1 /*
2 * Copyright (c) 2001, 2019, 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/cmsVMOperations.hpp"
36 #include "gc/cms/compactibleFreeListSpace.hpp"
37 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
38 #include "gc/cms/concurrentMarkSweepThread.hpp"
39 #include "gc/cms/parNewGeneration.hpp"
40 #include "gc/cms/promotionInfo.inline.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/owstTaskTerminator.hpp"
59 #include "gc/shared/referencePolicy.hpp"
60 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
61 #include "gc/shared/space.inline.hpp"
62 #include "gc/shared/strongRootsScope.hpp"
63 #include "gc/shared/taskqueue.inline.hpp"
64 #include "gc/shared/weakProcessor.hpp"
65 #include "gc/shared/workerPolicy.hpp"
66 #include "logging/log.hpp"
67 #include "logging/logStream.hpp"
68 #include "memory/allocation.hpp"
69 #include "memory/binaryTreeDictionary.inline.hpp"
70 #include "memory/iterator.inline.hpp"
71 #include "memory/padded.hpp"
72 #include "memory/resourceArea.hpp"
73 #include "oops/access.inline.hpp"
74 #include "oops/oop.inline.hpp"
75 #include "prims/jvmtiExport.hpp"
76 #include "runtime/atomic.hpp"
77 #include "runtime/flags/flagSetting.hpp"
78 #include "runtime/globals_extension.hpp"
79 #include "runtime/handles.inline.hpp"
80 #include "runtime/java.hpp"
81 #include "runtime/orderAccess.hpp"
82 #include "runtime/timer.hpp"
83 #include "runtime/vmThread.hpp"
84 #include "services/memoryService.hpp"
85 #include "services/runtimeService.hpp"
86 #include "utilities/align.hpp"
87 #include "utilities/stack.inline.hpp"
88
89 // statics
90 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
91 bool CMSCollector::_full_gc_requested = false;
92 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
93
94 //////////////////////////////////////////////////////////////////
95 // In support of CMS/VM thread synchronization
96 //////////////////////////////////////////////////////////////////
97 // We split use of the CGC_lock into 2 "levels".
98 // The low-level locking is of the usual CGC_lock monitor. We introduce
99 // a higher level "token" (hereafter "CMS token") built on top of the
100 // low level monitor (hereafter "CGC lock").
101 // The token-passing protocol gives priority to the VM thread. The
102 // CMS-lock doesn't provide any fairness guarantees, but clients
103 // should ensure that it is only held for very short, bounded
104 // durations.
105 //
106 // When either of the CMS thread or the VM thread is involved in
107 // collection operations during which it does not want the other
108 // thread to interfere, it obtains the CMS token.
109 //
110 // If either thread tries to get the token while the other has
111 // it, that thread waits. However, if the VM thread and CMS thread
112 // both want the token, then the VM thread gets priority while the
113 // CMS thread waits. This ensures, for instance, that the "concurrent"
114 // phases of the CMS thread's work do not block out the VM thread
115 // for long periods of time as the CMS thread continues to hog
116 // the token. (See bug 4616232).
117 //
118 // The baton-passing functions are, however, controlled by the
119 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
120 // and here the low-level CMS lock, not the high level token,
121 // ensures mutual exclusion.
122 //
123 // Two important conditions that we have to satisfy:
124 // 1. if a thread does a low-level wait on the CMS lock, then it
125 // relinquishes the CMS token if it were holding that token
126 // when it acquired the low-level CMS lock.
127 // 2. any low-level notifications on the low-level lock
128 // should only be sent when a thread has relinquished the token.
129 //
130 // In the absence of either property, we'd have potential deadlock.
131 //
132 // We protect each of the CMS (concurrent and sequential) phases
133 // with the CMS _token_, not the CMS _lock_.
134 //
135 // The only code protected by CMS lock is the token acquisition code
136 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
137 // baton-passing code.
138 //
139 // Unfortunately, i couldn't come up with a good abstraction to factor and
140 // hide the naked CGC_lock manipulation in the baton-passing code
141 // further below. That's something we should try to do. Also, the proof
142 // of correctness of this 2-level locking scheme is far from obvious,
143 // and potentially quite slippery. We have an uneasy suspicion, for instance,
144 // that there may be a theoretical possibility of delay/starvation in the
145 // low-level lock/wait/notify scheme used for the baton-passing because of
146 // potential interference with the priority scheme embodied in the
147 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
148 // invocation further below and marked with "XXX 20011219YSR".
149 // Indeed, as we note elsewhere, this may become yet more slippery
150 // in the presence of multiple CMS and/or multiple VM threads. XXX
151
152 class CMSTokenSync: public StackObj {
153 private:
154 bool _is_cms_thread;
155 public:
156 CMSTokenSync(bool is_cms_thread):
157 _is_cms_thread(is_cms_thread) {
158 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
159 "Incorrect argument to constructor");
160 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
161 }
162
163 ~CMSTokenSync() {
164 assert(_is_cms_thread ?
165 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
166 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
167 "Incorrect state");
168 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
169 }
170 };
171
172 // Convenience class that does a CMSTokenSync, and then acquires
173 // upto three locks.
174 class CMSTokenSyncWithLocks: public CMSTokenSync {
175 private:
176 // Note: locks are acquired in textual declaration order
177 // and released in the opposite order
178 MutexLockerEx _locker1, _locker2, _locker3;
179 public:
180 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
181 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
182 CMSTokenSync(is_cms_thread),
183 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
184 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
185 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
186 { }
187 };
188
189
190 //////////////////////////////////////////////////////////////////
191 // Concurrent Mark-Sweep Generation /////////////////////////////
192 //////////////////////////////////////////////////////////////////
193
194 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
195
196 // This struct contains per-thread things necessary to support parallel
197 // young-gen collection.
198 class CMSParGCThreadState: public CHeapObj<mtGC> {
199 public:
200 CompactibleFreeListSpaceLAB lab;
201 PromotionInfo promo;
202
203 // Constructor.
204 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
205 promo.setSpace(cfls);
206 }
207 };
208
209 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
210 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
211 CardGeneration(rs, initial_byte_size, ct),
212 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
213 _did_compact(false)
214 {
215 HeapWord* bottom = (HeapWord*) _virtual_space.low();
216 HeapWord* end = (HeapWord*) _virtual_space.high();
217
218 _direct_allocated_words = 0;
219 NOT_PRODUCT(
220 _numObjectsPromoted = 0;
221 _numWordsPromoted = 0;
222 _numObjectsAllocated = 0;
223 _numWordsAllocated = 0;
224 )
225
226 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
227 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
228 _cmsSpace->_old_gen = this;
229
230 _gc_stats = new CMSGCStats();
231
232 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
233 // offsets match. The ability to tell free chunks from objects
234 // depends on this property.
235 debug_only(
236 FreeChunk* junk = NULL;
237 assert(UseCompressedClassPointers ||
238 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
239 "Offset of FreeChunk::_prev within FreeChunk must match"
240 " that of OopDesc::_klass within OopDesc");
241 )
242
243 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
244 for (uint i = 0; i < ParallelGCThreads; i++) {
245 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
246 }
247
248 _incremental_collection_failed = false;
249 // The "dilatation_factor" is the expansion that can occur on
250 // account of the fact that the minimum object size in the CMS
251 // generation may be larger than that in, say, a contiguous young
252 // generation.
253 // Ideally, in the calculation below, we'd compute the dilatation
254 // factor as: MinChunkSize/(promoting_gen's min object size)
255 // Since we do not have such a general query interface for the
256 // promoting generation, we'll instead just use the minimum
257 // object size (which today is a header's worth of space);
258 // note that all arithmetic is in units of HeapWords.
259 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
260 assert(_dilatation_factor >= 1.0, "from previous assert");
261 }
262
263
264 // The field "_initiating_occupancy" represents the occupancy percentage
265 // at which we trigger a new collection cycle. Unless explicitly specified
266 // via CMSInitiatingOccupancyFraction (argument "io" below), it
267 // is calculated by:
268 //
269 // Let "f" be MinHeapFreeRatio in
270 //
271 // _initiating_occupancy = 100-f +
272 // f * (CMSTriggerRatio/100)
273 // where CMSTriggerRatio is the argument "tr" below.
274 //
275 // That is, if we assume the heap is at its desired maximum occupancy at the
276 // end of a collection, we let CMSTriggerRatio of the (purported) free
277 // space be allocated before initiating a new collection cycle.
278 //
279 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
280 assert(io <= 100 && tr <= 100, "Check the arguments");
281 if (io >= 0) {
282 _initiating_occupancy = (double)io / 100.0;
283 } else {
284 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
285 (double)(tr * MinHeapFreeRatio) / 100.0)
286 / 100.0;
287 }
288 }
289
290 void ConcurrentMarkSweepGeneration::ref_processor_init() {
291 assert(collector() != NULL, "no collector");
292 collector()->ref_processor_init();
293 }
294
295 void CMSCollector::ref_processor_init() {
296 if (_ref_processor == NULL) {
297 // Allocate and initialize a reference processor
298 _ref_processor =
299 new ReferenceProcessor(&_span_based_discoverer,
300 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
301 ParallelGCThreads, // mt processing degree
302 _cmsGen->refs_discovery_is_mt(), // mt discovery
303 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
304 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
305 &_is_alive_closure, // closure for liveness info
306 false); // disable adjusting number of processing threads
307 // Initialize the _ref_processor field of CMSGen
308 _cmsGen->set_ref_processor(_ref_processor);
309
310 }
311 }
312
313 AdaptiveSizePolicy* CMSCollector::size_policy() {
314 return CMSHeap::heap()->size_policy();
315 }
316
317 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
318
319 const char* gen_name = "old";
320 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
321 // Generation Counters - generation 1, 1 subspace
322 _gen_counters = new GenerationCounters(gen_name, 1, 1,
323 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
324
325 _space_counters = new GSpaceCounters(gen_name, 0,
326 _virtual_space.reserved_size(),
327 this, _gen_counters);
328 }
329
330 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
331 _cms_gen(cms_gen)
332 {
333 assert(alpha <= 100, "bad value");
334 _saved_alpha = alpha;
335
336 // Initialize the alphas to the bootstrap value of 100.
337 _gc0_alpha = _cms_alpha = 100;
338
339 _cms_begin_time.update();
340 _cms_end_time.update();
341
342 _gc0_duration = 0.0;
343 _gc0_period = 0.0;
344 _gc0_promoted = 0;
345
346 _cms_duration = 0.0;
347 _cms_period = 0.0;
348 _cms_allocated = 0;
349
350 _cms_used_at_gc0_begin = 0;
351 _cms_used_at_gc0_end = 0;
352 _allow_duty_cycle_reduction = false;
353 _valid_bits = 0;
354 }
355
356 double CMSStats::cms_free_adjustment_factor(size_t free) const {
357 // TBD: CR 6909490
358 return 1.0;
359 }
360
361 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
362 }
363
364 // If promotion failure handling is on use
365 // the padded average size of the promotion for each
366 // young generation collection.
367 double CMSStats::time_until_cms_gen_full() const {
368 size_t cms_free = _cms_gen->cmsSpace()->free();
369 CMSHeap* heap = CMSHeap::heap();
370 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
371 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
372 if (cms_free > expected_promotion) {
373 // Start a cms collection if there isn't enough space to promote
374 // for the next young collection. Use the padded average as
375 // a safety factor.
376 cms_free -= expected_promotion;
377
378 // Adjust by the safety factor.
379 double cms_free_dbl = (double)cms_free;
380 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
381 // Apply a further correction factor which tries to adjust
382 // for recent occurance of concurrent mode failures.
383 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
384 cms_free_dbl = cms_free_dbl * cms_adjustment;
385
386 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
387 cms_free, expected_promotion);
388 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
389 // Add 1 in case the consumption rate goes to zero.
390 return cms_free_dbl / (cms_consumption_rate() + 1.0);
391 }
392 return 0.0;
393 }
394
395 // Compare the duration of the cms collection to the
396 // time remaining before the cms generation is empty.
397 // Note that the time from the start of the cms collection
398 // to the start of the cms sweep (less than the total
399 // duration of the cms collection) can be used. This
400 // has been tried and some applications experienced
401 // promotion failures early in execution. This was
402 // possibly because the averages were not accurate
403 // enough at the beginning.
404 double CMSStats::time_until_cms_start() const {
405 // We add "gc0_period" to the "work" calculation
406 // below because this query is done (mostly) at the
407 // end of a scavenge, so we need to conservatively
408 // account for that much possible delay
409 // in the query so as to avoid concurrent mode failures
410 // due to starting the collection just a wee bit too
411 // late.
412 double work = cms_duration() + gc0_period();
413 double deadline = time_until_cms_gen_full();
414 // If a concurrent mode failure occurred recently, we want to be
415 // more conservative and halve our expected time_until_cms_gen_full()
416 if (work > deadline) {
417 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
418 cms_duration(), gc0_period(), time_until_cms_gen_full());
419 return 0.0;
420 }
421 return work - deadline;
422 }
423
424 #ifndef PRODUCT
425 void CMSStats::print_on(outputStream *st) const {
426 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
427 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
428 gc0_duration(), gc0_period(), gc0_promoted());
429 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
430 cms_duration(), cms_period(), cms_allocated());
431 st->print(",cms_since_beg=%g,cms_since_end=%g",
432 cms_time_since_begin(), cms_time_since_end());
433 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
434 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
435
436 if (valid()) {
437 st->print(",promo_rate=%g,cms_alloc_rate=%g",
438 promotion_rate(), cms_allocation_rate());
439 st->print(",cms_consumption_rate=%g,time_until_full=%g",
440 cms_consumption_rate(), time_until_cms_gen_full());
441 }
442 st->cr();
443 }
444 #endif // #ifndef PRODUCT
445
446 CMSCollector::CollectorState CMSCollector::_collectorState =
447 CMSCollector::Idling;
448 bool CMSCollector::_foregroundGCIsActive = false;
449 bool CMSCollector::_foregroundGCShouldWait = false;
450
451 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
452 CardTableRS* ct,
453 ConcurrentMarkSweepPolicy* cp):
454 _overflow_list(NULL),
455 _conc_workers(NULL), // may be set later
456 _completed_initialization(false),
457 _collection_count_start(0),
458 _should_unload_classes(CMSClassUnloadingEnabled),
459 _concurrent_cycles_since_last_unload(0),
460 _roots_scanning_options(GenCollectedHeap::SO_None),
461 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
462 _verifying(false),
463 _collector_policy(cp),
464 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
465 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
466 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
467 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
468 _cms_start_registered(false),
469 _cmsGen(cmsGen),
470 // Adjust span to cover old (cms) gen
471 _span(cmsGen->reserved()),
472 _ct(ct),
473 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
474 _modUnionTable((CardTable::card_shift - LogHeapWordSize),
475 -1 /* lock-free */, "No_lock" /* dummy */),
476 _restart_addr(NULL),
477 _ser_pmc_preclean_ovflw(0),
478 _ser_pmc_remark_ovflw(0),
479 _par_pmc_remark_ovflw(0),
480 _ser_kac_preclean_ovflw(0),
481 _ser_kac_ovflw(0),
482 _par_kac_ovflw(0),
483 #ifndef PRODUCT
484 _num_par_pushes(0),
485 #endif
486 _span_based_discoverer(_span),
487 _ref_processor(NULL), // will be set later
488 // Construct the is_alive_closure with _span & markBitMap
489 _is_alive_closure(_span, &_markBitMap),
490 _modUnionClosurePar(&_modUnionTable),
491 _between_prologue_and_epilogue(false),
492 _abort_preclean(false),
493 _start_sampling(false),
494 _stats(cmsGen),
495 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
496 //verify that this lock should be acquired with safepoint check.
497 Monitor::_safepoint_check_sometimes)),
498 _eden_chunk_array(NULL), // may be set in ctor body
499 _eden_chunk_index(0), // -- ditto --
500 _eden_chunk_capacity(0), // -- ditto --
501 _survivor_chunk_array(NULL), // -- ditto --
502 _survivor_chunk_index(0), // -- ditto --
503 _survivor_chunk_capacity(0), // -- ditto --
504 _survivor_plab_array(NULL) // -- ditto --
505 {
506 // Now expand the span and allocate the collection support structures
507 // (MUT, marking bit map etc.) to cover both generations subject to
508 // collection.
509
510 // For use by dirty card to oop closures.
511 _cmsGen->cmsSpace()->set_collector(this);
512
513 // Allocate MUT and marking bit map
514 {
515 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
516 if (!_markBitMap.allocate(_span)) {
517 log_warning(gc)("Failed to allocate CMS Bit Map");
518 return;
519 }
520 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
521 }
522 {
523 _modUnionTable.allocate(_span);
524 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
525 }
526
527 if (!_markStack.allocate(MarkStackSize)) {
528 log_warning(gc)("Failed to allocate CMS Marking Stack");
529 return;
530 }
531
532 // Support for multi-threaded concurrent phases
533 if (CMSConcurrentMTEnabled) {
534 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
535 // just for now
536 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
537 }
538 if (ConcGCThreads > 1) {
539 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
540 ConcGCThreads, true);
541 if (_conc_workers == NULL) {
542 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
543 CMSConcurrentMTEnabled = false;
544 } else {
545 _conc_workers->initialize_workers();
546 }
547 } else {
548 CMSConcurrentMTEnabled = false;
549 }
550 }
551 if (!CMSConcurrentMTEnabled) {
552 ConcGCThreads = 0;
553 } else {
554 // Turn off CMSCleanOnEnter optimization temporarily for
555 // the MT case where it's not fixed yet; see 6178663.
556 CMSCleanOnEnter = false;
557 }
558 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
559 "Inconsistency");
560 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
561 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
562
563 // Parallel task queues; these are shared for the
564 // concurrent and stop-world phases of CMS, but
565 // are not shared with parallel scavenge (ParNew).
566 {
567 uint i;
568 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
569
570 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
571 || ParallelRefProcEnabled)
572 && num_queues > 0) {
573 _task_queues = new OopTaskQueueSet(num_queues);
574 if (_task_queues == NULL) {
575 log_warning(gc)("task_queues allocation failure.");
576 return;
577 }
578 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
579 for (i = 0; i < num_queues; i++) {
580 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
581 if (q == NULL) {
582 log_warning(gc)("work_queue allocation failure.");
583 return;
584 }
585 _task_queues->register_queue(i, q);
586 }
587 for (i = 0; i < num_queues; i++) {
588 _task_queues->queue(i)->initialize();
589 }
590 }
591 }
592
593 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
594
595 // Clip CMSBootstrapOccupancy between 0 and 100.
596 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
597
598 // Now tell CMS generations the identity of their collector
599 ConcurrentMarkSweepGeneration::set_collector(this);
600
601 // Create & start a CMS thread for this CMS collector
602 _cmsThread = ConcurrentMarkSweepThread::start(this);
603 assert(cmsThread() != NULL, "CMS Thread should have been created");
604 assert(cmsThread()->collector() == this,
605 "CMS Thread should refer to this gen");
606 assert(CGC_lock != NULL, "Where's the CGC_lock?");
607
608 // Support for parallelizing young gen rescan
609 CMSHeap* heap = CMSHeap::heap();
610 _young_gen = heap->young_gen();
611 if (heap->supports_inline_contig_alloc()) {
612 _top_addr = heap->top_addr();
613 _end_addr = heap->end_addr();
614 assert(_young_gen != NULL, "no _young_gen");
615 _eden_chunk_index = 0;
616 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
617 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
618 }
619
620 // Support for parallelizing survivor space rescan
621 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
622 const size_t max_plab_samples =
623 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
624
625 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
626 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
627 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
628 _survivor_chunk_capacity = max_plab_samples;
629 for (uint i = 0; i < ParallelGCThreads; i++) {
630 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
631 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
632 assert(cur->end() == 0, "Should be 0");
633 assert(cur->array() == vec, "Should be vec");
634 assert(cur->capacity() == max_plab_samples, "Error");
635 }
636 }
637
638 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
639 _gc_counters = new CollectorCounters("CMS", 1);
640 _cgc_counters = new CollectorCounters("CMS stop-the-world phases", 2);
641 _completed_initialization = true;
642 _inter_sweep_timer.start(); // start of time
643 }
644
645 const char* ConcurrentMarkSweepGeneration::name() const {
646 return "concurrent mark-sweep generation";
647 }
648 void ConcurrentMarkSweepGeneration::update_counters() {
649 if (UsePerfData) {
650 _space_counters->update_all();
651 _gen_counters->update_all();
652 }
653 }
654
655 // this is an optimized version of update_counters(). it takes the
656 // used value as a parameter rather than computing it.
657 //
658 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
659 if (UsePerfData) {
660 _space_counters->update_used(used);
661 _space_counters->update_capacity();
662 _gen_counters->update_all();
663 }
664 }
665
666 void ConcurrentMarkSweepGeneration::print() const {
667 Generation::print();
668 cmsSpace()->print();
669 }
670
671 #ifndef PRODUCT
672 void ConcurrentMarkSweepGeneration::print_statistics() {
673 cmsSpace()->printFLCensus(0);
674 }
675 #endif
676
677 size_t
678 ConcurrentMarkSweepGeneration::contiguous_available() const {
679 // dld proposes an improvement in precision here. If the committed
680 // part of the space ends in a free block we should add that to
681 // uncommitted size in the calculation below. Will make this
682 // change later, staying with the approximation below for the
683 // time being. -- ysr.
684 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
685 }
686
687 size_t
688 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
689 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
690 }
691
692 size_t ConcurrentMarkSweepGeneration::max_available() const {
693 return free() + _virtual_space.uncommitted_size();
694 }
695
696 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
697 size_t available = max_available();
698 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
699 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
700 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
701 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
702 return res;
703 }
704
705 // At a promotion failure dump information on block layout in heap
706 // (cms old generation).
707 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
708 Log(gc, promotion) log;
709 if (log.is_trace()) {
710 LogStream ls(log.trace());
711 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
712 }
713 }
714
715 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
716 // Clear the promotion information. These pointers can be adjusted
717 // along with all the other pointers into the heap but
718 // compaction is expected to be a rare event with
719 // a heap using cms so don't do it without seeing the need.
720 for (uint i = 0; i < ParallelGCThreads; i++) {
721 _par_gc_thread_states[i]->promo.reset();
722 }
723 }
724
725 void ConcurrentMarkSweepGeneration::compute_new_size() {
726 assert_locked_or_safepoint(Heap_lock);
727
728 // If incremental collection failed, we just want to expand
729 // to the limit.
730 if (incremental_collection_failed()) {
731 clear_incremental_collection_failed();
732 grow_to_reserved();
733 return;
734 }
735
736 // The heap has been compacted but not reset yet.
737 // Any metric such as free() or used() will be incorrect.
738
739 CardGeneration::compute_new_size();
740
741 // Reset again after a possible resizing
742 if (did_compact()) {
743 cmsSpace()->reset_after_compaction();
744 }
745 }
746
747 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
748 assert_locked_or_safepoint(Heap_lock);
749
750 // If incremental collection failed, we just want to expand
751 // to the limit.
752 if (incremental_collection_failed()) {
753 clear_incremental_collection_failed();
754 grow_to_reserved();
755 return;
756 }
757
758 double free_percentage = ((double) free()) / capacity();
759 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
760 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
761
762 // compute expansion delta needed for reaching desired free percentage
763 if (free_percentage < desired_free_percentage) {
764 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
765 assert(desired_capacity >= capacity(), "invalid expansion size");
766 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
767 Log(gc) log;
768 if (log.is_trace()) {
769 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
770 log.trace("From compute_new_size: ");
771 log.trace(" Free fraction %f", free_percentage);
772 log.trace(" Desired free fraction %f", desired_free_percentage);
773 log.trace(" Maximum free fraction %f", maximum_free_percentage);
774 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
775 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
776 CMSHeap* heap = CMSHeap::heap();
777 size_t young_size = heap->young_gen()->capacity();
778 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
779 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
780 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
781 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
782 }
783 // safe if expansion fails
784 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
785 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
786 } else {
787 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
788 assert(desired_capacity <= capacity(), "invalid expansion size");
789 size_t shrink_bytes = capacity() - desired_capacity;
790 // Don't shrink unless the delta is greater than the minimum shrink we want
791 if (shrink_bytes >= MinHeapDeltaBytes) {
792 shrink_free_list_by(shrink_bytes);
793 }
794 }
795 }
796
797 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
798 return cmsSpace()->freelistLock();
799 }
800
801 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
802 CMSSynchronousYieldRequest yr;
803 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
804 return have_lock_and_allocate(size, tlab);
805 }
806
807 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
808 bool tlab /* ignored */) {
809 assert_lock_strong(freelistLock());
810 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
811 HeapWord* res = cmsSpace()->allocate(adjustedSize);
812 // Allocate the object live (grey) if the background collector has
813 // started marking. This is necessary because the marker may
814 // have passed this address and consequently this object will
815 // not otherwise be greyed and would be incorrectly swept up.
816 // Note that if this object contains references, the writing
817 // of those references will dirty the card containing this object
818 // allowing the object to be blackened (and its references scanned)
819 // either during a preclean phase or at the final checkpoint.
820 if (res != NULL) {
821 // We may block here with an uninitialized object with
822 // its mark-bit or P-bits not yet set. Such objects need
823 // to be safely navigable by block_start().
824 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
825 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
826 collector()->direct_allocated(res, adjustedSize);
827 _direct_allocated_words += adjustedSize;
828 // allocation counters
829 NOT_PRODUCT(
830 _numObjectsAllocated++;
831 _numWordsAllocated += (int)adjustedSize;
832 )
833 }
834 return res;
835 }
836
837 // In the case of direct allocation by mutators in a generation that
838 // is being concurrently collected, the object must be allocated
839 // live (grey) if the background collector has started marking.
840 // This is necessary because the marker may
841 // have passed this address and consequently this object will
842 // not otherwise be greyed and would be incorrectly swept up.
843 // Note that if this object contains references, the writing
844 // of those references will dirty the card containing this object
845 // allowing the object to be blackened (and its references scanned)
846 // either during a preclean phase or at the final checkpoint.
847 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
848 assert(_markBitMap.covers(start, size), "Out of bounds");
849 if (_collectorState >= Marking) {
850 MutexLockerEx y(_markBitMap.lock(),
851 Mutex::_no_safepoint_check_flag);
852 // [see comments preceding SweepClosure::do_blk() below for details]
853 //
854 // Can the P-bits be deleted now? JJJ
855 //
856 // 1. need to mark the object as live so it isn't collected
857 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
858 // 3. need to mark the end of the object so marking, precleaning or sweeping
859 // can skip over uninitialized or unparsable objects. An allocated
860 // object is considered uninitialized for our purposes as long as
861 // its klass word is NULL. All old gen objects are parsable
862 // as soon as they are initialized.)
863 _markBitMap.mark(start); // object is live
864 _markBitMap.mark(start + 1); // object is potentially uninitialized?
865 _markBitMap.mark(start + size - 1);
866 // mark end of object
867 }
868 // check that oop looks uninitialized
869 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
870 }
871
872 void CMSCollector::promoted(bool par, HeapWord* start,
873 bool is_obj_array, size_t obj_size) {
874 assert(_markBitMap.covers(start), "Out of bounds");
875 // See comment in direct_allocated() about when objects should
876 // be allocated live.
877 if (_collectorState >= Marking) {
878 // we already hold the marking bit map lock, taken in
879 // the prologue
880 if (par) {
881 _markBitMap.par_mark(start);
882 } else {
883 _markBitMap.mark(start);
884 }
885 // We don't need to mark the object as uninitialized (as
886 // in direct_allocated above) because this is being done with the
887 // world stopped and the object will be initialized by the
888 // time the marking, precleaning or sweeping get to look at it.
889 // But see the code for copying objects into the CMS generation,
890 // where we need to ensure that concurrent readers of the
891 // block offset table are able to safely navigate a block that
892 // is in flux from being free to being allocated (and in
893 // transition while being copied into) and subsequently
894 // becoming a bona-fide object when the copy/promotion is complete.
895 assert(SafepointSynchronize::is_at_safepoint(),
896 "expect promotion only at safepoints");
897
898 if (_collectorState < Sweeping) {
899 // Mark the appropriate cards in the modUnionTable, so that
900 // this object gets scanned before the sweep. If this is
901 // not done, CMS generation references in the object might
902 // not get marked.
903 // For the case of arrays, which are otherwise precisely
904 // marked, we need to dirty the entire array, not just its head.
905 if (is_obj_array) {
906 // The [par_]mark_range() method expects mr.end() below to
907 // be aligned to the granularity of a bit's representation
908 // in the heap. In the case of the MUT below, that's a
909 // card size.
910 MemRegion mr(start,
911 align_up(start + obj_size,
912 CardTable::card_size /* bytes */));
913 if (par) {
914 _modUnionTable.par_mark_range(mr);
915 } else {
916 _modUnionTable.mark_range(mr);
917 }
918 } else { // not an obj array; we can just mark the head
919 if (par) {
920 _modUnionTable.par_mark(start);
921 } else {
922 _modUnionTable.mark(start);
923 }
924 }
925 }
926 }
927 }
928
929 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
930 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
931 // allocate, copy and if necessary update promoinfo --
932 // delegate to underlying space.
933 assert_lock_strong(freelistLock());
934
935 #ifndef PRODUCT
936 if (CMSHeap::heap()->promotion_should_fail()) {
937 return NULL;
938 }
939 #endif // #ifndef PRODUCT
940
941 oop res = _cmsSpace->promote(obj, obj_size);
942 if (res == NULL) {
943 // expand and retry
944 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
945 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
946 // Since this is the old generation, we don't try to promote
947 // into a more senior generation.
948 res = _cmsSpace->promote(obj, obj_size);
949 }
950 if (res != NULL) {
951 // See comment in allocate() about when objects should
952 // be allocated live.
953 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
954 collector()->promoted(false, // Not parallel
955 (HeapWord*)res, obj->is_objArray(), obj_size);
956 // promotion counters
957 NOT_PRODUCT(
958 _numObjectsPromoted++;
959 _numWordsPromoted +=
960 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
961 )
962 }
963 return res;
964 }
965
966
967 // IMPORTANT: Notes on object size recognition in CMS.
968 // ---------------------------------------------------
969 // A block of storage in the CMS generation is always in
970 // one of three states. A free block (FREE), an allocated
971 // object (OBJECT) whose size() method reports the correct size,
972 // and an intermediate state (TRANSIENT) in which its size cannot
973 // be accurately determined.
974 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
975 // -----------------------------------------------------
976 // FREE: klass_word & 1 == 1; mark_word holds block size
977 //
978 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
979 // obj->size() computes correct size
980 //
981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
982 //
983 // STATE IDENTIFICATION: (64 bit+COOPS)
984 // ------------------------------------
985 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
986 //
987 // OBJECT: klass_word installed; klass_word != 0;
988 // obj->size() computes correct size
989 //
990 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
991 //
992 //
993 // STATE TRANSITION DIAGRAM
994 //
995 // mut / parnew mut / parnew
996 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
997 // ^ |
998 // |------------------------ DEAD <------------------------------------|
999 // sweep mut
1000 //
1001 // While a block is in TRANSIENT state its size cannot be determined
1002 // so readers will either need to come back later or stall until
1003 // the size can be determined. Note that for the case of direct
1004 // allocation, P-bits, when available, may be used to determine the
1005 // size of an object that may not yet have been initialized.
1006
1007 // Things to support parallel young-gen collection.
1008 oop
1009 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1010 oop old, markOop m,
1011 size_t word_sz) {
1012 #ifndef PRODUCT
1013 if (CMSHeap::heap()->promotion_should_fail()) {
1014 return NULL;
1015 }
1016 #endif // #ifndef PRODUCT
1017
1018 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1019 PromotionInfo* promoInfo = &ps->promo;
1020 // if we are tracking promotions, then first ensure space for
1021 // promotion (including spooling space for saving header if necessary).
1022 // then allocate and copy, then track promoted info if needed.
1023 // When tracking (see PromotionInfo::track()), the mark word may
1024 // be displaced and in this case restoration of the mark word
1025 // occurs in the (oop_since_save_marks_)iterate phase.
1026 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1027 // Out of space for allocating spooling buffers;
1028 // try expanding and allocating spooling buffers.
1029 if (!expand_and_ensure_spooling_space(promoInfo)) {
1030 return NULL;
1031 }
1032 }
1033 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1034 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1035 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1036 if (obj_ptr == NULL) {
1037 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1038 if (obj_ptr == NULL) {
1039 return NULL;
1040 }
1041 }
1042 oop obj = oop(obj_ptr);
1043 OrderAccess::storestore();
1044 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1045 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1046 // IMPORTANT: See note on object initialization for CMS above.
1047 // Otherwise, copy the object. Here we must be careful to insert the
1048 // klass pointer last, since this marks the block as an allocated object.
1049 // Except with compressed oops it's the mark word.
1050 HeapWord* old_ptr = (HeapWord*)old;
1051 // Restore the mark word copied above.
1052 obj->set_mark_raw(m);
1053 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1054 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1055 OrderAccess::storestore();
1056
1057 if (UseCompressedClassPointers) {
1058 // Copy gap missed by (aligned) header size calculation below
1059 obj->set_klass_gap(old->klass_gap());
1060 }
1061 if (word_sz > (size_t)oopDesc::header_size()) {
1062 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1063 obj_ptr + oopDesc::header_size(),
1064 word_sz - oopDesc::header_size());
1065 }
1066
1067 // Now we can track the promoted object, if necessary. We take care
1068 // to delay the transition from uninitialized to full object
1069 // (i.e., insertion of klass pointer) until after, so that it
1070 // atomically becomes a promoted object.
1071 if (promoInfo->tracking()) {
1072 promoInfo->track((PromotedObject*)obj, old->klass());
1073 }
1074 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1075 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1076 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1077
1078 // Finally, install the klass pointer (this should be volatile).
1079 OrderAccess::storestore();
1080 obj->set_klass(old->klass());
1081 // We should now be able to calculate the right size for this object
1082 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1083
1084 collector()->promoted(true, // parallel
1085 obj_ptr, old->is_objArray(), word_sz);
1086
1087 NOT_PRODUCT(
1088 Atomic::inc(&_numObjectsPromoted);
1089 Atomic::add(alloc_sz, &_numWordsPromoted);
1090 )
1091
1092 return obj;
1093 }
1094
1095 void
1096 ConcurrentMarkSweepGeneration::
1097 par_promote_alloc_done(int thread_num) {
1098 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1099 ps->lab.retire(thread_num);
1100 }
1101
1102 void
1103 ConcurrentMarkSweepGeneration::
1104 par_oop_since_save_marks_iterate_done(int thread_num) {
1105 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1106 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1107 ps->promo.promoted_oops_iterate(dummy_cl);
1108
1109 // Because card-scanning has been completed, subsequent phases
1110 // (e.g., reference processing) will not need to recognize which
1111 // objects have been promoted during this GC. So, we can now disable
1112 // promotion tracking.
