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::used_stable() const {
696 return cmsSpace()->used_stable();
697 }
698
699 size_t ConcurrentMarkSweepGeneration::max_available() const {
700 return free() + _virtual_space.uncommitted_size();
701 }
702
703 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
704 size_t available = max_available();
705 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
706 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
707 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
708 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
709 return res;
710 }
711
712 // At a promotion failure dump information on block layout in heap
713 // (cms old generation).
714 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
715 Log(gc, promotion) log;
716 if (log.is_trace()) {
717 LogStream ls(log.trace());
718 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
719 }
720 }
721
722 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
723 // Clear the promotion information. These pointers can be adjusted
724 // along with all the other pointers into the heap but
725 // compaction is expected to be a rare event with
726 // a heap using cms so don't do it without seeing the need.
727 for (uint i = 0; i < ParallelGCThreads; i++) {
728 _par_gc_thread_states[i]->promo.reset();
729 }
730 }
731
732 void ConcurrentMarkSweepGeneration::compute_new_size() {
733 assert_locked_or_safepoint(Heap_lock);
734
735 // If incremental collection failed, we just want to expand
736 // to the limit.
737 if (incremental_collection_failed()) {
738 clear_incremental_collection_failed();
739 grow_to_reserved();
740 return;
741 }
742
743 // The heap has been compacted but not reset yet.
744 // Any metric such as free() or used() will be incorrect.
745
746 CardGeneration::compute_new_size();
747
748 // Reset again after a possible resizing
749 if (did_compact()) {
750 cmsSpace()->reset_after_compaction();
751 }
752 }
753
754 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
755 assert_locked_or_safepoint(Heap_lock);
756
757 // If incremental collection failed, we just want to expand
758 // to the limit.
759 if (incremental_collection_failed()) {
760 clear_incremental_collection_failed();
761 grow_to_reserved();
762 return;
763 }
764
765 double free_percentage = ((double) free()) / capacity();
766 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
767 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
768
769 // compute expansion delta needed for reaching desired free percentage
770 if (free_percentage < desired_free_percentage) {
771 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
772 assert(desired_capacity >= capacity(), "invalid expansion size");
773 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
774 Log(gc) log;
775 if (log.is_trace()) {
776 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
777 log.trace("From compute_new_size: ");
778 log.trace(" Free fraction %f", free_percentage);
779 log.trace(" Desired free fraction %f", desired_free_percentage);
780 log.trace(" Maximum free fraction %f", maximum_free_percentage);
781 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
782 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
783 CMSHeap* heap = CMSHeap::heap();
784 size_t young_size = heap->young_gen()->capacity();
785 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
786 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
787 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
788 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
789 }
790 // safe if expansion fails
791 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
792 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
793 } else {
794 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
795 assert(desired_capacity <= capacity(), "invalid expansion size");
796 size_t shrink_bytes = capacity() - desired_capacity;
797 // Don't shrink unless the delta is greater than the minimum shrink we want
798 if (shrink_bytes >= MinHeapDeltaBytes) {
799 shrink_free_list_by(shrink_bytes);
800 }
801 }
802 }
803
804 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
805 return cmsSpace()->freelistLock();
806 }
807
808 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
809 CMSSynchronousYieldRequest yr;
810 MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
811 return have_lock_and_allocate(size, tlab);
812 }
813
814 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
815 bool tlab /* ignored */) {
816 assert_lock_strong(freelistLock());
817 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
818 HeapWord* res = cmsSpace()->allocate(adjustedSize);
819 // Allocate the object live (grey) if the background collector has
820 // started marking. This is necessary because the marker may
821 // have passed this address and consequently this object will
822 // not otherwise be greyed and would be incorrectly swept up.
823 // Note that if this object contains references, the writing
824 // of those references will dirty the card containing this object
825 // allowing the object to be blackened (and its references scanned)
826 // either during a preclean phase or at the final checkpoint.
827 if (res != NULL) {
828 // We may block here with an uninitialized object with
829 // its mark-bit or P-bits not yet set. Such objects need
830 // to be safely navigable by block_start().
831 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
832 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
833 collector()->direct_allocated(res, adjustedSize);
834 _direct_allocated_words += adjustedSize;
835 // allocation counters
836 NOT_PRODUCT(
837 _numObjectsAllocated++;
838 _numWordsAllocated += (int)adjustedSize;
839 )
840 }
841 return res;
842 }
843
844 // In the case of direct allocation by mutators in a generation that
845 // is being concurrently collected, the object must be allocated
846 // live (grey) if the background collector has started marking.
847 // This is necessary because the marker may
848 // have passed this address and consequently this object will
849 // not otherwise be greyed and would be incorrectly swept up.
850 // Note that if this object contains references, the writing
851 // of those references will dirty the card containing this object
852 // allowing the object to be blackened (and its references scanned)
853 // either during a preclean phase or at the final checkpoint.
854 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
855 assert(_markBitMap.covers(start, size), "Out of bounds");
856 if (_collectorState >= Marking) {
857 MutexLocker y(_markBitMap.lock(),
858 Mutex::_no_safepoint_check_flag);
859 // [see comments preceding SweepClosure::do_blk() below for details]
860 //
861 // Can the P-bits be deleted now? JJJ
862 //
863 // 1. need to mark the object as live so it isn't collected
864 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
865 // 3. need to mark the end of the object so marking, precleaning or sweeping
866 // can skip over uninitialized or unparsable objects. An allocated
867 // object is considered uninitialized for our purposes as long as
868 // its klass word is NULL. All old gen objects are parsable
869 // as soon as they are initialized.)
870 _markBitMap.mark(start); // object is live
871 _markBitMap.mark(start + 1); // object is potentially uninitialized?
872 _markBitMap.mark(start + size - 1);
873 // mark end of object
874 }
875 // check that oop looks uninitialized
876 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
877 }
878
879 void CMSCollector::promoted(bool par, HeapWord* start,
880 bool is_obj_array, size_t obj_size) {
881 assert(_markBitMap.covers(start), "Out of bounds");
882 // See comment in direct_allocated() about when objects should
883 // be allocated live.
884 if (_collectorState >= Marking) {
885 // we already hold the marking bit map lock, taken in
886 // the prologue
887 if (par) {
888 _markBitMap.par_mark(start);
889 } else {
890 _markBitMap.mark(start);
891 }
892 // We don't need to mark the object as uninitialized (as
893 // in direct_allocated above) because this is being done with the
894 // world stopped and the object will be initialized by the
895 // time the marking, precleaning or sweeping get to look at it.
896 // But see the code for copying objects into the CMS generation,
897 // where we need to ensure that concurrent readers of the
898 // block offset table are able to safely navigate a block that
899 // is in flux from being free to being allocated (and in
900 // transition while being copied into) and subsequently
901 // becoming a bona-fide object when the copy/promotion is complete.
902 assert(SafepointSynchronize::is_at_safepoint(),
903 "expect promotion only at safepoints");
904
905 if (_collectorState < Sweeping) {
906 // Mark the appropriate cards in the modUnionTable, so that
907 // this object gets scanned before the sweep. If this is
908 // not done, CMS generation references in the object might
909 // not get marked.
910 // For the case of arrays, which are otherwise precisely
911 // marked, we need to dirty the entire array, not just its head.
912 if (is_obj_array) {
913 // The [par_]mark_range() method expects mr.end() below to
914 // be aligned to the granularity of a bit's representation
915 // in the heap. In the case of the MUT below, that's a
916 // card size.
917 MemRegion mr(start,
918 align_up(start + obj_size,
919 CardTable::card_size /* bytes */));
920 if (par) {
921 _modUnionTable.par_mark_range(mr);
922 } else {
923 _modUnionTable.mark_range(mr);
924 }
925 } else { // not an obj array; we can just mark the head
926 if (par) {
927 _modUnionTable.par_mark(start);
928 } else {
929 _modUnionTable.mark(start);
930 }
931 }
932 }
933 }
934 }
935
936 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
937 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
938 // allocate, copy and if necessary update promoinfo --
939 // delegate to underlying space.
940 assert_lock_strong(freelistLock());
941
942 #ifndef PRODUCT
943 if (CMSHeap::heap()->promotion_should_fail()) {
944 return NULL;
945 }
946 #endif // #ifndef PRODUCT
947
948 oop res = _cmsSpace->promote(obj, obj_size);
949 if (res == NULL) {
950 // expand and retry
951 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
952 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
953 // Since this is the old generation, we don't try to promote
954 // into a more senior generation.
955 res = _cmsSpace->promote(obj, obj_size);
956 }
957 if (res != NULL) {
958 // See comment in allocate() about when objects should
959 // be allocated live.
960 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
961 collector()->promoted(false, // Not parallel
962 (HeapWord*)res, obj->is_objArray(), obj_size);
963 // promotion counters
964 NOT_PRODUCT(
965 _numObjectsPromoted++;
966 _numWordsPromoted +=
967 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
968 )
969 }
970 return res;
971 }
972
973
974 // IMPORTANT: Notes on object size recognition in CMS.
975 // ---------------------------------------------------
976 // A block of storage in the CMS generation is always in
977 // one of three states. A free block (FREE), an allocated
978 // object (OBJECT) whose size() method reports the correct size,
979 // and an intermediate state (TRANSIENT) in which its size cannot
980 // be accurately determined.
981 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
982 // -----------------------------------------------------
983 // FREE: klass_word & 1 == 1; mark_word holds block size
984 //
985 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
986 // obj->size() computes correct size
987 //
988 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
989 //
990 // STATE IDENTIFICATION: (64 bit+COOPS)
991 // ------------------------------------
992 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
993 //
994 // OBJECT: klass_word installed; klass_word != 0;
995 // obj->size() computes correct size
996 //
997 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
998 //
999 //
1000 // STATE TRANSITION DIAGRAM
1001 //
1002 // mut / parnew mut / parnew
1003 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1004 // ^ |
1005 // |------------------------ DEAD <------------------------------------|
1006 // sweep mut
1007 //
1008 // While a block is in TRANSIENT state its size cannot be determined
1009 // so readers will either need to come back later or stall until
1010 // the size can be determined. Note that for the case of direct
1011 // allocation, P-bits, when available, may be used to determine the
1012 // size of an object that may not yet have been initialized.
1013
1014 // Things to support parallel young-gen collection.
1015 oop
1016 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1017 oop old, markOop m,
1018 size_t word_sz) {
1019 #ifndef PRODUCT
1020 if (CMSHeap::heap()->promotion_should_fail()) {
1021 return NULL;
1022 }
1023 #endif // #ifndef PRODUCT
1024
1025 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1026 PromotionInfo* promoInfo = &ps->promo;
1027 // if we are tracking promotions, then first ensure space for
1028 // promotion (including spooling space for saving header if necessary).
1029 // then allocate and copy, then track promoted info if needed.
1030 // When tracking (see PromotionInfo::track()), the mark word may
1031 // be displaced and in this case restoration of the mark word
1032 // occurs in the (oop_since_save_marks_)iterate phase.
1033 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1034 // Out of space for allocating spooling buffers;
1035 // try expanding and allocating spooling buffers.
1036 if (!expand_and_ensure_spooling_space(promoInfo)) {
1037 return NULL;
1038 }
1039 }
1040 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1041 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1042 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1043 if (obj_ptr == NULL) {
1044 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1045 if (obj_ptr == NULL) {
1046 return NULL;
1047 }
1048 }
1049 oop obj = oop(obj_ptr);
1050 OrderAccess::storestore();
1051 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1052 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1053 // IMPORTANT: See note on object initialization for CMS above.
1054 // Otherwise, copy the object. Here we must be careful to insert the
1055 // klass pointer last, since this marks the block as an allocated object.
1056 // Except with compressed oops it's the mark word.
1057 HeapWord* old_ptr = (HeapWord*)old;
1058 // Restore the mark word copied above.
1059 obj->set_mark_raw(m);
1060 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1061 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1062 OrderAccess::storestore();
1063
1064 if (UseCompressedClassPointers) {
1065 // Copy gap missed by (aligned) header size calculation below
1066 obj->set_klass_gap(old->klass_gap());
1067 }
1068 if (word_sz > (size_t)oopDesc::header_size()) {
1069 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1070 obj_ptr + oopDesc::header_size(),
1071 word_sz - oopDesc::header_size());
1072 }
1073
1074 // Now we can track the promoted object, if necessary. We take care
1075 // to delay the transition from uninitialized to full object
1076 // (i.e., insertion of klass pointer) until after, so that it
1077 // atomically becomes a promoted object.
1078 if (promoInfo->tracking()) {
1079 promoInfo->track((PromotedObject*)obj, old->klass());
1080 }
1081 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1084
1085 // Finally, install the klass pointer (this should be volatile).
1086 OrderAccess::storestore();
1087 obj->set_klass(old->klass());
1088 // We should now be able to calculate the right size for this object
1089 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1090
1091 collector()->promoted(true, // parallel
1092 obj_ptr, old->is_objArray(), word_sz);
1093
1094 NOT_PRODUCT(
1095 Atomic::inc(&_numObjectsPromoted);
1096 Atomic::add(alloc_sz, &_numWordsPromoted);
1097 )
1098
1099 return obj;
1100 }
1101
1102 void
1103 ConcurrentMarkSweepGeneration::
1104 par_promote_alloc_done(int thread_num) {
1105 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1106 ps->lab.retire(thread_num);
1107 }
1108
1109 void
1110 ConcurrentMarkSweepGeneration::
1111 par_oop_since_save_marks_iterate_done(int thread_num) {
1112 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1113 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1114 ps->promo.promoted_oops_iterate(dummy_cl);
1115
1116 // Because card-scanning has been completed, subsequent phases
1117 // (e.g., reference processing) will not need to recognize which
1118 // objects have been promoted during this GC. So, we can now disable
1119 // promotion tracking.
1120 ps->promo.stopTrackingPromotions();
1121 }
1122
1123 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1124 size_t size,
1125 bool tlab)
1126 {
1127 // We allow a STW collection only if a full
1128 // collection was requested.
1129 return full || should_allocate(size, tlab); // FIX ME !!!
1130 // This and promotion failure handling are connected at the
1131 // hip and should be fixed by untying them.
1132 }
1133
1134 bool CMSCollector::shouldConcurrentCollect() {
1135 LogTarget(Trace, gc) log;
1136
1137 if (_full_gc_requested) {
1138 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1139 return true;
1140 }
1141
1142 FreelistLocker x(this);
1143 // ------------------------------------------------------------------
1144 // Print out lots of information which affects the initiation of
1145 // a collection.
1146 if (log.is_enabled() && stats().valid()) {
1147 log.print("CMSCollector shouldConcurrentCollect: ");
1148
1149 LogStream out(log);
1150 stats().print_on(&out);
1151
1152 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1153 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1154 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1155 log.print("promotion_rate=%g", stats().promotion_rate());
1156 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1157 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1158 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1159 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1160 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1161 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1162 }
1163 // ------------------------------------------------------------------
1164
1165 // If the estimated time to complete a cms collection (cms_duration())
1166 // is less than the estimated time remaining until the cms generation
1167 // is full, start a collection.
1168 if (!UseCMSInitiatingOccupancyOnly) {
1169 if (stats().valid()) {
1170 if (stats().time_until_cms_start() == 0.0) {
1171 return true;
1172 }
1173 } else {
1174 // We want to conservatively collect somewhat early in order
1175 // to try and "bootstrap" our CMS/promotion statistics;
1176 // this branch will not fire after the first successful CMS
1177 // collection because the stats should then be valid.
1178 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1179 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1180 _cmsGen->occupancy(), _bootstrap_occupancy);
1181 return true;
1182 }
1183 }
1184 }
1185
1186 // Otherwise, we start a collection cycle if
1187 // old gen want a collection cycle started. Each may use
1188 // an appropriate criterion for making this decision.
1189 // XXX We need to make sure that the gen expansion
1190 // criterion dovetails well with this. XXX NEED TO FIX THIS
1191 if (_cmsGen->should_concurrent_collect()) {
1192 log.print("CMS old gen initiated");
1193 return true;
1194 }
1195
1196 // We start a collection if we believe an incremental collection may fail;
1197 // this is not likely to be productive in practice because it's probably too
1198 // late anyway.
1199 CMSHeap* heap = CMSHeap::heap();
1200 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1201 log.print("CMSCollector: collect because incremental collection will fail ");
1202 return true;
1203 }
1204
1205 if (MetaspaceGC::should_concurrent_collect()) {
1206 log.print("CMSCollector: collect for metadata allocation ");
1207 return true;
1208 }
1209
1210 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1211 if (CMSTriggerInterval >= 0) {
1212 if (CMSTriggerInterval == 0) {
1213 // Trigger always
1214 return true;
1215 }
1216
1217 // Check the CMS time since begin (we do not check the stats validity
1218 // as we want to be able to trigger the first CMS cycle as well)
1219 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1220 if (stats().valid()) {
1221 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1222 stats().cms_time_since_begin());
1223 } else {
1224 log.print("CMSCollector: collect because of trigger interval (first collection)");
1225 }
1226 return true;
1227 }
1228 }
1229
1230 return false;
1231 }
1232
1233 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1234
1235 // Clear _expansion_cause fields of constituent generations
1236 void CMSCollector::clear_expansion_cause() {
1237 _cmsGen->clear_expansion_cause();
1238 }
1239
1240 // We should be conservative in starting a collection cycle. To
1241 // start too eagerly runs the risk of collecting too often in the
1242 // extreme. To collect too rarely falls back on full collections,
1243 // which works, even if not optimum in terms of concurrent work.
1244 // As a work around for too eagerly collecting, use the flag
1245 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1246 // giving the user an easily understandable way of controlling the
1247 // collections.
1248 // We want to start a new collection cycle if any of the following
1249 // conditions hold:
1250 // . our current occupancy exceeds the configured initiating occupancy
1251 // for this generation, or
1252 // . we recently needed to expand this space and have not, since that
1253 // expansion, done a collection of this generation, or
1254 // . the underlying space believes that it may be a good idea to initiate
1255 // a concurrent collection (this may be based on criteria such as the
1256 // following: the space uses linear allocation and linear allocation is
1257 // going to fail, or there is believed to be excessive fragmentation in
1258 // the generation, etc... or ...
1259 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1260 // the case of the old generation; see CR 6543076):
1261 // we may be approaching a point at which allocation requests may fail because
1262 // we will be out of sufficient free space given allocation rate estimates.]
1263 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1264
1265 assert_lock_strong(freelistLock());
1266 if (occupancy() > initiating_occupancy()) {
1267 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1268 short_name(), occupancy(), initiating_occupancy());
1269 return true;
1270 }
1271 if (UseCMSInitiatingOccupancyOnly) {
1272 return false;
1273 }
1274 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1275 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1276 return true;
1277 }
1278 return false;
1279 }
1280
1281 void ConcurrentMarkSweepGeneration::collect(bool full,
1282 bool clear_all_soft_refs,
1283 size_t size,
1284 bool tlab)
1285 {
1286 collector()->collect(full, clear_all_soft_refs, size, tlab);
1287 }
1288
1289 void CMSCollector::collect(bool full,
1290 bool clear_all_soft_refs,
1291 size_t size,
1292 bool tlab)
1293 {
1294 // The following "if" branch is present for defensive reasons.
1295 // In the current uses of this interface, it can be replaced with:
1296 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1297 // But I am not placing that assert here to allow future
1298 // generality in invoking this interface.
1299 if (GCLocker::is_active()) {
1300 // A consistency test for GCLocker
1301 assert(GCLocker::needs_gc(), "Should have been set already");
1302 // Skip this foreground collection, instead
1303 // expanding the heap if necessary.
1304 // Need the free list locks for the call to free() in compute_new_size()
1305 compute_new_size();
1306 return;
1307 }
1308 acquire_control_and_collect(full, clear_all_soft_refs);
1309 }
1310
1311 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1312 CMSHeap* heap = CMSHeap::heap();
1313 unsigned int gc_count = heap->total_full_collections();
1314 if (gc_count == full_gc_count) {
1315 MutexLocker y(CGC_lock, Mutex::_no_safepoint_check_flag);
1316 _full_gc_requested = true;
1317 _full_gc_cause = cause;
1318 CGC_lock->notify(); // nudge CMS thread
1319 } else {
1320 assert(gc_count > full_gc_count, "Error: causal loop");
1321 }
1322 }
1323
1324 bool CMSCollector::is_external_interruption() {
1325 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1326 return GCCause::is_user_requested_gc(cause) ||
1327 GCCause::is_serviceability_requested_gc(cause);
1328 }
1329
1330 void CMSCollector::report_concurrent_mode_interruption() {
1331 if (is_external_interruption()) {
1332 log_debug(gc)("Concurrent mode interrupted");
1333 } else {
1334 log_debug(gc)("Concurrent mode failure");
1335 _gc_tracer_cm->report_concurrent_mode_failure();
1336 }
1337 }
1338
1339
1340 // The foreground and background collectors need to coordinate in order
1341 // to make sure that they do not mutually interfere with CMS collections.
1342 // When a background collection is active,
1343 // the foreground collector may need to take over (preempt) and
1344 // synchronously complete an ongoing collection. Depending on the
1345 // frequency of the background collections and the heap usage
1346 // of the application, this preemption can be seldom or frequent.
1347 // There are only certain
1348 // points in the background collection that the "collection-baton"
1349 // can be passed to the foreground collector.
1350 //
1351 // The foreground collector will wait for the baton before
1352 // starting any part of the collection. The foreground collector
1353 // will only wait at one location.
1354 //
1355 // The background collector will yield the baton before starting a new
1356 // phase of the collection (e.g., before initial marking, marking from roots,
1357 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1358 // of the loop which switches the phases. The background collector does some
1359 // of the phases (initial mark, final re-mark) with the world stopped.
1360 // Because of locking involved in stopping the world,
1361 // the foreground collector should not block waiting for the background
1362 // collector when it is doing a stop-the-world phase. The background
1363 // collector will yield the baton at an additional point just before
1364 // it enters a stop-the-world phase. Once the world is stopped, the
1365 // background collector checks the phase of the collection. If the
1366 // phase has not changed, it proceeds with the collection. If the
1367 // phase has changed, it skips that phase of the collection. See
1368 // the comments on the use of the Heap_lock in collect_in_background().
1369 //
1370 // Variable used in baton passing.
1371 // _foregroundGCIsActive - Set to true by the foreground collector when
1372 // it wants the baton. The foreground clears it when it has finished
1373 // the collection.
1374 // _foregroundGCShouldWait - Set to true by the background collector
1375 // when it is running. The foreground collector waits while
1376 // _foregroundGCShouldWait is true.
1377 // CGC_lock - monitor used to protect access to the above variables
1378 // and to notify the foreground and background collectors.
1379 // _collectorState - current state of the CMS collection.
1380 //
1381 // The foreground collector
1382 // acquires the CGC_lock
1383 // sets _foregroundGCIsActive
1384 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1385 // various locks acquired in preparation for the collection
1386 // are released so as not to block the background collector
1387 // that is in the midst of a collection
1388 // proceeds with the collection
1389 // clears _foregroundGCIsActive
1390 // returns
1391 //
1392 // The background collector in a loop iterating on the phases of the
1393 // collection
1394 // acquires the CGC_lock
1395 // sets _foregroundGCShouldWait
1396 // if _foregroundGCIsActive is set
1397 // clears _foregroundGCShouldWait, notifies _CGC_lock
1398 // waits on _CGC_lock for _foregroundGCIsActive to become false
1399 // and exits the loop.
1400 // otherwise
1401 // proceed with that phase of the collection
1402 // if the phase is a stop-the-world phase,
1403 // yield the baton once more just before enqueueing
1404 // the stop-world CMS operation (executed by the VM thread).
1405 // returns after all phases of the collection are done
1406 //
1407
1408 void CMSCollector::acquire_control_and_collect(bool full,
1409 bool clear_all_soft_refs) {
1410 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1411 assert(!Thread::current()->is_ConcurrentGC_thread(),
1412 "shouldn't try to acquire control from self!");
1413
1414 // Start the protocol for acquiring control of the
1415 // collection from the background collector (aka CMS thread).
1416 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1417 "VM thread should have CMS token");
1418 // Remember the possibly interrupted state of an ongoing
1419 // concurrent collection
1420 CollectorState first_state = _collectorState;
1421
1422 // Signal to a possibly ongoing concurrent collection that
1423 // we want to do a foreground collection.
1424 _foregroundGCIsActive = true;
1425
1426 // release locks and wait for a notify from the background collector
1427 // releasing the locks in only necessary for phases which
1428 // do yields to improve the granularity of the collection.
1429 assert_lock_strong(bitMapLock());
1430 // We need to lock the Free list lock for the space that we are
1431 // currently collecting.
1432 assert(haveFreelistLocks(), "Must be holding free list locks");
1433 bitMapLock()->unlock();
1434 releaseFreelistLocks();
1435 {
1436 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1437 if (_foregroundGCShouldWait) {
1438 // We are going to be waiting for action for the CMS thread;
1439 // it had better not be gone (for instance at shutdown)!
1440 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1441 "CMS thread must be running");
1442 // Wait here until the background collector gives us the go-ahead
1443 ConcurrentMarkSweepThread::clear_CMS_flag(
1444 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1445 // Get a possibly blocked CMS thread going:
1446 // Note that we set _foregroundGCIsActive true above,
1447 // without protection of the CGC_lock.
1448 CGC_lock->notify();
1449 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1450 "Possible deadlock");
1451 while (_foregroundGCShouldWait) {
1452 // wait for notification
1453 CGC_lock->wait_without_safepoint_check();
1454 // Possibility of delay/starvation here, since CMS token does
1455 // not know to give priority to VM thread? Actually, i think
1456 // there wouldn't be any delay/starvation, but the proof of
1457 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1458 }
1459 ConcurrentMarkSweepThread::set_CMS_flag(
1460 ConcurrentMarkSweepThread::CMS_vm_has_token);
1461 }
1462 }
1463 // The CMS_token is already held. Get back the other locks.
1464 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465 "VM thread should have CMS token");
1466 getFreelistLocks();
1467 bitMapLock()->lock_without_safepoint_check();
1468 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1469 p2i(Thread::current()), first_state);
1470 log_debug(gc, state)(" gets control with state %d", _collectorState);
1471
1472 // Inform cms gen if this was due to partial collection failing.
1473 // The CMS gen may use this fact to determine its expansion policy.
1474 CMSHeap* heap = CMSHeap::heap();
1475 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1476 assert(!_cmsGen->incremental_collection_failed(),
1477 "Should have been noticed, reacted to and cleared");
1478 _cmsGen->set_incremental_collection_failed();
1479 }
1480
1481 if (first_state > Idling) {
1482 report_concurrent_mode_interruption();
1483 }
1484
1485 set_did_compact(true);
1486
1487 // If the collection is being acquired from the background
1488 // collector, there may be references on the discovered
1489 // references lists. Abandon those references, since some
1490 // of them may have become unreachable after concurrent
1491 // discovery; the STW compacting collector will redo discovery
1492 // more precisely, without being subject to floating garbage.
1493 // Leaving otherwise unreachable references in the discovered
1494 // lists would require special handling.
1495 ref_processor()->disable_discovery();
1496 ref_processor()->abandon_partial_discovery();
1497 ref_processor()->verify_no_references_recorded();
1498
1499 if (first_state > Idling) {
1500 save_heap_summary();
1501 }
1502
1503 do_compaction_work(clear_all_soft_refs);
1504
1505 // Has the GC time limit been exceeded?
1506 size_t max_eden_size = _young_gen->max_eden_size();
1507 GCCause::Cause gc_cause = heap->gc_cause();
1508 size_policy()->check_gc_overhead_limit(_young_gen->eden()->used(),
1509 _cmsGen->max_capacity(),
1510 max_eden_size,
1511 full,
1512 gc_cause,
1513 heap->soft_ref_policy());
1514
1515 // Reset the expansion cause, now that we just completed
1516 // a collection cycle.
1517 clear_expansion_cause();
1518 _foregroundGCIsActive = false;
1519 return;
1520 }
1521
1522 // Resize the tenured generation
1523 // after obtaining the free list locks for the
1524 // two generations.
1525 void CMSCollector::compute_new_size() {
1526 assert_locked_or_safepoint(Heap_lock);
1527 FreelistLocker z(this);
1528 MetaspaceGC::compute_new_size();
1529 _cmsGen->compute_new_size_free_list();
1530 // recalculate CMS used space after CMS collection
1531 _cmsGen->cmsSpace()->recalculate_used_stable();
1532 }
1533
1534 // A work method used by the foreground collector to do
1535 // a mark-sweep-compact.
1536 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1537 CMSHeap* heap = CMSHeap::heap();
1538
1539 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1540 gc_timer->register_gc_start();
1541
1542 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1543 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1544
1545 heap->pre_full_gc_dump(gc_timer);
1546
1547 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1548
1549 // Temporarily widen the span of the weak reference processing to
1550 // the entire heap.
1551 MemRegion new_span(CMSHeap::heap()->reserved_region());
1552 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1553 // Temporarily, clear the "is_alive_non_header" field of the
1554 // reference processor.
1555 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1556 // Temporarily make reference _processing_ single threaded (non-MT).
1557 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1558 // Temporarily make refs discovery atomic
1559 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1560 // Temporarily make reference _discovery_ single threaded (non-MT)
1561 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1562
1563 ref_processor()->set_enqueuing_is_done(false);
1564 ref_processor()->enable_discovery();
1565 ref_processor()->setup_policy(clear_all_soft_refs);
1566 // If an asynchronous collection finishes, the _modUnionTable is
1567 // all clear. If we are assuming the collection from an asynchronous
1568 // collection, clear the _modUnionTable.
1569 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1570 "_modUnionTable should be clear if the baton was not passed");
1571 _modUnionTable.clear_all();
1572 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1573 "mod union for klasses should be clear if the baton was passed");
1574 _ct->cld_rem_set()->clear_mod_union();
1575
1576
1577 // We must adjust the allocation statistics being maintained
1578 // in the free list space. We do so by reading and clearing
1579 // the sweep timer and updating the block flux rate estimates below.
1580 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1581 if (_inter_sweep_timer.is_active()) {
1582 _inter_sweep_timer.stop();
1583 // Note that we do not use this sample to update the _inter_sweep_estimate.
1584 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1585 _inter_sweep_estimate.padded_average(),
1586 _intra_sweep_estimate.padded_average());
1587 }
1588
1589 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1590 #ifdef ASSERT
1591 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1592 size_t free_size = cms_space->free();
1593 assert(free_size ==
1594 pointer_delta(cms_space->end(), cms_space->compaction_top())
1595 * HeapWordSize,
1596 "All the free space should be compacted into one chunk at top");
1597 assert(cms_space->dictionary()->total_chunk_size(
1598 debug_only(cms_space->freelistLock())) == 0 ||
1599 cms_space->totalSizeInIndexedFreeLists() == 0,
1600 "All the free space should be in a single chunk");
1601 size_t num = cms_space->totalCount();
1602 assert((free_size == 0 && num == 0) ||
1603 (free_size > 0 && (num == 1 || num == 2)),
1604 "There should be at most 2 free chunks after compaction");
1605 #endif // ASSERT
1606 _collectorState = Resetting;
1607 assert(_restart_addr == NULL,
1608 "Should have been NULL'd before baton was passed");
1609 reset_stw();
1610 _cmsGen->reset_after_compaction();
1611 _concurrent_cycles_since_last_unload = 0;
1612
1613 // Clear any data recorded in the PLAB chunk arrays.
1614 if (_survivor_plab_array != NULL) {
1615 reset_survivor_plab_arrays();
1616 }
1617
1618 // Adjust the per-size allocation stats for the next epoch.
1619 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1620 // Restart the "inter sweep timer" for the next epoch.
1621 _inter_sweep_timer.reset();
1622 _inter_sweep_timer.start();
1623
1624 // No longer a need to do a concurrent collection for Metaspace.
1625 MetaspaceGC::set_should_concurrent_collect(false);
1626
1627 heap->post_full_gc_dump(gc_timer);
1628
1629 gc_timer->register_gc_end();
1630
1631 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1632
1633 // For a mark-sweep-compact, compute_new_size() will be called
1634 // in the heap's do_collection() method.
