1 /*
2 * Copyright (c) 2001, 2018, 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/classLoaderDataGraph.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsGCStats.hpp"
33 #include "gc/cms/cmsHeap.hpp"
34 #include "gc/cms/cmsOopClosures.inline.hpp"
35 #include "gc/cms/compactibleFreeListSpace.hpp"
36 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
37 #include "gc/cms/concurrentMarkSweepThread.hpp"
38 #include "gc/cms/parNewGeneration.hpp"
39 #include "gc/cms/promotionInfo.inline.hpp"
40 #include "gc/cms/vmCMSOperations.hpp"
41 #include "gc/serial/genMarkSweep.hpp"
42 #include "gc/serial/tenuredGeneration.hpp"
43 #include "gc/shared/adaptiveSizePolicy.hpp"
44 #include "gc/shared/cardGeneration.inline.hpp"
45 #include "gc/shared/cardTableRS.hpp"
46 #include "gc/shared/collectedHeap.inline.hpp"
47 #include "gc/shared/collectorCounters.hpp"
48 #include "gc/shared/collectorPolicy.hpp"
49 #include "gc/shared/gcLocker.hpp"
50 #include "gc/shared/gcPolicyCounters.hpp"
51 #include "gc/shared/gcTimer.hpp"
52 #include "gc/shared/gcTrace.hpp"
53 #include "gc/shared/gcTraceTime.inline.hpp"
54 #include "gc/shared/genCollectedHeap.hpp"
55 #include "gc/shared/genOopClosures.inline.hpp"
56 #include "gc/shared/isGCActiveMark.hpp"
57 #include "gc/shared/oopStorageParState.hpp"
58 #include "gc/shared/referencePolicy.hpp"
59 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
60 #include "gc/shared/space.inline.hpp"
61 #include "gc/shared/strongRootsScope.hpp"
62 #include "gc/shared/taskqueue.inline.hpp"
63 #include "gc/shared/weakProcessor.hpp"
64 #include "logging/log.hpp"
65 #include "logging/logStream.hpp"
66 #include "memory/allocation.hpp"
67 #include "memory/binaryTreeDictionary.inline.hpp"
68 #include "memory/iterator.inline.hpp"
69 #include "memory/padded.hpp"
70 #include "memory/resourceArea.hpp"
71 #include "oops/access.inline.hpp"
72 #include "oops/oop.inline.hpp"
73 #include "prims/jvmtiExport.hpp"
74 #include "runtime/atomic.hpp"
75 #include "runtime/flags/flagSetting.hpp"
76 #include "runtime/globals_extension.hpp"
77 #include "runtime/handles.inline.hpp"
78 #include "runtime/java.hpp"
79 #include "runtime/orderAccess.hpp"
80 #include "runtime/timer.hpp"
81 #include "runtime/vmThread.hpp"
82 #include "services/memoryService.hpp"
83 #include "services/runtimeService.hpp"
84 #include "utilities/align.hpp"
85 #include "utilities/stack.inline.hpp"
86
87 // statics
88 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
89 bool CMSCollector::_full_gc_requested = false;
90 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
91
92 //////////////////////////////////////////////////////////////////
93 // In support of CMS/VM thread synchronization
94 //////////////////////////////////////////////////////////////////
95 // We split use of the CGC_lock into 2 "levels".
96 // The low-level locking is of the usual CGC_lock monitor. We introduce
97 // a higher level "token" (hereafter "CMS token") built on top of the
98 // low level monitor (hereafter "CGC lock").
99 // The token-passing protocol gives priority to the VM thread. The
100 // CMS-lock doesn't provide any fairness guarantees, but clients
101 // should ensure that it is only held for very short, bounded
102 // durations.
103 //
104 // When either of the CMS thread or the VM thread is involved in
105 // collection operations during which it does not want the other
106 // thread to interfere, it obtains the CMS token.
107 //
108 // If either thread tries to get the token while the other has
109 // it, that thread waits. However, if the VM thread and CMS thread
110 // both want the token, then the VM thread gets priority while the
111 // CMS thread waits. This ensures, for instance, that the "concurrent"
112 // phases of the CMS thread's work do not block out the VM thread
113 // for long periods of time as the CMS thread continues to hog
114 // the token. (See bug 4616232).
115 //
116 // The baton-passing functions are, however, controlled by the
117 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
118 // and here the low-level CMS lock, not the high level token,
119 // ensures mutual exclusion.
120 //
121 // Two important conditions that we have to satisfy:
122 // 1. if a thread does a low-level wait on the CMS lock, then it
123 // relinquishes the CMS token if it were holding that token
124 // when it acquired the low-level CMS lock.
125 // 2. any low-level notifications on the low-level lock
126 // should only be sent when a thread has relinquished the token.
127 //
128 // In the absence of either property, we'd have potential deadlock.
129 //
130 // We protect each of the CMS (concurrent and sequential) phases
131 // with the CMS _token_, not the CMS _lock_.
132 //
133 // The only code protected by CMS lock is the token acquisition code
134 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
135 // baton-passing code.
136 //
137 // Unfortunately, i couldn't come up with a good abstraction to factor and
138 // hide the naked CGC_lock manipulation in the baton-passing code
139 // further below. That's something we should try to do. Also, the proof
140 // of correctness of this 2-level locking scheme is far from obvious,
141 // and potentially quite slippery. We have an uneasy suspicion, for instance,
142 // that there may be a theoretical possibility of delay/starvation in the
143 // low-level lock/wait/notify scheme used for the baton-passing because of
144 // potential interference with the priority scheme embodied in the
145 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
146 // invocation further below and marked with "XXX 20011219YSR".
147 // Indeed, as we note elsewhere, this may become yet more slippery
148 // in the presence of multiple CMS and/or multiple VM threads. XXX
149
150 class CMSTokenSync: public StackObj {
151 private:
152 bool _is_cms_thread;
153 public:
154 CMSTokenSync(bool is_cms_thread):
155 _is_cms_thread(is_cms_thread) {
156 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
157 "Incorrect argument to constructor");
158 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
159 }
160
161 ~CMSTokenSync() {
162 assert(_is_cms_thread ?
163 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
164 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
165 "Incorrect state");
166 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
167 }
168 };
169
170 // Convenience class that does a CMSTokenSync, and then acquires
171 // upto three locks.
172 class CMSTokenSyncWithLocks: public CMSTokenSync {
173 private:
174 // Note: locks are acquired in textual declaration order
175 // and released in the opposite order
176 MutexLockerEx _locker1, _locker2, _locker3;
177 public:
178 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
179 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
180 CMSTokenSync(is_cms_thread),
181 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
182 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
183 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
184 { }
185 };
186
187
188 //////////////////////////////////////////////////////////////////
189 // Concurrent Mark-Sweep Generation /////////////////////////////
190 //////////////////////////////////////////////////////////////////
191
192 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
193
194 // This struct contains per-thread things necessary to support parallel
195 // young-gen collection.
196 class CMSParGCThreadState: public CHeapObj<mtGC> {
197 public:
198 CompactibleFreeListSpaceLAB lab;
199 PromotionInfo promo;
200
201 // Constructor.
202 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
203 promo.setSpace(cfls);
204 }
205 };
206
207 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
208 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
209 CardGeneration(rs, initial_byte_size, ct),
210 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
211 _did_compact(false)
212 {
213 HeapWord* bottom = (HeapWord*) _virtual_space.low();
214 HeapWord* end = (HeapWord*) _virtual_space.high();
215
216 _direct_allocated_words = 0;
217 NOT_PRODUCT(
218 _numObjectsPromoted = 0;
219 _numWordsPromoted = 0;
220 _numObjectsAllocated = 0;
221 _numWordsAllocated = 0;
222 )
223
224 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
225 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
226 _cmsSpace->_old_gen = this;
227
228 _gc_stats = new CMSGCStats();
229
230 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
231 // offsets match. The ability to tell free chunks from objects
232 // depends on this property.
233 debug_only(
234 FreeChunk* junk = NULL;
235 assert(UseCompressedClassPointers ||
236 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
237 "Offset of FreeChunk::_prev within FreeChunk must match"
238 " that of OopDesc::_klass within OopDesc");
239 )
240
241 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
242 for (uint i = 0; i < ParallelGCThreads; i++) {
243 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
244 }
245
246 _incremental_collection_failed = false;
247 // The "dilatation_factor" is the expansion that can occur on
248 // account of the fact that the minimum object size in the CMS
249 // generation may be larger than that in, say, a contiguous young
250 // generation.
251 // Ideally, in the calculation below, we'd compute the dilatation
252 // factor as: MinChunkSize/(promoting_gen's min object size)
253 // Since we do not have such a general query interface for the
254 // promoting generation, we'll instead just use the minimum
255 // object size (which today is a header's worth of space);
256 // note that all arithmetic is in units of HeapWords.
257 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
258 assert(_dilatation_factor >= 1.0, "from previous assert");
259 }
260
261
262 // The field "_initiating_occupancy" represents the occupancy percentage
263 // at which we trigger a new collection cycle. Unless explicitly specified
264 // via CMSInitiatingOccupancyFraction (argument "io" below), it
265 // is calculated by:
266 //
267 // Let "f" be MinHeapFreeRatio in
268 //
269 // _initiating_occupancy = 100-f +
270 // f * (CMSTriggerRatio/100)
271 // where CMSTriggerRatio is the argument "tr" below.
272 //
273 // That is, if we assume the heap is at its desired maximum occupancy at the
274 // end of a collection, we let CMSTriggerRatio of the (purported) free
275 // space be allocated before initiating a new collection cycle.
276 //
277 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
278 assert(io <= 100 && tr <= 100, "Check the arguments");
279 if (io >= 0) {
280 _initiating_occupancy = (double)io / 100.0;
281 } else {
282 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
283 (double)(tr * MinHeapFreeRatio) / 100.0)
284 / 100.0;
285 }
286 }
287
288 void ConcurrentMarkSweepGeneration::ref_processor_init() {
289 assert(collector() != NULL, "no collector");
290 collector()->ref_processor_init();
291 }
292
293 void CMSCollector::ref_processor_init() {
294 if (_ref_processor == NULL) {
295 // Allocate and initialize a reference processor
296 _ref_processor =
297 new ReferenceProcessor(&_span_based_discoverer,
298 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
299 ParallelGCThreads, // mt processing degree
300 _cmsGen->refs_discovery_is_mt(), // mt discovery
301 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
302 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
303 &_is_alive_closure, // closure for liveness info
304 false); // disable adjusting number of processing threads
305 // Initialize the _ref_processor field of CMSGen
306 _cmsGen->set_ref_processor(_ref_processor);
307
308 }
309 }
310
311 AdaptiveSizePolicy* CMSCollector::size_policy() {
312 return CMSHeap::heap()->size_policy();
313 }
314
315 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
316
317 const char* gen_name = "old";
318 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
319 // Generation Counters - generation 1, 1 subspace
320 _gen_counters = new GenerationCounters(gen_name, 1, 1,
321 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
322
323 _space_counters = new GSpaceCounters(gen_name, 0,
324 _virtual_space.reserved_size(),
325 this, _gen_counters);
326 }
327
328 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
329 _cms_gen(cms_gen)
330 {
331 assert(alpha <= 100, "bad value");
332 _saved_alpha = alpha;
333
334 // Initialize the alphas to the bootstrap value of 100.
335 _gc0_alpha = _cms_alpha = 100;
336
337 _cms_begin_time.update();
338 _cms_end_time.update();
339
340 _gc0_duration = 0.0;
341 _gc0_period = 0.0;
342 _gc0_promoted = 0;
343
344 _cms_duration = 0.0;
345 _cms_period = 0.0;
346 _cms_allocated = 0;
347
348 _cms_used_at_gc0_begin = 0;
349 _cms_used_at_gc0_end = 0;
350 _allow_duty_cycle_reduction = false;
351 _valid_bits = 0;
352 }
353
354 double CMSStats::cms_free_adjustment_factor(size_t free) const {
355 // TBD: CR 6909490
356 return 1.0;
357 }
358
359 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
360 }
361
362 // If promotion failure handling is on use
363 // the padded average size of the promotion for each
364 // young generation collection.
365 double CMSStats::time_until_cms_gen_full() const {
366 size_t cms_free = _cms_gen->cmsSpace()->free();
367 CMSHeap* heap = CMSHeap::heap();
368 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
369 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
370 if (cms_free > expected_promotion) {
371 // Start a cms collection if there isn't enough space to promote
372 // for the next young collection. Use the padded average as
373 // a safety factor.
374 cms_free -= expected_promotion;
375
376 // Adjust by the safety factor.
377 double cms_free_dbl = (double)cms_free;
378 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
379 // Apply a further correction factor which tries to adjust
380 // for recent occurance of concurrent mode failures.
381 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
382 cms_free_dbl = cms_free_dbl * cms_adjustment;
383
384 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
385 cms_free, expected_promotion);
386 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
387 // Add 1 in case the consumption rate goes to zero.
388 return cms_free_dbl / (cms_consumption_rate() + 1.0);
389 }
390 return 0.0;
391 }
392
393 // Compare the duration of the cms collection to the
394 // time remaining before the cms generation is empty.
395 // Note that the time from the start of the cms collection
396 // to the start of the cms sweep (less than the total
397 // duration of the cms collection) can be used. This
398 // has been tried and some applications experienced
399 // promotion failures early in execution. This was
400 // possibly because the averages were not accurate
401 // enough at the beginning.
402 double CMSStats::time_until_cms_start() const {
403 // We add "gc0_period" to the "work" calculation
404 // below because this query is done (mostly) at the
405 // end of a scavenge, so we need to conservatively
406 // account for that much possible delay
407 // in the query so as to avoid concurrent mode failures
408 // due to starting the collection just a wee bit too
409 // late.
410 double work = cms_duration() + gc0_period();
411 double deadline = time_until_cms_gen_full();
412 // If a concurrent mode failure occurred recently, we want to be
413 // more conservative and halve our expected time_until_cms_gen_full()
414 if (work > deadline) {
415 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
416 cms_duration(), gc0_period(), time_until_cms_gen_full());
417 return 0.0;
418 }
419 return work - deadline;
420 }
421
422 #ifndef PRODUCT
423 void CMSStats::print_on(outputStream *st) const {
424 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
425 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
426 gc0_duration(), gc0_period(), gc0_promoted());
427 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
428 cms_duration(), cms_period(), cms_allocated());
429 st->print(",cms_since_beg=%g,cms_since_end=%g",
430 cms_time_since_begin(), cms_time_since_end());
431 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
432 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
433
434 if (valid()) {
435 st->print(",promo_rate=%g,cms_alloc_rate=%g",
436 promotion_rate(), cms_allocation_rate());
437 st->print(",cms_consumption_rate=%g,time_until_full=%g",
438 cms_consumption_rate(), time_until_cms_gen_full());
439 }
440 st->cr();
441 }
442 #endif // #ifndef PRODUCT
443
444 CMSCollector::CollectorState CMSCollector::_collectorState =
445 CMSCollector::Idling;
446 bool CMSCollector::_foregroundGCIsActive = false;
447 bool CMSCollector::_foregroundGCShouldWait = false;
448
449 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
450 CardTableRS* ct,
451 ConcurrentMarkSweepPolicy* cp):
452 _overflow_list(NULL),
453 _conc_workers(NULL), // may be set later
454 _completed_initialization(false),
455 _collection_count_start(0),
456 _should_unload_classes(CMSClassUnloadingEnabled),
457 _concurrent_cycles_since_last_unload(0),
458 _roots_scanning_options(GenCollectedHeap::SO_None),
459 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
460 _verifying(false),
461 _collector_policy(cp),
462 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
463 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
464 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
465 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
466 _cms_start_registered(false),
467 _cmsGen(cmsGen),
468 // Adjust span to cover old (cms) gen
469 _span(cmsGen->reserved()),
470 _ct(ct),
471 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
472 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
473 -1 /* lock-free */, "No_lock" /* dummy */),
474 _restart_addr(NULL),
475 _ser_pmc_preclean_ovflw(0),
476 _ser_pmc_remark_ovflw(0),
477 _par_pmc_remark_ovflw(0),
478 _ser_kac_preclean_ovflw(0),
479 _ser_kac_ovflw(0),
480 _par_kac_ovflw(0),
481 #ifndef PRODUCT
482 _num_par_pushes(0),
483 #endif
484 _span_based_discoverer(_span),
485 _ref_processor(NULL), // will be set later
486 // Construct the is_alive_closure with _span & markBitMap
487 _is_alive_closure(_span, &_markBitMap),
488 _modUnionClosurePar(&_modUnionTable),
489 _between_prologue_and_epilogue(false),
490 _abort_preclean(false),
491 _start_sampling(false),
492 _stats(cmsGen),
493 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
494 //verify that this lock should be acquired with safepoint check.
495 Monitor::_safepoint_check_sometimes)),
496 _eden_chunk_array(NULL), // may be set in ctor body
497 _eden_chunk_index(0), // -- ditto --
498 _eden_chunk_capacity(0), // -- ditto --
499 _survivor_chunk_array(NULL), // -- ditto --
500 _survivor_chunk_index(0), // -- ditto --
501 _survivor_chunk_capacity(0), // -- ditto --
502 _survivor_plab_array(NULL) // -- ditto --
503 {
504 // Now expand the span and allocate the collection support structures
505 // (MUT, marking bit map etc.) to cover both generations subject to
506 // collection.
507
508 // For use by dirty card to oop closures.
509 _cmsGen->cmsSpace()->set_collector(this);
510
511 // Allocate MUT and marking bit map
512 {
513 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
514 if (!_markBitMap.allocate(_span)) {
515 log_warning(gc)("Failed to allocate CMS Bit Map");
516 return;
517 }
518 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
519 }
520 {
521 _modUnionTable.allocate(_span);
522 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
523 }
524
525 if (!_markStack.allocate(MarkStackSize)) {
526 log_warning(gc)("Failed to allocate CMS Marking Stack");
527 return;
528 }
529
530 // Support for multi-threaded concurrent phases
531 if (CMSConcurrentMTEnabled) {
532 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
533 // just for now
534 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
535 }
536 if (ConcGCThreads > 1) {
537 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
538 ConcGCThreads, true);
539 if (_conc_workers == NULL) {
540 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
541 CMSConcurrentMTEnabled = false;
542 } else {
543 _conc_workers->initialize_workers();
544 }
545 } else {
546 CMSConcurrentMTEnabled = false;
547 }
548 }
549 if (!CMSConcurrentMTEnabled) {
550 ConcGCThreads = 0;
551 } else {
552 // Turn off CMSCleanOnEnter optimization temporarily for
553 // the MT case where it's not fixed yet; see 6178663.
554 CMSCleanOnEnter = false;
555 }
556 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
557 "Inconsistency");
558 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
559 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
560
561 // Parallel task queues; these are shared for the
562 // concurrent and stop-world phases of CMS, but
563 // are not shared with parallel scavenge (ParNew).
564 {
565 uint i;
566 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
567
568 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
569 || ParallelRefProcEnabled)
570 && num_queues > 0) {
571 _task_queues = new OopTaskQueueSet(num_queues);
572 if (_task_queues == NULL) {
573 log_warning(gc)("task_queues allocation failure.");
574 return;
575 }
576 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
577 for (i = 0; i < num_queues; i++) {
578 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
579 if (q == NULL) {
580 log_warning(gc)("work_queue allocation failure.");
581 return;
582 }
583 _task_queues->register_queue(i, q);
584 }
585 for (i = 0; i < num_queues; i++) {
586 _task_queues->queue(i)->initialize();
587 }
588 }
589 }
590
591 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
592
593 // Clip CMSBootstrapOccupancy between 0 and 100.
594 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
595
596 // Now tell CMS generations the identity of their collector
597 ConcurrentMarkSweepGeneration::set_collector(this);
598
599 // Create & start a CMS thread for this CMS collector
600 _cmsThread = ConcurrentMarkSweepThread::start(this);
601 assert(cmsThread() != NULL, "CMS Thread should have been created");
602 assert(cmsThread()->collector() == this,
603 "CMS Thread should refer to this gen");
604 assert(CGC_lock != NULL, "Where's the CGC_lock?");
605
606 // Support for parallelizing young gen rescan
607 CMSHeap* heap = CMSHeap::heap();
608 _young_gen = heap->young_gen();
609 if (heap->supports_inline_contig_alloc()) {
610 _top_addr = heap->top_addr();
611 _end_addr = heap->end_addr();
612 assert(_young_gen != NULL, "no _young_gen");
613 _eden_chunk_index = 0;
614 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
615 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
616 }
617
618 // Support for parallelizing survivor space rescan
619 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
620 const size_t max_plab_samples =
621 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
622
623 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
624 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
625 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
626 _survivor_chunk_capacity = max_plab_samples;
627 for (uint i = 0; i < ParallelGCThreads; i++) {
628 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
629 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
630 assert(cur->end() == 0, "Should be 0");
631 assert(cur->array() == vec, "Should be vec");
632 assert(cur->capacity() == max_plab_samples, "Error");
633 }
634 }
635
636 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
637 _gc_counters = new CollectorCounters("CMS", 1);
638 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
639 _completed_initialization = true;
640 _inter_sweep_timer.start(); // start of time
641 }
642
643 const char* ConcurrentMarkSweepGeneration::name() const {
644 return "concurrent mark-sweep generation";
645 }
646 void ConcurrentMarkSweepGeneration::update_counters() {
647 if (UsePerfData) {
648 _space_counters->update_all();
649 _gen_counters->update_all();
650 }
651 }
652
653 // this is an optimized version of update_counters(). it takes the
654 // used value as a parameter rather than computing it.
655 //
656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
657 if (UsePerfData) {
658 _space_counters->update_used(used);
659 _space_counters->update_capacity();
660 _gen_counters->update_all();
661 }
662 }
663
664 void ConcurrentMarkSweepGeneration::print() const {
665 Generation::print();
666 cmsSpace()->print();
667 }
668
669 #ifndef PRODUCT
670 void ConcurrentMarkSweepGeneration::print_statistics() {
671 cmsSpace()->printFLCensus(0);
672 }
673 #endif
674
675 size_t
676 ConcurrentMarkSweepGeneration::contiguous_available() const {
677 // dld proposes an improvement in precision here. If the committed
678 // part of the space ends in a free block we should add that to
679 // uncommitted size in the calculation below. Will make this
680 // change later, staying with the approximation below for the
681 // time being. -- ysr.
682 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
683 }
684
685 size_t
686 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
687 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
688 }
689
690 size_t ConcurrentMarkSweepGeneration::max_available() const {
691 return free() + _virtual_space.uncommitted_size();
692 }
693
694 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
695 size_t available = max_available();
696 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
697 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
698 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
699 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
700 return res;
701 }
702
703 // At a promotion failure dump information on block layout in heap
704 // (cms old generation).
705 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
706 Log(gc, promotion) log;
707 if (log.is_trace()) {
708 LogStream ls(log.trace());
709 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
710 }
711 }
712
713 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
714 // Clear the promotion information. These pointers can be adjusted
715 // along with all the other pointers into the heap but
716 // compaction is expected to be a rare event with
717 // a heap using cms so don't do it without seeing the need.
718 for (uint i = 0; i < ParallelGCThreads; i++) {
719 _par_gc_thread_states[i]->promo.reset();
720 }
721 }
722
723 void ConcurrentMarkSweepGeneration::compute_new_size() {
724 assert_locked_or_safepoint(Heap_lock);
725
726 // If incremental collection failed, we just want to expand
727 // to the limit.
728 if (incremental_collection_failed()) {
729 clear_incremental_collection_failed();
730 grow_to_reserved();
731 return;
732 }
733
734 // The heap has been compacted but not reset yet.
735 // Any metric such as free() or used() will be incorrect.
736
737 CardGeneration::compute_new_size();
738
739 // Reset again after a possible resizing
740 if (did_compact()) {
741 cmsSpace()->reset_after_compaction();
742 }
743 }
744
745 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
746 assert_locked_or_safepoint(Heap_lock);
747
748 // If incremental collection failed, we just want to expand
749 // to the limit.
750 if (incremental_collection_failed()) {
751 clear_incremental_collection_failed();
752 grow_to_reserved();
753 return;
754 }
755
756 double free_percentage = ((double) free()) / capacity();
757 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
758 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
759
760 // compute expansion delta needed for reaching desired free percentage
761 if (free_percentage < desired_free_percentage) {
762 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
763 assert(desired_capacity >= capacity(), "invalid expansion size");
764 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
765 Log(gc) log;
766 if (log.is_trace()) {
767 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
768 log.trace("From compute_new_size: ");
769 log.trace(" Free fraction %f", free_percentage);
770 log.trace(" Desired free fraction %f", desired_free_percentage);
771 log.trace(" Maximum free fraction %f", maximum_free_percentage);
772 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
773 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
774 CMSHeap* heap = CMSHeap::heap();
775 size_t young_size = heap->young_gen()->capacity();
776 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
777 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
778 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
779 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
780 }
781 // safe if expansion fails
782 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
783 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
784 } else {
785 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
786 assert(desired_capacity <= capacity(), "invalid expansion size");
787 size_t shrink_bytes = capacity() - desired_capacity;
788 // Don't shrink unless the delta is greater than the minimum shrink we want
789 if (shrink_bytes >= MinHeapDeltaBytes) {
790 shrink_free_list_by(shrink_bytes);
791 }
792 }
793 }
794
795 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
796 return cmsSpace()->freelistLock();
797 }
798
799 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
800 CMSSynchronousYieldRequest yr;
801 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
802 return have_lock_and_allocate(size, tlab);
803 }
804
805 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
806 bool tlab /* ignored */) {
807 assert_lock_strong(freelistLock());
808 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
809 HeapWord* res = cmsSpace()->allocate(adjustedSize);
810 // Allocate the object live (grey) if the background collector has
811 // started marking. This is necessary because the marker may
812 // have passed this address and consequently this object will
813 // not otherwise be greyed and would be incorrectly swept up.
814 // Note that if this object contains references, the writing
815 // of those references will dirty the card containing this object
816 // allowing the object to be blackened (and its references scanned)
817 // either during a preclean phase or at the final checkpoint.
818 if (res != NULL) {
819 // We may block here with an uninitialized object with
820 // its mark-bit or P-bits not yet set. Such objects need
821 // to be safely navigable by block_start().
822 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
823 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
824 collector()->direct_allocated(res, adjustedSize);
825 _direct_allocated_words += adjustedSize;
826 // allocation counters
827 NOT_PRODUCT(
828 _numObjectsAllocated++;
829 _numWordsAllocated += (int)adjustedSize;
830 )
831 }
832 return res;
833 }
834
835 // In the case of direct allocation by mutators in a generation that
836 // is being concurrently collected, the object must be allocated
837 // live (grey) if the background collector has started marking.
838 // This is necessary because the marker may
839 // have passed this address and consequently this object will
840 // not otherwise be greyed and would be incorrectly swept up.
841 // Note that if this object contains references, the writing
842 // of those references will dirty the card containing this object
843 // allowing the object to be blackened (and its references scanned)
844 // either during a preclean phase or at the final checkpoint.
845 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
846 assert(_markBitMap.covers(start, size), "Out of bounds");
847 if (_collectorState >= Marking) {
848 MutexLockerEx y(_markBitMap.lock(),
849 Mutex::_no_safepoint_check_flag);
850 // [see comments preceding SweepClosure::do_blk() below for details]
851 //
852 // Can the P-bits be deleted now? JJJ
853 //
854 // 1. need to mark the object as live so it isn't collected
855 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
856 // 3. need to mark the end of the object so marking, precleaning or sweeping
857 // can skip over uninitialized or unparsable objects. An allocated
858 // object is considered uninitialized for our purposes as long as
859 // its klass word is NULL. All old gen objects are parsable
860 // as soon as they are initialized.)
861 _markBitMap.mark(start); // object is live
862 _markBitMap.mark(start + 1); // object is potentially uninitialized?
863 _markBitMap.mark(start + size - 1);
864 // mark end of object
865 }
866 // check that oop looks uninitialized
867 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
868 }
869
870 void CMSCollector::promoted(bool par, HeapWord* start,
871 bool is_obj_array, size_t obj_size) {
872 assert(_markBitMap.covers(start), "Out of bounds");
873 // See comment in direct_allocated() about when objects should
874 // be allocated live.
875 if (_collectorState >= Marking) {
876 // we already hold the marking bit map lock, taken in
877 // the prologue
878 if (par) {
879 _markBitMap.par_mark(start);
880 } else {
881 _markBitMap.mark(start);
882 }
883 // We don't need to mark the object as uninitialized (as
884 // in direct_allocated above) because this is being done with the
885 // world stopped and the object will be initialized by the
886 // time the marking, precleaning or sweeping get to look at it.
887 // But see the code for copying objects into the CMS generation,
888 // where we need to ensure that concurrent readers of the
889 // block offset table are able to safely navigate a block that
890 // is in flux from being free to being allocated (and in
891 // transition while being copied into) and subsequently
892 // becoming a bona-fide object when the copy/promotion is complete.
893 assert(SafepointSynchronize::is_at_safepoint(),
894 "expect promotion only at safepoints");
895
896 if (_collectorState < Sweeping) {
897 // Mark the appropriate cards in the modUnionTable, so that
898 // this object gets scanned before the sweep. If this is
899 // not done, CMS generation references in the object might
900 // not get marked.
901 // For the case of arrays, which are otherwise precisely
902 // marked, we need to dirty the entire array, not just its head.
903 if (is_obj_array) {
904 // The [par_]mark_range() method expects mr.end() below to
905 // be aligned to the granularity of a bit's representation
906 // in the heap. In the case of the MUT below, that's a
907 // card size.
908 MemRegion mr(start,
909 align_up(start + obj_size,
910 CardTable::card_size /* bytes */));
911 if (par) {
912 _modUnionTable.par_mark_range(mr);
913 } else {
914 _modUnionTable.mark_range(mr);
915 }
916 } else { // not an obj array; we can just mark the head
917 if (par) {
918 _modUnionTable.par_mark(start);
919 } else {
920 _modUnionTable.mark(start);
921 }
922 }
923 }
924 }
925 }
926
927 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
928 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
929 // allocate, copy and if necessary update promoinfo --
930 // delegate to underlying space.
931 assert_lock_strong(freelistLock());
932
933 #ifndef PRODUCT
934 if (CMSHeap::heap()->promotion_should_fail()) {
935 return NULL;
936 }
937 #endif // #ifndef PRODUCT
938
939 oop res = _cmsSpace->promote(obj, obj_size);
940 if (res == NULL) {
941 // expand and retry
942 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
943 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
944 // Since this is the old generation, we don't try to promote
945 // into a more senior generation.
946 res = _cmsSpace->promote(obj, obj_size);
947 }
948 if (res != NULL) {
949 // See comment in allocate() about when objects should
950 // be allocated live.
951 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
952 collector()->promoted(false, // Not parallel
953 (HeapWord*)res, obj->is_objArray(), obj_size);
954 // promotion counters
955 NOT_PRODUCT(
956 _numObjectsPromoted++;
957 _numWordsPromoted +=
958 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
959 )
960 }
961 return res;
962 }
963
964
965 // IMPORTANT: Notes on object size recognition in CMS.
966 // ---------------------------------------------------
967 // A block of storage in the CMS generation is always in
968 // one of three states. A free block (FREE), an allocated
969 // object (OBJECT) whose size() method reports the correct size,
970 // and an intermediate state (TRANSIENT) in which its size cannot
971 // be accurately determined.
972 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
973 // -----------------------------------------------------
974 // FREE: klass_word & 1 == 1; mark_word holds block size
975 //
976 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
977 // obj->size() computes correct size
978 //
979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
980 //
981 // STATE IDENTIFICATION: (64 bit+COOPS)
982 // ------------------------------------
983 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
984 //
985 // OBJECT: klass_word installed; klass_word != 0;
986 // obj->size() computes correct size
987 //
988 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
989 //
990 //
991 // STATE TRANSITION DIAGRAM
992 //
993 // mut / parnew mut / parnew
994 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
995 // ^ |
996 // |------------------------ DEAD <------------------------------------|
997 // sweep mut
998 //
999 // While a block is in TRANSIENT state its size cannot be determined
1000 // so readers will either need to come back later or stall until
1001 // the size can be determined. Note that for the case of direct
1002 // allocation, P-bits, when available, may be used to determine the
1003 // size of an object that may not yet have been initialized.
1004
1005 // Things to support parallel young-gen collection.
1006 oop
1007 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1008 oop old, markOop m,
1009 size_t word_sz) {
1010 #ifndef PRODUCT
1011 if (CMSHeap::heap()->promotion_should_fail()) {
1012 return NULL;
1013 }
1014 #endif // #ifndef PRODUCT
1015
1016 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1017 PromotionInfo* promoInfo = &ps->promo;
1018 // if we are tracking promotions, then first ensure space for
1019 // promotion (including spooling space for saving header if necessary).
1020 // then allocate and copy, then track promoted info if needed.
1021 // When tracking (see PromotionInfo::track()), the mark word may
1022 // be displaced and in this case restoration of the mark word
1023 // occurs in the (oop_since_save_marks_)iterate phase.
1024 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1025 // Out of space for allocating spooling buffers;
1026 // try expanding and allocating spooling buffers.
1027 if (!expand_and_ensure_spooling_space(promoInfo)) {
1028 return NULL;
1029 }
1030 }
1031 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1032 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1033 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1034 if (obj_ptr == NULL) {
1035 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1036 if (obj_ptr == NULL) {
1037 return NULL;
1038 }
1039 }
1040 oop obj = oop(obj_ptr);
1041 OrderAccess::storestore();
1042 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044 // IMPORTANT: See note on object initialization for CMS above.
1045 // Otherwise, copy the object. Here we must be careful to insert the
1046 // klass pointer last, since this marks the block as an allocated object.
1047 // Except with compressed oops it's the mark word.
1048 HeapWord* old_ptr = (HeapWord*)old;
1049 // Restore the mark word copied above.
1050 obj->set_mark_raw(m);
1051 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1052 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1053 OrderAccess::storestore();
1054
1055 if (UseCompressedClassPointers) {
1056 // Copy gap missed by (aligned) header size calculation below
1057 obj->set_klass_gap(old->klass_gap());
1058 }
1059 if (word_sz > (size_t)oopDesc::header_size()) {
1060 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1061 obj_ptr + oopDesc::header_size(),
1062 word_sz - oopDesc::header_size());
1063 }
1064
1065 // Now we can track the promoted object, if necessary. We take care
1066 // to delay the transition from uninitialized to full object
1067 // (i.e., insertion of klass pointer) until after, so that it
1068 // atomically becomes a promoted object.
1069 if (promoInfo->tracking()) {
1070 promoInfo->track((PromotedObject*)obj, old->klass());
1071 }
1072 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1075
1076 // Finally, install the klass pointer (this should be volatile).
