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