1635 }
1636
1637 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1638 Log(gc, heap) log;
1639 if (!log.is_trace()) {
1640 return;
1641 }
1642
1643 ContiguousSpace* eden_space = _young_gen->eden();
1644 ContiguousSpace* from_space = _young_gen->from();
1645 ContiguousSpace* to_space = _young_gen->to();
1646 // Eden
1647 if (_eden_chunk_array != NULL) {
1648 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1649 p2i(eden_space->bottom()), p2i(eden_space->top()),
1650 p2i(eden_space->end()), eden_space->capacity());
1651 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1652 _eden_chunk_index, _eden_chunk_capacity);
1653 for (size_t i = 0; i < _eden_chunk_index; i++) {
1654 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1655 }
1656 }
1657 // Survivor
1658 if (_survivor_chunk_array != NULL) {
1659 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1660 p2i(from_space->bottom()), p2i(from_space->top()),
1661 p2i(from_space->end()), from_space->capacity());
1662 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1663 _survivor_chunk_index, _survivor_chunk_capacity);
1664 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1665 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1666 }
1667 }
1668 }
1669
1670 void CMSCollector::getFreelistLocks() const {
1671 // Get locks for all free lists in all generations that this
1672 // collector is responsible for
1673 _cmsGen->freelistLock()->lock_without_safepoint_check();
1674 }
1675
1676 void CMSCollector::releaseFreelistLocks() const {
1677 // Release locks for all free lists in all generations that this
1678 // collector is responsible for
1679 _cmsGen->freelistLock()->unlock();
1680 }
1681
1682 bool CMSCollector::haveFreelistLocks() const {
1683 // Check locks for all free lists in all generations that this
1684 // collector is responsible for
1685 assert_lock_strong(_cmsGen->freelistLock());
1686 PRODUCT_ONLY(ShouldNotReachHere());
1687 return true;
1688 }
1689
1690 // A utility class that is used by the CMS collector to
1691 // temporarily "release" the foreground collector from its
1692 // usual obligation to wait for the background collector to
1693 // complete an ongoing phase before proceeding.
1694 class ReleaseForegroundGC: public StackObj {
1695 private:
1696 CMSCollector* _c;
1697 public:
1698 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1699 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1700 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1701 // allow a potentially blocked foreground collector to proceed
1702 _c->_foregroundGCShouldWait = false;
1703 if (_c->_foregroundGCIsActive) {
1704 CGC_lock->notify();
1705 }
1706 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1707 "Possible deadlock");
1708 }
1709
1710 ~ReleaseForegroundGC() {
1711 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1712 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1713 _c->_foregroundGCShouldWait = true;
1714 }
1715 };
1716
1717 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1718 assert(Thread::current()->is_ConcurrentGC_thread(),
1719 "A CMS asynchronous collection is only allowed on a CMS thread.");
1720
1721 CMSHeap* heap = CMSHeap::heap();
1722 {
1723 MutexLocker hl(Heap_lock, Mutex::_no_safepoint_check_flag);
1724 FreelistLocker fll(this);
1725 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1726 if (_foregroundGCIsActive) {
1727 // The foreground collector is. Skip this
1728 // background collection.
1729 assert(!_foregroundGCShouldWait, "Should be clear");
1730 return;
1731 } else {
1732 assert(_collectorState == Idling, "Should be idling before start.");
1733 _collectorState = InitialMarking;
1734 register_gc_start(cause);
1735 // Reset the expansion cause, now that we are about to begin
1736 // a new cycle.
1737 clear_expansion_cause();
1738
1739 // Clear the MetaspaceGC flag since a concurrent collection
1740 // is starting but also clear it after the collection.
1741 MetaspaceGC::set_should_concurrent_collect(false);
1742 }
1743 // Decide if we want to enable class unloading as part of the
1744 // ensuing concurrent GC cycle.
1745 update_should_unload_classes();
1746 _full_gc_requested = false; // acks all outstanding full gc requests
1747 _full_gc_cause = GCCause::_no_gc;
1748 // Signal that we are about to start a collection
1749 heap->increment_total_full_collections(); // ... starting a collection cycle
1750 _collection_count_start = heap->total_full_collections();
1751 }
1752
1753 size_t prev_used = _cmsGen->used();
1754 _cmsGen->cmsSpace()->recalculate_used_stable();
1755
1756 // The change of the collection state is normally done at this level;
1757 // the exceptions are phases that are executed while the world is
1758 // stopped. For those phases the change of state is done while the
1759 // world is stopped. For baton passing purposes this allows the
1760 // background collector to finish the phase and change state atomically.
1761 // The foreground collector cannot wait on a phase that is done
1762 // while the world is stopped because the foreground collector already
1763 // has the world stopped and would deadlock.
1764 while (_collectorState != Idling) {
1765 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1766 p2i(Thread::current()), _collectorState);
1767 // The foreground collector
1768 // holds the Heap_lock throughout its collection.
1769 // holds the CMS token (but not the lock)
1770 // except while it is waiting for the background collector to yield.
1771 //
1772 // The foreground collector should be blocked (not for long)
1773 // if the background collector is about to start a phase
1774 // executed with world stopped. If the background
1775 // collector has already started such a phase, the
1776 // foreground collector is blocked waiting for the
1777 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1778 // are executed in the VM thread.
1779 //
1780 // The locking order is
1781 // PendingListLock (PLL) -- if applicable (FinalMarking)
1782 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1783 // CMS token (claimed in
1784 // stop_world_and_do() -->
1785 // safepoint_synchronize() -->
1786 // CMSThread::synchronize())
1787
1788 {
1789 // Check if the FG collector wants us to yield.
1790 CMSTokenSync x(true); // is cms thread
1791 if (waitForForegroundGC()) {
1792 // We yielded to a foreground GC, nothing more to be
1793 // done this round.
1794 assert(_foregroundGCShouldWait == false, "We set it to false in "
1795 "waitForForegroundGC()");
1796 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1797 p2i(Thread::current()), _collectorState);
1798 return;
1799 } else {
1800 // The background collector can run but check to see if the
1801 // foreground collector has done a collection while the
1802 // background collector was waiting to get the CGC_lock
1803 // above. If yes, break so that _foregroundGCShouldWait
1804 // is cleared before returning.
1805 if (_collectorState == Idling) {
1806 break;
1807 }
1808 }
1809 }
1810
1811 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1812 "should be waiting");
1813
1814 switch (_collectorState) {
1815 case InitialMarking:
1816 {
1817 ReleaseForegroundGC x(this);
1818 stats().record_cms_begin();
1819 VM_CMS_Initial_Mark initial_mark_op(this);
1820 VMThread::execute(&initial_mark_op);
1821 }
1822 // The collector state may be any legal state at this point
1823 // since the background collector may have yielded to the
1824 // foreground collector.
1825 break;
1826 case Marking:
1827 // initial marking in checkpointRootsInitialWork has been completed
1828 if (markFromRoots()) { // we were successful
1829 assert(_collectorState == Precleaning, "Collector state should "
1830 "have changed");
1831 } else {
1832 assert(_foregroundGCIsActive, "Internal state inconsistency");
1833 }
1834 break;
1835 case Precleaning:
1836 // marking from roots in markFromRoots has been completed
1837 preclean();
1838 assert(_collectorState == AbortablePreclean ||
1839 _collectorState == FinalMarking,
1840 "Collector state should have changed");
1841 break;
1842 case AbortablePreclean:
1843 abortable_preclean();
1844 assert(_collectorState == FinalMarking, "Collector state should "
1845 "have changed");
1846 break;
1847 case FinalMarking:
1848 {
1849 ReleaseForegroundGC x(this);
1850
1851 VM_CMS_Final_Remark final_remark_op(this);
1852 VMThread::execute(&final_remark_op);
1853 }
1854 assert(_foregroundGCShouldWait, "block post-condition");
1855 break;
1856 case Sweeping:
1857 // final marking in checkpointRootsFinal has been completed
1858 sweep();
1859 assert(_collectorState == Resizing, "Collector state change "
1860 "to Resizing must be done under the free_list_lock");
1861
1862 case Resizing: {
1863 // Sweeping has been completed...
1864 // At this point the background collection has completed.
1865 // Don't move the call to compute_new_size() down
1866 // into code that might be executed if the background
1867 // collection was preempted.
1868 {
1869 ReleaseForegroundGC x(this); // unblock FG collection
1870 MutexLocker y(Heap_lock, Mutex::_no_safepoint_check_flag);
1871 CMSTokenSync z(true); // not strictly needed.
1872 if (_collectorState == Resizing) {
1873 compute_new_size();
1874 save_heap_summary();
1875 _collectorState = Resetting;
1876 } else {
1877 assert(_collectorState == Idling, "The state should only change"
1878 " because the foreground collector has finished the collection");
1879 }
1880 }
1881 break;
1882 }
1883 case Resetting:
1884 // CMS heap resizing has been completed
1885 reset_concurrent();
1886 assert(_collectorState == Idling, "Collector state should "
1887 "have changed");
1888
1889 MetaspaceGC::set_should_concurrent_collect(false);
1890
1891 stats().record_cms_end();
1892 // Don't move the concurrent_phases_end() and compute_new_size()
1893 // calls to here because a preempted background collection
1894 // has it's state set to "Resetting".
1895 break;
1896 case Idling:
1897 default:
1898 ShouldNotReachHere();
1899 break;
1900 }
1901 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1902 p2i(Thread::current()), _collectorState);
1903 assert(_foregroundGCShouldWait, "block post-condition");
1904 }
1905
1906 // Should this be in gc_epilogue?
1907 heap->counters()->update_counters();
1908
1909 {
1910 // Clear _foregroundGCShouldWait and, in the event that the
1911 // foreground collector is waiting, notify it, before
1912 // returning.
1913 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1914 _foregroundGCShouldWait = false;
1915 if (_foregroundGCIsActive) {
1916 CGC_lock->notify();
1917 }
1918 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1919 "Possible deadlock");
1920 }
1921 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1922 p2i(Thread::current()), _collectorState);
1923 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1924 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1925 }
1926
1927 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1928 _cms_start_registered = true;
1929 _gc_timer_cm->register_gc_start();
1930 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1931 }
1932
1933 void CMSCollector::register_gc_end() {
1934 if (_cms_start_registered) {
1935 report_heap_summary(GCWhen::AfterGC);
1936
1937 _gc_timer_cm->register_gc_end();
1938 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1939 _cms_start_registered = false;
1940 }
1941 }
1942
1943 void CMSCollector::save_heap_summary() {
1944 CMSHeap* heap = CMSHeap::heap();
1945 _last_heap_summary = heap->create_heap_summary();
1946 _last_metaspace_summary = heap->create_metaspace_summary();
1947 }
1948
1949 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1950 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1951 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1952 }
1953
1954 bool CMSCollector::waitForForegroundGC() {
1955 bool res = false;
1956 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1957 "CMS thread should have CMS token");
1958 // Block the foreground collector until the
1959 // background collectors decides whether to
1960 // yield.
1961 MutexLocker x(CGC_lock, Mutex::_no_safepoint_check_flag);
1962 _foregroundGCShouldWait = true;
1963 if (_foregroundGCIsActive) {
1964 // The background collector yields to the
1965 // foreground collector and returns a value
1966 // indicating that it has yielded. The foreground
1967 // collector can proceed.
1968 res = true;
1969 _foregroundGCShouldWait = false;
1970 ConcurrentMarkSweepThread::clear_CMS_flag(
1971 ConcurrentMarkSweepThread::CMS_cms_has_token);
1972 ConcurrentMarkSweepThread::set_CMS_flag(
1973 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1974 // Get a possibly blocked foreground thread going
1975 CGC_lock->notify();
1976 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1977 p2i(Thread::current()), _collectorState);
1978 while (_foregroundGCIsActive) {
1979 CGC_lock->wait_without_safepoint_check();
1980 }
1981 ConcurrentMarkSweepThread::set_CMS_flag(
1982 ConcurrentMarkSweepThread::CMS_cms_has_token);
1983 ConcurrentMarkSweepThread::clear_CMS_flag(
1984 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1985 }
1986 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1987 p2i(Thread::current()), _collectorState);
1988 return res;
1989 }
1990
1991 // Because of the need to lock the free lists and other structures in
1992 // the collector, common to all the generations that the collector is
1993 // collecting, we need the gc_prologues of individual CMS generations
1994 // delegate to their collector. It may have been simpler had the
1995 // current infrastructure allowed one to call a prologue on a
1996 // collector. In the absence of that we have the generation's
1997 // prologue delegate to the collector, which delegates back
1998 // some "local" work to a worker method in the individual generations
1999 // that it's responsible for collecting, while itself doing any
2000 // work common to all generations it's responsible for. A similar
2001 // comment applies to the gc_epilogue()'s.
2002 // The role of the variable _between_prologue_and_epilogue is to
2003 // enforce the invocation protocol.
2004 void CMSCollector::gc_prologue(bool full) {
2005 // Call gc_prologue_work() for the CMSGen
2006 // we are responsible for.
2007
2008 // The following locking discipline assumes that we are only called
2009 // when the world is stopped.
2010 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2011
2012 // The CMSCollector prologue must call the gc_prologues for the
2013 // "generations" that it's responsible
2014 // for.
2015
2016 assert( Thread::current()->is_VM_thread()
2017 || ( CMSScavengeBeforeRemark
2018 && Thread::current()->is_ConcurrentGC_thread()),
2019 "Incorrect thread type for prologue execution");
2020
2021 if (_between_prologue_and_epilogue) {
2022 // We have already been invoked; this is a gc_prologue delegation
2023 // from yet another CMS generation that we are responsible for, just
2024 // ignore it since all relevant work has already been done.
2025 return;
2026 }
2027
2028 // set a bit saying prologue has been called; cleared in epilogue
2029 _between_prologue_and_epilogue = true;
2030 // Claim locks for common data structures, then call gc_prologue_work()
2031 // for each CMSGen.
2032
2033 getFreelistLocks(); // gets free list locks on constituent spaces
2034 bitMapLock()->lock_without_safepoint_check();
2035
2036 // Should call gc_prologue_work() for all cms gens we are responsible for
2037 bool duringMarking = _collectorState >= Marking
2038 && _collectorState < Sweeping;
2039
2040 // The young collections clear the modified oops state, which tells if
2041 // there are any modified oops in the class. The remark phase also needs
2042 // that information. Tell the young collection to save the union of all
2043 // modified klasses.
2044 if (duringMarking) {
2045 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2046 }
2047
2048 bool registerClosure = duringMarking;
2049
2050 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2051
2052 if (!full) {
2053 stats().record_gc0_begin();
2054 }
2055 }
2056
2057 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2058
2059 _capacity_at_prologue = capacity();
2060 _used_at_prologue = used();
2061 _cmsSpace->recalculate_used_stable();
2062
2063 // We enable promotion tracking so that card-scanning can recognize
2064 // which objects have been promoted during this GC and skip them.
2065 for (uint i = 0; i < ParallelGCThreads; i++) {
2066 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2067 }
2068
2069 // Delegate to CMScollector which knows how to coordinate between
2070 // this and any other CMS generations that it is responsible for
2071 // collecting.
2072 collector()->gc_prologue(full);
2073 }
2074
2075 // This is a "private" interface for use by this generation's CMSCollector.
2076 // Not to be called directly by any other entity (for instance,
2077 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2078 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2079 bool registerClosure, ModUnionClosure* modUnionClosure) {
2080 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2081 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2082 "Should be NULL");
2083 if (registerClosure) {
2084 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2085 }
2086 cmsSpace()->gc_prologue();
2087 // Clear stat counters
2088 NOT_PRODUCT(
2089 assert(_numObjectsPromoted == 0, "check");
2090 assert(_numWordsPromoted == 0, "check");
2091 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2092 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2093 _numObjectsAllocated = 0;
2094 _numWordsAllocated = 0;
2095 )
2096 }
2097
2098 void CMSCollector::gc_epilogue(bool full) {
2099 // The following locking discipline assumes that we are only called
2100 // when the world is stopped.
2101 assert(SafepointSynchronize::is_at_safepoint(),
2102 "world is stopped assumption");
2103
2104 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2105 // if linear allocation blocks need to be appropriately marked to allow the
2106 // the blocks to be parsable. We also check here whether we need to nudge the
2107 // CMS collector thread to start a new cycle (if it's not already active).
2108 assert( Thread::current()->is_VM_thread()
2109 || ( CMSScavengeBeforeRemark
2110 && Thread::current()->is_ConcurrentGC_thread()),
2111 "Incorrect thread type for epilogue execution");
2112
2113 if (!_between_prologue_and_epilogue) {
2114 // We have already been invoked; this is a gc_epilogue delegation
2115 // from yet another CMS generation that we are responsible for, just
2116 // ignore it since all relevant work has already been done.
2117 return;
2118 }
2119 assert(haveFreelistLocks(), "must have freelist locks");
2120 assert_lock_strong(bitMapLock());
2121
2122 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2123
2124 _cmsGen->gc_epilogue_work(full);
2125
2126 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2127 // in case sampling was not already enabled, enable it
2128 _start_sampling = true;
2129 }
2130 // reset _eden_chunk_array so sampling starts afresh
2131 _eden_chunk_index = 0;
2132
2133 size_t cms_used = _cmsGen->cmsSpace()->used();
2134 _cmsGen->cmsSpace()->recalculate_used_stable();
2135
2136 // update performance counters - this uses a special version of
2137 // update_counters() that allows the utilization to be passed as a
2138 // parameter, avoiding multiple calls to used().
2139 //
2140 _cmsGen->update_counters(cms_used);
2141
2142 bitMapLock()->unlock();
2143 releaseFreelistLocks();
2144
2145 if (!CleanChunkPoolAsync) {
2146 Chunk::clean_chunk_pool();
2147 }
2148
2149 set_did_compact(false);
2150 _between_prologue_and_epilogue = false; // ready for next cycle
2151 }
2152
2153 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2154 collector()->gc_epilogue(full);
2155
2156 // When using ParNew, promotion tracking should have already been
2157 // disabled. However, the prologue (which enables promotion
2158 // tracking) and epilogue are called irrespective of the type of
2159 // GC. So they will also be called before and after Full GCs, during
2160 // which promotion tracking will not be explicitly disabled. So,
2161 // it's safer to also disable it here too (to be symmetric with
2162 // enabling it in the prologue).
2163 for (uint i = 0; i < ParallelGCThreads; i++) {
2164 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2165 }
2166 }
2167
2168 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2169 assert(!incremental_collection_failed(), "Should have been cleared");
2170 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2171 cmsSpace()->gc_epilogue();
2172 // Print stat counters
2173 NOT_PRODUCT(
2174 assert(_numObjectsAllocated == 0, "check");
2175 assert(_numWordsAllocated == 0, "check");
2176 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2177 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2178 _numObjectsPromoted = 0;
2179 _numWordsPromoted = 0;
2180 )
2181
2182 // Call down the chain in contiguous_available needs the freelistLock
2183 // so print this out before releasing the freeListLock.
2184 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2185 }
2186
2187 #ifndef PRODUCT
2188 bool CMSCollector::have_cms_token() {
2189 Thread* thr = Thread::current();
2190 if (thr->is_VM_thread()) {
2191 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2192 } else if (thr->is_ConcurrentGC_thread()) {
2193 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2194 } else if (thr->is_GC_task_thread()) {
2195 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2196 ParGCRareEvent_lock->owned_by_self();
2197 }
2198 return false;
2199 }
2200
2201 // Check reachability of the given heap address in CMS generation,
2202 // treating all other generations as roots.
2203 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2204 // We could "guarantee" below, rather than assert, but I'll
2205 // leave these as "asserts" so that an adventurous debugger
2206 // could try this in the product build provided some subset of
2207 // the conditions were met, provided they were interested in the
2208 // results and knew that the computation below wouldn't interfere
2209 // with other concurrent computations mutating the structures
2210 // being read or written.
2211 assert(SafepointSynchronize::is_at_safepoint(),
2212 "Else mutations in object graph will make answer suspect");
2213 assert(have_cms_token(), "Should hold cms token");
2214 assert(haveFreelistLocks(), "must hold free list locks");
2215 assert_lock_strong(bitMapLock());
2216
2217 // Clear the marking bit map array before starting, but, just
2218 // for kicks, first report if the given address is already marked
2219 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2220 _markBitMap.isMarked(addr) ? "" : " not");
2221
2222 if (verify_after_remark()) {
2223 MutexLocker x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2224 bool result = verification_mark_bm()->isMarked(addr);
2225 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2226 result ? "IS" : "is NOT");
2227 return result;
2228 } else {
2229 tty->print_cr("Could not compute result");
2230 return false;
2231 }
2232 }
2233 #endif
2234
2235 void
2236 CMSCollector::print_on_error(outputStream* st) {
2237 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2238 if (collector != NULL) {
2239 CMSBitMap* bitmap = &collector->_markBitMap;
2240 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2241 bitmap->print_on_error(st, " Bits: ");
2242
2243 st->cr();
2244
2245 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2246 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2247 mut_bitmap->print_on_error(st, " Bits: ");
2248 }
2249 }
2250
2251 ////////////////////////////////////////////////////////
2252 // CMS Verification Support
2253 ////////////////////////////////////////////////////////
2254 // Following the remark phase, the following invariant
2255 // should hold -- each object in the CMS heap which is
2256 // marked in markBitMap() should be marked in the verification_mark_bm().
2257
2258 class VerifyMarkedClosure: public BitMapClosure {
2259 CMSBitMap* _marks;
2260 bool _failed;
2261
2262 public:
2263 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2264
2265 bool do_bit(size_t offset) {
2266 HeapWord* addr = _marks->offsetToHeapWord(offset);
2267 if (!_marks->isMarked(addr)) {
2268 Log(gc, verify) log;
2269 ResourceMark rm;
2270 LogStream ls(log.error());
2271 oop(addr)->print_on(&ls);
2272 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2273 _failed = true;
2274 }
2275 return true;
2276 }
2277
2278 bool failed() { return _failed; }
2279 };
2280
2281 bool CMSCollector::verify_after_remark() {
2282 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2283 MutexLocker ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2284 static bool init = false;
2285
2286 assert(SafepointSynchronize::is_at_safepoint(),
2287 "Else mutations in object graph will make answer suspect");
2288 assert(have_cms_token(),
2289 "Else there may be mutual interference in use of "
2290 " verification data structures");
2291 assert(_collectorState > Marking && _collectorState <= Sweeping,
2292 "Else marking info checked here may be obsolete");
2293 assert(haveFreelistLocks(), "must hold free list locks");
2294 assert_lock_strong(bitMapLock());
2295
2296
2297 // Allocate marking bit map if not already allocated
2298 if (!init) { // first time
2299 if (!verification_mark_bm()->allocate(_span)) {
2300 return false;
2301 }
2302 init = true;
2303 }
2304
2305 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2306
2307 // Turn off refs discovery -- so we will be tracing through refs.
2308 // This is as intended, because by this time
2309 // GC must already have cleared any refs that need to be cleared,
2310 // and traced those that need to be marked; moreover,
2311 // the marking done here is not going to interfere in any
2312 // way with the marking information used by GC.
2313 NoRefDiscovery no_discovery(ref_processor());
2314
2315 #if COMPILER2_OR_JVMCI
2316 DerivedPointerTableDeactivate dpt_deact;
2317 #endif
2318
2319 // Clear any marks from a previous round
2320 verification_mark_bm()->clear_all();
2321 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2322 verify_work_stacks_empty();
2323
2324 CMSHeap* heap = CMSHeap::heap();
2325 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2326 // Update the saved marks which may affect the root scans.
2327 heap->save_marks();
2328
2329 if (CMSRemarkVerifyVariant == 1) {
2330 // In this first variant of verification, we complete
2331 // all marking, then check if the new marks-vector is
2332 // a subset of the CMS marks-vector.
2333 verify_after_remark_work_1();
2334 } else {
2335 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2336 // In this second variant of verification, we flag an error
2337 // (i.e. an object reachable in the new marks-vector not reachable
2338 // in the CMS marks-vector) immediately, also indicating the
2339 // identify of an object (A) that references the unmarked object (B) --
2340 // presumably, a mutation to A failed to be picked up by preclean/remark?
2341 verify_after_remark_work_2();
2342 }
2343
2344 return true;
2345 }
2346
2347 void CMSCollector::verify_after_remark_work_1() {
2348 ResourceMark rm;
2349 HandleMark hm;
2350 CMSHeap* heap = CMSHeap::heap();
2351
2352 // Get a clear set of claim bits for the roots processing to work with.
2353 ClassLoaderDataGraph::clear_claimed_marks();
2354
2355 // Mark from roots one level into CMS
2356 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2357 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2358
2359 {
2360 StrongRootsScope srs(1);
2361
2362 heap->cms_process_roots(&srs,
2363 true, // young gen as roots
2364 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2365 should_unload_classes(),
2366 ¬Older,
2367 NULL);
2368 }
2369
2370 // Now mark from the roots
2371 MarkFromRootsClosure markFromRootsClosure(this, _span,
2372 verification_mark_bm(), verification_mark_stack(),
2373 false /* don't yield */, true /* verifying */);
2374 assert(_restart_addr == NULL, "Expected pre-condition");
2375 verification_mark_bm()->iterate(&markFromRootsClosure);
2376 while (_restart_addr != NULL) {
2377 // Deal with stack overflow: by restarting at the indicated
2378 // address.
2379 HeapWord* ra = _restart_addr;
2380 markFromRootsClosure.reset(ra);
2381 _restart_addr = NULL;
2382 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2383 }
2384 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2385 verify_work_stacks_empty();
2386
2387 // Marking completed -- now verify that each bit marked in
2388 // verification_mark_bm() is also marked in markBitMap(); flag all
2389 // errors by printing corresponding objects.
2390 VerifyMarkedClosure vcl(markBitMap());
2391 verification_mark_bm()->iterate(&vcl);
2392 if (vcl.failed()) {
2393 Log(gc, verify) log;
2394 log.error("Failed marking verification after remark");
2395 ResourceMark rm;
2396 LogStream ls(log.error());
2397 heap->print_on(&ls);
2398 fatal("CMS: failed marking verification after remark");
2399 }
2400 }
2401
2402 class VerifyCLDOopsCLDClosure : public CLDClosure {
2403 class VerifyCLDOopsClosure : public OopClosure {
2404 CMSBitMap* _bitmap;
2405 public:
2406 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2407 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2408 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2409 } _oop_closure;
2410 public:
2411 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2412 void do_cld(ClassLoaderData* cld) {
2413 cld->oops_do(&_oop_closure, ClassLoaderData::_claim_none, false);
2414 }
2415 };
2416
2417 void CMSCollector::verify_after_remark_work_2() {
2418 ResourceMark rm;
2419 HandleMark hm;
2420 CMSHeap* heap = CMSHeap::heap();
2421
2422 // Get a clear set of claim bits for the roots processing to work with.
2423 ClassLoaderDataGraph::clear_claimed_marks();
2424
2425 // Mark from roots one level into CMS
2426 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2427 markBitMap());
2428 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2429
2430 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2431
2432 {
2433 StrongRootsScope srs(1);
2434
2435 heap->cms_process_roots(&srs,
2436 true, // young gen as roots
2437 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2438 should_unload_classes(),
2439 ¬Older,
2440 &cld_closure);
2441 }
2442
2443 // Now mark from the roots
2444 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2445 verification_mark_bm(), markBitMap(), verification_mark_stack());
2446 assert(_restart_addr == NULL, "Expected pre-condition");
2447 verification_mark_bm()->iterate(&markFromRootsClosure);
2448 while (_restart_addr != NULL) {
2449 // Deal with stack overflow: by restarting at the indicated
2450 // address.
2451 HeapWord* ra = _restart_addr;
2452 markFromRootsClosure.reset(ra);
2453 _restart_addr = NULL;
2454 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2455 }
2456 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2457 verify_work_stacks_empty();
2458
2459 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2460 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2461
2462 // Marking completed -- now verify that each bit marked in
2463 // verification_mark_bm() is also marked in markBitMap(); flag all
2464 // errors by printing corresponding objects.
2465 VerifyMarkedClosure vcl(markBitMap());
2466 verification_mark_bm()->iterate(&vcl);
2467 assert(!vcl.failed(), "Else verification above should not have succeeded");
2468 }
2469
2470 void ConcurrentMarkSweepGeneration::save_marks() {
2471 // delegate to CMS space
2472 cmsSpace()->save_marks();
2473 }
2474
2475 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2476 return cmsSpace()->no_allocs_since_save_marks();
2477 }
2478
2479 void
2480 ConcurrentMarkSweepGeneration::oop_iterate(OopIterateClosure* cl) {
2481 if (freelistLock()->owned_by_self()) {
2482 Generation::oop_iterate(cl);
2483 } else {
2484 MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2485 Generation::oop_iterate(cl);
2486 }
2487 }
2488
2489 void
2490 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2491 if (freelistLock()->owned_by_self()) {
2492 Generation::object_iterate(cl);
2493 } else {
2494 MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2495 Generation::object_iterate(cl);
2496 }
2497 }
2498
2499 void
2500 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2501 if (freelistLock()->owned_by_self()) {
2502 Generation::safe_object_iterate(cl);
2503 } else {
2504 MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2505 Generation::safe_object_iterate(cl);
2506 }
2507 }
2508
2509 void
2510 ConcurrentMarkSweepGeneration::post_compact() {
2511 }
2512
2513 void
2514 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2515 // Fix the linear allocation blocks to look like free blocks.
2516
2517 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2518 // are not called when the heap is verified during universe initialization and
2519 // at vm shutdown.
2520 if (freelistLock()->owned_by_self()) {
2521 cmsSpace()->prepare_for_verify();
2522 } else {
2523 MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2524 cmsSpace()->prepare_for_verify();
2525 }
2526 }
2527
2528 void
2529 ConcurrentMarkSweepGeneration::verify() {
2530 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2531 // are not called when the heap is verified during universe initialization and
2532 // at vm shutdown.
2533 if (freelistLock()->owned_by_self()) {
2534 cmsSpace()->verify();
2535 } else {
2536 MutexLocker fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2537 cmsSpace()->verify();
2538 }
2539 }
2540
2541 void CMSCollector::verify() {
2542 _cmsGen->verify();
2543 }
2544
2545 #ifndef PRODUCT
2546 bool CMSCollector::overflow_list_is_empty() const {
2547 assert(_num_par_pushes >= 0, "Inconsistency");
2548 if (_overflow_list == NULL) {
2549 assert(_num_par_pushes == 0, "Inconsistency");
2550 }
2551 return _overflow_list == NULL;
2552 }
2553
2554 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2555 // merely consolidate assertion checks that appear to occur together frequently.
2556 void CMSCollector::verify_work_stacks_empty() const {
2557 assert(_markStack.isEmpty(), "Marking stack should be empty");
2558 assert(overflow_list_is_empty(), "Overflow list should be empty");
2559 }
2560
2561 void CMSCollector::verify_overflow_empty() const {
2562 assert(overflow_list_is_empty(), "Overflow list should be empty");
2563 assert(no_preserved_marks(), "No preserved marks");
2564 }
2565 #endif // PRODUCT
2566
2567 // Decide if we want to enable class unloading as part of the
2568 // ensuing concurrent GC cycle. We will collect and
2569 // unload classes if it's the case that:
2570 // (a) class unloading is enabled at the command line, and
2571 // (b) old gen is getting really full
2572 // NOTE: Provided there is no change in the state of the heap between
2573 // calls to this method, it should have idempotent results. Moreover,
2574 // its results should be monotonically increasing (i.e. going from 0 to 1,
2575 // but not 1 to 0) between successive calls between which the heap was
2576 // not collected. For the implementation below, it must thus rely on
2577 // the property that concurrent_cycles_since_last_unload()
2578 // will not decrease unless a collection cycle happened and that
2579 // _cmsGen->is_too_full() are
2580 // themselves also monotonic in that sense. See check_monotonicity()
2581 // below.
2582 void CMSCollector::update_should_unload_classes() {
2583 _should_unload_classes = false;
2584 if (CMSClassUnloadingEnabled) {
2585 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2586 CMSClassUnloadingMaxInterval)
2587 || _cmsGen->is_too_full();
2588 }
2589 }
2590
2591 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2592 bool res = should_concurrent_collect();
2593 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2594 return res;
2595 }
2596
2597 void CMSCollector::setup_cms_unloading_and_verification_state() {
2598 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2599 || VerifyBeforeExit;
2600 const int rso = GenCollectedHeap::SO_AllCodeCache;
2601
2602 // We set the proper root for this CMS cycle here.
2603 if (should_unload_classes()) { // Should unload classes this cycle
2604 remove_root_scanning_option(rso); // Shrink the root set appropriately
2605 set_verifying(should_verify); // Set verification state for this cycle
2606 return; // Nothing else needs to be done at this time
2607 }
2608
2609 // Not unloading classes this cycle
2610 assert(!should_unload_classes(), "Inconsistency!");
2611
2612 // If we are not unloading classes then add SO_AllCodeCache to root
2613 // scanning options.
2614 add_root_scanning_option(rso);
2615
2616 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2617 set_verifying(true);
2618 } else if (verifying() && !should_verify) {
2619 // We were verifying, but some verification flags got disabled.
2620 set_verifying(false);
2621 // Exclude symbols, strings and code cache elements from root scanning to
2622 // reduce IM and RM pauses.
