1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_old_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1,
310 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
358 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
359 if (cms_free > expected_promotion) {
360 // Start a cms collection if there isn't enough space to promote
361 // for the next young collection. Use the padded average as
362 // a safety factor.
363 cms_free -= expected_promotion;
364
365 // Adjust by the safety factor.
366 double cms_free_dbl = (double)cms_free;
367 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
368 // Apply a further correction factor which tries to adjust
369 // for recent occurance of concurrent mode failures.
370 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
371 cms_free_dbl = cms_free_dbl * cms_adjustment;
372
373 if (PrintGCDetails && Verbose) {
374 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
375 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
376 cms_free, expected_promotion);
377 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
378 cms_free_dbl, cms_consumption_rate() + 1.0);
379 }
380 // Add 1 in case the consumption rate goes to zero.
381 return cms_free_dbl / (cms_consumption_rate() + 1.0);
382 }
383 return 0.0;
384 }
385
386 // Compare the duration of the cms collection to the
387 // time remaining before the cms generation is empty.
388 // Note that the time from the start of the cms collection
389 // to the start of the cms sweep (less than the total
390 // duration of the cms collection) can be used. This
391 // has been tried and some applications experienced
392 // promotion failures early in execution. This was
393 // possibly because the averages were not accurate
394 // enough at the beginning.
395 double CMSStats::time_until_cms_start() const {
396 // We add "gc0_period" to the "work" calculation
397 // below because this query is done (mostly) at the
398 // end of a scavenge, so we need to conservatively
399 // account for that much possible delay
400 // in the query so as to avoid concurrent mode failures
401 // due to starting the collection just a wee bit too
402 // late.
403 double work = cms_duration() + gc0_period();
404 double deadline = time_until_cms_gen_full();
405 // If a concurrent mode failure occurred recently, we want to be
406 // more conservative and halve our expected time_until_cms_gen_full()
407 if (work > deadline) {
408 if (Verbose && PrintGCDetails) {
409 gclog_or_tty->print(
410 " CMSCollector: collect because of anticipated promotion "
411 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
412 gc0_period(), time_until_cms_gen_full());
413 }
414 return 0.0;
415 }
416 return work - deadline;
417 }
418
419 #ifndef PRODUCT
420 void CMSStats::print_on(outputStream *st) const {
421 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
422 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
423 gc0_duration(), gc0_period(), gc0_promoted());
424 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
425 cms_duration(), cms_period(), cms_allocated());
426 st->print(",cms_since_beg=%g,cms_since_end=%g",
427 cms_time_since_begin(), cms_time_since_end());
428 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
429 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
430
431 if (valid()) {
432 st->print(",promo_rate=%g,cms_alloc_rate=%g",
433 promotion_rate(), cms_allocation_rate());
434 st->print(",cms_consumption_rate=%g,time_until_full=%g",
435 cms_consumption_rate(), time_until_cms_gen_full());
436 }
437 st->print(" ");
438 }
439 #endif // #ifndef PRODUCT
440
441 CMSCollector::CollectorState CMSCollector::_collectorState =
442 CMSCollector::Idling;
443 bool CMSCollector::_foregroundGCIsActive = false;
444 bool CMSCollector::_foregroundGCShouldWait = false;
445
446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
447 CardTableRS* ct,
448 ConcurrentMarkSweepPolicy* cp):
449 _cmsGen(cmsGen),
450 _ct(ct),
451 _ref_processor(NULL), // will be set later
452 _conc_workers(NULL), // may be set later
453 _abort_preclean(false),
454 _start_sampling(false),
455 _between_prologue_and_epilogue(false),
456 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
457 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
458 -1 /* lock-free */, "No_lock" /* dummy */),
459 _modUnionClosurePar(&_modUnionTable),
460 // Adjust my span to cover old (cms) gen
461 _span(cmsGen->reserved()),
462 // Construct the is_alive_closure with _span & markBitMap
463 _is_alive_closure(_span, &_markBitMap),
464 _restart_addr(NULL),
465 _overflow_list(NULL),
466 _stats(cmsGen),
467 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
468 //verify that this lock should be acquired with safepoint check.
469 Monitor::_safepoint_check_sometimes)),
470 _eden_chunk_array(NULL), // may be set in ctor body
471 _eden_chunk_capacity(0), // -- ditto --
472 _eden_chunk_index(0), // -- ditto --
473 _survivor_plab_array(NULL), // -- ditto --
474 _survivor_chunk_array(NULL), // -- ditto --
475 _survivor_chunk_capacity(0), // -- ditto --
476 _survivor_chunk_index(0), // -- ditto --
477 _ser_pmc_preclean_ovflw(0),
478 _ser_kac_preclean_ovflw(0),
479 _ser_pmc_remark_ovflw(0),
480 _par_pmc_remark_ovflw(0),
481 _ser_kac_ovflw(0),
482 _par_kac_ovflw(0),
483 #ifndef PRODUCT
484 _num_par_pushes(0),
485 #endif
486 _collection_count_start(0),
487 _verifying(false),
488 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
489 _completed_initialization(false),
490 _collector_policy(cp),
491 _should_unload_classes(CMSClassUnloadingEnabled),
492 _concurrent_cycles_since_last_unload(0),
493 _roots_scanning_options(GenCollectedHeap::SO_None),
494 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
495 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
497 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
498 _cms_start_registered(false)
499 {
500 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
501 ExplicitGCInvokesConcurrent = true;
502 }
503 // Now expand the span and allocate the collection support structures
504 // (MUT, marking bit map etc.) to cover both generations subject to
505 // collection.
506
507 // For use by dirty card to oop closures.
508 _cmsGen->cmsSpace()->set_collector(this);
509
510 // Allocate MUT and marking bit map
511 {
512 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
513 if (!_markBitMap.allocate(_span)) {
514 warning("Failed to allocate CMS Bit Map");
515 return;
516 }
517 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
518 }
519 {
520 _modUnionTable.allocate(_span);
521 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
522 }
523
524 if (!_markStack.allocate(MarkStackSize)) {
525 warning("Failed to allocate CMS Marking Stack");
526 return;
527 }
528
529 // Support for multi-threaded concurrent phases
530 if (CMSConcurrentMTEnabled) {
531 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
532 // just for now
533 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
534 }
535 if (ConcGCThreads > 1) {
536 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
537 ConcGCThreads, true);
538 if (_conc_workers == NULL) {
539 warning("GC/CMS: _conc_workers allocation failure: "
540 "forcing -CMSConcurrentMTEnabled");
541 CMSConcurrentMTEnabled = false;
542 } else {
543 _conc_workers->initialize_workers();
544 }
545 } else {
546 CMSConcurrentMTEnabled = false;
547 }
548 }
549 if (!CMSConcurrentMTEnabled) {
550 ConcGCThreads = 0;
551 } else {
552 // Turn off CMSCleanOnEnter optimization temporarily for
553 // the MT case where it's not fixed yet; see 6178663.
554 CMSCleanOnEnter = false;
555 }
556 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
557 "Inconsistency");
558
559 // Parallel task queues; these are shared for the
560 // concurrent and stop-world phases of CMS, but
561 // are not shared with parallel scavenge (ParNew).
562 {
563 uint i;
564 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
565
566 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
567 || ParallelRefProcEnabled)
568 && num_queues > 0) {
569 _task_queues = new OopTaskQueueSet(num_queues);
570 if (_task_queues == NULL) {
571 warning("task_queues allocation failure.");
572 return;
573 }
574 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
575 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
576 for (i = 0; i < num_queues; i++) {
577 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
578 if (q == NULL) {
579 warning("work_queue allocation failure.");
580 return;
581 }
582 _task_queues->register_queue(i, q);
583 }
584 for (i = 0; i < num_queues; i++) {
585 _task_queues->queue(i)->initialize();
586 _hash_seed[i] = 17; // copied from ParNew
587 }
588 }
589 }
590
591 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
592
593 // Clip CMSBootstrapOccupancy between 0 and 100.
594 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
595
596 // Now tell CMS generations the identity of their collector
597 ConcurrentMarkSweepGeneration::set_collector(this);
598
599 // Create & start a CMS thread for this CMS collector
600 _cmsThread = ConcurrentMarkSweepThread::start(this);
601 assert(cmsThread() != NULL, "CMS Thread should have been created");
602 assert(cmsThread()->collector() == this,
603 "CMS Thread should refer to this gen");
604 assert(CGC_lock != NULL, "Where's the CGC_lock?");
605
606 // Support for parallelizing young gen rescan
607 GenCollectedHeap* gch = GenCollectedHeap::heap();
608 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
609 _young_gen = (ParNewGeneration*)gch->young_gen();
610 if (gch->supports_inline_contig_alloc()) {
611 _top_addr = gch->top_addr();
612 _end_addr = gch->end_addr();
613 assert(_young_gen != NULL, "no _young_gen");
614 _eden_chunk_index = 0;
615 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
616 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
617 }
618
619 // Support for parallelizing survivor space rescan
620 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
621 const size_t max_plab_samples =
622 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
623
624 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
625 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
627 _survivor_chunk_capacity = max_plab_samples;
628 for (uint i = 0; i < ParallelGCThreads; i++) {
629 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
631 assert(cur->end() == 0, "Should be 0");
632 assert(cur->array() == vec, "Should be vec");
633 assert(cur->capacity() == max_plab_samples, "Error");
634 }
635 }
636
637 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
638 _gc_counters = new CollectorCounters("CMS", 1);
639 _completed_initialization = true;
640 _inter_sweep_timer.start(); // start of time
641 }
642
643 const char* ConcurrentMarkSweepGeneration::name() const {
644 return "concurrent mark-sweep generation";
645 }
646 void ConcurrentMarkSweepGeneration::update_counters() {
647 if (UsePerfData) {
648 _space_counters->update_all();
649 _gen_counters->update_all();
650 }
651 }
652
653 // this is an optimized version of update_counters(). it takes the
654 // used value as a parameter rather than computing it.
655 //
656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
657 if (UsePerfData) {
658 _space_counters->update_used(used);
659 _space_counters->update_capacity();
660 _gen_counters->update_all();
661 }
662 }
663
664 void ConcurrentMarkSweepGeneration::print() const {
665 Generation::print();
666 cmsSpace()->print();
667 }
668
669 #ifndef PRODUCT
670 void ConcurrentMarkSweepGeneration::print_statistics() {
671 cmsSpace()->printFLCensus(0);
672 }
673 #endif
674
675 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
676 GenCollectedHeap* gch = GenCollectedHeap::heap();
677 if (PrintGCDetails) {
678 // I didn't want to change the logging when removing the level concept,
679 // but I guess this logging could say "old" or something instead of "1".
680 assert(gch->is_old_gen(this),
681 "The CMS generation should be the old generation");
682 uint level = 1;
683 if (Verbose) {
684 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
685 level, short_name(), s, used(), capacity());
686 } else {
687 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
688 level, short_name(), s, used() / K, capacity() / K);
689 }
690 }
691 if (Verbose) {
692 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
693 gch->used(), gch->capacity());
694 } else {
695 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
696 gch->used() / K, gch->capacity() / K);
697 }
698 }
699
700 size_t
701 ConcurrentMarkSweepGeneration::contiguous_available() const {
702 // dld proposes an improvement in precision here. If the committed
703 // part of the space ends in a free block we should add that to
704 // uncommitted size in the calculation below. Will make this
705 // change later, staying with the approximation below for the
706 // time being. -- ysr.
707 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
708 }
709
710 size_t
711 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
712 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
713 }
714
715 size_t ConcurrentMarkSweepGeneration::max_available() const {
716 return free() + _virtual_space.uncommitted_size();
717 }
718
719 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
720 size_t available = max_available();
721 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
722 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
723 if (Verbose && PrintGCDetails) {
724 gclog_or_tty->print_cr(
725 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
726 "max_promo(" SIZE_FORMAT ")",
727 res? "":" not", available, res? ">=":"<",
728 av_promo, max_promotion_in_bytes);
729 }
730 return res;
731 }
732
733 // At a promotion failure dump information on block layout in heap
734 // (cms old generation).
735 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
736 if (CMSDumpAtPromotionFailure) {
737 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
738 }
739 }
740
741 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
742 // Clear the promotion information. These pointers can be adjusted
743 // along with all the other pointers into the heap but
744 // compaction is expected to be a rare event with
745 // a heap using cms so don't do it without seeing the need.
746 for (uint i = 0; i < ParallelGCThreads; i++) {
747 _par_gc_thread_states[i]->promo.reset();
748 }
749 }
750
751 void ConcurrentMarkSweepGeneration::compute_new_size() {
752 assert_locked_or_safepoint(Heap_lock);
753
754 // If incremental collection failed, we just want to expand
755 // to the limit.
756 if (incremental_collection_failed()) {
757 clear_incremental_collection_failed();
758 grow_to_reserved();
759 return;
760 }
761
762 // The heap has been compacted but not reset yet.
763 // Any metric such as free() or used() will be incorrect.
764
765 CardGeneration::compute_new_size();
766
767 // Reset again after a possible resizing
768 if (did_compact()) {
769 cmsSpace()->reset_after_compaction();
770 }
771 }
772
773 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
774 assert_locked_or_safepoint(Heap_lock);
775
776 // If incremental collection failed, we just want to expand
777 // to the limit.
778 if (incremental_collection_failed()) {
779 clear_incremental_collection_failed();
780 grow_to_reserved();
781 return;
782 }
783
784 double free_percentage = ((double) free()) / capacity();
785 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
786 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
787
788 // compute expansion delta needed for reaching desired free percentage
789 if (free_percentage < desired_free_percentage) {
790 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
791 assert(desired_capacity >= capacity(), "invalid expansion size");
792 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
793 if (PrintGCDetails && Verbose) {
794 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
795 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
796 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
797 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
798 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
799 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
800 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
801 GenCollectedHeap* gch = GenCollectedHeap::heap();
802 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
803 size_t young_size = gch->young_gen()->capacity();
804 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
805 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
806 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
807 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
808 }
809 // safe if expansion fails
810 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
811 if (PrintGCDetails && Verbose) {
812 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
813 }
814 } else {
815 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
816 assert(desired_capacity <= capacity(), "invalid expansion size");
817 size_t shrink_bytes = capacity() - desired_capacity;
818 // Don't shrink unless the delta is greater than the minimum shrink we want
819 if (shrink_bytes >= MinHeapDeltaBytes) {
820 shrink_free_list_by(shrink_bytes);
821 }
822 }
823 }
824
825 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
826 return cmsSpace()->freelistLock();
827 }
828
829 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
830 CMSSynchronousYieldRequest yr;
831 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
832 return have_lock_and_allocate(size, tlab);
833 }
834
835 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
836 bool tlab /* ignored */) {
837 assert_lock_strong(freelistLock());
838 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
839 HeapWord* res = cmsSpace()->allocate(adjustedSize);
840 // Allocate the object live (grey) if the background collector has
841 // started marking. This is necessary because the marker may
842 // have passed this address and consequently this object will
843 // not otherwise be greyed and would be incorrectly swept up.
844 // Note that if this object contains references, the writing
845 // of those references will dirty the card containing this object
846 // allowing the object to be blackened (and its references scanned)
847 // either during a preclean phase or at the final checkpoint.
848 if (res != NULL) {
849 // We may block here with an uninitialized object with
850 // its mark-bit or P-bits not yet set. Such objects need
851 // to be safely navigable by block_start().
852 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
853 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
854 collector()->direct_allocated(res, adjustedSize);
855 _direct_allocated_words += adjustedSize;
856 // allocation counters
857 NOT_PRODUCT(
858 _numObjectsAllocated++;
859 _numWordsAllocated += (int)adjustedSize;
860 )
861 }
862 return res;
863 }
864
865 // In the case of direct allocation by mutators in a generation that
866 // is being concurrently collected, the object must be allocated
867 // live (grey) if the background collector has started marking.
868 // This is necessary because the marker may
869 // have passed this address and consequently this object will
870 // not otherwise be greyed and would be incorrectly swept up.
871 // Note that if this object contains references, the writing
872 // of those references will dirty the card containing this object
873 // allowing the object to be blackened (and its references scanned)
874 // either during a preclean phase or at the final checkpoint.
875 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
876 assert(_markBitMap.covers(start, size), "Out of bounds");
877 if (_collectorState >= Marking) {
878 MutexLockerEx y(_markBitMap.lock(),
879 Mutex::_no_safepoint_check_flag);
880 // [see comments preceding SweepClosure::do_blk() below for details]
881 //
882 // Can the P-bits be deleted now? JJJ
883 //
884 // 1. need to mark the object as live so it isn't collected
885 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
886 // 3. need to mark the end of the object so marking, precleaning or sweeping
887 // can skip over uninitialized or unparsable objects. An allocated
888 // object is considered uninitialized for our purposes as long as
889 // its klass word is NULL. All old gen objects are parsable
890 // as soon as they are initialized.)
891 _markBitMap.mark(start); // object is live
892 _markBitMap.mark(start + 1); // object is potentially uninitialized?
893 _markBitMap.mark(start + size - 1);
894 // mark end of object
895 }
896 // check that oop looks uninitialized
897 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
898 }
899
900 void CMSCollector::promoted(bool par, HeapWord* start,
901 bool is_obj_array, size_t obj_size) {
902 assert(_markBitMap.covers(start), "Out of bounds");
903 // See comment in direct_allocated() about when objects should
904 // be allocated live.
905 if (_collectorState >= Marking) {
906 // we already hold the marking bit map lock, taken in
907 // the prologue
908 if (par) {
909 _markBitMap.par_mark(start);
910 } else {
911 _markBitMap.mark(start);
912 }
913 // We don't need to mark the object as uninitialized (as
914 // in direct_allocated above) because this is being done with the
915 // world stopped and the object will be initialized by the
916 // time the marking, precleaning or sweeping get to look at it.
917 // But see the code for copying objects into the CMS generation,
918 // where we need to ensure that concurrent readers of the
919 // block offset table are able to safely navigate a block that
920 // is in flux from being free to being allocated (and in
921 // transition while being copied into) and subsequently
922 // becoming a bona-fide object when the copy/promotion is complete.
923 assert(SafepointSynchronize::is_at_safepoint(),
924 "expect promotion only at safepoints");
925
926 if (_collectorState < Sweeping) {
927 // Mark the appropriate cards in the modUnionTable, so that
928 // this object gets scanned before the sweep. If this is
929 // not done, CMS generation references in the object might
930 // not get marked.
931 // For the case of arrays, which are otherwise precisely
932 // marked, we need to dirty the entire array, not just its head.
933 if (is_obj_array) {
934 // The [par_]mark_range() method expects mr.end() below to
935 // be aligned to the granularity of a bit's representation
936 // in the heap. In the case of the MUT below, that's a
937 // card size.
938 MemRegion mr(start,
939 (HeapWord*)round_to((intptr_t)(start + obj_size),
940 CardTableModRefBS::card_size /* bytes */));
941 if (par) {
942 _modUnionTable.par_mark_range(mr);
943 } else {
944 _modUnionTable.mark_range(mr);
945 }
946 } else { // not an obj array; we can just mark the head
947 if (par) {
948 _modUnionTable.par_mark(start);
949 } else {
950 _modUnionTable.mark(start);
951 }
952 }
953 }
954 }
955 }
956
957 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
958 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
959 // allocate, copy and if necessary update promoinfo --
960 // delegate to underlying space.
961 assert_lock_strong(freelistLock());
962
963 #ifndef PRODUCT
964 if (GenCollectedHeap::heap()->promotion_should_fail()) {
965 return NULL;
966 }
967 #endif // #ifndef PRODUCT
968
969 oop res = _cmsSpace->promote(obj, obj_size);
970 if (res == NULL) {
971 // expand and retry
972 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
973 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
974 // Since this is the old generation, we don't try to promote
975 // into a more senior generation.
976 res = _cmsSpace->promote(obj, obj_size);
977 }
978 if (res != NULL) {
979 // See comment in allocate() about when objects should
980 // be allocated live.
981 assert(obj->is_oop(), "Will dereference klass pointer below");
982 collector()->promoted(false, // Not parallel
983 (HeapWord*)res, obj->is_objArray(), obj_size);
984 // promotion counters
985 NOT_PRODUCT(
986 _numObjectsPromoted++;
987 _numWordsPromoted +=
988 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
989 )
990 }
991 return res;
992 }
993
994
995 // IMPORTANT: Notes on object size recognition in CMS.
