full, clear_all_soft_refs, size, tlab);
1650 }
1651
1652 void CMSCollector::collect(bool full,
1653 bool clear_all_soft_refs,
1654 size_t size,
1655 bool tlab)
1656 {
1657 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1658 // For debugging purposes skip the collection if the state
1659 // is not currently idle
1660 if (TraceCMSState) {
1661 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1662 Thread::current(), full, _collectorState);
1663 }
1664 return;
1665 }
1666
1667 // The following "if" branch is present for defensive reasons.
1668 // In the current uses of this interface, it can be replaced with:
1669 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1670 // But I am not placing that assert here to allow future
1671 // generality in invoking this interface.
1672 if (GC_locker::is_active()) {
1673 // A consistency test for GC_locker
1674 assert(GC_locker::needs_gc(), "Should have been set already");
1675 // Skip this foreground collection, instead
1676 // expanding the heap if necessary.
1677 // Need the free list locks for the call to free() in compute_new_size()
1678 compute_new_size();
1679 return;
1680 }
1681 acquire_control_and_collect(full, clear_all_soft_refs);
1682 _full_gcs_since_conc_gc++;
1683
1684 }
1685
1686 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1687 GenCollectedHeap* gch = GenCollectedHeap::heap();
1688 unsigned int gc_count = gch->total_full_collections();
1689 if (gc_count == full_gc_count) {
1690 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1691 _full_gc_requested = true;
1692 CGC_lock->notify(); // nudge CMS thread
1693 } else {
1694 assert(gc_count > full_gc_count, "Error: causal loop");
1695 }
1696 }
1697
1698
1699 // The foreground and background collectors need to coordinate in order
1700 // to make sure that they do not mutually interfere with CMS collections.
1701 // When a background collection is active,
1702 // the foreground collector may need to take over (preempt) and
1703 // synchronously complete an ongoing collection. Depending on the
1704 // frequency of the background collections and the heap usage
1705 // of the application, this preemption can be seldom or frequent.
1706 // There are only certain
1707 // points in the background collection that the "collection-baton"
1708 // can be passed to the foreground collector.
1709 //
1710 // The foreground collector will wait for the baton before
1711 // starting any part of the collection. The foreground collector
1712 // will only wait at one location.
1713 //
1714 // The background collector will yield the baton before starting a new
1715 // phase of the collection (e.g., before initial marking, marking from roots,
1716 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1717 // of the loop which switches the phases. The background collector does some
1718 // of the phases (initial mark, final re-mark) with the world stopped.
1719 // Because of locking involved in stopping the world,
1720 // the foreground collector should not block waiting for the background
1721 // collector when it is doing a stop-the-world phase. The background
1722 // collector will yield the baton at an additional point just before
1723 // it enters a stop-the-world phase. Once the world is stopped, the
1724 // background collector checks the phase of the collection. If the
1725 // phase has not changed, it proceeds with the collection. If the
1726 // phase has changed, it skips that phase of the collection. See
1727 // the comments on the use of the Heap_lock in collect_in_background().
1728 //
1729 // Variable used in baton passing.
1730 // _foregroundGCIsActive - Set to true by the foreground collector when
1731 // it wants the baton. The foreground clears it when it has finished
1732 // the collection.
1733 // _foregroundGCShouldWait - Set to true by the background collector
1734 // when it is running. The foreground collector waits while
1735 // _foregroundGCShouldWait is true.
1736 // CGC_lock - monitor used to protect access to the above variables
1737 // and to notify the foreground and background collectors.
1738 // _collectorState - current state of the CMS collection.
1739 //
1740 // The foreground collector
1741 // acquires the CGC_lock
1742 // sets _foregroundGCIsActive
1743 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1744 // various locks acquired in preparation for the collection
1745 // are released so as not to block the background collector
1746 // that is in the midst of a collection
1747 // proceeds with the collection
1748 // clears _foregroundGCIsActive
1749 // returns
1750 //
1751 // The background collector in a loop iterating on the phases of the
1752 // collection
1753 // acquires the CGC_lock
1754 // sets _foregroundGCShouldWait
1755 // if _foregroundGCIsActive is set
1756 // clears _foregroundGCShouldWait, notifies _CGC_lock
1757 // waits on _CGC_lock for _foregroundGCIsActive to become false
1758 // and exits the loop.
1759 // otherwise
1760 // proceed with that phase of the collection
1761 // if the phase is a stop-the-world phase,
1762 // yield the baton once more just before enqueueing
1763 // the stop-world CMS operation (executed by the VM thread).
1764 // returns after all phases of the collection are done
1765 //
1766
1767 void CMSCollector::acquire_control_and_collect(bool full,
1768 bool clear_all_soft_refs) {
1769 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1770 assert(!Thread::current()->is_ConcurrentGC_thread(),
1771 "shouldn't try to acquire control from self!");
1772
1773 // Start the protocol for acquiring control of the
1774 // collection from the background collector (aka CMS thread).
1775 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1776 "VM thread should have CMS token");
1777 // Remember the possibly interrupted state of an ongoing
1778 // concurrent collection
1779 CollectorState first_state = _collectorState;
1780
1781 // Signal to a possibly ongoing concurrent collection that
1782 // we want to do a foreground collection.
1783 _foregroundGCIsActive = true;
1784
1785 // Disable incremental mode during a foreground collection.
1786 ICMSDisabler icms_disabler;
1787
1788 // release locks and wait for a notify from the background collector
1789 // releasing the locks in only necessary for phases which
1790 // do yields to improve the granularity of the collection.
1791 assert_lock_strong(bitMapLock());
1792 // We need to lock the Free list lock for the space that we are
1793 // currently collecting.
1794 assert(haveFreelistLocks(), "Must be holding free list locks");
1795 bitMapLock()->unlock();
1796 releaseFreelistLocks();
1797 {
1798 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1799 if (_foregroundGCShouldWait) {
1800 // We are going to be waiting for action for the CMS thread;
1801 // it had better not be gone (for instance at shutdown)!
1802 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1803 "CMS thread must be running");
1804 // Wait here until the background collector gives us the go-ahead
1805 ConcurrentMarkSweepThread::clear_CMS_flag(
1806 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1807 // Get a possibly blocked CMS thread going:
1808 // Note that we set _foregroundGCIsActive true above,
1809 // without protection of the CGC_lock.
1810 CGC_lock->notify();
1811 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1812 "Possible deadlock");
1813 while (_foregroundGCShouldWait) {
1814 // wait for notification
1815 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1816 // Possibility of delay/starvation here, since CMS token does
1817 // not know to give priority to VM thread? Actually, i think
1818 // there wouldn't be any delay/starvation, but the proof of
1819 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1820 }
1821 ConcurrentMarkSweepThread::set_CMS_flag(
1822 ConcurrentMarkSweepThread::CMS_vm_has_token);
1823 }
1824 }
1825 // The CMS_token is already held. Get back the other locks.
1826 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1827 "VM thread should have CMS token");
1828 getFreelistLocks();
1829 bitMapLock()->lock_without_safepoint_check();
1830 if (TraceCMSState) {
1831 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1832 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1833 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1834 }
1835
1836 // Check if we need to do a compaction, or if not, whether
1837 // we need to start the mark-sweep from scratch.
1838 bool should_compact = false;
1839 bool should_start_over = false;
1840 decide_foreground_collection_type(clear_all_soft_refs,
1841 &should_compact, &should_start_over);
1842
1843 NOT_PRODUCT(
1844 if (RotateCMSCollectionTypes) {
1845 if (_cmsGen->debug_collection_type() ==
1846 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1847 should_compact = true;
1848 } else if (_cmsGen->debug_collection_type() ==
1849 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1850 should_compact = false;
1851 }
1852 }
1853 )
1854
1855 if (PrintGCDetails && first_state > Idling) {
1856 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1857 if (GCCause::is_user_requested_gc(cause) ||
1858 GCCause::is_serviceability_requested_gc(cause)) {
1859 gclog_or_tty->print(" (concurrent mode interrupted)");
1860 } else {
1861 gclog_or_tty->print(" (concurrent mode failure)");
1862 }
1863 }
1864
1865 if (should_compact) {
1866 // If the collection is being acquired from the background
1867 // collector, there may be references on the discovered
1868 // references lists that have NULL referents (being those
1869 // that were concurrently cleared by a mutator) or
1870 // that are no longer active (having been enqueued concurrently
1871 // by the mutator).
1872 // Scrub the list of those references because Mark-Sweep-Compact
1873 // code assumes referents are not NULL and that all discovered
1874 // Reference objects are active.
1875 ref_processor()->clean_up_discovered_references();
1876
1877 do_compaction_work(clear_all_soft_refs);
1878
1879 // Has the GC time limit been exceeded?
1880 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1881 size_t max_eden_size = young_gen->max_capacity() -
1882 young_gen->to()->capacity() -
1883 young_gen->from()->capacity();
1884 GenCollectedHeap* gch = GenCollectedHeap::heap();
1885 GCCause::Cause gc_cause = gch->gc_cause();
1886 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1887 young_gen->eden()->used(),
1888 _cmsGen->max_capacity(),
1889 max_eden_size,
1890 full,
1891 gc_cause,
1892 gch->collector_policy());
1893 } else {
1894 do_mark_sweep_work(clear_all_soft_refs, first_state,
1895 should_start_over);
1896 }
1897 // Reset the expansion cause, now that we just completed
1898 // a collection cycle.
1899 clear_expansion_cause();
1900 _foregroundGCIsActive = false;
1901 return;
1902 }
1903
1904 // Resize the perm generation and the tenured generation
1905 // after obtaining the free list locks for the
1906 // two generations.
1907 void CMSCollector::compute_new_size() {
1908 assert_locked_or_safepoint(Heap_lock);
1909 FreelistLocker z(this);
1910 _permGen->compute_new_size();
1911 _cmsGen->compute_new_size();
1912 }
1913
1914 // A work method used by foreground collection to determine
1915 // what type of collection (compacting or not, continuing or fresh)
1916 // it should do.
1917 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1918 // and CMSCompactWhenClearAllSoftRefs the default in the future
1919 // and do away with the flags after a suitable period.
1920 void CMSCollector::decide_foreground_collection_type(
1921 bool clear_all_soft_refs, bool* should_compact,
1922 bool* should_start_over) {
1923 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1924 // flag is set, and we have either requested a System.gc() or
1925 // the number of full gc's since the last concurrent cycle
1926 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1927 // or if an incremental collection has failed
1928 GenCollectedHeap* gch = GenCollectedHeap::heap();
1929 assert(gch->collector_policy()->is_two_generation_policy(),
1930 "You may want to check the correctness of the following");
1931 // Inform cms gen if this was due to partial collection failing.
1932 // The CMS gen may use this fact to determine its expansion policy.
1933 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1934 assert(!_cmsGen->incremental_collection_failed(),
1935 "Should have been noticed, reacted to and cleared");
1936 _cmsGen->set_incremental_collection_failed();
1937 }
1938 *should_compact =
1939 UseCMSCompactAtFullCollection &&
1940 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1941 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1942 gch->incremental_collection_will_fail(true /* consult_young */));
1943 *should_start_over = false;
1944 if (clear_all_soft_refs && !*should_compact) {
1945 // We are about to do a last ditch collection attempt
1946 // so it would normally make sense to do a compaction
1947 // to reclaim as much space as possible.
1948 if (CMSCompactWhenClearAllSoftRefs) {
1949 // Default: The rationale is that in this case either
1950 // we are past the final marking phase, in which case
1951 // we'd have to start over, or so little has been done
1952 // that there's little point in saving that work. Compaction
1953 // appears to be the sensible choice in either case.
1954 *should_compact = true;
1955 } else {
1956 // We have been asked to clear all soft refs, but not to
1957 // compact. Make sure that we aren't past the final checkpoint
1958 // phase, for that is where we process soft refs. If we are already
1959 // past that phase, we'll need to redo the refs discovery phase and
1960 // if necessary clear soft refs that weren't previously
1961 // cleared. We do so by remembering the phase in which
1962 // we came in, and if we are past the refs processing
1963 // phase, we'll choose to just redo the mark-sweep
1964 // collection from scratch.
1965 if (_collectorState > FinalMarking) {
1966 // We are past the refs processing phase;
1967 // start over and do a fresh synchronous CMS cycle
1968 _collectorState = Resetting; // skip to reset to start new cycle
1969 reset(false /* == !asynch */);
1970 *should_start_over = true;
1971 } // else we can continue a possibly ongoing current cycle
1972 }
1973 }
1974 }
1975
1976 // A work method used by the foreground collector to do
1977 // a mark-sweep-compact.
1978 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1979 GenCollectedHeap* gch = GenCollectedHeap::heap();
1980
1981 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1982 gc_timer->register_gc_start(os::elapsed_counter());
1983
1984 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1985 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1986
1987 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1988 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1989 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1990 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1991 }
1992
1993 // Sample collection interval time and reset for collection pause.
1994 if (UseAdaptiveSizePolicy) {
1995 size_policy()->msc_collection_begin();
1996 }
1997
1998 // Temporarily widen the span of the weak reference processing to
1999 // the entire heap.
2000 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2001 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2002 // Temporarily, clear the "is_alive_non_header" field of the
2003 // reference processor.
2004 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2005 // Temporarily make reference _processing_ single threaded (non-MT).
2006 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2007 // Temporarily make refs discovery atomic
2008 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2009 // Temporarily make reference _discovery_ single threaded (non-MT)
2010 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2011
2012 ref_processor()->set_enqueuing_is_done(false);
2013 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2014 ref_processor()->setup_policy(clear_all_soft_refs);
2015 // If an asynchronous collection finishes, the _modUnionTable is
2016 // all clear. If we are assuming the collection from an asynchronous
2017 // collection, clear the _modUnionTable.
2018 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2019 "_modUnionTable should be clear if the baton was not passed");
2020 _modUnionTable.clear_all();
2021
2022 // We must adjust the allocation statistics being maintained
2023 // in the free list space. We do so by reading and clearing
2024 // the sweep timer and updating the block flux rate estimates below.
2025 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2026 if (_inter_sweep_timer.is_active()) {
2027 _inter_sweep_timer.stop();
2028 // Note that we do not use this sample to update the _inter_sweep_estimate.
2029 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2030 _inter_sweep_estimate.padded_average(),
2031 _intra_sweep_estimate.padded_average());
2032 }
2033
2034 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2035 ref_processor(), clear_all_soft_refs);
2036 #ifdef ASSERT
2037 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2038 size_t free_size = cms_space->free();
2039 assert(free_size ==
2040 pointer_delta(cms_space->end(), cms_space->compaction_top())
2041 * HeapWordSize,
2042 "All the free space should be compacted into one chunk at top");
2043 assert(cms_space->dictionary()->total_chunk_size(
2044 debug_only(cms_space->freelistLock())) == 0 ||
2045 cms_space->totalSizeInIndexedFreeLists() == 0,
2046 "All the free space should be in a single chunk");
2047 size_t num = cms_space->totalCount();
2048 assert((free_size == 0 && num == 0) ||
2049 (free_size > 0 && (num == 1 || num == 2)),
2050 "There should be at most 2 free chunks after compaction");
2051 #endif // ASSERT
2052 _collectorState = Resetting;
2053 assert(_restart_addr == NULL,
2054 "Should have been NULL'd before baton was passed");
2055 reset(false /* == !asynch */);
2056 _cmsGen->reset_after_compaction();
2057 _concurrent_cycles_since_last_unload = 0;
2058
2059 if (verifying() && !should_unload_classes()) {
2060 perm_gen_verify_bit_map()->clear_all();
2061 }
2062
2063 // Clear any data recorded in the PLAB chunk arrays.
2064 if (_survivor_plab_array != NULL) {
2065 reset_survivor_plab_arrays();
2066 }
2067
2068 // Adjust the per-size allocation stats for the next epoch.
2069 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2070 // Restart the "inter sweep timer" for the next epoch.
2071 _inter_sweep_timer.reset();
2072 _inter_sweep_timer.start();
2073
2074 // Sample collection pause time and reset for collection interval.
2075 if (UseAdaptiveSizePolicy) {
2076 size_policy()->msc_collection_end(gch->gc_cause());
2077 }
2078
2079 gc_timer->register_gc_end(os::elapsed_counter());
2080
2081 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2082
2083 // For a mark-sweep-compact, compute_new_size() will be called
2084 // in the heap's do_collection() method.
2085 }
2086
2087 // A work method used by the foreground collector to do
2088 // a mark-sweep, after taking over from a possibly on-going
2089 // concurrent mark-sweep collection.
2090 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2091 CollectorState first_state, bool should_start_over) {
2092 if (PrintGC && Verbose) {
2093 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2094 "collector with count %d",
2095 _full_gcs_since_conc_gc);
2096 }
2097 switch (_collectorState) {
2098 case Idling:
2099 if (first_state == Idling || should_start_over) {
2100 // The background GC was not active, or should
2101 // restarted from scratch; start the cycle.
2102 _collectorState = InitialMarking;
2103 }
2104 // If first_state was not Idling, then a background GC
2105 // was in progress and has now finished. No need to do it
2106 // again. Leave the state as Idling.
2107 break;
2108 case Precleaning:
2109 // In the foreground case don't do the precleaning since
2110 // it is not done concurrently and there is extra work
2111 // required.
2112 _collectorState = FinalMarking;
2113 }
2114 if (PrintGCDetails &&
2115 (_collectorState > Idling ||
2116 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2117 gclog_or_tty->print(" (concurrent mode failure)");
2118 }
2119 collect_in_foreground(clear_all_soft_refs);
2120
2121 // For a mark-sweep, compute_new_size() will be called
2122 // in the heap's do_collection() method.
2123 }
2124
2125
2126 void CMSCollector::getFreelistLocks() const {
2127 // Get locks for all free lists in all generations that this
2128 // collector is responsible for
2129 _cmsGen->freelistLock()->lock_without_safepoint_check();
2130 _permGen->freelistLock()->lock_without_safepoint_check();
2131 }
2132
2133 void CMSCollector::releaseFreelistLocks() const {
2134 // Release locks for all free lists in all generations that this
2135 // collector is responsible for
2136 _cmsGen->freelistLock()->unlock();
2137 _permGen->freelistLock()->unlock();
2138 }
2139
2140 bool CMSCollector::haveFreelistLocks() const {
2141 // Check locks for all free lists in all generations that this
2142 // collector is responsible for
2143 assert_lock_strong(_cmsGen->freelistLock());
2144 assert_lock_strong(_permGen->freelistLock());
2145 PRODUCT_ONLY(ShouldNotReachHere());
2146 return true;
2147 }
2148
2149 // A utility class that is used by the CMS collector to
2150 // temporarily "release" the foreground collector from its
2151 // usual obligation to wait for the background collector to
2152 // complete an ongoing phase before proceeding.
2153 class ReleaseForegroundGC: public StackObj {
2154 private:
2155 CMSCollector* _c;
2156 public:
2157 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2158 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2159 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2160 // allow a potentially blocked foreground collector to proceed
2161 _c->_foregroundGCShouldWait = false;
2162 if (_c->_foregroundGCIsActive) {
2163 CGC_lock->notify();
2164 }
2165 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2166 "Possible deadlock");
2167 }
2168
2169 ~ReleaseForegroundGC() {
2170 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2171 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2172 _c->_foregroundGCShouldWait = true;
2173 }
2174 };
2175
2176 // There are separate collect_in_background and collect_in_foreground because of
2177 // the different locking requirements of the background collector and the
2178 // foreground collector. There was originally an attempt to share
2179 // one "collect" method between the background collector and the foreground
2180 // collector but the if-then-else required made it cleaner to have
2181 // separate methods.
2182 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2183 assert(Thread::current()->is_ConcurrentGC_thread(),
2184 "A CMS asynchronous collection is only allowed on a CMS thread.");
2185
2186 GenCollectedHeap* gch = GenCollectedHeap::heap();
2187 {
2188 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2189 MutexLockerEx hl(Heap_lock, safepoint_check);
2190 FreelistLocker fll(this);
2191 MutexLockerEx x(CGC_lock, safepoint_check);
2192 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2193 // The foreground collector is active or we're
2194 // not using asynchronous collections. Skip this
2195 // background collection.
2196 assert(!_foregroundGCShouldWait, "Should be clear");
2197 return;
2198 } else {
2199 assert(_collectorState == Idling, "Should be idling before start.");
2200 _collectorState = InitialMarking;
2201 // Reset the expansion cause, now that we are about to begin
2202 // a new cycle.
2203 clear_expansion_cause();
2204 }
2205 // Decide if we want to enable class unloading as part of the
2206 // ensuing concurrent GC cycle.
2207 update_should_unload_classes();
2208 _full_gc_requested = false; // acks all outstanding full gc requests
2209 // Signal that we are about to start a collection
2210 gch->increment_total_full_collections(); // ... starting a collection cycle
2211 _collection_count_start = gch->total_full_collections();
2212 }
2213
2214 // Used for PrintGC
2215 size_t prev_used;
2216 if (PrintGC && Verbose) {
2217 prev_used = _cmsGen->used(); // XXXPERM
2218 }
2219
2220 // The change of the collection state is normally done at this level;
2221 // the exceptions are phases that are executed while the world is
2222 // stopped. For those phases the change of state is done while the
2223 // world is stopped. For baton passing purposes this allows the
2224 // background collector to finish the phase and change state atomically.
2225 // The foreground collector cannot wait on a phase that is done
2226 // while the world is stopped because the foreground collector already
2227 // has the world stopped and would deadlock.
2228 while (_collectorState != Idling) {
2229 if (TraceCMSState) {
2230 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2231 Thread::current(), _collectorState);
2232 }
2233 // The foreground collector
2234 // holds the Heap_lock throughout its collection.
2235 // holds the CMS token (but not the lock)
2236 // except while it is waiting for the background collector to yield.
2237 //
2238 // The foreground collector should be blocked (not for long)
2239 // if the background collector is about to start a phase
2240 // executed with world stopped. If the background
2241 // collector has already started such a phase, the
2242 // foreground collector is blocked waiting for the
2243 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2244 // are executed in the VM thread.
2245 //
2246 // The locking order is
2247 // PendingListLock (PLL) -- if applicable (FinalMarking)
2248 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2249 // CMS token (claimed in
2250 // stop_world_and_do() -->
2251 // safepoint_synchronize() -->
2252 // CMSThread::synchronize())
2253
2254 {
2255 // Check if the FG collector wants us to yield.
2256 CMSTokenSync x(true); // is cms thread
2257 if (waitForForegroundGC()) {
2258 // We yielded to a foreground GC, nothing more to be
2259 // done this round.
2260 assert(_foregroundGCShouldWait == false, "We set it to false in "
2261 "waitForForegroundGC()");
2262 if (TraceCMSState) {
2263 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2264 " exiting collection CMS state %d",
2265 Thread::current(), _collectorState);
2266 }
2267 return;
2268 } else {
2269 // The background collector can run but check to see if the
2270 // foreground collector has done a collection while the
2271 // background collector was waiting to get the CGC_lock
2272 // above. If yes, break so that _foregroundGCShouldWait
2273 // is cleared before returning.
2274 if (_collectorState == Idling) {
2275 break;
2276 }
2277 }
2278 }
2279
2280 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2281 "should be waiting");
2282
2283 switch (_collectorState) {
2284 case InitialMarking:
2285 {
2286 ReleaseForegroundGC x(this);
2287 stats().record_cms_begin();
2288 register_gc_start(GCCause::_cms_concurrent_mark);
2289
2290 VM_CMS_Initial_Mark initial_mark_op(this);
2291 VMThread::execute(&initial_mark_op);
2292 }
2293 // The collector state may be any legal state at this point
2294 // since the background collector may have yielded to the
2295 // foreground collector.
2296 break;
2297 case Marking:
2298 // initial marking in checkpointRootsInitialWork has been completed
2299 if (markFromRoots(true)) { // we were successful
2300 assert(_collectorState == Precleaning, "Collector state should "
2301 "have changed");
2302 } else {
2303 assert(_foregroundGCIsActive, "Internal state inconsistency");
2304 }
2305 break;
2306 case Precleaning:
2307 if (UseAdaptiveSizePolicy) {
2308 size_policy()->concurrent_precleaning_begin();
2309 }
2310 // marking from roots in markFromRoots has been completed
2311 preclean();
2312 if (UseAdaptiveSizePolicy) {
2313 size_policy()->concurrent_precleaning_end();
2314 }
2315 assert(_collectorState == AbortablePreclean ||
2316 _collectorState == FinalMarking,
2317 "Collector state should have changed");
2318 break;
2319 case AbortablePreclean:
2320 if (UseAdaptiveSizePolicy) {
2321 size_policy()->concurrent_phases_resume();
2322 }
2323 abortable_preclean();
2324 if (UseAdaptiveSizePolicy) {
2325 size_policy()->concurrent_precleaning_end();
2326 }
2327 assert(_collectorState == FinalMarking, "Collector state should "
2328 "have changed");
2329 break;
2330 case FinalMarking:
2331 {
2332 ReleaseForegroundGC x(this);
2333
2334 VM_CMS_Final_Remark final_remark_op(this);
2335 VMThread::execute(&final_remark_op);
2336 }
2337 assert(_foregroundGCShouldWait, "block post-condition");
2338 break;
2339 case Sweeping:
2340 if (UseAdaptiveSizePolicy) {
2341 size_policy()->concurrent_sweeping_begin();
2342 }
2343 // final marking in checkpointRootsFinal has been completed
2344 sweep(true);
2345 assert(_collectorState == Resizing, "Collector state change "
2346 "to Resizing must be done under the free_list_lock");
2347 _full_gcs_since_conc_gc = 0;
2348
2349 // Stop the timers for adaptive size policy for the concurrent phases
2350 if (UseAdaptiveSizePolicy) {
2351 size_policy()->concurrent_sweeping_end();
2352 size_policy()->concurrent_phases_end(gch->gc_cause(),
2353 gch->prev_gen(_cmsGen)->capacity(),
2354 _cmsGen->free());
2355 }
2356
2357 case Resizing: {
2358 // Sweeping has been completed...
2359 // At this point the background collection has completed.
2360 // Don't move the call to compute_new_size() down
2361 // into code that might be executed if the background
2362 // collection was preempted.
2363 {
2364 ReleaseForegroundGC x(this); // unblock FG collection
2365 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2366 CMSTokenSync z(true); // not strictly needed.
2367 if (_collectorState == Resizing) {
2368 compute_new_size();
2369 _collectorState = Resetting;
2370 } else {
2371 assert(_collectorState == Idling, "The state should only change"
2372 " because the foreground collector has finished the collection");
2373 }
2374 }
2375 break;
2376 }
2377 case Resetting:
2378 // CMS heap resizing has been completed
2379 reset(true);
2380 assert(_collectorState == Idling, "Collector state should "
2381 "have changed");
2382 stats().record_cms_end();
2383 // Don't move the concurrent_phases_end() and compute_new_size()
2384 // calls to here because a preempted background collection
2385 // has it's state set to "Resetting".
2386 break;
2387 case Idling:
2388 default:
2389 ShouldNotReachHere();
2390 break;
2391 }
2392 if (TraceCMSState) {
2393 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2394 Thread::current(), _collectorState);
2395 }
2396 assert(_foregroundGCShouldWait, "block post-condition");
2397 }
2398
2399 // Should this be in gc_epilogue?
2400 collector_policy()->counters()->update_counters();
2401
2402 {
2403 // Clear _foregroundGCShouldWait and, in the event that the
2404 // foreground collector is waiting, notify it, before
2405 // returning.
2406 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2407 _foregroundGCShouldWait = false;
2408 if (_foregroundGCIsActive) {
2409 CGC_lock->notify();
2410 }
2411 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2412 "Possible deadlock");
2413 }
2414 if (TraceCMSState) {
2415 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2416 " exiting collection CMS state %d",
2417 Thread::current(), _collectorState);
2418 }
2419 if (PrintGC && Verbose) {
2420 _cmsGen->print_heap_change(prev_used);
2421 }
2422 }
2423
2424 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2425 _cms_start_registered = true;
2426 CollectedHeap* heap = GenCollectedHeap::heap();
2427 _gc_timer_cm->register_gc_start(os::elapsed_counter());
2428 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2429 }
2430
2431 void CMSCollector::register_gc_end() {
2432 if (_cms_start_registered) {
2433 _gc_timer_cm->register_gc_end(os::elapsed_counter());
2434 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2435 _cms_start_registered = false;
2436 }
2437 }
2438
2439 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2440 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2441 "Foreground collector should be waiting, not executing");
2442 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2443 "may only be done by the VM Thread with the world stopped");
2444 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2445 "VM thread should have CMS token");
2446
2447 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2448 true, NULL);)
2449 if (UseAdaptiveSizePolicy) {
2450 size_policy()->ms_collection_begin();
2451 }
2452 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2453
2454 HandleMark hm; // Discard invalid handles created during verification
2455
2456 if (VerifyBeforeGC &&
2457 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2458 Universe::verify();
2459 }
2460
2461 // Snapshot the soft reference policy to be used in this collection cycle.
2462 ref_processor()->setup_policy(clear_all_soft_refs);
2463
2464 bool init_mark_was_synchronous = false; // until proven otherwise
2465 while (_collectorState != Idling) {
2466 if (TraceCMSState) {
2467 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2468 Thread::current(), _collectorState);
2469 }
2470 switch (_collectorState) {
2471 case InitialMarking:
2472 register_gc_start(GenCollectedHeap::heap()->gc_cause());
2473 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2474 checkpointRootsInitial(false);
2475 assert(_collectorState == Marking, "Collector state should have changed"
2476 " within checkpointRootsInitial()");
2477 break;
2478 case Marking:
2479 // initial marking in checkpointRootsInitialWork has been completed
2480 if (VerifyDuringGC &&
2481 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2482 gclog_or_tty->print("Verify before initial mark: ");
2483 Universe::verify();
2484 }
2485 {
2486 bool res = markFromRoots(false);
2487 assert(res && _collectorState == FinalMarking, "Collector state should "
2488 "have changed");
2489 break;
2490 }
2491 case FinalMarking:
2492 if (VerifyDuringGC &&
2493 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2494 gclog_or_tty->print("Verify before re-mark: ");
2495 Universe::verify();
2496 }
2497 checkpointRootsFinal(false, clear_all_soft_refs,
2498 init_mark_was_synchronous);
2499 assert(_collectorState == Sweeping, "Collector state should not "
2500 "have changed within checkpointRootsFinal()");
2501 break;
2502 case Sweeping:
2503 // final marking in checkpointRootsFinal has been completed
2504 if (VerifyDuringGC &&
2505 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2506 gclog_or_tty->print("Verify before sweep: ");
2507 Universe::verify();
2508 }
2509 sweep(false);
2510 assert(_collectorState == Resizing, "Incorrect state");
2511 break;
2512 case Resizing: {
2513 // Sweeping has been completed; the actual resize in this case
2514 // is done separately; nothing to be done in this state.
2515 _collectorState = Resetting;
2516 break;
2517 }
2518 case Resetting:
2519 // The heap has been resized.
2520 if (VerifyDuringGC &&
2521 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2522 gclog_or_tty->print("Verify before reset: ");
2523 Universe::verify();
2524 }
2525 reset(false);
2526 assert(_collectorState == Idling, "Collector state should "
2527 "have changed");
2528 break;
2529 case Precleaning:
2530 case AbortablePreclean:
2531 // Elide the preclean phase
2532 _collectorState = FinalMarking;
2533 break;
2534 default:
2535 ShouldNotReachHere();
2536 }
2537 if (TraceCMSState) {
2538 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2539 Thread::current(), _collectorState);
2540 }
2541 }
2542
2543 if (UseAdaptiveSizePolicy) {
2544 GenCollectedHeap* gch = GenCollectedHeap::heap();
2545 size_policy()->ms_collection_end(gch->gc_cause());
2546 }
2547
2548 if (VerifyAfterGC &&
2549 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2550 Universe::verify();
2551 }
2552 if (TraceCMSState) {
2553 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2554 " exiting collection CMS state %d",
2555 Thread::current(), _collectorState);
2556 }
2557 }
2558
2559 bool CMSCollector::waitForForegroundGC() {
2560 bool res = false;
2561 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2562 "CMS thread should have CMS token");
2563 // Block the foreground collector until the
2564 // background collectors decides whether to
2565 // yield.
2566 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2567 _foregroundGCShouldWait = true;
2568 if (_foregroundGCIsActive) {
2569 // The background collector yields to the
2570 // foreground collector and returns a value
2571 // indicating that it has yielded. The foreground
2572 // collector can proceed.
2573 res = true;
2574 _foregroundGCShouldWait = false;
2575 ConcurrentMarkSweepThread::clear_CMS_flag(
2576 ConcurrentMarkSweepThread::CMS_cms_has_token);
2577 ConcurrentMarkSweepThread::set_CMS_flag(
2578 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2579 // Get a possibly blocked foreground thread going
2580 CGC_lock->notify();
2581 if (TraceCMSState) {
2582 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2583 Thread::current(), _collectorState);
2584 }
2585 while (_foregroundGCIsActive) {
2586 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2587 }
2588 ConcurrentMarkSweepThread::set_CMS_flag(
2589 ConcurrentMarkSweepThread::CMS_cms_has_token);
2590 ConcurrentMarkSweepThread::clear_CMS_flag(
2591 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2592 }
2593 if (TraceCMSState) {
2594 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2595 Thread::current(), _collectorState);
2596 }
2597 return res;
2598 }
2599
2600 // Because of the need to lock the free lists and other structures in
2601 // the collector, common to all the generations that the collector is
2602 // collecting, we need the gc_prologues of individual CMS generations
2603 // delegate to their collector. It may have been simpler had the
2604 // current infrastructure allowed one to call a prologue on a
2605 // collector. In the absence of that we have the generation's
2606 // prologue delegate to the collector, which delegates back
2607 // some "local" work to a worker method in the individual generations
2608 // that it's responsible for collecting, while itself doing any
2609 // work common to all generations it's responsible for. A similar
2610 // comment applies to the gc_epilogue()'s.