2623 remove_root_scanning_option(rso);
2624 }
2625 }
2626
2627
2628 #ifndef PRODUCT
2629 HeapWord* CMSCollector::block_start(const void* p) const {
2630 const HeapWord* addr = (HeapWord*)p;
2631 if (_span.contains(p)) {
2632 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2633 return _cmsGen->cmsSpace()->block_start(p);
2634 }
2635 }
2636 return NULL;
2637 }
2638 #endif
2639
2640 HeapWord*
2641 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2642 bool tlab,
2643 bool parallel) {
2644 CMSSynchronousYieldRequest yr;
2645 assert(!tlab, "Can't deal with TLAB allocation");
2646 MutexLocker x(freelistLock(), Mutex::_no_safepoint_check_flag);
2647 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2648 if (GCExpandToAllocateDelayMillis > 0) {
2649 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2650 }
2651 return have_lock_and_allocate(word_size, tlab);
2652 }
2653
2654 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2655 size_t bytes,
2656 size_t expand_bytes,
2657 CMSExpansionCause::Cause cause)
2658 {
2659
2660 bool success = expand(bytes, expand_bytes);
2661
2662 // remember why we expanded; this information is used
2663 // by shouldConcurrentCollect() when making decisions on whether to start
2664 // a new CMS cycle.
2665 if (success) {
2666 set_expansion_cause(cause);
2667 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2668 }
2669 }
2670
2671 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2672 HeapWord* res = NULL;
2673 MutexLocker x(ParGCRareEvent_lock);
2674 while (true) {
2675 // Expansion by some other thread might make alloc OK now:
2676 res = ps->lab.alloc(word_sz);
2677 if (res != NULL) return res;
2678 // If there's not enough expansion space available, give up.
2679 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2680 return NULL;
2681 }
2682 // Otherwise, we try expansion.
2683 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2684 // Now go around the loop and try alloc again;
2685 // A competing par_promote might beat us to the expansion space,
2686 // so we may go around the loop again if promotion fails again.
2687 if (GCExpandToAllocateDelayMillis > 0) {
2688 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2689 }
2690 }
2691 }
2692
2693
2694 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2695 PromotionInfo* promo) {
2696 MutexLocker x(ParGCRareEvent_lock);
2697 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2698 while (true) {
2699 // Expansion by some other thread might make alloc OK now:
2700 if (promo->ensure_spooling_space()) {
2701 assert(promo->has_spooling_space(),
2702 "Post-condition of successful ensure_spooling_space()");
2703 return true;
2704 }
2705 // If there's not enough expansion space available, give up.
2706 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2707 return false;
2708 }
2709 // Otherwise, we try expansion.
2710 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2711 // Now go around the loop and try alloc again;
2712 // A competing allocation might beat us to the expansion space,
2713 // so we may go around the loop again if allocation fails again.
2714 if (GCExpandToAllocateDelayMillis > 0) {
2715 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2716 }
2717 }
2718 }
2719
2720 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2721 // Only shrink if a compaction was done so that all the free space
2722 // in the generation is in a contiguous block at the end.
2723 if (did_compact()) {
2724 CardGeneration::shrink(bytes);
2725 }
2726 }
2727
2728 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2729 assert_locked_or_safepoint(Heap_lock);
2730 }
2731
2732 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2733 assert_locked_or_safepoint(Heap_lock);
2734 assert_lock_strong(freelistLock());
2735 log_trace(gc)("Shrinking of CMS not yet implemented");
2736 return;
2737 }
2738
2739
2740 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2741 // phases.
2742 class CMSPhaseAccounting: public StackObj {
2743 public:
2744 CMSPhaseAccounting(CMSCollector *collector,
2745 const char *title);
2746 ~CMSPhaseAccounting();
2747
2748 private:
2749 CMSCollector *_collector;
2750 const char *_title;
2751 GCTraceConcTime(Info, gc) _trace_time;
2752
2753 public:
2754 // Not MT-safe; so do not pass around these StackObj's
2755 // where they may be accessed by other threads.
2756 double wallclock_millis() {
2757 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2758 }
2759 };
2760
2761 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2762 const char *title) :
2763 _collector(collector), _title(title), _trace_time(title) {
2764
2765 _collector->resetYields();
2766 _collector->resetTimer();
2767 _collector->startTimer();
2768 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2769 }
2770
2771 CMSPhaseAccounting::~CMSPhaseAccounting() {
2772 _collector->gc_timer_cm()->register_gc_concurrent_end();
2773 _collector->stopTimer();
2774 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_millis(_collector->timerTicks()));
2775 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2776 }
2777
2778 // CMS work
2779
2780 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2781 class CMSParMarkTask : public AbstractGangTask {
2782 protected:
2783 CMSCollector* _collector;
2784 uint _n_workers;
2785 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2786 AbstractGangTask(name),
2787 _collector(collector),
2788 _n_workers(n_workers) {}
2789 // Work method in support of parallel rescan ... of young gen spaces
2790 void do_young_space_rescan(OopsInGenClosure* cl,
2791 ContiguousSpace* space,
2792 HeapWord** chunk_array, size_t chunk_top);
2793 void work_on_young_gen_roots(OopsInGenClosure* cl);
2794 };
2795
2796 // Parallel initial mark task
2797 class CMSParInitialMarkTask: public CMSParMarkTask {
2798 StrongRootsScope* _strong_roots_scope;
2799 public:
2800 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2801 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2802 _strong_roots_scope(strong_roots_scope) {}
2803 void work(uint worker_id);
2804 };
2805
2806 // Checkpoint the roots into this generation from outside
2807 // this generation. [Note this initial checkpoint need only
2808 // be approximate -- we'll do a catch up phase subsequently.]
2809 void CMSCollector::checkpointRootsInitial() {
2810 assert(_collectorState == InitialMarking, "Wrong collector state");
2811 check_correct_thread_executing();
2812 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2813
2814 save_heap_summary();
2815 report_heap_summary(GCWhen::BeforeGC);
2816
2817 ReferenceProcessor* rp = ref_processor();
2818 assert(_restart_addr == NULL, "Control point invariant");
2819 {
2820 // acquire locks for subsequent manipulations
2821 MutexLocker x(bitMapLock(),
2822 Mutex::_no_safepoint_check_flag);
2823 checkpointRootsInitialWork();
2824 // enable ("weak") refs discovery
2825 rp->enable_discovery();
2826 _collectorState = Marking;
2827 }
2828
2829 _cmsGen->cmsSpace()->recalculate_used_stable();
2830 }
2831
2832 void CMSCollector::checkpointRootsInitialWork() {
2833 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2834 assert(_collectorState == InitialMarking, "just checking");
2835
2836 // Already have locks.
2837 assert_lock_strong(bitMapLock());
2838 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2839
2840 // Setup the verification and class unloading state for this
2841 // CMS collection cycle.
2842 setup_cms_unloading_and_verification_state();
2843
2844 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2845
2846 // Reset all the PLAB chunk arrays if necessary.
2847 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2848 reset_survivor_plab_arrays();
2849 }
2850
2851 ResourceMark rm;
2852 HandleMark hm;
2853
2854 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2855 CMSHeap* heap = CMSHeap::heap();
2856
2857 verify_work_stacks_empty();
2858 verify_overflow_empty();
2859
2860 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2861 // Update the saved marks which may affect the root scans.
2862 heap->save_marks();
2863
2864 // weak reference processing has not started yet.
2865 ref_processor()->set_enqueuing_is_done(false);
2866
2867 // Need to remember all newly created CLDs,
2868 // so that we can guarantee that the remark finds them.
2869 ClassLoaderDataGraph::remember_new_clds(true);
2870
2871 // Whenever a CLD is found, it will be claimed before proceeding to mark
2872 // the klasses. The claimed marks need to be cleared before marking starts.
2873 ClassLoaderDataGraph::clear_claimed_marks();
2874
2875 print_eden_and_survivor_chunk_arrays();
2876
2877 {
2878 #if COMPILER2_OR_JVMCI
2879 DerivedPointerTableDeactivate dpt_deact;
2880 #endif
2881 if (CMSParallelInitialMarkEnabled) {
2882 // The parallel version.
2883 WorkGang* workers = heap->workers();
2884 assert(workers != NULL, "Need parallel worker threads.");
2885 uint n_workers = workers->active_workers();
2886
2887 StrongRootsScope srs(n_workers);
2888
2889 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2890 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2891 // If the total workers is greater than 1, then multiple workers
2892 // may be used at some time and the initialization has been set
2893 // such that the single threaded path cannot be used.
2894 if (workers->total_workers() > 1) {
2895 workers->run_task(&tsk);
2896 } else {
2897 tsk.work(0);
2898 }
2899 } else {
2900 // The serial version.
2901 CLDToOopClosure cld_closure(¬Older, ClassLoaderData::_claim_strong);
2902 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2903
2904 StrongRootsScope srs(1);
2905
2906 heap->cms_process_roots(&srs,
2907 true, // young gen as roots
2908 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2909 should_unload_classes(),
2910 ¬Older,
2911 &cld_closure);
2912 }
2913 }
2914
2915 // Clear mod-union table; it will be dirtied in the prologue of
2916 // CMS generation per each young generation collection.
2917
2918 assert(_modUnionTable.isAllClear(),
2919 "Was cleared in most recent final checkpoint phase"
2920 " or no bits are set in the gc_prologue before the start of the next "
2921 "subsequent marking phase.");
2922
2923 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2924
2925 // Save the end of the used_region of the constituent generations
2926 // to be used to limit the extent of sweep in each generation.
2927 save_sweep_limits();
2928 verify_overflow_empty();
2929 }
2930
2931 bool CMSCollector::markFromRoots() {
2932 // we might be tempted to assert that:
2933 // assert(!SafepointSynchronize::is_at_safepoint(),
2934 // "inconsistent argument?");
2935 // However that wouldn't be right, because it's possible that
2936 // a safepoint is indeed in progress as a young generation
2937 // stop-the-world GC happens even as we mark in this generation.
2938 assert(_collectorState == Marking, "inconsistent state?");
2939 check_correct_thread_executing();
2940 verify_overflow_empty();
2941
2942 // Weak ref discovery note: We may be discovering weak
2943 // refs in this generation concurrent (but interleaved) with
2944 // weak ref discovery by the young generation collector.
2945
2946 CMSTokenSyncWithLocks ts(true, bitMapLock());
2947 GCTraceCPUTime tcpu;
2948 CMSPhaseAccounting pa(this, "Concurrent Mark");
2949 bool res = markFromRootsWork();
2950 if (res) {
2951 _collectorState = Precleaning;
2952 } else { // We failed and a foreground collection wants to take over
2953 assert(_foregroundGCIsActive, "internal state inconsistency");
2954 assert(_restart_addr == NULL, "foreground will restart from scratch");
2955 log_debug(gc)("bailing out to foreground collection");
2956 }
2957 verify_overflow_empty();
2958 return res;
2959 }
2960
2961 bool CMSCollector::markFromRootsWork() {
2962 // iterate over marked bits in bit map, doing a full scan and mark
2963 // from these roots using the following algorithm:
2964 // . if oop is to the right of the current scan pointer,
2965 // mark corresponding bit (we'll process it later)
2966 // . else (oop is to left of current scan pointer)
2967 // push oop on marking stack
2968 // . drain the marking stack
2969
2970 // Note that when we do a marking step we need to hold the
2971 // bit map lock -- recall that direct allocation (by mutators)
2972 // and promotion (by the young generation collector) is also
2973 // marking the bit map. [the so-called allocate live policy.]
2974 // Because the implementation of bit map marking is not
2975 // robust wrt simultaneous marking of bits in the same word,
2976 // we need to make sure that there is no such interference
2977 // between concurrent such updates.
2978
2979 // already have locks
2980 assert_lock_strong(bitMapLock());
2981
2982 verify_work_stacks_empty();
2983 verify_overflow_empty();
2984 bool result = false;
2985 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2986 result = do_marking_mt();
2987 } else {
2988 result = do_marking_st();
2989 }
2990 return result;
2991 }
2992
2993 // Forward decl
2994 class CMSConcMarkingTask;
2995
2996 class CMSConcMarkingParallelTerminator: public ParallelTaskTerminator {
2997 CMSCollector* _collector;
2998 CMSConcMarkingTask* _task;
2999 public:
3000 virtual void yield();
3001
3002 // "n_threads" is the number of threads to be terminated.
3003 // "queue_set" is a set of work queues of other threads.
3004 // "collector" is the CMS collector associated with this task terminator.
3005 // "yield" indicates whether we need the gang as a whole to yield.
3006 CMSConcMarkingParallelTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3007 ParallelTaskTerminator(n_threads, queue_set),
3008 _collector(collector) { }
3009
3010 void set_task(CMSConcMarkingTask* task) {
3011 _task = task;
3012 }
3013 };
3014
3015 class CMSConcMarkingOWSTTerminator: public OWSTTaskTerminator {
3016 CMSCollector* _collector;
3017 CMSConcMarkingTask* _task;
3018 public:
3019 virtual void yield();
3020
3021 // "n_threads" is the number of threads to be terminated.
3022 // "queue_set" is a set of work queues of other threads.
3023 // "collector" is the CMS collector associated with this task terminator.
3024 // "yield" indicates whether we need the gang as a whole to yield.
3025 CMSConcMarkingOWSTTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3026 OWSTTaskTerminator(n_threads, queue_set),
3027 _collector(collector) { }
3028
3029 void set_task(CMSConcMarkingTask* task) {
3030 _task = task;
3031 }
3032 };
3033
3034 class CMSConcMarkingTaskTerminator {
3035 private:
3036 ParallelTaskTerminator* _term;
3037 public:
3038 CMSConcMarkingTaskTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) {
3039 if (UseOWSTTaskTerminator) {
3040 _term = new CMSConcMarkingOWSTTerminator(n_threads, queue_set, collector);
3041 } else {
3042 _term = new CMSConcMarkingParallelTerminator(n_threads, queue_set, collector);
3043 }
3044 }
3045 ~CMSConcMarkingTaskTerminator() {
3046 assert(_term != NULL, "Must not be NULL");
3047 delete _term;
3048 }
3049
3050 void set_task(CMSConcMarkingTask* task);
3051 ParallelTaskTerminator* terminator() const { return _term; }
3052 };
3053
3054 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3055 CMSConcMarkingTask* _task;
3056 public:
3057 bool should_exit_termination();
3058 void set_task(CMSConcMarkingTask* task) {
3059 _task = task;
3060 }
3061 };
3062
3063 // MT Concurrent Marking Task
3064 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3065 CMSCollector* _collector;
3066 uint _n_workers; // requested/desired # workers
3067 bool _result;
3068 CompactibleFreeListSpace* _cms_space;
3069 char _pad_front[64]; // padding to ...
3070 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3071 char _pad_back[64];
3072 HeapWord* _restart_addr;
3073
3074 // Exposed here for yielding support
3075 Mutex* const _bit_map_lock;
3076
3077 // The per thread work queues, available here for stealing
3078 OopTaskQueueSet* _task_queues;
3079
3080 // Termination (and yielding) support
3081 CMSConcMarkingTaskTerminator _term;
3082 CMSConcMarkingTerminatorTerminator _term_term;
3083
3084 public:
3085 CMSConcMarkingTask(CMSCollector* collector,
3086 CompactibleFreeListSpace* cms_space,
3087 YieldingFlexibleWorkGang* workers,
3088 OopTaskQueueSet* task_queues):
3089 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3090 _collector(collector),
3091 _n_workers(0),
3092 _result(true),
3093 _cms_space(cms_space),
3094 _bit_map_lock(collector->bitMapLock()),
3095 _task_queues(task_queues),
3096 _term(_n_workers, task_queues, _collector)
3097 {
3098 _requested_size = _n_workers;
3099 _term.set_task(this);
3100 _term_term.set_task(this);
3101 _restart_addr = _global_finger = _cms_space->bottom();
3102 }
3103
3104
3105 OopTaskQueueSet* task_queues() { return _task_queues; }
3106
3107 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3108
3109 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3110
3111 ParallelTaskTerminator* terminator() { return _term.terminator(); }
3112
3113 virtual void set_for_termination(uint active_workers) {
3114 terminator()->reset_for_reuse(active_workers);
3115 }
3116
3117 void work(uint worker_id);
3118 bool should_yield() {
3119 return ConcurrentMarkSweepThread::should_yield()
3120 && !_collector->foregroundGCIsActive();
3121 }
3122
3123 virtual void coordinator_yield(); // stuff done by coordinator
3124 bool result() { return _result; }
3125
3126 void reset(HeapWord* ra) {
3127 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3128 _restart_addr = _global_finger = ra;
3129 _term.terminator()->reset_for_reuse();
3130 }
3131
3132 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3133 OopTaskQueue* work_q);
3134
3135 private:
3136 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3137 void do_work_steal(int i);
3138 void bump_global_finger(HeapWord* f);
3139 };
3140
3141 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3142 assert(_task != NULL, "Error");
3143 return _task->yielding();
3144 // Note that we do not need the disjunct || _task->should_yield() above
3145 // because we want terminating threads to yield only if the task
3146 // is already in the midst of yielding, which happens only after at least one
3147 // thread has yielded.
3148 }
3149
3150 void CMSConcMarkingParallelTerminator::yield() {
3151 if (_task->should_yield()) {
3152 _task->yield();
3153 } else {
3154 ParallelTaskTerminator::yield();
3155 }
3156 }
3157
3158 void CMSConcMarkingOWSTTerminator::yield() {
3159 if (_task->should_yield()) {
3160 _task->yield();
3161 } else {
3162 OWSTTaskTerminator::yield();
3163 }
3164 }
3165
3166 void CMSConcMarkingTaskTerminator::set_task(CMSConcMarkingTask* task) {
3167 if (UseOWSTTaskTerminator) {
3168 ((CMSConcMarkingOWSTTerminator*)_term)->set_task(task);
3169 } else {
3170 ((CMSConcMarkingParallelTerminator*)_term)->set_task(task);
3171 }
3172 }
3173
3174 ////////////////////////////////////////////////////////////////
3175 // Concurrent Marking Algorithm Sketch
3176 ////////////////////////////////////////////////////////////////
3177 // Until all tasks exhausted (both spaces):
3178 // -- claim next available chunk
3179 // -- bump global finger via CAS
3180 // -- find first object that starts in this chunk
3181 // and start scanning bitmap from that position
3182 // -- scan marked objects for oops
3183 // -- CAS-mark target, and if successful:
3184 // . if target oop is above global finger (volatile read)
3185 // nothing to do
3186 // . if target oop is in chunk and above local finger
3187 // then nothing to do
3188 // . else push on work-queue
3189 // -- Deal with possible overflow issues:
3190 // . local work-queue overflow causes stuff to be pushed on
3191 // global (common) overflow queue
3192 // . always first empty local work queue
3193 // . then get a batch of oops from global work queue if any
3194 // . then do work stealing
3195 // -- When all tasks claimed (both spaces)
3196 // and local work queue empty,
3197 // then in a loop do:
3198 // . check global overflow stack; steal a batch of oops and trace
3199 // . try to steal from other threads oif GOS is empty
3200 // . if neither is available, offer termination
3201 // -- Terminate and return result
3202 //
3203 void CMSConcMarkingTask::work(uint worker_id) {
3204 elapsedTimer _timer;
3205 ResourceMark rm;
3206 HandleMark hm;
3207
3208 DEBUG_ONLY(_collector->verify_overflow_empty();)
3209
3210 // Before we begin work, our work queue should be empty
3211 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3212 // Scan the bitmap covering _cms_space, tracing through grey objects.
3213 _timer.start();
3214 do_scan_and_mark(worker_id, _cms_space);
3215 _timer.stop();
3216 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3217
3218 // ... do work stealing
3219 _timer.reset();
3220 _timer.start();
3221 do_work_steal(worker_id);
3222 _timer.stop();
3223 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3224 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3225 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3226 // Note that under the current task protocol, the
3227 // following assertion is true even of the spaces
3228 // expanded since the completion of the concurrent
3229 // marking. XXX This will likely change under a strict
3230 // ABORT semantics.
3231 // After perm removal the comparison was changed to
3232 // greater than or equal to from strictly greater than.
3233 // Before perm removal the highest address sweep would
3234 // have been at the end of perm gen but now is at the
3235 // end of the tenured gen.
3236 assert(_global_finger >= _cms_space->end(),
3237 "All tasks have been completed");
3238 DEBUG_ONLY(_collector->verify_overflow_empty();)
3239 }
3240
3241 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3242 HeapWord* read = _global_finger;
3243 HeapWord* cur = read;
3244 while (f > read) {
3245 cur = read;
3246 read = Atomic::cmpxchg(f, &_global_finger, cur);
3247 if (cur == read) {
3248 // our cas succeeded
3249 assert(_global_finger >= f, "protocol consistency");
3250 break;
3251 }
3252 }
3253 }
3254
3255 // This is really inefficient, and should be redone by
3256 // using (not yet available) block-read and -write interfaces to the
3257 // stack and the work_queue. XXX FIX ME !!!
3258 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3259 OopTaskQueue* work_q) {
3260 // Fast lock-free check
3261 if (ovflw_stk->length() == 0) {
3262 return false;
3263 }
3264 assert(work_q->size() == 0, "Shouldn't steal");
3265 MutexLocker ml(ovflw_stk->par_lock(),
3266 Mutex::_no_safepoint_check_flag);
3267 // Grab up to 1/4 the size of the work queue
3268 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3269 (size_t)ParGCDesiredObjsFromOverflowList);
3270 num = MIN2(num, ovflw_stk->length());
3271 for (int i = (int) num; i > 0; i--) {
3272 oop cur = ovflw_stk->pop();
3273 assert(cur != NULL, "Counted wrong?");
3274 work_q->push(cur);
3275 }
3276 return num > 0;
3277 }
3278
3279 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3280 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3281 int n_tasks = pst->n_tasks();
3282 // We allow that there may be no tasks to do here because
3283 // we are restarting after a stack overflow.
3284 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3285 uint nth_task = 0;
3286
3287 HeapWord* aligned_start = sp->bottom();
3288 if (sp->used_region().contains(_restart_addr)) {
3289 // Align down to a card boundary for the start of 0th task
3290 // for this space.
3291 aligned_start = align_down(_restart_addr, CardTable::card_size);
3292 }
3293
3294 size_t chunk_size = sp->marking_task_size();
3295 while (pst->try_claim_task(/* reference */ nth_task)) {
3296 // Having claimed the nth task in this space,
3297 // compute the chunk that it corresponds to:
3298 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3299 aligned_start + (nth_task+1)*chunk_size);
3300 // Try and bump the global finger via a CAS;
3301 // note that we need to do the global finger bump
3302 // _before_ taking the intersection below, because
3303 // the task corresponding to that region will be
3304 // deemed done even if the used_region() expands
3305 // because of allocation -- as it almost certainly will
3306 // during start-up while the threads yield in the
3307 // closure below.
3308 HeapWord* finger = span.end();
3309 bump_global_finger(finger); // atomically
3310 // There are null tasks here corresponding to chunks
3311 // beyond the "top" address of the space.
3312 span = span.intersection(sp->used_region());
3313 if (!span.is_empty()) { // Non-null task
3314 HeapWord* prev_obj;
3315 assert(!span.contains(_restart_addr) || nth_task == 0,
3316 "Inconsistency");
3317 if (nth_task == 0) {
3318 // For the 0th task, we'll not need to compute a block_start.
3319 if (span.contains(_restart_addr)) {
3320 // In the case of a restart because of stack overflow,
3321 // we might additionally skip a chunk prefix.
3322 prev_obj = _restart_addr;
3323 } else {
3324 prev_obj = span.start();
3325 }
3326 } else {
3327 // We want to skip the first object because
3328 // the protocol is to scan any object in its entirety
3329 // that _starts_ in this span; a fortiori, any
3330 // object starting in an earlier span is scanned
3331 // as part of an earlier claimed task.
3332 // Below we use the "careful" version of block_start
3333 // so we do not try to navigate uninitialized objects.
3334 prev_obj = sp->block_start_careful(span.start());
3335 // Below we use a variant of block_size that uses the
3336 // Printezis bits to avoid waiting for allocated
3337 // objects to become initialized/parsable.
3338 while (prev_obj < span.start()) {
3339 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3340 if (sz > 0) {
3341 prev_obj += sz;
3342 } else {
3343 // In this case we may end up doing a bit of redundant
3344 // scanning, but that appears unavoidable, short of
3345 // locking the free list locks; see bug 6324141.
3346 break;
3347 }
3348 }
3349 }
3350 if (prev_obj < span.end()) {
3351 MemRegion my_span = MemRegion(prev_obj, span.end());
3352 // Do the marking work within a non-empty span --
3353 // the last argument to the constructor indicates whether the
3354 // iteration should be incremental with periodic yields.
3355 ParMarkFromRootsClosure cl(this, _collector, my_span,
3356 &_collector->_markBitMap,
3357 work_queue(i),
3358 &_collector->_markStack);
3359 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3360 } // else nothing to do for this task
3361 } // else nothing to do for this task
3362 }
3363 // We'd be tempted to assert here that since there are no
3364 // more tasks left to claim in this space, the global_finger
3365 // must exceed space->top() and a fortiori space->end(). However,
3366 // that would not quite be correct because the bumping of
3367 // global_finger occurs strictly after the claiming of a task,
3368 // so by the time we reach here the global finger may not yet
3369 // have been bumped up by the thread that claimed the last
3370 // task.
3371 pst->all_tasks_completed();
3372 }
3373
3374 class ParConcMarkingClosure: public MetadataVisitingOopIterateClosure {
3375 private:
3376 CMSCollector* _collector;
3377 CMSConcMarkingTask* _task;
3378 MemRegion _span;
3379 CMSBitMap* _bit_map;
3380 CMSMarkStack* _overflow_stack;
3381 OopTaskQueue* _work_queue;
3382 protected:
3383 DO_OOP_WORK_DEFN
3384 public:
3385 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3386 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3387 MetadataVisitingOopIterateClosure(collector->ref_processor()),
3388 _collector(collector),
3389 _task(task),
3390 _span(collector->_span),
3391 _bit_map(bit_map),
3392 _overflow_stack(overflow_stack),
3393 _work_queue(work_queue)
3394 { }
3395 virtual void do_oop(oop* p);
3396 virtual void do_oop(narrowOop* p);
3397
3398 void trim_queue(size_t max);
3399 void handle_stack_overflow(HeapWord* lost);
3400 void do_yield_check() {
3401 if (_task->should_yield()) {
3402 _task->yield();
3403 }
3404 }
3405 };
3406
3407 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3408
3409 // Grey object scanning during work stealing phase --
3410 // the salient assumption here is that any references
3411 // that are in these stolen objects being scanned must
3412 // already have been initialized (else they would not have
3413 // been published), so we do not need to check for
3414 // uninitialized objects before pushing here.
3415 void ParConcMarkingClosure::do_oop(oop obj) {
3416 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3417 HeapWord* addr = (HeapWord*)obj;
3418 // Check if oop points into the CMS generation
3419 // and is not marked
3420 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3421 // a white object ...
3422 // If we manage to "claim" the object, by being the
3423 // first thread to mark it, then we push it on our
3424 // marking stack
3425 if (_bit_map->par_mark(addr)) { // ... now grey
3426 // push on work queue (grey set)
3427 bool simulate_overflow = false;
3428 NOT_PRODUCT(
3429 if (CMSMarkStackOverflowALot &&
3430 _collector->simulate_overflow()) {
3431 // simulate a stack overflow
3432 simulate_overflow = true;
3433 }
3434 )
3435 if (simulate_overflow ||
3436 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3437 // stack overflow
3438 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3439 // We cannot assert that the overflow stack is full because
3440 // it may have been emptied since.
3441 assert(simulate_overflow ||
3442 _work_queue->size() == _work_queue->max_elems(),
3443 "Else push should have succeeded");
3444 handle_stack_overflow(addr);
3445 }
3446 } // Else, some other thread got there first
3447 do_yield_check();
3448 }
3449 }
3450
3451 void ParConcMarkingClosure::trim_queue(size_t max) {
3452 while (_work_queue->size() > max) {
3453 oop new_oop;
3454 if (_work_queue->pop_local(new_oop)) {
3455 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3456 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3457 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3458 new_oop->oop_iterate(this); // do_oop() above
3459 do_yield_check();
3460 }
3461 }
3462 }
3463
3464 // Upon stack overflow, we discard (part of) the stack,
3465 // remembering the least address amongst those discarded
3466 // in CMSCollector's _restart_address.
3467 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3468 // We need to do this under a mutex to prevent other
3469 // workers from interfering with the work done below.
3470 MutexLocker ml(_overflow_stack->par_lock(),
3471 Mutex::_no_safepoint_check_flag);
3472 // Remember the least grey address discarded
3473 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3474 _collector->lower_restart_addr(ra);
3475 _overflow_stack->reset(); // discard stack contents
3476 _overflow_stack->expand(); // expand the stack if possible
3477 }
3478
3479
3480 void CMSConcMarkingTask::do_work_steal(int i) {
3481 OopTaskQueue* work_q = work_queue(i);
3482 oop obj_to_scan;
3483 CMSBitMap* bm = &(_collector->_markBitMap);
3484 CMSMarkStack* ovflw = &(_collector->_markStack);
3485 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3486 while (true) {
3487 cl.trim_queue(0);
3488 assert(work_q->size() == 0, "Should have been emptied above");
3489 if (get_work_from_overflow_stack(ovflw, work_q)) {
3490 // Can't assert below because the work obtained from the
3491 // overflow stack may already have been stolen from us.
3492 // assert(work_q->size() > 0, "Work from overflow stack");
3493 continue;
3494 } else if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
3495 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3496 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3497 obj_to_scan->oop_iterate(&cl);
3498 } else if (terminator()->offer_termination(&_term_term)) {
3499 assert(work_q->size() == 0, "Impossible!");
3500 break;
3501 } else if (yielding() || should_yield()) {
3502 yield();
3503 }
3504 }
3505 }
3506
3507 // This is run by the CMS (coordinator) thread.
3508 void CMSConcMarkingTask::coordinator_yield() {
3509 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3510 "CMS thread should hold CMS token");
3511 // First give up the locks, then yield, then re-lock
3512 // We should probably use a constructor/destructor idiom to
3513 // do this unlock/lock or modify the MutexUnlocker class to
3514 // serve our purpose. XXX
3515 assert_lock_strong(_bit_map_lock);
3516 _bit_map_lock->unlock();
3517 ConcurrentMarkSweepThread::desynchronize(true);
3518 _collector->stopTimer();
3519 _collector->incrementYields();
3520
3521 // It is possible for whichever thread initiated the yield request
3522 // not to get a chance to wake up and take the bitmap lock between
3523 // this thread releasing it and reacquiring it. So, while the
3524 // should_yield() flag is on, let's sleep for a bit to give the
3525 // other thread a chance to wake up. The limit imposed on the number
3526 // of iterations is defensive, to avoid any unforseen circumstances
3527 // putting us into an infinite loop. Since it's always been this
3528 // (coordinator_yield()) method that was observed to cause the
3529 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3530 // which is by default non-zero. For the other seven methods that
3531 // also perform the yield operation, as are using a different
3532 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3533 // can enable the sleeping for those methods too, if necessary.
3534 // See 6442774.
3535 //
3536 // We really need to reconsider the synchronization between the GC
3537 // thread and the yield-requesting threads in the future and we
3538 // should really use wait/notify, which is the recommended
3539 // way of doing this type of interaction. Additionally, we should
3540 // consolidate the eight methods that do the yield operation and they
3541 // are almost identical into one for better maintainability and
3542 // readability. See 6445193.
3543 //
3544 // Tony 2006.06.29
3545 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3546 ConcurrentMarkSweepThread::should_yield() &&
3547 !CMSCollector::foregroundGCIsActive(); ++i) {
3548 os::sleep(Thread::current(), 1, false);
3549 }
3550
3551 ConcurrentMarkSweepThread::synchronize(true);
3552 _bit_map_lock->lock_without_safepoint_check();
3553 _collector->startTimer();
3554 }
3555
3556 bool CMSCollector::do_marking_mt() {
3557 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3558 uint num_workers = WorkerPolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3559 conc_workers()->active_workers(),
3560 Threads::number_of_non_daemon_threads());
3561 num_workers = conc_workers()->update_active_workers(num_workers);
3562 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3563
3564 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3565
3566 CMSConcMarkingTask tsk(this,
3567 cms_space,
3568 conc_workers(),
3569 task_queues());
3570
3571 // Since the actual number of workers we get may be different
3572 // from the number we requested above, do we need to do anything different
3573 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3574 // class?? XXX
3575 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3576
3577 // Refs discovery is already non-atomic.
3578 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3579 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3580 conc_workers()->start_task(&tsk);
3581 while (tsk.yielded()) {
3582 tsk.coordinator_yield();
3583 conc_workers()->continue_task(&tsk);
3584 }
3585 // If the task was aborted, _restart_addr will be non-NULL
3586 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3587 while (_restart_addr != NULL) {
3588 // XXX For now we do not make use of ABORTED state and have not
3589 // yet implemented the right abort semantics (even in the original
3590 // single-threaded CMS case). That needs some more investigation
3591 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3592 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3593 // If _restart_addr is non-NULL, a marking stack overflow
3594 // occurred; we need to do a fresh marking iteration from the
3595 // indicated restart address.