996 // ---------------------------------------------------
997 // A block of storage in the CMS generation is always in
998 // one of three states. A free block (FREE), an allocated
999 // object (OBJECT) whose size() method reports the correct size,
1000 // and an intermediate state (TRANSIENT) in which its size cannot
1001 // be accurately determined.
1002 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1003 // -----------------------------------------------------
1004 // FREE: klass_word & 1 == 1; mark_word holds block size
1005 //
1006 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1007 // obj->size() computes correct size
1008 //
1009 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1010 //
1011 // STATE IDENTIFICATION: (64 bit+COOPS)
1012 // ------------------------------------
1013 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1014 //
1015 // OBJECT: klass_word installed; klass_word != 0;
1016 // obj->size() computes correct size
1017 //
1018 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1019 //
1020 //
1021 // STATE TRANSITION DIAGRAM
1022 //
1023 // mut / parnew mut / parnew
1024 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1025 // ^ |
1026 // |------------------------ DEAD <------------------------------------|
1027 // sweep mut
1028 //
1029 // While a block is in TRANSIENT state its size cannot be determined
1030 // so readers will either need to come back later or stall until
1031 // the size can be determined. Note that for the case of direct
1032 // allocation, P-bits, when available, may be used to determine the
1033 // size of an object that may not yet have been initialized.
1034
1035 // Things to support parallel young-gen collection.
1036 oop
1037 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1038 oop old, markOop m,
1039 size_t word_sz) {
1040 #ifndef PRODUCT
1041 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1042 return NULL;
1043 }
1044 #endif // #ifndef PRODUCT
1045
1046 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1047 PromotionInfo* promoInfo = &ps->promo;
1048 // if we are tracking promotions, then first ensure space for
1049 // promotion (including spooling space for saving header if necessary).
1050 // then allocate and copy, then track promoted info if needed.
1051 // When tracking (see PromotionInfo::track()), the mark word may
1052 // be displaced and in this case restoration of the mark word
1053 // occurs in the (oop_since_save_marks_)iterate phase.
1054 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1055 // Out of space for allocating spooling buffers;
1056 // try expanding and allocating spooling buffers.
1057 if (!expand_and_ensure_spooling_space(promoInfo)) {
1058 return NULL;
1059 }
1060 }
1061 assert(promoInfo->has_spooling_space(), "Control point invariant");
1062 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1063 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1064 if (obj_ptr == NULL) {
1065 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1066 if (obj_ptr == NULL) {
1067 return NULL;
1068 }
1069 }
1070 oop obj = oop(obj_ptr);
1071 OrderAccess::storestore();
1072 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074 // IMPORTANT: See note on object initialization for CMS above.
1075 // Otherwise, copy the object. Here we must be careful to insert the
1076 // klass pointer last, since this marks the block as an allocated object.
1077 // Except with compressed oops it's the mark word.
1078 HeapWord* old_ptr = (HeapWord*)old;
1079 // Restore the mark word copied above.
1080 obj->set_mark(m);
1081 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083 OrderAccess::storestore();
1084
1085 if (UseCompressedClassPointers) {
1086 // Copy gap missed by (aligned) header size calculation below
1087 obj->set_klass_gap(old->klass_gap());
1088 }
1089 if (word_sz > (size_t)oopDesc::header_size()) {
1090 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1091 obj_ptr + oopDesc::header_size(),
1092 word_sz - oopDesc::header_size());
1093 }
1094
1095 // Now we can track the promoted object, if necessary. We take care
1096 // to delay the transition from uninitialized to full object
1097 // (i.e., insertion of klass pointer) until after, so that it
1098 // atomically becomes a promoted object.
1099 if (promoInfo->tracking()) {
1100 promoInfo->track((PromotedObject*)obj, old->klass());
1101 }
1102 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1103 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1104 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1105
1106 // Finally, install the klass pointer (this should be volatile).
1107 OrderAccess::storestore();
1108 obj->set_klass(old->klass());
1109 // We should now be able to calculate the right size for this object
1110 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1111
1112 collector()->promoted(true, // parallel
1113 obj_ptr, old->is_objArray(), word_sz);
1114
1115 NOT_PRODUCT(
1116 Atomic::inc_ptr(&_numObjectsPromoted);
1117 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1118 )
1119
1120 return obj;
1121 }
1122
1123 void
1124 ConcurrentMarkSweepGeneration::
1125 par_promote_alloc_done(int thread_num) {
1126 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1127 ps->lab.retire(thread_num);
1128 }
1129
1130 void
1131 ConcurrentMarkSweepGeneration::
1132 par_oop_since_save_marks_iterate_done(int thread_num) {
1133 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1134 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1135 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1136 }
1137
1138 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1139 size_t size,
1140 bool tlab)
1141 {
1142 // We allow a STW collection only if a full
1143 // collection was requested.
1144 return full || should_allocate(size, tlab); // FIX ME !!!
1145 // This and promotion failure handling are connected at the
1146 // hip and should be fixed by untying them.
1147 }
1148
1149 bool CMSCollector::shouldConcurrentCollect() {
1150 if (_full_gc_requested) {
1151 if (Verbose && PrintGCDetails) {
1152 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1153 " gc request (or gc_locker)");
1154 }
1155 return true;
1156 }
1157
1158 FreelistLocker x(this);
1159 // ------------------------------------------------------------------
1160 // Print out lots of information which affects the initiation of
1161 // a collection.
1162 if (PrintCMSInitiationStatistics && stats().valid()) {
1163 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1164 gclog_or_tty->stamp();
1165 gclog_or_tty->cr();
1166 stats().print_on(gclog_or_tty);
1167 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1168 stats().time_until_cms_gen_full());
1169 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1170 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1171 _cmsGen->contiguous_available());
1172 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1173 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1174 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1175 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1176 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1177 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1178 gclog_or_tty->print_cr("metadata initialized %d",
1179 MetaspaceGC::should_concurrent_collect());
1180 }
1181 // ------------------------------------------------------------------
1182
1183 // If the estimated time to complete a cms collection (cms_duration())
1184 // is less than the estimated time remaining until the cms generation
1185 // is full, start a collection.
1186 if (!UseCMSInitiatingOccupancyOnly) {
1187 if (stats().valid()) {
1188 if (stats().time_until_cms_start() == 0.0) {
1189 return true;
1190 }
1191 } else {
1192 // We want to conservatively collect somewhat early in order
1193 // to try and "bootstrap" our CMS/promotion statistics;
1194 // this branch will not fire after the first successful CMS
1195 // collection because the stats should then be valid.
1196 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1197 if (Verbose && PrintGCDetails) {
1198 gclog_or_tty->print_cr(
1199 " CMSCollector: collect for bootstrapping statistics:"
1200 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1201 _bootstrap_occupancy);
1202 }
1203 return true;
1204 }
1205 }
1206 }
1207
1208 // Otherwise, we start a collection cycle if
1209 // old gen want a collection cycle started. Each may use
1210 // an appropriate criterion for making this decision.
1211 // XXX We need to make sure that the gen expansion
1212 // criterion dovetails well with this. XXX NEED TO FIX THIS
1213 if (_cmsGen->should_concurrent_collect()) {
1214 if (Verbose && PrintGCDetails) {
1215 gclog_or_tty->print_cr("CMS old gen initiated");
1216 }
1217 return true;
1218 }
1219
1220 // We start a collection if we believe an incremental collection may fail;
1221 // this is not likely to be productive in practice because it's probably too
1222 // late anyway.
1223 GenCollectedHeap* gch = GenCollectedHeap::heap();
1224 assert(gch->collector_policy()->is_generation_policy(),
1225 "You may want to check the correctness of the following");
1226 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1227 if (Verbose && PrintGCDetails) {
1228 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1229 }
1230 return true;
1231 }
1232
1233 if (MetaspaceGC::should_concurrent_collect()) {
1234 if (Verbose && PrintGCDetails) {
1235 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1236 }
1237 return true;
1238 }
1239
1240 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1241 if (CMSTriggerInterval >= 0) {
1242 if (CMSTriggerInterval == 0) {
1243 // Trigger always
1244 return true;
1245 }
1246
1247 // Check the CMS time since begin (we do not check the stats validity
1248 // as we want to be able to trigger the first CMS cycle as well)
1249 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1250 if (Verbose && PrintGCDetails) {
1251 if (stats().valid()) {
1252 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1253 stats().cms_time_since_begin());
1254 } else {
1255 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1256 }
1257 }
1258 return true;
1259 }
1260 }
1261
1262 return false;
1263 }
1264
1265 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1266
1267 // Clear _expansion_cause fields of constituent generations
1268 void CMSCollector::clear_expansion_cause() {
1269 _cmsGen->clear_expansion_cause();
1270 }
1271
1272 // We should be conservative in starting a collection cycle. To
1273 // start too eagerly runs the risk of collecting too often in the
1274 // extreme. To collect too rarely falls back on full collections,
1275 // which works, even if not optimum in terms of concurrent work.
1276 // As a work around for too eagerly collecting, use the flag
1277 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1278 // giving the user an easily understandable way of controlling the
1279 // collections.
1280 // We want to start a new collection cycle if any of the following
1281 // conditions hold:
1282 // . our current occupancy exceeds the configured initiating occupancy
1283 // for this generation, or
1284 // . we recently needed to expand this space and have not, since that
1285 // expansion, done a collection of this generation, or
1286 // . the underlying space believes that it may be a good idea to initiate
1287 // a concurrent collection (this may be based on criteria such as the
1288 // following: the space uses linear allocation and linear allocation is
1289 // going to fail, or there is believed to be excessive fragmentation in
1290 // the generation, etc... or ...
1291 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1292 // the case of the old generation; see CR 6543076):
1293 // we may be approaching a point at which allocation requests may fail because
1294 // we will be out of sufficient free space given allocation rate estimates.]
1295 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1296
1297 assert_lock_strong(freelistLock());
1298 if (occupancy() > initiating_occupancy()) {
1299 if (PrintGCDetails && Verbose) {
1300 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1301 short_name(), occupancy(), initiating_occupancy());
1302 }
1303 return true;
1304 }
1305 if (UseCMSInitiatingOccupancyOnly) {
1306 return false;
1307 }
1308 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1309 if (PrintGCDetails && Verbose) {
1310 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1311 short_name());
1312 }
1313 return true;
1314 }
1315 if (_cmsSpace->should_concurrent_collect()) {
1316 if (PrintGCDetails && Verbose) {
1317 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1318 short_name());
1319 }
1320 return true;
1321 }
1322 return false;
1323 }
1324
1325 void ConcurrentMarkSweepGeneration::collect(bool full,
1326 bool clear_all_soft_refs,
1327 size_t size,
1328 bool tlab)
1329 {
1330 collector()->collect(full, clear_all_soft_refs, size, tlab);
1331 }
1332
1333 void CMSCollector::collect(bool full,
1334 bool clear_all_soft_refs,
1335 size_t size,
1336 bool tlab)
1337 {
1338 // The following "if" branch is present for defensive reasons.
1339 // In the current uses of this interface, it can be replaced with:
1340 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1341 // But I am not placing that assert here to allow future
1342 // generality in invoking this interface.
1343 if (GC_locker::is_active()) {
1344 // A consistency test for GC_locker
1345 assert(GC_locker::needs_gc(), "Should have been set already");
1346 // Skip this foreground collection, instead
1347 // expanding the heap if necessary.
1348 // Need the free list locks for the call to free() in compute_new_size()
1349 compute_new_size();
1350 return;
1351 }
1352 acquire_control_and_collect(full, clear_all_soft_refs);
1353 }
1354
1355 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1356 GenCollectedHeap* gch = GenCollectedHeap::heap();
1357 unsigned int gc_count = gch->total_full_collections();
1358 if (gc_count == full_gc_count) {
1359 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1360 _full_gc_requested = true;
1361 _full_gc_cause = cause;
1362 CGC_lock->notify(); // nudge CMS thread
1363 } else {
1364 assert(gc_count > full_gc_count, "Error: causal loop");
1365 }
1366 }
1367
1368 bool CMSCollector::is_external_interruption() {
1369 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1370 return GCCause::is_user_requested_gc(cause) ||
1371 GCCause::is_serviceability_requested_gc(cause);
1372 }
1373
1374 void CMSCollector::report_concurrent_mode_interruption() {
1375 if (is_external_interruption()) {
1376 if (PrintGCDetails) {
1377 gclog_or_tty->print(" (concurrent mode interrupted)");
1378 }
1379 } else {
1380 if (PrintGCDetails) {
1381 gclog_or_tty->print(" (concurrent mode failure)");
1382 }
1383 _gc_tracer_cm->report_concurrent_mode_failure();
1384 }
1385 }
1386
1387
1388 // The foreground and background collectors need to coordinate in order
1389 // to make sure that they do not mutually interfere with CMS collections.
1390 // When a background collection is active,
1391 // the foreground collector may need to take over (preempt) and
1392 // synchronously complete an ongoing collection. Depending on the
1393 // frequency of the background collections and the heap usage
1394 // of the application, this preemption can be seldom or frequent.
1395 // There are only certain
1396 // points in the background collection that the "collection-baton"
1397 // can be passed to the foreground collector.
1398 //
1399 // The foreground collector will wait for the baton before
1400 // starting any part of the collection. The foreground collector
1401 // will only wait at one location.
1402 //
1403 // The background collector will yield the baton before starting a new
1404 // phase of the collection (e.g., before initial marking, marking from roots,
1405 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1406 // of the loop which switches the phases. The background collector does some
1407 // of the phases (initial mark, final re-mark) with the world stopped.
1408 // Because of locking involved in stopping the world,
1409 // the foreground collector should not block waiting for the background
1410 // collector when it is doing a stop-the-world phase. The background
1411 // collector will yield the baton at an additional point just before
1412 // it enters a stop-the-world phase. Once the world is stopped, the
1413 // background collector checks the phase of the collection. If the
1414 // phase has not changed, it proceeds with the collection. If the
1415 // phase has changed, it skips that phase of the collection. See
1416 // the comments on the use of the Heap_lock in collect_in_background().
1417 //
1418 // Variable used in baton passing.
1419 // _foregroundGCIsActive - Set to true by the foreground collector when
1420 // it wants the baton. The foreground clears it when it has finished
1421 // the collection.
1422 // _foregroundGCShouldWait - Set to true by the background collector
1423 // when it is running. The foreground collector waits while
1424 // _foregroundGCShouldWait is true.
1425 // CGC_lock - monitor used to protect access to the above variables
1426 // and to notify the foreground and background collectors.
1427 // _collectorState - current state of the CMS collection.
1428 //
1429 // The foreground collector
1430 // acquires the CGC_lock
1431 // sets _foregroundGCIsActive
1432 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1433 // various locks acquired in preparation for the collection
1434 // are released so as not to block the background collector
1435 // that is in the midst of a collection
1436 // proceeds with the collection
1437 // clears _foregroundGCIsActive
1438 // returns
1439 //
1440 // The background collector in a loop iterating on the phases of the
1441 // collection
1442 // acquires the CGC_lock
1443 // sets _foregroundGCShouldWait
1444 // if _foregroundGCIsActive is set
1445 // clears _foregroundGCShouldWait, notifies _CGC_lock
1446 // waits on _CGC_lock for _foregroundGCIsActive to become false
1447 // and exits the loop.
1448 // otherwise
1449 // proceed with that phase of the collection
1450 // if the phase is a stop-the-world phase,
1451 // yield the baton once more just before enqueueing
1452 // the stop-world CMS operation (executed by the VM thread).
1453 // returns after all phases of the collection are done
1454 //
1455
1456 void CMSCollector::acquire_control_and_collect(bool full,
1457 bool clear_all_soft_refs) {
1458 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1459 assert(!Thread::current()->is_ConcurrentGC_thread(),
1460 "shouldn't try to acquire control from self!");
1461
1462 // Start the protocol for acquiring control of the
1463 // collection from the background collector (aka CMS thread).
1464 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465 "VM thread should have CMS token");
1466 // Remember the possibly interrupted state of an ongoing
1467 // concurrent collection
1468 CollectorState first_state = _collectorState;
1469
1470 // Signal to a possibly ongoing concurrent collection that
1471 // we want to do a foreground collection.
1472 _foregroundGCIsActive = true;
1473
1474 // release locks and wait for a notify from the background collector
1475 // releasing the locks in only necessary for phases which
1476 // do yields to improve the granularity of the collection.
1477 assert_lock_strong(bitMapLock());
1478 // We need to lock the Free list lock for the space that we are
1479 // currently collecting.
1480 assert(haveFreelistLocks(), "Must be holding free list locks");
1481 bitMapLock()->unlock();
1482 releaseFreelistLocks();
1483 {
1484 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1485 if (_foregroundGCShouldWait) {
1486 // We are going to be waiting for action for the CMS thread;
1487 // it had better not be gone (for instance at shutdown)!
1488 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1489 "CMS thread must be running");
1490 // Wait here until the background collector gives us the go-ahead
1491 ConcurrentMarkSweepThread::clear_CMS_flag(
1492 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1493 // Get a possibly blocked CMS thread going:
1494 // Note that we set _foregroundGCIsActive true above,
1495 // without protection of the CGC_lock.
1496 CGC_lock->notify();
1497 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1498 "Possible deadlock");
1499 while (_foregroundGCShouldWait) {
1500 // wait for notification
1501 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1502 // Possibility of delay/starvation here, since CMS token does
1503 // not know to give priority to VM thread? Actually, i think
1504 // there wouldn't be any delay/starvation, but the proof of
1505 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1506 }
1507 ConcurrentMarkSweepThread::set_CMS_flag(
1508 ConcurrentMarkSweepThread::CMS_vm_has_token);
1509 }
1510 }
1511 // The CMS_token is already held. Get back the other locks.
1512 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1513 "VM thread should have CMS token");
1514 getFreelistLocks();
1515 bitMapLock()->lock_without_safepoint_check();
1516 if (TraceCMSState) {
1517 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1518 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1519 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1520 }
1521
1522 // Inform cms gen if this was due to partial collection failing.
1523 // The CMS gen may use this fact to determine its expansion policy.
1524 GenCollectedHeap* gch = GenCollectedHeap::heap();
1525 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1526 assert(!_cmsGen->incremental_collection_failed(),
1527 "Should have been noticed, reacted to and cleared");
1528 _cmsGen->set_incremental_collection_failed();
1529 }
1530
1531 if (first_state > Idling) {
1532 report_concurrent_mode_interruption();
1533 }
1534
1535 set_did_compact(true);
1536
1537 // If the collection is being acquired from the background
1538 // collector, there may be references on the discovered
1539 // references lists. Abandon those references, since some
1540 // of them may have become unreachable after concurrent
1541 // discovery; the STW compacting collector will redo discovery
1542 // more precisely, without being subject to floating garbage.
1543 // Leaving otherwise unreachable references in the discovered
1544 // lists would require special handling.
1545 ref_processor()->disable_discovery();
1546 ref_processor()->abandon_partial_discovery();
1547 ref_processor()->verify_no_references_recorded();
1548
1549 if (first_state > Idling) {
1550 save_heap_summary();
1551 }
1552
1553 do_compaction_work(clear_all_soft_refs);
1554
1555 // Has the GC time limit been exceeded?
1556 size_t max_eden_size = _young_gen->max_capacity() -
1557 _young_gen->to()->capacity() -
1558 _young_gen->from()->capacity();
1559 GCCause::Cause gc_cause = gch->gc_cause();
1560 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1561 _young_gen->eden()->used(),
1562 _cmsGen->max_capacity(),
1563 max_eden_size,
1564 full,
1565 gc_cause,
1566 gch->collector_policy());
1567
1568 // Reset the expansion cause, now that we just completed
1569 // a collection cycle.
1570 clear_expansion_cause();
1571 _foregroundGCIsActive = false;
1572 return;
1573 }
1574
1575 // Resize the tenured generation
1576 // after obtaining the free list locks for the
1577 // two generations.
1578 void CMSCollector::compute_new_size() {
1579 assert_locked_or_safepoint(Heap_lock);
1580 FreelistLocker z(this);
1581 MetaspaceGC::compute_new_size();
1582 _cmsGen->compute_new_size_free_list();
1583 }
1584
1585 // A work method used by the foreground collector to do
1586 // a mark-sweep-compact.
1587 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1588 GenCollectedHeap* gch = GenCollectedHeap::heap();
1589
1590 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1591 gc_timer->register_gc_start();
1592
1593 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1594 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1595
1596 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1597
1598 // Temporarily widen the span of the weak reference processing to
1599 // the entire heap.
1600 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1601 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1602 // Temporarily, clear the "is_alive_non_header" field of the
1603 // reference processor.
