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