1 /*
2 * Copyright (c) 2001, 2015, 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/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
308
309 // Generation Counters - generation 1, 1 subspace
310 _gen_counters = new GenerationCounters(gen_name, 1, 1,
311 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
312
313 _space_counters = new GSpaceCounters(gen_name, 0,
314 _virtual_space.reserved_size(),
315 this, _gen_counters);
316 }
317
318 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
319 _cms_gen(cms_gen)
320 {
321 assert(alpha <= 100, "bad value");
322 _saved_alpha = alpha;
323
324 // Initialize the alphas to the bootstrap value of 100.
325 _gc0_alpha = _cms_alpha = 100;
326
327 _cms_begin_time.update();
328 _cms_end_time.update();
329
330 _gc0_duration = 0.0;
331 _gc0_period = 0.0;
332 _gc0_promoted = 0;
333
334 _cms_duration = 0.0;
335 _cms_period = 0.0;
336 _cms_allocated = 0;
337
338 _cms_used_at_gc0_begin = 0;
339 _cms_used_at_gc0_end = 0;
340 _allow_duty_cycle_reduction = false;
341 _valid_bits = 0;
342 }
343
344 double CMSStats::cms_free_adjustment_factor(size_t free) const {
345 // TBD: CR 6909490
346 return 1.0;
347 }
348
349 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
350 }
351
352 // If promotion failure handling is on use
353 // the padded average size of the promotion for each
354 // young generation collection.
355 double CMSStats::time_until_cms_gen_full() const {
356 size_t cms_free = _cms_gen->cmsSpace()->free();
357 GenCollectedHeap* gch = GenCollectedHeap::heap();
358 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
359 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
360 if (cms_free > expected_promotion) {
361 // Start a cms collection if there isn't enough space to promote
362 // for the next minor collection. Use the padded average as
363 // a safety factor.
364 cms_free -= expected_promotion;
365
366 // Adjust by the safety factor.
367 double cms_free_dbl = (double)cms_free;
368 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
369 // Apply a further correction factor which tries to adjust
370 // for recent occurance of concurrent mode failures.
371 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
372 cms_free_dbl = cms_free_dbl * cms_adjustment;
373
374 if (PrintGCDetails && Verbose) {
375 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
376 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
377 cms_free, expected_promotion);
378 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
379 cms_free_dbl, cms_consumption_rate() + 1.0);
380 }
381 // Add 1 in case the consumption rate goes to zero.
382 return cms_free_dbl / (cms_consumption_rate() + 1.0);
383 }
384 return 0.0;
385 }
386
387 // Compare the duration of the cms collection to the
388 // time remaining before the cms generation is empty.
389 // Note that the time from the start of the cms collection
390 // to the start of the cms sweep (less than the total
391 // duration of the cms collection) can be used. This
392 // has been tried and some applications experienced
393 // promotion failures early in execution. This was
394 // possibly because the averages were not accurate
395 // enough at the beginning.
396 double CMSStats::time_until_cms_start() const {
397 // We add "gc0_period" to the "work" calculation
398 // below because this query is done (mostly) at the
399 // end of a scavenge, so we need to conservatively
400 // account for that much possible delay
401 // in the query so as to avoid concurrent mode failures
402 // due to starting the collection just a wee bit too
403 // late.
404 double work = cms_duration() + gc0_period();
405 double deadline = time_until_cms_gen_full();
406 // If a concurrent mode failure occurred recently, we want to be
407 // more conservative and halve our expected time_until_cms_gen_full()
408 if (work > deadline) {
409 if (Verbose && PrintGCDetails) {
410 gclog_or_tty->print(
411 " CMSCollector: collect because of anticipated promotion "
412 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
413 gc0_period(), time_until_cms_gen_full());
414 }
415 return 0.0;
416 }
417 return work - deadline;
418 }
419
420 #ifndef PRODUCT
421 void CMSStats::print_on(outputStream *st) const {
422 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
423 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
424 gc0_duration(), gc0_period(), gc0_promoted());
425 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
426 cms_duration(), cms_period(), cms_allocated());
427 st->print(",cms_since_beg=%g,cms_since_end=%g",
428 cms_time_since_begin(), cms_time_since_end());
429 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
430 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
431
432 if (valid()) {
433 st->print(",promo_rate=%g,cms_alloc_rate=%g",
434 promotion_rate(), cms_allocation_rate());
435 st->print(",cms_consumption_rate=%g,time_until_full=%g",
436 cms_consumption_rate(), time_until_cms_gen_full());
437 }
438 st->print(" ");
439 }
440 #endif // #ifndef PRODUCT
441
442 CMSCollector::CollectorState CMSCollector::_collectorState =
443 CMSCollector::Idling;
444 bool CMSCollector::_foregroundGCIsActive = false;
445 bool CMSCollector::_foregroundGCShouldWait = false;
446
447 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
448 CardTableRS* ct,
449 ConcurrentMarkSweepPolicy* cp):
450 _cmsGen(cmsGen),
451 _ct(ct),
452 _ref_processor(NULL), // will be set later
453 _conc_workers(NULL), // may be set later
454 _abort_preclean(false),
455 _start_sampling(false),
456 _between_prologue_and_epilogue(false),
457 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock",
458 CMSParallelFullGC && ShareCMSMarkBitMapWithParallelFullGC),
459 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
460 -1 /* lock-free */, "No_lock" /* dummy */),
461 _modUnionClosurePar(&_modUnionTable),
462 // Adjust my span to cover old (cms) gen
463 _span(cmsGen->reserved()),
464 // Construct the is_alive_closure with _span & markBitMap
465 _is_alive_closure(_span, &_markBitMap),
466 _restart_addr(NULL),
467 _overflow_list(NULL),
468 _stats(cmsGen),
469 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
470 //verify that this lock should be acquired with safepoint check.
471 Monitor::_safepoint_check_sometimes)),
472 _eden_chunk_array(NULL), // may be set in ctor body
473 _eden_chunk_capacity(0), // -- ditto --
474 _eden_chunk_index(0), // -- ditto --
475 _survivor_plab_array(NULL), // -- ditto --
476 _survivor_chunk_array(NULL), // -- ditto --
477 _survivor_chunk_capacity(0), // -- ditto --
478 _survivor_chunk_index(0), // -- ditto --
479 _ser_pmc_preclean_ovflw(0),
480 _ser_kac_preclean_ovflw(0),
481 _ser_pmc_remark_ovflw(0),
482 _par_pmc_remark_ovflw(0),
483 _ser_kac_ovflw(0),
484 _par_kac_ovflw(0),
485 #ifndef PRODUCT
486 _num_par_pushes(0),
487 #endif
488 _collection_count_start(0),
489 _verifying(false),
490 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
491 _completed_initialization(false),
492 _collector_policy(cp),
493 _should_unload_classes(CMSClassUnloadingEnabled),
494 _concurrent_cycles_since_last_unload(0),
495 _roots_scanning_options(GenCollectedHeap::SO_None),
496 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
497 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
498 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
499 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
500 _cms_start_registered(false)
501 {
502 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
503 ExplicitGCInvokesConcurrent = true;
504 }
505 // Now expand the span and allocate the collection support structures
506 // (MUT, marking bit map etc.) to cover both generations subject to
507 // collection.
508
509 // For use by dirty card to oop closures.
510 _cmsGen->cmsSpace()->set_collector(this);
511
512 // Allocate MUT and marking bit map
513 {
514 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
515 if (!_markBitMap.allocate(_span)) {
516 warning("Failed to allocate CMS Bit Map");
517 return;
518 }
519 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
520 }
521 {
522 _modUnionTable.allocate(_span);
523 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
524 }
525
526 if (!_markStack.allocate(MarkStackSize)) {
527 warning("Failed to allocate CMS Marking Stack");
528 return;
529 }
530
531 // Support for multi-threaded concurrent phases
532 if (CMSConcurrentMTEnabled) {
533 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
534 // just for now
535 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
536 }
537 if (ConcGCThreads > 1) {
538 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
539 ConcGCThreads, true);
540 if (_conc_workers == NULL) {
541 warning("GC/CMS: _conc_workers allocation failure: "
542 "forcing -CMSConcurrentMTEnabled");
543 CMSConcurrentMTEnabled = false;
544 } else {
545 _conc_workers->initialize_workers();
546 }
547 } else {
548 CMSConcurrentMTEnabled = false;
549 }
550 }
551 if (!CMSConcurrentMTEnabled) {
552 ConcGCThreads = 0;
553 } else {
554 // Turn off CMSCleanOnEnter optimization temporarily for
555 // the MT case where it's not fixed yet; see 6178663.
556 CMSCleanOnEnter = false;
557 }
558 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
559 "Inconsistency");
560
561 // Parallel task queues; these are shared for the
562 // concurrent and stop-world phases of CMS, but
563 // are not shared with parallel scavenge (ParNew).
564 {
565 uint i;
566 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
567
568 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
569 || ParallelRefProcEnabled)
570 && num_queues > 0) {
571 _task_queues = new OopTaskQueueSet(num_queues);
572 if (_task_queues == NULL) {
573 warning("task_queues allocation failure.");
574 return;
575 }
576 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
577 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
578 for (i = 0; i < num_queues; i++) {
579 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
580 if (q == NULL) {
581 warning("work_queue allocation failure.");
582 return;
583 }
584 _task_queues->register_queue(i, q);
585 }
586 for (i = 0; i < num_queues; i++) {
587 _task_queues->queue(i)->initialize();
588 _hash_seed[i] = 17; // copied from ParNew
589 }
590 }
591 }
592
593 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
594
595 // Clip CMSBootstrapOccupancy between 0 and 100.
596 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
597
598 // Now tell CMS generations the identity of their collector
599 ConcurrentMarkSweepGeneration::set_collector(this);
600
601 // Create & start a CMS thread for this CMS collector
602 _cmsThread = ConcurrentMarkSweepThread::start(this);
603 assert(cmsThread() != NULL, "CMS Thread should have been created");
604 assert(cmsThread()->collector() == this,
605 "CMS Thread should refer to this gen");
606 assert(CGC_lock != NULL, "Where's the CGC_lock?");
607
608 // Support for parallelizing young gen rescan
609 GenCollectedHeap* gch = GenCollectedHeap::heap();
610 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
611 _young_gen = (ParNewGeneration*)gch->young_gen();
612 if (gch->supports_inline_contig_alloc()) {
613 _top_addr = gch->top_addr();
614 _end_addr = gch->end_addr();
615 assert(_young_gen != NULL, "no _young_gen");
616 _eden_chunk_index = 0;
617 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
618 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
619 }
620
621 // Support for parallelizing survivor space rescan
622 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
623 const size_t max_plab_samples =
624 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
625
626 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
627 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
628 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
629 _survivor_chunk_capacity = 2*max_plab_samples;
630 for (uint i = 0; i < ParallelGCThreads; i++) {
631 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
632 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
633 assert(cur->end() == 0, "Should be 0");
634 assert(cur->array() == vec, "Should be vec");
635 assert(cur->capacity() == max_plab_samples, "Error");
636 }
637 }
638
639 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
640 _gc_counters = new CollectorCounters("CMS", 1);
641 _completed_initialization = true;
642 _inter_sweep_timer.start(); // start of time
643 }
644
645 size_t CMSCollector::plab_sample_minimum_size() {
646 // The default value of MinTLABSize is 2k, but there is
647 // no way to get the default value if the flag has been overridden.
648 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
649 }
650
651 const char* ConcurrentMarkSweepGeneration::name() const {
652 return "concurrent mark-sweep generation";
653 }
654 void ConcurrentMarkSweepGeneration::update_counters() {
655 if (UsePerfData) {
656 _space_counters->update_all();
657 _gen_counters->update_all();
658 }
659 }
660
661 // this is an optimized version of update_counters(). it takes the
662 // used value as a parameter rather than computing it.
663 //
664 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
665 if (UsePerfData) {
666 _space_counters->update_used(used);
667 _space_counters->update_capacity();
668 _gen_counters->update_all();
669 }
670 }
671
672 void ConcurrentMarkSweepGeneration::print() const {
673 Generation::print();
674 cmsSpace()->print();
675 }
676
677 #ifndef PRODUCT
678 void ConcurrentMarkSweepGeneration::print_statistics() {
679 cmsSpace()->printFLCensus(0);
680 }
681 #endif
682
683 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
684 GenCollectedHeap* gch = GenCollectedHeap::heap();
685 if (PrintGCDetails) {
686 // I didn't want to change the logging when removing the level concept,
687 // but I guess this logging could say "old" or something instead of "1".
688 assert(gch->is_old_gen(this),
689 "The CMS generation should be the old generation");
690 uint level = 1;
691 if (Verbose) {
692 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
693 level, short_name(), s, used(), capacity());
694 } else {
695 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
696 level, short_name(), s, used() / K, capacity() / K);
697 }
698 }
699 if (Verbose) {
700 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
701 gch->used(), gch->capacity());
702 } else {
703 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
704 gch->used() / K, gch->capacity() / K);
705 }
706 }
707
708 size_t
709 ConcurrentMarkSweepGeneration::contiguous_available() const {
710 // dld proposes an improvement in precision here. If the committed
711 // part of the space ends in a free block we should add that to
712 // uncommitted size in the calculation below. Will make this
713 // change later, staying with the approximation below for the
714 // time being. -- ysr.
715 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
716 }
717
718 size_t
719 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
720 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
721 }
722
723 size_t ConcurrentMarkSweepGeneration::max_available() const {
724 return free() + _virtual_space.uncommitted_size();
725 }
726
727 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
728 size_t available = max_available();
729 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
730 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
731 if (Verbose && PrintGCDetails) {
732 gclog_or_tty->print_cr(
733 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
734 "max_promo(" SIZE_FORMAT ")",
735 res? "":" not", available, res? ">=":"<",
736 av_promo, max_promotion_in_bytes);
737 }
738 return res;
739 }
740
741 // At a promotion failure dump information on block layout in heap
742 // (cms old generation).
743 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
744 if (CMSDumpAtPromotionFailure) {
745 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
746 }
747 }
748
749 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
750 // Clear the promotion information. These pointers can be adjusted
751 // along with all the other pointers into the heap but
752 // compaction is expected to be a rare event with
753 // a heap using cms so don't do it without seeing the need.
754 for (uint i = 0; i < ParallelGCThreads; i++) {
755 _par_gc_thread_states[i]->promo.reset();
756 }
757 }
758
759 void ConcurrentMarkSweepGeneration::compute_new_size() {
760 assert_locked_or_safepoint(Heap_lock);
761
762 // If incremental collection failed, we just want to expand
763 // to the limit.
764 if (incremental_collection_failed()) {
765 clear_incremental_collection_failed();
766 grow_to_reserved();
767 return;
768 }
769
770 // The heap has been compacted but not reset yet.
771 // Any metric such as free() or used() will be incorrect.
772
773 CardGeneration::compute_new_size();
774
775 // Reset again after a possible resizing
776 if (did_compact()) {
777 cmsSpace()->reset_after_compaction();
778 }
779 }
780
781 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
782 assert_locked_or_safepoint(Heap_lock);
783
784 // If incremental collection failed, we just want to expand
785 // to the limit.
786 if (incremental_collection_failed()) {
787 clear_incremental_collection_failed();
788 grow_to_reserved();
789 return;
790 }
791
792 double free_percentage = ((double) free()) / capacity();
793 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
794 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
795
796 // compute expansion delta needed for reaching desired free percentage
797 if (free_percentage < desired_free_percentage) {
798 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
799 assert(desired_capacity >= capacity(), "invalid expansion size");
800 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
801 if (PrintGCDetails && Verbose) {
802 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
803 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
804 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
805 gclog_or_tty->print_cr(" Desired free fraction %f",
806 desired_free_percentage);
807 gclog_or_tty->print_cr(" Maximum free fraction %f",
808 maximum_free_percentage);
809 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity()/1000);
810 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT,
811 desired_capacity/1000);
812 GenCollectedHeap* gch = GenCollectedHeap::heap();
813 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
814 size_t young_size = gch->young_gen()->capacity();
815 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
816 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT,
817 unsafe_max_alloc_nogc()/1000);
818 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT,
819 contiguous_available()/1000);
820 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)",
821 expand_bytes);
822 }
823 // safe if expansion fails
824 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
825 if (PrintGCDetails && Verbose) {
826 gclog_or_tty->print_cr(" Expanded free fraction %f",
827 ((double) free()) / capacity());
828 }
829 } else {
830 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
831 assert(desired_capacity <= capacity(), "invalid expansion size");
832 size_t shrink_bytes = capacity() - desired_capacity;
833 // Don't shrink unless the delta is greater than the minimum shrink we want
834 if (shrink_bytes >= MinHeapDeltaBytes) {
835 shrink_free_list_by(shrink_bytes);
836 }
837 }
838 }
839
840 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
841 return cmsSpace()->freelistLock();
842 }
843
844 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
845 bool tlab) {
846 CMSSynchronousYieldRequest yr;
847 MutexLockerEx x(freelistLock(),
848 Mutex::_no_safepoint_check_flag);
849 return have_lock_and_allocate(size, tlab);
850 }
851
852 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
853 bool tlab /* ignored */) {
854 assert_lock_strong(freelistLock());
855 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
856 HeapWord* res = cmsSpace()->allocate(adjustedSize);
857 // Allocate the object live (grey) if the background collector has
858 // started marking. This is necessary because the marker may
859 // have passed this address and consequently this object will
860 // not otherwise be greyed and would be incorrectly swept up.
861 // Note that if this object contains references, the writing
862 // of those references will dirty the card containing this object
863 // allowing the object to be blackened (and its references scanned)
864 // either during a preclean phase or at the final checkpoint.
865 if (res != NULL) {
866 // We may block here with an uninitialized object with
867 // its mark-bit or P-bits not yet set. Such objects need
868 // to be safely navigable by block_start().
869 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
870 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
871 collector()->direct_allocated(res, adjustedSize);
872 _direct_allocated_words += adjustedSize;
873 // allocation counters
874 NOT_PRODUCT(
875 _numObjectsAllocated++;
876 _numWordsAllocated += (int)adjustedSize;
877 )
878 }
879 return res;
880 }
881
882 // In the case of direct allocation by mutators in a generation that
883 // is being concurrently collected, the object must be allocated
884 // live (grey) if the background collector has started marking.
885 // This is necessary because the marker may
886 // have passed this address and consequently this object will
887 // not otherwise be greyed and would be incorrectly swept up.
888 // Note that if this object contains references, the writing
889 // of those references will dirty the card containing this object
890 // allowing the object to be blackened (and its references scanned)
891 // either during a preclean phase or at the final checkpoint.
892 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
893 assert(_markBitMap.covers(start, size), "Out of bounds");
894 if (_collectorState >= Marking) {
895 MutexLockerEx y(_markBitMap.lock(),
896 Mutex::_no_safepoint_check_flag);
897 // [see comments preceding SweepClosure::do_blk() below for details]
898 //
899 // Can the P-bits be deleted now? JJJ
900 //
901 // 1. need to mark the object as live so it isn't collected
902 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
903 // 3. need to mark the end of the object so marking, precleaning or sweeping
904 // can skip over uninitialized or unparsable objects. An allocated
905 // object is considered uninitialized for our purposes as long as
906 // its klass word is NULL. All old gen objects are parsable
907 // as soon as they are initialized.)
908 _markBitMap.mark(start); // object is live
909 _markBitMap.mark(start + 1); // object is potentially uninitialized?
910 _markBitMap.mark(start + size - 1);
911 // mark end of object
912 }
913 // check that oop looks uninitialized
914 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
915 }
916
917 void CMSCollector::promoted(bool par, HeapWord* start,
918 bool is_obj_array, size_t obj_size) {
919 assert(_markBitMap.covers(start), "Out of bounds");
920 // See comment in direct_allocated() about when objects should
921 // be allocated live.
922 if (_collectorState >= Marking) {
923 // we already hold the marking bit map lock, taken in
924 // the prologue
925 if (par) {
926 _markBitMap.par_mark(start);
927 } else {
928 _markBitMap.mark(start);
929 }
930 // We don't need to mark the object as uninitialized (as
931 // in direct_allocated above) because this is being done with the
932 // world stopped and the object will be initialized by the
933 // time the marking, precleaning or sweeping get to look at it.
934 // But see the code for copying objects into the CMS generation,
935 // where we need to ensure that concurrent readers of the
936 // block offset table are able to safely navigate a block that
937 // is in flux from being free to being allocated (and in
938 // transition while being copied into) and subsequently
939 // becoming a bona-fide object when the copy/promotion is complete.
940 assert(SafepointSynchronize::is_at_safepoint(),
941 "expect promotion only at safepoints");
942
943 if (_collectorState < Sweeping) {
944 // Mark the appropriate cards in the modUnionTable, so that
945 // this object gets scanned before the sweep. If this is
946 // not done, CMS generation references in the object might
947 // not get marked.
948 // For the case of arrays, which are otherwise precisely
949 // marked, we need to dirty the entire array, not just its head.
950 if (is_obj_array) {
951 // The [par_]mark_range() method expects mr.end() below to
952 // be aligned to the granularity of a bit's representation
953 // in the heap. In the case of the MUT below, that's a
954 // card size.
955 MemRegion mr(start,
956 (HeapWord*)round_to((intptr_t)(start + obj_size),
957 CardTableModRefBS::card_size /* bytes */));
958 if (par) {
959 _modUnionTable.par_mark_range(mr);
960 } else {
961 _modUnionTable.mark_range(mr);
962 }
963 } else { // not an obj array; we can just mark the head
964 if (par) {
965 _modUnionTable.par_mark(start);
966 } else {
967 _modUnionTable.mark(start);
968 }
969 }
970 }
971 }
972 }
973
974 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
975 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
976 // allocate, copy and if necessary update promoinfo --
977 // delegate to underlying space.
978 assert_lock_strong(freelistLock());
979
980 #ifndef PRODUCT
981 if (GenCollectedHeap::heap()->promotion_should_fail()) {
982 return NULL;
983 }
984 #endif // #ifndef PRODUCT
985
986 oop res = _cmsSpace->promote(obj, obj_size);
987 if (res == NULL) {
988 // expand and retry
989 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
990 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
991 // Since this is the old generation, we don't try to promote
992 // into a more senior generation.
993 res = _cmsSpace->promote(obj, obj_size);
994 }
995 if (res != NULL) {
996 // See comment in allocate() about when objects should
997 // be allocated live.
998 assert(obj->is_oop(), "Will dereference klass pointer below");
999 collector()->promoted(false, // Not parallel
1000 (HeapWord*)res, obj->is_objArray(), obj_size);
1001 // promotion counters
1002 NOT_PRODUCT(
1003 _numObjectsPromoted++;
1004 _numWordsPromoted +=
1005 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1006 )
1007 }
1008 return res;
1009 }
1010
1011
1012 // IMPORTANT: Notes on object size recognition in CMS.
1013 // ---------------------------------------------------
1014 // A block of storage in the CMS generation is always in
1015 // one of three states. A free block (FREE), an allocated
1016 // object (OBJECT) whose size() method reports the correct size,
1017 // and an intermediate state (TRANSIENT) in which its size cannot
1018 // be accurately determined.
1019 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1020 // -----------------------------------------------------
1021 // FREE: klass_word & 1 == 1; mark_word holds block size
1022 //
1023 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1024 // obj->size() computes correct size
1025 //
1026 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1027 //
1028 // STATE IDENTIFICATION: (64 bit+COOPS)
1029 // ------------------------------------
1030 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1031 //
1032 // OBJECT: klass_word installed; klass_word != 0;
1033 // obj->size() computes correct size
1034 //
1035 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1036 //
1037 //
1038 // STATE TRANSITION DIAGRAM
1039 //
1040 // mut / parnew mut / parnew
1041 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1042 // ^ |
1043 // |------------------------ DEAD <------------------------------------|
1044 // sweep mut
1045 //
1046 // While a block is in TRANSIENT state its size cannot be determined
1047 // so readers will either need to come back later or stall until
1048 // the size can be determined. Note that for the case of direct
1049 // allocation, P-bits, when available, may be used to determine the
1050 // size of an object that may not yet have been initialized.
1051
1052 // Things to support parallel young-gen collection.
1053 oop
1054 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1055 oop old, markOop m,
1056 size_t word_sz) {
1057 #ifndef PRODUCT
1058 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1059 return NULL;
1060 }
1061 #endif // #ifndef PRODUCT
1062
1063 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1064 PromotionInfo* promoInfo = &ps->promo;
1065 // if we are tracking promotions, then first ensure space for
1066 // promotion (including spooling space for saving header if necessary).
1067 // then allocate and copy, then track promoted info if needed.
1068 // When tracking (see PromotionInfo::track()), the mark word may
1069 // be displaced and in this case restoration of the mark word
1070 // occurs in the (oop_since_save_marks_)iterate phase.
1071 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1072 // Out of space for allocating spooling buffers;
1073 // try expanding and allocating spooling buffers.
1074 if (!expand_and_ensure_spooling_space(promoInfo)) {
1075 return NULL;
1076 }
1077 }
1078 assert(promoInfo->has_spooling_space(), "Control point invariant");
1079 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1080 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1081 if (obj_ptr == NULL) {
1082 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1083 if (obj_ptr == NULL) {
1084 return NULL;
1085 }
1086 }
1087 oop obj = oop(obj_ptr);
1088 OrderAccess::storestore();
1089 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1090 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1091 // IMPORTANT: See note on object initialization for CMS above.
1092 // Otherwise, copy the object. Here we must be careful to insert the
1093 // klass pointer last, since this marks the block as an allocated object.
1094 // Except with compressed oops it's the mark word.
1095 HeapWord* old_ptr = (HeapWord*)old;
1096 // Restore the mark word copied above.
1097 obj->set_mark(m);
1098 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1099 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1100 OrderAccess::storestore();
1101
1102 if (UseCompressedClassPointers) {
1103 // Copy gap missed by (aligned) header size calculation below
1104 obj->set_klass_gap(old->klass_gap());
1105 }
1106 if (word_sz > (size_t)oopDesc::header_size()) {
1107 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1108 obj_ptr + oopDesc::header_size(),
1109 word_sz - oopDesc::header_size());
1110 }
1111
1112 // Now we can track the promoted object, if necessary. We take care
1113 // to delay the transition from uninitialized to full object
1114 // (i.e., insertion of klass pointer) until after, so that it
1115 // atomically becomes a promoted object.
1116 if (promoInfo->tracking()) {
1117 promoInfo->track((PromotedObject*)obj, old->klass());
1118 }
1119 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1120 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1121 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1122
1123 // Finally, install the klass pointer (this should be volatile).
1124 OrderAccess::storestore();
1125 obj->set_klass(old->klass());
1126 // We should now be able to calculate the right size for this object
1127 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1128
1129 collector()->promoted(true, // parallel
1130 obj_ptr, old->is_objArray(), word_sz);
1131
1132 NOT_PRODUCT(
1133 Atomic::inc_ptr(&_numObjectsPromoted);
1134 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1135 )
1136
1137 return obj;
1138 }
1139
1140 void
1141 ConcurrentMarkSweepGeneration::
1142 par_promote_alloc_done(int thread_num) {
1143 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1144 ps->lab.retire(thread_num);
1145 }
1146
1147 void
1148 ConcurrentMarkSweepGeneration::
1149 par_oop_since_save_marks_iterate_done(int thread_num) {
1150 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1151 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1152 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1153 }
1154
1155 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1156 size_t size,
1157 bool tlab)
1158 {
1159 // We allow a STW collection only if a full
1160 // collection was requested.
1161 return full || should_allocate(size, tlab); // FIX ME !!!
1162 // This and promotion failure handling are connected at the
1163 // hip and should be fixed by untying them.
1164 }
1165
1166 bool CMSCollector::shouldConcurrentCollect() {
1167 if (_full_gc_requested) {
1168 if (Verbose && PrintGCDetails) {
1169 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1170 " gc request (or gc_locker)");
1171 }
1172 return true;
1173 }
1174
1175 FreelistLocker x(this);
1176 // ------------------------------------------------------------------
1177 // Print out lots of information which affects the initiation of
1178 // a collection.
1179 if (PrintCMSInitiationStatistics && stats().valid()) {
1180 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1181 gclog_or_tty->stamp();
1182 gclog_or_tty->cr();
1183 stats().print_on(gclog_or_tty);
1184 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1185 stats().time_until_cms_gen_full());
1186 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1187 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1188 _cmsGen->contiguous_available());
1189 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1190 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1191 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1192 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1193 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1194 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1195 gclog_or_tty->print_cr("metadata initialized %d",
1196 MetaspaceGC::should_concurrent_collect());
1197 }
1198 // ------------------------------------------------------------------
1199
1200 // If the estimated time to complete a cms collection (cms_duration())
1201 // is less than the estimated time remaining until the cms generation
1202 // is full, start a collection.
1203 if (!UseCMSInitiatingOccupancyOnly) {
1204 if (stats().valid()) {
1205 if (stats().time_until_cms_start() == 0.0) {
1206 return true;
1207 }
1208 } else {
1209 // We want to conservatively collect somewhat early in order
1210 // to try and "bootstrap" our CMS/promotion statistics;
1211 // this branch will not fire after the first successful CMS
1212 // collection because the stats should then be valid.
1213 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1214 if (Verbose && PrintGCDetails) {
1215 gclog_or_tty->print_cr(
1216 " CMSCollector: collect for bootstrapping statistics:"
1217 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1218 _bootstrap_occupancy);
1219 }
1220 return true;
1221 }
1222 }
1223 }
1224
1225 // Otherwise, we start a collection cycle if
1226 // old gen want a collection cycle started. Each may use
1227 // an appropriate criterion for making this decision.
1228 // XXX We need to make sure that the gen expansion
1229 // criterion dovetails well with this. XXX NEED TO FIX THIS
1230 if (_cmsGen->should_concurrent_collect()) {
1231 if (Verbose && PrintGCDetails) {
1232 gclog_or_tty->print_cr("CMS old gen initiated");
1233 }
1234 return true;
1235 }
1236
1237 // We start a collection if we believe an incremental collection may fail;
1238 // this is not likely to be productive in practice because it's probably too
1239 // late anyway.
1240 GenCollectedHeap* gch = GenCollectedHeap::heap();
1241 assert(gch->collector_policy()->is_generation_policy(),
1242 "You may want to check the correctness of the following");
1243 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1244 if (Verbose && PrintGCDetails) {
1245 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1246 }
1247 return true;
1248 }
1249
1250 if (MetaspaceGC::should_concurrent_collect()) {
1251 if (Verbose && PrintGCDetails) {
1252 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1253 }
1254 return true;
1255 }
1256
1257 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1258 if (CMSTriggerInterval >= 0) {
1259 if (CMSTriggerInterval == 0) {
1260 // Trigger always
1261 return true;
1262 }
1263
1264 // Check the CMS time since begin (we do not check the stats validity
1265 // as we want to be able to trigger the first CMS cycle as well)
1266 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1267 if (Verbose && PrintGCDetails) {
1268 if (stats().valid()) {
1269 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1270 stats().cms_time_since_begin());
1271 } else {
1272 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1273 }
1274 }
1275 return true;
1276 }
1277 }
1278
1279 return false;
1280 }
1281
1282 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1283
1284 // Clear _expansion_cause fields of constituent generations
1285 void CMSCollector::clear_expansion_cause() {
1286 _cmsGen->clear_expansion_cause();
1287 }
1288
1289 // We should be conservative in starting a collection cycle. To
1290 // start too eagerly runs the risk of collecting too often in the
1291 // extreme. To collect too rarely falls back on full collections,
1292 // which works, even if not optimum in terms of concurrent work.
1293 // As a work around for too eagerly collecting, use the flag
1294 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1295 // giving the user an easily understandable way of controlling the
1296 // collections.
1297 // We want to start a new collection cycle if any of the following
1298 // conditions hold:
1299 // . our current occupancy exceeds the configured initiating occupancy
1300 // for this generation, or
1301 // . we recently needed to expand this space and have not, since that
1302 // expansion, done a collection of this generation, or
1303 // . the underlying space believes that it may be a good idea to initiate
1304 // a concurrent collection (this may be based on criteria such as the
1305 // following: the space uses linear allocation and linear allocation is
1306 // going to fail, or there is believed to be excessive fragmentation in
1307 // the generation, etc... or ...
1308 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1309 // the case of the old generation; see CR 6543076):
1310 // we may be approaching a point at which allocation requests may fail because
1311 // we will be out of sufficient free space given allocation rate estimates.]
1312 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1313
1314 assert_lock_strong(freelistLock());
1315 if (occupancy() > initiating_occupancy()) {
1316 if (PrintGCDetails && Verbose) {
1317 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1318 short_name(), occupancy(), initiating_occupancy());
1319 }
1320 return true;
1321 }
1322 if (UseCMSInitiatingOccupancyOnly) {
1323 return false;
1324 }
1325 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1326 if (PrintGCDetails && Verbose) {
1327 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1328 short_name());
1329 }
1330 return true;
1331 }
1332 if (_cmsSpace->should_concurrent_collect()) {
1333 if (PrintGCDetails && Verbose) {
1334 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1335 short_name());
1336 }
1337 return true;
1338 }
1339 return false;
1340 }
1341
1342 void ConcurrentMarkSweepGeneration::collect(bool full,
1343 bool clear_all_soft_refs,
1344 size_t size,
1345 bool tlab)
1346 {
1347 collector()->collect(full, clear_all_soft_refs, size, tlab);
1348 }
1349
1350 void CMSCollector::collect(bool full,
1351 bool clear_all_soft_refs,
1352 size_t size,
1353 bool tlab)
1354 {
1355 // The following "if" branch is present for defensive reasons.
1356 // In the current uses of this interface, it can be replaced with:
1357 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1358 // But I am not placing that assert here to allow future
1359 // generality in invoking this interface.
1360 if (GC_locker::is_active()) {
1361 // A consistency test for GC_locker
1362 assert(GC_locker::needs_gc(), "Should have been set already");
1363 // Skip this foreground collection, instead
1364 // expanding the heap if necessary.
1365 // Need the free list locks for the call to free() in compute_new_size()
1366 compute_new_size();
1367 return;
1368 }
1369 acquire_control_and_collect(full, clear_all_soft_refs);
1370 }
1371
1372 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1373 GenCollectedHeap* gch = GenCollectedHeap::heap();
1374 unsigned int gc_count = gch->total_full_collections();
1375 if (gc_count == full_gc_count) {
1376 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1377 _full_gc_requested = true;
1378 _full_gc_cause = cause;
1379 CGC_lock->notify(); // nudge CMS thread
1380 } else {
1381 assert(gc_count > full_gc_count, "Error: causal loop");
1382 }
1383 }
1384
1385 bool CMSCollector::is_external_interruption() {
1386 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1387 return GCCause::is_user_requested_gc(cause) ||
1388 GCCause::is_serviceability_requested_gc(cause);
1389 }
1390
1391 void CMSCollector::report_concurrent_mode_interruption() {
1392 if (is_external_interruption()) {
1393 if (PrintGCDetails) {
1394 gclog_or_tty->print(" (concurrent mode interrupted)");
1395 }
1396 } else {
1397 if (PrintGCDetails) {
1398 gclog_or_tty->print(" (concurrent mode failure)");
1399 }
1400 _gc_tracer_cm->report_concurrent_mode_failure();
1401 }
1402 }
1403
1404
1405 // The foreground and background collectors need to coordinate in order
1406 // to make sure that they do not mutually interfere with CMS collections.
1407 // When a background collection is active,
1408 // the foreground collector may need to take over (preempt) and
1409 // synchronously complete an ongoing collection. Depending on the
1410 // frequency of the background collections and the heap usage
1411 // of the application, this preemption can be seldom or frequent.