1604 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1605 // Temporarily make reference _processing_ single threaded (non-MT).
1606 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1607 // Temporarily make refs discovery atomic
1608 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1609 // Temporarily make reference _discovery_ single threaded (non-MT)
1610 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1611
1612 ref_processor()->set_enqueuing_is_done(false);
1613 ref_processor()->enable_discovery();
1614 ref_processor()->setup_policy(clear_all_soft_refs);
1615 // If an asynchronous collection finishes, the _modUnionTable is
1616 // all clear. If we are assuming the collection from an asynchronous
1617 // collection, clear the _modUnionTable.
1618 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1619 "_modUnionTable should be clear if the baton was not passed");
1620 _modUnionTable.clear_all();
1621 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1622 "mod union for klasses should be clear if the baton was passed");
1623 _ct->klass_rem_set()->clear_mod_union();
1624
1625 // We must adjust the allocation statistics being maintained
1626 // in the free list space. We do so by reading and clearing
1627 // the sweep timer and updating the block flux rate estimates below.
1628 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1629 if (_inter_sweep_timer.is_active()) {
1630 _inter_sweep_timer.stop();
1631 // Note that we do not use this sample to update the _inter_sweep_estimate.
1632 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1633 _inter_sweep_estimate.padded_average(),
1634 _intra_sweep_estimate.padded_average());
1635 }
1636
1637 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1638 #ifdef ASSERT
1639 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1640 size_t free_size = cms_space->free();
1641 assert(free_size ==
1642 pointer_delta(cms_space->end(), cms_space->compaction_top())
1643 * HeapWordSize,
1644 "All the free space should be compacted into one chunk at top");
1645 assert(cms_space->dictionary()->total_chunk_size(
1646 debug_only(cms_space->freelistLock())) == 0 ||
1647 cms_space->totalSizeInIndexedFreeLists() == 0,
1648 "All the free space should be in a single chunk");
1649 size_t num = cms_space->totalCount();
1650 assert((free_size == 0 && num == 0) ||
1651 (free_size > 0 && (num == 1 || num == 2)),
1652 "There should be at most 2 free chunks after compaction");
1653 #endif // ASSERT
1654 _collectorState = Resetting;
1655 assert(_restart_addr == NULL,
1656 "Should have been NULL'd before baton was passed");
1657 reset(false /* == !concurrent */);
1658 _cmsGen->reset_after_compaction();
1659 _concurrent_cycles_since_last_unload = 0;
1660
1661 // Clear any data recorded in the PLAB chunk arrays.
1662 if (_survivor_plab_array != NULL) {
1663 reset_survivor_plab_arrays();
1664 }
1665
1666 // Adjust the per-size allocation stats for the next epoch.
1667 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1668 // Restart the "inter sweep timer" for the next epoch.
1669 _inter_sweep_timer.reset();
1670 _inter_sweep_timer.start();
1671
1672 gc_timer->register_gc_end();
1673
1674 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1675
1676 // For a mark-sweep-compact, compute_new_size() will be called
1677 // in the heap's do_collection() method.
1678 }
1679
1680 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1681 ContiguousSpace* eden_space = _young_gen->eden();
1682 ContiguousSpace* from_space = _young_gen->from();
1683 ContiguousSpace* to_space = _young_gen->to();
1684 // Eden
1685 if (_eden_chunk_array != NULL) {
1686 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1687 p2i(eden_space->bottom()), p2i(eden_space->top()),
1688 p2i(eden_space->end()), eden_space->capacity());
1689 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1690 "_eden_chunk_capacity=" SIZE_FORMAT,
1691 _eden_chunk_index, _eden_chunk_capacity);
1692 for (size_t i = 0; i < _eden_chunk_index; i++) {
1693 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1694 i, p2i(_eden_chunk_array[i]));
1695 }
1696 }
1697 // Survivor
1698 if (_survivor_chunk_array != NULL) {
1699 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1700 p2i(from_space->bottom()), p2i(from_space->top()),
1701 p2i(from_space->end()), from_space->capacity());
1702 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1703 "_survivor_chunk_capacity=" SIZE_FORMAT,
1704 _survivor_chunk_index, _survivor_chunk_capacity);
1705 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1706 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1707 i, p2i(_survivor_chunk_array[i]));
1708 }
1709 }
1710 }
1711
1712 void CMSCollector::getFreelistLocks() const {
1713 // Get locks for all free lists in all generations that this
1714 // collector is responsible for
1715 _cmsGen->freelistLock()->lock_without_safepoint_check();
1716 }
1717
1718 void CMSCollector::releaseFreelistLocks() const {
1719 // Release locks for all free lists in all generations that this
1720 // collector is responsible for
1721 _cmsGen->freelistLock()->unlock();
1722 }
1723
1724 bool CMSCollector::haveFreelistLocks() const {
1725 // Check locks for all free lists in all generations that this
1726 // collector is responsible for
1727 assert_lock_strong(_cmsGen->freelistLock());
1728 PRODUCT_ONLY(ShouldNotReachHere());
1729 return true;
1730 }
1731
1732 // A utility class that is used by the CMS collector to
1733 // temporarily "release" the foreground collector from its
1734 // usual obligation to wait for the background collector to
1735 // complete an ongoing phase before proceeding.
1736 class ReleaseForegroundGC: public StackObj {
1737 private:
1738 CMSCollector* _c;
1739 public:
1740 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1741 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1742 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1743 // allow a potentially blocked foreground collector to proceed
1744 _c->_foregroundGCShouldWait = false;
1745 if (_c->_foregroundGCIsActive) {
1746 CGC_lock->notify();
1747 }
1748 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1749 "Possible deadlock");
1750 }
1751
1752 ~ReleaseForegroundGC() {
1753 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1754 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1755 _c->_foregroundGCShouldWait = true;
1756 }
1757 };
1758
1759 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1760 assert(Thread::current()->is_ConcurrentGC_thread(),
1761 "A CMS asynchronous collection is only allowed on a CMS thread.");
1762
1763 GenCollectedHeap* gch = GenCollectedHeap::heap();
1764 {
1765 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1766 MutexLockerEx hl(Heap_lock, safepoint_check);
1767 FreelistLocker fll(this);
1768 MutexLockerEx x(CGC_lock, safepoint_check);
1769 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1770 // The foreground collector is active or we're
1771 // not using asynchronous collections. Skip this
1772 // background collection.
1773 assert(!_foregroundGCShouldWait, "Should be clear");
1774 return;
1775 } else {
1776 assert(_collectorState == Idling, "Should be idling before start.");
1777 _collectorState = InitialMarking;
1778 register_gc_start(cause);
1779 // Reset the expansion cause, now that we are about to begin
1780 // a new cycle.
1781 clear_expansion_cause();
1782
1783 // Clear the MetaspaceGC flag since a concurrent collection
1784 // is starting but also clear it after the collection.
1785 MetaspaceGC::set_should_concurrent_collect(false);
1786 }
1787 // Decide if we want to enable class unloading as part of the
1788 // ensuing concurrent GC cycle.
1789 update_should_unload_classes();
1790 _full_gc_requested = false; // acks all outstanding full gc requests
1791 _full_gc_cause = GCCause::_no_gc;
1792 // Signal that we are about to start a collection
1793 gch->increment_total_full_collections(); // ... starting a collection cycle
1794 _collection_count_start = gch->total_full_collections();
1795 }
1796
1797 // Used for PrintGC
1798 size_t prev_used;
1799 if (PrintGC && Verbose) {
1800 prev_used = _cmsGen->used();
1801 }
1802
1803 // The change of the collection state is normally done at this level;
1804 // the exceptions are phases that are executed while the world is
1805 // stopped. For those phases the change of state is done while the
1806 // world is stopped. For baton passing purposes this allows the
1807 // background collector to finish the phase and change state atomically.
1808 // The foreground collector cannot wait on a phase that is done
1809 // while the world is stopped because the foreground collector already
1810 // has the world stopped and would deadlock.
1811 while (_collectorState != Idling) {
1812 if (TraceCMSState) {
1813 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1814 p2i(Thread::current()), _collectorState);
1815 }
1816 // The foreground collector
1817 // holds the Heap_lock throughout its collection.
1818 // holds the CMS token (but not the lock)
1819 // except while it is waiting for the background collector to yield.
1820 //
1821 // The foreground collector should be blocked (not for long)
1822 // if the background collector is about to start a phase
1823 // executed with world stopped. If the background
1824 // collector has already started such a phase, the
1825 // foreground collector is blocked waiting for the
1826 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1827 // are executed in the VM thread.
1828 //
1829 // The locking order is
1830 // PendingListLock (PLL) -- if applicable (FinalMarking)
1831 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1832 // CMS token (claimed in
1833 // stop_world_and_do() -->
1834 // safepoint_synchronize() -->
1835 // CMSThread::synchronize())
1836
1837 {
1838 // Check if the FG collector wants us to yield.
1839 CMSTokenSync x(true); // is cms thread
1840 if (waitForForegroundGC()) {
1841 // We yielded to a foreground GC, nothing more to be
1842 // done this round.
1843 assert(_foregroundGCShouldWait == false, "We set it to false in "
1844 "waitForForegroundGC()");
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1847 " exiting collection CMS state %d",
1848 p2i(Thread::current()), _collectorState);
1849 }
1850 return;
1851 } else {
1852 // The background collector can run but check to see if the
1853 // foreground collector has done a collection while the
1854 // background collector was waiting to get the CGC_lock
1855 // above. If yes, break so that _foregroundGCShouldWait
1856 // is cleared before returning.
1857 if (_collectorState == Idling) {
1858 break;
1859 }
1860 }
1861 }
1862
1863 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1864 "should be waiting");
1865
1866 switch (_collectorState) {
1867 case InitialMarking:
1868 {
1869 ReleaseForegroundGC x(this);
1870 stats().record_cms_begin();
1871 VM_CMS_Initial_Mark initial_mark_op(this);
1872 VMThread::execute(&initial_mark_op);
1873 }
1874 // The collector state may be any legal state at this point
1875 // since the background collector may have yielded to the
1876 // foreground collector.
1877 break;
1878 case Marking:
1879 // initial marking in checkpointRootsInitialWork has been completed
1880 if (markFromRoots()) { // we were successful
1881 assert(_collectorState == Precleaning, "Collector state should "
1882 "have changed");
1883 } else {
1884 assert(_foregroundGCIsActive, "Internal state inconsistency");
1885 }
1886 break;
1887 case Precleaning:
1888 // marking from roots in markFromRoots has been completed
1889 preclean();
1890 assert(_collectorState == AbortablePreclean ||
1891 _collectorState == FinalMarking,
1892 "Collector state should have changed");
1893 break;
1894 case AbortablePreclean:
1895 abortable_preclean();
1896 assert(_collectorState == FinalMarking, "Collector state should "
1897 "have changed");
1898 break;
1899 case FinalMarking:
1900 {
1901 ReleaseForegroundGC x(this);
1902
1903 VM_CMS_Final_Remark final_remark_op(this);
1904 VMThread::execute(&final_remark_op);
1905 }
1906 assert(_foregroundGCShouldWait, "block post-condition");
1907 break;
1908 case Sweeping:
1909 // final marking in checkpointRootsFinal has been completed
1910 sweep();
1911 assert(_collectorState == Resizing, "Collector state change "
1912 "to Resizing must be done under the free_list_lock");
1913
1914 case Resizing: {
1915 // Sweeping has been completed...
1916 // At this point the background collection has completed.
1917 // Don't move the call to compute_new_size() down
1918 // into code that might be executed if the background
1919 // collection was preempted.
1920 {
1921 ReleaseForegroundGC x(this); // unblock FG collection
1922 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1923 CMSTokenSync z(true); // not strictly needed.
1924 if (_collectorState == Resizing) {
1925 compute_new_size();
1926 save_heap_summary();
1927 _collectorState = Resetting;
1928 } else {
1929 assert(_collectorState == Idling, "The state should only change"
1930 " because the foreground collector has finished the collection");
1931 }
1932 }
1933 break;
1934 }
1935 case Resetting:
1936 // CMS heap resizing has been completed
1937 reset(true);
1938 assert(_collectorState == Idling, "Collector state should "
1939 "have changed");
1940
1941 MetaspaceGC::set_should_concurrent_collect(false);
1942
1943 stats().record_cms_end();
1944 // Don't move the concurrent_phases_end() and compute_new_size()
1945 // calls to here because a preempted background collection
1946 // has it's state set to "Resetting".
1947 break;
1948 case Idling:
1949 default:
1950 ShouldNotReachHere();
1951 break;
1952 }
1953 if (TraceCMSState) {
1954 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1955 p2i(Thread::current()), _collectorState);
1956 }
1957 assert(_foregroundGCShouldWait, "block post-condition");
1958 }
1959
1960 // Should this be in gc_epilogue?
1961 collector_policy()->counters()->update_counters();
1962
1963 {
1964 // Clear _foregroundGCShouldWait and, in the event that the
1965 // foreground collector is waiting, notify it, before
1966 // returning.
1967 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1968 _foregroundGCShouldWait = false;
1969 if (_foregroundGCIsActive) {
1970 CGC_lock->notify();
1971 }
1972 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1973 "Possible deadlock");
1974 }
1975 if (TraceCMSState) {
1976 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1977 " exiting collection CMS state %d",
1978 p2i(Thread::current()), _collectorState);
1979 }
1980 if (PrintGC && Verbose) {
1981 _cmsGen->print_heap_change(prev_used);
1982 }
1983 }
1984
1985 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1986 _cms_start_registered = true;
1987 _gc_timer_cm->register_gc_start();
1988 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1989 }
1990
1991 void CMSCollector::register_gc_end() {
1992 if (_cms_start_registered) {
1993 report_heap_summary(GCWhen::AfterGC);
1994
1995 _gc_timer_cm->register_gc_end();
1996 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1997 _cms_start_registered = false;
1998 }
1999 }
2000
2001 void CMSCollector::save_heap_summary() {
2002 GenCollectedHeap* gch = GenCollectedHeap::heap();
2003 _last_heap_summary = gch->create_heap_summary();
2004 _last_metaspace_summary = gch->create_metaspace_summary();
2005 }
2006
2007 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2008 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2009 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2010 }
2011
2012 bool CMSCollector::waitForForegroundGC() {
2013 bool res = false;
2014 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2015 "CMS thread should have CMS token");
2016 // Block the foreground collector until the
2017 // background collectors decides whether to
2018 // yield.
2019 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2020 _foregroundGCShouldWait = true;
2021 if (_foregroundGCIsActive) {
2022 // The background collector yields to the
2023 // foreground collector and returns a value
2024 // indicating that it has yielded. The foreground
2025 // collector can proceed.
2026 res = true;
2027 _foregroundGCShouldWait = false;
2028 ConcurrentMarkSweepThread::clear_CMS_flag(
2029 ConcurrentMarkSweepThread::CMS_cms_has_token);
2030 ConcurrentMarkSweepThread::set_CMS_flag(
2031 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2032 // Get a possibly blocked foreground thread going
2033 CGC_lock->notify();
2034 if (TraceCMSState) {
2035 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2036 p2i(Thread::current()), _collectorState);
2037 }
2038 while (_foregroundGCIsActive) {
2039 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2040 }
2041 ConcurrentMarkSweepThread::set_CMS_flag(
2042 ConcurrentMarkSweepThread::CMS_cms_has_token);
2043 ConcurrentMarkSweepThread::clear_CMS_flag(
2044 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2045 }
2046 if (TraceCMSState) {
2047 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2048 p2i(Thread::current()), _collectorState);
2049 }
2050 return res;
2051 }
2052
2053 // Because of the need to lock the free lists and other structures in
2054 // the collector, common to all the generations that the collector is
2055 // collecting, we need the gc_prologues of individual CMS generations
2056 // delegate to their collector. It may have been simpler had the
2057 // current infrastructure allowed one to call a prologue on a
2058 // collector. In the absence of that we have the generation's
2059 // prologue delegate to the collector, which delegates back
2060 // some "local" work to a worker method in the individual generations
2061 // that it's responsible for collecting, while itself doing any
2062 // work common to all generations it's responsible for. A similar
2063 // comment applies to the gc_epilogue()'s.
2064 // The role of the variable _between_prologue_and_epilogue is to
2065 // enforce the invocation protocol.
2066 void CMSCollector::gc_prologue(bool full) {
2067 // Call gc_prologue_work() for the CMSGen
2068 // we are responsible for.
2069
2070 // The following locking discipline assumes that we are only called
2071 // when the world is stopped.
2072 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2073
2074 // The CMSCollector prologue must call the gc_prologues for the
2075 // "generations" that it's responsible
2076 // for.
2077
2078 assert( Thread::current()->is_VM_thread()
2079 || ( CMSScavengeBeforeRemark
2080 && Thread::current()->is_ConcurrentGC_thread()),
2081 "Incorrect thread type for prologue execution");
2082
2083 if (_between_prologue_and_epilogue) {
2084 // We have already been invoked; this is a gc_prologue delegation
2085 // from yet another CMS generation that we are responsible for, just
2086 // ignore it since all relevant work has already been done.
2087 return;
2088 }
2089
2090 // set a bit saying prologue has been called; cleared in epilogue
2091 _between_prologue_and_epilogue = true;
2092 // Claim locks for common data structures, then call gc_prologue_work()
2093 // for each CMSGen.
2094
2095 getFreelistLocks(); // gets free list locks on constituent spaces
2096 bitMapLock()->lock_without_safepoint_check();
2097
2098 // Should call gc_prologue_work() for all cms gens we are responsible for
2099 bool duringMarking = _collectorState >= Marking
2100 && _collectorState < Sweeping;
2101
2102 // The young collections clear the modified oops state, which tells if
2103 // there are any modified oops in the class. The remark phase also needs
2104 // that information. Tell the young collection to save the union of all
2105 // modified klasses.
2106 if (duringMarking) {
2107 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2108 }
2109
2110 bool registerClosure = duringMarking;
2111
2112 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2113
2114 if (!full) {
2115 stats().record_gc0_begin();
2116 }
2117 }
2118
2119 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2120
2121 _capacity_at_prologue = capacity();
2122 _used_at_prologue = used();
2123
2124 // Delegate to CMScollector which knows how to coordinate between
2125 // this and any other CMS generations that it is responsible for
2126 // collecting.
2127 collector()->gc_prologue(full);
2128 }
2129
2130 // This is a "private" interface for use by this generation's CMSCollector.
2131 // Not to be called directly by any other entity (for instance,
2132 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2133 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2134 bool registerClosure, ModUnionClosure* modUnionClosure) {
2135 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2136 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2137 "Should be NULL");
2138 if (registerClosure) {
2139 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2140 }
2141 cmsSpace()->gc_prologue();
2142 // Clear stat counters
2143 NOT_PRODUCT(
2144 assert(_numObjectsPromoted == 0, "check");
2145 assert(_numWordsPromoted == 0, "check");
2146 if (Verbose && PrintGC) {
2147 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2148 SIZE_FORMAT " bytes concurrently",
2149 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2150 }
2151 _numObjectsAllocated = 0;
2152 _numWordsAllocated = 0;
2153 )
2154 }
2155
2156 void CMSCollector::gc_epilogue(bool full) {
2157 // The following locking discipline assumes that we are only called
2158 // when the world is stopped.
2159 assert(SafepointSynchronize::is_at_safepoint(),
2160 "world is stopped assumption");
2161
2162 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2163 // if linear allocation blocks need to be appropriately marked to allow the
2164 // the blocks to be parsable. We also check here whether we need to nudge the
2165 // CMS collector thread to start a new cycle (if it's not already active).
2166 assert( Thread::current()->is_VM_thread()
2167 || ( CMSScavengeBeforeRemark
2168 && Thread::current()->is_ConcurrentGC_thread()),
2169 "Incorrect thread type for epilogue execution");
2170
2171 if (!_between_prologue_and_epilogue) {
2172 // We have already been invoked; this is a gc_epilogue delegation
2173 // from yet another CMS generation that we are responsible for, just
2174 // ignore it since all relevant work has already been done.
2175 return;
2176 }
2177 assert(haveFreelistLocks(), "must have freelist locks");
2178 assert_lock_strong(bitMapLock());
2179
2180 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2181
2182 _cmsGen->gc_epilogue_work(full);
2183
2184 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2185 // in case sampling was not already enabled, enable it
2186 _start_sampling = true;
2187 }
2188 // reset _eden_chunk_array so sampling starts afresh
2189 _eden_chunk_index = 0;
2190
2191 size_t cms_used = _cmsGen->cmsSpace()->used();
2192
2193 // update performance counters - this uses a special version of
2194 // update_counters() that allows the utilization to be passed as a
2195 // parameter, avoiding multiple calls to used().
