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