1412 // There are only certain
1413 // points in the background collection that the "collection-baton"
1414 // can be passed to the foreground collector.
1415 //
1416 // The foreground collector will wait for the baton before
1417 // starting any part of the collection. The foreground collector
1418 // will only wait at one location.
1419 //
1420 // The background collector will yield the baton before starting a new
1421 // phase of the collection (e.g., before initial marking, marking from roots,
1422 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1423 // of the loop which switches the phases. The background collector does some
1424 // of the phases (initial mark, final re-mark) with the world stopped.
1425 // Because of locking involved in stopping the world,
1426 // the foreground collector should not block waiting for the background
1427 // collector when it is doing a stop-the-world phase. The background
1428 // collector will yield the baton at an additional point just before
1429 // it enters a stop-the-world phase. Once the world is stopped, the
1430 // background collector checks the phase of the collection. If the
1431 // phase has not changed, it proceeds with the collection. If the
1432 // phase has changed, it skips that phase of the collection. See
1433 // the comments on the use of the Heap_lock in collect_in_background().
1434 //
1435 // Variable used in baton passing.
1436 // _foregroundGCIsActive - Set to true by the foreground collector when
1437 // it wants the baton. The foreground clears it when it has finished
1438 // the collection.
1439 // _foregroundGCShouldWait - Set to true by the background collector
1440 // when it is running. The foreground collector waits while
1441 // _foregroundGCShouldWait is true.
1442 // CGC_lock - monitor used to protect access to the above variables
1443 // and to notify the foreground and background collectors.
1444 // _collectorState - current state of the CMS collection.
1445 //
1446 // The foreground collector
1447 // acquires the CGC_lock
1448 // sets _foregroundGCIsActive
1449 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1450 // various locks acquired in preparation for the collection
1451 // are released so as not to block the background collector
1452 // that is in the midst of a collection
1453 // proceeds with the collection
1454 // clears _foregroundGCIsActive
1455 // returns
1456 //
1457 // The background collector in a loop iterating on the phases of the
1458 // collection
1459 // acquires the CGC_lock
1460 // sets _foregroundGCShouldWait
1461 // if _foregroundGCIsActive is set
1462 // clears _foregroundGCShouldWait, notifies _CGC_lock
1463 // waits on _CGC_lock for _foregroundGCIsActive to become false
1464 // and exits the loop.
1465 // otherwise
1466 // proceed with that phase of the collection
1467 // if the phase is a stop-the-world phase,
1468 // yield the baton once more just before enqueueing
1469 // the stop-world CMS operation (executed by the VM thread).
1470 // returns after all phases of the collection are done
1471 //
1472
1473 void CMSCollector::acquire_control_and_collect(bool full,
1474 bool clear_all_soft_refs) {
1475 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1476 assert(!Thread::current()->is_ConcurrentGC_thread(),
1477 "shouldn't try to acquire control from self!");
1478
1479 // Start the protocol for acquiring control of the
1480 // collection from the background collector (aka CMS thread).
1481 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1482 "VM thread should have CMS token");
1483 // Remember the possibly interrupted state of an ongoing
1484 // concurrent collection
1485 CollectorState first_state = _collectorState;
1486
1487 // Signal to a possibly ongoing concurrent collection that
1488 // we want to do a foreground collection.
1489 _foregroundGCIsActive = true;
1490
1491 // release locks and wait for a notify from the background collector
1492 // releasing the locks in only necessary for phases which
1493 // do yields to improve the granularity of the collection.
1494 assert_lock_strong(bitMapLock());
1495 // We need to lock the Free list lock for the space that we are
1496 // currently collecting.
1497 assert(haveFreelistLocks(), "Must be holding free list locks");
1498 bitMapLock()->unlock();
1499 releaseFreelistLocks();
1500 {
1501 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1502 if (_foregroundGCShouldWait) {
1503 // We are going to be waiting for action for the CMS thread;
1504 // it had better not be gone (for instance at shutdown)!
1505 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1506 "CMS thread must be running");
1507 // Wait here until the background collector gives us the go-ahead
1508 ConcurrentMarkSweepThread::clear_CMS_flag(
1509 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1510 // Get a possibly blocked CMS thread going:
1511 // Note that we set _foregroundGCIsActive true above,
1512 // without protection of the CGC_lock.
1513 CGC_lock->notify();
1514 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1515 "Possible deadlock");
1516 while (_foregroundGCShouldWait) {
1517 // wait for notification
1518 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1519 // Possibility of delay/starvation here, since CMS token does
1520 // not know to give priority to VM thread? Actually, i think
1521 // there wouldn't be any delay/starvation, but the proof of
1522 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1523 }
1524 ConcurrentMarkSweepThread::set_CMS_flag(
1525 ConcurrentMarkSweepThread::CMS_vm_has_token);
1526 }
1527 }
1528 // The CMS_token is already held. Get back the other locks.
1529 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1530 "VM thread should have CMS token");
1531 getFreelistLocks();
1532 bitMapLock()->lock_without_safepoint_check();
1533 if (TraceCMSState) {
1534 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1535 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1536 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1537 }
1538
1539 // Inform cms gen if this was due to partial collection failing.
1540 // The CMS gen may use this fact to determine its expansion policy.
1541 GenCollectedHeap* gch = GenCollectedHeap::heap();
1542 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1543 assert(!_cmsGen->incremental_collection_failed(),
1544 "Should have been noticed, reacted to and cleared");
1545 _cmsGen->set_incremental_collection_failed();
1546 }
1547
1548 if (first_state > Idling) {
1549 report_concurrent_mode_interruption();
1550 }
1551
1552 set_did_compact(true);
1553
1554 // If the collection is being acquired from the background
1555 // collector, there may be references on the discovered
1556 // references lists. Abandon those references, since some
1557 // of them may have become unreachable after concurrent
1558 // discovery; the STW compacting collector will redo discovery
1559 // more precisely, without being subject to floating garbage.
1560 // Leaving otherwise unreachable references in the discovered
1561 // lists would require special handling.
1562 ref_processor()->disable_discovery();
1563 ref_processor()->abandon_partial_discovery();
1564 ref_processor()->verify_no_references_recorded();
1565
1566 if (first_state > Idling) {
1567 save_heap_summary();
1568 }
1569
1570 do_compaction_work(clear_all_soft_refs);
1571
1572 // Has the GC time limit been exceeded?
1573 size_t max_eden_size = _young_gen->max_capacity() -
1574 _young_gen->to()->capacity() -
1575 _young_gen->from()->capacity();
1576 GCCause::Cause gc_cause = gch->gc_cause();
1577 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1578 _young_gen->eden()->used(),
1579 _cmsGen->max_capacity(),
1580 max_eden_size,
1581 full,
1582 gc_cause,
1583 gch->collector_policy());
1584
1585 // Reset the expansion cause, now that we just completed
1586 // a collection cycle.
1587 clear_expansion_cause();
1588 _foregroundGCIsActive = false;
1589 return;
1590 }
1591
1592 // Resize the tenured generation
1593 // after obtaining the free list locks for the
1594 // two generations.
1595 void CMSCollector::compute_new_size() {
1596 assert_locked_or_safepoint(Heap_lock);
1597 FreelistLocker z(this);
1598 MetaspaceGC::compute_new_size();
1599 _cmsGen->compute_new_size_free_list();
1600 }
1601
1602 // A work method used by the foreground collector to do
1603 // a mark-sweep-compact.
1604 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1605 GenCollectedHeap* gch = GenCollectedHeap::heap();
1606
1607 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1608 gc_timer->register_gc_start();
1609
1610 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1611 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1612
1613 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1614
1615 // Temporarily widen the span of the weak reference processing to
1616 // the entire heap.
1617 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1618 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1619 // Temporarily, clear the "is_alive_non_header" field of the
1620 // reference processor.
1621 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1622 // Temporarily make reference _processing_ single threaded or MT as
1623 // per CMSParallelFullGC
1624 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), CMSParallelFullGC);
1625 // Temporarily make refs discovery atomic
1626 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1627 // Temporarily make reference _discovery_ single threaded or MT as
1628 // per CMSParallelFullGC
1629 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), CMSParallelFullGC);
1630
1631 ref_processor()->set_enqueuing_is_done(false);
1632 ref_processor()->enable_discovery();
1633 ref_processor()->setup_policy(clear_all_soft_refs);
1634 // If an asynchronous collection finishes, the _modUnionTable is
1635 // all clear. If we are assuming the collection from an asynchronous
1636 // collection, clear the _modUnionTable.
1637 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1638 "_modUnionTable should be clear if the baton was not passed");
1639 _modUnionTable.clear_all();
1640 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1641 "mod union for klasses should be clear if the baton was passed");
1642 _ct->klass_rem_set()->clear_mod_union();
1643
1644 // We must adjust the allocation statistics being maintained
1645 // in the free list space. We do so by reading and clearing
1646 // the sweep timer and updating the block flux rate estimates below.
1647 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1648 if (_inter_sweep_timer.is_active()) {
1649 _inter_sweep_timer.stop();
1650 // Note that we do not use this sample to update the _inter_sweep_estimate.
1651 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1652 _inter_sweep_estimate.padded_average(),
1653 _intra_sweep_estimate.padded_average());
1654 }
1655
1656 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1657 #ifdef ASSERT
1658 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1659 size_t free_size = cms_space->free();
1660 assert(free_size ==
1661 pointer_delta(cms_space->end(), cms_space->compaction_top())
1662 * HeapWordSize,
1663 "All the free space should be compacted into one chunk at top");
1664 assert(cms_space->dictionary()->total_chunk_size(
1665 debug_only(cms_space->freelistLock())) == 0 ||
1666 cms_space->totalSizeInIndexedFreeLists() == 0,
1667 "All the free space should be in a single chunk");
1668 size_t num = cms_space->totalCount();
1669 assert((free_size == 0 && num == 0) ||
1670 (free_size > 0 && (num == 1 || num == 2)),
1671 "There should be at most 2 free chunks after compaction");
1672 #endif // ASSERT
1673 _collectorState = Resetting;
1674 assert(_restart_addr == NULL,
1675 "Should have been NULL'd before baton was passed");
1676 reset(false /* == !concurrent */);
1677 _cmsGen->reset_after_compaction();
1678 _concurrent_cycles_since_last_unload = 0;
1679
1680 // Clear any data recorded in the PLAB chunk arrays.
1681 if (_survivor_plab_array != NULL) {
1682 reset_survivor_plab_arrays();
1683 }
1684
1685 // Adjust the per-size allocation stats for the next epoch.
1686 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1687 // Restart the "inter sweep timer" for the next epoch.
1688 _inter_sweep_timer.reset();
1689 _inter_sweep_timer.start();
1690
1691 gc_timer->register_gc_end();
1692
1693 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1694
1695 // For a mark-sweep-compact, compute_new_size() will be called
1696 // in the heap's do_collection() method.
1697 }
1698
1699 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1700 ContiguousSpace* eden_space = _young_gen->eden();
1701 ContiguousSpace* from_space = _young_gen->from();
1702 ContiguousSpace* to_space = _young_gen->to();
1703 // Eden
1704 if (_eden_chunk_array != NULL) {
1705 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1706 p2i(eden_space->bottom()), p2i(eden_space->top()),
1707 p2i(eden_space->end()), eden_space->capacity());
1708 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1709 "_eden_chunk_capacity=" SIZE_FORMAT,
1710 _eden_chunk_index, _eden_chunk_capacity);
1711 for (size_t i = 0; i < _eden_chunk_index; i++) {
1712 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1713 i, p2i(_eden_chunk_array[i]));
1714 }
1715 }
1716 // Survivor
1717 if (_survivor_chunk_array != NULL) {
1718 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1719 p2i(from_space->bottom()), p2i(from_space->top()),
1720 p2i(from_space->end()), from_space->capacity());
1721 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1722 "_survivor_chunk_capacity=" SIZE_FORMAT,
1723 _survivor_chunk_index, _survivor_chunk_capacity);
1724 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1725 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1726 i, p2i(_survivor_chunk_array[i]));
1727 }
1728 }
1729 }
1730
1731 void CMSCollector::getFreelistLocks() const {
1732 // Get locks for all free lists in all generations that this
1733 // collector is responsible for
1734 _cmsGen->freelistLock()->lock_without_safepoint_check();
1735 }
1736
1737 void CMSCollector::releaseFreelistLocks() const {
1738 // Release locks for all free lists in all generations that this
1739 // collector is responsible for
1740 _cmsGen->freelistLock()->unlock();
1741 }
1742
1743 bool CMSCollector::haveFreelistLocks() const {
1744 // Check locks for all free lists in all generations that this
1745 // collector is responsible for
1746 assert_lock_strong(_cmsGen->freelistLock());
1747 PRODUCT_ONLY(ShouldNotReachHere());
1748 return true;
1749 }
1750
1751 // A utility class that is used by the CMS collector to
1752 // temporarily "release" the foreground collector from its
1753 // usual obligation to wait for the background collector to
1754 // complete an ongoing phase before proceeding.
1755 class ReleaseForegroundGC: public StackObj {
1756 private:
1757 CMSCollector* _c;
1758 public:
1759 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1760 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1761 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1762 // allow a potentially blocked foreground collector to proceed
1763 _c->_foregroundGCShouldWait = false;
1764 if (_c->_foregroundGCIsActive) {
1765 CGC_lock->notify();
1766 }
1767 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1768 "Possible deadlock");
1769 }
1770
1771 ~ReleaseForegroundGC() {
1772 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1773 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1774 _c->_foregroundGCShouldWait = true;
1775 }
1776 };
1777
1778 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1779 assert(Thread::current()->is_ConcurrentGC_thread(),
1780 "A CMS asynchronous collection is only allowed on a CMS thread.");
1781
1782 GenCollectedHeap* gch = GenCollectedHeap::heap();
1783 {
1784 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1785 MutexLockerEx hl(Heap_lock, safepoint_check);
1786 FreelistLocker fll(this);
1787 MutexLockerEx x(CGC_lock, safepoint_check);
1788 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1789 // The foreground collector is active or we're
1790 // not using asynchronous collections. Skip this
1791 // background collection.
1792 assert(!_foregroundGCShouldWait, "Should be clear");
1793 return;
1794 } else {
1795 assert(_collectorState == Idling, "Should be idling before start.");
1796 _collectorState = InitialMarking;
1797 register_gc_start(cause);
1798 // Reset the expansion cause, now that we are about to begin
1799 // a new cycle.
1800 clear_expansion_cause();
1801
1802 // Clear the MetaspaceGC flag since a concurrent collection
1803 // is starting but also clear it after the collection.
1804 MetaspaceGC::set_should_concurrent_collect(false);
1805 }
1806 // Decide if we want to enable class unloading as part of the
1807 // ensuing concurrent GC cycle.
1808 update_should_unload_classes();
1809 _full_gc_requested = false; // acks all outstanding full gc requests
1810 _full_gc_cause = GCCause::_no_gc;
1811 // Signal that we are about to start a collection
1812 gch->increment_total_full_collections(); // ... starting a collection cycle
1813 _collection_count_start = gch->total_full_collections();
1814 }
1815
1816 // Used for PrintGC
1817 size_t prev_used;
1818 if (PrintGC && Verbose) {
1819 prev_used = _cmsGen->used();
1820 }
1821
1822 // The change of the collection state is normally done at this level;
1823 // the exceptions are phases that are executed while the world is
1824 // stopped. For those phases the change of state is done while the
1825 // world is stopped. For baton passing purposes this allows the
1826 // background collector to finish the phase and change state atomically.
1827 // The foreground collector cannot wait on a phase that is done
1828 // while the world is stopped because the foreground collector already
1829 // has the world stopped and would deadlock.
1830 while (_collectorState != Idling) {
1831 if (TraceCMSState) {
1832 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1833 p2i(Thread::current()), _collectorState);
1834 }
1835 // The foreground collector
1836 // holds the Heap_lock throughout its collection.
1837 // holds the CMS token (but not the lock)
1838 // except while it is waiting for the background collector to yield.
1839 //
1840 // The foreground collector should be blocked (not for long)
1841 // if the background collector is about to start a phase
1842 // executed with world stopped. If the background
1843 // collector has already started such a phase, the
1844 // foreground collector is blocked waiting for the
1845 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1846 // are executed in the VM thread.
1847 //
1848 // The locking order is
1849 // PendingListLock (PLL) -- if applicable (FinalMarking)
1850 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1851 // CMS token (claimed in
1852 // stop_world_and_do() -->
1853 // safepoint_synchronize() -->
1854 // CMSThread::synchronize())
1855
1856 {
1857 // Check if the FG collector wants us to yield.
1858 CMSTokenSync x(true); // is cms thread
1859 if (waitForForegroundGC()) {
1860 // We yielded to a foreground GC, nothing more to be
1861 // done this round.
1862 assert(_foregroundGCShouldWait == false, "We set it to false in "
1863 "waitForForegroundGC()");
1864 if (TraceCMSState) {
1865 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1866 " exiting collection CMS state %d",
1867 p2i(Thread::current()), _collectorState);
1868 }
1869 return;
1870 } else {
1871 // The background collector can run but check to see if the
1872 // foreground collector has done a collection while the
1873 // background collector was waiting to get the CGC_lock
1874 // above. If yes, break so that _foregroundGCShouldWait
1875 // is cleared before returning.
1876 if (_collectorState == Idling) {
1877 break;
1878 }
1879 }
1880 }
1881
1882 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1883 "should be waiting");
1884
1885 switch (_collectorState) {
1886 case InitialMarking:
1887 {
1888 ReleaseForegroundGC x(this);
1889 stats().record_cms_begin();
1890 VM_CMS_Initial_Mark initial_mark_op(this);
1891 VMThread::execute(&initial_mark_op);
1892 }
1893 // The collector state may be any legal state at this point
1894 // since the background collector may have yielded to the
1895 // foreground collector.
1896 break;
1897 case Marking:
1898 // initial marking in checkpointRootsInitialWork has been completed
1899 if (markFromRoots()) { // we were successful
1900 assert(_collectorState == Precleaning, "Collector state should "
1901 "have changed");
1902 } else {
1903 assert(_foregroundGCIsActive, "Internal state inconsistency");
1904 }
1905 break;
1906 case Precleaning:
1907 // marking from roots in markFromRoots has been completed
1908 preclean();
1909 assert(_collectorState == AbortablePreclean ||
1910 _collectorState == FinalMarking,
1911 "Collector state should have changed");
1912 break;
1913 case AbortablePreclean:
1914 abortable_preclean();
1915 assert(_collectorState == FinalMarking, "Collector state should "
1916 "have changed");
1917 break;
1918 case FinalMarking:
1919 {
1920 ReleaseForegroundGC x(this);
1921
1922 VM_CMS_Final_Remark final_remark_op(this);
1923 VMThread::execute(&final_remark_op);
1924 }
1925 assert(_foregroundGCShouldWait, "block post-condition");
1926 break;
1927 case Sweeping:
1928 // final marking in checkpointRootsFinal has been completed
1929 sweep();
1930 assert(_collectorState == Resizing, "Collector state change "
1931 "to Resizing must be done under the free_list_lock");
1932
1933 case Resizing: {
1934 // Sweeping has been completed...
1935 // At this point the background collection has completed.
1936 // Don't move the call to compute_new_size() down
1937 // into code that might be executed if the background
1938 // collection was preempted.
1939 {
1940 ReleaseForegroundGC x(this); // unblock FG collection
1941 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1942 CMSTokenSync z(true); // not strictly needed.
1943 if (_collectorState == Resizing) {
1944 compute_new_size();
1945 save_heap_summary();
1946 _collectorState = Resetting;
1947 } else {
1948 assert(_collectorState == Idling, "The state should only change"
1949 " because the foreground collector has finished the collection");
1950 }
1951 }
1952 break;
1953 }
1954 case Resetting:
1955 // CMS heap resizing has been completed
1956 reset(true);
1957 assert(_collectorState == Idling, "Collector state should "
1958 "have changed");
1959
1960 MetaspaceGC::set_should_concurrent_collect(false);
1961
1962 stats().record_cms_end();
1963 // Don't move the concurrent_phases_end() and compute_new_size()
1964 // calls to here because a preempted background collection
1965 // has it's state set to "Resetting".
1966 break;
1967 case Idling:
1968 default:
1969 ShouldNotReachHere();
1970 break;
1971 }
1972 if (TraceCMSState) {
1973 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1974 p2i(Thread::current()), _collectorState);
1975 }
1976 assert(_foregroundGCShouldWait, "block post-condition");
1977 }
1978
1979 // Should this be in gc_epilogue?
1980 collector_policy()->counters()->update_counters();
1981
1982 {
1983 // Clear _foregroundGCShouldWait and, in the event that the
1984 // foreground collector is waiting, notify it, before
1985 // returning.
1986 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1987 _foregroundGCShouldWait = false;
1988 if (_foregroundGCIsActive) {
1989 CGC_lock->notify();
1990 }
1991 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1992 "Possible deadlock");
1993 }
1994 if (TraceCMSState) {
1995 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1996 " exiting collection CMS state %d",
1997 p2i(Thread::current()), _collectorState);
1998 }
1999 if (PrintGC && Verbose) {
2000 _cmsGen->print_heap_change(prev_used);
2001 }
2002 }
2003
2004 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2005 _cms_start_registered = true;
2006 _gc_timer_cm->register_gc_start();
2007 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2008 }
2009
2010 void CMSCollector::register_gc_end() {
2011 if (_cms_start_registered) {
2012 report_heap_summary(GCWhen::AfterGC);
2013
2014 _gc_timer_cm->register_gc_end();
2015 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2016 _cms_start_registered = false;
2017 }
2018 }
2019
2020 void CMSCollector::save_heap_summary() {
2021 GenCollectedHeap* gch = GenCollectedHeap::heap();
2022 _last_heap_summary = gch->create_heap_summary();
2023 _last_metaspace_summary = gch->create_metaspace_summary();
2024 }
2025
2026 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2027 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2028 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2029 }
2030
2031 bool CMSCollector::waitForForegroundGC() {
2032 bool res = false;
2033 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2034 "CMS thread should have CMS token");
2035 // Block the foreground collector until the
2036 // background collectors decides whether to
2037 // yield.
2038 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2039 _foregroundGCShouldWait = true;
2040 if (_foregroundGCIsActive) {
2041 // The background collector yields to the
2042 // foreground collector and returns a value
2043 // indicating that it has yielded. The foreground
2044 // collector can proceed.
2045 res = true;
2046 _foregroundGCShouldWait = false;
2047 ConcurrentMarkSweepThread::clear_CMS_flag(
2048 ConcurrentMarkSweepThread::CMS_cms_has_token);
2049 ConcurrentMarkSweepThread::set_CMS_flag(
2050 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2051 // Get a possibly blocked foreground thread going
2052 CGC_lock->notify();
2053 if (TraceCMSState) {
2054 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2055 p2i(Thread::current()), _collectorState);
2056 }
2057 while (_foregroundGCIsActive) {
2058 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2059 }
2060 ConcurrentMarkSweepThread::set_CMS_flag(
2061 ConcurrentMarkSweepThread::CMS_cms_has_token);
2062 ConcurrentMarkSweepThread::clear_CMS_flag(
2063 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2064 }
2065 if (TraceCMSState) {
2066 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2067 p2i(Thread::current()), _collectorState);
2068 }
2069 return res;
2070 }
2071
2072 // Because of the need to lock the free lists and other structures in
2073 // the collector, common to all the generations that the collector is
2074 // collecting, we need the gc_prologues of individual CMS generations
2075 // delegate to their collector. It may have been simpler had the
2076 // current infrastructure allowed one to call a prologue on a
2077 // collector. In the absence of that we have the generation's
2078 // prologue delegate to the collector, which delegates back
2079 // some "local" work to a worker method in the individual generations
2080 // that it's responsible for collecting, while itself doing any
2081 // work common to all generations it's responsible for. A similar
2082 // comment applies to the gc_epilogue()'s.
2083 // The role of the variable _between_prologue_and_epilogue is to
2084 // enforce the invocation protocol.
2085 void CMSCollector::gc_prologue(bool full) {
2086 // Call gc_prologue_work() for the CMSGen
2087 // we are responsible for.
2088
2089 // The following locking discipline assumes that we are only called
2090 // when the world is stopped.
2091 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2092
2093 // The CMSCollector prologue must call the gc_prologues for the
2094 // "generations" that it's responsible
2095 // for.
2096
2097 assert( Thread::current()->is_VM_thread()
2098 || ( CMSScavengeBeforeRemark
2099 && Thread::current()->is_ConcurrentGC_thread()),
2100 "Incorrect thread type for prologue execution");
2101
2102 if (_between_prologue_and_epilogue) {
2103 // We have already been invoked; this is a gc_prologue delegation
2104 // from yet another CMS generation that we are responsible for, just
2105 // ignore it since all relevant work has already been done.
2106 return;
2107 }
2108
2109 // set a bit saying prologue has been called; cleared in epilogue
2110 _between_prologue_and_epilogue = true;
2111 // Claim locks for common data structures, then call gc_prologue_work()
2112 // for each CMSGen.
2113
2114 getFreelistLocks(); // gets free list locks on constituent spaces
2115 bitMapLock()->lock_without_safepoint_check();
2116
2117 // Should call gc_prologue_work() for all cms gens we are responsible for
2118 bool duringMarking = _collectorState >= Marking
2119 && _collectorState < Sweeping;
2120
2121 // The young collections clear the modified oops state, which tells if
2122 // there are any modified oops in the class. The remark phase also needs
2123 // that information. Tell the young collection to save the union of all
2124 // modified klasses.
2125 if (duringMarking) {
2126 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2127 }
2128
2129 bool registerClosure = duringMarking;
2130
2131 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2132
2133 if (!full) {
2134 stats().record_gc0_begin();
2135 }
2136 }
2137
2138 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2139
2140 _capacity_at_prologue = capacity();
2141 _used_at_prologue = used();
2142
2143 // Delegate to CMScollector which knows how to coordinate between
2144 // this and any other CMS generations that it is responsible for
2145 // collecting.
2146 collector()->gc_prologue(full);
2147 }
2148
2149 // This is a "private" interface for use by this generation's CMSCollector.
2150 // Not to be called directly by any other entity (for instance,
2151 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2152 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2153 bool registerClosure, ModUnionClosure* modUnionClosure) {
2154 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2155 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2156 "Should be NULL");
2157 if (registerClosure) {
2158 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2159 }
2160 cmsSpace()->gc_prologue();
2161 // Clear stat counters
2162 NOT_PRODUCT(
2163 assert(_numObjectsPromoted == 0, "check");
2164 assert(_numWordsPromoted == 0, "check");
2165 if (Verbose && PrintGC) {
2166 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2167 SIZE_FORMAT " bytes concurrently",
2168 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2169 }
2170 _numObjectsAllocated = 0;
2171 _numWordsAllocated = 0;
2172 )
2173 }
2174
2175 void CMSCollector::gc_epilogue(bool full) {
2176 // The following locking discipline assumes that we are only called
2177 // when the world is stopped.
2178 assert(SafepointSynchronize::is_at_safepoint(),
2179 "world is stopped assumption");
2180
2181 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2182 // if linear allocation blocks need to be appropriately marked to allow the
2183 // the blocks to be parsable. We also check here whether we need to nudge the
2184 // CMS collector thread to start a new cycle (if it's not already active).
2185 assert( Thread::current()->is_VM_thread()
2186 || ( CMSScavengeBeforeRemark
2187 && Thread::current()->is_ConcurrentGC_thread()),
2188 "Incorrect thread type for epilogue execution");
2189
2190 if (!_between_prologue_and_epilogue) {
2191 // We have already been invoked; this is a gc_epilogue delegation
2192 // from yet another CMS generation that we are responsible for, just
2193 // ignore it since all relevant work has already been done.
2194 return;
2195 }
2196 assert(haveFreelistLocks(), "must have freelist locks");
2197 assert_lock_strong(bitMapLock());
2198
2199 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2200
2201 _cmsGen->gc_epilogue_work(full);
2202
2203 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2204 // in case sampling was not already enabled, enable it
2205 _start_sampling = true;
2206 }
2207 // reset _eden_chunk_array so sampling starts afresh
2208 _eden_chunk_index = 0;
2209
2210 size_t cms_used = _cmsGen->cmsSpace()->used();
2211
2212 // update performance counters - this uses a special version of
2213 // update_counters() that allows the utilization to be passed as a
2214 // parameter, avoiding multiple calls to used().
2215 //
2216 _cmsGen->update_counters(cms_used);
2217
2218 bitMapLock()->unlock();
2219 releaseFreelistLocks();
2220
2221 if (!CleanChunkPoolAsync) {
2222 Chunk::clean_chunk_pool();
2223 }
2224
2225 set_did_compact(false);
2226 _between_prologue_and_epilogue = false; // ready for next cycle
2227 }
2228
2229 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2230 collector()->gc_epilogue(full);
2231
2232 // Also reset promotion tracking in par gc thread states.
2233 for (uint i = 0; i < ParallelGCThreads; i++) {
2234 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2235 }
2236 }
2237
2238 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2239 assert(!incremental_collection_failed(), "Should have been cleared");
2240 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2241 cmsSpace()->gc_epilogue();
2242 // Print stat counters
2243 NOT_PRODUCT(
2244 assert(_numObjectsAllocated == 0, "check");
2245 assert(_numWordsAllocated == 0, "check");
2246 if (Verbose && PrintGC) {
2247 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2248 SIZE_FORMAT " bytes",
2249 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2250 }
2251 _numObjectsPromoted = 0;
2252 _numWordsPromoted = 0;
2253 )
2254
2255 if (PrintGC && Verbose) {
2256 // Call down the chain in contiguous_available needs the freelistLock
2257 // so print this out before releasing the freeListLock.
2258 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2259 contiguous_available());
2260 }
2261 }
2262
2263 #ifndef PRODUCT
2264 bool CMSCollector::have_cms_token() {
2265 Thread* thr = Thread::current();
2266 if (thr->is_VM_thread()) {
2267 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2268 } else if (thr->is_ConcurrentGC_thread()) {
2269 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2270 } else if (thr->is_GC_task_thread()) {
2271 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2272 ParGCRareEvent_lock->owned_by_self();
2273 }
2274 return false;
2275 }
2276 #endif
2277
2278 // Check reachability of the given heap address in CMS generation,
2279 // treating all other generations as roots.
2280 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2281 // We could "guarantee" below, rather than assert, but I'll
2282 // leave these as "asserts" so that an adventurous debugger
2283 // could try this in the product build provided some subset of
2284 // the conditions were met, provided they were interested in the
2285 // results and knew that the computation below wouldn't interfere
2286 // with other concurrent computations mutating the structures
2287 // being read or written.
2288 assert(SafepointSynchronize::is_at_safepoint(),
2289 "Else mutations in object graph will make answer suspect");
2290 assert(have_cms_token(), "Should hold cms token");
2291 assert(haveFreelistLocks(), "must hold free list locks");
2292 assert_lock_strong(bitMapLock());
2293
2294 // Clear the marking bit map array before starting, but, just
2295 // for kicks, first report if the given address is already marked
2296 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2297 _markBitMap.isMarked(addr) ? "" : " not");
2298
2299 if (verify_after_remark()) {
2300 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2301 bool result = verification_mark_bm()->isMarked(addr);
2302 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2303 result ? "IS" : "is NOT");
2304 return result;
2305 } else {
2306 gclog_or_tty->print_cr("Could not compute result");
2307 return false;
2308 }
2309 }
2310
2311
2312 void
2313 CMSCollector::print_on_error(outputStream* st) {
2314 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2315 if (collector != NULL) {
2316 CMSBitMap* bitmap = &collector->_markBitMap;
2317 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2318 bitmap->print_on_error(st, " Bits: ");
2319
2320 st->cr();
2321
2322 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2323 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2324 mut_bitmap->print_on_error(st, " Bits: ");
2325 }
2326 }
2327
2328 ////////////////////////////////////////////////////////
2329 // CMS Verification Support
2330 ////////////////////////////////////////////////////////
2331 // Following the remark phase, the following invariant
2332 // should hold -- each object in the CMS heap which is
2333 // marked in markBitMap() should be marked in the verification_mark_bm().
2334
2335 class VerifyMarkedClosure: public BitMapClosure {
2336 CMSBitMap* _marks;
2337 bool _failed;
2338
2339 public:
2340 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2341
2342 bool do_bit(size_t offset) {
2343 HeapWord* addr = _marks->offsetToHeapWord(offset);
2344 if (!_marks->isMarked(addr)) {
2345 oop(addr)->print_on(gclog_or_tty);
2346 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2347 _failed = true;
2348 }
2349 return true;
2350 }
2351
2352 bool failed() { return _failed; }
2353 };
2354
2355 bool CMSCollector::verify_after_remark(bool silent) {
2356 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2357 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2358 static bool init = false;
2359
2360 assert(SafepointSynchronize::is_at_safepoint(),
2361 "Else mutations in object graph will make answer suspect");
2362 assert(have_cms_token(),
2363 "Else there may be mutual interference in use of "
2364 " verification data structures");
2365 assert(_collectorState > Marking && _collectorState <= Sweeping,
2366 "Else marking info checked here may be obsolete");
2367 assert(haveFreelistLocks(), "must hold free list locks");
2368 assert_lock_strong(bitMapLock());
2369
2370
2371 // Allocate marking bit map if not already allocated
2372 if (!init) { // first time
2373 if (!verification_mark_bm()->allocate(_span)) {
2374 return false;
2375 }
2376 init = true;
2377 }
2378
2379 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2380
2381 // Turn off refs discovery -- so we will be tracing through refs.
2382 // This is as intended, because by this time
2383 // GC must already have cleared any refs that need to be cleared,
2384 // and traced those that need to be marked; moreover,
2385 // the marking done here is not going to interfere in any
2386 // way with the marking information used by GC.
2387 NoRefDiscovery no_discovery(ref_processor());
2388
2389 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2390
2391 // Clear any marks from a previous round
2392 verification_mark_bm()->clear_all();
2393 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2394 verify_work_stacks_empty();
2395
2396 GenCollectedHeap* gch = GenCollectedHeap::heap();
2397 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2398 // Update the saved marks which may affect the root scans.
2399 gch->save_marks();
2400
2401 if (CMSRemarkVerifyVariant == 1) {
2402 // In this first variant of verification, we complete
2403 // all marking, then check if the new marks-vector is
2404 // a subset of the CMS marks-vector.
2405 verify_after_remark_work_1();
2406 } else if (CMSRemarkVerifyVariant == 2) {
2407 // In this second variant of verification, we flag an error
2408 // (i.e. an object reachable in the new marks-vector not reachable
2409 // in the CMS marks-vector) immediately, also indicating the
2410 // identify of an object (A) that references the unmarked object (B) --
2411 // presumably, a mutation to A failed to be picked up by preclean/remark?
2412 verify_after_remark_work_2();
2413 } else {
2414 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2415 CMSRemarkVerifyVariant);
2416 }
2417 if (!silent) gclog_or_tty->print(" done] ");
2418 return true;
2419 }
2420
2421 void CMSCollector::verify_after_remark_work_1() {
2422 ResourceMark rm;
2423 HandleMark hm;
2424 GenCollectedHeap* gch = GenCollectedHeap::heap();
2425
2426 // Get a clear set of claim bits for the roots processing to work with.
2427 ClassLoaderDataGraph::clear_claimed_marks();
2428
2429 // Mark from roots one level into CMS
2430 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2431 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2432
2433 {
2434 StrongRootsScope srs(1);
2435
2436 gch->gen_process_roots(&srs,
2437 GenCollectedHeap::OldGen,
2438 true, // younger gens are roots
2439 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2440 should_unload_classes(),
2441 ¬Older,
2442 NULL,
2443 NULL);
2444 }
2445
2446 // Now mark from the roots
2447 MarkFromRootsClosure markFromRootsClosure(this, _span,
2448 verification_mark_bm(), verification_mark_stack(),
2449 false /* don't yield */, true /* verifying */);
2450 assert(_restart_addr == NULL, "Expected pre-condition");
2451 verification_mark_bm()->iterate(&markFromRootsClosure);
2452 while (_restart_addr != NULL) {
2453 // Deal with stack overflow: by restarting at the indicated
2454 // address.