2196 //
2197 _cmsGen->update_counters(cms_used);
2198
2199 bitMapLock()->unlock();
2200 releaseFreelistLocks();
2201
2202 if (!CleanChunkPoolAsync) {
2203 Chunk::clean_chunk_pool();
2204 }
2205
2206 set_did_compact(false);
2207 _between_prologue_and_epilogue = false; // ready for next cycle
2208 }
2209
2210 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2211 collector()->gc_epilogue(full);
2212
2213 // Also reset promotion tracking in par gc thread states.
2214 for (uint i = 0; i < ParallelGCThreads; i++) {
2215 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2216 }
2217 }
2218
2219 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2220 assert(!incremental_collection_failed(), "Should have been cleared");
2221 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2222 cmsSpace()->gc_epilogue();
2223 // Print stat counters
2224 NOT_PRODUCT(
2225 assert(_numObjectsAllocated == 0, "check");
2226 assert(_numWordsAllocated == 0, "check");
2227 if (Verbose && PrintGC) {
2228 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2229 SIZE_FORMAT " bytes",
2230 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2231 }
2232 _numObjectsPromoted = 0;
2233 _numWordsPromoted = 0;
2234 )
2235
2236 if (PrintGC && Verbose) {
2237 // Call down the chain in contiguous_available needs the freelistLock
2238 // so print this out before releasing the freeListLock.
2239 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2240 contiguous_available());
2241 }
2242 }
2243
2244 #ifndef PRODUCT
2245 bool CMSCollector::have_cms_token() {
2246 Thread* thr = Thread::current();
2247 if (thr->is_VM_thread()) {
2248 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2249 } else if (thr->is_ConcurrentGC_thread()) {
2250 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2251 } else if (thr->is_GC_task_thread()) {
2252 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2253 ParGCRareEvent_lock->owned_by_self();
2254 }
2255 return false;
2256 }
2257 #endif
2258
2259 // Check reachability of the given heap address in CMS generation,
2260 // treating all other generations as roots.
2261 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2262 // We could "guarantee" below, rather than assert, but I'll
2263 // leave these as "asserts" so that an adventurous debugger
2264 // could try this in the product build provided some subset of
2265 // the conditions were met, provided they were interested in the
2266 // results and knew that the computation below wouldn't interfere
2267 // with other concurrent computations mutating the structures
2268 // being read or written.
2269 assert(SafepointSynchronize::is_at_safepoint(),
2270 "Else mutations in object graph will make answer suspect");
2271 assert(have_cms_token(), "Should hold cms token");
2272 assert(haveFreelistLocks(), "must hold free list locks");
2273 assert_lock_strong(bitMapLock());
2274
2275 // Clear the marking bit map array before starting, but, just
2276 // for kicks, first report if the given address is already marked
2277 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2278 _markBitMap.isMarked(addr) ? "" : " not");
2279
2280 if (verify_after_remark()) {
2281 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2282 bool result = verification_mark_bm()->isMarked(addr);
2283 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2284 result ? "IS" : "is NOT");
2285 return result;
2286 } else {
2287 gclog_or_tty->print_cr("Could not compute result");
2288 return false;
2289 }
2290 }
2291
2292
2293 void
2294 CMSCollector::print_on_error(outputStream* st) {
2295 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2296 if (collector != NULL) {
2297 CMSBitMap* bitmap = &collector->_markBitMap;
2298 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2299 bitmap->print_on_error(st, " Bits: ");
2300
2301 st->cr();
2302
2303 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2304 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2305 mut_bitmap->print_on_error(st, " Bits: ");
2306 }
2307 }
2308
2309 ////////////////////////////////////////////////////////
2310 // CMS Verification Support
2311 ////////////////////////////////////////////////////////
2312 // Following the remark phase, the following invariant
2313 // should hold -- each object in the CMS heap which is
2314 // marked in markBitMap() should be marked in the verification_mark_bm().
2315
2316 class VerifyMarkedClosure: public BitMapClosure {
2317 CMSBitMap* _marks;
2318 bool _failed;
2319
2320 public:
2321 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2322
2323 bool do_bit(size_t offset) {
2324 HeapWord* addr = _marks->offsetToHeapWord(offset);
2325 if (!_marks->isMarked(addr)) {
2326 oop(addr)->print_on(gclog_or_tty);
2327 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2328 _failed = true;
2329 }
2330 return true;
2331 }
2332
2333 bool failed() { return _failed; }
2334 };
2335
2336 bool CMSCollector::verify_after_remark(bool silent) {
2337 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2338 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2339 static bool init = false;
2340
2341 assert(SafepointSynchronize::is_at_safepoint(),
2342 "Else mutations in object graph will make answer suspect");
2343 assert(have_cms_token(),
2344 "Else there may be mutual interference in use of "
2345 " verification data structures");
2346 assert(_collectorState > Marking && _collectorState <= Sweeping,
2347 "Else marking info checked here may be obsolete");
2348 assert(haveFreelistLocks(), "must hold free list locks");
2349 assert_lock_strong(bitMapLock());
2350
2351
2352 // Allocate marking bit map if not already allocated
2353 if (!init) { // first time
2354 if (!verification_mark_bm()->allocate(_span)) {
2355 return false;
2356 }
2357 init = true;
2358 }
2359
2360 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2361
2362 // Turn off refs discovery -- so we will be tracing through refs.
2363 // This is as intended, because by this time
2364 // GC must already have cleared any refs that need to be cleared,
2365 // and traced those that need to be marked; moreover,
2366 // the marking done here is not going to interfere in any
2367 // way with the marking information used by GC.
2368 NoRefDiscovery no_discovery(ref_processor());
2369
2370 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2371
2372 // Clear any marks from a previous round
2373 verification_mark_bm()->clear_all();
2374 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2375 verify_work_stacks_empty();
2376
2377 GenCollectedHeap* gch = GenCollectedHeap::heap();
2378 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2379 // Update the saved marks which may affect the root scans.
2380 gch->save_marks();
2381
2382 if (CMSRemarkVerifyVariant == 1) {
2383 // In this first variant of verification, we complete
2384 // all marking, then check if the new marks-vector is
2385 // a subset of the CMS marks-vector.
2386 verify_after_remark_work_1();
2387 } else if (CMSRemarkVerifyVariant == 2) {
2388 // In this second variant of verification, we flag an error
2389 // (i.e. an object reachable in the new marks-vector not reachable
2390 // in the CMS marks-vector) immediately, also indicating the
2391 // identify of an object (A) that references the unmarked object (B) --
2392 // presumably, a mutation to A failed to be picked up by preclean/remark?
2393 verify_after_remark_work_2();
2394 } else {
2395 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2396 CMSRemarkVerifyVariant);
2397 }
2398 if (!silent) gclog_or_tty->print(" done] ");
2399 return true;
2400 }
2401
2402 void CMSCollector::verify_after_remark_work_1() {
2403 ResourceMark rm;
2404 HandleMark hm;
2405 GenCollectedHeap* gch = GenCollectedHeap::heap();
2406
2407 // Get a clear set of claim bits for the roots processing to work with.
2408 ClassLoaderDataGraph::clear_claimed_marks();
2409
2410 // Mark from roots one level into CMS
2411 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2412 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2413
2414 {
2415 StrongRootsScope srs(1);
2416
2417 gch->gen_process_roots(&srs,
2418 GenCollectedHeap::OldGen,
2419 true, // young gen as roots
2420 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2421 should_unload_classes(),
2422 ¬Older,
2423 NULL,
2424 NULL);
2425 }
2426
2427 // Now mark from the roots
2428 MarkFromRootsClosure markFromRootsClosure(this, _span,
2429 verification_mark_bm(), verification_mark_stack(),
2430 false /* don't yield */, true /* verifying */);
2431 assert(_restart_addr == NULL, "Expected pre-condition");
2432 verification_mark_bm()->iterate(&markFromRootsClosure);
2433 while (_restart_addr != NULL) {
2434 // Deal with stack overflow: by restarting at the indicated
2435 // address.
2436 HeapWord* ra = _restart_addr;
2437 markFromRootsClosure.reset(ra);
2438 _restart_addr = NULL;
2439 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2440 }
2441 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2442 verify_work_stacks_empty();
2443
2444 // Marking completed -- now verify that each bit marked in
2445 // verification_mark_bm() is also marked in markBitMap(); flag all
2446 // errors by printing corresponding objects.
2447 VerifyMarkedClosure vcl(markBitMap());
2448 verification_mark_bm()->iterate(&vcl);
2449 if (vcl.failed()) {
2450 gclog_or_tty->print("Verification failed");
2451 gch->print_on(gclog_or_tty);
2452 fatal("CMS: failed marking verification after remark");
2453 }
2454 }
2455
2456 class VerifyKlassOopsKlassClosure : public KlassClosure {
2457 class VerifyKlassOopsClosure : public OopClosure {
2458 CMSBitMap* _bitmap;
2459 public:
2460 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2461 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2462 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2463 } _oop_closure;
2464 public:
2465 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2466 void do_klass(Klass* k) {
2467 k->oops_do(&_oop_closure);
2468 }
2469 };
2470
2471 void CMSCollector::verify_after_remark_work_2() {
2472 ResourceMark rm;
2473 HandleMark hm;
2474 GenCollectedHeap* gch = GenCollectedHeap::heap();
2475
2476 // Get a clear set of claim bits for the roots processing to work with.
2477 ClassLoaderDataGraph::clear_claimed_marks();
2478
2479 // Mark from roots one level into CMS
2480 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2481 markBitMap());
2482 CLDToOopClosure cld_closure(¬Older, true);
2483
2484 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2485
2486 {
2487 StrongRootsScope srs(1);
2488
2489 gch->gen_process_roots(&srs,
2490 GenCollectedHeap::OldGen,
2491 true, // young gen as roots
2492 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2493 should_unload_classes(),
2494 ¬Older,
2495 NULL,
2496 &cld_closure);
2497 }
2498
2499 // Now mark from the roots
2500 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2501 verification_mark_bm(), markBitMap(), verification_mark_stack());
2502 assert(_restart_addr == NULL, "Expected pre-condition");
2503 verification_mark_bm()->iterate(&markFromRootsClosure);
2504 while (_restart_addr != NULL) {
2505 // Deal with stack overflow: by restarting at the indicated
2506 // address.
2507 HeapWord* ra = _restart_addr;
2508 markFromRootsClosure.reset(ra);
2509 _restart_addr = NULL;
2510 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2511 }
2512 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2513 verify_work_stacks_empty();
2514
2515 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2516 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2517
2518 // Marking completed -- now verify that each bit marked in
2519 // verification_mark_bm() is also marked in markBitMap(); flag all
2520 // errors by printing corresponding objects.
2521 VerifyMarkedClosure vcl(markBitMap());
2522 verification_mark_bm()->iterate(&vcl);
2523 assert(!vcl.failed(), "Else verification above should not have succeeded");
2524 }
2525
2526 void ConcurrentMarkSweepGeneration::save_marks() {
2527 // delegate to CMS space
2528 cmsSpace()->save_marks();
2529 for (uint i = 0; i < ParallelGCThreads; i++) {
2530 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2531 }
2532 }
2533
2534 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2535 return cmsSpace()->no_allocs_since_save_marks();
2536 }
2537
2538 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2539 \
2540 void ConcurrentMarkSweepGeneration:: \
2541 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2542 cl->set_generation(this); \
2543 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2544 cl->reset_generation(); \
2545 save_marks(); \
2546 }
2547
2548 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2549
2550 void
2551 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2552 if (freelistLock()->owned_by_self()) {
2553 Generation::oop_iterate(cl);
2554 } else {
2555 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2556 Generation::oop_iterate(cl);
2557 }
2558 }
2559
2560 void
2561 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2562 if (freelistLock()->owned_by_self()) {
2563 Generation::object_iterate(cl);
2564 } else {
2565 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2566 Generation::object_iterate(cl);
2567 }
2568 }
2569
2570 void
2571 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2572 if (freelistLock()->owned_by_self()) {
2573 Generation::safe_object_iterate(cl);
2574 } else {
2575 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2576 Generation::safe_object_iterate(cl);
2577 }
2578 }
2579
2580 void
2581 ConcurrentMarkSweepGeneration::post_compact() {
2582 }
2583
2584 void
2585 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2586 // Fix the linear allocation blocks to look like free blocks.
2587
2588 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2589 // are not called when the heap is verified during universe initialization and
2590 // at vm shutdown.
2591 if (freelistLock()->owned_by_self()) {
2592 cmsSpace()->prepare_for_verify();
2593 } else {
2594 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2595 cmsSpace()->prepare_for_verify();
2596 }
2597 }
2598
2599 void
2600 ConcurrentMarkSweepGeneration::verify() {
2601 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2602 // are not called when the heap is verified during universe initialization and
2603 // at vm shutdown.
2604 if (freelistLock()->owned_by_self()) {
2605 cmsSpace()->verify();
2606 } else {
2607 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2608 cmsSpace()->verify();
2609 }
2610 }
2611
2612 void CMSCollector::verify() {
2613 _cmsGen->verify();
2614 }
2615
2616 #ifndef PRODUCT
2617 bool CMSCollector::overflow_list_is_empty() const {
2618 assert(_num_par_pushes >= 0, "Inconsistency");
2619 if (_overflow_list == NULL) {
2620 assert(_num_par_pushes == 0, "Inconsistency");
2621 }
2622 return _overflow_list == NULL;
2623 }
2624
2625 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2626 // merely consolidate assertion checks that appear to occur together frequently.
2627 void CMSCollector::verify_work_stacks_empty() const {
2628 assert(_markStack.isEmpty(), "Marking stack should be empty");
2629 assert(overflow_list_is_empty(), "Overflow list should be empty");
2630 }
2631
2632 void CMSCollector::verify_overflow_empty() const {
2633 assert(overflow_list_is_empty(), "Overflow list should be empty");
2634 assert(no_preserved_marks(), "No preserved marks");
2635 }
2636 #endif // PRODUCT
2637
2638 // Decide if we want to enable class unloading as part of the
2639 // ensuing concurrent GC cycle. We will collect and
2640 // unload classes if it's the case that:
2641 // (1) an explicit gc request has been made and the flag
2642 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2643 // (2) (a) class unloading is enabled at the command line, and
2644 // (b) old gen is getting really full
2645 // NOTE: Provided there is no change in the state of the heap between
2646 // calls to this method, it should have idempotent results. Moreover,
2647 // its results should be monotonically increasing (i.e. going from 0 to 1,
2648 // but not 1 to 0) between successive calls between which the heap was
2649 // not collected. For the implementation below, it must thus rely on
2650 // the property that concurrent_cycles_since_last_unload()
2651 // will not decrease unless a collection cycle happened and that
2652 // _cmsGen->is_too_full() are
2653 // themselves also monotonic in that sense. See check_monotonicity()
2654 // below.
2655 void CMSCollector::update_should_unload_classes() {
2656 _should_unload_classes = false;
2657 // Condition 1 above
2658 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2659 _should_unload_classes = true;
2660 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2661 // Disjuncts 2.b.(i,ii,iii) above
2662 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2663 CMSClassUnloadingMaxInterval)
2664 || _cmsGen->is_too_full();
2665 }
2666 }
2667
2668 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2669 bool res = should_concurrent_collect();
2670 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2671 return res;
2672 }
2673
2674 void CMSCollector::setup_cms_unloading_and_verification_state() {
2675 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2676 || VerifyBeforeExit;
2677 const int rso = GenCollectedHeap::SO_AllCodeCache;
2678
2679 // We set the proper root for this CMS cycle here.
2680 if (should_unload_classes()) { // Should unload classes this cycle
2681 remove_root_scanning_option(rso); // Shrink the root set appropriately
2682 set_verifying(should_verify); // Set verification state for this cycle
2683 return; // Nothing else needs to be done at this time
2684 }
2685
2686 // Not unloading classes this cycle
2687 assert(!should_unload_classes(), "Inconsistency!");
2688
2689 // If we are not unloading classes then add SO_AllCodeCache to root
2690 // scanning options.
2691 add_root_scanning_option(rso);
2692
2693 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2694 set_verifying(true);
2695 } else if (verifying() && !should_verify) {
2696 // We were verifying, but some verification flags got disabled.
2697 set_verifying(false);
2698 // Exclude symbols, strings and code cache elements from root scanning to
2699 // reduce IM and RM pauses.
2700 remove_root_scanning_option(rso);
2701 }
2702 }
2703
2704
2705 #ifndef PRODUCT
2706 HeapWord* CMSCollector::block_start(const void* p) const {
2707 const HeapWord* addr = (HeapWord*)p;
2708 if (_span.contains(p)) {
2709 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2710 return _cmsGen->cmsSpace()->block_start(p);
2711 }
2712 }
2713 return NULL;
2714 }
2715 #endif
2716
2717 HeapWord*
2718 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2719 bool tlab,
2720 bool parallel) {
2721 CMSSynchronousYieldRequest yr;
2722 assert(!tlab, "Can't deal with TLAB allocation");
2723 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2724 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2725 if (GCExpandToAllocateDelayMillis > 0) {
2726 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2727 }
2728 return have_lock_and_allocate(word_size, tlab);
2729 }
2730
2731 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2732 size_t bytes,
2733 size_t expand_bytes,
2734 CMSExpansionCause::Cause cause)
2735 {
2736
2737 bool success = expand(bytes, expand_bytes);
2738
2739 // remember why we expanded; this information is used
2740 // by shouldConcurrentCollect() when making decisions on whether to start
2741 // a new CMS cycle.
2742 if (success) {
2743 set_expansion_cause(cause);
2744 if (PrintGCDetails && Verbose) {
2745 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2746 CMSExpansionCause::to_string(cause));
2747 }
2748 }
2749 }
2750
2751 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2752 HeapWord* res = NULL;
2753 MutexLocker x(ParGCRareEvent_lock);
2754 while (true) {
2755 // Expansion by some other thread might make alloc OK now:
2756 res = ps->lab.alloc(word_sz);
2757 if (res != NULL) return res;
2758 // If there's not enough expansion space available, give up.
2759 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2760 return NULL;
2761 }
2762 // Otherwise, we try expansion.
2763 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2764 // Now go around the loop and try alloc again;
2765 // A competing par_promote might beat us to the expansion space,
2766 // so we may go around the loop again if promotion fails again.
2767 if (GCExpandToAllocateDelayMillis > 0) {
2768 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2769 }
2770 }
2771 }
2772
2773
2774 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2775 PromotionInfo* promo) {
2776 MutexLocker x(ParGCRareEvent_lock);
2777 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2778 while (true) {
2779 // Expansion by some other thread might make alloc OK now:
2780 if (promo->ensure_spooling_space()) {
2781 assert(promo->has_spooling_space(),
2782 "Post-condition of successful ensure_spooling_space()");
2783 return true;
2784 }
2785 // If there's not enough expansion space available, give up.
2786 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2787 return false;
2788 }
2789 // Otherwise, we try expansion.
2790 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2791 // Now go around the loop and try alloc again;
2792 // A competing allocation might beat us to the expansion space,
2793 // so we may go around the loop again if allocation fails again.
2794 if (GCExpandToAllocateDelayMillis > 0) {
2795 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2796 }
2797 }
2798 }
2799
2800 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2801 // Only shrink if a compaction was done so that all the free space
2802 // in the generation is in a contiguous block at the end.
2803 if (did_compact()) {
2804 CardGeneration::shrink(bytes);
2805 }
2806 }
2807
2808 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2809 assert_locked_or_safepoint(Heap_lock);
2810 }
2811
2812 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2813 assert_locked_or_safepoint(Heap_lock);
2814 assert_lock_strong(freelistLock());
2815 if (PrintGCDetails && Verbose) {
2816 warning("Shrinking of CMS not yet implemented");
2817 }
2818 return;
2819 }
2820
2821
2822 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2823 // phases.
2824 class CMSPhaseAccounting: public StackObj {
2825 public:
2826 CMSPhaseAccounting(CMSCollector *collector,
2827 const char *phase,
2828 const GCId gc_id,
2829 bool print_cr = true);
2830 ~CMSPhaseAccounting();
2831
2832 private:
2833 CMSCollector *_collector;
2834 const char *_phase;
2835 elapsedTimer _wallclock;
2836 bool _print_cr;
2837 const GCId _gc_id;
2838
2839 public:
2840 // Not MT-safe; so do not pass around these StackObj's
2841 // where they may be accessed by other threads.