2611 // The role of the varaible _between_prologue_and_epilogue is to
2612 // enforce the invocation protocol.
2613 void CMSCollector::gc_prologue(bool full) {
2614 // Call gc_prologue_work() for each CMSGen and PermGen that
2615 // we are responsible for.
2616
2617 // The following locking discipline assumes that we are only called
2618 // when the world is stopped.
2619 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2620
2621 // The CMSCollector prologue must call the gc_prologues for the
2622 // "generations" (including PermGen if any) that it's responsible
2623 // for.
2624
2625 assert( Thread::current()->is_VM_thread()
2626 || ( CMSScavengeBeforeRemark
2627 && Thread::current()->is_ConcurrentGC_thread()),
2628 "Incorrect thread type for prologue execution");
2629
2630 if (_between_prologue_and_epilogue) {
2631 // We have already been invoked; this is a gc_prologue delegation
2632 // from yet another CMS generation that we are responsible for, just
2633 // ignore it since all relevant work has already been done.
2634 return;
2635 }
2636
2637 // set a bit saying prologue has been called; cleared in epilogue
2638 _between_prologue_and_epilogue = true;
2639 // Claim locks for common data structures, then call gc_prologue_work()
2640 // for each CMSGen and PermGen that we are responsible for.
2641
2642 getFreelistLocks(); // gets free list locks on constituent spaces
2643 bitMapLock()->lock_without_safepoint_check();
2644
2645 // Should call gc_prologue_work() for all cms gens we are responsible for
2646 bool registerClosure = _collectorState >= Marking
2647 && _collectorState < Sweeping;
2648 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2649 &_modUnionClosurePar
2650 : &_modUnionClosure;
2651 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2652 _permGen->gc_prologue_work(full, registerClosure, muc);
2653
2654 if (!full) {
2655 stats().record_gc0_begin();
2656 }
2657 }
2658
2659 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2660 // Delegate to CMScollector which knows how to coordinate between
2661 // this and any other CMS generations that it is responsible for
2662 // collecting.
2663 collector()->gc_prologue(full);
2664 }
2665
2666 // This is a "private" interface for use by this generation's CMSCollector.
2667 // Not to be called directly by any other entity (for instance,
2668 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2669 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2670 bool registerClosure, ModUnionClosure* modUnionClosure) {
2671 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2672 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2673 "Should be NULL");
2674 if (registerClosure) {
2675 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2676 }
2677 cmsSpace()->gc_prologue();
2678 // Clear stat counters
2679 NOT_PRODUCT(
2680 assert(_numObjectsPromoted == 0, "check");
2681 assert(_numWordsPromoted == 0, "check");
2682 if (Verbose && PrintGC) {
2683 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2684 SIZE_FORMAT" bytes concurrently",
2685 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2686 }
2687 _numObjectsAllocated = 0;
2688 _numWordsAllocated = 0;
2689 )
2690 }
2691
2692 void CMSCollector::gc_epilogue(bool full) {
2693 // The following locking discipline assumes that we are only called
2694 // when the world is stopped.
2695 assert(SafepointSynchronize::is_at_safepoint(),
2696 "world is stopped assumption");
2697
2698 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2699 // if linear allocation blocks need to be appropriately marked to allow the
2700 // the blocks to be parsable. We also check here whether we need to nudge the
2701 // CMS collector thread to start a new cycle (if it's not already active).
2702 assert( Thread::current()->is_VM_thread()
2703 || ( CMSScavengeBeforeRemark
2704 && Thread::current()->is_ConcurrentGC_thread()),
2705 "Incorrect thread type for epilogue execution");
2706
2707 if (!_between_prologue_and_epilogue) {
2708 // We have already been invoked; this is a gc_epilogue delegation
2709 // from yet another CMS generation that we are responsible for, just
2710 // ignore it since all relevant work has already been done.
2711 return;
2712 }
2713 assert(haveFreelistLocks(), "must have freelist locks");
2714 assert_lock_strong(bitMapLock());
2715
2716 _cmsGen->gc_epilogue_work(full);
2717 _permGen->gc_epilogue_work(full);
2718
2719 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2720 // in case sampling was not already enabled, enable it
2721 _start_sampling = true;
2722 }
2723 // reset _eden_chunk_array so sampling starts afresh
2724 _eden_chunk_index = 0;
2725
2726 size_t cms_used = _cmsGen->cmsSpace()->used();
2727 size_t perm_used = _permGen->cmsSpace()->used();
2728
2729 // update performance counters - this uses a special version of
2730 // update_counters() that allows the utilization to be passed as a
2731 // parameter, avoiding multiple calls to used().
2732 //
2733 _cmsGen->update_counters(cms_used);
2734 _permGen->update_counters(perm_used);
2735
2736 if (CMSIncrementalMode) {
2737 icms_update_allocation_limits();
2738 }
2739
2740 bitMapLock()->unlock();
2741 releaseFreelistLocks();
2742
2743 if (!CleanChunkPoolAsync) {
2744 Chunk::clean_chunk_pool();
2745 }
2746
2747 _between_prologue_and_epilogue = false; // ready for next cycle
2748 }
2749
2750 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2751 collector()->gc_epilogue(full);
2752
2753 // Also reset promotion tracking in par gc thread states.
2754 if (CollectedHeap::use_parallel_gc_threads()) {
2755 for (uint i = 0; i < ParallelGCThreads; i++) {
2756 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2757 }
2758 }
2759 }
2760
2761 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2762 assert(!incremental_collection_failed(), "Should have been cleared");
2763 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2764 cmsSpace()->gc_epilogue();
2765 // Print stat counters
2766 NOT_PRODUCT(
2767 assert(_numObjectsAllocated == 0, "check");
2768 assert(_numWordsAllocated == 0, "check");
2769 if (Verbose && PrintGC) {
2770 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2771 SIZE_FORMAT" bytes",
2772 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2773 }
2774 _numObjectsPromoted = 0;
2775 _numWordsPromoted = 0;
2776 )
2777
2778 if (PrintGC && Verbose) {
2779 // Call down the chain in contiguous_available needs the freelistLock
2780 // so print this out before releasing the freeListLock.
2781 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2782 contiguous_available());
2783 }
2784 }
2785
2786 #ifndef PRODUCT
2787 bool CMSCollector::have_cms_token() {
2788 Thread* thr = Thread::current();
2789 if (thr->is_VM_thread()) {
2790 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2791 } else if (thr->is_ConcurrentGC_thread()) {
2792 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2793 } else if (thr->is_GC_task_thread()) {
2794 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2795 ParGCRareEvent_lock->owned_by_self();
2796 }
2797 return false;
2798 }
2799 #endif
2800
2801 // Check reachability of the given heap address in CMS generation,
2802 // treating all other generations as roots.
2803 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2804 // We could "guarantee" below, rather than assert, but i'll
2805 // leave these as "asserts" so that an adventurous debugger
2806 // could try this in the product build provided some subset of
2807 // the conditions were met, provided they were intersted in the
2808 // results and knew that the computation below wouldn't interfere
2809 // with other concurrent computations mutating the structures
2810 // being read or written.
2811 assert(SafepointSynchronize::is_at_safepoint(),
2812 "Else mutations in object graph will make answer suspect");
2813 assert(have_cms_token(), "Should hold cms token");
2814 assert(haveFreelistLocks(), "must hold free list locks");
2815 assert_lock_strong(bitMapLock());
2816
2817 // Clear the marking bit map array before starting, but, just
2818 // for kicks, first report if the given address is already marked
2819 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2820 _markBitMap.isMarked(addr) ? "" : " not");
2821
2822 if (verify_after_remark()) {
2823 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2824 bool result = verification_mark_bm()->isMarked(addr);
2825 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2826 result ? "IS" : "is NOT");
2827 return result;
2828 } else {
2829 gclog_or_tty->print_cr("Could not compute result");
2830 return false;
2831 }
2832 }
2833
2834 ////////////////////////////////////////////////////////
2835 // CMS Verification Support
2836 ////////////////////////////////////////////////////////
2837 // Following the remark phase, the following invariant
2838 // should hold -- each object in the CMS heap which is
2839 // marked in markBitMap() should be marked in the verification_mark_bm().
2840
2841 class VerifyMarkedClosure: public BitMapClosure {
2842 CMSBitMap* _marks;
2843 bool _failed;
2844
2845 public:
2846 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2847
2848 bool do_bit(size_t offset) {
2849 HeapWord* addr = _marks->offsetToHeapWord(offset);
2850 if (!_marks->isMarked(addr)) {
2851 oop(addr)->print_on(gclog_or_tty);
2852 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2853 _failed = true;
2854 }
2855 return true;
2856 }
2857
2858 bool failed() { return _failed; }
2859 };
2860
2861 bool CMSCollector::verify_after_remark() {
2862 gclog_or_tty->print(" [Verifying CMS Marking... ");
2863 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2864 static bool init = false;
2865
2866 assert(SafepointSynchronize::is_at_safepoint(),
2867 "Else mutations in object graph will make answer suspect");
2868 assert(have_cms_token(),
2869 "Else there may be mutual interference in use of "
2870 " verification data structures");
2871 assert(_collectorState > Marking && _collectorState <= Sweeping,
2872 "Else marking info checked here may be obsolete");
2873 assert(haveFreelistLocks(), "must hold free list locks");
2874 assert_lock_strong(bitMapLock());
2875
2876
2877 // Allocate marking bit map if not already allocated
2878 if (!init) { // first time
2879 if (!verification_mark_bm()->allocate(_span)) {
2880 return false;
2881 }
2882 init = true;
2883 }
2884
2885 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2886
2887 // Turn off refs discovery -- so we will be tracing through refs.
2888 // This is as intended, because by this time
2889 // GC must already have cleared any refs that need to be cleared,
2890 // and traced those that need to be marked; moreover,
2891 // the marking done here is not going to intefere in any
2892 // way with the marking information used by GC.
2893 NoRefDiscovery no_discovery(ref_processor());
2894
2895 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2896
2897 // Clear any marks from a previous round
2898 verification_mark_bm()->clear_all();
2899 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2900 verify_work_stacks_empty();
2901
2902 GenCollectedHeap* gch = GenCollectedHeap::heap();
2903 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2904 // Update the saved marks which may affect the root scans.
2905 gch->save_marks();
2906
2907 if (CMSRemarkVerifyVariant == 1) {
2908 // In this first variant of verification, we complete
2909 // all marking, then check if the new marks-verctor is
2910 // a subset of the CMS marks-vector.
2911 verify_after_remark_work_1();
2912 } else if (CMSRemarkVerifyVariant == 2) {
2913 // In this second variant of verification, we flag an error
2914 // (i.e. an object reachable in the new marks-vector not reachable
2915 // in the CMS marks-vector) immediately, also indicating the
2916 // identify of an object (A) that references the unmarked object (B) --
2917 // presumably, a mutation to A failed to be picked up by preclean/remark?
2918 verify_after_remark_work_2();
2919 } else {
2920 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2921 CMSRemarkVerifyVariant);
2922 }
2923 gclog_or_tty->print(" done] ");
2924 return true;
2925 }
2926
2927 void CMSCollector::verify_after_remark_work_1() {
2928 ResourceMark rm;
2929 HandleMark hm;
2930 GenCollectedHeap* gch = GenCollectedHeap::heap();
2931
2932 // Mark from roots one level into CMS
2933 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2934 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2935
2936 gch->gen_process_strong_roots(_cmsGen->level(),
2937 true, // younger gens are roots
2938 true, // activate StrongRootsScope
2939 true, // collecting perm gen
2940 SharedHeap::ScanningOption(roots_scanning_options()),
2941 ¬Older,
2942 true, // walk code active on stacks
2943 NULL);
2944
2945 // Now mark from the roots
2946 assert(_revisitStack.isEmpty(), "Should be empty");
2947 MarkFromRootsClosure markFromRootsClosure(this, _span,
2948 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2949 false /* don't yield */, true /* verifying */);
2950 assert(_restart_addr == NULL, "Expected pre-condition");
2951 verification_mark_bm()->iterate(&markFromRootsClosure);
2952 while (_restart_addr != NULL) {
2953 // Deal with stack overflow: by restarting at the indicated
2954 // address.
2955 HeapWord* ra = _restart_addr;
2956 markFromRootsClosure.reset(ra);
2957 _restart_addr = NULL;
2958 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2959 }
2960 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2961 verify_work_stacks_empty();
2962 // Should reset the revisit stack above, since no class tree
2963 // surgery is forthcoming.
2964 _revisitStack.reset(); // throwing away all contents
2965
2966 // Marking completed -- now verify that each bit marked in
2967 // verification_mark_bm() is also marked in markBitMap(); flag all
2968 // errors by printing corresponding objects.
2969 VerifyMarkedClosure vcl(markBitMap());
2970 verification_mark_bm()->iterate(&vcl);
2971 if (vcl.failed()) {
2972 gclog_or_tty->print("Verification failed");
2973 Universe::heap()->print_on(gclog_or_tty);
2974 fatal("CMS: failed marking verification after remark");
2975 }
2976 }
2977
2978 void CMSCollector::verify_after_remark_work_2() {
2979 ResourceMark rm;
2980 HandleMark hm;
2981 GenCollectedHeap* gch = GenCollectedHeap::heap();
2982
2983 // Mark from roots one level into CMS
2984 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2985 markBitMap());
2986 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2987 gch->gen_process_strong_roots(_cmsGen->level(),
2988 true, // younger gens are roots
2989 true, // activate StrongRootsScope
2990 true, // collecting perm gen
2991 SharedHeap::ScanningOption(roots_scanning_options()),
2992 ¬Older,
2993 true, // walk code active on stacks
2994 NULL);
2995
2996 // Now mark from the roots
2997 assert(_revisitStack.isEmpty(), "Should be empty");
2998 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2999 verification_mark_bm(), markBitMap(), verification_mark_stack());
3000 assert(_restart_addr == NULL, "Expected pre-condition");
3001 verification_mark_bm()->iterate(&markFromRootsClosure);
3002 while (_restart_addr != NULL) {
3003 // Deal with stack overflow: by restarting at the indicated
3004 // address.
3005 HeapWord* ra = _restart_addr;
3006 markFromRootsClosure.reset(ra);
3007 _restart_addr = NULL;
3008 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3009 }
3010 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3011 verify_work_stacks_empty();
3012 // Should reset the revisit stack above, since no class tree
3013 // surgery is forthcoming.
3014 _revisitStack.reset(); // throwing away all contents
3015
3016 // Marking completed -- now verify that each bit marked in
3017 // verification_mark_bm() is also marked in markBitMap(); flag all
3018 // errors by printing corresponding objects.
3019 VerifyMarkedClosure vcl(markBitMap());
3020 verification_mark_bm()->iterate(&vcl);
3021 assert(!vcl.failed(), "Else verification above should not have succeeded");
3022 }
3023
3024 void ConcurrentMarkSweepGeneration::save_marks() {
3025 // delegate to CMS space
3026 cmsSpace()->save_marks();
3027 for (uint i = 0; i < ParallelGCThreads; i++) {
3028 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3029 }
3030 }
3031
3032 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3033 return cmsSpace()->no_allocs_since_save_marks();
3034 }
3035
3036 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3037 \
3038 void ConcurrentMarkSweepGeneration:: \
3039 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3040 cl->set_generation(this); \
3041 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3042 cl->reset_generation(); \
3043 save_marks(); \
3044 }
3045
3046 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3047
3048 void
3049 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3050 {
3051 // Not currently implemented; need to do the following. -- ysr.
3052 // dld -- I think that is used for some sort of allocation profiler. So it
3053 // really means the objects allocated by the mutator since the last
3054 // GC. We could potentially implement this cheaply by recording only
3055 // the direct allocations in a side data structure.
3056 //
3057 // I think we probably ought not to be required to support these
3058 // iterations at any arbitrary point; I think there ought to be some
3059 // call to enable/disable allocation profiling in a generation/space,
3060 // and the iterator ought to return the objects allocated in the
3061 // gen/space since the enable call, or the last iterator call (which
3062 // will probably be at a GC.) That way, for gens like CM&S that would
3063 // require some extra data structure to support this, we only pay the
3064 // cost when it's in use...
3065 cmsSpace()->object_iterate_since_last_GC(blk);
3066 }
3067
3068 void
3069 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3070 cl->set_generation(this);
3071 younger_refs_in_space_iterate(_cmsSpace, cl);
3072 cl->reset_generation();
3073 }
3074
3075 void
3076 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3077 if (freelistLock()->owned_by_self()) {
3078 Generation::oop_iterate(mr, cl);
3079 } else {
3080 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3081 Generation::oop_iterate(mr, cl);
3082 }
3083 }
3084
3085 void
3086 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3087 if (freelistLock()->owned_by_self()) {
3088 Generation::oop_iterate(cl);
3089 } else {
3090 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3091 Generation::oop_iterate(cl);
3092 }
3093 }
3094
3095 void
3096 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3097 if (freelistLock()->owned_by_self()) {
3098 Generation::object_iterate(cl);
3099 } else {
3100 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3101 Generation::object_iterate(cl);
3102 }
3103 }
3104
3105 void
3106 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3107 if (freelistLock()->owned_by_self()) {
3108 Generation::safe_object_iterate(cl);
3109 } else {
3110 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3111 Generation::safe_object_iterate(cl);
3112 }
3113 }
3114
3115 void
3116 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3117 }
3118
3119 void
3120 ConcurrentMarkSweepGeneration::post_compact() {
3121 }
3122
3123 void
3124 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3125 // Fix the linear allocation blocks to look like free blocks.
3126
3127 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3128 // are not called when the heap is verified during universe initialization and
3129 // at vm shutdown.
3130 if (freelistLock()->owned_by_self()) {
3131 cmsSpace()->prepare_for_verify();
3132 } else {
3133 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3134 cmsSpace()->prepare_for_verify();
3135 }
3136 }
3137
3138 void
3139 ConcurrentMarkSweepGeneration::verify() {
3140 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3141 // are not called when the heap is verified during universe initialization and
3142 // at vm shutdown.
3143 if (freelistLock()->owned_by_self()) {
3144 cmsSpace()->verify();
3145 } else {
3146 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3147 cmsSpace()->verify();
3148 }
3149 }
3150
3151 void CMSCollector::verify() {
3152 _cmsGen->verify();
3153 _permGen->verify();
3154 }
3155
3156 #ifndef PRODUCT
3157 bool CMSCollector::overflow_list_is_empty() const {
3158 assert(_num_par_pushes >= 0, "Inconsistency");
3159 if (_overflow_list == NULL) {
3160 assert(_num_par_pushes == 0, "Inconsistency");
3161 }
3162 return _overflow_list == NULL;
3163 }
3164
3165 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3166 // merely consolidate assertion checks that appear to occur together frequently.
3167 void CMSCollector::verify_work_stacks_empty() const {
3168 assert(_markStack.isEmpty(), "Marking stack should be empty");
3169 assert(overflow_list_is_empty(), "Overflow list should be empty");
3170 }
3171
3172 void CMSCollector::verify_overflow_empty() const {
3173 assert(overflow_list_is_empty(), "Overflow list should be empty");
3174 assert(no_preserved_marks(), "No preserved marks");
3175 }
3176 #endif // PRODUCT
3177
3178 // Decide if we want to enable class unloading as part of the
3179 // ensuing concurrent GC cycle. We will collect the perm gen and
3180 // unload classes if it's the case that:
3181 // (1) an explicit gc request has been made and the flag
3182 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3183 // (2) (a) class unloading is enabled at the command line, and
3184 // (b) (i) perm gen threshold has been crossed, or
3185 // (ii) old gen is getting really full, or
3186 // (iii) the previous N CMS collections did not collect the
3187 // perm gen
3188 // NOTE: Provided there is no change in the state of the heap between
3189 // calls to this method, it should have idempotent results. Moreover,
3190 // its results should be monotonically increasing (i.e. going from 0 to 1,
3191 // but not 1 to 0) between successive calls between which the heap was
3192 // not collected. For the implementation below, it must thus rely on
3193 // the property that concurrent_cycles_since_last_unload()
3194 // will not decrease unless a collection cycle happened and that
3195 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3196 // themselves also monotonic in that sense. See check_monotonicity()
3197 // below.
3198 bool CMSCollector::update_should_unload_classes() {
3199 _should_unload_classes = false;
3200 // Condition 1 above
3201 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3202 _should_unload_classes = true;
3203 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3204 // Disjuncts 2.b.(i,ii,iii) above
3205 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3206 CMSClassUnloadingMaxInterval)
3207 || _permGen->should_concurrent_collect()
3208 || _cmsGen->is_too_full();
3209 }
3210 return _should_unload_classes;
3211 }
3212
3213 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3214 bool res = should_concurrent_collect();
3215 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3216 return res;
3217 }
3218
3219 void CMSCollector::setup_cms_unloading_and_verification_state() {
3220 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3221 || VerifyBeforeExit;
3222 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3223
3224 if (should_unload_classes()) { // Should unload classes this cycle
3225 remove_root_scanning_option(rso); // Shrink the root set appropriately
3226 set_verifying(should_verify); // Set verification state for this cycle
3227 return; // Nothing else needs to be done at this time
3228 }
3229
3230 // Not unloading classes this cycle
3231 assert(!should_unload_classes(), "Inconsitency!");
3232 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3233 // We were not verifying, or we _were_ unloading classes in the last cycle,
3234 // AND some verification options are enabled this cycle; in this case,
3235 // we must make sure that the deadness map is allocated if not already so,
3236 // and cleared (if already allocated previously --
3237 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3238 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3239 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3240 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3241 "permanent generation verification disabled");
3242 return; // Note that we leave verification disabled, so we'll retry this
3243 // allocation next cycle. We _could_ remember this failure
3244 // and skip further attempts and permanently disable verification
3245 // attempts if that is considered more desirable.
3246 }
3247 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3248 "_perm_gen_ver_bit_map inconsistency?");
3249 } else {
3250 perm_gen_verify_bit_map()->clear_all();
3251 }
3252 // Include symbols, strings and code cache elements to prevent their resurrection.
3253 add_root_scanning_option(rso);
3254 set_verifying(true);
3255 } else if (verifying() && !should_verify) {
3256 // We were verifying, but some verification flags got disabled.
3257 set_verifying(false);
3258 // Exclude symbols, strings and code cache elements from root scanning to
3259 // reduce IM and RM pauses.
3260 remove_root_scanning_option(rso);
3261 }
3262 }
3263
3264
3265 #ifndef PRODUCT
3266 HeapWord* CMSCollector::block_start(const void* p) const {
3267 const HeapWord* addr = (HeapWord*)p;
3268 if (_span.contains(p)) {
3269 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3270 return _cmsGen->cmsSpace()->block_start(p);
3271 } else {
3272 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3273 "Inconsistent _span?");
3274 return _permGen->cmsSpace()->block_start(p);
3275 }
3276 }
3277 return NULL;
3278 }
3279 #endif
3280
3281 HeapWord*
3282 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3283 bool tlab,
3284 bool parallel) {
3285 CMSSynchronousYieldRequest yr;
3286 assert(!tlab, "Can't deal with TLAB allocation");
3287 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3288 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3289 CMSExpansionCause::_satisfy_allocation);
3290 if (GCExpandToAllocateDelayMillis > 0) {
3291 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3292 }
3293 return have_lock_and_allocate(word_size, tlab);
3294 }
3295
3296 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3297 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3298 // to CardGeneration and share it...
3299 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3300 return CardGeneration::expand(bytes, expand_bytes);
3301 }
3302
3303 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3304 CMSExpansionCause::Cause cause)
3305 {
3306
3307 bool success = expand(bytes, expand_bytes);
3308
3309 // remember why we expanded; this information is used
3310 // by shouldConcurrentCollect() when making decisions on whether to start
3311 // a new CMS cycle.
3312 if (success) {
3313 set_expansion_cause(cause);
3314 if (PrintGCDetails && Verbose) {
3315 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3316 CMSExpansionCause::to_string(cause));
3317 }
3318 }
3319 }
3320
3321 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3322 HeapWord* res = NULL;
3323 MutexLocker x(ParGCRareEvent_lock);
3324 while (true) {
3325 // Expansion by some other thread might make alloc OK now:
3326 res = ps->lab.alloc(word_sz);
3327 if (res != NULL) return res;
3328 // If there's not enough expansion space available, give up.
3329 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3330 return NULL;
3331 }
3332 // Otherwise, we try expansion.
3333 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3334 CMSExpansionCause::_allocate_par_lab);
3335 // Now go around the loop and try alloc again;
3336 // A competing par_promote might beat us to the expansion space,
3337 // so we may go around the loop again if promotion fails agaion.
3338 if (GCExpandToAllocateDelayMillis > 0) {
3339 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3340 }
3341 }
3342 }
3343
3344
3345 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3346 PromotionInfo* promo) {
3347 MutexLocker x(ParGCRareEvent_lock);
3348 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3349 while (true) {
3350 // Expansion by some other thread might make alloc OK now:
3351 if (promo->ensure_spooling_space()) {
3352 assert(promo->has_spooling_space(),
3353 "Post-condition of successful ensure_spooling_space()");
3354 return true;
3355 }
3356 // If there's not enough expansion space available, give up.
3357 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3358 return false;
3359 }
3360 // Otherwise, we try expansion.
3361 expand(refill_size_bytes, MinHeapDeltaBytes,
3362 CMSExpansionCause::_allocate_par_spooling_space);
3363 // Now go around the loop and try alloc again;
3364 // A competing allocation might beat us to the expansion space,
3365 // so we may go around the loop again if allocation fails again.
3366 if (GCExpandToAllocateDelayMillis > 0) {
3367 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3368 }
3369 }
3370 }
3371
3372
3373
3374 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3375 assert_locked_or_safepoint(Heap_lock);
3376 size_t size = ReservedSpace::page_align_size_down(bytes);
3377 if (size > 0) {
3378 shrink_by(size);
3379 }
3380 }
3381
3382 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3383 assert_locked_or_safepoint(Heap_lock);
3384 bool result = _virtual_space.expand_by(bytes);
3385 if (result) {
3386 HeapWord* old_end = _cmsSpace->end();
3387 size_t new_word_size =
3388 heap_word_size(_virtual_space.committed_size());
3389 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3390 _bts->resize(new_word_size); // resize the block offset shared array
3391 Universe::heap()->barrier_set()->resize_covered_region(mr);
3392 // Hmmmm... why doesn't CFLS::set_end verify locking?
3393 // This is quite ugly; FIX ME XXX
3394 _cmsSpace->assert_locked(freelistLock());
3395 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3396
3397 // update the space and generation capacity counters
3398 if (UsePerfData) {
3399 _space_counters->update_capacity();
3400 _gen_counters->update_all();
3401 }
3402
3403 if (Verbose && PrintGC) {
3404 size_t new_mem_size = _virtual_space.committed_size();
3405 size_t old_mem_size = new_mem_size - bytes;
3406 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3407 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3408 }
3409 }
3410 return result;
3411 }
3412
3413 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3414 assert_locked_or_safepoint(Heap_lock);
3415 bool success = true;
3416 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3417 if (remaining_bytes > 0) {
3418 success = grow_by(remaining_bytes);
3419 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3420 }
3421 return success;
3422 }
3423
3424 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3425 assert_locked_or_safepoint(Heap_lock);
3426 assert_lock_strong(freelistLock());
3427 // XXX Fix when compaction is implemented.
3428 warning("Shrinking of CMS not yet implemented");
3429 return;
3430 }
3431
3432
3433 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3434 // phases.
3435 class CMSPhaseAccounting: public StackObj {
3436 public:
3437 CMSPhaseAccounting(CMSCollector *collector,
3438 const char *phase,
3439 bool print_cr = true);
3440 ~CMSPhaseAccounting();
3441
3442 private:
3443 CMSCollector *_collector;
3444 const char *_phase;
3445 elapsedTimer _wallclock;
3446 bool _print_cr;
3447
3448 public:
3449 // Not MT-safe; so do not pass around these StackObj's
3450 // where they may be accessed by other threads.
3451 jlong wallclock_millis() {
3452 assert(_wallclock.is_active(), "Wall clock should not stop");
3453 _wallclock.stop(); // to record time
3454 jlong ret = _wallclock.milliseconds();
3455 _wallclock.start(); // restart
3456 return ret;
3457 }
3458 };
3459
3460 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3461 const char *phase,
3462 bool print_cr) :
3463 _collector(collector), _phase(phase), _print_cr(print_cr) {
3464
3465 if (PrintCMSStatistics != 0) {
3466 _collector->resetYields();
3467 }
3468 if (PrintGCDetails && PrintGCTimeStamps) {
3469 gclog_or_tty->date_stamp(PrintGCDateStamps);
3470 gclog_or_tty->stamp();
3471 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3472 _collector->cmsGen()->short_name(), _phase);
3473 }
3474 _collector->resetTimer();
3475 _wallclock.start();
3476 _collector->startTimer();
3477 }
3478
3479 CMSPhaseAccounting::~CMSPhaseAccounting() {
3480 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3481 _collector->stopTimer();
3482 _wallclock.stop();
3483 if (PrintGCDetails) {
3484 gclog_or_tty->date_stamp(PrintGCDateStamps);
3485 gclog_or_tty->stamp(PrintGCTimeStamps);
3486 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3487 _collector->cmsGen()->short_name(),
3488 _phase, _collector->timerValue(), _wallclock.seconds());
3489 if (_print_cr) {
3490 gclog_or_tty->print_cr("");
3491 }
3492 if (PrintCMSStatistics != 0) {
3493 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3494 _collector->yields());
3495 }
3496 }
3497 }
3498
3499 // CMS work
3500
3501 // Checkpoint the roots into this generation from outside
3502 // this generation. [Note this initial checkpoint need only
3503 // be approximate -- we'll do a catch up phase subsequently.]
3504 void CMSCollector::checkpointRootsInitial(bool asynch) {
3505 assert(_collectorState == InitialMarking, "Wrong collector state");
3506 check_correct_thread_executing();
3507 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3508
3509 ReferenceProcessor* rp = ref_processor();
3510 SpecializationStats::clear();
3511 assert(_restart_addr == NULL, "Control point invariant");
3512 if (asynch) {
3513 // acquire locks for subsequent manipulations
3514 MutexLockerEx x(bitMapLock(),
3515 Mutex::_no_safepoint_check_flag);
3516 checkpointRootsInitialWork(asynch);
3517 // enable ("weak") refs discovery
3518 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3519 _collectorState = Marking;
3520 } else {
3521 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3522 // which recognizes if we are a CMS generation, and doesn't try to turn on
3523 // discovery; verify that they aren't meddling.
3524 assert(!rp->discovery_is_atomic(),
3525 "incorrect setting of discovery predicate");
3526 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3527 "ref discovery for this generation kind");
3528 // already have locks
3529 checkpointRootsInitialWork(asynch);
3530 // now enable ("weak") refs discovery
3531 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3532 _collectorState = Marking;
3533 }
3534 SpecializationStats::print();
3535 }
3536
3537 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3538 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3539 assert(_collectorState == InitialMarking, "just checking");
3540
3541 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3542 // precede our marking with a collection of all
3543 // younger generations to keep floating garbage to a minimum.
3544 // XXX: we won't do this for now -- it's an optimization to be done later.
3545
3546 // already have locks
3547 assert_lock_strong(bitMapLock());
3548 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3549
3550 // Setup the verification and class unloading state for this
3551 // CMS collection cycle.
3552 setup_cms_unloading_and_verification_state();
3553
3554 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3555 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3556 if (UseAdaptiveSizePolicy) {
3557 size_policy()->checkpoint_roots_initial_begin();
3558 }
3559
3560 // Reset all the PLAB chunk arrays if necessary.
3561 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3562 reset_survivor_plab_arrays();
3563 }
3564
3565 ResourceMark rm;
3566 HandleMark hm;
3567
3568 FalseClosure falseClosure;
3569 // In the case of a synchronous collection, we will elide the
3570 // remark step, so it's important to catch all the nmethod oops
3571 // in this step.
3572 // The final 'true' flag to gen_process_strong_roots will ensure this.
3573 // If 'async' is true, we can relax the nmethod tracing.
3574 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3575 GenCollectedHeap* gch = GenCollectedHeap::heap();
3576
3577 verify_work_stacks_empty();
3578 verify_overflow_empty();
3579
3580 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3581 // Update the saved marks which may affect the root scans.
3582 gch->save_marks();
3583
3584 // weak reference processing has not started yet.
3585 ref_processor()->set_enqueuing_is_done(false);
3586
3587 {
3588 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3589 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3590 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3591 gch->gen_process_strong_roots(_cmsGen->level(),
3592 true, // younger gens are roots
3593 true, // activate StrongRootsScope
3594 true, // collecting perm gen
3595 SharedHeap::ScanningOption(roots_scanning_options()),
3596 ¬Older,
3597 true, // walk all of code cache if (so & SO_CodeCache)
3598 NULL);
3599 }
3600
3601 // Clear mod-union table; it will be dirtied in the prologue of
3602 // CMS generation per each younger generation collection.
3603
3604 assert(_modUnionTable.isAllClear(),
3605 "Was cleared in most recent final checkpoint phase"
3606 " or no bits are set in the gc_prologue before the start of the next "
3607 "subsequent marking phase.");
3608
3609 // Save the end of the used_region of the constituent generations
3610 // to be used to limit the extent of sweep in each generation.
3611 save_sweep_limits();
3612 if (UseAdaptiveSizePolicy) {
3613 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3614 }
3615 verify_overflow_empty();
3616 }
3617
3618 bool CMSCollector::markFromRoots(bool asynch) {
3619 // we might be tempted to assert that:
3620 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3621 // "inconsistent argument?");
3622 // However that wouldn't be right, because it's possible that
3623 // a safepoint is indeed in progress as a younger generation
3624 // stop-the-world GC happens even as we mark in this generation.