1113 ps->promo.stopTrackingPromotions();
1114 }
1115
1116 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1117 size_t size,
1118 bool tlab)
1119 {
1120 // We allow a STW collection only if a full
1121 // collection was requested.
1122 return full || should_allocate(size, tlab); // FIX ME !!!
1123 // This and promotion failure handling are connected at the
1124 // hip and should be fixed by untying them.
1125 }
1126
1127 bool CMSCollector::shouldConcurrentCollect() {
1128 LogTarget(Trace, gc) log;
1129
1130 if (_full_gc_requested) {
1131 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1132 return true;
1133 }
1134
1135 FreelistLocker x(this);
1136 // ------------------------------------------------------------------
1137 // Print out lots of information which affects the initiation of
1138 // a collection.
1139 if (log.is_enabled() && stats().valid()) {
1140 log.print("CMSCollector shouldConcurrentCollect: ");
1141
1142 LogStream out(log);
1143 stats().print_on(&out);
1144
1145 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1146 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1147 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1148 log.print("promotion_rate=%g", stats().promotion_rate());
1149 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1150 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1151 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1152 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1153 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1154 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1155 }
1156 // ------------------------------------------------------------------
1157
1158 // If the estimated time to complete a cms collection (cms_duration())
1159 // is less than the estimated time remaining until the cms generation
1160 // is full, start a collection.
1161 if (!UseCMSInitiatingOccupancyOnly) {
1162 if (stats().valid()) {
1163 if (stats().time_until_cms_start() == 0.0) {
1164 return true;
1165 }
1166 } else {
1167 // We want to conservatively collect somewhat early in order
1168 // to try and "bootstrap" our CMS/promotion statistics;
1169 // this branch will not fire after the first successful CMS
1170 // collection because the stats should then be valid.
1171 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1172 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1173 _cmsGen->occupancy(), _bootstrap_occupancy);
1174 return true;
1175 }
1176 }
1177 }
1178
1179 // Otherwise, we start a collection cycle if
1180 // old gen want a collection cycle started. Each may use
1181 // an appropriate criterion for making this decision.
1182 // XXX We need to make sure that the gen expansion
1183 // criterion dovetails well with this. XXX NEED TO FIX THIS
1184 if (_cmsGen->should_concurrent_collect()) {
1185 log.print("CMS old gen initiated");
1186 return true;
1187 }
1188
1189 // We start a collection if we believe an incremental collection may fail;
1190 // this is not likely to be productive in practice because it's probably too
1191 // late anyway.
1192 CMSHeap* heap = CMSHeap::heap();
1193 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1194 log.print("CMSCollector: collect because incremental collection will fail ");
1195 return true;
1196 }
1197
1198 if (MetaspaceGC::should_concurrent_collect()) {
1199 log.print("CMSCollector: collect for metadata allocation ");
1200 return true;
1201 }
1202
1203 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1204 if (CMSTriggerInterval >= 0) {
1205 if (CMSTriggerInterval == 0) {
1206 // Trigger always
1207 return true;
1208 }
1209
1210 // Check the CMS time since begin (we do not check the stats validity
1211 // as we want to be able to trigger the first CMS cycle as well)
1212 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1213 if (stats().valid()) {
1214 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1215 stats().cms_time_since_begin());
1216 } else {
1217 log.print("CMSCollector: collect because of trigger interval (first collection)");
1218 }
1219 return true;
1220 }
1221 }
1222
1223 return false;
1224 }
1225
1226 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1227
1228 // Clear _expansion_cause fields of constituent generations
1229 void CMSCollector::clear_expansion_cause() {
1230 _cmsGen->clear_expansion_cause();
1231 }
1232
1233 // We should be conservative in starting a collection cycle. To
1234 // start too eagerly runs the risk of collecting too often in the
1235 // extreme. To collect too rarely falls back on full collections,
1236 // which works, even if not optimum in terms of concurrent work.
1237 // As a work around for too eagerly collecting, use the flag
1238 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1239 // giving the user an easily understandable way of controlling the
1240 // collections.
1241 // We want to start a new collection cycle if any of the following
1242 // conditions hold:
1243 // . our current occupancy exceeds the configured initiating occupancy
1244 // for this generation, or
1245 // . we recently needed to expand this space and have not, since that
1246 // expansion, done a collection of this generation, or
1247 // . the underlying space believes that it may be a good idea to initiate
1248 // a concurrent collection (this may be based on criteria such as the
1249 // following: the space uses linear allocation and linear allocation is
1250 // going to fail, or there is believed to be excessive fragmentation in
1251 // the generation, etc... or ...
1252 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1253 // the case of the old generation; see CR 6543076):
1254 // we may be approaching a point at which allocation requests may fail because
1255 // we will be out of sufficient free space given allocation rate estimates.]
1256 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1257
1258 assert_lock_strong(freelistLock());
1259 if (occupancy() > initiating_occupancy()) {
1260 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1261 short_name(), occupancy(), initiating_occupancy());
1262 return true;
1263 }
1264 if (UseCMSInitiatingOccupancyOnly) {
1265 return false;
1266 }
1267 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1268 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1269 return true;
1270 }
1271 return false;
1272 }
1273
1274 void ConcurrentMarkSweepGeneration::collect(bool full,
1275 bool clear_all_soft_refs,
1276 size_t size,
1277 bool tlab)
1278 {
1279 collector()->collect(full, clear_all_soft_refs, size, tlab);
1280 }
1281
1282 void CMSCollector::collect(bool full,
1283 bool clear_all_soft_refs,
1284 size_t size,
1285 bool tlab)
1286 {
1287 // The following "if" branch is present for defensive reasons.
1288 // In the current uses of this interface, it can be replaced with:
1289 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1290 // But I am not placing that assert here to allow future
1291 // generality in invoking this interface.
1292 if (GCLocker::is_active()) {
1293 // A consistency test for GCLocker
1294 assert(GCLocker::needs_gc(), "Should have been set already");
1295 // Skip this foreground collection, instead
1296 // expanding the heap if necessary.
1297 // Need the free list locks for the call to free() in compute_new_size()
1298 compute_new_size();
1299 return;
1300 }
1301 acquire_control_and_collect(full, clear_all_soft_refs);
1302 }
1303
1304 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1305 CMSHeap* heap = CMSHeap::heap();
1306 unsigned int gc_count = heap->total_full_collections();
1307 if (gc_count == full_gc_count) {
1308 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1309 _full_gc_requested = true;
1310 _full_gc_cause = cause;
1311 CGC_lock->notify(); // nudge CMS thread
1312 } else {
1313 assert(gc_count > full_gc_count, "Error: causal loop");
1314 }
1315 }
1316
1317 bool CMSCollector::is_external_interruption() {
1318 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1319 return GCCause::is_user_requested_gc(cause) ||
1320 GCCause::is_serviceability_requested_gc(cause);
1321 }
1322
1323 void CMSCollector::report_concurrent_mode_interruption() {
1324 if (is_external_interruption()) {
1325 log_debug(gc)("Concurrent mode interrupted");
1326 } else {
1327 log_debug(gc)("Concurrent mode failure");
1328 _gc_tracer_cm->report_concurrent_mode_failure();
1329 }
1330 }
1331
1332
1333 // The foreground and background collectors need to coordinate in order
1334 // to make sure that they do not mutually interfere with CMS collections.
1335 // When a background collection is active,
1336 // the foreground collector may need to take over (preempt) and
1337 // synchronously complete an ongoing collection. Depending on the
1338 // frequency of the background collections and the heap usage
1339 // of the application, this preemption can be seldom or frequent.
1340 // There are only certain
1341 // points in the background collection that the "collection-baton"
1342 // can be passed to the foreground collector.
1343 //
1344 // The foreground collector will wait for the baton before
1345 // starting any part of the collection. The foreground collector
1346 // will only wait at one location.
1347 //
1348 // The background collector will yield the baton before starting a new
1349 // phase of the collection (e.g., before initial marking, marking from roots,
1350 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1351 // of the loop which switches the phases. The background collector does some
1352 // of the phases (initial mark, final re-mark) with the world stopped.
1353 // Because of locking involved in stopping the world,
1354 // the foreground collector should not block waiting for the background
1355 // collector when it is doing a stop-the-world phase. The background
1356 // collector will yield the baton at an additional point just before
1357 // it enters a stop-the-world phase. Once the world is stopped, the
1358 // background collector checks the phase of the collection. If the
1359 // phase has not changed, it proceeds with the collection. If the
1360 // phase has changed, it skips that phase of the collection. See
1361 // the comments on the use of the Heap_lock in collect_in_background().
1362 //
1363 // Variable used in baton passing.
1364 // _foregroundGCIsActive - Set to true by the foreground collector when
1365 // it wants the baton. The foreground clears it when it has finished
1366 // the collection.
1367 // _foregroundGCShouldWait - Set to true by the background collector
1368 // when it is running. The foreground collector waits while
1369 // _foregroundGCShouldWait is true.
1370 // CGC_lock - monitor used to protect access to the above variables
1371 // and to notify the foreground and background collectors.
1372 // _collectorState - current state of the CMS collection.
1373 //
1374 // The foreground collector
1375 // acquires the CGC_lock
1376 // sets _foregroundGCIsActive
1377 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1378 // various locks acquired in preparation for the collection
1379 // are released so as not to block the background collector
1380 // that is in the midst of a collection
1381 // proceeds with the collection
1382 // clears _foregroundGCIsActive
1383 // returns
1384 //
1385 // The background collector in a loop iterating on the phases of the
1386 // collection
1387 // acquires the CGC_lock
1388 // sets _foregroundGCShouldWait
1389 // if _foregroundGCIsActive is set
1390 // clears _foregroundGCShouldWait, notifies _CGC_lock
1391 // waits on _CGC_lock for _foregroundGCIsActive to become false
1392 // and exits the loop.
1393 // otherwise
1394 // proceed with that phase of the collection
1395 // if the phase is a stop-the-world phase,
1396 // yield the baton once more just before enqueueing
1397 // the stop-world CMS operation (executed by the VM thread).
1398 // returns after all phases of the collection are done
1399 //
1400
1401 void CMSCollector::acquire_control_and_collect(bool full,
1402 bool clear_all_soft_refs) {
1403 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1404 assert(!Thread::current()->is_ConcurrentGC_thread(),
1405 "shouldn't try to acquire control from self!");
1406
1407 // Start the protocol for acquiring control of the
1408 // collection from the background collector (aka CMS thread).
1409 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1410 "VM thread should have CMS token");
1411 // Remember the possibly interrupted state of an ongoing
1412 // concurrent collection
1413 CollectorState first_state = _collectorState;
1414
1415 // Signal to a possibly ongoing concurrent collection that
1416 // we want to do a foreground collection.
1417 _foregroundGCIsActive = true;
1418
1419 // release locks and wait for a notify from the background collector
1420 // releasing the locks in only necessary for phases which
1421 // do yields to improve the granularity of the collection.
1422 assert_lock_strong(bitMapLock());
1423 // We need to lock the Free list lock for the space that we are
1424 // currently collecting.
1425 assert(haveFreelistLocks(), "Must be holding free list locks");
1426 bitMapLock()->unlock();
1427 releaseFreelistLocks();
1428 {
1429 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1430 if (_foregroundGCShouldWait) {
1431 // We are going to be waiting for action for the CMS thread;
1432 // it had better not be gone (for instance at shutdown)!
1433 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1434 "CMS thread must be running");
1435 // Wait here until the background collector gives us the go-ahead
1436 ConcurrentMarkSweepThread::clear_CMS_flag(
1437 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1438 // Get a possibly blocked CMS thread going:
1439 // Note that we set _foregroundGCIsActive true above,
1440 // without protection of the CGC_lock.
1441 CGC_lock->notify();
1442 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1443 "Possible deadlock");
1444 while (_foregroundGCShouldWait) {
1445 // wait for notification
1446 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1447 // Possibility of delay/starvation here, since CMS token does
1448 // not know to give priority to VM thread? Actually, i think
1449 // there wouldn't be any delay/starvation, but the proof of
1450 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1451 }
1452 ConcurrentMarkSweepThread::set_CMS_flag(
1453 ConcurrentMarkSweepThread::CMS_vm_has_token);
1454 }
1455 }
1456 // The CMS_token is already held. Get back the other locks.
1457 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1458 "VM thread should have CMS token");
1459 getFreelistLocks();
1460 bitMapLock()->lock_without_safepoint_check();
1461 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1462 p2i(Thread::current()), first_state);
1463 log_debug(gc, state)(" gets control with state %d", _collectorState);
1464
1465 // Inform cms gen if this was due to partial collection failing.
1466 // The CMS gen may use this fact to determine its expansion policy.
1467 CMSHeap* heap = CMSHeap::heap();
1468 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1469 assert(!_cmsGen->incremental_collection_failed(),
1470 "Should have been noticed, reacted to and cleared");
1471 _cmsGen->set_incremental_collection_failed();
1472 }
1473
1474 if (first_state > Idling) {
1475 report_concurrent_mode_interruption();
1476 }
1477
1478 set_did_compact(true);
1479
1480 // If the collection is being acquired from the background
1481 // collector, there may be references on the discovered
1482 // references lists. Abandon those references, since some
1483 // of them may have become unreachable after concurrent
1484 // discovery; the STW compacting collector will redo discovery
1485 // more precisely, without being subject to floating garbage.
1486 // Leaving otherwise unreachable references in the discovered
1487 // lists would require special handling.
1488 ref_processor()->disable_discovery();
1489 ref_processor()->abandon_partial_discovery();
1490 ref_processor()->verify_no_references_recorded();
1491
1492 if (first_state > Idling) {
1493 save_heap_summary();
1494 }
1495
1496 do_compaction_work(clear_all_soft_refs);
1497
1498 // Has the GC time limit been exceeded?
1499 size_t max_eden_size = _young_gen->max_eden_size();
1500 GCCause::Cause gc_cause = heap->gc_cause();
1501 size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1502 _cmsGen->max_capacity(),
1503 max_eden_size,
1504 full,
1505 gc_cause,
1506 heap->soft_ref_policy());
1507
1508 // Reset the expansion cause, now that we just completed
1509 // a collection cycle.
1510 clear_expansion_cause();
1511 _foregroundGCIsActive = false;
1512 return;
1513 }
1514
1515 // Resize the tenured generation
1516 // after obtaining the free list locks for the
1517 // two generations.
1518 void CMSCollector::compute_new_size() {
1519 assert_locked_or_safepoint(Heap_lock);
1520 FreelistLocker z(this);
1521 MetaspaceGC::compute_new_size();
1522 _cmsGen->compute_new_size_free_list();
1523 }
1524
1525 // A work method used by the foreground collector to do
1526 // a mark-sweep-compact.
1527 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1528 CMSHeap* heap = CMSHeap::heap();
1529
1530 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1531 gc_timer->register_gc_start();
1532
1533 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1534 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1535
1536 heap->pre_full_gc_dump(gc_timer);
1537
1538 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1539
1540 // Temporarily widen the span of the weak reference processing to
1541 // the entire heap.
1542 MemRegion new_span(CMSHeap::heap()->reserved_region());
1543 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1544 // Temporarily, clear the "is_alive_non_header" field of the
1545 // reference processor.
1546 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1547 // Temporarily make reference _processing_ single threaded (non-MT).
1548 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1549 // Temporarily make refs discovery atomic
1550 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1551 // Temporarily make reference _discovery_ single threaded (non-MT)
1552 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1553
1554 ref_processor()->set_enqueuing_is_done(false);
1555 ref_processor()->enable_discovery();
1556 ref_processor()->setup_policy(clear_all_soft_refs);
1557 // If an asynchronous collection finishes, the _modUnionTable is
1558 // all clear. If we are assuming the collection from an asynchronous
1559 // collection, clear the _modUnionTable.
1560 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1561 "_modUnionTable should be clear if the baton was not passed");
1562 _modUnionTable.clear_all();
1563 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1564 "mod union for klasses should be clear if the baton was passed");
1565 _ct->cld_rem_set()->clear_mod_union();
1566
1567
1568 // We must adjust the allocation statistics being maintained
1569 // in the free list space. We do so by reading and clearing
1570 // the sweep timer and updating the block flux rate estimates below.
1571 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1572 if (_inter_sweep_timer.is_active()) {
1573 _inter_sweep_timer.stop();
1574 // Note that we do not use this sample to update the _inter_sweep_estimate.
1575 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1576 _inter_sweep_estimate.padded_average(),
1577 _intra_sweep_estimate.padded_average());
1578 }
1579
1580 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1581 #ifdef ASSERT
1582 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1583 size_t free_size = cms_space->free();
1584 assert(free_size ==
1585 pointer_delta(cms_space->end(), cms_space->compaction_top())
1586 * HeapWordSize,
1587 "All the free space should be compacted into one chunk at top");
1588 assert(cms_space->dictionary()->total_chunk_size(
1589 debug_only(cms_space->freelistLock())) == 0 ||
1590 cms_space->totalSizeInIndexedFreeLists() == 0,
1591 "All the free space should be in a single chunk");
1592 size_t num = cms_space->totalCount();
1593 assert((free_size == 0 && num == 0) ||
1594 (free_size > 0 && (num == 1 || num == 2)),
1595 "There should be at most 2 free chunks after compaction");
1596 #endif // ASSERT
1597 _collectorState = Resetting;
1598 assert(_restart_addr == NULL,
1599 "Should have been NULL'd before baton was passed");
1600 reset_stw();
1601 _cmsGen->reset_after_compaction();
1602 _concurrent_cycles_since_last_unload = 0;
1603
1604 // Clear any data recorded in the PLAB chunk arrays.
1605 if (_survivor_plab_array != NULL) {
1606 reset_survivor_plab_arrays();
1607 }
1608
1609 // Adjust the per-size allocation stats for the next epoch.
1610 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1611 // Restart the "inter sweep timer" for the next epoch.
1612 _inter_sweep_timer.reset();
1613 _inter_sweep_timer.start();
1614
1615 // No longer a need to do a concurrent collection for Metaspace.
1616 MetaspaceGC::set_should_concurrent_collect(false);
1617
1618 heap->post_full_gc_dump(gc_timer);
1619
1620 gc_timer->register_gc_end();
1621
1622 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1623
1624 // For a mark-sweep-compact, compute_new_size() will be called
1625 // in the heap's do_collection() method.
1626 }
1627
1628 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1629 Log(gc, heap) log;
1630 if (!log.is_trace()) {
1631 return;
1632 }
1633
1634 ContiguousSpace* eden_space = _young_gen->eden();
1635 ContiguousSpace* from_space = _young_gen->from();
1636 ContiguousSpace* to_space = _young_gen->to();
1637 // Eden
1638 if (_eden_chunk_array != NULL) {
1639 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1640 p2i(eden_space->bottom()), p2i(eden_space->top()),
1641 p2i(eden_space->end()), eden_space->capacity());
1642 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1643 _eden_chunk_index, _eden_chunk_capacity);
1644 for (size_t i = 0; i < _eden_chunk_index; i++) {
1645 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1646 }
1647 }
1648 // Survivor
1649 if (_survivor_chunk_array != NULL) {
1650 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1651 p2i(from_space->bottom()), p2i(from_space->top()),
1652 p2i(from_space->end()), from_space->capacity());
1653 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1654 _survivor_chunk_index, _survivor_chunk_capacity);
1655 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1656 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1657 }
1658 }
1659 }
1660
1661 void CMSCollector::getFreelistLocks() const {
1662 // Get locks for all free lists in all generations that this
1663 // collector is responsible for
1664 _cmsGen->freelistLock()->lock_without_safepoint_check();
1665 }
1666
1667 void CMSCollector::releaseFreelistLocks() const {
1668 // Release locks for all free lists in all generations that this
1669 // collector is responsible for
1670 _cmsGen->freelistLock()->unlock();
1671 }
1672
1673 bool CMSCollector::haveFreelistLocks() const {
1674 // Check locks for all free lists in all generations that this
1675 // collector is responsible for
1676 assert_lock_strong(_cmsGen->freelistLock());
1677 PRODUCT_ONLY(ShouldNotReachHere());
1678 return true;
1679 }
1680
1681 // A utility class that is used by the CMS collector to
1682 // temporarily "release" the foreground collector from its
1683 // usual obligation to wait for the background collector to
1684 // complete an ongoing phase before proceeding.
1685 class ReleaseForegroundGC: public StackObj {
1686 private:
1687 CMSCollector* _c;
1688 public:
1689 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1690 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1691 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1692 // allow a potentially blocked foreground collector to proceed
1693 _c->_foregroundGCShouldWait = false;
1694 if (_c->_foregroundGCIsActive) {
1695 CGC_lock->notify();
1696 }
1697 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1698 "Possible deadlock");
1699 }
1700
1701 ~ReleaseForegroundGC() {
1702 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1703 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1704 _c->_foregroundGCShouldWait = true;
1705 }
1706 };
1707
1708 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1709 assert(Thread::current()->is_ConcurrentGC_thread(),
1710 "A CMS asynchronous collection is only allowed on a CMS thread.");
1711
1712 CMSHeap* heap = CMSHeap::heap();
1713 {
1714 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1715 MutexLockerEx hl(Heap_lock, safepoint_check);
1716 FreelistLocker fll(this);
1717 MutexLockerEx x(CGC_lock, safepoint_check);
1718 if (_foregroundGCIsActive) {
1719 // The foreground collector is. Skip this
1720 // background collection.
1721 assert(!_foregroundGCShouldWait, "Should be clear");
1722 return;
1723 } else {
1724 assert(_collectorState == Idling, "Should be idling before start.");
1725 _collectorState = InitialMarking;
1726 register_gc_start(cause);
1727 // Reset the expansion cause, now that we are about to begin
1728 // a new cycle.
1729 clear_expansion_cause();
1730
1731 // Clear the MetaspaceGC flag since a concurrent collection
1732 // is starting but also clear it after the collection.
1733 MetaspaceGC::set_should_concurrent_collect(false);
1734 }
1735 // Decide if we want to enable class unloading as part of the
1736 // ensuing concurrent GC cycle.
1737 update_should_unload_classes();
1738 _full_gc_requested = false; // acks all outstanding full gc requests
1739 _full_gc_cause = GCCause::_no_gc;
1740 // Signal that we are about to start a collection
1741 heap->increment_total_full_collections(); // ... starting a collection cycle
1742 _collection_count_start = heap->total_full_collections();
1743 }
1744
1745 size_t prev_used = _cmsGen->used();
1746
1747 // The change of the collection state is normally done at this level;
1748 // the exceptions are phases that are executed while the world is
1749 // stopped. For those phases the change of state is done while the
1750 // world is stopped. For baton passing purposes this allows the
1751 // background collector to finish the phase and change state atomically.
1752 // The foreground collector cannot wait on a phase that is done
1753 // while the world is stopped because the foreground collector already
1754 // has the world stopped and would deadlock.
1755 while (_collectorState != Idling) {
1756 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1757 p2i(Thread::current()), _collectorState);
1758 // The foreground collector
1759 // holds the Heap_lock throughout its collection.
1760 // holds the CMS token (but not the lock)
1761 // except while it is waiting for the background collector to yield.
1762 //
1763 // The foreground collector should be blocked (not for long)
1764 // if the background collector is about to start a phase
1765 // executed with world stopped. If the background
1766 // collector has already started such a phase, the
1767 // foreground collector is blocked waiting for the
1768 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1769 // are executed in the VM thread.
1770 //
1771 // The locking order is
1772 // PendingListLock (PLL) -- if applicable (FinalMarking)
1773 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1774 // CMS token (claimed in
1775 // stop_world_and_do() -->
1776 // safepoint_synchronize() -->
1777 // CMSThread::synchronize())
1778
1779 {
1780 // Check if the FG collector wants us to yield.
1781 CMSTokenSync x(true); // is cms thread
1782 if (waitForForegroundGC()) {
1783 // We yielded to a foreground GC, nothing more to be
1784 // done this round.
1785 assert(_foregroundGCShouldWait == false, "We set it to false in "
1786 "waitForForegroundGC()");
1787 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1788 p2i(Thread::current()), _collectorState);
1789 return;
1790 } else {
1791 // The background collector can run but check to see if the
1792 // foreground collector has done a collection while the
1793 // background collector was waiting to get the CGC_lock
1794 // above. If yes, break so that _foregroundGCShouldWait
1795 // is cleared before returning.
1796 if (_collectorState == Idling) {
1797 break;
1798 }
1799 }
1800 }
1801
1802 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1803 "should be waiting");
1804
1805 switch (_collectorState) {
1806 case InitialMarking:
1807 {
1808 ReleaseForegroundGC x(this);
1809 stats().record_cms_begin();
1810 VM_CMS_Initial_Mark initial_mark_op(this);
1811 VMThread::execute(&initial_mark_op);
1812 }
1813 // The collector state may be any legal state at this point
1814 // since the background collector may have yielded to the
1815 // foreground collector.
1816 break;
1817 case Marking:
1818 // initial marking in checkpointRootsInitialWork has been completed
1819 if (markFromRoots()) { // we were successful
1820 assert(_collectorState == Precleaning, "Collector state should "
1821 "have changed");
1822 } else {
1823 assert(_foregroundGCIsActive, "Internal state inconsistency");
1824 }
1825 break;
1826 case Precleaning:
1827 // marking from roots in markFromRoots has been completed
1828 preclean();
1829 assert(_collectorState == AbortablePreclean ||
1830 _collectorState == FinalMarking,
1831 "Collector state should have changed");
1832 break;
1833 case AbortablePreclean:
1834 abortable_preclean();
1835 assert(_collectorState == FinalMarking, "Collector state should "
1836 "have changed");
1837 break;
1838 case FinalMarking:
1839 {
1840 ReleaseForegroundGC x(this);
1841
1842 VM_CMS_Final_Remark final_remark_op(this);
1843 VMThread::execute(&final_remark_op);
1844 }
1845 assert(_foregroundGCShouldWait, "block post-condition");
1846 break;
1847 case Sweeping:
1848 // final marking in checkpointRootsFinal has been completed
1849 sweep();
1850 assert(_collectorState == Resizing, "Collector state change "
1851 "to Resizing must be done under the free_list_lock");
1852
1853 case Resizing: {
1854 // Sweeping has been completed...
1855 // At this point the background collection has completed.
1856 // Don't move the call to compute_new_size() down
1857 // into code that might be executed if the background
1858 // collection was preempted.
1859 {
1860 ReleaseForegroundGC x(this); // unblock FG collection
1861 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1862 CMSTokenSync z(true); // not strictly needed.
1863 if (_collectorState == Resizing) {
1864 compute_new_size();
1865 save_heap_summary();
1866 _collectorState = Resetting;
1867 } else {
1868 assert(_collectorState == Idling, "The state should only change"
1869 " because the foreground collector has finished the collection");
1870 }
1871 }
1872 break;
1873 }
1874 case Resetting:
1875 // CMS heap resizing has been completed
1876 reset_concurrent();
1877 assert(_collectorState == Idling, "Collector state should "
1878 "have changed");
1879
1880 MetaspaceGC::set_should_concurrent_collect(false);
1881
1882 stats().record_cms_end();
1883 // Don't move the concurrent_phases_end() and compute_new_size()
1884 // calls to here because a preempted background collection
1885 // has it's state set to "Resetting".
1886 break;
1887 case Idling:
1888 default:
1889 ShouldNotReachHere();
1890 break;
1891 }
1892 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1893 p2i(Thread::current()), _collectorState);
1894 assert(_foregroundGCShouldWait, "block post-condition");
1895 }
1896
1897 // Should this be in gc_epilogue?
1898 heap->counters()->update_counters();
1899
1900 {
1901 // Clear _foregroundGCShouldWait and, in the event that the
1902 // foreground collector is waiting, notify it, before
1903 // returning.
1904 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1905 _foregroundGCShouldWait = false;
1906 if (_foregroundGCIsActive) {
1907 CGC_lock->notify();
1908 }
1909 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1910 "Possible deadlock");
1911 }
1912 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1913 p2i(Thread::current()), _collectorState);
1914 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1915 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1916 }
1917
1918 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1919 _cms_start_registered = true;
1920 _gc_timer_cm->register_gc_start();
1921 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1922 }
1923
1924 void CMSCollector::register_gc_end() {
1925 if (_cms_start_registered) {
1926 report_heap_summary(GCWhen::AfterGC);
1927
1928 _gc_timer_cm->register_gc_end();
1929 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1930 _cms_start_registered = false;
1931 }
1932 }
1933
1934 void CMSCollector::save_heap_summary() {
1935 CMSHeap* heap = CMSHeap::heap();
1936 _last_heap_summary = heap->create_heap_summary();
1937 _last_metaspace_summary = heap->create_metaspace_summary();
1938 }
1939
1940 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1941 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1942 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1943 }
1944
1945 bool CMSCollector::waitForForegroundGC() {
1946 bool res = false;
1947 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1948 "CMS thread should have CMS token");
1949 // Block the foreground collector until the
1950 // background collectors decides whether to
1951 // yield.
1952 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1953 _foregroundGCShouldWait = true;
1954 if (_foregroundGCIsActive) {
1955 // The background collector yields to the
1956 // foreground collector and returns a value
1957 // indicating that it has yielded. The foreground
1958 // collector can proceed.
1959 res = true;
1960 _foregroundGCShouldWait = false;
1961 ConcurrentMarkSweepThread::clear_CMS_flag(
1962 ConcurrentMarkSweepThread::CMS_cms_has_token);
1963 ConcurrentMarkSweepThread::set_CMS_flag(
1964 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1965 // Get a possibly blocked foreground thread going
1966 CGC_lock->notify();
1967 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1968 p2i(Thread::current()), _collectorState);
1969 while (_foregroundGCIsActive) {
1970 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1971 }
1972 ConcurrentMarkSweepThread::set_CMS_flag(
1973 ConcurrentMarkSweepThread::CMS_cms_has_token);
1974 ConcurrentMarkSweepThread::clear_CMS_flag(
1975 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1976 }
1977 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1978 p2i(Thread::current()), _collectorState);
1979 return res;
1980 }
1981
1982 // Because of the need to lock the free lists and other structures in
1983 // the collector, common to all the generations that the collector is
1984 // collecting, we need the gc_prologues of individual CMS generations
1985 // delegate to their collector. It may have been simpler had the
1986 // current infrastructure allowed one to call a prologue on a
1987 // collector. In the absence of that we have the generation's
1988 // prologue delegate to the collector, which delegates back
1989 // some "local" work to a worker method in the individual generations
1990 // that it's responsible for collecting, while itself doing any
1991 // work common to all generations it's responsible for. A similar
1992 // comment applies to the gc_epilogue()'s.
1993 // The role of the variable _between_prologue_and_epilogue is to
1994 // enforce the invocation protocol.
1995 void CMSCollector::gc_prologue(bool full) {
1996 // Call gc_prologue_work() for the CMSGen
1997 // we are responsible for.
1998
1999 // The following locking discipline assumes that we are only called
2000 // when the world is stopped.
2001 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2002
2003 // The CMSCollector prologue must call the gc_prologues for the
2004 // "generations" that it's responsible
2005 // for.
2006
2007 assert( Thread::current()->is_VM_thread()
2008 || ( CMSScavengeBeforeRemark
2009 && Thread::current()->is_ConcurrentGC_thread()),
2010 "Incorrect thread type for prologue execution");
2011
2012 if (_between_prologue_and_epilogue) {
2013 // We have already been invoked; this is a gc_prologue delegation
2014 // from yet another CMS generation that we are responsible for, just
2015 // ignore it since all relevant work has already been done.
2016 return;
2017 }
2018
2019 // set a bit saying prologue has been called; cleared in epilogue
2020 _between_prologue_and_epilogue = true;
2021 // Claim locks for common data structures, then call gc_prologue_work()
2022 // for each CMSGen.
2023
2024 getFreelistLocks(); // gets free list locks on constituent spaces
2025 bitMapLock()->lock_without_safepoint_check();
2026
2027 // Should call gc_prologue_work() for all cms gens we are responsible for
2028 bool duringMarking = _collectorState >= Marking
2029 && _collectorState < Sweeping;
2030
2031 // The young collections clear the modified oops state, which tells if
2032 // there are any modified oops in the class. The remark phase also needs
2033 // that information. Tell the young collection to save the union of all
2034 // modified klasses.
2035 if (duringMarking) {
2036 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2037 }
2038
2039 bool registerClosure = duringMarking;
2040
2041 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2042
2043 if (!full) {
2044 stats().record_gc0_begin();
2045 }
2046 }
2047
2048 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2049
2050 _capacity_at_prologue = capacity();
2051 _used_at_prologue = used();
2052
2053 // We enable promotion tracking so that card-scanning can recognize
2054 // which objects have been promoted during this GC and skip them.
2055 for (uint i = 0; i < ParallelGCThreads; i++) {
2056 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2057 }
2058
2059 // Delegate to CMScollector which knows how to coordinate between
2060 // this and any other CMS generations that it is responsible for
2061 // collecting.
2062 collector()->gc_prologue(full);
2063 }
2064
2065 // This is a "private" interface for use by this generation's CMSCollector.
2066 // Not to be called directly by any other entity (for instance,
2067 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2068 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2069 bool registerClosure, ModUnionClosure* modUnionClosure) {
2070 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2071 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2072 "Should be NULL");
2073 if (registerClosure) {
2074 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2075 }
2076 cmsSpace()->gc_prologue();
2077 // Clear stat counters
2078 NOT_PRODUCT(
2079 assert(_numObjectsPromoted == 0, "check");
2080 assert(_numWordsPromoted == 0, "check");
2081 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2082 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2083 _numObjectsAllocated = 0;
2084 _numWordsAllocated = 0;
2085 )
2086 }
2087
2088 void CMSCollector::gc_epilogue(bool full) {
2089 // The following locking discipline assumes that we are only called
2090 // when the world is stopped.
2091 assert(SafepointSynchronize::is_at_safepoint(),
2092 "world is stopped assumption");
2093
2094 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2095 // if linear allocation blocks need to be appropriately marked to allow the
2096 // the blocks to be parsable. We also check here whether we need to nudge the
2097 // CMS collector thread to start a new cycle (if it's not already active).
2098 assert( Thread::current()->is_VM_thread()
2099 || ( CMSScavengeBeforeRemark
2100 && Thread::current()->is_ConcurrentGC_thread()),
2101 "Incorrect thread type for epilogue execution");
2102
2103 if (!_between_prologue_and_epilogue) {
2104 // We have already been invoked; this is a gc_epilogue delegation
2105 // from yet another CMS generation that we are responsible for, just
2106 // ignore it since all relevant work has already been done.
2107 return;
2108 }
2109 assert(haveFreelistLocks(), "must have freelist locks");
2110 assert_lock_strong(bitMapLock());
2111
2112 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2113
2114 _cmsGen->gc_epilogue_work(full);
2115
2116 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2117 // in case sampling was not already enabled, enable it
2118 _start_sampling = true;
2119 }
2120 // reset _eden_chunk_array so sampling starts afresh
2121 _eden_chunk_index = 0;
2122
2123 size_t cms_used = _cmsGen->cmsSpace()->used();
2124
2125 // update performance counters - this uses a special version of
2126 // update_counters() that allows the utilization to be passed as a
2127 // parameter, avoiding multiple calls to used().