3596 if (_foregroundGCIsActive) {
3597 // We may be running into repeated stack overflows, having
3598 // reached the limit of the stack size, while making very
3599 // slow forward progress. It may be best to bail out and
3600 // let the foreground collector do its job.
3601 // Clear _restart_addr, so that foreground GC
3602 // works from scratch. This avoids the headache of
3603 // a "rescan" which would otherwise be needed because
3604 // of the dirty mod union table & card table.
3605 _restart_addr = NULL;
3606 return false;
3607 }
3608 // Adjust the task to restart from _restart_addr
3609 tsk.reset(_restart_addr);
3610 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3611 _restart_addr);
3612 _restart_addr = NULL;
3613 // Get the workers going again
3614 conc_workers()->start_task(&tsk);
3615 while (tsk.yielded()) {
3616 tsk.coordinator_yield();
3617 conc_workers()->continue_task(&tsk);
3618 }
3619 }
3620 assert(tsk.completed(), "Inconsistency");
3621 assert(tsk.result() == true, "Inconsistency");
3622 return true;
3623 }
3624
3625 bool CMSCollector::do_marking_st() {
3626 ResourceMark rm;
3627 HandleMark hm;
3628
3629 // Temporarily make refs discovery single threaded (non-MT)
3630 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3631 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3632 &_markStack, CMSYield);
3633 // the last argument to iterate indicates whether the iteration
3634 // should be incremental with periodic yields.
3635 _markBitMap.iterate(&markFromRootsClosure);
3636 // If _restart_addr is non-NULL, a marking stack overflow
3637 // occurred; we need to do a fresh iteration from the
3638 // indicated restart address.
3639 while (_restart_addr != NULL) {
3640 if (_foregroundGCIsActive) {
3641 // We may be running into repeated stack overflows, having
3642 // reached the limit of the stack size, while making very
3643 // slow forward progress. It may be best to bail out and
3644 // let the foreground collector do its job.
3645 // Clear _restart_addr, so that foreground GC
3646 // works from scratch. This avoids the headache of
3647 // a "rescan" which would otherwise be needed because
3648 // of the dirty mod union table & card table.
3649 _restart_addr = NULL;
3650 return false; // indicating failure to complete marking
3651 }
3652 // Deal with stack overflow:
3653 // we restart marking from _restart_addr
3654 HeapWord* ra = _restart_addr;
3655 markFromRootsClosure.reset(ra);
3656 _restart_addr = NULL;
3657 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3658 }
3659 return true;
3660 }
3661
3662 void CMSCollector::preclean() {
3663 check_correct_thread_executing();
3664 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3665 verify_work_stacks_empty();
3666 verify_overflow_empty();
3667 _abort_preclean = false;
3668 if (CMSPrecleaningEnabled) {
3669 if (!CMSEdenChunksRecordAlways) {
3670 _eden_chunk_index = 0;
3671 }
3672 size_t used = get_eden_used();
3673 size_t capacity = get_eden_capacity();
3674 // Don't start sampling unless we will get sufficiently
3675 // many samples.
3676 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3677 * CMSScheduleRemarkEdenPenetration)) {
3678 _start_sampling = true;
3679 } else {
3680 _start_sampling = false;
3681 }
3682 GCTraceCPUTime tcpu;
3683 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3684 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3685 }
3686 CMSTokenSync x(true); // is cms thread
3687 if (CMSPrecleaningEnabled) {
3688 sample_eden();
3689 _collectorState = AbortablePreclean;
3690 } else {
3691 _collectorState = FinalMarking;
3692 }
3693 verify_work_stacks_empty();
3694 verify_overflow_empty();
3695 }
3696
3697 // Try and schedule the remark such that young gen
3698 // occupancy is CMSScheduleRemarkEdenPenetration %.
3699 void CMSCollector::abortable_preclean() {
3700 check_correct_thread_executing();
3701 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3702 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3703
3704 // If Eden's current occupancy is below this threshold,
3705 // immediately schedule the remark; else preclean
3706 // past the next scavenge in an effort to
3707 // schedule the pause as described above. By choosing
3708 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3709 // we will never do an actual abortable preclean cycle.
3710 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3711 GCTraceCPUTime tcpu;
3712 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3713 // We need more smarts in the abortable preclean
3714 // loop below to deal with cases where allocation
3715 // in young gen is very very slow, and our precleaning
3716 // is running a losing race against a horde of
3717 // mutators intent on flooding us with CMS updates
3718 // (dirty cards).
3719 // One, admittedly dumb, strategy is to give up
3720 // after a certain number of abortable precleaning loops
3721 // or after a certain maximum time. We want to make
3722 // this smarter in the next iteration.
3723 // XXX FIX ME!!! YSR
3724 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3725 while (!(should_abort_preclean() ||
3726 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3727 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3728 cumworkdone += workdone;
3729 loops++;
3730 // Voluntarily terminate abortable preclean phase if we have
3731 // been at it for too long.
3732 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3733 loops >= CMSMaxAbortablePrecleanLoops) {
3734 log_debug(gc)(" CMS: abort preclean due to loops ");
3735 break;
3736 }
3737 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3738 log_debug(gc)(" CMS: abort preclean due to time ");
3739 break;
3740 }
3741 // If we are doing little work each iteration, we should
3742 // take a short break.
3743 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3744 // Sleep for some time, waiting for work to accumulate
3745 stopTimer();
3746 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3747 startTimer();
3748 waited++;
3749 }
3750 }
3751 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3752 loops, waited, cumworkdone);
3753 }
3754 CMSTokenSync x(true); // is cms thread
3755 if (_collectorState != Idling) {
3756 assert(_collectorState == AbortablePreclean,
3757 "Spontaneous state transition?");
3758 _collectorState = FinalMarking;
3759 } // Else, a foreground collection completed this CMS cycle.
3760 return;
3761 }
3762
3763 // Respond to an Eden sampling opportunity
3764 void CMSCollector::sample_eden() {
3765 // Make sure a young gc cannot sneak in between our
3766 // reading and recording of a sample.
3767 assert(Thread::current()->is_ConcurrentGC_thread(),
3768 "Only the cms thread may collect Eden samples");
3769 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3770 "Should collect samples while holding CMS token");
3771 if (!_start_sampling) {
3772 return;
3773 }
3774 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3775 // is populated by the young generation.
3776 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3777 if (_eden_chunk_index < _eden_chunk_capacity) {
3778 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3779 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3780 "Unexpected state of Eden");
3781 // We'd like to check that what we just sampled is an oop-start address;
3782 // however, we cannot do that here since the object may not yet have been
3783 // initialized. So we'll instead do the check when we _use_ this sample
3784 // later.
3785 if (_eden_chunk_index == 0 ||
3786 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3787 _eden_chunk_array[_eden_chunk_index-1])
3788 >= CMSSamplingGrain)) {
3789 _eden_chunk_index++; // commit sample
3790 }
3791 }
3792 }
3793 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3794 size_t used = get_eden_used();
3795 size_t capacity = get_eden_capacity();
3796 assert(used <= capacity, "Unexpected state of Eden");
3797 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3798 _abort_preclean = true;
3799 }
3800 }
3801 }
3802
3803 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3804 assert(_collectorState == Precleaning ||
3805 _collectorState == AbortablePreclean, "incorrect state");
3806 ResourceMark rm;
3807 HandleMark hm;
3808
3809 // Precleaning is currently not MT but the reference processor
3810 // may be set for MT. Disable it temporarily here.
3811 ReferenceProcessor* rp = ref_processor();
3812 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3813
3814 // Do one pass of scrubbing the discovered reference lists
3815 // to remove any reference objects with strongly-reachable
3816 // referents.
3817 if (clean_refs) {
3818 CMSPrecleanRefsYieldClosure yield_cl(this);
3819 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
3820 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3821 &_markStack, true /* preclean */);
3822 CMSDrainMarkingStackClosure complete_trace(this,
3823 _span, &_markBitMap, &_markStack,
3824 &keep_alive, true /* preclean */);
3825
3826 // We don't want this step to interfere with a young
3827 // collection because we don't want to take CPU
3828 // or memory bandwidth away from the young GC threads
3829 // (which may be as many as there are CPUs).
3830 // Note that we don't need to protect ourselves from
3831 // interference with mutators because they can't
3832 // manipulate the discovered reference lists nor affect
3833 // the computed reachability of the referents, the
3834 // only properties manipulated by the precleaning
3835 // of these reference lists.
3836 stopTimer();
3837 CMSTokenSyncWithLocks x(true /* is cms thread */,
3838 bitMapLock());
3839 startTimer();
3840 sample_eden();
3841
3842 // The following will yield to allow foreground
3843 // collection to proceed promptly. XXX YSR:
3844 // The code in this method may need further
3845 // tweaking for better performance and some restructuring
3846 // for cleaner interfaces.
3847 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3848 rp->preclean_discovered_references(
3849 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3850 gc_timer);
3851 }
3852
3853 if (clean_survivor) { // preclean the active survivor space(s)
3854 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3855 &_markBitMap, &_modUnionTable,
3856 &_markStack, true /* precleaning phase */);
3857 stopTimer();
3858 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3859 bitMapLock());
3860 startTimer();
3861 unsigned int before_count =
3862 CMSHeap::heap()->total_collections();
3863 SurvivorSpacePrecleanClosure
3864 sss_cl(this, _span, &_markBitMap, &_markStack,
3865 &pam_cl, before_count, CMSYield);
3866 _young_gen->from()->object_iterate_careful(&sss_cl);
3867 _young_gen->to()->object_iterate_careful(&sss_cl);
3868 }
3869 MarkRefsIntoAndScanClosure
3870 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3871 &_markStack, this, CMSYield,
3872 true /* precleaning phase */);
3873 // CAUTION: The following closure has persistent state that may need to
3874 // be reset upon a decrease in the sequence of addresses it
3875 // processes.
3876 ScanMarkedObjectsAgainCarefullyClosure
3877 smoac_cl(this, _span,
3878 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3879
3880 // Preclean dirty cards in ModUnionTable and CardTable using
3881 // appropriate convergence criterion;
3882 // repeat CMSPrecleanIter times unless we find that
3883 // we are losing.
3884 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3885 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3886 "Bad convergence multiplier");
3887 assert(CMSPrecleanThreshold >= 100,
3888 "Unreasonably low CMSPrecleanThreshold");
3889
3890 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3891 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3892 numIter < CMSPrecleanIter;
3893 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3894 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3895 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3896 // Either there are very few dirty cards, so re-mark
3897 // pause will be small anyway, or our pre-cleaning isn't
3898 // that much faster than the rate at which cards are being
3899 // dirtied, so we might as well stop and re-mark since
3900 // precleaning won't improve our re-mark time by much.
3901 if (curNumCards <= CMSPrecleanThreshold ||
3902 (numIter > 0 &&
3903 (curNumCards * CMSPrecleanDenominator >
3904 lastNumCards * CMSPrecleanNumerator))) {
3905 numIter++;
3906 cumNumCards += curNumCards;
3907 break;
3908 }
3909 }
3910
3911 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3912
3913 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3914 cumNumCards += curNumCards;
3915 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3916 curNumCards, cumNumCards, numIter);
3917 return cumNumCards; // as a measure of useful work done
3918 }
3919
3920 // PRECLEANING NOTES:
3921 // Precleaning involves:
3922 // . reading the bits of the modUnionTable and clearing the set bits.
3923 // . For the cards corresponding to the set bits, we scan the
3924 // objects on those cards. This means we need the free_list_lock
3925 // so that we can safely iterate over the CMS space when scanning
3926 // for oops.
3927 // . When we scan the objects, we'll be both reading and setting
3928 // marks in the marking bit map, so we'll need the marking bit map.
3929 // . For protecting _collector_state transitions, we take the CGC_lock.
3930 // Note that any races in the reading of of card table entries by the
3931 // CMS thread on the one hand and the clearing of those entries by the
3932 // VM thread or the setting of those entries by the mutator threads on the
3933 // other are quite benign. However, for efficiency it makes sense to keep
3934 // the VM thread from racing with the CMS thread while the latter is
3935 // dirty card info to the modUnionTable. We therefore also use the
3936 // CGC_lock to protect the reading of the card table and the mod union
3937 // table by the CM thread.
3938 // . We run concurrently with mutator updates, so scanning
3939 // needs to be done carefully -- we should not try to scan
3940 // potentially uninitialized objects.
3941 //
3942 // Locking strategy: While holding the CGC_lock, we scan over and
3943 // reset a maximal dirty range of the mod union / card tables, then lock
3944 // the free_list_lock and bitmap lock to do a full marking, then
3945 // release these locks; and repeat the cycle. This allows for a
3946 // certain amount of fairness in the sharing of these locks between
3947 // the CMS collector on the one hand, and the VM thread and the
3948 // mutators on the other.
3949
3950 // NOTE: preclean_mod_union_table() and preclean_card_table()
3951 // further below are largely identical; if you need to modify
3952 // one of these methods, please check the other method too.
3953
3954 size_t CMSCollector::preclean_mod_union_table(
3955 ConcurrentMarkSweepGeneration* old_gen,
3956 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3957 verify_work_stacks_empty();
3958 verify_overflow_empty();
3959
3960 // strategy: starting with the first card, accumulate contiguous
3961 // ranges of dirty cards; clear these cards, then scan the region
3962 // covered by these cards.
3963
3964 // Since all of the MUT is committed ahead, we can just use
3965 // that, in case the generations expand while we are precleaning.
3966 // It might also be fine to just use the committed part of the
3967 // generation, but we might potentially miss cards when the
3968 // generation is rapidly expanding while we are in the midst
3969 // of precleaning.
3970 HeapWord* startAddr = old_gen->reserved().start();
3971 HeapWord* endAddr = old_gen->reserved().end();
3972
3973 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3974
3975 size_t numDirtyCards, cumNumDirtyCards;
3976 HeapWord *nextAddr, *lastAddr;
3977 for (cumNumDirtyCards = numDirtyCards = 0,
3978 nextAddr = lastAddr = startAddr;
3979 nextAddr < endAddr;
3980 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3981
3982 ResourceMark rm;
3983 HandleMark hm;
3984
3985 MemRegion dirtyRegion;
3986 {
3987 stopTimer();
3988 // Potential yield point
3989 CMSTokenSync ts(true);
3990 startTimer();
3991 sample_eden();
3992 // Get dirty region starting at nextOffset (inclusive),
3993 // simultaneously clearing it.
3994 dirtyRegion =
3995 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3996 assert(dirtyRegion.start() >= nextAddr,
3997 "returned region inconsistent?");
3998 }
3999 // Remember where the next search should begin.
4000 // The returned region (if non-empty) is a right open interval,
4001 // so lastOffset is obtained from the right end of that
4002 // interval.
4003 lastAddr = dirtyRegion.end();
4004 // Should do something more transparent and less hacky XXX
4005 numDirtyCards =
4006 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4007
4008 // We'll scan the cards in the dirty region (with periodic
4009 // yields for foreground GC as needed).
4010 if (!dirtyRegion.is_empty()) {
4011 assert(numDirtyCards > 0, "consistency check");
4012 HeapWord* stop_point = NULL;
4013 stopTimer();
4014 // Potential yield point
4015 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4016 bitMapLock());
4017 startTimer();
4018 {
4019 verify_work_stacks_empty();
4020 verify_overflow_empty();
4021 sample_eden();
4022 stop_point =
4023 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4024 }
4025 if (stop_point != NULL) {
4026 // The careful iteration stopped early either because it found an
4027 // uninitialized object, or because we were in the midst of an
4028 // "abortable preclean", which should now be aborted. Redirty
4029 // the bits corresponding to the partially-scanned or unscanned
4030 // cards. We'll either restart at the next block boundary or
4031 // abort the preclean.
4032 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4033 "Should only be AbortablePreclean.");
4034 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4035 if (should_abort_preclean()) {
4036 break; // out of preclean loop
4037 } else {
4038 // Compute the next address at which preclean should pick up;
4039 // might need bitMapLock in order to read P-bits.
4040 lastAddr = next_card_start_after_block(stop_point);
4041 }
4042 }
4043 } else {
4044 assert(lastAddr == endAddr, "consistency check");
4045 assert(numDirtyCards == 0, "consistency check");
4046 break;
4047 }
4048 }
4049 verify_work_stacks_empty();
4050 verify_overflow_empty();
4051 return cumNumDirtyCards;
4052 }
4053
4054 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4055 // below are largely identical; if you need to modify
4056 // one of these methods, please check the other method too.
4057
4058 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4059 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4060 // strategy: it's similar to precleamModUnionTable above, in that
4061 // we accumulate contiguous ranges of dirty cards, mark these cards
4062 // precleaned, then scan the region covered by these cards.
4063 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4064 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4065
4066 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4067
4068 size_t numDirtyCards, cumNumDirtyCards;
4069 HeapWord *lastAddr, *nextAddr;
4070
4071 for (cumNumDirtyCards = numDirtyCards = 0,
4072 nextAddr = lastAddr = startAddr;
4073 nextAddr < endAddr;
4074 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4075
4076 ResourceMark rm;
4077 HandleMark hm;
4078
4079 MemRegion dirtyRegion;
4080 {
4081 // See comments in "Precleaning notes" above on why we
4082 // do this locking. XXX Could the locking overheads be
4083 // too high when dirty cards are sparse? [I don't think so.]
4084 stopTimer();
4085 CMSTokenSync x(true); // is cms thread
4086 startTimer();
4087 sample_eden();
4088 // Get and clear dirty region from card table
4089 dirtyRegion = _ct->dirty_card_range_after_reset(MemRegion(nextAddr, endAddr),
4090 true,
4091 CardTable::precleaned_card_val());
4092
4093 assert(dirtyRegion.start() >= nextAddr,
4094 "returned region inconsistent?");
4095 }
4096 lastAddr = dirtyRegion.end();
4097 numDirtyCards =
4098 dirtyRegion.word_size()/CardTable::card_size_in_words;
4099
4100 if (!dirtyRegion.is_empty()) {
4101 stopTimer();
4102 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4103 startTimer();
4104 sample_eden();
4105 verify_work_stacks_empty();
4106 verify_overflow_empty();
4107 HeapWord* stop_point =
4108 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4109 if (stop_point != NULL) {
4110 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4111 "Should only be AbortablePreclean.");
4112 _ct->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4113 if (should_abort_preclean()) {
4114 break; // out of preclean loop
4115 } else {
4116 // Compute the next address at which preclean should pick up.
4117 lastAddr = next_card_start_after_block(stop_point);
4118 }
4119 }
4120 } else {
4121 break;
4122 }
4123 }
4124 verify_work_stacks_empty();
4125 verify_overflow_empty();
4126 return cumNumDirtyCards;
4127 }
4128
4129 class PrecleanCLDClosure : public CLDClosure {
4130 MetadataVisitingOopsInGenClosure* _cm_closure;
4131 public:
4132 PrecleanCLDClosure(MetadataVisitingOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4133 void do_cld(ClassLoaderData* cld) {
4134 if (cld->has_accumulated_modified_oops()) {
4135 cld->clear_accumulated_modified_oops();
4136
4137 _cm_closure->do_cld(cld);
4138 }
4139 }
4140 };
4141
4142 // The freelist lock is needed to prevent asserts, is it really needed?
4143 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4144 // Needed to walk CLDG
4145 MutexLocker ml(ClassLoaderDataGraph_lock);
4146
4147 cl->set_freelistLock(freelistLock);
4148
4149 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4150
4151 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4152 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4153 PrecleanCLDClosure preclean_closure(cl);
4154 ClassLoaderDataGraph::cld_do(&preclean_closure);
4155
4156 verify_work_stacks_empty();
4157 verify_overflow_empty();
4158 }
4159
4160 void CMSCollector::checkpointRootsFinal() {
4161 assert(_collectorState == FinalMarking, "incorrect state transition?");
4162 check_correct_thread_executing();
4163 // world is stopped at this checkpoint
4164 assert(SafepointSynchronize::is_at_safepoint(),
4165 "world should be stopped");
4166 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4167
4168 verify_work_stacks_empty();
4169 verify_overflow_empty();
4170
4171 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4172 _young_gen->used() / K, _young_gen->capacity() / K);
4173 {
4174 if (CMSScavengeBeforeRemark) {
4175 CMSHeap* heap = CMSHeap::heap();
4176 // Temporarily set flag to false, GCH->do_collection will
4177 // expect it to be false and set to true
4178 FlagSetting fl(heap->_is_gc_active, false);
4179
4180 heap->do_collection(true, // full (i.e. force, see below)
4181 false, // !clear_all_soft_refs
4182 0, // size
4183 false, // is_tlab
4184 GenCollectedHeap::YoungGen // type
4185 );
4186 }
4187 FreelistLocker x(this);
4188 MutexLocker y(bitMapLock(),
4189 Mutex::_no_safepoint_check_flag);
4190 checkpointRootsFinalWork();
4191 _cmsGen->cmsSpace()->recalculate_used_stable();
4192 }
4193 verify_work_stacks_empty();
4194 verify_overflow_empty();
4195 }
4196
4197 void CMSCollector::checkpointRootsFinalWork() {
4198 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4199
4200 assert(haveFreelistLocks(), "must have free list locks");
4201 assert_lock_strong(bitMapLock());
4202
4203 ResourceMark rm;
4204 HandleMark hm;
4205
4206 CMSHeap* heap = CMSHeap::heap();
4207
4208 assert(haveFreelistLocks(), "must have free list locks");
4209 assert_lock_strong(bitMapLock());
4210
4211 // We might assume that we need not fill TLAB's when
4212 // CMSScavengeBeforeRemark is set, because we may have just done
4213 // a scavenge which would have filled all TLAB's -- and besides
4214 // Eden would be empty. This however may not always be the case --
4215 // for instance although we asked for a scavenge, it may not have
4216 // happened because of a JNI critical section. We probably need
4217 // a policy for deciding whether we can in that case wait until
4218 // the critical section releases and then do the remark following
4219 // the scavenge, and skip it here. In the absence of that policy,
4220 // or of an indication of whether the scavenge did indeed occur,
4221 // we cannot rely on TLAB's having been filled and must do
4222 // so here just in case a scavenge did not happen.
4223 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4224 // Update the saved marks which may affect the root scans.
4225 heap->save_marks();
4226
4227 print_eden_and_survivor_chunk_arrays();
4228
4229 {
4230 #if COMPILER2_OR_JVMCI
4231 DerivedPointerTableDeactivate dpt_deact;
4232 #endif
4233
4234 // Note on the role of the mod union table:
4235 // Since the marker in "markFromRoots" marks concurrently with
4236 // mutators, it is possible for some reachable objects not to have been
4237 // scanned. For instance, an only reference to an object A was
4238 // placed in object B after the marker scanned B. Unless B is rescanned,
4239 // A would be collected. Such updates to references in marked objects
4240 // are detected via the mod union table which is the set of all cards
4241 // dirtied since the first checkpoint in this GC cycle and prior to
4242 // the most recent young generation GC, minus those cleaned up by the
4243 // concurrent precleaning.
4244 if (CMSParallelRemarkEnabled) {
4245 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4246 do_remark_parallel();
4247 } else {
4248 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4249 do_remark_non_parallel();
4250 }
4251 }
4252 verify_work_stacks_empty();
4253 verify_overflow_empty();
4254
4255 {
4256 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4257 refProcessingWork();
4258 }
4259 verify_work_stacks_empty();
4260 verify_overflow_empty();
4261
4262 if (should_unload_classes()) {
4263 heap->prune_scavengable_nmethods();
4264 }
4265 JvmtiExport::gc_epilogue();
4266
4267 // If we encountered any (marking stack / work queue) overflow
4268 // events during the current CMS cycle, take appropriate
4269 // remedial measures, where possible, so as to try and avoid
4270 // recurrence of that condition.
4271 assert(_markStack.isEmpty(), "No grey objects");
4272 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4273 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4274 if (ser_ovflw > 0) {
4275 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4276 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4277 _markStack.expand();
4278 _ser_pmc_remark_ovflw = 0;
4279 _ser_pmc_preclean_ovflw = 0;
4280 _ser_kac_preclean_ovflw = 0;
4281 _ser_kac_ovflw = 0;
4282 }
4283 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4284 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4285 _par_pmc_remark_ovflw, _par_kac_ovflw);
4286 _par_pmc_remark_ovflw = 0;
4287 _par_kac_ovflw = 0;
4288 }
4289 if (_markStack._hit_limit > 0) {
4290 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4291 _markStack._hit_limit);
4292 }
4293 if (_markStack._failed_double > 0) {
4294 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4295 _markStack._failed_double, _markStack.capacity());
4296 }
4297 _markStack._hit_limit = 0;
4298 _markStack._failed_double = 0;
4299
4300 if ((VerifyAfterGC || VerifyDuringGC) &&
4301 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4302 verify_after_remark();
4303 }
4304
4305 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4306
4307 // Change under the freelistLocks.
4308 _collectorState = Sweeping;
4309 // Call isAllClear() under bitMapLock
4310 assert(_modUnionTable.isAllClear(),
4311 "Should be clear by end of the final marking");
4312 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4313 "Should be clear by end of the final marking");
4314 }
4315
4316 void CMSParInitialMarkTask::work(uint worker_id) {
4317 elapsedTimer _timer;
4318 ResourceMark rm;
4319 HandleMark hm;
4320
4321 // ---------- scan from roots --------------
4322 _timer.start();
4323 CMSHeap* heap = CMSHeap::heap();
4324 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4325
4326 // ---------- young gen roots --------------
4327 {
4328 work_on_young_gen_roots(&par_mri_cl);
4329 _timer.stop();
4330 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4331 }
4332
4333 // ---------- remaining roots --------------
4334 _timer.reset();
4335 _timer.start();
4336
4337 CLDToOopClosure cld_closure(&par_mri_cl, ClassLoaderData::_claim_strong);
4338
4339 heap->cms_process_roots(_strong_roots_scope,
4340 false, // yg was scanned above
4341 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4342 _collector->should_unload_classes(),
4343 &par_mri_cl,
4344 &cld_closure);
4345
4346 assert(_collector->should_unload_classes()
4347 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4348 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4349 _timer.stop();
4350 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4351 }
4352
4353 // Parallel remark task
4354 class CMSParRemarkTask: public CMSParMarkTask {
4355 CompactibleFreeListSpace* _cms_space;
4356
4357 // The per-thread work queues, available here for stealing.
4358 OopTaskQueueSet* _task_queues;
4359 TaskTerminator _term;
4360 StrongRootsScope* _strong_roots_scope;
4361
4362 public:
4363 // A value of 0 passed to n_workers will cause the number of
4364 // workers to be taken from the active workers in the work gang.
4365 CMSParRemarkTask(CMSCollector* collector,
4366 CompactibleFreeListSpace* cms_space,
4367 uint n_workers, WorkGang* workers,
4368 OopTaskQueueSet* task_queues,
4369 StrongRootsScope* strong_roots_scope):
4370 CMSParMarkTask("Rescan roots and grey objects in parallel",
4371 collector, n_workers),
4372 _cms_space(cms_space),
4373 _task_queues(task_queues),
4374 _term(n_workers, task_queues),
4375 _strong_roots_scope(strong_roots_scope) { }
4376
4377 OopTaskQueueSet* task_queues() { return _task_queues; }
4378
4379 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4380
4381 ParallelTaskTerminator* terminator() { return _term.terminator(); }
4382 uint n_workers() { return _n_workers; }
4383
4384 void work(uint worker_id);
4385
4386 private:
4387 // ... of dirty cards in old space
4388 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4389 ParMarkRefsIntoAndScanClosure* cl);
4390
4391 // ... work stealing for the above
4392 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl);
4393 };
4394
4395 class RemarkCLDClosure : public CLDClosure {
4396 CLDToOopClosure _cm_closure;
4397 public:
4398 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure, ClassLoaderData::_claim_strong) {}
4399 void do_cld(ClassLoaderData* cld) {
4400 // Check if we have modified any oops in the CLD during the concurrent marking.
4401 if (cld->has_accumulated_modified_oops()) {
4402 cld->clear_accumulated_modified_oops();
4403
4404 // We could have transfered the current modified marks to the accumulated marks,
4405 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4406 } else if (cld->has_modified_oops()) {
4407 // Don't clear anything, this info is needed by the next young collection.
4408 } else {
4409 // No modified oops in the ClassLoaderData.
4410 return;
4411 }
4412
4413 // The klass has modified fields, need to scan the klass.
4414 _cm_closure.do_cld(cld);
4415 }
4416 };
4417
4418 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4419 ParNewGeneration* young_gen = _collector->_young_gen;
4420 ContiguousSpace* eden_space = young_gen->eden();
4421 ContiguousSpace* from_space = young_gen->from();
4422 ContiguousSpace* to_space = young_gen->to();
4423
4424 HeapWord** eca = _collector->_eden_chunk_array;
4425 size_t ect = _collector->_eden_chunk_index;
4426 HeapWord** sca = _collector->_survivor_chunk_array;
4427 size_t sct = _collector->_survivor_chunk_index;
4428
4429 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4430 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4431
4432 do_young_space_rescan(cl, to_space, NULL, 0);
4433 do_young_space_rescan(cl, from_space, sca, sct);
4434 do_young_space_rescan(cl, eden_space, eca, ect);
4435 }
4436
4437 // work_queue(i) is passed to the closure
4438 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4439 // also is passed to do_dirty_card_rescan_tasks() and to
4440 // do_work_steal() to select the i-th task_queue.
4441
4442 void CMSParRemarkTask::work(uint worker_id) {
4443 elapsedTimer _timer;
4444 ResourceMark rm;
4445 HandleMark hm;
4446
4447 // ---------- rescan from roots --------------
4448 _timer.start();
4449 CMSHeap* heap = CMSHeap::heap();
4450 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4451 _collector->_span, _collector->ref_processor(),
4452 &(_collector->_markBitMap),
4453 work_queue(worker_id));
4454
4455 // Rescan young gen roots first since these are likely
4456 // coarsely partitioned and may, on that account, constitute
4457 // the critical path; thus, it's best to start off that
4458 // work first.
4459 // ---------- young gen roots --------------
4460 {
4461 work_on_young_gen_roots(&par_mrias_cl);
4462 _timer.stop();
4463 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4464 }
4465
4466 // ---------- remaining roots --------------
4467 _timer.reset();
4468 _timer.start();
4469 heap->cms_process_roots(_strong_roots_scope,
4470 false, // yg was scanned above
4471 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4472 _collector->should_unload_classes(),
4473 &par_mrias_cl,
4474 NULL); // The dirty klasses will be handled below
4475
4476 assert(_collector->should_unload_classes()
4477 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4478 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4479 _timer.stop();
4480 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4481
4482 // ---------- unhandled CLD scanning ----------
4483 if (worker_id == 0) { // Single threaded at the moment.
4484 _timer.reset();
4485 _timer.start();
4486
4487 // Scan all new class loader data objects and new dependencies that were
4488 // introduced during concurrent marking.
4489 ResourceMark rm;
4490 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4491 for (int i = 0; i < array->length(); i++) {
4492 Devirtualizer::do_cld(&par_mrias_cl, array->at(i));
4493 }
4494
4495 // We don't need to keep track of new CLDs anymore.
4496 ClassLoaderDataGraph::remember_new_clds(false);
4497
4498 _timer.stop();
4499 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4500 }
4501
4502 // We might have added oops to ClassLoaderData::_handles during the
4503 // concurrent marking phase. These oops do not always point to newly allocated objects
4504 // that are guaranteed to be kept alive. Hence,
4505 // we do have to revisit the _handles block during the remark phase.
4506
4507 // ---------- dirty CLD scanning ----------
4508 if (worker_id == 0) { // Single threaded at the moment.
4509 _timer.reset();
4510 _timer.start();
4511
4512 // Scan all classes that was dirtied during the concurrent marking phase.
4513 RemarkCLDClosure remark_closure(&par_mrias_cl);
4514 ClassLoaderDataGraph::cld_do(&remark_closure);
4515
4516 _timer.stop();
4517 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4518 }
4519
4520
4521 // ---------- rescan dirty cards ------------
4522 _timer.reset();
4523 _timer.start();
4524
4525 // Do the rescan tasks for each of the two spaces
4526 // (cms_space) in turn.
4527 // "worker_id" is passed to select the task_queue for "worker_id"
4528 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4529 _timer.stop();
4530 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4531
4532 // ---------- steal work from other threads ...
4533 // ---------- ... and drain overflow list.