1077 OrderAccess::storestore();
1078 obj->set_klass(old->klass());
1079 // We should now be able to calculate the right size for this object
1080 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1081
1082 collector()->promoted(true, // parallel
1083 obj_ptr, old->is_objArray(), word_sz);
1084
1085 NOT_PRODUCT(
1086 Atomic::inc(&_numObjectsPromoted);
1087 Atomic::add(alloc_sz, &_numWordsPromoted);
1088 )
1089
1090 return obj;
1091 }
1092
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_promote_alloc_done(int thread_num) {
1096 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097 ps->lab.retire(thread_num);
1098 }
1099
1100 void
1101 ConcurrentMarkSweepGeneration::
1102 par_oop_since_save_marks_iterate_done(int thread_num) {
1103 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1104 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1105 ps->promo.promoted_oops_iterate(dummy_cl);
1106
1107 // Because card-scanning has been completed, subsequent phases
1108 // (e.g., reference processing) will not need to recognize which
1109 // objects have been promoted during this GC. So, we can now disable
1110 // promotion tracking.
1111 ps->promo.stopTrackingPromotions();
1112 }
1113
1114 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1115 size_t size,
1116 bool tlab)
1117 {
1118 // We allow a STW collection only if a full
1119 // collection was requested.
1120 return full || should_allocate(size, tlab); // FIX ME !!!
1121 // This and promotion failure handling are connected at the
1122 // hip and should be fixed by untying them.
1123 }
1124
1125 bool CMSCollector::shouldConcurrentCollect() {
1126 LogTarget(Trace, gc) log;
1127
1128 if (_full_gc_requested) {
1129 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1130 return true;
1131 }
1132
1133 FreelistLocker x(this);
1134 // ------------------------------------------------------------------
1135 // Print out lots of information which affects the initiation of
1136 // a collection.
1137 if (log.is_enabled() && stats().valid()) {
1138 log.print("CMSCollector shouldConcurrentCollect: ");
1139
1140 LogStream out(log);
1141 stats().print_on(&out);
1142
1143 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1144 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1145 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1146 log.print("promotion_rate=%g", stats().promotion_rate());
1147 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1148 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1149 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1150 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1151 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1152 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1153 }
1154 // ------------------------------------------------------------------
1155
1156 // If the estimated time to complete a cms collection (cms_duration())
1157 // is less than the estimated time remaining until the cms generation
1158 // is full, start a collection.
1159 if (!UseCMSInitiatingOccupancyOnly) {
1160 if (stats().valid()) {
1161 if (stats().time_until_cms_start() == 0.0) {
1162 return true;
1163 }
1164 } else {
1165 // We want to conservatively collect somewhat early in order
1166 // to try and "bootstrap" our CMS/promotion statistics;
1167 // this branch will not fire after the first successful CMS
1168 // collection because the stats should then be valid.
1169 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1170 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1171 _cmsGen->occupancy(), _bootstrap_occupancy);
1172 return true;
1173 }
1174 }
1175 }
1176
1177 // Otherwise, we start a collection cycle if
1178 // old gen want a collection cycle started. Each may use
1179 // an appropriate criterion for making this decision.
1180 // XXX We need to make sure that the gen expansion
1181 // criterion dovetails well with this. XXX NEED TO FIX THIS
1182 if (_cmsGen->should_concurrent_collect()) {
1183 log.print("CMS old gen initiated");
1184 return true;
1185 }
1186
1187 // We start a collection if we believe an incremental collection may fail;
1188 // this is not likely to be productive in practice because it's probably too
1189 // late anyway.
1190 CMSHeap* heap = CMSHeap::heap();
1191 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1192 log.print("CMSCollector: collect because incremental collection will fail ");
1193 return true;
1194 }
1195
1196 if (MetaspaceGC::should_concurrent_collect()) {
1197 log.print("CMSCollector: collect for metadata allocation ");
1198 return true;
1199 }
1200
1201 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1202 if (CMSTriggerInterval >= 0) {
1203 if (CMSTriggerInterval == 0) {
1204 // Trigger always
1205 return true;
1206 }
1207
1208 // Check the CMS time since begin (we do not check the stats validity
1209 // as we want to be able to trigger the first CMS cycle as well)
1210 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1211 if (stats().valid()) {
1212 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1213 stats().cms_time_since_begin());
1214 } else {
1215 log.print("CMSCollector: collect because of trigger interval (first collection)");
1216 }
1217 return true;
1218 }
1219 }
1220
1221 return false;
1222 }
1223
1224 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1225
1226 // Clear _expansion_cause fields of constituent generations
1227 void CMSCollector::clear_expansion_cause() {
1228 _cmsGen->clear_expansion_cause();
1229 }
1230
1231 // We should be conservative in starting a collection cycle. To
1232 // start too eagerly runs the risk of collecting too often in the
1233 // extreme. To collect too rarely falls back on full collections,
1234 // which works, even if not optimum in terms of concurrent work.
1235 // As a work around for too eagerly collecting, use the flag
1236 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1237 // giving the user an easily understandable way of controlling the
1238 // collections.
1239 // We want to start a new collection cycle if any of the following
1240 // conditions hold:
1241 // . our current occupancy exceeds the configured initiating occupancy
1242 // for this generation, or
1243 // . we recently needed to expand this space and have not, since that
1244 // expansion, done a collection of this generation, or
1245 // . the underlying space believes that it may be a good idea to initiate
1246 // a concurrent collection (this may be based on criteria such as the
1247 // following: the space uses linear allocation and linear allocation is
1248 // going to fail, or there is believed to be excessive fragmentation in
1249 // the generation, etc... or ...
1250 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1251 // the case of the old generation; see CR 6543076):
1252 // we may be approaching a point at which allocation requests may fail because
1253 // we will be out of sufficient free space given allocation rate estimates.]
1254 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1255
1256 assert_lock_strong(freelistLock());
1257 if (occupancy() > initiating_occupancy()) {
1258 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1259 short_name(), occupancy(), initiating_occupancy());
1260 return true;
1261 }
1262 if (UseCMSInitiatingOccupancyOnly) {
1263 return false;
1264 }
1265 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1266 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1267 return true;
1268 }
1269 return false;
1270 }
1271
1272 void ConcurrentMarkSweepGeneration::collect(bool full,
1273 bool clear_all_soft_refs,
1274 size_t size,
1275 bool tlab)
1276 {
1277 collector()->collect(full, clear_all_soft_refs, size, tlab);
1278 }
1279
1280 void CMSCollector::collect(bool full,
1281 bool clear_all_soft_refs,
1282 size_t size,
1283 bool tlab)
1284 {
1285 // The following "if" branch is present for defensive reasons.
1286 // In the current uses of this interface, it can be replaced with:
1287 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1288 // But I am not placing that assert here to allow future
1289 // generality in invoking this interface.
1290 if (GCLocker::is_active()) {
1291 // A consistency test for GCLocker
1292 assert(GCLocker::needs_gc(), "Should have been set already");
1293 // Skip this foreground collection, instead
1294 // expanding the heap if necessary.
1295 // Need the free list locks for the call to free() in compute_new_size()
1296 compute_new_size();
1297 return;
1298 }
1299 acquire_control_and_collect(full, clear_all_soft_refs);
1300 }
1301
1302 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1303 CMSHeap* heap = CMSHeap::heap();
1304 unsigned int gc_count = heap->total_full_collections();
1305 if (gc_count == full_gc_count) {
1306 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1307 _full_gc_requested = true;
1308 _full_gc_cause = cause;
1309 CGC_lock->notify(); // nudge CMS thread
1310 } else {
1311 assert(gc_count > full_gc_count, "Error: causal loop");
1312 }
1313 }
1314
1315 bool CMSCollector::is_external_interruption() {
1316 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1317 return GCCause::is_user_requested_gc(cause) ||
1318 GCCause::is_serviceability_requested_gc(cause);
1319 }
1320
1321 void CMSCollector::report_concurrent_mode_interruption() {
1322 if (is_external_interruption()) {
1323 log_debug(gc)("Concurrent mode interrupted");
1324 } else {
1325 log_debug(gc)("Concurrent mode failure");
1326 _gc_tracer_cm->report_concurrent_mode_failure();
1327 }
1328 }
1329
1330
1331 // The foreground and background collectors need to coordinate in order
1332 // to make sure that they do not mutually interfere with CMS collections.
1333 // When a background collection is active,
1334 // the foreground collector may need to take over (preempt) and
1335 // synchronously complete an ongoing collection. Depending on the
1336 // frequency of the background collections and the heap usage
1337 // of the application, this preemption can be seldom or frequent.
1338 // There are only certain
1339 // points in the background collection that the "collection-baton"
1340 // can be passed to the foreground collector.
1341 //
1342 // The foreground collector will wait for the baton before
1343 // starting any part of the collection. The foreground collector
1344 // will only wait at one location.
1345 //
1346 // The background collector will yield the baton before starting a new
1347 // phase of the collection (e.g., before initial marking, marking from roots,
1348 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1349 // of the loop which switches the phases. The background collector does some
1350 // of the phases (initial mark, final re-mark) with the world stopped.
1351 // Because of locking involved in stopping the world,
1352 // the foreground collector should not block waiting for the background
1353 // collector when it is doing a stop-the-world phase. The background
1354 // collector will yield the baton at an additional point just before
1355 // it enters a stop-the-world phase. Once the world is stopped, the
1356 // background collector checks the phase of the collection. If the
1357 // phase has not changed, it proceeds with the collection. If the
1358 // phase has changed, it skips that phase of the collection. See
1359 // the comments on the use of the Heap_lock in collect_in_background().
1360 //
1361 // Variable used in baton passing.
1362 // _foregroundGCIsActive - Set to true by the foreground collector when
1363 // it wants the baton. The foreground clears it when it has finished
1364 // the collection.
1365 // _foregroundGCShouldWait - Set to true by the background collector
1366 // when it is running. The foreground collector waits while
1367 // _foregroundGCShouldWait is true.
1368 // CGC_lock - monitor used to protect access to the above variables
1369 // and to notify the foreground and background collectors.
1370 // _collectorState - current state of the CMS collection.
1371 //
1372 // The foreground collector
1373 // acquires the CGC_lock
1374 // sets _foregroundGCIsActive
1375 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1376 // various locks acquired in preparation for the collection
1377 // are released so as not to block the background collector
1378 // that is in the midst of a collection
1379 // proceeds with the collection
1380 // clears _foregroundGCIsActive
1381 // returns
1382 //
1383 // The background collector in a loop iterating on the phases of the
1384 // collection
1385 // acquires the CGC_lock
1386 // sets _foregroundGCShouldWait
1387 // if _foregroundGCIsActive is set
1388 // clears _foregroundGCShouldWait, notifies _CGC_lock
1389 // waits on _CGC_lock for _foregroundGCIsActive to become false
1390 // and exits the loop.
1391 // otherwise
1392 // proceed with that phase of the collection
1393 // if the phase is a stop-the-world phase,
1394 // yield the baton once more just before enqueueing
1395 // the stop-world CMS operation (executed by the VM thread).
1396 // returns after all phases of the collection are done
1397 //
1398
1399 void CMSCollector::acquire_control_and_collect(bool full,
1400 bool clear_all_soft_refs) {
1401 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1402 assert(!Thread::current()->is_ConcurrentGC_thread(),
1403 "shouldn't try to acquire control from self!");
1404
1405 // Start the protocol for acquiring control of the
1406 // collection from the background collector (aka CMS thread).
1407 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1408 "VM thread should have CMS token");
1409 // Remember the possibly interrupted state of an ongoing
1410 // concurrent collection
1411 CollectorState first_state = _collectorState;
1412
1413 // Signal to a possibly ongoing concurrent collection that
1414 // we want to do a foreground collection.
1415 _foregroundGCIsActive = true;
1416
1417 // release locks and wait for a notify from the background collector
1418 // releasing the locks in only necessary for phases which
1419 // do yields to improve the granularity of the collection.
1420 assert_lock_strong(bitMapLock());
1421 // We need to lock the Free list lock for the space that we are
1422 // currently collecting.
1423 assert(haveFreelistLocks(), "Must be holding free list locks");
1424 bitMapLock()->unlock();
1425 releaseFreelistLocks();
1426 {
1427 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1428 if (_foregroundGCShouldWait) {
1429 // We are going to be waiting for action for the CMS thread;
1430 // it had better not be gone (for instance at shutdown)!
1431 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1432 "CMS thread must be running");
1433 // Wait here until the background collector gives us the go-ahead
1434 ConcurrentMarkSweepThread::clear_CMS_flag(
1435 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1436 // Get a possibly blocked CMS thread going:
1437 // Note that we set _foregroundGCIsActive true above,
1438 // without protection of the CGC_lock.
1439 CGC_lock->notify();
1440 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1441 "Possible deadlock");
1442 while (_foregroundGCShouldWait) {
1443 // wait for notification
1444 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1445 // Possibility of delay/starvation here, since CMS token does
1446 // not know to give priority to VM thread? Actually, i think
1447 // there wouldn't be any delay/starvation, but the proof of
1448 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1449 }
1450 ConcurrentMarkSweepThread::set_CMS_flag(
1451 ConcurrentMarkSweepThread::CMS_vm_has_token);
1452 }
1453 }
1454 // The CMS_token is already held. Get back the other locks.
1455 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1456 "VM thread should have CMS token");
1457 getFreelistLocks();
1458 bitMapLock()->lock_without_safepoint_check();
1459 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1460 p2i(Thread::current()), first_state);
1461 log_debug(gc, state)(" gets control with state %d", _collectorState);
1462
1463 // Inform cms gen if this was due to partial collection failing.
1464 // The CMS gen may use this fact to determine its expansion policy.
1465 CMSHeap* heap = CMSHeap::heap();
1466 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1467 assert(!_cmsGen->incremental_collection_failed(),
1468 "Should have been noticed, reacted to and cleared");
1469 _cmsGen->set_incremental_collection_failed();
1470 }
1471
1472 if (first_state > Idling) {
1473 report_concurrent_mode_interruption();
1474 }
1475
1476 set_did_compact(true);
1477
1478 // If the collection is being acquired from the background
1479 // collector, there may be references on the discovered
1480 // references lists. Abandon those references, since some
1481 // of them may have become unreachable after concurrent
1482 // discovery; the STW compacting collector will redo discovery
1483 // more precisely, without being subject to floating garbage.
1484 // Leaving otherwise unreachable references in the discovered
1485 // lists would require special handling.
1486 ref_processor()->disable_discovery();
1487 ref_processor()->abandon_partial_discovery();
1488 ref_processor()->verify_no_references_recorded();
1489
1490 if (first_state > Idling) {
1491 save_heap_summary();
1492 }
1493
1494 do_compaction_work(clear_all_soft_refs);
1495
1496 // Has the GC time limit been exceeded?
1497 size_t max_eden_size = _young_gen->max_eden_size();
1498 GCCause::Cause gc_cause = heap->gc_cause();
1499 size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1500 _cmsGen->max_capacity(),
1501 max_eden_size,
1502 full,
1503 gc_cause,
1504 heap->soft_ref_policy());
1505
1506 // Reset the expansion cause, now that we just completed
1507 // a collection cycle.
1508 clear_expansion_cause();
1509 _foregroundGCIsActive = false;
1510 return;
1511 }
1512
1513 // Resize the tenured generation
1514 // after obtaining the free list locks for the
1515 // two generations.
1516 void CMSCollector::compute_new_size() {
1517 assert_locked_or_safepoint(Heap_lock);
1518 FreelistLocker z(this);
1519 MetaspaceGC::compute_new_size();
1520 _cmsGen->compute_new_size_free_list();
1521 }
1522
1523 // A work method used by the foreground collector to do
1524 // a mark-sweep-compact.
1525 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1526 CMSHeap* heap = CMSHeap::heap();
1527
1528 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1529 gc_timer->register_gc_start();
1530
1531 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1532 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1533
1534 heap->pre_full_gc_dump(gc_timer);
1535
1536 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1537
1538 // Temporarily widen the span of the weak reference processing to
1539 // the entire heap.
1540 MemRegion new_span(CMSHeap::heap()->reserved_region());
1541 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1542 // Temporarily, clear the "is_alive_non_header" field of the
1543 // reference processor.
1544 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1545 // Temporarily make reference _processing_ single threaded (non-MT).
1546 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1547 // Temporarily make refs discovery atomic
1548 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1549 // Temporarily make reference _discovery_ single threaded (non-MT)
1550 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1551
1552 ref_processor()->set_enqueuing_is_done(false);
1553 ref_processor()->enable_discovery();
1554 ref_processor()->setup_policy(clear_all_soft_refs);
1555 // If an asynchronous collection finishes, the _modUnionTable is
1556 // all clear. If we are assuming the collection from an asynchronous
1557 // collection, clear the _modUnionTable.
1558 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1559 "_modUnionTable should be clear if the baton was not passed");
1560 _modUnionTable.clear_all();
1561 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1562 "mod union for klasses should be clear if the baton was passed");
1563 _ct->cld_rem_set()->clear_mod_union();
1564
1565
1566 // We must adjust the allocation statistics being maintained
1567 // in the free list space. We do so by reading and clearing
1568 // the sweep timer and updating the block flux rate estimates below.
1569 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1570 if (_inter_sweep_timer.is_active()) {
1571 _inter_sweep_timer.stop();
1572 // Note that we do not use this sample to update the _inter_sweep_estimate.
1573 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1574 _inter_sweep_estimate.padded_average(),
1575 _intra_sweep_estimate.padded_average());
1576 }
1577
1578 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1579 #ifdef ASSERT
1580 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1581 size_t free_size = cms_space->free();
1582 assert(free_size ==
1583 pointer_delta(cms_space->end(), cms_space->compaction_top())
1584 * HeapWordSize,
1585 "All the free space should be compacted into one chunk at top");
1586 assert(cms_space->dictionary()->total_chunk_size(
1587 debug_only(cms_space->freelistLock())) == 0 ||
1588 cms_space->totalSizeInIndexedFreeLists() == 0,
1589 "All the free space should be in a single chunk");
1590 size_t num = cms_space->totalCount();
1591 assert((free_size == 0 && num == 0) ||
1592 (free_size > 0 && (num == 1 || num == 2)),
1593 "There should be at most 2 free chunks after compaction");
1594 #endif // ASSERT
1595 _collectorState = Resetting;
1596 assert(_restart_addr == NULL,
1597 "Should have been NULL'd before baton was passed");
1598 reset_stw();
1599 _cmsGen->reset_after_compaction();
1600 _concurrent_cycles_since_last_unload = 0;
1601
1602 // Clear any data recorded in the PLAB chunk arrays.
1603 if (_survivor_plab_array != NULL) {
1604 reset_survivor_plab_arrays();
1605 }
1606
1607 // Adjust the per-size allocation stats for the next epoch.
1608 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1609 // Restart the "inter sweep timer" for the next epoch.
1610 _inter_sweep_timer.reset();
1611 _inter_sweep_timer.start();
1612
1613 // No longer a need to do a concurrent collection for Metaspace.
1614 MetaspaceGC::set_should_concurrent_collect(false);
1615
1616 heap->post_full_gc_dump(gc_timer);
1617
1618 gc_timer->register_gc_end();
1619
1620 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1621
1622 // For a mark-sweep-compact, compute_new_size() will be called
1623 // in the heap's do_collection() method.
1624 }
1625
1626 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1627 Log(gc, heap) log;
1628 if (!log.is_trace()) {
1629 return;
1630 }
1631
1632 ContiguousSpace* eden_space = _young_gen->eden();
1633 ContiguousSpace* from_space = _young_gen->from();
1634 ContiguousSpace* to_space = _young_gen->to();
1635 // Eden
1636 if (_eden_chunk_array != NULL) {
1637 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1638 p2i(eden_space->bottom()), p2i(eden_space->top()),
1639 p2i(eden_space->end()), eden_space->capacity());
1640 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1641 _eden_chunk_index, _eden_chunk_capacity);
1642 for (size_t i = 0; i < _eden_chunk_index; i++) {
1643 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1644 }
1645 }
1646 // Survivor
1647 if (_survivor_chunk_array != NULL) {
1648 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1649 p2i(from_space->bottom()), p2i(from_space->top()),
1650 p2i(from_space->end()), from_space->capacity());
1651 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1652 _survivor_chunk_index, _survivor_chunk_capacity);
1653 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1654 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1655 }
1656 }
1657 }
1658
1659 void CMSCollector::getFreelistLocks() const {
1660 // Get locks for all free lists in all generations that this
1661 // collector is responsible for
1662 _cmsGen->freelistLock()->lock_without_safepoint_check();
1663 }
1664
1665 void CMSCollector::releaseFreelistLocks() const {
1666 // Release locks for all free lists in all generations that this
1667 // collector is responsible for
1668 _cmsGen->freelistLock()->unlock();
1669 }
1670
1671 bool CMSCollector::haveFreelistLocks() const {
1672 // Check locks for all free lists in all generations that this
1673 // collector is responsible for
1674 assert_lock_strong(_cmsGen->freelistLock());
1675 PRODUCT_ONLY(ShouldNotReachHere());
1676 return true;
1677 }
1678
1679 // A utility class that is used by the CMS collector to
1680 // temporarily "release" the foreground collector from its
1681 // usual obligation to wait for the background collector to
1682 // complete an ongoing phase before proceeding.
1683 class ReleaseForegroundGC: public StackObj {
1684 private:
1685 CMSCollector* _c;
1686 public:
1687 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1688 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1689 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1690 // allow a potentially blocked foreground collector to proceed
1691 _c->_foregroundGCShouldWait = false;
1692 if (_c->_foregroundGCIsActive) {
1693 CGC_lock->notify();
1694 }
1695 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1696 "Possible deadlock");
1697 }
1698
1699 ~ReleaseForegroundGC() {
1700 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1701 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1702 _c->_foregroundGCShouldWait = true;
1703 }
1704 };
1705
1706 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1707 assert(Thread::current()->is_ConcurrentGC_thread(),
1708 "A CMS asynchronous collection is only allowed on a CMS thread.");
1709
1710 CMSHeap* heap = CMSHeap::heap();
1711 {
1712 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1713 MutexLockerEx hl(Heap_lock, safepoint_check);
1714 FreelistLocker fll(this);
1715 MutexLockerEx x(CGC_lock, safepoint_check);
1716 if (_foregroundGCIsActive) {
1717 // The foreground collector is. Skip this
1718 // background collection.
1719 assert(!_foregroundGCShouldWait, "Should be clear");
1720 return;
1721 } else {
1722 assert(_collectorState == Idling, "Should be idling before start.");
1723 _collectorState = InitialMarking;
1724 register_gc_start(cause);
1725 // Reset the expansion cause, now that we are about to begin
1726 // a new cycle.
1727 clear_expansion_cause();
1728
1729 // Clear the MetaspaceGC flag since a concurrent collection
1730 // is starting but also clear it after the collection.
1731 MetaspaceGC::set_should_concurrent_collect(false);
1732 }
1733 // Decide if we want to enable class unloading as part of the
1734 // ensuing concurrent GC cycle.
1735 update_should_unload_classes();
1736 _full_gc_requested = false; // acks all outstanding full gc requests
1737 _full_gc_cause = GCCause::_no_gc;
1738 // Signal that we are about to start a collection
1739 heap->increment_total_full_collections(); // ... starting a collection cycle
1740 _collection_count_start = heap->total_full_collections();
1741 }
1742
1743 size_t prev_used = _cmsGen->used();
1744
1745 // The change of the collection state is normally done at this level;
1746 // the exceptions are phases that are executed while the world is
1747 // stopped. For those phases the change of state is done while the
1748 // world is stopped. For baton passing purposes this allows the
1749 // background collector to finish the phase and change state atomically.
1750 // The foreground collector cannot wait on a phase that is done
1751 // while the world is stopped because the foreground collector already
1752 // has the world stopped and would deadlock.
1753 while (_collectorState != Idling) {
1754 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1755 p2i(Thread::current()), _collectorState);
1756 // The foreground collector
1757 // holds the Heap_lock throughout its collection.
1758 // holds the CMS token (but not the lock)
1759 // except while it is waiting for the background collector to yield.
1760 //
1761 // The foreground collector should be blocked (not for long)
1762 // if the background collector is about to start a phase
1763 // executed with world stopped. If the background
1764 // collector has already started such a phase, the
1765 // foreground collector is blocked waiting for the
1766 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1767 // are executed in the VM thread.
1768 //
1769 // The locking order is
1770 // PendingListLock (PLL) -- if applicable (FinalMarking)
1771 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1772 // CMS token (claimed in
1773 // stop_world_and_do() -->
1774 // safepoint_synchronize() -->
1775 // CMSThread::synchronize())
1776
1777 {
1778 // Check if the FG collector wants us to yield.
1779 CMSTokenSync x(true); // is cms thread
1780 if (waitForForegroundGC()) {
1781 // We yielded to a foreground GC, nothing more to be
1782 // done this round.
1783 assert(_foregroundGCShouldWait == false, "We set it to false in "
1784 "waitForForegroundGC()");
1785 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1786 p2i(Thread::current()), _collectorState);
1787 return;
1788 } else {
1789 // The background collector can run but check to see if the
1790 // foreground collector has done a collection while the
1791 // background collector was waiting to get the CGC_lock
1792 // above. If yes, break so that _foregroundGCShouldWait
1793 // is cleared before returning.
1794 if (_collectorState == Idling) {
1795 break;
1796 }
1797 }
1798 }
1799
1800 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1801 "should be waiting");
1802
1803 switch (_collectorState) {
1804 case InitialMarking:
1805 {
1806 ReleaseForegroundGC x(this);
1807 stats().record_cms_begin();
1808 VM_CMS_Initial_Mark initial_mark_op(this);
1809 VMThread::execute(&initial_mark_op);
1810 }
1811 // The collector state may be any legal state at this point
1812 // since the background collector may have yielded to the
1813 // foreground collector.
1814 break;
1815 case Marking:
1816 // initial marking in checkpointRootsInitialWork has been completed
1817 if (markFromRoots()) { // we were successful
1818 assert(_collectorState == Precleaning, "Collector state should "
1819 "have changed");
1820 } else {
1821 assert(_foregroundGCIsActive, "Internal state inconsistency");
1822 }
1823 break;
1824 case Precleaning:
1825 // marking from roots in markFromRoots has been completed
1826 preclean();
1827 assert(_collectorState == AbortablePreclean ||
1828 _collectorState == FinalMarking,
1829 "Collector state should have changed");
1830 break;
1831 case AbortablePreclean:
1832 abortable_preclean();
1833 assert(_collectorState == FinalMarking, "Collector state should "
1834 "have changed");
1835 break;
1836 case FinalMarking:
1837 {
1838 ReleaseForegroundGC x(this);
1839
1840 VM_CMS_Final_Remark final_remark_op(this);
1841 VMThread::execute(&final_remark_op);
1842 }
1843 assert(_foregroundGCShouldWait, "block post-condition");
1844 break;
1845 case Sweeping:
1846 // final marking in checkpointRootsFinal has been completed
1847 sweep();
1848 assert(_collectorState == Resizing, "Collector state change "
1849 "to Resizing must be done under the free_list_lock");
1850
1851 case Resizing: {
1852 // Sweeping has been completed...
1853 // At this point the background collection has completed.
1854 // Don't move the call to compute_new_size() down
1855 // into code that might be executed if the background
1856 // collection was preempted.
1857 {
1858 ReleaseForegroundGC x(this); // unblock FG collection
1859 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1860 CMSTokenSync z(true); // not strictly needed.
1861 if (_collectorState == Resizing) {
1862 compute_new_size();
1863 save_heap_summary();
1864 _collectorState = Resetting;
1865 } else {
1866 assert(_collectorState == Idling, "The state should only change"
1867 " because the foreground collector has finished the collection");
1868 }
1869 }
1870 break;
1871 }
1872 case Resetting:
1873 // CMS heap resizing has been completed
1874 reset_concurrent();
1875 assert(_collectorState == Idling, "Collector state should "
1876 "have changed");
1877
1878 MetaspaceGC::set_should_concurrent_collect(false);
1879
1880 stats().record_cms_end();
1881 // Don't move the concurrent_phases_end() and compute_new_size()
1882 // calls to here because a preempted background collection
1883 // has it's state set to "Resetting".
1884 break;
1885 case Idling:
1886 default:
1887 ShouldNotReachHere();
1888 break;
1889 }
1890 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1891 p2i(Thread::current()), _collectorState);
1892 assert(_foregroundGCShouldWait, "block post-condition");
1893 }
1894
1895 // Should this be in gc_epilogue?
1896 heap->counters()->update_counters();
1897
1898 {
1899 // Clear _foregroundGCShouldWait and, in the event that the
1900 // foreground collector is waiting, notify it, before
1901 // returning.
1902 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1903 _foregroundGCShouldWait = false;
1904 if (_foregroundGCIsActive) {
1905 CGC_lock->notify();
1906 }
1907 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1908 "Possible deadlock");
1909 }
1910 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1911 p2i(Thread::current()), _collectorState);
1912 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1913 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1914 }
1915
1916 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1917 _cms_start_registered = true;
1918 _gc_timer_cm->register_gc_start();
1919 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1920 }
1921
1922 void CMSCollector::register_gc_end() {
1923 if (_cms_start_registered) {
1924 report_heap_summary(GCWhen::AfterGC);
1925
1926 _gc_timer_cm->register_gc_end();
1927 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1928 _cms_start_registered = false;
1929 }
1930 }
1931
1932 void CMSCollector::save_heap_summary() {
1933 CMSHeap* heap = CMSHeap::heap();
1934 _last_heap_summary = heap->create_heap_summary();
1935 _last_metaspace_summary = heap->create_metaspace_summary();
1936 }
1937
1938 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1939 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1940 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1941 }
1942
1943 bool CMSCollector::waitForForegroundGC() {
1944 bool res = false;
1945 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1946 "CMS thread should have CMS token");
1947 // Block the foreground collector until the
1948 // background collectors decides whether to
1949 // yield.
1950 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1951 _foregroundGCShouldWait = true;
1952 if (_foregroundGCIsActive) {
1953 // The background collector yields to the
1954 // foreground collector and returns a value
1955 // indicating that it has yielded. The foreground
1956 // collector can proceed.
1957 res = true;
1958 _foregroundGCShouldWait = false;
1959 ConcurrentMarkSweepThread::clear_CMS_flag(
1960 ConcurrentMarkSweepThread::CMS_cms_has_token);
1961 ConcurrentMarkSweepThread::set_CMS_flag(
1962 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1963 // Get a possibly blocked foreground thread going
1964 CGC_lock->notify();
1965 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1966 p2i(Thread::current()), _collectorState);
1967 while (_foregroundGCIsActive) {
1968 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1969 }
1970 ConcurrentMarkSweepThread::set_CMS_flag(
1971 ConcurrentMarkSweepThread::CMS_cms_has_token);
1972 ConcurrentMarkSweepThread::clear_CMS_flag(
1973 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1974 }
1975 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1976 p2i(Thread::current()), _collectorState);
1977 return res;
1978 }
1979
1980 // Because of the need to lock the free lists and other structures in
1981 // the collector, common to all the generations that the collector is
1982 // collecting, we need the gc_prologues of individual CMS generations
1983 // delegate to their collector. It may have been simpler had the
1984 // current infrastructure allowed one to call a prologue on a
1985 // collector. In the absence of that we have the generation's
1986 // prologue delegate to the collector, which delegates back
1987 // some "local" work to a worker method in the individual generations
1988 // that it's responsible for collecting, while itself doing any
1989 // work common to all generations it's responsible for. A similar
1990 // comment applies to the gc_epilogue()'s.
1991 // The role of the variable _between_prologue_and_epilogue is to
1992 // enforce the invocation protocol.
1993 void CMSCollector::gc_prologue(bool full) {
1994 // Call gc_prologue_work() for the CMSGen
1995 // we are responsible for.
1996
1997 // The following locking discipline assumes that we are only called
1998 // when the world is stopped.
1999 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2000
2001 // The CMSCollector prologue must call the gc_prologues for the
2002 // "generations" that it's responsible
2003 // for.
2004
2005 assert( Thread::current()->is_VM_thread()
2006 || ( CMSScavengeBeforeRemark
2007 && Thread::current()->is_ConcurrentGC_thread()),
2008 "Incorrect thread type for prologue execution");
2009
2010 if (_between_prologue_and_epilogue) {
2011 // We have already been invoked; this is a gc_prologue delegation
2012 // from yet another CMS generation that we are responsible for, just
2013 // ignore it since all relevant work has already been done.
2014 return;
2015 }
2016
2017 // set a bit saying prologue has been called; cleared in epilogue
2018 _between_prologue_and_epilogue = true;
2019 // Claim locks for common data structures, then call gc_prologue_work()
2020 // for each CMSGen.
2021
2022 getFreelistLocks(); // gets free list locks on constituent spaces
2023 bitMapLock()->lock_without_safepoint_check();
2024
2025 // Should call gc_prologue_work() for all cms gens we are responsible for
2026 bool duringMarking = _collectorState >= Marking
2027 && _collectorState < Sweeping;
2028
2029 // The young collections clear the modified oops state, which tells if
2030 // there are any modified oops in the class. The remark phase also needs
2031 // that information. Tell the young collection to save the union of all
2032 // modified klasses.
2033 if (duringMarking) {
2034 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2035 }
2036
2037 bool registerClosure = duringMarking;
2038
2039 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2040
2041 if (!full) {
2042 stats().record_gc0_begin();
2043 }
2044 }
2045
2046 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2047
2048 _capacity_at_prologue = capacity();
2049 _used_at_prologue = used();
2050
2051 // We enable promotion tracking so that card-scanning can recognize
2052 // which objects have been promoted during this GC and skip them.
2053 for (uint i = 0; i < ParallelGCThreads; i++) {
2054 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2055 }
2056
2057 // Delegate to CMScollector which knows how to coordinate between
2058 // this and any other CMS generations that it is responsible for
2059 // collecting.
2060 collector()->gc_prologue(full);
2061 }
2062
2063 // This is a "private" interface for use by this generation's CMSCollector.
2064 // Not to be called directly by any other entity (for instance,
2065 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2066 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2067 bool registerClosure, ModUnionClosure* modUnionClosure) {
2068 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2069 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2070 "Should be NULL");
2071 if (registerClosure) {
2072 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2073 }
2074 cmsSpace()->gc_prologue();
2075 // Clear stat counters
2076 NOT_PRODUCT(
2077 assert(_numObjectsPromoted == 0, "check");
2078 assert(_numWordsPromoted == 0, "check");
2079 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2080 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2081 _numObjectsAllocated = 0;
2082 _numWordsAllocated = 0;
2083 )
2084 }
2085
2086 void CMSCollector::gc_epilogue(bool full) {
2087 // The following locking discipline assumes that we are only called
2088 // when the world is stopped.
2089 assert(SafepointSynchronize::is_at_safepoint(),
2090 "world is stopped assumption");
2091
2092 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2093 // if linear allocation blocks need to be appropriately marked to allow the
2094 // the blocks to be parsable. We also check here whether we need to nudge the
2095 // CMS collector thread to start a new cycle (if it's not already active).