2842 jlong wallclock_millis() {
2843 assert(_wallclock.is_active(), "Wall clock should not stop");
2844 _wallclock.stop(); // to record time
2845 jlong ret = _wallclock.milliseconds();
2846 _wallclock.start(); // restart
2847 return ret;
2848 }
2849 };
2850
2851 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2852 const char *phase,
2853 const GCId gc_id,
2854 bool print_cr) :
2855 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2856
2857 if (PrintCMSStatistics != 0) {
2858 _collector->resetYields();
2859 }
2860 if (PrintGCDetails) {
2861 gclog_or_tty->gclog_stamp(_gc_id);
2862 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2863 _collector->cmsGen()->short_name(), _phase);
2864 }
2865 _collector->resetTimer();
2866 _wallclock.start();
2867 _collector->startTimer();
2868 }
2869
2870 CMSPhaseAccounting::~CMSPhaseAccounting() {
2871 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2872 _collector->stopTimer();
2873 _wallclock.stop();
2874 if (PrintGCDetails) {
2875 gclog_or_tty->gclog_stamp(_gc_id);
2876 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2877 _collector->cmsGen()->short_name(),
2878 _phase, _collector->timerValue(), _wallclock.seconds());
2879 if (_print_cr) {
2880 gclog_or_tty->cr();
2881 }
2882 if (PrintCMSStatistics != 0) {
2883 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2884 _collector->yields());
2885 }
2886 }
2887 }
2888
2889 // CMS work
2890
2891 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2892 class CMSParMarkTask : public AbstractGangTask {
2893 protected:
2894 CMSCollector* _collector;
2895 uint _n_workers;
2896 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2897 AbstractGangTask(name),
2898 _collector(collector),
2899 _n_workers(n_workers) {}
2900 // Work method in support of parallel rescan ... of young gen spaces
2901 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2902 ContiguousSpace* space,
2903 HeapWord** chunk_array, size_t chunk_top);
2904 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2905 };
2906
2907 // Parallel initial mark task
2908 class CMSParInitialMarkTask: public CMSParMarkTask {
2909 StrongRootsScope* _strong_roots_scope;
2910 public:
2911 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2912 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2913 _strong_roots_scope(strong_roots_scope) {}
2914 void work(uint worker_id);
2915 };
2916
2917 // Checkpoint the roots into this generation from outside
2918 // this generation. [Note this initial checkpoint need only
2919 // be approximate -- we'll do a catch up phase subsequently.]
2920 void CMSCollector::checkpointRootsInitial() {
2921 assert(_collectorState == InitialMarking, "Wrong collector state");
2922 check_correct_thread_executing();
2923 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2924
2925 save_heap_summary();
2926 report_heap_summary(GCWhen::BeforeGC);
2927
2928 ReferenceProcessor* rp = ref_processor();
2929 assert(_restart_addr == NULL, "Control point invariant");
2930 {
2931 // acquire locks for subsequent manipulations
2932 MutexLockerEx x(bitMapLock(),
2933 Mutex::_no_safepoint_check_flag);
2934 checkpointRootsInitialWork();
2935 // enable ("weak") refs discovery
2936 rp->enable_discovery();
2937 _collectorState = Marking;
2938 }
2939 }
2940
2941 void CMSCollector::checkpointRootsInitialWork() {
2942 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2943 assert(_collectorState == InitialMarking, "just checking");
2944
2945 // Already have locks.
2946 assert_lock_strong(bitMapLock());
2947 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2948
2949 // Setup the verification and class unloading state for this
2950 // CMS collection cycle.
2951 setup_cms_unloading_and_verification_state();
2952
2953 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2954 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2955
2956 // Reset all the PLAB chunk arrays if necessary.
2957 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2958 reset_survivor_plab_arrays();
2959 }
2960
2961 ResourceMark rm;
2962 HandleMark hm;
2963
2964 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2965 GenCollectedHeap* gch = GenCollectedHeap::heap();
2966
2967 verify_work_stacks_empty();
2968 verify_overflow_empty();
2969
2970 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2971 // Update the saved marks which may affect the root scans.
2972 gch->save_marks();
2973
2974 // weak reference processing has not started yet.
2975 ref_processor()->set_enqueuing_is_done(false);
2976
2977 // Need to remember all newly created CLDs,
2978 // so that we can guarantee that the remark finds them.
2979 ClassLoaderDataGraph::remember_new_clds(true);
2980
2981 // Whenever a CLD is found, it will be claimed before proceeding to mark
2982 // the klasses. The claimed marks need to be cleared before marking starts.
2983 ClassLoaderDataGraph::clear_claimed_marks();
2984
2985 if (CMSPrintEdenSurvivorChunks) {
2986 print_eden_and_survivor_chunk_arrays();
2987 }
2988
2989 {
2990 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2991 if (CMSParallelInitialMarkEnabled) {
2992 // The parallel version.
2993 WorkGang* workers = gch->workers();
2994 assert(workers != NULL, "Need parallel worker threads.");
2995 uint n_workers = workers->active_workers();
2996
2997 StrongRootsScope srs(n_workers);
2998
2999 CMSParInitialMarkTask tsk(this, &srs, n_workers);
3000 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3001 if (n_workers > 1) {
3002 workers->run_task(&tsk);
3003 } else {
3004 tsk.work(0);
3005 }
3006 } else {
3007 // The serial version.
3008 CLDToOopClosure cld_closure(¬Older, true);
3009 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3010
3011 StrongRootsScope srs(1);
3012
3013 gch->gen_process_roots(&srs,
3014 GenCollectedHeap::OldGen,
3015 true, // young gen as roots
3016 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3017 should_unload_classes(),
3018 ¬Older,
3019 NULL,
3020 &cld_closure);
3021 }
3022 }
3023
3024 // Clear mod-union table; it will be dirtied in the prologue of
3025 // CMS generation per each young generation collection.
3026
3027 assert(_modUnionTable.isAllClear(),
3028 "Was cleared in most recent final checkpoint phase"
3029 " or no bits are set in the gc_prologue before the start of the next "
3030 "subsequent marking phase.");
3031
3032 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3033
3034 // Save the end of the used_region of the constituent generations
3035 // to be used to limit the extent of sweep in each generation.
3036 save_sweep_limits();
3037 verify_overflow_empty();
3038 }
3039
3040 bool CMSCollector::markFromRoots() {
3041 // we might be tempted to assert that:
3042 // assert(!SafepointSynchronize::is_at_safepoint(),
3043 // "inconsistent argument?");
3044 // However that wouldn't be right, because it's possible that
3045 // a safepoint is indeed in progress as a young generation
3046 // stop-the-world GC happens even as we mark in this generation.
3047 assert(_collectorState == Marking, "inconsistent state?");
3048 check_correct_thread_executing();
3049 verify_overflow_empty();
3050
3051 // Weak ref discovery note: We may be discovering weak
3052 // refs in this generation concurrent (but interleaved) with
3053 // weak ref discovery by the young generation collector.
3054
3055 CMSTokenSyncWithLocks ts(true, bitMapLock());
3056 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3057 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3058 bool res = markFromRootsWork();
3059 if (res) {
3060 _collectorState = Precleaning;
3061 } else { // We failed and a foreground collection wants to take over
3062 assert(_foregroundGCIsActive, "internal state inconsistency");
3063 assert(_restart_addr == NULL, "foreground will restart from scratch");
3064 if (PrintGCDetails) {
3065 gclog_or_tty->print_cr("bailing out to foreground collection");
3066 }
3067 }
3068 verify_overflow_empty();
3069 return res;
3070 }
3071
3072 bool CMSCollector::markFromRootsWork() {
3073 // iterate over marked bits in bit map, doing a full scan and mark
3074 // from these roots using the following algorithm:
3075 // . if oop is to the right of the current scan pointer,
3076 // mark corresponding bit (we'll process it later)
3077 // . else (oop is to left of current scan pointer)
3078 // push oop on marking stack
3079 // . drain the marking stack
3080
3081 // Note that when we do a marking step we need to hold the
3082 // bit map lock -- recall that direct allocation (by mutators)
3083 // and promotion (by the young generation collector) is also
3084 // marking the bit map. [the so-called allocate live policy.]
3085 // Because the implementation of bit map marking is not
3086 // robust wrt simultaneous marking of bits in the same word,
3087 // we need to make sure that there is no such interference
3088 // between concurrent such updates.
3089
3090 // already have locks
3091 assert_lock_strong(bitMapLock());
3092
3093 verify_work_stacks_empty();
3094 verify_overflow_empty();
3095 bool result = false;
3096 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3097 result = do_marking_mt();
3098 } else {
3099 result = do_marking_st();
3100 }
3101 return result;
3102 }
3103
3104 // Forward decl
3105 class CMSConcMarkingTask;
3106
3107 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3108 CMSCollector* _collector;
3109 CMSConcMarkingTask* _task;
3110 public:
3111 virtual void yield();
3112
3113 // "n_threads" is the number of threads to be terminated.
3114 // "queue_set" is a set of work queues of other threads.
3115 // "collector" is the CMS collector associated with this task terminator.
3116 // "yield" indicates whether we need the gang as a whole to yield.
3117 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3118 ParallelTaskTerminator(n_threads, queue_set),
3119 _collector(collector) { }
3120
3121 void set_task(CMSConcMarkingTask* task) {
3122 _task = task;
3123 }
3124 };
3125
3126 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3127 CMSConcMarkingTask* _task;
3128 public:
3129 bool should_exit_termination();
3130 void set_task(CMSConcMarkingTask* task) {
3131 _task = task;
3132 }
3133 };
3134
3135 // MT Concurrent Marking Task
3136 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3137 CMSCollector* _collector;
3138 uint _n_workers; // requested/desired # workers
3139 bool _result;
3140 CompactibleFreeListSpace* _cms_space;
3141 char _pad_front[64]; // padding to ...
3142 HeapWord* _global_finger; // ... avoid sharing cache line
3143 char _pad_back[64];
3144 HeapWord* _restart_addr;
3145
3146 // Exposed here for yielding support
3147 Mutex* const _bit_map_lock;
3148
3149 // The per thread work queues, available here for stealing
3150 OopTaskQueueSet* _task_queues;
3151
3152 // Termination (and yielding) support
3153 CMSConcMarkingTerminator _term;
3154 CMSConcMarkingTerminatorTerminator _term_term;
3155
3156 public:
3157 CMSConcMarkingTask(CMSCollector* collector,
3158 CompactibleFreeListSpace* cms_space,
3159 YieldingFlexibleWorkGang* workers,
3160 OopTaskQueueSet* task_queues):
3161 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3162 _collector(collector),
3163 _cms_space(cms_space),
3164 _n_workers(0), _result(true),
3165 _task_queues(task_queues),
3166 _term(_n_workers, task_queues, _collector),
3167 _bit_map_lock(collector->bitMapLock())
3168 {
3169 _requested_size = _n_workers;
3170 _term.set_task(this);
3171 _term_term.set_task(this);
3172 _restart_addr = _global_finger = _cms_space->bottom();
3173 }
3174
3175
3176 OopTaskQueueSet* task_queues() { return _task_queues; }
3177
3178 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3179
3180 HeapWord** global_finger_addr() { return &_global_finger; }
3181
3182 CMSConcMarkingTerminator* terminator() { return &_term; }
3183
3184 virtual void set_for_termination(uint active_workers) {
3185 terminator()->reset_for_reuse(active_workers);
3186 }
3187
3188 void work(uint worker_id);
3189 bool should_yield() {
3190 return ConcurrentMarkSweepThread::should_yield()
3191 && !_collector->foregroundGCIsActive();
3192 }
3193
3194 virtual void coordinator_yield(); // stuff done by coordinator
3195 bool result() { return _result; }
3196
3197 void reset(HeapWord* ra) {
3198 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3199 _restart_addr = _global_finger = ra;
3200 _term.reset_for_reuse();
3201 }
3202
3203 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3204 OopTaskQueue* work_q);
3205
3206 private:
3207 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3208 void do_work_steal(int i);
3209 void bump_global_finger(HeapWord* f);
3210 };
3211
3212 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3213 assert(_task != NULL, "Error");
3214 return _task->yielding();
3215 // Note that we do not need the disjunct || _task->should_yield() above
3216 // because we want terminating threads to yield only if the task
3217 // is already in the midst of yielding, which happens only after at least one
3218 // thread has yielded.
3219 }
3220
3221 void CMSConcMarkingTerminator::yield() {
3222 if (_task->should_yield()) {
3223 _task->yield();
3224 } else {
3225 ParallelTaskTerminator::yield();
3226 }
3227 }
3228
3229 ////////////////////////////////////////////////////////////////
3230 // Concurrent Marking Algorithm Sketch
3231 ////////////////////////////////////////////////////////////////
3232 // Until all tasks exhausted (both spaces):
3233 // -- claim next available chunk
3234 // -- bump global finger via CAS
3235 // -- find first object that starts in this chunk
3236 // and start scanning bitmap from that position
3237 // -- scan marked objects for oops
3238 // -- CAS-mark target, and if successful:
3239 // . if target oop is above global finger (volatile read)
3240 // nothing to do
3241 // . if target oop is in chunk and above local finger
3242 // then nothing to do
3243 // . else push on work-queue
3244 // -- Deal with possible overflow issues:
3245 // . local work-queue overflow causes stuff to be pushed on
3246 // global (common) overflow queue
3247 // . always first empty local work queue
3248 // . then get a batch of oops from global work queue if any
3249 // . then do work stealing
3250 // -- When all tasks claimed (both spaces)
3251 // and local work queue empty,
3252 // then in a loop do:
3253 // . check global overflow stack; steal a batch of oops and trace
3254 // . try to steal from other threads oif GOS is empty
3255 // . if neither is available, offer termination
3256 // -- Terminate and return result
3257 //
3258 void CMSConcMarkingTask::work(uint worker_id) {
3259 elapsedTimer _timer;
3260 ResourceMark rm;
3261 HandleMark hm;
3262
3263 DEBUG_ONLY(_collector->verify_overflow_empty();)
3264
3265 // Before we begin work, our work queue should be empty
3266 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3267 // Scan the bitmap covering _cms_space, tracing through grey objects.
3268 _timer.start();
3269 do_scan_and_mark(worker_id, _cms_space);
3270 _timer.stop();
3271 if (PrintCMSStatistics != 0) {
3272 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3273 worker_id, _timer.seconds());
3274 // XXX: need xxx/xxx type of notation, two timers
3275 }
3276
3277 // ... do work stealing
3278 _timer.reset();
3279 _timer.start();
3280 do_work_steal(worker_id);
3281 _timer.stop();
3282 if (PrintCMSStatistics != 0) {
3283 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3284 worker_id, _timer.seconds());
3285 // XXX: need xxx/xxx type of notation, two timers
3286 }
3287 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3288 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3289 // Note that under the current task protocol, the
3290 // following assertion is true even of the spaces
3291 // expanded since the completion of the concurrent
3292 // marking. XXX This will likely change under a strict
3293 // ABORT semantics.
3294 // After perm removal the comparison was changed to
3295 // greater than or equal to from strictly greater than.
3296 // Before perm removal the highest address sweep would
3297 // have been at the end of perm gen but now is at the
3298 // end of the tenured gen.
3299 assert(_global_finger >= _cms_space->end(),
3300 "All tasks have been completed");
3301 DEBUG_ONLY(_collector->verify_overflow_empty();)
3302 }
3303
3304 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3305 HeapWord* read = _global_finger;
3306 HeapWord* cur = read;
3307 while (f > read) {
3308 cur = read;
3309 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3310 if (cur == read) {
3311 // our cas succeeded
3312 assert(_global_finger >= f, "protocol consistency");
3313 break;
3314 }
3315 }
3316 }
3317
3318 // This is really inefficient, and should be redone by
3319 // using (not yet available) block-read and -write interfaces to the
3320 // stack and the work_queue. XXX FIX ME !!!
3321 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3322 OopTaskQueue* work_q) {
3323 // Fast lock-free check
3324 if (ovflw_stk->length() == 0) {
3325 return false;
3326 }
3327 assert(work_q->size() == 0, "Shouldn't steal");
3328 MutexLockerEx ml(ovflw_stk->par_lock(),
3329 Mutex::_no_safepoint_check_flag);
3330 // Grab up to 1/4 the size of the work queue
3331 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3332 (size_t)ParGCDesiredObjsFromOverflowList);
3333 num = MIN2(num, ovflw_stk->length());
3334 for (int i = (int) num; i > 0; i--) {
3335 oop cur = ovflw_stk->pop();
3336 assert(cur != NULL, "Counted wrong?");
3337 work_q->push(cur);
3338 }
3339 return num > 0;
3340 }
3341
3342 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3343 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3344 int n_tasks = pst->n_tasks();
3345 // We allow that there may be no tasks to do here because
3346 // we are restarting after a stack overflow.
3347 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3348 uint nth_task = 0;
3349
3350 HeapWord* aligned_start = sp->bottom();
3351 if (sp->used_region().contains(_restart_addr)) {
3352 // Align down to a card boundary for the start of 0th task
3353 // for this space.
3354 aligned_start =
3355 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3356 CardTableModRefBS::card_size);
3357 }
3358
3359 size_t chunk_size = sp->marking_task_size();
3360 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3361 // Having claimed the nth task in this space,
3362 // compute the chunk that it corresponds to:
3363 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3364 aligned_start + (nth_task+1)*chunk_size);
3365 // Try and bump the global finger via a CAS;
3366 // note that we need to do the global finger bump
3367 // _before_ taking the intersection below, because
3368 // the task corresponding to that region will be
3369 // deemed done even if the used_region() expands
3370 // because of allocation -- as it almost certainly will
3371 // during start-up while the threads yield in the
3372 // closure below.
3373 HeapWord* finger = span.end();
3374 bump_global_finger(finger); // atomically
3375 // There are null tasks here corresponding to chunks
3376 // beyond the "top" address of the space.
3377 span = span.intersection(sp->used_region());
3378 if (!span.is_empty()) { // Non-null task
3379 HeapWord* prev_obj;
3380 assert(!span.contains(_restart_addr) || nth_task == 0,
3381 "Inconsistency");
3382 if (nth_task == 0) {
3383 // For the 0th task, we'll not need to compute a block_start.
3384 if (span.contains(_restart_addr)) {
3385 // In the case of a restart because of stack overflow,
3386 // we might additionally skip a chunk prefix.
3387 prev_obj = _restart_addr;
3388 } else {
3389 prev_obj = span.start();
3390 }
3391 } else {
3392 // We want to skip the first object because
3393 // the protocol is to scan any object in its entirety
3394 // that _starts_ in this span; a fortiori, any
3395 // object starting in an earlier span is scanned
3396 // as part of an earlier claimed task.
3397 // Below we use the "careful" version of block_start
3398 // so we do not try to navigate uninitialized objects.
3399 prev_obj = sp->block_start_careful(span.start());
3400 // Below we use a variant of block_size that uses the
3401 // Printezis bits to avoid waiting for allocated
3402 // objects to become initialized/parsable.
3403 while (prev_obj < span.start()) {
3404 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3405 if (sz > 0) {
3406 prev_obj += sz;
3407 } else {
3408 // In this case we may end up doing a bit of redundant
3409 // scanning, but that appears unavoidable, short of
3410 // locking the free list locks; see bug 6324141.
3411 break;
3412 }
3413 }
3414 }
3415 if (prev_obj < span.end()) {
3416 MemRegion my_span = MemRegion(prev_obj, span.end());
3417 // Do the marking work within a non-empty span --
3418 // the last argument to the constructor indicates whether the
3419 // iteration should be incremental with periodic yields.
3420 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3421 &_collector->_markBitMap,
3422 work_queue(i),
3423 &_collector->_markStack);
3424 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3425 } // else nothing to do for this task
3426 } // else nothing to do for this task
3427 }
3428 // We'd be tempted to assert here that since there are no
3429 // more tasks left to claim in this space, the global_finger
3430 // must exceed space->top() and a fortiori space->end(). However,
3431 // that would not quite be correct because the bumping of
3432 // global_finger occurs strictly after the claiming of a task,
3433 // so by the time we reach here the global finger may not yet
3434 // have been bumped up by the thread that claimed the last
3435 // task.