4534 _timer.reset();
4535 _timer.start();
4536 do_work_steal(worker_id, &par_mrias_cl);
4537 _timer.stop();
4538 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4539 }
4540
4541 void
4542 CMSParMarkTask::do_young_space_rescan(
4543 OopsInGenClosure* cl, ContiguousSpace* space,
4544 HeapWord** chunk_array, size_t chunk_top) {
4545 // Until all tasks completed:
4546 // . claim an unclaimed task
4547 // . compute region boundaries corresponding to task claimed
4548 // using chunk_array
4549 // . par_oop_iterate(cl) over that region
4550
4551 ResourceMark rm;
4552 HandleMark hm;
4553
4554 SequentialSubTasksDone* pst = space->par_seq_tasks();
4555
4556 uint nth_task = 0;
4557 uint n_tasks = pst->n_tasks();
4558
4559 if (n_tasks > 0) {
4560 assert(pst->valid(), "Uninitialized use?");
4561 HeapWord *start, *end;
4562 while (pst->try_claim_task(/* reference */ nth_task)) {
4563 // We claimed task # nth_task; compute its boundaries.
4564 if (chunk_top == 0) { // no samples were taken
4565 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4566 start = space->bottom();
4567 end = space->top();
4568 } else if (nth_task == 0) {
4569 start = space->bottom();
4570 end = chunk_array[nth_task];
4571 } else if (nth_task < (uint)chunk_top) {
4572 assert(nth_task >= 1, "Control point invariant");
4573 start = chunk_array[nth_task - 1];
4574 end = chunk_array[nth_task];
4575 } else {
4576 assert(nth_task == (uint)chunk_top, "Control point invariant");
4577 start = chunk_array[chunk_top - 1];
4578 end = space->top();
4579 }
4580 MemRegion mr(start, end);
4581 // Verify that mr is in space
4582 assert(mr.is_empty() || space->used_region().contains(mr),
4583 "Should be in space");
4584 // Verify that "start" is an object boundary
4585 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4586 "Should be an oop");
4587 space->par_oop_iterate(mr, cl);
4588 }
4589 pst->all_tasks_completed();
4590 }
4591 }
4592
4593 void
4594 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4595 CompactibleFreeListSpace* sp, int i,
4596 ParMarkRefsIntoAndScanClosure* cl) {
4597 // Until all tasks completed:
4598 // . claim an unclaimed task
4599 // . compute region boundaries corresponding to task claimed
4600 // . transfer dirty bits ct->mut for that region
4601 // . apply rescanclosure to dirty mut bits for that region
4602
4603 ResourceMark rm;
4604 HandleMark hm;
4605
4606 OopTaskQueue* work_q = work_queue(i);
4607 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4608 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4609 // CAUTION: This closure has state that persists across calls to
4610 // the work method dirty_range_iterate_clear() in that it has
4611 // embedded in it a (subtype of) UpwardsObjectClosure. The
4612 // use of that state in the embedded UpwardsObjectClosure instance
4613 // assumes that the cards are always iterated (even if in parallel
4614 // by several threads) in monotonically increasing order per each
4615 // thread. This is true of the implementation below which picks
4616 // card ranges (chunks) in monotonically increasing order globally
4617 // and, a-fortiori, in monotonically increasing order per thread
4618 // (the latter order being a subsequence of the former).
4619 // If the work code below is ever reorganized into a more chaotic
4620 // work-partitioning form than the current "sequential tasks"
4621 // paradigm, the use of that persistent state will have to be
4622 // revisited and modified appropriately. See also related
4623 // bug 4756801 work on which should examine this code to make
4624 // sure that the changes there do not run counter to the
4625 // assumptions made here and necessary for correctness and
4626 // efficiency. Note also that this code might yield inefficient
4627 // behavior in the case of very large objects that span one or
4628 // more work chunks. Such objects would potentially be scanned
4629 // several times redundantly. Work on 4756801 should try and
4630 // address that performance anomaly if at all possible. XXX
4631 MemRegion full_span = _collector->_span;
4632 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4633 MarkFromDirtyCardsClosure
4634 greyRescanClosure(_collector, full_span, // entire span of interest
4635 sp, bm, work_q, cl);
4636
4637 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4638 assert(pst->valid(), "Uninitialized use?");
4639 uint nth_task = 0;
4640 const int alignment = CardTable::card_size * BitsPerWord;
4641 MemRegion span = sp->used_region();
4642 HeapWord* start_addr = span.start();
4643 HeapWord* end_addr = align_up(span.end(), alignment);
4644 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4645 assert(is_aligned(start_addr, alignment), "Check alignment");
4646 assert(is_aligned(chunk_size, alignment), "Check alignment");
4647
4648 while (pst->try_claim_task(/* reference */ nth_task)) {
4649 // Having claimed the nth_task, compute corresponding mem-region,
4650 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4651 // The alignment restriction ensures that we do not need any
4652 // synchronization with other gang-workers while setting or
4653 // clearing bits in thus chunk of the MUT.
4654 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4655 start_addr + (nth_task+1)*chunk_size);
4656 // The last chunk's end might be way beyond end of the
4657 // used region. In that case pull back appropriately.
4658 if (this_span.end() > end_addr) {
4659 this_span.set_end(end_addr);
4660 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4661 }
4662 // Iterate over the dirty cards covering this chunk, marking them
4663 // precleaned, and setting the corresponding bits in the mod union
4664 // table. Since we have been careful to partition at Card and MUT-word
4665 // boundaries no synchronization is needed between parallel threads.
4666 _collector->_ct->dirty_card_iterate(this_span,
4667 &modUnionClosure);
4668
4669 // Having transferred these marks into the modUnionTable,
4670 // rescan the marked objects on the dirty cards in the modUnionTable.
4671 // Even if this is at a synchronous collection, the initial marking
4672 // may have been done during an asynchronous collection so there
4673 // may be dirty bits in the mod-union table.
4674 _collector->_modUnionTable.dirty_range_iterate_clear(
4675 this_span, &greyRescanClosure);
4676 _collector->_modUnionTable.verifyNoOneBitsInRange(
4677 this_span.start(),
4678 this_span.end());
4679 }
4680 pst->all_tasks_completed(); // declare that i am done
4681 }
4682
4683 // . see if we can share work_queues with ParNew? XXX
4684 void
4685 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl) {
4686 OopTaskQueue* work_q = work_queue(i);
4687 NOT_PRODUCT(int num_steals = 0;)
4688 oop obj_to_scan;
4689 CMSBitMap* bm = &(_collector->_markBitMap);
4690
4691 while (true) {
4692 // Completely finish any left over work from (an) earlier round(s)
4693 cl->trim_queue(0);
4694 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4695 (size_t)ParGCDesiredObjsFromOverflowList);
4696 // Now check if there's any work in the overflow list
4697 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4698 // only affects the number of attempts made to get work from the
4699 // overflow list and does not affect the number of workers. Just
4700 // pass ParallelGCThreads so this behavior is unchanged.
4701 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4702 work_q,
4703 ParallelGCThreads)) {
4704 // found something in global overflow list;
4705 // not yet ready to go stealing work from others.
4706 // We'd like to assert(work_q->size() != 0, ...)
4707 // because we just took work from the overflow list,
4708 // but of course we can't since all of that could have
4709 // been already stolen from us.
4710 // "He giveth and He taketh away."
4711 continue;
4712 }
4713 // Verify that we have no work before we resort to stealing
4714 assert(work_q->size() == 0, "Have work, shouldn't steal");
4715 // Try to steal from other queues that have work
4716 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
4717 NOT_PRODUCT(num_steals++;)
4718 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4719 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4720 // Do scanning work
4721 obj_to_scan->oop_iterate(cl);
4722 // Loop around, finish this work, and try to steal some more
4723 } else if (terminator()->offer_termination()) {
4724 break; // nirvana from the infinite cycle
4725 }
4726 }
4727 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4728 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4729 "Else our work is not yet done");
4730 }
4731
4732 // Record object boundaries in _eden_chunk_array by sampling the eden
4733 // top in the slow-path eden object allocation code path and record
4734 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4735 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4736 // sampling in sample_eden() that activates during the part of the
4737 // preclean phase.
4738 void CMSCollector::sample_eden_chunk() {
4739 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4740 if (_eden_chunk_lock->try_lock()) {
4741 // Record a sample. This is the critical section. The contents
4742 // of the _eden_chunk_array have to be non-decreasing in the
4743 // address order.
4744 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4745 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4746 "Unexpected state of Eden");
4747 if (_eden_chunk_index == 0 ||
4748 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4749 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4750 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4751 _eden_chunk_index++; // commit sample
4752 }
4753 _eden_chunk_lock->unlock();
4754 }
4755 }
4756 }
4757
4758 // Return a thread-local PLAB recording array, as appropriate.
4759 void* CMSCollector::get_data_recorder(int thr_num) {
4760 if (_survivor_plab_array != NULL &&
4761 (CMSPLABRecordAlways ||
4762 (_collectorState > Marking && _collectorState < FinalMarking))) {
4763 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4764 ChunkArray* ca = &_survivor_plab_array[thr_num];
4765 ca->reset(); // clear it so that fresh data is recorded
4766 return (void*) ca;
4767 } else {
4768 return NULL;
4769 }
4770 }
4771
4772 // Reset all the thread-local PLAB recording arrays
4773 void CMSCollector::reset_survivor_plab_arrays() {
4774 for (uint i = 0; i < ParallelGCThreads; i++) {
4775 _survivor_plab_array[i].reset();
4776 }
4777 }
4778
4779 // Merge the per-thread plab arrays into the global survivor chunk
4780 // array which will provide the partitioning of the survivor space
4781 // for CMS initial scan and rescan.
4782 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4783 int no_of_gc_threads) {
4784 assert(_survivor_plab_array != NULL, "Error");
4785 assert(_survivor_chunk_array != NULL, "Error");
4786 assert(_collectorState == FinalMarking ||
4787 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4788 for (int j = 0; j < no_of_gc_threads; j++) {
4789 _cursor[j] = 0;
4790 }
4791 HeapWord* top = surv->top();
4792 size_t i;
4793 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4794 HeapWord* min_val = top; // Higher than any PLAB address
4795 uint min_tid = 0; // position of min_val this round
4796 for (int j = 0; j < no_of_gc_threads; j++) {
4797 ChunkArray* cur_sca = &_survivor_plab_array[j];
4798 if (_cursor[j] == cur_sca->end()) {
4799 continue;
4800 }
4801 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4802 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4803 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4804 if (cur_val < min_val) {
4805 min_tid = j;
4806 min_val = cur_val;
4807 } else {
4808 assert(cur_val < top, "All recorded addresses should be less");
4809 }
4810 }
4811 // At this point min_val and min_tid are respectively
4812 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4813 // and the thread (j) that witnesses that address.
4814 // We record this address in the _survivor_chunk_array[i]
4815 // and increment _cursor[min_tid] prior to the next round i.
4816 if (min_val == top) {
4817 break;
4818 }
4819 _survivor_chunk_array[i] = min_val;
4820 _cursor[min_tid]++;
4821 }
4822 // We are all done; record the size of the _survivor_chunk_array
4823 _survivor_chunk_index = i; // exclusive: [0, i)
4824 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4825 // Verify that we used up all the recorded entries
4826 #ifdef ASSERT
4827 size_t total = 0;
4828 for (int j = 0; j < no_of_gc_threads; j++) {
4829 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4830 total += _cursor[j];
4831 }
4832 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4833 // Check that the merged array is in sorted order
4834 if (total > 0) {
4835 for (size_t i = 0; i < total - 1; i++) {
4836 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4837 i, p2i(_survivor_chunk_array[i]));
4838 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4839 "Not sorted");
4840 }
4841 }
4842 #endif // ASSERT
4843 }
4844
4845 // Set up the space's par_seq_tasks structure for work claiming
4846 // for parallel initial scan and rescan of young gen.
4847 // See ParRescanTask where this is currently used.
4848 void
4849 CMSCollector::
4850 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4851 assert(n_threads > 0, "Unexpected n_threads argument");
4852
4853 // Eden space
4854 if (!_young_gen->eden()->is_empty()) {
4855 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4856 assert(!pst->valid(), "Clobbering existing data?");
4857 // Each valid entry in [0, _eden_chunk_index) represents a task.
4858 size_t n_tasks = _eden_chunk_index + 1;
4859 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4860 // Sets the condition for completion of the subtask (how many threads
4861 // need to finish in order to be done).
4862 pst->set_n_threads(n_threads);
4863 pst->set_n_tasks((int)n_tasks);
4864 }
4865
4866 // Merge the survivor plab arrays into _survivor_chunk_array
4867 if (_survivor_plab_array != NULL) {
4868 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4869 } else {
4870 assert(_survivor_chunk_index == 0, "Error");
4871 }
4872
4873 // To space
4874 {
4875 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4876 assert(!pst->valid(), "Clobbering existing data?");
4877 // Sets the condition for completion of the subtask (how many threads
4878 // need to finish in order to be done).
4879 pst->set_n_threads(n_threads);
4880 pst->set_n_tasks(1);
4881 assert(pst->valid(), "Error");
4882 }
4883
4884 // From space
4885 {
4886 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4887 assert(!pst->valid(), "Clobbering existing data?");
4888 size_t n_tasks = _survivor_chunk_index + 1;
4889 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4890 // Sets the condition for completion of the subtask (how many threads
4891 // need to finish in order to be done).
4892 pst->set_n_threads(n_threads);
4893 pst->set_n_tasks((int)n_tasks);
4894 assert(pst->valid(), "Error");
4895 }
4896 }
4897
4898 // Parallel version of remark
4899 void CMSCollector::do_remark_parallel() {
4900 CMSHeap* heap = CMSHeap::heap();
4901 WorkGang* workers = heap->workers();
4902 assert(workers != NULL, "Need parallel worker threads.");
4903 // Choose to use the number of GC workers most recently set
4904 // into "active_workers".
4905 uint n_workers = workers->active_workers();
4906
4907 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4908
4909 StrongRootsScope srs(n_workers);
4910
4911 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4912
4913 // We won't be iterating over the cards in the card table updating
4914 // the younger_gen cards, so we shouldn't call the following else
4915 // the verification code as well as subsequent younger_refs_iterate
4916 // code would get confused. XXX
4917 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4918
4919 // The young gen rescan work will not be done as part of
4920 // process_roots (which currently doesn't know how to
4921 // parallelize such a scan), but rather will be broken up into
4922 // a set of parallel tasks (via the sampling that the [abortable]
4923 // preclean phase did of eden, plus the [two] tasks of
4924 // scanning the [two] survivor spaces. Further fine-grain
4925 // parallelization of the scanning of the survivor spaces
4926 // themselves, and of precleaning of the young gen itself
4927 // is deferred to the future.
4928 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4929
4930 // The dirty card rescan work is broken up into a "sequence"
4931 // of parallel tasks (per constituent space) that are dynamically
4932 // claimed by the parallel threads.
4933 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4934
4935 // It turns out that even when we're using 1 thread, doing the work in a
4936 // separate thread causes wide variance in run times. We can't help this
4937 // in the multi-threaded case, but we special-case n=1 here to get
4938 // repeatable measurements of the 1-thread overhead of the parallel code.
4939 if (n_workers > 1) {
4940 // Make refs discovery MT-safe, if it isn't already: it may not
4941 // necessarily be so, since it's possible that we are doing
4942 // ST marking.
4943 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4944 workers->run_task(&tsk);
4945 } else {
4946 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4947 tsk.work(0);
4948 }
4949
4950 // restore, single-threaded for now, any preserved marks
4951 // as a result of work_q overflow
4952 restore_preserved_marks_if_any();
4953 }
4954
4955 // Non-parallel version of remark
4956 void CMSCollector::do_remark_non_parallel() {
4957 ResourceMark rm;
4958 HandleMark hm;
4959 CMSHeap* heap = CMSHeap::heap();
4960 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4961
4962 MarkRefsIntoAndScanClosure
4963 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4964 &_markStack, this,
4965 false /* should_yield */, false /* not precleaning */);
4966 MarkFromDirtyCardsClosure
4967 markFromDirtyCardsClosure(this, _span,
4968 NULL, // space is set further below
4969 &_markBitMap, &_markStack, &mrias_cl);
4970 {
4971 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4972 // Iterate over the dirty cards, setting the corresponding bits in the
4973 // mod union table.
4974 {
4975 ModUnionClosure modUnionClosure(&_modUnionTable);
4976 _ct->dirty_card_iterate(_cmsGen->used_region(),
4977 &modUnionClosure);
4978 }
4979 // Having transferred these marks into the modUnionTable, we just need
4980 // to rescan the marked objects on the dirty cards in the modUnionTable.
4981 // The initial marking may have been done during an asynchronous
4982 // collection so there may be dirty bits in the mod-union table.
4983 const int alignment = CardTable::card_size * BitsPerWord;
4984 {
4985 // ... First handle dirty cards in CMS gen
4986 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4987 MemRegion ur = _cmsGen->used_region();
4988 HeapWord* lb = ur.start();
4989 HeapWord* ub = align_up(ur.end(), alignment);
4990 MemRegion cms_span(lb, ub);
4991 _modUnionTable.dirty_range_iterate_clear(cms_span,
4992 &markFromDirtyCardsClosure);
4993 verify_work_stacks_empty();
4994 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4995 }
4996 }
4997 if (VerifyDuringGC &&
4998 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4999 HandleMark hm; // Discard invalid handles created during verification
5000 Universe::verify();
5001 }
5002 {
5003 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
5004
5005 verify_work_stacks_empty();
5006
5007 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5008 StrongRootsScope srs(1);
5009
5010 heap->cms_process_roots(&srs,
5011 true, // young gen as roots
5012 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5013 should_unload_classes(),
5014 &mrias_cl,
5015 NULL); // The dirty klasses will be handled below
5016
5017 assert(should_unload_classes()
5018 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5019 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5020 }
5021
5022 {
5023 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
5024
5025 verify_work_stacks_empty();
5026
5027 // Scan all class loader data objects that might have been introduced
5028 // during concurrent marking.
5029 ResourceMark rm;
5030 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5031 for (int i = 0; i < array->length(); i++) {
5032 Devirtualizer::do_cld(&mrias_cl, array->at(i));
5033 }
5034
5035 // We don't need to keep track of new CLDs anymore.
5036 ClassLoaderDataGraph::remember_new_clds(false);
5037
5038 verify_work_stacks_empty();
5039 }
5040
5041 // We might have added oops to ClassLoaderData::_handles during the
5042 // concurrent marking phase. These oops do not point to newly allocated objects
5043 // that are guaranteed to be kept alive. Hence,
5044 // we do have to revisit the _handles block during the remark phase.
5045 {
5046 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
5047
5048 verify_work_stacks_empty();
5049
5050 RemarkCLDClosure remark_closure(&mrias_cl);
5051 ClassLoaderDataGraph::cld_do(&remark_closure);
5052
5053 verify_work_stacks_empty();
5054 }
5055
5056 verify_work_stacks_empty();
5057 // Restore evacuated mark words, if any, used for overflow list links
5058 restore_preserved_marks_if_any();
5059
5060 verify_overflow_empty();
5061 }
5062
5063 ////////////////////////////////////////////////////////
5064 // Parallel Reference Processing Task Proxy Class
5065 ////////////////////////////////////////////////////////
5066 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5067 OopTaskQueueSet* _queues;
5068 TaskTerminator _terminator;
5069 public:
5070 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5071 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5072 ParallelTaskTerminator* terminator() { return _terminator.terminator(); }
5073 OopTaskQueueSet* queues() { return _queues; }
5074 };
5075
5076 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5077 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5078 CMSCollector* _collector;
5079 CMSBitMap* _mark_bit_map;
5080 const MemRegion _span;
5081 ProcessTask& _task;
5082
5083 public:
5084 CMSRefProcTaskProxy(ProcessTask& task,
5085 CMSCollector* collector,
5086 const MemRegion& span,
5087 CMSBitMap* mark_bit_map,
5088 AbstractWorkGang* workers,
5089 OopTaskQueueSet* task_queues):
5090 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5091 task_queues,
5092 workers->active_workers()),
5093 _collector(collector),
5094 _mark_bit_map(mark_bit_map),
5095 _span(span),
5096 _task(task)
5097 {
5098 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5099 "Inconsistency in _span");
5100 }
5101
5102 OopTaskQueueSet* task_queues() { return queues(); }
5103
5104 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5105
5106 void do_work_steal(int i,
5107 CMSParDrainMarkingStackClosure* drain,
5108 CMSParKeepAliveClosure* keep_alive);
5109
5110 virtual void work(uint worker_id);
5111 };
5112
5113 void CMSRefProcTaskProxy::work(uint worker_id) {
5114 ResourceMark rm;
5115 HandleMark hm;
5116 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5117 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5118 _mark_bit_map,
5119 work_queue(worker_id));
5120 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5121 _mark_bit_map,
5122 work_queue(worker_id));
5123 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5124 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5125 if (_task.marks_oops_alive()) {
5126 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive);
5127 }
5128 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5129 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5130 }
5131
5132 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5133 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5134 _span(span),
5135 _work_queue(work_queue),
5136 _bit_map(bit_map),
5137 _mark_and_push(collector, span, bit_map, work_queue),
5138 _low_water_mark(MIN2((work_queue->max_elems()/4),
5139 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5140 { }
5141
5142 // . see if we can share work_queues with ParNew? XXX
5143 void CMSRefProcTaskProxy::do_work_steal(int i,
5144 CMSParDrainMarkingStackClosure* drain,
5145 CMSParKeepAliveClosure* keep_alive) {
5146 OopTaskQueue* work_q = work_queue(i);
5147 NOT_PRODUCT(int num_steals = 0;)
5148 oop obj_to_scan;
5149
5150 while (true) {
5151 // Completely finish any left over work from (an) earlier round(s)
5152 drain->trim_queue(0);
5153 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5154 (size_t)ParGCDesiredObjsFromOverflowList);
5155 // Now check if there's any work in the overflow list
5156 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5157 // only affects the number of attempts made to get work from the
5158 // overflow list and does not affect the number of workers. Just
5159 // pass ParallelGCThreads so this behavior is unchanged.
5160 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5161 work_q,
5162 ParallelGCThreads)) {
5163 // Found something in global overflow list;
5164 // not yet ready to go stealing work from others.
5165 // We'd like to assert(work_q->size() != 0, ...)
5166 // because we just took work from the overflow list,
5167 // but of course we can't, since all of that might have
5168 // been already stolen from us.
5169 continue;
5170 }
5171 // Verify that we have no work before we resort to stealing
5172 assert(work_q->size() == 0, "Have work, shouldn't steal");
5173 // Try to steal from other queues that have work
5174 if (task_queues()->steal(i, /* reference */ obj_to_scan)) {
5175 NOT_PRODUCT(num_steals++;)
5176 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5177 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5178 // Do scanning work
5179 obj_to_scan->oop_iterate(keep_alive);
5180 // Loop around, finish this work, and try to steal some more
5181 } else if (terminator()->offer_termination()) {
5182 break; // nirvana from the infinite cycle
5183 }
5184 }
5185 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5186 }
5187
5188 void CMSRefProcTaskExecutor::execute(ProcessTask& task, uint ergo_workers) {
5189 CMSHeap* heap = CMSHeap::heap();
5190 WorkGang* workers = heap->workers();
5191 assert(workers != NULL, "Need parallel worker threads.");
5192 assert(workers->active_workers() == ergo_workers,
5193 "Ergonomically chosen workers (%u) must be equal to active workers (%u)",
5194 ergo_workers, workers->active_workers());
5195 CMSRefProcTaskProxy rp_task(task, &_collector,
5196 _collector.ref_processor_span(),
5197 _collector.markBitMap(),
5198 workers, _collector.task_queues());
5199 workers->run_task(&rp_task, workers->active_workers());
5200 }
5201
5202 void CMSCollector::refProcessingWork() {
5203 ResourceMark rm;
5204 HandleMark hm;
5205
5206 ReferenceProcessor* rp = ref_processor();
5207 assert(_span_based_discoverer.span().equals(_span), "Spans should be equal");
5208 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5209 // Process weak references.
5210 rp->setup_policy(false);
5211 verify_work_stacks_empty();
5212
5213 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->max_num_queues());
5214 {
5215 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5216
5217 // Setup keep_alive and complete closures.
5218 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5219 &_markStack, false /* !preclean */);
5220 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5221 _span, &_markBitMap, &_markStack,
5222 &cmsKeepAliveClosure, false /* !preclean */);
5223
5224 ReferenceProcessorStats stats;
5225 if (rp->processing_is_mt()) {
5226 // Set the degree of MT here. If the discovery is done MT, there
5227 // may have been a different number of threads doing the discovery
5228 // and a different number of discovered lists may have Ref objects.
5229 // That is OK as long as the Reference lists are balanced (see
5230 // balance_all_queues() and balance_queues()).
5231 CMSHeap* heap = CMSHeap::heap();
5232 uint active_workers = ParallelGCThreads;
5233 WorkGang* workers = heap->workers();
5234 if (workers != NULL) {
5235 active_workers = workers->active_workers();
5236 // The expectation is that active_workers will have already
5237 // been set to a reasonable value. If it has not been set,
5238 // investigate.
5239 assert(active_workers > 0, "Should have been set during scavenge");
5240 }
5241 rp->set_active_mt_degree(active_workers);
5242 CMSRefProcTaskExecutor task_executor(*this);
5243 stats = rp->process_discovered_references(&_is_alive_closure,
5244 &cmsKeepAliveClosure,
5245 &cmsDrainMarkingStackClosure,
5246 &task_executor,
5247 &pt);
5248 } else {
5249 stats = rp->process_discovered_references(&_is_alive_closure,
5250 &cmsKeepAliveClosure,
5251 &cmsDrainMarkingStackClosure,
5252 NULL,
5253 &pt);
5254 }
5255 _gc_tracer_cm->report_gc_reference_stats(stats);
5256 pt.print_all_references();
5257 }
5258
5259 // This is the point where the entire marking should have completed.
5260 verify_work_stacks_empty();
5261
5262 {
5263 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5264 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5265 }
5266
5267 if (should_unload_classes()) {
5268 {
5269 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5270
5271 // Unload classes and purge the SystemDictionary.
5272 bool purged_class = SystemDictionary::do_unloading(_gc_timer_cm);
5273
5274 // Unload nmethods.
5275 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5276
5277 // Prune dead klasses from subklass/sibling/implementor lists.
5278 Klass::clean_weak_klass_links(purged_class);
5279
5280 // Clean JVMCI metadata handles.
5281 JVMCI_ONLY(JVMCI::do_unloading(purged_class));
5282 }
5283 }
5284
5285 // Restore any preserved marks as a result of mark stack or
5286 // work queue overflow
5287 restore_preserved_marks_if_any(); // done single-threaded for now
5288
5289 rp->set_enqueuing_is_done(true);
5290 rp->verify_no_references_recorded();
5291 }
5292
5293 #ifndef PRODUCT
5294 void CMSCollector::check_correct_thread_executing() {
5295 Thread* t = Thread::current();
5296 // Only the VM thread or the CMS thread should be here.
5297 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5298 "Unexpected thread type");
5299 // If this is the vm thread, the foreground process
5300 // should not be waiting. Note that _foregroundGCIsActive is
5301 // true while the foreground collector is waiting.
5302 if (_foregroundGCShouldWait) {
5303 // We cannot be the VM thread
5304 assert(t->is_ConcurrentGC_thread(),
5305 "Should be CMS thread");
5306 } else {
5307 // We can be the CMS thread only if we are in a stop-world
5308 // phase of CMS collection.
5309 if (t->is_ConcurrentGC_thread()) {
5310 assert(_collectorState == InitialMarking ||
5311 _collectorState == FinalMarking,
5312 "Should be a stop-world phase");
5313 // The CMS thread should be holding the CMS_token.
5314 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5315 "Potential interference with concurrently "
5316 "executing VM thread");
5317 }
5318 }
5319 }
5320 #endif
5321
5322 void CMSCollector::sweep() {
5323 assert(_collectorState == Sweeping, "just checking");
5324 check_correct_thread_executing();
5325 verify_work_stacks_empty();
5326 verify_overflow_empty();
5327 increment_sweep_count();
5328 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5329
5330 _inter_sweep_timer.stop();
5331 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5332
5333 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5334 _intra_sweep_timer.reset();
5335 _intra_sweep_timer.start();
5336 {
5337 GCTraceCPUTime tcpu;
5338 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5339 // First sweep the old gen
5340 {
5341 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5342 bitMapLock());
5343 sweepWork(_cmsGen);
5344 }
5345
5346 // Update Universe::_heap_*_at_gc figures.
5347 // We need all the free list locks to make the abstract state
5348 // transition from Sweeping to Resetting. See detailed note
5349 // further below.
5350 {
5351 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5352
5353 // Update heap occupancy information which is used as
5354 // input to soft ref clearing policy at the next gc.
5355 Universe::update_heap_info_at_gc();
5356
5357 // recalculate CMS used space after CMS collection
5358 _cmsGen->cmsSpace()->recalculate_used_stable();
5359
5360 _collectorState = Resizing;
5361 }
5362 }
5363 verify_work_stacks_empty();
5364 verify_overflow_empty();
5365
5366 if (should_unload_classes()) {
5367 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5368 // requires that the virtual spaces are stable and not deleted.
5369 ClassLoaderDataGraph::set_should_purge(true);
5370 }
5371
5372 _intra_sweep_timer.stop();
5373 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5374
5375 _inter_sweep_timer.reset();
5376 _inter_sweep_timer.start();
5377
5378 // We need to use a monotonically non-decreasing time in ms
5379 // or we will see time-warp warnings and os::javaTimeMillis()
5380 // does not guarantee monotonicity.
5381 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5382 update_time_of_last_gc(now);
5383
5384 // NOTE on abstract state transitions:
5385 // Mutators allocate-live and/or mark the mod-union table dirty
5386 // based on the state of the collection. The former is done in
5387 // the interval [Marking, Sweeping] and the latter in the interval
5388 // [Marking, Sweeping). Thus the transitions into the Marking state
5389 // and out of the Sweeping state must be synchronously visible
5390 // globally to the mutators.
5391 // The transition into the Marking state happens with the world
5392 // stopped so the mutators will globally see it. Sweeping is
5393 // done asynchronously by the background collector so the transition
5394 // from the Sweeping state to the Resizing state must be done
5395 // under the freelistLock (as is the check for whether to
5396 // allocate-live and whether to dirty the mod-union table).
5397 assert(_collectorState == Resizing, "Change of collector state to"
5398 " Resizing must be done under the freelistLocks (plural)");
5399
5400 // Now that sweeping has been completed, we clear
5401 // the incremental_collection_failed flag,
5402 // thus inviting a younger gen collection to promote into
5403 // this generation. If such a promotion may still fail,
5404 // the flag will be set again when a young collection is
5405 // attempted.
5406 CMSHeap* heap = CMSHeap::heap();
5407 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5408 heap->update_full_collections_completed(_collection_count_start);
5409 }
5410
5411 // FIX ME!!! Looks like this belongs in CFLSpace, with
5412 // CMSGen merely delegating to it.
5413 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5414 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5415 HeapWord* minAddr = _cmsSpace->bottom();
5416 HeapWord* largestAddr =
5417 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5418 if (largestAddr == NULL) {
5419 // The dictionary appears to be empty. In this case
5420 // try to coalesce at the end of the heap.
5421 largestAddr = _cmsSpace->end();
5422 }
5423 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5424 size_t nearLargestOffset =
5425 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5426 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5427 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5428 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5429 }
5430
5431 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5432 return addr >= _cmsSpace->nearLargestChunk();
5433 }
5434
5435 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5436 return _cmsSpace->find_chunk_at_end();
5437 }
5438
5439 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5440 bool full) {
5441 // If the young generation has been collected, gather any statistics
5442 // that are of interest at this point.
5443 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5444 if (!full && current_is_young) {
5445 // Gather statistics on the young generation collection.
5446 collector()->stats().record_gc0_end(used());
5447 }
5448 _cmsSpace->recalculate_used_stable();
5449 }
5450
5451 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5452 // We iterate over the space(s) underlying this generation,
5453 // checking the mark bit map to see if the bits corresponding
5454 // to specific blocks are marked or not. Blocks that are
5455 // marked are live and are not swept up. All remaining blocks
5456 // are swept up, with coalescing on-the-fly as we sweep up
5457 // contiguous free and/or garbage blocks:
5458 // We need to ensure that the sweeper synchronizes with allocators
5459 // and stop-the-world collectors. In particular, the following
5460 // locks are used:
5461 // . CMS token: if this is held, a stop the world collection cannot occur
5462 // . freelistLock: if this is held no allocation can occur from this
5463 // generation by another thread
5464 // . bitMapLock: if this is held, no other thread can access or update
5465 //
5466
5467 // Note that we need to hold the freelistLock if we use
5468 // block iterate below; else the iterator might go awry if
5469 // a mutator (or promotion) causes block contents to change
5470 // (for instance if the allocator divvies up a block).