3625 assert(_collectorState == Marking, "inconsistent state?");
3626 check_correct_thread_executing();
3627 verify_overflow_empty();
3628
3629 bool res;
3630 if (asynch) {
3631
3632 // Start the timers for adaptive size policy for the concurrent phases
3633 // Do it here so that the foreground MS can use the concurrent
3634 // timer since a foreground MS might has the sweep done concurrently
3635 // or STW.
3636 if (UseAdaptiveSizePolicy) {
3637 size_policy()->concurrent_marking_begin();
3638 }
3639
3640 // Weak ref discovery note: We may be discovering weak
3641 // refs in this generation concurrent (but interleaved) with
3642 // weak ref discovery by a younger generation collector.
3643
3644 CMSTokenSyncWithLocks ts(true, bitMapLock());
3645 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3646 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3647 res = markFromRootsWork(asynch);
3648 if (res) {
3649 _collectorState = Precleaning;
3650 } else { // We failed and a foreground collection wants to take over
3651 assert(_foregroundGCIsActive, "internal state inconsistency");
3652 assert(_restart_addr == NULL, "foreground will restart from scratch");
3653 if (PrintGCDetails) {
3654 gclog_or_tty->print_cr("bailing out to foreground collection");
3655 }
3656 }
3657 if (UseAdaptiveSizePolicy) {
3658 size_policy()->concurrent_marking_end();
3659 }
3660 } else {
3661 assert(SafepointSynchronize::is_at_safepoint(),
3662 "inconsistent with asynch == false");
3663 if (UseAdaptiveSizePolicy) {
3664 size_policy()->ms_collection_marking_begin();
3665 }
3666 // already have locks
3667 res = markFromRootsWork(asynch);
3668 _collectorState = FinalMarking;
3669 if (UseAdaptiveSizePolicy) {
3670 GenCollectedHeap* gch = GenCollectedHeap::heap();
3671 size_policy()->ms_collection_marking_end(gch->gc_cause());
3672 }
3673 }
3674 verify_overflow_empty();
3675 return res;
3676 }
3677
3678 bool CMSCollector::markFromRootsWork(bool asynch) {
3679 // iterate over marked bits in bit map, doing a full scan and mark
3680 // from these roots using the following algorithm:
3681 // . if oop is to the right of the current scan pointer,
3682 // mark corresponding bit (we'll process it later)
3683 // . else (oop is to left of current scan pointer)
3684 // push oop on marking stack
3685 // . drain the marking stack
3686
3687 // Note that when we do a marking step we need to hold the
3688 // bit map lock -- recall that direct allocation (by mutators)
3689 // and promotion (by younger generation collectors) is also
3690 // marking the bit map. [the so-called allocate live policy.]
3691 // Because the implementation of bit map marking is not
3692 // robust wrt simultaneous marking of bits in the same word,
3693 // we need to make sure that there is no such interference
3694 // between concurrent such updates.
3695
3696 // already have locks
3697 assert_lock_strong(bitMapLock());
3698
3699 // Clear the revisit stack, just in case there are any
3700 // obsolete contents from a short-circuited previous CMS cycle.
3701 _revisitStack.reset();
3702 verify_work_stacks_empty();
3703 verify_overflow_empty();
3704 assert(_revisitStack.isEmpty(), "tabula rasa");
3705 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3706 bool result = false;
3707 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3708 result = do_marking_mt(asynch);
3709 } else {
3710 result = do_marking_st(asynch);
3711 }
3712 return result;
3713 }
3714
3715 // Forward decl
3716 class CMSConcMarkingTask;
3717
3718 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3719 CMSCollector* _collector;
3720 CMSConcMarkingTask* _task;
3721 public:
3722 virtual void yield();
3723
3724 // "n_threads" is the number of threads to be terminated.
3725 // "queue_set" is a set of work queues of other threads.
3726 // "collector" is the CMS collector associated with this task terminator.
3727 // "yield" indicates whether we need the gang as a whole to yield.
3728 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3729 ParallelTaskTerminator(n_threads, queue_set),
3730 _collector(collector) { }
3731
3732 void set_task(CMSConcMarkingTask* task) {
3733 _task = task;
3734 }
3735 };
3736
3737 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3738 CMSConcMarkingTask* _task;
3739 public:
3740 bool should_exit_termination();
3741 void set_task(CMSConcMarkingTask* task) {
3742 _task = task;
3743 }
3744 };
3745
3746 // MT Concurrent Marking Task
3747 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3748 CMSCollector* _collector;
3749 int _n_workers; // requested/desired # workers
3750 bool _asynch;
3751 bool _result;
3752 CompactibleFreeListSpace* _cms_space;
3753 CompactibleFreeListSpace* _perm_space;
3754 char _pad_front[64]; // padding to ...
3755 HeapWord* _global_finger; // ... avoid sharing cache line
3756 char _pad_back[64];
3757 HeapWord* _restart_addr;
3758
3759 // Exposed here for yielding support
3760 Mutex* const _bit_map_lock;
3761
3762 // The per thread work queues, available here for stealing
3763 OopTaskQueueSet* _task_queues;
3764
3765 // Termination (and yielding) support
3766 CMSConcMarkingTerminator _term;
3767 CMSConcMarkingTerminatorTerminator _term_term;
3768
3769 public:
3770 CMSConcMarkingTask(CMSCollector* collector,
3771 CompactibleFreeListSpace* cms_space,
3772 CompactibleFreeListSpace* perm_space,
3773 bool asynch,
3774 YieldingFlexibleWorkGang* workers,
3775 OopTaskQueueSet* task_queues):
3776 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3777 _collector(collector),
3778 _cms_space(cms_space),
3779 _perm_space(perm_space),
3780 _asynch(asynch), _n_workers(0), _result(true),
3781 _task_queues(task_queues),
3782 _term(_n_workers, task_queues, _collector),
3783 _bit_map_lock(collector->bitMapLock())
3784 {
3785 _requested_size = _n_workers;
3786 _term.set_task(this);
3787 _term_term.set_task(this);
3788 assert(_cms_space->bottom() < _perm_space->bottom(),
3789 "Finger incorrectly initialized below");
3790 _restart_addr = _global_finger = _cms_space->bottom();
3791 }
3792
3793
3794 OopTaskQueueSet* task_queues() { return _task_queues; }
3795
3796 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3797
3798 HeapWord** global_finger_addr() { return &_global_finger; }
3799
3800 CMSConcMarkingTerminator* terminator() { return &_term; }
3801
3802 virtual void set_for_termination(int active_workers) {
3803 terminator()->reset_for_reuse(active_workers);
3804 }
3805
3806 void work(uint worker_id);
3807 bool should_yield() {
3808 return ConcurrentMarkSweepThread::should_yield()
3809 && !_collector->foregroundGCIsActive()
3810 && _asynch;
3811 }
3812
3813 virtual void coordinator_yield(); // stuff done by coordinator
3814 bool result() { return _result; }
3815
3816 void reset(HeapWord* ra) {
3817 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3818 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3819 assert(ra < _perm_space->end(), "ra too large");
3820 _restart_addr = _global_finger = ra;
3821 _term.reset_for_reuse();
3822 }
3823
3824 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3825 OopTaskQueue* work_q);
3826
3827 private:
3828 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3829 void do_work_steal(int i);
3830 void bump_global_finger(HeapWord* f);
3831 };
3832
3833 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3834 assert(_task != NULL, "Error");
3835 return _task->yielding();
3836 // Note that we do not need the disjunct || _task->should_yield() above
3837 // because we want terminating threads to yield only if the task
3838 // is already in the midst of yielding, which happens only after at least one
3839 // thread has yielded.
3840 }
3841
3842 void CMSConcMarkingTerminator::yield() {
3843 if (_task->should_yield()) {
3844 _task->yield();
3845 } else {
3846 ParallelTaskTerminator::yield();
3847 }
3848 }
3849
3850 ////////////////////////////////////////////////////////////////
3851 // Concurrent Marking Algorithm Sketch
3852 ////////////////////////////////////////////////////////////////
3853 // Until all tasks exhausted (both spaces):
3854 // -- claim next available chunk
3855 // -- bump global finger via CAS
3856 // -- find first object that starts in this chunk
3857 // and start scanning bitmap from that position
3858 // -- scan marked objects for oops
3859 // -- CAS-mark target, and if successful:
3860 // . if target oop is above global finger (volatile read)
3861 // nothing to do
3862 // . if target oop is in chunk and above local finger
3863 // then nothing to do
3864 // . else push on work-queue
3865 // -- Deal with possible overflow issues:
3866 // . local work-queue overflow causes stuff to be pushed on
3867 // global (common) overflow queue
3868 // . always first empty local work queue
3869 // . then get a batch of oops from global work queue if any
3870 // . then do work stealing
3871 // -- When all tasks claimed (both spaces)
3872 // and local work queue empty,
3873 // then in a loop do:
3874 // . check global overflow stack; steal a batch of oops and trace
3875 // . try to steal from other threads oif GOS is empty
3876 // . if neither is available, offer termination
3877 // -- Terminate and return result
3878 //
3879 void CMSConcMarkingTask::work(uint worker_id) {
3880 elapsedTimer _timer;
3881 ResourceMark rm;
3882 HandleMark hm;
3883
3884 DEBUG_ONLY(_collector->verify_overflow_empty();)
3885
3886 // Before we begin work, our work queue should be empty
3887 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3888 // Scan the bitmap covering _cms_space, tracing through grey objects.
3889 _timer.start();
3890 do_scan_and_mark(worker_id, _cms_space);
3891 _timer.stop();
3892 if (PrintCMSStatistics != 0) {
3893 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3894 worker_id, _timer.seconds());
3895 // XXX: need xxx/xxx type of notation, two timers
3896 }
3897
3898 // ... do the same for the _perm_space
3899 _timer.reset();
3900 _timer.start();
3901 do_scan_and_mark(worker_id, _perm_space);
3902 _timer.stop();
3903 if (PrintCMSStatistics != 0) {
3904 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3905 worker_id, _timer.seconds());
3906 // XXX: need xxx/xxx type of notation, two timers
3907 }
3908
3909 // ... do work stealing
3910 _timer.reset();
3911 _timer.start();
3912 do_work_steal(worker_id);
3913 _timer.stop();
3914 if (PrintCMSStatistics != 0) {
3915 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3916 worker_id, _timer.seconds());
3917 // XXX: need xxx/xxx type of notation, two timers
3918 }
3919 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3920 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3921 // Note that under the current task protocol, the
3922 // following assertion is true even of the spaces
3923 // expanded since the completion of the concurrent
3924 // marking. XXX This will likely change under a strict
3925 // ABORT semantics.
3926 assert(_global_finger > _cms_space->end() &&
3927 _global_finger >= _perm_space->end(),
3928 "All tasks have been completed");
3929 DEBUG_ONLY(_collector->verify_overflow_empty();)
3930 }
3931
3932 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3933 HeapWord* read = _global_finger;
3934 HeapWord* cur = read;
3935 while (f > read) {
3936 cur = read;
3937 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3938 if (cur == read) {
3939 // our cas succeeded
3940 assert(_global_finger >= f, "protocol consistency");
3941 break;
3942 }
3943 }
3944 }
3945
3946 // This is really inefficient, and should be redone by
3947 // using (not yet available) block-read and -write interfaces to the
3948 // stack and the work_queue. XXX FIX ME !!!
3949 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3950 OopTaskQueue* work_q) {
3951 // Fast lock-free check
3952 if (ovflw_stk->length() == 0) {
3953 return false;
3954 }
3955 assert(work_q->size() == 0, "Shouldn't steal");
3956 MutexLockerEx ml(ovflw_stk->par_lock(),
3957 Mutex::_no_safepoint_check_flag);
3958 // Grab up to 1/4 the size of the work queue
3959 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3960 (size_t)ParGCDesiredObjsFromOverflowList);
3961 num = MIN2(num, ovflw_stk->length());
3962 for (int i = (int) num; i > 0; i--) {
3963 oop cur = ovflw_stk->pop();
3964 assert(cur != NULL, "Counted wrong?");
3965 work_q->push(cur);
3966 }
3967 return num > 0;
3968 }
3969
3970 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3971 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3972 int n_tasks = pst->n_tasks();
3973 // We allow that there may be no tasks to do here because
3974 // we are restarting after a stack overflow.
3975 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3976 uint nth_task = 0;
3977
3978 HeapWord* aligned_start = sp->bottom();
3979 if (sp->used_region().contains(_restart_addr)) {
3980 // Align down to a card boundary for the start of 0th task
3981 // for this space.
3982 aligned_start =
3983 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3984 CardTableModRefBS::card_size);
3985 }
3986
3987 size_t chunk_size = sp->marking_task_size();
3988 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3989 // Having claimed the nth task in this space,
3990 // compute the chunk that it corresponds to:
3991 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3992 aligned_start + (nth_task+1)*chunk_size);
3993 // Try and bump the global finger via a CAS;
3994 // note that we need to do the global finger bump
3995 // _before_ taking the intersection below, because
3996 // the task corresponding to that region will be
3997 // deemed done even if the used_region() expands
3998 // because of allocation -- as it almost certainly will
3999 // during start-up while the threads yield in the
4000 // closure below.
4001 HeapWord* finger = span.end();
4002 bump_global_finger(finger); // atomically
4003 // There are null tasks here corresponding to chunks
4004 // beyond the "top" address of the space.
4005 span = span.intersection(sp->used_region());
4006 if (!span.is_empty()) { // Non-null task
4007 HeapWord* prev_obj;
4008 assert(!span.contains(_restart_addr) || nth_task == 0,
4009 "Inconsistency");
4010 if (nth_task == 0) {
4011 // For the 0th task, we'll not need to compute a block_start.
4012 if (span.contains(_restart_addr)) {
4013 // In the case of a restart because of stack overflow,
4014 // we might additionally skip a chunk prefix.
4015 prev_obj = _restart_addr;
4016 } else {
4017 prev_obj = span.start();
4018 }
4019 } else {
4020 // We want to skip the first object because
4021 // the protocol is to scan any object in its entirety
4022 // that _starts_ in this span; a fortiori, any
4023 // object starting in an earlier span is scanned
4024 // as part of an earlier claimed task.
4025 // Below we use the "careful" version of block_start
4026 // so we do not try to navigate uninitialized objects.
4027 prev_obj = sp->block_start_careful(span.start());
4028 // Below we use a variant of block_size that uses the
4029 // Printezis bits to avoid waiting for allocated
4030 // objects to become initialized/parsable.
4031 while (prev_obj < span.start()) {
4032 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4033 if (sz > 0) {
4034 prev_obj += sz;
4035 } else {
4036 // In this case we may end up doing a bit of redundant
4037 // scanning, but that appears unavoidable, short of
4038 // locking the free list locks; see bug 6324141.
4039 break;
4040 }
4041 }
4042 }
4043 if (prev_obj < span.end()) {
4044 MemRegion my_span = MemRegion(prev_obj, span.end());
4045 // Do the marking work within a non-empty span --
4046 // the last argument to the constructor indicates whether the
4047 // iteration should be incremental with periodic yields.
4048 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4049 &_collector->_markBitMap,
4050 work_queue(i),
4051 &_collector->_markStack,
4052 &_collector->_revisitStack,
4053 _asynch);
4054 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4055 } // else nothing to do for this task
4056 } // else nothing to do for this task
4057 }
4058 // We'd be tempted to assert here that since there are no
4059 // more tasks left to claim in this space, the global_finger
4060 // must exceed space->top() and a fortiori space->end(). However,
4061 // that would not quite be correct because the bumping of
4062 // global_finger occurs strictly after the claiming of a task,
4063 // so by the time we reach here the global finger may not yet
4064 // have been bumped up by the thread that claimed the last
4065 // task.
4066 pst->all_tasks_completed();
4067 }
4068
4069 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4070 private:
4071 CMSConcMarkingTask* _task;
4072 MemRegion _span;
4073 CMSBitMap* _bit_map;
4074 CMSMarkStack* _overflow_stack;
4075 OopTaskQueue* _work_queue;
4076 protected:
4077 DO_OOP_WORK_DEFN
4078 public:
4079 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4080 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4081 CMSMarkStack* revisit_stack):
4082 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4083 _task(task),
4084 _span(collector->_span),
4085 _work_queue(work_queue),
4086 _bit_map(bit_map),
4087 _overflow_stack(overflow_stack)
4088 { }
4089 virtual void do_oop(oop* p);
4090 virtual void do_oop(narrowOop* p);
4091 void trim_queue(size_t max);
4092 void handle_stack_overflow(HeapWord* lost);
4093 void do_yield_check() {
4094 if (_task->should_yield()) {
4095 _task->yield();
4096 }
4097 }
4098 };
4099
4100 // Grey object scanning during work stealing phase --
4101 // the salient assumption here is that any references
4102 // that are in these stolen objects being scanned must
4103 // already have been initialized (else they would not have
4104 // been published), so we do not need to check for
4105 // uninitialized objects before pushing here.
4106 void Par_ConcMarkingClosure::do_oop(oop obj) {
4107 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4108 HeapWord* addr = (HeapWord*)obj;
4109 // Check if oop points into the CMS generation
4110 // and is not marked
4111 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4112 // a white object ...
4113 // If we manage to "claim" the object, by being the
4114 // first thread to mark it, then we push it on our
4115 // marking stack
4116 if (_bit_map->par_mark(addr)) { // ... now grey
4117 // push on work queue (grey set)
4118 bool simulate_overflow = false;
4119 NOT_PRODUCT(
4120 if (CMSMarkStackOverflowALot &&
4121 _collector->simulate_overflow()) {
4122 // simulate a stack overflow
4123 simulate_overflow = true;
4124 }
4125 )
4126 if (simulate_overflow ||
4127 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4128 // stack overflow
4129 if (PrintCMSStatistics != 0) {
4130 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4131 SIZE_FORMAT, _overflow_stack->capacity());
4132 }
4133 // We cannot assert that the overflow stack is full because
4134 // it may have been emptied since.
4135 assert(simulate_overflow ||
4136 _work_queue->size() == _work_queue->max_elems(),
4137 "Else push should have succeeded");
4138 handle_stack_overflow(addr);
4139 }
4140 } // Else, some other thread got there first
4141 do_yield_check();
4142 }
4143 }
4144
4145 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4146 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4147
4148 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4149 while (_work_queue->size() > max) {
4150 oop new_oop;
4151 if (_work_queue->pop_local(new_oop)) {
4152 assert(new_oop->is_oop(), "Should be an oop");
4153 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4154 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4155 assert(new_oop->is_parsable(), "Should be parsable");
4156 new_oop->oop_iterate(this); // do_oop() above
4157 do_yield_check();
4158 }
4159 }
4160 }
4161
4162 // Upon stack overflow, we discard (part of) the stack,
4163 // remembering the least address amongst those discarded
4164 // in CMSCollector's _restart_address.
4165 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4166 // We need to do this under a mutex to prevent other
4167 // workers from interfering with the work done below.
4168 MutexLockerEx ml(_overflow_stack->par_lock(),
4169 Mutex::_no_safepoint_check_flag);
4170 // Remember the least grey address discarded
4171 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4172 _collector->lower_restart_addr(ra);
4173 _overflow_stack->reset(); // discard stack contents
4174 _overflow_stack->expand(); // expand the stack if possible
4175 }
4176
4177
4178 void CMSConcMarkingTask::do_work_steal(int i) {
4179 OopTaskQueue* work_q = work_queue(i);
4180 oop obj_to_scan;
4181 CMSBitMap* bm = &(_collector->_markBitMap);
4182 CMSMarkStack* ovflw = &(_collector->_markStack);
4183 CMSMarkStack* revisit = &(_collector->_revisitStack);
4184 int* seed = _collector->hash_seed(i);
4185 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4186 while (true) {
4187 cl.trim_queue(0);
4188 assert(work_q->size() == 0, "Should have been emptied above");
4189 if (get_work_from_overflow_stack(ovflw, work_q)) {
4190 // Can't assert below because the work obtained from the
4191 // overflow stack may already have been stolen from us.
4192 // assert(work_q->size() > 0, "Work from overflow stack");
4193 continue;
4194 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4195 assert(obj_to_scan->is_oop(), "Should be an oop");
4196 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4197 obj_to_scan->oop_iterate(&cl);
4198 } else if (terminator()->offer_termination(&_term_term)) {
4199 assert(work_q->size() == 0, "Impossible!");
4200 break;
4201 } else if (yielding() || should_yield()) {
4202 yield();
4203 }
4204 }
4205 }
4206
4207 // This is run by the CMS (coordinator) thread.
4208 void CMSConcMarkingTask::coordinator_yield() {
4209 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4210 "CMS thread should hold CMS token");
4211 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4212 // First give up the locks, then yield, then re-lock
4213 // We should probably use a constructor/destructor idiom to
4214 // do this unlock/lock or modify the MutexUnlocker class to
4215 // serve our purpose. XXX
4216 assert_lock_strong(_bit_map_lock);
4217 _bit_map_lock->unlock();
4218 ConcurrentMarkSweepThread::desynchronize(true);
4219 ConcurrentMarkSweepThread::acknowledge_yield_request();
4220 _collector->stopTimer();
4221 if (PrintCMSStatistics != 0) {
4222 _collector->incrementYields();
4223 }
4224 _collector->icms_wait();
4225
4226 // It is possible for whichever thread initiated the yield request
4227 // not to get a chance to wake up and take the bitmap lock between
4228 // this thread releasing it and reacquiring it. So, while the
4229 // should_yield() flag is on, let's sleep for a bit to give the
4230 // other thread a chance to wake up. The limit imposed on the number
4231 // of iterations is defensive, to avoid any unforseen circumstances
4232 // putting us into an infinite loop. Since it's always been this
4233 // (coordinator_yield()) method that was observed to cause the
4234 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4235 // which is by default non-zero. For the other seven methods that
4236 // also perform the yield operation, as are using a different
4237 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4238 // can enable the sleeping for those methods too, if necessary.
4239 // See 6442774.
4240 //
4241 // We really need to reconsider the synchronization between the GC
4242 // thread and the yield-requesting threads in the future and we
4243 // should really use wait/notify, which is the recommended
4244 // way of doing this type of interaction. Additionally, we should
4245 // consolidate the eight methods that do the yield operation and they
4246 // are almost identical into one for better maintenability and
4247 // readability. See 6445193.
4248 //
4249 // Tony 2006.06.29
4250 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4251 ConcurrentMarkSweepThread::should_yield() &&
4252 !CMSCollector::foregroundGCIsActive(); ++i) {
4253 os::sleep(Thread::current(), 1, false);
4254 ConcurrentMarkSweepThread::acknowledge_yield_request();
4255 }
4256
4257 ConcurrentMarkSweepThread::synchronize(true);
4258 _bit_map_lock->lock_without_safepoint_check();
4259 _collector->startTimer();
4260 }
4261
4262 bool CMSCollector::do_marking_mt(bool asynch) {
4263 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4264 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4265 conc_workers()->total_workers(),
4266 conc_workers()->active_workers(),
4267 Threads::number_of_non_daemon_threads());
4268 conc_workers()->set_active_workers(num_workers);
4269
4270 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4271 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4272
4273 CMSConcMarkingTask tsk(this,
4274 cms_space,
4275 perm_space,
4276 asynch,
4277 conc_workers(),
4278 task_queues());
4279
4280 // Since the actual number of workers we get may be different
4281 // from the number we requested above, do we need to do anything different
4282 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4283 // class?? XXX
4284 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4285 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4286
4287 // Refs discovery is already non-atomic.
4288 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4289 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4290 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4291 conc_workers()->start_task(&tsk);
4292 while (tsk.yielded()) {
4293 tsk.coordinator_yield();
4294 conc_workers()->continue_task(&tsk);
4295 }
4296 // If the task was aborted, _restart_addr will be non-NULL
4297 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4298 while (_restart_addr != NULL) {
4299 // XXX For now we do not make use of ABORTED state and have not
4300 // yet implemented the right abort semantics (even in the original
4301 // single-threaded CMS case). That needs some more investigation
4302 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4303 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4304 // If _restart_addr is non-NULL, a marking stack overflow
4305 // occurred; we need to do a fresh marking iteration from the
4306 // indicated restart address.
4307 if (_foregroundGCIsActive && asynch) {
4308 // We may be running into repeated stack overflows, having
4309 // reached the limit of the stack size, while making very
4310 // slow forward progress. It may be best to bail out and
4311 // let the foreground collector do its job.
4312 // Clear _restart_addr, so that foreground GC
4313 // works from scratch. This avoids the headache of
4314 // a "rescan" which would otherwise be needed because
4315 // of the dirty mod union table & card table.
4316 _restart_addr = NULL;
4317 return false;
4318 }
4319 // Adjust the task to restart from _restart_addr
4320 tsk.reset(_restart_addr);
4321 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4322 _restart_addr);
4323 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4324 _restart_addr);
4325 _restart_addr = NULL;
4326 // Get the workers going again
4327 conc_workers()->start_task(&tsk);
4328 while (tsk.yielded()) {
4329 tsk.coordinator_yield();
4330 conc_workers()->continue_task(&tsk);
4331 }
4332 }
4333 assert(tsk.completed(), "Inconsistency");
4334 assert(tsk.result() == true, "Inconsistency");
4335 return true;
4336 }
4337
4338 bool CMSCollector::do_marking_st(bool asynch) {
4339 ResourceMark rm;
4340 HandleMark hm;
4341
4342 // Temporarily make refs discovery single threaded (non-MT)
4343 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4344 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4345 &_markStack, &_revisitStack, CMSYield && asynch);
4346 // the last argument to iterate indicates whether the iteration
4347 // should be incremental with periodic yields.
4348 _markBitMap.iterate(&markFromRootsClosure);
4349 // If _restart_addr is non-NULL, a marking stack overflow
4350 // occurred; we need to do a fresh iteration from the
4351 // indicated restart address.
4352 while (_restart_addr != NULL) {
4353 if (_foregroundGCIsActive && asynch) {
4354 // We may be running into repeated stack overflows, having
4355 // reached the limit of the stack size, while making very
4356 // slow forward progress. It may be best to bail out and
4357 // let the foreground collector do its job.
4358 // Clear _restart_addr, so that foreground GC
4359 // works from scratch. This avoids the headache of
4360 // a "rescan" which would otherwise be needed because
4361 // of the dirty mod union table & card table.
4362 _restart_addr = NULL;
4363 return false; // indicating failure to complete marking
4364 }
4365 // Deal with stack overflow:
4366 // we restart marking from _restart_addr
4367 HeapWord* ra = _restart_addr;
4368 markFromRootsClosure.reset(ra);
4369 _restart_addr = NULL;
4370 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4371 }
4372 return true;
4373 }
4374
4375 void CMSCollector::preclean() {
4376 check_correct_thread_executing();
4377 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4378 verify_work_stacks_empty();
4379 verify_overflow_empty();
4380 _abort_preclean = false;
4381 if (CMSPrecleaningEnabled) {
4382 _eden_chunk_index = 0;
4383 size_t used = get_eden_used();
4384 size_t capacity = get_eden_capacity();
4385 // Don't start sampling unless we will get sufficiently
4386 // many samples.
4387 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4388 * CMSScheduleRemarkEdenPenetration)) {
4389 _start_sampling = true;
4390 } else {
4391 _start_sampling = false;
4392 }
4393 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4394 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4395 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4396 }
4397 CMSTokenSync x(true); // is cms thread
4398 if (CMSPrecleaningEnabled) {
4399 sample_eden();
4400 _collectorState = AbortablePreclean;
4401 } else {
4402 _collectorState = FinalMarking;
4403 }
4404 verify_work_stacks_empty();
4405 verify_overflow_empty();
4406 }
4407
4408 // Try and schedule the remark such that young gen
4409 // occupancy is CMSScheduleRemarkEdenPenetration %.
4410 void CMSCollector::abortable_preclean() {
4411 check_correct_thread_executing();
4412 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4413 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4414
4415 // If Eden's current occupancy is below this threshold,
4416 // immediately schedule the remark; else preclean
4417 // past the next scavenge in an effort to
4418 // schedule the pause as described avove. By choosing
4419 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4420 // we will never do an actual abortable preclean cycle.
4421 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4422 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4423 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4424 // We need more smarts in the abortable preclean
4425 // loop below to deal with cases where allocation
4426 // in young gen is very very slow, and our precleaning
4427 // is running a losing race against a horde of
4428 // mutators intent on flooding us with CMS updates
4429 // (dirty cards).
4430 // One, admittedly dumb, strategy is to give up
4431 // after a certain number of abortable precleaning loops
4432 // or after a certain maximum time. We want to make
4433 // this smarter in the next iteration.
4434 // XXX FIX ME!!! YSR
4435 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4436 while (!(should_abort_preclean() ||
4437 ConcurrentMarkSweepThread::should_terminate())) {
4438 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4439 cumworkdone += workdone;
4440 loops++;
4441 // Voluntarily terminate abortable preclean phase if we have
4442 // been at it for too long.
4443 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4444 loops >= CMSMaxAbortablePrecleanLoops) {
4445 if (PrintGCDetails) {
4446 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4447 }
4448 break;
4449 }
4450 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4451 if (PrintGCDetails) {
4452 gclog_or_tty->print(" CMS: abort preclean due to time ");
4453 }
4454 break;
4455 }
4456 // If we are doing little work each iteration, we should
4457 // take a short break.
4458 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4459 // Sleep for some time, waiting for work to accumulate
4460 stopTimer();
4461 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4462 startTimer();
4463 waited++;
4464 }
4465 }
4466 if (PrintCMSStatistics > 0) {
4467 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4468 loops, waited, cumworkdone);
4469 }
4470 }
4471 CMSTokenSync x(true); // is cms thread
4472 if (_collectorState != Idling) {
4473 assert(_collectorState == AbortablePreclean,
4474 "Spontaneous state transition?");
4475 _collectorState = FinalMarking;
4476 } // Else, a foreground collection completed this CMS cycle.
4477 return;
4478 }
4479
4480 // Respond to an Eden sampling opportunity
4481 void CMSCollector::sample_eden() {
4482 // Make sure a young gc cannot sneak in between our
4483 // reading and recording of a sample.
4484 assert(Thread::current()->is_ConcurrentGC_thread(),
4485 "Only the cms thread may collect Eden samples");
4486 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4487 "Should collect samples while holding CMS token");
4488 if (!_start_sampling) {
4489 return;
4490 }
4491 if (_eden_chunk_array) {
4492 if (_eden_chunk_index < _eden_chunk_capacity) {
4493 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4494 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4495 "Unexpected state of Eden");
4496 // We'd like to check that what we just sampled is an oop-start address;
4497 // however, we cannot do that here since the object may not yet have been
4498 // initialized. So we'll instead do the check when we _use_ this sample
4499 // later.
4500 if (_eden_chunk_index == 0 ||
4501 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4502 _eden_chunk_array[_eden_chunk_index-1])
4503 >= CMSSamplingGrain)) {
4504 _eden_chunk_index++; // commit sample
4505 }
4506 }
4507 }
4508 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4509 size_t used = get_eden_used();
4510 size_t capacity = get_eden_capacity();
4511 assert(used <= capacity, "Unexpected state of Eden");
4512 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4513 _abort_preclean = true;
4514 }
4515 }
4516 }
4517
4518
4519 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4520 assert(_collectorState == Precleaning ||
4521 _collectorState == AbortablePreclean, "incorrect state");
4522 ResourceMark rm;
4523 HandleMark hm;
4524
4525 // Precleaning is currently not MT but the reference processor
4526 // may be set for MT. Disable it temporarily here.
4527 ReferenceProcessor* rp = ref_processor();
4528 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4529
4530 // Do one pass of scrubbing the discovered reference lists
4531 // to remove any reference objects with strongly-reachable
4532 // referents.
4533 if (clean_refs) {
4534 CMSPrecleanRefsYieldClosure yield_cl(this);
4535 assert(rp->span().equals(_span), "Spans should be equal");
4536 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4537 &_markStack, &_revisitStack,
4538 true /* preclean */);
4539 CMSDrainMarkingStackClosure complete_trace(this,
4540 _span, &_markBitMap, &_markStack,
4541 &keep_alive, true /* preclean */);
4542
4543 // We don't want this step to interfere with a young
4544 // collection because we don't want to take CPU
4545 // or memory bandwidth away from the young GC threads
4546 // (which may be as many as there are CPUs).
4547 // Note that we don't need to protect ourselves from
4548 // interference with mutators because they can't
4549 // manipulate the discovered reference lists nor affect
4550 // the computed reachability of the referents, the
4551 // only properties manipulated by the precleaning
4552 // of these reference lists.
4553 stopTimer();
4554 CMSTokenSyncWithLocks x(true /* is cms thread */,
4555 bitMapLock());
4556 startTimer();
4557 sample_eden();
4558
4559 // The following will yield to allow foreground
4560 // collection to proceed promptly. XXX YSR:
4561 // The code in this method may need further
4562 // tweaking for better performance and some restructuring
4563 // for cleaner interfaces.
4564 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4565 rp->preclean_discovered_references(
4566 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4567 &yield_cl, should_unload_classes(), gc_timer);
4568 }
4569
4570 if (clean_survivor) { // preclean the active survivor space(s)
4571 assert(_young_gen->kind() == Generation::DefNew ||
4572 _young_gen->kind() == Generation::ParNew ||
4573 _young_gen->kind() == Generation::ASParNew,
4574 "incorrect type for cast");
4575 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4576 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4577 &_markBitMap, &_modUnionTable,
4578 &_markStack, &_revisitStack,
4579 true /* precleaning phase */);
4580 stopTimer();
4581 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4582 bitMapLock());
4583 startTimer();
4584 unsigned int before_count =
4585 GenCollectedHeap::heap()->total_collections();
4586 SurvivorSpacePrecleanClosure
4587 sss_cl(this, _span, &_markBitMap, &_markStack,
4588 &pam_cl, before_count, CMSYield);
4589 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4590 dng->from()->object_iterate_careful(&sss_cl);
4591 dng->to()->object_iterate_careful(&sss_cl);
4592 }
4593 MarkRefsIntoAndScanClosure
4594 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4595 &_markStack, &_revisitStack, this, CMSYield,
4596 true /* precleaning phase */);
4597 // CAUTION: The following closure has persistent state that may need to
4598 // be reset upon a decrease in the sequence of addresses it
4599 // processes.