2455 HeapWord* ra = _restart_addr;
2456 markFromRootsClosure.reset(ra);
2457 _restart_addr = NULL;
2458 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2459 }
2460 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2461 verify_work_stacks_empty();
2462
2463 // Marking completed -- now verify that each bit marked in
2464 // verification_mark_bm() is also marked in markBitMap(); flag all
2465 // errors by printing corresponding objects.
2466 VerifyMarkedClosure vcl(markBitMap());
2467 verification_mark_bm()->iterate(&vcl);
2468 if (vcl.failed()) {
2469 gclog_or_tty->print("Verification failed");
2470 gch->print_on(gclog_or_tty);
2471 fatal("CMS: failed marking verification after remark");
2472 }
2473 }
2474
2475 class VerifyKlassOopsKlassClosure : public KlassClosure {
2476 class VerifyKlassOopsClosure : public OopClosure {
2477 CMSBitMap* _bitmap;
2478 public:
2479 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2480 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2481 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2482 } _oop_closure;
2483 public:
2484 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2485 void do_klass(Klass* k) {
2486 k->oops_do(&_oop_closure);
2487 }
2488 };
2489
2490 void CMSCollector::verify_after_remark_work_2() {
2491 ResourceMark rm;
2492 HandleMark hm;
2493 GenCollectedHeap* gch = GenCollectedHeap::heap();
2494
2495 // Get a clear set of claim bits for the roots processing to work with.
2496 ClassLoaderDataGraph::clear_claimed_marks();
2497
2498 // Mark from roots one level into CMS
2499 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2500 markBitMap());
2501 CLDToOopClosure cld_closure(¬Older, true);
2502
2503 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2504
2505 {
2506 StrongRootsScope srs(1);
2507
2508 gch->gen_process_roots(&srs,
2509 GenCollectedHeap::OldGen,
2510 true, // younger gens are roots
2511 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2512 should_unload_classes(),
2513 ¬Older,
2514 NULL,
2515 &cld_closure);
2516 }
2517
2518 // Now mark from the roots
2519 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2520 verification_mark_bm(), markBitMap(), verification_mark_stack());
2521 assert(_restart_addr == NULL, "Expected pre-condition");
2522 verification_mark_bm()->iterate(&markFromRootsClosure);
2523 while (_restart_addr != NULL) {
2524 // Deal with stack overflow: by restarting at the indicated
2525 // address.
2526 HeapWord* ra = _restart_addr;
2527 markFromRootsClosure.reset(ra);
2528 _restart_addr = NULL;
2529 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2530 }
2531 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2532 verify_work_stacks_empty();
2533
2534 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2535 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2536
2537 // Marking completed -- now verify that each bit marked in
2538 // verification_mark_bm() is also marked in markBitMap(); flag all
2539 // errors by printing corresponding objects.
2540 VerifyMarkedClosure vcl(markBitMap());
2541 verification_mark_bm()->iterate(&vcl);
2542 assert(!vcl.failed(), "Else verification above should not have succeeded");
2543 }
2544
2545 void ConcurrentMarkSweepGeneration::save_marks() {
2546 // delegate to CMS space
2547 cmsSpace()->save_marks();
2548 for (uint i = 0; i < ParallelGCThreads; i++) {
2549 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2550 }
2551 }
2552
2553 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2554 return cmsSpace()->no_allocs_since_save_marks();
2555 }
2556
2557 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2558 \
2559 void ConcurrentMarkSweepGeneration:: \
2560 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2561 cl->set_generation(this); \
2562 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2563 cl->reset_generation(); \
2564 save_marks(); \
2565 }
2566
2567 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2568
2569 void
2570 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2571 if (freelistLock()->owned_by_self()) {
2572 Generation::oop_iterate(cl);
2573 } else {
2574 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2575 Generation::oop_iterate(cl);
2576 }
2577 }
2578
2579 void
2580 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2581 if (freelistLock()->owned_by_self()) {
2582 Generation::object_iterate(cl);
2583 } else {
2584 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2585 Generation::object_iterate(cl);
2586 }
2587 }
2588
2589 void
2590 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2591 if (freelistLock()->owned_by_self()) {
2592 Generation::safe_object_iterate(cl);
2593 } else {
2594 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2595 Generation::safe_object_iterate(cl);
2596 }
2597 }
2598
2599 void
2600 ConcurrentMarkSweepGeneration::post_compact() {
2601 }
2602
2603 void
2604 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2605 // Fix the linear allocation blocks to look like free blocks.
2606
2607 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2608 // are not called when the heap is verified during universe initialization and
2609 // at vm shutdown.
2610 if (freelistLock()->owned_by_self()) {
2611 cmsSpace()->prepare_for_verify();
2612 } else {
2613 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2614 cmsSpace()->prepare_for_verify();
2615 }
2616 }
2617
2618 void
2619 ConcurrentMarkSweepGeneration::verify() {
2620 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2621 // are not called when the heap is verified during universe initialization and
2622 // at vm shutdown.
2623 if (freelistLock()->owned_by_self()) {
2624 cmsSpace()->verify();
2625 } else {
2626 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2627 cmsSpace()->verify();
2628 }
2629 }
2630
2631 void CMSCollector::verify() {
2632 _cmsGen->verify();
2633 }
2634
2635 #ifndef PRODUCT
2636 bool CMSCollector::overflow_list_is_empty() const {
2637 assert(_num_par_pushes >= 0, "Inconsistency");
2638 if (_overflow_list == NULL) {
2639 assert(_num_par_pushes == 0, "Inconsistency");
2640 }
2641 return _overflow_list == NULL;
2642 }
2643
2644 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2645 // merely consolidate assertion checks that appear to occur together frequently.
2646 void CMSCollector::verify_work_stacks_empty() const {
2647 assert(_markStack.isEmpty(), "Marking stack should be empty");
2648 assert(overflow_list_is_empty(), "Overflow list should be empty");
2649 }
2650
2651 void CMSCollector::verify_overflow_empty() const {
2652 assert(overflow_list_is_empty(), "Overflow list should be empty");
2653 assert(no_preserved_marks(), "No preserved marks");
2654 }
2655 #endif // PRODUCT
2656
2657 // Decide if we want to enable class unloading as part of the
2658 // ensuing concurrent GC cycle. We will collect and
2659 // unload classes if it's the case that:
2660 // (1) an explicit gc request has been made and the flag
2661 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2662 // (2) (a) class unloading is enabled at the command line, and
2663 // (b) old gen is getting really full
2664 // NOTE: Provided there is no change in the state of the heap between
2665 // calls to this method, it should have idempotent results. Moreover,
2666 // its results should be monotonically increasing (i.e. going from 0 to 1,
2667 // but not 1 to 0) between successive calls between which the heap was
2668 // not collected. For the implementation below, it must thus rely on
2669 // the property that concurrent_cycles_since_last_unload()
2670 // will not decrease unless a collection cycle happened and that
2671 // _cmsGen->is_too_full() are
2672 // themselves also monotonic in that sense. See check_monotonicity()
2673 // below.
2674 void CMSCollector::update_should_unload_classes() {
2675 _should_unload_classes = false;
2676 // Condition 1 above
2677 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2678 _should_unload_classes = true;
2679 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2680 // Disjuncts 2.b.(i,ii,iii) above
2681 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2682 CMSClassUnloadingMaxInterval)
2683 || _cmsGen->is_too_full();
2684 }
2685 }
2686
2687 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2688 bool res = should_concurrent_collect();
2689 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2690 return res;
2691 }
2692
2693 void CMSCollector::setup_cms_unloading_and_verification_state() {
2694 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2695 || VerifyBeforeExit;
2696 const int rso = GenCollectedHeap::SO_AllCodeCache;
2697
2698 // We set the proper root for this CMS cycle here.
2699 if (should_unload_classes()) { // Should unload classes this cycle
2700 remove_root_scanning_option(rso); // Shrink the root set appropriately
2701 set_verifying(should_verify); // Set verification state for this cycle
2702 return; // Nothing else needs to be done at this time
2703 }
2704
2705 // Not unloading classes this cycle
2706 assert(!should_unload_classes(), "Inconsistency!");
2707
2708 // If we are not unloading classes then add SO_AllCodeCache to root
2709 // scanning options.
2710 add_root_scanning_option(rso);
2711
2712 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2713 set_verifying(true);
2714 } else if (verifying() && !should_verify) {
2715 // We were verifying, but some verification flags got disabled.
2716 set_verifying(false);
2717 // Exclude symbols, strings and code cache elements from root scanning to
2718 // reduce IM and RM pauses.
2719 remove_root_scanning_option(rso);
2720 }
2721 }
2722
2723
2724 #ifndef PRODUCT
2725 HeapWord* CMSCollector::block_start(const void* p) const {
2726 const HeapWord* addr = (HeapWord*)p;
2727 if (_span.contains(p)) {
2728 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2729 return _cmsGen->cmsSpace()->block_start(p);
2730 }
2731 }
2732 return NULL;
2733 }
2734 #endif
2735
2736 HeapWord*
2737 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2738 bool tlab,
2739 bool parallel) {
2740 CMSSynchronousYieldRequest yr;
2741 assert(!tlab, "Can't deal with TLAB allocation");
2742 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2743 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2744 if (GCExpandToAllocateDelayMillis > 0) {
2745 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2746 }
2747 return have_lock_and_allocate(word_size, tlab);
2748 }
2749
2750 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2751 size_t bytes,
2752 size_t expand_bytes,
2753 CMSExpansionCause::Cause cause)
2754 {
2755
2756 bool success = expand(bytes, expand_bytes);
2757
2758 // remember why we expanded; this information is used
2759 // by shouldConcurrentCollect() when making decisions on whether to start
2760 // a new CMS cycle.
2761 if (success) {
2762 set_expansion_cause(cause);
2763 if (PrintGCDetails && Verbose) {
2764 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2765 CMSExpansionCause::to_string(cause));
2766 }
2767 }
2768 }
2769
2770 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2771 HeapWord* res = NULL;
2772 MutexLocker x(ParGCRareEvent_lock);
2773 while (true) {
2774 // Expansion by some other thread might make alloc OK now:
2775 res = ps->lab.alloc(word_sz);
2776 if (res != NULL) return res;
2777 // If there's not enough expansion space available, give up.
2778 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2779 return NULL;
2780 }
2781 // Otherwise, we try expansion.
2782 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2783 // Now go around the loop and try alloc again;
2784 // A competing par_promote might beat us to the expansion space,
2785 // so we may go around the loop again if promotion fails again.
2786 if (GCExpandToAllocateDelayMillis > 0) {
2787 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2788 }
2789 }
2790 }
2791
2792
2793 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2794 PromotionInfo* promo) {
2795 MutexLocker x(ParGCRareEvent_lock);
2796 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2797 while (true) {
2798 // Expansion by some other thread might make alloc OK now:
2799 if (promo->ensure_spooling_space()) {
2800 assert(promo->has_spooling_space(),
2801 "Post-condition of successful ensure_spooling_space()");
2802 return true;
2803 }
2804 // If there's not enough expansion space available, give up.
2805 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2806 return false;
2807 }
2808 // Otherwise, we try expansion.
2809 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2810 // Now go around the loop and try alloc again;
2811 // A competing allocation might beat us to the expansion space,
2812 // so we may go around the loop again if allocation fails again.
2813 if (GCExpandToAllocateDelayMillis > 0) {
2814 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2815 }
2816 }
2817 }
2818
2819 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2820 // Only shrink if a compaction was done so that all the free space
2821 // in the generation is in a contiguous block at the end.
2822 if (did_compact()) {
2823 CardGeneration::shrink(bytes);
2824 }
2825 }
2826
2827 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2828 assert_locked_or_safepoint(Heap_lock);
2829 }
2830
2831 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2832 assert_locked_or_safepoint(Heap_lock);
2833 assert_lock_strong(freelistLock());
2834 if (PrintGCDetails && Verbose) {
2835 warning("Shrinking of CMS not yet implemented");
2836 }
2837 return;
2838 }
2839
2840
2841 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2842 // phases.
2843 class CMSPhaseAccounting: public StackObj {
2844 public:
2845 CMSPhaseAccounting(CMSCollector *collector,
2846 const char *phase,
2847 const GCId gc_id,
2848 bool print_cr = true);
2849 ~CMSPhaseAccounting();
2850
2851 private:
2852 CMSCollector *_collector;
2853 const char *_phase;
2854 elapsedTimer _wallclock;
2855 bool _print_cr;
2856 const GCId _gc_id;
2857
2858 public:
2859 // Not MT-safe; so do not pass around these StackObj's
2860 // where they may be accessed by other threads.
2861 jlong wallclock_millis() {
2862 assert(_wallclock.is_active(), "Wall clock should not stop");
2863 _wallclock.stop(); // to record time
2864 jlong ret = _wallclock.milliseconds();
2865 _wallclock.start(); // restart
2866 return ret;
2867 }
2868 };
2869
2870 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2871 const char *phase,
2872 const GCId gc_id,
2873 bool print_cr) :
2874 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2875
2876 if (PrintCMSStatistics != 0) {
2877 _collector->resetYields();
2878 }
2879 if (PrintGCDetails) {
2880 gclog_or_tty->gclog_stamp(_gc_id);
2881 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2882 _collector->cmsGen()->short_name(), _phase);
2883 }
2884 _collector->resetTimer();
2885 _wallclock.start();
2886 _collector->startTimer();
2887 }
2888
2889 CMSPhaseAccounting::~CMSPhaseAccounting() {
2890 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2891 _collector->stopTimer();
2892 _wallclock.stop();
2893 if (PrintGCDetails) {
2894 gclog_or_tty->gclog_stamp(_gc_id);
2895 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2896 _collector->cmsGen()->short_name(),
2897 _phase, _collector->timerValue(), _wallclock.seconds());
2898 if (_print_cr) {
2899 gclog_or_tty->cr();
2900 }
2901 if (PrintCMSStatistics != 0) {
2902 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2903 _collector->yields());
2904 }
2905 }
2906 }
2907
2908 // CMS work
2909
2910 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2911 class CMSParMarkTask : public AbstractGangTask {
2912 protected:
2913 CMSCollector* _collector;
2914 uint _n_workers;
2915 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2916 AbstractGangTask(name),
2917 _collector(collector),
2918 _n_workers(n_workers) {}
2919 // Work method in support of parallel rescan ... of young gen spaces
2920 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2921 ContiguousSpace* space,
2922 HeapWord** chunk_array, size_t chunk_top);
2923 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2924 };
2925
2926 // Parallel initial mark task
2927 class CMSParInitialMarkTask: public CMSParMarkTask {
2928 StrongRootsScope* _strong_roots_scope;
2929 public:
2930 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2931 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2932 _strong_roots_scope(strong_roots_scope) {}
2933 void work(uint worker_id);
2934 };
2935
2936 // Checkpoint the roots into this generation from outside
2937 // this generation. [Note this initial checkpoint need only
2938 // be approximate -- we'll do a catch up phase subsequently.]
2939 void CMSCollector::checkpointRootsInitial() {
2940 assert(_collectorState == InitialMarking, "Wrong collector state");
2941 check_correct_thread_executing();
2942 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2943
2944 save_heap_summary();
2945 report_heap_summary(GCWhen::BeforeGC);
2946
2947 ReferenceProcessor* rp = ref_processor();
2948 assert(_restart_addr == NULL, "Control point invariant");
2949 {
2950 // acquire locks for subsequent manipulations
2951 MutexLockerEx x(bitMapLock(),
2952 Mutex::_no_safepoint_check_flag);
2953 checkpointRootsInitialWork();
2954 // enable ("weak") refs discovery
2955 rp->enable_discovery();
2956 _collectorState = Marking;
2957 }
2958 }
2959
2960 void CMSCollector::checkpointRootsInitialWork() {
2961 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2962 assert(_collectorState == InitialMarking, "just checking");
2963
2964 // If there has not been a GC[n-1] since last GC[n] cycle completed,
2965 // precede our marking with a collection of all
2966 // younger generations to keep floating garbage to a minimum.
2967 // XXX: we won't do this for now -- it's an optimization to be done later.
2968
2969 // already have locks
2970 assert_lock_strong(bitMapLock());
2971 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2972
2973 // Setup the verification and class unloading state for this
2974 // CMS collection cycle.
2975 setup_cms_unloading_and_verification_state();
2976
2977 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2978 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2979
2980 // Reset all the PLAB chunk arrays if necessary.
2981 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2982 reset_survivor_plab_arrays();
2983 }
2984
2985 ResourceMark rm;
2986 HandleMark hm;
2987
2988 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2989 GenCollectedHeap* gch = GenCollectedHeap::heap();
2990
2991 verify_work_stacks_empty();
2992 verify_overflow_empty();
2993
2994 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2995 // Update the saved marks which may affect the root scans.
2996 gch->save_marks();
2997
2998 // weak reference processing has not started yet.
2999 ref_processor()->set_enqueuing_is_done(false);
3000
3001 // Need to remember all newly created CLDs,
3002 // so that we can guarantee that the remark finds them.
3003 ClassLoaderDataGraph::remember_new_clds(true);
3004
3005 // Whenever a CLD is found, it will be claimed before proceeding to mark
3006 // the klasses. The claimed marks need to be cleared before marking starts.
3007 ClassLoaderDataGraph::clear_claimed_marks();
3008
3009 if (CMSPrintEdenSurvivorChunks) {
3010 print_eden_and_survivor_chunk_arrays();
3011 }
3012
3013 {
3014 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3015 if (CMSParallelInitialMarkEnabled) {
3016 // The parallel version.
3017 FlexibleWorkGang* workers = gch->workers();
3018 assert(workers != NULL, "Need parallel worker threads.");
3019 uint n_workers = workers->active_workers();
3020
3021 StrongRootsScope srs(n_workers);
3022
3023 CMSParInitialMarkTask tsk(this, &srs, n_workers);
3024 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3025 if (n_workers > 1) {
3026 workers->run_task(&tsk);
3027 } else {
3028 tsk.work(0);
3029 }
3030 } else {
3031 // The serial version.
3032 CLDToOopClosure cld_closure(¬Older, true);
3033 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3034
3035 StrongRootsScope srs(1);
3036
3037 gch->gen_process_roots(&srs,
3038 GenCollectedHeap::OldGen,
3039 true, // younger gens are roots
3040 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3041 should_unload_classes(),
3042 ¬Older,
3043 NULL,
3044 &cld_closure);
3045 }
3046 }
3047
3048 // Clear mod-union table; it will be dirtied in the prologue of
3049 // CMS generation per each younger generation collection.
3050
3051 assert(_modUnionTable.isAllClear(),
3052 "Was cleared in most recent final checkpoint phase"
3053 " or no bits are set in the gc_prologue before the start of the next "
3054 "subsequent marking phase.");
3055
3056 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3057
3058 // Save the end of the used_region of the constituent generations
3059 // to be used to limit the extent of sweep in each generation.
3060 save_sweep_limits();
3061 verify_overflow_empty();
3062 }
3063
3064 bool CMSCollector::markFromRoots() {
3065 // we might be tempted to assert that:
3066 // assert(!SafepointSynchronize::is_at_safepoint(),
3067 // "inconsistent argument?");
3068 // However that wouldn't be right, because it's possible that
3069 // a safepoint is indeed in progress as a younger generation
3070 // stop-the-world GC happens even as we mark in this generation.
3071 assert(_collectorState == Marking, "inconsistent state?");
3072 check_correct_thread_executing();
3073 verify_overflow_empty();
3074
3075 // Weak ref discovery note: We may be discovering weak
3076 // refs in this generation concurrent (but interleaved) with
3077 // weak ref discovery by a younger generation collector.
3078
3079 CMSTokenSyncWithLocks ts(true, bitMapLock());
3080 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3081 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3082 bool res = markFromRootsWork();
3083 if (res) {
3084 _collectorState = Precleaning;
3085 } else { // We failed and a foreground collection wants to take over
3086 assert(_foregroundGCIsActive, "internal state inconsistency");
3087 assert(_restart_addr == NULL, "foreground will restart from scratch");
3088 if (PrintGCDetails) {
3089 gclog_or_tty->print_cr("bailing out to foreground collection");
3090 }
3091 }
3092 verify_overflow_empty();
3093 return res;
3094 }
3095
3096 bool CMSCollector::markFromRootsWork() {
3097 // iterate over marked bits in bit map, doing a full scan and mark
3098 // from these roots using the following algorithm:
3099 // . if oop is to the right of the current scan pointer,
3100 // mark corresponding bit (we'll process it later)
3101 // . else (oop is to left of current scan pointer)
3102 // push oop on marking stack
3103 // . drain the marking stack
3104
3105 // Note that when we do a marking step we need to hold the
3106 // bit map lock -- recall that direct allocation (by mutators)
3107 // and promotion (by younger generation collectors) is also
3108 // marking the bit map. [the so-called allocate live policy.]
3109 // Because the implementation of bit map marking is not
3110 // robust wrt simultaneous marking of bits in the same word,
3111 // we need to make sure that there is no such interference
3112 // between concurrent such updates.
3113
3114 // already have locks
3115 assert_lock_strong(bitMapLock());
3116
3117 verify_work_stacks_empty();
3118 verify_overflow_empty();
3119 bool result = false;
3120 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3121 result = do_marking_mt();
3122 } else {
3123 result = do_marking_st();
3124 }
3125 return result;
3126 }
3127
3128 // Forward decl
3129 class CMSConcMarkingTask;
3130
3131 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3132 CMSCollector* _collector;
3133 CMSConcMarkingTask* _task;
3134 public:
3135 virtual void yield();
3136
3137 // "n_threads" is the number of threads to be terminated.
3138 // "queue_set" is a set of work queues of other threads.
3139 // "collector" is the CMS collector associated with this task terminator.
3140 // "yield" indicates whether we need the gang as a whole to yield.
3141 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3142 ParallelTaskTerminator(n_threads, queue_set),
3143 _collector(collector) { }
3144
3145 void set_task(CMSConcMarkingTask* task) {
3146 _task = task;
3147 }
3148 };
3149
3150 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3151 CMSConcMarkingTask* _task;
3152 public:
3153 bool should_exit_termination();
3154 void set_task(CMSConcMarkingTask* task) {
3155 _task = task;
3156 }
3157 };
3158
3159 // MT Concurrent Marking Task
3160 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3161 CMSCollector* _collector;
3162 uint _n_workers; // requested/desired # workers
3163 bool _result;
3164 CompactibleFreeListSpace* _cms_space;
3165 char _pad_front[64]; // padding to ...
3166 HeapWord* _global_finger; // ... avoid sharing cache line
3167 char _pad_back[64];
3168 HeapWord* _restart_addr;
3169
3170 // Exposed here for yielding support
3171 Mutex* const _bit_map_lock;
3172
3173 // The per thread work queues, available here for stealing
3174 OopTaskQueueSet* _task_queues;
3175
3176 // Termination (and yielding) support
3177 CMSConcMarkingTerminator _term;
3178 CMSConcMarkingTerminatorTerminator _term_term;
3179
3180 public:
3181 CMSConcMarkingTask(CMSCollector* collector,
3182 CompactibleFreeListSpace* cms_space,
3183 YieldingFlexibleWorkGang* workers,
3184 OopTaskQueueSet* task_queues):
3185 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3186 _collector(collector),
3187 _cms_space(cms_space),
3188 _n_workers(0), _result(true),
3189 _task_queues(task_queues),
3190 _term(_n_workers, task_queues, _collector),
3191 _bit_map_lock(collector->bitMapLock())
3192 {
3193 _requested_size = _n_workers;
3194 _term.set_task(this);
3195 _term_term.set_task(this);
3196 _restart_addr = _global_finger = _cms_space->bottom();
3197 }
3198
3199
3200 OopTaskQueueSet* task_queues() { return _task_queues; }
3201
3202 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3203
3204 HeapWord** global_finger_addr() { return &_global_finger; }
3205
3206 CMSConcMarkingTerminator* terminator() { return &_term; }
3207
3208 virtual void set_for_termination(uint active_workers) {
3209 terminator()->reset_for_reuse(active_workers);
3210 }
3211
3212 void work(uint worker_id);
3213 bool should_yield() {
3214 return ConcurrentMarkSweepThread::should_yield()
3215 && !_collector->foregroundGCIsActive();
3216 }
3217
3218 virtual void coordinator_yield(); // stuff done by coordinator
3219 bool result() { return _result; }
3220
3221 void reset(HeapWord* ra) {
3222 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3223 _restart_addr = _global_finger = ra;
3224 _term.reset_for_reuse();
3225 }
3226
3227 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3228 OopTaskQueue* work_q);
3229
3230 private:
3231 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3232 void do_work_steal(int i);
3233 void bump_global_finger(HeapWord* f);
3234 };
3235
3236 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3237 assert(_task != NULL, "Error");
3238 return _task->yielding();
3239 // Note that we do not need the disjunct || _task->should_yield() above
3240 // because we want terminating threads to yield only if the task
3241 // is already in the midst of yielding, which happens only after at least one
3242 // thread has yielded.
3243 }
3244
3245 void CMSConcMarkingTerminator::yield() {
3246 if (_task->should_yield()) {
3247 _task->yield();
3248 } else {
3249 ParallelTaskTerminator::yield();
3250 }
3251 }
3252
3253 ////////////////////////////////////////////////////////////////
3254 // Concurrent Marking Algorithm Sketch
3255 ////////////////////////////////////////////////////////////////
3256 // Until all tasks exhausted (both spaces):
3257 // -- claim next available chunk
3258 // -- bump global finger via CAS
3259 // -- find first object that starts in this chunk
3260 // and start scanning bitmap from that position
3261 // -- scan marked objects for oops
3262 // -- CAS-mark target, and if successful:
3263 // . if target oop is above global finger (volatile read)
3264 // nothing to do
3265 // . if target oop is in chunk and above local finger
3266 // then nothing to do
3267 // . else push on work-queue
3268 // -- Deal with possible overflow issues:
3269 // . local work-queue overflow causes stuff to be pushed on
3270 // global (common) overflow queue
3271 // . always first empty local work queue
3272 // . then get a batch of oops from global work queue if any
3273 // . then do work stealing
3274 // -- When all tasks claimed (both spaces)
3275 // and local work queue empty,
3276 // then in a loop do:
3277 // . check global overflow stack; steal a batch of oops and trace
3278 // . try to steal from other threads oif GOS is empty
3279 // . if neither is available, offer termination
3280 // -- Terminate and return result
3281 //
3282 void CMSConcMarkingTask::work(uint worker_id) {
3283 elapsedTimer _timer;
3284 ResourceMark rm;
3285 HandleMark hm;
3286
3287 DEBUG_ONLY(_collector->verify_overflow_empty();)
3288
3289 // Before we begin work, our work queue should be empty
3290 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3291 // Scan the bitmap covering _cms_space, tracing through grey objects.
3292 _timer.start();
3293 do_scan_and_mark(worker_id, _cms_space);
3294 _timer.stop();
3295 if (PrintCMSStatistics != 0) {
3296 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3297 worker_id, _timer.seconds());
3298 // XXX: need xxx/xxx type of notation, two timers
3299 }
3300
3301 // ... do work stealing
3302 _timer.reset();
3303 _timer.start();
3304 do_work_steal(worker_id);
3305 _timer.stop();
3306 if (PrintCMSStatistics != 0) {
3307 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3308 worker_id, _timer.seconds());
3309 // XXX: need xxx/xxx type of notation, two timers
3310 }
3311 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3312 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3313 // Note that under the current task protocol, the
3314 // following assertion is true even of the spaces
3315 // expanded since the completion of the concurrent
3316 // marking. XXX This will likely change under a strict
3317 // ABORT semantics.
3318 // After perm removal the comparison was changed to
3319 // greater than or equal to from strictly greater than.
3320 // Before perm removal the highest address sweep would
3321 // have been at the end of perm gen but now is at the
3322 // end of the tenured gen.
3323 assert(_global_finger >= _cms_space->end(),
3324 "All tasks have been completed");
3325 DEBUG_ONLY(_collector->verify_overflow_empty();)
3326 }
3327
3328 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3329 HeapWord* read = _global_finger;
3330 HeapWord* cur = read;
3331 while (f > read) {
3332 cur = read;
3333 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3334 if (cur == read) {
3335 // our cas succeeded
3336 assert(_global_finger >= f, "protocol consistency");
3337 break;
3338 }
3339 }
3340 }
3341
3342 // This is really inefficient, and should be redone by
3343 // using (not yet available) block-read and -write interfaces to the
3344 // stack and the work_queue. XXX FIX ME !!!
3345 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3346 OopTaskQueue* work_q) {
3347 // Fast lock-free check
3348 if (ovflw_stk->length() == 0) {
3349 return false;
3350 }
3351 assert(work_q->size() == 0, "Shouldn't steal");
3352 MutexLockerEx ml(ovflw_stk->par_lock(),
3353 Mutex::_no_safepoint_check_flag);
3354 // Grab up to 1/4 the size of the work queue
3355 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3356 (size_t)ParGCDesiredObjsFromOverflowList);
3357 num = MIN2(num, ovflw_stk->length());
3358 for (int i = (int) num; i > 0; i--) {
3359 oop cur = ovflw_stk->pop();
3360 assert(cur != NULL, "Counted wrong?");
3361 work_q->push(cur);
3362 }
3363 return num > 0;
3364 }
3365
3366 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3367 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3368 int n_tasks = pst->n_tasks();
3369 // We allow that there may be no tasks to do here because
3370 // we are restarting after a stack overflow.
3371 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3372 uint nth_task = 0;
3373
3374 HeapWord* aligned_start = sp->bottom();
3375 if (sp->used_region().contains(_restart_addr)) {
3376 // Align down to a card boundary for the start of 0th task
3377 // for this space.
3378 aligned_start =
3379 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3380 CardTableModRefBS::card_size);
3381 }
3382
3383 size_t chunk_size = sp->marking_task_size();
3384 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3385 // Having claimed the nth task in this space,
3386 // compute the chunk that it corresponds to:
3387 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3388 aligned_start + (nth_task+1)*chunk_size);
3389 // Try and bump the global finger via a CAS;
3390 // note that we need to do the global finger bump
3391 // _before_ taking the intersection below, because
3392 // the task corresponding to that region will be
3393 // deemed done even if the used_region() expands
3394 // because of allocation -- as it almost certainly will
3395 // during start-up while the threads yield in the
3396 // closure below.
3397 HeapWord* finger = span.end();
3398 bump_global_finger(finger); // atomically
3399 // There are null tasks here corresponding to chunks
3400 // beyond the "top" address of the space.
3401 span = span.intersection(sp->used_region());
3402 if (!span.is_empty()) { // Non-null task
3403 HeapWord* prev_obj;
3404 assert(!span.contains(_restart_addr) || nth_task == 0,
3405 "Inconsistency");
3406 if (nth_task == 0) {
3407 // For the 0th task, we'll not need to compute a block_start.
3408 if (span.contains(_restart_addr)) {
3409 // In the case of a restart because of stack overflow,
3410 // we might additionally skip a chunk prefix.
3411 prev_obj = _restart_addr;
3412 } else {
3413 prev_obj = span.start();
3414 }
3415 } else {
3416 // We want to skip the first object because
3417 // the protocol is to scan any object in its entirety
3418 // that _starts_ in this span; a fortiori, any
3419 // object starting in an earlier span is scanned
3420 // as part of an earlier claimed task.
3421 // Below we use the "careful" version of block_start
3422 // so we do not try to navigate uninitialized objects.
3423 prev_obj = sp->block_start_careful(span.start());
3424 // Below we use a variant of block_size that uses the
3425 // Printezis bits to avoid waiting for allocated
3426 // objects to become initialized/parsable.
3427 while (prev_obj < span.start()) {
3428 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3429 if (sz > 0) {
3430 prev_obj += sz;
3431 } else {
3432 // In this case we may end up doing a bit of redundant
3433 // scanning, but that appears unavoidable, short of
3434 // locking the free list locks; see bug 6324141.
3435 break;
3436 }
3437 }
3438 }
3439 if (prev_obj < span.end()) {
3440 MemRegion my_span = MemRegion(prev_obj, span.end());
3441 // Do the marking work within a non-empty span --
3442 // the last argument to the constructor indicates whether the
3443 // iteration should be incremental with periodic yields.
3444 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3445 &_collector->_markBitMap,
3446 work_queue(i),
3447 &_collector->_markStack);
3448 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3449 } // else nothing to do for this task
3450 } // else nothing to do for this task
3451 }
3452 // We'd be tempted to assert here that since there are no
3453 // more tasks left to claim in this space, the global_finger
3454 // must exceed space->top() and a fortiori space->end(). However,
3455 // that would not quite be correct because the bumping of
3456 // global_finger occurs strictly after the claiming of a task,
3457 // so by the time we reach here the global finger may not yet
3458 // have been bumped up by the thread that claimed the last
3459 // task.
3460 pst->all_tasks_completed();
3461 }
3462
3463 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3464 private:
3465 CMSCollector* _collector;
3466 CMSConcMarkingTask* _task;
3467 MemRegion _span;
3468 CMSBitMap* _bit_map;
3469 CMSMarkStack* _overflow_stack;
3470 OopTaskQueue* _work_queue;
3471 protected:
3472 DO_OOP_WORK_DEFN
3473 public:
3474 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3475 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3476 MetadataAwareOopClosure(collector->ref_processor()),
3477 _collector(collector),
3478 _task(task),
3479 _span(collector->_span),
3480 _work_queue(work_queue),
3481 _bit_map(bit_map),
3482 _overflow_stack(overflow_stack)
3483 { }
3484 virtual void do_oop(oop* p);
3485 virtual void do_oop(narrowOop* p);
3486
3487 void trim_queue(size_t max);
3488 void handle_stack_overflow(HeapWord* lost);
3489 void do_yield_check() {
3490 if (_task->should_yield()) {
3491 _task->yield();
3492 }
3493 }
3494 };
3495
3496 // Grey object scanning during work stealing phase --
3497 // the salient assumption here is that any references
3498 // that are in these stolen objects being scanned must
3499 // already have been initialized (else they would not have
3500 // been published), so we do not need to check for
3501 // uninitialized objects before pushing here.
3502 void Par_ConcMarkingClosure::do_oop(oop obj) {
3503 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3504 HeapWord* addr = (HeapWord*)obj;
3505 // Check if oop points into the CMS generation
3506 // and is not marked
3507 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3508 // a white object ...
3509 // If we manage to "claim" the object, by being the
3510 // first thread to mark it, then we push it on our
3511 // marking stack
3512 if (_bit_map->par_mark(addr)) { // ... now grey
3513 // push on work queue (grey set)
3514 bool simulate_overflow = false;
3515 NOT_PRODUCT(
3516 if (CMSMarkStackOverflowALot &&
3517 _collector->simulate_overflow()) {
3518 // simulate a stack overflow
3519 simulate_overflow = true;
3520 }
3521 )
3522 if (simulate_overflow ||
3523 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3524 // stack overflow
3525 if (PrintCMSStatistics != 0) {
3526 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3527 SIZE_FORMAT, _overflow_stack->capacity());
3528 }
3529 // We cannot assert that the overflow stack is full because
3530 // it may have been emptied since.