5471 // If we hold the free list lock, for all practical purposes
5472 // young generation GC's can't occur (they'll usually need to
5473 // promote), so we might as well prevent all young generation
5474 // GC's while we do a sweeping step. For the same reason, we might
5475 // as well take the bit map lock for the entire duration
5476
5477 // check that we hold the requisite locks
5478 assert(have_cms_token(), "Should hold cms token");
5479 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5480 assert_lock_strong(old_gen->freelistLock());
5481 assert_lock_strong(bitMapLock());
5482
5483 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5484 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5485 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5486 _inter_sweep_estimate.padded_average(),
5487 _intra_sweep_estimate.padded_average());
5488 old_gen->setNearLargestChunk();
5489
5490 {
5491 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5492 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5493 // We need to free-up/coalesce garbage/blocks from a
5494 // co-terminal free run. This is done in the SweepClosure
5495 // destructor; so, do not remove this scope, else the
5496 // end-of-sweep-census below will be off by a little bit.
5497 }
5498 old_gen->cmsSpace()->sweep_completed();
5499 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5500 if (should_unload_classes()) { // unloaded classes this cycle,
5501 _concurrent_cycles_since_last_unload = 0; // ... reset count
5502 } else { // did not unload classes,
5503 _concurrent_cycles_since_last_unload++; // ... increment count
5504 }
5505 }
5506
5507 // Reset CMS data structures (for now just the marking bit map)
5508 // preparatory for the next cycle.
5509 void CMSCollector::reset_concurrent() {
5510 CMSTokenSyncWithLocks ts(true, bitMapLock());
5511
5512 // If the state is not "Resetting", the foreground thread
5513 // has done a collection and the resetting.
5514 if (_collectorState != Resetting) {
5515 assert(_collectorState == Idling, "The state should only change"
5516 " because the foreground collector has finished the collection");
5517 return;
5518 }
5519
5520 {
5521 // Clear the mark bitmap (no grey objects to start with)
5522 // for the next cycle.
5523 GCTraceCPUTime tcpu;
5524 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5525
5526 HeapWord* curAddr = _markBitMap.startWord();
5527 while (curAddr < _markBitMap.endWord()) {
5528 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5529 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5530 _markBitMap.clear_large_range(chunk);
5531 if (ConcurrentMarkSweepThread::should_yield() &&
5532 !foregroundGCIsActive() &&
5533 CMSYield) {
5534 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5535 "CMS thread should hold CMS token");
5536 assert_lock_strong(bitMapLock());
5537 bitMapLock()->unlock();
5538 ConcurrentMarkSweepThread::desynchronize(true);
5539 stopTimer();
5540 incrementYields();
5541
5542 // See the comment in coordinator_yield()
5543 for (unsigned i = 0; i < CMSYieldSleepCount &&
5544 ConcurrentMarkSweepThread::should_yield() &&
5545 !CMSCollector::foregroundGCIsActive(); ++i) {
5546 os::sleep(Thread::current(), 1, false);
5547 }
5548
5549 ConcurrentMarkSweepThread::synchronize(true);
5550 bitMapLock()->lock_without_safepoint_check();
5551 startTimer();
5552 }
5553 curAddr = chunk.end();
5554 }
5555 // A successful mostly concurrent collection has been done.
5556 // Because only the full (i.e., concurrent mode failure) collections
5557 // are being measured for gc overhead limits, clean the "near" flag
5558 // and count.
5559 size_policy()->reset_gc_overhead_limit_count();
5560 _collectorState = Idling;
5561 }
5562
5563 register_gc_end();
5564 }
5565
5566 // Same as above but for STW paths
5567 void CMSCollector::reset_stw() {
5568 // already have the lock
5569 assert(_collectorState == Resetting, "just checking");
5570 assert_lock_strong(bitMapLock());
5571 GCIdMark gc_id_mark(_cmsThread->gc_id());
5572 _markBitMap.clear_all();
5573 _collectorState = Idling;
5574 register_gc_end();
5575 }
5576
5577 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5578 GCTraceCPUTime tcpu;
5579 TraceCollectorStats tcs_cgc(cgc_counters());
5580
5581 switch (op) {
5582 case CMS_op_checkpointRootsInitial: {
5583 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5584 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5585 checkpointRootsInitial();
5586 break;
5587 }
5588 case CMS_op_checkpointRootsFinal: {
5589 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5590 SvcGCMarker sgcm(SvcGCMarker::CONCURRENT);
5591 checkpointRootsFinal();
5592 break;
5593 }
5594 default:
5595 fatal("No such CMS_op");
5596 }
5597 }
5598
5599 #ifndef PRODUCT
5600 size_t const CMSCollector::skip_header_HeapWords() {
5601 return FreeChunk::header_size();
5602 }
5603
5604 // Try and collect here conditions that should hold when
5605 // CMS thread is exiting. The idea is that the foreground GC
5606 // thread should not be blocked if it wants to terminate
5607 // the CMS thread and yet continue to run the VM for a while
5608 // after that.
5609 void CMSCollector::verify_ok_to_terminate() const {
5610 assert(Thread::current()->is_ConcurrentGC_thread(),
5611 "should be called by CMS thread");
5612 assert(!_foregroundGCShouldWait, "should be false");
5613 // We could check here that all the various low-level locks
5614 // are not held by the CMS thread, but that is overkill; see
5615 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5616 // is checked.
5617 }
5618 #endif
5619
5620 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5621 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5622 "missing Printezis mark?");
5623 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5624 size_t size = pointer_delta(nextOneAddr + 1, addr);
5625 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5626 "alignment problem");
5627 assert(size >= 3, "Necessary for Printezis marks to work");
5628 return size;
5629 }
5630
5631 // A variant of the above (block_size_using_printezis_bits()) except
5632 // that we return 0 if the P-bits are not yet set.
5633 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5634 if (_markBitMap.isMarked(addr + 1)) {
5635 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5636 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5637 size_t size = pointer_delta(nextOneAddr + 1, addr);
5638 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5639 "alignment problem");
5640 assert(size >= 3, "Necessary for Printezis marks to work");
5641 return size;
5642 }
5643 return 0;
5644 }
5645
5646 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5647 size_t sz = 0;
5648 oop p = (oop)addr;
5649 if (p->klass_or_null_acquire() != NULL) {
5650 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5651 } else {
5652 sz = block_size_using_printezis_bits(addr);
5653 }
5654 assert(sz > 0, "size must be nonzero");
5655 HeapWord* next_block = addr + sz;
5656 HeapWord* next_card = align_up(next_block, CardTable::card_size);
5657 assert(align_down((uintptr_t)addr, CardTable::card_size) <
5658 align_down((uintptr_t)next_card, CardTable::card_size),
5659 "must be different cards");
5660 return next_card;
5661 }
5662
5663
5664 // CMS Bit Map Wrapper /////////////////////////////////////////
5665
5666 // Construct a CMS bit map infrastructure, but don't create the
5667 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5668 // further below.
5669 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5670 _shifter(shifter),
5671 _bm(),
5672 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5673 Monitor::_safepoint_check_never) : NULL)
5674 {
5675 _bmStartWord = 0;
5676 _bmWordSize = 0;
5677 }
5678
5679 bool CMSBitMap::allocate(MemRegion mr) {
5680 _bmStartWord = mr.start();
5681 _bmWordSize = mr.word_size();
5682 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5683 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5684 if (!brs.is_reserved()) {
5685 log_warning(gc)("CMS bit map allocation failure");
5686 return false;
5687 }
5688 // For now we'll just commit all of the bit map up front.
5689 // Later on we'll try to be more parsimonious with swap.
5690 if (!_virtual_space.initialize(brs, brs.size())) {
5691 log_warning(gc)("CMS bit map backing store failure");
5692 return false;
5693 }
5694 assert(_virtual_space.committed_size() == brs.size(),
5695 "didn't reserve backing store for all of CMS bit map?");
5696 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5697 _bmWordSize, "inconsistency in bit map sizing");
5698 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5699
5700 // bm.clear(); // can we rely on getting zero'd memory? verify below
5701 assert(isAllClear(),
5702 "Expected zero'd memory from ReservedSpace constructor");
5703 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5704 "consistency check");
5705 return true;
5706 }
5707
5708 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5709 HeapWord *next_addr, *end_addr, *last_addr;
5710 assert_locked();
5711 assert(covers(mr), "out-of-range error");
5712 // XXX assert that start and end are appropriately aligned
5713 for (next_addr = mr.start(), end_addr = mr.end();
5714 next_addr < end_addr; next_addr = last_addr) {
5715 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5716 last_addr = dirty_region.end();
5717 if (!dirty_region.is_empty()) {
5718 cl->do_MemRegion(dirty_region);
5719 } else {
5720 assert(last_addr == end_addr, "program logic");
5721 return;
5722 }
5723 }
5724 }
5725
5726 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5727 _bm.print_on_error(st, prefix);
5728 }
5729
5730 #ifndef PRODUCT
5731 void CMSBitMap::assert_locked() const {
5732 CMSLockVerifier::assert_locked(lock());
5733 }
5734
5735 bool CMSBitMap::covers(MemRegion mr) const {
5736 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5737 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5738 "size inconsistency");
5739 return (mr.start() >= _bmStartWord) &&
5740 (mr.end() <= endWord());
5741 }
5742
5743 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5744 return (start >= _bmStartWord && (start + size) <= endWord());
5745 }
5746
5747 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5748 // verify that there are no 1 bits in the interval [left, right)
5749 FalseBitMapClosure falseBitMapClosure;
5750 iterate(&falseBitMapClosure, left, right);
5751 }
5752
5753 void CMSBitMap::region_invariant(MemRegion mr)
5754 {
5755 assert_locked();
5756 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5757 assert(!mr.is_empty(), "unexpected empty region");
5758 assert(covers(mr), "mr should be covered by bit map");
5759 // convert address range into offset range
5760 size_t start_ofs = heapWordToOffset(mr.start());
5761 // Make sure that end() is appropriately aligned
5762 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5763 "Misaligned mr.end()");
5764 size_t end_ofs = heapWordToOffset(mr.end());
5765 assert(end_ofs > start_ofs, "Should mark at least one bit");
5766 }
5767
5768 #endif
5769
5770 bool CMSMarkStack::allocate(size_t size) {
5771 // allocate a stack of the requisite depth
5772 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5773 size * sizeof(oop)));
5774 if (!rs.is_reserved()) {
5775 log_warning(gc)("CMSMarkStack allocation failure");
5776 return false;
5777 }
5778 if (!_virtual_space.initialize(rs, rs.size())) {
5779 log_warning(gc)("CMSMarkStack backing store failure");
5780 return false;
5781 }
5782 assert(_virtual_space.committed_size() == rs.size(),
5783 "didn't reserve backing store for all of CMS stack?");
5784 _base = (oop*)(_virtual_space.low());
5785 _index = 0;
5786 _capacity = size;
5787 NOT_PRODUCT(_max_depth = 0);
5788 return true;
5789 }
5790
5791 // XXX FIX ME !!! In the MT case we come in here holding a
5792 // leaf lock. For printing we need to take a further lock
5793 // which has lower rank. We need to recalibrate the two
5794 // lock-ranks involved in order to be able to print the
5795 // messages below. (Or defer the printing to the caller.
5796 // For now we take the expedient path of just disabling the
5797 // messages for the problematic case.)
5798 void CMSMarkStack::expand() {
5799 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5800 if (_capacity == MarkStackSizeMax) {
5801 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5802 // We print a warning message only once per CMS cycle.
5803 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5804 }
5805 return;
5806 }
5807 // Double capacity if possible
5808 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5809 // Do not give up existing stack until we have managed to
5810 // get the double capacity that we desired.
5811 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5812 new_capacity * sizeof(oop)));
5813 if (rs.is_reserved()) {
5814 // Release the backing store associated with old stack
5815 _virtual_space.release();
5816 // Reinitialize virtual space for new stack
5817 if (!_virtual_space.initialize(rs, rs.size())) {
5818 fatal("Not enough swap for expanded marking stack");
5819 }
5820 _base = (oop*)(_virtual_space.low());
5821 _index = 0;
5822 _capacity = new_capacity;
5823 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5824 // Failed to double capacity, continue;
5825 // we print a detail message only once per CMS cycle.
5826 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5827 _capacity / K, new_capacity / K);
5828 }
5829 }
5830
5831
5832 // Closures
5833 // XXX: there seems to be a lot of code duplication here;
5834 // should refactor and consolidate common code.
5835
5836 // This closure is used to mark refs into the CMS generation in
5837 // the CMS bit map. Called at the first checkpoint. This closure
5838 // assumes that we do not need to re-mark dirty cards; if the CMS
5839 // generation on which this is used is not an oldest
5840 // generation then this will lose younger_gen cards!
5841
5842 MarkRefsIntoClosure::MarkRefsIntoClosure(
5843 MemRegion span, CMSBitMap* bitMap):
5844 _span(span),
5845 _bitMap(bitMap)
5846 {
5847 assert(ref_discoverer() == NULL, "deliberately left NULL");
5848 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5849 }
5850
5851 void MarkRefsIntoClosure::do_oop(oop obj) {
5852 // if p points into _span, then mark corresponding bit in _markBitMap
5853 assert(oopDesc::is_oop(obj), "expected an oop");
5854 HeapWord* addr = (HeapWord*)obj;
5855 if (_span.contains(addr)) {
5856 // this should be made more efficient
5857 _bitMap->mark(addr);
5858 }
5859 }
5860
5861 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5862 MemRegion span, CMSBitMap* bitMap):
5863 _span(span),
5864 _bitMap(bitMap)
5865 {
5866 assert(ref_discoverer() == NULL, "deliberately left NULL");
5867 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5868 }
5869
5870 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5871 // if p points into _span, then mark corresponding bit in _markBitMap
5872 assert(oopDesc::is_oop(obj), "expected an oop");
5873 HeapWord* addr = (HeapWord*)obj;
5874 if (_span.contains(addr)) {
5875 // this should be made more efficient
5876 _bitMap->par_mark(addr);
5877 }
5878 }
5879
5880 // A variant of the above, used for CMS marking verification.
5881 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5882 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5883 _span(span),
5884 _verification_bm(verification_bm),
5885 _cms_bm(cms_bm)
5886 {
5887 assert(ref_discoverer() == NULL, "deliberately left NULL");
5888 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5889 }
5890
5891 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5892 // if p points into _span, then mark corresponding bit in _markBitMap
5893 assert(oopDesc::is_oop(obj), "expected an oop");
5894 HeapWord* addr = (HeapWord*)obj;
5895 if (_span.contains(addr)) {
5896 _verification_bm->mark(addr);
5897 if (!_cms_bm->isMarked(addr)) {
5898 Log(gc, verify) log;
5899 ResourceMark rm;
5900 LogStream ls(log.error());
5901 oop(addr)->print_on(&ls);
5902 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5903 fatal("... aborting");
5904 }
5905 }
5906 }
5907
5908 //////////////////////////////////////////////////
5909 // MarkRefsIntoAndScanClosure
5910 //////////////////////////////////////////////////
5911
5912 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5913 ReferenceDiscoverer* rd,
5914 CMSBitMap* bit_map,
5915 CMSBitMap* mod_union_table,
5916 CMSMarkStack* mark_stack,
5917 CMSCollector* collector,
5918 bool should_yield,
5919 bool concurrent_precleaning):
5920 _span(span),
5921 _bit_map(bit_map),
5922 _mark_stack(mark_stack),
5923 _pushAndMarkClosure(collector, span, rd, bit_map, mod_union_table,
5924 mark_stack, concurrent_precleaning),
5925 _collector(collector),
5926 _freelistLock(NULL),
5927 _yield(should_yield),
5928 _concurrent_precleaning(concurrent_precleaning)
5929 {
5930 // FIXME: Should initialize in base class constructor.
5931 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
5932 set_ref_discoverer_internal(rd);
5933 }
5934
5935 // This closure is used to mark refs into the CMS generation at the
5936 // second (final) checkpoint, and to scan and transitively follow
5937 // the unmarked oops. It is also used during the concurrent precleaning
5938 // phase while scanning objects on dirty cards in the CMS generation.
5939 // The marks are made in the marking bit map and the marking stack is
5940 // used for keeping the (newly) grey objects during the scan.
5941 // The parallel version (Par_...) appears further below.
5942 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5943 if (obj != NULL) {
5944 assert(oopDesc::is_oop(obj), "expected an oop");
5945 HeapWord* addr = (HeapWord*)obj;
5946 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5947 assert(_collector->overflow_list_is_empty(),
5948 "overflow list should be empty");
5949 if (_span.contains(addr) &&
5950 !_bit_map->isMarked(addr)) {
5951 // mark bit map (object is now grey)
5952 _bit_map->mark(addr);
5953 // push on marking stack (stack should be empty), and drain the
5954 // stack by applying this closure to the oops in the oops popped
5955 // from the stack (i.e. blacken the grey objects)
5956 bool res = _mark_stack->push(obj);
5957 assert(res, "Should have space to push on empty stack");
5958 do {
5959 oop new_oop = _mark_stack->pop();
5960 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5961 assert(_bit_map->isMarked((HeapWord*)new_oop),
5962 "only grey objects on this stack");
5963 // iterate over the oops in this oop, marking and pushing
5964 // the ones in CMS heap (i.e. in _span).
5965 new_oop->oop_iterate(&_pushAndMarkClosure);
5966 // check if it's time to yield
5967 do_yield_check();
5968 } while (!_mark_stack->isEmpty() ||
5969 (!_concurrent_precleaning && take_from_overflow_list()));
5970 // if marking stack is empty, and we are not doing this
5971 // during precleaning, then check the overflow list
5972 }
5973 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5974 assert(_collector->overflow_list_is_empty(),
5975 "overflow list was drained above");
5976
5977 assert(_collector->no_preserved_marks(),
5978 "All preserved marks should have been restored above");
5979 }
5980 }
5981
5982 void MarkRefsIntoAndScanClosure::do_yield_work() {
5983 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5984 "CMS thread should hold CMS token");
5985 assert_lock_strong(_freelistLock);
5986 assert_lock_strong(_bit_map->lock());
5987 // relinquish the free_list_lock and bitMaplock()
5988 _bit_map->lock()->unlock();
5989 _freelistLock->unlock();
5990 ConcurrentMarkSweepThread::desynchronize(true);
5991 _collector->stopTimer();
5992 _collector->incrementYields();
5993
5994 // See the comment in coordinator_yield()
5995 for (unsigned i = 0;
5996 i < CMSYieldSleepCount &&
5997 ConcurrentMarkSweepThread::should_yield() &&
5998 !CMSCollector::foregroundGCIsActive();
5999 ++i) {
6000 os::sleep(Thread::current(), 1, false);
6001 }
6002
6003 ConcurrentMarkSweepThread::synchronize(true);
6004 _freelistLock->lock_without_safepoint_check();
6005 _bit_map->lock()->lock_without_safepoint_check();
6006 _collector->startTimer();
6007 }
6008
6009 ///////////////////////////////////////////////////////////
6010 // ParMarkRefsIntoAndScanClosure: a parallel version of
6011 // MarkRefsIntoAndScanClosure
6012 ///////////////////////////////////////////////////////////
6013 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6014 CMSCollector* collector, MemRegion span, ReferenceDiscoverer* rd,
6015 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6016 _span(span),
6017 _bit_map(bit_map),
6018 _work_queue(work_queue),
6019 _low_water_mark(MIN2((work_queue->max_elems()/4),
6020 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6021 _parPushAndMarkClosure(collector, span, rd, bit_map, work_queue)
6022 {
6023 // FIXME: Should initialize in base class constructor.
6024 assert(rd != NULL, "ref_discoverer shouldn't be NULL");
6025 set_ref_discoverer_internal(rd);
6026 }
6027
6028 // This closure is used to mark refs into the CMS generation at the
6029 // second (final) checkpoint, and to scan and transitively follow
6030 // the unmarked oops. The marks are made in the marking bit map and
6031 // the work_queue is used for keeping the (newly) grey objects during
6032 // the scan phase whence they are also available for stealing by parallel
6033 // threads. Since the marking bit map is shared, updates are
6034 // synchronized (via CAS).
6035 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6036 if (obj != NULL) {
6037 // Ignore mark word because this could be an already marked oop
6038 // that may be chained at the end of the overflow list.
6039 assert(oopDesc::is_oop(obj, true), "expected an oop");
6040 HeapWord* addr = (HeapWord*)obj;
6041 if (_span.contains(addr) &&
6042 !_bit_map->isMarked(addr)) {
6043 // mark bit map (object will become grey):
6044 // It is possible for several threads to be
6045 // trying to "claim" this object concurrently;
6046 // the unique thread that succeeds in marking the
6047 // object first will do the subsequent push on
6048 // to the work queue (or overflow list).
6049 if (_bit_map->par_mark(addr)) {
6050 // push on work_queue (which may not be empty), and trim the
6051 // queue to an appropriate length by applying this closure to
6052 // the oops in the oops popped from the stack (i.e. blacken the
6053 // grey objects)
6054 bool res = _work_queue->push(obj);
6055 assert(res, "Low water mark should be less than capacity?");
6056 trim_queue(_low_water_mark);
6057 } // Else, another thread claimed the object
6058 }
6059 }
6060 }
6061
6062 // This closure is used to rescan the marked objects on the dirty cards
6063 // in the mod union table and the card table proper.
6064 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6065 oop p, MemRegion mr) {
6066
6067 size_t size = 0;
6068 HeapWord* addr = (HeapWord*)p;
6069 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6070 assert(_span.contains(addr), "we are scanning the CMS generation");
6071 // check if it's time to yield
6072 if (do_yield_check()) {
6073 // We yielded for some foreground stop-world work,
6074 // and we have been asked to abort this ongoing preclean cycle.
6075 return 0;
6076 }
6077 if (_bitMap->isMarked(addr)) {
6078 // it's marked; is it potentially uninitialized?
6079 if (p->klass_or_null_acquire() != NULL) {
6080 // an initialized object; ignore mark word in verification below
6081 // since we are running concurrent with mutators
6082 assert(oopDesc::is_oop(p, true), "should be an oop");
6083 if (p->is_objArray()) {
6084 // objArrays are precisely marked; restrict scanning
6085 // to dirty cards only.
6086 size = CompactibleFreeListSpace::adjustObjectSize(
6087 p->oop_iterate_size(_scanningClosure, mr));
6088 } else {
6089 // A non-array may have been imprecisely marked; we need
6090 // to scan object in its entirety.
6091 size = CompactibleFreeListSpace::adjustObjectSize(
6092 p->oop_iterate_size(_scanningClosure));
6093 }
6094 #ifdef ASSERT
6095 size_t direct_size =
6096 CompactibleFreeListSpace::adjustObjectSize(p->size());
6097 assert(size == direct_size, "Inconsistency in size");
6098 assert(size >= 3, "Necessary for Printezis marks to work");
6099 HeapWord* start_pbit = addr + 1;
6100 HeapWord* end_pbit = addr + size - 1;
6101 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6102 "inconsistent Printezis mark");
6103 // Verify inner mark bits (between Printezis bits) are clear,
6104 // but don't repeat if there are multiple dirty regions for
6105 // the same object, to avoid potential O(N^2) performance.
6106 if (addr != _last_scanned_object) {
6107 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6108 _last_scanned_object = addr;
6109 }
6110 #endif // ASSERT
6111 } else {
6112 // An uninitialized object.
6113 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6114 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6115 size = pointer_delta(nextOneAddr + 1, addr);
6116 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6117 "alignment problem");
6118 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6119 // will dirty the card when the klass pointer is installed in the
6120 // object (signaling the completion of initialization).
6121 }
6122 } else {
6123 // Either a not yet marked object or an uninitialized object
6124 if (p->klass_or_null_acquire() == NULL) {
6125 // An uninitialized object, skip to the next card, since
6126 // we may not be able to read its P-bits yet.
6127 assert(size == 0, "Initial value");
6128 } else {
6129 // An object not (yet) reached by marking: we merely need to
6130 // compute its size so as to go look at the next block.
6131 assert(oopDesc::is_oop(p, true), "should be an oop");
6132 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6133 }
6134 }
6135 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6136 return size;
6137 }
6138
6139 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6140 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6141 "CMS thread should hold CMS token");
6142 assert_lock_strong(_freelistLock);
6143 assert_lock_strong(_bitMap->lock());
6144 // relinquish the free_list_lock and bitMaplock()
6145 _bitMap->lock()->unlock();
6146 _freelistLock->unlock();
6147 ConcurrentMarkSweepThread::desynchronize(true);
6148 _collector->stopTimer();
6149 _collector->incrementYields();
6150
6151 // See the comment in coordinator_yield()
6152 for (unsigned i = 0; i < CMSYieldSleepCount &&
6153 ConcurrentMarkSweepThread::should_yield() &&
6154 !CMSCollector::foregroundGCIsActive(); ++i) {
6155 os::sleep(Thread::current(), 1, false);
6156 }
6157
6158 ConcurrentMarkSweepThread::synchronize(true);
6159 _freelistLock->lock_without_safepoint_check();
6160 _bitMap->lock()->lock_without_safepoint_check();
6161 _collector->startTimer();
6162 }
6163
6164
6165 //////////////////////////////////////////////////////////////////
6166 // SurvivorSpacePrecleanClosure
6167 //////////////////////////////////////////////////////////////////
6168 // This (single-threaded) closure is used to preclean the oops in
6169 // the survivor spaces.
6170 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6171
6172 HeapWord* addr = (HeapWord*)p;
6173 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6174 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6175 assert(p->klass_or_null() != NULL, "object should be initialized");
6176 // an initialized object; ignore mark word in verification below
6177 // since we are running concurrent with mutators
6178 assert(oopDesc::is_oop(p, true), "should be an oop");
6179 // Note that we do not yield while we iterate over
6180 // the interior oops of p, pushing the relevant ones
6181 // on our marking stack.
6182 size_t size = p->oop_iterate_size(_scanning_closure);
6183 do_yield_check();
6184 // Observe that below, we do not abandon the preclean
6185 // phase as soon as we should; rather we empty the
6186 // marking stack before returning. This is to satisfy
6187 // some existing assertions. In general, it may be a
6188 // good idea to abort immediately and complete the marking
6189 // from the grey objects at a later time.
6190 while (!_mark_stack->isEmpty()) {
6191 oop new_oop = _mark_stack->pop();
6192 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6193 assert(_bit_map->isMarked((HeapWord*)new_oop),
6194 "only grey objects on this stack");
6195 // iterate over the oops in this oop, marking and pushing
6196 // the ones in CMS heap (i.e. in _span).
6197 new_oop->oop_iterate(_scanning_closure);
6198 // check if it's time to yield
6199 do_yield_check();
6200 }
6201 unsigned int after_count =
6202 CMSHeap::heap()->total_collections();
6203 bool abort = (_before_count != after_count) ||
6204 _collector->should_abort_preclean();
6205 return abort ? 0 : size;
6206 }
6207
6208 void SurvivorSpacePrecleanClosure::do_yield_work() {
6209 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6210 "CMS thread should hold CMS token");
6211 assert_lock_strong(_bit_map->lock());
6212 // Relinquish the bit map lock
6213 _bit_map->lock()->unlock();
6214 ConcurrentMarkSweepThread::desynchronize(true);
6215 _collector->stopTimer();
6216 _collector->incrementYields();
6217
6218 // See the comment in coordinator_yield()
6219 for (unsigned i = 0; i < CMSYieldSleepCount &&
6220 ConcurrentMarkSweepThread::should_yield() &&
6221 !CMSCollector::foregroundGCIsActive(); ++i) {
6222 os::sleep(Thread::current(), 1, false);
6223 }
6224
6225 ConcurrentMarkSweepThread::synchronize(true);
6226 _bit_map->lock()->lock_without_safepoint_check();
6227 _collector->startTimer();
6228 }
6229
6230 // This closure is used to rescan the marked objects on the dirty cards
6231 // in the mod union table and the card table proper. In the parallel
6232 // case, although the bitMap is shared, we do a single read so the
6233 // isMarked() query is "safe".
6234 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6235 // Ignore mark word because we are running concurrent with mutators
6236 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6237 HeapWord* addr = (HeapWord*)p;
6238 assert(_span.contains(addr), "we are scanning the CMS generation");
6239 bool is_obj_array = false;
6240 #ifdef ASSERT
6241 if (!_parallel) {
6242 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6243 assert(_collector->overflow_list_is_empty(),
6244 "overflow list should be empty");
6245
6246 }
6247 #endif // ASSERT
6248 if (_bit_map->isMarked(addr)) {
6249 // Obj arrays are precisely marked, non-arrays are not;
6250 // so we scan objArrays precisely and non-arrays in their
6251 // entirety.
6252 if (p->is_objArray()) {
6253 is_obj_array = true;
6254 if (_parallel) {
6255 p->oop_iterate(_par_scan_closure, mr);
6256 } else {
6257 p->oop_iterate(_scan_closure, mr);
6258 }
6259 } else {
6260 if (_parallel) {
6261 p->oop_iterate(_par_scan_closure);
6262 } else {
6263 p->oop_iterate(_scan_closure);
6264 }
6265 }
6266 }
6267 #ifdef ASSERT
6268 if (!_parallel) {
6269 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6270 assert(_collector->overflow_list_is_empty(),
6271 "overflow list should be empty");
6272
6273 }
6274 #endif // ASSERT
6275 return is_obj_array;
6276 }
6277
6278 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6279 MemRegion span,
6280 CMSBitMap* bitMap, CMSMarkStack* markStack,
6281 bool should_yield, bool verifying):
6282 _collector(collector),
6283 _span(span),
6284 _bitMap(bitMap),
6285 _mut(&collector->_modUnionTable),
6286 _markStack(markStack),
6287 _yield(should_yield),
6288 _skipBits(0)
6289 {
6290 assert(_markStack->isEmpty(), "stack should be empty");
6291 _finger = _bitMap->startWord();
6292 _threshold = _finger;
6293 assert(_collector->_restart_addr == NULL, "Sanity check");
6294 assert(_span.contains(_finger), "Out of bounds _finger?");
6295 DEBUG_ONLY(_verifying = verifying;)
6296 }
6297
6298 void MarkFromRootsClosure::reset(HeapWord* addr) {
6299 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6300 assert(_span.contains(addr), "Out of bounds _finger?");
6301 _finger = addr;
6302 _threshold = align_up(_finger, CardTable::card_size);
6303 }
6304
6305 // Should revisit to see if this should be restructured for
6306 // greater efficiency.
6307 bool MarkFromRootsClosure::do_bit(size_t offset) {
6308 if (_skipBits > 0) {
6309 _skipBits--;
6310 return true;
6311 }
6312 // convert offset into a HeapWord*
6313 HeapWord* addr = _bitMap->startWord() + offset;
6314 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6315 "address out of range");
6316 assert(_bitMap->isMarked(addr), "tautology");
6317 if (_bitMap->isMarked(addr+1)) {
6318 // this is an allocated but not yet initialized object
6319 assert(_skipBits == 0, "tautology");
6320 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6321 oop p = oop(addr);
6322 if (p->klass_or_null_acquire() == NULL) {
6323 DEBUG_ONLY(if (!_verifying) {)
6324 // We re-dirty the cards on which this object lies and increase
6325 // the _threshold so that we'll come back to scan this object
6326 // during the preclean or remark phase. (CMSCleanOnEnter)
6327 if (CMSCleanOnEnter) {
6328 size_t sz = _collector->block_size_using_printezis_bits(addr);
6329 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6330 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6331 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6332 // Bump _threshold to end_card_addr; note that
6333 // _threshold cannot possibly exceed end_card_addr, anyhow.
6334 // This prevents future clearing of the card as the scan proceeds
6335 // to the right.
6336 assert(_threshold <= end_card_addr,
6337 "Because we are just scanning into this object");
6338 if (_threshold < end_card_addr) {
6339 _threshold = end_card_addr;
6340 }
6341 if (p->klass_or_null_acquire() != NULL) {
6342 // Redirty the range of cards...
6343 _mut->mark_range(redirty_range);
6344 } // ...else the setting of klass will dirty the card anyway.
6345 }
6346 DEBUG_ONLY(})
6347 return true;
6348 }
6349 }
6350 scanOopsInOop(addr);
6351 return true;
6352 }
6353
6354 // We take a break if we've been at this for a while,
6355 // so as to avoid monopolizing the locks involved.
6356 void MarkFromRootsClosure::do_yield_work() {
6357 // First give up the locks, then yield, then re-lock
6358 // We should probably use a constructor/destructor idiom to
6359 // do this unlock/lock or modify the MutexUnlocker class to
6360 // serve our purpose. XXX
6361 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6362 "CMS thread should hold CMS token");
6363 assert_lock_strong(_bitMap->lock());
6364 _bitMap->lock()->unlock();
6365 ConcurrentMarkSweepThread::desynchronize(true);
6366 _collector->stopTimer();
6367 _collector->incrementYields();
6368
6369 // See the comment in coordinator_yield()
6370 for (unsigned i = 0; i < CMSYieldSleepCount &&
6371 ConcurrentMarkSweepThread::should_yield() &&
6372 !CMSCollector::foregroundGCIsActive(); ++i) {
6373 os::sleep(Thread::current(), 1, false);
6374 }
6375
6376 ConcurrentMarkSweepThread::synchronize(true);
6377 _bitMap->lock()->lock_without_safepoint_check();
6378 _collector->startTimer();
6379 }
6380
6381 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6382 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6383 assert(_markStack->isEmpty(),
6384 "should drain stack to limit stack usage");
6385 // convert ptr to an oop preparatory to scanning
6386 oop obj = oop(ptr);
6387 // Ignore mark word in verification below, since we
6388 // may be running concurrent with mutators.