4600 ScanMarkedObjectsAgainCarefullyClosure
4601 smoac_cl(this, _span,
4602 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4603
4604 // Preclean dirty cards in ModUnionTable and CardTable using
4605 // appropriate convergence criterion;
4606 // repeat CMSPrecleanIter times unless we find that
4607 // we are losing.
4608 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4609 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4610 "Bad convergence multiplier");
4611 assert(CMSPrecleanThreshold >= 100,
4612 "Unreasonably low CMSPrecleanThreshold");
4613
4614 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4615 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4616 numIter < CMSPrecleanIter;
4617 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4618 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4619 if (CMSPermGenPrecleaningEnabled) {
4620 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4621 }
4622 if (Verbose && PrintGCDetails) {
4623 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4624 }
4625 // Either there are very few dirty cards, so re-mark
4626 // pause will be small anyway, or our pre-cleaning isn't
4627 // that much faster than the rate at which cards are being
4628 // dirtied, so we might as well stop and re-mark since
4629 // precleaning won't improve our re-mark time by much.
4630 if (curNumCards <= CMSPrecleanThreshold ||
4631 (numIter > 0 &&
4632 (curNumCards * CMSPrecleanDenominator >
4633 lastNumCards * CMSPrecleanNumerator))) {
4634 numIter++;
4635 cumNumCards += curNumCards;
4636 break;
4637 }
4638 }
4639 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4640 if (CMSPermGenPrecleaningEnabled) {
4641 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4642 }
4643 cumNumCards += curNumCards;
4644 if (PrintGCDetails && PrintCMSStatistics != 0) {
4645 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4646 curNumCards, cumNumCards, numIter);
4647 }
4648 return cumNumCards; // as a measure of useful work done
4649 }
4650
4651 // PRECLEANING NOTES:
4652 // Precleaning involves:
4653 // . reading the bits of the modUnionTable and clearing the set bits.
4654 // . For the cards corresponding to the set bits, we scan the
4655 // objects on those cards. This means we need the free_list_lock
4656 // so that we can safely iterate over the CMS space when scanning
4657 // for oops.
4658 // . When we scan the objects, we'll be both reading and setting
4659 // marks in the marking bit map, so we'll need the marking bit map.
4660 // . For protecting _collector_state transitions, we take the CGC_lock.
4661 // Note that any races in the reading of of card table entries by the
4662 // CMS thread on the one hand and the clearing of those entries by the
4663 // VM thread or the setting of those entries by the mutator threads on the
4664 // other are quite benign. However, for efficiency it makes sense to keep
4665 // the VM thread from racing with the CMS thread while the latter is
4666 // dirty card info to the modUnionTable. We therefore also use the
4667 // CGC_lock to protect the reading of the card table and the mod union
4668 // table by the CM thread.
4669 // . We run concurrently with mutator updates, so scanning
4670 // needs to be done carefully -- we should not try to scan
4671 // potentially uninitialized objects.
4672 //
4673 // Locking strategy: While holding the CGC_lock, we scan over and
4674 // reset a maximal dirty range of the mod union / card tables, then lock
4675 // the free_list_lock and bitmap lock to do a full marking, then
4676 // release these locks; and repeat the cycle. This allows for a
4677 // certain amount of fairness in the sharing of these locks between
4678 // the CMS collector on the one hand, and the VM thread and the
4679 // mutators on the other.
4680
4681 // NOTE: preclean_mod_union_table() and preclean_card_table()
4682 // further below are largely identical; if you need to modify
4683 // one of these methods, please check the other method too.
4684
4685 size_t CMSCollector::preclean_mod_union_table(
4686 ConcurrentMarkSweepGeneration* gen,
4687 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4688 verify_work_stacks_empty();
4689 verify_overflow_empty();
4690
4691 // Turn off checking for this method but turn it back on
4692 // selectively. There are yield points in this method
4693 // but it is difficult to turn the checking off just around
4694 // the yield points. It is simpler to selectively turn
4695 // it on.
4696 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4697
4698 // strategy: starting with the first card, accumulate contiguous
4699 // ranges of dirty cards; clear these cards, then scan the region
4700 // covered by these cards.
4701
4702 // Since all of the MUT is committed ahead, we can just use
4703 // that, in case the generations expand while we are precleaning.
4704 // It might also be fine to just use the committed part of the
4705 // generation, but we might potentially miss cards when the
4706 // generation is rapidly expanding while we are in the midst
4707 // of precleaning.
4708 HeapWord* startAddr = gen->reserved().start();
4709 HeapWord* endAddr = gen->reserved().end();
4710
4711 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4712
4713 size_t numDirtyCards, cumNumDirtyCards;
4714 HeapWord *nextAddr, *lastAddr;
4715 for (cumNumDirtyCards = numDirtyCards = 0,
4716 nextAddr = lastAddr = startAddr;
4717 nextAddr < endAddr;
4718 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4719
4720 ResourceMark rm;
4721 HandleMark hm;
4722
4723 MemRegion dirtyRegion;
4724 {
4725 stopTimer();
4726 // Potential yield point
4727 CMSTokenSync ts(true);
4728 startTimer();
4729 sample_eden();
4730 // Get dirty region starting at nextOffset (inclusive),
4731 // simultaneously clearing it.
4732 dirtyRegion =
4733 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4734 assert(dirtyRegion.start() >= nextAddr,
4735 "returned region inconsistent?");
4736 }
4737 // Remember where the next search should begin.
4738 // The returned region (if non-empty) is a right open interval,
4739 // so lastOffset is obtained from the right end of that
4740 // interval.
4741 lastAddr = dirtyRegion.end();
4742 // Should do something more transparent and less hacky XXX
4743 numDirtyCards =
4744 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4745
4746 // We'll scan the cards in the dirty region (with periodic
4747 // yields for foreground GC as needed).
4748 if (!dirtyRegion.is_empty()) {
4749 assert(numDirtyCards > 0, "consistency check");
4750 HeapWord* stop_point = NULL;
4751 stopTimer();
4752 // Potential yield point
4753 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4754 bitMapLock());
4755 startTimer();
4756 {
4757 verify_work_stacks_empty();
4758 verify_overflow_empty();
4759 sample_eden();
4760 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4761 stop_point =
4762 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4763 }
4764 if (stop_point != NULL) {
4765 // The careful iteration stopped early either because it found an
4766 // uninitialized object, or because we were in the midst of an
4767 // "abortable preclean", which should now be aborted. Redirty
4768 // the bits corresponding to the partially-scanned or unscanned
4769 // cards. We'll either restart at the next block boundary or
4770 // abort the preclean.
4771 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4772 (_collectorState == AbortablePreclean && should_abort_preclean()),
4773 "Unparsable objects should only be in perm gen.");
4774 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4775 if (should_abort_preclean()) {
4776 break; // out of preclean loop
4777 } else {
4778 // Compute the next address at which preclean should pick up;
4779 // might need bitMapLock in order to read P-bits.
4780 lastAddr = next_card_start_after_block(stop_point);
4781 }
4782 }
4783 } else {
4784 assert(lastAddr == endAddr, "consistency check");
4785 assert(numDirtyCards == 0, "consistency check");
4786 break;
4787 }
4788 }
4789 verify_work_stacks_empty();
4790 verify_overflow_empty();
4791 return cumNumDirtyCards;
4792 }
4793
4794 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4795 // below are largely identical; if you need to modify
4796 // one of these methods, please check the other method too.
4797
4798 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4799 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4800 // strategy: it's similar to precleamModUnionTable above, in that
4801 // we accumulate contiguous ranges of dirty cards, mark these cards
4802 // precleaned, then scan the region covered by these cards.
4803 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4804 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4805
4806 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4807
4808 size_t numDirtyCards, cumNumDirtyCards;
4809 HeapWord *lastAddr, *nextAddr;
4810
4811 for (cumNumDirtyCards = numDirtyCards = 0,
4812 nextAddr = lastAddr = startAddr;
4813 nextAddr < endAddr;
4814 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4815
4816 ResourceMark rm;
4817 HandleMark hm;
4818
4819 MemRegion dirtyRegion;
4820 {
4821 // See comments in "Precleaning notes" above on why we
4822 // do this locking. XXX Could the locking overheads be
4823 // too high when dirty cards are sparse? [I don't think so.]
4824 stopTimer();
4825 CMSTokenSync x(true); // is cms thread
4826 startTimer();
4827 sample_eden();
4828 // Get and clear dirty region from card table
4829 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4830 MemRegion(nextAddr, endAddr),
4831 true,
4832 CardTableModRefBS::precleaned_card_val());
4833
4834 assert(dirtyRegion.start() >= nextAddr,
4835 "returned region inconsistent?");
4836 }
4837 lastAddr = dirtyRegion.end();
4838 numDirtyCards =
4839 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4840
4841 if (!dirtyRegion.is_empty()) {
4842 stopTimer();
4843 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4844 startTimer();
4845 sample_eden();
4846 verify_work_stacks_empty();
4847 verify_overflow_empty();
4848 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4849 HeapWord* stop_point =
4850 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4851 if (stop_point != NULL) {
4852 // The careful iteration stopped early because it found an
4853 // uninitialized object. Redirty the bits corresponding to the
4854 // partially-scanned or unscanned cards, and start again at the
4855 // next block boundary.
4856 assert(CMSPermGenPrecleaningEnabled ||
4857 (_collectorState == AbortablePreclean && should_abort_preclean()),
4858 "Unparsable objects should only be in perm gen.");
4859 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4860 if (should_abort_preclean()) {
4861 break; // out of preclean loop
4862 } else {
4863 // Compute the next address at which preclean should pick up.
4864 lastAddr = next_card_start_after_block(stop_point);
4865 }
4866 }
4867 } else {
4868 break;
4869 }
4870 }
4871 verify_work_stacks_empty();
4872 verify_overflow_empty();
4873 return cumNumDirtyCards;
4874 }
4875
4876 void CMSCollector::checkpointRootsFinal(bool asynch,
4877 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4878 assert(_collectorState == FinalMarking, "incorrect state transition?");
4879 check_correct_thread_executing();
4880 // world is stopped at this checkpoint
4881 assert(SafepointSynchronize::is_at_safepoint(),
4882 "world should be stopped");
4883 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4884
4885 verify_work_stacks_empty();
4886 verify_overflow_empty();
4887
4888 SpecializationStats::clear();
4889 if (PrintGCDetails) {
4890 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4891 _young_gen->used() / K,
4892 _young_gen->capacity() / K);
4893 }
4894 if (asynch) {
4895 if (CMSScavengeBeforeRemark) {
4896 GenCollectedHeap* gch = GenCollectedHeap::heap();
4897 // Temporarily set flag to false, GCH->do_collection will
4898 // expect it to be false and set to true
4899 FlagSetting fl(gch->_is_gc_active, false);
4900 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4901 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4902 int level = _cmsGen->level() - 1;
4903 if (level >= 0) {
4904 gch->do_collection(true, // full (i.e. force, see below)
4905 false, // !clear_all_soft_refs
4906 0, // size
4907 false, // is_tlab
4908 level // max_level
4909 );
4910 }
4911 }
4912 FreelistLocker x(this);
4913 MutexLockerEx y(bitMapLock(),
4914 Mutex::_no_safepoint_check_flag);
4915 assert(!init_mark_was_synchronous, "but that's impossible!");
4916 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4917 } else {
4918 // already have all the locks
4919 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4920 init_mark_was_synchronous);
4921 }
4922 verify_work_stacks_empty();
4923 verify_overflow_empty();
4924 SpecializationStats::print();
4925 }
4926
4927 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4928 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4929
4930 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4931
4932 assert(haveFreelistLocks(), "must have free list locks");
4933 assert_lock_strong(bitMapLock());
4934
4935 if (UseAdaptiveSizePolicy) {
4936 size_policy()->checkpoint_roots_final_begin();
4937 }
4938
4939 ResourceMark rm;
4940 HandleMark hm;
4941
4942 GenCollectedHeap* gch = GenCollectedHeap::heap();
4943
4944 if (should_unload_classes()) {
4945 CodeCache::gc_prologue();
4946 }
4947 assert(haveFreelistLocks(), "must have free list locks");
4948 assert_lock_strong(bitMapLock());
4949
4950 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4951 if (!init_mark_was_synchronous) {
4952 // We might assume that we need not fill TLAB's when
4953 // CMSScavengeBeforeRemark is set, because we may have just done
4954 // a scavenge which would have filled all TLAB's -- and besides
4955 // Eden would be empty. This however may not always be the case --
4956 // for instance although we asked for a scavenge, it may not have
4957 // happened because of a JNI critical section. We probably need
4958 // a policy for deciding whether we can in that case wait until
4959 // the critical section releases and then do the remark following
4960 // the scavenge, and skip it here. In the absence of that policy,
4961 // or of an indication of whether the scavenge did indeed occur,
4962 // we cannot rely on TLAB's having been filled and must do
4963 // so here just in case a scavenge did not happen.
4964 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4965 // Update the saved marks which may affect the root scans.
4966 gch->save_marks();
4967
4968 {
4969 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4970
4971 // Note on the role of the mod union table:
4972 // Since the marker in "markFromRoots" marks concurrently with
4973 // mutators, it is possible for some reachable objects not to have been
4974 // scanned. For instance, an only reference to an object A was
4975 // placed in object B after the marker scanned B. Unless B is rescanned,
4976 // A would be collected. Such updates to references in marked objects
4977 // are detected via the mod union table which is the set of all cards
4978 // dirtied since the first checkpoint in this GC cycle and prior to
4979 // the most recent young generation GC, minus those cleaned up by the
4980 // concurrent precleaning.
4981 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4982 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4983 do_remark_parallel();
4984 } else {
4985 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4986 _gc_timer_cm);
4987 do_remark_non_parallel();
4988 }
4989 }
4990 } else {
4991 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4992 // The initial mark was stop-world, so there's no rescanning to
4993 // do; go straight on to the next step below.
4994 }
4995 verify_work_stacks_empty();
4996 verify_overflow_empty();
4997
4998 {
4999 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5000 refProcessingWork(asynch, clear_all_soft_refs);
5001 }
5002 verify_work_stacks_empty();
5003 verify_overflow_empty();
5004
5005 if (should_unload_classes()) {
5006 CodeCache::gc_epilogue();
5007 }
5008 JvmtiExport::gc_epilogue();
5009
5010 // If we encountered any (marking stack / work queue) overflow
5011 // events during the current CMS cycle, take appropriate
5012 // remedial measures, where possible, so as to try and avoid
5013 // recurrence of that condition.
5014 assert(_markStack.isEmpty(), "No grey objects");
5015 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5016 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5017 if (ser_ovflw > 0) {
5018 if (PrintCMSStatistics != 0) {
5019 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5020 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5021 ", kac_preclean="SIZE_FORMAT")",
5022 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5023 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5024 }
5025 _markStack.expand();
5026 _ser_pmc_remark_ovflw = 0;
5027 _ser_pmc_preclean_ovflw = 0;
5028 _ser_kac_preclean_ovflw = 0;
5029 _ser_kac_ovflw = 0;
5030 }
5031 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5032 if (PrintCMSStatistics != 0) {
5033 gclog_or_tty->print_cr("Work queue overflow (benign) "
5034 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5035 _par_pmc_remark_ovflw, _par_kac_ovflw);
5036 }
5037 _par_pmc_remark_ovflw = 0;
5038 _par_kac_ovflw = 0;
5039 }
5040 if (PrintCMSStatistics != 0) {
5041 if (_markStack._hit_limit > 0) {
5042 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5043 _markStack._hit_limit);
5044 }
5045 if (_markStack._failed_double > 0) {
5046 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5047 " current capacity "SIZE_FORMAT,
5048 _markStack._failed_double,
5049 _markStack.capacity());
5050 }
5051 }
5052 _markStack._hit_limit = 0;
5053 _markStack._failed_double = 0;
5054
5055 // Check that all the klasses have been checked
5056 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5057
5058 if ((VerifyAfterGC || VerifyDuringGC) &&
5059 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5060 verify_after_remark();
5061 }
5062
5063 // Change under the freelistLocks.
5064 _collectorState = Sweeping;
5065 // Call isAllClear() under bitMapLock
5066 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5067 " final marking");
5068 if (UseAdaptiveSizePolicy) {
5069 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5070 }
5071 }
5072
5073 // Parallel remark task
5074 class CMSParRemarkTask: public AbstractGangTask {
5075 CMSCollector* _collector;
5076 int _n_workers;
5077 CompactibleFreeListSpace* _cms_space;
5078 CompactibleFreeListSpace* _perm_space;
5079
5080 // The per-thread work queues, available here for stealing.
5081 OopTaskQueueSet* _task_queues;
5082 ParallelTaskTerminator _term;
5083
5084 public:
5085 // A value of 0 passed to n_workers will cause the number of
5086 // workers to be taken from the active workers in the work gang.
5087 CMSParRemarkTask(CMSCollector* collector,
5088 CompactibleFreeListSpace* cms_space,
5089 CompactibleFreeListSpace* perm_space,
5090 int n_workers, FlexibleWorkGang* workers,
5091 OopTaskQueueSet* task_queues):
5092 AbstractGangTask("Rescan roots and grey objects in parallel"),
5093 _collector(collector),
5094 _cms_space(cms_space), _perm_space(perm_space),
5095 _n_workers(n_workers),
5096 _task_queues(task_queues),
5097 _term(n_workers, task_queues) { }
5098
5099 OopTaskQueueSet* task_queues() { return _task_queues; }
5100
5101 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5102
5103 ParallelTaskTerminator* terminator() { return &_term; }
5104 int n_workers() { return _n_workers; }
5105
5106 void work(uint worker_id);
5107
5108 private:
5109 // Work method in support of parallel rescan ... of young gen spaces
5110 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5111 ContiguousSpace* space,
5112 HeapWord** chunk_array, size_t chunk_top);
5113
5114 // ... of dirty cards in old space
5115 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5116 Par_MarkRefsIntoAndScanClosure* cl);
5117
5118 // ... work stealing for the above
5119 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5120 };
5121
5122 // work_queue(i) is passed to the closure
5123 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5124 // also is passed to do_dirty_card_rescan_tasks() and to
5125 // do_work_steal() to select the i-th task_queue.
5126
5127 void CMSParRemarkTask::work(uint worker_id) {
5128 elapsedTimer _timer;
5129 ResourceMark rm;
5130 HandleMark hm;
5131
5132 // ---------- rescan from roots --------------
5133 _timer.start();
5134 GenCollectedHeap* gch = GenCollectedHeap::heap();
5135 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5136 _collector->_span, _collector->ref_processor(),
5137 &(_collector->_markBitMap),
5138 work_queue(worker_id), &(_collector->_revisitStack));
5139
5140 // Rescan young gen roots first since these are likely
5141 // coarsely partitioned and may, on that account, constitute
5142 // the critical path; thus, it's best to start off that
5143 // work first.
5144 // ---------- young gen roots --------------
5145 {
5146 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5147 EdenSpace* eden_space = dng->eden();
5148 ContiguousSpace* from_space = dng->from();
5149 ContiguousSpace* to_space = dng->to();
5150
5151 HeapWord** eca = _collector->_eden_chunk_array;
5152 size_t ect = _collector->_eden_chunk_index;
5153 HeapWord** sca = _collector->_survivor_chunk_array;
5154 size_t sct = _collector->_survivor_chunk_index;
5155
5156 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5157 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5158
5159 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5160 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5161 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5162
5163 _timer.stop();
5164 if (PrintCMSStatistics != 0) {
5165 gclog_or_tty->print_cr(
5166 "Finished young gen rescan work in %dth thread: %3.3f sec",
5167 worker_id, _timer.seconds());
5168 }
5169 }
5170
5171 // ---------- remaining roots --------------
5172 _timer.reset();
5173 _timer.start();
5174 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5175 false, // yg was scanned above
5176 false, // this is parallel code
5177 true, // collecting perm gen
5178 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5179 &par_mrias_cl,
5180 true, // walk all of code cache if (so & SO_CodeCache)
5181 NULL);
5182 assert(_collector->should_unload_classes()
5183 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5184 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5185 _timer.stop();
5186 if (PrintCMSStatistics != 0) {
5187 gclog_or_tty->print_cr(
5188 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5189 worker_id, _timer.seconds());
5190 }
5191
5192 // ---------- rescan dirty cards ------------
5193 _timer.reset();
5194 _timer.start();
5195
5196 // Do the rescan tasks for each of the two spaces
5197 // (cms_space and perm_space) in turn.
5198 // "worker_id" is passed to select the task_queue for "worker_id"
5199 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5200 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5201 _timer.stop();
5202 if (PrintCMSStatistics != 0) {
5203 gclog_or_tty->print_cr(
5204 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5205 worker_id, _timer.seconds());
5206 }
5207
5208 // ---------- steal work from other threads ...
5209 // ---------- ... and drain overflow list.
5210 _timer.reset();
5211 _timer.start();
5212 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5213 _timer.stop();
5214 if (PrintCMSStatistics != 0) {
5215 gclog_or_tty->print_cr(
5216 "Finished work stealing in %dth thread: %3.3f sec",
5217 worker_id, _timer.seconds());
5218 }
5219 }
5220
5221 // Note that parameter "i" is not used.
5222 void
5223 CMSParRemarkTask::do_young_space_rescan(int i,
5224 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5225 HeapWord** chunk_array, size_t chunk_top) {
5226 // Until all tasks completed:
5227 // . claim an unclaimed task
5228 // . compute region boundaries corresponding to task claimed
5229 // using chunk_array
5230 // . par_oop_iterate(cl) over that region
5231
5232 ResourceMark rm;
5233 HandleMark hm;
5234
5235 SequentialSubTasksDone* pst = space->par_seq_tasks();
5236 assert(pst->valid(), "Uninitialized use?");
5237
5238 uint nth_task = 0;
5239 uint n_tasks = pst->n_tasks();
5240
5241 HeapWord *start, *end;
5242 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5243 // We claimed task # nth_task; compute its boundaries.
5244 if (chunk_top == 0) { // no samples were taken
5245 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5246 start = space->bottom();
5247 end = space->top();
5248 } else if (nth_task == 0) {
5249 start = space->bottom();
5250 end = chunk_array[nth_task];
5251 } else if (nth_task < (uint)chunk_top) {
5252 assert(nth_task >= 1, "Control point invariant");
5253 start = chunk_array[nth_task - 1];
5254 end = chunk_array[nth_task];
5255 } else {
5256 assert(nth_task == (uint)chunk_top, "Control point invariant");
5257 start = chunk_array[chunk_top - 1];
5258 end = space->top();
5259 }
5260 MemRegion mr(start, end);
5261 // Verify that mr is in space
5262 assert(mr.is_empty() || space->used_region().contains(mr),
5263 "Should be in space");
5264 // Verify that "start" is an object boundary
5265 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5266 "Should be an oop");
5267 space->par_oop_iterate(mr, cl);
5268 }
5269 pst->all_tasks_completed();
5270 }
5271
5272 void
5273 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5274 CompactibleFreeListSpace* sp, int i,
5275 Par_MarkRefsIntoAndScanClosure* cl) {
5276 // Until all tasks completed:
5277 // . claim an unclaimed task
5278 // . compute region boundaries corresponding to task claimed
5279 // . transfer dirty bits ct->mut for that region
5280 // . apply rescanclosure to dirty mut bits for that region
5281
5282 ResourceMark rm;
5283 HandleMark hm;
5284
5285 OopTaskQueue* work_q = work_queue(i);
5286 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5287 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5288 // CAUTION: This closure has state that persists across calls to
5289 // the work method dirty_range_iterate_clear() in that it has
5290 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5291 // use of that state in the imbedded UpwardsObjectClosure instance
5292 // assumes that the cards are always iterated (even if in parallel
5293 // by several threads) in monotonically increasing order per each
5294 // thread. This is true of the implementation below which picks
5295 // card ranges (chunks) in monotonically increasing order globally
5296 // and, a-fortiori, in monotonically increasing order per thread
5297 // (the latter order being a subsequence of the former).
5298 // If the work code below is ever reorganized into a more chaotic
5299 // work-partitioning form than the current "sequential tasks"
5300 // paradigm, the use of that persistent state will have to be
5301 // revisited and modified appropriately. See also related
5302 // bug 4756801 work on which should examine this code to make
5303 // sure that the changes there do not run counter to the
5304 // assumptions made here and necessary for correctness and
5305 // efficiency. Note also that this code might yield inefficient
5306 // behaviour in the case of very large objects that span one or
5307 // more work chunks. Such objects would potentially be scanned
5308 // several times redundantly. Work on 4756801 should try and
5309 // address that performance anomaly if at all possible. XXX
5310 MemRegion full_span = _collector->_span;
5311 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5312 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5313 MarkFromDirtyCardsClosure
5314 greyRescanClosure(_collector, full_span, // entire span of interest
5315 sp, bm, work_q, rs, cl);
5316
5317 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5318 assert(pst->valid(), "Uninitialized use?");
5319 uint nth_task = 0;
5320 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5321 MemRegion span = sp->used_region();
5322 HeapWord* start_addr = span.start();
5323 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5324 alignment);
5325 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5326 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5327 start_addr, "Check alignment");
5328 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5329 chunk_size, "Check alignment");
5330
5331 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5332 // Having claimed the nth_task, compute corresponding mem-region,
5333 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5334 // The alignment restriction ensures that we do not need any
5335 // synchronization with other gang-workers while setting or
5336 // clearing bits in thus chunk of the MUT.
5337 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5338 start_addr + (nth_task+1)*chunk_size);
5339 // The last chunk's end might be way beyond end of the
5340 // used region. In that case pull back appropriately.
5341 if (this_span.end() > end_addr) {
5342 this_span.set_end(end_addr);
5343 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5344 }
5345 // Iterate over the dirty cards covering this chunk, marking them
5346 // precleaned, and setting the corresponding bits in the mod union
5347 // table. Since we have been careful to partition at Card and MUT-word
5348 // boundaries no synchronization is needed between parallel threads.
5349 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5350 &modUnionClosure);
5351
5352 // Having transferred these marks into the modUnionTable,
5353 // rescan the marked objects on the dirty cards in the modUnionTable.
5354 // Even if this is at a synchronous collection, the initial marking
5355 // may have been done during an asynchronous collection so there
5356 // may be dirty bits in the mod-union table.
5357 _collector->_modUnionTable.dirty_range_iterate_clear(
5358 this_span, &greyRescanClosure);
5359 _collector->_modUnionTable.verifyNoOneBitsInRange(
5360 this_span.start(),
5361 this_span.end());
5362 }
5363 pst->all_tasks_completed(); // declare that i am done
5364 }
5365
5366 // . see if we can share work_queues with ParNew? XXX
5367 void
5368 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5369 int* seed) {
5370 OopTaskQueue* work_q = work_queue(i);
5371 NOT_PRODUCT(int num_steals = 0;)
5372 oop obj_to_scan;
5373 CMSBitMap* bm = &(_collector->_markBitMap);
5374
5375 while (true) {
5376 // Completely finish any left over work from (an) earlier round(s)
5377 cl->trim_queue(0);
5378 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5379 (size_t)ParGCDesiredObjsFromOverflowList);
5380 // Now check if there's any work in the overflow list
5381 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5382 // only affects the number of attempts made to get work from the
5383 // overflow list and does not affect the number of workers. Just
5384 // pass ParallelGCThreads so this behavior is unchanged.
5385 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5386 work_q,
5387 ParallelGCThreads)) {
5388 // found something in global overflow list;
5389 // not yet ready to go stealing work from others.
5390 // We'd like to assert(work_q->size() != 0, ...)
5391 // because we just took work from the overflow list,
5392 // but of course we can't since all of that could have
5393 // been already stolen from us.
5394 // "He giveth and He taketh away."
5395 continue;
5396 }
5397 // Verify that we have no work before we resort to stealing
5398 assert(work_q->size() == 0, "Have work, shouldn't steal");
5399 // Try to steal from other queues that have work
5400 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5401 NOT_PRODUCT(num_steals++;)
5402 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5403 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5404 // Do scanning work
5405 obj_to_scan->oop_iterate(cl);
5406 // Loop around, finish this work, and try to steal some more
5407 } else if (terminator()->offer_termination()) {
5408 break; // nirvana from the infinite cycle
5409 }
5410 }
5411 NOT_PRODUCT(
5412 if (PrintCMSStatistics != 0) {
5413 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5414 }
5415 )
5416 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5417 "Else our work is not yet done");
5418 }
5419
5420 // Return a thread-local PLAB recording array, as appropriate.
5421 void* CMSCollector::get_data_recorder(int thr_num) {
5422 if (_survivor_plab_array != NULL &&
5423 (CMSPLABRecordAlways ||
5424 (_collectorState > Marking && _collectorState < FinalMarking))) {
5425 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5426 ChunkArray* ca = &_survivor_plab_array[thr_num];
5427 ca->reset(); // clear it so that fresh data is recorded
5428 return (void*) ca;
5429 } else {
5430 return NULL;
5431 }
5432 }
5433
5434 // Reset all the thread-local PLAB recording arrays
5435 void CMSCollector::reset_survivor_plab_arrays() {
5436 for (uint i = 0; i < ParallelGCThreads; i++) {
5437 _survivor_plab_array[i].reset();
5438 }
5439 }
5440
5441 // Merge the per-thread plab arrays into the global survivor chunk
5442 // array which will provide the partitioning of the survivor space
5443 // for CMS rescan.
5444 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5445 int no_of_gc_threads) {
5446 assert(_survivor_plab_array != NULL, "Error");
5447 assert(_survivor_chunk_array != NULL, "Error");
5448 assert(_collectorState == FinalMarking, "Error");
5449 for (int j = 0; j < no_of_gc_threads; j++) {
5450 _cursor[j] = 0;
5451 }
5452 HeapWord* top = surv->top();
5453 size_t i;
5454 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5455 HeapWord* min_val = top; // Higher than any PLAB address
5456 uint min_tid = 0; // position of min_val this round
5457 for (int j = 0; j < no_of_gc_threads; j++) {
5458 ChunkArray* cur_sca = &_survivor_plab_array[j];
5459 if (_cursor[j] == cur_sca->end()) {
5460 continue;
5461 }
5462 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5463 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5464 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5465 if (cur_val < min_val) {
5466 min_tid = j;
5467 min_val = cur_val;
5468 } else {
5469 assert(cur_val < top, "All recorded addresses should be less");
5470 }
5471 }
5472 // At this point min_val and min_tid are respectively
5473 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5474 // and the thread (j) that witnesses that address.
5475 // We record this address in the _survivor_chunk_array[i]
5476 // and increment _cursor[min_tid] prior to the next round i.
5477 if (min_val == top) {
5478 break;
5479 }
5480 _survivor_chunk_array[i] = min_val;
5481 _cursor[min_tid]++;
5482 }
5483 // We are all done; record the size of the _survivor_chunk_array
5484 _survivor_chunk_index = i; // exclusive: [0, i)
5485 if (PrintCMSStatistics > 0) {
5486 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5487 }
5488 // Verify that we used up all the recorded entries
5489 #ifdef ASSERT
5490 size_t total = 0;
5491 for (int j = 0; j < no_of_gc_threads; j++) {
5492 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5493 total += _cursor[j];
5494 }
5495 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5496 // Check that the merged array is in sorted order
5497 if (total > 0) {
5498 for (size_t i = 0; i < total - 1; i++) {
5499 if (PrintCMSStatistics > 0) {
5500 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5501 i, _survivor_chunk_array[i]);
5502 }
5503 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5504 "Not sorted");
5505 }
5506 }
5507 #endif // ASSERT
5508 }
5509
5510 // Set up the space's par_seq_tasks structure for work claiming
5511 // for parallel rescan of young gen.
5512 // See ParRescanTask where this is currently used.
5513 void
5514 CMSCollector::
5515 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5516 assert(n_threads > 0, "Unexpected n_threads argument");
5517 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5518
5519 // Eden space
5520 {
5521 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5522 assert(!pst->valid(), "Clobbering existing data?");
5523 // Each valid entry in [0, _eden_chunk_index) represents a task.
5524 size_t n_tasks = _eden_chunk_index + 1;
5525 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5526 // Sets the condition for completion of the subtask (how many threads
5527 // need to finish in order to be done).
5528 pst->set_n_threads(n_threads);
5529 pst->set_n_tasks((int)n_tasks);
5530 }
5531
5532 // Merge the survivor plab arrays into _survivor_chunk_array
5533 if (_survivor_plab_array != NULL) {
5534 merge_survivor_plab_arrays(dng->from(), n_threads);
5535 } else {
5536 assert(_survivor_chunk_index == 0, "Error");
5537 }
5538
5539 // To space
5540 {
5541 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5542 assert(!pst->valid(), "Clobbering existing data?");
5543 // Sets the condition for completion of the subtask (how many threads
5544 // need to finish in order to be done).
5545 pst->set_n_threads(n_threads);
5546 pst->set_n_tasks(1);
5547 assert(pst->valid(), "Error");
5548 }
5549
5550 // From space
5551 {
5552 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5553 assert(!pst->valid(), "Clobbering existing data?");
5554 size_t n_tasks = _survivor_chunk_index + 1;
5555 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5556 // Sets the condition for completion of the subtask (how many threads
5557 // need to finish in order to be done).
5558 pst->set_n_threads(n_threads);
5559 pst->set_n_tasks((int)n_tasks);
5560 assert(pst->valid(), "Error");
5561 }
5562 }
5563
5564 // Parallel version of remark
5565 void CMSCollector::do_remark_parallel() {
5566 GenCollectedHeap* gch = GenCollectedHeap::heap();
5567 FlexibleWorkGang* workers = gch->workers();
5568 assert(workers != NULL, "Need parallel worker threads.");
5569 // Choose to use the number of GC workers most recently set
5570 // into "active_workers". If active_workers is not set, set it
5571 // to ParallelGCThreads.