3531 assert(simulate_overflow ||
3532 _work_queue->size() == _work_queue->max_elems(),
3533 "Else push should have succeeded");
3534 handle_stack_overflow(addr);
3535 }
3536 } // Else, some other thread got there first
3537 do_yield_check();
3538 }
3539 }
3540
3541 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3542 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3543
3544 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3545 while (_work_queue->size() > max) {
3546 oop new_oop;
3547 if (_work_queue->pop_local(new_oop)) {
3548 assert(new_oop->is_oop(), "Should be an oop");
3549 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3550 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3551 new_oop->oop_iterate(this); // do_oop() above
3552 do_yield_check();
3553 }
3554 }
3555 }
3556
3557 // Upon stack overflow, we discard (part of) the stack,
3558 // remembering the least address amongst those discarded
3559 // in CMSCollector's _restart_address.
3560 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3561 // We need to do this under a mutex to prevent other
3562 // workers from interfering with the work done below.
3563 MutexLockerEx ml(_overflow_stack->par_lock(),
3564 Mutex::_no_safepoint_check_flag);
3565 // Remember the least grey address discarded
3566 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3567 _collector->lower_restart_addr(ra);
3568 _overflow_stack->reset(); // discard stack contents
3569 _overflow_stack->expand(); // expand the stack if possible
3570 }
3571
3572
3573 void CMSConcMarkingTask::do_work_steal(int i) {
3574 OopTaskQueue* work_q = work_queue(i);
3575 oop obj_to_scan;
3576 CMSBitMap* bm = &(_collector->_markBitMap);
3577 CMSMarkStack* ovflw = &(_collector->_markStack);
3578 int* seed = _collector->hash_seed(i);
3579 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3580 while (true) {
3581 cl.trim_queue(0);
3582 assert(work_q->size() == 0, "Should have been emptied above");
3583 if (get_work_from_overflow_stack(ovflw, work_q)) {
3584 // Can't assert below because the work obtained from the
3585 // overflow stack may already have been stolen from us.
3586 // assert(work_q->size() > 0, "Work from overflow stack");
3587 continue;
3588 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3589 assert(obj_to_scan->is_oop(), "Should be an oop");
3590 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3591 obj_to_scan->oop_iterate(&cl);
3592 } else if (terminator()->offer_termination(&_term_term)) {
3593 assert(work_q->size() == 0, "Impossible!");
3594 break;
3595 } else if (yielding() || should_yield()) {
3596 yield();
3597 }
3598 }
3599 }
3600
3601 // This is run by the CMS (coordinator) thread.
3602 void CMSConcMarkingTask::coordinator_yield() {
3603 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3604 "CMS thread should hold CMS token");
3605 // First give up the locks, then yield, then re-lock
3606 // We should probably use a constructor/destructor idiom to
3607 // do this unlock/lock or modify the MutexUnlocker class to
3608 // serve our purpose. XXX
3609 assert_lock_strong(_bit_map_lock);
3610 _bit_map_lock->unlock();
3611 ConcurrentMarkSweepThread::desynchronize(true);
3612 _collector->stopTimer();
3613 if (PrintCMSStatistics != 0) {
3614 _collector->incrementYields();
3615 }
3616
3617 // It is possible for whichever thread initiated the yield request
3618 // not to get a chance to wake up and take the bitmap lock between
3619 // this thread releasing it and reacquiring it. So, while the
3620 // should_yield() flag is on, let's sleep for a bit to give the
3621 // other thread a chance to wake up. The limit imposed on the number
3622 // of iterations is defensive, to avoid any unforseen circumstances
3623 // putting us into an infinite loop. Since it's always been this
3624 // (coordinator_yield()) method that was observed to cause the
3625 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3626 // which is by default non-zero. For the other seven methods that
3627 // also perform the yield operation, as are using a different
3628 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3629 // can enable the sleeping for those methods too, if necessary.
3630 // See 6442774.
3631 //
3632 // We really need to reconsider the synchronization between the GC
3633 // thread and the yield-requesting threads in the future and we
3634 // should really use wait/notify, which is the recommended
3635 // way of doing this type of interaction. Additionally, we should
3636 // consolidate the eight methods that do the yield operation and they
3637 // are almost identical into one for better maintainability and
3638 // readability. See 6445193.
3639 //
3640 // Tony 2006.06.29
3641 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3642 ConcurrentMarkSweepThread::should_yield() &&
3643 !CMSCollector::foregroundGCIsActive(); ++i) {
3644 os::sleep(Thread::current(), 1, false);
3645 }
3646
3647 ConcurrentMarkSweepThread::synchronize(true);
3648 _bit_map_lock->lock_without_safepoint_check();
3649 _collector->startTimer();
3650 }
3651
3652 bool CMSCollector::do_marking_mt() {
3653 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3654 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3655 conc_workers()->active_workers(),
3656 Threads::number_of_non_daemon_threads());
3657 conc_workers()->set_active_workers(num_workers);
3658
3659 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3660
3661 CMSConcMarkingTask tsk(this,
3662 cms_space,
3663 conc_workers(),
3664 task_queues());
3665
3666 // Since the actual number of workers we get may be different
3667 // from the number we requested above, do we need to do anything different
3668 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3669 // class?? XXX
3670 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3671
3672 // Refs discovery is already non-atomic.
3673 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3674 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3675 conc_workers()->start_task(&tsk);
3676 while (tsk.yielded()) {
3677 tsk.coordinator_yield();
3678 conc_workers()->continue_task(&tsk);
3679 }
3680 // If the task was aborted, _restart_addr will be non-NULL
3681 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3682 while (_restart_addr != NULL) {
3683 // XXX For now we do not make use of ABORTED state and have not
3684 // yet implemented the right abort semantics (even in the original
3685 // single-threaded CMS case). That needs some more investigation
3686 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3687 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3688 // If _restart_addr is non-NULL, a marking stack overflow
3689 // occurred; we need to do a fresh marking iteration from the
3690 // indicated restart address.
3691 if (_foregroundGCIsActive) {
3692 // We may be running into repeated stack overflows, having
3693 // reached the limit of the stack size, while making very
3694 // slow forward progress. It may be best to bail out and
3695 // let the foreground collector do its job.
3696 // Clear _restart_addr, so that foreground GC
3697 // works from scratch. This avoids the headache of
3698 // a "rescan" which would otherwise be needed because
3699 // of the dirty mod union table & card table.
3700 _restart_addr = NULL;
3701 return false;
3702 }
3703 // Adjust the task to restart from _restart_addr
3704 tsk.reset(_restart_addr);
3705 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3706 _restart_addr);
3707 _restart_addr = NULL;
3708 // Get the workers going again
3709 conc_workers()->start_task(&tsk);
3710 while (tsk.yielded()) {
3711 tsk.coordinator_yield();
3712 conc_workers()->continue_task(&tsk);
3713 }
3714 }
3715 assert(tsk.completed(), "Inconsistency");
3716 assert(tsk.result() == true, "Inconsistency");
3717 return true;
3718 }
3719
3720 bool CMSCollector::do_marking_st() {
3721 ResourceMark rm;
3722 HandleMark hm;
3723
3724 // Temporarily make refs discovery single threaded (non-MT)
3725 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3726 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3727 &_markStack, CMSYield);
3728 // the last argument to iterate indicates whether the iteration
3729 // should be incremental with periodic yields.
3730 _markBitMap.iterate(&markFromRootsClosure);
3731 // If _restart_addr is non-NULL, a marking stack overflow
3732 // occurred; we need to do a fresh iteration from the
3733 // indicated restart address.
3734 while (_restart_addr != NULL) {
3735 if (_foregroundGCIsActive) {
3736 // We may be running into repeated stack overflows, having
3737 // reached the limit of the stack size, while making very
3738 // slow forward progress. It may be best to bail out and
3739 // let the foreground collector do its job.
3740 // Clear _restart_addr, so that foreground GC
3741 // works from scratch. This avoids the headache of
3742 // a "rescan" which would otherwise be needed because
3743 // of the dirty mod union table & card table.
3744 _restart_addr = NULL;
3745 return false; // indicating failure to complete marking
3746 }
3747 // Deal with stack overflow:
3748 // we restart marking from _restart_addr
3749 HeapWord* ra = _restart_addr;
3750 markFromRootsClosure.reset(ra);
3751 _restart_addr = NULL;
3752 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3753 }
3754 return true;
3755 }
3756
3757 void CMSCollector::preclean() {
3758 check_correct_thread_executing();
3759 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3760 verify_work_stacks_empty();
3761 verify_overflow_empty();
3762 _abort_preclean = false;
3763 if (CMSPrecleaningEnabled) {
3764 if (!CMSEdenChunksRecordAlways) {
3765 _eden_chunk_index = 0;
3766 }
3767 size_t used = get_eden_used();
3768 size_t capacity = get_eden_capacity();
3769 // Don't start sampling unless we will get sufficiently
3770 // many samples.
3771 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3772 * CMSScheduleRemarkEdenPenetration)) {
3773 _start_sampling = true;
3774 } else {
3775 _start_sampling = false;
3776 }
3777 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3778 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3779 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3780 }
3781 CMSTokenSync x(true); // is cms thread
3782 if (CMSPrecleaningEnabled) {
3783 sample_eden();
3784 _collectorState = AbortablePreclean;
3785 } else {
3786 _collectorState = FinalMarking;
3787 }
3788 verify_work_stacks_empty();
3789 verify_overflow_empty();
3790 }
3791
3792 // Try and schedule the remark such that young gen
3793 // occupancy is CMSScheduleRemarkEdenPenetration %.
3794 void CMSCollector::abortable_preclean() {
3795 check_correct_thread_executing();
3796 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3797 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3798
3799 // If Eden's current occupancy is below this threshold,
3800 // immediately schedule the remark; else preclean
3801 // past the next scavenge in an effort to
3802 // schedule the pause as described above. By choosing
3803 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3804 // we will never do an actual abortable preclean cycle.
3805 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3806 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3807 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3808 // We need more smarts in the abortable preclean
3809 // loop below to deal with cases where allocation
3810 // in young gen is very very slow, and our precleaning
3811 // is running a losing race against a horde of
3812 // mutators intent on flooding us with CMS updates
3813 // (dirty cards).
3814 // One, admittedly dumb, strategy is to give up
3815 // after a certain number of abortable precleaning loops
3816 // or after a certain maximum time. We want to make
3817 // this smarter in the next iteration.
3818 // XXX FIX ME!!! YSR
3819 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3820 while (!(should_abort_preclean() ||
3821 ConcurrentMarkSweepThread::should_terminate())) {
3822 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3823 cumworkdone += workdone;
3824 loops++;
3825 // Voluntarily terminate abortable preclean phase if we have
3826 // been at it for too long.
3827 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3828 loops >= CMSMaxAbortablePrecleanLoops) {
3829 if (PrintGCDetails) {
3830 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3831 }
3832 break;
3833 }
3834 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3835 if (PrintGCDetails) {
3836 gclog_or_tty->print(" CMS: abort preclean due to time ");
3837 }
3838 break;
3839 }
3840 // If we are doing little work each iteration, we should
3841 // take a short break.
3842 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3843 // Sleep for some time, waiting for work to accumulate
3844 stopTimer();
3845 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3846 startTimer();
3847 waited++;
3848 }
3849 }
3850 if (PrintCMSStatistics > 0) {
3851 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3852 loops, waited, cumworkdone);
3853 }
3854 }
3855 CMSTokenSync x(true); // is cms thread
3856 if (_collectorState != Idling) {
3857 assert(_collectorState == AbortablePreclean,
3858 "Spontaneous state transition?");
3859 _collectorState = FinalMarking;
3860 } // Else, a foreground collection completed this CMS cycle.
3861 return;
3862 }
3863
3864 // Respond to an Eden sampling opportunity
3865 void CMSCollector::sample_eden() {
3866 // Make sure a young gc cannot sneak in between our
3867 // reading and recording of a sample.
3868 assert(Thread::current()->is_ConcurrentGC_thread(),
3869 "Only the cms thread may collect Eden samples");
3870 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3871 "Should collect samples while holding CMS token");
3872 if (!_start_sampling) {
3873 return;
3874 }
3875 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3876 // is populated by the young generation.
3877 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3878 if (_eden_chunk_index < _eden_chunk_capacity) {
3879 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3880 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3881 "Unexpected state of Eden");
3882 // We'd like to check that what we just sampled is an oop-start address;
3883 // however, we cannot do that here since the object may not yet have been
3884 // initialized. So we'll instead do the check when we _use_ this sample
3885 // later.
3886 if (_eden_chunk_index == 0 ||
3887 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3888 _eden_chunk_array[_eden_chunk_index-1])
3889 >= CMSSamplingGrain)) {
3890 _eden_chunk_index++; // commit sample
3891 }
3892 }
3893 }
3894 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3895 size_t used = get_eden_used();
3896 size_t capacity = get_eden_capacity();
3897 assert(used <= capacity, "Unexpected state of Eden");
3898 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3899 _abort_preclean = true;
3900 }
3901 }
3902 }
3903
3904
3905 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3906 assert(_collectorState == Precleaning ||
3907 _collectorState == AbortablePreclean, "incorrect state");
3908 ResourceMark rm;
3909 HandleMark hm;
3910
3911 // Precleaning is currently not MT but the reference processor
3912 // may be set for MT. Disable it temporarily here.
3913 ReferenceProcessor* rp = ref_processor();
3914 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3915
3916 // Do one pass of scrubbing the discovered reference lists
3917 // to remove any reference objects with strongly-reachable
3918 // referents.
3919 if (clean_refs) {
3920 CMSPrecleanRefsYieldClosure yield_cl(this);
3921 assert(rp->span().equals(_span), "Spans should be equal");
3922 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3923 &_markStack, true /* preclean */);
3924 CMSDrainMarkingStackClosure complete_trace(this,
3925 _span, &_markBitMap, &_markStack,
3926 &keep_alive, true /* preclean */);
3927
3928 // We don't want this step to interfere with a young
3929 // collection because we don't want to take CPU
3930 // or memory bandwidth away from the young GC threads
3931 // (which may be as many as there are CPUs).
3932 // Note that we don't need to protect ourselves from
3933 // interference with mutators because they can't
3934 // manipulate the discovered reference lists nor affect
3935 // the computed reachability of the referents, the
3936 // only properties manipulated by the precleaning
3937 // of these reference lists.
3938 stopTimer();
3939 CMSTokenSyncWithLocks x(true /* is cms thread */,
3940 bitMapLock());
3941 startTimer();
3942 sample_eden();
3943
3944 // The following will yield to allow foreground
3945 // collection to proceed promptly. XXX YSR:
3946 // The code in this method may need further
3947 // tweaking for better performance and some restructuring
3948 // for cleaner interfaces.
3949 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3950 rp->preclean_discovered_references(
3951 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3952 gc_timer, _gc_tracer_cm->gc_id());
3953 }
3954
3955 if (clean_survivor) { // preclean the active survivor space(s)
3956 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3957 &_markBitMap, &_modUnionTable,
3958 &_markStack, true /* precleaning phase */);
3959 stopTimer();
3960 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3961 bitMapLock());
3962 startTimer();
3963 unsigned int before_count =
3964 GenCollectedHeap::heap()->total_collections();
3965 SurvivorSpacePrecleanClosure
3966 sss_cl(this, _span, &_markBitMap, &_markStack,
3967 &pam_cl, before_count, CMSYield);
3968 _young_gen->from()->object_iterate_careful(&sss_cl);
3969 _young_gen->to()->object_iterate_careful(&sss_cl);
3970 }
3971 MarkRefsIntoAndScanClosure
3972 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3973 &_markStack, this, CMSYield,
3974 true /* precleaning phase */);
3975 // CAUTION: The following closure has persistent state that may need to
3976 // be reset upon a decrease in the sequence of addresses it
3977 // processes.
3978 ScanMarkedObjectsAgainCarefullyClosure
3979 smoac_cl(this, _span,
3980 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3981
3982 // Preclean dirty cards in ModUnionTable and CardTable using
3983 // appropriate convergence criterion;
3984 // repeat CMSPrecleanIter times unless we find that
3985 // we are losing.
3986 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3987 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3988 "Bad convergence multiplier");
3989 assert(CMSPrecleanThreshold >= 100,
3990 "Unreasonably low CMSPrecleanThreshold");
3991
3992 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3993 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3994 numIter < CMSPrecleanIter;
3995 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3996 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3997 if (Verbose && PrintGCDetails) {
3998 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3999 }
4000 // Either there are very few dirty cards, so re-mark
4001 // pause will be small anyway, or our pre-cleaning isn't
4002 // that much faster than the rate at which cards are being
4003 // dirtied, so we might as well stop and re-mark since
4004 // precleaning won't improve our re-mark time by much.
4005 if (curNumCards <= CMSPrecleanThreshold ||
4006 (numIter > 0 &&
4007 (curNumCards * CMSPrecleanDenominator >
4008 lastNumCards * CMSPrecleanNumerator))) {
4009 numIter++;
4010 cumNumCards += curNumCards;
4011 break;
4012 }
4013 }
4014
4015 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4016
4017 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4018 cumNumCards += curNumCards;
4019 if (PrintGCDetails && PrintCMSStatistics != 0) {
4020 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4021 curNumCards, cumNumCards, numIter);
4022 }
4023 return cumNumCards; // as a measure of useful work done
4024 }
4025
4026 // PRECLEANING NOTES:
4027 // Precleaning involves:
4028 // . reading the bits of the modUnionTable and clearing the set bits.
4029 // . For the cards corresponding to the set bits, we scan the
4030 // objects on those cards. This means we need the free_list_lock
4031 // so that we can safely iterate over the CMS space when scanning
4032 // for oops.
4033 // . When we scan the objects, we'll be both reading and setting
4034 // marks in the marking bit map, so we'll need the marking bit map.
4035 // . For protecting _collector_state transitions, we take the CGC_lock.
4036 // Note that any races in the reading of of card table entries by the
4037 // CMS thread on the one hand and the clearing of those entries by the
4038 // VM thread or the setting of those entries by the mutator threads on the
4039 // other are quite benign. However, for efficiency it makes sense to keep
4040 // the VM thread from racing with the CMS thread while the latter is
4041 // dirty card info to the modUnionTable. We therefore also use the
4042 // CGC_lock to protect the reading of the card table and the mod union
4043 // table by the CM thread.
4044 // . We run concurrently with mutator updates, so scanning
4045 // needs to be done carefully -- we should not try to scan
4046 // potentially uninitialized objects.
4047 //
4048 // Locking strategy: While holding the CGC_lock, we scan over and
4049 // reset a maximal dirty range of the mod union / card tables, then lock
4050 // the free_list_lock and bitmap lock to do a full marking, then
4051 // release these locks; and repeat the cycle. This allows for a
4052 // certain amount of fairness in the sharing of these locks between
4053 // the CMS collector on the one hand, and the VM thread and the
4054 // mutators on the other.
4055
4056 // NOTE: preclean_mod_union_table() and preclean_card_table()
4057 // further below are largely identical; if you need to modify
4058 // one of these methods, please check the other method too.
4059
4060 size_t CMSCollector::preclean_mod_union_table(
4061 ConcurrentMarkSweepGeneration* gen,
4062 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4063 verify_work_stacks_empty();
4064 verify_overflow_empty();
4065
4066 // strategy: starting with the first card, accumulate contiguous
4067 // ranges of dirty cards; clear these cards, then scan the region
4068 // covered by these cards.
4069
4070 // Since all of the MUT is committed ahead, we can just use
4071 // that, in case the generations expand while we are precleaning.
4072 // It might also be fine to just use the committed part of the
4073 // generation, but we might potentially miss cards when the
4074 // generation is rapidly expanding while we are in the midst
4075 // of precleaning.
4076 HeapWord* startAddr = gen->reserved().start();
4077 HeapWord* endAddr = gen->reserved().end();
4078
4079 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4080
4081 size_t numDirtyCards, cumNumDirtyCards;
4082 HeapWord *nextAddr, *lastAddr;
4083 for (cumNumDirtyCards = numDirtyCards = 0,
4084 nextAddr = lastAddr = startAddr;
4085 nextAddr < endAddr;
4086 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4087
4088 ResourceMark rm;
4089 HandleMark hm;
4090
4091 MemRegion dirtyRegion;
4092 {
4093 stopTimer();
4094 // Potential yield point
4095 CMSTokenSync ts(true);
4096 startTimer();
4097 sample_eden();
4098 // Get dirty region starting at nextOffset (inclusive),
4099 // simultaneously clearing it.
4100 dirtyRegion =
4101 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4102 assert(dirtyRegion.start() >= nextAddr,
4103 "returned region inconsistent?");
4104 }
4105 // Remember where the next search should begin.
4106 // The returned region (if non-empty) is a right open interval,
4107 // so lastOffset is obtained from the right end of that
4108 // interval.
4109 lastAddr = dirtyRegion.end();
4110 // Should do something more transparent and less hacky XXX
4111 numDirtyCards =
4112 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4113
4114 // We'll scan the cards in the dirty region (with periodic
4115 // yields for foreground GC as needed).
4116 if (!dirtyRegion.is_empty()) {
4117 assert(numDirtyCards > 0, "consistency check");
4118 HeapWord* stop_point = NULL;
4119 stopTimer();
4120 // Potential yield point
4121 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4122 bitMapLock());
4123 startTimer();
4124 {
4125 verify_work_stacks_empty();
4126 verify_overflow_empty();
4127 sample_eden();
4128 stop_point =
4129 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4130 }
4131 if (stop_point != NULL) {
4132 // The careful iteration stopped early either because it found an
4133 // uninitialized object, or because we were in the midst of an
4134 // "abortable preclean", which should now be aborted. Redirty
4135 // the bits corresponding to the partially-scanned or unscanned
4136 // cards. We'll either restart at the next block boundary or
4137 // abort the preclean.
4138 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4139 "Should only be AbortablePreclean.");
4140 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4141 if (should_abort_preclean()) {
4142 break; // out of preclean loop
4143 } else {
4144 // Compute the next address at which preclean should pick up;
4145 // might need bitMapLock in order to read P-bits.
4146 lastAddr = next_card_start_after_block(stop_point);
4147 }
4148 }
4149 } else {
4150 assert(lastAddr == endAddr, "consistency check");
4151 assert(numDirtyCards == 0, "consistency check");
4152 break;
4153 }
4154 }
4155 verify_work_stacks_empty();
4156 verify_overflow_empty();
4157 return cumNumDirtyCards;
4158 }
4159
4160 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4161 // below are largely identical; if you need to modify
4162 // one of these methods, please check the other method too.
4163
4164 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4165 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4166 // strategy: it's similar to precleamModUnionTable above, in that
4167 // we accumulate contiguous ranges of dirty cards, mark these cards
4168 // precleaned, then scan the region covered by these cards.
4169 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4170 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4171
4172 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4173
4174 size_t numDirtyCards, cumNumDirtyCards;
4175 HeapWord *lastAddr, *nextAddr;
4176
4177 for (cumNumDirtyCards = numDirtyCards = 0,
4178 nextAddr = lastAddr = startAddr;
4179 nextAddr < endAddr;
4180 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4181
4182 ResourceMark rm;
4183 HandleMark hm;
4184
4185 MemRegion dirtyRegion;
4186 {
4187 // See comments in "Precleaning notes" above on why we
4188 // do this locking. XXX Could the locking overheads be
4189 // too high when dirty cards are sparse? [I don't think so.]
4190 stopTimer();
4191 CMSTokenSync x(true); // is cms thread
4192 startTimer();
4193 sample_eden();
4194 // Get and clear dirty region from card table
4195 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4196 MemRegion(nextAddr, endAddr),
4197 true,
4198 CardTableModRefBS::precleaned_card_val());
4199
4200 assert(dirtyRegion.start() >= nextAddr,
4201 "returned region inconsistent?");
4202 }
4203 lastAddr = dirtyRegion.end();
4204 numDirtyCards =
4205 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4206
4207 if (!dirtyRegion.is_empty()) {
4208 stopTimer();
4209 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4210 startTimer();
4211 sample_eden();
4212 verify_work_stacks_empty();
4213 verify_overflow_empty();
4214 HeapWord* stop_point =
4215 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4216 if (stop_point != NULL) {
4217 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4218 "Should only be AbortablePreclean.");
4219 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4220 if (should_abort_preclean()) {
4221 break; // out of preclean loop
4222 } else {
4223 // Compute the next address at which preclean should pick up.
4224 lastAddr = next_card_start_after_block(stop_point);
4225 }
4226 }
4227 } else {
4228 break;
4229 }
4230 }
4231 verify_work_stacks_empty();
4232 verify_overflow_empty();
4233 return cumNumDirtyCards;
4234 }
4235
4236 class PrecleanKlassClosure : public KlassClosure {
4237 KlassToOopClosure _cm_klass_closure;
4238 public:
4239 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4240 void do_klass(Klass* k) {
4241 if (k->has_accumulated_modified_oops()) {
4242 k->clear_accumulated_modified_oops();
4243
4244 _cm_klass_closure.do_klass(k);
4245 }
4246 }
4247 };
4248
4249 // The freelist lock is needed to prevent asserts, is it really needed?
4250 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4251
4252 cl->set_freelistLock(freelistLock);
4253
4254 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4255
4256 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4257 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4258 PrecleanKlassClosure preclean_klass_closure(cl);
4259 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4260
4261 verify_work_stacks_empty();
4262 verify_overflow_empty();
4263 }
4264
4265 void CMSCollector::checkpointRootsFinal() {
4266 assert(_collectorState == FinalMarking, "incorrect state transition?");
4267 check_correct_thread_executing();
4268 // world is stopped at this checkpoint
4269 assert(SafepointSynchronize::is_at_safepoint(),
4270 "world should be stopped");
4271 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4272
4273 verify_work_stacks_empty();
4274 verify_overflow_empty();
4275
4276 if (PrintGCDetails) {
4277 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4278 _young_gen->used() / K,
4279 _young_gen->capacity() / K);
4280 }
4281 {
4282 if (CMSScavengeBeforeRemark) {
4283 GenCollectedHeap* gch = GenCollectedHeap::heap();
4284 // Temporarily set flag to false, GCH->do_collection will
4285 // expect it to be false and set to true
4286 FlagSetting fl(gch->_is_gc_active, false);
4287 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4288 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4289 gch->do_collection(true, // full (i.e. force, see below)
4290 false, // !clear_all_soft_refs
4291 0, // size
4292 false, // is_tlab
4293 GenCollectedHeap::YoungGen // type
4294 );
4295 }
4296 FreelistLocker x(this);
4297 MutexLockerEx y(bitMapLock(),
4298 Mutex::_no_safepoint_check_flag);
4299 checkpointRootsFinalWork();
4300 }
4301 verify_work_stacks_empty();
4302 verify_overflow_empty();
4303 }
4304
4305 void CMSCollector::checkpointRootsFinalWork() {
4306 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4307
4308 assert(haveFreelistLocks(), "must have free list locks");
4309 assert_lock_strong(bitMapLock());
4310
4311 ResourceMark rm;
4312 HandleMark hm;
4313
4314 GenCollectedHeap* gch = GenCollectedHeap::heap();
4315
4316 if (should_unload_classes()) {
4317 CodeCache::gc_prologue();
4318 }
4319 assert(haveFreelistLocks(), "must have free list locks");
4320 assert_lock_strong(bitMapLock());
4321
4322 // We might assume that we need not fill TLAB's when
4323 // CMSScavengeBeforeRemark is set, because we may have just done
4324 // a scavenge which would have filled all TLAB's -- and besides
4325 // Eden would be empty. This however may not always be the case --
4326 // for instance although we asked for a scavenge, it may not have
4327 // happened because of a JNI critical section. We probably need
4328 // a policy for deciding whether we can in that case wait until
4329 // the critical section releases and then do the remark following
4330 // the scavenge, and skip it here. In the absence of that policy,
4331 // or of an indication of whether the scavenge did indeed occur,
4332 // we cannot rely on TLAB's having been filled and must do
4333 // so here just in case a scavenge did not happen.
4334 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4335 // Update the saved marks which may affect the root scans.
4336 gch->save_marks();
4337
4338 if (CMSPrintEdenSurvivorChunks) {
4339 print_eden_and_survivor_chunk_arrays();
4340 }
4341
4342 {
4343 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4344
4345 // Note on the role of the mod union table:
4346 // Since the marker in "markFromRoots" marks concurrently with
4347 // mutators, it is possible for some reachable objects not to have been
4348 // scanned. For instance, an only reference to an object A was
4349 // placed in object B after the marker scanned B. Unless B is rescanned,
4350 // A would be collected. Such updates to references in marked objects
4351 // are detected via the mod union table which is the set of all cards
4352 // dirtied since the first checkpoint in this GC cycle and prior to
4353 // the most recent young generation GC, minus those cleaned up by the
4354 // concurrent precleaning.
4355 if (CMSParallelRemarkEnabled) {
4356 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4357 do_remark_parallel();
4358 } else {
4359 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4360 _gc_timer_cm, _gc_tracer_cm->gc_id());
4361 do_remark_non_parallel();
4362 }
4363 }
4364 verify_work_stacks_empty();
4365 verify_overflow_empty();
4366
4367 {
4368 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4369 refProcessingWork();
4370 }
4371 verify_work_stacks_empty();
4372 verify_overflow_empty();
4373
4374 if (should_unload_classes()) {
4375 CodeCache::gc_epilogue();
4376 }
4377 JvmtiExport::gc_epilogue();
4378
4379 // If we encountered any (marking stack / work queue) overflow
4380 // events during the current CMS cycle, take appropriate
4381 // remedial measures, where possible, so as to try and avoid
4382 // recurrence of that condition.
4383 assert(_markStack.isEmpty(), "No grey objects");
4384 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4385 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4386 if (ser_ovflw > 0) {
4387 if (PrintCMSStatistics != 0) {
4388 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4389 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4390 ", kac_preclean=" SIZE_FORMAT ")",
4391 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4392 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4393 }
4394 _markStack.expand();
4395 _ser_pmc_remark_ovflw = 0;
4396 _ser_pmc_preclean_ovflw = 0;
4397 _ser_kac_preclean_ovflw = 0;
4398 _ser_kac_ovflw = 0;
4399 }
4400 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4401 if (PrintCMSStatistics != 0) {
4402 gclog_or_tty->print_cr("Work queue overflow (benign) "
4403 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4404 _par_pmc_remark_ovflw, _par_kac_ovflw);
4405 }
4406 _par_pmc_remark_ovflw = 0;
4407 _par_kac_ovflw = 0;
4408 }
4409 if (PrintCMSStatistics != 0) {
4410 if (_markStack._hit_limit > 0) {
4411 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4412 _markStack._hit_limit);
4413 }
4414 if (_markStack._failed_double > 0) {
4415 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4416 " current capacity " SIZE_FORMAT,
4417 _markStack._failed_double,
4418 _markStack.capacity());
4419 }
4420 }
4421 _markStack._hit_limit = 0;
4422 _markStack._failed_double = 0;
4423
4424 if ((VerifyAfterGC || VerifyDuringGC) &&
4425 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4426 verify_after_remark();
4427 }
4428
4429 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4430
4431 // Change under the freelistLocks.
4432 _collectorState = Sweeping;
4433 // Call isAllClear() under bitMapLock
4434 assert(_modUnionTable.isAllClear(),
4435 "Should be clear by end of the final marking");
4436 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4437 "Should be clear by end of the final marking");
4438 }
4439
4440 void CMSParInitialMarkTask::work(uint worker_id) {
4441 elapsedTimer _timer;
4442 ResourceMark rm;
4443 HandleMark hm;
4444
4445 // ---------- scan from roots --------------
4446 _timer.start();
4447 GenCollectedHeap* gch = GenCollectedHeap::heap();
4448 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4449
4450 // ---------- young gen roots --------------
4451 {
4452 work_on_young_gen_roots(worker_id, &par_mri_cl);
4453 _timer.stop();
4454 if (PrintCMSStatistics != 0) {
4455 gclog_or_tty->print_cr(
4456 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4457 worker_id, _timer.seconds());
4458 }
4459 }
4460
4461 // ---------- remaining roots --------------
4462 _timer.reset();
4463 _timer.start();
4464
4465 CLDToOopClosure cld_closure(&par_mri_cl, true);
4466
4467 gch->gen_process_roots(_strong_roots_scope,
4468 GenCollectedHeap::OldGen,
4469 false, // yg was scanned above
4470 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4471 _collector->should_unload_classes(),
4472 &par_mri_cl,
4473 NULL,
4474 &cld_closure);
4475 assert(_collector->should_unload_classes()
4476 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4477 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4478 _timer.stop();
4479 if (PrintCMSStatistics != 0) {
4480 gclog_or_tty->print_cr(
4481 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4482 worker_id, _timer.seconds());
4483 }
4484 }
4485
4486 // Parallel remark task
4487 class CMSParRemarkTask: public CMSParMarkTask {
4488 CompactibleFreeListSpace* _cms_space;
4489
4490 // The per-thread work queues, available here for stealing.
4491 OopTaskQueueSet* _task_queues;
4492 ParallelTaskTerminator _term;
4493 StrongRootsScope* _strong_roots_scope;
4494
4495 public:
4496 // A value of 0 passed to n_workers will cause the number of
4497 // workers to be taken from the active workers in the work gang.
4498 CMSParRemarkTask(CMSCollector* collector,
4499 CompactibleFreeListSpace* cms_space,
4500 uint n_workers, FlexibleWorkGang* workers,
4501 OopTaskQueueSet* task_queues,
4502 StrongRootsScope* strong_roots_scope):
4503 CMSParMarkTask("Rescan roots and grey objects in parallel",
4504 collector, n_workers),
4505 _cms_space(cms_space),
4506 _task_queues(task_queues),
4507 _term(n_workers, task_queues),
4508 _strong_roots_scope(strong_roots_scope) { }
4509
4510 OopTaskQueueSet* task_queues() { return _task_queues; }
4511
4512 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4513
4514 ParallelTaskTerminator* terminator() { return &_term; }
4515 uint n_workers() { return _n_workers; }
4516
4517 void work(uint worker_id);
4518
4519 private:
4520 // ... of dirty cards in old space
4521 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4522 Par_MarkRefsIntoAndScanClosure* cl);
4523
4524 // ... work stealing for the above
4525 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4526 };
4527
4528 class RemarkKlassClosure : public KlassClosure {
4529 KlassToOopClosure _cm_klass_closure;
4530 public:
4531 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4532 void do_klass(Klass* k) {
4533 // Check if we have modified any oops in the Klass during the concurrent marking.
4534 if (k->has_accumulated_modified_oops()) {
4535 k->clear_accumulated_modified_oops();
4536
4537 // We could have transfered the current modified marks to the accumulated marks,
4538 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4539 } else if (k->has_modified_oops()) {
4540 // Don't clear anything, this info is needed by the next young collection.
4541 } else {
4542 // No modified oops in the Klass.
4543 return;
4544 }
4545
4546 // The klass has modified fields, need to scan the klass.
4547 _cm_klass_closure.do_klass(k);
4548 }
4549 };
4550
4551 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4552 ParNewGeneration* young_gen = _collector->_young_gen;
4553 ContiguousSpace* eden_space = young_gen->eden();
4554 ContiguousSpace* from_space = young_gen->from();
4555 ContiguousSpace* to_space = young_gen->to();
4556
4557 HeapWord** eca = _collector->_eden_chunk_array;
4558 size_t ect = _collector->_eden_chunk_index;
4559 HeapWord** sca = _collector->_survivor_chunk_array;
4560 size_t sct = _collector->_survivor_chunk_index;
4561
4562 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4563 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4564
4565 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4566 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4567 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4568 }
4569
4570 // work_queue(i) is passed to the closure
4571 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4572 // also is passed to do_dirty_card_rescan_tasks() and to
4573 // do_work_steal() to select the i-th task_queue.