3436 pst->all_tasks_completed();
3437 }
3438
3439 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3440 private:
3441 CMSCollector* _collector;
3442 CMSConcMarkingTask* _task;
3443 MemRegion _span;
3444 CMSBitMap* _bit_map;
3445 CMSMarkStack* _overflow_stack;
3446 OopTaskQueue* _work_queue;
3447 protected:
3448 DO_OOP_WORK_DEFN
3449 public:
3450 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3451 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3452 MetadataAwareOopClosure(collector->ref_processor()),
3453 _collector(collector),
3454 _task(task),
3455 _span(collector->_span),
3456 _work_queue(work_queue),
3457 _bit_map(bit_map),
3458 _overflow_stack(overflow_stack)
3459 { }
3460 virtual void do_oop(oop* p);
3461 virtual void do_oop(narrowOop* p);
3462
3463 void trim_queue(size_t max);
3464 void handle_stack_overflow(HeapWord* lost);
3465 void do_yield_check() {
3466 if (_task->should_yield()) {
3467 _task->yield();
3468 }
3469 }
3470 };
3471
3472 // Grey object scanning during work stealing phase --
3473 // the salient assumption here is that any references
3474 // that are in these stolen objects being scanned must
3475 // already have been initialized (else they would not have
3476 // been published), so we do not need to check for
3477 // uninitialized objects before pushing here.
3478 void Par_ConcMarkingClosure::do_oop(oop obj) {
3479 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3480 HeapWord* addr = (HeapWord*)obj;
3481 // Check if oop points into the CMS generation
3482 // and is not marked
3483 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3484 // a white object ...
3485 // If we manage to "claim" the object, by being the
3486 // first thread to mark it, then we push it on our
3487 // marking stack
3488 if (_bit_map->par_mark(addr)) { // ... now grey
3489 // push on work queue (grey set)
3490 bool simulate_overflow = false;
3491 NOT_PRODUCT(
3492 if (CMSMarkStackOverflowALot &&
3493 _collector->simulate_overflow()) {
3494 // simulate a stack overflow
3495 simulate_overflow = true;
3496 }
3497 )
3498 if (simulate_overflow ||
3499 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3500 // stack overflow
3501 if (PrintCMSStatistics != 0) {
3502 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3503 SIZE_FORMAT, _overflow_stack->capacity());
3504 }
3505 // We cannot assert that the overflow stack is full because
3506 // it may have been emptied since.
3507 assert(simulate_overflow ||
3508 _work_queue->size() == _work_queue->max_elems(),
3509 "Else push should have succeeded");
3510 handle_stack_overflow(addr);
3511 }
3512 } // Else, some other thread got there first
3513 do_yield_check();
3514 }
3515 }
3516
3517 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3518 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3519
3520 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3521 while (_work_queue->size() > max) {
3522 oop new_oop;
3523 if (_work_queue->pop_local(new_oop)) {
3524 assert(new_oop->is_oop(), "Should be an oop");
3525 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3526 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3527 new_oop->oop_iterate(this); // do_oop() above
3528 do_yield_check();
3529 }
3530 }
3531 }
3532
3533 // Upon stack overflow, we discard (part of) the stack,
3534 // remembering the least address amongst those discarded
3535 // in CMSCollector's _restart_address.
3536 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3537 // We need to do this under a mutex to prevent other
3538 // workers from interfering with the work done below.
3539 MutexLockerEx ml(_overflow_stack->par_lock(),
3540 Mutex::_no_safepoint_check_flag);
3541 // Remember the least grey address discarded
3542 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3543 _collector->lower_restart_addr(ra);
3544 _overflow_stack->reset(); // discard stack contents
3545 _overflow_stack->expand(); // expand the stack if possible
3546 }
3547
3548
3549 void CMSConcMarkingTask::do_work_steal(int i) {
3550 OopTaskQueue* work_q = work_queue(i);
3551 oop obj_to_scan;
3552 CMSBitMap* bm = &(_collector->_markBitMap);
3553 CMSMarkStack* ovflw = &(_collector->_markStack);
3554 int* seed = _collector->hash_seed(i);
3555 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3556 while (true) {
3557 cl.trim_queue(0);
3558 assert(work_q->size() == 0, "Should have been emptied above");
3559 if (get_work_from_overflow_stack(ovflw, work_q)) {
3560 // Can't assert below because the work obtained from the
3561 // overflow stack may already have been stolen from us.
3562 // assert(work_q->size() > 0, "Work from overflow stack");
3563 continue;
3564 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3565 assert(obj_to_scan->is_oop(), "Should be an oop");
3566 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3567 obj_to_scan->oop_iterate(&cl);
3568 } else if (terminator()->offer_termination(&_term_term)) {
3569 assert(work_q->size() == 0, "Impossible!");
3570 break;
3571 } else if (yielding() || should_yield()) {
3572 yield();
3573 }
3574 }
3575 }
3576
3577 // This is run by the CMS (coordinator) thread.
3578 void CMSConcMarkingTask::coordinator_yield() {
3579 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3580 "CMS thread should hold CMS token");
3581 // First give up the locks, then yield, then re-lock
3582 // We should probably use a constructor/destructor idiom to
3583 // do this unlock/lock or modify the MutexUnlocker class to
3584 // serve our purpose. XXX
3585 assert_lock_strong(_bit_map_lock);
3586 _bit_map_lock->unlock();
3587 ConcurrentMarkSweepThread::desynchronize(true);
3588 _collector->stopTimer();
3589 if (PrintCMSStatistics != 0) {
3590 _collector->incrementYields();
3591 }
3592
3593 // It is possible for whichever thread initiated the yield request
3594 // not to get a chance to wake up and take the bitmap lock between
3595 // this thread releasing it and reacquiring it. So, while the
3596 // should_yield() flag is on, let's sleep for a bit to give the
3597 // other thread a chance to wake up. The limit imposed on the number
3598 // of iterations is defensive, to avoid any unforseen circumstances
3599 // putting us into an infinite loop. Since it's always been this
3600 // (coordinator_yield()) method that was observed to cause the
3601 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3602 // which is by default non-zero. For the other seven methods that
3603 // also perform the yield operation, as are using a different
3604 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3605 // can enable the sleeping for those methods too, if necessary.
3606 // See 6442774.
3607 //
3608 // We really need to reconsider the synchronization between the GC
3609 // thread and the yield-requesting threads in the future and we
3610 // should really use wait/notify, which is the recommended
3611 // way of doing this type of interaction. Additionally, we should
3612 // consolidate the eight methods that do the yield operation and they
3613 // are almost identical into one for better maintainability and
3614 // readability. See 6445193.
3615 //
3616 // Tony 2006.06.29
3617 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3618 ConcurrentMarkSweepThread::should_yield() &&
3619 !CMSCollector::foregroundGCIsActive(); ++i) {
3620 os::sleep(Thread::current(), 1, false);
3621 }
3622
3623 ConcurrentMarkSweepThread::synchronize(true);
3624 _bit_map_lock->lock_without_safepoint_check();
3625 _collector->startTimer();
3626 }
3627
3628 bool CMSCollector::do_marking_mt() {
3629 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3630 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3631 conc_workers()->active_workers(),
3632 Threads::number_of_non_daemon_threads());
3633 conc_workers()->set_active_workers(num_workers);
3634
3635 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3636
3637 CMSConcMarkingTask tsk(this,
3638 cms_space,
3639 conc_workers(),
3640 task_queues());
3641
3642 // Since the actual number of workers we get may be different
3643 // from the number we requested above, do we need to do anything different
3644 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3645 // class?? XXX
3646 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3647
3648 // Refs discovery is already non-atomic.
3649 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3650 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3651 conc_workers()->start_task(&tsk);
3652 while (tsk.yielded()) {
3653 tsk.coordinator_yield();
3654 conc_workers()->continue_task(&tsk);
3655 }
3656 // If the task was aborted, _restart_addr will be non-NULL
3657 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3658 while (_restart_addr != NULL) {
3659 // XXX For now we do not make use of ABORTED state and have not
3660 // yet implemented the right abort semantics (even in the original
3661 // single-threaded CMS case). That needs some more investigation
3662 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3663 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3664 // If _restart_addr is non-NULL, a marking stack overflow
3665 // occurred; we need to do a fresh marking iteration from the
3666 // indicated restart address.
3667 if (_foregroundGCIsActive) {
3668 // We may be running into repeated stack overflows, having
3669 // reached the limit of the stack size, while making very
3670 // slow forward progress. It may be best to bail out and
3671 // let the foreground collector do its job.
3672 // Clear _restart_addr, so that foreground GC
3673 // works from scratch. This avoids the headache of
3674 // a "rescan" which would otherwise be needed because
3675 // of the dirty mod union table & card table.
3676 _restart_addr = NULL;
3677 return false;
3678 }
3679 // Adjust the task to restart from _restart_addr
3680 tsk.reset(_restart_addr);
3681 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3682 _restart_addr);
3683 _restart_addr = NULL;
3684 // Get the workers going again
3685 conc_workers()->start_task(&tsk);
3686 while (tsk.yielded()) {
3687 tsk.coordinator_yield();
3688 conc_workers()->continue_task(&tsk);
3689 }
3690 }
3691 assert(tsk.completed(), "Inconsistency");
3692 assert(tsk.result() == true, "Inconsistency");
3693 return true;
3694 }
3695
3696 bool CMSCollector::do_marking_st() {
3697 ResourceMark rm;
3698 HandleMark hm;
3699
3700 // Temporarily make refs discovery single threaded (non-MT)
3701 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3702 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3703 &_markStack, CMSYield);
3704 // the last argument to iterate indicates whether the iteration
3705 // should be incremental with periodic yields.
3706 _markBitMap.iterate(&markFromRootsClosure);
3707 // If _restart_addr is non-NULL, a marking stack overflow
3708 // occurred; we need to do a fresh iteration from the
3709 // indicated restart address.
3710 while (_restart_addr != NULL) {
3711 if (_foregroundGCIsActive) {
3712 // We may be running into repeated stack overflows, having
3713 // reached the limit of the stack size, while making very
3714 // slow forward progress. It may be best to bail out and
3715 // let the foreground collector do its job.
3716 // Clear _restart_addr, so that foreground GC
3717 // works from scratch. This avoids the headache of
3718 // a "rescan" which would otherwise be needed because
3719 // of the dirty mod union table & card table.
3720 _restart_addr = NULL;
3721 return false; // indicating failure to complete marking
3722 }
3723 // Deal with stack overflow:
3724 // we restart marking from _restart_addr
3725 HeapWord* ra = _restart_addr;
3726 markFromRootsClosure.reset(ra);
3727 _restart_addr = NULL;
3728 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3729 }
3730 return true;
3731 }
3732
3733 void CMSCollector::preclean() {
3734 check_correct_thread_executing();
3735 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3736 verify_work_stacks_empty();
3737 verify_overflow_empty();
3738 _abort_preclean = false;
3739 if (CMSPrecleaningEnabled) {
3740 if (!CMSEdenChunksRecordAlways) {
3741 _eden_chunk_index = 0;
3742 }
3743 size_t used = get_eden_used();
3744 size_t capacity = get_eden_capacity();
3745 // Don't start sampling unless we will get sufficiently
3746 // many samples.
3747 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3748 * CMSScheduleRemarkEdenPenetration)) {
3749 _start_sampling = true;
3750 } else {
3751 _start_sampling = false;
3752 }
3753 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3754 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3755 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3756 }
3757 CMSTokenSync x(true); // is cms thread
3758 if (CMSPrecleaningEnabled) {
3759 sample_eden();
3760 _collectorState = AbortablePreclean;
3761 } else {
3762 _collectorState = FinalMarking;
3763 }
3764 verify_work_stacks_empty();
3765 verify_overflow_empty();
3766 }
3767
3768 // Try and schedule the remark such that young gen
3769 // occupancy is CMSScheduleRemarkEdenPenetration %.
3770 void CMSCollector::abortable_preclean() {
3771 check_correct_thread_executing();
3772 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3773 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3774
3775 // If Eden's current occupancy is below this threshold,
3776 // immediately schedule the remark; else preclean
3777 // past the next scavenge in an effort to
3778 // schedule the pause as described above. By choosing
3779 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3780 // we will never do an actual abortable preclean cycle.
3781 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3782 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3783 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3784 // We need more smarts in the abortable preclean
3785 // loop below to deal with cases where allocation
3786 // in young gen is very very slow, and our precleaning
3787 // is running a losing race against a horde of
3788 // mutators intent on flooding us with CMS updates
3789 // (dirty cards).
3790 // One, admittedly dumb, strategy is to give up
3791 // after a certain number of abortable precleaning loops
3792 // or after a certain maximum time. We want to make
3793 // this smarter in the next iteration.
3794 // XXX FIX ME!!! YSR
3795 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3796 while (!(should_abort_preclean() ||
3797 ConcurrentMarkSweepThread::should_terminate())) {
3798 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3799 cumworkdone += workdone;
3800 loops++;
3801 // Voluntarily terminate abortable preclean phase if we have
3802 // been at it for too long.
3803 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3804 loops >= CMSMaxAbortablePrecleanLoops) {
3805 if (PrintGCDetails) {
3806 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3807 }
3808 break;
3809 }
3810 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3811 if (PrintGCDetails) {
3812 gclog_or_tty->print(" CMS: abort preclean due to time ");
3813 }
3814 break;
3815 }
3816 // If we are doing little work each iteration, we should
3817 // take a short break.
3818 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3819 // Sleep for some time, waiting for work to accumulate
3820 stopTimer();
3821 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3822 startTimer();
3823 waited++;
3824 }
3825 }
3826 if (PrintCMSStatistics > 0) {
3827 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3828 loops, waited, cumworkdone);
3829 }
3830 }
3831 CMSTokenSync x(true); // is cms thread
3832 if (_collectorState != Idling) {
3833 assert(_collectorState == AbortablePreclean,
3834 "Spontaneous state transition?");
3835 _collectorState = FinalMarking;
3836 } // Else, a foreground collection completed this CMS cycle.
3837 return;
3838 }
3839
3840 // Respond to an Eden sampling opportunity
3841 void CMSCollector::sample_eden() {
3842 // Make sure a young gc cannot sneak in between our
3843 // reading and recording of a sample.
3844 assert(Thread::current()->is_ConcurrentGC_thread(),
3845 "Only the cms thread may collect Eden samples");
3846 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3847 "Should collect samples while holding CMS token");
3848 if (!_start_sampling) {
3849 return;
3850 }
3851 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3852 // is populated by the young generation.
3853 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3854 if (_eden_chunk_index < _eden_chunk_capacity) {
3855 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3856 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3857 "Unexpected state of Eden");
3858 // We'd like to check that what we just sampled is an oop-start address;
3859 // however, we cannot do that here since the object may not yet have been
3860 // initialized. So we'll instead do the check when we _use_ this sample
3861 // later.
3862 if (_eden_chunk_index == 0 ||
3863 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3864 _eden_chunk_array[_eden_chunk_index-1])
3865 >= CMSSamplingGrain)) {
3866 _eden_chunk_index++; // commit sample
3867 }
3868 }
3869 }
3870 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3871 size_t used = get_eden_used();
3872 size_t capacity = get_eden_capacity();
3873 assert(used <= capacity, "Unexpected state of Eden");
3874 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3875 _abort_preclean = true;
3876 }
3877 }
3878 }
3879
3880
3881 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3882 assert(_collectorState == Precleaning ||
3883 _collectorState == AbortablePreclean, "incorrect state");
3884 ResourceMark rm;
3885 HandleMark hm;
3886
3887 // Precleaning is currently not MT but the reference processor
3888 // may be set for MT. Disable it temporarily here.
3889 ReferenceProcessor* rp = ref_processor();
3890 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3891
3892 // Do one pass of scrubbing the discovered reference lists
3893 // to remove any reference objects with strongly-reachable
3894 // referents.
3895 if (clean_refs) {
3896 CMSPrecleanRefsYieldClosure yield_cl(this);
3897 assert(rp->span().equals(_span), "Spans should be equal");
3898 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3899 &_markStack, true /* preclean */);
3900 CMSDrainMarkingStackClosure complete_trace(this,
3901 _span, &_markBitMap, &_markStack,
3902 &keep_alive, true /* preclean */);
3903
3904 // We don't want this step to interfere with a young
3905 // collection because we don't want to take CPU
3906 // or memory bandwidth away from the young GC threads
3907 // (which may be as many as there are CPUs).
3908 // Note that we don't need to protect ourselves from
3909 // interference with mutators because they can't
3910 // manipulate the discovered reference lists nor affect
3911 // the computed reachability of the referents, the
3912 // only properties manipulated by the precleaning
3913 // of these reference lists.
3914 stopTimer();
3915 CMSTokenSyncWithLocks x(true /* is cms thread */,
3916 bitMapLock());
3917 startTimer();
3918 sample_eden();
3919
3920 // The following will yield to allow foreground
3921 // collection to proceed promptly. XXX YSR:
3922 // The code in this method may need further
3923 // tweaking for better performance and some restructuring
3924 // for cleaner interfaces.
3925 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3926 rp->preclean_discovered_references(
3927 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3928 gc_timer, _gc_tracer_cm->gc_id());
3929 }
3930
3931 if (clean_survivor) { // preclean the active survivor space(s)
3932 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3933 &_markBitMap, &_modUnionTable,
3934 &_markStack, true /* precleaning phase */);
3935 stopTimer();
3936 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3937 bitMapLock());
3938 startTimer();
3939 unsigned int before_count =
3940 GenCollectedHeap::heap()->total_collections();
3941 SurvivorSpacePrecleanClosure
3942 sss_cl(this, _span, &_markBitMap, &_markStack,
3943 &pam_cl, before_count, CMSYield);
3944 _young_gen->from()->object_iterate_careful(&sss_cl);
3945 _young_gen->to()->object_iterate_careful(&sss_cl);
3946 }
3947 MarkRefsIntoAndScanClosure
3948 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3949 &_markStack, this, CMSYield,
3950 true /* precleaning phase */);
3951 // CAUTION: The following closure has persistent state that may need to
3952 // be reset upon a decrease in the sequence of addresses it
3953 // processes.
3954 ScanMarkedObjectsAgainCarefullyClosure
3955 smoac_cl(this, _span,
3956 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3957
3958 // Preclean dirty cards in ModUnionTable and CardTable using
3959 // appropriate convergence criterion;
3960 // repeat CMSPrecleanIter times unless we find that
3961 // we are losing.
3962 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3963 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3964 "Bad convergence multiplier");
3965 assert(CMSPrecleanThreshold >= 100,
3966 "Unreasonably low CMSPrecleanThreshold");
3967
3968 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3969 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3970 numIter < CMSPrecleanIter;
3971 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3972 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3973 if (Verbose && PrintGCDetails) {
3974 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3975 }
3976 // Either there are very few dirty cards, so re-mark
3977 // pause will be small anyway, or our pre-cleaning isn't
3978 // that much faster than the rate at which cards are being
3979 // dirtied, so we might as well stop and re-mark since
3980 // precleaning won't improve our re-mark time by much.
3981 if (curNumCards <= CMSPrecleanThreshold ||
3982 (numIter > 0 &&
3983 (curNumCards * CMSPrecleanDenominator >
3984 lastNumCards * CMSPrecleanNumerator))) {
3985 numIter++;
3986 cumNumCards += curNumCards;
3987 break;
3988 }
3989 }
3990
3991 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3992
3993 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3994 cumNumCards += curNumCards;
3995 if (PrintGCDetails && PrintCMSStatistics != 0) {
3996 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3997 curNumCards, cumNumCards, numIter);
3998 }
3999 return cumNumCards; // as a measure of useful work done
4000 }
4001
4002 // PRECLEANING NOTES:
4003 // Precleaning involves:
4004 // . reading the bits of the modUnionTable and clearing the set bits.
4005 // . For the cards corresponding to the set bits, we scan the
4006 // objects on those cards. This means we need the free_list_lock
4007 // so that we can safely iterate over the CMS space when scanning
4008 // for oops.
4009 // . When we scan the objects, we'll be both reading and setting
4010 // marks in the marking bit map, so we'll need the marking bit map.
4011 // . For protecting _collector_state transitions, we take the CGC_lock.
4012 // Note that any races in the reading of of card table entries by the
4013 // CMS thread on the one hand and the clearing of those entries by the
4014 // VM thread or the setting of those entries by the mutator threads on the
4015 // other are quite benign. However, for efficiency it makes sense to keep
4016 // the VM thread from racing with the CMS thread while the latter is
4017 // dirty card info to the modUnionTable. We therefore also use the
4018 // CGC_lock to protect the reading of the card table and the mod union
4019 // table by the CM thread.
4020 // . We run concurrently with mutator updates, so scanning
4021 // needs to be done carefully -- we should not try to scan
4022 // potentially uninitialized objects.