5572 int n_workers = workers->active_workers();
5573 if (n_workers == 0) {
5574 assert(n_workers > 0, "Should have been set during scavenge");
5575 n_workers = ParallelGCThreads;
5576 workers->set_active_workers(n_workers);
5577 }
5578 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5579 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5580
5581 CMSParRemarkTask tsk(this,
5582 cms_space, perm_space,
5583 n_workers, workers, task_queues());
5584
5585 // Set up for parallel process_strong_roots work.
5586 gch->set_par_threads(n_workers);
5587 // We won't be iterating over the cards in the card table updating
5588 // the younger_gen cards, so we shouldn't call the following else
5589 // the verification code as well as subsequent younger_refs_iterate
5590 // code would get confused. XXX
5591 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5592
5593 // The young gen rescan work will not be done as part of
5594 // process_strong_roots (which currently doesn't knw how to
5595 // parallelize such a scan), but rather will be broken up into
5596 // a set of parallel tasks (via the sampling that the [abortable]
5597 // preclean phase did of EdenSpace, plus the [two] tasks of
5598 // scanning the [two] survivor spaces. Further fine-grain
5599 // parallelization of the scanning of the survivor spaces
5600 // themselves, and of precleaning of the younger gen itself
5601 // is deferred to the future.
5602 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5603
5604 // The dirty card rescan work is broken up into a "sequence"
5605 // of parallel tasks (per constituent space) that are dynamically
5606 // claimed by the parallel threads.
5607 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5608 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5609
5610 // It turns out that even when we're using 1 thread, doing the work in a
5611 // separate thread causes wide variance in run times. We can't help this
5612 // in the multi-threaded case, but we special-case n=1 here to get
5613 // repeatable measurements of the 1-thread overhead of the parallel code.
5614 if (n_workers > 1) {
5615 // Make refs discovery MT-safe, if it isn't already: it may not
5616 // necessarily be so, since it's possible that we are doing
5617 // ST marking.
5618 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5619 GenCollectedHeap::StrongRootsScope srs(gch);
5620 workers->run_task(&tsk);
5621 } else {
5622 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5623 GenCollectedHeap::StrongRootsScope srs(gch);
5624 tsk.work(0);
5625 }
5626 gch->set_par_threads(0); // 0 ==> non-parallel.
5627 // restore, single-threaded for now, any preserved marks
5628 // as a result of work_q overflow
5629 restore_preserved_marks_if_any();
5630 }
5631
5632 // Non-parallel version of remark
5633 void CMSCollector::do_remark_non_parallel() {
5634 ResourceMark rm;
5635 HandleMark hm;
5636 GenCollectedHeap* gch = GenCollectedHeap::heap();
5637 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5638
5639 MarkRefsIntoAndScanClosure
5640 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5641 &_markStack, &_revisitStack, this,
5642 false /* should_yield */, false /* not precleaning */);
5643 MarkFromDirtyCardsClosure
5644 markFromDirtyCardsClosure(this, _span,
5645 NULL, // space is set further below
5646 &_markBitMap, &_markStack, &_revisitStack,
5647 &mrias_cl);
5648 {
5649 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5650 // Iterate over the dirty cards, setting the corresponding bits in the
5651 // mod union table.
5652 {
5653 ModUnionClosure modUnionClosure(&_modUnionTable);
5654 _ct->ct_bs()->dirty_card_iterate(
5655 _cmsGen->used_region(),
5656 &modUnionClosure);
5657 _ct->ct_bs()->dirty_card_iterate(
5658 _permGen->used_region(),
5659 &modUnionClosure);
5660 }
5661 // Having transferred these marks into the modUnionTable, we just need
5662 // to rescan the marked objects on the dirty cards in the modUnionTable.
5663 // The initial marking may have been done during an asynchronous
5664 // collection so there may be dirty bits in the mod-union table.
5665 const int alignment =
5666 CardTableModRefBS::card_size * BitsPerWord;
5667 {
5668 // ... First handle dirty cards in CMS gen
5669 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5670 MemRegion ur = _cmsGen->used_region();
5671 HeapWord* lb = ur.start();
5672 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5673 MemRegion cms_span(lb, ub);
5674 _modUnionTable.dirty_range_iterate_clear(cms_span,
5675 &markFromDirtyCardsClosure);
5676 verify_work_stacks_empty();
5677 if (PrintCMSStatistics != 0) {
5678 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5679 markFromDirtyCardsClosure.num_dirty_cards());
5680 }
5681 }
5682 {
5683 // .. and then repeat for dirty cards in perm gen
5684 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5685 MemRegion ur = _permGen->used_region();
5686 HeapWord* lb = ur.start();
5687 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5688 MemRegion perm_span(lb, ub);
5689 _modUnionTable.dirty_range_iterate_clear(perm_span,
5690 &markFromDirtyCardsClosure);
5691 verify_work_stacks_empty();
5692 if (PrintCMSStatistics != 0) {
5693 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5694 markFromDirtyCardsClosure.num_dirty_cards());
5695 }
5696 }
5697 }
5698 if (VerifyDuringGC &&
5699 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5700 HandleMark hm; // Discard invalid handles created during verification
5701 Universe::verify();
5702 }
5703 {
5704 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5705
5706 verify_work_stacks_empty();
5707
5708 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5709 GenCollectedHeap::StrongRootsScope srs(gch);
5710 gch->gen_process_strong_roots(_cmsGen->level(),
5711 true, // younger gens as roots
5712 false, // use the local StrongRootsScope
5713 true, // collecting perm gen
5714 SharedHeap::ScanningOption(roots_scanning_options()),
5715 &mrias_cl,
5716 true, // walk code active on stacks
5717 NULL);
5718 assert(should_unload_classes()
5719 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5720 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5721 }
5722 verify_work_stacks_empty();
5723 // Restore evacuated mark words, if any, used for overflow list links
5724 if (!CMSOverflowEarlyRestoration) {
5725 restore_preserved_marks_if_any();
5726 }
5727 verify_overflow_empty();
5728 }
5729
5730 ////////////////////////////////////////////////////////
5731 // Parallel Reference Processing Task Proxy Class
5732 ////////////////////////////////////////////////////////
5733 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5734 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5735 CMSCollector* _collector;
5736 CMSBitMap* _mark_bit_map;
5737 const MemRegion _span;
5738 ProcessTask& _task;
5739
5740 public:
5741 CMSRefProcTaskProxy(ProcessTask& task,
5742 CMSCollector* collector,
5743 const MemRegion& span,
5744 CMSBitMap* mark_bit_map,
5745 AbstractWorkGang* workers,
5746 OopTaskQueueSet* task_queues):
5747 // XXX Should superclass AGTWOQ also know about AWG since it knows
5748 // about the task_queues used by the AWG? Then it could initialize
5749 // the terminator() object. See 6984287. The set_for_termination()
5750 // below is a temporary band-aid for the regression in 6984287.
5751 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5752 task_queues),
5753 _task(task),
5754 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5755 {
5756 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5757 "Inconsistency in _span");
5758 set_for_termination(workers->active_workers());
5759 }
5760
5761 OopTaskQueueSet* task_queues() { return queues(); }
5762
5763 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5764
5765 void do_work_steal(int i,
5766 CMSParDrainMarkingStackClosure* drain,
5767 CMSParKeepAliveClosure* keep_alive,
5768 int* seed);
5769
5770 virtual void work(uint worker_id);
5771 };
5772
5773 void CMSRefProcTaskProxy::work(uint worker_id) {
5774 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5775 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5776 _mark_bit_map,
5777 &_collector->_revisitStack,
5778 work_queue(worker_id));
5779 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5780 _mark_bit_map,
5781 &_collector->_revisitStack,
5782 work_queue(worker_id));
5783 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5784 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5785 if (_task.marks_oops_alive()) {
5786 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5787 _collector->hash_seed(worker_id));
5788 }
5789 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5790 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5791 }
5792
5793 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5794 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5795 EnqueueTask& _task;
5796
5797 public:
5798 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5799 : AbstractGangTask("Enqueue reference objects in parallel"),
5800 _task(task)
5801 { }
5802
5803 virtual void work(uint worker_id)
5804 {
5805 _task.work(worker_id);
5806 }
5807 };
5808
5809 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5810 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5811 OopTaskQueue* work_queue):
5812 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5813 _span(span),
5814 _bit_map(bit_map),
5815 _work_queue(work_queue),
5816 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5817 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5818 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5819 { }
5820
5821 // . see if we can share work_queues with ParNew? XXX
5822 void CMSRefProcTaskProxy::do_work_steal(int i,
5823 CMSParDrainMarkingStackClosure* drain,
5824 CMSParKeepAliveClosure* keep_alive,
5825 int* seed) {
5826 OopTaskQueue* work_q = work_queue(i);
5827 NOT_PRODUCT(int num_steals = 0;)
5828 oop obj_to_scan;
5829
5830 while (true) {
5831 // Completely finish any left over work from (an) earlier round(s)
5832 drain->trim_queue(0);
5833 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5834 (size_t)ParGCDesiredObjsFromOverflowList);
5835 // Now check if there's any work in the overflow list
5836 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5837 // only affects the number of attempts made to get work from the
5838 // overflow list and does not affect the number of workers. Just
5839 // pass ParallelGCThreads so this behavior is unchanged.
5840 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5841 work_q,
5842 ParallelGCThreads)) {
5843 // Found something in global overflow list;
5844 // not yet ready to go stealing work from others.
5845 // We'd like to assert(work_q->size() != 0, ...)
5846 // because we just took work from the overflow list,
5847 // but of course we can't, since all of that might have
5848 // been already stolen from us.
5849 continue;
5850 }
5851 // Verify that we have no work before we resort to stealing
5852 assert(work_q->size() == 0, "Have work, shouldn't steal");
5853 // Try to steal from other queues that have work
5854 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5855 NOT_PRODUCT(num_steals++;)
5856 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5857 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5858 // Do scanning work
5859 obj_to_scan->oop_iterate(keep_alive);
5860 // Loop around, finish this work, and try to steal some more
5861 } else if (terminator()->offer_termination()) {
5862 break; // nirvana from the infinite cycle
5863 }
5864 }
5865 NOT_PRODUCT(
5866 if (PrintCMSStatistics != 0) {
5867 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5868 }
5869 )
5870 }
5871
5872 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5873 {
5874 GenCollectedHeap* gch = GenCollectedHeap::heap();
5875 FlexibleWorkGang* workers = gch->workers();
5876 assert(workers != NULL, "Need parallel worker threads.");
5877 CMSRefProcTaskProxy rp_task(task, &_collector,
5878 _collector.ref_processor()->span(),
5879 _collector.markBitMap(),
5880 workers, _collector.task_queues());
5881 workers->run_task(&rp_task);
5882 }
5883
5884 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5885 {
5886
5887 GenCollectedHeap* gch = GenCollectedHeap::heap();
5888 FlexibleWorkGang* workers = gch->workers();
5889 assert(workers != NULL, "Need parallel worker threads.");
5890 CMSRefEnqueueTaskProxy enq_task(task);
5891 workers->run_task(&enq_task);
5892 }
5893
5894 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5895
5896 ResourceMark rm;
5897 HandleMark hm;
5898
5899 ReferenceProcessor* rp = ref_processor();
5900 assert(rp->span().equals(_span), "Spans should be equal");
5901 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5902 // Process weak references.
5903 rp->setup_policy(clear_all_soft_refs);
5904 verify_work_stacks_empty();
5905
5906 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5907 &_markStack, &_revisitStack,
5908 false /* !preclean */);
5909 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5910 _span, &_markBitMap, &_markStack,
5911 &cmsKeepAliveClosure, false /* !preclean */);
5912 {
5913 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5914 if (rp->processing_is_mt()) {
5915 // Set the degree of MT here. If the discovery is done MT, there
5916 // may have been a different number of threads doing the discovery
5917 // and a different number of discovered lists may have Ref objects.
5918 // That is OK as long as the Reference lists are balanced (see
5919 // balance_all_queues() and balance_queues()).
5920 GenCollectedHeap* gch = GenCollectedHeap::heap();
5921 int active_workers = ParallelGCThreads;
5922 FlexibleWorkGang* workers = gch->workers();
5923 if (workers != NULL) {
5924 active_workers = workers->active_workers();
5925 // The expectation is that active_workers will have already
5926 // been set to a reasonable value. If it has not been set,
5927 // investigate.
5928 assert(active_workers > 0, "Should have been set during scavenge");
5929 }
5930 rp->set_active_mt_degree(active_workers);
5931 CMSRefProcTaskExecutor task_executor(*this);
5932 rp->process_discovered_references(&_is_alive_closure,
5933 &cmsKeepAliveClosure,
5934 &cmsDrainMarkingStackClosure,
5935 &task_executor,
5936 _gc_timer_cm);
5937 } else {
5938 rp->process_discovered_references(&_is_alive_closure,
5939 &cmsKeepAliveClosure,
5940 &cmsDrainMarkingStackClosure,
5941 NULL,
5942 _gc_timer_cm);
5943 }
5944 verify_work_stacks_empty();
5945 }
5946
5947 if (should_unload_classes()) {
5948 {
5949 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5950
5951 // Follow SystemDictionary roots and unload classes
5952 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5953
5954 // Follow CodeCache roots and unload any methods marked for unloading
5955 CodeCache::do_unloading(&_is_alive_closure,
5956 &cmsKeepAliveClosure,
5957 purged_class);
5958
5959 cmsDrainMarkingStackClosure.do_void();
5960 verify_work_stacks_empty();
5961
5962 // Update subklass/sibling/implementor links in KlassKlass descendants
5963 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5964 oop k;
5965 while ((k = _revisitStack.pop()) != NULL) {
5966 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5967 &_is_alive_closure,
5968 &cmsKeepAliveClosure);
5969 }
5970 assert(!ClassUnloading ||
5971 (_markStack.isEmpty() && overflow_list_is_empty()),
5972 "Should not have found new reachable objects");
5973 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5974 cmsDrainMarkingStackClosure.do_void();
5975 verify_work_stacks_empty();
5976 }
5977
5978 {
5979 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5980 // Clean up unreferenced symbols in symbol table.
5981 SymbolTable::unlink();
5982 }
5983 }
5984
5985 if (should_unload_classes() || !JavaObjectsInPerm) {
5986 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5987 // Now clean up stale oops in StringTable
5988 StringTable::unlink(&_is_alive_closure);
5989 }
5990
5991 verify_work_stacks_empty();
5992 // Restore any preserved marks as a result of mark stack or
5993 // work queue overflow
5994 restore_preserved_marks_if_any(); // done single-threaded for now
5995
5996 rp->set_enqueuing_is_done(true);
5997 if (rp->processing_is_mt()) {
5998 rp->balance_all_queues();
5999 CMSRefProcTaskExecutor task_executor(*this);
6000 rp->enqueue_discovered_references(&task_executor);
6001 } else {
6002 rp->enqueue_discovered_references(NULL);
6003 }
6004 rp->verify_no_references_recorded();
6005 assert(!rp->discovery_enabled(), "should have been disabled");
6006 }
6007
6008 #ifndef PRODUCT
6009 void CMSCollector::check_correct_thread_executing() {
6010 Thread* t = Thread::current();
6011 // Only the VM thread or the CMS thread should be here.
6012 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6013 "Unexpected thread type");
6014 // If this is the vm thread, the foreground process
6015 // should not be waiting. Note that _foregroundGCIsActive is
6016 // true while the foreground collector is waiting.
6017 if (_foregroundGCShouldWait) {
6018 // We cannot be the VM thread
6019 assert(t->is_ConcurrentGC_thread(),
6020 "Should be CMS thread");
6021 } else {
6022 // We can be the CMS thread only if we are in a stop-world
6023 // phase of CMS collection.
6024 if (t->is_ConcurrentGC_thread()) {
6025 assert(_collectorState == InitialMarking ||
6026 _collectorState == FinalMarking,
6027 "Should be a stop-world phase");
6028 // The CMS thread should be holding the CMS_token.
6029 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6030 "Potential interference with concurrently "
6031 "executing VM thread");
6032 }
6033 }
6034 }
6035 #endif
6036
6037 void CMSCollector::sweep(bool asynch) {
6038 assert(_collectorState == Sweeping, "just checking");
6039 check_correct_thread_executing();
6040 verify_work_stacks_empty();
6041 verify_overflow_empty();
6042 increment_sweep_count();
6043 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6044
6045 _inter_sweep_timer.stop();
6046 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6047 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6048
6049 // PermGen verification support: If perm gen sweeping is disabled in
6050 // this cycle, we preserve the perm gen object "deadness" information
6051 // in the perm_gen_verify_bit_map. In order to do that we traverse
6052 // all blocks in perm gen and mark all dead objects.
6053 if (verifying() && !should_unload_classes()) {
6054 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6055 "Should have already been allocated");
6056 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6057 markBitMap(), perm_gen_verify_bit_map());
6058 if (asynch) {
6059 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6060 bitMapLock());
6061 _permGen->cmsSpace()->blk_iterate(&mdo);
6062 } else {
6063 // In the case of synchronous sweep, we already have
6064 // the requisite locks/tokens.
6065 _permGen->cmsSpace()->blk_iterate(&mdo);
6066 }
6067 }
6068
6069 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6070 _intra_sweep_timer.reset();
6071 _intra_sweep_timer.start();
6072 if (asynch) {
6073 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6074 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6075 // First sweep the old gen then the perm gen
6076 {
6077 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6078 bitMapLock());
6079 sweepWork(_cmsGen, asynch);
6080 }
6081
6082 // Now repeat for perm gen
6083 if (should_unload_classes()) {
6084 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6085 bitMapLock());
6086 sweepWork(_permGen, asynch);
6087 }
6088
6089 // Update Universe::_heap_*_at_gc figures.
6090 // We need all the free list locks to make the abstract state
6091 // transition from Sweeping to Resetting. See detailed note
6092 // further below.
6093 {
6094 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6095 _permGen->freelistLock());
6096 // Update heap occupancy information which is used as
6097 // input to soft ref clearing policy at the next gc.
6098 Universe::update_heap_info_at_gc();
6099 _collectorState = Resizing;
6100 }
6101 } else {
6102 // already have needed locks
6103 sweepWork(_cmsGen, asynch);
6104
6105 if (should_unload_classes()) {
6106 sweepWork(_permGen, asynch);
6107 }
6108 // Update heap occupancy information which is used as
6109 // input to soft ref clearing policy at the next gc.
6110 Universe::update_heap_info_at_gc();
6111 _collectorState = Resizing;
6112 }
6113 verify_work_stacks_empty();
6114 verify_overflow_empty();
6115
6116 _intra_sweep_timer.stop();
6117 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6118
6119 _inter_sweep_timer.reset();
6120 _inter_sweep_timer.start();
6121
6122 // We need to use a monotonically non-deccreasing time in ms
6123 // or we will see time-warp warnings and os::javaTimeMillis()
6124 // does not guarantee monotonicity.
6125 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6126 update_time_of_last_gc(now);
6127
6128 // NOTE on abstract state transitions:
6129 // Mutators allocate-live and/or mark the mod-union table dirty
6130 // based on the state of the collection. The former is done in
6131 // the interval [Marking, Sweeping] and the latter in the interval
6132 // [Marking, Sweeping). Thus the transitions into the Marking state
6133 // and out of the Sweeping state must be synchronously visible
6134 // globally to the mutators.
6135 // The transition into the Marking state happens with the world
6136 // stopped so the mutators will globally see it. Sweeping is
6137 // done asynchronously by the background collector so the transition
6138 // from the Sweeping state to the Resizing state must be done
6139 // under the freelistLock (as is the check for whether to
6140 // allocate-live and whether to dirty the mod-union table).
6141 assert(_collectorState == Resizing, "Change of collector state to"
6142 " Resizing must be done under the freelistLocks (plural)");
6143
6144 // Now that sweeping has been completed, we clear
6145 // the incremental_collection_failed flag,
6146 // thus inviting a younger gen collection to promote into
6147 // this generation. If such a promotion may still fail,
6148 // the flag will be set again when a young collection is
6149 // attempted.
6150 GenCollectedHeap* gch = GenCollectedHeap::heap();
6151 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6152 gch->update_full_collections_completed(_collection_count_start);
6153 }
6154
6155 // FIX ME!!! Looks like this belongs in CFLSpace, with
6156 // CMSGen merely delegating to it.
6157 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6158 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6159 HeapWord* minAddr = _cmsSpace->bottom();
6160 HeapWord* largestAddr =
6161 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6162 if (largestAddr == NULL) {
6163 // The dictionary appears to be empty. In this case
6164 // try to coalesce at the end of the heap.
6165 largestAddr = _cmsSpace->end();
6166 }
6167 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6168 size_t nearLargestOffset =
6169 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6170 if (PrintFLSStatistics != 0) {
6171 gclog_or_tty->print_cr(
6172 "CMS: Large Block: " PTR_FORMAT ";"
6173 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6174 largestAddr,
6175 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6176 }
6177 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6178 }
6179
6180 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6181 return addr >= _cmsSpace->nearLargestChunk();
6182 }
6183
6184 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6185 return _cmsSpace->find_chunk_at_end();
6186 }
6187
6188 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6189 bool full) {
6190 // The next lower level has been collected. Gather any statistics
6191 // that are of interest at this point.
6192 if (!full && (current_level + 1) == level()) {
6193 // Gather statistics on the young generation collection.
6194 collector()->stats().record_gc0_end(used());
6195 }
6196 }
6197
6198 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6199 GenCollectedHeap* gch = GenCollectedHeap::heap();
6200 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6201 "Wrong type of heap");
6202 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6203 gch->gen_policy()->size_policy();
6204 assert(sp->is_gc_cms_adaptive_size_policy(),
6205 "Wrong type of size policy");
6206 return sp;
6207 }
6208
6209 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6210 if (PrintGCDetails && Verbose) {
6211 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6212 }
6213 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6214 _debug_collection_type =
6215 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6216 if (PrintGCDetails && Verbose) {
6217 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6218 }
6219 }
6220
6221 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6222 bool asynch) {
6223 // We iterate over the space(s) underlying this generation,
6224 // checking the mark bit map to see if the bits corresponding
6225 // to specific blocks are marked or not. Blocks that are
6226 // marked are live and are not swept up. All remaining blocks
6227 // are swept up, with coalescing on-the-fly as we sweep up
6228 // contiguous free and/or garbage blocks:
6229 // We need to ensure that the sweeper synchronizes with allocators
6230 // and stop-the-world collectors. In particular, the following
6231 // locks are used:
6232 // . CMS token: if this is held, a stop the world collection cannot occur
6233 // . freelistLock: if this is held no allocation can occur from this
6234 // generation by another thread
6235 // . bitMapLock: if this is held, no other thread can access or update
6236 //
6237
6238 // Note that we need to hold the freelistLock if we use
6239 // block iterate below; else the iterator might go awry if
6240 // a mutator (or promotion) causes block contents to change
6241 // (for instance if the allocator divvies up a block).
6242 // If we hold the free list lock, for all practical purposes
6243 // young generation GC's can't occur (they'll usually need to
6244 // promote), so we might as well prevent all young generation
6245 // GC's while we do a sweeping step. For the same reason, we might
6246 // as well take the bit map lock for the entire duration
6247
6248 // check that we hold the requisite locks
6249 assert(have_cms_token(), "Should hold cms token");
6250 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6251 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6252 "Should possess CMS token to sweep");
6253 assert_lock_strong(gen->freelistLock());
6254 assert_lock_strong(bitMapLock());
6255
6256 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6257 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6258 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6259 _inter_sweep_estimate.padded_average(),
6260 _intra_sweep_estimate.padded_average());
6261 gen->setNearLargestChunk();
6262
6263 {
6264 SweepClosure sweepClosure(this, gen, &_markBitMap,
6265 CMSYield && asynch);
6266 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6267 // We need to free-up/coalesce garbage/blocks from a
6268 // co-terminal free run. This is done in the SweepClosure
6269 // destructor; so, do not remove this scope, else the
6270 // end-of-sweep-census below will be off by a little bit.
6271 }
6272 gen->cmsSpace()->sweep_completed();
6273 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6274 if (should_unload_classes()) { // unloaded classes this cycle,
6275 _concurrent_cycles_since_last_unload = 0; // ... reset count
6276 } else { // did not unload classes,
6277 _concurrent_cycles_since_last_unload++; // ... increment count
6278 }
6279 }
6280
6281 // Reset CMS data structures (for now just the marking bit map)
6282 // preparatory for the next cycle.
6283 void CMSCollector::reset(bool asynch) {
6284 GenCollectedHeap* gch = GenCollectedHeap::heap();
6285 CMSAdaptiveSizePolicy* sp = size_policy();
6286 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6287 if (asynch) {
6288 CMSTokenSyncWithLocks ts(true, bitMapLock());
6289
6290 // If the state is not "Resetting", the foreground thread
6291 // has done a collection and the resetting.
6292 if (_collectorState != Resetting) {
6293 assert(_collectorState == Idling, "The state should only change"
6294 " because the foreground collector has finished the collection");
6295 return;
6296 }
6297
6298 // Clear the mark bitmap (no grey objects to start with)
6299 // for the next cycle.
6300 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6301 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6302
6303 HeapWord* curAddr = _markBitMap.startWord();
6304 while (curAddr < _markBitMap.endWord()) {
6305 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6306 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6307 _markBitMap.clear_large_range(chunk);
6308 if (ConcurrentMarkSweepThread::should_yield() &&
6309 !foregroundGCIsActive() &&
6310 CMSYield) {
6311 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6312 "CMS thread should hold CMS token");
6313 assert_lock_strong(bitMapLock());
6314 bitMapLock()->unlock();
6315 ConcurrentMarkSweepThread::desynchronize(true);
6316 ConcurrentMarkSweepThread::acknowledge_yield_request();
6317 stopTimer();
6318 if (PrintCMSStatistics != 0) {
6319 incrementYields();
6320 }
6321 icms_wait();
6322
6323 // See the comment in coordinator_yield()
6324 for (unsigned i = 0; i < CMSYieldSleepCount &&
6325 ConcurrentMarkSweepThread::should_yield() &&
6326 !CMSCollector::foregroundGCIsActive(); ++i) {
6327 os::sleep(Thread::current(), 1, false);
6328 ConcurrentMarkSweepThread::acknowledge_yield_request();
6329 }
6330
6331 ConcurrentMarkSweepThread::synchronize(true);
6332 bitMapLock()->lock_without_safepoint_check();
6333 startTimer();
6334 }
6335 curAddr = chunk.end();
6336 }
6337 // A successful mostly concurrent collection has been done.
6338 // Because only the full (i.e., concurrent mode failure) collections
6339 // are being measured for gc overhead limits, clean the "near" flag
6340 // and count.
6341 sp->reset_gc_overhead_limit_count();
6342 _collectorState = Idling;
6343 } else {
6344 // already have the lock
6345 assert(_collectorState == Resetting, "just checking");
6346 assert_lock_strong(bitMapLock());
6347 _markBitMap.clear_all();
6348 _collectorState = Idling;
6349 }
6350
6351 // Stop incremental mode after a cycle completes, so that any future cycles
6352 // are triggered by allocation.
6353 stop_icms();
6354
6355 NOT_PRODUCT(
6356 if (RotateCMSCollectionTypes) {
6357 _cmsGen->rotate_debug_collection_type();
6358 }
6359 )
6360
6361 register_gc_end();
6362 }
6363
6364 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6365 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6366 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6367 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6368 TraceCollectorStats tcs(counters());
6369
6370 switch (op) {
6371 case CMS_op_checkpointRootsInitial: {
6372 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6373 checkpointRootsInitial(true); // asynch
6374 if (PrintGC) {
6375 _cmsGen->printOccupancy("initial-mark");
6376 }
6377 break;
6378 }
6379 case CMS_op_checkpointRootsFinal: {
6380 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6381 checkpointRootsFinal(true, // asynch
6382 false, // !clear_all_soft_refs
6383 false); // !init_mark_was_synchronous
6384 if (PrintGC) {
6385 _cmsGen->printOccupancy("remark");
6386 }
6387 break;
6388 }
6389 default:
6390 fatal("No such CMS_op");
6391 }
6392 }
6393
6394 #ifndef PRODUCT
6395 size_t const CMSCollector::skip_header_HeapWords() {
6396 return FreeChunk::header_size();
6397 }
6398
6399 // Try and collect here conditions that should hold when
6400 // CMS thread is exiting. The idea is that the foreground GC
6401 // thread should not be blocked if it wants to terminate
6402 // the CMS thread and yet continue to run the VM for a while
6403 // after that.
6404 void CMSCollector::verify_ok_to_terminate() const {
6405 assert(Thread::current()->is_ConcurrentGC_thread(),
6406 "should be called by CMS thread");
6407 assert(!_foregroundGCShouldWait, "should be false");
6408 // We could check here that all the various low-level locks
6409 // are not held by the CMS thread, but that is overkill; see
6410 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6411 // is checked.
6412 }
6413 #endif
6414
6415 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6416 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6417 "missing Printezis mark?");
6418 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6419 size_t size = pointer_delta(nextOneAddr + 1, addr);
6420 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6421 "alignment problem");
6422 assert(size >= 3, "Necessary for Printezis marks to work");
6423 return size;
6424 }
6425
6426 // A variant of the above (block_size_using_printezis_bits()) except
6427 // that we return 0 if the P-bits are not yet set.
6428 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6429 if (_markBitMap.isMarked(addr + 1)) {
6430 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6431 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6432 size_t size = pointer_delta(nextOneAddr + 1, addr);
6433 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6434 "alignment problem");
6435 assert(size >= 3, "Necessary for Printezis marks to work");
6436 return size;
6437 }
6438 return 0;
6439 }
6440
6441 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6442 size_t sz = 0;
6443 oop p = (oop)addr;
6444 if (p->klass_or_null() != NULL && p->is_parsable()) {
6445 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6446 } else {
6447 sz = block_size_using_printezis_bits(addr);
6448 }
6449 assert(sz > 0, "size must be nonzero");
6450 HeapWord* next_block = addr + sz;
6451 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6452 CardTableModRefBS::card_size);
6453 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6454 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6455 "must be different cards");
6456 return next_card;
6457 }
6458
6459
6460 // CMS Bit Map Wrapper /////////////////////////////////////////
6461
6462 // Construct a CMS bit map infrastructure, but don't create the
6463 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6464 // further below.
6465 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6466 _bm(),
6467 _shifter(shifter),
6468 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6469 {
6470 _bmStartWord = 0;
6471 _bmWordSize = 0;
6472 }
6473
6474 bool CMSBitMap::allocate(MemRegion mr) {
6475 _bmStartWord = mr.start();
6476 _bmWordSize = mr.word_size();
6477 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6478 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6479 if (!brs.is_reserved()) {
6480 warning("CMS bit map allocation failure");
6481 return false;
6482 }
6483 // For now we'll just commit all of the bit map up fromt.
6484 // Later on we'll try to be more parsimonious with swap.
6485 if (!_virtual_space.initialize(brs, brs.size())) {
6486 warning("CMS bit map backing store failure");
6487 return false;
6488 }
6489 assert(_virtual_space.committed_size() == brs.size(),
6490 "didn't reserve backing store for all of CMS bit map?");
6491 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6492 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6493 _bmWordSize, "inconsistency in bit map sizing");
6494 _bm.set_size(_bmWordSize >> _shifter);
6495
6496 // bm.clear(); // can we rely on getting zero'd memory? verify below
6497 assert(isAllClear(),
6498 "Expected zero'd memory from ReservedSpace constructor");
6499 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6500 "consistency check");
6501 return true;
6502 }
6503
6504 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6505 HeapWord *next_addr, *end_addr, *last_addr;
6506 assert_locked();
6507 assert(covers(mr), "out-of-range error");
6508 // XXX assert that start and end are appropriately aligned
6509 for (next_addr = mr.start(), end_addr = mr.end();
6510 next_addr < end_addr; next_addr = last_addr) {
6511 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6512 last_addr = dirty_region.end();
6513 if (!dirty_region.is_empty()) {
6514 cl->do_MemRegion(dirty_region);
6515 } else {
6516 assert(last_addr == end_addr, "program logic");
6517 return;
6518 }
6519 }
6520 }
6521
6522 #ifndef PRODUCT
6523 void CMSBitMap::assert_locked() const {
6524 CMSLockVerifier::assert_locked(lock());
6525 }
6526
6527 bool CMSBitMap::covers(MemRegion mr) const {
6528 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6529 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6530 "size inconsistency");
6531 return (mr.start() >= _bmStartWord) &&
6532 (mr.end() <= endWord());
6533 }
6534
6535 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6536 return (start >= _bmStartWord && (start + size) <= endWord());
6537 }
6538
6539 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6540 // verify that there are no 1 bits in the interval [left, right)
6541 FalseBitMapClosure falseBitMapClosure;
6542 iterate(&falseBitMapClosure, left, right);
6543 }
6544
6545 void CMSBitMap::region_invariant(MemRegion mr)
6546 {
6547 assert_locked();
6548 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6549 assert(!mr.is_empty(), "unexpected empty region");
6550 assert(covers(mr), "mr should be covered by bit map");
6551 // convert address range into offset range
6552 size_t start_ofs = heapWordToOffset(mr.start());
6553 // Make sure that end() is appropriately aligned
6554 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6555 (1 << (_shifter+LogHeapWordSize))),
6556 "Misaligned mr.end()");
6557 size_t end_ofs = heapWordToOffset(mr.end());
6558 assert(end_ofs > start_ofs, "Should mark at least one bit");
6559 }
6560
6561 #endif
6562
6563 bool CMSMarkStack::allocate(size_t size) {
6564 // allocate a stack of the requisite depth
6565 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6566 size * sizeof(oop)));
6567 if (!rs.is_reserved()) {
6568 warning("CMSMarkStack allocation failure");
6569 return false;
6570 }
6571 if (!_virtual_space.initialize(rs, rs.size())) {
6572 warning("CMSMarkStack backing store failure");
6573 return false;
6574 }
6575 assert(_virtual_space.committed_size() == rs.size(),
6576 "didn't reserve backing store for all of CMS stack?");
6577 _base = (oop*)(_virtual_space.low());
6578 _index = 0;
6579 _capacity = size;
6580 NOT_PRODUCT(_max_depth = 0);
6581 return true;
6582 }
6583
6584 // XXX FIX ME !!! In the MT case we come in here holding a
6585 // leaf lock. For printing we need to take a further lock
6586 // which has lower rank. We need to recallibrate the two
6587 // lock-ranks involved in order to be able to rpint the
6588 // messages below. (Or defer the printing to the caller.