4574
4575 void CMSParRemarkTask::work(uint worker_id) {
4576 elapsedTimer _timer;
4577 ResourceMark rm;
4578 HandleMark hm;
4579
4580 // ---------- rescan from roots --------------
4581 _timer.start();
4582 GenCollectedHeap* gch = GenCollectedHeap::heap();
4583 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4584 _collector->_span, _collector->ref_processor(),
4585 &(_collector->_markBitMap),
4586 work_queue(worker_id));
4587
4588 // Rescan young gen roots first since these are likely
4589 // coarsely partitioned and may, on that account, constitute
4590 // the critical path; thus, it's best to start off that
4591 // work first.
4592 // ---------- young gen roots --------------
4593 {
4594 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4595 _timer.stop();
4596 if (PrintCMSStatistics != 0) {
4597 gclog_or_tty->print_cr(
4598 "Finished young gen rescan work in %dth thread: %3.3f sec",
4599 worker_id, _timer.seconds());
4600 }
4601 }
4602
4603 // ---------- remaining roots --------------
4604 _timer.reset();
4605 _timer.start();
4606 gch->gen_process_roots(_strong_roots_scope,
4607 GenCollectedHeap::OldGen,
4608 false, // yg was scanned above
4609 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4610 _collector->should_unload_classes(),
4611 &par_mrias_cl,
4612 NULL,
4613 NULL); // The dirty klasses will be handled below
4614
4615 assert(_collector->should_unload_classes()
4616 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4617 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4618 _timer.stop();
4619 if (PrintCMSStatistics != 0) {
4620 gclog_or_tty->print_cr(
4621 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4622 worker_id, _timer.seconds());
4623 }
4624
4625 // ---------- unhandled CLD scanning ----------
4626 if (worker_id == 0) { // Single threaded at the moment.
4627 _timer.reset();
4628 _timer.start();
4629
4630 // Scan all new class loader data objects and new dependencies that were
4631 // introduced during concurrent marking.
4632 ResourceMark rm;
4633 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4634 for (int i = 0; i < array->length(); i++) {
4635 par_mrias_cl.do_class_loader_data(array->at(i));
4636 }
4637
4638 // We don't need to keep track of new CLDs anymore.
4639 ClassLoaderDataGraph::remember_new_clds(false);
4640
4641 _timer.stop();
4642 if (PrintCMSStatistics != 0) {
4643 gclog_or_tty->print_cr(
4644 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4645 worker_id, _timer.seconds());
4646 }
4647 }
4648
4649 // ---------- dirty klass scanning ----------
4650 if (worker_id == 0) { // Single threaded at the moment.
4651 _timer.reset();
4652 _timer.start();
4653
4654 // Scan all classes that was dirtied during the concurrent marking phase.
4655 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4656 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4657
4658 _timer.stop();
4659 if (PrintCMSStatistics != 0) {
4660 gclog_or_tty->print_cr(
4661 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4662 worker_id, _timer.seconds());
4663 }
4664 }
4665
4666 // We might have added oops to ClassLoaderData::_handles during the
4667 // concurrent marking phase. These oops point to newly allocated objects
4668 // that are guaranteed to be kept alive. Either by the direct allocation
4669 // code, or when the young collector processes the roots. Hence,
4670 // we don't have to revisit the _handles block during the remark phase.
4671
4672 // ---------- rescan dirty cards ------------
4673 _timer.reset();
4674 _timer.start();
4675
4676 // Do the rescan tasks for each of the two spaces
4677 // (cms_space) in turn.
4678 // "worker_id" is passed to select the task_queue for "worker_id"
4679 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4680 _timer.stop();
4681 if (PrintCMSStatistics != 0) {
4682 gclog_or_tty->print_cr(
4683 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4684 worker_id, _timer.seconds());
4685 }
4686
4687 // ---------- steal work from other threads ...
4688 // ---------- ... and drain overflow list.
4689 _timer.reset();
4690 _timer.start();
4691 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4692 _timer.stop();
4693 if (PrintCMSStatistics != 0) {
4694 gclog_or_tty->print_cr(
4695 "Finished work stealing in %dth thread: %3.3f sec",
4696 worker_id, _timer.seconds());
4697 }
4698 }
4699
4700 // Note that parameter "i" is not used.
4701 void
4702 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4703 OopsInGenClosure* cl, ContiguousSpace* space,
4704 HeapWord** chunk_array, size_t chunk_top) {
4705 // Until all tasks completed:
4706 // . claim an unclaimed task
4707 // . compute region boundaries corresponding to task claimed
4708 // using chunk_array
4709 // . par_oop_iterate(cl) over that region
4710
4711 ResourceMark rm;
4712 HandleMark hm;
4713
4714 SequentialSubTasksDone* pst = space->par_seq_tasks();
4715
4716 uint nth_task = 0;
4717 uint n_tasks = pst->n_tasks();
4718
4719 if (n_tasks > 0) {
4720 assert(pst->valid(), "Uninitialized use?");
4721 HeapWord *start, *end;
4722 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4723 // We claimed task # nth_task; compute its boundaries.
4724 if (chunk_top == 0) { // no samples were taken
4725 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4726 start = space->bottom();
4727 end = space->top();
4728 } else if (nth_task == 0) {
4729 start = space->bottom();
4730 end = chunk_array[nth_task];
4731 } else if (nth_task < (uint)chunk_top) {
4732 assert(nth_task >= 1, "Control point invariant");
4733 start = chunk_array[nth_task - 1];
4734 end = chunk_array[nth_task];
4735 } else {
4736 assert(nth_task == (uint)chunk_top, "Control point invariant");
4737 start = chunk_array[chunk_top - 1];
4738 end = space->top();
4739 }
4740 MemRegion mr(start, end);
4741 // Verify that mr is in space
4742 assert(mr.is_empty() || space->used_region().contains(mr),
4743 "Should be in space");
4744 // Verify that "start" is an object boundary
4745 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4746 "Should be an oop");
4747 space->par_oop_iterate(mr, cl);
4748 }
4749 pst->all_tasks_completed();
4750 }
4751 }
4752
4753 void
4754 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4755 CompactibleFreeListSpace* sp, int i,
4756 Par_MarkRefsIntoAndScanClosure* cl) {
4757 // Until all tasks completed:
4758 // . claim an unclaimed task
4759 // . compute region boundaries corresponding to task claimed
4760 // . transfer dirty bits ct->mut for that region
4761 // . apply rescanclosure to dirty mut bits for that region
4762
4763 ResourceMark rm;
4764 HandleMark hm;
4765
4766 OopTaskQueue* work_q = work_queue(i);
4767 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4768 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4769 // CAUTION: This closure has state that persists across calls to
4770 // the work method dirty_range_iterate_clear() in that it has
4771 // embedded in it a (subtype of) UpwardsObjectClosure. The
4772 // use of that state in the embedded UpwardsObjectClosure instance
4773 // assumes that the cards are always iterated (even if in parallel
4774 // by several threads) in monotonically increasing order per each
4775 // thread. This is true of the implementation below which picks
4776 // card ranges (chunks) in monotonically increasing order globally
4777 // and, a-fortiori, in monotonically increasing order per thread
4778 // (the latter order being a subsequence of the former).
4779 // If the work code below is ever reorganized into a more chaotic
4780 // work-partitioning form than the current "sequential tasks"
4781 // paradigm, the use of that persistent state will have to be
4782 // revisited and modified appropriately. See also related
4783 // bug 4756801 work on which should examine this code to make
4784 // sure that the changes there do not run counter to the
4785 // assumptions made here and necessary for correctness and
4786 // efficiency. Note also that this code might yield inefficient
4787 // behavior in the case of very large objects that span one or
4788 // more work chunks. Such objects would potentially be scanned
4789 // several times redundantly. Work on 4756801 should try and
4790 // address that performance anomaly if at all possible. XXX
4791 MemRegion full_span = _collector->_span;
4792 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4793 MarkFromDirtyCardsClosure
4794 greyRescanClosure(_collector, full_span, // entire span of interest
4795 sp, bm, work_q, cl);
4796
4797 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4798 assert(pst->valid(), "Uninitialized use?");
4799 uint nth_task = 0;
4800 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4801 MemRegion span = sp->used_region();
4802 HeapWord* start_addr = span.start();
4803 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4804 alignment);
4805 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4806 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4807 start_addr, "Check alignment");
4808 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4809 chunk_size, "Check alignment");
4810
4811 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4812 // Having claimed the nth_task, compute corresponding mem-region,
4813 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4814 // The alignment restriction ensures that we do not need any
4815 // synchronization with other gang-workers while setting or
4816 // clearing bits in thus chunk of the MUT.
4817 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4818 start_addr + (nth_task+1)*chunk_size);
4819 // The last chunk's end might be way beyond end of the
4820 // used region. In that case pull back appropriately.
4821 if (this_span.end() > end_addr) {
4822 this_span.set_end(end_addr);
4823 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4824 }
4825 // Iterate over the dirty cards covering this chunk, marking them
4826 // precleaned, and setting the corresponding bits in the mod union
4827 // table. Since we have been careful to partition at Card and MUT-word
4828 // boundaries no synchronization is needed between parallel threads.
4829 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4830 &modUnionClosure);
4831
4832 // Having transferred these marks into the modUnionTable,
4833 // rescan the marked objects on the dirty cards in the modUnionTable.
4834 // Even if this is at a synchronous collection, the initial marking
4835 // may have been done during an asynchronous collection so there
4836 // may be dirty bits in the mod-union table.
4837 _collector->_modUnionTable.dirty_range_iterate_clear(
4838 this_span, &greyRescanClosure);
4839 _collector->_modUnionTable.verifyNoOneBitsInRange(
4840 this_span.start(),
4841 this_span.end());
4842 }
4843 pst->all_tasks_completed(); // declare that i am done
4844 }
4845
4846 // . see if we can share work_queues with ParNew? XXX
4847 void
4848 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4849 int* seed) {
4850 OopTaskQueue* work_q = work_queue(i);
4851 NOT_PRODUCT(int num_steals = 0;)
4852 oop obj_to_scan;
4853 CMSBitMap* bm = &(_collector->_markBitMap);
4854
4855 while (true) {
4856 // Completely finish any left over work from (an) earlier round(s)
4857 cl->trim_queue(0);
4858 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4859 (size_t)ParGCDesiredObjsFromOverflowList);
4860 // Now check if there's any work in the overflow list
4861 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4862 // only affects the number of attempts made to get work from the
4863 // overflow list and does not affect the number of workers. Just
4864 // pass ParallelGCThreads so this behavior is unchanged.
4865 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4866 work_q,
4867 ParallelGCThreads)) {
4868 // found something in global overflow list;
4869 // not yet ready to go stealing work from others.
4870 // We'd like to assert(work_q->size() != 0, ...)
4871 // because we just took work from the overflow list,
4872 // but of course we can't since all of that could have
4873 // been already stolen from us.
4874 // "He giveth and He taketh away."
4875 continue;
4876 }
4877 // Verify that we have no work before we resort to stealing
4878 assert(work_q->size() == 0, "Have work, shouldn't steal");
4879 // Try to steal from other queues that have work
4880 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4881 NOT_PRODUCT(num_steals++;)
4882 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4883 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4884 // Do scanning work
4885 obj_to_scan->oop_iterate(cl);
4886 // Loop around, finish this work, and try to steal some more
4887 } else if (terminator()->offer_termination()) {
4888 break; // nirvana from the infinite cycle
4889 }
4890 }
4891 NOT_PRODUCT(
4892 if (PrintCMSStatistics != 0) {
4893 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4894 }
4895 )
4896 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4897 "Else our work is not yet done");
4898 }
4899
4900 // Record object boundaries in _eden_chunk_array by sampling the eden
4901 // top in the slow-path eden object allocation code path and record
4902 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4903 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4904 // sampling in sample_eden() that activates during the part of the
4905 // preclean phase.
4906 void CMSCollector::sample_eden_chunk() {
4907 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4908 if (_eden_chunk_lock->try_lock()) {
4909 // Record a sample. This is the critical section. The contents
4910 // of the _eden_chunk_array have to be non-decreasing in the
4911 // address order.
4912 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4913 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4914 "Unexpected state of Eden");
4915 if (_eden_chunk_index == 0 ||
4916 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4917 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4918 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4919 _eden_chunk_index++; // commit sample
4920 }
4921 _eden_chunk_lock->unlock();
4922 }
4923 }
4924 }
4925
4926 // Return a thread-local PLAB recording array, as appropriate.
4927 void* CMSCollector::get_data_recorder(int thr_num) {
4928 if (_survivor_plab_array != NULL &&
4929 (CMSPLABRecordAlways ||
4930 (_collectorState > Marking && _collectorState < FinalMarking))) {
4931 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4932 ChunkArray* ca = &_survivor_plab_array[thr_num];
4933 ca->reset(); // clear it so that fresh data is recorded
4934 return (void*) ca;
4935 } else {
4936 return NULL;
4937 }
4938 }
4939
4940 // Reset all the thread-local PLAB recording arrays
4941 void CMSCollector::reset_survivor_plab_arrays() {
4942 for (uint i = 0; i < ParallelGCThreads; i++) {
4943 _survivor_plab_array[i].reset();
4944 }
4945 }
4946
4947 // Merge the per-thread plab arrays into the global survivor chunk
4948 // array which will provide the partitioning of the survivor space
4949 // for CMS initial scan and rescan.
4950 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4951 int no_of_gc_threads) {
4952 assert(_survivor_plab_array != NULL, "Error");
4953 assert(_survivor_chunk_array != NULL, "Error");
4954 assert(_collectorState == FinalMarking ||
4955 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4956 for (int j = 0; j < no_of_gc_threads; j++) {
4957 _cursor[j] = 0;
4958 }
4959 HeapWord* top = surv->top();
4960 size_t i;
4961 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4962 HeapWord* min_val = top; // Higher than any PLAB address
4963 uint min_tid = 0; // position of min_val this round
4964 for (int j = 0; j < no_of_gc_threads; j++) {
4965 ChunkArray* cur_sca = &_survivor_plab_array[j];
4966 if (_cursor[j] == cur_sca->end()) {
4967 continue;
4968 }
4969 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4970 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4971 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4972 if (cur_val < min_val) {
4973 min_tid = j;
4974 min_val = cur_val;
4975 } else {
4976 assert(cur_val < top, "All recorded addresses should be less");
4977 }
4978 }
4979 // At this point min_val and min_tid are respectively
4980 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4981 // and the thread (j) that witnesses that address.
4982 // We record this address in the _survivor_chunk_array[i]
4983 // and increment _cursor[min_tid] prior to the next round i.
4984 if (min_val == top) {
4985 break;
4986 }
4987 _survivor_chunk_array[i] = min_val;
4988 _cursor[min_tid]++;
4989 }
4990 // We are all done; record the size of the _survivor_chunk_array
4991 _survivor_chunk_index = i; // exclusive: [0, i)
4992 if (PrintCMSStatistics > 0) {
4993 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4994 }
4995 // Verify that we used up all the recorded entries
4996 #ifdef ASSERT
4997 size_t total = 0;
4998 for (int j = 0; j < no_of_gc_threads; j++) {
4999 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5000 total += _cursor[j];
5001 }
5002 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5003 // Check that the merged array is in sorted order
5004 if (total > 0) {
5005 for (size_t i = 0; i < total - 1; i++) {
5006 if (PrintCMSStatistics > 0) {
5007 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5008 i, p2i(_survivor_chunk_array[i]));
5009 }
5010 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5011 "Not sorted");
5012 }
5013 }
5014 #endif // ASSERT
5015 }
5016
5017 // Set up the space's par_seq_tasks structure for work claiming
5018 // for parallel initial scan and rescan of young gen.
5019 // See ParRescanTask where this is currently used.
5020 void
5021 CMSCollector::
5022 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5023 assert(n_threads > 0, "Unexpected n_threads argument");
5024
5025 // Eden space
5026 if (!_young_gen->eden()->is_empty()) {
5027 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5028 assert(!pst->valid(), "Clobbering existing data?");
5029 // Each valid entry in [0, _eden_chunk_index) represents a task.
5030 size_t n_tasks = _eden_chunk_index + 1;
5031 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5032 // Sets the condition for completion of the subtask (how many threads
5033 // need to finish in order to be done).
5034 pst->set_n_threads(n_threads);
5035 pst->set_n_tasks((int)n_tasks);
5036 }
5037
5038 // Merge the survivor plab arrays into _survivor_chunk_array
5039 if (_survivor_plab_array != NULL) {
5040 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5041 } else {
5042 assert(_survivor_chunk_index == 0, "Error");
5043 }
5044
5045 // To space
5046 {
5047 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5048 assert(!pst->valid(), "Clobbering existing data?");
5049 // Sets the condition for completion of the subtask (how many threads
5050 // need to finish in order to be done).
5051 pst->set_n_threads(n_threads);
5052 pst->set_n_tasks(1);
5053 assert(pst->valid(), "Error");
5054 }
5055
5056 // From space
5057 {
5058 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5059 assert(!pst->valid(), "Clobbering existing data?");
5060 size_t n_tasks = _survivor_chunk_index + 1;
5061 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5062 // Sets the condition for completion of the subtask (how many threads
5063 // need to finish in order to be done).
5064 pst->set_n_threads(n_threads);
5065 pst->set_n_tasks((int)n_tasks);
5066 assert(pst->valid(), "Error");
5067 }
5068 }
5069
5070 // Parallel version of remark
5071 void CMSCollector::do_remark_parallel() {
5072 GenCollectedHeap* gch = GenCollectedHeap::heap();
5073 FlexibleWorkGang* workers = gch->workers();
5074 assert(workers != NULL, "Need parallel worker threads.");
5075 // Choose to use the number of GC workers most recently set
5076 // into "active_workers".
5077 uint n_workers = workers->active_workers();
5078
5079 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5080
5081 StrongRootsScope srs(n_workers);
5082
5083 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5084
5085 // We won't be iterating over the cards in the card table updating
5086 // the younger_gen cards, so we shouldn't call the following else
5087 // the verification code as well as subsequent younger_refs_iterate
5088 // code would get confused. XXX
5089 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5090
5091 // The young gen rescan work will not be done as part of
5092 // process_roots (which currently doesn't know how to
5093 // parallelize such a scan), but rather will be broken up into
5094 // a set of parallel tasks (via the sampling that the [abortable]
5095 // preclean phase did of eden, plus the [two] tasks of
5096 // scanning the [two] survivor spaces. Further fine-grain
5097 // parallelization of the scanning of the survivor spaces
5098 // themselves, and of precleaning of the younger gen itself
5099 // is deferred to the future.
5100 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5101
5102 // The dirty card rescan work is broken up into a "sequence"
5103 // of parallel tasks (per constituent space) that are dynamically
5104 // claimed by the parallel threads.
5105 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5106
5107 // It turns out that even when we're using 1 thread, doing the work in a
5108 // separate thread causes wide variance in run times. We can't help this
5109 // in the multi-threaded case, but we special-case n=1 here to get
5110 // repeatable measurements of the 1-thread overhead of the parallel code.
5111 if (n_workers > 1) {
5112 // Make refs discovery MT-safe, if it isn't already: it may not
5113 // necessarily be so, since it's possible that we are doing
5114 // ST marking.
5115 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5116 workers->run_task(&tsk);
5117 } else {
5118 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5119 tsk.work(0);
5120 }
5121
5122 // restore, single-threaded for now, any preserved marks
5123 // as a result of work_q overflow
5124 restore_preserved_marks_if_any();
5125 }
5126
5127 // Non-parallel version of remark
5128 void CMSCollector::do_remark_non_parallel() {
5129 ResourceMark rm;
5130 HandleMark hm;
5131 GenCollectedHeap* gch = GenCollectedHeap::heap();
5132 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5133
5134 MarkRefsIntoAndScanClosure
5135 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5136 &_markStack, this,
5137 false /* should_yield */, false /* not precleaning */);
5138 MarkFromDirtyCardsClosure
5139 markFromDirtyCardsClosure(this, _span,
5140 NULL, // space is set further below
5141 &_markBitMap, &_markStack, &mrias_cl);
5142 {
5143 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5144 // Iterate over the dirty cards, setting the corresponding bits in the
5145 // mod union table.
5146 {
5147 ModUnionClosure modUnionClosure(&_modUnionTable);
5148 _ct->ct_bs()->dirty_card_iterate(
5149 _cmsGen->used_region(),
5150 &modUnionClosure);
5151 }
5152 // Having transferred these marks into the modUnionTable, we just need
5153 // to rescan the marked objects on the dirty cards in the modUnionTable.
5154 // The initial marking may have been done during an asynchronous
5155 // collection so there may be dirty bits in the mod-union table.
5156 const int alignment =
5157 CardTableModRefBS::card_size * BitsPerWord;
5158 {
5159 // ... First handle dirty cards in CMS gen
5160 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5161 MemRegion ur = _cmsGen->used_region();
5162 HeapWord* lb = ur.start();
5163 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5164 MemRegion cms_span(lb, ub);
5165 _modUnionTable.dirty_range_iterate_clear(cms_span,
5166 &markFromDirtyCardsClosure);
5167 verify_work_stacks_empty();
5168 if (PrintCMSStatistics != 0) {
5169 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5170 markFromDirtyCardsClosure.num_dirty_cards());
5171 }
5172 }
5173 }
5174 if (VerifyDuringGC &&
5175 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5176 HandleMark hm; // Discard invalid handles created during verification
5177 Universe::verify();
5178 }
5179 {
5180 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5181
5182 verify_work_stacks_empty();
5183
5184 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5185 StrongRootsScope srs(1);
5186
5187 gch->gen_process_roots(&srs,
5188 GenCollectedHeap::OldGen,
5189 true, // younger gens as roots
5190 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5191 should_unload_classes(),
5192 &mrias_cl,
5193 NULL,
5194 NULL); // The dirty klasses will be handled below
5195
5196 assert(should_unload_classes()
5197 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5198 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5199 }
5200
5201 {
5202 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5203
5204 verify_work_stacks_empty();
5205
5206 // Scan all class loader data objects that might have been introduced
5207 // during concurrent marking.
5208 ResourceMark rm;
5209 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5210 for (int i = 0; i < array->length(); i++) {
5211 mrias_cl.do_class_loader_data(array->at(i));
5212 }
5213
5214 // We don't need to keep track of new CLDs anymore.
5215 ClassLoaderDataGraph::remember_new_clds(false);
5216
5217 verify_work_stacks_empty();
5218 }
5219
5220 {
5221 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5222
5223 verify_work_stacks_empty();
5224
5225 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5226 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5227
5228 verify_work_stacks_empty();
5229 }
5230
5231 // We might have added oops to ClassLoaderData::_handles during the
5232 // concurrent marking phase. These oops point to newly allocated objects
5233 // that are guaranteed to be kept alive. Either by the direct allocation
5234 // code, or when the young collector processes the roots. Hence,
5235 // we don't have to revisit the _handles block during the remark phase.
5236
5237 verify_work_stacks_empty();
5238 // Restore evacuated mark words, if any, used for overflow list links
5239 if (!CMSOverflowEarlyRestoration) {
5240 restore_preserved_marks_if_any();
5241 }
5242 verify_overflow_empty();
5243 }
5244
5245 ////////////////////////////////////////////////////////
5246 // Parallel Reference Processing Task Proxy Class
5247 ////////////////////////////////////////////////////////
5248 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5249 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5250 CMSCollector* _collector;
5251 CMSBitMap* _mark_bit_map;
5252 const MemRegion _span;
5253 ProcessTask& _task;
5254
5255 public:
5256 CMSRefProcTaskProxy(ProcessTask& task,
5257 CMSCollector* collector,
5258 const MemRegion& span,
5259 CMSBitMap* mark_bit_map,
5260 AbstractWorkGang* workers,
5261 OopTaskQueueSet* task_queues):
5262 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5263 task_queues,
5264 workers->active_workers()),
5265 _task(task),
5266 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5267 {
5268 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5269 "Inconsistency in _span");
5270 }
5271
5272 OopTaskQueueSet* task_queues() { return queues(); }
5273
5274 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5275
5276 void do_work_steal(int i,
5277 CMSParDrainMarkingStackClosure* drain,
5278 CMSParKeepAliveClosure* keep_alive,
5279 int* seed);
5280
5281 virtual void work(uint worker_id);
5282 };
5283
5284 void CMSRefProcTaskProxy::work(uint worker_id) {
5285 ResourceMark rm;
5286 HandleMark hm;
5287 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5288 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5289 _mark_bit_map,
5290 work_queue(worker_id));
5291 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5292 _mark_bit_map,
5293 work_queue(worker_id));
5294 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5295 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5296 if (_task.marks_oops_alive()) {
5297 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5298 _collector->hash_seed(worker_id));
5299 }
5300 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5301 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5302 }
5303
5304 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5305 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5306 EnqueueTask& _task;
5307
5308 public:
5309 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5310 : AbstractGangTask("Enqueue reference objects in parallel"),
5311 _task(task)
5312 { }
5313
5314 virtual void work(uint worker_id)
5315 {
5316 _task.work(worker_id);
5317 }
5318 };
5319
5320 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5321 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5322 _span(span),
5323 _bit_map(bit_map),
5324 _work_queue(work_queue),
5325 _mark_and_push(collector, span, bit_map, work_queue),
5326 _low_water_mark(MIN2((work_queue->max_elems()/4),
5327 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5328 { }
5329
5330 // . see if we can share work_queues with ParNew? XXX
5331 void CMSRefProcTaskProxy::do_work_steal(int i,
5332 CMSParDrainMarkingStackClosure* drain,
5333 CMSParKeepAliveClosure* keep_alive,
5334 int* seed) {
5335 OopTaskQueue* work_q = work_queue(i);
5336 NOT_PRODUCT(int num_steals = 0;)
5337 oop obj_to_scan;
5338
5339 while (true) {
5340 // Completely finish any left over work from (an) earlier round(s)
5341 drain->trim_queue(0);
5342 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5343 (size_t)ParGCDesiredObjsFromOverflowList);
5344 // Now check if there's any work in the overflow list
5345 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5346 // only affects the number of attempts made to get work from the
5347 // overflow list and does not affect the number of workers. Just
5348 // pass ParallelGCThreads so this behavior is unchanged.
5349 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5350 work_q,
5351 ParallelGCThreads)) {
5352 // Found something in global overflow list;
5353 // not yet ready to go stealing work from others.
5354 // We'd like to assert(work_q->size() != 0, ...)
5355 // because we just took work from the overflow list,
5356 // but of course we can't, since all of that might have
5357 // been already stolen from us.
5358 continue;
5359 }
5360 // Verify that we have no work before we resort to stealing
5361 assert(work_q->size() == 0, "Have work, shouldn't steal");
5362 // Try to steal from other queues that have work
5363 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5364 NOT_PRODUCT(num_steals++;)
5365 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5366 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5367 // Do scanning work
5368 obj_to_scan->oop_iterate(keep_alive);
5369 // Loop around, finish this work, and try to steal some more
5370 } else if (terminator()->offer_termination()) {
5371 break; // nirvana from the infinite cycle
5372 }
5373 }
5374 NOT_PRODUCT(
5375 if (PrintCMSStatistics != 0) {
5376 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5377 }
5378 )
5379 }
5380
5381 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5382 {
5383 GenCollectedHeap* gch = GenCollectedHeap::heap();
5384 FlexibleWorkGang* workers = gch->workers();
5385 assert(workers != NULL, "Need parallel worker threads.");
5386 CMSRefProcTaskProxy rp_task(task, &_collector,
5387 _collector.ref_processor()->span(),
5388 _collector.markBitMap(),
5389 workers, _collector.task_queues());
5390 workers->run_task(&rp_task);
5391 }
5392
5393 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5394 {
5395
5396 GenCollectedHeap* gch = GenCollectedHeap::heap();
5397 FlexibleWorkGang* workers = gch->workers();
5398 assert(workers != NULL, "Need parallel worker threads.");
5399 CMSRefEnqueueTaskProxy enq_task(task);
5400 workers->run_task(&enq_task);
5401 }
5402
5403 void CMSCollector::refProcessingWork() {
5404 ResourceMark rm;
5405 HandleMark hm;
5406
5407 ReferenceProcessor* rp = ref_processor();
5408 assert(rp->span().equals(_span), "Spans should be equal");
5409 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5410 // Process weak references.
5411 rp->setup_policy(false);
5412 verify_work_stacks_empty();
5413
5414 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5415 &_markStack, false /* !preclean */);
5416 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5417 _span, &_markBitMap, &_markStack,
5418 &cmsKeepAliveClosure, false /* !preclean */);
5419 {
5420 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5421
5422 ReferenceProcessorStats stats;
5423 if (rp->processing_is_mt()) {
5424 // Set the degree of MT here. If the discovery is done MT, there
5425 // may have been a different number of threads doing the discovery
5426 // and a different number of discovered lists may have Ref objects.
5427 // That is OK as long as the Reference lists are balanced (see
5428 // balance_all_queues() and balance_queues()).
5429 GenCollectedHeap* gch = GenCollectedHeap::heap();
5430 uint active_workers = ParallelGCThreads;
5431 FlexibleWorkGang* workers = gch->workers();
5432 if (workers != NULL) {
5433 active_workers = workers->active_workers();
5434 // The expectation is that active_workers will have already
5435 // been set to a reasonable value. If it has not been set,
5436 // investigate.
5437 assert(active_workers > 0, "Should have been set during scavenge");
5438 }
5439 rp->set_active_mt_degree(active_workers);
5440 CMSRefProcTaskExecutor task_executor(*this);
5441 stats = rp->process_discovered_references(&_is_alive_closure,
5442 &cmsKeepAliveClosure,
5443 &cmsDrainMarkingStackClosure,
5444 &task_executor,
5445 _gc_timer_cm,
5446 _gc_tracer_cm->gc_id());
5447 } else {
5448 stats = rp->process_discovered_references(&_is_alive_closure,
5449 &cmsKeepAliveClosure,
5450 &cmsDrainMarkingStackClosure,
5451 NULL,
5452 _gc_timer_cm,
5453 _gc_tracer_cm->gc_id());
5454 }
5455 _gc_tracer_cm->report_gc_reference_stats(stats);
5456
5457 }
5458
5459 // This is the point where the entire marking should have completed.
5460 verify_work_stacks_empty();
5461
5462 if (should_unload_classes()) {
5463 {
5464 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5465
5466 // Unload classes and purge the SystemDictionary.
5467 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5468
5469 // Unload nmethods.
5470 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5471
5472 // Prune dead klasses from subklass/sibling/implementor lists.
5473 Klass::clean_weak_klass_links(&_is_alive_closure);
5474 }
5475
5476 {
5477 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5478 // Clean up unreferenced symbols in symbol table.
5479 SymbolTable::unlink();
5480 }
5481
5482 {
5483 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5484 // Delete entries for dead interned strings.
5485 StringTable::unlink(&_is_alive_closure);
5486 }
5487 }
5488
5489
5490 // Restore any preserved marks as a result of mark stack or
5491 // work queue overflow
5492 restore_preserved_marks_if_any(); // done single-threaded for now
5493
5494 rp->set_enqueuing_is_done(true);
5495 if (rp->processing_is_mt()) {
5496 rp->balance_all_queues();
5497 CMSRefProcTaskExecutor task_executor(*this);
5498 rp->enqueue_discovered_references(&task_executor);
5499 } else {
5500 rp->enqueue_discovered_references(NULL);
5501 }
5502 rp->verify_no_references_recorded();
5503 assert(!rp->discovery_enabled(), "should have been disabled");
5504 }
5505
5506 #ifndef PRODUCT
5507 void CMSCollector::check_correct_thread_executing() {
5508 Thread* t = Thread::current();
5509 // Only the VM thread or the CMS thread should be here.
5510 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5511 "Unexpected thread type");
5512 // If this is the vm thread, the foreground process
5513 // should not be waiting. Note that _foregroundGCIsActive is
5514 // true while the foreground collector is waiting.
5515 if (_foregroundGCShouldWait) {
5516 // We cannot be the VM thread
5517 assert(t->is_ConcurrentGC_thread(),
5518 "Should be CMS thread");
5519 } else {
5520 // We can be the CMS thread only if we are in a stop-world
5521 // phase of CMS collection.
5522 if (t->is_ConcurrentGC_thread()) {
5523 assert(_collectorState == InitialMarking ||
5524 _collectorState == FinalMarking,
5525 "Should be a stop-world phase");
5526 // The CMS thread should be holding the CMS_token.
5527 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5528 "Potential interference with concurrently "
5529 "executing VM thread");
5530 }
5531 }
5532 }
5533 #endif
5534
5535 void CMSCollector::sweep() {
5536 assert(_collectorState == Sweeping, "just checking");
5537 check_correct_thread_executing();
5538 verify_work_stacks_empty();
5539 verify_overflow_empty();
5540 increment_sweep_count();
5541 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5542
5543 _inter_sweep_timer.stop();
5544 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5545
5546 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5547 _intra_sweep_timer.reset();
5548 _intra_sweep_timer.start();
5549 {
5550 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5551 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5552 // First sweep the old gen
5553 {
5554 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5555 bitMapLock());
5556 sweepWork(_cmsGen);
5557 }
5558
5559 // Update Universe::_heap_*_at_gc figures.
5560 // We need all the free list locks to make the abstract state
5561 // transition from Sweeping to Resetting. See detailed note
5562 // further below.
5563 {
5564 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5565 // Update heap occupancy information which is used as
5566 // input to soft ref clearing policy at the next gc.
5567 Universe::update_heap_info_at_gc();
5568 _collectorState = Resizing;
5569 }
5570 }
5571 verify_work_stacks_empty();
5572 verify_overflow_empty();
5573
5574 if (should_unload_classes()) {
5575 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5576 // requires that the virtual spaces are stable and not deleted.
5577 ClassLoaderDataGraph::set_should_purge(true);
5578 }
5579
5580 _intra_sweep_timer.stop();
5581 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5582
5583 _inter_sweep_timer.reset();
5584 _inter_sweep_timer.start();
5585
5586 // We need to use a monotonically non-decreasing time in ms
5587 // or we will see time-warp warnings and os::javaTimeMillis()
5588 // does not guarantee monotonicity.
5589 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5590 update_time_of_last_gc(now);
5591
5592 // NOTE on abstract state transitions:
5593 // Mutators allocate-live and/or mark the mod-union table dirty
5594 // based on the state of the collection. The former is done in
5595 // the interval [Marking, Sweeping] and the latter in the interval
5596 // [Marking, Sweeping). Thus the transitions into the Marking state
5597 // and out of the Sweeping state must be synchronously visible
5598 // globally to the mutators.
5599 // The transition into the Marking state happens with the world
5600 // stopped so the mutators will globally see it. Sweeping is
5601 // done asynchronously by the background collector so the transition
5602 // from the Sweeping state to the Resizing state must be done
5603 // under the freelistLock (as is the check for whether to
5604 // allocate-live and whether to dirty the mod-union table).
5605 assert(_collectorState == Resizing, "Change of collector state to"
5606 " Resizing must be done under the freelistLocks (plural)");
5607
5608 // Now that sweeping has been completed, we clear
5609 // the incremental_collection_failed flag,
5610 // thus inviting a younger gen collection to promote into
5611 // this generation. If such a promotion may still fail,
5612 // the flag will be set again when a young collection is
5613 // attempted.
5614 GenCollectedHeap* gch = GenCollectedHeap::heap();
5615 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5616 gch->update_full_collections_completed(_collection_count_start);
5617 }
5618
5619 // FIX ME!!! Looks like this belongs in CFLSpace, with
5620 // CMSGen merely delegating to it.
5621 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5622 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5623 HeapWord* minAddr = _cmsSpace->bottom();
5624 HeapWord* largestAddr =
5625 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5626 if (largestAddr == NULL) {
5627 // The dictionary appears to be empty. In this case
5628 // try to coalesce at the end of the heap.