2096 assert( Thread::current()->is_VM_thread()
2097 || ( CMSScavengeBeforeRemark
2098 && Thread::current()->is_ConcurrentGC_thread()),
2099 "Incorrect thread type for epilogue execution");
2100
2101 if (!_between_prologue_and_epilogue) {
2102 // We have already been invoked; this is a gc_epilogue delegation
2103 // from yet another CMS generation that we are responsible for, just
2104 // ignore it since all relevant work has already been done.
2105 return;
2106 }
2107 assert(haveFreelistLocks(), "must have freelist locks");
2108 assert_lock_strong(bitMapLock());
2109
2110 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2111
2112 _cmsGen->gc_epilogue_work(full);
2113
2114 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2115 // in case sampling was not already enabled, enable it
2116 _start_sampling = true;
2117 }
2118 // reset _eden_chunk_array so sampling starts afresh
2119 _eden_chunk_index = 0;
2120
2121 size_t cms_used = _cmsGen->cmsSpace()->used();
2122
2123 // update performance counters - this uses a special version of
2124 // update_counters() that allows the utilization to be passed as a
2125 // parameter, avoiding multiple calls to used().
2126 //
2127 _cmsGen->update_counters(cms_used);
2128
2129 bitMapLock()->unlock();
2130 releaseFreelistLocks();
2131
2132 if (!CleanChunkPoolAsync) {
2133 Chunk::clean_chunk_pool();
2134 }
2135
2136 set_did_compact(false);
2137 _between_prologue_and_epilogue = false; // ready for next cycle
2138 }
2139
2140 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2141 collector()->gc_epilogue(full);
2142
2143 // When using ParNew, promotion tracking should have already been
2144 // disabled. However, the prologue (which enables promotion
2145 // tracking) and epilogue are called irrespective of the type of
2146 // GC. So they will also be called before and after Full GCs, during
2147 // which promotion tracking will not be explicitly disabled. So,
2148 // it's safer to also disable it here too (to be symmetric with
2149 // enabling it in the prologue).
2150 for (uint i = 0; i < ParallelGCThreads; i++) {
2151 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2152 }
2153 }
2154
2155 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2156 assert(!incremental_collection_failed(), "Should have been cleared");
2157 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2158 cmsSpace()->gc_epilogue();
2159 // Print stat counters
2160 NOT_PRODUCT(
2161 assert(_numObjectsAllocated == 0, "check");
2162 assert(_numWordsAllocated == 0, "check");
2163 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2164 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2165 _numObjectsPromoted = 0;
2166 _numWordsPromoted = 0;
2167 )
2168
2169 // Call down the chain in contiguous_available needs the freelistLock
2170 // so print this out before releasing the freeListLock.
2171 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2172 }
2173
2174 #ifndef PRODUCT
2175 bool CMSCollector::have_cms_token() {
2176 Thread* thr = Thread::current();
2177 if (thr->is_VM_thread()) {
2178 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2179 } else if (thr->is_ConcurrentGC_thread()) {
2180 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2181 } else if (thr->is_GC_task_thread()) {
2182 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2183 ParGCRareEvent_lock->owned_by_self();
2184 }
2185 return false;
2186 }
2187
2188 // Check reachability of the given heap address in CMS generation,
2189 // treating all other generations as roots.
2190 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2191 // We could "guarantee" below, rather than assert, but I'll
2192 // leave these as "asserts" so that an adventurous debugger
2193 // could try this in the product build provided some subset of
2194 // the conditions were met, provided they were interested in the
2195 // results and knew that the computation below wouldn't interfere
2196 // with other concurrent computations mutating the structures
2197 // being read or written.
2198 assert(SafepointSynchronize::is_at_safepoint(),
2199 "Else mutations in object graph will make answer suspect");
2200 assert(have_cms_token(), "Should hold cms token");
2201 assert(haveFreelistLocks(), "must hold free list locks");
2202 assert_lock_strong(bitMapLock());
2203
2204 // Clear the marking bit map array before starting, but, just
2205 // for kicks, first report if the given address is already marked
2206 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2207 _markBitMap.isMarked(addr) ? "" : " not");
2208
2209 if (verify_after_remark()) {
2210 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2211 bool result = verification_mark_bm()->isMarked(addr);
2212 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2213 result ? "IS" : "is NOT");
2214 return result;
2215 } else {
2216 tty->print_cr("Could not compute result");
2217 return false;
2218 }
2219 }
2220 #endif
2221
2222 void
2223 CMSCollector::print_on_error(outputStream* st) {
2224 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2225 if (collector != NULL) {
2226 CMSBitMap* bitmap = &collector->_markBitMap;
2227 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2228 bitmap->print_on_error(st, " Bits: ");
2229
2230 st->cr();
2231
2232 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2233 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2234 mut_bitmap->print_on_error(st, " Bits: ");
2235 }
2236 }
2237
2238 ////////////////////////////////////////////////////////
2239 // CMS Verification Support
2240 ////////////////////////////////////////////////////////
2241 // Following the remark phase, the following invariant
2242 // should hold -- each object in the CMS heap which is
2243 // marked in markBitMap() should be marked in the verification_mark_bm().
2244
2245 class VerifyMarkedClosure: public BitMapClosure {
2246 CMSBitMap* _marks;
2247 bool _failed;
2248
2249 public:
2250 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2251
2252 bool do_bit(size_t offset) {
2253 HeapWord* addr = _marks->offsetToHeapWord(offset);
2254 if (!_marks->isMarked(addr)) {
2255 Log(gc, verify) log;
2256 ResourceMark rm;
2257 LogStream ls(log.error());
2258 oop(addr)->print_on(&ls);
2259 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2260 _failed = true;
2261 }
2262 return true;
2263 }
2264
2265 bool failed() { return _failed; }
2266 };
2267
2268 bool CMSCollector::verify_after_remark() {
2269 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2270 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2271 static bool init = false;
2272
2273 assert(SafepointSynchronize::is_at_safepoint(),
2274 "Else mutations in object graph will make answer suspect");
2275 assert(have_cms_token(),
2276 "Else there may be mutual interference in use of "
2277 " verification data structures");
2278 assert(_collectorState > Marking && _collectorState <= Sweeping,
2279 "Else marking info checked here may be obsolete");
2280 assert(haveFreelistLocks(), "must hold free list locks");
2281 assert_lock_strong(bitMapLock());
2282
2283
2284 // Allocate marking bit map if not already allocated
2285 if (!init) { // first time
2286 if (!verification_mark_bm()->allocate(_span)) {
2287 return false;
2288 }
2289 init = true;
2290 }
2291
2292 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2293
2294 // Turn off refs discovery -- so we will be tracing through refs.
2295 // This is as intended, because by this time
2296 // GC must already have cleared any refs that need to be cleared,
2297 // and traced those that need to be marked; moreover,
2298 // the marking done here is not going to interfere in any
2299 // way with the marking information used by GC.
2300 NoRefDiscovery no_discovery(ref_processor());
2301
2302 #if COMPILER2_OR_JVMCI
2303 DerivedPointerTableDeactivate dpt_deact;
2304 #endif
2305
2306 // Clear any marks from a previous round
2307 verification_mark_bm()->clear_all();
2308 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2309 verify_work_stacks_empty();
2310
2311 CMSHeap* heap = CMSHeap::heap();
2312 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2313 // Update the saved marks which may affect the root scans.
2314 heap->save_marks();
2315
2316 if (CMSRemarkVerifyVariant == 1) {
2317 // In this first variant of verification, we complete
2318 // all marking, then check if the new marks-vector is
2319 // a subset of the CMS marks-vector.
2320 verify_after_remark_work_1();
2321 } else {
2322 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2323 // In this second variant of verification, we flag an error
2324 // (i.e. an object reachable in the new marks-vector not reachable
2325 // in the CMS marks-vector) immediately, also indicating the
2326 // identify of an object (A) that references the unmarked object (B) --
2327 // presumably, a mutation to A failed to be picked up by preclean/remark?
2328 verify_after_remark_work_2();
2329 }
2330
2331 return true;
2332 }
2333
2334 void CMSCollector::verify_after_remark_work_1() {
2335 ResourceMark rm;
2336 HandleMark hm;
2337 CMSHeap* heap = CMSHeap::heap();
2338
2339 // Get a clear set of claim bits for the roots processing to work with.
2340 ClassLoaderDataGraph::clear_claimed_marks();
2341
2342 // Mark from roots one level into CMS
2343 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2344 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2345
2346 {
2347 StrongRootsScope srs(1);
2348
2349 heap->cms_process_roots(&srs,
2350 true, // young gen as roots
2351 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2352 should_unload_classes(),
2353 ¬Older,
2354 NULL);
2355 }
2356
2357 // Now mark from the roots
2358 MarkFromRootsClosure markFromRootsClosure(this, _span,
2359 verification_mark_bm(), verification_mark_stack(),
2360 false /* don't yield */, true /* verifying */);
2361 assert(_restart_addr == NULL, "Expected pre-condition");
2362 verification_mark_bm()->iterate(&markFromRootsClosure);
2363 while (_restart_addr != NULL) {
2364 // Deal with stack overflow: by restarting at the indicated
2365 // address.
2366 HeapWord* ra = _restart_addr;
2367 markFromRootsClosure.reset(ra);
2368 _restart_addr = NULL;
2369 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2370 }
2371 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2372 verify_work_stacks_empty();
2373
2374 // Marking completed -- now verify that each bit marked in
2375 // verification_mark_bm() is also marked in markBitMap(); flag all
2376 // errors by printing corresponding objects.
2377 VerifyMarkedClosure vcl(markBitMap());
2378 verification_mark_bm()->iterate(&vcl);
2379 if (vcl.failed()) {
2380 Log(gc, verify) log;
2381 log.error("Failed marking verification after remark");
2382 ResourceMark rm;
2383 LogStream ls(log.error());
2384 heap->print_on(&ls);
2385 fatal("CMS: failed marking verification after remark");
2386 }
2387 }
2388
2389 class VerifyCLDOopsCLDClosure : public CLDClosure {
2390 class VerifyCLDOopsClosure : public OopClosure {
2391 CMSBitMap* _bitmap;
2392 public:
2393 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2394 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2395 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2396 } _oop_closure;
2397 public:
2398 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2399 void do_cld(ClassLoaderData* cld) {
2400 cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2401 }
2402 };
2403
2404 void CMSCollector::verify_after_remark_work_2() {
2405 ResourceMark rm;
2406 HandleMark hm;
2407 CMSHeap* heap = CMSHeap::heap();
2408
2409 // Get a clear set of claim bits for the roots processing to work with.
2410 ClassLoaderDataGraph::clear_claimed_marks();
2411
2412 // Mark from roots one level into CMS
2413 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2414 markBitMap());
2415 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2416
2417 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2418
2419 {
2420 StrongRootsScope srs(1);
2421
2422 heap->cms_process_roots(&srs,
2423 true, // young gen as roots
2424 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2425 should_unload_classes(),
2426 ¬Older,
2427 &cld_closure);
2428 }
2429
2430 // Now mark from the roots
2431 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2432 verification_mark_bm(), markBitMap(), verification_mark_stack());
2433 assert(_restart_addr == NULL, "Expected pre-condition");
2434 verification_mark_bm()->iterate(&markFromRootsClosure);
2435 while (_restart_addr != NULL) {
2436 // Deal with stack overflow: by restarting at the indicated
2437 // address.
2438 HeapWord* ra = _restart_addr;
2439 markFromRootsClosure.reset(ra);
2440 _restart_addr = NULL;
2441 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2442 }
2443 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2444 verify_work_stacks_empty();
2445
2446 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2447 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2448
2449 // Marking completed -- now verify that each bit marked in
2450 // verification_mark_bm() is also marked in markBitMap(); flag all
2451 // errors by printing corresponding objects.
2452 VerifyMarkedClosure vcl(markBitMap());
2453 verification_mark_bm()->iterate(&vcl);
2454 assert(!vcl.failed(), "Else verification above should not have succeeded");
2455 }
2456
2457 void ConcurrentMarkSweepGeneration::save_marks() {
2458 // delegate to CMS space
2459 cmsSpace()->save_marks();
2460 }
2461
2462 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2463 return cmsSpace()->no_allocs_since_save_marks();
2464 }
2465
2466 void
2467 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2468 if (freelistLock()->owned_by_self()) {
2469 Generation::oop_iterate(cl);
2470 } else {
2471 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2472 Generation::oop_iterate(cl);
2473 }
2474 }
2475
2476 void
2477 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2478 if (freelistLock()->owned_by_self()) {
2479 Generation::object_iterate(cl);
2480 } else {
2481 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2482 Generation::object_iterate(cl);
2483 }
2484 }
2485
2486 void
2487 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2488 if (freelistLock()->owned_by_self()) {
2489 Generation::safe_object_iterate(cl);
2490 } else {
2491 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2492 Generation::safe_object_iterate(cl);
2493 }
2494 }
2495
2496 void
2497 ConcurrentMarkSweepGeneration::post_compact() {
2498 }
2499
2500 void
2501 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2502 // Fix the linear allocation blocks to look like free blocks.
2503
2504 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2505 // are not called when the heap is verified during universe initialization and
2506 // at vm shutdown.
2507 if (freelistLock()->owned_by_self()) {
2508 cmsSpace()->prepare_for_verify();
2509 } else {
2510 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2511 cmsSpace()->prepare_for_verify();
2512 }
2513 }
2514
2515 void
2516 ConcurrentMarkSweepGeneration::verify() {
2517 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2518 // are not called when the heap is verified during universe initialization and
2519 // at vm shutdown.
2520 if (freelistLock()->owned_by_self()) {
2521 cmsSpace()->verify();
2522 } else {
2523 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2524 cmsSpace()->verify();
2525 }
2526 }
2527
2528 void CMSCollector::verify() {
2529 _cmsGen->verify();
2530 }
2531
2532 #ifndef PRODUCT
2533 bool CMSCollector::overflow_list_is_empty() const {
2534 assert(_num_par_pushes >= 0, "Inconsistency");
2535 if (_overflow_list == NULL) {
2536 assert(_num_par_pushes == 0, "Inconsistency");
2537 }
2538 return _overflow_list == NULL;
2539 }
2540
2541 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2542 // merely consolidate assertion checks that appear to occur together frequently.
2543 void CMSCollector::verify_work_stacks_empty() const {
2544 assert(_markStack.isEmpty(), "Marking stack should be empty");
2545 assert(overflow_list_is_empty(), "Overflow list should be empty");
2546 }
2547
2548 void CMSCollector::verify_overflow_empty() const {
2549 assert(overflow_list_is_empty(), "Overflow list should be empty");
2550 assert(no_preserved_marks(), "No preserved marks");
2551 }
2552 #endif // PRODUCT
2553
2554 // Decide if we want to enable class unloading as part of the
2555 // ensuing concurrent GC cycle. We will collect and
2556 // unload classes if it's the case that:
2557 // (a) class unloading is enabled at the command line, and
2558 // (b) old gen is getting really full
2559 // NOTE: Provided there is no change in the state of the heap between
2560 // calls to this method, it should have idempotent results. Moreover,
2561 // its results should be monotonically increasing (i.e. going from 0 to 1,
2562 // but not 1 to 0) between successive calls between which the heap was
2563 // not collected. For the implementation below, it must thus rely on
2564 // the property that concurrent_cycles_since_last_unload()
2565 // will not decrease unless a collection cycle happened and that
2566 // _cmsGen->is_too_full() are
2567 // themselves also monotonic in that sense. See check_monotonicity()
2568 // below.
2569 void CMSCollector::update_should_unload_classes() {
2570 _should_unload_classes = false;
2571 if (CMSClassUnloadingEnabled) {
2572 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2573 CMSClassUnloadingMaxInterval)
2574 || _cmsGen->is_too_full();
2575 }
2576 }
2577
2578 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2579 bool res = should_concurrent_collect();
2580 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2581 return res;
2582 }
2583
2584 void CMSCollector::setup_cms_unloading_and_verification_state() {
2585 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2586 || VerifyBeforeExit;
2587 const int rso = GenCollectedHeap::SO_AllCodeCache;
2588
2589 // We set the proper root for this CMS cycle here.
2590 if (should_unload_classes()) { // Should unload classes this cycle
2591 remove_root_scanning_option(rso); // Shrink the root set appropriately
2592 set_verifying(should_verify); // Set verification state for this cycle
2593 return; // Nothing else needs to be done at this time
2594 }
2595
2596 // Not unloading classes this cycle
2597 assert(!should_unload_classes(), "Inconsistency!");
2598
2599 // If we are not unloading classes then add SO_AllCodeCache to root
2600 // scanning options.
2601 add_root_scanning_option(rso);
2602
2603 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2604 set_verifying(true);
2605 } else if (verifying() && !should_verify) {
2606 // We were verifying, but some verification flags got disabled.
2607 set_verifying(false);
2608 // Exclude symbols, strings and code cache elements from root scanning to
2609 // reduce IM and RM pauses.
2610 remove_root_scanning_option(rso);
2611 }
2612 }
2613
2614
2615 #ifndef PRODUCT
2616 HeapWord* CMSCollector::block_start(const void* p) const {
2617 const HeapWord* addr = (HeapWord*)p;
2618 if (_span.contains(p)) {
2619 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2620 return _cmsGen->cmsSpace()->block_start(p);
2621 }
2622 }
2623 return NULL;
2624 }
2625 #endif
2626
2627 HeapWord*
2628 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2629 bool tlab,
2630 bool parallel) {
2631 CMSSynchronousYieldRequest yr;
2632 assert(!tlab, "Can't deal with TLAB allocation");
2633 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2634 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2635 if (GCExpandToAllocateDelayMillis > 0) {
2636 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2637 }
2638 return have_lock_and_allocate(word_size, tlab);
2639 }
2640
2641 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2642 size_t bytes,
2643 size_t expand_bytes,
2644 CMSExpansionCause::Cause cause)
2645 {
2646
2647 bool success = expand(bytes, expand_bytes);
2648
2649 // remember why we expanded; this information is used
2650 // by shouldConcurrentCollect() when making decisions on whether to start
2651 // a new CMS cycle.
2652 if (success) {
2653 set_expansion_cause(cause);
2654 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2655 }
2656 }
2657
2658 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2659 HeapWord* res = NULL;
2660 MutexLocker x(ParGCRareEvent_lock);
2661 while (true) {
2662 // Expansion by some other thread might make alloc OK now:
2663 res = ps->lab.alloc(word_sz);
2664 if (res != NULL) return res;
2665 // If there's not enough expansion space available, give up.
2666 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2667 return NULL;
2668 }
2669 // Otherwise, we try expansion.
2670 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2671 // Now go around the loop and try alloc again;
2672 // A competing par_promote might beat us to the expansion space,
2673 // so we may go around the loop again if promotion fails again.
2674 if (GCExpandToAllocateDelayMillis > 0) {
2675 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2676 }
2677 }
2678 }
2679
2680
2681 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2682 PromotionInfo* promo) {
2683 MutexLocker x(ParGCRareEvent_lock);
2684 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2685 while (true) {
2686 // Expansion by some other thread might make alloc OK now:
2687 if (promo->ensure_spooling_space()) {
2688 assert(promo->has_spooling_space(),
2689 "Post-condition of successful ensure_spooling_space()");
2690 return true;
2691 }
2692 // If there's not enough expansion space available, give up.
2693 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2694 return false;
2695 }
2696 // Otherwise, we try expansion.
2697 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2698 // Now go around the loop and try alloc again;
2699 // A competing allocation might beat us to the expansion space,
2700 // so we may go around the loop again if allocation fails again.
2701 if (GCExpandToAllocateDelayMillis > 0) {
2702 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2703 }
2704 }
2705 }
2706
2707 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2708 // Only shrink if a compaction was done so that all the free space
2709 // in the generation is in a contiguous block at the end.
2710 if (did_compact()) {
2711 CardGeneration::shrink(bytes);
2712 }
2713 }
2714
2715 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2716 assert_locked_or_safepoint(Heap_lock);
2717 }
2718
2719 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2720 assert_locked_or_safepoint(Heap_lock);
2721 assert_lock_strong(freelistLock());
2722 log_trace(gc)("Shrinking of CMS not yet implemented");
2723 return;
2724 }
2725
2726
2727 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2728 // phases.
2729 class CMSPhaseAccounting: public StackObj {
2730 public:
2731 CMSPhaseAccounting(CMSCollector *collector,
2732 const char *title);
2733 ~CMSPhaseAccounting();
2734
2735 private:
2736 CMSCollector *_collector;
2737 const char *_title;
2738 GCTraceConcTime(Info, gc) _trace_time;
2739
2740 public:
2741 // Not MT-safe; so do not pass around these StackObj's
2742 // where they may be accessed by other threads.
2743 double wallclock_millis() {
2744 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2745 }
2746 };
2747
2748 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2749 const char *title) :
2750 _collector(collector), _title(title), _trace_time(title) {
2751
2752 _collector->resetYields();
2753 _collector->resetTimer();
2754 _collector->startTimer();
2755 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2756 }
2757
2758 CMSPhaseAccounting::~CMSPhaseAccounting() {
2759 _collector->gc_timer_cm()->register_gc_concurrent_end();
2760 _collector->stopTimer();
2761 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2762 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2763 }
2764
2765 // CMS work
2766
2767 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2768 class CMSParMarkTask : public AbstractGangTask {
2769 protected:
2770 CMSCollector* _collector;
2771 uint _n_workers;
2772 OopStorage::ParState<false, false> _par_state_string;
2773 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2774 AbstractGangTask(name),
2775 _collector(collector),
2776 _n_workers(n_workers),
2777 _par_state_string(StringTable::weak_storage()) {}
2778 // Work method in support of parallel rescan ... of young gen spaces
2779 void do_young_space_rescan(OopsInGenClosure* cl,
2780 ContiguousSpace* space,
2781 HeapWord** chunk_array, size_t chunk_top);
2782 void work_on_young_gen_roots(OopsInGenClosure* cl);
2783 };
2784
2785 // Parallel initial mark task
2786 class CMSParInitialMarkTask: public CMSParMarkTask {
2787 StrongRootsScope* _strong_roots_scope;
2788 public:
2789 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2790 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2791 _strong_roots_scope(strong_roots_scope) {}
2792 void work(uint worker_id);
2793 };
2794
2795 // Checkpoint the roots into this generation from outside
2796 // this generation. [Note this initial checkpoint need only
2797 // be approximate -- we'll do a catch up phase subsequently.]
2798 void CMSCollector::checkpointRootsInitial() {
2799 assert(_collectorState == InitialMarking, "Wrong collector state");
2800 check_correct_thread_executing();
2801 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2802
2803 save_heap_summary();
2804 report_heap_summary(GCWhen::BeforeGC);
2805
2806 ReferenceProcessor* rp = ref_processor();
2807 assert(_restart_addr == NULL, "Control point invariant");
2808 {
2809 // acquire locks for subsequent manipulations
2810 MutexLockerEx x(bitMapLock(),
2811 Mutex::_no_safepoint_check_flag);
2812 checkpointRootsInitialWork();
2813 // enable ("weak") refs discovery
2814 rp->enable_discovery();
2815 _collectorState = Marking;
2816 }
2817 }
2818
2819 void CMSCollector::checkpointRootsInitialWork() {
2820 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2821 assert(_collectorState == InitialMarking, "just checking");
2822
2823 // Already have locks.
2824 assert_lock_strong(bitMapLock());
2825 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2826
2827 // Setup the verification and class unloading state for this
2828 // CMS collection cycle.
2829 setup_cms_unloading_and_verification_state();
2830
2831 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2832
2833 // Reset all the PLAB chunk arrays if necessary.
2834 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2835 reset_survivor_plab_arrays();
2836 }
2837
2838 ResourceMark rm;
2839 HandleMark hm;
2840
2841 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2842 CMSHeap* heap = CMSHeap::heap();
2843
2844 verify_work_stacks_empty();
2845 verify_overflow_empty();
2846
2847 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2848 // Update the saved marks which may affect the root scans.
2849 heap->save_marks();
2850
2851 // weak reference processing has not started yet.
2852 ref_processor()->set_enqueuing_is_done(false);
2853
2854 // Need to remember all newly created CLDs,
2855 // so that we can guarantee that the remark finds them.
2856 ClassLoaderDataGraph::remember_new_clds(true);
2857
2858 // Whenever a CLD is found, it will be claimed before proceeding to mark
2859 // the klasses. The claimed marks need to be cleared before marking starts.
2860 ClassLoaderDataGraph::clear_claimed_marks();
2861
2862 print_eden_and_survivor_chunk_arrays();
2863
2864 {
2865 #if COMPILER2_OR_JVMCI
2866 DerivedPointerTableDeactivate dpt_deact;
2867 #endif
2868 if (CMSParallelInitialMarkEnabled) {
2869 // The parallel version.
2870 WorkGang* workers = heap->workers();
2871 assert(workers != NULL, "Need parallel worker threads.");
2872 uint n_workers = workers->active_workers();
2873
2874 StrongRootsScope srs(n_workers);
2875
2876 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2877 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2878 // If the total workers is greater than 1, then multiple workers
2879 // may be used at some time and the initialization has been set
2880 // such that the single threaded path cannot be used.
2881 if (workers->total_workers() > 1) {
2882 workers->run_task(&tsk);
2883 } else {
2884 tsk.work(0);
2885 }
2886 } else {
2887 // The serial version.
2888 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2889 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2890
2891 StrongRootsScope srs(1);
2892
2893 heap->cms_process_roots(&srs,
2894 true, // young gen as roots
2895 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2896 should_unload_classes(),
2897 ¬Older,
2898 &cld_closure);
2899 }
2900 }
2901
2902 // Clear mod-union table; it will be dirtied in the prologue of
2903 // CMS generation per each young generation collection.
2904
2905 assert(_modUnionTable.isAllClear(),
2906 "Was cleared in most recent final checkpoint phase"
2907 " or no bits are set in the gc_prologue before the start of the next "
2908 "subsequent marking phase.");
2909
2910 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2911
2912 // Save the end of the used_region of the constituent generations
2913 // to be used to limit the extent of sweep in each generation.
2914 save_sweep_limits();
2915 verify_overflow_empty();
2916 }
2917
2918 bool CMSCollector::markFromRoots() {
2919 // we might be tempted to assert that:
2920 // assert(!SafepointSynchronize::is_at_safepoint(),
2921 // "inconsistent argument?");
2922 // However that wouldn't be right, because it's possible that
2923 // a safepoint is indeed in progress as a young generation
2924 // stop-the-world GC happens even as we mark in this generation.
2925 assert(_collectorState == Marking, "inconsistent state?");
2926 check_correct_thread_executing();
2927 verify_overflow_empty();
2928
2929 // Weak ref discovery note: We may be discovering weak
2930 // refs in this generation concurrent (but interleaved) with
2931 // weak ref discovery by the young generation collector.
2932
2933 CMSTokenSyncWithLocks ts(true, bitMapLock());
2934 GCTraceCPUTime tcpu;
2935 CMSPhaseAccounting pa(this, "Concurrent Mark");
2936 bool res = markFromRootsWork();
2937 if (res) {
2938 _collectorState = Precleaning;
2939 } else { // We failed and a foreground collection wants to take over
2940 assert(_foregroundGCIsActive, "internal state inconsistency");
2941 assert(_restart_addr == NULL, "foreground will restart from scratch");
2942 log_debug(gc)("bailing out to foreground collection");
2943 }
2944 verify_overflow_empty();
2945 return res;
2946 }
2947
2948 bool CMSCollector::markFromRootsWork() {
2949 // iterate over marked bits in bit map, doing a full scan and mark
2950 // from these roots using the following algorithm:
2951 // . if oop is to the right of the current scan pointer,
2952 // mark corresponding bit (we'll process it later)
2953 // . else (oop is to left of current scan pointer)
2954 // push oop on marking stack
2955 // . drain the marking stack
2956
2957 // Note that when we do a marking step we need to hold the
2958 // bit map lock -- recall that direct allocation (by mutators)
2959 // and promotion (by the young generation collector) is also
2960 // marking the bit map. [the so-called allocate live policy.]
2961 // Because the implementation of bit map marking is not
2962 // robust wrt simultaneous marking of bits in the same word,
2963 // we need to make sure that there is no such interference
2964 // between concurrent such updates.
2965
2966 // already have locks
2967 assert_lock_strong(bitMapLock());
2968
2969 verify_work_stacks_empty();
2970 verify_overflow_empty();
2971 bool result = false;
2972 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2973 result = do_marking_mt();
2974 } else {
2975 result = do_marking_st();
2976 }
2977 return result;
2978 }
2979
2980 // Forward decl
2981 class CMSConcMarkingTask;
2982
2983 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2984 CMSCollector* _collector;
2985 CMSConcMarkingTask* _task;
2986 public:
2987 virtual void yield();
2988
2989 // "n_threads" is the number of threads to be terminated.
2990 // "queue_set" is a set of work queues of other threads.
2991 // "collector" is the CMS collector associated with this task terminator.
2992 // "yield" indicates whether we need the gang as a whole to yield.
2993 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2994 ParallelTaskTerminator(n_threads, queue_set),
2995 _collector(collector) { }
2996
2997 void set_task(CMSConcMarkingTask* task) {
2998 _task = task;
2999 }
3000 };
3001
3002 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3003 CMSConcMarkingTask* _task;
3004 public:
3005 bool should_exit_termination();
3006 void set_task(CMSConcMarkingTask* task) {
3007 _task = task;
3008 }
3009 };
3010
3011 // MT Concurrent Marking Task
3012 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3013 CMSCollector* _collector;
3014 uint _n_workers; // requested/desired # workers
3015 bool _result;
3016 CompactibleFreeListSpace* _cms_space;
3017 char _pad_front[64]; // padding to ...
3018 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3019 char _pad_back[64];
3020 HeapWord* _restart_addr;
3021
3022 // Exposed here for yielding support
3023 Mutex* const _bit_map_lock;
3024
3025 // The per thread work queues, available here for stealing
3026 OopTaskQueueSet* _task_queues;
3027
3028 // Termination (and yielding) support
3029 CMSConcMarkingTerminator _term;
3030 CMSConcMarkingTerminatorTerminator _term_term;
3031
3032 public:
3033 CMSConcMarkingTask(CMSCollector* collector,
3034 CompactibleFreeListSpace* cms_space,
3035 YieldingFlexibleWorkGang* workers,
3036 OopTaskQueueSet* task_queues):
3037 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3038 _collector(collector),
3039 _n_workers(0),
3040 _result(true),
3041 _cms_space(cms_space),
3042 _bit_map_lock(collector->bitMapLock()),
3043 _task_queues(task_queues),
3044 _term(_n_workers, task_queues, _collector)
3045 {
3046 _requested_size = _n_workers;
3047 _term.set_task(this);
3048 _term_term.set_task(this);
3049 _restart_addr = _global_finger = _cms_space->bottom();
3050 }
3051
3052
3053 OopTaskQueueSet* task_queues() { return _task_queues; }
3054
3055 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3056
3057 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3058
3059 CMSConcMarkingTerminator* terminator() { return &_term; }
3060
3061 virtual void set_for_termination(uint active_workers) {
3062 terminator()->reset_for_reuse(active_workers);
3063 }
3064
3065 void work(uint worker_id);
3066 bool should_yield() {
3067 return ConcurrentMarkSweepThread::should_yield()
3068 && !_collector->foregroundGCIsActive();
3069 }
3070
3071 virtual void coordinator_yield(); // stuff done by coordinator
3072 bool result() { return _result; }
3073
3074 void reset(HeapWord* ra) {
3075 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3076 _restart_addr = _global_finger = ra;
3077 _term.reset_for_reuse();
3078 }
3079
3080 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3081 OopTaskQueue* work_q);
3082
3083 private:
3084 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3085 void do_work_steal(int i);
3086 void bump_global_finger(HeapWord* f);
3087 };
3088
3089 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3090 assert(_task != NULL, "Error");
3091 return _task->yielding();
3092 // Note that we do not need the disjunct || _task->should_yield() above
3093 // because we want terminating threads to yield only if the task
3094 // is already in the midst of yielding, which happens only after at least one
3095 // thread has yielded.
3096 }
3097
3098 void CMSConcMarkingTerminator::yield() {
3099 if (_task->should_yield()) {
3100 _task->yield();
3101 } else {
3102 ParallelTaskTerminator::yield();
3103 }
3104 }
3105
3106 ////////////////////////////////////////////////////////////////
3107 // Concurrent Marking Algorithm Sketch
3108 ////////////////////////////////////////////////////////////////
3109 // Until all tasks exhausted (both spaces):
3110 // -- claim next available chunk
3111 // -- bump global finger via CAS
3112 // -- find first object that starts in this chunk
3113 // and start scanning bitmap from that position
3114 // -- scan marked objects for oops
3115 // -- CAS-mark target, and if successful:
3116 // . if target oop is above global finger (volatile read)
3117 // nothing to do
3118 // . if target oop is in chunk and above local finger
3119 // then nothing to do
3120 // . else push on work-queue
3121 // -- Deal with possible overflow issues:
3122 // . local work-queue overflow causes stuff to be pushed on
3123 // global (common) overflow queue
3124 // . always first empty local work queue
3125 // . then get a batch of oops from global work queue if any
3126 // . then do work stealing
3127 // -- When all tasks claimed (both spaces)
3128 // and local work queue empty,
3129 // then in a loop do:
3130 // . check global overflow stack; steal a batch of oops and trace
3131 // . try to steal from other threads oif GOS is empty
3132 // . if neither is available, offer termination
3133 // -- Terminate and return result
3134 //
3135 void CMSConcMarkingTask::work(uint worker_id) {
3136 elapsedTimer _timer;
3137 ResourceMark rm;
3138 HandleMark hm;
3139
3140 DEBUG_ONLY(_collector->verify_overflow_empty();)
3141
3142 // Before we begin work, our work queue should be empty
3143 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3144 // Scan the bitmap covering _cms_space, tracing through grey objects.
3145 _timer.start();
3146 do_scan_and_mark(worker_id, _cms_space);
3147 _timer.stop();
3148 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3149
3150 // ... do work stealing
3151 _timer.reset();
3152 _timer.start();
3153 do_work_steal(worker_id);
3154 _timer.stop();
3155 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3156 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3157 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3158 // Note that under the current task protocol, the
3159 // following assertion is true even of the spaces
3160 // expanded since the completion of the concurrent
3161 // marking. XXX This will likely change under a strict
3162 // ABORT semantics.
3163 // After perm removal the comparison was changed to
3164 // greater than or equal to from strictly greater than.
3165 // Before perm removal the highest address sweep would
3166 // have been at the end of perm gen but now is at the
3167 // end of the tenured gen.