6589 // For now we take the expedient path of just disabling the
6590 // messages for the problematic case.)
6591 void CMSMarkStack::expand() {
6592 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6593 if (_capacity == MarkStackSizeMax) {
6594 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6595 // We print a warning message only once per CMS cycle.
6596 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6597 }
6598 return;
6599 }
6600 // Double capacity if possible
6601 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6602 // Do not give up existing stack until we have managed to
6603 // get the double capacity that we desired.
6604 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6605 new_capacity * sizeof(oop)));
6606 if (rs.is_reserved()) {
6607 // Release the backing store associated with old stack
6608 _virtual_space.release();
6609 // Reinitialize virtual space for new stack
6610 if (!_virtual_space.initialize(rs, rs.size())) {
6611 fatal("Not enough swap for expanded marking stack");
6612 }
6613 _base = (oop*)(_virtual_space.low());
6614 _index = 0;
6615 _capacity = new_capacity;
6616 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6617 // Failed to double capacity, continue;
6618 // we print a detail message only once per CMS cycle.
6619 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6620 SIZE_FORMAT"K",
6621 _capacity / K, new_capacity / K);
6622 }
6623 }
6624
6625
6626 // Closures
6627 // XXX: there seems to be a lot of code duplication here;
6628 // should refactor and consolidate common code.
6629
6630 // This closure is used to mark refs into the CMS generation in
6631 // the CMS bit map. Called at the first checkpoint. This closure
6632 // assumes that we do not need to re-mark dirty cards; if the CMS
6633 // generation on which this is used is not an oldest (modulo perm gen)
6634 // generation then this will lose younger_gen cards!
6635
6636 MarkRefsIntoClosure::MarkRefsIntoClosure(
6637 MemRegion span, CMSBitMap* bitMap):
6638 _span(span),
6639 _bitMap(bitMap)
6640 {
6641 assert(_ref_processor == NULL, "deliberately left NULL");
6642 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6643 }
6644
6645 void MarkRefsIntoClosure::do_oop(oop obj) {
6646 // if p points into _span, then mark corresponding bit in _markBitMap
6647 assert(obj->is_oop(), "expected an oop");
6648 HeapWord* addr = (HeapWord*)obj;
6649 if (_span.contains(addr)) {
6650 // this should be made more efficient
6651 _bitMap->mark(addr);
6652 }
6653 }
6654
6655 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6656 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6657
6658 // A variant of the above, used for CMS marking verification.
6659 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6660 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6661 _span(span),
6662 _verification_bm(verification_bm),
6663 _cms_bm(cms_bm)
6664 {
6665 assert(_ref_processor == NULL, "deliberately left NULL");
6666 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6667 }
6668
6669 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6670 // if p points into _span, then mark corresponding bit in _markBitMap
6671 assert(obj->is_oop(), "expected an oop");
6672 HeapWord* addr = (HeapWord*)obj;
6673 if (_span.contains(addr)) {
6674 _verification_bm->mark(addr);
6675 if (!_cms_bm->isMarked(addr)) {
6676 oop(addr)->print();
6677 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6678 fatal("... aborting");
6679 }
6680 }
6681 }
6682
6683 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6684 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6685
6686 //////////////////////////////////////////////////
6687 // MarkRefsIntoAndScanClosure
6688 //////////////////////////////////////////////////
6689
6690 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6691 ReferenceProcessor* rp,
6692 CMSBitMap* bit_map,
6693 CMSBitMap* mod_union_table,
6694 CMSMarkStack* mark_stack,
6695 CMSMarkStack* revisit_stack,
6696 CMSCollector* collector,
6697 bool should_yield,
6698 bool concurrent_precleaning):
6699 _collector(collector),
6700 _span(span),
6701 _bit_map(bit_map),
6702 _mark_stack(mark_stack),
6703 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6704 mark_stack, revisit_stack, concurrent_precleaning),
6705 _yield(should_yield),
6706 _concurrent_precleaning(concurrent_precleaning),
6707 _freelistLock(NULL)
6708 {
6709 _ref_processor = rp;
6710 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6711 }
6712
6713 // This closure is used to mark refs into the CMS generation at the
6714 // second (final) checkpoint, and to scan and transitively follow
6715 // the unmarked oops. It is also used during the concurrent precleaning
6716 // phase while scanning objects on dirty cards in the CMS generation.
6717 // The marks are made in the marking bit map and the marking stack is
6718 // used for keeping the (newly) grey objects during the scan.
6719 // The parallel version (Par_...) appears further below.
6720 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6721 if (obj != NULL) {
6722 assert(obj->is_oop(), "expected an oop");
6723 HeapWord* addr = (HeapWord*)obj;
6724 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6725 assert(_collector->overflow_list_is_empty(),
6726 "overflow list should be empty");
6727 if (_span.contains(addr) &&
6728 !_bit_map->isMarked(addr)) {
6729 // mark bit map (object is now grey)
6730 _bit_map->mark(addr);
6731 // push on marking stack (stack should be empty), and drain the
6732 // stack by applying this closure to the oops in the oops popped
6733 // from the stack (i.e. blacken the grey objects)
6734 bool res = _mark_stack->push(obj);
6735 assert(res, "Should have space to push on empty stack");
6736 do {
6737 oop new_oop = _mark_stack->pop();
6738 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6739 assert(new_oop->is_parsable(), "Found unparsable oop");
6740 assert(_bit_map->isMarked((HeapWord*)new_oop),
6741 "only grey objects on this stack");
6742 // iterate over the oops in this oop, marking and pushing
6743 // the ones in CMS heap (i.e. in _span).
6744 new_oop->oop_iterate(&_pushAndMarkClosure);
6745 // check if it's time to yield
6746 do_yield_check();
6747 } while (!_mark_stack->isEmpty() ||
6748 (!_concurrent_precleaning && take_from_overflow_list()));
6749 // if marking stack is empty, and we are not doing this
6750 // during precleaning, then check the overflow list
6751 }
6752 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6753 assert(_collector->overflow_list_is_empty(),
6754 "overflow list was drained above");
6755 // We could restore evacuated mark words, if any, used for
6756 // overflow list links here because the overflow list is
6757 // provably empty here. That would reduce the maximum
6758 // size requirements for preserved_{oop,mark}_stack.
6759 // But we'll just postpone it until we are all done
6760 // so we can just stream through.
6761 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6762 _collector->restore_preserved_marks_if_any();
6763 assert(_collector->no_preserved_marks(), "No preserved marks");
6764 }
6765 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6766 "All preserved marks should have been restored above");
6767 }
6768 }
6769
6770 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6771 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6772
6773 void MarkRefsIntoAndScanClosure::do_yield_work() {
6774 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6775 "CMS thread should hold CMS token");
6776 assert_lock_strong(_freelistLock);
6777 assert_lock_strong(_bit_map->lock());
6778 // relinquish the free_list_lock and bitMaplock()
6779 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6780 _bit_map->lock()->unlock();
6781 _freelistLock->unlock();
6782 ConcurrentMarkSweepThread::desynchronize(true);
6783 ConcurrentMarkSweepThread::acknowledge_yield_request();
6784 _collector->stopTimer();
6785 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6786 if (PrintCMSStatistics != 0) {
6787 _collector->incrementYields();
6788 }
6789 _collector->icms_wait();
6790
6791 // See the comment in coordinator_yield()
6792 for (unsigned i = 0;
6793 i < CMSYieldSleepCount &&
6794 ConcurrentMarkSweepThread::should_yield() &&
6795 !CMSCollector::foregroundGCIsActive();
6796 ++i) {
6797 os::sleep(Thread::current(), 1, false);
6798 ConcurrentMarkSweepThread::acknowledge_yield_request();
6799 }
6800
6801 ConcurrentMarkSweepThread::synchronize(true);
6802 _freelistLock->lock_without_safepoint_check();
6803 _bit_map->lock()->lock_without_safepoint_check();
6804 _collector->startTimer();
6805 }
6806
6807 ///////////////////////////////////////////////////////////
6808 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6809 // MarkRefsIntoAndScanClosure
6810 ///////////////////////////////////////////////////////////
6811 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6812 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6813 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6814 _span(span),
6815 _bit_map(bit_map),
6816 _work_queue(work_queue),
6817 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6818 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6819 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6820 revisit_stack)
6821 {
6822 _ref_processor = rp;
6823 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6824 }
6825
6826 // This closure is used to mark refs into the CMS generation at the
6827 // second (final) checkpoint, and to scan and transitively follow
6828 // the unmarked oops. The marks are made in the marking bit map and
6829 // the work_queue is used for keeping the (newly) grey objects during
6830 // the scan phase whence they are also available for stealing by parallel
6831 // threads. Since the marking bit map is shared, updates are
6832 // synchronized (via CAS).
6833 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6834 if (obj != NULL) {
6835 // Ignore mark word because this could be an already marked oop
6836 // that may be chained at the end of the overflow list.
6837 assert(obj->is_oop(true), "expected an oop");
6838 HeapWord* addr = (HeapWord*)obj;
6839 if (_span.contains(addr) &&
6840 !_bit_map->isMarked(addr)) {
6841 // mark bit map (object will become grey):
6842 // It is possible for several threads to be
6843 // trying to "claim" this object concurrently;
6844 // the unique thread that succeeds in marking the
6845 // object first will do the subsequent push on
6846 // to the work queue (or overflow list).
6847 if (_bit_map->par_mark(addr)) {
6848 // push on work_queue (which may not be empty), and trim the
6849 // queue to an appropriate length by applying this closure to
6850 // the oops in the oops popped from the stack (i.e. blacken the
6851 // grey objects)
6852 bool res = _work_queue->push(obj);
6853 assert(res, "Low water mark should be less than capacity?");
6854 trim_queue(_low_water_mark);
6855 } // Else, another thread claimed the object
6856 }
6857 }
6858 }
6859
6860 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6861 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6862
6863 // This closure is used to rescan the marked objects on the dirty cards
6864 // in the mod union table and the card table proper.
6865 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6866 oop p, MemRegion mr) {
6867
6868 size_t size = 0;
6869 HeapWord* addr = (HeapWord*)p;
6870 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6871 assert(_span.contains(addr), "we are scanning the CMS generation");
6872 // check if it's time to yield
6873 if (do_yield_check()) {
6874 // We yielded for some foreground stop-world work,
6875 // and we have been asked to abort this ongoing preclean cycle.
6876 return 0;
6877 }
6878 if (_bitMap->isMarked(addr)) {
6879 // it's marked; is it potentially uninitialized?
6880 if (p->klass_or_null() != NULL) {
6881 // If is_conc_safe is false, the object may be undergoing
6882 // change by the VM outside a safepoint. Don't try to
6883 // scan it, but rather leave it for the remark phase.
6884 if (CMSPermGenPrecleaningEnabled &&
6885 (!p->is_conc_safe() || !p->is_parsable())) {
6886 // Signal precleaning to redirty the card since
6887 // the klass pointer is already installed.
6888 assert(size == 0, "Initial value");
6889 } else {
6890 assert(p->is_parsable(), "must be parsable.");
6891 // an initialized object; ignore mark word in verification below
6892 // since we are running concurrent with mutators
6893 assert(p->is_oop(true), "should be an oop");
6894 if (p->is_objArray()) {
6895 // objArrays are precisely marked; restrict scanning
6896 // to dirty cards only.
6897 size = CompactibleFreeListSpace::adjustObjectSize(
6898 p->oop_iterate(_scanningClosure, mr));
6899 } else {
6900 // A non-array may have been imprecisely marked; we need
6901 // to scan object in its entirety.
6902 size = CompactibleFreeListSpace::adjustObjectSize(
6903 p->oop_iterate(_scanningClosure));
6904 }
6905 #ifdef DEBUG
6906 size_t direct_size =
6907 CompactibleFreeListSpace::adjustObjectSize(p->size());
6908 assert(size == direct_size, "Inconsistency in size");
6909 assert(size >= 3, "Necessary for Printezis marks to work");
6910 if (!_bitMap->isMarked(addr+1)) {
6911 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6912 } else {
6913 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6914 assert(_bitMap->isMarked(addr+size-1),
6915 "inconsistent Printezis mark");
6916 }
6917 #endif // DEBUG
6918 }
6919 } else {
6920 // an unitialized object
6921 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6922 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6923 size = pointer_delta(nextOneAddr + 1, addr);
6924 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6925 "alignment problem");
6926 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6927 // will dirty the card when the klass pointer is installed in the
6928 // object (signalling the completion of initialization).
6929 }
6930 } else {
6931 // Either a not yet marked object or an uninitialized object
6932 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6933 // An uninitialized object, skip to the next card, since
6934 // we may not be able to read its P-bits yet.
6935 assert(size == 0, "Initial value");
6936 } else {
6937 // An object not (yet) reached by marking: we merely need to
6938 // compute its size so as to go look at the next block.
6939 assert(p->is_oop(true), "should be an oop");
6940 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6941 }
6942 }
6943 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6944 return size;
6945 }
6946
6947 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6948 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6949 "CMS thread should hold CMS token");
6950 assert_lock_strong(_freelistLock);
6951 assert_lock_strong(_bitMap->lock());
6952 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6953 // relinquish the free_list_lock and bitMaplock()
6954 _bitMap->lock()->unlock();
6955 _freelistLock->unlock();
6956 ConcurrentMarkSweepThread::desynchronize(true);
6957 ConcurrentMarkSweepThread::acknowledge_yield_request();
6958 _collector->stopTimer();
6959 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6960 if (PrintCMSStatistics != 0) {
6961 _collector->incrementYields();
6962 }
6963 _collector->icms_wait();
6964
6965 // See the comment in coordinator_yield()
6966 for (unsigned i = 0; i < CMSYieldSleepCount &&
6967 ConcurrentMarkSweepThread::should_yield() &&
6968 !CMSCollector::foregroundGCIsActive(); ++i) {
6969 os::sleep(Thread::current(), 1, false);
6970 ConcurrentMarkSweepThread::acknowledge_yield_request();
6971 }
6972
6973 ConcurrentMarkSweepThread::synchronize(true);
6974 _freelistLock->lock_without_safepoint_check();
6975 _bitMap->lock()->lock_without_safepoint_check();
6976 _collector->startTimer();
6977 }
6978
6979
6980 //////////////////////////////////////////////////////////////////
6981 // SurvivorSpacePrecleanClosure
6982 //////////////////////////////////////////////////////////////////
6983 // This (single-threaded) closure is used to preclean the oops in
6984 // the survivor spaces.
6985 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6986
6987 HeapWord* addr = (HeapWord*)p;
6988 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6989 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6990 assert(p->klass_or_null() != NULL, "object should be initializd");
6991 assert(p->is_parsable(), "must be parsable.");
6992 // an initialized object; ignore mark word in verification below
6993 // since we are running concurrent with mutators
6994 assert(p->is_oop(true), "should be an oop");
6995 // Note that we do not yield while we iterate over
6996 // the interior oops of p, pushing the relevant ones
6997 // on our marking stack.
6998 size_t size = p->oop_iterate(_scanning_closure);
6999 do_yield_check();
7000 // Observe that below, we do not abandon the preclean
7001 // phase as soon as we should; rather we empty the
7002 // marking stack before returning. This is to satisfy
7003 // some existing assertions. In general, it may be a
7004 // good idea to abort immediately and complete the marking
7005 // from the grey objects at a later time.
7006 while (!_mark_stack->isEmpty()) {
7007 oop new_oop = _mark_stack->pop();
7008 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7009 assert(new_oop->is_parsable(), "Found unparsable oop");
7010 assert(_bit_map->isMarked((HeapWord*)new_oop),
7011 "only grey objects on this stack");
7012 // iterate over the oops in this oop, marking and pushing
7013 // the ones in CMS heap (i.e. in _span).
7014 new_oop->oop_iterate(_scanning_closure);
7015 // check if it's time to yield
7016 do_yield_check();
7017 }
7018 unsigned int after_count =
7019 GenCollectedHeap::heap()->total_collections();
7020 bool abort = (_before_count != after_count) ||
7021 _collector->should_abort_preclean();
7022 return abort ? 0 : size;
7023 }
7024
7025 void SurvivorSpacePrecleanClosure::do_yield_work() {
7026 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7027 "CMS thread should hold CMS token");
7028 assert_lock_strong(_bit_map->lock());
7029 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7030 // Relinquish the bit map lock
7031 _bit_map->lock()->unlock();
7032 ConcurrentMarkSweepThread::desynchronize(true);
7033 ConcurrentMarkSweepThread::acknowledge_yield_request();
7034 _collector->stopTimer();
7035 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7036 if (PrintCMSStatistics != 0) {
7037 _collector->incrementYields();
7038 }
7039 _collector->icms_wait();
7040
7041 // See the comment in coordinator_yield()
7042 for (unsigned i = 0; i < CMSYieldSleepCount &&
7043 ConcurrentMarkSweepThread::should_yield() &&
7044 !CMSCollector::foregroundGCIsActive(); ++i) {
7045 os::sleep(Thread::current(), 1, false);
7046 ConcurrentMarkSweepThread::acknowledge_yield_request();
7047 }
7048
7049 ConcurrentMarkSweepThread::synchronize(true);
7050 _bit_map->lock()->lock_without_safepoint_check();
7051 _collector->startTimer();
7052 }
7053
7054 // This closure is used to rescan the marked objects on the dirty cards
7055 // in the mod union table and the card table proper. In the parallel
7056 // case, although the bitMap is shared, we do a single read so the
7057 // isMarked() query is "safe".
7058 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7059 // Ignore mark word because we are running concurrent with mutators
7060 assert(p->is_oop_or_null(true), "expected an oop or null");
7061 HeapWord* addr = (HeapWord*)p;
7062 assert(_span.contains(addr), "we are scanning the CMS generation");
7063 bool is_obj_array = false;
7064 #ifdef DEBUG
7065 if (!_parallel) {
7066 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7067 assert(_collector->overflow_list_is_empty(),
7068 "overflow list should be empty");
7069
7070 }
7071 #endif // DEBUG
7072 if (_bit_map->isMarked(addr)) {
7073 // Obj arrays are precisely marked, non-arrays are not;
7074 // so we scan objArrays precisely and non-arrays in their
7075 // entirety.
7076 if (p->is_objArray()) {
7077 is_obj_array = true;
7078 if (_parallel) {
7079 p->oop_iterate(_par_scan_closure, mr);
7080 } else {
7081 p->oop_iterate(_scan_closure, mr);
7082 }
7083 } else {
7084 if (_parallel) {
7085 p->oop_iterate(_par_scan_closure);
7086 } else {
7087 p->oop_iterate(_scan_closure);
7088 }
7089 }
7090 }
7091 #ifdef DEBUG
7092 if (!_parallel) {
7093 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7094 assert(_collector->overflow_list_is_empty(),
7095 "overflow list should be empty");
7096
7097 }
7098 #endif // DEBUG
7099 return is_obj_array;
7100 }
7101
7102 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7103 MemRegion span,
7104 CMSBitMap* bitMap, CMSMarkStack* markStack,
7105 CMSMarkStack* revisitStack,
7106 bool should_yield, bool verifying):
7107 _collector(collector),
7108 _span(span),
7109 _bitMap(bitMap),
7110 _mut(&collector->_modUnionTable),
7111 _markStack(markStack),
7112 _revisitStack(revisitStack),
7113 _yield(should_yield),
7114 _skipBits(0)
7115 {
7116 assert(_markStack->isEmpty(), "stack should be empty");
7117 _finger = _bitMap->startWord();
7118 _threshold = _finger;
7119 assert(_collector->_restart_addr == NULL, "Sanity check");
7120 assert(_span.contains(_finger), "Out of bounds _finger?");
7121 DEBUG_ONLY(_verifying = verifying;)
7122 }
7123
7124 void MarkFromRootsClosure::reset(HeapWord* addr) {
7125 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7126 assert(_span.contains(addr), "Out of bounds _finger?");
7127 _finger = addr;
7128 _threshold = (HeapWord*)round_to(
7129 (intptr_t)_finger, CardTableModRefBS::card_size);
7130 }
7131
7132 // Should revisit to see if this should be restructured for
7133 // greater efficiency.
7134 bool MarkFromRootsClosure::do_bit(size_t offset) {
7135 if (_skipBits > 0) {
7136 _skipBits--;
7137 return true;
7138 }
7139 // convert offset into a HeapWord*
7140 HeapWord* addr = _bitMap->startWord() + offset;
7141 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7142 "address out of range");
7143 assert(_bitMap->isMarked(addr), "tautology");
7144 if (_bitMap->isMarked(addr+1)) {
7145 // this is an allocated but not yet initialized object
7146 assert(_skipBits == 0, "tautology");
7147 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7148 oop p = oop(addr);
7149 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7150 DEBUG_ONLY(if (!_verifying) {)
7151 // We re-dirty the cards on which this object lies and increase
7152 // the _threshold so that we'll come back to scan this object
7153 // during the preclean or remark phase. (CMSCleanOnEnter)
7154 if (CMSCleanOnEnter) {
7155 size_t sz = _collector->block_size_using_printezis_bits(addr);
7156 HeapWord* end_card_addr = (HeapWord*)round_to(
7157 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7158 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7159 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7160 // Bump _threshold to end_card_addr; note that
7161 // _threshold cannot possibly exceed end_card_addr, anyhow.
7162 // This prevents future clearing of the card as the scan proceeds
7163 // to the right.
7164 assert(_threshold <= end_card_addr,
7165 "Because we are just scanning into this object");
7166 if (_threshold < end_card_addr) {
7167 _threshold = end_card_addr;
7168 }
7169 if (p->klass_or_null() != NULL) {
7170 // Redirty the range of cards...
7171 _mut->mark_range(redirty_range);
7172 } // ...else the setting of klass will dirty the card anyway.
7173 }
7174 DEBUG_ONLY(})
7175 return true;
7176 }
7177 }
7178 scanOopsInOop(addr);
7179 return true;
7180 }
7181
7182 // We take a break if we've been at this for a while,
7183 // so as to avoid monopolizing the locks involved.
7184 void MarkFromRootsClosure::do_yield_work() {
7185 // First give up the locks, then yield, then re-lock
7186 // We should probably use a constructor/destructor idiom to
7187 // do this unlock/lock or modify the MutexUnlocker class to
7188 // serve our purpose. XXX
7189 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7190 "CMS thread should hold CMS token");
7191 assert_lock_strong(_bitMap->lock());
7192 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7193 _bitMap->lock()->unlock();
7194 ConcurrentMarkSweepThread::desynchronize(true);
7195 ConcurrentMarkSweepThread::acknowledge_yield_request();
7196 _collector->stopTimer();
7197 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7198 if (PrintCMSStatistics != 0) {
7199 _collector->incrementYields();
7200 }
7201 _collector->icms_wait();
7202
7203 // See the comment in coordinator_yield()
7204 for (unsigned i = 0; i < CMSYieldSleepCount &&
7205 ConcurrentMarkSweepThread::should_yield() &&
7206 !CMSCollector::foregroundGCIsActive(); ++i) {
7207 os::sleep(Thread::current(), 1, false);
7208 ConcurrentMarkSweepThread::acknowledge_yield_request();
7209 }
7210
7211 ConcurrentMarkSweepThread::synchronize(true);
7212 _bitMap->lock()->lock_without_safepoint_check();
7213 _collector->startTimer();
7214 }
7215
7216 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7217 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7218 assert(_markStack->isEmpty(),
7219 "should drain stack to limit stack usage");
7220 // convert ptr to an oop preparatory to scanning
7221 oop obj = oop(ptr);
7222 // Ignore mark word in verification below, since we
7223 // may be running concurrent with mutators.
7224 assert(obj->is_oop(true), "should be an oop");
7225 assert(_finger <= ptr, "_finger runneth ahead");
7226 // advance the finger to right end of this object
7227 _finger = ptr + obj->size();
7228 assert(_finger > ptr, "we just incremented it above");
7229 // On large heaps, it may take us some time to get through
7230 // the marking phase (especially if running iCMS). During
7231 // this time it's possible that a lot of mutations have
7232 // accumulated in the card table and the mod union table --
7233 // these mutation records are redundant until we have
7234 // actually traced into the corresponding card.
7235 // Here, we check whether advancing the finger would make
7236 // us cross into a new card, and if so clear corresponding
7237 // cards in the MUT (preclean them in the card-table in the
7238 // future).
7239
7240 DEBUG_ONLY(if (!_verifying) {)
7241 // The clean-on-enter optimization is disabled by default,
7242 // until we fix 6178663.
7243 if (CMSCleanOnEnter && (_finger > _threshold)) {
7244 // [_threshold, _finger) represents the interval
7245 // of cards to be cleared in MUT (or precleaned in card table).
7246 // The set of cards to be cleared is all those that overlap
7247 // with the interval [_threshold, _finger); note that
7248 // _threshold is always kept card-aligned but _finger isn't
7249 // always card-aligned.
7250 HeapWord* old_threshold = _threshold;
7251 assert(old_threshold == (HeapWord*)round_to(
7252 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7253 "_threshold should always be card-aligned");
7254 _threshold = (HeapWord*)round_to(
7255 (intptr_t)_finger, CardTableModRefBS::card_size);
7256 MemRegion mr(old_threshold, _threshold);
7257 assert(!mr.is_empty(), "Control point invariant");
7258 assert(_span.contains(mr), "Should clear within span");
7259 // XXX When _finger crosses from old gen into perm gen
7260 // we may be doing unnecessary cleaning; do better in the
7261 // future by detecting that condition and clearing fewer
7262 // MUT/CT entries.
7263 _mut->clear_range(mr);
7264 }
7265 DEBUG_ONLY(})
7266 // Note: the finger doesn't advance while we drain
7267 // the stack below.
7268 PushOrMarkClosure pushOrMarkClosure(_collector,
7269 _span, _bitMap, _markStack,
7270 _revisitStack,
7271 _finger, this);
7272 bool res = _markStack->push(obj);
7273 assert(res, "Empty non-zero size stack should have space for single push");
7274 while (!_markStack->isEmpty()) {
7275 oop new_oop = _markStack->pop();
7276 // Skip verifying header mark word below because we are
7277 // running concurrent with mutators.
7278 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7279 // now scan this oop's oops
7280 new_oop->oop_iterate(&pushOrMarkClosure);
7281 do_yield_check();
7282 }
7283 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7284 }
7285
7286 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7287 CMSCollector* collector, MemRegion span,
7288 CMSBitMap* bit_map,
7289 OopTaskQueue* work_queue,
7290 CMSMarkStack* overflow_stack,
7291 CMSMarkStack* revisit_stack,
7292 bool should_yield):
7293 _collector(collector),
7294 _whole_span(collector->_span),
7295 _span(span),
7296 _bit_map(bit_map),
7297 _mut(&collector->_modUnionTable),
7298 _work_queue(work_queue),
7299 _overflow_stack(overflow_stack),
7300 _revisit_stack(revisit_stack),
7301 _yield(should_yield),
7302 _skip_bits(0),
7303 _task(task)
7304 {
7305 assert(_work_queue->size() == 0, "work_queue should be empty");
7306 _finger = span.start();
7307 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7308 assert(_span.contains(_finger), "Out of bounds _finger?");
7309 }
7310
7311 // Should revisit to see if this should be restructured for
7312 // greater efficiency.
7313 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7314 if (_skip_bits > 0) {
7315 _skip_bits--;
7316 return true;
7317 }
7318 // convert offset into a HeapWord*
7319 HeapWord* addr = _bit_map->startWord() + offset;
7320 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7321 "address out of range");
7322 assert(_bit_map->isMarked(addr), "tautology");
7323 if (_bit_map->isMarked(addr+1)) {
7324 // this is an allocated object that might not yet be initialized
7325 assert(_skip_bits == 0, "tautology");
7326 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7327 oop p = oop(addr);
7328 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7329 // in the case of Clean-on-Enter optimization, redirty card
7330 // and avoid clearing card by increasing the threshold.
7331 return true;
7332 }
7333 }
7334 scan_oops_in_oop(addr);
7335 return true;
7336 }
7337
7338 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7339 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7340 // Should we assert that our work queue is empty or
7341 // below some drain limit?
7342 assert(_work_queue->size() == 0,
7343 "should drain stack to limit stack usage");
7344 // convert ptr to an oop preparatory to scanning
7345 oop obj = oop(ptr);
7346 // Ignore mark word in verification below, since we
7347 // may be running concurrent with mutators.
7348 assert(obj->is_oop(true), "should be an oop");
7349 assert(_finger <= ptr, "_finger runneth ahead");
7350 // advance the finger to right end of this object
7351 _finger = ptr + obj->size();
7352 assert(_finger > ptr, "we just incremented it above");
7353 // On large heaps, it may take us some time to get through
7354 // the marking phase (especially if running iCMS). During
7355 // this time it's possible that a lot of mutations have
7356 // accumulated in the card table and the mod union table --
7357 // these mutation records are redundant until we have
7358 // actually traced into the corresponding card.
7359 // Here, we check whether advancing the finger would make
7360 // us cross into a new card, and if so clear corresponding
7361 // cards in the MUT (preclean them in the card-table in the
7362 // future).
7363
7364 // The clean-on-enter optimization is disabled by default,
7365 // until we fix 6178663.
7366 if (CMSCleanOnEnter && (_finger > _threshold)) {
7367 // [_threshold, _finger) represents the interval
7368 // of cards to be cleared in MUT (or precleaned in card table).
7369 // The set of cards to be cleared is all those that overlap
7370 // with the interval [_threshold, _finger); note that
7371 // _threshold is always kept card-aligned but _finger isn't
7372 // always card-aligned.
7373 HeapWord* old_threshold = _threshold;
7374 assert(old_threshold == (HeapWord*)round_to(
7375 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7376 "_threshold should always be card-aligned");
7377 _threshold = (HeapWord*)round_to(
7378 (intptr_t)_finger, CardTableModRefBS::card_size);
7379 MemRegion mr(old_threshold, _threshold);
7380 assert(!mr.is_empty(), "Control point invariant");
7381 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7382 // XXX When _finger crosses from old gen into perm gen
7383 // we may be doing unnecessary cleaning; do better in the
7384 // future by detecting that condition and clearing fewer
7385 // MUT/CT entries.
7386 _mut->clear_range(mr);
7387 }
7388
7389 // Note: the local finger doesn't advance while we drain
7390 // the stack below, but the global finger sure can and will.
7391 HeapWord** gfa = _task->global_finger_addr();
7392 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7393 _span, _bit_map,
7394 _work_queue,
7395 _overflow_stack,
7396 _revisit_stack,
7397 _finger,
7398 gfa, this);
7399 bool res = _work_queue->push(obj); // overflow could occur here
7400 assert(res, "Will hold once we use workqueues");
7401 while (true) {
7402 oop new_oop;
7403 if (!_work_queue->pop_local(new_oop)) {
7404 // We emptied our work_queue; check if there's stuff that can
7405 // be gotten from the overflow stack.
7406 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7407 _overflow_stack, _work_queue)) {
7408 do_yield_check();
7409 continue;
7410 } else { // done
7411 break;
7412 }
7413 }
7414 // Skip verifying header mark word below because we are
7415 // running concurrent with mutators.
7416 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7417 // now scan this oop's oops
7418 new_oop->oop_iterate(&pushOrMarkClosure);
7419 do_yield_check();
7420 }
7421 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7422 }
7423
7424 // Yield in response to a request from VM Thread or
7425 // from mutators.
7426 void Par_MarkFromRootsClosure::do_yield_work() {
7427 assert(_task != NULL, "sanity");
7428 _task->yield();
7429 }
7430
7431 // A variant of the above used for verifying CMS marking work.
7432 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7433 MemRegion span,
7434 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7435 CMSMarkStack* mark_stack):
7436 _collector(collector),
7437 _span(span),
7438 _verification_bm(verification_bm),
7439 _cms_bm(cms_bm),
7440 _mark_stack(mark_stack),
7441 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7442 mark_stack)
7443 {
7444 assert(_mark_stack->isEmpty(), "stack should be empty");
7445 _finger = _verification_bm->startWord();
7446 assert(_collector->_restart_addr == NULL, "Sanity check");
7447 assert(_span.contains(_finger), "Out of bounds _finger?");
7448 }
7449
7450 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7451 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7452 assert(_span.contains(addr), "Out of bounds _finger?");
7453 _finger = addr;
7454 }
7455
7456 // Should revisit to see if this should be restructured for
7457 // greater efficiency.
7458 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7459 // convert offset into a HeapWord*
7460 HeapWord* addr = _verification_bm->startWord() + offset;
7461 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7462 "address out of range");
7463 assert(_verification_bm->isMarked(addr), "tautology");
7464 assert(_cms_bm->isMarked(addr), "tautology");
7465
7466 assert(_mark_stack->isEmpty(),
7467 "should drain stack to limit stack usage");
7468 // convert addr to an oop preparatory to scanning
7469 oop obj = oop(addr);
7470 assert(obj->is_oop(), "should be an oop");
7471 assert(_finger <= addr, "_finger runneth ahead");
7472 // advance the finger to right end of this object
7473 _finger = addr + obj->size();
7474 assert(_finger > addr, "we just incremented it above");
7475 // Note: the finger doesn't advance while we drain
7476 // the stack below.