2128 //
2129 _cmsGen->update_counters(cms_used);
2130
2131 bitMapLock()->unlock();
2132 releaseFreelistLocks();
2133
2134 if (!CleanChunkPoolAsync) {
2135 Chunk::clean_chunk_pool();
2136 }
2137
2138 set_did_compact(false);
2139 _between_prologue_and_epilogue = false; // ready for next cycle
2140 }
2141
2142 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2143 collector()->gc_epilogue(full);
2144
2145 // When using ParNew, promotion tracking should have already been
2146 // disabled. However, the prologue (which enables promotion
2147 // tracking) and epilogue are called irrespective of the type of
2148 // GC. So they will also be called before and after Full GCs, during
2149 // which promotion tracking will not be explicitly disabled. So,
2150 // it's safer to also disable it here too (to be symmetric with
2151 // enabling it in the prologue).
2152 for (uint i = 0; i < ParallelGCThreads; i++) {
2153 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2154 }
2155 }
2156
2157 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2158 assert(!incremental_collection_failed(), "Should have been cleared");
2159 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2160 cmsSpace()->gc_epilogue();
2161 // Print stat counters
2162 NOT_PRODUCT(
2163 assert(_numObjectsAllocated == 0, "check");
2164 assert(_numWordsAllocated == 0, "check");
2165 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2166 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2167 _numObjectsPromoted = 0;
2168 _numWordsPromoted = 0;
2169 )
2170
2171 // Call down the chain in contiguous_available needs the freelistLock
2172 // so print this out before releasing the freeListLock.
2173 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2174 }
2175
2176 #ifndef PRODUCT
2177 bool CMSCollector::have_cms_token() {
2178 Thread* thr = Thread::current();
2179 if (thr->is_VM_thread()) {
2180 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2181 } else if (thr->is_ConcurrentGC_thread()) {
2182 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2183 } else if (thr->is_GC_task_thread()) {
2184 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2185 ParGCRareEvent_lock->owned_by_self();
2186 }
2187 return false;
2188 }
2189
2190 // Check reachability of the given heap address in CMS generation,
2191 // treating all other generations as roots.
2192 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2193 // We could "guarantee" below, rather than assert, but I'll
2194 // leave these as "asserts" so that an adventurous debugger
2195 // could try this in the product build provided some subset of
2196 // the conditions were met, provided they were interested in the
2197 // results and knew that the computation below wouldn't interfere
2198 // with other concurrent computations mutating the structures
2199 // being read or written.
2200 assert(SafepointSynchronize::is_at_safepoint(),
2201 "Else mutations in object graph will make answer suspect");
2202 assert(have_cms_token(), "Should hold cms token");
2203 assert(haveFreelistLocks(), "must hold free list locks");
2204 assert_lock_strong(bitMapLock());
2205
2206 // Clear the marking bit map array before starting, but, just
2207 // for kicks, first report if the given address is already marked
2208 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2209 _markBitMap.isMarked(addr) ? "" : " not");
2210
2211 if (verify_after_remark()) {
2212 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2213 bool result = verification_mark_bm()->isMarked(addr);
2214 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2215 result ? "IS" : "is NOT");
2216 return result;
2217 } else {
2218 tty->print_cr("Could not compute result");
2219 return false;
2220 }
2221 }
2222 #endif
2223
2224 void
2225 CMSCollector::print_on_error(outputStream* st) {
2226 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2227 if (collector != NULL) {
2228 CMSBitMap* bitmap = &collector->_markBitMap;
2229 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2230 bitmap->print_on_error(st, " Bits: ");
2231
2232 st->cr();
2233
2234 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2235 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2236 mut_bitmap->print_on_error(st, " Bits: ");
2237 }
2238 }
2239
2240 ////////////////////////////////////////////////////////
2241 // CMS Verification Support
2242 ////////////////////////////////////////////////////////
2243 // Following the remark phase, the following invariant
2244 // should hold -- each object in the CMS heap which is
2245 // marked in markBitMap() should be marked in the verification_mark_bm().
2246
2247 class VerifyMarkedClosure: public BitMapClosure {
2248 CMSBitMap* _marks;
2249 bool _failed;
2250
2251 public:
2252 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2253
2254 bool do_bit(size_t offset) {
2255 HeapWord* addr = _marks->offsetToHeapWord(offset);
2256 if (!_marks->isMarked(addr)) {
2257 Log(gc, verify) log;
2258 ResourceMark rm;
2259 LogStream ls(log.error());
2260 oop(addr)->print_on(&ls);
2261 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2262 _failed = true;
2263 }
2264 return true;
2265 }
2266
2267 bool failed() { return _failed; }
2268 };
2269
2270 bool CMSCollector::verify_after_remark() {
2271 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2272 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2273 static bool init = false;
2274
2275 assert(SafepointSynchronize::is_at_safepoint(),
2276 "Else mutations in object graph will make answer suspect");
2277 assert(have_cms_token(),
2278 "Else there may be mutual interference in use of "
2279 " verification data structures");
2280 assert(_collectorState > Marking && _collectorState <= Sweeping,
2281 "Else marking info checked here may be obsolete");
2282 assert(haveFreelistLocks(), "must hold free list locks");
2283 assert_lock_strong(bitMapLock());
2284
2285
2286 // Allocate marking bit map if not already allocated
2287 if (!init) { // first time
2288 if (!verification_mark_bm()->allocate(_span)) {
2289 return false;
2290 }
2291 init = true;
2292 }
2293
2294 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2295
2296 // Turn off refs discovery -- so we will be tracing through refs.
2297 // This is as intended, because by this time
2298 // GC must already have cleared any refs that need to be cleared,
2299 // and traced those that need to be marked; moreover,
2300 // the marking done here is not going to interfere in any
2301 // way with the marking information used by GC.
2302 NoRefDiscovery no_discovery(ref_processor());
2303
2304 #if COMPILER2_OR_JVMCI
2305 DerivedPointerTableDeactivate dpt_deact;
2306 #endif
2307
2308 // Clear any marks from a previous round
2309 verification_mark_bm()->clear_all();
2310 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2311 verify_work_stacks_empty();
2312
2313 CMSHeap* heap = CMSHeap::heap();
2314 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2315 // Update the saved marks which may affect the root scans.
2316 heap->save_marks();
2317
2318 if (CMSRemarkVerifyVariant == 1) {
2319 // In this first variant of verification, we complete
2320 // all marking, then check if the new marks-vector is
2321 // a subset of the CMS marks-vector.
2322 verify_after_remark_work_1();
2323 } else {
2324 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2325 // In this second variant of verification, we flag an error
2326 // (i.e. an object reachable in the new marks-vector not reachable
2327 // in the CMS marks-vector) immediately, also indicating the
2328 // identify of an object (A) that references the unmarked object (B) --
2329 // presumably, a mutation to A failed to be picked up by preclean/remark?
2330 verify_after_remark_work_2();
2331 }
2332
2333 return true;
2334 }
2335
2336 void CMSCollector::verify_after_remark_work_1() {
2337 ResourceMark rm;
2338 HandleMark hm;
2339 CMSHeap* heap = CMSHeap::heap();
2340
2341 // Get a clear set of claim bits for the roots processing to work with.
2342 ClassLoaderDataGraph::clear_claimed_marks();
2343
2344 // Mark from roots one level into CMS
2345 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2346 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2347
2348 {
2349 StrongRootsScope srs(1);
2350
2351 heap->cms_process_roots(&srs,
2352 true, // young gen as roots
2353 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2354 should_unload_classes(),
2355 ¬Older,
2356 NULL);
2357 }
2358
2359 // Now mark from the roots
2360 MarkFromRootsClosure markFromRootsClosure(this, _span,
2361 verification_mark_bm(), verification_mark_stack(),
2362 false /* don't yield */, true /* verifying */);
2363 assert(_restart_addr == NULL, "Expected pre-condition");
2364 verification_mark_bm()->iterate(&markFromRootsClosure);
2365 while (_restart_addr != NULL) {
2366 // Deal with stack overflow: by restarting at the indicated
2367 // address.
2368 HeapWord* ra = _restart_addr;
2369 markFromRootsClosure.reset(ra);
2370 _restart_addr = NULL;
2371 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2372 }
2373 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2374 verify_work_stacks_empty();
2375
2376 // Marking completed -- now verify that each bit marked in
2377 // verification_mark_bm() is also marked in markBitMap(); flag all
2378 // errors by printing corresponding objects.
2379 VerifyMarkedClosure vcl(markBitMap());
2380 verification_mark_bm()->iterate(&vcl);
2381 if (vcl.failed()) {
2382 Log(gc, verify) log;
2383 log.error("Failed marking verification after remark");
2384 ResourceMark rm;
2385 LogStream ls(log.error());
2386 heap->print_on(&ls);
2387 fatal("CMS: failed marking verification after remark");
2388 }
2389 }
2390
2391 class VerifyCLDOopsCLDClosure : public CLDClosure {
2392 class VerifyCLDOopsClosure : public OopClosure {
2393 CMSBitMap* _bitmap;
2394 public:
2395 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2396 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2397 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2398 } _oop_closure;
2399 public:
2400 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2401 void do_cld(ClassLoaderData* cld) {
2402 cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2403 }
2404 };
2405
2406 void CMSCollector::verify_after_remark_work_2() {
2407 ResourceMark rm;
2408 HandleMark hm;
2409 CMSHeap* heap = CMSHeap::heap();
2410
2411 // Get a clear set of claim bits for the roots processing to work with.
2412 ClassLoaderDataGraph::clear_claimed_marks();
2413
2414 // Mark from roots one level into CMS
2415 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2416 markBitMap());
2417 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2418
2419 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2420
2421 {
2422 StrongRootsScope srs(1);
2423
2424 heap->cms_process_roots(&srs,
2425 true, // young gen as roots
2426 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2427 should_unload_classes(),
2428 ¬Older,
2429 &cld_closure);
2430 }
2431
2432 // Now mark from the roots
2433 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2434 verification_mark_bm(), markBitMap(), verification_mark_stack());
2435 assert(_restart_addr == NULL, "Expected pre-condition");
2436 verification_mark_bm()->iterate(&markFromRootsClosure);
2437 while (_restart_addr != NULL) {
2438 // Deal with stack overflow: by restarting at the indicated
2439 // address.
2440 HeapWord* ra = _restart_addr;
2441 markFromRootsClosure.reset(ra);
2442 _restart_addr = NULL;
2443 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2444 }
2445 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2446 verify_work_stacks_empty();
2447
2448 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2449 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2450
2451 // Marking completed -- now verify that each bit marked in
2452 // verification_mark_bm() is also marked in markBitMap(); flag all
2453 // errors by printing corresponding objects.
2454 VerifyMarkedClosure vcl(markBitMap());
2455 verification_mark_bm()->iterate(&vcl);
2456 assert(!vcl.failed(), "Else verification above should not have succeeded");
2457 }
2458
2459 void ConcurrentMarkSweepGeneration::save_marks() {
2460 // delegate to CMS space
2461 cmsSpace()->save_marks();
2462 }
2463
2464 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2465 return cmsSpace()->no_allocs_since_save_marks();
2466 }
2467
2468 void
2469 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2470 if (freelistLock()->owned_by_self()) {
2471 Generation::oop_iterate(cl);
2472 } else {
2473 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2474 Generation::oop_iterate(cl);
2475 }
2476 }
2477
2478 void
2479 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2480 if (freelistLock()->owned_by_self()) {
2481 Generation::object_iterate(cl);
2482 } else {
2483 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2484 Generation::object_iterate(cl);
2485 }
2486 }
2487
2488 void
2489 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2490 if (freelistLock()->owned_by_self()) {
2491 Generation::safe_object_iterate(cl);
2492 } else {
2493 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2494 Generation::safe_object_iterate(cl);
2495 }
2496 }
2497
2498 void
2499 ConcurrentMarkSweepGeneration::post_compact() {
2500 }
2501
2502 void
2503 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2504 // Fix the linear allocation blocks to look like free blocks.
2505
2506 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507 // are not called when the heap is verified during universe initialization and
2508 // at vm shutdown.
2509 if (freelistLock()->owned_by_self()) {
2510 cmsSpace()->prepare_for_verify();
2511 } else {
2512 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513 cmsSpace()->prepare_for_verify();
2514 }
2515 }
2516
2517 void
2518 ConcurrentMarkSweepGeneration::verify() {
2519 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2520 // are not called when the heap is verified during universe initialization and
2521 // at vm shutdown.
2522 if (freelistLock()->owned_by_self()) {
2523 cmsSpace()->verify();
2524 } else {
2525 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2526 cmsSpace()->verify();
2527 }
2528 }
2529
2530 void CMSCollector::verify() {
2531 _cmsGen->verify();
2532 }
2533
2534 #ifndef PRODUCT
2535 bool CMSCollector::overflow_list_is_empty() const {
2536 assert(_num_par_pushes >= 0, "Inconsistency");
2537 if (_overflow_list == NULL) {
2538 assert(_num_par_pushes == 0, "Inconsistency");
2539 }
2540 return _overflow_list == NULL;
2541 }
2542
2543 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2544 // merely consolidate assertion checks that appear to occur together frequently.
2545 void CMSCollector::verify_work_stacks_empty() const {
2546 assert(_markStack.isEmpty(), "Marking stack should be empty");
2547 assert(overflow_list_is_empty(), "Overflow list should be empty");
2548 }
2549
2550 void CMSCollector::verify_overflow_empty() const {
2551 assert(overflow_list_is_empty(), "Overflow list should be empty");
2552 assert(no_preserved_marks(), "No preserved marks");
2553 }
2554 #endif // PRODUCT
2555
2556 // Decide if we want to enable class unloading as part of the
2557 // ensuing concurrent GC cycle. We will collect and
2558 // unload classes if it's the case that:
2559 // (a) class unloading is enabled at the command line, and
2560 // (b) old gen is getting really full
2561 // NOTE: Provided there is no change in the state of the heap between
2562 // calls to this method, it should have idempotent results. Moreover,
2563 // its results should be monotonically increasing (i.e. going from 0 to 1,
2564 // but not 1 to 0) between successive calls between which the heap was
2565 // not collected. For the implementation below, it must thus rely on
2566 // the property that concurrent_cycles_since_last_unload()
2567 // will not decrease unless a collection cycle happened and that
2568 // _cmsGen->is_too_full() are
2569 // themselves also monotonic in that sense. See check_monotonicity()
2570 // below.
2571 void CMSCollector::update_should_unload_classes() {
2572 _should_unload_classes = false;
2573 if (CMSClassUnloadingEnabled) {
2574 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2575 CMSClassUnloadingMaxInterval)
2576 || _cmsGen->is_too_full();
2577 }
2578 }
2579
2580 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2581 bool res = should_concurrent_collect();
2582 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2583 return res;
2584 }
2585
2586 void CMSCollector::setup_cms_unloading_and_verification_state() {
2587 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2588 || VerifyBeforeExit;
2589 const int rso = GenCollectedHeap::SO_AllCodeCache;
2590
2591 // We set the proper root for this CMS cycle here.
2592 if (should_unload_classes()) { // Should unload classes this cycle
2593 remove_root_scanning_option(rso); // Shrink the root set appropriately
2594 set_verifying(should_verify); // Set verification state for this cycle
2595 return; // Nothing else needs to be done at this time
2596 }
2597
2598 // Not unloading classes this cycle
2599 assert(!should_unload_classes(), "Inconsistency!");
2600
2601 // If we are not unloading classes then add SO_AllCodeCache to root
2602 // scanning options.
2603 add_root_scanning_option(rso);
2604
2605 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2606 set_verifying(true);
2607 } else if (verifying() && !should_verify) {
2608 // We were verifying, but some verification flags got disabled.
2609 set_verifying(false);
2610 // Exclude symbols, strings and code cache elements from root scanning to
2611 // reduce IM and RM pauses.
2612 remove_root_scanning_option(rso);
2613 }
2614 }
2615
2616
2617 #ifndef PRODUCT
2618 HeapWord* CMSCollector::block_start(const void* p) const {
2619 const HeapWord* addr = (HeapWord*)p;
2620 if (_span.contains(p)) {
2621 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2622 return _cmsGen->cmsSpace()->block_start(p);
2623 }
2624 }
2625 return NULL;
2626 }
2627 #endif
2628
2629 HeapWord*
2630 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2631 bool tlab,
2632 bool parallel) {
2633 CMSSynchronousYieldRequest yr;
2634 assert(!tlab, "Can't deal with TLAB allocation");
2635 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2636 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2637 if (GCExpandToAllocateDelayMillis > 0) {
2638 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2639 }
2640 return have_lock_and_allocate(word_size, tlab);
2641 }
2642
2643 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2644 size_t bytes,
2645 size_t expand_bytes,
2646 CMSExpansionCause::Cause cause)
2647 {
2648
2649 bool success = expand(bytes, expand_bytes);
2650
2651 // remember why we expanded; this information is used
2652 // by shouldConcurrentCollect() when making decisions on whether to start
2653 // a new CMS cycle.
2654 if (success) {
2655 set_expansion_cause(cause);
2656 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2657 }
2658 }
2659
2660 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2661 HeapWord* res = NULL;
2662 MutexLocker x(ParGCRareEvent_lock);
2663 while (true) {
2664 // Expansion by some other thread might make alloc OK now:
2665 res = ps->lab.alloc(word_sz);
2666 if (res != NULL) return res;
2667 // If there's not enough expansion space available, give up.
2668 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2669 return NULL;
2670 }
2671 // Otherwise, we try expansion.
2672 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2673 // Now go around the loop and try alloc again;
2674 // A competing par_promote might beat us to the expansion space,
2675 // so we may go around the loop again if promotion fails again.
2676 if (GCExpandToAllocateDelayMillis > 0) {
2677 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2678 }
2679 }
2680 }
2681
2682
2683 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2684 PromotionInfo* promo) {
2685 MutexLocker x(ParGCRareEvent_lock);
2686 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2687 while (true) {
2688 // Expansion by some other thread might make alloc OK now:
2689 if (promo->ensure_spooling_space()) {
2690 assert(promo->has_spooling_space(),
2691 "Post-condition of successful ensure_spooling_space()");
2692 return true;
2693 }
2694 // If there's not enough expansion space available, give up.
2695 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2696 return false;
2697 }
2698 // Otherwise, we try expansion.
2699 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2700 // Now go around the loop and try alloc again;
2701 // A competing allocation might beat us to the expansion space,
2702 // so we may go around the loop again if allocation fails again.
2703 if (GCExpandToAllocateDelayMillis > 0) {
2704 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2705 }
2706 }
2707 }
2708
2709 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2710 // Only shrink if a compaction was done so that all the free space
2711 // in the generation is in a contiguous block at the end.
2712 if (did_compact()) {
2713 CardGeneration::shrink(bytes);
2714 }
2715 }
2716
2717 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2718 assert_locked_or_safepoint(Heap_lock);
2719 }
2720
2721 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2722 assert_locked_or_safepoint(Heap_lock);
2723 assert_lock_strong(freelistLock());
2724 log_trace(gc)("Shrinking of CMS not yet implemented");
2725 return;
2726 }
2727
2728
2729 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2730 // phases.
2731 class CMSPhaseAccounting: public StackObj {
2732 public:
2733 CMSPhaseAccounting(CMSCollector *collector,
2734 const char *title);
2735 ~CMSPhaseAccounting();
2736
2737 private:
2738 CMSCollector *_collector;
2739 const char *_title;
2740 GCTraceConcTime(Info, gc) _trace_time;
2741
2742 public:
2743 // Not MT-safe; so do not pass around these StackObj's
2744 // where they may be accessed by other threads.
2745 double wallclock_millis() {
2746 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2747 }
2748 };
2749
2750 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2751 const char *title) :
2752 _collector(collector), _title(title), _trace_time(title) {
2753
2754 _collector->resetYields();
2755 _collector->resetTimer();
2756 _collector->startTimer();
2757 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2758 }
2759
2760 CMSPhaseAccounting::~CMSPhaseAccounting() {
2761 _collector->gc_timer_cm()->register_gc_concurrent_end();
2762 _collector->stopTimer();
2763 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2764 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2765 }
2766
2767 // CMS work
2768
2769 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2770 class CMSParMarkTask : public AbstractGangTask {
2771 protected:
2772 CMSCollector* _collector;
2773 uint _n_workers;
2774 OopStorage::ParState<false, false> _par_state_string;
2775 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2776 AbstractGangTask(name),
2777 _collector(collector),
2778 _n_workers(n_workers),
2779 _par_state_string(StringTable::weak_storage()) {}
2780 // Work method in support of parallel rescan ... of young gen spaces
2781 void do_young_space_rescan(OopsInGenClosure* cl,
2782 ContiguousSpace* space,
2783 HeapWord** chunk_array, size_t chunk_top);
2784 void work_on_young_gen_roots(OopsInGenClosure* cl);
2785 };
2786
2787 // Parallel initial mark task
2788 class CMSParInitialMarkTask: public CMSParMarkTask {
2789 StrongRootsScope* _strong_roots_scope;
2790 public:
2791 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2792 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2793 _strong_roots_scope(strong_roots_scope) {}
2794 void work(uint worker_id);
2795 };
2796
2797 // Checkpoint the roots into this generation from outside
2798 // this generation. [Note this initial checkpoint need only
2799 // be approximate -- we'll do a catch up phase subsequently.]
2800 void CMSCollector::checkpointRootsInitial() {
2801 assert(_collectorState == InitialMarking, "Wrong collector state");
2802 check_correct_thread_executing();
2803 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2804
2805 save_heap_summary();
2806 report_heap_summary(GCWhen::BeforeGC);
2807
2808 ReferenceProcessor* rp = ref_processor();
2809 assert(_restart_addr == NULL, "Control point invariant");
2810 {
2811 // acquire locks for subsequent manipulations
2812 MutexLockerEx x(bitMapLock(),
2813 Mutex::_no_safepoint_check_flag);
2814 checkpointRootsInitialWork();
2815 // enable ("weak") refs discovery
2816 rp->enable_discovery();
2817 _collectorState = Marking;
2818 }
2819 }
2820
2821 void CMSCollector::checkpointRootsInitialWork() {
2822 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2823 assert(_collectorState == InitialMarking, "just checking");
2824
2825 // Already have locks.
2826 assert_lock_strong(bitMapLock());
2827 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2828
2829 // Setup the verification and class unloading state for this
2830 // CMS collection cycle.
2831 setup_cms_unloading_and_verification_state();
2832
2833 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2834
2835 // Reset all the PLAB chunk arrays if necessary.
2836 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2837 reset_survivor_plab_arrays();
2838 }
2839
2840 ResourceMark rm;
2841 HandleMark hm;
2842
2843 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2844 CMSHeap* heap = CMSHeap::heap();
2845
2846 verify_work_stacks_empty();
2847 verify_overflow_empty();
2848
2849 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2850 // Update the saved marks which may affect the root scans.
2851 heap->save_marks();
2852
2853 // weak reference processing has not started yet.
2854 ref_processor()->set_enqueuing_is_done(false);
2855
2856 // Need to remember all newly created CLDs,
2857 // so that we can guarantee that the remark finds them.
2858 ClassLoaderDataGraph::remember_new_clds(true);
2859
2860 // Whenever a CLD is found, it will be claimed before proceeding to mark
2861 // the klasses. The claimed marks need to be cleared before marking starts.
2862 ClassLoaderDataGraph::clear_claimed_marks();
2863
2864 print_eden_and_survivor_chunk_arrays();
2865
2866 {
2867 #if COMPILER2_OR_JVMCI
2868 DerivedPointerTableDeactivate dpt_deact;
2869 #endif
2870 if (CMSParallelInitialMarkEnabled) {
2871 // The parallel version.
2872 WorkGang* workers = heap->workers();
2873 assert(workers != NULL, "Need parallel worker threads.");
2874 uint n_workers = workers->active_workers();
2875
2876 StrongRootsScope srs(n_workers);
2877
2878 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2879 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2880 // If the total workers is greater than 1, then multiple workers
2881 // may be used at some time and the initialization has been set
2882 // such that the single threaded path cannot be used.
2883 if (workers->total_workers() > 1) {
2884 workers->run_task(&tsk);
2885 } else {
2886 tsk.work(0);
2887 }
2888 } else {
2889 // The serial version.
2890 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2891 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2892
2893 StrongRootsScope srs(1);
2894
2895 heap->cms_process_roots(&srs,
2896 true, // young gen as roots
2897 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2898 should_unload_classes(),
2899 ¬Older,
2900 &cld_closure);
2901 }
2902 }
2903
2904 // Clear mod-union table; it will be dirtied in the prologue of
2905 // CMS generation per each young generation collection.
2906
2907 assert(_modUnionTable.isAllClear(),
2908 "Was cleared in most recent final checkpoint phase"
2909 " or no bits are set in the gc_prologue before the start of the next "
2910 "subsequent marking phase.");
2911
2912 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2913
2914 // Save the end of the used_region of the constituent generations
2915 // to be used to limit the extent of sweep in each generation.
2916 save_sweep_limits();
2917 verify_overflow_empty();
2918 }
2919
2920 bool CMSCollector::markFromRoots() {
2921 // we might be tempted to assert that:
2922 // assert(!SafepointSynchronize::is_at_safepoint(),
2923 // "inconsistent argument?");
2924 // However that wouldn't be right, because it's possible that
2925 // a safepoint is indeed in progress as a young generation
2926 // stop-the-world GC happens even as we mark in this generation.
2927 assert(_collectorState == Marking, "inconsistent state?");
2928 check_correct_thread_executing();
2929 verify_overflow_empty();
2930
2931 // Weak ref discovery note: We may be discovering weak
2932 // refs in this generation concurrent (but interleaved) with
2933 // weak ref discovery by the young generation collector.
2934
2935 CMSTokenSyncWithLocks ts(true, bitMapLock());
2936 GCTraceCPUTime tcpu;
2937 CMSPhaseAccounting pa(this, "Concurrent Mark");
2938 bool res = markFromRootsWork();
2939 if (res) {
2940 _collectorState = Precleaning;
2941 } else { // We failed and a foreground collection wants to take over
2942 assert(_foregroundGCIsActive, "internal state inconsistency");
2943 assert(_restart_addr == NULL, "foreground will restart from scratch");
2944 log_debug(gc)("bailing out to foreground collection");
2945 }
2946 verify_overflow_empty();
2947 return res;
2948 }
2949
2950 bool CMSCollector::markFromRootsWork() {
2951 // iterate over marked bits in bit map, doing a full scan and mark
2952 // from these roots using the following algorithm:
2953 // . if oop is to the right of the current scan pointer,
2954 // mark corresponding bit (we'll process it later)
2955 // . else (oop is to left of current scan pointer)
2956 // push oop on marking stack
2957 // . drain the marking stack
2958
2959 // Note that when we do a marking step we need to hold the
2960 // bit map lock -- recall that direct allocation (by mutators)
2961 // and promotion (by the young generation collector) is also
2962 // marking the bit map. [the so-called allocate live policy.]
2963 // Because the implementation of bit map marking is not
2964 // robust wrt simultaneous marking of bits in the same word,
2965 // we need to make sure that there is no such interference
2966 // between concurrent such updates.
2967
2968 // already have locks
2969 assert_lock_strong(bitMapLock());
2970
2971 verify_work_stacks_empty();
2972 verify_overflow_empty();
2973 bool result = false;
2974 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2975 result = do_marking_mt();
2976 } else {
2977 result = do_marking_st();
2978 }
2979 return result;
2980 }
2981
2982 // Forward decl
2983 class CMSConcMarkingTask;
2984
2985 class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator {
2986 CMSCollector* _collector;
2987 CMSConcMarkingTask* _task;
2988 public:
2989 virtual void yield();
2990
2991 // "n_threads" is the number of threads to be terminated.
2992 // "queue_set" is a set of work queues of other threads.
2993 // "collector" is the CMS collector associated with this task terminator.
2994 // "yield" indicates whether we need the gang as a whole to yield.
2995 CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2996 ParallelTaskTerminator(n_threads, queue_set),
2997 _collector(collector) { }
2998
2999 void set_task(CMSConcMarkingTask* task) {
3000 _task = task;
3001 }
3002 };
3003
3004 class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator {
3005 CMSCollector* _collector;
3006 CMSConcMarkingTask* _task;
3007 public:
3008 virtual void yield();
3009
3010 // "n_threads" is the number of threads to be terminated.
3011 // "queue_set" is a set of work queues of other threads.
3012 // "collector" is the CMS collector associated with this task terminator.
3013 // "yield" indicates whether we need the gang as a whole to yield.
3014 CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3015 OWSTTaskTerminator(n_threads, queue_set),
3016 _collector(collector) { }
3017
3018 void set_task(CMSConcMarkingTask* task) {
3019 _task = task;
3020 }
3021 };
3022
3023 class CMSConcMarkingTaskTerminator {
3024 private:
3025 ParallelTaskTerminator* _term;
3026 public:
3027 CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) {
3028 if (UseOWSTTaskTerminator) {
3029 _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector);
3030 } else {
3031 _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector);
3032 }
3033 }
3034 ~CMSConcMarkingTaskTerminator() {
3035 assert(_term != NULL, "Must not be NULL");
3036 delete _term;
3037 }
3038
3039 void set_task(CMSConcMarkingTask* task);
3040 ParallelTaskTerminator* terminator() const { return _term; }
3041 };
3042
3043 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3044 CMSConcMarkingTask* _task;
3045 public:
3046 bool should_exit_termination();
3047 void set_task(CMSConcMarkingTask* task) {
3048 _task = task;
3049 }
3050 };
3051
3052 // MT Concurrent Marking Task
3053 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3054 CMSCollector* _collector;
3055 uint _n_workers; // requested/desired # workers
3056 bool _result;
3057 CompactibleFreeListSpace* _cms_space;
3058 char _pad_front[64]; // padding to ...
3059 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3060 char _pad_back[64];
3061 HeapWord* _restart_addr;
3062
3063 // Exposed here for yielding support
3064 Mutex* const _bit_map_lock;
3065
3066 // The per thread work queues, available here for stealing
3067 OopTaskQueueSet* _task_queues;
3068
3069 // Termination (and yielding) support
3070 CMSConcMarkingTaskTerminator _term;
3071 CMSConcMarkingTerminatorTerminator _term_term;
3072
3073 public:
3074 CMSConcMarkingTask(CMSCollector* collector,
3075 CompactibleFreeListSpace* cms_space,
3076 YieldingFlexibleWorkGang* workers,
3077 OopTaskQueueSet* task_queues):
3078 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3079 _collector(collector),
3080 _n_workers(0),
3081 _result(true),
3082 _cms_space(cms_space),
3083 _bit_map_lock(collector->bitMapLock()),
3084 _task_queues(task_queues),
3085 _term(_n_workers, task_queues, _collector)
3086 {
3087 _requested_size = _n_workers;
3088 _term.set_task(this);
3089 _term_term.set_task(this);
3090 _restart_addr = _global_finger = _cms_space->bottom();
3091 }
3092
3093
3094 OopTaskQueueSet* task_queues() { return _task_queues; }
3095
3096 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3097
3098 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3099
3100 ParallelTaskTerminator* terminator() { return _term.terminator(); }
3101
3102 virtual void set_for_termination(uint active_workers) {
3103 terminator()->reset_for_reuse(active_workers);
3104 }
3105
3106 void work(uint worker_id);
3107 bool should_yield() {
3108 return ConcurrentMarkSweepThread::should_yield()
3109 && !_collector->foregroundGCIsActive();
3110 }
3111
3112 virtual void coordinator_yield(); // stuff done by coordinator
3113 bool result() { return _result; }
3114
3115 void reset(HeapWord* ra) {
3116 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3117 _restart_addr = _global_finger = ra;
3118 _term.terminator()->reset_for_reuse();
3119 }
3120
3121 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3122 OopTaskQueue* work_q);
3123
3124 private:
3125 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3126 void do_work_steal(int i);
3127 void bump_global_finger(HeapWord* f);
3128 };
3129
3130 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3131 assert(_task != NULL, "Error");
3132 return _task->yielding();
3133 // Note that we do not need the disjunct || _task->should_yield() above
3134 // because we want terminating threads to yield only if the task
3135 // is already in the midst of yielding, which happens only after at least one
3136 // thread has yielded.
3137 }
3138
3139 void CMSConcMarkingParallelTerminator::yield() {
3140 if (_task->should_yield()) {
3141 _task->yield();
3142 } else {
3143 ParallelTaskTerminator::yield();
3144 }
3145 }
3146
3147 void CMSConcMarkingOWSTTerminator::yield() {
3148 if (_task->should_yield()) {
3149 _task->yield();
3150 } else {
3151 OWSTTaskTerminator::yield();
3152 }
3153 }
3154
3155 void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) {
3156 if (UseOWSTTaskTerminator) {
3157 ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task);
3158 } else {
3159 ((CMSConcMarkingParallelTerminator*)_term)->set_task(task);
3160 }
3161 }
3162
3163 ////////////////////////////////////////////////////////////////
3164 // Concurrent Marking Algorithm Sketch
3165 ////////////////////////////////////////////////////////////////
3166 // Until all tasks exhausted (both spaces):
3167 // -- claim next available chunk
3168 // -- bump global finger via CAS
3169 // -- find first object that starts in this chunk
3170 // and start scanning bitmap from that position
3171 // -- scan marked objects for oops
3172 // -- CAS-mark target, and if successful:
3173 // . if target oop is above global finger (volatile read)
3174 // nothing to do
3175 // . if target oop is in chunk and above local finger
3176 // then nothing to do
3177 // . else push on work-queue
3178 // -- Deal with possible overflow issues:
3179 // . local work-queue overflow causes stuff to be pushed on
3180 // global (common) overflow queue
3181 // . always first empty local work queue
3182 // . then get a batch of oops from global work queue if any
3183 // . then do work stealing
3184 // -- When all tasks claimed (both spaces)
3185 // and local work queue empty,
3186 // then in a loop do:
3187 // . check global overflow stack; steal a batch of oops and trace
3188 // . try to steal from other threads oif GOS is empty
3189 // . if neither is available, offer termination
3190 // -- Terminate and return result
3191 //
3192 void CMSConcMarkingTask::work(uint worker_id) {
3193 elapsedTimer _timer;
3194 ResourceMark rm;
3195 HandleMark hm;
3196
3197 DEBUG_ONLY(_collector->verify_overflow_empty();)
3198
3199 // Before we begin work, our work queue should be empty
3200 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3201 // Scan the bitmap covering _cms_space, tracing through grey objects.
3202 _timer.start();
3203 do_scan_and_mark(worker_id, _cms_space);
3204 _timer.stop();
3205 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3206
3207 // ... do work stealing
3208 _timer.reset();
3209 _timer.start();
3210 do_work_steal(worker_id);
3211 _timer.stop();
3212 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3213 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3214 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3215 // Note that under the current task protocol, the
3216 // following assertion is true even of the spaces
3217 // expanded since the completion of the concurrent
3218 // marking. XXX This will likely change under a strict
3219 // ABORT semantics.