3168 assert(_global_finger >= _cms_space->end(),
3169 "All tasks have been completed");
3170 DEBUG_ONLY(_collector->verify_overflow_empty();)
3171 }
3172
3173 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3174 HeapWord* read = _global_finger;
3175 HeapWord* cur = read;
3176 while (f > read) {
3177 cur = read;
3178 read = Atomic::cmpxchg(f, &_global_finger, cur);
3179 if (cur == read) {
3180 // our cas succeeded
3181 assert(_global_finger >= f, "protocol consistency");
3182 break;
3183 }
3184 }
3185 }
3186
3187 // This is really inefficient, and should be redone by
3188 // using (not yet available) block-read and -write interfaces to the
3189 // stack and the work_queue. XXX FIX ME !!!
3190 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3191 OopTaskQueue* work_q) {
3192 // Fast lock-free check
3193 if (ovflw_stk->length() == 0) {
3194 return false;
3195 }
3196 assert(work_q->size() == 0, "Shouldn't steal");
3197 MutexLockerEx ml(ovflw_stk->par_lock(),
3198 Mutex::_no_safepoint_check_flag);
3199 // Grab up to 1/4 the size of the work queue
3200 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3201 (size_t)ParGCDesiredObjsFromOverflowList);
3202 num = MIN2(num, ovflw_stk->length());
3203 for (int i = (int) num; i > 0; i--) {
3204 oop cur = ovflw_stk->pop();
3205 assert(cur != NULL, "Counted wrong?");
3206 work_q->push(cur);
3207 }
3208 return num > 0;
3209 }
3210
3211 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3212 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3213 int n_tasks = pst->n_tasks();
3214 // We allow that there may be no tasks to do here because
3215 // we are restarting after a stack overflow.
3216 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3217 uint nth_task = 0;
3218
3219 HeapWord* aligned_start = sp->bottom();
3220 if (sp->used_region().contains(_restart_addr)) {
3221 // Align down to a card boundary for the start of 0th task
3222 // for this space.
3223 aligned_start = align_down(_restart_addr, CardTable::card_size);
3224 }
3225
3226 size_t chunk_size = sp->marking_task_size();
3227 while (pst->try_claim_task(/* reference */ nth_task)) {
3228 // Having claimed the nth task in this space,
3229 // compute the chunk that it corresponds to:
3230 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3231 aligned_start + (nth_task+1)*chunk_size);
3232 // Try and bump the global finger via a CAS;
3233 // note that we need to do the global finger bump
3234 // _before_ taking the intersection below, because
3235 // the task corresponding to that region will be
3236 // deemed done even if the used_region() expands
3237 // because of allocation -- as it almost certainly will
3238 // during start-up while the threads yield in the
3239 // closure below.
3240 HeapWord* finger = span.end();
3241 bump_global_finger(finger); // atomically
3242 // There are null tasks here corresponding to chunks
3243 // beyond the "top" address of the space.
3244 span = span.intersection(sp->used_region());
3245 if (!span.is_empty()) { // Non-null task
3246 HeapWord* prev_obj;
3247 assert(!span.contains(_restart_addr) || nth_task == 0,
3248 "Inconsistency");
3249 if (nth_task == 0) {
3250 // For the 0th task, we'll not need to compute a block_start.
3251 if (span.contains(_restart_addr)) {
3252 // In the case of a restart because of stack overflow,
3253 // we might additionally skip a chunk prefix.
3254 prev_obj = _restart_addr;
3255 } else {
3256 prev_obj = span.start();
3257 }
3258 } else {
3259 // We want to skip the first object because
3260 // the protocol is to scan any object in its entirety
3261 // that _starts_ in this span; a fortiori, any
3262 // object starting in an earlier span is scanned
3263 // as part of an earlier claimed task.
3264 // Below we use the "careful" version of block_start
3265 // so we do not try to navigate uninitialized objects.
3266 prev_obj = sp->block_start_careful(span.start());
3267 // Below we use a variant of block_size that uses the
3268 // Printezis bits to avoid waiting for allocated
3269 // objects to become initialized/parsable.
3270 while (prev_obj < span.start()) {
3271 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3272 if (sz > 0) {
3273 prev_obj += sz;
3274 } else {
3275 // In this case we may end up doing a bit of redundant
3276 // scanning, but that appears unavoidable, short of
3277 // locking the free list locks; see bug 6324141.
3278 break;
3279 }
3280 }
3281 }
3282 if (prev_obj < span.end()) {
3283 MemRegion my_span = MemRegion(prev_obj, span.end());
3284 // Do the marking work within a non-empty span --
3285 // the last argument to the constructor indicates whether the
3286 // iteration should be incremental with periodic yields.
3287 ParMarkFromRootsClosure cl(this, _collector, my_span,
3288 &_collector->_markBitMap,
3289 work_queue(i),
3290 &_collector->_markStack);
3291 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3292 } // else nothing to do for this task
3293 } // else nothing to do for this task
3294 }
3295 // We'd be tempted to assert here that since there are no
3296 // more tasks left to claim in this space, the global_finger
3297 // must exceed space->top() and a fortiori space->end(). However,
3298 // that would not quite be correct because the bumping of
3299 // global_finger occurs strictly after the claiming of a task,
3300 // so by the time we reach here the global finger may not yet
3301 // have been bumped up by the thread that claimed the last
3302 // task.
3303 pst->all_tasks_completed();
3304 }
3305
3306 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3307 private:
3308 CMSCollector* _collector;
3309 CMSConcMarkingTask* _task;
3310 MemRegion _span;
3311 CMSBitMap* _bit_map;
3312 CMSMarkStack* _overflow_stack;
3313 OopTaskQueue* _work_queue;
3314 protected:
3315 DO_OOP_WORK_DEFN
3316 public:
3317 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3318 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3319 MetadataVisitingOopIterateClosure(collector->ref_processor()),
3320 _collector(collector),
3321 _task(task),
3322 _span(collector->_span),
3323 _bit_map(bit_map),
3324 _overflow_stack(overflow_stack),
3325 _work_queue(work_queue)
3326 { }
3327 virtual void do_oop(oop* p);
3328 virtual void do_oop(narrowOop* p);
3329
3330 void trim_queue(size_t max);
3331 void handle_stack_overflow(HeapWord* lost);
3332 void do_yield_check() {
3333 if (_task->should_yield()) {
3334 _task->yield();
3335 }
3336 }
3337 };
3338
3339 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3340
3341 // Grey object scanning during work stealing phase --
3342 // the salient assumption here is that any references
3343 // that are in these stolen objects being scanned must
3344 // already have been initialized (else they would not have
3345 // been published), so we do not need to check for
3346 // uninitialized objects before pushing here.
3347 void ParConcMarkingClosure::do_oop(oop obj) {
3348 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3349 HeapWord* addr = (HeapWord*)obj;
3350 // Check if oop points into the CMS generation
3351 // and is not marked
3352 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3353 // a white object ...
3354 // If we manage to "claim" the object, by being the
3355 // first thread to mark it, then we push it on our
3356 // marking stack
3357 if (_bit_map->par_mark(addr)) { // ... now grey
3358 // push on work queue (grey set)
3359 bool simulate_overflow = false;
3360 NOT_PRODUCT(
3361 if (CMSMarkStackOverflowALot &&
3362 _collector->simulate_overflow()) {
3363 // simulate a stack overflow
3364 simulate_overflow = true;
3365 }
3366 )
3367 if (simulate_overflow ||
3368 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3369 // stack overflow
3370 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3371 // We cannot assert that the overflow stack is full because
3372 // it may have been emptied since.
3373 assert(simulate_overflow ||
3374 _work_queue->size() == _work_queue->max_elems(),
3375 "Else push should have succeeded");
3376 handle_stack_overflow(addr);
3377 }
3378 } // Else, some other thread got there first
3379 do_yield_check();
3380 }
3381 }
3382
3383 void ParConcMarkingClosure::trim_queue(size_t max) {
3384 while (_work_queue->size() > max) {
3385 oop new_oop;
3386 if (_work_queue->pop_local(new_oop)) {
3387 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3388 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3389 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3390 new_oop->oop_iterate(this); // do_oop() above
3391 do_yield_check();
3392 }
3393 }
3394 }
3395
3396 // Upon stack overflow, we discard (part of) the stack,
3397 // remembering the least address amongst those discarded
3398 // in CMSCollector's _restart_address.
3399 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3400 // We need to do this under a mutex to prevent other
3401 // workers from interfering with the work done below.
3402 MutexLockerEx ml(_overflow_stack->par_lock(),
3403 Mutex::_no_safepoint_check_flag);
3404 // Remember the least grey address discarded
3405 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3406 _collector->lower_restart_addr(ra);
3407 _overflow_stack->reset(); // discard stack contents
3408 _overflow_stack->expand(); // expand the stack if possible
3409 }
3410
3411
3412 void CMSConcMarkingTask::do_work_steal(int i) {
3413 OopTaskQueue* work_q = work_queue(i);
3414 oop obj_to_scan;
3415 CMSBitMap* bm = &(_collector->_markBitMap);
3416 CMSMarkStack* ovflw = &(_collector->_markStack);
3417 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3418 while (true) {
3419 cl.trim_queue(0);
3420 assert(work_q->size() == 0, "Should have been emptied above");
3421 if (get_work_from_overflow_stack(ovflw, work_q)) {
3422 // Can't assert below because the work obtained from the
3423 // overflow stack may already have been stolen from us.
3424 // assert(work_q->size() > 0, "Work from overflow stack");
3425 continue;
3426 } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3427 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3428 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3429 obj_to_scan->oop_iterate(&cl);
3430 } else if (terminator()->offer_termination(&_term_term)) {
3431 assert(work_q->size() == 0, "Impossible!");
3432 break;
3433 } else if (yielding() || should_yield()) {
3434 yield();
3435 }
3436 }
3437 }
3438
3439 // This is run by the CMS (coordinator) thread.
3440 void CMSConcMarkingTask::coordinator_yield() {
3441 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3442 "CMS thread should hold CMS token");
3443 // First give up the locks, then yield, then re-lock
3444 // We should probably use a constructor/destructor idiom to
3445 // do this unlock/lock or modify the MutexUnlocker class to
3446 // serve our purpose. XXX
3447 assert_lock_strong(_bit_map_lock);
3448 _bit_map_lock->unlock();
3449 ConcurrentMarkSweepThread::desynchronize(true);
3450 _collector->stopTimer();
3451 _collector->incrementYields();
3452
3453 // It is possible for whichever thread initiated the yield request
3454 // not to get a chance to wake up and take the bitmap lock between
3455 // this thread releasing it and reacquiring it. So, while the
3456 // should_yield() flag is on, let's sleep for a bit to give the
3457 // other thread a chance to wake up. The limit imposed on the number
3458 // of iterations is defensive, to avoid any unforseen circumstances
3459 // putting us into an infinite loop. Since it's always been this
3460 // (coordinator_yield()) method that was observed to cause the
3461 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3462 // which is by default non-zero. For the other seven methods that
3463 // also perform the yield operation, as are using a different
3464 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3465 // can enable the sleeping for those methods too, if necessary.
3466 // See 6442774.
3467 //
3468 // We really need to reconsider the synchronization between the GC
3469 // thread and the yield-requesting threads in the future and we
3470 // should really use wait/notify, which is the recommended
3471 // way of doing this type of interaction. Additionally, we should
3472 // consolidate the eight methods that do the yield operation and they
3473 // are almost identical into one for better maintainability and
3474 // readability. See 6445193.
3475 //
3476 // Tony 2006.06.29
3477 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3478 ConcurrentMarkSweepThread::should_yield() &&
3479 !CMSCollector::foregroundGCIsActive(); ++i) {
3480 os::sleep(Thread::current(), 1, false);
3481 }
3482
3483 ConcurrentMarkSweepThread::synchronize(true);
3484 _bit_map_lock->lock_without_safepoint_check();
3485 _collector->startTimer();
3486 }
3487
3488 bool CMSCollector::do_marking_mt() {
3489 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3490 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3491 conc_workers()->active_workers(),
3492 Threads::number_of_non_daemon_threads());
3493 num_workers = conc_workers()->update_active_workers(num_workers);
3494 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3495
3496 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3497
3498 CMSConcMarkingTask tsk(this,
3499 cms_space,
3500 conc_workers(),
3501 task_queues());
3502
3503 // Since the actual number of workers we get may be different
3504 // from the number we requested above, do we need to do anything different
3505 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3506 // class?? XXX
3507 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3508
3509 // Refs discovery is already non-atomic.
3510 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3511 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3512 conc_workers()->start_task(&tsk);
3513 while (tsk.yielded()) {
3514 tsk.coordinator_yield();
3515 conc_workers()->continue_task(&tsk);
3516 }
3517 // If the task was aborted, _restart_addr will be non-NULL
3518 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3519 while (_restart_addr != NULL) {
3520 // XXX For now we do not make use of ABORTED state and have not
3521 // yet implemented the right abort semantics (even in the original
3522 // single-threaded CMS case). That needs some more investigation
3523 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3524 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3525 // If _restart_addr is non-NULL, a marking stack overflow
3526 // occurred; we need to do a fresh marking iteration from the
3527 // indicated restart address.
3528 if (_foregroundGCIsActive) {
3529 // We may be running into repeated stack overflows, having
3530 // reached the limit of the stack size, while making very
3531 // slow forward progress. It may be best to bail out and
3532 // let the foreground collector do its job.
3533 // Clear _restart_addr, so that foreground GC
3534 // works from scratch. This avoids the headache of
3535 // a "rescan" which would otherwise be needed because
3536 // of the dirty mod union table & card table.
3537 _restart_addr = NULL;
3538 return false;
3539 }
3540 // Adjust the task to restart from _restart_addr
3541 tsk.reset(_restart_addr);
3542 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3543 _restart_addr);
3544 _restart_addr = NULL;
3545 // Get the workers going again
3546 conc_workers()->start_task(&tsk);
3547 while (tsk.yielded()) {
3548 tsk.coordinator_yield();
3549 conc_workers()->continue_task(&tsk);
3550 }
3551 }
3552 assert(tsk.completed(), "Inconsistency");
3553 assert(tsk.result() == true, "Inconsistency");
3554 return true;
3555 }
3556
3557 bool CMSCollector::do_marking_st() {
3558 ResourceMark rm;
3559 HandleMark hm;
3560
3561 // Temporarily make refs discovery single threaded (non-MT)
3562 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3563 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3564 &_markStack, CMSYield);
3565 // the last argument to iterate indicates whether the iteration
3566 // should be incremental with periodic yields.
3567 _markBitMap.iterate(&markFromRootsClosure);
3568 // If _restart_addr is non-NULL, a marking stack overflow
3569 // occurred; we need to do a fresh iteration from the
3570 // indicated restart address.
3571 while (_restart_addr != NULL) {
3572 if (_foregroundGCIsActive) {
3573 // We may be running into repeated stack overflows, having
3574 // reached the limit of the stack size, while making very
3575 // slow forward progress. It may be best to bail out and
3576 // let the foreground collector do its job.
3577 // Clear _restart_addr, so that foreground GC
3578 // works from scratch. This avoids the headache of
3579 // a "rescan" which would otherwise be needed because
3580 // of the dirty mod union table & card table.
3581 _restart_addr = NULL;
3582 return false; // indicating failure to complete marking
3583 }
3584 // Deal with stack overflow:
3585 // we restart marking from _restart_addr
3586 HeapWord* ra = _restart_addr;
3587 markFromRootsClosure.reset(ra);
3588 _restart_addr = NULL;
3589 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3590 }
3591 return true;
3592 }
3593
3594 void CMSCollector::preclean() {
3595 check_correct_thread_executing();
3596 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3597 verify_work_stacks_empty();
3598 verify_overflow_empty();
3599 _abort_preclean = false;
3600 if (CMSPrecleaningEnabled) {
3601 if (!CMSEdenChunksRecordAlways) {
3602 _eden_chunk_index = 0;
3603 }
3604 size_t used = get_eden_used();
3605 size_t capacity = get_eden_capacity();
3606 // Don't start sampling unless we will get sufficiently
3607 // many samples.
3608 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3609 * CMSScheduleRemarkEdenPenetration)) {
3610 _start_sampling = true;
3611 } else {
3612 _start_sampling = false;
3613 }
3614 GCTraceCPUTime tcpu;
3615 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3616 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3617 }
3618 CMSTokenSync x(true); // is cms thread
3619 if (CMSPrecleaningEnabled) {
3620 sample_eden();
3621 _collectorState = AbortablePreclean;
3622 } else {
3623 _collectorState = FinalMarking;
3624 }
3625 verify_work_stacks_empty();
3626 verify_overflow_empty();
3627 }
3628
3629 // Try and schedule the remark such that young gen
3630 // occupancy is CMSScheduleRemarkEdenPenetration %.
3631 void CMSCollector::abortable_preclean() {
3632 check_correct_thread_executing();
3633 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3634 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3635
3636 // If Eden's current occupancy is below this threshold,
3637 // immediately schedule the remark; else preclean
3638 // past the next scavenge in an effort to
3639 // schedule the pause as described above. By choosing
3640 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3641 // we will never do an actual abortable preclean cycle.
3642 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3643 GCTraceCPUTime tcpu;
3644 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3645 // We need more smarts in the abortable preclean
3646 // loop below to deal with cases where allocation
3647 // in young gen is very very slow, and our precleaning
3648 // is running a losing race against a horde of
3649 // mutators intent on flooding us with CMS updates
3650 // (dirty cards).
3651 // One, admittedly dumb, strategy is to give up
3652 // after a certain number of abortable precleaning loops
3653 // or after a certain maximum time. We want to make
3654 // this smarter in the next iteration.
3655 // XXX FIX ME!!! YSR
3656 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3657 while (!(should_abort_preclean() ||
3658 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3659 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3660 cumworkdone += workdone;
3661 loops++;
3662 // Voluntarily terminate abortable preclean phase if we have
3663 // been at it for too long.
3664 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3665 loops >= CMSMaxAbortablePrecleanLoops) {
3666 log_debug(gc)(" CMS: abort preclean due to loops ");
3667 break;
3668 }
3669 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3670 log_debug(gc)(" CMS: abort preclean due to time ");
3671 break;
3672 }
3673 // If we are doing little work each iteration, we should
3674 // take a short break.
3675 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3676 // Sleep for some time, waiting for work to accumulate
3677 stopTimer();
3678 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3679 startTimer();
3680 waited++;
3681 }
3682 }
3683 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3684 loops, waited, cumworkdone);
3685 }
3686 CMSTokenSync x(true); // is cms thread
3687 if (_collectorState != Idling) {
3688 assert(_collectorState == AbortablePreclean,
3689 "Spontaneous state transition?");
3690 _collectorState = FinalMarking;
3691 } // Else, a foreground collection completed this CMS cycle.
3692 return;
3693 }
3694
3695 // Respond to an Eden sampling opportunity
3696 void CMSCollector::sample_eden() {
3697 // Make sure a young gc cannot sneak in between our
3698 // reading and recording of a sample.
3699 assert(Thread::current()->is_ConcurrentGC_thread(),
3700 "Only the cms thread may collect Eden samples");
3701 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3702 "Should collect samples while holding CMS token");
3703 if (!_start_sampling) {
3704 return;
3705 }
3706 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3707 // is populated by the young generation.
3708 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3709 if (_eden_chunk_index < _eden_chunk_capacity) {
3710 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3711 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3712 "Unexpected state of Eden");
3713 // We'd like to check that what we just sampled is an oop-start address;
3714 // however, we cannot do that here since the object may not yet have been
3715 // initialized. So we'll instead do the check when we _use_ this sample
3716 // later.
3717 if (_eden_chunk_index == 0 ||
3718 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3719 _eden_chunk_array[_eden_chunk_index-1])
3720 >= CMSSamplingGrain)) {
3721 _eden_chunk_index++; // commit sample
3722 }
3723 }
3724 }
3725 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3726 size_t used = get_eden_used();
3727 size_t capacity = get_eden_capacity();
3728 assert(used <= capacity, "Unexpected state of Eden");
3729 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3730 _abort_preclean = true;
3731 }
3732 }
3733 }
3734
3735 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3736 assert(_collectorState == Precleaning ||
3737 _collectorState == AbortablePreclean, "incorrect state");
3738 ResourceMark rm;
3739 HandleMark hm;
3740
3741 // Precleaning is currently not MT but the reference processor
3742 // may be set for MT. Disable it temporarily here.
3743 ReferenceProcessor* rp = ref_processor();
3744 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3745
3746 // Do one pass of scrubbing the discovered reference lists
3747 // to remove any reference objects with strongly-reachable
3748 // referents.
3749 if (clean_refs) {
3750 CMSPrecleanRefsYieldClosure yield_cl(this);
3751 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3752 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3753 &_markStack, true /* preclean */);
3754 CMSDrainMarkingStackClosure complete_trace(this,
3755 _span, &_markBitMap, &_markStack,
3756 &keep_alive, true /* preclean */);
3757
3758 // We don't want this step to interfere with a young
3759 // collection because we don't want to take CPU
3760 // or memory bandwidth away from the young GC threads
3761 // (which may be as many as there are CPUs).
3762 // Note that we don't need to protect ourselves from
3763 // interference with mutators because they can't
3764 // manipulate the discovered reference lists nor affect
3765 // the computed reachability of the referents, the
3766 // only properties manipulated by the precleaning
3767 // of these reference lists.
3768 stopTimer();
3769 CMSTokenSyncWithLocks x(true /* is cms thread */,
3770 bitMapLock());
3771 startTimer();
3772 sample_eden();
3773
3774 // The following will yield to allow foreground
3775 // collection to proceed promptly. XXX YSR:
3776 // The code in this method may need further
3777 // tweaking for better performance and some restructuring
3778 // for cleaner interfaces.
3779 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3780 rp->preclean_discovered_references(
3781 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3782 gc_timer);
3783 }
3784
3785 if (clean_survivor) { // preclean the active survivor space(s)
3786 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3787 &_markBitMap, &_modUnionTable,
3788 &_markStack, true /* precleaning phase */);
3789 stopTimer();
3790 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3791 bitMapLock());
3792 startTimer();
3793 unsigned int before_count =
3794 CMSHeap::heap()->total_collections();
3795 SurvivorSpacePrecleanClosure
3796 sss_cl(this, _span, &_markBitMap, &_markStack,
3797 &pam_cl, before_count, CMSYield);
3798 _young_gen->from()->object_iterate_careful(&sss_cl);
3799 _young_gen->to()->object_iterate_careful(&sss_cl);
3800 }
3801 MarkRefsIntoAndScanClosure
3802 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3803 &_markStack, this, CMSYield,
3804 true /* precleaning phase */);
3805 // CAUTION: The following closure has persistent state that may need to
3806 // be reset upon a decrease in the sequence of addresses it
3807 // processes.
3808 ScanMarkedObjectsAgainCarefullyClosure
3809 smoac_cl(this, _span,
3810 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3811
3812 // Preclean dirty cards in ModUnionTable and CardTable using
3813 // appropriate convergence criterion;
3814 // repeat CMSPrecleanIter times unless we find that
3815 // we are losing.
3816 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3817 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3818 "Bad convergence multiplier");
3819 assert(CMSPrecleanThreshold >= 100,
3820 "Unreasonably low CMSPrecleanThreshold");
3821
3822 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3823 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3824 numIter < CMSPrecleanIter;
3825 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3826 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3827 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3828 // Either there are very few dirty cards, so re-mark
3829 // pause will be small anyway, or our pre-cleaning isn't
3830 // that much faster than the rate at which cards are being
3831 // dirtied, so we might as well stop and re-mark since
3832 // precleaning won't improve our re-mark time by much.
3833 if (curNumCards <= CMSPrecleanThreshold ||
3834 (numIter > 0 &&
3835 (curNumCards * CMSPrecleanDenominator >
3836 lastNumCards * CMSPrecleanNumerator))) {
3837 numIter++;
3838 cumNumCards += curNumCards;
3839 break;
3840 }
3841 }
3842
3843 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3844
3845 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3846 cumNumCards += curNumCards;
3847 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3848 curNumCards, cumNumCards, numIter);
3849 return cumNumCards; // as a measure of useful work done
3850 }
3851
3852 // PRECLEANING NOTES:
3853 // Precleaning involves:
3854 // . reading the bits of the modUnionTable and clearing the set bits.
3855 // . For the cards corresponding to the set bits, we scan the
3856 // objects on those cards. This means we need the free_list_lock
3857 // so that we can safely iterate over the CMS space when scanning
3858 // for oops.
3859 // . When we scan the objects, we'll be both reading and setting
3860 // marks in the marking bit map, so we'll need the marking bit map.
3861 // . For protecting _collector_state transitions, we take the CGC_lock.
3862 // Note that any races in the reading of of card table entries by the
3863 // CMS thread on the one hand and the clearing of those entries by the
3864 // VM thread or the setting of those entries by the mutator threads on the
3865 // other are quite benign. However, for efficiency it makes sense to keep
3866 // the VM thread from racing with the CMS thread while the latter is
3867 // dirty card info to the modUnionTable. We therefore also use the
3868 // CGC_lock to protect the reading of the card table and the mod union
3869 // table by the CM thread.
3870 // . We run concurrently with mutator updates, so scanning
3871 // needs to be done carefully -- we should not try to scan
3872 // potentially uninitialized objects.
3873 //
3874 // Locking strategy: While holding the CGC_lock, we scan over and
3875 // reset a maximal dirty range of the mod union / card tables, then lock
3876 // the free_list_lock and bitmap lock to do a full marking, then
3877 // release these locks; and repeat the cycle. This allows for a
3878 // certain amount of fairness in the sharing of these locks between
3879 // the CMS collector on the one hand, and the VM thread and the
3880 // mutators on the other.
3881
3882 // NOTE: preclean_mod_union_table() and preclean_card_table()
3883 // further below are largely identical; if you need to modify
3884 // one of these methods, please check the other method too.
3885
3886 size_t CMSCollector::preclean_mod_union_table(
3887 ConcurrentMarkSweepGeneration* old_gen,
3888 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3889 verify_work_stacks_empty();
3890 verify_overflow_empty();
3891
3892 // strategy: starting with the first card, accumulate contiguous
3893 // ranges of dirty cards; clear these cards, then scan the region
3894 // covered by these cards.
3895
3896 // Since all of the MUT is committed ahead, we can just use
3897 // that, in case the generations expand while we are precleaning.
3898 // It might also be fine to just use the committed part of the
3899 // generation, but we might potentially miss cards when the
3900 // generation is rapidly expanding while we are in the midst
3901 // of precleaning.
3902 HeapWord* startAddr = old_gen->reserved().start();
3903 HeapWord* endAddr = old_gen->reserved().end();
3904
3905 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3906
3907 size_t numDirtyCards, cumNumDirtyCards;
3908 HeapWord *nextAddr, *lastAddr;
3909 for (cumNumDirtyCards = numDirtyCards = 0,
3910 nextAddr = lastAddr = startAddr;
3911 nextAddr < endAddr;
3912 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3913
3914 ResourceMark rm;
3915 HandleMark hm;
3916
3917 MemRegion dirtyRegion;
3918 {
3919 stopTimer();
3920 // Potential yield point
3921 CMSTokenSync ts(true);
3922 startTimer();
3923 sample_eden();
3924 // Get dirty region starting at nextOffset (inclusive),
3925 // simultaneously clearing it.
3926 dirtyRegion =
3927 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3928 assert(dirtyRegion.start() >= nextAddr,
3929 "returned region inconsistent?");
3930 }
3931 // Remember where the next search should begin.
3932 // The returned region (if non-empty) is a right open interval,
3933 // so lastOffset is obtained from the right end of that
3934 // interval.
3935 lastAddr = dirtyRegion.end();
3936 // Should do something more transparent and less hacky XXX
3937 numDirtyCards =
3938 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3939
3940 // We'll scan the cards in the dirty region (with periodic
3941 // yields for foreground GC as needed).
3942 if (!dirtyRegion.is_empty()) {
3943 assert(numDirtyCards > 0, "consistency check");
3944 HeapWord* stop_point = NULL;
3945 stopTimer();
3946 // Potential yield point
3947 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3948 bitMapLock());
3949 startTimer();
3950 {
3951 verify_work_stacks_empty();
3952 verify_overflow_empty();
3953 sample_eden();
3954 stop_point =
3955 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3956 }
3957 if (stop_point != NULL) {
3958 // The careful iteration stopped early either because it found an
3959 // uninitialized object, or because we were in the midst of an
3960 // "abortable preclean", which should now be aborted. Redirty
3961 // the bits corresponding to the partially-scanned or unscanned
3962 // cards. We'll either restart at the next block boundary or
3963 // abort the preclean.
3964 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3965 "Should only be AbortablePreclean.");
3966 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3967 if (should_abort_preclean()) {
3968 break; // out of preclean loop
3969 } else {
3970 // Compute the next address at which preclean should pick up;
3971 // might need bitMapLock in order to read P-bits.
3972 lastAddr = next_card_start_after_block(stop_point);
3973 }
3974 }
3975 } else {
3976 assert(lastAddr == endAddr, "consistency check");
3977 assert(numDirtyCards == 0, "consistency check");
3978 break;
3979 }
3980 }
3981 verify_work_stacks_empty();
3982 verify_overflow_empty();
3983 return cumNumDirtyCards;
3984 }
3985
3986 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3987 // below are largely identical; if you need to modify
3988 // one of these methods, please check the other method too.
3989
3990 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3991 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3992 // strategy: it's similar to precleamModUnionTable above, in that
3993 // we accumulate contiguous ranges of dirty cards, mark these cards
3994 // precleaned, then scan the region covered by these cards.
3995 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3996 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3997
3998 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3999
4000 size_t numDirtyCards, cumNumDirtyCards;
4001 HeapWord *lastAddr, *nextAddr;
4002
4003 for (cumNumDirtyCards = numDirtyCards = 0,
4004 nextAddr = lastAddr = startAddr;
4005 nextAddr < endAddr;
4006 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4007
4008 ResourceMark rm;
4009 HandleMark hm;
4010
4011 MemRegion dirtyRegion;
4012 {
4013 // See comments in "Precleaning notes" above on why we
4014 // do this locking. XXX Could the locking overheads be
4015 // too high when dirty cards are sparse? [I don't think so.]
4016 stopTimer();
4017 CMSTokenSync x(true); // is cms thread
4018 startTimer();
4019 sample_eden();
4020 // Get and clear dirty region from card table
4021 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4022 true,
4023 CardTable::precleaned_card_val());
4024
4025 assert(dirtyRegion.start() >= nextAddr,
4026 "returned region inconsistent?");
4027 }
4028 lastAddr = dirtyRegion.end();
4029 numDirtyCards =
4030 dirtyRegion.word_size()/CardTable::card_size_in_words;
4031
4032 if (!dirtyRegion.is_empty()) {
4033 stopTimer();
4034 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4035 startTimer();
4036 sample_eden();
4037 verify_work_stacks_empty();
4038 verify_overflow_empty();
4039 HeapWord* stop_point =
4040 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4041 if (stop_point != NULL) {
4042 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4043 "Should only be AbortablePreclean.");
4044 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4045 if (should_abort_preclean()) {
4046 break; // out of preclean loop
4047 } else {
4048 // Compute the next address at which preclean should pick up.
4049 lastAddr = next_card_start_after_block(stop_point);
4050 }
4051 }
4052 } else {
4053 break;
4054 }
4055 }
4056 verify_work_stacks_empty();
4057 verify_overflow_empty();
4058 return cumNumDirtyCards;
4059 }
4060
4061 class PrecleanCLDClosure : public CLDClosure {
4062 MetadataVisitingOopsInGenClosure* _cm_closure;
4063 public:
4064 PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4065 void do_cld(ClassLoaderData* cld) {
4066 if (cld->has_accumulated_modified_oops()) {
4067 cld->clear_accumulated_modified_oops();
4068
4069 _cm_closure->do_cld(cld);
4070 }
4071 }
4072 };
4073
4074 // The freelist lock is needed to prevent asserts, is it really needed?
4075 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4076 // Needed to walk CLDG
4077 MutexLocker ml(ClassLoaderDataGraph_lock);
4078
4079 cl->set_freelistLock(freelistLock);
4080
4081 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4082
4083 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4084 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4085 PrecleanCLDClosure preclean_closure(cl);
4086 ClassLoaderDataGraph::cld_do(&preclean_closure);
4087
4088 verify_work_stacks_empty();
4089 verify_overflow_empty();
4090 }
4091
4092 void CMSCollector::checkpointRootsFinal() {
4093 assert(_collectorState == FinalMarking, "incorrect state transition?");
4094 check_correct_thread_executing();
4095 // world is stopped at this checkpoint
4096 assert(SafepointSynchronize::is_at_safepoint(),
4097 "world should be stopped");
4098 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4099
4100 verify_work_stacks_empty();
4101 verify_overflow_empty();
4102
4103 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4104 _young_gen->used() / K, _young_gen->capacity() / K);
4105 {
4106 if (CMSScavengeBeforeRemark) {
4107 CMSHeap* heap = CMSHeap::heap();
4108 // Temporarily set flag to false, GCH->do_collection will
4109 // expect it to be false and set to true
4110 FlagSetting fl(heap->_is_gc_active, false);
4111
4112 heap->do_collection(true, // full (i.e. force, see below)
4113 false, // !clear_all_soft_refs
4114 0, // size
4115 false, // is_tlab
4116 GenCollectedHeap::YoungGen // type
4117 );
4118 }
4119 FreelistLocker x(this);
4120 MutexLockerEx y(bitMapLock(),
4121 Mutex::_no_safepoint_check_flag);
4122 checkpointRootsFinalWork();
4123 }
4124 verify_work_stacks_empty();
4125 verify_overflow_empty();
4126 }
4127
4128 void CMSCollector::checkpointRootsFinalWork() {
4129 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4130
4131 assert(haveFreelistLocks(), "must have free list locks");
4132 assert_lock_strong(bitMapLock());
4133
4134 ResourceMark rm;
4135 HandleMark hm;
4136
4137 CMSHeap* heap = CMSHeap::heap();
4138
4139 if (should_unload_classes()) {
4140 CodeCache::gc_prologue();
4141 }
4142 assert(haveFreelistLocks(), "must have free list locks");
4143 assert_lock_strong(bitMapLock());
4144
4145 // We might assume that we need not fill TLAB's when
4146 // CMSScavengeBeforeRemark is set, because we may have just done
4147 // a scavenge which would have filled all TLAB's -- and besides
4148 // Eden would be empty. This however may not always be the case --
4149 // for instance although we asked for a scavenge, it may not have
4150 // happened because of a JNI critical section. We probably need
4151 // a policy for deciding whether we can in that case wait until
4152 // the critical section releases and then do the remark following
4153 // the scavenge, and skip it here. In the absence of that policy,
4154 // or of an indication of whether the scavenge did indeed occur,
4155 // we cannot rely on TLAB's having been filled and must do
4156 // so here just in case a scavenge did not happen.
4157 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4158 // Update the saved marks which may affect the root scans.