7477 bool res = _mark_stack->push(obj);
7478 assert(res, "Empty non-zero size stack should have space for single push");
7479 while (!_mark_stack->isEmpty()) {
7480 oop new_oop = _mark_stack->pop();
7481 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7482 // now scan this oop's oops
7483 new_oop->oop_iterate(&_pam_verify_closure);
7484 }
7485 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7486 return true;
7487 }
7488
7489 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7490 CMSCollector* collector, MemRegion span,
7491 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7492 CMSMarkStack* mark_stack):
7493 OopClosure(collector->ref_processor()),
7494 _collector(collector),
7495 _span(span),
7496 _verification_bm(verification_bm),
7497 _cms_bm(cms_bm),
7498 _mark_stack(mark_stack)
7499 { }
7500
7501 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7502 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7503
7504 // Upon stack overflow, we discard (part of) the stack,
7505 // remembering the least address amongst those discarded
7506 // in CMSCollector's _restart_address.
7507 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7508 // Remember the least grey address discarded
7509 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7510 _collector->lower_restart_addr(ra);
7511 _mark_stack->reset(); // discard stack contents
7512 _mark_stack->expand(); // expand the stack if possible
7513 }
7514
7515 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7516 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7517 HeapWord* addr = (HeapWord*)obj;
7518 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7519 // Oop lies in _span and isn't yet grey or black
7520 _verification_bm->mark(addr); // now grey
7521 if (!_cms_bm->isMarked(addr)) {
7522 oop(addr)->print();
7523 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7524 addr);
7525 fatal("... aborting");
7526 }
7527
7528 if (!_mark_stack->push(obj)) { // stack overflow
7529 if (PrintCMSStatistics != 0) {
7530 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7531 SIZE_FORMAT, _mark_stack->capacity());
7532 }
7533 assert(_mark_stack->isFull(), "Else push should have succeeded");
7534 handle_stack_overflow(addr);
7535 }
7536 // anything including and to the right of _finger
7537 // will be scanned as we iterate over the remainder of the
7538 // bit map
7539 }
7540 }
7541
7542 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7543 MemRegion span,
7544 CMSBitMap* bitMap, CMSMarkStack* markStack,
7545 CMSMarkStack* revisitStack,
7546 HeapWord* finger, MarkFromRootsClosure* parent) :
7547 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7548 _span(span),
7549 _bitMap(bitMap),
7550 _markStack(markStack),
7551 _finger(finger),
7552 _parent(parent)
7553 { }
7554
7555 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7556 MemRegion span,
7557 CMSBitMap* bit_map,
7558 OopTaskQueue* work_queue,
7559 CMSMarkStack* overflow_stack,
7560 CMSMarkStack* revisit_stack,
7561 HeapWord* finger,
7562 HeapWord** global_finger_addr,
7563 Par_MarkFromRootsClosure* parent) :
7564 Par_KlassRememberingOopClosure(collector,
7565 collector->ref_processor(),
7566 revisit_stack),
7567 _whole_span(collector->_span),
7568 _span(span),
7569 _bit_map(bit_map),
7570 _work_queue(work_queue),
7571 _overflow_stack(overflow_stack),
7572 _finger(finger),
7573 _global_finger_addr(global_finger_addr),
7574 _parent(parent)
7575 { }
7576
7577 // Assumes thread-safe access by callers, who are
7578 // responsible for mutual exclusion.
7579 void CMSCollector::lower_restart_addr(HeapWord* low) {
7580 assert(_span.contains(low), "Out of bounds addr");
7581 if (_restart_addr == NULL) {
7582 _restart_addr = low;
7583 } else {
7584 _restart_addr = MIN2(_restart_addr, low);
7585 }
7586 }
7587
7588 // Upon stack overflow, we discard (part of) the stack,
7589 // remembering the least address amongst those discarded
7590 // in CMSCollector's _restart_address.
7591 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7592 // Remember the least grey address discarded
7593 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7594 _collector->lower_restart_addr(ra);
7595 _markStack->reset(); // discard stack contents
7596 _markStack->expand(); // expand the stack if possible
7597 }
7598
7599 // Upon stack overflow, we discard (part of) the stack,
7600 // remembering the least address amongst those discarded
7601 // in CMSCollector's _restart_address.
7602 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7603 // We need to do this under a mutex to prevent other
7604 // workers from interfering with the work done below.
7605 MutexLockerEx ml(_overflow_stack->par_lock(),
7606 Mutex::_no_safepoint_check_flag);
7607 // Remember the least grey address discarded
7608 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7609 _collector->lower_restart_addr(ra);
7610 _overflow_stack->reset(); // discard stack contents
7611 _overflow_stack->expand(); // expand the stack if possible
7612 }
7613
7614 void PushOrMarkClosure::do_oop(oop obj) {
7615 // Ignore mark word because we are running concurrent with mutators.
7616 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7617 HeapWord* addr = (HeapWord*)obj;
7618 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7619 // Oop lies in _span and isn't yet grey or black
7620 _bitMap->mark(addr); // now grey
7621 if (addr < _finger) {
7622 // the bit map iteration has already either passed, or
7623 // sampled, this bit in the bit map; we'll need to
7624 // use the marking stack to scan this oop's oops.
7625 bool simulate_overflow = false;
7626 NOT_PRODUCT(
7627 if (CMSMarkStackOverflowALot &&
7628 _collector->simulate_overflow()) {
7629 // simulate a stack overflow
7630 simulate_overflow = true;
7631 }
7632 )
7633 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7634 if (PrintCMSStatistics != 0) {
7635 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7636 SIZE_FORMAT, _markStack->capacity());
7637 }
7638 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7639 handle_stack_overflow(addr);
7640 }
7641 }
7642 // anything including and to the right of _finger
7643 // will be scanned as we iterate over the remainder of the
7644 // bit map
7645 do_yield_check();
7646 }
7647 }
7648
7649 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7650 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7651
7652 void Par_PushOrMarkClosure::do_oop(oop obj) {
7653 // Ignore mark word because we are running concurrent with mutators.
7654 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7655 HeapWord* addr = (HeapWord*)obj;
7656 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7657 // Oop lies in _span and isn't yet grey or black
7658 // We read the global_finger (volatile read) strictly after marking oop
7659 bool res = _bit_map->par_mark(addr); // now grey
7660 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7661 // Should we push this marked oop on our stack?
7662 // -- if someone else marked it, nothing to do
7663 // -- if target oop is above global finger nothing to do
7664 // -- if target oop is in chunk and above local finger
7665 // then nothing to do
7666 // -- else push on work queue
7667 if ( !res // someone else marked it, they will deal with it
7668 || (addr >= *gfa) // will be scanned in a later task
7669 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7670 return;
7671 }
7672 // the bit map iteration has already either passed, or
7673 // sampled, this bit in the bit map; we'll need to
7674 // use the marking stack to scan this oop's oops.
7675 bool simulate_overflow = false;
7676 NOT_PRODUCT(
7677 if (CMSMarkStackOverflowALot &&
7678 _collector->simulate_overflow()) {
7679 // simulate a stack overflow
7680 simulate_overflow = true;
7681 }
7682 )
7683 if (simulate_overflow ||
7684 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7685 // stack overflow
7686 if (PrintCMSStatistics != 0) {
7687 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7688 SIZE_FORMAT, _overflow_stack->capacity());
7689 }
7690 // We cannot assert that the overflow stack is full because
7691 // it may have been emptied since.
7692 assert(simulate_overflow ||
7693 _work_queue->size() == _work_queue->max_elems(),
7694 "Else push should have succeeded");
7695 handle_stack_overflow(addr);
7696 }
7697 do_yield_check();
7698 }
7699 }
7700
7701 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7702 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7703
7704 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7705 ReferenceProcessor* rp,
7706 CMSMarkStack* revisit_stack) :
7707 OopClosure(rp),
7708 _collector(collector),
7709 _revisit_stack(revisit_stack),
7710 _should_remember_klasses(collector->should_unload_classes()) {}
7711
7712 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7713 MemRegion span,
7714 ReferenceProcessor* rp,
7715 CMSBitMap* bit_map,
7716 CMSBitMap* mod_union_table,
7717 CMSMarkStack* mark_stack,
7718 CMSMarkStack* revisit_stack,
7719 bool concurrent_precleaning):
7720 KlassRememberingOopClosure(collector, rp, revisit_stack),
7721 _span(span),
7722 _bit_map(bit_map),
7723 _mod_union_table(mod_union_table),
7724 _mark_stack(mark_stack),
7725 _concurrent_precleaning(concurrent_precleaning)
7726 {
7727 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7728 }
7729
7730 // Grey object rescan during pre-cleaning and second checkpoint phases --
7731 // the non-parallel version (the parallel version appears further below.)
7732 void PushAndMarkClosure::do_oop(oop obj) {
7733 // Ignore mark word verification. If during concurrent precleaning,
7734 // the object monitor may be locked. If during the checkpoint
7735 // phases, the object may already have been reached by a different
7736 // path and may be at the end of the global overflow list (so
7737 // the mark word may be NULL).
7738 assert(obj->is_oop_or_null(true /* ignore mark word */),
7739 "expected an oop or NULL");
7740 HeapWord* addr = (HeapWord*)obj;
7741 // Check if oop points into the CMS generation
7742 // and is not marked
7743 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7744 // a white object ...
7745 _bit_map->mark(addr); // ... now grey
7746 // push on the marking stack (grey set)
7747 bool simulate_overflow = false;
7748 NOT_PRODUCT(
7749 if (CMSMarkStackOverflowALot &&
7750 _collector->simulate_overflow()) {
7751 // simulate a stack overflow
7752 simulate_overflow = true;
7753 }
7754 )
7755 if (simulate_overflow || !_mark_stack->push(obj)) {
7756 if (_concurrent_precleaning) {
7757 // During precleaning we can just dirty the appropriate card(s)
7758 // in the mod union table, thus ensuring that the object remains
7759 // in the grey set and continue. In the case of object arrays
7760 // we need to dirty all of the cards that the object spans,
7761 // since the rescan of object arrays will be limited to the
7762 // dirty cards.
7763 // Note that no one can be intefering with us in this action
7764 // of dirtying the mod union table, so no locking or atomics
7765 // are required.
7766 if (obj->is_objArray()) {
7767 size_t sz = obj->size();
7768 HeapWord* end_card_addr = (HeapWord*)round_to(
7769 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7770 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7771 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7772 _mod_union_table->mark_range(redirty_range);
7773 } else {
7774 _mod_union_table->mark(addr);
7775 }
7776 _collector->_ser_pmc_preclean_ovflw++;
7777 } else {
7778 // During the remark phase, we need to remember this oop
7779 // in the overflow list.
7780 _collector->push_on_overflow_list(obj);
7781 _collector->_ser_pmc_remark_ovflw++;
7782 }
7783 }
7784 }
7785 }
7786
7787 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7788 MemRegion span,
7789 ReferenceProcessor* rp,
7790 CMSBitMap* bit_map,
7791 OopTaskQueue* work_queue,
7792 CMSMarkStack* revisit_stack):
7793 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7794 _span(span),
7795 _bit_map(bit_map),
7796 _work_queue(work_queue)
7797 {
7798 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7799 }
7800
7801 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7802 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7803
7804 // Grey object rescan during second checkpoint phase --
7805 // the parallel version.
7806 void Par_PushAndMarkClosure::do_oop(oop obj) {
7807 // In the assert below, we ignore the mark word because
7808 // this oop may point to an already visited object that is
7809 // on the overflow stack (in which case the mark word has
7810 // been hijacked for chaining into the overflow stack --
7811 // if this is the last object in the overflow stack then
7812 // its mark word will be NULL). Because this object may
7813 // have been subsequently popped off the global overflow
7814 // stack, and the mark word possibly restored to the prototypical
7815 // value, by the time we get to examined this failing assert in
7816 // the debugger, is_oop_or_null(false) may subsequently start
7817 // to hold.
7818 assert(obj->is_oop_or_null(true),
7819 "expected an oop or NULL");
7820 HeapWord* addr = (HeapWord*)obj;
7821 // Check if oop points into the CMS generation
7822 // and is not marked
7823 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7824 // a white object ...
7825 // If we manage to "claim" the object, by being the
7826 // first thread to mark it, then we push it on our
7827 // marking stack
7828 if (_bit_map->par_mark(addr)) { // ... now grey
7829 // push on work queue (grey set)
7830 bool simulate_overflow = false;
7831 NOT_PRODUCT(
7832 if (CMSMarkStackOverflowALot &&
7833 _collector->par_simulate_overflow()) {
7834 // simulate a stack overflow
7835 simulate_overflow = true;
7836 }
7837 )
7838 if (simulate_overflow || !_work_queue->push(obj)) {
7839 _collector->par_push_on_overflow_list(obj);
7840 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7841 }
7842 } // Else, some other thread got there first
7843 }
7844 }
7845
7846 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7847 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7848
7849 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7850 // TBD
7851 }
7852
7853 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7854 // TBD
7855 }
7856
7857 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7858 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7859 Mutex* bml = _collector->bitMapLock();
7860 assert_lock_strong(bml);
7861 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7862 "CMS thread should hold CMS token");
7863
7864 bml->unlock();
7865 ConcurrentMarkSweepThread::desynchronize(true);
7866
7867 ConcurrentMarkSweepThread::acknowledge_yield_request();
7868
7869 _collector->stopTimer();
7870 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7871 if (PrintCMSStatistics != 0) {
7872 _collector->incrementYields();
7873 }
7874 _collector->icms_wait();
7875
7876 // See the comment in coordinator_yield()
7877 for (unsigned i = 0; i < CMSYieldSleepCount &&
7878 ConcurrentMarkSweepThread::should_yield() &&
7879 !CMSCollector::foregroundGCIsActive(); ++i) {
7880 os::sleep(Thread::current(), 1, false);
7881 ConcurrentMarkSweepThread::acknowledge_yield_request();
7882 }
7883
7884 ConcurrentMarkSweepThread::synchronize(true);
7885 bml->lock();
7886
7887 _collector->startTimer();
7888 }
7889
7890 bool CMSPrecleanRefsYieldClosure::should_return() {
7891 if (ConcurrentMarkSweepThread::should_yield()) {
7892 do_yield_work();
7893 }
7894 return _collector->foregroundGCIsActive();
7895 }
7896
7897 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7898 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7899 "mr should be aligned to start at a card boundary");
7900 // We'd like to assert:
7901 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7902 // "mr should be a range of cards");
7903 // However, that would be too strong in one case -- the last
7904 // partition ends at _unallocated_block which, in general, can be
7905 // an arbitrary boundary, not necessarily card aligned.
7906 if (PrintCMSStatistics != 0) {
7907 _num_dirty_cards +=
7908 mr.word_size()/CardTableModRefBS::card_size_in_words;
7909 }
7910 _space->object_iterate_mem(mr, &_scan_cl);
7911 }
7912
7913 SweepClosure::SweepClosure(CMSCollector* collector,
7914 ConcurrentMarkSweepGeneration* g,
7915 CMSBitMap* bitMap, bool should_yield) :
7916 _collector(collector),
7917 _g(g),
7918 _sp(g->cmsSpace()),
7919 _limit(_sp->sweep_limit()),
7920 _freelistLock(_sp->freelistLock()),
7921 _bitMap(bitMap),
7922 _yield(should_yield),
7923 _inFreeRange(false), // No free range at beginning of sweep
7924 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7925 _lastFreeRangeCoalesced(false),
7926 _freeFinger(g->used_region().start())
7927 {
7928 NOT_PRODUCT(
7929 _numObjectsFreed = 0;
7930 _numWordsFreed = 0;
7931 _numObjectsLive = 0;
7932 _numWordsLive = 0;
7933 _numObjectsAlreadyFree = 0;
7934 _numWordsAlreadyFree = 0;
7935 _last_fc = NULL;
7936
7937 _sp->initializeIndexedFreeListArrayReturnedBytes();
7938 _sp->dictionary()->initialize_dict_returned_bytes();
7939 )
7940 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7941 "sweep _limit out of bounds");
7942 if (CMSTraceSweeper) {
7943 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7944 _limit);
7945 }
7946 }
7947
7948 void SweepClosure::print_on(outputStream* st) const {
7949 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7950 _sp->bottom(), _sp->end());
7951 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7952 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7953 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7954 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7955 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7956 }
7957
7958 #ifndef PRODUCT
7959 // Assertion checking only: no useful work in product mode --
7960 // however, if any of the flags below become product flags,
7961 // you may need to review this code to see if it needs to be
7962 // enabled in product mode.
7963 SweepClosure::~SweepClosure() {
7964 assert_lock_strong(_freelistLock);
7965 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7966 "sweep _limit out of bounds");
7967 if (inFreeRange()) {
7968 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7969 print();
7970 ShouldNotReachHere();
7971 }
7972 if (Verbose && PrintGC) {
7973 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7974 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7975 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7976 SIZE_FORMAT" bytes "
7977 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7978 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7979 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7980 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7981 * sizeof(HeapWord);
7982 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7983
7984 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7985 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7986 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7987 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7988 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7989 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7990 indexListReturnedBytes);
7991 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7992 dict_returned_bytes);
7993 }
7994 }
7995 if (CMSTraceSweeper) {
7996 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7997 _limit);
7998 }
7999 }
8000 #endif // PRODUCT
8001
8002 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8003 bool freeRangeInFreeLists) {
8004 if (CMSTraceSweeper) {
8005 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8006 freeFinger, freeRangeInFreeLists);
8007 }
8008 assert(!inFreeRange(), "Trampling existing free range");
8009 set_inFreeRange(true);
8010 set_lastFreeRangeCoalesced(false);
8011
8012 set_freeFinger(freeFinger);
8013 set_freeRangeInFreeLists(freeRangeInFreeLists);
8014 if (CMSTestInFreeList) {
8015 if (freeRangeInFreeLists) {
8016 FreeChunk* fc = (FreeChunk*) freeFinger;
8017 assert(fc->is_free(), "A chunk on the free list should be free.");
8018 assert(fc->size() > 0, "Free range should have a size");
8019 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8020 }
8021 }
8022 }
8023
8024 // Note that the sweeper runs concurrently with mutators. Thus,
8025 // it is possible for direct allocation in this generation to happen
8026 // in the middle of the sweep. Note that the sweeper also coalesces
8027 // contiguous free blocks. Thus, unless the sweeper and the allocator
8028 // synchronize appropriately freshly allocated blocks may get swept up.
8029 // This is accomplished by the sweeper locking the free lists while
8030 // it is sweeping. Thus blocks that are determined to be free are
8031 // indeed free. There is however one additional complication:
8032 // blocks that have been allocated since the final checkpoint and
8033 // mark, will not have been marked and so would be treated as
8034 // unreachable and swept up. To prevent this, the allocator marks
8035 // the bit map when allocating during the sweep phase. This leads,
8036 // however, to a further complication -- objects may have been allocated
8037 // but not yet initialized -- in the sense that the header isn't yet
8038 // installed. The sweeper can not then determine the size of the block
8039 // in order to skip over it. To deal with this case, we use a technique
8040 // (due to Printezis) to encode such uninitialized block sizes in the
8041 // bit map. Since the bit map uses a bit per every HeapWord, but the
8042 // CMS generation has a minimum object size of 3 HeapWords, it follows
8043 // that "normal marks" won't be adjacent in the bit map (there will
8044 // always be at least two 0 bits between successive 1 bits). We make use
8045 // of these "unused" bits to represent uninitialized blocks -- the bit
8046 // corresponding to the start of the uninitialized object and the next
8047 // bit are both set. Finally, a 1 bit marks the end of the object that
8048 // started with the two consecutive 1 bits to indicate its potentially
8049 // uninitialized state.
8050
8051 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8052 FreeChunk* fc = (FreeChunk*)addr;
8053 size_t res;
8054
8055 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8056 // than "addr == _limit" because although _limit was a block boundary when
8057 // we started the sweep, it may no longer be one because heap expansion
8058 // may have caused us to coalesce the block ending at the address _limit
8059 // with a newly expanded chunk (this happens when _limit was set to the
8060 // previous _end of the space), so we may have stepped past _limit:
8061 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8062 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8063 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8064 "sweep _limit out of bounds");
8065 assert(addr < _sp->end(), "addr out of bounds");
8066 // Flush any free range we might be holding as a single
8067 // coalesced chunk to the appropriate free list.
8068 if (inFreeRange()) {
8069 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8070 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8071 flush_cur_free_chunk(freeFinger(),
8072 pointer_delta(addr, freeFinger()));
8073 if (CMSTraceSweeper) {
8074 gclog_or_tty->print("Sweep: last chunk: ");
8075 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8076 "[coalesced:"SIZE_FORMAT"]\n",
8077 freeFinger(), pointer_delta(addr, freeFinger()),
8078 lastFreeRangeCoalesced());
8079 }
8080 }
8081
8082 // help the iterator loop finish
8083 return pointer_delta(_sp->end(), addr);
8084 }
8085
8086 assert(addr < _limit, "sweep invariant");
8087 // check if we should yield
8088 do_yield_check(addr);
8089 if (fc->is_free()) {
8090 // Chunk that is already free
8091 res = fc->size();
8092 do_already_free_chunk(fc);
8093 debug_only(_sp->verifyFreeLists());
8094 // If we flush the chunk at hand in lookahead_and_flush()
8095 // and it's coalesced with a preceding chunk, then the
8096 // process of "mangling" the payload of the coalesced block
8097 // will cause erasure of the size information from the
8098 // (erstwhile) header of all the coalesced blocks but the
8099 // first, so the first disjunct in the assert will not hold
8100 // in that specific case (in which case the second disjunct
8101 // will hold).
8102 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8103 "Otherwise the size info doesn't change at this step");
8104 NOT_PRODUCT(
8105 _numObjectsAlreadyFree++;
8106 _numWordsAlreadyFree += res;
8107 )
8108 NOT_PRODUCT(_last_fc = fc;)
8109 } else if (!_bitMap->isMarked(addr)) {
8110 // Chunk is fresh garbage
8111 res = do_garbage_chunk(fc);
8112 debug_only(_sp->verifyFreeLists());
8113 NOT_PRODUCT(
8114 _numObjectsFreed++;
8115 _numWordsFreed += res;
8116 )
8117 } else {
8118 // Chunk that is alive.
8119 res = do_live_chunk(fc);
8120 debug_only(_sp->verifyFreeLists());
8121 NOT_PRODUCT(
8122 _numObjectsLive++;
8123 _numWordsLive += res;
8124 )
8125 }
8126 return res;
8127 }
8128
8129 // For the smart allocation, record following
8130 // split deaths - a free chunk is removed from its free list because
8131 // it is being split into two or more chunks.
8132 // split birth - a free chunk is being added to its free list because
8133 // a larger free chunk has been split and resulted in this free chunk.
8134 // coal death - a free chunk is being removed from its free list because
8135 // it is being coalesced into a large free chunk.
8136 // coal birth - a free chunk is being added to its free list because
8137 // it was created when two or more free chunks where coalesced into
8138 // this free chunk.
8139 //
8140 // These statistics are used to determine the desired number of free
8141 // chunks of a given size. The desired number is chosen to be relative
8142 // to the end of a CMS sweep. The desired number at the end of a sweep
8143 // is the
8144 // count-at-end-of-previous-sweep (an amount that was enough)
8145 // - count-at-beginning-of-current-sweep (the excess)
8146 // + split-births (gains in this size during interval)
8147 // - split-deaths (demands on this size during interval)
8148 // where the interval is from the end of one sweep to the end of the
8149 // next.
8150 //
8151 // When sweeping the sweeper maintains an accumulated chunk which is
8152 // the chunk that is made up of chunks that have been coalesced. That
8153 // will be termed the left-hand chunk. A new chunk of garbage that
8154 // is being considered for coalescing will be referred to as the
8155 // right-hand chunk.
8156 //
8157 // When making a decision on whether to coalesce a right-hand chunk with
8158 // the current left-hand chunk, the current count vs. the desired count
8159 // of the left-hand chunk is considered. Also if the right-hand chunk
8160 // is near the large chunk at the end of the heap (see
8161 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8162 // left-hand chunk is coalesced.
8163 //
8164 // When making a decision about whether to split a chunk, the desired count
8165 // vs. the current count of the candidate to be split is also considered.
8166 // If the candidate is underpopulated (currently fewer chunks than desired)
8167 // a chunk of an overpopulated (currently more chunks than desired) size may
8168 // be chosen. The "hint" associated with a free list, if non-null, points
8169 // to a free list which may be overpopulated.
8170 //
8171
8172 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8173 const size_t size = fc->size();
8174 // Chunks that cannot be coalesced are not in the
8175 // free lists.
8176 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8177 assert(_sp->verify_chunk_in_free_list(fc),
8178 "free chunk should be in free lists");
8179 }
8180 // a chunk that is already free, should not have been
8181 // marked in the bit map
8182 HeapWord* const addr = (HeapWord*) fc;
8183 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8184 // Verify that the bit map has no bits marked between
8185 // addr and purported end of this block.
8186 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8187
8188 // Some chunks cannot be coalesced under any circumstances.
8189 // See the definition of cantCoalesce().
8190 if (!fc->cantCoalesce()) {
8191 // This chunk can potentially be coalesced.
8192 if (_sp->adaptive_freelists()) {
8193 // All the work is done in
8194 do_post_free_or_garbage_chunk(fc, size);
8195 } else { // Not adaptive free lists
8196 // this is a free chunk that can potentially be coalesced by the sweeper;
8197 if (!inFreeRange()) {
8198 // if the next chunk is a free block that can't be coalesced
8199 // it doesn't make sense to remove this chunk from the free lists
8200 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8201 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8202 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8203 nextChunk->is_free() && // ... which is free...
8204 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8205 // nothing to do
8206 } else {
8207 // Potentially the start of a new free range:
8208 // Don't eagerly remove it from the free lists.
8209 // No need to remove it if it will just be put
8210 // back again. (Also from a pragmatic point of view
8211 // if it is a free block in a region that is beyond
8212 // any allocated blocks, an assertion will fail)
8213 // Remember the start of a free run.
8214 initialize_free_range(addr, true);
8215 // end - can coalesce with next chunk
8216 }
8217 } else {
8218 // the midst of a free range, we are coalescing
8219 print_free_block_coalesced(fc);
8220 if (CMSTraceSweeper) {
8221 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8222 }
8223 // remove it from the free lists
8224 _sp->removeFreeChunkFromFreeLists(fc);
8225 set_lastFreeRangeCoalesced(true);
8226 // If the chunk is being coalesced and the current free range is
8227 // in the free lists, remove the current free range so that it
8228 // will be returned to the free lists in its entirety - all
8229 // the coalesced pieces included.
8230 if (freeRangeInFreeLists()) {
8231 FreeChunk* ffc = (FreeChunk*) freeFinger();
8232 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8233 "Size of free range is inconsistent with chunk size.");
8234 if (CMSTestInFreeList) {
8235 assert(_sp->verify_chunk_in_free_list(ffc),
8236 "free range is not in free lists");
8237 }
8238 _sp->removeFreeChunkFromFreeLists(ffc);
8239 set_freeRangeInFreeLists(false);
8240 }
8241 }
8242 }
8243 // Note that if the chunk is not coalescable (the else arm
8244 // below), we unconditionally flush, without needing to do
8245 // a "lookahead," as we do below.
8246 if (inFreeRange()) lookahead_and_flush(fc, size);
8247 } else {
8248 // Code path common to both original and adaptive free lists.
8249
8250 // cant coalesce with previous block; this should be treated
8251 // as the end of a free run if any
8252 if (inFreeRange()) {
8253 // we kicked some butt; time to pick up the garbage
8254 assert(freeFinger() < addr, "freeFinger points too high");
8255 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8256 }
8257 // else, nothing to do, just continue
8258 }
8259 }
8260
8261 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8262 // This is a chunk of garbage. It is not in any free list.
8263 // Add it to a free list or let it possibly be coalesced into
8264 // a larger chunk.
8265 HeapWord* const addr = (HeapWord*) fc;
8266 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8267
8268 if (_sp->adaptive_freelists()) {
8269 // Verify that the bit map has no bits marked between
8270 // addr and purported end of just dead object.
8271 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8272
8273 do_post_free_or_garbage_chunk(fc, size);
8274 } else {
8275 if (!inFreeRange()) {
8276 // start of a new free range
8277 assert(size > 0, "A free range should have a size");
8278 initialize_free_range(addr, false);
8279 } else {
8280 // this will be swept up when we hit the end of the
8281 // free range
8282 if (CMSTraceSweeper) {
8283 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8284 }
8285 // If the chunk is being coalesced and the current free range is
8286 // in the free lists, remove the current free range so that it
8287 // will be returned to the free lists in its entirety - all
8288 // the coalesced pieces included.
8289 if (freeRangeInFreeLists()) {
8290 FreeChunk* ffc = (FreeChunk*)freeFinger();
8291 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8292 "Size of free range is inconsistent with chunk size.");
8293 if (CMSTestInFreeList) {
8294 assert(_sp->verify_chunk_in_free_list(ffc),
8295 "free range is not in free lists");
8296 }
8297 _sp->removeFreeChunkFromFreeLists(ffc);
8298 set_freeRangeInFreeLists(false);
8299 }
8300 set_lastFreeRangeCoalesced(true);
8301 }
8302 // this will be swept up when we hit the end of the free range
8303
8304 // Verify that the bit map has no bits marked between
8305 // addr and purported end of just dead object.
8306 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8307 }
8308 assert(_limit >= addr + size,
8309 "A freshly garbage chunk can't possibly straddle over _limit");
8310 if (inFreeRange()) lookahead_and_flush(fc, size);
8311 return size;
8312 }
8313
8314 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8315 HeapWord* addr = (HeapWord*) fc;
8316 // The sweeper has just found a live object. Return any accumulated
8317 // left hand chunk to the free lists.
8318 if (inFreeRange()) {
8319 assert(freeFinger() < addr, "freeFinger points too high");
8320 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8321 }
8322
8323 // This object is live: we'd normally expect this to be
8324 // an oop, and like to assert the following:
8325 // assert(oop(addr)->is_oop(), "live block should be an oop");
8326 // However, as we commented above, this may be an object whose
8327 // header hasn't yet been initialized.
8328 size_t size;
8329 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8330 if (_bitMap->isMarked(addr + 1)) {
8331 // Determine the size from the bit map, rather than trying to
8332 // compute it from the object header.
8333 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8334 size = pointer_delta(nextOneAddr + 1, addr);
8335 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8336 "alignment problem");
8337
8338 #ifdef DEBUG
8339 if (oop(addr)->klass_or_null() != NULL &&
8340 ( !_collector->should_unload_classes()
8341 || (oop(addr)->is_parsable()) &&
8342 oop(addr)->is_conc_safe())) {
8343 // Ignore mark word because we are running concurrent with mutators
8344 assert(oop(addr)->is_oop(true), "live block should be an oop");
8345 // is_conc_safe is checked before performing this assertion
8346 // because an object that is not is_conc_safe may yet have
8347 // the return from size() correct.
8348 assert(size ==
8349 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8350 "P-mark and computed size do not agree");
8351 }
8352 #endif
8353
8354 } else {
8355 // This should be an initialized object that's alive.
8356 assert(oop(addr)->klass_or_null() != NULL &&
8357 (!_collector->should_unload_classes()
8358 || oop(addr)->is_parsable()),
8359 "Should be an initialized object");
8360 // Note that there are objects used during class redefinition,
8361 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8362 // which are discarded with their is_conc_safe state still
8363 // false. These object may be floating garbage so may be
8364 // seen here. If they are floating garbage their size
8365 // should be attainable from their klass. Do not that
8366 // is_conc_safe() is true for oop(addr).
8367 // Ignore mark word because we are running concurrent with mutators
8368 assert(oop(addr)->is_oop(true), "live block should be an oop");
8369 // Verify that the bit map has no bits marked between
8370 // addr and purported end of this block.
8371 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8372 assert(size >= 3, "Necessary for Printezis marks to work");
8373 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8374 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8375 }
8376 return size;
8377 }
8378
8379 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8380 size_t chunkSize) {
8381 // do_post_free_or_garbage_chunk() should only be called in the case
8382 // of the adaptive free list allocator.
8383 const bool fcInFreeLists = fc->is_free();
8384 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8385 assert((HeapWord*)fc <= _limit, "sweep invariant");
8386 if (CMSTestInFreeList && fcInFreeLists) {
8387 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8388 }
8389
8390 if (CMSTraceSweeper) {
8391 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8392 }
8393
8394 HeapWord* const fc_addr = (HeapWord*) fc;
8395
8396 bool coalesce;
8397 const size_t left = pointer_delta(fc_addr, freeFinger());
8398 const size_t right = chunkSize;
8399 switch (FLSCoalescePolicy) {
8400 // numeric value forms a coalition aggressiveness metric
8401 case 0: { // never coalesce
8402 coalesce = false;
8403 break;
8404 }
8405 case 1: { // coalesce if left & right chunks on overpopulated lists
8406 coalesce = _sp->coalOverPopulated(left) &&
8407 _sp->coalOverPopulated(right);
8408 break;
8409 }
8410 case 2: { // coalesce if left chunk on overpopulated list (default)
8411 coalesce = _sp->coalOverPopulated(left);
8412 break;
8413 }
8414 case 3: { // coalesce if left OR right chunk on overpopulated list
8415 coalesce = _sp->coalOverPopulated(left) ||
8416 _sp->coalOverPopulated(right);
8417 break;
8418 }
8419 case 4: { // always coalesce
8420 coalesce = true;
8421 break;
8422 }
8423 default:
8424 ShouldNotReachHere();
8425 }
8426
8427 // Should the current free range be coalesced?
8428 // If the chunk is in a free range and either we decided to coalesce above
8429 // or the chunk is near the large block at the end of the heap
8430 // (isNearLargestChunk() returns true), then coalesce this chunk.
8431 const bool doCoalesce = inFreeRange()
8432 && (coalesce || _g->isNearLargestChunk(fc_addr));
8433 if (doCoalesce) {
8434 // Coalesce the current free range on the left with the new
8435 // chunk on the right. If either is on a free list,
8436 // it must be removed from the list and stashed in the closure.