3220 // After perm removal the comparison was changed to
3221 // greater than or equal to from strictly greater than.
3222 // Before perm removal the highest address sweep would
3223 // have been at the end of perm gen but now is at the
3224 // end of the tenured gen.
3225 assert(_global_finger >= _cms_space->end(),
3226 "All tasks have been completed");
3227 DEBUG_ONLY(_collector->verify_overflow_empty();)
3228 }
3229
3230 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3231 HeapWord* read = _global_finger;
3232 HeapWord* cur = read;
3233 while (f > read) {
3234 cur = read;
3235 read = Atomic::cmpxchg(f, &_global_finger, cur);
3236 if (cur == read) {
3237 // our cas succeeded
3238 assert(_global_finger >= f, "protocol consistency");
3239 break;
3240 }
3241 }
3242 }
3243
3244 // This is really inefficient, and should be redone by
3245 // using (not yet available) block-read and -write interfaces to the
3246 // stack and the work_queue. XXX FIX ME !!!
3247 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3248 OopTaskQueue* work_q) {
3249 // Fast lock-free check
3250 if (ovflw_stk->length() == 0) {
3251 return false;
3252 }
3253 assert(work_q->size() == 0, "Shouldn't steal");
3254 MutexLockerEx ml(ovflw_stk->par_lock(),
3255 Mutex::_no_safepoint_check_flag);
3256 // Grab up to 1/4 the size of the work queue
3257 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3258 (size_t)ParGCDesiredObjsFromOverflowList);
3259 num = MIN2(num, ovflw_stk->length());
3260 for (int i = (int) num; i > 0; i--) {
3261 oop cur = ovflw_stk->pop();
3262 assert(cur != NULL, "Counted wrong?");
3263 work_q->push(cur);
3264 }
3265 return num > 0;
3266 }
3267
3268 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3269 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3270 int n_tasks = pst->n_tasks();
3271 // We allow that there may be no tasks to do here because
3272 // we are restarting after a stack overflow.
3273 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3274 uint nth_task = 0;
3275
3276 HeapWord* aligned_start = sp->bottom();
3277 if (sp->used_region().contains(_restart_addr)) {
3278 // Align down to a card boundary for the start of 0th task
3279 // for this space.
3280 aligned_start = align_down(_restart_addr, CardTable::card_size);
3281 }
3282
3283 size_t chunk_size = sp->marking_task_size();
3284 while (pst->try_claim_task(/* reference */ nth_task)) {
3285 // Having claimed the nth task in this space,
3286 // compute the chunk that it corresponds to:
3287 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3288 aligned_start + (nth_task+1)*chunk_size);
3289 // Try and bump the global finger via a CAS;
3290 // note that we need to do the global finger bump
3291 // _before_ taking the intersection below, because
3292 // the task corresponding to that region will be
3293 // deemed done even if the used_region() expands
3294 // because of allocation -- as it almost certainly will
3295 // during start-up while the threads yield in the
3296 // closure below.
3297 HeapWord* finger = span.end();
3298 bump_global_finger(finger); // atomically
3299 // There are null tasks here corresponding to chunks
3300 // beyond the "top" address of the space.
3301 span = span.intersection(sp->used_region());
3302 if (!span.is_empty()) { // Non-null task
3303 HeapWord* prev_obj;
3304 assert(!span.contains(_restart_addr) || nth_task == 0,
3305 "Inconsistency");
3306 if (nth_task == 0) {
3307 // For the 0th task, we'll not need to compute a block_start.
3308 if (span.contains(_restart_addr)) {
3309 // In the case of a restart because of stack overflow,
3310 // we might additionally skip a chunk prefix.
3311 prev_obj = _restart_addr;
3312 } else {
3313 prev_obj = span.start();
3314 }
3315 } else {
3316 // We want to skip the first object because
3317 // the protocol is to scan any object in its entirety
3318 // that _starts_ in this span; a fortiori, any
3319 // object starting in an earlier span is scanned
3320 // as part of an earlier claimed task.
3321 // Below we use the "careful" version of block_start
3322 // so we do not try to navigate uninitialized objects.
3323 prev_obj = sp->block_start_careful(span.start());
3324 // Below we use a variant of block_size that uses the
3325 // Printezis bits to avoid waiting for allocated
3326 // objects to become initialized/parsable.
3327 while (prev_obj < span.start()) {
3328 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3329 if (sz > 0) {
3330 prev_obj += sz;
3331 } else {
3332 // In this case we may end up doing a bit of redundant
3333 // scanning, but that appears unavoidable, short of
3334 // locking the free list locks; see bug 6324141.
3335 break;
3336 }
3337 }
3338 }
3339 if (prev_obj < span.end()) {
3340 MemRegion my_span = MemRegion(prev_obj, span.end());
3341 // Do the marking work within a non-empty span --
3342 // the last argument to the constructor indicates whether the
3343 // iteration should be incremental with periodic yields.
3344 ParMarkFromRootsClosure cl(this, _collector, my_span,
3345 &_collector->_markBitMap,
3346 work_queue(i),
3347 &_collector->_markStack);
3348 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3349 } // else nothing to do for this task
3350 } // else nothing to do for this task
3351 }
3352 // We'd be tempted to assert here that since there are no
3353 // more tasks left to claim in this space, the global_finger
3354 // must exceed space->top() and a fortiori space->end(). However,
3355 // that would not quite be correct because the bumping of
3356 // global_finger occurs strictly after the claiming of a task,
3357 // so by the time we reach here the global finger may not yet
3358 // have been bumped up by the thread that claimed the last
3359 // task.
3360 pst->all_tasks_completed();
3361 }
3362
3363 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3364 private:
3365 CMSCollector* _collector;
3366 CMSConcMarkingTask* _task;
3367 MemRegion _span;
3368 CMSBitMap* _bit_map;
3369 CMSMarkStack* _overflow_stack;
3370 OopTaskQueue* _work_queue;
3371 protected:
3372 DO_OOP_WORK_DEFN
3373 public:
3374 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3375 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3376 MetadataVisitingOopIterateClosure(collector->ref_processor()),
3377 _collector(collector),
3378 _task(task),
3379 _span(collector->_span),
3380 _bit_map(bit_map),
3381 _overflow_stack(overflow_stack),
3382 _work_queue(work_queue)
3383 { }
3384 virtual void do_oop(oop* p);
3385 virtual void do_oop(narrowOop* p);
3386
3387 void trim_queue(size_t max);
3388 void handle_stack_overflow(HeapWord* lost);
3389 void do_yield_check() {
3390 if (_task->should_yield()) {
3391 _task->yield();
3392 }
3393 }
3394 };
3395
3396 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3397
3398 // Grey object scanning during work stealing phase --
3399 // the salient assumption here is that any references
3400 // that are in these stolen objects being scanned must
3401 // already have been initialized (else they would not have
3402 // been published), so we do not need to check for
3403 // uninitialized objects before pushing here.
3404 void ParConcMarkingClosure::do_oop(oop obj) {
3405 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3406 HeapWord* addr = (HeapWord*)obj;
3407 // Check if oop points into the CMS generation
3408 // and is not marked
3409 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3410 // a white object ...
3411 // If we manage to "claim" the object, by being the
3412 // first thread to mark it, then we push it on our
3413 // marking stack
3414 if (_bit_map->par_mark(addr)) { // ... now grey
3415 // push on work queue (grey set)
3416 bool simulate_overflow = false;
3417 NOT_PRODUCT(
3418 if (CMSMarkStackOverflowALot &&
3419 _collector->simulate_overflow()) {
3420 // simulate a stack overflow
3421 simulate_overflow = true;
3422 }
3423 )
3424 if (simulate_overflow ||
3425 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3426 // stack overflow
3427 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3428 // We cannot assert that the overflow stack is full because
3429 // it may have been emptied since.
3430 assert(simulate_overflow ||
3431 _work_queue->size() == _work_queue->max_elems(),
3432 "Else push should have succeeded");
3433 handle_stack_overflow(addr);
3434 }
3435 } // Else, some other thread got there first
3436 do_yield_check();
3437 }
3438 }
3439
3440 void ParConcMarkingClosure::trim_queue(size_t max) {
3441 while (_work_queue->size() > max) {
3442 oop new_oop;
3443 if (_work_queue->pop_local(new_oop)) {
3444 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3445 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3446 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3447 new_oop->oop_iterate(this); // do_oop() above
3448 do_yield_check();
3449 }
3450 }
3451 }
3452
3453 // Upon stack overflow, we discard (part of) the stack,
3454 // remembering the least address amongst those discarded
3455 // in CMSCollector's _restart_address.
3456 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3457 // We need to do this under a mutex to prevent other
3458 // workers from interfering with the work done below.
3459 MutexLockerEx ml(_overflow_stack->par_lock(),
3460 Mutex::_no_safepoint_check_flag);
3461 // Remember the least grey address discarded
3462 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3463 _collector->lower_restart_addr(ra);
3464 _overflow_stack->reset(); // discard stack contents
3465 _overflow_stack->expand(); // expand the stack if possible
3466 }
3467
3468
3469 void CMSConcMarkingTask::do_work_steal(int i) {
3470 OopTaskQueue* work_q = work_queue(i);
3471 oop obj_to_scan;
3472 CMSBitMap* bm = &(_collector->_markBitMap);
3473 CMSMarkStack* ovflw = &(_collector->_markStack);
3474 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3475 while (true) {
3476 cl.trim_queue(0);
3477 assert(work_q->size() == 0, "Should have been emptied above");
3478 if (get_work_from_overflow_stack(ovflw, work_q)) {
3479 // Can't assert below because the work obtained from the
3480 // overflow stack may already have been stolen from us.
3481 // assert(work_q->size() > 0, "Work from overflow stack");
3482 continue;
3483 } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3484 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3485 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3486 obj_to_scan->oop_iterate(&cl);
3487 } else if (terminator()->offer_termination(&_term_term)) {
3488 assert(work_q->size() == 0, "Impossible!");
3489 break;
3490 } else if (yielding() || should_yield()) {
3491 yield();
3492 }
3493 }
3494 }
3495
3496 // This is run by the CMS (coordinator) thread.
3497 void CMSConcMarkingTask::coordinator_yield() {
3498 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3499 "CMS thread should hold CMS token");
3500 // First give up the locks, then yield, then re-lock
3501 // We should probably use a constructor/destructor idiom to
3502 // do this unlock/lock or modify the MutexUnlocker class to
3503 // serve our purpose. XXX
3504 assert_lock_strong(_bit_map_lock);
3505 _bit_map_lock->unlock();
3506 ConcurrentMarkSweepThread::desynchronize(true);
3507 _collector->stopTimer();
3508 _collector->incrementYields();
3509
3510 // It is possible for whichever thread initiated the yield request
3511 // not to get a chance to wake up and take the bitmap lock between
3512 // this thread releasing it and reacquiring it. So, while the
3513 // should_yield() flag is on, let's sleep for a bit to give the
3514 // other thread a chance to wake up. The limit imposed on the number
3515 // of iterations is defensive, to avoid any unforseen circumstances
3516 // putting us into an infinite loop. Since it's always been this
3517 // (coordinator_yield()) method that was observed to cause the
3518 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3519 // which is by default non-zero. For the other seven methods that
3520 // also perform the yield operation, as are using a different
3521 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3522 // can enable the sleeping for those methods too, if necessary.
3523 // See 6442774.
3524 //
3525 // We really need to reconsider the synchronization between the GC
3526 // thread and the yield-requesting threads in the future and we
3527 // should really use wait/notify, which is the recommended
3528 // way of doing this type of interaction. Additionally, we should
3529 // consolidate the eight methods that do the yield operation and they
3530 // are almost identical into one for better maintainability and
3531 // readability. See 6445193.
3532 //
3533 // Tony 2006.06.29
3534 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3535 ConcurrentMarkSweepThread::should_yield() &&
3536 !CMSCollector::foregroundGCIsActive(); ++i) {
3537 os::sleep(Thread::current(), 1, false);
3538 }
3539
3540 ConcurrentMarkSweepThread::synchronize(true);
3541 _bit_map_lock->lock_without_safepoint_check();
3542 _collector->startTimer();
3543 }
3544
3545 bool CMSCollector::do_marking_mt() {
3546 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3547 uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3548 conc_workers()->active_workers(),
3549 Threads::number_of_non_daemon_threads());
3550 num_workers = conc_workers()->update_active_workers(num_workers);
3551 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3552
3553 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3554
3555 CMSConcMarkingTask tsk(this,
3556 cms_space,
3557 conc_workers(),
3558 task_queues());
3559
3560 // Since the actual number of workers we get may be different
3561 // from the number we requested above, do we need to do anything different
3562 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3563 // class?? XXX
3564 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3565
3566 // Refs discovery is already non-atomic.
3567 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3568 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3569 conc_workers()->start_task(&tsk);
3570 while (tsk.yielded()) {
3571 tsk.coordinator_yield();
3572 conc_workers()->continue_task(&tsk);
3573 }
3574 // If the task was aborted, _restart_addr will be non-NULL
3575 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3576 while (_restart_addr != NULL) {
3577 // XXX For now we do not make use of ABORTED state and have not
3578 // yet implemented the right abort semantics (even in the original
3579 // single-threaded CMS case). That needs some more investigation
3580 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3581 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3582 // If _restart_addr is non-NULL, a marking stack overflow
3583 // occurred; we need to do a fresh marking iteration from the
3584 // indicated restart address.
3585 if (_foregroundGCIsActive) {
3586 // We may be running into repeated stack overflows, having
3587 // reached the limit of the stack size, while making very
3588 // slow forward progress. It may be best to bail out and
3589 // let the foreground collector do its job.
3590 // Clear _restart_addr, so that foreground GC
3591 // works from scratch. This avoids the headache of
3592 // a "rescan" which would otherwise be needed because
3593 // of the dirty mod union table & card table.
3594 _restart_addr = NULL;
3595 return false;
3596 }
3597 // Adjust the task to restart from _restart_addr
3598 tsk.reset(_restart_addr);
3599 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3600 _restart_addr);
3601 _restart_addr = NULL;
3602 // Get the workers going again
3603 conc_workers()->start_task(&tsk);
3604 while (tsk.yielded()) {
3605 tsk.coordinator_yield();
3606 conc_workers()->continue_task(&tsk);
3607 }
3608 }
3609 assert(tsk.completed(), "Inconsistency");
3610 assert(tsk.result() == true, "Inconsistency");
3611 return true;
3612 }
3613
3614 bool CMSCollector::do_marking_st() {
3615 ResourceMark rm;
3616 HandleMark hm;
3617
3618 // Temporarily make refs discovery single threaded (non-MT)
3619 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3620 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3621 &_markStack, CMSYield);
3622 // the last argument to iterate indicates whether the iteration
3623 // should be incremental with periodic yields.
3624 _markBitMap.iterate(&markFromRootsClosure);
3625 // If _restart_addr is non-NULL, a marking stack overflow
3626 // occurred; we need to do a fresh iteration from the
3627 // indicated restart address.
3628 while (_restart_addr != NULL) {
3629 if (_foregroundGCIsActive) {
3630 // We may be running into repeated stack overflows, having
3631 // reached the limit of the stack size, while making very
3632 // slow forward progress. It may be best to bail out and
3633 // let the foreground collector do its job.
3634 // Clear _restart_addr, so that foreground GC
3635 // works from scratch. This avoids the headache of
3636 // a "rescan" which would otherwise be needed because
3637 // of the dirty mod union table & card table.
3638 _restart_addr = NULL;
3639 return false; // indicating failure to complete marking
3640 }
3641 // Deal with stack overflow:
3642 // we restart marking from _restart_addr
3643 HeapWord* ra = _restart_addr;
3644 markFromRootsClosure.reset(ra);
3645 _restart_addr = NULL;
3646 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3647 }
3648 return true;
3649 }
3650
3651 void CMSCollector::preclean() {
3652 check_correct_thread_executing();
3653 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3654 verify_work_stacks_empty();
3655 verify_overflow_empty();
3656 _abort_preclean = false;
3657 if (CMSPrecleaningEnabled) {
3658 if (!CMSEdenChunksRecordAlways) {
3659 _eden_chunk_index = 0;
3660 }
3661 size_t used = get_eden_used();
3662 size_t capacity = get_eden_capacity();
3663 // Don't start sampling unless we will get sufficiently
3664 // many samples.
3665 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3666 * CMSScheduleRemarkEdenPenetration)) {
3667 _start_sampling = true;
3668 } else {
3669 _start_sampling = false;
3670 }
3671 GCTraceCPUTime tcpu;
3672 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3673 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3674 }
3675 CMSTokenSync x(true); // is cms thread
3676 if (CMSPrecleaningEnabled) {
3677 sample_eden();
3678 _collectorState = AbortablePreclean;
3679 } else {
3680 _collectorState = FinalMarking;
3681 }
3682 verify_work_stacks_empty();
3683 verify_overflow_empty();
3684 }
3685
3686 // Try and schedule the remark such that young gen
3687 // occupancy is CMSScheduleRemarkEdenPenetration %.
3688 void CMSCollector::abortable_preclean() {
3689 check_correct_thread_executing();
3690 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3691 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3692
3693 // If Eden's current occupancy is below this threshold,
3694 // immediately schedule the remark; else preclean
3695 // past the next scavenge in an effort to
3696 // schedule the pause as described above. By choosing
3697 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3698 // we will never do an actual abortable preclean cycle.
3699 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3700 GCTraceCPUTime tcpu;
3701 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3702 // We need more smarts in the abortable preclean
3703 // loop below to deal with cases where allocation
3704 // in young gen is very very slow, and our precleaning
3705 // is running a losing race against a horde of
3706 // mutators intent on flooding us with CMS updates
3707 // (dirty cards).
3708 // One, admittedly dumb, strategy is to give up
3709 // after a certain number of abortable precleaning loops
3710 // or after a certain maximum time. We want to make
3711 // this smarter in the next iteration.
3712 // XXX FIX ME!!! YSR
3713 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3714 while (!(should_abort_preclean() ||
3715 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3716 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3717 cumworkdone += workdone;
3718 loops++;
3719 // Voluntarily terminate abortable preclean phase if we have
3720 // been at it for too long.
3721 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3722 loops >= CMSMaxAbortablePrecleanLoops) {
3723 log_debug(gc)(" CMS: abort preclean due to loops ");
3724 break;
3725 }
3726 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3727 log_debug(gc)(" CMS: abort preclean due to time ");
3728 break;
3729 }
3730 // If we are doing little work each iteration, we should
3731 // take a short break.
3732 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3733 // Sleep for some time, waiting for work to accumulate
3734 stopTimer();
3735 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3736 startTimer();
3737 waited++;
3738 }
3739 }
3740 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3741 loops, waited, cumworkdone);
3742 }
3743 CMSTokenSync x(true); // is cms thread
3744 if (_collectorState != Idling) {
3745 assert(_collectorState == AbortablePreclean,
3746 "Spontaneous state transition?");
3747 _collectorState = FinalMarking;
3748 } // Else, a foreground collection completed this CMS cycle.
3749 return;
3750 }
3751
3752 // Respond to an Eden sampling opportunity
3753 void CMSCollector::sample_eden() {
3754 // Make sure a young gc cannot sneak in between our
3755 // reading and recording of a sample.
3756 assert(Thread::current()->is_ConcurrentGC_thread(),
3757 "Only the cms thread may collect Eden samples");
3758 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3759 "Should collect samples while holding CMS token");
3760 if (!_start_sampling) {
3761 return;
3762 }
3763 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3764 // is populated by the young generation.
3765 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3766 if (_eden_chunk_index < _eden_chunk_capacity) {
3767 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3768 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3769 "Unexpected state of Eden");
3770 // We'd like to check that what we just sampled is an oop-start address;
3771 // however, we cannot do that here since the object may not yet have been
3772 // initialized. So we'll instead do the check when we _use_ this sample
3773 // later.
3774 if (_eden_chunk_index == 0 ||
3775 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3776 _eden_chunk_array[_eden_chunk_index-1])
3777 >= CMSSamplingGrain)) {
3778 _eden_chunk_index++; // commit sample
3779 }
3780 }
3781 }
3782 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3783 size_t used = get_eden_used();
3784 size_t capacity = get_eden_capacity();
3785 assert(used <= capacity, "Unexpected state of Eden");
3786 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3787 _abort_preclean = true;
3788 }
3789 }
3790 }
3791
3792 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3793 assert(_collectorState == Precleaning ||
3794 _collectorState == AbortablePreclean, "incorrect state");
3795 ResourceMark rm;
3796 HandleMark hm;
3797
3798 // Precleaning is currently not MT but the reference processor
3799 // may be set for MT. Disable it temporarily here.
3800 ReferenceProcessor* rp = ref_processor();
3801 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3802
3803 // Do one pass of scrubbing the discovered reference lists
3804 // to remove any reference objects with strongly-reachable
3805 // referents.
3806 if (clean_refs) {
3807 CMSPrecleanRefsYieldClosure yield_cl(this);
3808 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3809 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3810 &_markStack, true /* preclean */);
3811 CMSDrainMarkingStackClosure complete_trace(this,
3812 _span, &_markBitMap, &_markStack,
3813 &keep_alive, true /* preclean */);
3814
3815 // We don't want this step to interfere with a young
3816 // collection because we don't want to take CPU
3817 // or memory bandwidth away from the young GC threads
3818 // (which may be as many as there are CPUs).
3819 // Note that we don't need to protect ourselves from
3820 // interference with mutators because they can't
3821 // manipulate the discovered reference lists nor affect
3822 // the computed reachability of the referents, the
3823 // only properties manipulated by the precleaning
3824 // of these reference lists.
3825 stopTimer();
3826 CMSTokenSyncWithLocks x(true /* is cms thread */,
3827 bitMapLock());
3828 startTimer();
3829 sample_eden();
3830
3831 // The following will yield to allow foreground
3832 // collection to proceed promptly. XXX YSR:
3833 // The code in this method may need further
3834 // tweaking for better performance and some restructuring
3835 // for cleaner interfaces.
3836 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3837 rp->preclean_discovered_references(
3838 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3839 gc_timer);
3840 }
3841
3842 if (clean_survivor) { // preclean the active survivor space(s)
3843 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3844 &_markBitMap, &_modUnionTable,
3845 &_markStack, true /* precleaning phase */);
3846 stopTimer();
3847 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3848 bitMapLock());
3849 startTimer();
3850 unsigned int before_count =
3851 CMSHeap::heap()->total_collections();
3852 SurvivorSpacePrecleanClosure
3853 sss_cl(this, _span, &_markBitMap, &_markStack,
3854 &pam_cl, before_count, CMSYield);
3855 _young_gen->from()->object_iterate_careful(&sss_cl);
3856 _young_gen->to()->object_iterate_careful(&sss_cl);
3857 }
3858 MarkRefsIntoAndScanClosure
3859 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3860 &_markStack, this, CMSYield,
3861 true /* precleaning phase */);
3862 // CAUTION: The following closure has persistent state that may need to
3863 // be reset upon a decrease in the sequence of addresses it
3864 // processes.
3865 ScanMarkedObjectsAgainCarefullyClosure
3866 smoac_cl(this, _span,
3867 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3868
3869 // Preclean dirty cards in ModUnionTable and CardTable using
3870 // appropriate convergence criterion;
3871 // repeat CMSPrecleanIter times unless we find that
3872 // we are losing.
3873 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3874 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3875 "Bad convergence multiplier");
3876 assert(CMSPrecleanThreshold >= 100,
3877 "Unreasonably low CMSPrecleanThreshold");
3878
3879 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3880 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3881 numIter < CMSPrecleanIter;
3882 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3883 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3884 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3885 // Either there are very few dirty cards, so re-mark
3886 // pause will be small anyway, or our pre-cleaning isn't
3887 // that much faster than the rate at which cards are being
3888 // dirtied, so we might as well stop and re-mark since
3889 // precleaning won't improve our re-mark time by much.
3890 if (curNumCards <= CMSPrecleanThreshold ||
3891 (numIter > 0 &&
3892 (curNumCards * CMSPrecleanDenominator >
3893 lastNumCards * CMSPrecleanNumerator))) {
3894 numIter++;
3895 cumNumCards += curNumCards;
3896 break;
3897 }
3898 }
3899
3900 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3901
3902 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3903 cumNumCards += curNumCards;
3904 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3905 curNumCards, cumNumCards, numIter);
3906 return cumNumCards; // as a measure of useful work done
3907 }
3908
3909 // PRECLEANING NOTES:
3910 // Precleaning involves:
3911 // . reading the bits of the modUnionTable and clearing the set bits.
3912 // . For the cards corresponding to the set bits, we scan the
3913 // objects on those cards. This means we need the free_list_lock
3914 // so that we can safely iterate over the CMS space when scanning
3915 // for oops.
3916 // . When we scan the objects, we'll be both reading and setting
3917 // marks in the marking bit map, so we'll need the marking bit map.
3918 // . For protecting _collector_state transitions, we take the CGC_lock.
3919 // Note that any races in the reading of of card table entries by the
3920 // CMS thread on the one hand and the clearing of those entries by the
3921 // VM thread or the setting of those entries by the mutator threads on the
3922 // other are quite benign. However, for efficiency it makes sense to keep
3923 // the VM thread from racing with the CMS thread while the latter is
3924 // dirty card info to the modUnionTable. We therefore also use the
3925 // CGC_lock to protect the reading of the card table and the mod union
3926 // table by the CM thread.
3927 // . We run concurrently with mutator updates, so scanning
3928 // needs to be done carefully -- we should not try to scan
3929 // potentially uninitialized objects.
3930 //
3931 // Locking strategy: While holding the CGC_lock, we scan over and
3932 // reset a maximal dirty range of the mod union / card tables, then lock
3933 // the free_list_lock and bitmap lock to do a full marking, then
3934 // release these locks; and repeat the cycle. This allows for a
3935 // certain amount of fairness in the sharing of these locks between
3936 // the CMS collector on the one hand, and the VM thread and the
3937 // mutators on the other.
3938
3939 // NOTE: preclean_mod_union_table() and preclean_card_table()
3940 // further below are largely identical; if you need to modify
3941 // one of these methods, please check the other method too.
3942
3943 size_t CMSCollector::preclean_mod_union_table(
3944 ConcurrentMarkSweepGeneration* old_gen,
3945 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3946 verify_work_stacks_empty();
3947 verify_overflow_empty();
3948
3949 // strategy: starting with the first card, accumulate contiguous
3950 // ranges of dirty cards; clear these cards, then scan the region
3951 // covered by these cards.
3952
3953 // Since all of the MUT is committed ahead, we can just use
3954 // that, in case the generations expand while we are precleaning.
3955 // It might also be fine to just use the committed part of the
3956 // generation, but we might potentially miss cards when the
3957 // generation is rapidly expanding while we are in the midst
3958 // of precleaning.
3959 HeapWord* startAddr = old_gen->reserved().start();
3960 HeapWord* endAddr = old_gen->reserved().end();
3961
3962 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3963
3964 size_t numDirtyCards, cumNumDirtyCards;
3965 HeapWord *nextAddr, *lastAddr;
3966 for (cumNumDirtyCards = numDirtyCards = 0,
3967 nextAddr = lastAddr = startAddr;
3968 nextAddr < endAddr;
3969 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3970
3971 ResourceMark rm;
3972 HandleMark hm;
3973
3974 MemRegion dirtyRegion;
3975 {
3976 stopTimer();
3977 // Potential yield point
3978 CMSTokenSync ts(true);
3979 startTimer();
3980 sample_eden();
3981 // Get dirty region starting at nextOffset (inclusive),
3982 // simultaneously clearing it.
3983 dirtyRegion =
3984 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3985 assert(dirtyRegion.start() >= nextAddr,
3986 "returned region inconsistent?");
3987 }
3988 // Remember where the next search should begin.
3989 // The returned region (if non-empty) is a right open interval,
3990 // so lastOffset is obtained from the right end of that
3991 // interval.
3992 lastAddr = dirtyRegion.end();
3993 // Should do something more transparent and less hacky XXX
3994 numDirtyCards =
3995 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3996
3997 // We'll scan the cards in the dirty region (with periodic
3998 // yields for foreground GC as needed).
3999 if (!dirtyRegion.is_empty()) {
4000 assert(numDirtyCards > 0, "consistency check");
4001 HeapWord* stop_point = NULL;
4002 stopTimer();
4003 // Potential yield point
4004 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4005 bitMapLock());
4006 startTimer();
4007 {
4008 verify_work_stacks_empty();
4009 verify_overflow_empty();
4010 sample_eden();
4011 stop_point =
4012 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4013 }
4014 if (stop_point != NULL) {
4015 // The careful iteration stopped early either because it found an
4016 // uninitialized object, or because we were in the midst of an
4017 // "abortable preclean", which should now be aborted. Redirty
4018 // the bits corresponding to the partially-scanned or unscanned
4019 // cards. We'll either restart at the next block boundary or
4020 // abort the preclean.
4021 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4022 "Should only be AbortablePreclean.");
4023 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4024 if (should_abort_preclean()) {
4025 break; // out of preclean loop
4026 } else {
4027 // Compute the next address at which preclean should pick up;
4028 // might need bitMapLock in order to read P-bits.
4029 lastAddr = next_card_start_after_block(stop_point);
4030 }
4031 }
4032 } else {
4033 assert(lastAddr == endAddr, "consistency check");
4034 assert(numDirtyCards == 0, "consistency check");
4035 break;
4036 }
4037 }
4038 verify_work_stacks_empty();
4039 verify_overflow_empty();
4040 return cumNumDirtyCards;
4041 }
4042
4043 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4044 // below are largely identical; if you need to modify
4045 // one of these methods, please check the other method too.
4046
4047 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4048 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4049 // strategy: it's similar to precleamModUnionTable above, in that
4050 // we accumulate contiguous ranges of dirty cards, mark these cards
4051 // precleaned, then scan the region covered by these cards.
4052 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4053 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4054
4055 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4056
4057 size_t numDirtyCards, cumNumDirtyCards;
4058 HeapWord *lastAddr, *nextAddr;
4059
4060 for (cumNumDirtyCards = numDirtyCards = 0,
4061 nextAddr = lastAddr = startAddr;
4062 nextAddr < endAddr;
4063 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4064
4065 ResourceMark rm;
4066 HandleMark hm;
4067
4068 MemRegion dirtyRegion;
4069 {
4070 // See comments in "Precleaning notes" above on why we
4071 // do this locking. XXX Could the locking overheads be
4072 // too high when dirty cards are sparse? [I don't think so.]
4073 stopTimer();
4074 CMSTokenSync x(true); // is cms thread
4075 startTimer();
4076 sample_eden();
4077 // Get and clear dirty region from card table
4078 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4079 true,
4080 CardTable::precleaned_card_val());
4081
4082 assert(dirtyRegion.start() >= nextAddr,
4083 "returned region inconsistent?");
4084 }
4085 lastAddr = dirtyRegion.end();
4086 numDirtyCards =
4087 dirtyRegion.word_size()/CardTable::card_size_in_words;
4088
4089 if (!dirtyRegion.is_empty()) {
4090 stopTimer();
4091 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4092 startTimer();
4093 sample_eden();
4094 verify_work_stacks_empty();
4095 verify_overflow_empty();
4096 HeapWord* stop_point =
4097 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4098 if (stop_point != NULL) {
4099 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4100 "Should only be AbortablePreclean.");
4101 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4102 if (should_abort_preclean()) {
4103 break; // out of preclean loop
4104 } else {
4105 // Compute the next address at which preclean should pick up.
4106 lastAddr = next_card_start_after_block(stop_point);
4107 }
4108 }
4109 } else {
4110 break;
4111 }
4112 }
4113 verify_work_stacks_empty();
4114 verify_overflow_empty();
4115 return cumNumDirtyCards;
4116 }
4117
4118 class PrecleanCLDClosure : public CLDClosure {
4119 MetadataVisitingOopsInGenClosure* _cm_closure;
4120 public:
4121 PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4122 void do_cld(ClassLoaderData* cld) {
4123 if (cld->has_accumulated_modified_oops()) {
4124 cld->clear_accumulated_modified_oops();
4125
4126 _cm_closure->do_cld(cld);
4127 }
4128 }
4129 };
4130
4131 // The freelist lock is needed to prevent asserts, is it really needed?
4132 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4133 // Needed to walk CLDG
4134 MutexLocker ml(ClassLoaderDataGraph_lock);
4135
4136 cl->set_freelistLock(freelistLock);
4137
4138 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4139
4140 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4141 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4142 PrecleanCLDClosure preclean_closure(cl);
4143 ClassLoaderDataGraph::cld_do(&preclean_closure);
4144
4145 verify_work_stacks_empty();
4146 verify_overflow_empty();
4147 }
4148
4149 void CMSCollector::checkpointRootsFinal() {
4150 assert(_collectorState == FinalMarking, "incorrect state transition?");
4151 check_correct_thread_executing();
4152 // world is stopped at this checkpoint
4153 assert(SafepointSynchronize::is_at_safepoint(),
4154 "world should be stopped");
4155 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4156
4157 verify_work_stacks_empty();
4158 verify_overflow_empty();
4159
4160 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4161 _young_gen->used() / K, _young_gen->capacity() / K);
4162 {
4163 if (CMSScavengeBeforeRemark) {
4164 CMSHeap* heap = CMSHeap::heap();
4165 // Temporarily set flag to false, GCH->do_collection will
4166 // expect it to be false and set to true
4167 FlagSetting fl(heap->_is_gc_active, false);
4168
4169 heap->do_collection(true, // full (i.e. force, see below)
4170 false, // !clear_all_soft_refs
4171 0, // size
4172 false, // is_tlab
4173 GenCollectedHeap::YoungGen // type
4174 );
4175 }
4176 FreelistLocker x(this);
4177 MutexLockerEx y(bitMapLock(),
4178 Mutex::_no_safepoint_check_flag);
4179 checkpointRootsFinalWork();
4180 }
4181 verify_work_stacks_empty();
4182 verify_overflow_empty();
4183 }
4184
4185 void CMSCollector::checkpointRootsFinalWork() {
4186 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4187
4188 assert(haveFreelistLocks(), "must have free list locks");
4189 assert_lock_strong(bitMapLock());
4190
4191 ResourceMark rm;
4192 HandleMark hm;
4193
4194 CMSHeap* heap = CMSHeap::heap();
4195
4196 if (should_unload_classes()) {
4197 CodeCache::gc_prologue();
4198 }
4199 assert(haveFreelistLocks(), "must have free list locks");
4200 assert_lock_strong(bitMapLock());
4201
4202 // We might assume that we need not fill TLAB's when
4203 // CMSScavengeBeforeRemark is set, because we may have just done
4204 // a scavenge which would have filled all TLAB's -- and besides
4205 // Eden would be empty. This however may not always be the case --
4206 // for instance although we asked for a scavenge, it may not have
4207 // happened because of a JNI critical section. We probably need
4208 // a policy for deciding whether we can in that case wait until
4209 // the critical section releases and then do the remark following
4210 // the scavenge, and skip it here. In the absence of that policy,
4211 // or of an indication of whether the scavenge did indeed occur,
4212 // we cannot rely on TLAB's having been filled and must do
4213 // so here just in case a scavenge did not happen.