4159 heap->save_marks();
4160
4161 print_eden_and_survivor_chunk_arrays();
4162
4163 {
4164 #if COMPILER2_OR_JVMCI
4165 DerivedPointerTableDeactivate dpt_deact;
4166 #endif
4167
4168 // Note on the role of the mod union table:
4169 // Since the marker in "markFromRoots" marks concurrently with
4170 // mutators, it is possible for some reachable objects not to have been
4171 // scanned. For instance, an only reference to an object A was
4172 // placed in object B after the marker scanned B. Unless B is rescanned,
4173 // A would be collected. Such updates to references in marked objects
4174 // are detected via the mod union table which is the set of all cards
4175 // dirtied since the first checkpoint in this GC cycle and prior to
4176 // the most recent young generation GC, minus those cleaned up by the
4177 // concurrent precleaning.
4178 if (CMSParallelRemarkEnabled) {
4179 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4180 do_remark_parallel();
4181 } else {
4182 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4183 do_remark_non_parallel();
4184 }
4185 }
4186 verify_work_stacks_empty();
4187 verify_overflow_empty();
4188
4189 {
4190 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4191 refProcessingWork();
4192 }
4193 verify_work_stacks_empty();
4194 verify_overflow_empty();
4195
4196 if (should_unload_classes()) {
4197 CodeCache::gc_epilogue();
4198 }
4199 JvmtiExport::gc_epilogue();
4200
4201 // If we encountered any (marking stack / work queue) overflow
4202 // events during the current CMS cycle, take appropriate
4203 // remedial measures, where possible, so as to try and avoid
4204 // recurrence of that condition.
4205 assert(_markStack.isEmpty(), "No grey objects");
4206 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4207 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4208 if (ser_ovflw > 0) {
4209 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4210 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4211 _markStack.expand();
4212 _ser_pmc_remark_ovflw = 0;
4213 _ser_pmc_preclean_ovflw = 0;
4214 _ser_kac_preclean_ovflw = 0;
4215 _ser_kac_ovflw = 0;
4216 }
4217 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4218 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4219 _par_pmc_remark_ovflw, _par_kac_ovflw);
4220 _par_pmc_remark_ovflw = 0;
4221 _par_kac_ovflw = 0;
4222 }
4223 if (_markStack._hit_limit > 0) {
4224 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4225 _markStack._hit_limit);
4226 }
4227 if (_markStack._failed_double > 0) {
4228 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4229 _markStack._failed_double, _markStack.capacity());
4230 }
4231 _markStack._hit_limit = 0;
4232 _markStack._failed_double = 0;
4233
4234 if ((VerifyAfterGC || VerifyDuringGC) &&
4235 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4236 verify_after_remark();
4237 }
4238
4239 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4240
4241 // Change under the freelistLocks.
4242 _collectorState = Sweeping;
4243 // Call isAllClear() under bitMapLock
4244 assert(_modUnionTable.isAllClear(),
4245 "Should be clear by end of the final marking");
4246 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4247 "Should be clear by end of the final marking");
4248 }
4249
4250 void CMSParInitialMarkTask::work(uint worker_id) {
4251 elapsedTimer _timer;
4252 ResourceMark rm;
4253 HandleMark hm;
4254
4255 // ---------- scan from roots --------------
4256 _timer.start();
4257 CMSHeap* heap = CMSHeap::heap();
4258 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4259
4260 // ---------- young gen roots --------------
4261 {
4262 work_on_young_gen_roots(&par_mri_cl);
4263 _timer.stop();
4264 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4265 }
4266
4267 // ---------- remaining roots --------------
4268 _timer.reset();
4269 _timer.start();
4270
4271 CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4272
4273 heap->cms_process_roots(_strong_roots_scope,
4274 false, // yg was scanned above
4275 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4276 _collector->should_unload_classes(),
4277 &par_mri_cl,
4278 &cld_closure,
4279 &_par_state_string);
4280
4281 assert(_collector->should_unload_classes()
4282 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4283 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4284 _timer.stop();
4285 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4286 }
4287
4288 // Parallel remark task
4289 class CMSParRemarkTask: public CMSParMarkTask {
4290 CompactibleFreeListSpace* _cms_space;
4291
4292 // The per-thread work queues, available here for stealing.
4293 OopTaskQueueSet* _task_queues;
4294 ParallelTaskTerminator _term;
4295 StrongRootsScope* _strong_roots_scope;
4296
4297 public:
4298 // A value of 0 passed to n_workers will cause the number of
4299 // workers to be taken from the active workers in the work gang.
4300 CMSParRemarkTask(CMSCollector* collector,
4301 CompactibleFreeListSpace* cms_space,
4302 uint n_workers, WorkGang* workers,
4303 OopTaskQueueSet* task_queues,
4304 StrongRootsScope* strong_roots_scope):
4305 CMSParMarkTask("Rescan roots and grey objects in parallel",
4306 collector, n_workers),
4307 _cms_space(cms_space),
4308 _task_queues(task_queues),
4309 _term(n_workers, task_queues),
4310 _strong_roots_scope(strong_roots_scope) { }
4311
4312 OopTaskQueueSet* task_queues() { return _task_queues; }
4313
4314 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4315
4316 ParallelTaskTerminator* terminator() { return &_term; }
4317 uint n_workers() { return _n_workers; }
4318
4319 void work(uint worker_id);
4320
4321 private:
4322 // ... of dirty cards in old space
4323 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4324 ParMarkRefsIntoAndScanClosure* cl);
4325
4326 // ... work stealing for the above
4327 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4328 };
4329
4330 class RemarkCLDClosure : public CLDClosure {
4331 CLDToOopClosure _cm_closure;
4332 public:
4333 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4334 void do_cld(ClassLoaderData* cld) {
4335 // Check if we have modified any oops in the CLD during the concurrent marking.
4336 if (cld->has_accumulated_modified_oops()) {
4337 cld->clear_accumulated_modified_oops();
4338
4339 // We could have transfered the current modified marks to the accumulated marks,
4340 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4341 } else if (cld->has_modified_oops()) {
4342 // Don't clear anything, this info is needed by the next young collection.
4343 } else {
4344 // No modified oops in the ClassLoaderData.
4345 return;
4346 }
4347
4348 // The klass has modified fields, need to scan the klass.
4349 _cm_closure.do_cld(cld);
4350 }
4351 };
4352
4353 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4354 ParNewGeneration* young_gen = _collector->_young_gen;
4355 ContiguousSpace* eden_space = young_gen->eden();
4356 ContiguousSpace* from_space = young_gen->from();
4357 ContiguousSpace* to_space = young_gen->to();
4358
4359 HeapWord** eca = _collector->_eden_chunk_array;
4360 size_t ect = _collector->_eden_chunk_index;
4361 HeapWord** sca = _collector->_survivor_chunk_array;
4362 size_t sct = _collector->_survivor_chunk_index;
4363
4364 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4365 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4366
4367 do_young_space_rescan(cl, to_space, NULL, 0);
4368 do_young_space_rescan(cl, from_space, sca, sct);
4369 do_young_space_rescan(cl, eden_space, eca, ect);
4370 }
4371
4372 // work_queue(i) is passed to the closure
4373 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4374 // also is passed to do_dirty_card_rescan_tasks() and to
4375 // do_work_steal() to select the i-th task_queue.
4376
4377 void CMSParRemarkTask::work(uint worker_id) {
4378 elapsedTimer _timer;
4379 ResourceMark rm;
4380 HandleMark hm;
4381
4382 // ---------- rescan from roots --------------
4383 _timer.start();
4384 CMSHeap* heap = CMSHeap::heap();
4385 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4386 _collector->_span, _collector->ref_processor(),
4387 &(_collector->_markBitMap),
4388 work_queue(worker_id));
4389
4390 // Rescan young gen roots first since these are likely
4391 // coarsely partitioned and may, on that account, constitute
4392 // the critical path; thus, it's best to start off that
4393 // work first.
4394 // ---------- young gen roots --------------
4395 {
4396 work_on_young_gen_roots(&par_mrias_cl);
4397 _timer.stop();
4398 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4399 }
4400
4401 // ---------- remaining roots --------------
4402 _timer.reset();
4403 _timer.start();
4404 heap->cms_process_roots(_strong_roots_scope,
4405 false, // yg was scanned above
4406 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4407 _collector->should_unload_classes(),
4408 &par_mrias_cl,
4409 NULL, // The dirty klasses will be handled below
4410 &_par_state_string);
4411
4412 assert(_collector->should_unload_classes()
4413 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4414 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4415 _timer.stop();
4416 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4417
4418 // ---------- unhandled CLD scanning ----------
4419 if (worker_id == 0) { // Single threaded at the moment.
4420 _timer.reset();
4421 _timer.start();
4422
4423 // Scan all new class loader data objects and new dependencies that were
4424 // introduced during concurrent marking.
4425 ResourceMark rm;
4426 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4427 for (int i = 0; i < array->length(); i++) {
4428 Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4429 }
4430
4431 // We don't need to keep track of new CLDs anymore.
4432 ClassLoaderDataGraph::remember_new_clds(false);
4433
4434 _timer.stop();
4435 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4436 }
4437
4438 // We might have added oops to ClassLoaderData::_handles during the
4439 // concurrent marking phase. These oops do not always point to newly allocated objects
4440 // that are guaranteed to be kept alive. Hence,
4441 // we do have to revisit the _handles block during the remark phase.
4442
4443 // ---------- dirty CLD scanning ----------
4444 if (worker_id == 0) { // Single threaded at the moment.
4445 _timer.reset();
4446 _timer.start();
4447
4448 // Scan all classes that was dirtied during the concurrent marking phase.
4449 RemarkCLDClosure remark_closure(&par_mrias_cl);
4450 ClassLoaderDataGraph::cld_do(&remark_closure);
4451
4452 _timer.stop();
4453 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4454 }
4455
4456
4457 // ---------- rescan dirty cards ------------
4458 _timer.reset();
4459 _timer.start();
4460
4461 // Do the rescan tasks for each of the two spaces
4462 // (cms_space) in turn.
4463 // "worker_id" is passed to select the task_queue for "worker_id"
4464 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4465 _timer.stop();
4466 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4467
4468 // ---------- steal work from other threads ...
4469 // ---------- ... and drain overflow list.
4470 _timer.reset();
4471 _timer.start();
4472 do_work_steal(worker_id, &par_mrias_cl);
4473 _timer.stop();
4474 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4475 }
4476
4477 void
4478 CMSParMarkTask::do_young_space_rescan(
4479 OopsInGenClosure* cl, ContiguousSpace* space,
4480 HeapWord** chunk_array, size_t chunk_top) {
4481 // Until all tasks completed:
4482 // . claim an unclaimed task
4483 // . compute region boundaries corresponding to task claimed
4484 // using chunk_array
4485 // . par_oop_iterate(cl) over that region
4486
4487 ResourceMark rm;
4488 HandleMark hm;
4489
4490 SequentialSubTasksDone* pst = space->par_seq_tasks();
4491
4492 uint nth_task = 0;
4493 uint n_tasks = pst->n_tasks();
4494
4495 if (n_tasks > 0) {
4496 assert(pst->valid(), "Uninitialized use?");
4497 HeapWord *start, *end;
4498 while (pst->try_claim_task(/* reference */ nth_task)) {
4499 // We claimed task # nth_task; compute its boundaries.
4500 if (chunk_top == 0) { // no samples were taken
4501 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4502 start = space->bottom();
4503 end = space->top();
4504 } else if (nth_task == 0) {
4505 start = space->bottom();
4506 end = chunk_array[nth_task];
4507 } else if (nth_task < (uint)chunk_top) {
4508 assert(nth_task >= 1, "Control point invariant");
4509 start = chunk_array[nth_task - 1];
4510 end = chunk_array[nth_task];
4511 } else {
4512 assert(nth_task == (uint)chunk_top, "Control point invariant");
4513 start = chunk_array[chunk_top - 1];
4514 end = space->top();
4515 }
4516 MemRegion mr(start, end);
4517 // Verify that mr is in space
4518 assert(mr.is_empty() || space->used_region().contains(mr),
4519 "Should be in space");
4520 // Verify that "start" is an object boundary
4521 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4522 "Should be an oop");
4523 space->par_oop_iterate(mr, cl);
4524 }
4525 pst->all_tasks_completed();
4526 }
4527 }
4528
4529 void
4530 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4531 CompactibleFreeListSpace* sp, int i,
4532 ParMarkRefsIntoAndScanClosure* cl) {
4533 // Until all tasks completed:
4534 // . claim an unclaimed task
4535 // . compute region boundaries corresponding to task claimed
4536 // . transfer dirty bits ct->mut for that region
4537 // . apply rescanclosure to dirty mut bits for that region
4538
4539 ResourceMark rm;
4540 HandleMark hm;
4541
4542 OopTaskQueue* work_q = work_queue(i);
4543 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4544 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4545 // CAUTION: This closure has state that persists across calls to
4546 // the work method dirty_range_iterate_clear() in that it has
4547 // embedded in it a (subtype of) UpwardsObjectClosure. The
4548 // use of that state in the embedded UpwardsObjectClosure instance
4549 // assumes that the cards are always iterated (even if in parallel
4550 // by several threads) in monotonically increasing order per each
4551 // thread. This is true of the implementation below which picks
4552 // card ranges (chunks) in monotonically increasing order globally
4553 // and, a-fortiori, in monotonically increasing order per thread
4554 // (the latter order being a subsequence of the former).
4555 // If the work code below is ever reorganized into a more chaotic
4556 // work-partitioning form than the current "sequential tasks"
4557 // paradigm, the use of that persistent state will have to be
4558 // revisited and modified appropriately. See also related
4559 // bug 4756801 work on which should examine this code to make
4560 // sure that the changes there do not run counter to the
4561 // assumptions made here and necessary for correctness and
4562 // efficiency. Note also that this code might yield inefficient
4563 // behavior in the case of very large objects that span one or
4564 // more work chunks. Such objects would potentially be scanned
4565 // several times redundantly. Work on 4756801 should try and
4566 // address that performance anomaly if at all possible. XXX
4567 MemRegion full_span = _collector->_span;
4568 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4569 MarkFromDirtyCardsClosure
4570 greyRescanClosure(_collector, full_span, // entire span of interest
4571 sp, bm, work_q, cl);
4572
4573 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4574 assert(pst->valid(), "Uninitialized use?");
4575 uint nth_task = 0;
4576 const int alignment = CardTable::card_size * BitsPerWord;
4577 MemRegion span = sp->used_region();
4578 HeapWord* start_addr = span.start();
4579 HeapWord* end_addr = align_up(span.end(), alignment);
4580 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4581 assert(is_aligned(start_addr, alignment), "Check alignment");
4582 assert(is_aligned(chunk_size, alignment), "Check alignment");
4583
4584 while (pst->try_claim_task(/* reference */ nth_task)) {
4585 // Having claimed the nth_task, compute corresponding mem-region,
4586 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4587 // The alignment restriction ensures that we do not need any
4588 // synchronization with other gang-workers while setting or
4589 // clearing bits in thus chunk of the MUT.
4590 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4591 start_addr + (nth_task+1)*chunk_size);
4592 // The last chunk's end might be way beyond end of the
4593 // used region. In that case pull back appropriately.
4594 if (this_span.end() > end_addr) {
4595 this_span.set_end(end_addr);
4596 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4597 }
4598 // Iterate over the dirty cards covering this chunk, marking them
4599 // precleaned, and setting the corresponding bits in the mod union
4600 // table. Since we have been careful to partition at Card and MUT-word
4601 // boundaries no synchronization is needed between parallel threads.
4602 _collector->_ct->dirty_card_iterate(this_span,
4603 &modUnionClosure);
4604
4605 // Having transferred these marks into the modUnionTable,
4606 // rescan the marked objects on the dirty cards in the modUnionTable.
4607 // Even if this is at a synchronous collection, the initial marking
4608 // may have been done during an asynchronous collection so there
4609 // may be dirty bits in the mod-union table.
4610 _collector->_modUnionTable.dirty_range_iterate_clear(
4611 this_span, &greyRescanClosure);
4612 _collector->_modUnionTable.verifyNoOneBitsInRange(
4613 this_span.start(),
4614 this_span.end());
4615 }
4616 pst->all_tasks_completed(); // declare that i am done
4617 }
4618
4619 // . see if we can share work_queues with ParNew? XXX
4620 void
4621 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4622 OopTaskQueue* work_q = work_queue(i);
4623 NOT_PRODUCT(int num_steals = 0;)
4624 oop obj_to_scan;
4625 CMSBitMap* bm = &(_collector->_markBitMap);
4626
4627 while (true) {
4628 // Completely finish any left over work from (an) earlier round(s)
4629 cl->trim_queue(0);
4630 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4631 (size_t)ParGCDesiredObjsFromOverflowList);
4632 // Now check if there's any work in the overflow list
4633 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4634 // only affects the number of attempts made to get work from the
4635 // overflow list and does not affect the number of workers. Just
4636 // pass ParallelGCThreads so this behavior is unchanged.
4637 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4638 work_q,
4639 ParallelGCThreads)) {
4640 // found something in global overflow list;
4641 // not yet ready to go stealing work from others.
4642 // We'd like to assert(work_q->size() != 0, ...)
4643 // because we just took work from the overflow list,
4644 // but of course we can't since all of that could have
4645 // been already stolen from us.
4646 // "He giveth and He taketh away."
4647 continue;
4648 }
4649 // Verify that we have no work before we resort to stealing
4650 assert(work_q->size() == 0, "Have work, shouldn't steal");
4651 // Try to steal from other queues that have work
4652 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4653 NOT_PRODUCT(num_steals++;)
4654 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4655 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4656 // Do scanning work
4657 obj_to_scan->oop_iterate(cl);
4658 // Loop around, finish this work, and try to steal some more
4659 } else if (terminator()->offer_termination()) {
4660 break; // nirvana from the infinite cycle
4661 }
4662 }
4663 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4664 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4665 "Else our work is not yet done");
4666 }
4667
4668 // Record object boundaries in _eden_chunk_array by sampling the eden
4669 // top in the slow-path eden object allocation code path and record
4670 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4671 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4672 // sampling in sample_eden() that activates during the part of the
4673 // preclean phase.
4674 void CMSCollector::sample_eden_chunk() {
4675 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4676 if (_eden_chunk_lock->try_lock()) {
4677 // Record a sample. This is the critical section. The contents
4678 // of the _eden_chunk_array have to be non-decreasing in the
4679 // address order.
4680 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4681 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4682 "Unexpected state of Eden");
4683 if (_eden_chunk_index == 0 ||
4684 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4685 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4686 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4687 _eden_chunk_index++; // commit sample
4688 }
4689 _eden_chunk_lock->unlock();
4690 }
4691 }
4692 }
4693
4694 // Return a thread-local PLAB recording array, as appropriate.
4695 void* CMSCollector::get_data_recorder(int thr_num) {
4696 if (_survivor_plab_array != NULL &&
4697 (CMSPLABRecordAlways ||
4698 (_collectorState > Marking && _collectorState < FinalMarking))) {
4699 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4700 ChunkArray* ca = &_survivor_plab_array[thr_num];
4701 ca->reset(); // clear it so that fresh data is recorded
4702 return (void*) ca;
4703 } else {
4704 return NULL;
4705 }
4706 }
4707
4708 // Reset all the thread-local PLAB recording arrays
4709 void CMSCollector::reset_survivor_plab_arrays() {
4710 for (uint i = 0; i < ParallelGCThreads; i++) {
4711 _survivor_plab_array[i].reset();
4712 }
4713 }
4714
4715 // Merge the per-thread plab arrays into the global survivor chunk
4716 // array which will provide the partitioning of the survivor space
4717 // for CMS initial scan and rescan.
4718 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4719 int no_of_gc_threads) {
4720 assert(_survivor_plab_array != NULL, "Error");
4721 assert(_survivor_chunk_array != NULL, "Error");
4722 assert(_collectorState == FinalMarking ||
4723 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4724 for (int j = 0; j < no_of_gc_threads; j++) {
4725 _cursor[j] = 0;
4726 }
4727 HeapWord* top = surv->top();
4728 size_t i;
4729 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4730 HeapWord* min_val = top; // Higher than any PLAB address
4731 uint min_tid = 0; // position of min_val this round
4732 for (int j = 0; j < no_of_gc_threads; j++) {
4733 ChunkArray* cur_sca = &_survivor_plab_array[j];
4734 if (_cursor[j] == cur_sca->end()) {
4735 continue;
4736 }
4737 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4738 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4739 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4740 if (cur_val < min_val) {
4741 min_tid = j;
4742 min_val = cur_val;
4743 } else {
4744 assert(cur_val < top, "All recorded addresses should be less");
4745 }
4746 }
4747 // At this point min_val and min_tid are respectively
4748 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4749 // and the thread (j) that witnesses that address.
4750 // We record this address in the _survivor_chunk_array[i]
4751 // and increment _cursor[min_tid] prior to the next round i.
4752 if (min_val == top) {
4753 break;
4754 }
4755 _survivor_chunk_array[i] = min_val;
4756 _cursor[min_tid]++;
4757 }
4758 // We are all done; record the size of the _survivor_chunk_array
4759 _survivor_chunk_index = i; // exclusive: [0, i)
4760 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4761 // Verify that we used up all the recorded entries
4762 #ifdef ASSERT
4763 size_t total = 0;
4764 for (int j = 0; j < no_of_gc_threads; j++) {
4765 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4766 total += _cursor[j];
4767 }
4768 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4769 // Check that the merged array is in sorted order
4770 if (total > 0) {
4771 for (size_t i = 0; i < total - 1; i++) {
4772 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4773 i, p2i(_survivor_chunk_array[i]));
4774 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4775 "Not sorted");
4776 }
4777 }
4778 #endif // ASSERT
4779 }
4780
4781 // Set up the space's par_seq_tasks structure for work claiming
4782 // for parallel initial scan and rescan of young gen.
4783 // See ParRescanTask where this is currently used.
4784 void
4785 CMSCollector::
4786 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4787 assert(n_threads > 0, "Unexpected n_threads argument");
4788
4789 // Eden space
4790 if (!_young_gen->eden()->is_empty()) {
4791 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4792 assert(!pst->valid(), "Clobbering existing data?");
4793 // Each valid entry in [0, _eden_chunk_index) represents a task.
4794 size_t n_tasks = _eden_chunk_index + 1;
4795 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4796 // Sets the condition for completion of the subtask (how many threads
4797 // need to finish in order to be done).
4798 pst->set_n_threads(n_threads);
4799 pst->set_n_tasks((int)n_tasks);
4800 }
4801
4802 // Merge the survivor plab arrays into _survivor_chunk_array
4803 if (_survivor_plab_array != NULL) {
4804 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4805 } else {
4806 assert(_survivor_chunk_index == 0, "Error");
4807 }
4808
4809 // To space
4810 {
4811 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4812 assert(!pst->valid(), "Clobbering existing data?");
4813 // Sets the condition for completion of the subtask (how many threads
4814 // need to finish in order to be done).
4815 pst->set_n_threads(n_threads);
4816 pst->set_n_tasks(1);
4817 assert(pst->valid(), "Error");
4818 }
4819
4820 // From space
4821 {
4822 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4823 assert(!pst->valid(), "Clobbering existing data?");
4824 size_t n_tasks = _survivor_chunk_index + 1;
4825 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4826 // Sets the condition for completion of the subtask (how many threads
4827 // need to finish in order to be done).
4828 pst->set_n_threads(n_threads);
4829 pst->set_n_tasks((int)n_tasks);
4830 assert(pst->valid(), "Error");
4831 }
4832 }
4833
4834 // Parallel version of remark
4835 void CMSCollector::do_remark_parallel() {
4836 CMSHeap* heap = CMSHeap::heap();
4837 WorkGang* workers = heap->workers();
4838 assert(workers != NULL, "Need parallel worker threads.");
4839 // Choose to use the number of GC workers most recently set
4840 // into "active_workers".
4841 uint n_workers = workers->active_workers();
4842
4843 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4844
4845 StrongRootsScope srs(n_workers);
4846
4847 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4848
4849 // We won't be iterating over the cards in the card table updating
4850 // the younger_gen cards, so we shouldn't call the following else
4851 // the verification code as well as subsequent younger_refs_iterate
4852 // code would get confused. XXX
4853 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4854
4855 // The young gen rescan work will not be done as part of
4856 // process_roots (which currently doesn't know how to
4857 // parallelize such a scan), but rather will be broken up into
4858 // a set of parallel tasks (via the sampling that the [abortable]
4859 // preclean phase did of eden, plus the [two] tasks of
4860 // scanning the [two] survivor spaces. Further fine-grain
4861 // parallelization of the scanning of the survivor spaces
4862 // themselves, and of precleaning of the young gen itself
4863 // is deferred to the future.
4864 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4865
4866 // The dirty card rescan work is broken up into a "sequence"
4867 // of parallel tasks (per constituent space) that are dynamically
4868 // claimed by the parallel threads.
4869 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4870
4871 // It turns out that even when we're using 1 thread, doing the work in a
4872 // separate thread causes wide variance in run times. We can't help this
4873 // in the multi-threaded case, but we special-case n=1 here to get
4874 // repeatable measurements of the 1-thread overhead of the parallel code.
4875 if (n_workers > 1) {
4876 // Make refs discovery MT-safe, if it isn't already: it may not
4877 // necessarily be so, since it's possible that we are doing
4878 // ST marking.
4879 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4880 workers->run_task(&tsk);
4881 } else {
4882 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4883 tsk.work(0);
4884 }
4885
4886 // restore, single-threaded for now, any preserved marks
4887 // as a result of work_q overflow
4888 restore_preserved_marks_if_any();
4889 }
4890
4891 // Non-parallel version of remark
4892 void CMSCollector::do_remark_non_parallel() {
4893 ResourceMark rm;
4894 HandleMark hm;
4895 CMSHeap* heap = CMSHeap::heap();
4896 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4897
4898 MarkRefsIntoAndScanClosure
4899 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4900 &_markStack, this,
4901 false /* should_yield */, false /* not precleaning */);
4902 MarkFromDirtyCardsClosure
4903 markFromDirtyCardsClosure(this, _span,
4904 NULL, // space is set further below
4905 &_markBitMap, &_markStack, &mrias_cl);
4906 {
4907 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4908 // Iterate over the dirty cards, setting the corresponding bits in the
4909 // mod union table.
4910 {
4911 ModUnionClosure modUnionClosure(&_modUnionTable);
4912 _ct->dirty_card_iterate(_cmsGen->used_region(),
4913 &modUnionClosure);
4914 }
4915 // Having transferred these marks into the modUnionTable, we just need
4916 // to rescan the marked objects on the dirty cards in the modUnionTable.
4917 // The initial marking may have been done during an asynchronous
4918 // collection so there may be dirty bits in the mod-union table.
4919 const int alignment = CardTable::card_size * BitsPerWord;
4920 {
4921 // ... First handle dirty cards in CMS gen
4922 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4923 MemRegion ur = _cmsGen->used_region();
4924 HeapWord* lb = ur.start();
4925 HeapWord* ub = align_up(ur.end(), alignment);
4926 MemRegion cms_span(lb, ub);
4927 _modUnionTable.dirty_range_iterate_clear(cms_span,
4928 &markFromDirtyCardsClosure);
4929 verify_work_stacks_empty();
4930 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4931 }
4932 }
4933 if (VerifyDuringGC &&
4934 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4935 HandleMark hm; // Discard invalid handles created during verification
4936 Universe::verify();
4937 }
4938 {
4939 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4940
4941 verify_work_stacks_empty();
4942
4943 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4944 StrongRootsScope srs(1);
4945
4946 heap->cms_process_roots(&srs,
4947 true, // young gen as roots
4948 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4949 should_unload_classes(),
4950 &mrias_cl,
4951 NULL); // The dirty klasses will be handled below
4952
4953 assert(should_unload_classes()
4954 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4955 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4956 }
4957
4958 {
4959 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4960
4961 verify_work_stacks_empty();
4962
4963 // Scan all class loader data objects that might have been introduced
4964 // during concurrent marking.
4965 ResourceMark rm;
4966 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4967 for (int i = 0; i < array->length(); i++) {
4968 Devirtualizer::do_cld(&mrias_cl, array->at(i));
4969 }
4970
4971 // We don't need to keep track of new CLDs anymore.
4972 ClassLoaderDataGraph::remember_new_clds(false);
4973
4974 verify_work_stacks_empty();
4975 }
4976
4977 // We might have added oops to ClassLoaderData::_handles during the
4978 // concurrent marking phase. These oops do not point to newly allocated objects
4979 // that are guaranteed to be kept alive. Hence,
4980 // we do have to revisit the _handles block during the remark phase.
4981 {
4982 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4983
4984 verify_work_stacks_empty();
4985
4986 RemarkCLDClosure remark_closure(&mrias_cl);
4987 ClassLoaderDataGraph::cld_do(&remark_closure);
4988
4989 verify_work_stacks_empty();
4990 }
4991
4992 verify_work_stacks_empty();
4993 // Restore evacuated mark words, if any, used for overflow list links
4994 restore_preserved_marks_if_any();
4995
4996 verify_overflow_empty();
4997 }
4998
4999 ////////////////////////////////////////////////////////
5000 // Parallel Reference Processing Task Proxy Class
5001 ////////////////////////////////////////////////////////
5002 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5003 OopTaskQueueSet* _queues;
5004 ParallelTaskTerminator _terminator;
5005 public:
5006 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5007 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5008 ParallelTaskTerminator* terminator() { return &_terminator; }
5009 OopTaskQueueSet* queues() { return _queues; }
5010 };
5011
5012 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5013 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5014 CMSCollector* _collector;
5015 CMSBitMap* _mark_bit_map;
5016 const MemRegion _span;
5017 ProcessTask& _task;
5018
5019 public:
5020 CMSRefProcTaskProxy(ProcessTask& task,
5021 CMSCollector* collector,
5022 const MemRegion& span,
5023 CMSBitMap* mark_bit_map,
5024 AbstractWorkGang* workers,
5025 OopTaskQueueSet* task_queues):
5026 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5027 task_queues,
5028 workers->active_workers()),
5029 _collector(collector),
5030 _mark_bit_map(mark_bit_map),
5031 _span(span),
5032 _task(task)
5033 {
5034 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5035 "Inconsistency in _span");
5036 }
5037
5038 OopTaskQueueSet* task_queues() { return queues(); }
5039
5040 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5041
5042 void do_work_steal(int i,
5043 CMSParDrainMarkingStackClosure* drain,
5044 CMSParKeepAliveClosure* keep_alive);
5045
5046 virtual void work(uint worker_id);
5047 };
5048
5049 void CMSRefProcTaskProxy::work(uint worker_id) {
5050 ResourceMark rm;
5051 HandleMark hm;
5052 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5053 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5054 _mark_bit_map,
5055 work_queue(worker_id));
5056 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5057 _mark_bit_map,
5058 work_queue(worker_id));
5059 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5060 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5061 if (_task.marks_oops_alive()) {
5062 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5063 }
5064 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5065 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5066 }
5067
5068 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5069 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5070 _span(span),
5071 _work_queue(work_queue),
5072 _bit_map(bit_map),
5073 _mark_and_push(collector, span, bit_map, work_queue),
5074 _low_water_mark(MIN2((work_queue->max_elems()/4),
5075 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5076 { }
5077
5078 // . see if we can share work_queues with ParNew? XXX
5079 void CMSRefProcTaskProxy::do_work_steal(int i,
5080 CMSParDrainMarkingStackClosure* drain,
5081 CMSParKeepAliveClosure* keep_alive) {
5082 OopTaskQueue* work_q = work_queue(i);
5083 NOT_PRODUCT(int num_steals = 0;)
5084 oop obj_to_scan;
5085
5086 while (true) {
5087 // Completely finish any left over work from (an) earlier round(s)
5088 drain->trim_queue(0);
5089 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5090 (size_t)ParGCDesiredObjsFromOverflowList);
5091 // Now check if there's any work in the overflow list
5092 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5093 // only affects the number of attempts made to get work from the
5094 // overflow list and does not affect the number of workers. Just
5095 // pass ParallelGCThreads so this behavior is unchanged.
5096 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5097 work_q,
5098 ParallelGCThreads)) {
5099 // Found something in global overflow list;
5100 // not yet ready to go stealing work from others.
5101 // We'd like to assert(work_q->size() != 0, ...)
5102 // because we just took work from the overflow list,
5103 // but of course we can't, since all of that might have
5104 // been already stolen from us.
5105 continue;
5106 }
5107 // Verify that we have no work before we resort to stealing
5108 assert(work_q->size() == 0, "Have work, shouldn't steal");
5109 // Try to steal from other queues that have work
5110 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5111 NOT_PRODUCT(num_steals++;)
5112 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5113 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5114 // Do scanning work
5115 obj_to_scan->oop_iterate(keep_alive);
5116 // Loop around, finish this work, and try to steal some more
5117 } else if (terminator()->offer_termination()) {
5118 break; // nirvana from the infinite cycle
5119 }
5120 }
5121 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5122 }
5123
5124 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5125 CMSHeap* heap = CMSHeap::heap();
5126 WorkGang* workers = heap->workers();
5127 assert(workers != NULL, "Need parallel worker threads.");
5128 assert(workers->active_workers() == ergo_workers,
5129 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5130 ergo_workers, workers->active_workers());
5131 CMSRefProcTaskProxy rp_task(task, &_collector,
5132 _collector.ref_processor_span(),
5133 _collector.markBitMap(),
5134 workers, _collector.task_queues());
5135 workers->run_task(&rp_task, workers->active_workers());
5136 }
5137
5138 void CMSCollector::refProcessingWork() {
5139 ResourceMark rm;
5140 HandleMark hm;
5141
5142 ReferenceProcessor* rp = ref_processor();
5143 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5144 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5145 // Process weak references.
5146 rp->setup_policy(false);
5147 verify_work_stacks_empty();
5148
5149 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5150 {
5151 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5152
5153 // Setup keep_alive and complete closures.
5154 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5155 &_markStack, false /* !preclean */);
5156 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5157 _span, &_markBitMap, &_markStack,
5158 &cmsKeepAliveClosure, false /* !preclean */);
5159
5160 ReferenceProcessorStats stats;
5161 if (rp->processing_is_mt()) {
5162 // Set the degree of MT here. If the discovery is done MT, there
5163 // may have been a different number of threads doing the discovery
5164 // and a different number of discovered lists may have Ref objects.
5165 // That is OK as long as the Reference lists are balanced (see
5166 // balance_all_queues() and balance_queues()).
5167 CMSHeap* heap = CMSHeap::heap();
5168 uint active_workers = ParallelGCThreads;
5169 WorkGang* workers = heap->workers();
5170 if (workers != NULL) {
5171 active_workers = workers->active_workers();
5172 // The expectation is that active_workers will have already
5173 // been set to a reasonable value. If it has not been set,
5174 // investigate.