6389 assert(oopDesc::is_oop(obj, true), "should be an oop");
6390 assert(_finger <= ptr, "_finger runneth ahead");
6391 // advance the finger to right end of this object
6392 _finger = ptr + obj->size();
6393 assert(_finger > ptr, "we just incremented it above");
6394 // On large heaps, it may take us some time to get through
6395 // the marking phase. During
6396 // this time it's possible that a lot of mutations have
6397 // accumulated in the card table and the mod union table --
6398 // these mutation records are redundant until we have
6399 // actually traced into the corresponding card.
6400 // Here, we check whether advancing the finger would make
6401 // us cross into a new card, and if so clear corresponding
6402 // cards in the MUT (preclean them in the card-table in the
6403 // future).
6404
6405 DEBUG_ONLY(if (!_verifying) {)
6406 // The clean-on-enter optimization is disabled by default,
6407 // until we fix 6178663.
6408 if (CMSCleanOnEnter && (_finger > _threshold)) {
6409 // [_threshold, _finger) represents the interval
6410 // of cards to be cleared in MUT (or precleaned in card table).
6411 // The set of cards to be cleared is all those that overlap
6412 // with the interval [_threshold, _finger); note that
6413 // _threshold is always kept card-aligned but _finger isn't
6414 // always card-aligned.
6415 HeapWord* old_threshold = _threshold;
6416 assert(is_aligned(old_threshold, CardTable::card_size),
6417 "_threshold should always be card-aligned");
6418 _threshold = align_up(_finger, CardTable::card_size);
6419 MemRegion mr(old_threshold, _threshold);
6420 assert(!mr.is_empty(), "Control point invariant");
6421 assert(_span.contains(mr), "Should clear within span");
6422 _mut->clear_range(mr);
6423 }
6424 DEBUG_ONLY(})
6425 // Note: the finger doesn't advance while we drain
6426 // the stack below.
6427 PushOrMarkClosure pushOrMarkClosure(_collector,
6428 _span, _bitMap, _markStack,
6429 _finger, this);
6430 bool res = _markStack->push(obj);
6431 assert(res, "Empty non-zero size stack should have space for single push");
6432 while (!_markStack->isEmpty()) {
6433 oop new_oop = _markStack->pop();
6434 // Skip verifying header mark word below because we are
6435 // running concurrent with mutators.
6436 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6437 // now scan this oop's oops
6438 new_oop->oop_iterate(&pushOrMarkClosure);
6439 do_yield_check();
6440 }
6441 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6442 }
6443
6444 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6445 CMSCollector* collector, MemRegion span,
6446 CMSBitMap* bit_map,
6447 OopTaskQueue* work_queue,
6448 CMSMarkStack* overflow_stack):
6449 _collector(collector),
6450 _whole_span(collector->_span),
6451 _span(span),
6452 _bit_map(bit_map),
6453 _mut(&collector->_modUnionTable),
6454 _work_queue(work_queue),
6455 _overflow_stack(overflow_stack),
6456 _skip_bits(0),
6457 _task(task)
6458 {
6459 assert(_work_queue->size() == 0, "work_queue should be empty");
6460 _finger = span.start();
6461 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6462 assert(_span.contains(_finger), "Out of bounds _finger?");
6463 }
6464
6465 // Should revisit to see if this should be restructured for
6466 // greater efficiency.
6467 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6468 if (_skip_bits > 0) {
6469 _skip_bits--;
6470 return true;
6471 }
6472 // convert offset into a HeapWord*
6473 HeapWord* addr = _bit_map->startWord() + offset;
6474 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6475 "address out of range");
6476 assert(_bit_map->isMarked(addr), "tautology");
6477 if (_bit_map->isMarked(addr+1)) {
6478 // this is an allocated object that might not yet be initialized
6479 assert(_skip_bits == 0, "tautology");
6480 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6481 oop p = oop(addr);
6482 if (p->klass_or_null_acquire() == NULL) {
6483 // in the case of Clean-on-Enter optimization, redirty card
6484 // and avoid clearing card by increasing the threshold.
6485 return true;
6486 }
6487 }
6488 scan_oops_in_oop(addr);
6489 return true;
6490 }
6491
6492 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6493 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6494 // Should we assert that our work queue is empty or
6495 // below some drain limit?
6496 assert(_work_queue->size() == 0,
6497 "should drain stack to limit stack usage");
6498 // convert ptr to an oop preparatory to scanning
6499 oop obj = oop(ptr);
6500 // Ignore mark word in verification below, since we
6501 // may be running concurrent with mutators.
6502 assert(oopDesc::is_oop(obj, true), "should be an oop");
6503 assert(_finger <= ptr, "_finger runneth ahead");
6504 // advance the finger to right end of this object
6505 _finger = ptr + obj->size();
6506 assert(_finger > ptr, "we just incremented it above");
6507 // On large heaps, it may take us some time to get through
6508 // the marking phase. During
6509 // this time it's possible that a lot of mutations have
6510 // accumulated in the card table and the mod union table --
6511 // these mutation records are redundant until we have
6512 // actually traced into the corresponding card.
6513 // Here, we check whether advancing the finger would make
6514 // us cross into a new card, and if so clear corresponding
6515 // cards in the MUT (preclean them in the card-table in the
6516 // future).
6517
6518 // The clean-on-enter optimization is disabled by default,
6519 // until we fix 6178663.
6520 if (CMSCleanOnEnter && (_finger > _threshold)) {
6521 // [_threshold, _finger) represents the interval
6522 // of cards to be cleared in MUT (or precleaned in card table).
6523 // The set of cards to be cleared is all those that overlap
6524 // with the interval [_threshold, _finger); note that
6525 // _threshold is always kept card-aligned but _finger isn't
6526 // always card-aligned.
6527 HeapWord* old_threshold = _threshold;
6528 assert(is_aligned(old_threshold, CardTable::card_size),
6529 "_threshold should always be card-aligned");
6530 _threshold = align_up(_finger, CardTable::card_size);
6531 MemRegion mr(old_threshold, _threshold);
6532 assert(!mr.is_empty(), "Control point invariant");
6533 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6534 _mut->clear_range(mr);
6535 }
6536
6537 // Note: the local finger doesn't advance while we drain
6538 // the stack below, but the global finger sure can and will.
6539 HeapWord* volatile* gfa = _task->global_finger_addr();
6540 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6541 _span, _bit_map,
6542 _work_queue,
6543 _overflow_stack,
6544 _finger,
6545 gfa, this);
6546 bool res = _work_queue->push(obj); // overflow could occur here
6547 assert(res, "Will hold once we use workqueues");
6548 while (true) {
6549 oop new_oop;
6550 if (!_work_queue->pop_local(new_oop)) {
6551 // We emptied our work_queue; check if there's stuff that can
6552 // be gotten from the overflow stack.
6553 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6554 _overflow_stack, _work_queue)) {
6555 do_yield_check();
6556 continue;
6557 } else { // done
6558 break;
6559 }
6560 }
6561 // Skip verifying header mark word below because we are
6562 // running concurrent with mutators.
6563 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6564 // now scan this oop's oops
6565 new_oop->oop_iterate(&pushOrMarkClosure);
6566 do_yield_check();
6567 }
6568 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6569 }
6570
6571 // Yield in response to a request from VM Thread or
6572 // from mutators.
6573 void ParMarkFromRootsClosure::do_yield_work() {
6574 assert(_task != NULL, "sanity");
6575 _task->yield();
6576 }
6577
6578 // A variant of the above used for verifying CMS marking work.
6579 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6580 MemRegion span,
6581 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6582 CMSMarkStack* mark_stack):
6583 _collector(collector),
6584 _span(span),
6585 _verification_bm(verification_bm),
6586 _cms_bm(cms_bm),
6587 _mark_stack(mark_stack),
6588 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6589 mark_stack)
6590 {
6591 assert(_mark_stack->isEmpty(), "stack should be empty");
6592 _finger = _verification_bm->startWord();
6593 assert(_collector->_restart_addr == NULL, "Sanity check");
6594 assert(_span.contains(_finger), "Out of bounds _finger?");
6595 }
6596
6597 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6598 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6599 assert(_span.contains(addr), "Out of bounds _finger?");
6600 _finger = addr;
6601 }
6602
6603 // Should revisit to see if this should be restructured for
6604 // greater efficiency.
6605 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6606 // convert offset into a HeapWord*
6607 HeapWord* addr = _verification_bm->startWord() + offset;
6608 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6609 "address out of range");
6610 assert(_verification_bm->isMarked(addr), "tautology");
6611 assert(_cms_bm->isMarked(addr), "tautology");
6612
6613 assert(_mark_stack->isEmpty(),
6614 "should drain stack to limit stack usage");
6615 // convert addr to an oop preparatory to scanning
6616 oop obj = oop(addr);
6617 assert(oopDesc::is_oop(obj), "should be an oop");
6618 assert(_finger <= addr, "_finger runneth ahead");
6619 // advance the finger to right end of this object
6620 _finger = addr + obj->size();
6621 assert(_finger > addr, "we just incremented it above");
6622 // Note: the finger doesn't advance while we drain
6623 // the stack below.
6624 bool res = _mark_stack->push(obj);
6625 assert(res, "Empty non-zero size stack should have space for single push");
6626 while (!_mark_stack->isEmpty()) {
6627 oop new_oop = _mark_stack->pop();
6628 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6629 // now scan this oop's oops
6630 new_oop->oop_iterate(&_pam_verify_closure);
6631 }
6632 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6633 return true;
6634 }
6635
6636 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6637 CMSCollector* collector, MemRegion span,
6638 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6639 CMSMarkStack* mark_stack):
6640 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6641 _collector(collector),
6642 _span(span),
6643 _verification_bm(verification_bm),
6644 _cms_bm(cms_bm),
6645 _mark_stack(mark_stack)
6646 { }
6647
6648 template <class T> void PushAndMarkVerifyClosure::do_oop_work(T *p) {
6649 oop obj = RawAccess<>::oop_load(p);
6650 do_oop(obj);
6651 }
6652
6653 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6654 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6655
6656 // Upon stack overflow, we discard (part of) the stack,
6657 // remembering the least address amongst those discarded
6658 // in CMSCollector's _restart_address.
6659 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6660 // Remember the least grey address discarded
6661 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6662 _collector->lower_restart_addr(ra);
6663 _mark_stack->reset(); // discard stack contents
6664 _mark_stack->expand(); // expand the stack if possible
6665 }
6666
6667 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6668 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6669 HeapWord* addr = (HeapWord*)obj;
6670 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6671 // Oop lies in _span and isn't yet grey or black
6672 _verification_bm->mark(addr); // now grey
6673 if (!_cms_bm->isMarked(addr)) {
6674 Log(gc, verify) log;
6675 ResourceMark rm;
6676 LogStream ls(log.error());
6677 oop(addr)->print_on(&ls);
6678 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6679 fatal("... aborting");
6680 }
6681
6682 if (!_mark_stack->push(obj)) { // stack overflow
6683 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6684 assert(_mark_stack->isFull(), "Else push should have succeeded");
6685 handle_stack_overflow(addr);
6686 }
6687 // anything including and to the right of _finger
6688 // will be scanned as we iterate over the remainder of the
6689 // bit map
6690 }
6691 }
6692
6693 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6694 MemRegion span,
6695 CMSBitMap* bitMap, CMSMarkStack* markStack,
6696 HeapWord* finger, MarkFromRootsClosure* parent) :
6697 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6698 _collector(collector),
6699 _span(span),
6700 _bitMap(bitMap),
6701 _markStack(markStack),
6702 _finger(finger),
6703 _parent(parent)
6704 { }
6705
6706 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6707 MemRegion span,
6708 CMSBitMap* bit_map,
6709 OopTaskQueue* work_queue,
6710 CMSMarkStack* overflow_stack,
6711 HeapWord* finger,
6712 HeapWord* volatile* global_finger_addr,
6713 ParMarkFromRootsClosure* parent) :
6714 MetadataVisitingOopIterateClosure(collector->ref_processor()),
6715 _collector(collector),
6716 _whole_span(collector->_span),
6717 _span(span),
6718 _bit_map(bit_map),
6719 _work_queue(work_queue),
6720 _overflow_stack(overflow_stack),
6721 _finger(finger),
6722 _global_finger_addr(global_finger_addr),
6723 _parent(parent)
6724 { }
6725
6726 // Assumes thread-safe access by callers, who are
6727 // responsible for mutual exclusion.
6728 void CMSCollector::lower_restart_addr(HeapWord* low) {
6729 assert(_span.contains(low), "Out of bounds addr");
6730 if (_restart_addr == NULL) {
6731 _restart_addr = low;
6732 } else {
6733 _restart_addr = MIN2(_restart_addr, low);
6734 }
6735 }
6736
6737 // Upon stack overflow, we discard (part of) the stack,
6738 // remembering the least address amongst those discarded
6739 // in CMSCollector's _restart_address.
6740 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6741 // Remember the least grey address discarded
6742 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6743 _collector->lower_restart_addr(ra);
6744 _markStack->reset(); // discard stack contents
6745 _markStack->expand(); // expand the stack if possible
6746 }
6747
6748 // Upon stack overflow, we discard (part of) the stack,
6749 // remembering the least address amongst those discarded
6750 // in CMSCollector's _restart_address.
6751 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6752 // We need to do this under a mutex to prevent other
6753 // workers from interfering with the work done below.
6754 MutexLocker ml(_overflow_stack->par_lock(),
6755 Mutex::_no_safepoint_check_flag);
6756 // Remember the least grey address discarded
6757 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6758 _collector->lower_restart_addr(ra);
6759 _overflow_stack->reset(); // discard stack contents
6760 _overflow_stack->expand(); // expand the stack if possible
6761 }
6762
6763 void PushOrMarkClosure::do_oop(oop obj) {
6764 // Ignore mark word because we are running concurrent with mutators.
6765 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6766 HeapWord* addr = (HeapWord*)obj;
6767 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6768 // Oop lies in _span and isn't yet grey or black
6769 _bitMap->mark(addr); // now grey
6770 if (addr < _finger) {
6771 // the bit map iteration has already either passed, or
6772 // sampled, this bit in the bit map; we'll need to
6773 // use the marking stack to scan this oop's oops.
6774 bool simulate_overflow = false;
6775 NOT_PRODUCT(
6776 if (CMSMarkStackOverflowALot &&
6777 _collector->simulate_overflow()) {
6778 // simulate a stack overflow
6779 simulate_overflow = true;
6780 }
6781 )
6782 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6783 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6784 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6785 handle_stack_overflow(addr);
6786 }
6787 }
6788 // anything including and to the right of _finger
6789 // will be scanned as we iterate over the remainder of the
6790 // bit map
6791 do_yield_check();
6792 }
6793 }
6794
6795 void ParPushOrMarkClosure::do_oop(oop obj) {
6796 // Ignore mark word because we are running concurrent with mutators.
6797 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6798 HeapWord* addr = (HeapWord*)obj;
6799 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6800 // Oop lies in _span and isn't yet grey or black
6801 // We read the global_finger (volatile read) strictly after marking oop
6802 bool res = _bit_map->par_mark(addr); // now grey
6803 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6804 // Should we push this marked oop on our stack?
6805 // -- if someone else marked it, nothing to do
6806 // -- if target oop is above global finger nothing to do
6807 // -- if target oop is in chunk and above local finger
6808 // then nothing to do
6809 // -- else push on work queue
6810 if ( !res // someone else marked it, they will deal with it
6811 || (addr >= *gfa) // will be scanned in a later task
6812 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6813 return;
6814 }
6815 // the bit map iteration has already either passed, or
6816 // sampled, this bit in the bit map; we'll need to
6817 // use the marking stack to scan this oop's oops.
6818 bool simulate_overflow = false;
6819 NOT_PRODUCT(
6820 if (CMSMarkStackOverflowALot &&
6821 _collector->simulate_overflow()) {
6822 // simulate a stack overflow
6823 simulate_overflow = true;
6824 }
6825 )
6826 if (simulate_overflow ||
6827 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6828 // stack overflow
6829 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6830 // We cannot assert that the overflow stack is full because
6831 // it may have been emptied since.
6832 assert(simulate_overflow ||
6833 _work_queue->size() == _work_queue->max_elems(),
6834 "Else push should have succeeded");
6835 handle_stack_overflow(addr);
6836 }
6837 do_yield_check();
6838 }
6839 }
6840
6841 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6842 MemRegion span,
6843 ReferenceDiscoverer* rd,
6844 CMSBitMap* bit_map,
6845 CMSBitMap* mod_union_table,
6846 CMSMarkStack* mark_stack,
6847 bool concurrent_precleaning):
6848 MetadataVisitingOopIterateClosure(rd),
6849 _collector(collector),
6850 _span(span),
6851 _bit_map(bit_map),
6852 _mod_union_table(mod_union_table),
6853 _mark_stack(mark_stack),
6854 _concurrent_precleaning(concurrent_precleaning)
6855 {
6856 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6857 }
6858
6859 // Grey object rescan during pre-cleaning and second checkpoint phases --
6860 // the non-parallel version (the parallel version appears further below.)
6861 void PushAndMarkClosure::do_oop(oop obj) {
6862 // Ignore mark word verification. If during concurrent precleaning,
6863 // the object monitor may be locked. If during the checkpoint
6864 // phases, the object may already have been reached by a different
6865 // path and may be at the end of the global overflow list (so
6866 // the mark word may be NULL).
6867 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6868 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6869 HeapWord* addr = (HeapWord*)obj;
6870 // Check if oop points into the CMS generation
6871 // and is not marked
6872 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6873 // a white object ...
6874 _bit_map->mark(addr); // ... now grey
6875 // push on the marking stack (grey set)
6876 bool simulate_overflow = false;
6877 NOT_PRODUCT(
6878 if (CMSMarkStackOverflowALot &&
6879 _collector->simulate_overflow()) {
6880 // simulate a stack overflow
6881 simulate_overflow = true;
6882 }
6883 )
6884 if (simulate_overflow || !_mark_stack->push(obj)) {
6885 if (_concurrent_precleaning) {
6886 // During precleaning we can just dirty the appropriate card(s)
6887 // in the mod union table, thus ensuring that the object remains
6888 // in the grey set and continue. In the case of object arrays
6889 // we need to dirty all of the cards that the object spans,
6890 // since the rescan of object arrays will be limited to the
6891 // dirty cards.
6892 // Note that no one can be interfering with us in this action
6893 // of dirtying the mod union table, so no locking or atomics
6894 // are required.
6895 if (obj->is_objArray()) {
6896 size_t sz = obj->size();
6897 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
6898 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6899 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6900 _mod_union_table->mark_range(redirty_range);
6901 } else {
6902 _mod_union_table->mark(addr);
6903 }
6904 _collector->_ser_pmc_preclean_ovflw++;
6905 } else {
6906 // During the remark phase, we need to remember this oop
6907 // in the overflow list.
6908 _collector->push_on_overflow_list(obj);
6909 _collector->_ser_pmc_remark_ovflw++;
6910 }
6911 }
6912 }
6913 }
6914
6915 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6916 MemRegion span,
6917 ReferenceDiscoverer* rd,
6918 CMSBitMap* bit_map,
6919 OopTaskQueue* work_queue):
6920 MetadataVisitingOopIterateClosure(rd),
6921 _collector(collector),
6922 _span(span),
6923 _bit_map(bit_map),
6924 _work_queue(work_queue)
6925 {
6926 assert(ref_discoverer() != NULL, "ref_discoverer shouldn't be NULL");
6927 }
6928
6929 // Grey object rescan during second checkpoint phase --
6930 // the parallel version.
6931 void ParPushAndMarkClosure::do_oop(oop obj) {
6932 // In the assert below, we ignore the mark word because
6933 // this oop may point to an already visited object that is
6934 // on the overflow stack (in which case the mark word has
6935 // been hijacked for chaining into the overflow stack --
6936 // if this is the last object in the overflow stack then
6937 // its mark word will be NULL). Because this object may
6938 // have been subsequently popped off the global overflow
6939 // stack, and the mark word possibly restored to the prototypical
6940 // value, by the time we get to examined this failing assert in
6941 // the debugger, is_oop_or_null(false) may subsequently start
6942 // to hold.
6943 assert(oopDesc::is_oop_or_null(obj, true),
6944 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6945 HeapWord* addr = (HeapWord*)obj;
6946 // Check if oop points into the CMS generation
6947 // and is not marked
6948 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6949 // a white object ...
6950 // If we manage to "claim" the object, by being the
6951 // first thread to mark it, then we push it on our
6952 // marking stack
6953 if (_bit_map->par_mark(addr)) { // ... now grey
6954 // push on work queue (grey set)
6955 bool simulate_overflow = false;
6956 NOT_PRODUCT(
6957 if (CMSMarkStackOverflowALot &&
6958 _collector->par_simulate_overflow()) {
6959 // simulate a stack overflow
6960 simulate_overflow = true;
6961 }
6962 )
6963 if (simulate_overflow || !_work_queue->push(obj)) {
6964 _collector->par_push_on_overflow_list(obj);
6965 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6966 }
6967 } // Else, some other thread got there first
6968 }
6969 }
6970
6971 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6972 Mutex* bml = _collector->bitMapLock();
6973 assert_lock_strong(bml);
6974 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6975 "CMS thread should hold CMS token");
6976
6977 bml->unlock();
6978 ConcurrentMarkSweepThread::desynchronize(true);
6979
6980 _collector->stopTimer();
6981 _collector->incrementYields();
6982
6983 // See the comment in coordinator_yield()
6984 for (unsigned i = 0; i < CMSYieldSleepCount &&
6985 ConcurrentMarkSweepThread::should_yield() &&
6986 !CMSCollector::foregroundGCIsActive(); ++i) {
6987 os::sleep(Thread::current(), 1, false);
6988 }
6989
6990 ConcurrentMarkSweepThread::synchronize(true);
6991 bml->lock();
6992
6993 _collector->startTimer();
6994 }
6995
6996 bool CMSPrecleanRefsYieldClosure::should_return() {
6997 if (ConcurrentMarkSweepThread::should_yield()) {
6998 do_yield_work();
6999 }
7000 return _collector->foregroundGCIsActive();
7001 }
7002
7003 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7004 assert(((size_t)mr.start())%CardTable::card_size_in_words == 0,
7005 "mr should be aligned to start at a card boundary");
7006 // We'd like to assert:
7007 // assert(mr.word_size()%CardTable::card_size_in_words == 0,
7008 // "mr should be a range of cards");
7009 // However, that would be too strong in one case -- the last
7010 // partition ends at _unallocated_block which, in general, can be
7011 // an arbitrary boundary, not necessarily card aligned.
7012 _num_dirty_cards += mr.word_size()/CardTable::card_size_in_words;
7013 _space->object_iterate_mem(mr, &_scan_cl);
7014 }
7015
7016 SweepClosure::SweepClosure(CMSCollector* collector,
7017 ConcurrentMarkSweepGeneration* g,
7018 CMSBitMap* bitMap, bool should_yield) :
7019 _collector(collector),
7020 _g(g),
7021 _sp(g->cmsSpace()),
7022 _limit(_sp->sweep_limit()),
7023 _freelistLock(_sp->freelistLock()),
7024 _bitMap(bitMap),
7025 _inFreeRange(false), // No free range at beginning of sweep
7026 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7027 _lastFreeRangeCoalesced(false),
7028 _yield(should_yield),
7029 _freeFinger(g->used_region().start())
7030 {
7031 NOT_PRODUCT(
7032 _numObjectsFreed = 0;
7033 _numWordsFreed = 0;
7034 _numObjectsLive = 0;
7035 _numWordsLive = 0;
7036 _numObjectsAlreadyFree = 0;
7037 _numWordsAlreadyFree = 0;
7038 _last_fc = NULL;
7039
7040 _sp->initializeIndexedFreeListArrayReturnedBytes();
7041 _sp->dictionary()->initialize_dict_returned_bytes();
7042 )
7043 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7044 "sweep _limit out of bounds");
7045 log_develop_trace(gc, sweep)("====================");
7046 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7047 }
7048
7049 void SweepClosure::print_on(outputStream* st) const {
7050 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7051 p2i(_sp->bottom()), p2i(_sp->end()));
7052 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7053 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7054 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7055 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7056 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7057 }
7058
7059 #ifndef PRODUCT
7060 // Assertion checking only: no useful work in product mode --
7061 // however, if any of the flags below become product flags,
7062 // you may need to review this code to see if it needs to be
7063 // enabled in product mode.
7064 SweepClosure::~SweepClosure() {
7065 assert_lock_strong(_freelistLock);
7066 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7067 "sweep _limit out of bounds");
7068 if (inFreeRange()) {
7069 Log(gc, sweep) log;
7070 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7071 ResourceMark rm;
7072 LogStream ls(log.error());
7073 print_on(&ls);
7074 ShouldNotReachHere();
7075 }
7076
7077 if (log_is_enabled(Debug, gc, sweep)) {
7078 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7079 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7080 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7081 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7082 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7083 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7084 }
7085
7086 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7087 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7088 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7089 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7090 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7091 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7092 }
7093 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7094 log_develop_trace(gc, sweep)("================");
7095 }
7096 #endif // PRODUCT
7097
7098 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7099 bool freeRangeInFreeLists) {
7100 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7101 p2i(freeFinger), freeRangeInFreeLists);
7102 assert(!inFreeRange(), "Trampling existing free range");
7103 set_inFreeRange(true);
7104 set_lastFreeRangeCoalesced(false);
7105
7106 set_freeFinger(freeFinger);
7107 set_freeRangeInFreeLists(freeRangeInFreeLists);
7108 if (CMSTestInFreeList) {
7109 if (freeRangeInFreeLists) {
7110 FreeChunk* fc = (FreeChunk*) freeFinger;
7111 assert(fc->is_free(), "A chunk on the free list should be free.");
7112 assert(fc->size() > 0, "Free range should have a size");
7113 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7114 }
7115 }
7116 }
7117
7118 // Note that the sweeper runs concurrently with mutators. Thus,
7119 // it is possible for direct allocation in this generation to happen
7120 // in the middle of the sweep. Note that the sweeper also coalesces
7121 // contiguous free blocks. Thus, unless the sweeper and the allocator
7122 // synchronize appropriately freshly allocated blocks may get swept up.
7123 // This is accomplished by the sweeper locking the free lists while
7124 // it is sweeping. Thus blocks that are determined to be free are
7125 // indeed free. There is however one additional complication:
7126 // blocks that have been allocated since the final checkpoint and
7127 // mark, will not have been marked and so would be treated as
7128 // unreachable and swept up. To prevent this, the allocator marks
7129 // the bit map when allocating during the sweep phase. This leads,
7130 // however, to a further complication -- objects may have been allocated
7131 // but not yet initialized -- in the sense that the header isn't yet
7132 // installed. The sweeper can not then determine the size of the block
7133 // in order to skip over it. To deal with this case, we use a technique
7134 // (due to Printezis) to encode such uninitialized block sizes in the
7135 // bit map. Since the bit map uses a bit per every HeapWord, but the
7136 // CMS generation has a minimum object size of 3 HeapWords, it follows
7137 // that "normal marks" won't be adjacent in the bit map (there will
7138 // always be at least two 0 bits between successive 1 bits). We make use
7139 // of these "unused" bits to represent uninitialized blocks -- the bit
7140 // corresponding to the start of the uninitialized object and the next
7141 // bit are both set. Finally, a 1 bit marks the end of the object that
7142 // started with the two consecutive 1 bits to indicate its potentially
7143 // uninitialized state.
7144
7145 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7146 FreeChunk* fc = (FreeChunk*)addr;
7147 size_t res;
7148
7149 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7150 // than "addr == _limit" because although _limit was a block boundary when
7151 // we started the sweep, it may no longer be one because heap expansion
7152 // may have caused us to coalesce the block ending at the address _limit
7153 // with a newly expanded chunk (this happens when _limit was set to the
7154 // previous _end of the space), so we may have stepped past _limit:
7155 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7156 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7157 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7158 "sweep _limit out of bounds");
7159 assert(addr < _sp->end(), "addr out of bounds");
7160 // Flush any free range we might be holding as a single
7161 // coalesced chunk to the appropriate free list.
7162 if (inFreeRange()) {
7163 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7164 "freeFinger() " PTR_FORMAT " is out of bounds", p2i(freeFinger()));
7165 flush_cur_free_chunk(freeFinger(),
7166 pointer_delta(addr, freeFinger()));
7167 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7168 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7169 lastFreeRangeCoalesced() ? 1 : 0);
7170 }
7171
7172 // help the iterator loop finish
7173 return pointer_delta(_sp->end(), addr);
7174 }
7175
7176 assert(addr < _limit, "sweep invariant");
7177 // check if we should yield
7178 do_yield_check(addr);
7179 if (fc->is_free()) {
7180 // Chunk that is already free
7181 res = fc->size();
7182 do_already_free_chunk(fc);
7183 debug_only(_sp->verifyFreeLists());
7184 // If we flush the chunk at hand in lookahead_and_flush()
7185 // and it's coalesced with a preceding chunk, then the
7186 // process of "mangling" the payload of the coalesced block
7187 // will cause erasure of the size information from the
7188 // (erstwhile) header of all the coalesced blocks but the
7189 // first, so the first disjunct in the assert will not hold
7190 // in that specific case (in which case the second disjunct
7191 // will hold).
7192 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7193 "Otherwise the size info doesn't change at this step");
7194 NOT_PRODUCT(
7195 _numObjectsAlreadyFree++;
7196 _numWordsAlreadyFree += res;
7197 )
7198 NOT_PRODUCT(_last_fc = fc;)
7199 } else if (!_bitMap->isMarked(addr)) {
7200 // Chunk is fresh garbage
7201 res = do_garbage_chunk(fc);
7202 debug_only(_sp->verifyFreeLists());
7203 NOT_PRODUCT(
7204 _numObjectsFreed++;
7205 _numWordsFreed += res;
7206 )
7207 } else {
7208 // Chunk that is alive.
7209 res = do_live_chunk(fc);
7210 debug_only(_sp->verifyFreeLists());
7211 NOT_PRODUCT(
7212 _numObjectsLive++;
7213 _numWordsLive += res;
7214 )
7215 }
7216 return res;
7217 }
7218
7219 // For the smart allocation, record following
7220 // split deaths - a free chunk is removed from its free list because
7221 // it is being split into two or more chunks.
7222 // split birth - a free chunk is being added to its free list because
7223 // a larger free chunk has been split and resulted in this free chunk.
7224 // coal death - a free chunk is being removed from its free list because
7225 // it is being coalesced into a large free chunk.
7226 // coal birth - a free chunk is being added to its free list because
7227 // it was created when two or more free chunks where coalesced into
7228 // this free chunk.
7229 //
7230 // These statistics are used to determine the desired number of free
7231 // chunks of a given size. The desired number is chosen to be relative
7232 // to the end of a CMS sweep. The desired number at the end of a sweep
7233 // is the
7234 // count-at-end-of-previous-sweep (an amount that was enough)
7235 // - count-at-beginning-of-current-sweep (the excess)
7236 // + split-births (gains in this size during interval)
7237 // - split-deaths (demands on this size during interval)
7238 // where the interval is from the end of one sweep to the end of the
7239 // next.
7240 //
7241 // When sweeping the sweeper maintains an accumulated chunk which is
7242 // the chunk that is made up of chunks that have been coalesced. That
7243 // will be termed the left-hand chunk. A new chunk of garbage that
7244 // is being considered for coalescing will be referred to as the
7245 // right-hand chunk.
7246 //
7247 // When making a decision on whether to coalesce a right-hand chunk with
7248 // the current left-hand chunk, the current count vs. the desired count
7249 // of the left-hand chunk is considered. Also if the right-hand chunk
7250 // is near the large chunk at the end of the heap (see
7251 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7252 // left-hand chunk is coalesced.
7253 //
7254 // When making a decision about whether to split a chunk, the desired count
7255 // vs. the current count of the candidate to be split is also considered.
7256 // If the candidate is underpopulated (currently fewer chunks than desired)
7257 // a chunk of an overpopulated (currently more chunks than desired) size may
7258 // be chosen. The "hint" associated with a free list, if non-null, points
7259 // to a free list which may be overpopulated.
7260 //
7261
7262 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7263 const size_t size = fc->size();
7264 // Chunks that cannot be coalesced are not in the
7265 // free lists.