4214 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4215 // Update the saved marks which may affect the root scans.
4216 heap->save_marks();
4217
4218 print_eden_and_survivor_chunk_arrays();
4219
4220 {
4221 #if COMPILER2_OR_JVMCI
4222 DerivedPointerTableDeactivate dpt_deact;
4223 #endif
4224
4225 // Note on the role of the mod union table:
4226 // Since the marker in "markFromRoots" marks concurrently with
4227 // mutators, it is possible for some reachable objects not to have been
4228 // scanned. For instance, an only reference to an object A was
4229 // placed in object B after the marker scanned B. Unless B is rescanned,
4230 // A would be collected. Such updates to references in marked objects
4231 // are detected via the mod union table which is the set of all cards
4232 // dirtied since the first checkpoint in this GC cycle and prior to
4233 // the most recent young generation GC, minus those cleaned up by the
4234 // concurrent precleaning.
4235 if (CMSParallelRemarkEnabled) {
4236 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4237 do_remark_parallel();
4238 } else {
4239 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4240 do_remark_non_parallel();
4241 }
4242 }
4243 verify_work_stacks_empty();
4244 verify_overflow_empty();
4245
4246 {
4247 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4248 refProcessingWork();
4249 }
4250 verify_work_stacks_empty();
4251 verify_overflow_empty();
4252
4253 if (should_unload_classes()) {
4254 CodeCache::gc_epilogue();
4255 }
4256 JvmtiExport::gc_epilogue();
4257
4258 // If we encountered any (marking stack / work queue) overflow
4259 // events during the current CMS cycle, take appropriate
4260 // remedial measures, where possible, so as to try and avoid
4261 // recurrence of that condition.
4262 assert(_markStack.isEmpty(), "No grey objects");
4263 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4264 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4265 if (ser_ovflw > 0) {
4266 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4267 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4268 _markStack.expand();
4269 _ser_pmc_remark_ovflw = 0;
4270 _ser_pmc_preclean_ovflw = 0;
4271 _ser_kac_preclean_ovflw = 0;
4272 _ser_kac_ovflw = 0;
4273 }
4274 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4275 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4276 _par_pmc_remark_ovflw, _par_kac_ovflw);
4277 _par_pmc_remark_ovflw = 0;
4278 _par_kac_ovflw = 0;
4279 }
4280 if (_markStack._hit_limit > 0) {
4281 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4282 _markStack._hit_limit);
4283 }
4284 if (_markStack._failed_double > 0) {
4285 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4286 _markStack._failed_double, _markStack.capacity());
4287 }
4288 _markStack._hit_limit = 0;
4289 _markStack._failed_double = 0;
4290
4291 if ((VerifyAfterGC || VerifyDuringGC) &&
4292 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4293 verify_after_remark();
4294 }
4295
4296 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4297
4298 // Change under the freelistLocks.
4299 _collectorState = Sweeping;
4300 // Call isAllClear() under bitMapLock
4301 assert(_modUnionTable.isAllClear(),
4302 "Should be clear by end of the final marking");
4303 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4304 "Should be clear by end of the final marking");
4305 }
4306
4307 void CMSParInitialMarkTask::work(uint worker_id) {
4308 elapsedTimer _timer;
4309 ResourceMark rm;
4310 HandleMark hm;
4311
4312 // ---------- scan from roots --------------
4313 _timer.start();
4314 CMSHeap* heap = CMSHeap::heap();
4315 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4316
4317 // ---------- young gen roots --------------
4318 {
4319 work_on_young_gen_roots(&par_mri_cl);
4320 _timer.stop();
4321 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4322 }
4323
4324 // ---------- remaining roots --------------
4325 _timer.reset();
4326 _timer.start();
4327
4328 CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4329
4330 heap->cms_process_roots(_strong_roots_scope,
4331 false, // yg was scanned above
4332 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4333 _collector->should_unload_classes(),
4334 &par_mri_cl,
4335 &cld_closure,
4336 &_par_state_string);
4337
4338 assert(_collector->should_unload_classes()
4339 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4340 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4341 _timer.stop();
4342 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4343 }
4344
4345 // Parallel remark task
4346 class CMSParRemarkTask: public CMSParMarkTask {
4347 CompactibleFreeListSpace* _cms_space;
4348
4349 // The per-thread work queues, available here for stealing.
4350 OopTaskQueueSet* _task_queues;
4351 TaskTerminator _term;
4352 StrongRootsScope* _strong_roots_scope;
4353
4354 public:
4355 // A value of 0 passed to n_workers will cause the number of
4356 // workers to be taken from the active workers in the work gang.
4357 CMSParRemarkTask(CMSCollector* collector,
4358 CompactibleFreeListSpace* cms_space,
4359 uint n_workers, WorkGang* workers,
4360 OopTaskQueueSet* task_queues,
4361 StrongRootsScope* strong_roots_scope):
4362 CMSParMarkTask("Rescan roots and grey objects in parallel",
4363 collector, n_workers),
4364 _cms_space(cms_space),
4365 _task_queues(task_queues),
4366 _term(n_workers, task_queues),
4367 _strong_roots_scope(strong_roots_scope) { }
4368
4369 OopTaskQueueSet* task_queues() { return _task_queues; }
4370
4371 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4372
4373 ParallelTaskTerminator* terminator() { return _term.terminator(); }
4374 uint n_workers() { return _n_workers; }
4375
4376 void work(uint worker_id);
4377
4378 private:
4379 // ... of dirty cards in old space
4380 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4381 ParMarkRefsIntoAndScanClosure* cl);
4382
4383 // ... work stealing for the above
4384 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4385 };
4386
4387 class RemarkCLDClosure : public CLDClosure {
4388 CLDToOopClosure _cm_closure;
4389 public:
4390 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4391 void do_cld(ClassLoaderData* cld) {
4392 // Check if we have modified any oops in the CLD during the concurrent marking.
4393 if (cld->has_accumulated_modified_oops()) {
4394 cld->clear_accumulated_modified_oops();
4395
4396 // We could have transfered the current modified marks to the accumulated marks,
4397 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4398 } else if (cld->has_modified_oops()) {
4399 // Don't clear anything, this info is needed by the next young collection.
4400 } else {
4401 // No modified oops in the ClassLoaderData.
4402 return;
4403 }
4404
4405 // The klass has modified fields, need to scan the klass.
4406 _cm_closure.do_cld(cld);
4407 }
4408 };
4409
4410 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4411 ParNewGeneration* young_gen = _collector->_young_gen;
4412 ContiguousSpace* eden_space = young_gen->eden();
4413 ContiguousSpace* from_space = young_gen->from();
4414 ContiguousSpace* to_space = young_gen->to();
4415
4416 HeapWord** eca = _collector->_eden_chunk_array;
4417 size_t ect = _collector->_eden_chunk_index;
4418 HeapWord** sca = _collector->_survivor_chunk_array;
4419 size_t sct = _collector->_survivor_chunk_index;
4420
4421 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4422 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4423
4424 do_young_space_rescan(cl, to_space, NULL, 0);
4425 do_young_space_rescan(cl, from_space, sca, sct);
4426 do_young_space_rescan(cl, eden_space, eca, ect);
4427 }
4428
4429 // work_queue(i) is passed to the closure
4430 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4431 // also is passed to do_dirty_card_rescan_tasks() and to
4432 // do_work_steal() to select the i-th task_queue.
4433
4434 void CMSParRemarkTask::work(uint worker_id) {
4435 elapsedTimer _timer;
4436 ResourceMark rm;
4437 HandleMark hm;
4438
4439 // ---------- rescan from roots --------------
4440 _timer.start();
4441 CMSHeap* heap = CMSHeap::heap();
4442 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4443 _collector->_span, _collector->ref_processor(),
4444 &(_collector->_markBitMap),
4445 work_queue(worker_id));
4446
4447 // Rescan young gen roots first since these are likely
4448 // coarsely partitioned and may, on that account, constitute
4449 // the critical path; thus, it's best to start off that
4450 // work first.
4451 // ---------- young gen roots --------------
4452 {
4453 work_on_young_gen_roots(&par_mrias_cl);
4454 _timer.stop();
4455 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4456 }
4457
4458 // ---------- remaining roots --------------
4459 _timer.reset();
4460 _timer.start();
4461 heap->cms_process_roots(_strong_roots_scope,
4462 false, // yg was scanned above
4463 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4464 _collector->should_unload_classes(),
4465 &par_mrias_cl,
4466 NULL, // The dirty klasses will be handled below
4467 &_par_state_string);
4468
4469 assert(_collector->should_unload_classes()
4470 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4471 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4472 _timer.stop();
4473 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4474
4475 // ---------- unhandled CLD scanning ----------
4476 if (worker_id == 0) { // Single threaded at the moment.
4477 _timer.reset();
4478 _timer.start();
4479
4480 // Scan all new class loader data objects and new dependencies that were
4481 // introduced during concurrent marking.
4482 ResourceMark rm;
4483 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4484 for (int i = 0; i < array->length(); i++) {
4485 Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4486 }
4487
4488 // We don't need to keep track of new CLDs anymore.
4489 ClassLoaderDataGraph::remember_new_clds(false);
4490
4491 _timer.stop();
4492 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4493 }
4494
4495 // We might have added oops to ClassLoaderData::_handles during the
4496 // concurrent marking phase. These oops do not always point to newly allocated objects
4497 // that are guaranteed to be kept alive. Hence,
4498 // we do have to revisit the _handles block during the remark phase.
4499
4500 // ---------- dirty CLD scanning ----------
4501 if (worker_id == 0) { // Single threaded at the moment.
4502 _timer.reset();
4503 _timer.start();
4504
4505 // Scan all classes that was dirtied during the concurrent marking phase.
4506 RemarkCLDClosure remark_closure(&par_mrias_cl);
4507 ClassLoaderDataGraph::cld_do(&remark_closure);
4508
4509 _timer.stop();
4510 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4511 }
4512
4513
4514 // ---------- rescan dirty cards ------------
4515 _timer.reset();
4516 _timer.start();
4517
4518 // Do the rescan tasks for each of the two spaces
4519 // (cms_space) in turn.
4520 // "worker_id" is passed to select the task_queue for "worker_id"
4521 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4522 _timer.stop();
4523 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4524
4525 // ---------- steal work from other threads ...
4526 // ---------- ... and drain overflow list.
4527 _timer.reset();
4528 _timer.start();
4529 do_work_steal(worker_id, &par_mrias_cl);
4530 _timer.stop();
4531 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4532 }
4533
4534 void
4535 CMSParMarkTask::do_young_space_rescan(
4536 OopsInGenClosure* cl, ContiguousSpace* space,
4537 HeapWord** chunk_array, size_t chunk_top) {
4538 // Until all tasks completed:
4539 // . claim an unclaimed task
4540 // . compute region boundaries corresponding to task claimed
4541 // using chunk_array
4542 // . par_oop_iterate(cl) over that region
4543
4544 ResourceMark rm;
4545 HandleMark hm;
4546
4547 SequentialSubTasksDone* pst = space->par_seq_tasks();
4548
4549 uint nth_task = 0;
4550 uint n_tasks = pst->n_tasks();
4551
4552 if (n_tasks > 0) {
4553 assert(pst->valid(), "Uninitialized use?");
4554 HeapWord *start, *end;
4555 while (pst->try_claim_task(/* reference */ nth_task)) {
4556 // We claimed task # nth_task; compute its boundaries.
4557 if (chunk_top == 0) { // no samples were taken
4558 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4559 start = space->bottom();
4560 end = space->top();
4561 } else if (nth_task == 0) {
4562 start = space->bottom();
4563 end = chunk_array[nth_task];
4564 } else if (nth_task < (uint)chunk_top) {
4565 assert(nth_task >= 1, "Control point invariant");
4566 start = chunk_array[nth_task - 1];
4567 end = chunk_array[nth_task];
4568 } else {
4569 assert(nth_task == (uint)chunk_top, "Control point invariant");
4570 start = chunk_array[chunk_top - 1];
4571 end = space->top();
4572 }
4573 MemRegion mr(start, end);
4574 // Verify that mr is in space
4575 assert(mr.is_empty() || space->used_region().contains(mr),
4576 "Should be in space");
4577 // Verify that "start" is an object boundary
4578 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4579 "Should be an oop");
4580 space->par_oop_iterate(mr, cl);
4581 }
4582 pst->all_tasks_completed();
4583 }
4584 }
4585
4586 void
4587 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4588 CompactibleFreeListSpace* sp, int i,
4589 ParMarkRefsIntoAndScanClosure* cl) {
4590 // Until all tasks completed:
4591 // . claim an unclaimed task
4592 // . compute region boundaries corresponding to task claimed
4593 // . transfer dirty bits ct->mut for that region
4594 // . apply rescanclosure to dirty mut bits for that region
4595
4596 ResourceMark rm;
4597 HandleMark hm;
4598
4599 OopTaskQueue* work_q = work_queue(i);
4600 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4601 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4602 // CAUTION: This closure has state that persists across calls to
4603 // the work method dirty_range_iterate_clear() in that it has
4604 // embedded in it a (subtype of) UpwardsObjectClosure. The
4605 // use of that state in the embedded UpwardsObjectClosure instance
4606 // assumes that the cards are always iterated (even if in parallel
4607 // by several threads) in monotonically increasing order per each
4608 // thread. This is true of the implementation below which picks
4609 // card ranges (chunks) in monotonically increasing order globally
4610 // and, a-fortiori, in monotonically increasing order per thread
4611 // (the latter order being a subsequence of the former).
4612 // If the work code below is ever reorganized into a more chaotic
4613 // work-partitioning form than the current "sequential tasks"
4614 // paradigm, the use of that persistent state will have to be
4615 // revisited and modified appropriately. See also related
4616 // bug 4756801 work on which should examine this code to make
4617 // sure that the changes there do not run counter to the
4618 // assumptions made here and necessary for correctness and
4619 // efficiency. Note also that this code might yield inefficient
4620 // behavior in the case of very large objects that span one or
4621 // more work chunks. Such objects would potentially be scanned
4622 // several times redundantly. Work on 4756801 should try and
4623 // address that performance anomaly if at all possible. XXX
4624 MemRegion full_span = _collector->_span;
4625 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4626 MarkFromDirtyCardsClosure
4627 greyRescanClosure(_collector, full_span, // entire span of interest
4628 sp, bm, work_q, cl);
4629
4630 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4631 assert(pst->valid(), "Uninitialized use?");
4632 uint nth_task = 0;
4633 const int alignment = CardTable::card_size * BitsPerWord;
4634 MemRegion span = sp->used_region();
4635 HeapWord* start_addr = span.start();
4636 HeapWord* end_addr = align_up(span.end(), alignment);
4637 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4638 assert(is_aligned(start_addr, alignment), "Check alignment");
4639 assert(is_aligned(chunk_size, alignment), "Check alignment");
4640
4641 while (pst->try_claim_task(/* reference */ nth_task)) {
4642 // Having claimed the nth_task, compute corresponding mem-region,
4643 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4644 // The alignment restriction ensures that we do not need any
4645 // synchronization with other gang-workers while setting or
4646 // clearing bits in thus chunk of the MUT.
4647 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4648 start_addr + (nth_task+1)*chunk_size);
4649 // The last chunk's end might be way beyond end of the
4650 // used region. In that case pull back appropriately.
4651 if (this_span.end() > end_addr) {
4652 this_span.set_end(end_addr);
4653 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4654 }
4655 // Iterate over the dirty cards covering this chunk, marking them
4656 // precleaned, and setting the corresponding bits in the mod union
4657 // table. Since we have been careful to partition at Card and MUT-word
4658 // boundaries no synchronization is needed between parallel threads.
4659 _collector->_ct->dirty_card_iterate(this_span,
4660 &modUnionClosure);
4661
4662 // Having transferred these marks into the modUnionTable,
4663 // rescan the marked objects on the dirty cards in the modUnionTable.
4664 // Even if this is at a synchronous collection, the initial marking
4665 // may have been done during an asynchronous collection so there
4666 // may be dirty bits in the mod-union table.
4667 _collector->_modUnionTable.dirty_range_iterate_clear(
4668 this_span, &greyRescanClosure);
4669 _collector->_modUnionTable.verifyNoOneBitsInRange(
4670 this_span.start(),
4671 this_span.end());
4672 }
4673 pst->all_tasks_completed(); // declare that i am done
4674 }
4675
4676 // . see if we can share work_queues with ParNew? XXX
4677 void
4678 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4679 OopTaskQueue* work_q = work_queue(i);
4680 NOT_PRODUCT(int num_steals = 0;)
4681 oop obj_to_scan;
4682 CMSBitMap* bm = &(_collector->_markBitMap);
4683
4684 while (true) {
4685 // Completely finish any left over work from (an) earlier round(s)
4686 cl->trim_queue(0);
4687 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4688 (size_t)ParGCDesiredObjsFromOverflowList);
4689 // Now check if there's any work in the overflow list
4690 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4691 // only affects the number of attempts made to get work from the
4692 // overflow list and does not affect the number of workers. Just
4693 // pass ParallelGCThreads so this behavior is unchanged.
4694 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4695 work_q,
4696 ParallelGCThreads)) {
4697 // found something in global overflow list;
4698 // not yet ready to go stealing work from others.
4699 // We'd like to assert(work_q->size() != 0, ...)
4700 // because we just took work from the overflow list,
4701 // but of course we can't since all of that could have
4702 // been already stolen from us.
4703 // "He giveth and He taketh away."
4704 continue;
4705 }
4706 // Verify that we have no work before we resort to stealing
4707 assert(work_q->size() == 0, "Have work, shouldn't steal");
4708 // Try to steal from other queues that have work
4709 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4710 NOT_PRODUCT(num_steals++;)
4711 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4712 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4713 // Do scanning work
4714 obj_to_scan->oop_iterate(cl);
4715 // Loop around, finish this work, and try to steal some more
4716 } else if (terminator()->offer_termination()) {
4717 break; // nirvana from the infinite cycle
4718 }
4719 }
4720 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4721 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4722 "Else our work is not yet done");
4723 }
4724
4725 // Record object boundaries in _eden_chunk_array by sampling the eden
4726 // top in the slow-path eden object allocation code path and record
4727 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4728 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4729 // sampling in sample_eden() that activates during the part of the
4730 // preclean phase.
4731 void CMSCollector::sample_eden_chunk() {
4732 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4733 if (_eden_chunk_lock->try_lock()) {
4734 // Record a sample. This is the critical section. The contents
4735 // of the _eden_chunk_array have to be non-decreasing in the
4736 // address order.
4737 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4738 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4739 "Unexpected state of Eden");
4740 if (_eden_chunk_index == 0 ||
4741 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4742 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4743 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4744 _eden_chunk_index++; // commit sample
4745 }
4746 _eden_chunk_lock->unlock();
4747 }
4748 }
4749 }
4750
4751 // Return a thread-local PLAB recording array, as appropriate.
4752 void* CMSCollector::get_data_recorder(int thr_num) {
4753 if (_survivor_plab_array != NULL &&
4754 (CMSPLABRecordAlways ||
4755 (_collectorState > Marking && _collectorState < FinalMarking))) {
4756 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4757 ChunkArray* ca = &_survivor_plab_array[thr_num];
4758 ca->reset(); // clear it so that fresh data is recorded
4759 return (void*) ca;
4760 } else {
4761 return NULL;
4762 }
4763 }
4764
4765 // Reset all the thread-local PLAB recording arrays
4766 void CMSCollector::reset_survivor_plab_arrays() {
4767 for (uint i = 0; i < ParallelGCThreads; i++) {
4768 _survivor_plab_array[i].reset();
4769 }
4770 }
4771
4772 // Merge the per-thread plab arrays into the global survivor chunk
4773 // array which will provide the partitioning of the survivor space
4774 // for CMS initial scan and rescan.
4775 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4776 int no_of_gc_threads) {
4777 assert(_survivor_plab_array != NULL, "Error");
4778 assert(_survivor_chunk_array != NULL, "Error");
4779 assert(_collectorState == FinalMarking ||
4780 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4781 for (int j = 0; j < no_of_gc_threads; j++) {
4782 _cursor[j] = 0;
4783 }
4784 HeapWord* top = surv->top();
4785 size_t i;
4786 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4787 HeapWord* min_val = top; // Higher than any PLAB address
4788 uint min_tid = 0; // position of min_val this round
4789 for (int j = 0; j < no_of_gc_threads; j++) {
4790 ChunkArray* cur_sca = &_survivor_plab_array[j];
4791 if (_cursor[j] == cur_sca->end()) {
4792 continue;
4793 }
4794 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4795 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4796 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4797 if (cur_val < min_val) {
4798 min_tid = j;
4799 min_val = cur_val;
4800 } else {
4801 assert(cur_val < top, "All recorded addresses should be less");
4802 }
4803 }
4804 // At this point min_val and min_tid are respectively
4805 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4806 // and the thread (j) that witnesses that address.
4807 // We record this address in the _survivor_chunk_array[i]
4808 // and increment _cursor[min_tid] prior to the next round i.
4809 if (min_val == top) {
4810 break;
4811 }
4812 _survivor_chunk_array[i] = min_val;
4813 _cursor[min_tid]++;
4814 }
4815 // We are all done; record the size of the _survivor_chunk_array
4816 _survivor_chunk_index = i; // exclusive: [0, i)
4817 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4818 // Verify that we used up all the recorded entries
4819 #ifdef ASSERT
4820 size_t total = 0;
4821 for (int j = 0; j < no_of_gc_threads; j++) {
4822 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4823 total += _cursor[j];
4824 }
4825 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4826 // Check that the merged array is in sorted order
4827 if (total > 0) {
4828 for (size_t i = 0; i < total - 1; i++) {
4829 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4830 i, p2i(_survivor_chunk_array[i]));
4831 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4832 "Not sorted");
4833 }
4834 }
4835 #endif // ASSERT
4836 }
4837
4838 // Set up the space's par_seq_tasks structure for work claiming
4839 // for parallel initial scan and rescan of young gen.
4840 // See ParRescanTask where this is currently used.
4841 void
4842 CMSCollector::
4843 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4844 assert(n_threads > 0, "Unexpected n_threads argument");
4845
4846 // Eden space
4847 if (!_young_gen->eden()->is_empty()) {
4848 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4849 assert(!pst->valid(), "Clobbering existing data?");
4850 // Each valid entry in [0, _eden_chunk_index) represents a task.
4851 size_t n_tasks = _eden_chunk_index + 1;
4852 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4853 // Sets the condition for completion of the subtask (how many threads
4854 // need to finish in order to be done).
4855 pst->set_n_threads(n_threads);
4856 pst->set_n_tasks((int)n_tasks);
4857 }
4858
4859 // Merge the survivor plab arrays into _survivor_chunk_array
4860 if (_survivor_plab_array != NULL) {
4861 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4862 } else {
4863 assert(_survivor_chunk_index == 0, "Error");
4864 }
4865
4866 // To space
4867 {
4868 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4869 assert(!pst->valid(), "Clobbering existing data?");
4870 // Sets the condition for completion of the subtask (how many threads
4871 // need to finish in order to be done).
4872 pst->set_n_threads(n_threads);
4873 pst->set_n_tasks(1);
4874 assert(pst->valid(), "Error");
4875 }
4876
4877 // From space
4878 {
4879 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4880 assert(!pst->valid(), "Clobbering existing data?");
4881 size_t n_tasks = _survivor_chunk_index + 1;
4882 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4883 // Sets the condition for completion of the subtask (how many threads
4884 // need to finish in order to be done).
4885 pst->set_n_threads(n_threads);
4886 pst->set_n_tasks((int)n_tasks);
4887 assert(pst->valid(), "Error");
4888 }
4889 }
4890
4891 // Parallel version of remark
4892 void CMSCollector::do_remark_parallel() {
4893 CMSHeap* heap = CMSHeap::heap();
4894 WorkGang* workers = heap->workers();
4895 assert(workers != NULL, "Need parallel worker threads.");
4896 // Choose to use the number of GC workers most recently set
4897 // into "active_workers".
4898 uint n_workers = workers->active_workers();
4899
4900 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4901
4902 StrongRootsScope srs(n_workers);
4903
4904 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4905
4906 // We won't be iterating over the cards in the card table updating
4907 // the younger_gen cards, so we shouldn't call the following else
4908 // the verification code as well as subsequent younger_refs_iterate
4909 // code would get confused. XXX
4910 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4911
4912 // The young gen rescan work will not be done as part of
4913 // process_roots (which currently doesn't know how to
4914 // parallelize such a scan), but rather will be broken up into
4915 // a set of parallel tasks (via the sampling that the [abortable]
4916 // preclean phase did of eden, plus the [two] tasks of
4917 // scanning the [two] survivor spaces. Further fine-grain
4918 // parallelization of the scanning of the survivor spaces
4919 // themselves, and of precleaning of the young gen itself
4920 // is deferred to the future.
4921 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4922
4923 // The dirty card rescan work is broken up into a "sequence"
4924 // of parallel tasks (per constituent space) that are dynamically
4925 // claimed by the parallel threads.
4926 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4927
4928 // It turns out that even when we're using 1 thread, doing the work in a
4929 // separate thread causes wide variance in run times. We can't help this
4930 // in the multi-threaded case, but we special-case n=1 here to get
4931 // repeatable measurements of the 1-thread overhead of the parallel code.
4932 if (n_workers > 1) {
4933 // Make refs discovery MT-safe, if it isn't already: it may not
4934 // necessarily be so, since it's possible that we are doing
4935 // ST marking.
4936 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4937 workers->run_task(&tsk);
4938 } else {
4939 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4940 tsk.work(0);
4941 }
4942
4943 // restore, single-threaded for now, any preserved marks
4944 // as a result of work_q overflow
4945 restore_preserved_marks_if_any();
4946 }
4947
4948 // Non-parallel version of remark
4949 void CMSCollector::do_remark_non_parallel() {
4950 ResourceMark rm;
4951 HandleMark hm;
4952 CMSHeap* heap = CMSHeap::heap();
4953 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4954
4955 MarkRefsIntoAndScanClosure
4956 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4957 &_markStack, this,
4958 false /* should_yield */, false /* not precleaning */);
4959 MarkFromDirtyCardsClosure
4960 markFromDirtyCardsClosure(this, _span,
4961 NULL, // space is set further below
4962 &_markBitMap, &_markStack, &mrias_cl);
4963 {
4964 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4965 // Iterate over the dirty cards, setting the corresponding bits in the
4966 // mod union table.
4967 {
4968 ModUnionClosure modUnionClosure(&_modUnionTable);
4969 _ct->dirty_card_iterate(_cmsGen->used_region(),
4970 &modUnionClosure);
4971 }
4972 // Having transferred these marks into the modUnionTable, we just need
4973 // to rescan the marked objects on the dirty cards in the modUnionTable.
4974 // The initial marking may have been done during an asynchronous
4975 // collection so there may be dirty bits in the mod-union table.
4976 const int alignment = CardTable::card_size * BitsPerWord;
4977 {
4978 // ... First handle dirty cards in CMS gen
4979 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4980 MemRegion ur = _cmsGen->used_region();
4981 HeapWord* lb = ur.start();
4982 HeapWord* ub = align_up(ur.end(), alignment);
4983 MemRegion cms_span(lb, ub);
4984 _modUnionTable.dirty_range_iterate_clear(cms_span,
4985 &markFromDirtyCardsClosure);
4986 verify_work_stacks_empty();
4987 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4988 }
4989 }
4990 if (VerifyDuringGC &&
4991 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4992 HandleMark hm; // Discard invalid handles created during verification
4993 Universe::verify();
4994 }
4995 {
4996 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4997
4998 verify_work_stacks_empty();
4999
5000 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5001 StrongRootsScope srs(1);
5002
5003 heap->cms_process_roots(&srs,
5004 true, // young gen as roots
5005 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5006 should_unload_classes(),
5007 &mrias_cl,
5008 NULL); // The dirty klasses will be handled below
5009
5010 assert(should_unload_classes()
5011 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5012 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5013 }
5014
5015 {
5016 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
5017
5018 verify_work_stacks_empty();
5019
5020 // Scan all class loader data objects that might have been introduced
5021 // during concurrent marking.
5022 ResourceMark rm;
5023 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5024 for (int i = 0; i < array->length(); i++) {
5025 Devirtualizer::do_cld(&mrias_cl, array->at(i));
5026 }
5027
5028 // We don't need to keep track of new CLDs anymore.
5029 ClassLoaderDataGraph::remember_new_clds(false);
5030
5031 verify_work_stacks_empty();
5032 }
5033
5034 // We might have added oops to ClassLoaderData::_handles during the
5035 // concurrent marking phase. These oops do not point to newly allocated objects
5036 // that are guaranteed to be kept alive. Hence,
5037 // we do have to revisit the _handles block during the remark phase.
5038 {
5039 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
5040
5041 verify_work_stacks_empty();
5042
5043 RemarkCLDClosure remark_closure(&mrias_cl);
5044 ClassLoaderDataGraph::cld_do(&remark_closure);
5045
5046 verify_work_stacks_empty();
5047 }
5048
5049 verify_work_stacks_empty();
5050 // Restore evacuated mark words, if any, used for overflow list links
5051 restore_preserved_marks_if_any();
5052
5053 verify_overflow_empty();
5054 }
5055
5056 ////////////////////////////////////////////////////////
5057 // Parallel Reference Processing Task Proxy Class
5058 ////////////////////////////////////////////////////////
5059 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5060 OopTaskQueueSet* _queues;
5061 TaskTerminator _terminator;
5062 public:
5063 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5064 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5065 ParallelTaskTerminator* terminator() { return _terminator.terminator(); }
5066 OopTaskQueueSet* queues() { return _queues; }
5067 };
5068
5069 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5070 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5071 CMSCollector* _collector;
5072 CMSBitMap* _mark_bit_map;
5073 const MemRegion _span;
5074 ProcessTask& _task;
5075
5076 public:
5077 CMSRefProcTaskProxy(ProcessTask& task,
5078 CMSCollector* collector,
5079 const MemRegion& span,
5080 CMSBitMap* mark_bit_map,
5081 AbstractWorkGang* workers,
5082 OopTaskQueueSet* task_queues):
5083 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5084 task_queues,
5085 workers->active_workers()),
5086 _collector(collector),
5087 _mark_bit_map(mark_bit_map),
5088 _span(span),
5089 _task(task)
5090 {
5091 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5092 "Inconsistency in _span");
5093 }
5094
5095 OopTaskQueueSet* task_queues() { return queues(); }
5096
5097 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5098
5099 void do_work_steal(int i,
5100 CMSParDrainMarkingStackClosure* drain,
5101 CMSParKeepAliveClosure* keep_alive);
5102
5103 virtual void work(uint worker_id);
5104 };
5105
5106 void CMSRefProcTaskProxy::work(uint worker_id) {
5107 ResourceMark rm;
5108 HandleMark hm;
5109 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5110 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5111 _mark_bit_map,
5112 work_queue(worker_id));
5113 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5114 _mark_bit_map,
5115 work_queue(worker_id));
5116 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5117 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5118 if (_task.marks_oops_alive()) {
5119 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5120 }
5121 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5122 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5123 }
5124
5125 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5126 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5127 _span(span),
5128 _work_queue(work_queue),
5129 _bit_map(bit_map),
5130 _mark_and_push(collector, span, bit_map, work_queue),
5131 _low_water_mark(MIN2((work_queue->max_elems()/4),
5132 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5133 { }
5134
5135 // . see if we can share work_queues with ParNew? XXX
5136 void CMSRefProcTaskProxy::do_work_steal(int i,
5137 CMSParDrainMarkingStackClosure* drain,
5138 CMSParKeepAliveClosure* keep_alive) {
5139 OopTaskQueue* work_q = work_queue(i);
5140 NOT_PRODUCT(int num_steals = 0;)
5141 oop obj_to_scan;
5142
5143 while (true) {
5144 // Completely finish any left over work from (an) earlier round(s)
5145 drain->trim_queue(0);
5146 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5147 (size_t)ParGCDesiredObjsFromOverflowList);
5148 // Now check if there's any work in the overflow list
5149 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5150 // only affects the number of attempts made to get work from the
5151 // overflow list and does not affect the number of workers. Just
5152 // pass ParallelGCThreads so this behavior is unchanged.
5153 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5154 work_q,
5155 ParallelGCThreads)) {
5156 // Found something in global overflow list;
5157 // not yet ready to go stealing work from others.
5158 // We'd like to assert(work_q->size() != 0, ...)
5159 // because we just took work from the overflow list,
5160 // but of course we can't, since all of that might have
5161 // been already stolen from us.
5162 continue;
5163 }
5164 // Verify that we have no work before we resort to stealing
5165 assert(work_q->size() == 0, "Have work, shouldn't steal");
5166 // Try to steal from other queues that have work
5167 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5168 NOT_PRODUCT(num_steals++;)
5169 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5170 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5171 // Do scanning work
5172 obj_to_scan->oop_iterate(keep_alive);
5173 // Loop around, finish this work, and try to steal some more
5174 } else if (terminator()->offer_termination()) {
5175 break; // nirvana from the infinite cycle
5176 }
5177 }
5178 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5179 }
5180
5181 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5182 CMSHeap* heap = CMSHeap::heap();
5183 WorkGang* workers = heap->workers();
5184 assert(workers != NULL, "Need parallel worker threads.");
5185 assert(workers->active_workers() == ergo_workers,
5186 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5187 ergo_workers, workers->active_workers());
5188 CMSRefProcTaskProxy rp_task(task, &_collector,
5189 _collector.ref_processor_span(),
5190 _collector.markBitMap(),
5191 workers, _collector.task_queues());
5192 workers->run_task(&rp_task, workers->active_workers());
5193 }
5194
5195 void CMSCollector::refProcessingWork() {
5196 ResourceMark rm;
5197 HandleMark hm;
5198
5199 ReferenceProcessor* rp = ref_processor();
5200 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5201 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5202 // Process weak references.
5203 rp->setup_policy(false);
5204 verify_work_stacks_empty();
5205
5206 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5207 {
5208 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5209
5210 // Setup keep_alive and complete closures.
5211 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5212 &_markStack, false /* !preclean */);
5213 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5214 _span, &_markBitMap, &_markStack,
5215 &cmsKeepAliveClosure, false /* !preclean */);
5216
5217 ReferenceProcessorStats stats;
5218 if (rp->processing_is_mt()) {
5219 // Set the degree of MT here. If the discovery is done MT, there
5220 // may have been a different number of threads doing the discovery
5221 // and a different number of discovered lists may have Ref objects.
5222 // That is OK as long as the Reference lists are balanced (see
5223 // balance_all_queues() and balance_queues()).
5224 CMSHeap* heap = CMSHeap::heap();
5225 uint active_workers = ParallelGCThreads;
5226 WorkGang* workers = heap->workers();
5227 if (workers != NULL) {
5228 active_workers = workers->active_workers();
5229 // The expectation is that active_workers will have already
5230 // been set to a reasonable value. If it has not been set,
5231 // investigate.