8437 if (freeRangeInFreeLists()) {
8438 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8439 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8440 "Size of free range is inconsistent with chunk size.");
8441 if (CMSTestInFreeList) {
8442 assert(_sp->verify_chunk_in_free_list(ffc),
8443 "Chunk is not in free lists");
8444 }
8445 _sp->coalDeath(ffc->size());
8446 _sp->removeFreeChunkFromFreeLists(ffc);
8447 set_freeRangeInFreeLists(false);
8448 }
8449 if (fcInFreeLists) {
8450 _sp->coalDeath(chunkSize);
8451 assert(fc->size() == chunkSize,
8452 "The chunk has the wrong size or is not in the free lists");
8453 _sp->removeFreeChunkFromFreeLists(fc);
8454 }
8455 set_lastFreeRangeCoalesced(true);
8456 print_free_block_coalesced(fc);
8457 } else { // not in a free range and/or should not coalesce
8458 // Return the current free range and start a new one.
8459 if (inFreeRange()) {
8460 // In a free range but cannot coalesce with the right hand chunk.
8461 // Put the current free range into the free lists.
8462 flush_cur_free_chunk(freeFinger(),
8463 pointer_delta(fc_addr, freeFinger()));
8464 }
8465 // Set up for new free range. Pass along whether the right hand
8466 // chunk is in the free lists.
8467 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8468 }
8469 }
8470
8471 // Lookahead flush:
8472 // If we are tracking a free range, and this is the last chunk that
8473 // we'll look at because its end crosses past _limit, we'll preemptively
8474 // flush it along with any free range we may be holding on to. Note that
8475 // this can be the case only for an already free or freshly garbage
8476 // chunk. If this block is an object, it can never straddle
8477 // over _limit. The "straddling" occurs when _limit is set at
8478 // the previous end of the space when this cycle started, and
8479 // a subsequent heap expansion caused the previously co-terminal
8480 // free block to be coalesced with the newly expanded portion,
8481 // thus rendering _limit a non-block-boundary making it dangerous
8482 // for the sweeper to step over and examine.
8483 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8484 assert(inFreeRange(), "Should only be called if currently in a free range.");
8485 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8486 assert(_sp->used_region().contains(eob - 1),
8487 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8488 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8489 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8490 if (eob >= _limit) {
8491 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8492 if (CMSTraceSweeper) {
8493 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8494 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8495 "[" PTR_FORMAT "," PTR_FORMAT ")",
8496 _limit, fc, eob, _sp->bottom(), _sp->end());
8497 }
8498 // Return the storage we are tracking back into the free lists.
8499 if (CMSTraceSweeper) {
8500 gclog_or_tty->print_cr("Flushing ... ");
8501 }
8502 assert(freeFinger() < eob, "Error");
8503 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8504 }
8505 }
8506
8507 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8508 assert(inFreeRange(), "Should only be called if currently in a free range.");
8509 assert(size > 0,
8510 "A zero sized chunk cannot be added to the free lists.");
8511 if (!freeRangeInFreeLists()) {
8512 if (CMSTestInFreeList) {
8513 FreeChunk* fc = (FreeChunk*) chunk;
8514 fc->set_size(size);
8515 assert(!_sp->verify_chunk_in_free_list(fc),
8516 "chunk should not be in free lists yet");
8517 }
8518 if (CMSTraceSweeper) {
8519 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8520 chunk, size);
8521 }
8522 // A new free range is going to be starting. The current
8523 // free range has not been added to the free lists yet or
8524 // was removed so add it back.
8525 // If the current free range was coalesced, then the death
8526 // of the free range was recorded. Record a birth now.
8527 if (lastFreeRangeCoalesced()) {
8528 _sp->coalBirth(size);
8529 }
8530 _sp->addChunkAndRepairOffsetTable(chunk, size,
8531 lastFreeRangeCoalesced());
8532 } else if (CMSTraceSweeper) {
8533 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8534 }
8535 set_inFreeRange(false);
8536 set_freeRangeInFreeLists(false);
8537 }
8538
8539 // We take a break if we've been at this for a while,
8540 // so as to avoid monopolizing the locks involved.
8541 void SweepClosure::do_yield_work(HeapWord* addr) {
8542 // Return current free chunk being used for coalescing (if any)
8543 // to the appropriate freelist. After yielding, the next
8544 // free block encountered will start a coalescing range of
8545 // free blocks. If the next free block is adjacent to the
8546 // chunk just flushed, they will need to wait for the next
8547 // sweep to be coalesced.
8548 if (inFreeRange()) {
8549 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8550 }
8551
8552 // First give up the locks, then yield, then re-lock.
8553 // We should probably use a constructor/destructor idiom to
8554 // do this unlock/lock or modify the MutexUnlocker class to
8555 // serve our purpose. XXX
8556 assert_lock_strong(_bitMap->lock());
8557 assert_lock_strong(_freelistLock);
8558 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8559 "CMS thread should hold CMS token");
8560 _bitMap->lock()->unlock();
8561 _freelistLock->unlock();
8562 ConcurrentMarkSweepThread::desynchronize(true);
8563 ConcurrentMarkSweepThread::acknowledge_yield_request();
8564 _collector->stopTimer();
8565 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8566 if (PrintCMSStatistics != 0) {
8567 _collector->incrementYields();
8568 }
8569 _collector->icms_wait();
8570
8571 // See the comment in coordinator_yield()
8572 for (unsigned i = 0; i < CMSYieldSleepCount &&
8573 ConcurrentMarkSweepThread::should_yield() &&
8574 !CMSCollector::foregroundGCIsActive(); ++i) {
8575 os::sleep(Thread::current(), 1, false);
8576 ConcurrentMarkSweepThread::acknowledge_yield_request();
8577 }
8578
8579 ConcurrentMarkSweepThread::synchronize(true);
8580 _freelistLock->lock();
8581 _bitMap->lock()->lock_without_safepoint_check();
8582 _collector->startTimer();
8583 }
8584
8585 #ifndef PRODUCT
8586 // This is actually very useful in a product build if it can
8587 // be called from the debugger. Compile it into the product
8588 // as needed.
8589 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8590 return debug_cms_space->verify_chunk_in_free_list(fc);
8591 }
8592 #endif
8593
8594 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8595 if (CMSTraceSweeper) {
8596 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8597 fc, fc->size());
8598 }
8599 }
8600
8601 // CMSIsAliveClosure
8602 bool CMSIsAliveClosure::do_object_b(oop obj) {
8603 HeapWord* addr = (HeapWord*)obj;
8604 return addr != NULL &&
8605 (!_span.contains(addr) || _bit_map->isMarked(addr));
8606 }
8607
8608 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8609 MemRegion span,
8610 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8611 CMSMarkStack* revisit_stack, bool cpc):
8612 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8613 _span(span),
8614 _bit_map(bit_map),
8615 _mark_stack(mark_stack),
8616 _concurrent_precleaning(cpc) {
8617 assert(!_span.is_empty(), "Empty span could spell trouble");
8618 }
8619
8620
8621 // CMSKeepAliveClosure: the serial version
8622 void CMSKeepAliveClosure::do_oop(oop obj) {
8623 HeapWord* addr = (HeapWord*)obj;
8624 if (_span.contains(addr) &&
8625 !_bit_map->isMarked(addr)) {
8626 _bit_map->mark(addr);
8627 bool simulate_overflow = false;
8628 NOT_PRODUCT(
8629 if (CMSMarkStackOverflowALot &&
8630 _collector->simulate_overflow()) {
8631 // simulate a stack overflow
8632 simulate_overflow = true;
8633 }
8634 )
8635 if (simulate_overflow || !_mark_stack->push(obj)) {
8636 if (_concurrent_precleaning) {
8637 // We dirty the overflown object and let the remark
8638 // phase deal with it.
8639 assert(_collector->overflow_list_is_empty(), "Error");
8640 // In the case of object arrays, we need to dirty all of
8641 // the cards that the object spans. No locking or atomics
8642 // are needed since no one else can be mutating the mod union
8643 // table.
8644 if (obj->is_objArray()) {
8645 size_t sz = obj->size();
8646 HeapWord* end_card_addr =
8647 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8648 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8649 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8650 _collector->_modUnionTable.mark_range(redirty_range);
8651 } else {
8652 _collector->_modUnionTable.mark(addr);
8653 }
8654 _collector->_ser_kac_preclean_ovflw++;
8655 } else {
8656 _collector->push_on_overflow_list(obj);
8657 _collector->_ser_kac_ovflw++;
8658 }
8659 }
8660 }
8661 }
8662
8663 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8664 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8665
8666 // CMSParKeepAliveClosure: a parallel version of the above.
8667 // The work queues are private to each closure (thread),
8668 // but (may be) available for stealing by other threads.
8669 void CMSParKeepAliveClosure::do_oop(oop obj) {
8670 HeapWord* addr = (HeapWord*)obj;
8671 if (_span.contains(addr) &&
8672 !_bit_map->isMarked(addr)) {
8673 // In general, during recursive tracing, several threads
8674 // may be concurrently getting here; the first one to
8675 // "tag" it, claims it.
8676 if (_bit_map->par_mark(addr)) {
8677 bool res = _work_queue->push(obj);
8678 assert(res, "Low water mark should be much less than capacity");
8679 // Do a recursive trim in the hope that this will keep
8680 // stack usage lower, but leave some oops for potential stealers
8681 trim_queue(_low_water_mark);
8682 } // Else, another thread got there first
8683 }
8684 }
8685
8686 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8687 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8688
8689 void CMSParKeepAliveClosure::trim_queue(uint max) {
8690 while (_work_queue->size() > max) {
8691 oop new_oop;
8692 if (_work_queue->pop_local(new_oop)) {
8693 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8694 assert(_bit_map->isMarked((HeapWord*)new_oop),
8695 "no white objects on this stack!");
8696 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8697 // iterate over the oops in this oop, marking and pushing
8698 // the ones in CMS heap (i.e. in _span).
8699 new_oop->oop_iterate(&_mark_and_push);
8700 }
8701 }
8702 }
8703
8704 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8705 CMSCollector* collector,
8706 MemRegion span, CMSBitMap* bit_map,
8707 CMSMarkStack* revisit_stack,
8708 OopTaskQueue* work_queue):
8709 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8710 _span(span),
8711 _bit_map(bit_map),
8712 _work_queue(work_queue) { }
8713
8714 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8715 HeapWord* addr = (HeapWord*)obj;
8716 if (_span.contains(addr) &&
8717 !_bit_map->isMarked(addr)) {
8718 if (_bit_map->par_mark(addr)) {
8719 bool simulate_overflow = false;
8720 NOT_PRODUCT(
8721 if (CMSMarkStackOverflowALot &&
8722 _collector->par_simulate_overflow()) {
8723 // simulate a stack overflow
8724 simulate_overflow = true;
8725 }
8726 )
8727 if (simulate_overflow || !_work_queue->push(obj)) {
8728 _collector->par_push_on_overflow_list(obj);
8729 _collector->_par_kac_ovflw++;
8730 }
8731 } // Else another thread got there already
8732 }
8733 }
8734
8735 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8736 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8737
8738 //////////////////////////////////////////////////////////////////
8739 // CMSExpansionCause /////////////////////////////
8740 //////////////////////////////////////////////////////////////////
8741 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8742 switch (cause) {
8743 case _no_expansion:
8744 return "No expansion";
8745 case _satisfy_free_ratio:
8746 return "Free ratio";
8747 case _satisfy_promotion:
8748 return "Satisfy promotion";
8749 case _satisfy_allocation:
8750 return "allocation";
8751 case _allocate_par_lab:
8752 return "Par LAB";
8753 case _allocate_par_spooling_space:
8754 return "Par Spooling Space";
8755 case _adaptive_size_policy:
8756 return "Ergonomics";
8757 default:
8758 return "unknown";
8759 }
8760 }
8761
8762 void CMSDrainMarkingStackClosure::do_void() {
8763 // the max number to take from overflow list at a time
8764 const size_t num = _mark_stack->capacity()/4;
8765 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8766 "Overflow list should be NULL during concurrent phases");
8767 while (!_mark_stack->isEmpty() ||
8768 // if stack is empty, check the overflow list
8769 _collector->take_from_overflow_list(num, _mark_stack)) {
8770 oop obj = _mark_stack->pop();
8771 HeapWord* addr = (HeapWord*)obj;
8772 assert(_span.contains(addr), "Should be within span");
8773 assert(_bit_map->isMarked(addr), "Should be marked");
8774 assert(obj->is_oop(), "Should be an oop");
8775 obj->oop_iterate(_keep_alive);
8776 }
8777 }
8778
8779 void CMSParDrainMarkingStackClosure::do_void() {
8780 // drain queue
8781 trim_queue(0);
8782 }
8783
8784 // Trim our work_queue so its length is below max at return
8785 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8786 while (_work_queue->size() > max) {
8787 oop new_oop;
8788 if (_work_queue->pop_local(new_oop)) {
8789 assert(new_oop->is_oop(), "Expected an oop");
8790 assert(_bit_map->isMarked((HeapWord*)new_oop),
8791 "no white objects on this stack!");
8792 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8793 // iterate over the oops in this oop, marking and pushing
8794 // the ones in CMS heap (i.e. in _span).
8795 new_oop->oop_iterate(&_mark_and_push);
8796 }
8797 }
8798 }
8799
8800 ////////////////////////////////////////////////////////////////////
8801 // Support for Marking Stack Overflow list handling and related code
8802 ////////////////////////////////////////////////////////////////////
8803 // Much of the following code is similar in shape and spirit to the
8804 // code used in ParNewGC. We should try and share that code
8805 // as much as possible in the future.
8806
8807 #ifndef PRODUCT
8808 // Debugging support for CMSStackOverflowALot
8809
8810 // It's OK to call this multi-threaded; the worst thing
8811 // that can happen is that we'll get a bunch of closely
8812 // spaced simulated oveflows, but that's OK, in fact
8813 // probably good as it would exercise the overflow code
8814 // under contention.
8815 bool CMSCollector::simulate_overflow() {
8816 if (_overflow_counter-- <= 0) { // just being defensive
8817 _overflow_counter = CMSMarkStackOverflowInterval;
8818 return true;
8819 } else {
8820 return false;
8821 }
8822 }
8823
8824 bool CMSCollector::par_simulate_overflow() {
8825 return simulate_overflow();
8826 }
8827 #endif
8828
8829 // Single-threaded
8830 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8831 assert(stack->isEmpty(), "Expected precondition");
8832 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8833 size_t i = num;
8834 oop cur = _overflow_list;
8835 const markOop proto = markOopDesc::prototype();
8836 NOT_PRODUCT(ssize_t n = 0;)
8837 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8838 next = oop(cur->mark());
8839 cur->set_mark(proto); // until proven otherwise
8840 assert(cur->is_oop(), "Should be an oop");
8841 bool res = stack->push(cur);
8842 assert(res, "Bit off more than can chew?");
8843 NOT_PRODUCT(n++;)
8844 }
8845 _overflow_list = cur;
8846 #ifndef PRODUCT
8847 assert(_num_par_pushes >= n, "Too many pops?");
8848 _num_par_pushes -=n;
8849 #endif
8850 return !stack->isEmpty();
8851 }
8852
8853 #define BUSY (oop(0x1aff1aff))
8854 // (MT-safe) Get a prefix of at most "num" from the list.
8855 // The overflow list is chained through the mark word of
8856 // each object in the list. We fetch the entire list,
8857 // break off a prefix of the right size and return the
8858 // remainder. If other threads try to take objects from
8859 // the overflow list at that time, they will wait for
8860 // some time to see if data becomes available. If (and
8861 // only if) another thread places one or more object(s)
8862 // on the global list before we have returned the suffix
8863 // to the global list, we will walk down our local list
8864 // to find its end and append the global list to
8865 // our suffix before returning it. This suffix walk can
8866 // prove to be expensive (quadratic in the amount of traffic)
8867 // when there are many objects in the overflow list and
8868 // there is much producer-consumer contention on the list.
8869 // *NOTE*: The overflow list manipulation code here and
8870 // in ParNewGeneration:: are very similar in shape,
8871 // except that in the ParNew case we use the old (from/eden)
8872 // copy of the object to thread the list via its klass word.
8873 // Because of the common code, if you make any changes in
8874 // the code below, please check the ParNew version to see if
8875 // similar changes might be needed.
8876 // CR 6797058 has been filed to consolidate the common code.
8877 bool CMSCollector::par_take_from_overflow_list(size_t num,
8878 OopTaskQueue* work_q,
8879 int no_of_gc_threads) {
8880 assert(work_q->size() == 0, "First empty local work queue");
8881 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8882 if (_overflow_list == NULL) {
8883 return false;
8884 }
8885 // Grab the entire list; we'll put back a suffix
8886 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8887 Thread* tid = Thread::current();
8888 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8889 // set to ParallelGCThreads.
8890 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8891 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8892 // If the list is busy, we spin for a short while,
8893 // sleeping between attempts to get the list.
8894 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8895 os::sleep(tid, sleep_time_millis, false);
8896 if (_overflow_list == NULL) {
8897 // Nothing left to take
8898 return false;
8899 } else if (_overflow_list != BUSY) {
8900 // Try and grab the prefix
8901 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8902 }
8903 }
8904 // If the list was found to be empty, or we spun long
8905 // enough, we give up and return empty-handed. If we leave
8906 // the list in the BUSY state below, it must be the case that
8907 // some other thread holds the overflow list and will set it
8908 // to a non-BUSY state in the future.
8909 if (prefix == NULL || prefix == BUSY) {
8910 // Nothing to take or waited long enough
8911 if (prefix == NULL) {
8912 // Write back the NULL in case we overwrote it with BUSY above
8913 // and it is still the same value.
8914 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8915 }
8916 return false;
8917 }
8918 assert(prefix != NULL && prefix != BUSY, "Error");
8919 size_t i = num;
8920 oop cur = prefix;
8921 // Walk down the first "num" objects, unless we reach the end.
8922 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8923 if (cur->mark() == NULL) {
8924 // We have "num" or fewer elements in the list, so there
8925 // is nothing to return to the global list.
8926 // Write back the NULL in lieu of the BUSY we wrote
8927 // above, if it is still the same value.
8928 if (_overflow_list == BUSY) {
8929 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8930 }
8931 } else {
8932 // Chop off the suffix and rerturn it to the global list.
8933 assert(cur->mark() != BUSY, "Error");
8934 oop suffix_head = cur->mark(); // suffix will be put back on global list
8935 cur->set_mark(NULL); // break off suffix
8936 // It's possible that the list is still in the empty(busy) state
8937 // we left it in a short while ago; in that case we may be
8938 // able to place back the suffix without incurring the cost
8939 // of a walk down the list.
8940 oop observed_overflow_list = _overflow_list;
8941 oop cur_overflow_list = observed_overflow_list;
8942 bool attached = false;
8943 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8944 observed_overflow_list =
8945 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8946 if (cur_overflow_list == observed_overflow_list) {
8947 attached = true;
8948 break;
8949 } else cur_overflow_list = observed_overflow_list;
8950 }
8951 if (!attached) {
8952 // Too bad, someone else sneaked in (at least) an element; we'll need
8953 // to do a splice. Find tail of suffix so we can prepend suffix to global
8954 // list.
8955 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8956 oop suffix_tail = cur;
8957 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8958 "Tautology");
8959 observed_overflow_list = _overflow_list;
8960 do {
8961 cur_overflow_list = observed_overflow_list;
8962 if (cur_overflow_list != BUSY) {
8963 // Do the splice ...
8964 suffix_tail->set_mark(markOop(cur_overflow_list));
8965 } else { // cur_overflow_list == BUSY
8966 suffix_tail->set_mark(NULL);
8967 }
8968 // ... and try to place spliced list back on overflow_list ...
8969 observed_overflow_list =
8970 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8971 } while (cur_overflow_list != observed_overflow_list);
8972 // ... until we have succeeded in doing so.
8973 }
8974 }
8975
8976 // Push the prefix elements on work_q
8977 assert(prefix != NULL, "control point invariant");
8978 const markOop proto = markOopDesc::prototype();
8979 oop next;
8980 NOT_PRODUCT(ssize_t n = 0;)
8981 for (cur = prefix; cur != NULL; cur = next) {
8982 next = oop(cur->mark());
8983 cur->set_mark(proto); // until proven otherwise
8984 assert(cur->is_oop(), "Should be an oop");
8985 bool res = work_q->push(cur);
8986 assert(res, "Bit off more than we can chew?");
8987 NOT_PRODUCT(n++;)
8988 }
8989 #ifndef PRODUCT
8990 assert(_num_par_pushes >= n, "Too many pops?");
8991 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8992 #endif
8993 return true;
8994 }
8995
8996 // Single-threaded
8997 void CMSCollector::push_on_overflow_list(oop p) {
8998 NOT_PRODUCT(_num_par_pushes++;)
8999 assert(p->is_oop(), "Not an oop");
9000 preserve_mark_if_necessary(p);
9001 p->set_mark((markOop)_overflow_list);
9002 _overflow_list = p;
9003 }
9004
9005 // Multi-threaded; use CAS to prepend to overflow list
9006 void CMSCollector::par_push_on_overflow_list(oop p) {
9007 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9008 assert(p->is_oop(), "Not an oop");
9009 par_preserve_mark_if_necessary(p);
9010 oop observed_overflow_list = _overflow_list;
9011 oop cur_overflow_list;
9012 do {
9013 cur_overflow_list = observed_overflow_list;
9014 if (cur_overflow_list != BUSY) {
9015 p->set_mark(markOop(cur_overflow_list));
9016 } else {
9017 p->set_mark(NULL);
9018 }
9019 observed_overflow_list =
9020 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9021 } while (cur_overflow_list != observed_overflow_list);
9022 }
9023 #undef BUSY
9024
9025 // Single threaded
9026 // General Note on GrowableArray: pushes may silently fail
9027 // because we are (temporarily) out of C-heap for expanding
9028 // the stack. The problem is quite ubiquitous and affects
9029 // a lot of code in the JVM. The prudent thing for GrowableArray
9030 // to do (for now) is to exit with an error. However, that may
9031 // be too draconian in some cases because the caller may be
9032 // able to recover without much harm. For such cases, we
9033 // should probably introduce a "soft_push" method which returns
9034 // an indication of success or failure with the assumption that
9035 // the caller may be able to recover from a failure; code in
9036 // the VM can then be changed, incrementally, to deal with such
9037 // failures where possible, thus, incrementally hardening the VM
9038 // in such low resource situations.
9039 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9040 _preserved_oop_stack.push(p);
9041 _preserved_mark_stack.push(m);
9042 assert(m == p->mark(), "Mark word changed");
9043 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9044 "bijection");
9045 }
9046
9047 // Single threaded
9048 void CMSCollector::preserve_mark_if_necessary(oop p) {
9049 markOop m = p->mark();
9050 if (m->must_be_preserved(p)) {
9051 preserve_mark_work(p, m);
9052 }
9053 }
9054
9055 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9056 markOop m = p->mark();
9057 if (m->must_be_preserved(p)) {
9058 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9059 // Even though we read the mark word without holding
9060 // the lock, we are assured that it will not change
9061 // because we "own" this oop, so no other thread can
9062 // be trying to push it on the overflow list; see
9063 // the assertion in preserve_mark_work() that checks
9064 // that m == p->mark().
9065 preserve_mark_work(p, m);
9066 }
9067 }
9068
9069 // We should be able to do this multi-threaded,
9070 // a chunk of stack being a task (this is
9071 // correct because each oop only ever appears
9072 // once in the overflow list. However, it's
9073 // not very easy to completely overlap this with
9074 // other operations, so will generally not be done
9075 // until all work's been completed. Because we
9076 // expect the preserved oop stack (set) to be small,
9077 // it's probably fine to do this single-threaded.
9078 // We can explore cleverer concurrent/overlapped/parallel
9079 // processing of preserved marks if we feel the
9080 // need for this in the future. Stack overflow should
9081 // be so rare in practice and, when it happens, its
9082 // effect on performance so great that this will
9083 // likely just be in the noise anyway.
9084 void CMSCollector::restore_preserved_marks_if_any() {
9085 assert(SafepointSynchronize::is_at_safepoint(),
9086 "world should be stopped");
9087 assert(Thread::current()->is_ConcurrentGC_thread() ||
9088 Thread::current()->is_VM_thread(),
9089 "should be single-threaded");
9090 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9091 "bijection");
9092
9093 while (!_preserved_oop_stack.is_empty()) {
9094 oop p = _preserved_oop_stack.pop();
9095 assert(p->is_oop(), "Should be an oop");
9096 assert(_span.contains(p), "oop should be in _span");
9097 assert(p->mark() == markOopDesc::prototype(),
9098 "Set when taken from overflow list");
9099 markOop m = _preserved_mark_stack.pop();
9100 p->set_mark(m);
9101 }
9102 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9103 "stacks were cleared above");
9104 }
9105
9106 #ifndef PRODUCT
9107 bool CMSCollector::no_preserved_marks() const {
9108 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9109 }
9110 #endif
9111
9112 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9113 {
9114 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9115 CMSAdaptiveSizePolicy* size_policy =
9116 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9117 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9118 "Wrong type for size policy");
9119 return size_policy;
9120 }
9121
9122 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9123 size_t desired_promo_size) {
9124 if (cur_promo_size < desired_promo_size) {
9125 size_t expand_bytes = desired_promo_size - cur_promo_size;
9126 if (PrintAdaptiveSizePolicy && Verbose) {
9127 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9128 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9129 expand_bytes);
9130 }
9131 expand(expand_bytes,
9132 MinHeapDeltaBytes,
9133 CMSExpansionCause::_adaptive_size_policy);
9134 } else if (desired_promo_size < cur_promo_size) {
9135 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9136 if (PrintAdaptiveSizePolicy && Verbose) {
9137 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9138 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9139 shrink_bytes);
9140 }
9141 shrink(shrink_bytes);
9142 }
9143 }
9144
9145 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9146 GenCollectedHeap* gch = GenCollectedHeap::heap();
9147 CMSGCAdaptivePolicyCounters* counters =
9148 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9149 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9150 "Wrong kind of counters");
9151 return counters;
9152 }
9153
9154
9155 void ASConcurrentMarkSweepGeneration::update_counters() {
9156 if (UsePerfData) {
9157 _space_counters->update_all();
9158 _gen_counters->update_all();
9159 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9160 GenCollectedHeap* gch = GenCollectedHeap::heap();
9161 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9162 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9163 "Wrong gc statistics type");
9164 counters->update_counters(gc_stats_l);
9165 }
9166 }
9167
9168 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9169 if (UsePerfData) {
9170 _space_counters->update_used(used);
9171 _space_counters->update_capacity();
9172 _gen_counters->update_all();
9173
9174 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9175 GenCollectedHeap* gch = GenCollectedHeap::heap();
9176 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9177 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9178 "Wrong gc statistics type");
9179 counters->update_counters(gc_stats_l);
9180 }
9181 }
9182
9183 // The desired expansion delta is computed so that:
9184 // . desired free percentage or greater is used
9185 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9186 assert_locked_or_safepoint(Heap_lock);
9187
9188 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9189
9190 // If incremental collection failed, we just want to expand
9191 // to the limit.
9192 if (incremental_collection_failed()) {
9193 clear_incremental_collection_failed();
9194 grow_to_reserved();
9195 return;
9196 }
9197
9198 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9199
9200 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9201 "Wrong type of heap");
9202 int prev_level = level() - 1;
9203 assert(prev_level >= 0, "The cms generation is the lowest generation");
9204 Generation* prev_gen = gch->get_gen(prev_level);
9205 assert(prev_gen->kind() == Generation::ASParNew,
9206 "Wrong type of young generation");
9207 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9208 size_t cur_eden = younger_gen->eden()->capacity();
9209 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9210 size_t cur_promo = free();
9211 size_policy->compute_tenured_generation_free_space(cur_promo,
9212 max_available(),
9213 cur_eden);
9214 resize(cur_promo, size_policy->promo_size());
9215
9216 // Record the new size of the space in the cms generation
9217 // that is available for promotions. This is temporary.
9218 // It should be the desired promo size.
9219 size_policy->avg_cms_promo()->sample(free());
9220 size_policy->avg_old_live()->sample(used());
9221
9222 if (UsePerfData) {
9223 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9224 counters->update_cms_capacity_counter(capacity());
9225 }
9226 }
9227
9228 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9229 assert_locked_or_safepoint(Heap_lock);
9230 assert_lock_strong(freelistLock());
9231 HeapWord* old_end = _cmsSpace->end();
9232 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9233 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9234 FreeChunk* chunk_at_end = find_chunk_at_end();
9235 if (chunk_at_end == NULL) {
9236 // No room to shrink
9237 if (PrintGCDetails && Verbose) {
9238 gclog_or_tty->print_cr("No room to shrink: old_end "
9239 PTR_FORMAT " unallocated_start " PTR_FORMAT
9240 " chunk_at_end " PTR_FORMAT,
9241 old_end, unallocated_start, chunk_at_end);
9242 }
9243 return;
9244 } else {
9245
9246 // Find the chunk at the end of the space and determine
9247 // how much it can be shrunk.
9248 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9249 size_t aligned_shrinkable_size_in_bytes =
9250 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9251 assert(unallocated_start <= chunk_at_end->end(),
9252 "Inconsistent chunk at end of space");
9253 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9254 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9255
9256 // Shrink the underlying space
9257 _virtual_space.shrink_by(bytes);
9258 if (PrintGCDetails && Verbose) {
9259 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9260 " desired_bytes " SIZE_FORMAT
9261 " shrinkable_size_in_bytes " SIZE_FORMAT
9262 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9263 " bytes " SIZE_FORMAT,
9264 desired_bytes, shrinkable_size_in_bytes,
9265 aligned_shrinkable_size_in_bytes, bytes);
9266 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9267 " unallocated_start " SIZE_FORMAT,
9268 old_end, unallocated_start);
9269 }
9270
9271 // If the space did shrink (shrinking is not guaranteed),
9272 // shrink the chunk at the end by the appropriate amount.
9273 if (((HeapWord*)_virtual_space.high()) < old_end) {
9274 size_t new_word_size =
9275 heap_word_size(_virtual_space.committed_size());
9276
9277 // Have to remove the chunk from the dictionary because it is changing
9278 // size and might be someplace elsewhere in the dictionary.
9279
9280 // Get the chunk at end, shrink it, and put it
9281 // back.
9282 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9283 size_t word_size_change = word_size_before - new_word_size;
9284 size_t chunk_at_end_old_size = chunk_at_end->size();
9285 assert(chunk_at_end_old_size >= word_size_change,
9286 "Shrink is too large");
9287 chunk_at_end->set_size(chunk_at_end_old_size -
9288 word_size_change);
9289 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9290 word_size_change);
9291
9292 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9293
9294 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9295 _bts->resize(new_word_size); // resize the block offset shared array
9296 Universe::heap()->barrier_set()->resize_covered_region(mr);
9297 _cmsSpace->assert_locked();
9298 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9299
9300 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9301
9302 // update the space and generation capacity counters
9303 if (UsePerfData) {
9304 _space_counters->update_capacity();
9305 _gen_counters->update_all();
9306 }
9307
9308 if (Verbose && PrintGCDetails) {
9309 size_t new_mem_size = _virtual_space.committed_size();
9310 size_t old_mem_size = new_mem_size + bytes;
9311 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9312 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9313 }
9314 }
9315
9316 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9317 "Inconsistency at end of space");
9318 assert(chunk_at_end->end() == _cmsSpace->end(),
9319 "Shrinking is inconsistent");
9320 return;
9321 }
9322 }
9323
9324 // Transfer some number of overflown objects to usual marking
9325 // stack. Return true if some objects were transferred.
9326 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9327 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9328 (size_t)ParGCDesiredObjsFromOverflowList);
9329
9330 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9331 assert(_collector->overflow_list_is_empty() || res,
9332 "If list is not empty, we should have taken something");
9333 assert(!res || !_mark_stack->isEmpty(),
9334 "If we took something, it should now be on our stack");
9335 return res;
9336 }
9337
9338 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9339 size_t res = _sp->block_size_no_stall(addr, _collector);
9340 if (_sp->block_is_obj(addr)) {
9341 if (_live_bit_map->isMarked(addr)) {
9342 // It can't have been dead in a previous cycle
9343 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9344 } else {
9345 _dead_bit_map->mark(addr); // mark the dead object
9346 }
9347 }
9348 // Could be 0, if the block size could not be computed without stalling.
9349 return res;
9350 }
9351
9352 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9353
9354 switch (phase) {
9355 case CMSCollector::InitialMarking:
9356 initialize(true /* fullGC */ ,
9357 cause /* cause of the GC */,
9358 true /* recordGCBeginTime */,
9359 true /* recordPreGCUsage */,
9360 false /* recordPeakUsage */,
9361 false /* recordPostGCusage */,
9362 true /* recordAccumulatedGCTime */,
9363 false /* recordGCEndTime */,
9364 false /* countCollection */ );
9365 break;
9366
9367 case CMSCollector::FinalMarking:
9368 initialize(true /* fullGC */ ,
9369 cause /* cause of the GC */,
9370 false /* recordGCBeginTime */,
9371 false /* recordPreGCUsage */,
9372 false /* recordPeakUsage */,
9373 false /* recordPostGCusage */,
9374 true /* recordAccumulatedGCTime */,
9375 false /* recordGCEndTime */,
9376 false /* countCollection */ );
9377 break;
9378
9379 case CMSCollector::Sweeping:
9380 initialize(true /* fullGC */ ,
9381 cause /* cause of the GC */,
9382 false /* recordGCBeginTime */,
9383 false /* recordPreGCUsage */,
9384 true /* recordPeakUsage */,
9385 true /* recordPostGCusage */,
9386 false /* recordAccumulatedGCTime */,
9387 true /* recordGCEndTime */,
9388 true /* countCollection */ );
9389 break;
9390
9391 default:
9392 ShouldNotReachHere();
9393 }
9394 }
9395