5175 assert(active_workers > 0, "Should have been set during scavenge");
5176 }
5177 rp->set_active_mt_degree(active_workers);
5178 CMSRefProcTaskExecutor task_executor(*this);
5179 stats = rp->process_discovered_references(&_is_alive_closure,
5180 &cmsKeepAliveClosure,
5181 &cmsDrainMarkingStackClosure,
5182 &task_executor,
5183 &pt);
5184 } else {
5185 stats = rp->process_discovered_references(&_is_alive_closure,
5186 &cmsKeepAliveClosure,
5187 &cmsDrainMarkingStackClosure,
5188 NULL,
5189 &pt);
5190 }
5191 _gc_tracer_cm->report_gc_reference_stats(stats);
5192 pt.print_all_references();
5193 }
5194
5195 // This is the point where the entire marking should have completed.
5196 verify_work_stacks_empty();
5197
5198 {
5199 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5200 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5201 }
5202
5203 if (should_unload_classes()) {
5204 {
5205 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5206
5207 // Unload classes and purge the SystemDictionary.
5208 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5209
5210 // Unload nmethods.
5211 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5212
5213 // Prune dead klasses from subklass/sibling/implementor lists.
5214 Klass::clean_weak_klass_links(purged_class);
5215 }
5216
5217 {
5218 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5219 // Clean up unreferenced symbols in symbol table.
5220 SymbolTable::unlink();
5221 }
5222
5223 {
5224 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5225 // Delete entries for dead interned strings.
5226 StringTable::unlink(&_is_alive_closure);
5227 }
5228 }
5229
5230 // Restore any preserved marks as a result of mark stack or
5231 // work queue overflow
5232 restore_preserved_marks_if_any(); // done single-threaded for now
5233
5234 rp->set_enqueuing_is_done(true);
5235 rp->verify_no_references_recorded();
5236 }
5237
5238 #ifndef PRODUCT
5239 void CMSCollector::check_correct_thread_executing() {
5240 Thread* t = Thread::current();
5241 // Only the VM thread or the CMS thread should be here.
5242 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5243 "Unexpected thread type");
5244 // If this is the vm thread, the foreground process
5245 // should not be waiting. Note that _foregroundGCIsActive is
5246 // true while the foreground collector is waiting.
5247 if (_foregroundGCShouldWait) {
5248 // We cannot be the VM thread
5249 assert(t->is_ConcurrentGC_thread(),
5250 "Should be CMS thread");
5251 } else {
5252 // We can be the CMS thread only if we are in a stop-world
5253 // phase of CMS collection.
5254 if (t->is_ConcurrentGC_thread()) {
5255 assert(_collectorState == InitialMarking ||
5256 _collectorState == FinalMarking,
5257 "Should be a stop-world phase");
5258 // The CMS thread should be holding the CMS_token.
5259 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5260 "Potential interference with concurrently "
5261 "executing VM thread");
5262 }
5263 }
5264 }
5265 #endif
5266
5267 void CMSCollector::sweep() {
5268 assert(_collectorState == Sweeping, "just checking");
5269 check_correct_thread_executing();
5270 verify_work_stacks_empty();
5271 verify_overflow_empty();
5272 increment_sweep_count();
5273 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5274
5275 _inter_sweep_timer.stop();
5276 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5277
5278 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5279 _intra_sweep_timer.reset();
5280 _intra_sweep_timer.start();
5281 {
5282 GCTraceCPUTime tcpu;
5283 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5284 // First sweep the old gen
5285 {
5286 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5287 bitMapLock());
5288 sweepWork(_cmsGen);
5289 }
5290
5291 // Update Universe::_heap_*_at_gc figures.
5292 // We need all the free list locks to make the abstract state
5293 // transition from Sweeping to Resetting. See detailed note
5294 // further below.
5295 {
5296 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5297 // Update heap occupancy information which is used as
5298 // input to soft ref clearing policy at the next gc.
5299 Universe::update_heap_info_at_gc();
5300 _collectorState = Resizing;
5301 }
5302 }
5303 verify_work_stacks_empty();
5304 verify_overflow_empty();
5305
5306 if (should_unload_classes()) {
5307 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5308 // requires that the virtual spaces are stable and not deleted.
5309 ClassLoaderDataGraph::set_should_purge(true);
5310 }
5311
5312 _intra_sweep_timer.stop();
5313 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5314
5315 _inter_sweep_timer.reset();
5316 _inter_sweep_timer.start();
5317
5318 // We need to use a monotonically non-decreasing time in ms
5319 // or we will see time-warp warnings and os::javaTimeMillis()
5320 // does not guarantee monotonicity.
5321 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5322 update_time_of_last_gc(now);
5323
5324 // NOTE on abstract state transitions:
5325 // Mutators allocate-live and/or mark the mod-union table dirty
5326 // based on the state of the collection. The former is done in
5327 // the interval [Marking, Sweeping] and the latter in the interval
5328 // [Marking, Sweeping). Thus the transitions into the Marking state
5329 // and out of the Sweeping state must be synchronously visible
5330 // globally to the mutators.
5331 // The transition into the Marking state happens with the world
5332 // stopped so the mutators will globally see it. Sweeping is
5333 // done asynchronously by the background collector so the transition
5334 // from the Sweeping state to the Resizing state must be done
5335 // under the freelistLock (as is the check for whether to
5336 // allocate-live and whether to dirty the mod-union table).
5337 assert(_collectorState == Resizing, "Change of collector state to"
5338 " Resizing must be done under the freelistLocks (plural)");
5339
5340 // Now that sweeping has been completed, we clear
5341 // the incremental_collection_failed flag,
5342 // thus inviting a younger gen collection to promote into
5343 // this generation. If such a promotion may still fail,
5344 // the flag will be set again when a young collection is
5345 // attempted.
5346 CMSHeap* heap = CMSHeap::heap();
5347 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5348 heap->update_full_collections_completed(_collection_count_start);
5349 }
5350
5351 // FIX ME!!! Looks like this belongs in CFLSpace, with
5352 // CMSGen merely delegating to it.
5353 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5354 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5355 HeapWord* minAddr = _cmsSpace->bottom();
5356 HeapWord* largestAddr =
5357 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5358 if (largestAddr == NULL) {
5359 // The dictionary appears to be empty. In this case
5360 // try to coalesce at the end of the heap.
5361 largestAddr = _cmsSpace->end();
5362 }
5363 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5364 size_t nearLargestOffset =
5365 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5366 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5367 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5368 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5369 }
5370
5371 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5372 return addr >= _cmsSpace->nearLargestChunk();
5373 }
5374
5375 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5376 return _cmsSpace->find_chunk_at_end();
5377 }
5378
5379 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5380 bool full) {
5381 // If the young generation has been collected, gather any statistics
5382 // that are of interest at this point.
5383 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5384 if (!full && current_is_young) {
5385 // Gather statistics on the young generation collection.
5386 collector()->stats().record_gc0_end(used());
5387 }
5388 }
5389
5390 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5391 // We iterate over the space(s) underlying this generation,
5392 // checking the mark bit map to see if the bits corresponding
5393 // to specific blocks are marked or not. Blocks that are
5394 // marked are live and are not swept up. All remaining blocks
5395 // are swept up, with coalescing on-the-fly as we sweep up
5396 // contiguous free and/or garbage blocks:
5397 // We need to ensure that the sweeper synchronizes with allocators
5398 // and stop-the-world collectors. In particular, the following
5399 // locks are used:
5400 // . CMS token: if this is held, a stop the world collection cannot occur
5401 // . freelistLock: if this is held no allocation can occur from this
5402 // generation by another thread
5403 // . bitMapLock: if this is held, no other thread can access or update
5404 //
5405
5406 // Note that we need to hold the freelistLock if we use
5407 // block iterate below; else the iterator might go awry if
5408 // a mutator (or promotion) causes block contents to change
5409 // (for instance if the allocator divvies up a block).
5410 // If we hold the free list lock, for all practical purposes
5411 // young generation GC's can't occur (they'll usually need to
5412 // promote), so we might as well prevent all young generation
5413 // GC's while we do a sweeping step. For the same reason, we might
5414 // as well take the bit map lock for the entire duration
5415
5416 // check that we hold the requisite locks
5417 assert(have_cms_token(), "Should hold cms token");
5418 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5419 assert_lock_strong(old_gen->freelistLock());
5420 assert_lock_strong(bitMapLock());
5421
5422 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5423 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5424 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5425 _inter_sweep_estimate.padded_average(),
5426 _intra_sweep_estimate.padded_average());
5427 old_gen->setNearLargestChunk();
5428
5429 {
5430 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5431 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5432 // We need to free-up/coalesce garbage/blocks from a
5433 // co-terminal free run. This is done in the SweepClosure
5434 // destructor; so, do not remove this scope, else the
5435 // end-of-sweep-census below will be off by a little bit.
5436 }
5437 old_gen->cmsSpace()->sweep_completed();
5438 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5439 if (should_unload_classes()) { // unloaded classes this cycle,
5440 _concurrent_cycles_since_last_unload = 0; // ... reset count
5441 } else { // did not unload classes,
5442 _concurrent_cycles_since_last_unload++; // ... increment count
5443 }
5444 }
5445
5446 // Reset CMS data structures (for now just the marking bit map)
5447 // preparatory for the next cycle.
5448 void CMSCollector::reset_concurrent() {
5449 CMSTokenSyncWithLocks ts(true, bitMapLock());
5450
5451 // If the state is not "Resetting", the foreground thread
5452 // has done a collection and the resetting.
5453 if (_collectorState != Resetting) {
5454 assert(_collectorState == Idling, "The state should only change"
5455 " because the foreground collector has finished the collection");
5456 return;
5457 }
5458
5459 {
5460 // Clear the mark bitmap (no grey objects to start with)
5461 // for the next cycle.
5462 GCTraceCPUTime tcpu;
5463 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5464
5465 HeapWord* curAddr = _markBitMap.startWord();
5466 while (curAddr < _markBitMap.endWord()) {
5467 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5468 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5469 _markBitMap.clear_large_range(chunk);
5470 if (ConcurrentMarkSweepThread::should_yield() &&
5471 !foregroundGCIsActive() &&
5472 CMSYield) {
5473 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5474 "CMS thread should hold CMS token");
5475 assert_lock_strong(bitMapLock());
5476 bitMapLock()->unlock();
5477 ConcurrentMarkSweepThread::desynchronize(true);
5478 stopTimer();
5479 incrementYields();
5480
5481 // See the comment in coordinator_yield()
5482 for (unsigned i = 0; i < CMSYieldSleepCount &&
5483 ConcurrentMarkSweepThread::should_yield() &&
5484 !CMSCollector::foregroundGCIsActive(); ++i) {
5485 os::sleep(Thread::current(), 1, false);
5486 }
5487
5488 ConcurrentMarkSweepThread::synchronize(true);
5489 bitMapLock()->lock_without_safepoint_check();
5490 startTimer();
5491 }
5492 curAddr = chunk.end();
5493 }
5494 // A successful mostly concurrent collection has been done.
5495 // Because only the full (i.e., concurrent mode failure) collections
5496 // are being measured for gc overhead limits, clean the "near" flag
5497 // and count.
5498 size_policy()->reset_gc_overhead_limit_count();
5499 _collectorState = Idling;
5500 }
5501
5502 register_gc_end();
5503 }
5504
5505 // Same as above but for STW paths
5506 void CMSCollector::reset_stw() {
5507 // already have the lock
5508 assert(_collectorState == Resetting, "just checking");
5509 assert_lock_strong(bitMapLock());
5510 GCIdMark gc_id_mark(_cmsThread->gc_id());
5511 _markBitMap.clear_all();
5512 _collectorState = Idling;
5513 register_gc_end();
5514 }
5515
5516 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5517 GCTraceCPUTime tcpu;
5518 TraceCollectorStats tcs_cgc(cgc_counters());
5519
5520 switch (op) {
5521 case CMS_op_checkpointRootsInitial: {
5522 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5523 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5524 checkpointRootsInitial();
5525 break;
5526 }
5527 case CMS_op_checkpointRootsFinal: {
5528 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5529 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5530 checkpointRootsFinal();
5531 break;
5532 }
5533 default:
5534 fatal("No such CMS_op");
5535 }
5536 }
5537
5538 #ifndef PRODUCT
5539 size_t const CMSCollector::skip_header_HeapWords() {
5540 return FreeChunk::header_size();
5541 }
5542
5543 // Try and collect here conditions that should hold when
5544 // CMS thread is exiting. The idea is that the foreground GC
5545 // thread should not be blocked if it wants to terminate
5546 // the CMS thread and yet continue to run the VM for a while
5547 // after that.
5548 void CMSCollector::verify_ok_to_terminate() const {
5549 assert(Thread::current()->is_ConcurrentGC_thread(),
5550 "should be called by CMS thread");
5551 assert(!_foregroundGCShouldWait, "should be false");
5552 // We could check here that all the various low-level locks
5553 // are not held by the CMS thread, but that is overkill; see
5554 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5555 // is checked.
5556 }
5557 #endif
5558
5559 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5560 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5561 "missing Printezis mark?");
5562 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5563 size_t size = pointer_delta(nextOneAddr + 1, addr);
5564 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5565 "alignment problem");
5566 assert(size >= 3, "Necessary for Printezis marks to work");
5567 return size;
5568 }
5569
5570 // A variant of the above (block_size_using_printezis_bits()) except
5571 // that we return 0 if the P-bits are not yet set.
5572 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5573 if (_markBitMap.isMarked(addr + 1)) {
5574 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5575 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5576 size_t size = pointer_delta(nextOneAddr + 1, addr);
5577 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5578 "alignment problem");
5579 assert(size >= 3, "Necessary for Printezis marks to work");
5580 return size;
5581 }
5582 return 0;
5583 }
5584
5585 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5586 size_t sz = 0;
5587 oop p = (oop)addr;
5588 if (p->klass_or_null_acquire() != NULL) {
5589 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5590 } else {
5591 sz = block_size_using_printezis_bits(addr);
5592 }
5593 assert(sz > 0, "size must be nonzero");
5594 HeapWord* next_block = addr + sz;
5595 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5596 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5597 align_down((uintptr_t)next_card, CardTable::card_size),
5598 "must be different cards");
5599 return next_card;
5600 }
5601
5602
5603 // CMS Bit Map Wrapper /////////////////////////////////////////
5604
5605 // Construct a CMS bit map infrastructure, but don't create the
5606 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5607 // further below.
5608 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5609 _shifter(shifter),
5610 _bm(),
5611 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5612 Monitor::_safepoint_check_sometimes) : NULL)
5613 {
5614 _bmStartWord = 0;
5615 _bmWordSize = 0;
5616 }
5617
5618 bool CMSBitMap::allocate(MemRegion mr) {
5619 _bmStartWord = mr.start();
5620 _bmWordSize = mr.word_size();
5621 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5622 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5623 if (!brs.is_reserved()) {
5624 log_warning(gc)("CMS bit map allocation failure");
5625 return false;
5626 }
5627 // For now we'll just commit all of the bit map up front.
5628 // Later on we'll try to be more parsimonious with swap.
5629 if (!_virtual_space.initialize(brs, brs.size())) {
5630 log_warning(gc)("CMS bit map backing store failure");
5631 return false;
5632 }
5633 assert(_virtual_space.committed_size() == brs.size(),
5634 "didn't reserve backing store for all of CMS bit map?");
5635 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5636 _bmWordSize, "inconsistency in bit map sizing");
5637 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5638
5639 // bm.clear(); // can we rely on getting zero'd memory? verify below
5640 assert(isAllClear(),
5641 "Expected zero'd memory from ReservedSpace constructor");
5642 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5643 "consistency check");
5644 return true;
5645 }
5646
5647 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5648 HeapWord *next_addr, *end_addr, *last_addr;
5649 assert_locked();
5650 assert(covers(mr), "out-of-range error");
5651 // XXX assert that start and end are appropriately aligned
5652 for (next_addr = mr.start(), end_addr = mr.end();
5653 next_addr < end_addr; next_addr = last_addr) {
5654 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5655 last_addr = dirty_region.end();
5656 if (!dirty_region.is_empty()) {
5657 cl->do_MemRegion(dirty_region);
5658 } else {
5659 assert(last_addr == end_addr, "program logic");
5660 return;
5661 }
5662 }
5663 }
5664
5665 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5666 _bm.print_on_error(st, prefix);
5667 }
5668
5669 #ifndef PRODUCT
5670 void CMSBitMap::assert_locked() const {
5671 CMSLockVerifier::assert_locked(lock());
5672 }
5673
5674 bool CMSBitMap::covers(MemRegion mr) const {
5675 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5676 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5677 "size inconsistency");
5678 return (mr.start() >= _bmStartWord) &&
5679 (mr.end() <= endWord());
5680 }
5681
5682 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5683 return (start >= _bmStartWord && (start + size) <= endWord());
5684 }
5685
5686 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5687 // verify that there are no 1 bits in the interval [left, right)
5688 FalseBitMapClosure falseBitMapClosure;
5689 iterate(&falseBitMapClosure, left, right);
5690 }
5691
5692 void CMSBitMap::region_invariant(MemRegion mr)
5693 {
5694 assert_locked();
5695 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5696 assert(!mr.is_empty(), "unexpected empty region");
5697 assert(covers(mr), "mr should be covered by bit map");
5698 // convert address range into offset range
5699 size_t start_ofs = heapWordToOffset(mr.start());
5700 // Make sure that end() is appropriately aligned
5701 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5702 "Misaligned mr.end()");
5703 size_t end_ofs = heapWordToOffset(mr.end());
5704 assert(end_ofs > start_ofs, "Should mark at least one bit");
5705 }
5706
5707 #endif
5708
5709 bool CMSMarkStack::allocate(size_t size) {
5710 // allocate a stack of the requisite depth
5711 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5712 size * sizeof(oop)));
5713 if (!rs.is_reserved()) {
5714 log_warning(gc)("CMSMarkStack allocation failure");
5715 return false;
5716 }
5717 if (!_virtual_space.initialize(rs, rs.size())) {
5718 log_warning(gc)("CMSMarkStack backing store failure");
5719 return false;
5720 }
5721 assert(_virtual_space.committed_size() == rs.size(),
5722 "didn't reserve backing store for all of CMS stack?");
5723 _base = (oop*)(_virtual_space.low());
5724 _index = 0;
5725 _capacity = size;
5726 NOT_PRODUCT(_max_depth = 0);
5727 return true;
5728 }
5729
5730 // XXX FIX ME !!! In the MT case we come in here holding a
5731 // leaf lock. For printing we need to take a further lock
5732 // which has lower rank. We need to recalibrate the two
5733 // lock-ranks involved in order to be able to print the
5734 // messages below. (Or defer the printing to the caller.
5735 // For now we take the expedient path of just disabling the
5736 // messages for the problematic case.)
5737 void CMSMarkStack::expand() {
5738 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5739 if (_capacity == MarkStackSizeMax) {
5740 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5741 // We print a warning message only once per CMS cycle.
5742 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5743 }
5744 return;
5745 }
5746 // Double capacity if possible
5747 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5748 // Do not give up existing stack until we have managed to
5749 // get the double capacity that we desired.
5750 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5751 new_capacity * sizeof(oop)));
5752 if (rs.is_reserved()) {
5753 // Release the backing store associated with old stack
5754 _virtual_space.release();
5755 // Reinitialize virtual space for new stack
5756 if (!_virtual_space.initialize(rs, rs.size())) {
5757 fatal("Not enough swap for expanded marking stack");
5758 }
5759 _base = (oop*)(_virtual_space.low());
5760 _index = 0;
5761 _capacity = new_capacity;
5762 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5763 // Failed to double capacity, continue;
5764 // we print a detail message only once per CMS cycle.
5765 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5766 _capacity / K, new_capacity / K);
5767 }
5768 }
5769
5770
5771 // Closures
5772 // XXX: there seems to be a lot of code duplication here;
5773 // should refactor and consolidate common code.
5774
5775 // This closure is used to mark refs into the CMS generation in
5776 // the CMS bit map. Called at the first checkpoint. This closure
5777 // assumes that we do not need to re-mark dirty cards; if the CMS
5778 // generation on which this is used is not an oldest
5779 // generation then this will lose younger_gen cards!
5780
5781 MarkRefsIntoClosure::MarkRefsIntoClosure(
5782 MemRegion span, CMSBitMap* bitMap):
5783 _span(span),
5784 _bitMap(bitMap)
5785 {
5786 assert(ref_discoverer() == NULL, "deliberately left NULL");
5787 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5788 }
5789
5790 void MarkRefsIntoClosure::do_oop(oop obj) {
5791 // if p points into _span, then mark corresponding bit in _markBitMap
5792 assert(oopDesc::is_oop(obj), "expected an oop");
5793 HeapWord* addr = (HeapWord*)obj;
5794 if (_span.contains(addr)) {
5795 // this should be made more efficient
5796 _bitMap->mark(addr);
5797 }
5798 }
5799
5800 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5801 MemRegion span, CMSBitMap* bitMap):
5802 _span(span),
5803 _bitMap(bitMap)
5804 {
5805 assert(ref_discoverer() == NULL, "deliberately left NULL");
5806 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5807 }
5808
5809 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5810 // if p points into _span, then mark corresponding bit in _markBitMap
5811 assert(oopDesc::is_oop(obj), "expected an oop");
5812 HeapWord* addr = (HeapWord*)obj;
5813 if (_span.contains(addr)) {
5814 // this should be made more efficient
5815 _bitMap->par_mark(addr);
5816 }
5817 }
5818
5819 // A variant of the above, used for CMS marking verification.
5820 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5821 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5822 _span(span),
5823 _verification_bm(verification_bm),
5824 _cms_bm(cms_bm)
5825 {
5826 assert(ref_discoverer() == NULL, "deliberately left NULL");
5827 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5828 }
5829
5830 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5831 // if p points into _span, then mark corresponding bit in _markBitMap
5832 assert(oopDesc::is_oop(obj), "expected an oop");
5833 HeapWord* addr = (HeapWord*)obj;
5834 if (_span.contains(addr)) {
5835 _verification_bm->mark(addr);
5836 if (!_cms_bm->isMarked(addr)) {
5837 Log(gc, verify) log;
5838 ResourceMark rm;
5839 LogStream ls(log.error());
5840 oop(addr)->print_on(&ls);
5841 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5842 fatal("... aborting");
5843 }
5844 }
5845 }
5846
5847 //////////////////////////////////////////////////
5848 // MarkRefsIntoAndScanClosure
5849 //////////////////////////////////////////////////
5850
5851 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5852 ReferenceDiscoverer* rd,
5853 CMSBitMap* bit_map,
5854 CMSBitMap* mod_union_table,
5855 CMSMarkStack* mark_stack,
5856 CMSCollector* collector,
5857 bool should_yield,
5858 bool concurrent_precleaning):
5859 _span(span),
5860 _bit_map(bit_map),
5861 _mark_stack(mark_stack),
5862 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5863 mark_stack, concurrent_precleaning),
5864 _collector(collector),
5865 _freelistLock(NULL),
5866 _yield(should_yield),
5867 _concurrent_precleaning(concurrent_precleaning)
5868 {
5869 // FIXME: Should initialize in base class constructor.
5870 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5871 set_ref_discoverer_internal(rd);
5872 }
5873
5874 // This closure is used to mark refs into the CMS generation at the
5875 // second (final) checkpoint, and to scan and transitively follow
5876 // the unmarked oops. It is also used during the concurrent precleaning
5877 // phase while scanning objects on dirty cards in the CMS generation.
5878 // The marks are made in the marking bit map and the marking stack is
5879 // used for keeping the (newly) grey objects during the scan.
5880 // The parallel version (Par_...) appears further below.
5881 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5882 if (obj != NULL) {
5883 assert(oopDesc::is_oop(obj), "expected an oop");
5884 HeapWord* addr = (HeapWord*)obj;
5885 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5886 assert(_collector->overflow_list_is_empty(),
5887 "overflow list should be empty");
5888 if (_span.contains(addr) &&
5889 !_bit_map->isMarked(addr)) {
5890 // mark bit map (object is now grey)
5891 _bit_map->mark(addr);
5892 // push on marking stack (stack should be empty), and drain the
5893 // stack by applying this closure to the oops in the oops popped
5894 // from the stack (i.e. blacken the grey objects)
5895 bool res = _mark_stack->push(obj);
5896 assert(res, "Should have space to push on empty stack");
5897 do {
5898 oop new_oop = _mark_stack->pop();
5899 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5900 assert(_bit_map->isMarked((HeapWord*)new_oop),
5901 "only grey objects on this stack");
5902 // iterate over the oops in this oop, marking and pushing
5903 // the ones in CMS heap (i.e. in _span).
5904 new_oop->oop_iterate(&_pushAndMarkClosure);
5905 // check if it's time to yield
5906 do_yield_check();
5907 } while (!_mark_stack->isEmpty() ||
5908 (!_concurrent_precleaning && take_from_overflow_list()));
5909 // if marking stack is empty, and we are not doing this
5910 // during precleaning, then check the overflow list
5911 }
5912 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5913 assert(_collector->overflow_list_is_empty(),
5914 "overflow list was drained above");
5915
5916 assert(_collector->no_preserved_marks(),
5917 "All preserved marks should have been restored above");
5918 }
5919 }
5920
5921 void MarkRefsIntoAndScanClosure::do_yield_work() {
5922 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5923 "CMS thread should hold CMS token");
5924 assert_lock_strong(_freelistLock);
5925 assert_lock_strong(_bit_map->lock());
5926 // relinquish the free_list_lock and bitMaplock()
5927 _bit_map->lock()->unlock();
5928 _freelistLock->unlock();
5929 ConcurrentMarkSweepThread::desynchronize(true);
5930 _collector->stopTimer();
5931 _collector->incrementYields();
5932
5933 // See the comment in coordinator_yield()
5934 for (unsigned i = 0;
5935 i < CMSYieldSleepCount &&
5936 ConcurrentMarkSweepThread::should_yield() &&
5937 !CMSCollector::foregroundGCIsActive();
5938 ++i) {
5939 os::sleep(Thread::current(), 1, false);
5940 }
5941
5942 ConcurrentMarkSweepThread::synchronize(true);
5943 _freelistLock->lock_without_safepoint_check();
5944 _bit_map->lock()->lock_without_safepoint_check();
5945 _collector->startTimer();
5946 }
5947
5948 ///////////////////////////////////////////////////////////
5949 // ParMarkRefsIntoAndScanClosure: a parallel version of
5950 // MarkRefsIntoAndScanClosure
5951 ///////////////////////////////////////////////////////////
5952 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
5953 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
5954 CMSBitMap* bit_map, OopTaskQueue* work_queue):
5955 _span(span),
5956 _bit_map(bit_map),
5957 _work_queue(work_queue),
5958 _low_water_mark(MIN2((work_queue->max_elems()/4),
5959 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
5960 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
5961 {
5962 // FIXME: Should initialize in base class constructor.
5963 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5964 set_ref_discoverer_internal(rd);
5965 }
5966
5967 // This closure is used to mark refs into the CMS generation at the
5968 // second (final) checkpoint, and to scan and transitively follow
5969 // the unmarked oops. The marks are made in the marking bit map and
5970 // the work_queue is used for keeping the (newly) grey objects during
5971 // the scan phase whence they are also available for stealing by parallel
5972 // threads. Since the marking bit map is shared, updates are
5973 // synchronized (via CAS).
5974 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
5975 if (obj != NULL) {
5976 // Ignore mark word because this could be an already marked oop
5977 // that may be chained at the end of the overflow list.
5978 assert(oopDesc::is_oop(obj, true), "expected an oop");
5979 HeapWord* addr = (HeapWord*)obj;
5980 if (_span.contains(addr) &&
5981 !_bit_map->isMarked(addr)) {
5982 // mark bit map (object will become grey):
5983 // It is possible for several threads to be
5984 // trying to "claim" this object concurrently;
5985 // the unique thread that succeeds in marking the
5986 // object first will do the subsequent push on
5987 // to the work queue (or overflow list).
5988 if (_bit_map->par_mark(addr)) {
5989 // push on work_queue (which may not be empty), and trim the
5990 // queue to an appropriate length by applying this closure to
5991 // the oops in the oops popped from the stack (i.e. blacken the
5992 // grey objects)
5993 bool res = _work_queue->push(obj);
5994 assert(res, "Low water mark should be less than capacity?");
5995 trim_queue(_low_water_mark);
5996 } // Else, another thread claimed the object
5997 }
5998 }
5999 }
6000
6001 // This closure is used to rescan the marked objects on the dirty cards
6002 // in the mod union table and the card table proper.
6003 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6004 oop p, MemRegion mr) {
6005
6006 size_t size = 0;
6007 HeapWord* addr = (HeapWord*)p;
6008 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6009 assert(_span.contains(addr), "we are scanning the CMS generation");
6010 // check if it's time to yield
6011 if (do_yield_check()) {
6012 // We yielded for some foreground stop-world work,
6013 // and we have been asked to abort this ongoing preclean cycle.
6014 return 0;
6015 }
6016 if (_bitMap->isMarked(addr)) {
6017 // it's marked; is it potentially uninitialized?
6018 if (p->klass_or_null_acquire() != NULL) {
6019 // an initialized object; ignore mark word in verification below
6020 // since we are running concurrent with mutators
6021 assert(oopDesc::is_oop(p, true), "should be an oop");
6022 if (p->is_objArray()) {
6023 // objArrays are precisely marked; restrict scanning
6024 // to dirty cards only.
6025 size = CompactibleFreeListSpace::adjustObjectSize(
6026 p->oop_iterate_size(_scanningClosure, mr));
6027 } else {
6028 // A non-array may have been imprecisely marked; we need
6029 // to scan object in its entirety.
6030 size = CompactibleFreeListSpace::adjustObjectSize(
6031 p->oop_iterate_size(_scanningClosure));
6032 }
6033 #ifdef ASSERT
6034 size_t direct_size =
6035 CompactibleFreeListSpace::adjustObjectSize(p->size());
6036 assert(size == direct_size, "Inconsistency in size");
6037 assert(size >= 3, "Necessary for Printezis marks to work");
6038 HeapWord* start_pbit = addr + 1;
6039 HeapWord* end_pbit = addr + size - 1;
6040 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6041 "inconsistent Printezis mark");
6042 // Verify inner mark bits (between Printezis bits) are clear,
6043 // but don't repeat if there are multiple dirty regions for
6044 // the same object, to avoid potential O(N^2) performance.
6045 if (addr != _last_scanned_object) {
6046 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6047 _last_scanned_object = addr;
6048 }
6049 #endif // ASSERT
6050 } else {
6051 // An uninitialized object.
6052 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6053 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6054 size = pointer_delta(nextOneAddr + 1, addr);
6055 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6056 "alignment problem");
6057 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6058 // will dirty the card when the klass pointer is installed in the
6059 // object (signaling the completion of initialization).
6060 }
6061 } else {
6062 // Either a not yet marked object or an uninitialized object
6063 if (p->klass_or_null_acquire() == NULL) {
6064 // An uninitialized object, skip to the next card, since
6065 // we may not be able to read its P-bits yet.
6066 assert(size == 0, "Initial value");
6067 } else {
6068 // An object not (yet) reached by marking: we merely need to
6069 // compute its size so as to go look at the next block.
6070 assert(oopDesc::is_oop(p, true), "should be an oop");
6071 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6072 }
6073 }
6074 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6075 return size;
6076 }
6077
6078 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6079 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6080 "CMS thread should hold CMS token");
6081 assert_lock_strong(_freelistLock);
6082 assert_lock_strong(_bitMap->lock());
6083 // relinquish the free_list_lock and bitMaplock()
6084 _bitMap->lock()->unlock();
6085 _freelistLock->unlock();
6086 ConcurrentMarkSweepThread::desynchronize(true);
6087 _collector->stopTimer();
6088 _collector->incrementYields();
6089
6090 // See the comment in coordinator_yield()
6091 for (unsigned i = 0; i < CMSYieldSleepCount &&
6092 ConcurrentMarkSweepThread::should_yield() &&
6093 !CMSCollector::foregroundGCIsActive(); ++i) {
6094 os::sleep(Thread::current(), 1, false);
6095 }
6096
6097 ConcurrentMarkSweepThread::synchronize(true);
6098 _freelistLock->lock_without_safepoint_check();
6099 _bitMap->lock()->lock_without_safepoint_check();
6100 _collector->startTimer();
6101 }
6102
6103
6104 //////////////////////////////////////////////////////////////////
6105 // SurvivorSpacePrecleanClosure
6106 //////////////////////////////////////////////////////////////////
6107 // This (single-threaded) closure is used to preclean the oops in
6108 // the survivor spaces.
6109 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6110
6111 HeapWord* addr = (HeapWord*)p;
6112 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6113 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6114 assert(p->klass_or_null() != NULL, "object should be initialized");
6115 // an initialized object; ignore mark word in verification below
6116 // since we are running concurrent with mutators
6117 assert(oopDesc::is_oop(p, true), "should be an oop");
6118 // Note that we do not yield while we iterate over
6119 // the interior oops of p, pushing the relevant ones
6120 // on our marking stack.
6121 size_t size = p->oop_iterate_size(_scanning_closure);
6122 do_yield_check();
6123 // Observe that below, we do not abandon the preclean
6124 // phase as soon as we should; rather we empty the
6125 // marking stack before returning. This is to satisfy
6126 // some existing assertions. In general, it may be a
6127 // good idea to abort immediately and complete the marking
6128 // from the grey objects at a later time.
6129 while (!_mark_stack->isEmpty()) {
6130 oop new_oop = _mark_stack->pop();
6131 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6132 assert(_bit_map->isMarked((HeapWord*)new_oop),
6133 "only grey objects on this stack");
6134 // iterate over the oops in this oop, marking and pushing
6135 // the ones in CMS heap (i.e. in _span).
6136 new_oop->oop_iterate(_scanning_closure);
6137 // check if it's time to yield
6138 do_yield_check();
6139 }
6140 unsigned int after_count =
6141 CMSHeap::heap()->total_collections();
6142 bool abort = (_before_count != after_count) ||
6143 _collector->should_abort_preclean();
6144 return abort ? 0 : size;
6145 }
6146
6147 void SurvivorSpacePrecleanClosure::do_yield_work() {
6148 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6149 "CMS thread should hold CMS token");
6150 assert_lock_strong(_bit_map->lock());
6151 // Relinquish the bit map lock
6152 _bit_map->lock()->unlock();
6153 ConcurrentMarkSweepThread::desynchronize(true);
6154 _collector->stopTimer();
6155 _collector->incrementYields();
6156
6157 // See the comment in coordinator_yield()
6158 for (unsigned i = 0; i < CMSYieldSleepCount &&
6159 ConcurrentMarkSweepThread::should_yield() &&
6160 !CMSCollector::foregroundGCIsActive(); ++i) {
6161 os::sleep(Thread::current(), 1, false);
6162 }
6163
6164 ConcurrentMarkSweepThread::synchronize(true);
6165 _bit_map->lock()->lock_without_safepoint_check();
6166 _collector->startTimer();
6167 }
6168
6169 // This closure is used to rescan the marked objects on the dirty cards
6170 // in the mod union table and the card table proper. In the parallel
6171 // case, although the bitMap is shared, we do a single read so the
6172 // isMarked() query is "safe".