5232 assert(active_workers > 0, "Should have been set during scavenge");
5233 }
5234 rp->set_active_mt_degree(active_workers);
5235 CMSRefProcTaskExecutor task_executor(*this);
5236 stats = rp->process_discovered_references(&_is_alive_closure,
5237 &cmsKeepAliveClosure,
5238 &cmsDrainMarkingStackClosure,
5239 &task_executor,
5240 &pt);
5241 } else {
5242 stats = rp->process_discovered_references(&_is_alive_closure,
5243 &cmsKeepAliveClosure,
5244 &cmsDrainMarkingStackClosure,
5245 NULL,
5246 &pt);
5247 }
5248 _gc_tracer_cm->report_gc_reference_stats(stats);
5249 pt.print_all_references();
5250 }
5251
5252 // This is the point where the entire marking should have completed.
5253 verify_work_stacks_empty();
5254
5255 {
5256 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5257 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5258 }
5259
5260 if (should_unload_classes()) {
5261 {
5262 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5263
5264 // Unload classes and purge the SystemDictionary.
5265 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5266
5267 // Unload nmethods.
5268 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5269
5270 // Prune dead klasses from subklass/sibling/implementor lists.
5271 Klass::clean_weak_klass_links(purged_class);
5272 }
5273
5274 {
5275 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5276 // Clean up unreferenced symbols in symbol table.
5277 SymbolTable::unlink();
5278 }
5279
5280 {
5281 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5282 // Delete entries for dead interned strings.
5283 StringTable::unlink(&_is_alive_closure);
5284 }
5285 }
5286
5287 // Restore any preserved marks as a result of mark stack or
5288 // work queue overflow
5289 restore_preserved_marks_if_any(); // done single-threaded for now
5290
5291 rp->set_enqueuing_is_done(true);
5292 rp->verify_no_references_recorded();
5293 }
5294
5295 #ifndef PRODUCT
5296 void CMSCollector::check_correct_thread_executing() {
5297 Thread* t = Thread::current();
5298 // Only the VM thread or the CMS thread should be here.
5299 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5300 "Unexpected thread type");
5301 // If this is the vm thread, the foreground process
5302 // should not be waiting. Note that _foregroundGCIsActive is
5303 // true while the foreground collector is waiting.
5304 if (_foregroundGCShouldWait) {
5305 // We cannot be the VM thread
5306 assert(t->is_ConcurrentGC_thread(),
5307 "Should be CMS thread");
5308 } else {
5309 // We can be the CMS thread only if we are in a stop-world
5310 // phase of CMS collection.
5311 if (t->is_ConcurrentGC_thread()) {
5312 assert(_collectorState == InitialMarking ||
5313 _collectorState == FinalMarking,
5314 "Should be a stop-world phase");
5315 // The CMS thread should be holding the CMS_token.
5316 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5317 "Potential interference with concurrently "
5318 "executing VM thread");
5319 }
5320 }
5321 }
5322 #endif
5323
5324 void CMSCollector::sweep() {
5325 assert(_collectorState == Sweeping, "just checking");
5326 check_correct_thread_executing();
5327 verify_work_stacks_empty();
5328 verify_overflow_empty();
5329 increment_sweep_count();
5330 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5331
5332 _inter_sweep_timer.stop();
5333 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5334
5335 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5336 _intra_sweep_timer.reset();
5337 _intra_sweep_timer.start();
5338 {
5339 GCTraceCPUTime tcpu;
5340 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5341 // First sweep the old gen
5342 {
5343 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5344 bitMapLock());
5345 sweepWork(_cmsGen);
5346 }
5347
5348 // Update Universe::_heap_*_at_gc figures.
5349 // We need all the free list locks to make the abstract state
5350 // transition from Sweeping to Resetting. See detailed note
5351 // further below.
5352 {
5353 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5354 // Update heap occupancy information which is used as
5355 // input to soft ref clearing policy at the next gc.
5356 Universe::update_heap_info_at_gc();
5357 _collectorState = Resizing;
5358 }
5359 }
5360 verify_work_stacks_empty();
5361 verify_overflow_empty();
5362
5363 if (should_unload_classes()) {
5364 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5365 // requires that the virtual spaces are stable and not deleted.
5366 ClassLoaderDataGraph::set_should_purge(true);
5367 }
5368
5369 _intra_sweep_timer.stop();
5370 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5371
5372 _inter_sweep_timer.reset();
5373 _inter_sweep_timer.start();
5374
5375 // We need to use a monotonically non-decreasing time in ms
5376 // or we will see time-warp warnings and os::javaTimeMillis()
5377 // does not guarantee monotonicity.
5378 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5379 update_time_of_last_gc(now);
5380
5381 // NOTE on abstract state transitions:
5382 // Mutators allocate-live and/or mark the mod-union table dirty
5383 // based on the state of the collection. The former is done in
5384 // the interval [Marking, Sweeping] and the latter in the interval
5385 // [Marking, Sweeping). Thus the transitions into the Marking state
5386 // and out of the Sweeping state must be synchronously visible
5387 // globally to the mutators.
5388 // The transition into the Marking state happens with the world
5389 // stopped so the mutators will globally see it. Sweeping is
5390 // done asynchronously by the background collector so the transition
5391 // from the Sweeping state to the Resizing state must be done
5392 // under the freelistLock (as is the check for whether to
5393 // allocate-live and whether to dirty the mod-union table).
5394 assert(_collectorState == Resizing, "Change of collector state to"
5395 " Resizing must be done under the freelistLocks (plural)");
5396
5397 // Now that sweeping has been completed, we clear
5398 // the incremental_collection_failed flag,
5399 // thus inviting a younger gen collection to promote into
5400 // this generation. If such a promotion may still fail,
5401 // the flag will be set again when a young collection is
5402 // attempted.
5403 CMSHeap* heap = CMSHeap::heap();
5404 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5405 heap->update_full_collections_completed(_collection_count_start);
5406 }
5407
5408 // FIX ME!!! Looks like this belongs in CFLSpace, with
5409 // CMSGen merely delegating to it.
5410 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5411 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5412 HeapWord* minAddr = _cmsSpace->bottom();
5413 HeapWord* largestAddr =
5414 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5415 if (largestAddr == NULL) {
5416 // The dictionary appears to be empty. In this case
5417 // try to coalesce at the end of the heap.
5418 largestAddr = _cmsSpace->end();
5419 }
5420 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5421 size_t nearLargestOffset =
5422 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5423 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5424 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5425 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5426 }
5427
5428 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5429 return addr >= _cmsSpace->nearLargestChunk();
5430 }
5431
5432 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5433 return _cmsSpace->find_chunk_at_end();
5434 }
5435
5436 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5437 bool full) {
5438 // If the young generation has been collected, gather any statistics
5439 // that are of interest at this point.
5440 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5441 if (!full && current_is_young) {
5442 // Gather statistics on the young generation collection.
5443 collector()->stats().record_gc0_end(used());
5444 }
5445 }
5446
5447 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5448 // We iterate over the space(s) underlying this generation,
5449 // checking the mark bit map to see if the bits corresponding
5450 // to specific blocks are marked or not. Blocks that are
5451 // marked are live and are not swept up. All remaining blocks
5452 // are swept up, with coalescing on-the-fly as we sweep up
5453 // contiguous free and/or garbage blocks:
5454 // We need to ensure that the sweeper synchronizes with allocators
5455 // and stop-the-world collectors. In particular, the following
5456 // locks are used:
5457 // . CMS token: if this is held, a stop the world collection cannot occur
5458 // . freelistLock: if this is held no allocation can occur from this
5459 // generation by another thread
5460 // . bitMapLock: if this is held, no other thread can access or update
5461 //
5462
5463 // Note that we need to hold the freelistLock if we use
5464 // block iterate below; else the iterator might go awry if
5465 // a mutator (or promotion) causes block contents to change
5466 // (for instance if the allocator divvies up a block).
5467 // If we hold the free list lock, for all practical purposes
5468 // young generation GC's can't occur (they'll usually need to
5469 // promote), so we might as well prevent all young generation
5470 // GC's while we do a sweeping step. For the same reason, we might
5471 // as well take the bit map lock for the entire duration
5472
5473 // check that we hold the requisite locks
5474 assert(have_cms_token(), "Should hold cms token");
5475 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5476 assert_lock_strong(old_gen->freelistLock());
5477 assert_lock_strong(bitMapLock());
5478
5479 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5480 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5481 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5482 _inter_sweep_estimate.padded_average(),
5483 _intra_sweep_estimate.padded_average());
5484 old_gen->setNearLargestChunk();
5485
5486 {
5487 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5488 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5489 // We need to free-up/coalesce garbage/blocks from a
5490 // co-terminal free run. This is done in the SweepClosure
5491 // destructor; so, do not remove this scope, else the
5492 // end-of-sweep-census below will be off by a little bit.
5493 }
5494 old_gen->cmsSpace()->sweep_completed();
5495 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5496 if (should_unload_classes()) { // unloaded classes this cycle,
5497 _concurrent_cycles_since_last_unload = 0; // ... reset count
5498 } else { // did not unload classes,
5499 _concurrent_cycles_since_last_unload++; // ... increment count
5500 }
5501 }
5502
5503 // Reset CMS data structures (for now just the marking bit map)
5504 // preparatory for the next cycle.
5505 void CMSCollector::reset_concurrent() {
5506 CMSTokenSyncWithLocks ts(true, bitMapLock());
5507
5508 // If the state is not "Resetting", the foreground thread
5509 // has done a collection and the resetting.
5510 if (_collectorState != Resetting) {
5511 assert(_collectorState == Idling, "The state should only change"
5512 " because the foreground collector has finished the collection");
5513 return;
5514 }
5515
5516 {
5517 // Clear the mark bitmap (no grey objects to start with)
5518 // for the next cycle.
5519 GCTraceCPUTime tcpu;
5520 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5521
5522 HeapWord* curAddr = _markBitMap.startWord();
5523 while (curAddr < _markBitMap.endWord()) {
5524 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5525 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5526 _markBitMap.clear_large_range(chunk);
5527 if (ConcurrentMarkSweepThread::should_yield() &&
5528 !foregroundGCIsActive() &&
5529 CMSYield) {
5530 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5531 "CMS thread should hold CMS token");
5532 assert_lock_strong(bitMapLock());
5533 bitMapLock()->unlock();
5534 ConcurrentMarkSweepThread::desynchronize(true);
5535 stopTimer();
5536 incrementYields();
5537
5538 // See the comment in coordinator_yield()
5539 for (unsigned i = 0; i < CMSYieldSleepCount &&
5540 ConcurrentMarkSweepThread::should_yield() &&
5541 !CMSCollector::foregroundGCIsActive(); ++i) {
5542 os::sleep(Thread::current(), 1, false);
5543 }
5544
5545 ConcurrentMarkSweepThread::synchronize(true);
5546 bitMapLock()->lock_without_safepoint_check();
5547 startTimer();
5548 }
5549 curAddr = chunk.end();
5550 }
5551 // A successful mostly concurrent collection has been done.
5552 // Because only the full (i.e., concurrent mode failure) collections
5553 // are being measured for gc overhead limits, clean the "near" flag
5554 // and count.
5555 size_policy()->reset_gc_overhead_limit_count();
5556 _collectorState = Idling;
5557 }
5558
5559 register_gc_end();
5560 }
5561
5562 // Same as above but for STW paths
5563 void CMSCollector::reset_stw() {
5564 // already have the lock
5565 assert(_collectorState == Resetting, "just checking");
5566 assert_lock_strong(bitMapLock());
5567 GCIdMark gc_id_mark(_cmsThread->gc_id());
5568 _markBitMap.clear_all();
5569 _collectorState = Idling;
5570 register_gc_end();
5571 }
5572
5573 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5574 GCTraceCPUTime tcpu;
5575 TraceCollectorStats tcs_cgc(cgc_counters());
5576
5577 switch (op) {
5578 case CMS_op_checkpointRootsInitial: {
5579 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5580 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5581 checkpointRootsInitial();
5582 break;
5583 }
5584 case CMS_op_checkpointRootsFinal: {
5585 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5586 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5587 checkpointRootsFinal();
5588 break;
5589 }
5590 default:
5591 fatal("No such CMS_op");
5592 }
5593 }
5594
5595 #ifndef PRODUCT
5596 size_t const CMSCollector::skip_header_HeapWords() {
5597 return FreeChunk::header_size();
5598 }
5599
5600 // Try and collect here conditions that should hold when
5601 // CMS thread is exiting. The idea is that the foreground GC
5602 // thread should not be blocked if it wants to terminate
5603 // the CMS thread and yet continue to run the VM for a while
5604 // after that.
5605 void CMSCollector::verify_ok_to_terminate() const {
5606 assert(Thread::current()->is_ConcurrentGC_thread(),
5607 "should be called by CMS thread");
5608 assert(!_foregroundGCShouldWait, "should be false");
5609 // We could check here that all the various low-level locks
5610 // are not held by the CMS thread, but that is overkill; see
5611 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5612 // is checked.
5613 }
5614 #endif
5615
5616 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5617 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5618 "missing Printezis mark?");
5619 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5620 size_t size = pointer_delta(nextOneAddr + 1, addr);
5621 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5622 "alignment problem");
5623 assert(size >= 3, "Necessary for Printezis marks to work");
5624 return size;
5625 }
5626
5627 // A variant of the above (block_size_using_printezis_bits()) except
5628 // that we return 0 if the P-bits are not yet set.
5629 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5630 if (_markBitMap.isMarked(addr + 1)) {
5631 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5632 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5633 size_t size = pointer_delta(nextOneAddr + 1, addr);
5634 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5635 "alignment problem");
5636 assert(size >= 3, "Necessary for Printezis marks to work");
5637 return size;
5638 }
5639 return 0;
5640 }
5641
5642 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5643 size_t sz = 0;
5644 oop p = (oop)addr;
5645 if (p->klass_or_null_acquire() != NULL) {
5646 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5647 } else {
5648 sz = block_size_using_printezis_bits(addr);
5649 }
5650 assert(sz > 0, "size must be nonzero");
5651 HeapWord* next_block = addr + sz;
5652 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5653 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5654 align_down((uintptr_t)next_card, CardTable::card_size),
5655 "must be different cards");
5656 return next_card;
5657 }
5658
5659
5660 // CMS Bit Map Wrapper /////////////////////////////////////////
5661
5662 // Construct a CMS bit map infrastructure, but don't create the
5663 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5664 // further below.
5665 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5666 _shifter(shifter),
5667 _bm(),
5668 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5669 Monitor::_safepoint_check_sometimes) : NULL)
5670 {
5671 _bmStartWord = 0;
5672 _bmWordSize = 0;
5673 }
5674
5675 bool CMSBitMap::allocate(MemRegion mr) {
5676 _bmStartWord = mr.start();
5677 _bmWordSize = mr.word_size();
5678 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5679 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5680 if (!brs.is_reserved()) {
5681 log_warning(gc)("CMS bit map allocation failure");
5682 return false;
5683 }
5684 // For now we'll just commit all of the bit map up front.
5685 // Later on we'll try to be more parsimonious with swap.
5686 if (!_virtual_space.initialize(brs, brs.size())) {
5687 log_warning(gc)("CMS bit map backing store failure");
5688 return false;
5689 }
5690 assert(_virtual_space.committed_size() == brs.size(),
5691 "didn't reserve backing store for all of CMS bit map?");
5692 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5693 _bmWordSize, "inconsistency in bit map sizing");
5694 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5695
5696 // bm.clear(); // can we rely on getting zero'd memory? verify below
5697 assert(isAllClear(),
5698 "Expected zero'd memory from ReservedSpace constructor");
5699 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5700 "consistency check");
5701 return true;
5702 }
5703
5704 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5705 HeapWord *next_addr, *end_addr, *last_addr;
5706 assert_locked();
5707 assert(covers(mr), "out-of-range error");
5708 // XXX assert that start and end are appropriately aligned
5709 for (next_addr = mr.start(), end_addr = mr.end();
5710 next_addr < end_addr; next_addr = last_addr) {
5711 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5712 last_addr = dirty_region.end();
5713 if (!dirty_region.is_empty()) {
5714 cl->do_MemRegion(dirty_region);
5715 } else {
5716 assert(last_addr == end_addr, "program logic");
5717 return;
5718 }
5719 }
5720 }
5721
5722 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5723 _bm.print_on_error(st, prefix);
5724 }
5725
5726 #ifndef PRODUCT
5727 void CMSBitMap::assert_locked() const {
5728 CMSLockVerifier::assert_locked(lock());
5729 }
5730
5731 bool CMSBitMap::covers(MemRegion mr) const {
5732 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5733 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5734 "size inconsistency");
5735 return (mr.start() >= _bmStartWord) &&
5736 (mr.end() <= endWord());
5737 }
5738
5739 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5740 return (start >= _bmStartWord && (start + size) <= endWord());
5741 }
5742
5743 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5744 // verify that there are no 1 bits in the interval [left, right)
5745 FalseBitMapClosure falseBitMapClosure;
5746 iterate(&falseBitMapClosure, left, right);
5747 }
5748
5749 void CMSBitMap::region_invariant(MemRegion mr)
5750 {
5751 assert_locked();
5752 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5753 assert(!mr.is_empty(), "unexpected empty region");
5754 assert(covers(mr), "mr should be covered by bit map");
5755 // convert address range into offset range
5756 size_t start_ofs = heapWordToOffset(mr.start());
5757 // Make sure that end() is appropriately aligned
5758 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5759 "Misaligned mr.end()");
5760 size_t end_ofs = heapWordToOffset(mr.end());
5761 assert(end_ofs > start_ofs, "Should mark at least one bit");
5762 }
5763
5764 #endif
5765
5766 bool CMSMarkStack::allocate(size_t size) {
5767 // allocate a stack of the requisite depth
5768 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5769 size * sizeof(oop)));
5770 if (!rs.is_reserved()) {
5771 log_warning(gc)("CMSMarkStack allocation failure");
5772 return false;
5773 }
5774 if (!_virtual_space.initialize(rs, rs.size())) {
5775 log_warning(gc)("CMSMarkStack backing store failure");
5776 return false;
5777 }
5778 assert(_virtual_space.committed_size() == rs.size(),
5779 "didn't reserve backing store for all of CMS stack?");
5780 _base = (oop*)(_virtual_space.low());
5781 _index = 0;
5782 _capacity = size;
5783 NOT_PRODUCT(_max_depth = 0);
5784 return true;
5785 }
5786
5787 // XXX FIX ME !!! In the MT case we come in here holding a
5788 // leaf lock. For printing we need to take a further lock
5789 // which has lower rank. We need to recalibrate the two
5790 // lock-ranks involved in order to be able to print the
5791 // messages below. (Or defer the printing to the caller.
5792 // For now we take the expedient path of just disabling the
5793 // messages for the problematic case.)
5794 void CMSMarkStack::expand() {
5795 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5796 if (_capacity == MarkStackSizeMax) {
5797 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5798 // We print a warning message only once per CMS cycle.
5799 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5800 }
5801 return;
5802 }
5803 // Double capacity if possible
5804 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5805 // Do not give up existing stack until we have managed to
5806 // get the double capacity that we desired.
5807 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5808 new_capacity * sizeof(oop)));
5809 if (rs.is_reserved()) {
5810 // Release the backing store associated with old stack
5811 _virtual_space.release();
5812 // Reinitialize virtual space for new stack
5813 if (!_virtual_space.initialize(rs, rs.size())) {
5814 fatal("Not enough swap for expanded marking stack");
5815 }
5816 _base = (oop*)(_virtual_space.low());
5817 _index = 0;
5818 _capacity = new_capacity;
5819 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5820 // Failed to double capacity, continue;
5821 // we print a detail message only once per CMS cycle.
5822 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5823 _capacity / K, new_capacity / K);
5824 }
5825 }
5826
5827
5828 // Closures
5829 // XXX: there seems to be a lot of code duplication here;
5830 // should refactor and consolidate common code.
5831
5832 // This closure is used to mark refs into the CMS generation in
5833 // the CMS bit map. Called at the first checkpoint. This closure
5834 // assumes that we do not need to re-mark dirty cards; if the CMS
5835 // generation on which this is used is not an oldest
5836 // generation then this will lose younger_gen cards!
5837
5838 MarkRefsIntoClosure::MarkRefsIntoClosure(
5839 MemRegion span, CMSBitMap* bitMap):
5840 _span(span),
5841 _bitMap(bitMap)
5842 {
5843 assert(ref_discoverer() == NULL, "deliberately left NULL");
5844 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5845 }
5846
5847 void MarkRefsIntoClosure::do_oop(oop obj) {
5848 // if p points into _span, then mark corresponding bit in _markBitMap
5849 assert(oopDesc::is_oop(obj), "expected an oop");
5850 HeapWord* addr = (HeapWord*)obj;
5851 if (_span.contains(addr)) {
5852 // this should be made more efficient
5853 _bitMap->mark(addr);
5854 }
5855 }
5856
5857 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5858 MemRegion span, CMSBitMap* bitMap):
5859 _span(span),
5860 _bitMap(bitMap)
5861 {
5862 assert(ref_discoverer() == NULL, "deliberately left NULL");
5863 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5864 }
5865
5866 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5867 // if p points into _span, then mark corresponding bit in _markBitMap
5868 assert(oopDesc::is_oop(obj), "expected an oop");
5869 HeapWord* addr = (HeapWord*)obj;
5870 if (_span.contains(addr)) {
5871 // this should be made more efficient
5872 _bitMap->par_mark(addr);
5873 }
5874 }
5875
5876 // A variant of the above, used for CMS marking verification.
5877 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5878 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5879 _span(span),
5880 _verification_bm(verification_bm),
5881 _cms_bm(cms_bm)
5882 {
5883 assert(ref_discoverer() == NULL, "deliberately left NULL");
5884 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5885 }
5886
5887 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5888 // if p points into _span, then mark corresponding bit in _markBitMap
5889 assert(oopDesc::is_oop(obj), "expected an oop");
5890 HeapWord* addr = (HeapWord*)obj;
5891 if (_span.contains(addr)) {
5892 _verification_bm->mark(addr);
5893 if (!_cms_bm->isMarked(addr)) {
5894 Log(gc, verify) log;
5895 ResourceMark rm;
5896 LogStream ls(log.error());
5897 oop(addr)->print_on(&ls);
5898 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5899 fatal("... aborting");
5900 }
5901 }
5902 }
5903
5904 //////////////////////////////////////////////////
5905 // MarkRefsIntoAndScanClosure
5906 //////////////////////////////////////////////////
5907
5908 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5909 ReferenceDiscoverer* rd,
5910 CMSBitMap* bit_map,
5911 CMSBitMap* mod_union_table,
5912 CMSMarkStack* mark_stack,
5913 CMSCollector* collector,
5914 bool should_yield,
5915 bool concurrent_precleaning):
5916 _span(span),
5917 _bit_map(bit_map),
5918 _mark_stack(mark_stack),
5919 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5920 mark_stack, concurrent_precleaning),
5921 _collector(collector),
5922 _freelistLock(NULL),
5923 _yield(should_yield),
5924 _concurrent_precleaning(concurrent_precleaning)
5925 {
5926 // FIXME: Should initialize in base class constructor.
5927 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5928 set_ref_discoverer_internal(rd);
5929 }
5930
5931 // This closure is used to mark refs into the CMS generation at the
5932 // second (final) checkpoint, and to scan and transitively follow
5933 // the unmarked oops. It is also used during the concurrent precleaning
5934 // phase while scanning objects on dirty cards in the CMS generation.
5935 // The marks are made in the marking bit map and the marking stack is
5936 // used for keeping the (newly) grey objects during the scan.
5937 // The parallel version (Par_...) appears further below.
5938 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5939 if (obj != NULL) {
5940 assert(oopDesc::is_oop(obj), "expected an oop");
5941 HeapWord* addr = (HeapWord*)obj;
5942 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5943 assert(_collector->overflow_list_is_empty(),
5944 "overflow list should be empty");
5945 if (_span.contains(addr) &&
5946 !_bit_map->isMarked(addr)) {
5947 // mark bit map (object is now grey)
5948 _bit_map->mark(addr);
5949 // push on marking stack (stack should be empty), and drain the
5950 // stack by applying this closure to the oops in the oops popped
5951 // from the stack (i.e. blacken the grey objects)
5952 bool res = _mark_stack->push(obj);
5953 assert(res, "Should have space to push on empty stack");
5954 do {
5955 oop new_oop = _mark_stack->pop();
5956 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5957 assert(_bit_map->isMarked((HeapWord*)new_oop),
5958 "only grey objects on this stack");
5959 // iterate over the oops in this oop, marking and pushing
5960 // the ones in CMS heap (i.e. in _span).
5961 new_oop->oop_iterate(&_pushAndMarkClosure);
5962 // check if it's time to yield
5963 do_yield_check();
5964 } while (!_mark_stack->isEmpty() ||
5965 (!_concurrent_precleaning && take_from_overflow_list()));
5966 // if marking stack is empty, and we are not doing this
5967 // during precleaning, then check the overflow list
5968 }
5969 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5970 assert(_collector->overflow_list_is_empty(),
5971 "overflow list was drained above");
5972
5973 assert(_collector->no_preserved_marks(),
5974 "All preserved marks should have been restored above");
5975 }
5976 }
5977
5978 void MarkRefsIntoAndScanClosure::do_yield_work() {
5979 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5980 "CMS thread should hold CMS token");
5981 assert_lock_strong(_freelistLock);
5982 assert_lock_strong(_bit_map->lock());
5983 // relinquish the free_list_lock and bitMaplock()
5984 _bit_map->lock()->unlock();
5985 _freelistLock->unlock();
5986 ConcurrentMarkSweepThread::desynchronize(true);
5987 _collector->stopTimer();
5988 _collector->incrementYields();
5989
5990 // See the comment in coordinator_yield()
5991 for (unsigned i = 0;
5992 i < CMSYieldSleepCount &&
5993 ConcurrentMarkSweepThread::should_yield() &&
5994 !CMSCollector::foregroundGCIsActive();
5995 ++i) {
5996 os::sleep(Thread::current(), 1, false);
5997 }
5998
5999 ConcurrentMarkSweepThread::synchronize(true);
6000 _freelistLock->lock_without_safepoint_check();
6001 _bit_map->lock()->lock_without_safepoint_check();
6002 _collector->startTimer();
6003 }
6004
6005 ///////////////////////////////////////////////////////////
6006 // ParMarkRefsIntoAndScanClosure: a parallel version of
6007 // MarkRefsIntoAndScanClosure
6008 ///////////////////////////////////////////////////////////
6009 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6010 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6011 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6012 _span(span),
6013 _bit_map(bit_map),
6014 _work_queue(work_queue),
6015 _low_water_mark(MIN2((work_queue->max_elems()/4),
6016 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6017 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6018 {
6019 // FIXME: Should initialize in base class constructor.
6020 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6021 set_ref_discoverer_internal(rd);
6022 }
6023
6024 // This closure is used to mark refs into the CMS generation at the
6025 // second (final) checkpoint, and to scan and transitively follow
6026 // the unmarked oops. The marks are made in the marking bit map and
6027 // the work_queue is used for keeping the (newly) grey objects during
6028 // the scan phase whence they are also available for stealing by parallel
6029 // threads. Since the marking bit map is shared, updates are
6030 // synchronized (via CAS).
6031 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6032 if (obj != NULL) {
6033 // Ignore mark word because this could be an already marked oop
6034 // that may be chained at the end of the overflow list.
6035 assert(oopDesc::is_oop(obj, true), "expected an oop");
6036 HeapWord* addr = (HeapWord*)obj;
6037 if (_span.contains(addr) &&
6038 !_bit_map->isMarked(addr)) {
6039 // mark bit map (object will become grey):
6040 // It is possible for several threads to be
6041 // trying to "claim" this object concurrently;
6042 // the unique thread that succeeds in marking the
6043 // object first will do the subsequent push on
6044 // to the work queue (or overflow list).
6045 if (_bit_map->par_mark(addr)) {
6046 // push on work_queue (which may not be empty), and trim the
6047 // queue to an appropriate length by applying this closure to
6048 // the oops in the oops popped from the stack (i.e. blacken the
6049 // grey objects)
6050 bool res = _work_queue->push(obj);
6051 assert(res, "Low water mark should be less than capacity?");
6052 trim_queue(_low_water_mark);
6053 } // Else, another thread claimed the object
6054 }
6055 }
6056 }
6057
6058 // This closure is used to rescan the marked objects on the dirty cards
6059 // in the mod union table and the card table proper.
6060 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6061 oop p, MemRegion mr) {
6062
6063 size_t size = 0;
6064 HeapWord* addr = (HeapWord*)p;
6065 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6066 assert(_span.contains(addr), "we are scanning the CMS generation");
6067 // check if it's time to yield
6068 if (do_yield_check()) {
6069 // We yielded for some foreground stop-world work,
6070 // and we have been asked to abort this ongoing preclean cycle.
6071 return 0;
6072 }
6073 if (_bitMap->isMarked(addr)) {
6074 // it's marked; is it potentially uninitialized?
6075 if (p->klass_or_null_acquire() != NULL) {
6076 // an initialized object; ignore mark word in verification below
6077 // since we are running concurrent with mutators
6078 assert(oopDesc::is_oop(p, true), "should be an oop");
6079 if (p->is_objArray()) {
6080 // objArrays are precisely marked; restrict scanning
6081 // to dirty cards only.
6082 size = CompactibleFreeListSpace::adjustObjectSize(
6083 p->oop_iterate_size(_scanningClosure, mr));
6084 } else {
6085 // A non-array may have been imprecisely marked; we need
6086 // to scan object in its entirety.
6087 size = CompactibleFreeListSpace::adjustObjectSize(
6088 p->oop_iterate_size(_scanningClosure));
6089 }
6090 #ifdef ASSERT
6091 size_t direct_size =
6092 CompactibleFreeListSpace::adjustObjectSize(p->size());
6093 assert(size == direct_size, "Inconsistency in size");
6094 assert(size >= 3, "Necessary for Printezis marks to work");
6095 HeapWord* start_pbit = addr + 1;
6096 HeapWord* end_pbit = addr + size - 1;
6097 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6098 "inconsistent Printezis mark");
6099 // Verify inner mark bits (between Printezis bits) are clear,
6100 // but don't repeat if there are multiple dirty regions for
6101 // the same object, to avoid potential O(N^2) performance.
6102 if (addr != _last_scanned_object) {
6103 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6104 _last_scanned_object = addr;
6105 }
6106 #endif // ASSERT
6107 } else {
6108 // An uninitialized object.
6109 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6110 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6111 size = pointer_delta(nextOneAddr + 1, addr);
6112 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6113 "alignment problem");
6114 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6115 // will dirty the card when the klass pointer is installed in the
6116 // object (signaling the completion of initialization).
6117 }
6118 } else {
6119 // Either a not yet marked object or an uninitialized object
6120 if (p->klass_or_null_acquire() == NULL) {
6121 // An uninitialized object, skip to the next card, since
6122 // we may not be able to read its P-bits yet.
6123 assert(size == 0, "Initial value");
6124 } else {
6125 // An object not (yet) reached by marking: we merely need to
6126 // compute its size so as to go look at the next block.
6127 assert(oopDesc::is_oop(p, true), "should be an oop");
6128 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6129 }
6130 }
6131 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6132 return size;
6133 }
6134
6135 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6136 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6137 "CMS thread should hold CMS token");
6138 assert_lock_strong(_freelistLock);
6139 assert_lock_strong(_bitMap->lock());
6140 // relinquish the free_list_lock and bitMaplock()
6141 _bitMap->lock()->unlock();
6142 _freelistLock->unlock();
6143 ConcurrentMarkSweepThread::desynchronize(true);
6144 _collector->stopTimer();
6145 _collector->incrementYields();
6146
6147 // See the comment in coordinator_yield()
6148 for (unsigned i = 0; i < CMSYieldSleepCount &&
6149 ConcurrentMarkSweepThread::should_yield() &&
6150 !CMSCollector::foregroundGCIsActive(); ++i) {
6151 os::sleep(Thread::current(), 1, false);
6152 }
6153
6154 ConcurrentMarkSweepThread::synchronize(true);
6155 _freelistLock->lock_without_safepoint_check();
6156 _bitMap->lock()->lock_without_safepoint_check();
6157 _collector->startTimer();
6158 }
6159
6160
6161 //////////////////////////////////////////////////////////////////
6162 // SurvivorSpacePrecleanClosure
6163 //////////////////////////////////////////////////////////////////
6164 // This (single-threaded) closure is used to preclean the oops in
6165 // the survivor spaces.
6166 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6167
6168 HeapWord* addr = (HeapWord*)p;
6169 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6170 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6171 assert(p->klass_or_null() != NULL, "object should be initialized");
6172 // an initialized object; ignore mark word in verification below
6173 // since we are running concurrent with mutators
6174 assert(oopDesc::is_oop(p, true), "should be an oop");
6175 // Note that we do not yield while we iterate over
6176 // the interior oops of p, pushing the relevant ones
6177 // on our marking stack.
6178 size_t size = p->oop_iterate_size(_scanning_closure);
6179 do_yield_check();
6180 // Observe that below, we do not abandon the preclean
6181 // phase as soon as we should; rather we empty the
6182 // marking stack before returning. This is to satisfy
6183 // some existing assertions. In general, it may be a
6184 // good idea to abort immediately and complete the marking
6185 // from the grey objects at a later time.
6186 while (!_mark_stack->isEmpty()) {
6187 oop new_oop = _mark_stack->pop();
6188 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6189 assert(_bit_map->isMarked((HeapWord*)new_oop),
6190 "only grey objects on this stack");
6191 // iterate over the oops in this oop, marking and pushing
6192 // the ones in CMS heap (i.e. in _span).
6193 new_oop->oop_iterate(_scanning_closure);
6194 // check if it's time to yield
6195 do_yield_check();
6196 }
6197 unsigned int after_count =
6198 CMSHeap::heap()->total_collections();
6199 bool abort = (_before_count != after_count) ||
6200 _collector->should_abort_preclean();
6201 return abort ? 0 : size;
6202 }
6203
6204 void SurvivorSpacePrecleanClosure::do_yield_work() {
6205 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6206 "CMS thread should hold CMS token");
6207 assert_lock_strong(_bit_map->lock());
6208 // Relinquish the bit map lock
6209 _bit_map->lock()->unlock();
6210 ConcurrentMarkSweepThread::desynchronize(true);
6211 _collector->stopTimer();
6212 _collector->incrementYields();
6213
6214 // See the comment in coordinator_yield()
6215 for (unsigned i = 0; i < CMSYieldSleepCount &&
6216 ConcurrentMarkSweepThread::should_yield() &&
6217 !CMSCollector::foregroundGCIsActive(); ++i) {
6218 os::sleep(Thread::current(), 1, false);
6219 }
6220
6221 ConcurrentMarkSweepThread::synchronize(true);
6222 _bit_map->lock()->lock_without_safepoint_check();
6223 _collector->startTimer();
6224 }
6225
6226 // This closure is used to rescan the marked objects on the dirty cards
6227 // in the mod union table and the card table proper. In the parallel
6228 // case, although the bitMap is shared, we do a single read so the
6229 // isMarked() query is "safe".