5629 largestAddr = _cmsSpace->end();
5630 }
5631 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5632 size_t nearLargestOffset =
5633 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5634 if (PrintFLSStatistics != 0) {
5635 gclog_or_tty->print_cr(
5636 "CMS: Large Block: " PTR_FORMAT ";"
5637 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5638 p2i(largestAddr),
5639 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5640 }
5641 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5642 }
5643
5644 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5645 return addr >= _cmsSpace->nearLargestChunk();
5646 }
5647
5648 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5649 return _cmsSpace->find_chunk_at_end();
5650 }
5651
5652 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5653 bool full) {
5654 // If the young generation has been collected, gather any statistics
5655 // that are of interest at this point.
5656 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5657 if (!full && current_is_young) {
5658 // Gather statistics on the young generation collection.
5659 collector()->stats().record_gc0_end(used());
5660 }
5661 }
5662
5663 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5664 // We iterate over the space(s) underlying this generation,
5665 // checking the mark bit map to see if the bits corresponding
5666 // to specific blocks are marked or not. Blocks that are
5667 // marked are live and are not swept up. All remaining blocks
5668 // are swept up, with coalescing on-the-fly as we sweep up
5669 // contiguous free and/or garbage blocks:
5670 // We need to ensure that the sweeper synchronizes with allocators
5671 // and stop-the-world collectors. In particular, the following
5672 // locks are used:
5673 // . CMS token: if this is held, a stop the world collection cannot occur
5674 // . freelistLock: if this is held no allocation can occur from this
5675 // generation by another thread
5676 // . bitMapLock: if this is held, no other thread can access or update
5677 //
5678
5679 // Note that we need to hold the freelistLock if we use
5680 // block iterate below; else the iterator might go awry if
5681 // a mutator (or promotion) causes block contents to change
5682 // (for instance if the allocator divvies up a block).
5683 // If we hold the free list lock, for all practical purposes
5684 // young generation GC's can't occur (they'll usually need to
5685 // promote), so we might as well prevent all young generation
5686 // GC's while we do a sweeping step. For the same reason, we might
5687 // as well take the bit map lock for the entire duration
5688
5689 // check that we hold the requisite locks
5690 assert(have_cms_token(), "Should hold cms token");
5691 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5692 assert_lock_strong(gen->freelistLock());
5693 assert_lock_strong(bitMapLock());
5694
5695 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5696 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5697 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5698 _inter_sweep_estimate.padded_average(),
5699 _intra_sweep_estimate.padded_average());
5700 gen->setNearLargestChunk();
5701
5702 {
5703 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5704 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5705 // We need to free-up/coalesce garbage/blocks from a
5706 // co-terminal free run. This is done in the SweepClosure
5707 // destructor; so, do not remove this scope, else the
5708 // end-of-sweep-census below will be off by a little bit.
5709 }
5710 gen->cmsSpace()->sweep_completed();
5711 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5712 if (should_unload_classes()) { // unloaded classes this cycle,
5713 _concurrent_cycles_since_last_unload = 0; // ... reset count
5714 } else { // did not unload classes,
5715 _concurrent_cycles_since_last_unload++; // ... increment count
5716 }
5717 }
5718
5719 // Reset CMS data structures (for now just the marking bit map)
5720 // preparatory for the next cycle.
5721 void CMSCollector::reset(bool concurrent) {
5722 if (concurrent) {
5723 CMSTokenSyncWithLocks ts(true, bitMapLock());
5724
5725 // If the state is not "Resetting", the foreground thread
5726 // has done a collection and the resetting.
5727 if (_collectorState != Resetting) {
5728 assert(_collectorState == Idling, "The state should only change"
5729 " because the foreground collector has finished the collection");
5730 return;
5731 }
5732
5733 // Clear the mark bitmap (no grey objects to start with)
5734 // for the next cycle.
5735 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5736 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5737
5738 HeapWord* curAddr = _markBitMap.startWord();
5739 while (curAddr < _markBitMap.endWord()) {
5740 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5741 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5742 _markBitMap.clear_large_range(chunk);
5743 if (ConcurrentMarkSweepThread::should_yield() &&
5744 !foregroundGCIsActive() &&
5745 CMSYield) {
5746 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5747 "CMS thread should hold CMS token");
5748 assert_lock_strong(bitMapLock());
5749 bitMapLock()->unlock();
5750 ConcurrentMarkSweepThread::desynchronize(true);
5751 stopTimer();
5752 if (PrintCMSStatistics != 0) {
5753 incrementYields();
5754 }
5755
5756 // See the comment in coordinator_yield()
5757 for (unsigned i = 0; i < CMSYieldSleepCount &&
5758 ConcurrentMarkSweepThread::should_yield() &&
5759 !CMSCollector::foregroundGCIsActive(); ++i) {
5760 os::sleep(Thread::current(), 1, false);
5761 }
5762
5763 ConcurrentMarkSweepThread::synchronize(true);
5764 bitMapLock()->lock_without_safepoint_check();
5765 startTimer();
5766 }
5767 curAddr = chunk.end();
5768 }
5769 // A successful mostly concurrent collection has been done.
5770 // Because only the full (i.e., concurrent mode failure) collections
5771 // are being measured for gc overhead limits, clean the "near" flag
5772 // and count.
5773 size_policy()->reset_gc_overhead_limit_count();
5774 _collectorState = Idling;
5775 } else {
5776 // already have the lock
5777 assert(_collectorState == Resetting, "just checking");
5778 assert_lock_strong(bitMapLock());
5779 _markBitMap.clear_all();
5780 _collectorState = Idling;
5781 }
5782
5783 register_gc_end();
5784 }
5785
5786 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5787 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5788 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5789 TraceCollectorStats tcs(counters());
5790
5791 switch (op) {
5792 case CMS_op_checkpointRootsInitial: {
5793 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5794 checkpointRootsInitial();
5795 if (PrintGC) {
5796 _cmsGen->printOccupancy("initial-mark");
5797 }
5798 break;
5799 }
5800 case CMS_op_checkpointRootsFinal: {
5801 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5802 checkpointRootsFinal();
5803 if (PrintGC) {
5804 _cmsGen->printOccupancy("remark");
5805 }
5806 break;
5807 }
5808 default:
5809 fatal("No such CMS_op");
5810 }
5811 }
5812
5813 #ifndef PRODUCT
5814 size_t const CMSCollector::skip_header_HeapWords() {
5815 return FreeChunk::header_size();
5816 }
5817
5818 // Try and collect here conditions that should hold when
5819 // CMS thread is exiting. The idea is that the foreground GC
5820 // thread should not be blocked if it wants to terminate
5821 // the CMS thread and yet continue to run the VM for a while
5822 // after that.
5823 void CMSCollector::verify_ok_to_terminate() const {
5824 assert(Thread::current()->is_ConcurrentGC_thread(),
5825 "should be called by CMS thread");
5826 assert(!_foregroundGCShouldWait, "should be false");
5827 // We could check here that all the various low-level locks
5828 // are not held by the CMS thread, but that is overkill; see
5829 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5830 // is checked.
5831 }
5832 #endif
5833
5834 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5835 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5836 "missing Printezis mark?");
5837 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5838 size_t size = pointer_delta(nextOneAddr + 1, addr);
5839 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5840 "alignment problem");
5841 assert(size >= 3, "Necessary for Printezis marks to work");
5842 return size;
5843 }
5844
5845 // A variant of the above (block_size_using_printezis_bits()) except
5846 // that we return 0 if the P-bits are not yet set.
5847 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5848 if (_markBitMap.isMarked(addr + 1)) {
5849 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5850 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5851 size_t size = pointer_delta(nextOneAddr + 1, addr);
5852 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5853 "alignment problem");
5854 assert(size >= 3, "Necessary for Printezis marks to work");
5855 return size;
5856 }
5857 return 0;
5858 }
5859
5860 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5861 size_t sz = 0;
5862 oop p = (oop)addr;
5863 if (p->klass_or_null() != NULL) {
5864 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5865 } else {
5866 sz = block_size_using_printezis_bits(addr);
5867 }
5868 assert(sz > 0, "size must be nonzero");
5869 HeapWord* next_block = addr + sz;
5870 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5871 CardTableModRefBS::card_size);
5872 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5873 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5874 "must be different cards");
5875 return next_card;
5876 }
5877
5878
5879 // CMS Bit Map Wrapper /////////////////////////////////////////
5880
5881 // Construct a CMS bit map infrastructure, but don't create the
5882 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5883 // further below.
5884 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name,
5885 bool allocate_for_entire_heap):
5886 _bm(),
5887 _shifter(shifter),
5888 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5889 Monitor::_safepoint_check_sometimes) : NULL),
5890 _allocate_for_entire_heap(allocate_for_entire_heap)
5891 {
5892 _bmStartWord = 0;
5893 _bmWordSize = 0;
5894 }
5895
5896 bool CMSBitMap::allocate(MemRegion mr) {
5897 _bmStartWord = mr.start();
5898 _bmWordSize = mr.word_size();
5899 size_t reserved_size;
5900 MemRegion heap_mr = GenCollectedHeap::heap()->reserved_region();
5901 size_t heapWordSize = heap_mr.word_size();
5902 if (!_allocate_for_entire_heap) {
5903 reserved_size = ReservedSpace::allocation_align_size_up(
5904 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1);
5905 } else {
5906 // Allocate a bit map memory large enough to cover the entire heap
5907 // (as opposed to the OG and PG only.)
5908 assert(CMSParallelFullGC && ShareCMSMarkBitMapWithParallelFullGC,
5909 "Otherwise this code must not reachable.");
5910 assert(_shifter == 0, "Valid only for the mark bit map, not the mod union table.");
5911 assert(heap_mr.contains(mr),
5912 "The give MR (OG and PG) must be part of the heap");
5913 reserved_size = ReservedSpace::allocation_align_size_up(
5914 (heapWordSize >> (_shifter + LogBitsPerByte)) + 1);
5915 }
5916 ReservedSpace brs(reserved_size);
5917 if (!brs.is_reserved()) {
5918 warning("CMS bit map allocation failure");
5919 return false;
5920 }
5921 // For now we'll just commit all of the bit map up front.
5922 // Later on we'll try to be more parsimonious with swap.
5923 if (!_virtual_space.initialize(brs, brs.size())) {
5924 warning("CMS bit map backing store failure");
5925 return false;
5926 }
5927 assert(_virtual_space.committed_size() == brs.size(),
5928 "didn't reserve backing store for all of CMS bit map?");
5929 if (!_allocate_for_entire_heap) {
5930 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5931 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5932 _bmWordSize, "inconsistency in bit map sizing");
5933 } else {
5934 // First, verify that there is no alignment issue between the
5935 // heap, the generation boundaries, and the bit map because each
5936 // word in the bit map covers BitsPerWord heap words.
5937 assert(CMSParallelFullGC && ShareCMSMarkBitMapWithParallelFullGC,
5938 "Otherwise this code must not reachable.");
5939 assert(_shifter == 0, "Valid only for the mark bit map, not the mod union table.");
5940 assert((((intptr_t) heap_mr.start()) % BitsPerWord) == 0,
5941 "Assume the heap base is aligned by BitsPerWord");
5942 assert((((intptr_t) _bmStartWord) % BitsPerWord) == 0,
5943 "Assume the yg-og boundary is aligned by BitsPerWord");
5944 assert(heapWordSize % BitsPerByte == 0,
5945 "heap_mr.word_size() should be aligned by BitsPerByte");
5946 assert(_bmWordSize % BitsPerByte == 0,
5947 "_bmWordSize should be aligned by BitsPerByte");
5948 // Second, let _bm point to the OG and PG portion of the allocated
5949 // memory.
5950 size_t payload_size = (_bmWordSize >> (_shifter + LogBitsPerByte));
5951 size_t total_size = (heapWordSize >> (_shifter + LogBitsPerByte));
5952 size_t non_payload_size = total_size - payload_size;
5953 _bm.set_map((BitMap::bm_word_t*)(_virtual_space.low() + non_payload_size));
5954 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5955 heapWordSize, "inconsistency in bit map sizing");
5956 }
5957 _bm.set_size(_bmWordSize >> _shifter);
5958
5959 // bm.clear(); // can we rely on getting zero'd memory? verify below
5960 assert(isAllClear(),
5961 "Expected zero'd memory from ReservedSpace constructor");
5962 #ifdef ASSERT
5963 if (CMSParallelFullGC && ShareCMSMarkBitMapWithParallelFullGC) {
5964 // The above isAllClear() checks only for the portion visible to
5965 // _bm (OG and PG). Check that the entire backing memory including
5966 // the YG portion is all zero.
5967 char* brs_base = brs.base();
5968 size_t brs_size = brs.size();
5969 for (size_t p = 0; p < brs_size; p++) {
5970 char* a = brs_base + p;
5971 assert(*a == 0, "The backing memory of the CMSBitMap must be all zero at init.");
5972 }
5973 }
5974 #endif
5975 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5976 "consistency check");
5977 return true;
5978 }
5979
5980 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5981 HeapWord *next_addr, *end_addr, *last_addr;
5982 assert_locked();
5983 assert(covers(mr), "out-of-range error");
5984 // XXX assert that start and end are appropriately aligned
5985 for (next_addr = mr.start(), end_addr = mr.end();
5986 next_addr < end_addr; next_addr = last_addr) {
5987 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5988 last_addr = dirty_region.end();
5989 if (!dirty_region.is_empty()) {
5990 cl->do_MemRegion(dirty_region);
5991 } else {
5992 assert(last_addr == end_addr, "program logic");
5993 return;
5994 }
5995 }
5996 }
5997
5998 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5999 _bm.print_on_error(st, prefix);
6000 }
6001
6002 #ifndef PRODUCT
6003 void CMSBitMap::assert_locked() const {
6004 CMSLockVerifier::assert_locked(lock());
6005 }
6006
6007 bool CMSBitMap::covers(MemRegion mr) const {
6008 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6009 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6010 "size inconsistency");
6011 return (mr.start() >= _bmStartWord) &&
6012 (mr.end() <= endWord());
6013 }
6014
6015 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6016 return (start >= _bmStartWord && (start + size) <= endWord());
6017 }
6018
6019 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6020 // verify that there are no 1 bits in the interval [left, right)
6021 FalseBitMapClosure falseBitMapClosure;
6022 iterate(&falseBitMapClosure, left, right);
6023 }
6024
6025 void CMSBitMap::region_invariant(MemRegion mr)
6026 {
6027 assert_locked();
6028 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6029 assert(!mr.is_empty(), "unexpected empty region");
6030 assert(covers(mr), "mr should be covered by bit map");
6031 // convert address range into offset range
6032 size_t start_ofs = heapWordToOffset(mr.start());
6033 // Make sure that end() is appropriately aligned
6034 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6035 (1 << (_shifter+LogHeapWordSize))),
6036 "Misaligned mr.end()");
6037 size_t end_ofs = heapWordToOffset(mr.end());
6038 assert(end_ofs > start_ofs, "Should mark at least one bit");
6039 }
6040
6041 #endif
6042
6043 bool CMSMarkStack::allocate(size_t size) {
6044 // allocate a stack of the requisite depth
6045 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6046 size * sizeof(oop)));
6047 if (!rs.is_reserved()) {
6048 warning("CMSMarkStack allocation failure");
6049 return false;
6050 }
6051 if (!_virtual_space.initialize(rs, rs.size())) {
6052 warning("CMSMarkStack backing store failure");
6053 return false;
6054 }
6055 assert(_virtual_space.committed_size() == rs.size(),
6056 "didn't reserve backing store for all of CMS stack?");
6057 _base = (oop*)(_virtual_space.low());
6058 _index = 0;
6059 _capacity = size;
6060 NOT_PRODUCT(_max_depth = 0);
6061 return true;
6062 }
6063
6064 // XXX FIX ME !!! In the MT case we come in here holding a
6065 // leaf lock. For printing we need to take a further lock
6066 // which has lower rank. We need to recalibrate the two
6067 // lock-ranks involved in order to be able to print the
6068 // messages below. (Or defer the printing to the caller.
6069 // For now we take the expedient path of just disabling the
6070 // messages for the problematic case.)
6071 void CMSMarkStack::expand() {
6072 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6073 if (_capacity == MarkStackSizeMax) {
6074 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6075 // We print a warning message only once per CMS cycle.
6076 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6077 }
6078 return;
6079 }
6080 // Double capacity if possible
6081 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6082 // Do not give up existing stack until we have managed to
6083 // get the double capacity that we desired.
6084 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6085 new_capacity * sizeof(oop)));
6086 if (rs.is_reserved()) {
6087 // Release the backing store associated with old stack
6088 _virtual_space.release();
6089 // Reinitialize virtual space for new stack
6090 if (!_virtual_space.initialize(rs, rs.size())) {
6091 fatal("Not enough swap for expanded marking stack");
6092 }
6093 _base = (oop*)(_virtual_space.low());
6094 _index = 0;
6095 _capacity = new_capacity;
6096 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6097 // Failed to double capacity, continue;
6098 // we print a detail message only once per CMS cycle.
6099 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6100 SIZE_FORMAT "K",
6101 _capacity / K, new_capacity / K);
6102 }
6103 }
6104
6105
6106 // Closures
6107 // XXX: there seems to be a lot of code duplication here;
6108 // should refactor and consolidate common code.
6109
6110 // This closure is used to mark refs into the CMS generation in
6111 // the CMS bit map. Called at the first checkpoint. This closure
6112 // assumes that we do not need to re-mark dirty cards; if the CMS
6113 // generation on which this is used is not an oldest
6114 // generation then this will lose younger_gen cards!
6115
6116 MarkRefsIntoClosure::MarkRefsIntoClosure(
6117 MemRegion span, CMSBitMap* bitMap):
6118 _span(span),
6119 _bitMap(bitMap)
6120 {
6121 assert(_ref_processor == NULL, "deliberately left NULL");
6122 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6123 }
6124
6125 void MarkRefsIntoClosure::do_oop(oop obj) {
6126 // if p points into _span, then mark corresponding bit in _markBitMap
6127 assert(obj->is_oop(), "expected an oop");
6128 HeapWord* addr = (HeapWord*)obj;
6129 if (_span.contains(addr)) {
6130 // this should be made more efficient
6131 _bitMap->mark(addr);
6132 }
6133 }
6134
6135 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6136 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6137
6138 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6139 MemRegion span, CMSBitMap* bitMap):
6140 _span(span),
6141 _bitMap(bitMap)
6142 {
6143 assert(_ref_processor == NULL, "deliberately left NULL");
6144 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6145 }
6146
6147 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6148 // if p points into _span, then mark corresponding bit in _markBitMap
6149 assert(obj->is_oop(), "expected an oop");
6150 HeapWord* addr = (HeapWord*)obj;
6151 if (_span.contains(addr)) {
6152 // this should be made more efficient
6153 _bitMap->par_mark(addr);
6154 }
6155 }
6156
6157 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6158 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6159
6160 // A variant of the above, used for CMS marking verification.
6161 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6162 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6163 _span(span),
6164 _verification_bm(verification_bm),
6165 _cms_bm(cms_bm)
6166 {
6167 assert(_ref_processor == NULL, "deliberately left NULL");
6168 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6169 }
6170
6171 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6172 // if p points into _span, then mark corresponding bit in _markBitMap
6173 assert(obj->is_oop(), "expected an oop");
6174 HeapWord* addr = (HeapWord*)obj;
6175 if (_span.contains(addr)) {
6176 _verification_bm->mark(addr);
6177 if (!_cms_bm->isMarked(addr)) {
6178 oop(addr)->print();
6179 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6180 fatal("... aborting");
6181 }
6182 }
6183 }
6184
6185 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6186 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6187
6188 //////////////////////////////////////////////////
6189 // MarkRefsIntoAndScanClosure
6190 //////////////////////////////////////////////////
6191
6192 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6193 ReferenceProcessor* rp,
6194 CMSBitMap* bit_map,
6195 CMSBitMap* mod_union_table,
6196 CMSMarkStack* mark_stack,
6197 CMSCollector* collector,
6198 bool should_yield,
6199 bool concurrent_precleaning):
6200 _collector(collector),
6201 _span(span),
6202 _bit_map(bit_map),
6203 _mark_stack(mark_stack),
6204 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6205 mark_stack, concurrent_precleaning),
6206 _yield(should_yield),
6207 _concurrent_precleaning(concurrent_precleaning),
6208 _freelistLock(NULL)
6209 {
6210 _ref_processor = rp;
6211 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6212 }
6213
6214 // This closure is used to mark refs into the CMS generation at the
6215 // second (final) checkpoint, and to scan and transitively follow
6216 // the unmarked oops. It is also used during the concurrent precleaning
6217 // phase while scanning objects on dirty cards in the CMS generation.
6218 // The marks are made in the marking bit map and the marking stack is
6219 // used for keeping the (newly) grey objects during the scan.
6220 // The parallel version (Par_...) appears further below.
6221 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6222 if (obj != NULL) {
6223 assert(obj->is_oop(), "expected an oop");
6224 HeapWord* addr = (HeapWord*)obj;
6225 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6226 assert(_collector->overflow_list_is_empty(),
6227 "overflow list should be empty");
6228 if (_span.contains(addr) &&
6229 !_bit_map->isMarked(addr)) {
6230 // mark bit map (object is now grey)
6231 _bit_map->mark(addr);
6232 // push on marking stack (stack should be empty), and drain the
6233 // stack by applying this closure to the oops in the oops popped
6234 // from the stack (i.e. blacken the grey objects)
6235 bool res = _mark_stack->push(obj);
6236 assert(res, "Should have space to push on empty stack");
6237 do {
6238 oop new_oop = _mark_stack->pop();
6239 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6240 assert(_bit_map->isMarked((HeapWord*)new_oop),
6241 "only grey objects on this stack");
6242 // iterate over the oops in this oop, marking and pushing
6243 // the ones in CMS heap (i.e. in _span).
6244 new_oop->oop_iterate(&_pushAndMarkClosure);
6245 // check if it's time to yield
6246 do_yield_check();
6247 } while (!_mark_stack->isEmpty() ||
6248 (!_concurrent_precleaning && take_from_overflow_list()));
6249 // if marking stack is empty, and we are not doing this
6250 // during precleaning, then check the overflow list
6251 }
6252 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6253 assert(_collector->overflow_list_is_empty(),
6254 "overflow list was drained above");
6255 // We could restore evacuated mark words, if any, used for
6256 // overflow list links here because the overflow list is
6257 // provably empty here. That would reduce the maximum
6258 // size requirements for preserved_{oop,mark}_stack.
6259 // But we'll just postpone it until we are all done
6260 // so we can just stream through.
6261 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6262 _collector->restore_preserved_marks_if_any();
6263 assert(_collector->no_preserved_marks(), "No preserved marks");
6264 }
6265 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6266 "All preserved marks should have been restored above");
6267 }
6268 }
6269
6270 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6271 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6272
6273 void MarkRefsIntoAndScanClosure::do_yield_work() {
6274 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6275 "CMS thread should hold CMS token");
6276 assert_lock_strong(_freelistLock);
6277 assert_lock_strong(_bit_map->lock());
6278 // relinquish the free_list_lock and bitMaplock()
6279 _bit_map->lock()->unlock();
6280 _freelistLock->unlock();
6281 ConcurrentMarkSweepThread::desynchronize(true);
6282 _collector->stopTimer();
6283 if (PrintCMSStatistics != 0) {
6284 _collector->incrementYields();
6285 }
6286
6287 // See the comment in coordinator_yield()
6288 for (unsigned i = 0;
6289 i < CMSYieldSleepCount &&
6290 ConcurrentMarkSweepThread::should_yield() &&
6291 !CMSCollector::foregroundGCIsActive();
6292 ++i) {
6293 os::sleep(Thread::current(), 1, false);
6294 }
6295
6296 ConcurrentMarkSweepThread::synchronize(true);
6297 _freelistLock->lock_without_safepoint_check();
6298 _bit_map->lock()->lock_without_safepoint_check();
6299 _collector->startTimer();
6300 }
6301
6302 ///////////////////////////////////////////////////////////
6303 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6304 // MarkRefsIntoAndScanClosure
6305 ///////////////////////////////////////////////////////////
6306 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6307 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6308 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6309 _span(span),
6310 _bit_map(bit_map),
6311 _work_queue(work_queue),
6312 _low_water_mark(MIN2((work_queue->max_elems()/4),
6313 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6314 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6315 {
6316 _ref_processor = rp;
6317 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6318 }
6319
6320 // This closure is used to mark refs into the CMS generation at the
6321 // second (final) checkpoint, and to scan and transitively follow
6322 // the unmarked oops. The marks are made in the marking bit map and
6323 // the work_queue is used for keeping the (newly) grey objects during
6324 // the scan phase whence they are also available for stealing by parallel
6325 // threads. Since the marking bit map is shared, updates are
6326 // synchronized (via CAS).
6327 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6328 if (obj != NULL) {
6329 // Ignore mark word because this could be an already marked oop
6330 // that may be chained at the end of the overflow list.
6331 assert(obj->is_oop(true), "expected an oop");
6332 HeapWord* addr = (HeapWord*)obj;
6333 if (_span.contains(addr) &&
6334 !_bit_map->isMarked(addr)) {
6335 // mark bit map (object will become grey):
6336 // It is possible for several threads to be
6337 // trying to "claim" this object concurrently;
6338 // the unique thread that succeeds in marking the
6339 // object first will do the subsequent push on
6340 // to the work queue (or overflow list).
6341 if (_bit_map->par_mark(addr)) {
6342 // push on work_queue (which may not be empty), and trim the
6343 // queue to an appropriate length by applying this closure to
6344 // the oops in the oops popped from the stack (i.e. blacken the
6345 // grey objects)
6346 bool res = _work_queue->push(obj);
6347 assert(res, "Low water mark should be less than capacity?");
6348 trim_queue(_low_water_mark);
6349 } // Else, another thread claimed the object
6350 }
6351 }
6352 }
6353
6354 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6355 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6356
6357 // This closure is used to rescan the marked objects on the dirty cards
6358 // in the mod union table and the card table proper.
6359 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6360 oop p, MemRegion mr) {
6361
6362 size_t size = 0;
6363 HeapWord* addr = (HeapWord*)p;
6364 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6365 assert(_span.contains(addr), "we are scanning the CMS generation");
6366 // check if it's time to yield
6367 if (do_yield_check()) {
6368 // We yielded for some foreground stop-world work,
6369 // and we have been asked to abort this ongoing preclean cycle.
6370 return 0;
6371 }
6372 if (_bitMap->isMarked(addr)) {
6373 // it's marked; is it potentially uninitialized?
6374 if (p->klass_or_null() != NULL) {
6375 // an initialized object; ignore mark word in verification below
6376 // since we are running concurrent with mutators
6377 assert(p->is_oop(true), "should be an oop");
6378 if (p->is_objArray()) {
6379 // objArrays are precisely marked; restrict scanning
6380 // to dirty cards only.
6381 size = CompactibleFreeListSpace::adjustObjectSize(
6382 p->oop_iterate(_scanningClosure, mr));
6383 } else {
6384 // A non-array may have been imprecisely marked; we need
6385 // to scan object in its entirety.
6386 size = CompactibleFreeListSpace::adjustObjectSize(
6387 p->oop_iterate(_scanningClosure));
6388 }
6389 #ifdef ASSERT
6390 size_t direct_size =
6391 CompactibleFreeListSpace::adjustObjectSize(p->size());
6392 assert(size == direct_size, "Inconsistency in size");
6393 assert(size >= 3, "Necessary for Printezis marks to work");
6394 if (!_bitMap->isMarked(addr+1)) {
6395 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6396 } else {
6397 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6398 assert(_bitMap->isMarked(addr+size-1),
6399 "inconsistent Printezis mark");
6400 }
6401 #endif // ASSERT
6402 } else {
6403 // An uninitialized object.
6404 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6405 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6406 size = pointer_delta(nextOneAddr + 1, addr);
6407 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6408 "alignment problem");
6409 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6410 // will dirty the card when the klass pointer is installed in the
6411 // object (signaling the completion of initialization).
6412 }
6413 } else {
6414 // Either a not yet marked object or an uninitialized object
6415 if (p->klass_or_null() == NULL) {
6416 // An uninitialized object, skip to the next card, since
6417 // we may not be able to read its P-bits yet.
6418 assert(size == 0, "Initial value");
6419 } else {
6420 // An object not (yet) reached by marking: we merely need to
6421 // compute its size so as to go look at the next block.
6422 assert(p->is_oop(true), "should be an oop");
6423 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6424 }
6425 }
6426 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6427 return size;
6428 }
6429
6430 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6431 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6432 "CMS thread should hold CMS token");
6433 assert_lock_strong(_freelistLock);
6434 assert_lock_strong(_bitMap->lock());
6435 // relinquish the free_list_lock and bitMaplock()
6436 _bitMap->lock()->unlock();
6437 _freelistLock->unlock();
6438 ConcurrentMarkSweepThread::desynchronize(true);
6439 _collector->stopTimer();
6440 if (PrintCMSStatistics != 0) {
6441 _collector->incrementYields();
6442 }
6443
6444 // See the comment in coordinator_yield()
6445 for (unsigned i = 0; i < CMSYieldSleepCount &&
6446 ConcurrentMarkSweepThread::should_yield() &&
6447 !CMSCollector::foregroundGCIsActive(); ++i) {
6448 os::sleep(Thread::current(), 1, false);
6449 }
6450
6451 ConcurrentMarkSweepThread::synchronize(true);
6452 _freelistLock->lock_without_safepoint_check();
6453 _bitMap->lock()->lock_without_safepoint_check();
6454 _collector->startTimer();
6455 }
6456
6457
6458 //////////////////////////////////////////////////////////////////
6459 // SurvivorSpacePrecleanClosure
6460 //////////////////////////////////////////////////////////////////
6461 // This (single-threaded) closure is used to preclean the oops in
6462 // the survivor spaces.
6463 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6464
6465 HeapWord* addr = (HeapWord*)p;
6466 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6467 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6468 assert(p->klass_or_null() != NULL, "object should be initialized");
6469 // an initialized object; ignore mark word in verification below
6470 // since we are running concurrent with mutators
6471 assert(p->is_oop(true), "should be an oop");
6472 // Note that we do not yield while we iterate over
6473 // the interior oops of p, pushing the relevant ones
6474 // on our marking stack.
6475 size_t size = p->oop_iterate(_scanning_closure);
6476 do_yield_check();
6477 // Observe that below, we do not abandon the preclean
6478 // phase as soon as we should; rather we empty the
6479 // marking stack before returning. This is to satisfy
6480 // some existing assertions. In general, it may be a
6481 // good idea to abort immediately and complete the marking
6482 // from the grey objects at a later time.
6483 while (!_mark_stack->isEmpty()) {
6484 oop new_oop = _mark_stack->pop();
6485 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6486 assert(_bit_map->isMarked((HeapWord*)new_oop),
6487 "only grey objects on this stack");
6488 // iterate over the oops in this oop, marking and pushing
6489 // the ones in CMS heap (i.e. in _span).
6490 new_oop->oop_iterate(_scanning_closure);
6491 // check if it's time to yield
6492 do_yield_check();
6493 }
6494 unsigned int after_count =
6495 GenCollectedHeap::heap()->total_collections();
6496 bool abort = (_before_count != after_count) ||
6497 _collector->should_abort_preclean();
6498 return abort ? 0 : size;
6499 }
6500
6501 void SurvivorSpacePrecleanClosure::do_yield_work() {
6502 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6503 "CMS thread should hold CMS token");
6504 assert_lock_strong(_bit_map->lock());
6505 // Relinquish the bit map lock
6506 _bit_map->lock()->unlock();
6507 ConcurrentMarkSweepThread::desynchronize(true);
6508 _collector->stopTimer();
6509 if (PrintCMSStatistics != 0) {
6510 _collector->incrementYields();
6511 }
6512
6513 // See the comment in coordinator_yield()
6514 for (unsigned i = 0; i < CMSYieldSleepCount &&
6515 ConcurrentMarkSweepThread::should_yield() &&
6516 !CMSCollector::foregroundGCIsActive(); ++i) {
6517 os::sleep(Thread::current(), 1, false);
6518 }
6519
6520 ConcurrentMarkSweepThread::synchronize(true);
6521 _bit_map->lock()->lock_without_safepoint_check();
6522 _collector->startTimer();
6523 }
6524
6525 // This closure is used to rescan the marked objects on the dirty cards
6526 // in the mod union table and the card table proper. In the parallel
6527 // case, although the bitMap is shared, we do a single read so the
6528 // isMarked() query is "safe".
6529 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6530 // Ignore mark word because we are running concurrent with mutators
6531 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6532 HeapWord* addr = (HeapWord*)p;
6533 assert(_span.contains(addr), "we are scanning the CMS generation");
6534 bool is_obj_array = false;
6535 #ifdef ASSERT
6536 if (!_parallel) {
6537 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6538 assert(_collector->overflow_list_is_empty(),
6539 "overflow list should be empty");
6540
6541 }
6542 #endif // ASSERT
6543 if (_bit_map->isMarked(addr)) {
6544 // Obj arrays are precisely marked, non-arrays are not;
6545 // so we scan objArrays precisely and non-arrays in their
6546 // entirety.
6547 if (p->is_objArray()) {
6548 is_obj_array = true;
6549 if (_parallel) {
6550 p->oop_iterate(_par_scan_closure, mr);
6551 } else {
6552 p->oop_iterate(_scan_closure, mr);
6553 }
6554 } else {
6555 if (_parallel) {
6556 p->oop_iterate(_par_scan_closure);
6557 } else {
6558 p->oop_iterate(_scan_closure);
6559 }
6560 }
6561 }
6562 #ifdef ASSERT
6563 if (!_parallel) {
6564 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6565 assert(_collector->overflow_list_is_empty(),
6566 "overflow list should be empty");
6567
6568 }
6569 #endif // ASSERT
6570 return is_obj_array;
6571 }
6572
6573 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6574 MemRegion span,
6575 CMSBitMap* bitMap, CMSMarkStack* markStack,
6576 bool should_yield, bool verifying):
6577 _collector(collector),
6578 _span(span),
6579 _bitMap(bitMap),
6580 _mut(&collector->_modUnionTable),
6581 _markStack(markStack),
6582 _yield(should_yield),
6583 _skipBits(0)
6584 {
6585 assert(_markStack->isEmpty(), "stack should be empty");
6586 _finger = _bitMap->startWord();
6587 _threshold = _finger;
6588 assert(_collector->_restart_addr == NULL, "Sanity check");
6589 assert(_span.contains(_finger), "Out of bounds _finger?");
6590 DEBUG_ONLY(_verifying = verifying;)
6591 }
6592
6593 void MarkFromRootsClosure::reset(HeapWord* addr) {
6594 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6595 assert(_span.contains(addr), "Out of bounds _finger?");
6596 _finger = addr;
6597 _threshold = (HeapWord*)round_to(
6598 (intptr_t)_finger, CardTableModRefBS::card_size);
6599 }
6600
6601 // Should revisit to see if this should be restructured for
6602 // greater efficiency.
6603 bool MarkFromRootsClosure::do_bit(size_t offset) {
6604 if (_skipBits > 0) {
6605 _skipBits--;
6606 return true;
6607 }
6608 // convert offset into a HeapWord*
6609 HeapWord* addr = _bitMap->startWord() + offset;
6610 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6611 "address out of range");
6612 assert(_bitMap->isMarked(addr), "tautology");
6613 if (_bitMap->isMarked(addr+1)) {
6614 // this is an allocated but not yet initialized object
6615 assert(_skipBits == 0, "tautology");
6616 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6617 oop p = oop(addr);
6618 if (p->klass_or_null() == NULL) {
6619 DEBUG_ONLY(if (!_verifying) {)
6620 // We re-dirty the cards on which this object lies and increase
6621 // the _threshold so that we'll come back to scan this object
6622 // during the preclean or remark phase. (CMSCleanOnEnter)
6623 if (CMSCleanOnEnter) {
6624 size_t sz = _collector->block_size_using_printezis_bits(addr);
6625 HeapWord* end_card_addr = (HeapWord*)round_to(
6626 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6627 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6628 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6629 // Bump _threshold to end_card_addr; note that
6630 // _threshold cannot possibly exceed end_card_addr, anyhow.