6173 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6174 // Ignore mark word because we are running concurrent with mutators
6175 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6176 HeapWord* addr = (HeapWord*)p;
6177 assert(_span.contains(addr), "we are scanning the CMS generation");
6178 bool is_obj_array = false;
6179 #ifdef ASSERT
6180 if (!_parallel) {
6181 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6182 assert(_collector->overflow_list_is_empty(),
6183 "overflow list should be empty");
6184
6185 }
6186 #endif // ASSERT
6187 if (_bit_map->isMarked(addr)) {
6188 // Obj arrays are precisely marked, non-arrays are not;
6189 // so we scan objArrays precisely and non-arrays in their
6190 // entirety.
6191 if (p->is_objArray()) {
6192 is_obj_array = true;
6193 if (_parallel) {
6194 p->oop_iterate(_par_scan_closure, mr);
6195 } else {
6196 p->oop_iterate(_scan_closure, mr);
6197 }
6198 } else {
6199 if (_parallel) {
6200 p->oop_iterate(_par_scan_closure);
6201 } else {
6202 p->oop_iterate(_scan_closure);
6203 }
6204 }
6205 }
6206 #ifdef ASSERT
6207 if (!_parallel) {
6208 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6209 assert(_collector->overflow_list_is_empty(),
6210 "overflow list should be empty");
6211
6212 }
6213 #endif // ASSERT
6214 return is_obj_array;
6215 }
6216
6217 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6218 MemRegion span,
6219 CMSBitMap* bitMap, CMSMarkStack* markStack,
6220 bool should_yield, bool verifying):
6221 _collector(collector),
6222 _span(span),
6223 _bitMap(bitMap),
6224 _mut(&collector->_modUnionTable),
6225 _markStack(markStack),
6226 _yield(should_yield),
6227 _skipBits(0)
6228 {
6229 assert(_markStack->isEmpty(), "stack should be empty");
6230 _finger = _bitMap->startWord();
6231 _threshold = _finger;
6232 assert(_collector->_restart_addr == NULL, "Sanity check");
6233 assert(_span.contains(_finger), "Out of bounds _finger?");
6234 DEBUG_ONLY(_verifying = verifying;)
6235 }
6236
6237 void MarkFromRootsClosure::reset(HeapWord* addr) {
6238 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6239 assert(_span.contains(addr), "Out of bounds _finger?");
6240 _finger = addr;
6241 _threshold = align_up(_finger, CardTable::card_size);
6242 }
6243
6244 // Should revisit to see if this should be restructured for
6245 // greater efficiency.
6246 bool MarkFromRootsClosure::do_bit(size_t offset) {
6247 if (_skipBits > 0) {
6248 _skipBits--;
6249 return true;
6250 }
6251 // convert offset into a HeapWord*
6252 HeapWord* addr = _bitMap->startWord() + offset;
6253 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6254 "address out of range");
6255 assert(_bitMap->isMarked(addr), "tautology");
6256 if (_bitMap->isMarked(addr+1)) {
6257 // this is an allocated but not yet initialized object
6258 assert(_skipBits == 0, "tautology");
6259 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6260 oop p = oop(addr);
6261 if (p->klass_or_null_acquire() == NULL) {
6262 DEBUG_ONLY(if (!_verifying) {)
6263 // We re-dirty the cards on which this object lies and increase
6264 // the _threshold so that we'll come back to scan this object
6265 // during the preclean or remark phase. (CMSCleanOnEnter)
6266 if (CMSCleanOnEnter) {
6267 size_t sz = _collector->block_size_using_printezis_bits(addr);
6268 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6269 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6270 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6271 // Bump _threshold to end_card_addr; note that
6272 // _threshold cannot possibly exceed end_card_addr, anyhow.
6273 // This prevents future clearing of the card as the scan proceeds
6274 // to the right.
6275 assert(_threshold <= end_card_addr,
6276 "Because we are just scanning into this object");
6277 if (_threshold < end_card_addr) {
6278 _threshold = end_card_addr;
6279 }
6280 if (p->klass_or_null_acquire() != NULL) {
6281 // Redirty the range of cards...
6282 _mut->mark_range(redirty_range);
6283 } // ...else the setting of klass will dirty the card anyway.
6284 }
6285 DEBUG_ONLY(})
6286 return true;
6287 }
6288 }
6289 scanOopsInOop(addr);
6290 return true;
6291 }
6292
6293 // We take a break if we've been at this for a while,
6294 // so as to avoid monopolizing the locks involved.
6295 void MarkFromRootsClosure::do_yield_work() {
6296 // First give up the locks, then yield, then re-lock
6297 // We should probably use a constructor/destructor idiom to
6298 // do this unlock/lock or modify the MutexUnlocker class to
6299 // serve our purpose. XXX
6300 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6301 "CMS thread should hold CMS token");
6302 assert_lock_strong(_bitMap->lock());
6303 _bitMap->lock()->unlock();
6304 ConcurrentMarkSweepThread::desynchronize(true);
6305 _collector->stopTimer();
6306 _collector->incrementYields();
6307
6308 // See the comment in coordinator_yield()
6309 for (unsigned i = 0; i < CMSYieldSleepCount &&
6310 ConcurrentMarkSweepThread::should_yield() &&
6311 !CMSCollector::foregroundGCIsActive(); ++i) {
6312 os::sleep(Thread::current(), 1, false);
6313 }
6314
6315 ConcurrentMarkSweepThread::synchronize(true);
6316 _bitMap->lock()->lock_without_safepoint_check();
6317 _collector->startTimer();
6318 }
6319
6320 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6321 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6322 assert(_markStack->isEmpty(),
6323 "should drain stack to limit stack usage");
6324 // convert ptr to an oop preparatory to scanning
6325 oop obj = oop(ptr);
6326 // Ignore mark word in verification below, since we
6327 // may be running concurrent with mutators.
6328 assert(oopDesc::is_oop(obj, true), "should be an oop");
6329 assert(_finger <= ptr, "_finger runneth ahead");
6330 // advance the finger to right end of this object
6331 _finger = ptr + obj->size();
6332 assert(_finger > ptr, "we just incremented it above");
6333 // On large heaps, it may take us some time to get through
6334 // the marking phase. During
6335 // this time it's possible that a lot of mutations have
6336 // accumulated in the card table and the mod union table --
6337 // these mutation records are redundant until we have
6338 // actually traced into the corresponding card.
6339 // Here, we check whether advancing the finger would make
6340 // us cross into a new card, and if so clear corresponding
6341 // cards in the MUT (preclean them in the card-table in the
6342 // future).
6343
6344 DEBUG_ONLY(if (!_verifying) {)
6345 // The clean-on-enter optimization is disabled by default,
6346 // until we fix 6178663.
6347 if (CMSCleanOnEnter && (_finger > _threshold)) {
6348 // [_threshold, _finger) represents the interval
6349 // of cards to be cleared in MUT (or precleaned in card table).
6350 // The set of cards to be cleared is all those that overlap
6351 // with the interval [_threshold, _finger); note that
6352 // _threshold is always kept card-aligned but _finger isn't
6353 // always card-aligned.
6354 HeapWord* old_threshold = _threshold;
6355 assert(is_aligned(old_threshold, CardTable::card_size),
6356 "_threshold should always be card-aligned");
6357 _threshold = align_up(_finger, CardTable::card_size);
6358 MemRegion mr(old_threshold, _threshold);
6359 assert(!mr.is_empty(), "Control point invariant");
6360 assert(_span.contains(mr), "Should clear within span");
6361 _mut->clear_range(mr);
6362 }
6363 DEBUG_ONLY(})
6364 // Note: the finger doesn't advance while we drain
6365 // the stack below.
6366 PushOrMarkClosure pushOrMarkClosure(_collector,
6367 _span, _bitMap, _markStack,
6368 _finger, this);
6369 bool res = _markStack->push(obj);
6370 assert(res, "Empty non-zero size stack should have space for single push");
6371 while (!_markStack->isEmpty()) {
6372 oop new_oop = _markStack->pop();
6373 // Skip verifying header mark word below because we are
6374 // running concurrent with mutators.
6375 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6376 // now scan this oop's oops
6377 new_oop->oop_iterate(&pushOrMarkClosure);
6378 do_yield_check();
6379 }
6380 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6381 }
6382
6383 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6384 CMSCollector* collector, MemRegion span,
6385 CMSBitMap* bit_map,
6386 OopTaskQueue* work_queue,
6387 CMSMarkStack* overflow_stack):
6388 _collector(collector),
6389 _whole_span(collector->_span),
6390 _span(span),
6391 _bit_map(bit_map),
6392 _mut(&collector->_modUnionTable),
6393 _work_queue(work_queue),
6394 _overflow_stack(overflow_stack),
6395 _skip_bits(0),
6396 _task(task)
6397 {
6398 assert(_work_queue->size() == 0, "work_queue should be empty");
6399 _finger = span.start();
6400 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6401 assert(_span.contains(_finger), "Out of bounds _finger?");
6402 }
6403
6404 // Should revisit to see if this should be restructured for
6405 // greater efficiency.
6406 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6407 if (_skip_bits > 0) {
6408 _skip_bits--;
6409 return true;
6410 }
6411 // convert offset into a HeapWord*
6412 HeapWord* addr = _bit_map->startWord() + offset;
6413 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6414 "address out of range");
6415 assert(_bit_map->isMarked(addr), "tautology");
6416 if (_bit_map->isMarked(addr+1)) {
6417 // this is an allocated object that might not yet be initialized
6418 assert(_skip_bits == 0, "tautology");
6419 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6420 oop p = oop(addr);
6421 if (p->klass_or_null_acquire() == NULL) {
6422 // in the case of Clean-on-Enter optimization, redirty card
6423 // and avoid clearing card by increasing the threshold.
6424 return true;
6425 }
6426 }
6427 scan_oops_in_oop(addr);
6428 return true;
6429 }
6430
6431 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6432 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6433 // Should we assert that our work queue is empty or
6434 // below some drain limit?
6435 assert(_work_queue->size() == 0,
6436 "should drain stack to limit stack usage");
6437 // convert ptr to an oop preparatory to scanning
6438 oop obj = oop(ptr);
6439 // Ignore mark word in verification below, since we
6440 // may be running concurrent with mutators.
6441 assert(oopDesc::is_oop(obj, true), "should be an oop");
6442 assert(_finger <= ptr, "_finger runneth ahead");
6443 // advance the finger to right end of this object
6444 _finger = ptr + obj->size();
6445 assert(_finger > ptr, "we just incremented it above");
6446 // On large heaps, it may take us some time to get through
6447 // the marking phase. During
6448 // this time it's possible that a lot of mutations have
6449 // accumulated in the card table and the mod union table --
6450 // these mutation records are redundant until we have
6451 // actually traced into the corresponding card.
6452 // Here, we check whether advancing the finger would make
6453 // us cross into a new card, and if so clear corresponding
6454 // cards in the MUT (preclean them in the card-table in the
6455 // future).
6456
6457 // The clean-on-enter optimization is disabled by default,
6458 // until we fix 6178663.
6459 if (CMSCleanOnEnter && (_finger > _threshold)) {
6460 // [_threshold, _finger) represents the interval
6461 // of cards to be cleared in MUT (or precleaned in card table).
6462 // The set of cards to be cleared is all those that overlap
6463 // with the interval [_threshold, _finger); note that
6464 // _threshold is always kept card-aligned but _finger isn't
6465 // always card-aligned.
6466 HeapWord* old_threshold = _threshold;
6467 assert(is_aligned(old_threshold, CardTable::card_size),
6468 "_threshold should always be card-aligned");
6469 _threshold = align_up(_finger, CardTable::card_size);
6470 MemRegion mr(old_threshold, _threshold);
6471 assert(!mr.is_empty(), "Control point invariant");
6472 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6473 _mut->clear_range(mr);
6474 }
6475
6476 // Note: the local finger doesn't advance while we drain
6477 // the stack below, but the global finger sure can and will.
6478 HeapWord* volatile* gfa = _task->global_finger_addr();
6479 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6480 _span, _bit_map,
6481 _work_queue,
6482 _overflow_stack,
6483 _finger,
6484 gfa, this);
6485 bool res = _work_queue->push(obj); // overflow could occur here
6486 assert(res, "Will hold once we use workqueues");
6487 while (true) {
6488 oop new_oop;
6489 if (!_work_queue->pop_local(new_oop)) {
6490 // We emptied our work_queue; check if there's stuff that can
6491 // be gotten from the overflow stack.
6492 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6493 _overflow_stack, _work_queue)) {
6494 do_yield_check();
6495 continue;
6496 } else { // done
6497 break;
6498 }
6499 }
6500 // Skip verifying header mark word below because we are
6501 // running concurrent with mutators.
6502 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6503 // now scan this oop's oops
6504 new_oop->oop_iterate(&pushOrMarkClosure);
6505 do_yield_check();
6506 }
6507 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6508 }
6509
6510 // Yield in response to a request from VM Thread or
6511 // from mutators.
6512 void ParMarkFromRootsClosure::do_yield_work() {
6513 assert(_task != NULL, "sanity");
6514 _task->yield();
6515 }
6516
6517 // A variant of the above used for verifying CMS marking work.
6518 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6519 MemRegion span,
6520 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6521 CMSMarkStack* mark_stack):
6522 _collector(collector),
6523 _span(span),
6524 _verification_bm(verification_bm),
6525 _cms_bm(cms_bm),
6526 _mark_stack(mark_stack),
6527 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6528 mark_stack)
6529 {
6530 assert(_mark_stack->isEmpty(), "stack should be empty");
6531 _finger = _verification_bm->startWord();
6532 assert(_collector->_restart_addr == NULL, "Sanity check");
6533 assert(_span.contains(_finger), "Out of bounds _finger?");
6534 }
6535
6536 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6537 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6538 assert(_span.contains(addr), "Out of bounds _finger?");
6539 _finger = addr;
6540 }
6541
6542 // Should revisit to see if this should be restructured for
6543 // greater efficiency.
6544 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6545 // convert offset into a HeapWord*
6546 HeapWord* addr = _verification_bm->startWord() + offset;
6547 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6548 "address out of range");
6549 assert(_verification_bm->isMarked(addr), "tautology");
6550 assert(_cms_bm->isMarked(addr), "tautology");
6551
6552 assert(_mark_stack->isEmpty(),
6553 "should drain stack to limit stack usage");
6554 // convert addr to an oop preparatory to scanning
6555 oop obj = oop(addr);
6556 assert(oopDesc::is_oop(obj), "should be an oop");
6557 assert(_finger <= addr, "_finger runneth ahead");
6558 // advance the finger to right end of this object
6559 _finger = addr + obj->size();
6560 assert(_finger > addr, "we just incremented it above");
6561 // Note: the finger doesn't advance while we drain
6562 // the stack below.
6563 bool res = _mark_stack->push(obj);
6564 assert(res, "Empty non-zero size stack should have space for single push");
6565 while (!_mark_stack->isEmpty()) {
6566 oop new_oop = _mark_stack->pop();
6567 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6568 // now scan this oop's oops
6569 new_oop->oop_iterate(&_pam_verify_closure);
6570 }
6571 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6572 return true;
6573 }
6574
6575 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6576 CMSCollector* collector, MemRegion span,
6577 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6578 CMSMarkStack* mark_stack):
6579 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6580 _collector(collector),
6581 _span(span),
6582 _verification_bm(verification_bm),
6583 _cms_bm(cms_bm),
6584 _mark_stack(mark_stack)
6585 { }
6586
6587 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6588 oop obj = RawAccess<>::oop_load(p);
6589 do_oop(obj);
6590 }
6591
6592 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6593 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6594
6595 // Upon stack overflow, we discard (part of) the stack,
6596 // remembering the least address amongst those discarded
6597 // in CMSCollector's _restart_address.
6598 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6599 // Remember the least grey address discarded
6600 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6601 _collector->lower_restart_addr(ra);
6602 _mark_stack->reset(); // discard stack contents
6603 _mark_stack->expand(); // expand the stack if possible
6604 }
6605
6606 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6607 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6608 HeapWord* addr = (HeapWord*)obj;
6609 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6610 // Oop lies in _span and isn't yet grey or black
6611 _verification_bm->mark(addr); // now grey
6612 if (!_cms_bm->isMarked(addr)) {
6613 Log(gc, verify) log;
6614 ResourceMark rm;
6615 LogStream ls(log.error());
6616 oop(addr)->print_on(&ls);
6617 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6618 fatal("... aborting");
6619 }
6620
6621 if (!_mark_stack->push(obj)) { // stack overflow
6622 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6623 assert(_mark_stack->isFull(), "Else push should have succeeded");
6624 handle_stack_overflow(addr);
6625 }
6626 // anything including and to the right of _finger
6627 // will be scanned as we iterate over the remainder of the
6628 // bit map
6629 }
6630 }
6631
6632 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6633 MemRegion span,
6634 CMSBitMap* bitMap, CMSMarkStack* markStack,
6635 HeapWord* finger, MarkFromRootsClosure* parent) :
6636 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6637 _collector(collector),
6638 _span(span),
6639 _bitMap(bitMap),
6640 _markStack(markStack),
6641 _finger(finger),
6642 _parent(parent)
6643 { }
6644
6645 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6646 MemRegion span,
6647 CMSBitMap* bit_map,
6648 OopTaskQueue* work_queue,
6649 CMSMarkStack* overflow_stack,
6650 HeapWord* finger,
6651 HeapWord* volatile* global_finger_addr,
6652 ParMarkFromRootsClosure* parent) :
6653 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6654 _collector(collector),
6655 _whole_span(collector->_span),
6656 _span(span),
6657 _bit_map(bit_map),
6658 _work_queue(work_queue),
6659 _overflow_stack(overflow_stack),
6660 _finger(finger),
6661 _global_finger_addr(global_finger_addr),
6662 _parent(parent)
6663 { }
6664
6665 // Assumes thread-safe access by callers, who are
6666 // responsible for mutual exclusion.
6667 void CMSCollector::lower_restart_addr(HeapWord* low) {
6668 assert(_span.contains(low), "Out of bounds addr");
6669 if (_restart_addr == NULL) {
6670 _restart_addr = low;
6671 } else {
6672 _restart_addr = MIN2(_restart_addr, low);
6673 }
6674 }
6675
6676 // Upon stack overflow, we discard (part of) the stack,
6677 // remembering the least address amongst those discarded
6678 // in CMSCollector's _restart_address.
6679 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6680 // Remember the least grey address discarded
6681 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6682 _collector->lower_restart_addr(ra);
6683 _markStack->reset(); // discard stack contents
6684 _markStack->expand(); // expand the stack if possible
6685 }
6686
6687 // Upon stack overflow, we discard (part of) the stack,
6688 // remembering the least address amongst those discarded
6689 // in CMSCollector's _restart_address.
6690 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6691 // We need to do this under a mutex to prevent other
6692 // workers from interfering with the work done below.
6693 MutexLockerEx ml(_overflow_stack->par_lock(),
6694 Mutex::_no_safepoint_check_flag);
6695 // Remember the least grey address discarded
6696 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6697 _collector->lower_restart_addr(ra);
6698 _overflow_stack->reset(); // discard stack contents
6699 _overflow_stack->expand(); // expand the stack if possible
6700 }
6701
6702 void PushOrMarkClosure::do_oop(oop obj) {
6703 // Ignore mark word because we are running concurrent with mutators.
6704 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6705 HeapWord* addr = (HeapWord*)obj;
6706 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6707 // Oop lies in _span and isn't yet grey or black
6708 _bitMap->mark(addr); // now grey
6709 if (addr < _finger) {
6710 // the bit map iteration has already either passed, or
6711 // sampled, this bit in the bit map; we'll need to
6712 // use the marking stack to scan this oop's oops.
6713 bool simulate_overflow = false;
6714 NOT_PRODUCT(
6715 if (CMSMarkStackOverflowALot &&
6716 _collector->simulate_overflow()) {
6717 // simulate a stack overflow
6718 simulate_overflow = true;
6719 }
6720 )
6721 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6722 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6723 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6724 handle_stack_overflow(addr);
6725 }
6726 }
6727 // anything including and to the right of _finger
6728 // will be scanned as we iterate over the remainder of the
6729 // bit map
6730 do_yield_check();
6731 }
6732 }
6733
6734 void ParPushOrMarkClosure::do_oop(oop obj) {
6735 // Ignore mark word because we are running concurrent with mutators.
6736 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6737 HeapWord* addr = (HeapWord*)obj;
6738 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6739 // Oop lies in _span and isn't yet grey or black
6740 // We read the global_finger (volatile read) strictly after marking oop
6741 bool res = _bit_map->par_mark(addr); // now grey
6742 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6743 // Should we push this marked oop on our stack?
6744 // -- if someone else marked it, nothing to do
6745 // -- if target oop is above global finger nothing to do
6746 // -- if target oop is in chunk and above local finger
6747 // then nothing to do
6748 // -- else push on work queue
6749 if ( !res // someone else marked it, they will deal with it
6750 || (addr >= *gfa) // will be scanned in a later task
6751 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6752 return;
6753 }
6754 // the bit map iteration has already either passed, or
6755 // sampled, this bit in the bit map; we'll need to
6756 // use the marking stack to scan this oop's oops.
6757 bool simulate_overflow = false;
6758 NOT_PRODUCT(
6759 if (CMSMarkStackOverflowALot &&
6760 _collector->simulate_overflow()) {
6761 // simulate a stack overflow
6762 simulate_overflow = true;
6763 }
6764 )
6765 if (simulate_overflow ||
6766 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6767 // stack overflow
6768 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6769 // We cannot assert that the overflow stack is full because
6770 // it may have been emptied since.
6771 assert(simulate_overflow ||
6772 _work_queue->size() == _work_queue->max_elems(),
6773 "Else push should have succeeded");
6774 handle_stack_overflow(addr);
6775 }
6776 do_yield_check();
6777 }
6778 }
6779
6780 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6781 MemRegion span,
6782 ReferenceDiscoverer* rd,
6783 CMSBitMap* bit_map,
6784 CMSBitMap* mod_union_table,
6785 CMSMarkStack* mark_stack,
6786 bool concurrent_precleaning):
6787 MetadataVisitingOopIterateClosure(rd),
6788 _collector(collector),
6789 _span(span),
6790 _bit_map(bit_map),
6791 _mod_union_table(mod_union_table),
6792 _mark_stack(mark_stack),
6793 _concurrent_precleaning(concurrent_precleaning)
6794 {
6795 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6796 }
6797
6798 // Grey object rescan during pre-cleaning and second checkpoint phases --
6799 // the non-parallel version (the parallel version appears further below.)
6800 void PushAndMarkClosure::do_oop(oop obj) {
6801 // Ignore mark word verification. If during concurrent precleaning,
6802 // the object monitor may be locked. If during the checkpoint
6803 // phases, the object may already have been reached by a different
6804 // path and may be at the end of the global overflow list (so
6805 // the mark word may be NULL).
6806 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6807 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6808 HeapWord* addr = (HeapWord*)obj;
6809 // Check if oop points into the CMS generation
6810 // and is not marked
6811 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6812 // a white object ...
6813 _bit_map->mark(addr); // ... now grey
6814 // push on the marking stack (grey set)
6815 bool simulate_overflow = false;
6816 NOT_PRODUCT(
6817 if (CMSMarkStackOverflowALot &&
6818 _collector->simulate_overflow()) {
6819 // simulate a stack overflow
6820 simulate_overflow = true;
6821 }
6822 )
6823 if (simulate_overflow || !_mark_stack->push(obj)) {
6824 if (_concurrent_precleaning) {
6825 // During precleaning we can just dirty the appropriate card(s)
6826 // in the mod union table, thus ensuring that the object remains
6827 // in the grey set and continue. In the case of object arrays
6828 // we need to dirty all of the cards that the object spans,
6829 // since the rescan of object arrays will be limited to the
6830 // dirty cards.
6831 // Note that no one can be interfering with us in this action
6832 // of dirtying the mod union table, so no locking or atomics
6833 // are required.
6834 if (obj->is_objArray()) {
6835 size_t sz = obj->size();
6836 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6837 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6838 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6839 _mod_union_table->mark_range(redirty_range);
6840 } else {
6841 _mod_union_table->mark(addr);
6842 }
6843 _collector->_ser_pmc_preclean_ovflw++;
6844 } else {
6845 // During the remark phase, we need to remember this oop
6846 // in the overflow list.
6847 _collector->push_on_overflow_list(obj);
6848 _collector->_ser_pmc_remark_ovflw++;
6849 }
6850 }
6851 }
6852 }
6853
6854 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6855 MemRegion span,
6856 ReferenceDiscoverer* rd,
6857 CMSBitMap* bit_map,
6858 OopTaskQueue* work_queue):
6859 MetadataVisitingOopIterateClosure(rd),
6860 _collector(collector),
6861 _span(span),
6862 _bit_map(bit_map),
6863 _work_queue(work_queue)
6864 {
6865 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6866 }
6867
6868 // Grey object rescan during second checkpoint phase --
6869 // the parallel version.
6870 void ParPushAndMarkClosure::do_oop(oop obj) {
6871 // In the assert below, we ignore the mark word because
6872 // this oop may point to an already visited object that is
6873 // on the overflow stack (in which case the mark word has
6874 // been hijacked for chaining into the overflow stack --
6875 // if this is the last object in the overflow stack then
6876 // its mark word will be NULL). Because this object may
6877 // have been subsequently popped off the global overflow
6878 // stack, and the mark word possibly restored to the prototypical
6879 // value, by the time we get to examined this failing assert in
6880 // the debugger, is_oop_or_null(false) may subsequently start
6881 // to hold.
6882 assert(oopDesc::is_oop_or_null(obj, true),
6883 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6884 HeapWord* addr = (HeapWord*)obj;
6885 // Check if oop points into the CMS generation
6886 // and is not marked
6887 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6888 // a white object ...
6889 // If we manage to "claim" the object, by being the
6890 // first thread to mark it, then we push it on our
6891 // marking stack
6892 if (_bit_map->par_mark(addr)) { // ... now grey
6893 // push on work queue (grey set)
6894 bool simulate_overflow = false;
6895 NOT_PRODUCT(
6896 if (CMSMarkStackOverflowALot &&
6897 _collector->par_simulate_overflow()) {
6898 // simulate a stack overflow
6899 simulate_overflow = true;
6900 }
6901 )
6902 if (simulate_overflow || !_work_queue->push(obj)) {
6903 _collector->par_push_on_overflow_list(obj);
6904 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6905 }
6906 } // Else, some other thread got there first
6907 }
6908 }
6909
6910 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6911 Mutex* bml = _collector->bitMapLock();
6912 assert_lock_strong(bml);
6913 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6914 "CMS thread should hold CMS token");
6915
6916 bml->unlock();
6917 ConcurrentMarkSweepThread::desynchronize(true);
6918
6919 _collector->stopTimer();
6920 _collector->incrementYields();
6921
6922 // See the comment in coordinator_yield()
6923 for (unsigned i = 0; i < CMSYieldSleepCount &&
6924 ConcurrentMarkSweepThread::should_yield() &&
6925 !CMSCollector::foregroundGCIsActive(); ++i) {
6926 os::sleep(Thread::current(), 1, false);
6927 }
6928
6929 ConcurrentMarkSweepThread::synchronize(true);
6930 bml->lock();
6931
6932 _collector->startTimer();
6933 }
6934
6935 bool CMSPrecleanRefsYieldClosure::should_return() {
6936 if (ConcurrentMarkSweepThread::should_yield()) {
6937 do_yield_work();
6938 }
6939 return _collector->foregroundGCIsActive();
6940 }
6941
6942 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
6943 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
6944 "mr should be aligned to start at a card boundary");
6945 // We'd like to assert:
6946 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
6947 // "mr should be a range of cards");
6948 // However, that would be too strong in one case -- the last
6949 // partition ends at _unallocated_block which, in general, can be
6950 // an arbitrary boundary, not necessarily card aligned.
6951 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
6952 _space->object_iterate_mem(mr, &_scan_cl);
6953 }
6954
6955 SweepClosure::SweepClosure(CMSCollector* collector,
6956 ConcurrentMarkSweepGeneration* g,
6957 CMSBitMap* bitMap, bool should_yield) :
6958 _collector(collector),
6959 _g(g),
6960 _sp(g->cmsSpace()),
6961 _limit(_sp->sweep_limit()),
6962 _freelistLock(_sp->freelistLock()),
6963 _bitMap(bitMap),
6964 _inFreeRange(false), // No free range at beginning of sweep
6965 _freeRangeInFreeLists(false), // No free range at beginning of sweep
6966 _lastFreeRangeCoalesced(false),
6967 _yield(should_yield),
6968 _freeFinger(g->used_region().start())
6969 {
6970 NOT_PRODUCT(
6971 _numObjectsFreed = 0;
6972 _numWordsFreed = 0;
6973 _numObjectsLive = 0;
6974 _numWordsLive = 0;
6975 _numObjectsAlreadyFree = 0;
6976 _numWordsAlreadyFree = 0;
6977 _last_fc = NULL;
6978
6979 _sp->initializeIndexedFreeListArrayReturnedBytes();
6980 _sp->dictionary()->initialize_dict_returned_bytes();
6981 )
6982 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
6983 "sweep _limit out of bounds");
6984 log_develop_trace(gc, sweep)("====================");
6985 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
6986 }
6987
6988 void SweepClosure::print_on(outputStream* st) const {
6989 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
6990 p2i(_sp->bottom()), p2i(_sp->end()));
6991 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
6992 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
6993 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
6994 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
6995 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
6996 }
6997
6998 #ifndef PRODUCT
6999 // Assertion checking only: no useful work in product mode --
7000 // however, if any of the flags below become product flags,
7001 // you may need to review this code to see if it needs to be
7002 // enabled in product mode.
7003 SweepClosure::~SweepClosure() {
7004 assert_lock_strong(_freelistLock);
7005 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7006 "sweep _limit out of bounds");
7007 if (inFreeRange()) {
7008 Log(gc, sweep) log;
7009 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7010 ResourceMark rm;
7011 LogStream ls(log.error());
7012 print_on(&ls);
7013 ShouldNotReachHere();
7014 }
7015
7016 if (log_is_enabled(Debug, gc, sweep)) {
7017 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7018 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7019 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7020 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7021 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7022 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7023 }
7024
7025 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7026 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7027 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7028 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7029 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7030 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7031 }
7032 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7033 log_develop_trace(gc, sweep)("================");
7034 }
7035 #endif // PRODUCT
7036
7037 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7038 bool freeRangeInFreeLists) {
7039 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7040 p2i(freeFinger), freeRangeInFreeLists);
7041 assert(!inFreeRange(), "Trampling existing free range");
7042 set_inFreeRange(true);
7043 set_lastFreeRangeCoalesced(false);
7044
7045 set_freeFinger(freeFinger);
7046 set_freeRangeInFreeLists(freeRangeInFreeLists);
7047 if (CMSTestInFreeList) {
7048 if (freeRangeInFreeLists) {
7049 FreeChunk* fc = (FreeChunk*) freeFinger;
7050 assert(fc->is_free(), "A chunk on the free list should be free.");
7051 assert(fc->size() > 0, "Free range should have a size");
7052 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7053 }
7054 }
7055 }
7056
7057 // Note that the sweeper runs concurrently with mutators. Thus,
7058 // it is possible for direct allocation in this generation to happen
7059 // in the middle of the sweep. Note that the sweeper also coalesces
7060 // contiguous free blocks. Thus, unless the sweeper and the allocator
7061 // synchronize appropriately freshly allocated blocks may get swept up.
7062 // This is accomplished by the sweeper locking the free lists while
7063 // it is sweeping. Thus blocks that are determined to be free are
7064 // indeed free. There is however one additional complication:
7065 // blocks that have been allocated since the final checkpoint and
7066 // mark, will not have been marked and so would be treated as
7067 // unreachable and swept up. To prevent this, the allocator marks
7068 // the bit map when allocating during the sweep phase. This leads,
7069 // however, to a further complication -- objects may have been allocated
7070 // but not yet initialized -- in the sense that the header isn't yet
7071 // installed. The sweeper can not then determine the size of the block
7072 // in order to skip over it. To deal with this case, we use a technique
7073 // (due to Printezis) to encode such uninitialized block sizes in the
7074 // bit map. Since the bit map uses a bit per every HeapWord, but the
7075 // CMS generation has a minimum object size of 3 HeapWords, it follows
7076 // that "normal marks" won't be adjacent in the bit map (there will
7077 // always be at least two 0 bits between successive 1 bits). We make use
7078 // of these "unused" bits to represent uninitialized blocks -- the bit
7079 // corresponding to the start of the uninitialized object and the next
7080 // bit are both set. Finally, a 1 bit marks the end of the object that
7081 // started with the two consecutive 1 bits to indicate its potentially
7082 // uninitialized state.
7083
7084 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7085 FreeChunk* fc = (FreeChunk*)addr;
7086 size_t res;
7087
7088 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7089 // than "addr == _limit" because although _limit was a block boundary when
7090 // we started the sweep, it may no longer be one because heap expansion
7091 // may have caused us to coalesce the block ending at the address _limit
7092 // with a newly expanded chunk (this happens when _limit was set to the
7093 // previous _end of the space), so we may have stepped past _limit:
7094 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7095 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7096 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7097 "sweep _limit out of bounds");
7098 assert(addr < _sp->end(), "addr out of bounds");
7099 // Flush any free range we might be holding as a single
7100 // coalesced chunk to the appropriate free list.
7101 if (inFreeRange()) {
7102 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7103 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7104 flush_cur_free_chunk(freeFinger(),
7105 pointer_delta(addr, freeFinger()));
7106 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7107 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7108 lastFreeRangeCoalesced() ? 1 : 0);
7109 }
7110
7111 // help the iterator loop finish
7112 return pointer_delta(_sp->end(), addr);
7113 }
7114
7115 assert(addr < _limit, "sweep invariant");
7116 // check if we should yield
7117 do_yield_check(addr);
7118 if (fc->is_free()) {
7119 // Chunk that is already free
7120 res = fc->size();
7121 do_already_free_chunk(fc);
7122 debug_only(_sp->verifyFreeLists());
7123 // If we flush the chunk at hand in lookahead_and_flush()
7124 // and it's coalesced with a preceding chunk, then the
7125 // process of "mangling" the payload of the coalesced block
7126 // will cause erasure of the size information from the
7127 // (erstwhile) header of all the coalesced blocks but the
7128 // first, so the first disjunct in the assert will not hold
7129 // in that specific case (in which case the second disjunct
7130 // will hold).
7131 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7132 "Otherwise the size info doesn't change at this step");
7133 NOT_PRODUCT(
7134 _numObjectsAlreadyFree++;
7135 _numWordsAlreadyFree += res;
7136 )
7137 NOT_PRODUCT(_last_fc = fc;)
7138 } else if (!_bitMap->isMarked(addr)) {
7139 // Chunk is fresh garbage
7140 res = do_garbage_chunk(fc);
7141 debug_only(_sp->verifyFreeLists());
7142 NOT_PRODUCT(
7143 _numObjectsFreed++;
7144 _numWordsFreed += res;
7145 )
7146 } else {
7147 // Chunk that is alive.