6230 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6231 // Ignore mark word because we are running concurrent with mutators
6232 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6233 HeapWord* addr = (HeapWord*)p;
6234 assert(_span.contains(addr), "we are scanning the CMS generation");
6235 bool is_obj_array = false;
6236 #ifdef ASSERT
6237 if (!_parallel) {
6238 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6239 assert(_collector->overflow_list_is_empty(),
6240 "overflow list should be empty");
6241
6242 }
6243 #endif // ASSERT
6244 if (_bit_map->isMarked(addr)) {
6245 // Obj arrays are precisely marked, non-arrays are not;
6246 // so we scan objArrays precisely and non-arrays in their
6247 // entirety.
6248 if (p->is_objArray()) {
6249 is_obj_array = true;
6250 if (_parallel) {
6251 p->oop_iterate(_par_scan_closure, mr);
6252 } else {
6253 p->oop_iterate(_scan_closure, mr);
6254 }
6255 } else {
6256 if (_parallel) {
6257 p->oop_iterate(_par_scan_closure);
6258 } else {
6259 p->oop_iterate(_scan_closure);
6260 }
6261 }
6262 }
6263 #ifdef ASSERT
6264 if (!_parallel) {
6265 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6266 assert(_collector->overflow_list_is_empty(),
6267 "overflow list should be empty");
6268
6269 }
6270 #endif // ASSERT
6271 return is_obj_array;
6272 }
6273
6274 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6275 MemRegion span,
6276 CMSBitMap* bitMap, CMSMarkStack* markStack,
6277 bool should_yield, bool verifying):
6278 _collector(collector),
6279 _span(span),
6280 _bitMap(bitMap),
6281 _mut(&collector->_modUnionTable),
6282 _markStack(markStack),
6283 _yield(should_yield),
6284 _skipBits(0)
6285 {
6286 assert(_markStack->isEmpty(), "stack should be empty");
6287 _finger = _bitMap->startWord();
6288 _threshold = _finger;
6289 assert(_collector->_restart_addr == NULL, "Sanity check");
6290 assert(_span.contains(_finger), "Out of bounds _finger?");
6291 DEBUG_ONLY(_verifying = verifying;)
6292 }
6293
6294 void MarkFromRootsClosure::reset(HeapWord* addr) {
6295 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6296 assert(_span.contains(addr), "Out of bounds _finger?");
6297 _finger = addr;
6298 _threshold = align_up(_finger, CardTable::card_size);
6299 }
6300
6301 // Should revisit to see if this should be restructured for
6302 // greater efficiency.
6303 bool MarkFromRootsClosure::do_bit(size_t offset) {
6304 if (_skipBits > 0) {
6305 _skipBits--;
6306 return true;
6307 }
6308 // convert offset into a HeapWord*
6309 HeapWord* addr = _bitMap->startWord() + offset;
6310 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6311 "address out of range");
6312 assert(_bitMap->isMarked(addr), "tautology");
6313 if (_bitMap->isMarked(addr+1)) {
6314 // this is an allocated but not yet initialized object
6315 assert(_skipBits == 0, "tautology");
6316 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6317 oop p = oop(addr);
6318 if (p->klass_or_null_acquire() == NULL) {
6319 DEBUG_ONLY(if (!_verifying) {)
6320 // We re-dirty the cards on which this object lies and increase
6321 // the _threshold so that we'll come back to scan this object
6322 // during the preclean or remark phase. (CMSCleanOnEnter)
6323 if (CMSCleanOnEnter) {
6324 size_t sz = _collector->block_size_using_printezis_bits(addr);
6325 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6326 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6327 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6328 // Bump _threshold to end_card_addr; note that
6329 // _threshold cannot possibly exceed end_card_addr, anyhow.
6330 // This prevents future clearing of the card as the scan proceeds
6331 // to the right.
6332 assert(_threshold <= end_card_addr,
6333 "Because we are just scanning into this object");
6334 if (_threshold < end_card_addr) {
6335 _threshold = end_card_addr;
6336 }
6337 if (p->klass_or_null_acquire() != NULL) {
6338 // Redirty the range of cards...
6339 _mut->mark_range(redirty_range);
6340 } // ...else the setting of klass will dirty the card anyway.
6341 }
6342 DEBUG_ONLY(})
6343 return true;
6344 }
6345 }
6346 scanOopsInOop(addr);
6347 return true;
6348 }
6349
6350 // We take a break if we've been at this for a while,
6351 // so as to avoid monopolizing the locks involved.
6352 void MarkFromRootsClosure::do_yield_work() {
6353 // First give up the locks, then yield, then re-lock
6354 // We should probably use a constructor/destructor idiom to
6355 // do this unlock/lock or modify the MutexUnlocker class to
6356 // serve our purpose. XXX
6357 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6358 "CMS thread should hold CMS token");
6359 assert_lock_strong(_bitMap->lock());
6360 _bitMap->lock()->unlock();
6361 ConcurrentMarkSweepThread::desynchronize(true);
6362 _collector->stopTimer();
6363 _collector->incrementYields();
6364
6365 // See the comment in coordinator_yield()
6366 for (unsigned i = 0; i < CMSYieldSleepCount &&
6367 ConcurrentMarkSweepThread::should_yield() &&
6368 !CMSCollector::foregroundGCIsActive(); ++i) {
6369 os::sleep(Thread::current(), 1, false);
6370 }
6371
6372 ConcurrentMarkSweepThread::synchronize(true);
6373 _bitMap->lock()->lock_without_safepoint_check();
6374 _collector->startTimer();
6375 }
6376
6377 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6378 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6379 assert(_markStack->isEmpty(),
6380 "should drain stack to limit stack usage");
6381 // convert ptr to an oop preparatory to scanning
6382 oop obj = oop(ptr);
6383 // Ignore mark word in verification below, since we
6384 // may be running concurrent with mutators.
6385 assert(oopDesc::is_oop(obj, true), "should be an oop");
6386 assert(_finger <= ptr, "_finger runneth ahead");
6387 // advance the finger to right end of this object
6388 _finger = ptr + obj->size();
6389 assert(_finger > ptr, "we just incremented it above");
6390 // On large heaps, it may take us some time to get through
6391 // the marking phase. During
6392 // this time it's possible that a lot of mutations have
6393 // accumulated in the card table and the mod union table --
6394 // these mutation records are redundant until we have
6395 // actually traced into the corresponding card.
6396 // Here, we check whether advancing the finger would make
6397 // us cross into a new card, and if so clear corresponding
6398 // cards in the MUT (preclean them in the card-table in the
6399 // future).
6400
6401 DEBUG_ONLY(if (!_verifying) {)
6402 // The clean-on-enter optimization is disabled by default,
6403 // until we fix 6178663.
6404 if (CMSCleanOnEnter && (_finger > _threshold)) {
6405 // [_threshold, _finger) represents the interval
6406 // of cards to be cleared in MUT (or precleaned in card table).
6407 // The set of cards to be cleared is all those that overlap
6408 // with the interval [_threshold, _finger); note that
6409 // _threshold is always kept card-aligned but _finger isn't
6410 // always card-aligned.
6411 HeapWord* old_threshold = _threshold;
6412 assert(is_aligned(old_threshold, CardTable::card_size),
6413 "_threshold should always be card-aligned");
6414 _threshold = align_up(_finger, CardTable::card_size);
6415 MemRegion mr(old_threshold, _threshold);
6416 assert(!mr.is_empty(), "Control point invariant");
6417 assert(_span.contains(mr), "Should clear within span");
6418 _mut->clear_range(mr);
6419 }
6420 DEBUG_ONLY(})
6421 // Note: the finger doesn't advance while we drain
6422 // the stack below.
6423 PushOrMarkClosure pushOrMarkClosure(_collector,
6424 _span, _bitMap, _markStack,
6425 _finger, this);
6426 bool res = _markStack->push(obj);
6427 assert(res, "Empty non-zero size stack should have space for single push");
6428 while (!_markStack->isEmpty()) {
6429 oop new_oop = _markStack->pop();
6430 // Skip verifying header mark word below because we are
6431 // running concurrent with mutators.
6432 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6433 // now scan this oop's oops
6434 new_oop->oop_iterate(&pushOrMarkClosure);
6435 do_yield_check();
6436 }
6437 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6438 }
6439
6440 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6441 CMSCollector* collector, MemRegion span,
6442 CMSBitMap* bit_map,
6443 OopTaskQueue* work_queue,
6444 CMSMarkStack* overflow_stack):
6445 _collector(collector),
6446 _whole_span(collector->_span),
6447 _span(span),
6448 _bit_map(bit_map),
6449 _mut(&collector->_modUnionTable),
6450 _work_queue(work_queue),
6451 _overflow_stack(overflow_stack),
6452 _skip_bits(0),
6453 _task(task)
6454 {
6455 assert(_work_queue->size() == 0, "work_queue should be empty");
6456 _finger = span.start();
6457 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6458 assert(_span.contains(_finger), "Out of bounds _finger?");
6459 }
6460
6461 // Should revisit to see if this should be restructured for
6462 // greater efficiency.
6463 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6464 if (_skip_bits > 0) {
6465 _skip_bits--;
6466 return true;
6467 }
6468 // convert offset into a HeapWord*
6469 HeapWord* addr = _bit_map->startWord() + offset;
6470 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6471 "address out of range");
6472 assert(_bit_map->isMarked(addr), "tautology");
6473 if (_bit_map->isMarked(addr+1)) {
6474 // this is an allocated object that might not yet be initialized
6475 assert(_skip_bits == 0, "tautology");
6476 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6477 oop p = oop(addr);
6478 if (p->klass_or_null_acquire() == NULL) {
6479 // in the case of Clean-on-Enter optimization, redirty card
6480 // and avoid clearing card by increasing the threshold.
6481 return true;
6482 }
6483 }
6484 scan_oops_in_oop(addr);
6485 return true;
6486 }
6487
6488 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6489 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6490 // Should we assert that our work queue is empty or
6491 // below some drain limit?
6492 assert(_work_queue->size() == 0,
6493 "should drain stack to limit stack usage");
6494 // convert ptr to an oop preparatory to scanning
6495 oop obj = oop(ptr);
6496 // Ignore mark word in verification below, since we
6497 // may be running concurrent with mutators.
6498 assert(oopDesc::is_oop(obj, true), "should be an oop");
6499 assert(_finger <= ptr, "_finger runneth ahead");
6500 // advance the finger to right end of this object
6501 _finger = ptr + obj->size();
6502 assert(_finger > ptr, "we just incremented it above");
6503 // On large heaps, it may take us some time to get through
6504 // the marking phase. During
6505 // this time it's possible that a lot of mutations have
6506 // accumulated in the card table and the mod union table --
6507 // these mutation records are redundant until we have
6508 // actually traced into the corresponding card.
6509 // Here, we check whether advancing the finger would make
6510 // us cross into a new card, and if so clear corresponding
6511 // cards in the MUT (preclean them in the card-table in the
6512 // future).
6513
6514 // The clean-on-enter optimization is disabled by default,
6515 // until we fix 6178663.
6516 if (CMSCleanOnEnter && (_finger > _threshold)) {
6517 // [_threshold, _finger) represents the interval
6518 // of cards to be cleared in MUT (or precleaned in card table).
6519 // The set of cards to be cleared is all those that overlap
6520 // with the interval [_threshold, _finger); note that
6521 // _threshold is always kept card-aligned but _finger isn't
6522 // always card-aligned.
6523 HeapWord* old_threshold = _threshold;
6524 assert(is_aligned(old_threshold, CardTable::card_size),
6525 "_threshold should always be card-aligned");
6526 _threshold = align_up(_finger, CardTable::card_size);
6527 MemRegion mr(old_threshold, _threshold);
6528 assert(!mr.is_empty(), "Control point invariant");
6529 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6530 _mut->clear_range(mr);
6531 }
6532
6533 // Note: the local finger doesn't advance while we drain
6534 // the stack below, but the global finger sure can and will.
6535 HeapWord* volatile* gfa = _task->global_finger_addr();
6536 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6537 _span, _bit_map,
6538 _work_queue,
6539 _overflow_stack,
6540 _finger,
6541 gfa, this);
6542 bool res = _work_queue->push(obj); // overflow could occur here
6543 assert(res, "Will hold once we use workqueues");
6544 while (true) {
6545 oop new_oop;
6546 if (!_work_queue->pop_local(new_oop)) {
6547 // We emptied our work_queue; check if there's stuff that can
6548 // be gotten from the overflow stack.
6549 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6550 _overflow_stack, _work_queue)) {
6551 do_yield_check();
6552 continue;
6553 } else { // done
6554 break;
6555 }
6556 }
6557 // Skip verifying header mark word below because we are
6558 // running concurrent with mutators.
6559 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6560 // now scan this oop's oops
6561 new_oop->oop_iterate(&pushOrMarkClosure);
6562 do_yield_check();
6563 }
6564 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6565 }
6566
6567 // Yield in response to a request from VM Thread or
6568 // from mutators.
6569 void ParMarkFromRootsClosure::do_yield_work() {
6570 assert(_task != NULL, "sanity");
6571 _task->yield();
6572 }
6573
6574 // A variant of the above used for verifying CMS marking work.
6575 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6576 MemRegion span,
6577 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6578 CMSMarkStack* mark_stack):
6579 _collector(collector),
6580 _span(span),
6581 _verification_bm(verification_bm),
6582 _cms_bm(cms_bm),
6583 _mark_stack(mark_stack),
6584 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6585 mark_stack)
6586 {
6587 assert(_mark_stack->isEmpty(), "stack should be empty");
6588 _finger = _verification_bm->startWord();
6589 assert(_collector->_restart_addr == NULL, "Sanity check");
6590 assert(_span.contains(_finger), "Out of bounds _finger?");
6591 }
6592
6593 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6594 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6595 assert(_span.contains(addr), "Out of bounds _finger?");
6596 _finger = addr;
6597 }
6598
6599 // Should revisit to see if this should be restructured for
6600 // greater efficiency.
6601 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6602 // convert offset into a HeapWord*
6603 HeapWord* addr = _verification_bm->startWord() + offset;
6604 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6605 "address out of range");
6606 assert(_verification_bm->isMarked(addr), "tautology");
6607 assert(_cms_bm->isMarked(addr), "tautology");
6608
6609 assert(_mark_stack->isEmpty(),
6610 "should drain stack to limit stack usage");
6611 // convert addr to an oop preparatory to scanning
6612 oop obj = oop(addr);
6613 assert(oopDesc::is_oop(obj), "should be an oop");
6614 assert(_finger <= addr, "_finger runneth ahead");
6615 // advance the finger to right end of this object
6616 _finger = addr + obj->size();
6617 assert(_finger > addr, "we just incremented it above");
6618 // Note: the finger doesn't advance while we drain
6619 // the stack below.
6620 bool res = _mark_stack->push(obj);
6621 assert(res, "Empty non-zero size stack should have space for single push");
6622 while (!_mark_stack->isEmpty()) {
6623 oop new_oop = _mark_stack->pop();
6624 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6625 // now scan this oop's oops
6626 new_oop->oop_iterate(&_pam_verify_closure);
6627 }
6628 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6629 return true;
6630 }
6631
6632 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6633 CMSCollector* collector, MemRegion span,
6634 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6635 CMSMarkStack* mark_stack):
6636 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6637 _collector(collector),
6638 _span(span),
6639 _verification_bm(verification_bm),
6640 _cms_bm(cms_bm),
6641 _mark_stack(mark_stack)
6642 { }
6643
6644 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6645 oop obj = RawAccess<>::oop_load(p);
6646 do_oop(obj);
6647 }
6648
6649 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6650 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6651
6652 // Upon stack overflow, we discard (part of) the stack,
6653 // remembering the least address amongst those discarded
6654 // in CMSCollector's _restart_address.
6655 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6656 // Remember the least grey address discarded
6657 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6658 _collector->lower_restart_addr(ra);
6659 _mark_stack->reset(); // discard stack contents
6660 _mark_stack->expand(); // expand the stack if possible
6661 }
6662
6663 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6664 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6665 HeapWord* addr = (HeapWord*)obj;
6666 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6667 // Oop lies in _span and isn't yet grey or black
6668 _verification_bm->mark(addr); // now grey
6669 if (!_cms_bm->isMarked(addr)) {
6670 Log(gc, verify) log;
6671 ResourceMark rm;
6672 LogStream ls(log.error());
6673 oop(addr)->print_on(&ls);
6674 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6675 fatal("... aborting");
6676 }
6677
6678 if (!_mark_stack->push(obj)) { // stack overflow
6679 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6680 assert(_mark_stack->isFull(), "Else push should have succeeded");
6681 handle_stack_overflow(addr);
6682 }
6683 // anything including and to the right of _finger
6684 // will be scanned as we iterate over the remainder of the
6685 // bit map
6686 }
6687 }
6688
6689 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6690 MemRegion span,
6691 CMSBitMap* bitMap, CMSMarkStack* markStack,
6692 HeapWord* finger, MarkFromRootsClosure* parent) :
6693 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6694 _collector(collector),
6695 _span(span),
6696 _bitMap(bitMap),
6697 _markStack(markStack),
6698 _finger(finger),
6699 _parent(parent)
6700 { }
6701
6702 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6703 MemRegion span,
6704 CMSBitMap* bit_map,
6705 OopTaskQueue* work_queue,
6706 CMSMarkStack* overflow_stack,
6707 HeapWord* finger,
6708 HeapWord* volatile* global_finger_addr,
6709 ParMarkFromRootsClosure* parent) :
6710 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6711 _collector(collector),
6712 _whole_span(collector->_span),
6713 _span(span),
6714 _bit_map(bit_map),
6715 _work_queue(work_queue),
6716 _overflow_stack(overflow_stack),
6717 _finger(finger),
6718 _global_finger_addr(global_finger_addr),
6719 _parent(parent)
6720 { }
6721
6722 // Assumes thread-safe access by callers, who are
6723 // responsible for mutual exclusion.
6724 void CMSCollector::lower_restart_addr(HeapWord* low) {
6725 assert(_span.contains(low), "Out of bounds addr");
6726 if (_restart_addr == NULL) {
6727 _restart_addr = low;
6728 } else {
6729 _restart_addr = MIN2(_restart_addr, low);
6730 }
6731 }
6732
6733 // Upon stack overflow, we discard (part of) the stack,
6734 // remembering the least address amongst those discarded
6735 // in CMSCollector's _restart_address.
6736 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6737 // Remember the least grey address discarded
6738 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6739 _collector->lower_restart_addr(ra);
6740 _markStack->reset(); // discard stack contents
6741 _markStack->expand(); // expand the stack if possible
6742 }
6743
6744 // Upon stack overflow, we discard (part of) the stack,
6745 // remembering the least address amongst those discarded
6746 // in CMSCollector's _restart_address.
6747 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6748 // We need to do this under a mutex to prevent other
6749 // workers from interfering with the work done below.
6750 MutexLockerEx ml(_overflow_stack->par_lock(),
6751 Mutex::_no_safepoint_check_flag);
6752 // Remember the least grey address discarded
6753 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6754 _collector->lower_restart_addr(ra);
6755 _overflow_stack->reset(); // discard stack contents
6756 _overflow_stack->expand(); // expand the stack if possible
6757 }
6758
6759 void PushOrMarkClosure::do_oop(oop obj) {
6760 // Ignore mark word because we are running concurrent with mutators.
6761 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6762 HeapWord* addr = (HeapWord*)obj;
6763 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6764 // Oop lies in _span and isn't yet grey or black
6765 _bitMap->mark(addr); // now grey
6766 if (addr < _finger) {
6767 // the bit map iteration has already either passed, or
6768 // sampled, this bit in the bit map; we'll need to
6769 // use the marking stack to scan this oop's oops.
6770 bool simulate_overflow = false;
6771 NOT_PRODUCT(
6772 if (CMSMarkStackOverflowALot &&
6773 _collector->simulate_overflow()) {
6774 // simulate a stack overflow
6775 simulate_overflow = true;
6776 }
6777 )
6778 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6779 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6780 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6781 handle_stack_overflow(addr);
6782 }
6783 }
6784 // anything including and to the right of _finger
6785 // will be scanned as we iterate over the remainder of the
6786 // bit map
6787 do_yield_check();
6788 }
6789 }
6790
6791 void ParPushOrMarkClosure::do_oop(oop obj) {
6792 // Ignore mark word because we are running concurrent with mutators.
6793 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6794 HeapWord* addr = (HeapWord*)obj;
6795 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6796 // Oop lies in _span and isn't yet grey or black
6797 // We read the global_finger (volatile read) strictly after marking oop
6798 bool res = _bit_map->par_mark(addr); // now grey
6799 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6800 // Should we push this marked oop on our stack?
6801 // -- if someone else marked it, nothing to do
6802 // -- if target oop is above global finger nothing to do
6803 // -- if target oop is in chunk and above local finger
6804 // then nothing to do
6805 // -- else push on work queue
6806 if ( !res // someone else marked it, they will deal with it
6807 || (addr >= *gfa) // will be scanned in a later task
6808 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6809 return;
6810 }
6811 // the bit map iteration has already either passed, or
6812 // sampled, this bit in the bit map; we'll need to
6813 // use the marking stack to scan this oop's oops.
6814 bool simulate_overflow = false;
6815 NOT_PRODUCT(
6816 if (CMSMarkStackOverflowALot &&
6817 _collector->simulate_overflow()) {
6818 // simulate a stack overflow
6819 simulate_overflow = true;
6820 }
6821 )
6822 if (simulate_overflow ||
6823 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6824 // stack overflow
6825 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6826 // We cannot assert that the overflow stack is full because
6827 // it may have been emptied since.
6828 assert(simulate_overflow ||
6829 _work_queue->size() == _work_queue->max_elems(),
6830 "Else push should have succeeded");
6831 handle_stack_overflow(addr);
6832 }
6833 do_yield_check();
6834 }
6835 }
6836
6837 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6838 MemRegion span,
6839 ReferenceDiscoverer* rd,
6840 CMSBitMap* bit_map,
6841 CMSBitMap* mod_union_table,
6842 CMSMarkStack* mark_stack,
6843 bool concurrent_precleaning):
6844 MetadataVisitingOopIterateClosure(rd),
6845 _collector(collector),
6846 _span(span),
6847 _bit_map(bit_map),
6848 _mod_union_table(mod_union_table),
6849 _mark_stack(mark_stack),
6850 _concurrent_precleaning(concurrent_precleaning)
6851 {
6852 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6853 }
6854
6855 // Grey object rescan during pre-cleaning and second checkpoint phases --
6856 // the non-parallel version (the parallel version appears further below.)
6857 void PushAndMarkClosure::do_oop(oop obj) {
6858 // Ignore mark word verification. If during concurrent precleaning,
6859 // the object monitor may be locked. If during the checkpoint
6860 // phases, the object may already have been reached by a different
6861 // path and may be at the end of the global overflow list (so
6862 // the mark word may be NULL).
6863 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6864 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6865 HeapWord* addr = (HeapWord*)obj;
6866 // Check if oop points into the CMS generation
6867 // and is not marked
6868 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6869 // a white object ...
6870 _bit_map->mark(addr); // ... now grey
6871 // push on the marking stack (grey set)
6872 bool simulate_overflow = false;
6873 NOT_PRODUCT(
6874 if (CMSMarkStackOverflowALot &&
6875 _collector->simulate_overflow()) {
6876 // simulate a stack overflow
6877 simulate_overflow = true;
6878 }
6879 )
6880 if (simulate_overflow || !_mark_stack->push(obj)) {
6881 if (_concurrent_precleaning) {
6882 // During precleaning we can just dirty the appropriate card(s)
6883 // in the mod union table, thus ensuring that the object remains
6884 // in the grey set and continue. In the case of object arrays
6885 // we need to dirty all of the cards that the object spans,
6886 // since the rescan of object arrays will be limited to the
6887 // dirty cards.
6888 // Note that no one can be interfering with us in this action
6889 // of dirtying the mod union table, so no locking or atomics
6890 // are required.
6891 if (obj->is_objArray()) {
6892 size_t sz = obj->size();
6893 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6894 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6895 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6896 _mod_union_table->mark_range(redirty_range);
6897 } else {
6898 _mod_union_table->mark(addr);
6899 }
6900 _collector->_ser_pmc_preclean_ovflw++;
6901 } else {
6902 // During the remark phase, we need to remember this oop
6903 // in the overflow list.
6904 _collector->push_on_overflow_list(obj);
6905 _collector->_ser_pmc_remark_ovflw++;
6906 }
6907 }
6908 }
6909 }
6910
6911 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6912 MemRegion span,
6913 ReferenceDiscoverer* rd,
6914 CMSBitMap* bit_map,
6915 OopTaskQueue* work_queue):
6916 MetadataVisitingOopIterateClosure(rd),
6917 _collector(collector),
6918 _span(span),
6919 _bit_map(bit_map),
6920 _work_queue(work_queue)
6921 {
6922 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6923 }
6924
6925 // Grey object rescan during second checkpoint phase --
6926 // the parallel version.
6927 void ParPushAndMarkClosure::do_oop(oop obj) {
6928 // In the assert below, we ignore the mark word because
6929 // this oop may point to an already visited object that is
6930 // on the overflow stack (in which case the mark word has
6931 // been hijacked for chaining into the overflow stack --
6932 // if this is the last object in the overflow stack then
6933 // its mark word will be NULL). Because this object may
6934 // have been subsequently popped off the global overflow
6935 // stack, and the mark word possibly restored to the prototypical
6936 // value, by the time we get to examined this failing assert in
6937 // the debugger, is_oop_or_null(false) may subsequently start
6938 // to hold.
6939 assert(oopDesc::is_oop_or_null(obj, true),
6940 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6941 HeapWord* addr = (HeapWord*)obj;
6942 // Check if oop points into the CMS generation
6943 // and is not marked
6944 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6945 // a white object ...
6946 // If we manage to "claim" the object, by being the
6947 // first thread to mark it, then we push it on our
6948 // marking stack
6949 if (_bit_map->par_mark(addr)) { // ... now grey
6950 // push on work queue (grey set)
6951 bool simulate_overflow = false;
6952 NOT_PRODUCT(
6953 if (CMSMarkStackOverflowALot &&
6954 _collector->par_simulate_overflow()) {
6955 // simulate a stack overflow
6956 simulate_overflow = true;
6957 }
6958 )
6959 if (simulate_overflow || !_work_queue->push(obj)) {
6960 _collector->par_push_on_overflow_list(obj);
6961 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6962 }
6963 } // Else, some other thread got there first
6964 }
6965 }
6966
6967 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6968 Mutex* bml = _collector->bitMapLock();
6969 assert_lock_strong(bml);
6970 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6971 "CMS thread should hold CMS token");
6972
6973 bml->unlock();
6974 ConcurrentMarkSweepThread::desynchronize(true);
6975
6976 _collector->stopTimer();
6977 _collector->incrementYields();
6978
6979 // See the comment in coordinator_yield()
6980 for (unsigned i = 0; i < CMSYieldSleepCount &&
6981 ConcurrentMarkSweepThread::should_yield() &&
6982 !CMSCollector::foregroundGCIsActive(); ++i) {
6983 os::sleep(Thread::current(), 1, false);
6984 }
6985
6986 ConcurrentMarkSweepThread::synchronize(true);
6987 bml->lock();
6988
6989 _collector->startTimer();
6990 }
6991
6992 bool CMSPrecleanRefsYieldClosure::should_return() {
6993 if (ConcurrentMarkSweepThread::should_yield()) {
6994 do_yield_work();
6995 }
6996 return _collector->foregroundGCIsActive();
6997 }
6998
6999 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7000 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
7001 "mr should be aligned to start at a card boundary");
7002 // We'd like to assert:
7003 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
7004 // "mr should be a range of cards");
7005 // However, that would be too strong in one case -- the last
7006 // partition ends at _unallocated_block which, in general, can be
7007 // an arbitrary boundary, not necessarily card aligned.
7008 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7009 _space->object_iterate_mem(mr, &_scan_cl);
7010 }
7011
7012 SweepClosure::SweepClosure(CMSCollector* collector,
7013 ConcurrentMarkSweepGeneration* g,
7014 CMSBitMap* bitMap, bool should_yield) :
7015 _collector(collector),
7016 _g(g),
7017 _sp(g->cmsSpace()),
7018 _limit(_sp->sweep_limit()),
7019 _freelistLock(_sp->freelistLock()),
7020 _bitMap(bitMap),
7021 _inFreeRange(false), // No free range at beginning of sweep
7022 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7023 _lastFreeRangeCoalesced(false),
7024 _yield(should_yield),
7025 _freeFinger(g->used_region().start())
7026 {
7027 NOT_PRODUCT(
7028 _numObjectsFreed = 0;
7029 _numWordsFreed = 0;
7030 _numObjectsLive = 0;
7031 _numWordsLive = 0;
7032 _numObjectsAlreadyFree = 0;
7033 _numWordsAlreadyFree = 0;
7034 _last_fc = NULL;
7035
7036 _sp->initializeIndexedFreeListArrayReturnedBytes();
7037 _sp->dictionary()->initialize_dict_returned_bytes();
7038 )
7039 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7040 "sweep _limit out of bounds");
7041 log_develop_trace(gc, sweep)("====================");
7042 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7043 }
7044
7045 void SweepClosure::print_on(outputStream* st) const {
7046 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7047 p2i(_sp->bottom()), p2i(_sp->end()));
7048 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7049 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7050 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7051 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7052 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7053 }
7054
7055 #ifndef PRODUCT
7056 // Assertion checking only: no useful work in product mode --
7057 // however, if any of the flags below become product flags,
7058 // you may need to review this code to see if it needs to be
7059 // enabled in product mode.
7060 SweepClosure::~SweepClosure() {
7061 assert_lock_strong(_freelistLock);
7062 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7063 "sweep _limit out of bounds");
7064 if (inFreeRange()) {
7065 Log(gc, sweep) log;
7066 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7067 ResourceMark rm;
7068 LogStream ls(log.error());
7069 print_on(&ls);
7070 ShouldNotReachHere();
7071 }
7072
7073 if (log_is_enabled(Debug, gc, sweep)) {
7074 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7075 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7076 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7077 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7078 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7079 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7080 }
7081
7082 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7083 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7084 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7085 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7086 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7087 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7088 }
7089 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7090 log_develop_trace(gc, sweep)("================");
7091 }
7092 #endif // PRODUCT
7093
7094 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7095 bool freeRangeInFreeLists) {
7096 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7097 p2i(freeFinger), freeRangeInFreeLists);
7098 assert(!inFreeRange(), "Trampling existing free range");
7099 set_inFreeRange(true);
7100 set_lastFreeRangeCoalesced(false);
7101
7102 set_freeFinger(freeFinger);
7103 set_freeRangeInFreeLists(freeRangeInFreeLists);
7104 if (CMSTestInFreeList) {
7105 if (freeRangeInFreeLists) {
7106 FreeChunk* fc = (FreeChunk*) freeFinger;
7107 assert(fc->is_free(), "A chunk on the free list should be free.");
7108 assert(fc->size() > 0, "Free range should have a size");
7109 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7110 }
7111 }
7112 }
7113
7114 // Note that the sweeper runs concurrently with mutators. Thus,
7115 // it is possible for direct allocation in this generation to happen
7116 // in the middle of the sweep. Note that the sweeper also coalesces
7117 // contiguous free blocks. Thus, unless the sweeper and the allocator
7118 // synchronize appropriately freshly allocated blocks may get swept up.
7119 // This is accomplished by the sweeper locking the free lists while
7120 // it is sweeping. Thus blocks that are determined to be free are
7121 // indeed free. There is however one additional complication:
7122 // blocks that have been allocated since the final checkpoint and
7123 // mark, will not have been marked and so would be treated as
7124 // unreachable and swept up. To prevent this, the allocator marks
7125 // the bit map when allocating during the sweep phase. This leads,
7126 // however, to a further complication -- objects may have been allocated
7127 // but not yet initialized -- in the sense that the header isn't yet
7128 // installed. The sweeper can not then determine the size of the block
7129 // in order to skip over it. To deal with this case, we use a technique
7130 // (due to Printezis) to encode such uninitialized block sizes in the
7131 // bit map. Since the bit map uses a bit per every HeapWord, but the
7132 // CMS generation has a minimum object size of 3 HeapWords, it follows
7133 // that "normal marks" won't be adjacent in the bit map (there will
7134 // always be at least two 0 bits between successive 1 bits). We make use
7135 // of these "unused" bits to represent uninitialized blocks -- the bit
7136 // corresponding to the start of the uninitialized object and the next
7137 // bit are both set. Finally, a 1 bit marks the end of the object that
7138 // started with the two consecutive 1 bits to indicate its potentially
7139 // uninitialized state.
7140
7141 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7142 FreeChunk* fc = (FreeChunk*)addr;
7143 size_t res;
7144
7145 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7146 // than "addr == _limit" because although _limit was a block boundary when
7147 // we started the sweep, it may no longer be one because heap expansion
7148 // may have caused us to coalesce the block ending at the address _limit
7149 // with a newly expanded chunk (this happens when _limit was set to the
7150 // previous _end of the space), so we may have stepped past _limit:
7151 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7152 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7153 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7154 "sweep _limit out of bounds");
7155 assert(addr < _sp->end(), "addr out of bounds");
7156 // Flush any free range we might be holding as a single
7157 // coalesced chunk to the appropriate free list.
7158 if (inFreeRange()) {
7159 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7160 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7161 flush_cur_free_chunk(freeFinger(),
7162 pointer_delta(addr, freeFinger()));
7163 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7164 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7165 lastFreeRangeCoalesced() ? 1 : 0);
7166 }
7167
7168 // help the iterator loop finish
7169 return pointer_delta(_sp->end(), addr);
7170 }
7171
7172 assert(addr < _limit, "sweep invariant");
7173 // check if we should yield
7174 do_yield_check(addr);
7175 if (fc->is_free()) {
7176 // Chunk that is already free
7177 res = fc->size();
7178 do_already_free_chunk(fc);
7179 debug_only(_sp->verifyFreeLists());
7180 // If we flush the chunk at hand in lookahead_and_flush()
7181 // and it's coalesced with a preceding chunk, then the
7182 // process of "mangling" the payload of the coalesced block
7183 // will cause erasure of the size information from the
7184 // (erstwhile) header of all the coalesced blocks but the
7185 // first, so the first disjunct in the assert will not hold
7186 // in that specific case (in which case the second disjunct
7187 // will hold).
7188 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7189 "Otherwise the size info doesn't change at this step");
7190 NOT_PRODUCT(
7191 _numObjectsAlreadyFree++;
7192 _numWordsAlreadyFree += res;
7193 )
7194 NOT_PRODUCT(_last_fc = fc;)
7195 } else if (!_bitMap->isMarked(addr)) {
7196 // Chunk is fresh garbage
7197 res = do_garbage_chunk(fc);
7198 debug_only(_sp->verifyFreeLists());
7199 NOT_PRODUCT(
7200 _numObjectsFreed++;
7201 _numWordsFreed += res;
7202 )
7203 } else {
7204 // Chunk that is alive.