6631 // This prevents future clearing of the card as the scan proceeds
6632 // to the right.
6633 assert(_threshold <= end_card_addr,
6634 "Because we are just scanning into this object");
6635 if (_threshold < end_card_addr) {
6636 _threshold = end_card_addr;
6637 }
6638 if (p->klass_or_null() != NULL) {
6639 // Redirty the range of cards...
6640 _mut->mark_range(redirty_range);
6641 } // ...else the setting of klass will dirty the card anyway.
6642 }
6643 DEBUG_ONLY(})
6644 return true;
6645 }
6646 }
6647 scanOopsInOop(addr);
6648 return true;
6649 }
6650
6651 // We take a break if we've been at this for a while,
6652 // so as to avoid monopolizing the locks involved.
6653 void MarkFromRootsClosure::do_yield_work() {
6654 // First give up the locks, then yield, then re-lock
6655 // We should probably use a constructor/destructor idiom to
6656 // do this unlock/lock or modify the MutexUnlocker class to
6657 // serve our purpose. XXX
6658 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6659 "CMS thread should hold CMS token");
6660 assert_lock_strong(_bitMap->lock());
6661 _bitMap->lock()->unlock();
6662 ConcurrentMarkSweepThread::desynchronize(true);
6663 _collector->stopTimer();
6664 if (PrintCMSStatistics != 0) {
6665 _collector->incrementYields();
6666 }
6667
6668 // See the comment in coordinator_yield()
6669 for (unsigned i = 0; i < CMSYieldSleepCount &&
6670 ConcurrentMarkSweepThread::should_yield() &&
6671 !CMSCollector::foregroundGCIsActive(); ++i) {
6672 os::sleep(Thread::current(), 1, false);
6673 }
6674
6675 ConcurrentMarkSweepThread::synchronize(true);
6676 _bitMap->lock()->lock_without_safepoint_check();
6677 _collector->startTimer();
6678 }
6679
6680 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6681 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6682 assert(_markStack->isEmpty(),
6683 "should drain stack to limit stack usage");
6684 // convert ptr to an oop preparatory to scanning
6685 oop obj = oop(ptr);
6686 // Ignore mark word in verification below, since we
6687 // may be running concurrent with mutators.
6688 assert(obj->is_oop(true), "should be an oop");
6689 assert(_finger <= ptr, "_finger runneth ahead");
6690 // advance the finger to right end of this object
6691 _finger = ptr + obj->size();
6692 assert(_finger > ptr, "we just incremented it above");
6693 // On large heaps, it may take us some time to get through
6694 // the marking phase. During
6695 // this time it's possible that a lot of mutations have
6696 // accumulated in the card table and the mod union table --
6697 // these mutation records are redundant until we have
6698 // actually traced into the corresponding card.
6699 // Here, we check whether advancing the finger would make
6700 // us cross into a new card, and if so clear corresponding
6701 // cards in the MUT (preclean them in the card-table in the
6702 // future).
6703
6704 DEBUG_ONLY(if (!_verifying) {)
6705 // The clean-on-enter optimization is disabled by default,
6706 // until we fix 6178663.
6707 if (CMSCleanOnEnter && (_finger > _threshold)) {
6708 // [_threshold, _finger) represents the interval
6709 // of cards to be cleared in MUT (or precleaned in card table).
6710 // The set of cards to be cleared is all those that overlap
6711 // with the interval [_threshold, _finger); note that
6712 // _threshold is always kept card-aligned but _finger isn't
6713 // always card-aligned.
6714 HeapWord* old_threshold = _threshold;
6715 assert(old_threshold == (HeapWord*)round_to(
6716 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6717 "_threshold should always be card-aligned");
6718 _threshold = (HeapWord*)round_to(
6719 (intptr_t)_finger, CardTableModRefBS::card_size);
6720 MemRegion mr(old_threshold, _threshold);
6721 assert(!mr.is_empty(), "Control point invariant");
6722 assert(_span.contains(mr), "Should clear within span");
6723 _mut->clear_range(mr);
6724 }
6725 DEBUG_ONLY(})
6726 // Note: the finger doesn't advance while we drain
6727 // the stack below.
6728 PushOrMarkClosure pushOrMarkClosure(_collector,
6729 _span, _bitMap, _markStack,
6730 _finger, this);
6731 bool res = _markStack->push(obj);
6732 assert(res, "Empty non-zero size stack should have space for single push");
6733 while (!_markStack->isEmpty()) {
6734 oop new_oop = _markStack->pop();
6735 // Skip verifying header mark word below because we are
6736 // running concurrent with mutators.
6737 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6738 // now scan this oop's oops
6739 new_oop->oop_iterate(&pushOrMarkClosure);
6740 do_yield_check();
6741 }
6742 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6743 }
6744
6745 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6746 CMSCollector* collector, MemRegion span,
6747 CMSBitMap* bit_map,
6748 OopTaskQueue* work_queue,
6749 CMSMarkStack* overflow_stack):
6750 _collector(collector),
6751 _whole_span(collector->_span),
6752 _span(span),
6753 _bit_map(bit_map),
6754 _mut(&collector->_modUnionTable),
6755 _work_queue(work_queue),
6756 _overflow_stack(overflow_stack),
6757 _skip_bits(0),
6758 _task(task)
6759 {
6760 assert(_work_queue->size() == 0, "work_queue should be empty");
6761 _finger = span.start();
6762 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6763 assert(_span.contains(_finger), "Out of bounds _finger?");
6764 }
6765
6766 // Should revisit to see if this should be restructured for
6767 // greater efficiency.
6768 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6769 if (_skip_bits > 0) {
6770 _skip_bits--;
6771 return true;
6772 }
6773 // convert offset into a HeapWord*
6774 HeapWord* addr = _bit_map->startWord() + offset;
6775 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6776 "address out of range");
6777 assert(_bit_map->isMarked(addr), "tautology");
6778 if (_bit_map->isMarked(addr+1)) {
6779 // this is an allocated object that might not yet be initialized
6780 assert(_skip_bits == 0, "tautology");
6781 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6782 oop p = oop(addr);
6783 if (p->klass_or_null() == NULL) {
6784 // in the case of Clean-on-Enter optimization, redirty card
6785 // and avoid clearing card by increasing the threshold.
6786 return true;
6787 }
6788 }
6789 scan_oops_in_oop(addr);
6790 return true;
6791 }
6792
6793 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6794 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6795 // Should we assert that our work queue is empty or
6796 // below some drain limit?
6797 assert(_work_queue->size() == 0,
6798 "should drain stack to limit stack usage");
6799 // convert ptr to an oop preparatory to scanning
6800 oop obj = oop(ptr);
6801 // Ignore mark word in verification below, since we
6802 // may be running concurrent with mutators.
6803 assert(obj->is_oop(true), "should be an oop");
6804 assert(_finger <= ptr, "_finger runneth ahead");
6805 // advance the finger to right end of this object
6806 _finger = ptr + obj->size();
6807 assert(_finger > ptr, "we just incremented it above");
6808 // On large heaps, it may take us some time to get through
6809 // the marking phase. During
6810 // this time it's possible that a lot of mutations have
6811 // accumulated in the card table and the mod union table --
6812 // these mutation records are redundant until we have
6813 // actually traced into the corresponding card.
6814 // Here, we check whether advancing the finger would make
6815 // us cross into a new card, and if so clear corresponding
6816 // cards in the MUT (preclean them in the card-table in the
6817 // future).
6818
6819 // The clean-on-enter optimization is disabled by default,
6820 // until we fix 6178663.
6821 if (CMSCleanOnEnter && (_finger > _threshold)) {
6822 // [_threshold, _finger) represents the interval
6823 // of cards to be cleared in MUT (or precleaned in card table).
6824 // The set of cards to be cleared is all those that overlap
6825 // with the interval [_threshold, _finger); note that
6826 // _threshold is always kept card-aligned but _finger isn't
6827 // always card-aligned.
6828 HeapWord* old_threshold = _threshold;
6829 assert(old_threshold == (HeapWord*)round_to(
6830 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6831 "_threshold should always be card-aligned");
6832 _threshold = (HeapWord*)round_to(
6833 (intptr_t)_finger, CardTableModRefBS::card_size);
6834 MemRegion mr(old_threshold, _threshold);
6835 assert(!mr.is_empty(), "Control point invariant");
6836 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6837 _mut->clear_range(mr);
6838 }
6839
6840 // Note: the local finger doesn't advance while we drain
6841 // the stack below, but the global finger sure can and will.
6842 HeapWord** gfa = _task->global_finger_addr();
6843 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6844 _span, _bit_map,
6845 _work_queue,
6846 _overflow_stack,
6847 _finger,
6848 gfa, this);
6849 bool res = _work_queue->push(obj); // overflow could occur here
6850 assert(res, "Will hold once we use workqueues");
6851 while (true) {
6852 oop new_oop;
6853 if (!_work_queue->pop_local(new_oop)) {
6854 // We emptied our work_queue; check if there's stuff that can
6855 // be gotten from the overflow stack.
6856 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6857 _overflow_stack, _work_queue)) {
6858 do_yield_check();
6859 continue;
6860 } else { // done
6861 break;
6862 }
6863 }
6864 // Skip verifying header mark word below because we are
6865 // running concurrent with mutators.
6866 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6867 // now scan this oop's oops
6868 new_oop->oop_iterate(&pushOrMarkClosure);
6869 do_yield_check();
6870 }
6871 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6872 }
6873
6874 // Yield in response to a request from VM Thread or
6875 // from mutators.
6876 void Par_MarkFromRootsClosure::do_yield_work() {
6877 assert(_task != NULL, "sanity");
6878 _task->yield();
6879 }
6880
6881 // A variant of the above used for verifying CMS marking work.
6882 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6883 MemRegion span,
6884 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6885 CMSMarkStack* mark_stack):
6886 _collector(collector),
6887 _span(span),
6888 _verification_bm(verification_bm),
6889 _cms_bm(cms_bm),
6890 _mark_stack(mark_stack),
6891 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6892 mark_stack)
6893 {
6894 assert(_mark_stack->isEmpty(), "stack should be empty");
6895 _finger = _verification_bm->startWord();
6896 assert(_collector->_restart_addr == NULL, "Sanity check");
6897 assert(_span.contains(_finger), "Out of bounds _finger?");
6898 }
6899
6900 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6901 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6902 assert(_span.contains(addr), "Out of bounds _finger?");
6903 _finger = addr;
6904 }
6905
6906 // Should revisit to see if this should be restructured for
6907 // greater efficiency.
6908 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6909 // convert offset into a HeapWord*
6910 HeapWord* addr = _verification_bm->startWord() + offset;
6911 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6912 "address out of range");
6913 assert(_verification_bm->isMarked(addr), "tautology");
6914 assert(_cms_bm->isMarked(addr), "tautology");
6915
6916 assert(_mark_stack->isEmpty(),
6917 "should drain stack to limit stack usage");
6918 // convert addr to an oop preparatory to scanning
6919 oop obj = oop(addr);
6920 assert(obj->is_oop(), "should be an oop");
6921 assert(_finger <= addr, "_finger runneth ahead");
6922 // advance the finger to right end of this object
6923 _finger = addr + obj->size();
6924 assert(_finger > addr, "we just incremented it above");
6925 // Note: the finger doesn't advance while we drain
6926 // the stack below.
6927 bool res = _mark_stack->push(obj);
6928 assert(res, "Empty non-zero size stack should have space for single push");
6929 while (!_mark_stack->isEmpty()) {
6930 oop new_oop = _mark_stack->pop();
6931 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6932 // now scan this oop's oops
6933 new_oop->oop_iterate(&_pam_verify_closure);
6934 }
6935 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6936 return true;
6937 }
6938
6939 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6940 CMSCollector* collector, MemRegion span,
6941 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6942 CMSMarkStack* mark_stack):
6943 MetadataAwareOopClosure(collector->ref_processor()),
6944 _collector(collector),
6945 _span(span),
6946 _verification_bm(verification_bm),
6947 _cms_bm(cms_bm),
6948 _mark_stack(mark_stack)
6949 { }
6950
6951 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6952 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6953
6954 // Upon stack overflow, we discard (part of) the stack,
6955 // remembering the least address amongst those discarded
6956 // in CMSCollector's _restart_address.
6957 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6958 // Remember the least grey address discarded
6959 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6960 _collector->lower_restart_addr(ra);
6961 _mark_stack->reset(); // discard stack contents
6962 _mark_stack->expand(); // expand the stack if possible
6963 }
6964
6965 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6966 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6967 HeapWord* addr = (HeapWord*)obj;
6968 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6969 // Oop lies in _span and isn't yet grey or black
6970 _verification_bm->mark(addr); // now grey
6971 if (!_cms_bm->isMarked(addr)) {
6972 oop(addr)->print();
6973 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6974 p2i(addr));
6975 fatal("... aborting");
6976 }
6977
6978 if (!_mark_stack->push(obj)) { // stack overflow
6979 if (PrintCMSStatistics != 0) {
6980 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6981 SIZE_FORMAT, _mark_stack->capacity());
6982 }
6983 assert(_mark_stack->isFull(), "Else push should have succeeded");
6984 handle_stack_overflow(addr);
6985 }
6986 // anything including and to the right of _finger
6987 // will be scanned as we iterate over the remainder of the
6988 // bit map
6989 }
6990 }
6991
6992 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6993 MemRegion span,
6994 CMSBitMap* bitMap, CMSMarkStack* markStack,
6995 HeapWord* finger, MarkFromRootsClosure* parent) :
6996 MetadataAwareOopClosure(collector->ref_processor()),
6997 _collector(collector),
6998 _span(span),
6999 _bitMap(bitMap),
7000 _markStack(markStack),
7001 _finger(finger),
7002 _parent(parent)
7003 { }
7004
7005 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7006 MemRegion span,
7007 CMSBitMap* bit_map,
7008 OopTaskQueue* work_queue,
7009 CMSMarkStack* overflow_stack,
7010 HeapWord* finger,
7011 HeapWord** global_finger_addr,
7012 Par_MarkFromRootsClosure* parent) :
7013 MetadataAwareOopClosure(collector->ref_processor()),
7014 _collector(collector),
7015 _whole_span(collector->_span),
7016 _span(span),
7017 _bit_map(bit_map),
7018 _work_queue(work_queue),
7019 _overflow_stack(overflow_stack),
7020 _finger(finger),
7021 _global_finger_addr(global_finger_addr),
7022 _parent(parent)
7023 { }
7024
7025 // Assumes thread-safe access by callers, who are
7026 // responsible for mutual exclusion.
7027 void CMSCollector::lower_restart_addr(HeapWord* low) {
7028 assert(_span.contains(low), "Out of bounds addr");
7029 if (_restart_addr == NULL) {
7030 _restart_addr = low;
7031 } else {
7032 _restart_addr = MIN2(_restart_addr, low);
7033 }
7034 }
7035
7036 // Upon stack overflow, we discard (part of) the stack,
7037 // remembering the least address amongst those discarded
7038 // in CMSCollector's _restart_address.
7039 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7040 // Remember the least grey address discarded
7041 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7042 _collector->lower_restart_addr(ra);
7043 _markStack->reset(); // discard stack contents
7044 _markStack->expand(); // expand the stack if possible
7045 }
7046
7047 // Upon stack overflow, we discard (part of) the stack,
7048 // remembering the least address amongst those discarded
7049 // in CMSCollector's _restart_address.
7050 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7051 // We need to do this under a mutex to prevent other
7052 // workers from interfering with the work done below.
7053 MutexLockerEx ml(_overflow_stack->par_lock(),
7054 Mutex::_no_safepoint_check_flag);
7055 // Remember the least grey address discarded
7056 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7057 _collector->lower_restart_addr(ra);
7058 _overflow_stack->reset(); // discard stack contents
7059 _overflow_stack->expand(); // expand the stack if possible
7060 }
7061
7062 void PushOrMarkClosure::do_oop(oop obj) {
7063 // Ignore mark word because we are running concurrent with mutators.
7064 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7065 HeapWord* addr = (HeapWord*)obj;
7066 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7067 // Oop lies in _span and isn't yet grey or black
7068 _bitMap->mark(addr); // now grey
7069 if (addr < _finger) {
7070 // the bit map iteration has already either passed, or
7071 // sampled, this bit in the bit map; we'll need to
7072 // use the marking stack to scan this oop's oops.
7073 bool simulate_overflow = false;
7074 NOT_PRODUCT(
7075 if (CMSMarkStackOverflowALot &&
7076 _collector->simulate_overflow()) {
7077 // simulate a stack overflow
7078 simulate_overflow = true;
7079 }
7080 )
7081 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7082 if (PrintCMSStatistics != 0) {
7083 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7084 SIZE_FORMAT, _markStack->capacity());
7085 }
7086 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7087 handle_stack_overflow(addr);
7088 }
7089 }
7090 // anything including and to the right of _finger
7091 // will be scanned as we iterate over the remainder of the
7092 // bit map
7093 do_yield_check();
7094 }
7095 }
7096
7097 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7098 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7099
7100 void Par_PushOrMarkClosure::do_oop(oop obj) {
7101 // Ignore mark word because we are running concurrent with mutators.
7102 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7103 HeapWord* addr = (HeapWord*)obj;
7104 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7105 // Oop lies in _span and isn't yet grey or black
7106 // We read the global_finger (volatile read) strictly after marking oop
7107 bool res = _bit_map->par_mark(addr); // now grey
7108 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7109 // Should we push this marked oop on our stack?
7110 // -- if someone else marked it, nothing to do
7111 // -- if target oop is above global finger nothing to do
7112 // -- if target oop is in chunk and above local finger
7113 // then nothing to do
7114 // -- else push on work queue
7115 if ( !res // someone else marked it, they will deal with it
7116 || (addr >= *gfa) // will be scanned in a later task
7117 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7118 return;
7119 }
7120 // the bit map iteration has already either passed, or
7121 // sampled, this bit in the bit map; we'll need to
7122 // use the marking stack to scan this oop's oops.
7123 bool simulate_overflow = false;
7124 NOT_PRODUCT(
7125 if (CMSMarkStackOverflowALot &&
7126 _collector->simulate_overflow()) {
7127 // simulate a stack overflow
7128 simulate_overflow = true;
7129 }
7130 )
7131 if (simulate_overflow ||
7132 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7133 // stack overflow
7134 if (PrintCMSStatistics != 0) {
7135 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7136 SIZE_FORMAT, _overflow_stack->capacity());
7137 }
7138 // We cannot assert that the overflow stack is full because
7139 // it may have been emptied since.
7140 assert(simulate_overflow ||
7141 _work_queue->size() == _work_queue->max_elems(),
7142 "Else push should have succeeded");
7143 handle_stack_overflow(addr);
7144 }
7145 do_yield_check();
7146 }
7147 }
7148
7149 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7150 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7151
7152 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7153 MemRegion span,
7154 ReferenceProcessor* rp,
7155 CMSBitMap* bit_map,
7156 CMSBitMap* mod_union_table,
7157 CMSMarkStack* mark_stack,
7158 bool concurrent_precleaning):
7159 MetadataAwareOopClosure(rp),
7160 _collector(collector),
7161 _span(span),
7162 _bit_map(bit_map),
7163 _mod_union_table(mod_union_table),
7164 _mark_stack(mark_stack),
7165 _concurrent_precleaning(concurrent_precleaning)
7166 {
7167 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7168 }
7169
7170 // Grey object rescan during pre-cleaning and second checkpoint phases --
7171 // the non-parallel version (the parallel version appears further below.)
7172 void PushAndMarkClosure::do_oop(oop obj) {
7173 // Ignore mark word verification. If during concurrent precleaning,
7174 // the object monitor may be locked. If during the checkpoint
7175 // phases, the object may already have been reached by a different
7176 // path and may be at the end of the global overflow list (so
7177 // the mark word may be NULL).
7178 assert(obj->is_oop_or_null(true /* ignore mark word */),
7179 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7180 HeapWord* addr = (HeapWord*)obj;
7181 // Check if oop points into the CMS generation
7182 // and is not marked
7183 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7184 // a white object ...
7185 _bit_map->mark(addr); // ... now grey
7186 // push on the marking stack (grey set)
7187 bool simulate_overflow = false;
7188 NOT_PRODUCT(
7189 if (CMSMarkStackOverflowALot &&
7190 _collector->simulate_overflow()) {
7191 // simulate a stack overflow
7192 simulate_overflow = true;
7193 }
7194 )
7195 if (simulate_overflow || !_mark_stack->push(obj)) {
7196 if (_concurrent_precleaning) {
7197 // During precleaning we can just dirty the appropriate card(s)
7198 // in the mod union table, thus ensuring that the object remains
7199 // in the grey set and continue. In the case of object arrays
7200 // we need to dirty all of the cards that the object spans,
7201 // since the rescan of object arrays will be limited to the
7202 // dirty cards.
7203 // Note that no one can be interfering with us in this action
7204 // of dirtying the mod union table, so no locking or atomics
7205 // are required.
7206 if (obj->is_objArray()) {
7207 size_t sz = obj->size();
7208 HeapWord* end_card_addr = (HeapWord*)round_to(
7209 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7210 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7211 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7212 _mod_union_table->mark_range(redirty_range);
7213 } else {
7214 _mod_union_table->mark(addr);
7215 }
7216 _collector->_ser_pmc_preclean_ovflw++;
7217 } else {
7218 // During the remark phase, we need to remember this oop
7219 // in the overflow list.
7220 _collector->push_on_overflow_list(obj);
7221 _collector->_ser_pmc_remark_ovflw++;
7222 }
7223 }
7224 }
7225 }
7226
7227 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7228 MemRegion span,
7229 ReferenceProcessor* rp,
7230 CMSBitMap* bit_map,
7231 OopTaskQueue* work_queue):
7232 MetadataAwareOopClosure(rp),
7233 _collector(collector),
7234 _span(span),
7235 _bit_map(bit_map),
7236 _work_queue(work_queue)
7237 {
7238 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7239 }
7240
7241 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7242 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7243
7244 // Grey object rescan during second checkpoint phase --
7245 // the parallel version.
7246 void Par_PushAndMarkClosure::do_oop(oop obj) {
7247 // In the assert below, we ignore the mark word because
7248 // this oop may point to an already visited object that is
7249 // on the overflow stack (in which case the mark word has
7250 // been hijacked for chaining into the overflow stack --
7251 // if this is the last object in the overflow stack then
7252 // its mark word will be NULL). Because this object may
7253 // have been subsequently popped off the global overflow
7254 // stack, and the mark word possibly restored to the prototypical
7255 // value, by the time we get to examined this failing assert in
7256 // the debugger, is_oop_or_null(false) may subsequently start
7257 // to hold.
7258 assert(obj->is_oop_or_null(true),
7259 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7260 HeapWord* addr = (HeapWord*)obj;
7261 // Check if oop points into the CMS generation
7262 // and is not marked
7263 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7264 // a white object ...
7265 // If we manage to "claim" the object, by being the
7266 // first thread to mark it, then we push it on our
7267 // marking stack
7268 if (_bit_map->par_mark(addr)) { // ... now grey
7269 // push on work queue (grey set)
7270 bool simulate_overflow = false;
7271 NOT_PRODUCT(
7272 if (CMSMarkStackOverflowALot &&
7273 _collector->par_simulate_overflow()) {
7274 // simulate a stack overflow
7275 simulate_overflow = true;
7276 }
7277 )
7278 if (simulate_overflow || !_work_queue->push(obj)) {
7279 _collector->par_push_on_overflow_list(obj);
7280 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7281 }
7282 } // Else, some other thread got there first
7283 }
7284 }
7285
7286 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7287 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7288
7289 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7290 Mutex* bml = _collector->bitMapLock();
7291 assert_lock_strong(bml);
7292 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7293 "CMS thread should hold CMS token");
7294
7295 bml->unlock();
7296 ConcurrentMarkSweepThread::desynchronize(true);
7297
7298 _collector->stopTimer();
7299 if (PrintCMSStatistics != 0) {
7300 _collector->incrementYields();
7301 }
7302
7303 // See the comment in coordinator_yield()
7304 for (unsigned i = 0; i < CMSYieldSleepCount &&
7305 ConcurrentMarkSweepThread::should_yield() &&
7306 !CMSCollector::foregroundGCIsActive(); ++i) {
7307 os::sleep(Thread::current(), 1, false);
7308 }
7309
7310 ConcurrentMarkSweepThread::synchronize(true);
7311 bml->lock();
7312
7313 _collector->startTimer();
7314 }
7315
7316 bool CMSPrecleanRefsYieldClosure::should_return() {
7317 if (ConcurrentMarkSweepThread::should_yield()) {
7318 do_yield_work();
7319 }
7320 return _collector->foregroundGCIsActive();
7321 }
7322
7323 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7324 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7325 "mr should be aligned to start at a card boundary");
7326 // We'd like to assert:
7327 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7328 // "mr should be a range of cards");
7329 // However, that would be too strong in one case -- the last
7330 // partition ends at _unallocated_block which, in general, can be
7331 // an arbitrary boundary, not necessarily card aligned.
7332 if (PrintCMSStatistics != 0) {
7333 _num_dirty_cards +=
7334 mr.word_size()/CardTableModRefBS::card_size_in_words;
7335 }
7336 _space->object_iterate_mem(mr, &_scan_cl);
7337 }
7338
7339 SweepClosure::SweepClosure(CMSCollector* collector,
7340 ConcurrentMarkSweepGeneration* g,
7341 CMSBitMap* bitMap, bool should_yield) :
7342 _collector(collector),
7343 _g(g),
7344 _sp(g->cmsSpace()),
7345 _limit(_sp->sweep_limit()),
7346 _freelistLock(_sp->freelistLock()),
7347 _bitMap(bitMap),
7348 _yield(should_yield),
7349 _inFreeRange(false), // No free range at beginning of sweep
7350 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7351 _lastFreeRangeCoalesced(false),
7352 _freeFinger(g->used_region().start())
7353 {
7354 NOT_PRODUCT(
7355 _numObjectsFreed = 0;
7356 _numWordsFreed = 0;
7357 _numObjectsLive = 0;
7358 _numWordsLive = 0;
7359 _numObjectsAlreadyFree = 0;
7360 _numWordsAlreadyFree = 0;
7361 _last_fc = NULL;
7362
7363 _sp->initializeIndexedFreeListArrayReturnedBytes();
7364 _sp->dictionary()->initialize_dict_returned_bytes();
7365 )
7366 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7367 "sweep _limit out of bounds");
7368 if (CMSTraceSweeper) {
7369 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7370 p2i(_limit));
7371 }
7372 }
7373
7374 void SweepClosure::print_on(outputStream* st) const {
7375 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7376 p2i(_sp->bottom()), p2i(_sp->end()));
7377 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7378 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7379 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7380 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7381 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7382 }
7383
7384 #ifndef PRODUCT
7385 // Assertion checking only: no useful work in product mode --
7386 // however, if any of the flags below become product flags,
7387 // you may need to review this code to see if it needs to be
7388 // enabled in product mode.
7389 SweepClosure::~SweepClosure() {
7390 assert_lock_strong(_freelistLock);
7391 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7392 "sweep _limit out of bounds");
7393 if (inFreeRange()) {
7394 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7395 print();
7396 ShouldNotReachHere();
7397 }
7398 if (Verbose && PrintGC) {
7399 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7400 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7401 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7402 SIZE_FORMAT " bytes "
7403 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7404 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7405 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7406 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7407 * sizeof(HeapWord);
7408 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7409
7410 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7411 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7412 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7413 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7414 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7415 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7416 indexListReturnedBytes);
7417 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7418 dict_returned_bytes);
7419 }
7420 }
7421 if (CMSTraceSweeper) {
7422 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7423 p2i(_limit));
7424 }
7425 }
7426 #endif // PRODUCT
7427
7428 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7429 bool freeRangeInFreeLists) {
7430 if (CMSTraceSweeper) {
7431 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7432 p2i(freeFinger), freeRangeInFreeLists);
7433 }
7434 assert(!inFreeRange(), "Trampling existing free range");
7435 set_inFreeRange(true);
7436 set_lastFreeRangeCoalesced(false);
7437
7438 set_freeFinger(freeFinger);
7439 set_freeRangeInFreeLists(freeRangeInFreeLists);
7440 if (CMSTestInFreeList) {
7441 if (freeRangeInFreeLists) {
7442 FreeChunk* fc = (FreeChunk*) freeFinger;
7443 assert(fc->is_free(), "A chunk on the free list should be free.");
7444 assert(fc->size() > 0, "Free range should have a size");
7445 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7446 }
7447 }
7448 }
7449
7450 // Note that the sweeper runs concurrently with mutators. Thus,
7451 // it is possible for direct allocation in this generation to happen
7452 // in the middle of the sweep. Note that the sweeper also coalesces
7453 // contiguous free blocks. Thus, unless the sweeper and the allocator
7454 // synchronize appropriately freshly allocated blocks may get swept up.
7455 // This is accomplished by the sweeper locking the free lists while
7456 // it is sweeping. Thus blocks that are determined to be free are
7457 // indeed free. There is however one additional complication:
7458 // blocks that have been allocated since the final checkpoint and
7459 // mark, will not have been marked and so would be treated as
7460 // unreachable and swept up. To prevent this, the allocator marks
7461 // the bit map when allocating during the sweep phase. This leads,
7462 // however, to a further complication -- objects may have been allocated
7463 // but not yet initialized -- in the sense that the header isn't yet
7464 // installed. The sweeper can not then determine the size of the block
7465 // in order to skip over it. To deal with this case, we use a technique
7466 // (due to Printezis) to encode such uninitialized block sizes in the
7467 // bit map. Since the bit map uses a bit per every HeapWord, but the
7468 // CMS generation has a minimum object size of 3 HeapWords, it follows
7469 // that "normal marks" won't be adjacent in the bit map (there will
7470 // always be at least two 0 bits between successive 1 bits). We make use
7471 // of these "unused" bits to represent uninitialized blocks -- the bit
7472 // corresponding to the start of the uninitialized object and the next
7473 // bit are both set. Finally, a 1 bit marks the end of the object that
7474 // started with the two consecutive 1 bits to indicate its potentially
7475 // uninitialized state.
7476
7477 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7478 FreeChunk* fc = (FreeChunk*)addr;
7479 size_t res;
7480
7481 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7482 // than "addr == _limit" because although _limit was a block boundary when
7483 // we started the sweep, it may no longer be one because heap expansion
7484 // may have caused us to coalesce the block ending at the address _limit
7485 // with a newly expanded chunk (this happens when _limit was set to the
7486 // previous _end of the space), so we may have stepped past _limit:
7487 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7488 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7489 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7490 "sweep _limit out of bounds");
7491 assert(addr < _sp->end(), "addr out of bounds");
7492 // Flush any free range we might be holding as a single
7493 // coalesced chunk to the appropriate free list.
7494 if (inFreeRange()) {
7495 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7496 err_msg("freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())));
7497 flush_cur_free_chunk(freeFinger(),
7498 pointer_delta(addr, freeFinger()));
7499 if (CMSTraceSweeper) {
7500 gclog_or_tty->print("Sweep: last chunk: ");
7501 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7502 "[coalesced:%d]\n",
7503 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7504 lastFreeRangeCoalesced() ? 1 : 0);
7505 }
7506 }
7507
7508 // help the iterator loop finish
7509 return pointer_delta(_sp->end(), addr);
7510 }
7511
7512 assert(addr < _limit, "sweep invariant");
7513 // check if we should yield
7514 do_yield_check(addr);
7515 if (fc->is_free()) {
7516 // Chunk that is already free
7517 res = fc->size();
7518 do_already_free_chunk(fc);
7519 debug_only(_sp->verifyFreeLists());
7520 // If we flush the chunk at hand in lookahead_and_flush()
7521 // and it's coalesced with a preceding chunk, then the
7522 // process of "mangling" the payload of the coalesced block
7523 // will cause erasure of the size information from the
7524 // (erstwhile) header of all the coalesced blocks but the
7525 // first, so the first disjunct in the assert will not hold
7526 // in that specific case (in which case the second disjunct
7527 // will hold).
7528 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7529 "Otherwise the size info doesn't change at this step");
7530 NOT_PRODUCT(
7531 _numObjectsAlreadyFree++;
7532 _numWordsAlreadyFree += res;
7533 )
7534 NOT_PRODUCT(_last_fc = fc;)
7535 } else if (!_bitMap->isMarked(addr)) {
7536 // Chunk is fresh garbage
7537 res = do_garbage_chunk(fc);
7538 debug_only(_sp->verifyFreeLists());
7539 NOT_PRODUCT(
7540 _numObjectsFreed++;
7541 _numWordsFreed += res;
7542 )
7543 } else {
7544 // Chunk that is alive.
7545 res = do_live_chunk(fc);
7546 debug_only(_sp->verifyFreeLists());
7547 NOT_PRODUCT(
7548 _numObjectsLive++;
7549 _numWordsLive += res;
7550 )
7551 }
7552 return res;
7553 }
7554
7555 // For the smart allocation, record following
7556 // split deaths - a free chunk is removed from its free list because
7557 // it is being split into two or more chunks.
7558 // split birth - a free chunk is being added to its free list because
7559 // a larger free chunk has been split and resulted in this free chunk.
7560 // coal death - a free chunk is being removed from its free list because
7561 // it is being coalesced into a large free chunk.
7562 // coal birth - a free chunk is being added to its free list because
7563 // it was created when two or more free chunks where coalesced into
7564 // this free chunk.
7565 //
7566 // These statistics are used to determine the desired number of free
7567 // chunks of a given size. The desired number is chosen to be relative
7568 // to the end of a CMS sweep. The desired number at the end of a sweep
7569 // is the
7570 // count-at-end-of-previous-sweep (an amount that was enough)
7571 // - count-at-beginning-of-current-sweep (the excess)
7572 // + split-births (gains in this size during interval)
7573 // - split-deaths (demands on this size during interval)
7574 // where the interval is from the end of one sweep to the end of the
7575 // next.
7576 //
7577 // When sweeping the sweeper maintains an accumulated chunk which is
7578 // the chunk that is made up of chunks that have been coalesced. That
7579 // will be termed the left-hand chunk. A new chunk of garbage that
7580 // is being considered for coalescing will be referred to as the
7581 // right-hand chunk.
7582 //
7583 // When making a decision on whether to coalesce a right-hand chunk with
7584 // the current left-hand chunk, the current count vs. the desired count
7585 // of the left-hand chunk is considered. Also if the right-hand chunk
7586 // is near the large chunk at the end of the heap (see
7587 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7588 // left-hand chunk is coalesced.
7589 //
7590 // When making a decision about whether to split a chunk, the desired count
7591 // vs. the current count of the candidate to be split is also considered.
7592 // If the candidate is underpopulated (currently fewer chunks than desired)
7593 // a chunk of an overpopulated (currently more chunks than desired) size may
7594 // be chosen. The "hint" associated with a free list, if non-null, points
7595 // to a free list which may be overpopulated.
7596 //
7597
7598 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7599 const size_t size = fc->size();
7600 // Chunks that cannot be coalesced are not in the
7601 // free lists.