7148 res = do_live_chunk(fc);
7149 debug_only(_sp->verifyFreeLists());
7150 NOT_PRODUCT(
7151 _numObjectsLive++;
7152 _numWordsLive += res;
7153 )
7154 }
7155 return res;
7156 }
7157
7158 // For the smart allocation, record following
7159 // split deaths - a free chunk is removed from its free list because
7160 // it is being split into two or more chunks.
7161 // split birth - a free chunk is being added to its free list because
7162 // a larger free chunk has been split and resulted in this free chunk.
7163 // coal death - a free chunk is being removed from its free list because
7164 // it is being coalesced into a large free chunk.
7165 // coal birth - a free chunk is being added to its free list because
7166 // it was created when two or more free chunks where coalesced into
7167 // this free chunk.
7168 //
7169 // These statistics are used to determine the desired number of free
7170 // chunks of a given size. The desired number is chosen to be relative
7171 // to the end of a CMS sweep. The desired number at the end of a sweep
7172 // is the
7173 // count-at-end-of-previous-sweep (an amount that was enough)
7174 // - count-at-beginning-of-current-sweep (the excess)
7175 // + split-births (gains in this size during interval)
7176 // - split-deaths (demands on this size during interval)
7177 // where the interval is from the end of one sweep to the end of the
7178 // next.
7179 //
7180 // When sweeping the sweeper maintains an accumulated chunk which is
7181 // the chunk that is made up of chunks that have been coalesced. That
7182 // will be termed the left-hand chunk. A new chunk of garbage that
7183 // is being considered for coalescing will be referred to as the
7184 // right-hand chunk.
7185 //
7186 // When making a decision on whether to coalesce a right-hand chunk with
7187 // the current left-hand chunk, the current count vs. the desired count
7188 // of the left-hand chunk is considered. Also if the right-hand chunk
7189 // is near the large chunk at the end of the heap (see
7190 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7191 // left-hand chunk is coalesced.
7192 //
7193 // When making a decision about whether to split a chunk, the desired count
7194 // vs. the current count of the candidate to be split is also considered.
7195 // If the candidate is underpopulated (currently fewer chunks than desired)
7196 // a chunk of an overpopulated (currently more chunks than desired) size may
7197 // be chosen. The "hint" associated with a free list, if non-null, points
7198 // to a free list which may be overpopulated.
7199 //
7200
7201 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7202 const size_t size = fc->size();
7203 // Chunks that cannot be coalesced are not in the
7204 // free lists.
7205 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7206 assert(_sp->verify_chunk_in_free_list(fc),
7207 "free chunk should be in free lists");
7208 }
7209 // a chunk that is already free, should not have been
7210 // marked in the bit map
7211 HeapWord* const addr = (HeapWord*) fc;
7212 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7213 // Verify that the bit map has no bits marked between
7214 // addr and purported end of this block.
7215 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7216
7217 // Some chunks cannot be coalesced under any circumstances.
7218 // See the definition of cantCoalesce().
7219 if (!fc->cantCoalesce()) {
7220 // This chunk can potentially be coalesced.
7221 // All the work is done in
7222 do_post_free_or_garbage_chunk(fc, size);
7223 // Note that if the chunk is not coalescable (the else arm
7224 // below), we unconditionally flush, without needing to do
7225 // a "lookahead," as we do below.
7226 if (inFreeRange()) lookahead_and_flush(fc, size);
7227 } else {
7228 // Code path common to both original and adaptive free lists.
7229
7230 // cant coalesce with previous block; this should be treated
7231 // as the end of a free run if any
7232 if (inFreeRange()) {
7233 // we kicked some butt; time to pick up the garbage
7234 assert(freeFinger() < addr, "freeFinger points too high");
7235 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7236 }
7237 // else, nothing to do, just continue
7238 }
7239 }
7240
7241 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7242 // This is a chunk of garbage. It is not in any free list.
7243 // Add it to a free list or let it possibly be coalesced into
7244 // a larger chunk.
7245 HeapWord* const addr = (HeapWord*) fc;
7246 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7247
7248 // Verify that the bit map has no bits marked between
7249 // addr and purported end of just dead object.
7250 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7251 do_post_free_or_garbage_chunk(fc, size);
7252
7253 assert(_limit >= addr + size,
7254 "A freshly garbage chunk can't possibly straddle over _limit");
7255 if (inFreeRange()) lookahead_and_flush(fc, size);
7256 return size;
7257 }
7258
7259 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7260 HeapWord* addr = (HeapWord*) fc;
7261 // The sweeper has just found a live object. Return any accumulated
7262 // left hand chunk to the free lists.
7263 if (inFreeRange()) {
7264 assert(freeFinger() < addr, "freeFinger points too high");
7265 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7266 }
7267
7268 // This object is live: we'd normally expect this to be
7269 // an oop, and like to assert the following:
7270 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7271 // However, as we commented above, this may be an object whose
7272 // header hasn't yet been initialized.
7273 size_t size;
7274 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7275 if (_bitMap->isMarked(addr + 1)) {
7276 // Determine the size from the bit map, rather than trying to
7277 // compute it from the object header.
7278 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7279 size = pointer_delta(nextOneAddr + 1, addr);
7280 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7281 "alignment problem");
7282
7283 #ifdef ASSERT
7284 if (oop(addr)->klass_or_null_acquire() != NULL) {
7285 // Ignore mark word because we are running concurrent with mutators
7286 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7287 assert(size ==
7288 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7289 "P-mark and computed size do not agree");
7290 }
7291 #endif
7292
7293 } else {
7294 // This should be an initialized object that's alive.
7295 assert(oop(addr)->klass_or_null_acquire() != NULL,
7296 "Should be an initialized object");
7297 // Ignore mark word because we are running concurrent with mutators
7298 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7299 // Verify that the bit map has no bits marked between
7300 // addr and purported end of this block.
7301 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7302 assert(size >= 3, "Necessary for Printezis marks to work");
7303 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7304 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7305 }
7306 return size;
7307 }
7308
7309 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7310 size_t chunkSize) {
7311 // do_post_free_or_garbage_chunk() should only be called in the case
7312 // of the adaptive free list allocator.
7313 const bool fcInFreeLists = fc->is_free();
7314 assert((HeapWord*)fc <= _limit, "sweep invariant");
7315 if (CMSTestInFreeList && fcInFreeLists) {
7316 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7317 }
7318
7319 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7320
7321 HeapWord* const fc_addr = (HeapWord*) fc;
7322
7323 bool coalesce = false;
7324 const size_t left = pointer_delta(fc_addr, freeFinger());
7325 const size_t right = chunkSize;
7326 switch (FLSCoalescePolicy) {
7327 // numeric value forms a coalition aggressiveness metric
7328 case 0: { // never coalesce
7329 coalesce = false;
7330 break;
7331 }
7332 case 1: { // coalesce if left & right chunks on overpopulated lists
7333 coalesce = _sp->coalOverPopulated(left) &&
7334 _sp->coalOverPopulated(right);
7335 break;
7336 }
7337 case 2: { // coalesce if left chunk on overpopulated list (default)
7338 coalesce = _sp->coalOverPopulated(left);
7339 break;
7340 }
7341 case 3: { // coalesce if left OR right chunk on overpopulated list
7342 coalesce = _sp->coalOverPopulated(left) ||
7343 _sp->coalOverPopulated(right);
7344 break;
7345 }
7346 case 4: { // always coalesce
7347 coalesce = true;
7348 break;
7349 }
7350 default:
7351 ShouldNotReachHere();
7352 }
7353
7354 // Should the current free range be coalesced?
7355 // If the chunk is in a free range and either we decided to coalesce above
7356 // or the chunk is near the large block at the end of the heap
7357 // (isNearLargestChunk() returns true), then coalesce this chunk.
7358 const bool doCoalesce = inFreeRange()
7359 && (coalesce || _g->isNearLargestChunk(fc_addr));
7360 if (doCoalesce) {
7361 // Coalesce the current free range on the left with the new
7362 // chunk on the right. If either is on a free list,
7363 // it must be removed from the list and stashed in the closure.
7364 if (freeRangeInFreeLists()) {
7365 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7366 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7367 "Size of free range is inconsistent with chunk size.");
7368 if (CMSTestInFreeList) {
7369 assert(_sp->verify_chunk_in_free_list(ffc),
7370 "Chunk is not in free lists");
7371 }
7372 _sp->coalDeath(ffc->size());
7373 _sp->removeFreeChunkFromFreeLists(ffc);
7374 set_freeRangeInFreeLists(false);
7375 }
7376 if (fcInFreeLists) {
7377 _sp->coalDeath(chunkSize);
7378 assert(fc->size() == chunkSize,
7379 "The chunk has the wrong size or is not in the free lists");
7380 _sp->removeFreeChunkFromFreeLists(fc);
7381 }
7382 set_lastFreeRangeCoalesced(true);
7383 print_free_block_coalesced(fc);
7384 } else { // not in a free range and/or should not coalesce
7385 // Return the current free range and start a new one.
7386 if (inFreeRange()) {
7387 // In a free range but cannot coalesce with the right hand chunk.
7388 // Put the current free range into the free lists.
7389 flush_cur_free_chunk(freeFinger(),
7390 pointer_delta(fc_addr, freeFinger()));
7391 }
7392 // Set up for new free range. Pass along whether the right hand
7393 // chunk is in the free lists.
7394 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7395 }
7396 }
7397
7398 // Lookahead flush:
7399 // If we are tracking a free range, and this is the last chunk that
7400 // we'll look at because its end crosses past _limit, we'll preemptively
7401 // flush it along with any free range we may be holding on to. Note that
7402 // this can be the case only for an already free or freshly garbage
7403 // chunk. If this block is an object, it can never straddle
7404 // over _limit. The "straddling" occurs when _limit is set at
7405 // the previous end of the space when this cycle started, and
7406 // a subsequent heap expansion caused the previously co-terminal
7407 // free block to be coalesced with the newly expanded portion,
7408 // thus rendering _limit a non-block-boundary making it dangerous
7409 // for the sweeper to step over and examine.
7410 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7411 assert(inFreeRange(), "Should only be called if currently in a free range.");
7412 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7413 assert(_sp->used_region().contains(eob - 1),
7414 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7415 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7416 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7417 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7418 if (eob >= _limit) {
7419 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7420 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7421 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7422 "[" PTR_FORMAT "," PTR_FORMAT ")",
7423 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7424 // Return the storage we are tracking back into the free lists.
7425 log_develop_trace(gc, sweep)("Flushing ... ");
7426 assert(freeFinger() < eob, "Error");
7427 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7428 }
7429 }
7430
7431 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7432 assert(inFreeRange(), "Should only be called if currently in a free range.");
7433 assert(size > 0,
7434 "A zero sized chunk cannot be added to the free lists.");
7435 if (!freeRangeInFreeLists()) {
7436 if (CMSTestInFreeList) {
7437 FreeChunk* fc = (FreeChunk*) chunk;
7438 fc->set_size(size);
7439 assert(!_sp->verify_chunk_in_free_list(fc),
7440 "chunk should not be in free lists yet");
7441 }
7442 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7443 // A new free range is going to be starting. The current
7444 // free range has not been added to the free lists yet or
7445 // was removed so add it back.
7446 // If the current free range was coalesced, then the death
7447 // of the free range was recorded. Record a birth now.
7448 if (lastFreeRangeCoalesced()) {
7449 _sp->coalBirth(size);
7450 }
7451 _sp->addChunkAndRepairOffsetTable(chunk, size,
7452 lastFreeRangeCoalesced());
7453 } else {
7454 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7455 }
7456 set_inFreeRange(false);
7457 set_freeRangeInFreeLists(false);
7458 }
7459
7460 // We take a break if we've been at this for a while,
7461 // so as to avoid monopolizing the locks involved.
7462 void SweepClosure::do_yield_work(HeapWord* addr) {
7463 // Return current free chunk being used for coalescing (if any)
7464 // to the appropriate freelist. After yielding, the next
7465 // free block encountered will start a coalescing range of
7466 // free blocks. If the next free block is adjacent to the
7467 // chunk just flushed, they will need to wait for the next
7468 // sweep to be coalesced.
7469 if (inFreeRange()) {
7470 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7471 }
7472
7473 // First give up the locks, then yield, then re-lock.
7474 // We should probably use a constructor/destructor idiom to
7475 // do this unlock/lock or modify the MutexUnlocker class to
7476 // serve our purpose. XXX
7477 assert_lock_strong(_bitMap->lock());
7478 assert_lock_strong(_freelistLock);
7479 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7480 "CMS thread should hold CMS token");
7481 _bitMap->lock()->unlock();
7482 _freelistLock->unlock();
7483 ConcurrentMarkSweepThread::desynchronize(true);
7484 _collector->stopTimer();
7485 _collector->incrementYields();
7486
7487 // See the comment in coordinator_yield()
7488 for (unsigned i = 0; i < CMSYieldSleepCount &&
7489 ConcurrentMarkSweepThread::should_yield() &&
7490 !CMSCollector::foregroundGCIsActive(); ++i) {
7491 os::sleep(Thread::current(), 1, false);
7492 }
7493
7494 ConcurrentMarkSweepThread::synchronize(true);
7495 _freelistLock->lock();
7496 _bitMap->lock()->lock_without_safepoint_check();
7497 _collector->startTimer();
7498 }
7499
7500 #ifndef PRODUCT
7501 // This is actually very useful in a product build if it can
7502 // be called from the debugger. Compile it into the product
7503 // as needed.
7504 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7505 return debug_cms_space->verify_chunk_in_free_list(fc);
7506 }
7507 #endif
7508
7509 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7510 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7511 p2i(fc), fc->size());
7512 }
7513
7514 // CMSIsAliveClosure
7515 bool CMSIsAliveClosure::do_object_b(oop obj) {
7516 HeapWord* addr = (HeapWord*)obj;
7517 return addr != NULL &&
7518 (!_span.contains(addr) || _bit_map->isMarked(addr));
7519 }
7520
7521 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7522 MemRegion span,
7523 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7524 bool cpc):
7525 _collector(collector),
7526 _span(span),
7527 _mark_stack(mark_stack),
7528 _bit_map(bit_map),
7529 _concurrent_precleaning(cpc) {
7530 assert(!_span.is_empty(), "Empty span could spell trouble");
7531 }
7532
7533
7534 // CMSKeepAliveClosure: the serial version
7535 void CMSKeepAliveClosure::do_oop(oop obj) {
7536 HeapWord* addr = (HeapWord*)obj;
7537 if (_span.contains(addr) &&
7538 !_bit_map->isMarked(addr)) {
7539 _bit_map->mark(addr);
7540 bool simulate_overflow = false;
7541 NOT_PRODUCT(
7542 if (CMSMarkStackOverflowALot &&
7543 _collector->simulate_overflow()) {
7544 // simulate a stack overflow
7545 simulate_overflow = true;
7546 }
7547 )
7548 if (simulate_overflow || !_mark_stack->push(obj)) {
7549 if (_concurrent_precleaning) {
7550 // We dirty the overflown object and let the remark
7551 // phase deal with it.
7552 assert(_collector->overflow_list_is_empty(), "Error");
7553 // In the case of object arrays, we need to dirty all of
7554 // the cards that the object spans. No locking or atomics
7555 // are needed since no one else can be mutating the mod union
7556 // table.
7557 if (obj->is_objArray()) {
7558 size_t sz = obj->size();
7559 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7560 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7561 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7562 _collector->_modUnionTable.mark_range(redirty_range);
7563 } else {
7564 _collector->_modUnionTable.mark(addr);
7565 }
7566 _collector->_ser_kac_preclean_ovflw++;
7567 } else {
7568 _collector->push_on_overflow_list(obj);
7569 _collector->_ser_kac_ovflw++;
7570 }
7571 }
7572 }
7573 }
7574
7575 // CMSParKeepAliveClosure: a parallel version of the above.
7576 // The work queues are private to each closure (thread),
7577 // but (may be) available for stealing by other threads.
7578 void CMSParKeepAliveClosure::do_oop(oop obj) {
7579 HeapWord* addr = (HeapWord*)obj;
7580 if (_span.contains(addr) &&
7581 !_bit_map->isMarked(addr)) {
7582 // In general, during recursive tracing, several threads
7583 // may be concurrently getting here; the first one to
7584 // "tag" it, claims it.
7585 if (_bit_map->par_mark(addr)) {
7586 bool res = _work_queue->push(obj);
7587 assert(res, "Low water mark should be much less than capacity");
7588 // Do a recursive trim in the hope that this will keep
7589 // stack usage lower, but leave some oops for potential stealers
7590 trim_queue(_low_water_mark);
7591 } // Else, another thread got there first
7592 }
7593 }
7594
7595 void CMSParKeepAliveClosure::trim_queue(uint max) {
7596 while (_work_queue->size() > max) {
7597 oop new_oop;
7598 if (_work_queue->pop_local(new_oop)) {
7599 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7600 assert(_bit_map->isMarked((HeapWord*)new_oop),
7601 "no white objects on this stack!");
7602 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7603 // iterate over the oops in this oop, marking and pushing
7604 // the ones in CMS heap (i.e. in _span).
7605 new_oop->oop_iterate(&_mark_and_push);
7606 }
7607 }
7608 }
7609
7610 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7611 CMSCollector* collector,
7612 MemRegion span, CMSBitMap* bit_map,
7613 OopTaskQueue* work_queue):
7614 _collector(collector),
7615 _span(span),
7616 _work_queue(work_queue),
7617 _bit_map(bit_map) { }
7618
7619 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7620 HeapWord* addr = (HeapWord*)obj;
7621 if (_span.contains(addr) &&
7622 !_bit_map->isMarked(addr)) {
7623 if (_bit_map->par_mark(addr)) {
7624 bool simulate_overflow = false;
7625 NOT_PRODUCT(
7626 if (CMSMarkStackOverflowALot &&
7627 _collector->par_simulate_overflow()) {
7628 // simulate a stack overflow
7629 simulate_overflow = true;
7630 }
7631 )
7632 if (simulate_overflow || !_work_queue->push(obj)) {
7633 _collector->par_push_on_overflow_list(obj);
7634 _collector->_par_kac_ovflw++;
7635 }
7636 } // Else another thread got there already
7637 }
7638 }
7639
7640 //////////////////////////////////////////////////////////////////
7641 // CMSExpansionCause /////////////////////////////
7642 //////////////////////////////////////////////////////////////////
7643 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7644 switch (cause) {
7645 case _no_expansion:
7646 return "No expansion";
7647 case _satisfy_free_ratio:
7648 return "Free ratio";
7649 case _satisfy_promotion:
7650 return "Satisfy promotion";
7651 case _satisfy_allocation:
7652 return "allocation";
7653 case _allocate_par_lab:
7654 return "Par LAB";
7655 case _allocate_par_spooling_space:
7656 return "Par Spooling Space";
7657 case _adaptive_size_policy:
7658 return "Ergonomics";
7659 default:
7660 return "unknown";
7661 }
7662 }
7663
7664 void CMSDrainMarkingStackClosure::do_void() {
7665 // the max number to take from overflow list at a time
7666 const size_t num = _mark_stack->capacity()/4;
7667 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7668 "Overflow list should be NULL during concurrent phases");
7669 while (!_mark_stack->isEmpty() ||
7670 // if stack is empty, check the overflow list
7671 _collector->take_from_overflow_list(num, _mark_stack)) {
7672 oop obj = _mark_stack->pop();
7673 HeapWord* addr = (HeapWord*)obj;
7674 assert(_span.contains(addr), "Should be within span");
7675 assert(_bit_map->isMarked(addr), "Should be marked");
7676 assert(oopDesc::is_oop(obj), "Should be an oop");
7677 obj->oop_iterate(_keep_alive);
7678 }
7679 }
7680
7681 void CMSParDrainMarkingStackClosure::do_void() {
7682 // drain queue
7683 trim_queue(0);
7684 }
7685
7686 // Trim our work_queue so its length is below max at return
7687 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7688 while (_work_queue->size() > max) {
7689 oop new_oop;
7690 if (_work_queue->pop_local(new_oop)) {
7691 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7692 assert(_bit_map->isMarked((HeapWord*)new_oop),
7693 "no white objects on this stack!");
7694 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7695 // iterate over the oops in this oop, marking and pushing
7696 // the ones in CMS heap (i.e. in _span).
7697 new_oop->oop_iterate(&_mark_and_push);
7698 }
7699 }
7700 }
7701
7702 ////////////////////////////////////////////////////////////////////
7703 // Support for Marking Stack Overflow list handling and related code
7704 ////////////////////////////////////////////////////////////////////
7705 // Much of the following code is similar in shape and spirit to the
7706 // code used in ParNewGC. We should try and share that code
7707 // as much as possible in the future.
7708
7709 #ifndef PRODUCT
7710 // Debugging support for CMSStackOverflowALot
7711
7712 // It's OK to call this multi-threaded; the worst thing
7713 // that can happen is that we'll get a bunch of closely
7714 // spaced simulated overflows, but that's OK, in fact
7715 // probably good as it would exercise the overflow code
7716 // under contention.
7717 bool CMSCollector::simulate_overflow() {
7718 if (_overflow_counter-- <= 0) { // just being defensive
7719 _overflow_counter = CMSMarkStackOverflowInterval;
7720 return true;
7721 } else {
7722 return false;
7723 }
7724 }
7725
7726 bool CMSCollector::par_simulate_overflow() {
7727 return simulate_overflow();
7728 }
7729 #endif
7730
7731 // Single-threaded
7732 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7733 assert(stack->isEmpty(), "Expected precondition");
7734 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7735 size_t i = num;
7736 oop cur = _overflow_list;
7737 const markOop proto = markOopDesc::prototype();
7738 NOT_PRODUCT(ssize_t n = 0;)
7739 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7740 next = oop(cur->mark_raw());
7741 cur->set_mark_raw(proto); // until proven otherwise
7742 assert(oopDesc::is_oop(cur), "Should be an oop");
7743 bool res = stack->push(cur);
7744 assert(res, "Bit off more than can chew?");
7745 NOT_PRODUCT(n++;)
7746 }
7747 _overflow_list = cur;
7748 #ifndef PRODUCT
7749 assert(_num_par_pushes >= n, "Too many pops?");
7750 _num_par_pushes -=n;
7751 #endif
7752 return !stack->isEmpty();
7753 }
7754
7755 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7756 // (MT-safe) Get a prefix of at most "num" from the list.
7757 // The overflow list is chained through the mark word of
7758 // each object in the list. We fetch the entire list,
7759 // break off a prefix of the right size and return the
7760 // remainder. If other threads try to take objects from
7761 // the overflow list at that time, they will wait for
7762 // some time to see if data becomes available. If (and
7763 // only if) another thread places one or more object(s)
7764 // on the global list before we have returned the suffix
7765 // to the global list, we will walk down our local list
7766 // to find its end and append the global list to
7767 // our suffix before returning it. This suffix walk can
7768 // prove to be expensive (quadratic in the amount of traffic)
7769 // when there are many objects in the overflow list and
7770 // there is much producer-consumer contention on the list.
7771 // *NOTE*: The overflow list manipulation code here and
7772 // in ParNewGeneration:: are very similar in shape,
7773 // except that in the ParNew case we use the old (from/eden)
7774 // copy of the object to thread the list via its klass word.
7775 // Because of the common code, if you make any changes in
7776 // the code below, please check the ParNew version to see if
7777 // similar changes might be needed.
7778 // CR 6797058 has been filed to consolidate the common code.
7779 bool CMSCollector::par_take_from_overflow_list(size_t num,
7780 OopTaskQueue* work_q,
7781 int no_of_gc_threads) {
7782 assert(work_q->size() == 0, "First empty local work queue");
7783 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7784 if (_overflow_list == NULL) {
7785 return false;
7786 }
7787 // Grab the entire list; we'll put back a suffix
7788 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7789 Thread* tid = Thread::current();
7790 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7791 // set to ParallelGCThreads.
7792 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7793 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7794 // If the list is busy, we spin for a short while,
7795 // sleeping between attempts to get the list.
7796 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7797 os::sleep(tid, sleep_time_millis, false);
7798 if (_overflow_list == NULL) {
7799 // Nothing left to take
7800 return false;
7801 } else if (_overflow_list != BUSY) {
7802 // Try and grab the prefix
7803 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7804 }
7805 }
7806 // If the list was found to be empty, or we spun long
7807 // enough, we give up and return empty-handed. If we leave
7808 // the list in the BUSY state below, it must be the case that
7809 // some other thread holds the overflow list and will set it
7810 // to a non-BUSY state in the future.
7811 if (prefix == NULL || prefix == BUSY) {
7812 // Nothing to take or waited long enough
7813 if (prefix == NULL) {
7814 // Write back the NULL in case we overwrote it with BUSY above
7815 // and it is still the same value.
7816 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7817 }
7818 return false;
7819 }
7820 assert(prefix != NULL && prefix != BUSY, "Error");
7821 size_t i = num;
7822 oop cur = prefix;
7823 // Walk down the first "num" objects, unless we reach the end.
7824 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7825 if (cur->mark_raw() == NULL) {
7826 // We have "num" or fewer elements in the list, so there
7827 // is nothing to return to the global list.
7828 // Write back the NULL in lieu of the BUSY we wrote
7829 // above, if it is still the same value.
7830 if (_overflow_list == BUSY) {
7831 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7832 }
7833 } else {
7834 // Chop off the suffix and return it to the global list.
7835 assert(cur->mark_raw() != BUSY, "Error");
7836 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7837 cur->set_mark_raw(NULL); // break off suffix
7838 // It's possible that the list is still in the empty(busy) state
7839 // we left it in a short while ago; in that case we may be
7840 // able to place back the suffix without incurring the cost
7841 // of a walk down the list.
7842 oop observed_overflow_list = _overflow_list;
7843 oop cur_overflow_list = observed_overflow_list;
7844 bool attached = false;
7845 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7846 observed_overflow_list =
7847 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7848 if (cur_overflow_list == observed_overflow_list) {
7849 attached = true;
7850 break;
7851 } else cur_overflow_list = observed_overflow_list;
7852 }
7853 if (!attached) {
7854 // Too bad, someone else sneaked in (at least) an element; we'll need
7855 // to do a splice. Find tail of suffix so we can prepend suffix to global
7856 // list.
7857 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7858 oop suffix_tail = cur;
7859 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7860 "Tautology");
7861 observed_overflow_list = _overflow_list;
7862 do {
7863 cur_overflow_list = observed_overflow_list;
7864 if (cur_overflow_list != BUSY) {
7865 // Do the splice ...
7866 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7867 } else { // cur_overflow_list == BUSY
7868 suffix_tail->set_mark_raw(NULL);
7869 }
7870 // ... and try to place spliced list back on overflow_list ...
7871 observed_overflow_list =
7872 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7873 } while (cur_overflow_list != observed_overflow_list);
7874 // ... until we have succeeded in doing so.
7875 }
7876 }
7877
7878 // Push the prefix elements on work_q
7879 assert(prefix != NULL, "control point invariant");
7880 const markOop proto = markOopDesc::prototype();
7881 oop next;
7882 NOT_PRODUCT(ssize_t n = 0;)
7883 for (cur = prefix; cur != NULL; cur = next) {
7884 next = oop(cur->mark_raw());
7885 cur->set_mark_raw(proto); // until proven otherwise
7886 assert(oopDesc::is_oop(cur), "Should be an oop");
7887 bool res = work_q->push(cur);
7888 assert(res, "Bit off more than we can chew?");
7889 NOT_PRODUCT(n++;)
7890 }
7891 #ifndef PRODUCT
7892 assert(_num_par_pushes >= n, "Too many pops?");
7893 Atomic::sub(n, &_num_par_pushes);
7894 #endif
7895 return true;
7896 }
7897
7898 // Single-threaded
7899 void CMSCollector::push_on_overflow_list(oop p) {
7900 NOT_PRODUCT(_num_par_pushes++;)
7901 assert(oopDesc::is_oop(p), "Not an oop");
7902 preserve_mark_if_necessary(p);
7903 p->set_mark_raw((markOop)_overflow_list);
7904 _overflow_list = p;
7905 }
7906
7907 // Multi-threaded; use CAS to prepend to overflow list
7908 void CMSCollector::par_push_on_overflow_list(oop p) {
7909 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7910 assert(oopDesc::is_oop(p), "Not an oop");
7911 par_preserve_mark_if_necessary(p);
7912 oop observed_overflow_list = _overflow_list;
7913 oop cur_overflow_list;
7914 do {
7915 cur_overflow_list = observed_overflow_list;
7916 if (cur_overflow_list != BUSY) {
7917 p->set_mark_raw(markOop(cur_overflow_list));
7918 } else {
7919 p->set_mark_raw(NULL);
7920 }
7921 observed_overflow_list =
7922 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7923 } while (cur_overflow_list != observed_overflow_list);
7924 }
7925 #undef BUSY
7926
7927 // Single threaded
7928 // General Note on GrowableArray: pushes may silently fail
7929 // because we are (temporarily) out of C-heap for expanding
7930 // the stack. The problem is quite ubiquitous and affects
7931 // a lot of code in the JVM. The prudent thing for GrowableArray
7932 // to do (for now) is to exit with an error. However, that may
7933 // be too draconian in some cases because the caller may be
7934 // able to recover without much harm. For such cases, we
7935 // should probably introduce a "soft_push" method which returns
7936 // an indication of success or failure with the assumption that
7937 // the caller may be able to recover from a failure; code in
7938 // the VM can then be changed, incrementally, to deal with such
7939 // failures where possible, thus, incrementally hardening the VM
7940 // in such low resource situations.
7941 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7942 _preserved_oop_stack.push(p);
7943 _preserved_mark_stack.push(m);
7944 assert(m == p->mark_raw(), "Mark word changed");
7945 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7946 "bijection");
7947 }
7948
7949 // Single threaded
7950 void CMSCollector::preserve_mark_if_necessary(oop p) {
7951 markOop m = p->mark_raw();
7952 if (m->must_be_preserved(p)) {
7953 preserve_mark_work(p, m);
7954 }
7955 }
7956
7957 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
7958 markOop m = p->mark_raw();
7959 if (m->must_be_preserved(p)) {
7960 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
7961 // Even though we read the mark word without holding
7962 // the lock, we are assured that it will not change
7963 // because we "own" this oop, so no other thread can
7964 // be trying to push it on the overflow list; see
7965 // the assertion in preserve_mark_work() that checks
7966 // that m == p->mark_raw().
7967 preserve_mark_work(p, m);
7968 }
7969 }
7970
7971 // We should be able to do this multi-threaded,
7972 // a chunk of stack being a task (this is
7973 // correct because each oop only ever appears
7974 // once in the overflow list. However, it's
7975 // not very easy to completely overlap this with
7976 // other operations, so will generally not be done
7977 // until all work's been completed. Because we
7978 // expect the preserved oop stack (set) to be small,
7979 // it's probably fine to do this single-threaded.
7980 // We can explore cleverer concurrent/overlapped/parallel
7981 // processing of preserved marks if we feel the
7982 // need for this in the future. Stack overflow should
7983 // be so rare in practice and, when it happens, its
7984 // effect on performance so great that this will
7985 // likely just be in the noise anyway.
7986 void CMSCollector::restore_preserved_marks_if_any() {
7987 assert(SafepointSynchronize::is_at_safepoint(),
7988 "world should be stopped");
7989 assert(Thread::current()->is_ConcurrentGC_thread() ||
7990 Thread::current()->is_VM_thread(),
7991 "should be single-threaded");
7992 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
7993 "bijection");
7994
7995 while (!_preserved_oop_stack.is_empty()) {
7996 oop p = _preserved_oop_stack.pop();
7997 assert(oopDesc::is_oop(p), "Should be an oop");
7998 assert(_span.contains(p), "oop should be in _span");
7999 assert(p->mark_raw() == markOopDesc::prototype(),
8000 "Set when taken from overflow list");
8001 markOop m = _preserved_mark_stack.pop();
8002 p->set_mark_raw(m);
8003 }
8004 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8005 "stacks were cleared above");
8006 }
8007
8008 #ifndef PRODUCT
8009 bool CMSCollector::no_preserved_marks() const {
8010 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8011 }
8012 #endif
8013
8014 // Transfer some number of overflown objects to usual marking
8015 // stack. Return true if some objects were transferred.
8016 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8017 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8018 (size_t)ParGCDesiredObjsFromOverflowList);
8019
8020 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8021 assert(_collector->overflow_list_is_empty() || res,
8022 "If list is not empty, we should have taken something");
8023 assert(!res || !_mark_stack->isEmpty(),
8024 "If we took something, it should now be on our stack");
8025 return res;
8026 }
8027
8028 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8029 size_t res = _sp->block_size_no_stall(addr, _collector);
8030 if (_sp->block_is_obj(addr)) {
8031 if (_live_bit_map->isMarked(addr)) {
8032 // It can't have been dead in a previous cycle
8033 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8034 } else {
8035 _dead_bit_map->mark(addr); // mark the dead object
8036 }
8037 }
8038 // Could be 0, if the block size could not be computed without stalling.
8039 return res;
8040 }
8041
8042 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8043 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8044 switch (phase) {
8045 case CMSCollector::InitialMarking:
8046 initialize(manager /* GC manager */ ,
8047 cause /* cause of the GC */,
8048 true /* allMemoryPoolsAffected */,
8049 true /* recordGCBeginTime */,
8050 true /* recordPreGCUsage */,
8051 false /* recordPeakUsage */,
8052 false /* recordPostGCusage */,
8053 true /* recordAccumulatedGCTime */,
8054 false /* recordGCEndTime */,
8055 false /* countCollection */ );
8056 break;
8057
8058 case CMSCollector::FinalMarking:
8059 initialize(manager /* GC manager */ ,
8060 cause /* cause of the GC */,
8061 true /* allMemoryPoolsAffected */,
8062 false /* recordGCBeginTime */,
8063 false /* recordPreGCUsage */,
8064 false /* recordPeakUsage */,
8065 false /* recordPostGCusage */,
8066 true /* recordAccumulatedGCTime */,
8067 false /* recordGCEndTime */,
8068 false /* countCollection */ );
8069 break;
8070
8071 case CMSCollector::Sweeping:
8072 initialize(manager /* GC manager */ ,
8073 cause /* cause of the GC */,
8074 true /* allMemoryPoolsAffected */,
8075 false /* recordGCBeginTime */,
8076 false /* recordPreGCUsage */,
8077 true /* recordPeakUsage */,
8078 true /* recordPostGCusage */,
8079 false /* recordAccumulatedGCTime */,
8080 true /* recordGCEndTime */,
8081 true /* countCollection */ );
8082 break;
8083
8084 default:
8085 ShouldNotReachHere();
8086 }
8087 }