7205 res = do_live_chunk(fc);
7206 debug_only(_sp->verifyFreeLists());
7207 NOT_PRODUCT(
7208 _numObjectsLive++;
7209 _numWordsLive += res;
7210 )
7211 }
7212 return res;
7213 }
7214
7215 // For the smart allocation, record following
7216 // split deaths - a free chunk is removed from its free list because
7217 // it is being split into two or more chunks.
7218 // split birth - a free chunk is being added to its free list because
7219 // a larger free chunk has been split and resulted in this free chunk.
7220 // coal death - a free chunk is being removed from its free list because
7221 // it is being coalesced into a large free chunk.
7222 // coal birth - a free chunk is being added to its free list because
7223 // it was created when two or more free chunks where coalesced into
7224 // this free chunk.
7225 //
7226 // These statistics are used to determine the desired number of free
7227 // chunks of a given size. The desired number is chosen to be relative
7228 // to the end of a CMS sweep. The desired number at the end of a sweep
7229 // is the
7230 // count-at-end-of-previous-sweep (an amount that was enough)
7231 // - count-at-beginning-of-current-sweep (the excess)
7232 // + split-births (gains in this size during interval)
7233 // - split-deaths (demands on this size during interval)
7234 // where the interval is from the end of one sweep to the end of the
7235 // next.
7236 //
7237 // When sweeping the sweeper maintains an accumulated chunk which is
7238 // the chunk that is made up of chunks that have been coalesced. That
7239 // will be termed the left-hand chunk. A new chunk of garbage that
7240 // is being considered for coalescing will be referred to as the
7241 // right-hand chunk.
7242 //
7243 // When making a decision on whether to coalesce a right-hand chunk with
7244 // the current left-hand chunk, the current count vs. the desired count
7245 // of the left-hand chunk is considered. Also if the right-hand chunk
7246 // is near the large chunk at the end of the heap (see
7247 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7248 // left-hand chunk is coalesced.
7249 //
7250 // When making a decision about whether to split a chunk, the desired count
7251 // vs. the current count of the candidate to be split is also considered.
7252 // If the candidate is underpopulated (currently fewer chunks than desired)
7253 // a chunk of an overpopulated (currently more chunks than desired) size may
7254 // be chosen. The "hint" associated with a free list, if non-null, points
7255 // to a free list which may be overpopulated.
7256 //
7257
7258 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7259 const size_t size = fc->size();
7260 // Chunks that cannot be coalesced are not in the
7261 // free lists.
7262 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7263 assert(_sp->verify_chunk_in_free_list(fc),
7264 "free chunk should be in free lists");
7265 }
7266 // a chunk that is already free, should not have been
7267 // marked in the bit map
7268 HeapWord* const addr = (HeapWord*) fc;
7269 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7270 // Verify that the bit map has no bits marked between
7271 // addr and purported end of this block.
7272 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7273
7274 // Some chunks cannot be coalesced under any circumstances.
7275 // See the definition of cantCoalesce().
7276 if (!fc->cantCoalesce()) {
7277 // This chunk can potentially be coalesced.
7278 // All the work is done in
7279 do_post_free_or_garbage_chunk(fc, size);
7280 // Note that if the chunk is not coalescable (the else arm
7281 // below), we unconditionally flush, without needing to do
7282 // a "lookahead," as we do below.
7283 if (inFreeRange()) lookahead_and_flush(fc, size);
7284 } else {
7285 // Code path common to both original and adaptive free lists.
7286
7287 // cant coalesce with previous block; this should be treated
7288 // as the end of a free run if any
7289 if (inFreeRange()) {
7290 // we kicked some butt; time to pick up the garbage
7291 assert(freeFinger() < addr, "freeFinger points too high");
7292 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7293 }
7294 // else, nothing to do, just continue
7295 }
7296 }
7297
7298 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7299 // This is a chunk of garbage. It is not in any free list.
7300 // Add it to a free list or let it possibly be coalesced into
7301 // a larger chunk.
7302 HeapWord* const addr = (HeapWord*) fc;
7303 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7304
7305 // Verify that the bit map has no bits marked between
7306 // addr and purported end of just dead object.
7307 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7308 do_post_free_or_garbage_chunk(fc, size);
7309
7310 assert(_limit >= addr + size,
7311 "A freshly garbage chunk can't possibly straddle over _limit");
7312 if (inFreeRange()) lookahead_and_flush(fc, size);
7313 return size;
7314 }
7315
7316 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7317 HeapWord* addr = (HeapWord*) fc;
7318 // The sweeper has just found a live object. Return any accumulated
7319 // left hand chunk to the free lists.
7320 if (inFreeRange()) {
7321 assert(freeFinger() < addr, "freeFinger points too high");
7322 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7323 }
7324
7325 // This object is live: we'd normally expect this to be
7326 // an oop, and like to assert the following:
7327 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7328 // However, as we commented above, this may be an object whose
7329 // header hasn't yet been initialized.
7330 size_t size;
7331 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7332 if (_bitMap->isMarked(addr + 1)) {
7333 // Determine the size from the bit map, rather than trying to
7334 // compute it from the object header.
7335 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7336 size = pointer_delta(nextOneAddr + 1, addr);
7337 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7338 "alignment problem");
7339
7340 #ifdef ASSERT
7341 if (oop(addr)->klass_or_null_acquire() != NULL) {
7342 // Ignore mark word because we are running concurrent with mutators
7343 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7344 assert(size ==
7345 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7346 "P-mark and computed size do not agree");
7347 }
7348 #endif
7349
7350 } else {
7351 // This should be an initialized object that's alive.
7352 assert(oop(addr)->klass_or_null_acquire() != NULL,
7353 "Should be an initialized object");
7354 // Ignore mark word because we are running concurrent with mutators
7355 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7356 // Verify that the bit map has no bits marked between
7357 // addr and purported end of this block.
7358 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7359 assert(size >= 3, "Necessary for Printezis marks to work");
7360 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7361 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7362 }
7363 return size;
7364 }
7365
7366 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7367 size_t chunkSize) {
7368 // do_post_free_or_garbage_chunk() should only be called in the case
7369 // of the adaptive free list allocator.
7370 const bool fcInFreeLists = fc->is_free();
7371 assert((HeapWord*)fc <= _limit, "sweep invariant");
7372 if (CMSTestInFreeList && fcInFreeLists) {
7373 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7374 }
7375
7376 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7377
7378 HeapWord* const fc_addr = (HeapWord*) fc;
7379
7380 bool coalesce = false;
7381 const size_t left = pointer_delta(fc_addr, freeFinger());
7382 const size_t right = chunkSize;
7383 switch (FLSCoalescePolicy) {
7384 // numeric value forms a coalition aggressiveness metric
7385 case 0: { // never coalesce
7386 coalesce = false;
7387 break;
7388 }
7389 case 1: { // coalesce if left & right chunks on overpopulated lists
7390 coalesce = _sp->coalOverPopulated(left) &&
7391 _sp->coalOverPopulated(right);
7392 break;
7393 }
7394 case 2: { // coalesce if left chunk on overpopulated list (default)
7395 coalesce = _sp->coalOverPopulated(left);
7396 break;
7397 }
7398 case 3: { // coalesce if left OR right chunk on overpopulated list
7399 coalesce = _sp->coalOverPopulated(left) ||
7400 _sp->coalOverPopulated(right);
7401 break;
7402 }
7403 case 4: { // always coalesce
7404 coalesce = true;
7405 break;
7406 }
7407 default:
7408 ShouldNotReachHere();
7409 }
7410
7411 // Should the current free range be coalesced?
7412 // If the chunk is in a free range and either we decided to coalesce above
7413 // or the chunk is near the large block at the end of the heap
7414 // (isNearLargestChunk() returns true), then coalesce this chunk.
7415 const bool doCoalesce = inFreeRange()
7416 && (coalesce || _g->isNearLargestChunk(fc_addr));
7417 if (doCoalesce) {
7418 // Coalesce the current free range on the left with the new
7419 // chunk on the right. If either is on a free list,
7420 // it must be removed from the list and stashed in the closure.
7421 if (freeRangeInFreeLists()) {
7422 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7423 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7424 "Size of free range is inconsistent with chunk size.");
7425 if (CMSTestInFreeList) {
7426 assert(_sp->verify_chunk_in_free_list(ffc),
7427 "Chunk is not in free lists");
7428 }
7429 _sp->coalDeath(ffc->size());
7430 _sp->removeFreeChunkFromFreeLists(ffc);
7431 set_freeRangeInFreeLists(false);
7432 }
7433 if (fcInFreeLists) {
7434 _sp->coalDeath(chunkSize);
7435 assert(fc->size() == chunkSize,
7436 "The chunk has the wrong size or is not in the free lists");
7437 _sp->removeFreeChunkFromFreeLists(fc);
7438 }
7439 set_lastFreeRangeCoalesced(true);
7440 print_free_block_coalesced(fc);
7441 } else { // not in a free range and/or should not coalesce
7442 // Return the current free range and start a new one.
7443 if (inFreeRange()) {
7444 // In a free range but cannot coalesce with the right hand chunk.
7445 // Put the current free range into the free lists.
7446 flush_cur_free_chunk(freeFinger(),
7447 pointer_delta(fc_addr, freeFinger()));
7448 }
7449 // Set up for new free range. Pass along whether the right hand
7450 // chunk is in the free lists.
7451 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7452 }
7453 }
7454
7455 // Lookahead flush:
7456 // If we are tracking a free range, and this is the last chunk that
7457 // we'll look at because its end crosses past _limit, we'll preemptively
7458 // flush it along with any free range we may be holding on to. Note that
7459 // this can be the case only for an already free or freshly garbage
7460 // chunk. If this block is an object, it can never straddle
7461 // over _limit. The "straddling" occurs when _limit is set at
7462 // the previous end of the space when this cycle started, and
7463 // a subsequent heap expansion caused the previously co-terminal
7464 // free block to be coalesced with the newly expanded portion,
7465 // thus rendering _limit a non-block-boundary making it dangerous
7466 // for the sweeper to step over and examine.
7467 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7468 assert(inFreeRange(), "Should only be called if currently in a free range.");
7469 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7470 assert(_sp->used_region().contains(eob - 1),
7471 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7472 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7473 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7474 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7475 if (eob >= _limit) {
7476 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7477 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7478 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7479 "[" PTR_FORMAT "," PTR_FORMAT ")",
7480 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7481 // Return the storage we are tracking back into the free lists.
7482 log_develop_trace(gc, sweep)("Flushing ... ");
7483 assert(freeFinger() < eob, "Error");
7484 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7485 }
7486 }
7487
7488 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7489 assert(inFreeRange(), "Should only be called if currently in a free range.");
7490 assert(size > 0,
7491 "A zero sized chunk cannot be added to the free lists.");
7492 if (!freeRangeInFreeLists()) {
7493 if (CMSTestInFreeList) {
7494 FreeChunk* fc = (FreeChunk*) chunk;
7495 fc->set_size(size);
7496 assert(!_sp->verify_chunk_in_free_list(fc),
7497 "chunk should not be in free lists yet");
7498 }
7499 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7500 // A new free range is going to be starting. The current
7501 // free range has not been added to the free lists yet or
7502 // was removed so add it back.
7503 // If the current free range was coalesced, then the death
7504 // of the free range was recorded. Record a birth now.
7505 if (lastFreeRangeCoalesced()) {
7506 _sp->coalBirth(size);
7507 }
7508 _sp->addChunkAndRepairOffsetTable(chunk, size,
7509 lastFreeRangeCoalesced());
7510 } else {
7511 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7512 }
7513 set_inFreeRange(false);
7514 set_freeRangeInFreeLists(false);
7515 }
7516
7517 // We take a break if we've been at this for a while,
7518 // so as to avoid monopolizing the locks involved.
7519 void SweepClosure::do_yield_work(HeapWord* addr) {
7520 // Return current free chunk being used for coalescing (if any)
7521 // to the appropriate freelist. After yielding, the next
7522 // free block encountered will start a coalescing range of
7523 // free blocks. If the next free block is adjacent to the
7524 // chunk just flushed, they will need to wait for the next
7525 // sweep to be coalesced.
7526 if (inFreeRange()) {
7527 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7528 }
7529
7530 // First give up the locks, then yield, then re-lock.
7531 // We should probably use a constructor/destructor idiom to
7532 // do this unlock/lock or modify the MutexUnlocker class to
7533 // serve our purpose. XXX
7534 assert_lock_strong(_bitMap->lock());
7535 assert_lock_strong(_freelistLock);
7536 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7537 "CMS thread should hold CMS token");
7538 _bitMap->lock()->unlock();
7539 _freelistLock->unlock();
7540 ConcurrentMarkSweepThread::desynchronize(true);
7541 _collector->stopTimer();
7542 _collector->incrementYields();
7543
7544 // See the comment in coordinator_yield()
7545 for (unsigned i = 0; i < CMSYieldSleepCount &&
7546 ConcurrentMarkSweepThread::should_yield() &&
7547 !CMSCollector::foregroundGCIsActive(); ++i) {
7548 os::sleep(Thread::current(), 1, false);
7549 }
7550
7551 ConcurrentMarkSweepThread::synchronize(true);
7552 _freelistLock->lock();
7553 _bitMap->lock()->lock_without_safepoint_check();
7554 _collector->startTimer();
7555 }
7556
7557 #ifndef PRODUCT
7558 // This is actually very useful in a product build if it can
7559 // be called from the debugger. Compile it into the product
7560 // as needed.
7561 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7562 return debug_cms_space->verify_chunk_in_free_list(fc);
7563 }
7564 #endif
7565
7566 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7567 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7568 p2i(fc), fc->size());
7569 }
7570
7571 // CMSIsAliveClosure
7572 bool CMSIsAliveClosure::do_object_b(oop obj) {
7573 HeapWord* addr = (HeapWord*)obj;
7574 return addr != NULL &&
7575 (!_span.contains(addr) || _bit_map->isMarked(addr));
7576 }
7577
7578 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7579 MemRegion span,
7580 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7581 bool cpc):
7582 _collector(collector),
7583 _span(span),
7584 _mark_stack(mark_stack),
7585 _bit_map(bit_map),
7586 _concurrent_precleaning(cpc) {
7587 assert(!_span.is_empty(), "Empty span could spell trouble");
7588 }
7589
7590
7591 // CMSKeepAliveClosure: the serial version
7592 void CMSKeepAliveClosure::do_oop(oop obj) {
7593 HeapWord* addr = (HeapWord*)obj;
7594 if (_span.contains(addr) &&
7595 !_bit_map->isMarked(addr)) {
7596 _bit_map->mark(addr);
7597 bool simulate_overflow = false;
7598 NOT_PRODUCT(
7599 if (CMSMarkStackOverflowALot &&
7600 _collector->simulate_overflow()) {
7601 // simulate a stack overflow
7602 simulate_overflow = true;
7603 }
7604 )
7605 if (simulate_overflow || !_mark_stack->push(obj)) {
7606 if (_concurrent_precleaning) {
7607 // We dirty the overflown object and let the remark
7608 // phase deal with it.
7609 assert(_collector->overflow_list_is_empty(), "Error");
7610 // In the case of object arrays, we need to dirty all of
7611 // the cards that the object spans. No locking or atomics
7612 // are needed since no one else can be mutating the mod union
7613 // table.
7614 if (obj->is_objArray()) {
7615 size_t sz = obj->size();
7616 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7617 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7618 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7619 _collector->_modUnionTable.mark_range(redirty_range);
7620 } else {
7621 _collector->_modUnionTable.mark(addr);
7622 }
7623 _collector->_ser_kac_preclean_ovflw++;
7624 } else {
7625 _collector->push_on_overflow_list(obj);
7626 _collector->_ser_kac_ovflw++;
7627 }
7628 }
7629 }
7630 }
7631
7632 // CMSParKeepAliveClosure: a parallel version of the above.
7633 // The work queues are private to each closure (thread),
7634 // but (may be) available for stealing by other threads.
7635 void CMSParKeepAliveClosure::do_oop(oop obj) {
7636 HeapWord* addr = (HeapWord*)obj;
7637 if (_span.contains(addr) &&
7638 !_bit_map->isMarked(addr)) {
7639 // In general, during recursive tracing, several threads
7640 // may be concurrently getting here; the first one to
7641 // "tag" it, claims it.
7642 if (_bit_map->par_mark(addr)) {
7643 bool res = _work_queue->push(obj);
7644 assert(res, "Low water mark should be much less than capacity");
7645 // Do a recursive trim in the hope that this will keep
7646 // stack usage lower, but leave some oops for potential stealers
7647 trim_queue(_low_water_mark);
7648 } // Else, another thread got there first
7649 }
7650 }
7651
7652 void CMSParKeepAliveClosure::trim_queue(uint max) {
7653 while (_work_queue->size() > max) {
7654 oop new_oop;
7655 if (_work_queue->pop_local(new_oop)) {
7656 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7657 assert(_bit_map->isMarked((HeapWord*)new_oop),
7658 "no white objects on this stack!");
7659 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7660 // iterate over the oops in this oop, marking and pushing
7661 // the ones in CMS heap (i.e. in _span).
7662 new_oop->oop_iterate(&_mark_and_push);
7663 }
7664 }
7665 }
7666
7667 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7668 CMSCollector* collector,
7669 MemRegion span, CMSBitMap* bit_map,
7670 OopTaskQueue* work_queue):
7671 _collector(collector),
7672 _span(span),
7673 _work_queue(work_queue),
7674 _bit_map(bit_map) { }
7675
7676 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7677 HeapWord* addr = (HeapWord*)obj;
7678 if (_span.contains(addr) &&
7679 !_bit_map->isMarked(addr)) {
7680 if (_bit_map->par_mark(addr)) {
7681 bool simulate_overflow = false;
7682 NOT_PRODUCT(
7683 if (CMSMarkStackOverflowALot &&
7684 _collector->par_simulate_overflow()) {
7685 // simulate a stack overflow
7686 simulate_overflow = true;
7687 }
7688 )
7689 if (simulate_overflow || !_work_queue->push(obj)) {
7690 _collector->par_push_on_overflow_list(obj);
7691 _collector->_par_kac_ovflw++;
7692 }
7693 } // Else another thread got there already
7694 }
7695 }
7696
7697 //////////////////////////////////////////////////////////////////
7698 // CMSExpansionCause /////////////////////////////
7699 //////////////////////////////////////////////////////////////////
7700 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7701 switch (cause) {
7702 case _no_expansion:
7703 return "No expansion";
7704 case _satisfy_free_ratio:
7705 return "Free ratio";
7706 case _satisfy_promotion:
7707 return "Satisfy promotion";
7708 case _satisfy_allocation:
7709 return "allocation";
7710 case _allocate_par_lab:
7711 return "Par LAB";
7712 case _allocate_par_spooling_space:
7713 return "Par Spooling Space";
7714 case _adaptive_size_policy:
7715 return "Ergonomics";
7716 default:
7717 return "unknown";
7718 }
7719 }
7720
7721 void CMSDrainMarkingStackClosure::do_void() {
7722 // the max number to take from overflow list at a time
7723 const size_t num = _mark_stack->capacity()/4;
7724 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7725 "Overflow list should be NULL during concurrent phases");
7726 while (!_mark_stack->isEmpty() ||
7727 // if stack is empty, check the overflow list
7728 _collector->take_from_overflow_list(num, _mark_stack)) {
7729 oop obj = _mark_stack->pop();
7730 HeapWord* addr = (HeapWord*)obj;
7731 assert(_span.contains(addr), "Should be within span");
7732 assert(_bit_map->isMarked(addr), "Should be marked");
7733 assert(oopDesc::is_oop(obj), "Should be an oop");
7734 obj->oop_iterate(_keep_alive);
7735 }
7736 }
7737
7738 void CMSParDrainMarkingStackClosure::do_void() {
7739 // drain queue
7740 trim_queue(0);
7741 }
7742
7743 // Trim our work_queue so its length is below max at return
7744 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7745 while (_work_queue->size() > max) {
7746 oop new_oop;
7747 if (_work_queue->pop_local(new_oop)) {
7748 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7749 assert(_bit_map->isMarked((HeapWord*)new_oop),
7750 "no white objects on this stack!");
7751 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7752 // iterate over the oops in this oop, marking and pushing
7753 // the ones in CMS heap (i.e. in _span).
7754 new_oop->oop_iterate(&_mark_and_push);
7755 }
7756 }
7757 }
7758
7759 ////////////////////////////////////////////////////////////////////
7760 // Support for Marking Stack Overflow list handling and related code
7761 ////////////////////////////////////////////////////////////////////
7762 // Much of the following code is similar in shape and spirit to the
7763 // code used in ParNewGC. We should try and share that code
7764 // as much as possible in the future.
7765
7766 #ifndef PRODUCT
7767 // Debugging support for CMSStackOverflowALot
7768
7769 // It's OK to call this multi-threaded; the worst thing
7770 // that can happen is that we'll get a bunch of closely
7771 // spaced simulated overflows, but that's OK, in fact
7772 // probably good as it would exercise the overflow code
7773 // under contention.
7774 bool CMSCollector::simulate_overflow() {
7775 if (_overflow_counter-- <= 0) { // just being defensive
7776 _overflow_counter = CMSMarkStackOverflowInterval;
7777 return true;
7778 } else {
7779 return false;
7780 }
7781 }
7782
7783 bool CMSCollector::par_simulate_overflow() {
7784 return simulate_overflow();
7785 }
7786 #endif
7787
7788 // Single-threaded
7789 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7790 assert(stack->isEmpty(), "Expected precondition");
7791 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7792 size_t i = num;
7793 oop cur = _overflow_list;
7794 const markOop proto = markOopDesc::prototype();
7795 NOT_PRODUCT(ssize_t n = 0;)
7796 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7797 next = oop(cur->mark_raw());
7798 cur->set_mark_raw(proto); // until proven otherwise
7799 assert(oopDesc::is_oop(cur), "Should be an oop");
7800 bool res = stack->push(cur);
7801 assert(res, "Bit off more than can chew?");
7802 NOT_PRODUCT(n++;)
7803 }
7804 _overflow_list = cur;
7805 #ifndef PRODUCT
7806 assert(_num_par_pushes >= n, "Too many pops?");
7807 _num_par_pushes -=n;
7808 #endif
7809 return !stack->isEmpty();
7810 }
7811
7812 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7813 // (MT-safe) Get a prefix of at most "num" from the list.
7814 // The overflow list is chained through the mark word of
7815 // each object in the list. We fetch the entire list,
7816 // break off a prefix of the right size and return the
7817 // remainder. If other threads try to take objects from
7818 // the overflow list at that time, they will wait for
7819 // some time to see if data becomes available. If (and
7820 // only if) another thread places one or more object(s)
7821 // on the global list before we have returned the suffix
7822 // to the global list, we will walk down our local list
7823 // to find its end and append the global list to
7824 // our suffix before returning it. This suffix walk can
7825 // prove to be expensive (quadratic in the amount of traffic)
7826 // when there are many objects in the overflow list and
7827 // there is much producer-consumer contention on the list.
7828 // *NOTE*: The overflow list manipulation code here and
7829 // in ParNewGeneration:: are very similar in shape,
7830 // except that in the ParNew case we use the old (from/eden)
7831 // copy of the object to thread the list via its klass word.
7832 // Because of the common code, if you make any changes in
7833 // the code below, please check the ParNew version to see if
7834 // similar changes might be needed.
7835 // CR 6797058 has been filed to consolidate the common code.
7836 bool CMSCollector::par_take_from_overflow_list(size_t num,
7837 OopTaskQueue* work_q,
7838 int no_of_gc_threads) {
7839 assert(work_q->size() == 0, "First empty local work queue");
7840 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7841 if (_overflow_list == NULL) {
7842 return false;
7843 }
7844 // Grab the entire list; we'll put back a suffix
7845 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7846 Thread* tid = Thread::current();
7847 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7848 // set to ParallelGCThreads.
7849 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7850 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7851 // If the list is busy, we spin for a short while,
7852 // sleeping between attempts to get the list.
7853 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7854 os::sleep(tid, sleep_time_millis, false);
7855 if (_overflow_list == NULL) {
7856 // Nothing left to take
7857 return false;
7858 } else if (_overflow_list != BUSY) {
7859 // Try and grab the prefix
7860 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7861 }
7862 }
7863 // If the list was found to be empty, or we spun long
7864 // enough, we give up and return empty-handed. If we leave
7865 // the list in the BUSY state below, it must be the case that
7866 // some other thread holds the overflow list and will set it
7867 // to a non-BUSY state in the future.
7868 if (prefix == NULL || prefix == BUSY) {
7869 // Nothing to take or waited long enough
7870 if (prefix == NULL) {
7871 // Write back the NULL in case we overwrote it with BUSY above
7872 // and it is still the same value.
7873 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7874 }
7875 return false;
7876 }
7877 assert(prefix != NULL && prefix != BUSY, "Error");
7878 size_t i = num;
7879 oop cur = prefix;
7880 // Walk down the first "num" objects, unless we reach the end.
7881 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7882 if (cur->mark_raw() == NULL) {
7883 // We have "num" or fewer elements in the list, so there
7884 // is nothing to return to the global list.
7885 // Write back the NULL in lieu of the BUSY we wrote
7886 // above, if it is still the same value.
7887 if (_overflow_list == BUSY) {
7888 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7889 }
7890 } else {
7891 // Chop off the suffix and return it to the global list.
7892 assert(cur->mark_raw() != BUSY, "Error");
7893 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7894 cur->set_mark_raw(NULL); // break off suffix
7895 // It's possible that the list is still in the empty(busy) state
7896 // we left it in a short while ago; in that case we may be
7897 // able to place back the suffix without incurring the cost
7898 // of a walk down the list.
7899 oop observed_overflow_list = _overflow_list;
7900 oop cur_overflow_list = observed_overflow_list;
7901 bool attached = false;
7902 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7903 observed_overflow_list =
7904 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7905 if (cur_overflow_list == observed_overflow_list) {
7906 attached = true;
7907 break;
7908 } else cur_overflow_list = observed_overflow_list;
7909 }
7910 if (!attached) {
7911 // Too bad, someone else sneaked in (at least) an element; we'll need
7912 // to do a splice. Find tail of suffix so we can prepend suffix to global
7913 // list.
7914 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7915 oop suffix_tail = cur;
7916 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7917 "Tautology");
7918 observed_overflow_list = _overflow_list;
7919 do {
7920 cur_overflow_list = observed_overflow_list;
7921 if (cur_overflow_list != BUSY) {
7922 // Do the splice ...
7923 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7924 } else { // cur_overflow_list == BUSY
7925 suffix_tail->set_mark_raw(NULL);
7926 }
7927 // ... and try to place spliced list back on overflow_list ...
7928 observed_overflow_list =
7929 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7930 } while (cur_overflow_list != observed_overflow_list);
7931 // ... until we have succeeded in doing so.
7932 }
7933 }
7934
7935 // Push the prefix elements on work_q
7936 assert(prefix != NULL, "control point invariant");
7937 const markOop proto = markOopDesc::prototype();
7938 oop next;
7939 NOT_PRODUCT(ssize_t n = 0;)
7940 for (cur = prefix; cur != NULL; cur = next) {
7941 next = oop(cur->mark_raw());
7942 cur->set_mark_raw(proto); // until proven otherwise
7943 assert(oopDesc::is_oop(cur), "Should be an oop");
7944 bool res = work_q->push(cur);
7945 assert(res, "Bit off more than we can chew?");
7946 NOT_PRODUCT(n++;)
7947 }
7948 #ifndef PRODUCT
7949 assert(_num_par_pushes >= n, "Too many pops?");
7950 Atomic::sub(n, &_num_par_pushes);
7951 #endif
7952 return true;
7953 }
7954
7955 // Single-threaded
7956 void CMSCollector::push_on_overflow_list(oop p) {
7957 NOT_PRODUCT(_num_par_pushes++;)
7958 assert(oopDesc::is_oop(p), "Not an oop");
7959 preserve_mark_if_necessary(p);
7960 p->set_mark_raw((markOop)_overflow_list);
7961 _overflow_list = p;
7962 }
7963
7964 // Multi-threaded; use CAS to prepend to overflow list
7965 void CMSCollector::par_push_on_overflow_list(oop p) {
7966 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7967 assert(oopDesc::is_oop(p), "Not an oop");
7968 par_preserve_mark_if_necessary(p);
7969 oop observed_overflow_list = _overflow_list;
7970 oop cur_overflow_list;
7971 do {
7972 cur_overflow_list = observed_overflow_list;
7973 if (cur_overflow_list != BUSY) {
7974 p->set_mark_raw(markOop(cur_overflow_list));
7975 } else {
7976 p->set_mark_raw(NULL);
7977 }
7978 observed_overflow_list =
7979 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7980 } while (cur_overflow_list != observed_overflow_list);
7981 }
7982 #undef BUSY
7983
7984 // Single threaded
7985 // General Note on GrowableArray: pushes may silently fail
7986 // because we are (temporarily) out of C-heap for expanding
7987 // the stack. The problem is quite ubiquitous and affects
7988 // a lot of code in the JVM. The prudent thing for GrowableArray
7989 // to do (for now) is to exit with an error. However, that may
7990 // be too draconian in some cases because the caller may be
7991 // able to recover without much harm. For such cases, we
7992 // should probably introduce a "soft_push" method which returns
7993 // an indication of success or failure with the assumption that
7994 // the caller may be able to recover from a failure; code in
7995 // the VM can then be changed, incrementally, to deal with such
7996 // failures where possible, thus, incrementally hardening the VM
7997 // in such low resource situations.
7998 void CMSCollector::preserve_mark_work(oop p, markOop m) {
7999 _preserved_oop_stack.push(p);
8000 _preserved_mark_stack.push(m);
8001 assert(m == p->mark_raw(), "Mark word changed");
8002 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8003 "bijection");
8004 }
8005
8006 // Single threaded
8007 void CMSCollector::preserve_mark_if_necessary(oop p) {
8008 markOop m = p->mark_raw();
8009 if (m->must_be_preserved(p)) {
8010 preserve_mark_work(p, m);
8011 }
8012 }
8013
8014 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8015 markOop m = p->mark_raw();
8016 if (m->must_be_preserved(p)) {
8017 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8018 // Even though we read the mark word without holding
8019 // the lock, we are assured that it will not change
8020 // because we "own" this oop, so no other thread can
8021 // be trying to push it on the overflow list; see
8022 // the assertion in preserve_mark_work() that checks
8023 // that m == p->mark_raw().
8024 preserve_mark_work(p, m);
8025 }
8026 }
8027
8028 // We should be able to do this multi-threaded,
8029 // a chunk of stack being a task (this is
8030 // correct because each oop only ever appears
8031 // once in the overflow list. However, it's
8032 // not very easy to completely overlap this with
8033 // other operations, so will generally not be done
8034 // until all work's been completed. Because we
8035 // expect the preserved oop stack (set) to be small,
8036 // it's probably fine to do this single-threaded.
8037 // We can explore cleverer concurrent/overlapped/parallel
8038 // processing of preserved marks if we feel the
8039 // need for this in the future. Stack overflow should
8040 // be so rare in practice and, when it happens, its
8041 // effect on performance so great that this will
8042 // likely just be in the noise anyway.
8043 void CMSCollector::restore_preserved_marks_if_any() {
8044 assert(SafepointSynchronize::is_at_safepoint(),
8045 "world should be stopped");
8046 assert(Thread::current()->is_ConcurrentGC_thread() ||
8047 Thread::current()->is_VM_thread(),
8048 "should be single-threaded");
8049 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8050 "bijection");
8051
8052 while (!_preserved_oop_stack.is_empty()) {
8053 oop p = _preserved_oop_stack.pop();
8054 assert(oopDesc::is_oop(p), "Should be an oop");
8055 assert(_span.contains(p), "oop should be in _span");
8056 assert(p->mark_raw() == markOopDesc::prototype(),
8057 "Set when taken from overflow list");
8058 markOop m = _preserved_mark_stack.pop();
8059 p->set_mark_raw(m);
8060 }
8061 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8062 "stacks were cleared above");
8063 }
8064
8065 #ifndef PRODUCT
8066 bool CMSCollector::no_preserved_marks() const {
8067 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8068 }
8069 #endif
8070
8071 // Transfer some number of overflown objects to usual marking
8072 // stack. Return true if some objects were transferred.
8073 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8074 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8075 (size_t)ParGCDesiredObjsFromOverflowList);
8076
8077 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8078 assert(_collector->overflow_list_is_empty() || res,
8079 "If list is not empty, we should have taken something");
8080 assert(!res || !_mark_stack->isEmpty(),
8081 "If we took something, it should now be on our stack");
8082 return res;
8083 }
8084
8085 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8086 size_t res = _sp->block_size_no_stall(addr, _collector);
8087 if (_sp->block_is_obj(addr)) {
8088 if (_live_bit_map->isMarked(addr)) {
8089 // It can't have been dead in a previous cycle
8090 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8091 } else {
8092 _dead_bit_map->mark(addr); // mark the dead object
8093 }
8094 }
8095 // Could be 0, if the block size could not be computed without stalling.
8096 return res;
8097 }
8098
8099 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8100 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8101 switch (phase) {
8102 case CMSCollector::InitialMarking:
8103 initialize(manager /* GC manager */ ,
8104 cause /* cause of the GC */,
8105 true /* allMemoryPoolsAffected */,
8106 true /* recordGCBeginTime */,
8107 true /* recordPreGCUsage */,
8108 false /* recordPeakUsage */,
8109 false /* recordPostGCusage */,
8110 true /* recordAccumulatedGCTime */,
8111 false /* recordGCEndTime */,
8112 false /* countCollection */ );
8113 break;
8114
8115 case CMSCollector::FinalMarking:
8116 initialize(manager /* GC manager */ ,
8117 cause /* cause of the GC */,
8118 true /* allMemoryPoolsAffected */,
8119 false /* recordGCBeginTime */,
8120 false /* recordPreGCUsage */,
8121 false /* recordPeakUsage */,
8122 false /* recordPostGCusage */,
8123 true /* recordAccumulatedGCTime */,
8124 false /* recordGCEndTime */,
8125 false /* countCollection */ );
8126 break;
8127
8128 case CMSCollector::Sweeping:
8129 initialize(manager /* GC manager */ ,
8130 cause /* cause of the GC */,
8131 true /* allMemoryPoolsAffected */,
8132 false /* recordGCBeginTime */,
8133 false /* recordPreGCUsage */,
8134 true /* recordPeakUsage */,
8135 true /* recordPostGCusage */,
8136 false /* recordAccumulatedGCTime */,
8137 true /* recordGCEndTime */,
8138 true /* countCollection */ );
8139 break;
8140
8141 default:
8142 ShouldNotReachHere();
8143 }
8144 }