7602 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7603 assert(_sp->verify_chunk_in_free_list(fc),
7604 "free chunk should be in free lists");
7605 }
7606 // a chunk that is already free, should not have been
7607 // marked in the bit map
7608 HeapWord* const addr = (HeapWord*) fc;
7609 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7610 // Verify that the bit map has no bits marked between
7611 // addr and purported end of this block.
7612 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7613
7614 // Some chunks cannot be coalesced under any circumstances.
7615 // See the definition of cantCoalesce().
7616 if (!fc->cantCoalesce()) {
7617 // This chunk can potentially be coalesced.
7618 if (_sp->adaptive_freelists()) {
7619 // All the work is done in
7620 do_post_free_or_garbage_chunk(fc, size);
7621 } else { // Not adaptive free lists
7622 // this is a free chunk that can potentially be coalesced by the sweeper;
7623 if (!inFreeRange()) {
7624 // if the next chunk is a free block that can't be coalesced
7625 // it doesn't make sense to remove this chunk from the free lists
7626 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7627 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7628 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7629 nextChunk->is_free() && // ... which is free...
7630 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7631 // nothing to do
7632 } else {
7633 // Potentially the start of a new free range:
7634 // Don't eagerly remove it from the free lists.
7635 // No need to remove it if it will just be put
7636 // back again. (Also from a pragmatic point of view
7637 // if it is a free block in a region that is beyond
7638 // any allocated blocks, an assertion will fail)
7639 // Remember the start of a free run.
7640 initialize_free_range(addr, true);
7641 // end - can coalesce with next chunk
7642 }
7643 } else {
7644 // the midst of a free range, we are coalescing
7645 print_free_block_coalesced(fc);
7646 if (CMSTraceSweeper) {
7647 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7648 }
7649 // remove it from the free lists
7650 _sp->removeFreeChunkFromFreeLists(fc);
7651 set_lastFreeRangeCoalesced(true);
7652 // If the chunk is being coalesced and the current free range is
7653 // in the free lists, remove the current free range so that it
7654 // will be returned to the free lists in its entirety - all
7655 // the coalesced pieces included.
7656 if (freeRangeInFreeLists()) {
7657 FreeChunk* ffc = (FreeChunk*) freeFinger();
7658 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7659 "Size of free range is inconsistent with chunk size.");
7660 if (CMSTestInFreeList) {
7661 assert(_sp->verify_chunk_in_free_list(ffc),
7662 "free range is not in free lists");
7663 }
7664 _sp->removeFreeChunkFromFreeLists(ffc);
7665 set_freeRangeInFreeLists(false);
7666 }
7667 }
7668 }
7669 // Note that if the chunk is not coalescable (the else arm
7670 // below), we unconditionally flush, without needing to do
7671 // a "lookahead," as we do below.
7672 if (inFreeRange()) lookahead_and_flush(fc, size);
7673 } else {
7674 // Code path common to both original and adaptive free lists.
7675
7676 // cant coalesce with previous block; this should be treated
7677 // as the end of a free run if any
7678 if (inFreeRange()) {
7679 // we kicked some butt; time to pick up the garbage
7680 assert(freeFinger() < addr, "freeFinger points too high");
7681 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7682 }
7683 // else, nothing to do, just continue
7684 }
7685 }
7686
7687 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7688 // This is a chunk of garbage. It is not in any free list.
7689 // Add it to a free list or let it possibly be coalesced into
7690 // a larger chunk.
7691 HeapWord* const addr = (HeapWord*) fc;
7692 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7693
7694 if (_sp->adaptive_freelists()) {
7695 // Verify that the bit map has no bits marked between
7696 // addr and purported end of just dead object.
7697 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7698
7699 do_post_free_or_garbage_chunk(fc, size);
7700 } else {
7701 if (!inFreeRange()) {
7702 // start of a new free range
7703 assert(size > 0, "A free range should have a size");
7704 initialize_free_range(addr, false);
7705 } else {
7706 // this will be swept up when we hit the end of the
7707 // free range
7708 if (CMSTraceSweeper) {
7709 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7710 }
7711 // If the chunk is being coalesced and the current free range is
7712 // in the free lists, remove the current free range so that it
7713 // will be returned to the free lists in its entirety - all
7714 // the coalesced pieces included.
7715 if (freeRangeInFreeLists()) {
7716 FreeChunk* ffc = (FreeChunk*)freeFinger();
7717 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7718 "Size of free range is inconsistent with chunk size.");
7719 if (CMSTestInFreeList) {
7720 assert(_sp->verify_chunk_in_free_list(ffc),
7721 "free range is not in free lists");
7722 }
7723 _sp->removeFreeChunkFromFreeLists(ffc);
7724 set_freeRangeInFreeLists(false);
7725 }
7726 set_lastFreeRangeCoalesced(true);
7727 }
7728 // this will be swept up when we hit the end of the free range
7729
7730 // Verify that the bit map has no bits marked between
7731 // addr and purported end of just dead object.
7732 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7733 }
7734 assert(_limit >= addr + size,
7735 "A freshly garbage chunk can't possibly straddle over _limit");
7736 if (inFreeRange()) lookahead_and_flush(fc, size);
7737 return size;
7738 }
7739
7740 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7741 HeapWord* addr = (HeapWord*) fc;
7742 // The sweeper has just found a live object. Return any accumulated
7743 // left hand chunk to the free lists.
7744 if (inFreeRange()) {
7745 assert(freeFinger() < addr, "freeFinger points too high");
7746 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7747 }
7748
7749 // This object is live: we'd normally expect this to be
7750 // an oop, and like to assert the following:
7751 // assert(oop(addr)->is_oop(), "live block should be an oop");
7752 // However, as we commented above, this may be an object whose
7753 // header hasn't yet been initialized.
7754 size_t size;
7755 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7756 if (_bitMap->isMarked(addr + 1)) {
7757 // Determine the size from the bit map, rather than trying to
7758 // compute it from the object header.
7759 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7760 size = pointer_delta(nextOneAddr + 1, addr);
7761 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7762 "alignment problem");
7763
7764 #ifdef ASSERT
7765 if (oop(addr)->klass_or_null() != NULL) {
7766 // Ignore mark word because we are running concurrent with mutators
7767 assert(oop(addr)->is_oop(true), "live block should be an oop");
7768 assert(size ==
7769 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7770 "P-mark and computed size do not agree");
7771 }
7772 #endif
7773
7774 } else {
7775 // This should be an initialized object that's alive.
7776 assert(oop(addr)->klass_or_null() != NULL,
7777 "Should be an initialized object");
7778 // Ignore mark word because we are running concurrent with mutators
7779 assert(oop(addr)->is_oop(true), "live block should be an oop");
7780 // Verify that the bit map has no bits marked between
7781 // addr and purported end of this block.
7782 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7783 assert(size >= 3, "Necessary for Printezis marks to work");
7784 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7785 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7786 }
7787 return size;
7788 }
7789
7790 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7791 size_t chunkSize) {
7792 // do_post_free_or_garbage_chunk() should only be called in the case
7793 // of the adaptive free list allocator.
7794 const bool fcInFreeLists = fc->is_free();
7795 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7796 assert((HeapWord*)fc <= _limit, "sweep invariant");
7797 if (CMSTestInFreeList && fcInFreeLists) {
7798 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7799 }
7800
7801 if (CMSTraceSweeper) {
7802 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7803 }
7804
7805 HeapWord* const fc_addr = (HeapWord*) fc;
7806
7807 bool coalesce;
7808 const size_t left = pointer_delta(fc_addr, freeFinger());
7809 const size_t right = chunkSize;
7810 switch (FLSCoalescePolicy) {
7811 // numeric value forms a coalition aggressiveness metric
7812 case 0: { // never coalesce
7813 coalesce = false;
7814 break;
7815 }
7816 case 1: { // coalesce if left & right chunks on overpopulated lists
7817 coalesce = _sp->coalOverPopulated(left) &&
7818 _sp->coalOverPopulated(right);
7819 break;
7820 }
7821 case 2: { // coalesce if left chunk on overpopulated list (default)
7822 coalesce = _sp->coalOverPopulated(left);
7823 break;
7824 }
7825 case 3: { // coalesce if left OR right chunk on overpopulated list
7826 coalesce = _sp->coalOverPopulated(left) ||
7827 _sp->coalOverPopulated(right);
7828 break;
7829 }
7830 case 4: { // always coalesce
7831 coalesce = true;
7832 break;
7833 }
7834 default:
7835 ShouldNotReachHere();
7836 }
7837
7838 // Should the current free range be coalesced?
7839 // If the chunk is in a free range and either we decided to coalesce above
7840 // or the chunk is near the large block at the end of the heap
7841 // (isNearLargestChunk() returns true), then coalesce this chunk.
7842 const bool doCoalesce = inFreeRange()
7843 && (coalesce || _g->isNearLargestChunk(fc_addr));
7844 if (doCoalesce) {
7845 // Coalesce the current free range on the left with the new
7846 // chunk on the right. If either is on a free list,
7847 // it must be removed from the list and stashed in the closure.
7848 if (freeRangeInFreeLists()) {
7849 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7850 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7851 "Size of free range is inconsistent with chunk size.");
7852 if (CMSTestInFreeList) {
7853 assert(_sp->verify_chunk_in_free_list(ffc),
7854 "Chunk is not in free lists");
7855 }
7856 _sp->coalDeath(ffc->size());
7857 _sp->removeFreeChunkFromFreeLists(ffc);
7858 set_freeRangeInFreeLists(false);
7859 }
7860 if (fcInFreeLists) {
7861 _sp->coalDeath(chunkSize);
7862 assert(fc->size() == chunkSize,
7863 "The chunk has the wrong size or is not in the free lists");
7864 _sp->removeFreeChunkFromFreeLists(fc);
7865 }
7866 set_lastFreeRangeCoalesced(true);
7867 print_free_block_coalesced(fc);
7868 } else { // not in a free range and/or should not coalesce
7869 // Return the current free range and start a new one.
7870 if (inFreeRange()) {
7871 // In a free range but cannot coalesce with the right hand chunk.
7872 // Put the current free range into the free lists.
7873 flush_cur_free_chunk(freeFinger(),
7874 pointer_delta(fc_addr, freeFinger()));
7875 }
7876 // Set up for new free range. Pass along whether the right hand
7877 // chunk is in the free lists.
7878 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7879 }
7880 }
7881
7882 // Lookahead flush:
7883 // If we are tracking a free range, and this is the last chunk that
7884 // we'll look at because its end crosses past _limit, we'll preemptively
7885 // flush it along with any free range we may be holding on to. Note that
7886 // this can be the case only for an already free or freshly garbage
7887 // chunk. If this block is an object, it can never straddle
7888 // over _limit. The "straddling" occurs when _limit is set at
7889 // the previous end of the space when this cycle started, and
7890 // a subsequent heap expansion caused the previously co-terminal
7891 // free block to be coalesced with the newly expanded portion,
7892 // thus rendering _limit a non-block-boundary making it dangerous
7893 // for the sweeper to step over and examine.
7894 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7895 assert(inFreeRange(), "Should only be called if currently in a free range.");
7896 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7897 assert(_sp->used_region().contains(eob - 1),
7898 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7899 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7900 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7901 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7902 if (eob >= _limit) {
7903 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7904 if (CMSTraceSweeper) {
7905 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7906 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7907 "[" PTR_FORMAT "," PTR_FORMAT ")",
7908 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7909 }
7910 // Return the storage we are tracking back into the free lists.
7911 if (CMSTraceSweeper) {
7912 gclog_or_tty->print_cr("Flushing ... ");
7913 }
7914 assert(freeFinger() < eob, "Error");
7915 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7916 }
7917 }
7918
7919 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7920 assert(inFreeRange(), "Should only be called if currently in a free range.");
7921 assert(size > 0,
7922 "A zero sized chunk cannot be added to the free lists.");
7923 if (!freeRangeInFreeLists()) {
7924 if (CMSTestInFreeList) {
7925 FreeChunk* fc = (FreeChunk*) chunk;
7926 fc->set_size(size);
7927 assert(!_sp->verify_chunk_in_free_list(fc),
7928 "chunk should not be in free lists yet");
7929 }
7930 if (CMSTraceSweeper) {
7931 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7932 p2i(chunk), size);
7933 }
7934 // A new free range is going to be starting. The current
7935 // free range has not been added to the free lists yet or
7936 // was removed so add it back.
7937 // If the current free range was coalesced, then the death
7938 // of the free range was recorded. Record a birth now.
7939 if (lastFreeRangeCoalesced()) {
7940 _sp->coalBirth(size);
7941 }
7942 _sp->addChunkAndRepairOffsetTable(chunk, size,
7943 lastFreeRangeCoalesced());
7944 } else if (CMSTraceSweeper) {
7945 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7946 }
7947 set_inFreeRange(false);
7948 set_freeRangeInFreeLists(false);
7949 }
7950
7951 // We take a break if we've been at this for a while,
7952 // so as to avoid monopolizing the locks involved.
7953 void SweepClosure::do_yield_work(HeapWord* addr) {
7954 // Return current free chunk being used for coalescing (if any)
7955 // to the appropriate freelist. After yielding, the next
7956 // free block encountered will start a coalescing range of
7957 // free blocks. If the next free block is adjacent to the
7958 // chunk just flushed, they will need to wait for the next
7959 // sweep to be coalesced.
7960 if (inFreeRange()) {
7961 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7962 }
7963
7964 // First give up the locks, then yield, then re-lock.
7965 // We should probably use a constructor/destructor idiom to
7966 // do this unlock/lock or modify the MutexUnlocker class to
7967 // serve our purpose. XXX
7968 assert_lock_strong(_bitMap->lock());
7969 assert_lock_strong(_freelistLock);
7970 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7971 "CMS thread should hold CMS token");
7972 _bitMap->lock()->unlock();
7973 _freelistLock->unlock();
7974 ConcurrentMarkSweepThread::desynchronize(true);
7975 _collector->stopTimer();
7976 if (PrintCMSStatistics != 0) {
7977 _collector->incrementYields();
7978 }
7979
7980 // See the comment in coordinator_yield()
7981 for (unsigned i = 0; i < CMSYieldSleepCount &&
7982 ConcurrentMarkSweepThread::should_yield() &&
7983 !CMSCollector::foregroundGCIsActive(); ++i) {
7984 os::sleep(Thread::current(), 1, false);
7985 }
7986
7987 ConcurrentMarkSweepThread::synchronize(true);
7988 _freelistLock->lock();
7989 _bitMap->lock()->lock_without_safepoint_check();
7990 _collector->startTimer();
7991 }
7992
7993 #ifndef PRODUCT
7994 // This is actually very useful in a product build if it can
7995 // be called from the debugger. Compile it into the product
7996 // as needed.
7997 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7998 return debug_cms_space->verify_chunk_in_free_list(fc);
7999 }
8000 #endif
8001
8002 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8003 if (CMSTraceSweeper) {
8004 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8005 p2i(fc), fc->size());
8006 }
8007 }
8008
8009 // CMSIsAliveClosure
8010 bool CMSIsAliveClosure::do_object_b(oop obj) {
8011 HeapWord* addr = (HeapWord*)obj;
8012 return addr != NULL &&
8013 (!_span.contains(addr) || _bit_map->isMarked(addr));
8014 }
8015
8016
8017 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8018 MemRegion span,
8019 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8020 bool cpc):
8021 _collector(collector),
8022 _span(span),
8023 _bit_map(bit_map),
8024 _mark_stack(mark_stack),
8025 _concurrent_precleaning(cpc) {
8026 assert(!_span.is_empty(), "Empty span could spell trouble");
8027 }
8028
8029
8030 // CMSKeepAliveClosure: the serial version
8031 void CMSKeepAliveClosure::do_oop(oop obj) {
8032 HeapWord* addr = (HeapWord*)obj;
8033 if (_span.contains(addr) &&
8034 !_bit_map->isMarked(addr)) {
8035 _bit_map->mark(addr);
8036 bool simulate_overflow = false;
8037 NOT_PRODUCT(
8038 if (CMSMarkStackOverflowALot &&
8039 _collector->simulate_overflow()) {
8040 // simulate a stack overflow
8041 simulate_overflow = true;
8042 }
8043 )
8044 if (simulate_overflow || !_mark_stack->push(obj)) {
8045 if (_concurrent_precleaning) {
8046 // We dirty the overflown object and let the remark
8047 // phase deal with it.
8048 assert(_collector->overflow_list_is_empty(), "Error");
8049 // In the case of object arrays, we need to dirty all of
8050 // the cards that the object spans. No locking or atomics
8051 // are needed since no one else can be mutating the mod union
8052 // table.
8053 if (obj->is_objArray()) {
8054 size_t sz = obj->size();
8055 HeapWord* end_card_addr =
8056 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8057 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8058 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8059 _collector->_modUnionTable.mark_range(redirty_range);
8060 } else {
8061 _collector->_modUnionTable.mark(addr);
8062 }
8063 _collector->_ser_kac_preclean_ovflw++;
8064 } else {
8065 _collector->push_on_overflow_list(obj);
8066 _collector->_ser_kac_ovflw++;
8067 }
8068 }
8069 }
8070 }
8071
8072 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8073 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8074
8075 // CMSParKeepAliveClosure: a parallel version of the above.
8076 // The work queues are private to each closure (thread),
8077 // but (may be) available for stealing by other threads.
8078 void CMSParKeepAliveClosure::do_oop(oop obj) {
8079 HeapWord* addr = (HeapWord*)obj;
8080 if (_span.contains(addr) &&
8081 !_bit_map->isMarked(addr)) {
8082 // In general, during recursive tracing, several threads
8083 // may be concurrently getting here; the first one to
8084 // "tag" it, claims it.
8085 if (_bit_map->par_mark(addr)) {
8086 bool res = _work_queue->push(obj);
8087 assert(res, "Low water mark should be much less than capacity");
8088 // Do a recursive trim in the hope that this will keep
8089 // stack usage lower, but leave some oops for potential stealers
8090 trim_queue(_low_water_mark);
8091 } // Else, another thread got there first
8092 }
8093 }
8094
8095 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8096 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8097
8098 void CMSParKeepAliveClosure::trim_queue(uint max) {
8099 while (_work_queue->size() > max) {
8100 oop new_oop;
8101 if (_work_queue->pop_local(new_oop)) {
8102 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8103 assert(_bit_map->isMarked((HeapWord*)new_oop),
8104 "no white objects on this stack!");
8105 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8106 // iterate over the oops in this oop, marking and pushing
8107 // the ones in CMS heap (i.e. in _span).
8108 new_oop->oop_iterate(&_mark_and_push);
8109 }
8110 }
8111 }
8112
8113 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8114 CMSCollector* collector,
8115 MemRegion span, CMSBitMap* bit_map,
8116 OopTaskQueue* work_queue):
8117 _collector(collector),
8118 _span(span),
8119 _bit_map(bit_map),
8120 _work_queue(work_queue) { }
8121
8122 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8123 HeapWord* addr = (HeapWord*)obj;
8124 if (_span.contains(addr) &&
8125 !_bit_map->isMarked(addr)) {
8126 if (_bit_map->par_mark(addr)) {
8127 bool simulate_overflow = false;
8128 NOT_PRODUCT(
8129 if (CMSMarkStackOverflowALot &&
8130 _collector->par_simulate_overflow()) {
8131 // simulate a stack overflow
8132 simulate_overflow = true;
8133 }
8134 )
8135 if (simulate_overflow || !_work_queue->push(obj)) {
8136 _collector->par_push_on_overflow_list(obj);
8137 _collector->_par_kac_ovflw++;
8138 }
8139 } // Else another thread got there already
8140 }
8141 }
8142
8143 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8144 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8145
8146 //////////////////////////////////////////////////////////////////
8147 // CMSExpansionCause /////////////////////////////
8148 //////////////////////////////////////////////////////////////////
8149 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8150 switch (cause) {
8151 case _no_expansion:
8152 return "No expansion";
8153 case _satisfy_free_ratio:
8154 return "Free ratio";
8155 case _satisfy_promotion:
8156 return "Satisfy promotion";
8157 case _satisfy_allocation:
8158 return "allocation";
8159 case _allocate_par_lab:
8160 return "Par LAB";
8161 case _allocate_par_spooling_space:
8162 return "Par Spooling Space";
8163 case _adaptive_size_policy:
8164 return "Ergonomics";
8165 default:
8166 return "unknown";
8167 }
8168 }
8169
8170 void CMSDrainMarkingStackClosure::do_void() {
8171 // the max number to take from overflow list at a time
8172 const size_t num = _mark_stack->capacity()/4;
8173 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8174 "Overflow list should be NULL during concurrent phases");
8175 while (!_mark_stack->isEmpty() ||
8176 // if stack is empty, check the overflow list
8177 _collector->take_from_overflow_list(num, _mark_stack)) {
8178 oop obj = _mark_stack->pop();
8179 HeapWord* addr = (HeapWord*)obj;
8180 assert(_span.contains(addr), "Should be within span");
8181 assert(_bit_map->isMarked(addr), "Should be marked");
8182 assert(obj->is_oop(), "Should be an oop");
8183 obj->oop_iterate(_keep_alive);
8184 }
8185 }
8186
8187 void CMSParDrainMarkingStackClosure::do_void() {
8188 // drain queue
8189 trim_queue(0);
8190 }
8191
8192 // Trim our work_queue so its length is below max at return
8193 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8194 while (_work_queue->size() > max) {
8195 oop new_oop;
8196 if (_work_queue->pop_local(new_oop)) {
8197 assert(new_oop->is_oop(), "Expected an oop");
8198 assert(_bit_map->isMarked((HeapWord*)new_oop),
8199 "no white objects on this stack!");
8200 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8201 // iterate over the oops in this oop, marking and pushing
8202 // the ones in CMS heap (i.e. in _span).
8203 new_oop->oop_iterate(&_mark_and_push);
8204 }
8205 }
8206 }
8207
8208 ////////////////////////////////////////////////////////////////////
8209 // Support for Marking Stack Overflow list handling and related code
8210 ////////////////////////////////////////////////////////////////////
8211 // Much of the following code is similar in shape and spirit to the
8212 // code used in ParNewGC. We should try and share that code
8213 // as much as possible in the future.
8214
8215 #ifndef PRODUCT
8216 // Debugging support for CMSStackOverflowALot
8217
8218 // It's OK to call this multi-threaded; the worst thing
8219 // that can happen is that we'll get a bunch of closely
8220 // spaced simulated overflows, but that's OK, in fact
8221 // probably good as it would exercise the overflow code
8222 // under contention.
8223 bool CMSCollector::simulate_overflow() {
8224 if (_overflow_counter-- <= 0) { // just being defensive
8225 _overflow_counter = CMSMarkStackOverflowInterval;
8226 return true;
8227 } else {
8228 return false;
8229 }
8230 }
8231
8232 bool CMSCollector::par_simulate_overflow() {
8233 return simulate_overflow();
8234 }
8235 #endif
8236
8237 // Single-threaded
8238 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8239 assert(stack->isEmpty(), "Expected precondition");
8240 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8241 size_t i = num;
8242 oop cur = _overflow_list;
8243 const markOop proto = markOopDesc::prototype();
8244 NOT_PRODUCT(ssize_t n = 0;)
8245 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8246 next = oop(cur->mark());
8247 cur->set_mark(proto); // until proven otherwise
8248 assert(cur->is_oop(), "Should be an oop");
8249 bool res = stack->push(cur);
8250 assert(res, "Bit off more than can chew?");
8251 NOT_PRODUCT(n++;)
8252 }
8253 _overflow_list = cur;
8254 #ifndef PRODUCT
8255 assert(_num_par_pushes >= n, "Too many pops?");
8256 _num_par_pushes -=n;
8257 #endif
8258 return !stack->isEmpty();
8259 }
8260
8261 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8262 // (MT-safe) Get a prefix of at most "num" from the list.
8263 // The overflow list is chained through the mark word of
8264 // each object in the list. We fetch the entire list,
8265 // break off a prefix of the right size and return the
8266 // remainder. If other threads try to take objects from
8267 // the overflow list at that time, they will wait for
8268 // some time to see if data becomes available. If (and
8269 // only if) another thread places one or more object(s)
8270 // on the global list before we have returned the suffix
8271 // to the global list, we will walk down our local list
8272 // to find its end and append the global list to
8273 // our suffix before returning it. This suffix walk can
8274 // prove to be expensive (quadratic in the amount of traffic)
8275 // when there are many objects in the overflow list and
8276 // there is much producer-consumer contention on the list.
8277 // *NOTE*: The overflow list manipulation code here and
8278 // in ParNewGeneration:: are very similar in shape,
8279 // except that in the ParNew case we use the old (from/eden)
8280 // copy of the object to thread the list via its klass word.
8281 // Because of the common code, if you make any changes in
8282 // the code below, please check the ParNew version to see if
8283 // similar changes might be needed.
8284 // CR 6797058 has been filed to consolidate the common code.
8285 bool CMSCollector::par_take_from_overflow_list(size_t num,
8286 OopTaskQueue* work_q,
8287 int no_of_gc_threads) {
8288 assert(work_q->size() == 0, "First empty local work queue");
8289 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8290 if (_overflow_list == NULL) {
8291 return false;
8292 }
8293 // Grab the entire list; we'll put back a suffix
8294 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8295 Thread* tid = Thread::current();
8296 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8297 // set to ParallelGCThreads.
8298 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8299 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8300 // If the list is busy, we spin for a short while,
8301 // sleeping between attempts to get the list.
8302 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8303 os::sleep(tid, sleep_time_millis, false);
8304 if (_overflow_list == NULL) {
8305 // Nothing left to take
8306 return false;
8307 } else if (_overflow_list != BUSY) {
8308 // Try and grab the prefix
8309 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8310 }
8311 }
8312 // If the list was found to be empty, or we spun long
8313 // enough, we give up and return empty-handed. If we leave
8314 // the list in the BUSY state below, it must be the case that
8315 // some other thread holds the overflow list and will set it
8316 // to a non-BUSY state in the future.
8317 if (prefix == NULL || prefix == BUSY) {
8318 // Nothing to take or waited long enough
8319 if (prefix == NULL) {
8320 // Write back the NULL in case we overwrote it with BUSY above
8321 // and it is still the same value.
8322 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8323 }
8324 return false;
8325 }
8326 assert(prefix != NULL && prefix != BUSY, "Error");
8327 size_t i = num;
8328 oop cur = prefix;
8329 // Walk down the first "num" objects, unless we reach the end.
8330 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8331 if (cur->mark() == NULL) {
8332 // We have "num" or fewer elements in the list, so there
8333 // is nothing to return to the global list.
8334 // Write back the NULL in lieu of the BUSY we wrote
8335 // above, if it is still the same value.
8336 if (_overflow_list == BUSY) {
8337 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8338 }
8339 } else {
8340 // Chop off the suffix and return it to the global list.
8341 assert(cur->mark() != BUSY, "Error");
8342 oop suffix_head = cur->mark(); // suffix will be put back on global list
8343 cur->set_mark(NULL); // break off suffix
8344 // It's possible that the list is still in the empty(busy) state
8345 // we left it in a short while ago; in that case we may be
8346 // able to place back the suffix without incurring the cost
8347 // of a walk down the list.
8348 oop observed_overflow_list = _overflow_list;
8349 oop cur_overflow_list = observed_overflow_list;
8350 bool attached = false;
8351 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8352 observed_overflow_list =
8353 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8354 if (cur_overflow_list == observed_overflow_list) {
8355 attached = true;
8356 break;
8357 } else cur_overflow_list = observed_overflow_list;
8358 }
8359 if (!attached) {
8360 // Too bad, someone else sneaked in (at least) an element; we'll need
8361 // to do a splice. Find tail of suffix so we can prepend suffix to global
8362 // list.
8363 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8364 oop suffix_tail = cur;
8365 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8366 "Tautology");
8367 observed_overflow_list = _overflow_list;
8368 do {
8369 cur_overflow_list = observed_overflow_list;
8370 if (cur_overflow_list != BUSY) {
8371 // Do the splice ...
8372 suffix_tail->set_mark(markOop(cur_overflow_list));
8373 } else { // cur_overflow_list == BUSY
8374 suffix_tail->set_mark(NULL);
8375 }
8376 // ... and try to place spliced list back on overflow_list ...
8377 observed_overflow_list =
8378 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8379 } while (cur_overflow_list != observed_overflow_list);
8380 // ... until we have succeeded in doing so.
8381 }
8382 }
8383
8384 // Push the prefix elements on work_q
8385 assert(prefix != NULL, "control point invariant");
8386 const markOop proto = markOopDesc::prototype();
8387 oop next;
8388 NOT_PRODUCT(ssize_t n = 0;)
8389 for (cur = prefix; cur != NULL; cur = next) {
8390 next = oop(cur->mark());
8391 cur->set_mark(proto); // until proven otherwise
8392 assert(cur->is_oop(), "Should be an oop");
8393 bool res = work_q->push(cur);
8394 assert(res, "Bit off more than we can chew?");
8395 NOT_PRODUCT(n++;)
8396 }
8397 #ifndef PRODUCT
8398 assert(_num_par_pushes >= n, "Too many pops?");
8399 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8400 #endif
8401 return true;
8402 }
8403
8404 // Single-threaded
8405 void CMSCollector::push_on_overflow_list(oop p) {
8406 NOT_PRODUCT(_num_par_pushes++;)
8407 assert(p->is_oop(), "Not an oop");
8408 preserve_mark_if_necessary(p);
8409 p->set_mark((markOop)_overflow_list);
8410 _overflow_list = p;
8411 }
8412
8413 // Multi-threaded; use CAS to prepend to overflow list
8414 void CMSCollector::par_push_on_overflow_list(oop p) {
8415 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8416 assert(p->is_oop(), "Not an oop");
8417 par_preserve_mark_if_necessary(p);
8418 oop observed_overflow_list = _overflow_list;
8419 oop cur_overflow_list;
8420 do {
8421 cur_overflow_list = observed_overflow_list;
8422 if (cur_overflow_list != BUSY) {
8423 p->set_mark(markOop(cur_overflow_list));
8424 } else {
8425 p->set_mark(NULL);
8426 }
8427 observed_overflow_list =
8428 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8429 } while (cur_overflow_list != observed_overflow_list);
8430 }
8431 #undef BUSY
8432
8433 // Single threaded
8434 // General Note on GrowableArray: pushes may silently fail
8435 // because we are (temporarily) out of C-heap for expanding
8436 // the stack. The problem is quite ubiquitous and affects
8437 // a lot of code in the JVM. The prudent thing for GrowableArray
8438 // to do (for now) is to exit with an error. However, that may
8439 // be too draconian in some cases because the caller may be
8440 // able to recover without much harm. For such cases, we
8441 // should probably introduce a "soft_push" method which returns
8442 // an indication of success or failure with the assumption that
8443 // the caller may be able to recover from a failure; code in
8444 // the VM can then be changed, incrementally, to deal with such
8445 // failures where possible, thus, incrementally hardening the VM
8446 // in such low resource situations.
8447 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8448 _preserved_oop_stack.push(p);
8449 _preserved_mark_stack.push(m);
8450 assert(m == p->mark(), "Mark word changed");
8451 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8452 "bijection");
8453 }
8454
8455 // Single threaded
8456 void CMSCollector::preserve_mark_if_necessary(oop p) {
8457 markOop m = p->mark();
8458 if (m->must_be_preserved(p)) {
8459 preserve_mark_work(p, m);
8460 }
8461 }
8462
8463 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8464 markOop m = p->mark();
8465 if (m->must_be_preserved(p)) {
8466 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8467 // Even though we read the mark word without holding
8468 // the lock, we are assured that it will not change
8469 // because we "own" this oop, so no other thread can
8470 // be trying to push it on the overflow list; see
8471 // the assertion in preserve_mark_work() that checks
8472 // that m == p->mark().
8473 preserve_mark_work(p, m);
8474 }
8475 }
8476
8477 // We should be able to do this multi-threaded,
8478 // a chunk of stack being a task (this is
8479 // correct because each oop only ever appears
8480 // once in the overflow list. However, it's
8481 // not very easy to completely overlap this with
8482 // other operations, so will generally not be done
8483 // until all work's been completed. Because we
8484 // expect the preserved oop stack (set) to be small,
8485 // it's probably fine to do this single-threaded.
8486 // We can explore cleverer concurrent/overlapped/parallel
8487 // processing of preserved marks if we feel the
8488 // need for this in the future. Stack overflow should
8489 // be so rare in practice and, when it happens, its
8490 // effect on performance so great that this will
8491 // likely just be in the noise anyway.
8492 void CMSCollector::restore_preserved_marks_if_any() {
8493 assert(SafepointSynchronize::is_at_safepoint(),
8494 "world should be stopped");
8495 assert(Thread::current()->is_ConcurrentGC_thread() ||
8496 Thread::current()->is_VM_thread(),
8497 "should be single-threaded");
8498 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8499 "bijection");
8500
8501 while (!_preserved_oop_stack.is_empty()) {
8502 oop p = _preserved_oop_stack.pop();
8503 assert(p->is_oop(), "Should be an oop");
8504 assert(_span.contains(p), "oop should be in _span");
8505 assert(p->mark() == markOopDesc::prototype(),
8506 "Set when taken from overflow list");
8507 markOop m = _preserved_mark_stack.pop();
8508 p->set_mark(m);
8509 }
8510 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8511 "stacks were cleared above");
8512 }
8513
8514 #ifndef PRODUCT
8515 bool CMSCollector::no_preserved_marks() const {
8516 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8517 }
8518 #endif
8519
8520 // Transfer some number of overflown objects to usual marking
8521 // stack. Return true if some objects were transferred.
8522 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8523 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8524 (size_t)ParGCDesiredObjsFromOverflowList);
8525
8526 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8527 assert(_collector->overflow_list_is_empty() || res,
8528 "If list is not empty, we should have taken something");
8529 assert(!res || !_mark_stack->isEmpty(),
8530 "If we took something, it should now be on our stack");
8531 return res;
8532 }
8533
8534 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8535 size_t res = _sp->block_size_no_stall(addr, _collector);
8536 if (_sp->block_is_obj(addr)) {
8537 if (_live_bit_map->isMarked(addr)) {
8538 // It can't have been dead in a previous cycle
8539 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8540 } else {
8541 _dead_bit_map->mark(addr); // mark the dead object
8542 }
8543 }
8544 // Could be 0, if the block size could not be computed without stalling.
8545 return res;
8546 }
8547
8548 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8549
8550 switch (phase) {
8551 case CMSCollector::InitialMarking:
8552 initialize(true /* fullGC */ ,
8553 cause /* cause of the GC */,
8554 true /* recordGCBeginTime */,
8555 true /* recordPreGCUsage */,
8556 false /* recordPeakUsage */,
8557 false /* recordPostGCusage */,
8558 true /* recordAccumulatedGCTime */,
8559 false /* recordGCEndTime */,
8560 false /* countCollection */ );
8561 break;
8562
8563 case CMSCollector::FinalMarking:
8564 initialize(true /* fullGC */ ,
8565 cause /* cause of the GC */,
8566 false /* recordGCBeginTime */,
8567 false /* recordPreGCUsage */,
8568 false /* recordPeakUsage */,
8569 false /* recordPostGCusage */,
8570 true /* recordAccumulatedGCTime */,
8571 false /* recordGCEndTime */,
8572 false /* countCollection */ );
8573 break;
8574
8575 case CMSCollector::Sweeping:
8576 initialize(true /* fullGC */ ,
8577 cause /* cause of the GC */,
8578 false /* recordGCBeginTime */,
8579 false /* recordPreGCUsage */,
8580 true /* recordPeakUsage */,
8581 true /* recordPostGCusage */,
8582 false /* recordAccumulatedGCTime */,
8583 true /* recordGCEndTime */,
8584 true /* countCollection */ );
8585 break;
8586
8587 default:
8588 ShouldNotReachHere();
8589 }
8590 }