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