4023 //
4024 // Locking strategy: While holding the CGC_lock, we scan over and
4025 // reset a maximal dirty range of the mod union / card tables, then lock
4026 // the free_list_lock and bitmap lock to do a full marking, then
4027 // release these locks; and repeat the cycle. This allows for a
4028 // certain amount of fairness in the sharing of these locks between
4029 // the CMS collector on the one hand, and the VM thread and the
4030 // mutators on the other.
4031
4032 // NOTE: preclean_mod_union_table() and preclean_card_table()
4033 // further below are largely identical; if you need to modify
4034 // one of these methods, please check the other method too.
4035
4036 size_t CMSCollector::preclean_mod_union_table(
4037 ConcurrentMarkSweepGeneration* old_gen,
4038 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4039 verify_work_stacks_empty();
4040 verify_overflow_empty();
4041
4042 // strategy: starting with the first card, accumulate contiguous
4043 // ranges of dirty cards; clear these cards, then scan the region
4044 // covered by these cards.
4045
4046 // Since all of the MUT is committed ahead, we can just use
4047 // that, in case the generations expand while we are precleaning.
4048 // It might also be fine to just use the committed part of the
4049 // generation, but we might potentially miss cards when the
4050 // generation is rapidly expanding while we are in the midst
4051 // of precleaning.
4052 HeapWord* startAddr = old_gen->reserved().start();
4053 HeapWord* endAddr = old_gen->reserved().end();
4054
4055 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4056
4057 size_t numDirtyCards, cumNumDirtyCards;
4058 HeapWord *nextAddr, *lastAddr;
4059 for (cumNumDirtyCards = numDirtyCards = 0,
4060 nextAddr = lastAddr = startAddr;
4061 nextAddr < endAddr;
4062 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4063
4064 ResourceMark rm;
4065 HandleMark hm;
4066
4067 MemRegion dirtyRegion;
4068 {
4069 stopTimer();
4070 // Potential yield point
4071 CMSTokenSync ts(true);
4072 startTimer();
4073 sample_eden();
4074 // Get dirty region starting at nextOffset (inclusive),
4075 // simultaneously clearing it.
4076 dirtyRegion =
4077 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4078 assert(dirtyRegion.start() >= nextAddr,
4079 "returned region inconsistent?");
4080 }
4081 // Remember where the next search should begin.
4082 // The returned region (if non-empty) is a right open interval,
4083 // so lastOffset is obtained from the right end of that
4084 // interval.
4085 lastAddr = dirtyRegion.end();
4086 // Should do something more transparent and less hacky XXX
4087 numDirtyCards =
4088 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4089
4090 // We'll scan the cards in the dirty region (with periodic
4091 // yields for foreground GC as needed).
4092 if (!dirtyRegion.is_empty()) {
4093 assert(numDirtyCards > 0, "consistency check");
4094 HeapWord* stop_point = NULL;
4095 stopTimer();
4096 // Potential yield point
4097 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4098 bitMapLock());
4099 startTimer();
4100 {
4101 verify_work_stacks_empty();
4102 verify_overflow_empty();
4103 sample_eden();
4104 stop_point =
4105 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4106 }
4107 if (stop_point != NULL) {
4108 // The careful iteration stopped early either because it found an
4109 // uninitialized object, or because we were in the midst of an
4110 // "abortable preclean", which should now be aborted. Redirty
4111 // the bits corresponding to the partially-scanned or unscanned
4112 // cards. We'll either restart at the next block boundary or
4113 // abort the preclean.
4114 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4115 "Should only be AbortablePreclean.");
4116 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4117 if (should_abort_preclean()) {
4118 break; // out of preclean loop
4119 } else {
4120 // Compute the next address at which preclean should pick up;
4121 // might need bitMapLock in order to read P-bits.
4122 lastAddr = next_card_start_after_block(stop_point);
4123 }
4124 }
4125 } else {
4126 assert(lastAddr == endAddr, "consistency check");
4127 assert(numDirtyCards == 0, "consistency check");
4128 break;
4129 }
4130 }
4131 verify_work_stacks_empty();
4132 verify_overflow_empty();
4133 return cumNumDirtyCards;
4134 }
4135
4136 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4137 // below are largely identical; if you need to modify
4138 // one of these methods, please check the other method too.
4139
4140 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4141 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4142 // strategy: it's similar to precleamModUnionTable above, in that
4143 // we accumulate contiguous ranges of dirty cards, mark these cards
4144 // precleaned, then scan the region covered by these cards.
4145 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4146 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4147
4148 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4149
4150 size_t numDirtyCards, cumNumDirtyCards;
4151 HeapWord *lastAddr, *nextAddr;
4152
4153 for (cumNumDirtyCards = numDirtyCards = 0,
4154 nextAddr = lastAddr = startAddr;
4155 nextAddr < endAddr;
4156 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4157
4158 ResourceMark rm;
4159 HandleMark hm;
4160
4161 MemRegion dirtyRegion;
4162 {
4163 // See comments in "Precleaning notes" above on why we
4164 // do this locking. XXX Could the locking overheads be
4165 // too high when dirty cards are sparse? [I don't think so.]
4166 stopTimer();
4167 CMSTokenSync x(true); // is cms thread
4168 startTimer();
4169 sample_eden();
4170 // Get and clear dirty region from card table
4171 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4172 MemRegion(nextAddr, endAddr),
4173 true,
4174 CardTableModRefBS::precleaned_card_val());
4175
4176 assert(dirtyRegion.start() >= nextAddr,
4177 "returned region inconsistent?");
4178 }
4179 lastAddr = dirtyRegion.end();
4180 numDirtyCards =
4181 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4182
4183 if (!dirtyRegion.is_empty()) {
4184 stopTimer();
4185 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4186 startTimer();
4187 sample_eden();
4188 verify_work_stacks_empty();
4189 verify_overflow_empty();
4190 HeapWord* stop_point =
4191 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4192 if (stop_point != NULL) {
4193 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4194 "Should only be AbortablePreclean.");
4195 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4196 if (should_abort_preclean()) {
4197 break; // out of preclean loop
4198 } else {
4199 // Compute the next address at which preclean should pick up.
4200 lastAddr = next_card_start_after_block(stop_point);
4201 }
4202 }
4203 } else {
4204 break;
4205 }
4206 }
4207 verify_work_stacks_empty();
4208 verify_overflow_empty();
4209 return cumNumDirtyCards;
4210 }
4211
4212 class PrecleanKlassClosure : public KlassClosure {
4213 KlassToOopClosure _cm_klass_closure;
4214 public:
4215 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4216 void do_klass(Klass* k) {
4217 if (k->has_accumulated_modified_oops()) {
4218 k->clear_accumulated_modified_oops();
4219
4220 _cm_klass_closure.do_klass(k);
4221 }
4222 }
4223 };
4224
4225 // The freelist lock is needed to prevent asserts, is it really needed?
4226 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4227
4228 cl->set_freelistLock(freelistLock);
4229
4230 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4231
4232 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4233 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4234 PrecleanKlassClosure preclean_klass_closure(cl);
4235 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4236
4237 verify_work_stacks_empty();
4238 verify_overflow_empty();
4239 }
4240
4241 void CMSCollector::checkpointRootsFinal() {
4242 assert(_collectorState == FinalMarking, "incorrect state transition?");
4243 check_correct_thread_executing();
4244 // world is stopped at this checkpoint
4245 assert(SafepointSynchronize::is_at_safepoint(),
4246 "world should be stopped");
4247 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4248
4249 verify_work_stacks_empty();
4250 verify_overflow_empty();
4251
4252 if (PrintGCDetails) {
4253 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4254 _young_gen->used() / K,
4255 _young_gen->capacity() / K);
4256 }
4257 {
4258 if (CMSScavengeBeforeRemark) {
4259 GenCollectedHeap* gch = GenCollectedHeap::heap();
4260 // Temporarily set flag to false, GCH->do_collection will
4261 // expect it to be false and set to true
4262 FlagSetting fl(gch->_is_gc_active, false);
4263 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4264 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4265 gch->do_collection(true, // full (i.e. force, see below)
4266 false, // !clear_all_soft_refs
4267 0, // size
4268 false, // is_tlab
4269 GenCollectedHeap::YoungGen // type
4270 );
4271 }
4272 FreelistLocker x(this);
4273 MutexLockerEx y(bitMapLock(),
4274 Mutex::_no_safepoint_check_flag);
4275 checkpointRootsFinalWork();
4276 }
4277 verify_work_stacks_empty();
4278 verify_overflow_empty();
4279 }
4280
4281 void CMSCollector::checkpointRootsFinalWork() {
4282 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4283
4284 assert(haveFreelistLocks(), "must have free list locks");
4285 assert_lock_strong(bitMapLock());
4286
4287 ResourceMark rm;
4288 HandleMark hm;
4289
4290 GenCollectedHeap* gch = GenCollectedHeap::heap();
4291
4292 if (should_unload_classes()) {
4293 CodeCache::gc_prologue();
4294 }
4295 assert(haveFreelistLocks(), "must have free list locks");
4296 assert_lock_strong(bitMapLock());
4297
4298 // We might assume that we need not fill TLAB's when
4299 // CMSScavengeBeforeRemark is set, because we may have just done
4300 // a scavenge which would have filled all TLAB's -- and besides
4301 // Eden would be empty. This however may not always be the case --
4302 // for instance although we asked for a scavenge, it may not have
4303 // happened because of a JNI critical section. We probably need
4304 // a policy for deciding whether we can in that case wait until
4305 // the critical section releases and then do the remark following
4306 // the scavenge, and skip it here. In the absence of that policy,
4307 // or of an indication of whether the scavenge did indeed occur,
4308 // we cannot rely on TLAB's having been filled and must do
4309 // so here just in case a scavenge did not happen.
4310 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4311 // Update the saved marks which may affect the root scans.
4312 gch->save_marks();
4313
4314 if (CMSPrintEdenSurvivorChunks) {
4315 print_eden_and_survivor_chunk_arrays();
4316 }
4317
4318 {
4319 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4320
4321 // Note on the role of the mod union table:
4322 // Since the marker in "markFromRoots" marks concurrently with
4323 // mutators, it is possible for some reachable objects not to have been
4324 // scanned. For instance, an only reference to an object A was
4325 // placed in object B after the marker scanned B. Unless B is rescanned,
4326 // A would be collected. Such updates to references in marked objects
4327 // are detected via the mod union table which is the set of all cards
4328 // dirtied since the first checkpoint in this GC cycle and prior to
4329 // the most recent young generation GC, minus those cleaned up by the
4330 // concurrent precleaning.
4331 if (CMSParallelRemarkEnabled) {
4332 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4333 do_remark_parallel();
4334 } else {
4335 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4336 _gc_timer_cm, _gc_tracer_cm->gc_id());
4337 do_remark_non_parallel();
4338 }
4339 }
4340 verify_work_stacks_empty();
4341 verify_overflow_empty();
4342
4343 {
4344 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4345 refProcessingWork();
4346 }
4347 verify_work_stacks_empty();
4348 verify_overflow_empty();
4349
4350 if (should_unload_classes()) {
4351 CodeCache::gc_epilogue();
4352 }
4353 JvmtiExport::gc_epilogue();
4354
4355 // If we encountered any (marking stack / work queue) overflow
4356 // events during the current CMS cycle, take appropriate
4357 // remedial measures, where possible, so as to try and avoid
4358 // recurrence of that condition.
4359 assert(_markStack.isEmpty(), "No grey objects");
4360 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4361 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4362 if (ser_ovflw > 0) {
4363 if (PrintCMSStatistics != 0) {
4364 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4365 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4366 ", kac_preclean=" SIZE_FORMAT ")",
4367 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4368 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4369 }
4370 _markStack.expand();
4371 _ser_pmc_remark_ovflw = 0;
4372 _ser_pmc_preclean_ovflw = 0;
4373 _ser_kac_preclean_ovflw = 0;
4374 _ser_kac_ovflw = 0;
4375 }
4376 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4377 if (PrintCMSStatistics != 0) {
4378 gclog_or_tty->print_cr("Work queue overflow (benign) "
4379 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4380 _par_pmc_remark_ovflw, _par_kac_ovflw);
4381 }
4382 _par_pmc_remark_ovflw = 0;
4383 _par_kac_ovflw = 0;
4384 }
4385 if (PrintCMSStatistics != 0) {
4386 if (_markStack._hit_limit > 0) {
4387 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4388 _markStack._hit_limit);
4389 }
4390 if (_markStack._failed_double > 0) {
4391 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4392 " current capacity " SIZE_FORMAT,
4393 _markStack._failed_double,
4394 _markStack.capacity());
4395 }
4396 }
4397 _markStack._hit_limit = 0;
4398 _markStack._failed_double = 0;
4399
4400 if ((VerifyAfterGC || VerifyDuringGC) &&
4401 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4402 verify_after_remark();
4403 }
4404
4405 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4406
4407 // Change under the freelistLocks.
4408 _collectorState = Sweeping;
4409 // Call isAllClear() under bitMapLock
4410 assert(_modUnionTable.isAllClear(),
4411 "Should be clear by end of the final marking");
4412 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4413 "Should be clear by end of the final marking");
4414 }
4415
4416 void CMSParInitialMarkTask::work(uint worker_id) {
4417 elapsedTimer _timer;
4418 ResourceMark rm;
4419 HandleMark hm;
4420
4421 // ---------- scan from roots --------------
4422 _timer.start();
4423 GenCollectedHeap* gch = GenCollectedHeap::heap();
4424 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4425
4426 // ---------- young gen roots --------------
4427 {
4428 work_on_young_gen_roots(worker_id, &par_mri_cl);
4429 _timer.stop();
4430 if (PrintCMSStatistics != 0) {
4431 gclog_or_tty->print_cr(
4432 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4433 worker_id, _timer.seconds());
4434 }
4435 }
4436
4437 // ---------- remaining roots --------------
4438 _timer.reset();
4439 _timer.start();
4440
4441 CLDToOopClosure cld_closure(&par_mri_cl, true);
4442
4443 gch->gen_process_roots(_strong_roots_scope,
4444 GenCollectedHeap::OldGen,
4445 false, // yg was scanned above
4446 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4447 _collector->should_unload_classes(),
4448 &par_mri_cl,
4449 NULL,
4450 &cld_closure);
4451 assert(_collector->should_unload_classes()
4452 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4453 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4454 _timer.stop();
4455 if (PrintCMSStatistics != 0) {
4456 gclog_or_tty->print_cr(
4457 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4458 worker_id, _timer.seconds());
4459 }
4460 }
4461
4462 // Parallel remark task
4463 class CMSParRemarkTask: public CMSParMarkTask {
4464 CompactibleFreeListSpace* _cms_space;
4465
4466 // The per-thread work queues, available here for stealing.
4467 OopTaskQueueSet* _task_queues;
4468 ParallelTaskTerminator _term;
4469 StrongRootsScope* _strong_roots_scope;
4470
4471 public:
4472 // A value of 0 passed to n_workers will cause the number of
4473 // workers to be taken from the active workers in the work gang.
4474 CMSParRemarkTask(CMSCollector* collector,
4475 CompactibleFreeListSpace* cms_space,
4476 uint n_workers, WorkGang* workers,
4477 OopTaskQueueSet* task_queues,
4478 StrongRootsScope* strong_roots_scope):
4479 CMSParMarkTask("Rescan roots and grey objects in parallel",
4480 collector, n_workers),
4481 _cms_space(cms_space),
4482 _task_queues(task_queues),
4483 _term(n_workers, task_queues),
4484 _strong_roots_scope(strong_roots_scope) { }
4485
4486 OopTaskQueueSet* task_queues() { return _task_queues; }
4487
4488 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4489
4490 ParallelTaskTerminator* terminator() { return &_term; }
4491 uint n_workers() { return _n_workers; }
4492
4493 void work(uint worker_id);
4494
4495 private:
4496 // ... of dirty cards in old space
4497 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4498 Par_MarkRefsIntoAndScanClosure* cl);
4499
4500 // ... work stealing for the above
4501 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4502 };
4503
4504 class RemarkKlassClosure : public KlassClosure {
4505 KlassToOopClosure _cm_klass_closure;
4506 public:
4507 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4508 void do_klass(Klass* k) {
4509 // Check if we have modified any oops in the Klass during the concurrent marking.
4510 if (k->has_accumulated_modified_oops()) {
4511 k->clear_accumulated_modified_oops();
4512
4513 // We could have transfered the current modified marks to the accumulated marks,
4514 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4515 } else if (k->has_modified_oops()) {
4516 // Don't clear anything, this info is needed by the next young collection.
4517 } else {
4518 // No modified oops in the Klass.
4519 return;
4520 }
4521
4522 // The klass has modified fields, need to scan the klass.
4523 _cm_klass_closure.do_klass(k);
4524 }
4525 };
4526
4527 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4528 ParNewGeneration* young_gen = _collector->_young_gen;
4529 ContiguousSpace* eden_space = young_gen->eden();
4530 ContiguousSpace* from_space = young_gen->from();
4531 ContiguousSpace* to_space = young_gen->to();
4532
4533 HeapWord** eca = _collector->_eden_chunk_array;
4534 size_t ect = _collector->_eden_chunk_index;
4535 HeapWord** sca = _collector->_survivor_chunk_array;
4536 size_t sct = _collector->_survivor_chunk_index;
4537
4538 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4539 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4540
4541 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4542 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4543 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4544 }
4545
4546 // work_queue(i) is passed to the closure
4547 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4548 // also is passed to do_dirty_card_rescan_tasks() and to
4549 // do_work_steal() to select the i-th task_queue.
4550
4551 void CMSParRemarkTask::work(uint worker_id) {
4552 elapsedTimer _timer;
4553 ResourceMark rm;
4554 HandleMark hm;
4555
4556 // ---------- rescan from roots --------------
4557 _timer.start();
4558 GenCollectedHeap* gch = GenCollectedHeap::heap();
4559 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4560 _collector->_span, _collector->ref_processor(),
4561 &(_collector->_markBitMap),
4562 work_queue(worker_id));
4563
4564 // Rescan young gen roots first since these are likely
4565 // coarsely partitioned and may, on that account, constitute
4566 // the critical path; thus, it's best to start off that
4567 // work first.
4568 // ---------- young gen roots --------------
4569 {
4570 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4571 _timer.stop();
4572 if (PrintCMSStatistics != 0) {
4573 gclog_or_tty->print_cr(
4574 "Finished young gen rescan work in %dth thread: %3.3f sec",
4575 worker_id, _timer.seconds());
4576 }
4577 }
4578
4579 // ---------- remaining roots --------------
4580 _timer.reset();
4581 _timer.start();
4582 gch->gen_process_roots(_strong_roots_scope,
4583 GenCollectedHeap::OldGen,
4584 false, // yg was scanned above
4585 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4586 _collector->should_unload_classes(),
4587 &par_mrias_cl,
4588 NULL,
4589 NULL); // The dirty klasses will be handled below
4590
4591 assert(_collector->should_unload_classes()
4592 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4593 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4594 _timer.stop();
4595 if (PrintCMSStatistics != 0) {
4596 gclog_or_tty->print_cr(
4597 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4598 worker_id, _timer.seconds());
4599 }
4600
4601 // ---------- unhandled CLD scanning ----------
4602 if (worker_id == 0) { // Single threaded at the moment.
4603 _timer.reset();
4604 _timer.start();
4605
4606 // Scan all new class loader data objects and new dependencies that were
4607 // introduced during concurrent marking.
4608 ResourceMark rm;
4609 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4610 for (int i = 0; i < array->length(); i++) {
4611 par_mrias_cl.do_cld_nv(array->at(i));
4612 }
4613
4614 // We don't need to keep track of new CLDs anymore.
4615 ClassLoaderDataGraph::remember_new_clds(false);
4616
4617 _timer.stop();
4618 if (PrintCMSStatistics != 0) {
4619 gclog_or_tty->print_cr(
4620 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4621 worker_id, _timer.seconds());
4622 }
4623 }
4624
4625 // ---------- dirty klass scanning ----------
4626 if (worker_id == 0) { // Single threaded at the moment.
4627 _timer.reset();
4628 _timer.start();
4629
4630 // Scan all classes that was dirtied during the concurrent marking phase.