7266 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7267 assert(_sp->verify_chunk_in_free_list(fc),
7268 "free chunk should be in free lists");
7269 }
7270 // a chunk that is already free, should not have been
7271 // marked in the bit map
7272 HeapWord* const addr = (HeapWord*) fc;
7273 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7274 // Verify that the bit map has no bits marked between
7275 // addr and purported end of this block.
7276 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7277
7278 // Some chunks cannot be coalesced under any circumstances.
7279 // See the definition of cantCoalesce().
7280 if (!fc->cantCoalesce()) {
7281 // This chunk can potentially be coalesced.
7282 // All the work is done in
7283 do_post_free_or_garbage_chunk(fc, size);
7284 // Note that if the chunk is not coalescable (the else arm
7285 // below), we unconditionally flush, without needing to do
7286 // a "lookahead," as we do below.
7287 if (inFreeRange()) lookahead_and_flush(fc, size);
7288 } else {
7289 // Code path common to both original and adaptive free lists.
7290
7291 // cant coalesce with previous block; this should be treated
7292 // as the end of a free run if any
7293 if (inFreeRange()) {
7294 // we kicked some butt; time to pick up the garbage
7295 assert(freeFinger() < addr, "freeFinger points too high");
7296 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7297 }
7298 // else, nothing to do, just continue
7299 }
7300 }
7301
7302 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7303 // This is a chunk of garbage. It is not in any free list.
7304 // Add it to a free list or let it possibly be coalesced into
7305 // a larger chunk.
7306 HeapWord* const addr = (HeapWord*) fc;
7307 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7308
7309 // Verify that the bit map has no bits marked between
7310 // addr and purported end of just dead object.
7311 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7312 do_post_free_or_garbage_chunk(fc, size);
7313
7314 assert(_limit >= addr + size,
7315 "A freshly garbage chunk can't possibly straddle over _limit");
7316 if (inFreeRange()) lookahead_and_flush(fc, size);
7317 return size;
7318 }
7319
7320 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7321 HeapWord* addr = (HeapWord*) fc;
7322 // The sweeper has just found a live object. Return any accumulated
7323 // left hand chunk to the free lists.
7324 if (inFreeRange()) {
7325 assert(freeFinger() < addr, "freeFinger points too high");
7326 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7327 }
7328
7329 // This object is live: we'd normally expect this to be
7330 // an oop, and like to assert the following:
7331 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7332 // However, as we commented above, this may be an object whose
7333 // header hasn't yet been initialized.
7334 size_t size;
7335 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7336 if (_bitMap->isMarked(addr + 1)) {
7337 // Determine the size from the bit map, rather than trying to
7338 // compute it from the object header.
7339 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7340 size = pointer_delta(nextOneAddr + 1, addr);
7341 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7342 "alignment problem");
7343
7344 #ifdef ASSERT
7345 if (oop(addr)->klass_or_null_acquire() != NULL) {
7346 // Ignore mark word because we are running concurrent with mutators
7347 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7348 assert(size ==
7349 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7350 "P-mark and computed size do not agree");
7351 }
7352 #endif
7353
7354 } else {
7355 // This should be an initialized object that's alive.
7356 assert(oop(addr)->klass_or_null_acquire() != NULL,
7357 "Should be an initialized object");
7358 // Ignore mark word because we are running concurrent with mutators
7359 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7360 // Verify that the bit map has no bits marked between
7361 // addr and purported end of this block.
7362 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7363 assert(size >= 3, "Necessary for Printezis marks to work");
7364 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7365 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7366 }
7367 return size;
7368 }
7369
7370 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7371 size_t chunkSize) {
7372 // do_post_free_or_garbage_chunk() should only be called in the case
7373 // of the adaptive free list allocator.
7374 const bool fcInFreeLists = fc->is_free();
7375 assert((HeapWord*)fc <= _limit, "sweep invariant");
7376 if (CMSTestInFreeList && fcInFreeLists) {
7377 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7378 }
7379
7380 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7381
7382 HeapWord* const fc_addr = (HeapWord*) fc;
7383
7384 bool coalesce = false;
7385 const size_t left = pointer_delta(fc_addr, freeFinger());
7386 const size_t right = chunkSize;
7387 switch (FLSCoalescePolicy) {
7388 // numeric value forms a coalition aggressiveness metric
7389 case 0: { // never coalesce
7390 coalesce = false;
7391 break;
7392 }
7393 case 1: { // coalesce if left & right chunks on overpopulated lists
7394 coalesce = _sp->coalOverPopulated(left) &&
7395 _sp->coalOverPopulated(right);
7396 break;
7397 }
7398 case 2: { // coalesce if left chunk on overpopulated list (default)
7399 coalesce = _sp->coalOverPopulated(left);
7400 break;
7401 }
7402 case 3: { // coalesce if left OR right chunk on overpopulated list
7403 coalesce = _sp->coalOverPopulated(left) ||
7404 _sp->coalOverPopulated(right);
7405 break;
7406 }
7407 case 4: { // always coalesce
7408 coalesce = true;
7409 break;
7410 }
7411 default:
7412 ShouldNotReachHere();
7413 }
7414
7415 // Should the current free range be coalesced?
7416 // If the chunk is in a free range and either we decided to coalesce above
7417 // or the chunk is near the large block at the end of the heap
7418 // (isNearLargestChunk() returns true), then coalesce this chunk.
7419 const bool doCoalesce = inFreeRange()
7420 && (coalesce || _g->isNearLargestChunk(fc_addr));
7421 if (doCoalesce) {
7422 // Coalesce the current free range on the left with the new
7423 // chunk on the right. If either is on a free list,
7424 // it must be removed from the list and stashed in the closure.
7425 if (freeRangeInFreeLists()) {
7426 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7427 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7428 "Size of free range is inconsistent with chunk size.");
7429 if (CMSTestInFreeList) {
7430 assert(_sp->verify_chunk_in_free_list(ffc),
7431 "Chunk is not in free lists");
7432 }
7433 _sp->coalDeath(ffc->size());
7434 _sp->removeFreeChunkFromFreeLists(ffc);
7435 set_freeRangeInFreeLists(false);
7436 }
7437 if (fcInFreeLists) {
7438 _sp->coalDeath(chunkSize);
7439 assert(fc->size() == chunkSize,
7440 "The chunk has the wrong size or is not in the free lists");
7441 _sp->removeFreeChunkFromFreeLists(fc);
7442 }
7443 set_lastFreeRangeCoalesced(true);
7444 print_free_block_coalesced(fc);
7445 } else { // not in a free range and/or should not coalesce
7446 // Return the current free range and start a new one.
7447 if (inFreeRange()) {
7448 // In a free range but cannot coalesce with the right hand chunk.
7449 // Put the current free range into the free lists.
7450 flush_cur_free_chunk(freeFinger(),
7451 pointer_delta(fc_addr, freeFinger()));
7452 }
7453 // Set up for new free range. Pass along whether the right hand
7454 // chunk is in the free lists.
7455 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7456 }
7457 }
7458
7459 // Lookahead flush:
7460 // If we are tracking a free range, and this is the last chunk that
7461 // we'll look at because its end crosses past _limit, we'll preemptively
7462 // flush it along with any free range we may be holding on to. Note that
7463 // this can be the case only for an already free or freshly garbage
7464 // chunk. If this block is an object, it can never straddle
7465 // over _limit. The "straddling" occurs when _limit is set at
7466 // the previous end of the space when this cycle started, and
7467 // a subsequent heap expansion caused the previously co-terminal
7468 // free block to be coalesced with the newly expanded portion,
7469 // thus rendering _limit a non-block-boundary making it dangerous
7470 // for the sweeper to step over and examine.
7471 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7472 assert(inFreeRange(), "Should only be called if currently in a free range.");
7473 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7474 assert(_sp->used_region().contains(eob - 1),
7475 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7476 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7477 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7478 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7479 if (eob >= _limit) {
7480 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7481 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7482 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7483 "[" PTR_FORMAT "," PTR_FORMAT ")",
7484 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7485 // Return the storage we are tracking back into the free lists.
7486 log_develop_trace(gc, sweep)("Flushing ... ");
7487 assert(freeFinger() < eob, "Error");
7488 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7489 }
7490 }
7491
7492 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7493 assert(inFreeRange(), "Should only be called if currently in a free range.");
7494 assert(size > 0,
7495 "A zero sized chunk cannot be added to the free lists.");
7496 if (!freeRangeInFreeLists()) {
7497 if (CMSTestInFreeList) {
7498 FreeChunk* fc = (FreeChunk*) chunk;
7499 fc->set_size(size);
7500 assert(!_sp->verify_chunk_in_free_list(fc),
7501 "chunk should not be in free lists yet");
7502 }
7503 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7504 // A new free range is going to be starting. The current
7505 // free range has not been added to the free lists yet or
7506 // was removed so add it back.
7507 // If the current free range was coalesced, then the death
7508 // of the free range was recorded. Record a birth now.
7509 if (lastFreeRangeCoalesced()) {
7510 _sp->coalBirth(size);
7511 }
7512 _sp->addChunkAndRepairOffsetTable(chunk, size,
7513 lastFreeRangeCoalesced());
7514 } else {
7515 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7516 }
7517 set_inFreeRange(false);
7518 set_freeRangeInFreeLists(false);
7519 }
7520
7521 // We take a break if we've been at this for a while,
7522 // so as to avoid monopolizing the locks involved.
7523 void SweepClosure::do_yield_work(HeapWord* addr) {
7524 // Return current free chunk being used for coalescing (if any)
7525 // to the appropriate freelist. After yielding, the next
7526 // free block encountered will start a coalescing range of
7527 // free blocks. If the next free block is adjacent to the
7528 // chunk just flushed, they will need to wait for the next
7529 // sweep to be coalesced.
7530 if (inFreeRange()) {
7531 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7532 }
7533
7534 // First give up the locks, then yield, then re-lock.
7535 // We should probably use a constructor/destructor idiom to
7536 // do this unlock/lock or modify the MutexUnlocker class to
7537 // serve our purpose. XXX
7538 assert_lock_strong(_bitMap->lock());
7539 assert_lock_strong(_freelistLock);
7540 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7541 "CMS thread should hold CMS token");
7542 _bitMap->lock()->unlock();
7543 _freelistLock->unlock();
7544 ConcurrentMarkSweepThread::desynchronize(true);
7545 _collector->stopTimer();
7546 _collector->incrementYields();
7547
7548 // See the comment in coordinator_yield()
7549 for (unsigned i = 0; i < CMSYieldSleepCount &&
7550 ConcurrentMarkSweepThread::should_yield() &&
7551 !CMSCollector::foregroundGCIsActive(); ++i) {
7552 os::sleep(Thread::current(), 1, false);
7553 }
7554
7555 ConcurrentMarkSweepThread::synchronize(true);
7556 _freelistLock->lock_without_safepoint_check();
7557 _bitMap->lock()->lock_without_safepoint_check();
7558 _collector->startTimer();
7559 }
7560
7561 #ifndef PRODUCT
7562 // This is actually very useful in a product build if it can
7563 // be called from the debugger. Compile it into the product
7564 // as needed.
7565 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7566 return debug_cms_space->verify_chunk_in_free_list(fc);
7567 }
7568 #endif
7569
7570 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7571 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7572 p2i(fc), fc->size());
7573 }
7574
7575 // CMSIsAliveClosure
7576 bool CMSIsAliveClosure::do_object_b(oop obj) {
7577 HeapWord* addr = (HeapWord*)obj;
7578 return addr != NULL &&
7579 (!_span.contains(addr) || _bit_map->isMarked(addr));
7580 }
7581
7582 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7583 MemRegion span,
7584 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7585 bool cpc):
7586 _collector(collector),
7587 _span(span),
7588 _mark_stack(mark_stack),
7589 _bit_map(bit_map),
7590 _concurrent_precleaning(cpc) {
7591 assert(!_span.is_empty(), "Empty span could spell trouble");
7592 }
7593
7594
7595 // CMSKeepAliveClosure: the serial version
7596 void CMSKeepAliveClosure::do_oop(oop obj) {
7597 HeapWord* addr = (HeapWord*)obj;
7598 if (_span.contains(addr) &&
7599 !_bit_map->isMarked(addr)) {
7600 _bit_map->mark(addr);
7601 bool simulate_overflow = false;
7602 NOT_PRODUCT(
7603 if (CMSMarkStackOverflowALot &&
7604 _collector->simulate_overflow()) {
7605 // simulate a stack overflow
7606 simulate_overflow = true;
7607 }
7608 )
7609 if (simulate_overflow || !_mark_stack->push(obj)) {
7610 if (_concurrent_precleaning) {
7611 // We dirty the overflown object and let the remark
7612 // phase deal with it.
7613 assert(_collector->overflow_list_is_empty(), "Error");
7614 // In the case of object arrays, we need to dirty all of
7615 // the cards that the object spans. No locking or atomics
7616 // are needed since no one else can be mutating the mod union
7617 // table.
7618 if (obj->is_objArray()) {
7619 size_t sz = obj->size();
7620 HeapWord* end_card_addr = align_up(addr + sz, CardTable::card_size);
7621 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7622 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7623 _collector->_modUnionTable.mark_range(redirty_range);
7624 } else {
7625 _collector->_modUnionTable.mark(addr);
7626 }
7627 _collector->_ser_kac_preclean_ovflw++;
7628 } else {
7629 _collector->push_on_overflow_list(obj);
7630 _collector->_ser_kac_ovflw++;
7631 }
7632 }
7633 }
7634 }
7635
7636 // CMSParKeepAliveClosure: a parallel version of the above.
7637 // The work queues are private to each closure (thread),
7638 // but (may be) available for stealing by other threads.
7639 void CMSParKeepAliveClosure::do_oop(oop obj) {
7640 HeapWord* addr = (HeapWord*)obj;
7641 if (_span.contains(addr) &&
7642 !_bit_map->isMarked(addr)) {
7643 // In general, during recursive tracing, several threads
7644 // may be concurrently getting here; the first one to
7645 // "tag" it, claims it.
7646 if (_bit_map->par_mark(addr)) {
7647 bool res = _work_queue->push(obj);
7648 assert(res, "Low water mark should be much less than capacity");
7649 // Do a recursive trim in the hope that this will keep
7650 // stack usage lower, but leave some oops for potential stealers
7651 trim_queue(_low_water_mark);
7652 } // Else, another thread got there first
7653 }
7654 }
7655
7656 void CMSParKeepAliveClosure::trim_queue(uint max) {
7657 while (_work_queue->size() > max) {
7658 oop new_oop;
7659 if (_work_queue->pop_local(new_oop)) {
7660 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7661 assert(_bit_map->isMarked((HeapWord*)new_oop),
7662 "no white objects on this stack!");
7663 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7664 // iterate over the oops in this oop, marking and pushing
7665 // the ones in CMS heap (i.e. in _span).
7666 new_oop->oop_iterate(&_mark_and_push);
7667 }
7668 }
7669 }
7670
7671 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7672 CMSCollector* collector,
7673 MemRegion span, CMSBitMap* bit_map,
7674 OopTaskQueue* work_queue):
7675 _collector(collector),
7676 _span(span),
7677 _work_queue(work_queue),
7678 _bit_map(bit_map) { }
7679
7680 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7681 HeapWord* addr = (HeapWord*)obj;
7682 if (_span.contains(addr) &&
7683 !_bit_map->isMarked(addr)) {
7684 if (_bit_map->par_mark(addr)) {
7685 bool simulate_overflow = false;
7686 NOT_PRODUCT(
7687 if (CMSMarkStackOverflowALot &&
7688 _collector->par_simulate_overflow()) {
7689 // simulate a stack overflow
7690 simulate_overflow = true;
7691 }
7692 )
7693 if (simulate_overflow || !_work_queue->push(obj)) {
7694 _collector->par_push_on_overflow_list(obj);
7695 _collector->_par_kac_ovflw++;
7696 }
7697 } // Else another thread got there already
7698 }
7699 }
7700
7701 //////////////////////////////////////////////////////////////////
7702 // CMSExpansionCause /////////////////////////////
7703 //////////////////////////////////////////////////////////////////
7704 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7705 switch (cause) {
7706 case _no_expansion:
7707 return "No expansion";
7708 case _satisfy_free_ratio:
7709 return "Free ratio";
7710 case _satisfy_promotion:
7711 return "Satisfy promotion";
7712 case _satisfy_allocation:
7713 return "allocation";
7714 case _allocate_par_lab:
7715 return "Par LAB";
7716 case _allocate_par_spooling_space:
7717 return "Par Spooling Space";
7718 case _adaptive_size_policy:
7719 return "Ergonomics";
7720 default:
7721 return "unknown";
7722 }
7723 }
7724
7725 void CMSDrainMarkingStackClosure::do_void() {
7726 // the max number to take from overflow list at a time
7727 const size_t num = _mark_stack->capacity()/4;
7728 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7729 "Overflow list should be NULL during concurrent phases");
7730 while (!_mark_stack->isEmpty() ||
7731 // if stack is empty, check the overflow list
7732 _collector->take_from_overflow_list(num, _mark_stack)) {
7733 oop obj = _mark_stack->pop();
7734 HeapWord* addr = (HeapWord*)obj;
7735 assert(_span.contains(addr), "Should be within span");
7736 assert(_bit_map->isMarked(addr), "Should be marked");
7737 assert(oopDesc::is_oop(obj), "Should be an oop");
7738 obj->oop_iterate(_keep_alive);
7739 }
7740 }
7741
7742 void CMSParDrainMarkingStackClosure::do_void() {
7743 // drain queue
7744 trim_queue(0);
7745 }
7746
7747 // Trim our work_queue so its length is below max at return
7748 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7749 while (_work_queue->size() > max) {
7750 oop new_oop;
7751 if (_work_queue->pop_local(new_oop)) {
7752 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7753 assert(_bit_map->isMarked((HeapWord*)new_oop),
7754 "no white objects on this stack!");
7755 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7756 // iterate over the oops in this oop, marking and pushing
7757 // the ones in CMS heap (i.e. in _span).
7758 new_oop->oop_iterate(&_mark_and_push);
7759 }
7760 }
7761 }
7762
7763 ////////////////////////////////////////////////////////////////////
7764 // Support for Marking Stack Overflow list handling and related code
7765 ////////////////////////////////////////////////////////////////////
7766 // Much of the following code is similar in shape and spirit to the
7767 // code used in ParNewGC. We should try and share that code
7768 // as much as possible in the future.
7769
7770 #ifndef PRODUCT
7771 // Debugging support for CMSStackOverflowALot
7772
7773 // It's OK to call this multi-threaded; the worst thing
7774 // that can happen is that we'll get a bunch of closely
7775 // spaced simulated overflows, but that's OK, in fact
7776 // probably good as it would exercise the overflow code
7777 // under contention.
7778 bool CMSCollector::simulate_overflow() {
7779 if (_overflow_counter-- <= 0) { // just being defensive
7780 _overflow_counter = CMSMarkStackOverflowInterval;
7781 return true;
7782 } else {
7783 return false;
7784 }
7785 }
7786
7787 bool CMSCollector::par_simulate_overflow() {
7788 return simulate_overflow();
7789 }
7790 #endif
7791
7792 // Single-threaded
7793 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7794 assert(stack->isEmpty(), "Expected precondition");
7795 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7796 size_t i = num;
7797 oop cur = _overflow_list;
7798 const markOop proto = markOopDesc::prototype();
7799 NOT_PRODUCT(ssize_t n = 0;)
7800 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7801 next = oop(cur->mark_raw());
7802 cur->set_mark_raw(proto); // until proven otherwise
7803 assert(oopDesc::is_oop(cur), "Should be an oop");
7804 bool res = stack->push(cur);
7805 assert(res, "Bit off more than can chew?");
7806 NOT_PRODUCT(n++;)
7807 }
7808 _overflow_list = cur;
7809 #ifndef PRODUCT
7810 assert(_num_par_pushes >= n, "Too many pops?");
7811 _num_par_pushes -=n;
7812 #endif
7813 return !stack->isEmpty();
7814 }
7815
7816 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7817 // (MT-safe) Get a prefix of at most "num" from the list.
7818 // The overflow list is chained through the mark word of
7819 // each object in the list. We fetch the entire list,
7820 // break off a prefix of the right size and return the
7821 // remainder. If other threads try to take objects from
7822 // the overflow list at that time, they will wait for
7823 // some time to see if data becomes available. If (and
7824 // only if) another thread places one or more object(s)
7825 // on the global list before we have returned the suffix
7826 // to the global list, we will walk down our local list
7827 // to find its end and append the global list to
7828 // our suffix before returning it. This suffix walk can
7829 // prove to be expensive (quadratic in the amount of traffic)
7830 // when there are many objects in the overflow list and
7831 // there is much producer-consumer contention on the list.
7832 // *NOTE*: The overflow list manipulation code here and
7833 // in ParNewGeneration:: are very similar in shape,
7834 // except that in the ParNew case we use the old (from/eden)
7835 // copy of the object to thread the list via its klass word.
7836 // Because of the common code, if you make any changes in
7837 // the code below, please check the ParNew version to see if
7838 // similar changes might be needed.
7839 // CR 6797058 has been filed to consolidate the common code.
7840 bool CMSCollector::par_take_from_overflow_list(size_t num,
7841 OopTaskQueue* work_q,
7842 int no_of_gc_threads) {
7843 assert(work_q->size() == 0, "First empty local work queue");
7844 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7845 if (_overflow_list == NULL) {
7846 return false;
7847 }
7848 // Grab the entire list; we'll put back a suffix
7849 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7850 Thread* tid = Thread::current();
7851 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7852 // set to ParallelGCThreads.
7853 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7854 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7855 // If the list is busy, we spin for a short while,
7856 // sleeping between attempts to get the list.
7857 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7858 os::sleep(tid, sleep_time_millis, false);
7859 if (_overflow_list == NULL) {
7860 // Nothing left to take
7861 return false;
7862 } else if (_overflow_list != BUSY) {
7863 // Try and grab the prefix
7864 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7865 }
7866 }
7867 // If the list was found to be empty, or we spun long
7868 // enough, we give up and return empty-handed. If we leave
7869 // the list in the BUSY state below, it must be the case that
7870 // some other thread holds the overflow list and will set it
7871 // to a non-BUSY state in the future.
7872 if (prefix == NULL || prefix == BUSY) {
7873 // Nothing to take or waited long enough
7874 if (prefix == NULL) {
7875 // Write back the NULL in case we overwrote it with BUSY above
7876 // and it is still the same value.
7877 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7878 }
7879 return false;
7880 }
7881 assert(prefix != NULL && prefix != BUSY, "Error");
7882 size_t i = num;
7883 oop cur = prefix;
7884 // Walk down the first "num" objects, unless we reach the end.
7885 for (; i > 1 && cur->mark_raw() != NULL; cur = oop(cur->mark_raw()), i--);
7886 if (cur->mark_raw() == NULL) {
7887 // We have "num" or fewer elements in the list, so there
7888 // is nothing to return to the global list.
7889 // Write back the NULL in lieu of the BUSY we wrote
7890 // above, if it is still the same value.
7891 if (_overflow_list == BUSY) {
7892 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7893 }
7894 } else {
7895 // Chop off the suffix and return it to the global list.
7896 assert(cur->mark_raw() != BUSY, "Error");
7897 oop suffix_head = cur->mark_raw(); // suffix will be put back on global list
7898 cur->set_mark_raw(NULL); // break off suffix
7899 // It's possible that the list is still in the empty(busy) state
7900 // we left it in a short while ago; in that case we may be
7901 // able to place back the suffix without incurring the cost
7902 // of a walk down the list.
7903 oop observed_overflow_list = _overflow_list;
7904 oop cur_overflow_list = observed_overflow_list;
7905 bool attached = false;
7906 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7907 observed_overflow_list =
7908 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7909 if (cur_overflow_list == observed_overflow_list) {
7910 attached = true;
7911 break;
7912 } else cur_overflow_list = observed_overflow_list;
7913 }
7914 if (!attached) {
7915 // Too bad, someone else sneaked in (at least) an element; we'll need
7916 // to do a splice. Find tail of suffix so we can prepend suffix to global
7917 // list.
7918 for (cur = suffix_head; cur->mark_raw() != NULL; cur = (oop)(cur->mark_raw()));
7919 oop suffix_tail = cur;
7920 assert(suffix_tail != NULL && suffix_tail->mark_raw() == NULL,
7921 "Tautology");
7922 observed_overflow_list = _overflow_list;
7923 do {
7924 cur_overflow_list = observed_overflow_list;
7925 if (cur_overflow_list != BUSY) {
7926 // Do the splice ...
7927 suffix_tail->set_mark_raw(markOop(cur_overflow_list));
7928 } else { // cur_overflow_list == BUSY
7929 suffix_tail->set_mark_raw(NULL);
7930 }
7931 // ... and try to place spliced list back on overflow_list ...
7932 observed_overflow_list =
7933 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7934 } while (cur_overflow_list != observed_overflow_list);
7935 // ... until we have succeeded in doing so.
7936 }
7937 }
7938
7939 // Push the prefix elements on work_q
7940 assert(prefix != NULL, "control point invariant");
7941 const markOop proto = markOopDesc::prototype();
7942 oop next;
7943 NOT_PRODUCT(ssize_t n = 0;)
7944 for (cur = prefix; cur != NULL; cur = next) {
7945 next = oop(cur->mark_raw());
7946 cur->set_mark_raw(proto); // until proven otherwise
7947 assert(oopDesc::is_oop(cur), "Should be an oop");
7948 bool res = work_q->push(cur);
7949 assert(res, "Bit off more than we can chew?");
7950 NOT_PRODUCT(n++;)
7951 }
7952 #ifndef PRODUCT
7953 assert(_num_par_pushes >= n, "Too many pops?");
7954 Atomic::sub(n, &_num_par_pushes);
7955 #endif
7956 return true;
7957 }
7958
7959 // Single-threaded
7960 void CMSCollector::push_on_overflow_list(oop p) {
7961 NOT_PRODUCT(_num_par_pushes++;)
7962 assert(oopDesc::is_oop(p), "Not an oop");
7963 preserve_mark_if_necessary(p);
7964 p->set_mark_raw((markOop)_overflow_list);
7965 _overflow_list = p;
7966 }
7967
7968 // Multi-threaded; use CAS to prepend to overflow list
7969 void CMSCollector::par_push_on_overflow_list(oop p) {
7970 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7971 assert(oopDesc::is_oop(p), "Not an oop");
7972 par_preserve_mark_if_necessary(p);
7973 oop observed_overflow_list = _overflow_list;
7974 oop cur_overflow_list;
7975 do {
7976 cur_overflow_list = observed_overflow_list;
7977 if (cur_overflow_list != BUSY) {
7978 p->set_mark_raw(markOop(cur_overflow_list));
7979 } else {
7980 p->set_mark_raw(NULL);
7981 }
7982 observed_overflow_list =
7983 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7984 } while (cur_overflow_list != observed_overflow_list);
7985 }
7986 #undef BUSY
7987
7988 // Single threaded
7989 // General Note on GrowableArray: pushes may silently fail
7990 // because we are (temporarily) out of C-heap for expanding
7991 // the stack. The problem is quite ubiquitous and affects
7992 // a lot of code in the JVM. The prudent thing for GrowableArray
7993 // to do (for now) is to exit with an error. However, that may
7994 // be too draconian in some cases because the caller may be
7995 // able to recover without much harm. For such cases, we
7996 // should probably introduce a "soft_push" method which returns
7997 // an indication of success or failure with the assumption that
7998 // the caller may be able to recover from a failure; code in
7999 // the VM can then be changed, incrementally, to deal with such
8000 // failures where possible, thus, incrementally hardening the VM
8001 // in such low resource situations.
8002 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8003 _preserved_oop_stack.push(p);
8004 _preserved_mark_stack.push(m);
8005 assert(m == p->mark_raw(), "Mark word changed");
8006 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8007 "bijection");
8008 }
8009
8010 // Single threaded
8011 void CMSCollector::preserve_mark_if_necessary(oop p) {
8012 markOop m = p->mark_raw();
8013 if (m->must_be_preserved(p)) {
8014 preserve_mark_work(p, m);
8015 }
8016 }
8017
8018 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8019 markOop m = p->mark_raw();
8020 if (m->must_be_preserved(p)) {
8021 MutexLocker x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8022 // Even though we read the mark word without holding
8023 // the lock, we are assured that it will not change
8024 // because we "own" this oop, so no other thread can
8025 // be trying to push it on the overflow list; see
8026 // the assertion in preserve_mark_work() that checks
8027 // that m == p->mark_raw().
8028 preserve_mark_work(p, m);
8029 }
8030 }
8031
8032 // We should be able to do this multi-threaded,
8033 // a chunk of stack being a task (this is
8034 // correct because each oop only ever appears
8035 // once in the overflow list. However, it's
8036 // not very easy to completely overlap this with
8037 // other operations, so will generally not be done
8038 // until all work's been completed. Because we
8039 // expect the preserved oop stack (set) to be small,
8040 // it's probably fine to do this single-threaded.
8041 // We can explore cleverer concurrent/overlapped/parallel
8042 // processing of preserved marks if we feel the
8043 // need for this in the future. Stack overflow should
8044 // be so rare in practice and, when it happens, its
8045 // effect on performance so great that this will
8046 // likely just be in the noise anyway.
8047 void CMSCollector::restore_preserved_marks_if_any() {
8048 assert(SafepointSynchronize::is_at_safepoint(),
8049 "world should be stopped");
8050 assert(Thread::current()->is_ConcurrentGC_thread() ||
8051 Thread::current()->is_VM_thread(),
8052 "should be single-threaded");
8053 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8054 "bijection");
8055
8056 while (!_preserved_oop_stack.is_empty()) {
8057 oop p = _preserved_oop_stack.pop();
8058 assert(oopDesc::is_oop(p), "Should be an oop");
8059 assert(_span.contains(p), "oop should be in _span");
8060 assert(p->mark_raw() == markOopDesc::prototype(),
8061 "Set when taken from overflow list");
8062 markOop m = _preserved_mark_stack.pop();
8063 p->set_mark_raw(m);
8064 }
8065 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8066 "stacks were cleared above");
8067 }
8068
8069 #ifndef PRODUCT
8070 bool CMSCollector::no_preserved_marks() const {
8071 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8072 }
8073 #endif
8074
8075 // Transfer some number of overflown objects to usual marking
8076 // stack. Return true if some objects were transferred.
8077 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8078 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8079 (size_t)ParGCDesiredObjsFromOverflowList);
8080
8081 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8082 assert(_collector->overflow_list_is_empty() || res,
8083 "If list is not empty, we should have taken something");
8084 assert(!res || !_mark_stack->isEmpty(),
8085 "If we took something, it should now be on our stack");
8086 return res;
8087 }
8088
8089 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8090 size_t res = _sp->block_size_no_stall(addr, _collector);
8091 if (_sp->block_is_obj(addr)) {
8092 if (_live_bit_map->isMarked(addr)) {
8093 // It can't have been dead in a previous cycle
8094 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8095 } else {
8096 _dead_bit_map->mark(addr); // mark the dead object
8097 }
8098 }
8099 // Could be 0, if the block size could not be computed without stalling.
8100 return res;
8101 }
8102
8103 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8104 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8105 switch (phase) {
8106 case CMSCollector::InitialMarking:
8107 initialize(manager /* GC manager */ ,
8108 cause /* cause of the GC */,
8109 true /* allMemoryPoolsAffected */,
8110 true /* recordGCBeginTime */,
8111 true /* recordPreGCUsage */,
8112 false /* recordPeakUsage */,
8113 false /* recordPostGCusage */,
8114 true /* recordAccumulatedGCTime */,
8115 false /* recordGCEndTime */,
8116 false /* countCollection */ );
8117 break;
8118
8119 case CMSCollector::FinalMarking:
8120 initialize(manager /* GC manager */ ,
8121 cause /* cause of the GC */,
8122 true /* allMemoryPoolsAffected */,
8123 false /* recordGCBeginTime */,
8124 false /* recordPreGCUsage */,
8125 false /* recordPeakUsage */,
8126 false /* recordPostGCusage */,
8127 true /* recordAccumulatedGCTime */,
8128 false /* recordGCEndTime */,
8129 false /* countCollection */ );
8130 break;
8131
8132 case CMSCollector::Sweeping:
8133 initialize(manager /* GC manager */ ,
8134 cause /* cause of the GC */,
8135 true /* allMemoryPoolsAffected */,
8136 false /* recordGCBeginTime */,
8137 false /* recordPreGCUsage */,
8138 true /* recordPeakUsage */,
8139 true /* recordPostGCusage */,
8140 false /* recordAccumulatedGCTime */,
8141 true /* recordGCEndTime */,
8142 true /* countCollection */ );
8143 break;
8144
8145 default:
8146 ShouldNotReachHere();
8147 }
8148 }