4631 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4632 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4633
4634 _timer.stop();
4635 if (PrintCMSStatistics != 0) {
4636 gclog_or_tty->print_cr(
4637 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4638 worker_id, _timer.seconds());
4639 }
4640 }
4641
4642 // We might have added oops to ClassLoaderData::_handles during the
4643 // concurrent marking phase. These oops point to newly allocated objects
4644 // that are guaranteed to be kept alive. Either by the direct allocation
4645 // code, or when the young collector processes the roots. Hence,
4646 // we don't have to revisit the _handles block during the remark phase.
4647
4648 // ---------- rescan dirty cards ------------
4649 _timer.reset();
4650 _timer.start();
4651
4652 // Do the rescan tasks for each of the two spaces
4653 // (cms_space) in turn.
4654 // "worker_id" is passed to select the task_queue for "worker_id"
4655 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4656 _timer.stop();
4657 if (PrintCMSStatistics != 0) {
4658 gclog_or_tty->print_cr(
4659 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4660 worker_id, _timer.seconds());
4661 }
4662
4663 // ---------- steal work from other threads ...
4664 // ---------- ... and drain overflow list.
4665 _timer.reset();
4666 _timer.start();
4667 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4668 _timer.stop();
4669 if (PrintCMSStatistics != 0) {
4670 gclog_or_tty->print_cr(
4671 "Finished work stealing in %dth thread: %3.3f sec",
4672 worker_id, _timer.seconds());
4673 }
4674 }
4675
4676 // Note that parameter "i" is not used.
4677 void
4678 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4679 OopsInGenClosure* cl, ContiguousSpace* space,
4680 HeapWord** chunk_array, size_t chunk_top) {
4681 // Until all tasks completed:
4682 // . claim an unclaimed task
4683 // . compute region boundaries corresponding to task claimed
4684 // using chunk_array
4685 // . par_oop_iterate(cl) over that region
4686
4687 ResourceMark rm;
4688 HandleMark hm;
4689
4690 SequentialSubTasksDone* pst = space->par_seq_tasks();
4691
4692 uint nth_task = 0;
4693 uint n_tasks = pst->n_tasks();
4694
4695 if (n_tasks > 0) {
4696 assert(pst->valid(), "Uninitialized use?");
4697 HeapWord *start, *end;
4698 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4699 // We claimed task # nth_task; compute its boundaries.
4700 if (chunk_top == 0) { // no samples were taken
4701 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4702 start = space->bottom();
4703 end = space->top();
4704 } else if (nth_task == 0) {
4705 start = space->bottom();
4706 end = chunk_array[nth_task];
4707 } else if (nth_task < (uint)chunk_top) {
4708 assert(nth_task >= 1, "Control point invariant");
4709 start = chunk_array[nth_task - 1];
4710 end = chunk_array[nth_task];
4711 } else {
4712 assert(nth_task == (uint)chunk_top, "Control point invariant");
4713 start = chunk_array[chunk_top - 1];
4714 end = space->top();
4715 }
4716 MemRegion mr(start, end);
4717 // Verify that mr is in space
4718 assert(mr.is_empty() || space->used_region().contains(mr),
4719 "Should be in space");
4720 // Verify that "start" is an object boundary
4721 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4722 "Should be an oop");
4723 space->par_oop_iterate(mr, cl);
4724 }
4725 pst->all_tasks_completed();
4726 }
4727 }
4728
4729 void
4730 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4731 CompactibleFreeListSpace* sp, int i,
4732 Par_MarkRefsIntoAndScanClosure* cl) {
4733 // Until all tasks completed:
4734 // . claim an unclaimed task
4735 // . compute region boundaries corresponding to task claimed
4736 // . transfer dirty bits ct->mut for that region
4737 // . apply rescanclosure to dirty mut bits for that region
4738
4739 ResourceMark rm;
4740 HandleMark hm;
4741
4742 OopTaskQueue* work_q = work_queue(i);
4743 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4744 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4745 // CAUTION: This closure has state that persists across calls to
4746 // the work method dirty_range_iterate_clear() in that it has
4747 // embedded in it a (subtype of) UpwardsObjectClosure. The
4748 // use of that state in the embedded UpwardsObjectClosure instance
4749 // assumes that the cards are always iterated (even if in parallel
4750 // by several threads) in monotonically increasing order per each
4751 // thread. This is true of the implementation below which picks
4752 // card ranges (chunks) in monotonically increasing order globally
4753 // and, a-fortiori, in monotonically increasing order per thread
4754 // (the latter order being a subsequence of the former).
4755 // If the work code below is ever reorganized into a more chaotic
4756 // work-partitioning form than the current "sequential tasks"
4757 // paradigm, the use of that persistent state will have to be
4758 // revisited and modified appropriately. See also related
4759 // bug 4756801 work on which should examine this code to make
4760 // sure that the changes there do not run counter to the
4761 // assumptions made here and necessary for correctness and
4762 // efficiency. Note also that this code might yield inefficient
4763 // behavior in the case of very large objects that span one or
4764 // more work chunks. Such objects would potentially be scanned
4765 // several times redundantly. Work on 4756801 should try and
4766 // address that performance anomaly if at all possible. XXX
4767 MemRegion full_span = _collector->_span;
4768 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4769 MarkFromDirtyCardsClosure
4770 greyRescanClosure(_collector, full_span, // entire span of interest
4771 sp, bm, work_q, cl);
4772
4773 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4774 assert(pst->valid(), "Uninitialized use?");
4775 uint nth_task = 0;
4776 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4777 MemRegion span = sp->used_region();
4778 HeapWord* start_addr = span.start();
4779 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4780 alignment);
4781 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4782 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4783 start_addr, "Check alignment");
4784 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4785 chunk_size, "Check alignment");
4786
4787 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4788 // Having claimed the nth_task, compute corresponding mem-region,
4789 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4790 // The alignment restriction ensures that we do not need any
4791 // synchronization with other gang-workers while setting or
4792 // clearing bits in thus chunk of the MUT.
4793 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4794 start_addr + (nth_task+1)*chunk_size);
4795 // The last chunk's end might be way beyond end of the
4796 // used region. In that case pull back appropriately.
4797 if (this_span.end() > end_addr) {
4798 this_span.set_end(end_addr);
4799 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4800 }
4801 // Iterate over the dirty cards covering this chunk, marking them
4802 // precleaned, and setting the corresponding bits in the mod union
4803 // table. Since we have been careful to partition at Card and MUT-word
4804 // boundaries no synchronization is needed between parallel threads.
4805 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4806 &modUnionClosure);
4807
4808 // Having transferred these marks into the modUnionTable,
4809 // rescan the marked objects on the dirty cards in the modUnionTable.
4810 // Even if this is at a synchronous collection, the initial marking
4811 // may have been done during an asynchronous collection so there
4812 // may be dirty bits in the mod-union table.
4813 _collector->_modUnionTable.dirty_range_iterate_clear(
4814 this_span, &greyRescanClosure);
4815 _collector->_modUnionTable.verifyNoOneBitsInRange(
4816 this_span.start(),
4817 this_span.end());
4818 }
4819 pst->all_tasks_completed(); // declare that i am done
4820 }
4821
4822 // . see if we can share work_queues with ParNew? XXX
4823 void
4824 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4825 int* seed) {
4826 OopTaskQueue* work_q = work_queue(i);
4827 NOT_PRODUCT(int num_steals = 0;)
4828 oop obj_to_scan;
4829 CMSBitMap* bm = &(_collector->_markBitMap);
4830
4831 while (true) {
4832 // Completely finish any left over work from (an) earlier round(s)
4833 cl->trim_queue(0);
4834 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4835 (size_t)ParGCDesiredObjsFromOverflowList);
4836 // Now check if there's any work in the overflow list
4837 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4838 // only affects the number of attempts made to get work from the
4839 // overflow list and does not affect the number of workers. Just
4840 // pass ParallelGCThreads so this behavior is unchanged.
4841 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4842 work_q,
4843 ParallelGCThreads)) {
4844 // found something in global overflow list;
4845 // not yet ready to go stealing work from others.
4846 // We'd like to assert(work_q->size() != 0, ...)
4847 // because we just took work from the overflow list,
4848 // but of course we can't since all of that could have
4849 // been already stolen from us.
4850 // "He giveth and He taketh away."
4851 continue;
4852 }
4853 // Verify that we have no work before we resort to stealing
4854 assert(work_q->size() == 0, "Have work, shouldn't steal");
4855 // Try to steal from other queues that have work
4856 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4857 NOT_PRODUCT(num_steals++;)
4858 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4859 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4860 // Do scanning work
4861 obj_to_scan->oop_iterate(cl);
4862 // Loop around, finish this work, and try to steal some more
4863 } else if (terminator()->offer_termination()) {
4864 break; // nirvana from the infinite cycle
4865 }
4866 }
4867 NOT_PRODUCT(
4868 if (PrintCMSStatistics != 0) {
4869 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4870 }
4871 )
4872 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4873 "Else our work is not yet done");
4874 }
4875
4876 // Record object boundaries in _eden_chunk_array by sampling the eden
4877 // top in the slow-path eden object allocation code path and record
4878 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4879 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4880 // sampling in sample_eden() that activates during the part of the
4881 // preclean phase.
4882 void CMSCollector::sample_eden_chunk() {
4883 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4884 if (_eden_chunk_lock->try_lock()) {
4885 // Record a sample. This is the critical section. The contents
4886 // of the _eden_chunk_array have to be non-decreasing in the
4887 // address order.
4888 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4889 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4890 "Unexpected state of Eden");
4891 if (_eden_chunk_index == 0 ||
4892 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4893 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4894 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4895 _eden_chunk_index++; // commit sample
4896 }
4897 _eden_chunk_lock->unlock();
4898 }
4899 }
4900 }
4901
4902 // Return a thread-local PLAB recording array, as appropriate.
4903 void* CMSCollector::get_data_recorder(int thr_num) {
4904 if (_survivor_plab_array != NULL &&
4905 (CMSPLABRecordAlways ||
4906 (_collectorState > Marking && _collectorState < FinalMarking))) {
4907 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4908 ChunkArray* ca = &_survivor_plab_array[thr_num];
4909 ca->reset(); // clear it so that fresh data is recorded
4910 return (void*) ca;
4911 } else {
4912 return NULL;
4913 }
4914 }
4915
4916 // Reset all the thread-local PLAB recording arrays
4917 void CMSCollector::reset_survivor_plab_arrays() {
4918 for (uint i = 0; i < ParallelGCThreads; i++) {
4919 _survivor_plab_array[i].reset();
4920 }
4921 }
4922
4923 // Merge the per-thread plab arrays into the global survivor chunk
4924 // array which will provide the partitioning of the survivor space
4925 // for CMS initial scan and rescan.
4926 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4927 int no_of_gc_threads) {
4928 assert(_survivor_plab_array != NULL, "Error");
4929 assert(_survivor_chunk_array != NULL, "Error");
4930 assert(_collectorState == FinalMarking ||
4931 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4932 for (int j = 0; j < no_of_gc_threads; j++) {
4933 _cursor[j] = 0;
4934 }
4935 HeapWord* top = surv->top();
4936 size_t i;
4937 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4938 HeapWord* min_val = top; // Higher than any PLAB address
4939 uint min_tid = 0; // position of min_val this round
4940 for (int j = 0; j < no_of_gc_threads; j++) {
4941 ChunkArray* cur_sca = &_survivor_plab_array[j];
4942 if (_cursor[j] == cur_sca->end()) {
4943 continue;
4944 }
4945 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4946 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4947 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4948 if (cur_val < min_val) {
4949 min_tid = j;
4950 min_val = cur_val;
4951 } else {
4952 assert(cur_val < top, "All recorded addresses should be less");
4953 }
4954 }
4955 // At this point min_val and min_tid are respectively
4956 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4957 // and the thread (j) that witnesses that address.
4958 // We record this address in the _survivor_chunk_array[i]
4959 // and increment _cursor[min_tid] prior to the next round i.
4960 if (min_val == top) {
4961 break;
4962 }
4963 _survivor_chunk_array[i] = min_val;
4964 _cursor[min_tid]++;
4965 }
4966 // We are all done; record the size of the _survivor_chunk_array
4967 _survivor_chunk_index = i; // exclusive: [0, i)
4968 if (PrintCMSStatistics > 0) {
4969 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4970 }
4971 // Verify that we used up all the recorded entries
4972 #ifdef ASSERT
4973 size_t total = 0;
4974 for (int j = 0; j < no_of_gc_threads; j++) {
4975 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4976 total += _cursor[j];
4977 }
4978 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4979 // Check that the merged array is in sorted order
4980 if (total > 0) {
4981 for (size_t i = 0; i < total - 1; i++) {
4982 if (PrintCMSStatistics > 0) {
4983 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4984 i, p2i(_survivor_chunk_array[i]));
4985 }
4986 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4987 "Not sorted");
4988 }
4989 }
4990 #endif // ASSERT
4991 }
4992
4993 // Set up the space's par_seq_tasks structure for work claiming
4994 // for parallel initial scan and rescan of young gen.
4995 // See ParRescanTask where this is currently used.
4996 void
4997 CMSCollector::
4998 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4999 assert(n_threads > 0, "Unexpected n_threads argument");
5000
5001 // Eden space
5002 if (!_young_gen->eden()->is_empty()) {
5003 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5004 assert(!pst->valid(), "Clobbering existing data?");
5005 // Each valid entry in [0, _eden_chunk_index) represents a task.
5006 size_t n_tasks = _eden_chunk_index + 1;
5007 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5008 // Sets the condition for completion of the subtask (how many threads
5009 // need to finish in order to be done).
5010 pst->set_n_threads(n_threads);
5011 pst->set_n_tasks((int)n_tasks);
5012 }
5013
5014 // Merge the survivor plab arrays into _survivor_chunk_array
5015 if (_survivor_plab_array != NULL) {
5016 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5017 } else {
5018 assert(_survivor_chunk_index == 0, "Error");
5019 }
5020
5021 // To space
5022 {
5023 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5024 assert(!pst->valid(), "Clobbering existing data?");
5025 // Sets the condition for completion of the subtask (how many threads
5026 // need to finish in order to be done).
5027 pst->set_n_threads(n_threads);
5028 pst->set_n_tasks(1);
5029 assert(pst->valid(), "Error");
5030 }
5031
5032 // From space
5033 {
5034 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5035 assert(!pst->valid(), "Clobbering existing data?");
5036 size_t n_tasks = _survivor_chunk_index + 1;
5037 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5038 // Sets the condition for completion of the subtask (how many threads
5039 // need to finish in order to be done).
5040 pst->set_n_threads(n_threads);
5041 pst->set_n_tasks((int)n_tasks);
5042 assert(pst->valid(), "Error");
5043 }
5044 }
5045
5046 // Parallel version of remark
5047 void CMSCollector::do_remark_parallel() {
5048 GenCollectedHeap* gch = GenCollectedHeap::heap();
5049 WorkGang* workers = gch->workers();
5050 assert(workers != NULL, "Need parallel worker threads.");
5051 // Choose to use the number of GC workers most recently set
5052 // into "active_workers".
5053 uint n_workers = workers->active_workers();
5054
5055 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5056
5057 StrongRootsScope srs(n_workers);
5058
5059 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5060
5061 // We won't be iterating over the cards in the card table updating
5062 // the younger_gen cards, so we shouldn't call the following else
5063 // the verification code as well as subsequent younger_refs_iterate
5064 // code would get confused. XXX
5065 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5066
5067 // The young gen rescan work will not be done as part of
5068 // process_roots (which currently doesn't know how to
5069 // parallelize such a scan), but rather will be broken up into
5070 // a set of parallel tasks (via the sampling that the [abortable]
5071 // preclean phase did of eden, plus the [two] tasks of
5072 // scanning the [two] survivor spaces. Further fine-grain
5073 // parallelization of the scanning of the survivor spaces
5074 // themselves, and of precleaning of the young gen itself
5075 // is deferred to the future.
5076 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5077
5078 // The dirty card rescan work is broken up into a "sequence"
5079 // of parallel tasks (per constituent space) that are dynamically
5080 // claimed by the parallel threads.
5081 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5082
5083 // It turns out that even when we're using 1 thread, doing the work in a
5084 // separate thread causes wide variance in run times. We can't help this
5085 // in the multi-threaded case, but we special-case n=1 here to get
5086 // repeatable measurements of the 1-thread overhead of the parallel code.
5087 if (n_workers > 1) {
5088 // Make refs discovery MT-safe, if it isn't already: it may not
5089 // necessarily be so, since it's possible that we are doing
5090 // ST marking.
5091 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5092 workers->run_task(&tsk);
5093 } else {
5094 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5095 tsk.work(0);
5096 }
5097
5098 // restore, single-threaded for now, any preserved marks
5099 // as a result of work_q overflow
5100 restore_preserved_marks_if_any();
5101 }
5102
5103 // Non-parallel version of remark
5104 void CMSCollector::do_remark_non_parallel() {
5105 ResourceMark rm;
5106 HandleMark hm;
5107 GenCollectedHeap* gch = GenCollectedHeap::heap();
5108 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5109
5110 MarkRefsIntoAndScanClosure
5111 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5112 &_markStack, this,
5113 false /* should_yield */, false /* not precleaning */);
5114 MarkFromDirtyCardsClosure
5115 markFromDirtyCardsClosure(this, _span,
5116 NULL, // space is set further below
5117 &_markBitMap, &_markStack, &mrias_cl);
5118 {
5119 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5120 // Iterate over the dirty cards, setting the corresponding bits in the
5121 // mod union table.
5122 {
5123 ModUnionClosure modUnionClosure(&_modUnionTable);
5124 _ct->ct_bs()->dirty_card_iterate(
5125 _cmsGen->used_region(),
5126 &modUnionClosure);
5127 }
5128 // Having transferred these marks into the modUnionTable, we just need
5129 // to rescan the marked objects on the dirty cards in the modUnionTable.
5130 // The initial marking may have been done during an asynchronous
5131 // collection so there may be dirty bits in the mod-union table.
5132 const int alignment =
5133 CardTableModRefBS::card_size * BitsPerWord;
5134 {
5135 // ... First handle dirty cards in CMS gen
5136 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5137 MemRegion ur = _cmsGen->used_region();
5138 HeapWord* lb = ur.start();
5139 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5140 MemRegion cms_span(lb, ub);
5141 _modUnionTable.dirty_range_iterate_clear(cms_span,
5142 &markFromDirtyCardsClosure);
5143 verify_work_stacks_empty();
5144 if (PrintCMSStatistics != 0) {
5145 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5146 markFromDirtyCardsClosure.num_dirty_cards());
5147 }
5148 }
5149 }
5150 if (VerifyDuringGC &&
5151 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5152 HandleMark hm; // Discard invalid handles created during verification
5153 Universe::verify();
5154 }
5155 {
5156 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5157
5158 verify_work_stacks_empty();
5159
5160 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5161 StrongRootsScope srs(1);
5162
5163 gch->gen_process_roots(&srs,
5164 GenCollectedHeap::OldGen,
5165 true, // young gen as roots
5166 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5167 should_unload_classes(),
5168 &mrias_cl,
5169 NULL,
5170 NULL); // The dirty klasses will be handled below
5171
5172 assert(should_unload_classes()
5173 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5174 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5175 }
5176
5177 {
5178 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5179
5180 verify_work_stacks_empty();
5181
5182 // Scan all class loader data objects that might have been introduced
5183 // during concurrent marking.
5184 ResourceMark rm;
5185 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5186 for (int i = 0; i < array->length(); i++) {
5187 mrias_cl.do_cld_nv(array->at(i));
5188 }
5189
5190 // We don't need to keep track of new CLDs anymore.
5191 ClassLoaderDataGraph::remember_new_clds(false);
5192
5193 verify_work_stacks_empty();
5194 }
5195
5196 {
5197 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5198
5199 verify_work_stacks_empty();
5200
5201 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5202 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5203
5204 verify_work_stacks_empty();
5205 }
5206
5207 // We might have added oops to ClassLoaderData::_handles during the
5208 // concurrent marking phase. These oops point to newly allocated objects
5209 // that are guaranteed to be kept alive. Either by the direct allocation
5210 // code, or when the young collector processes the roots. Hence,
5211 // we don't have to revisit the _handles block during the remark phase.
5212
5213 verify_work_stacks_empty();
5214 // Restore evacuated mark words, if any, used for overflow list links
5215 if (!CMSOverflowEarlyRestoration) {
5216 restore_preserved_marks_if_any();
5217 }
5218 verify_overflow_empty();
5219 }
5220
5221 ////////////////////////////////////////////////////////
5222 // Parallel Reference Processing Task Proxy Class
5223 ////////////////////////////////////////////////////////
5224 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5225 OopTaskQueueSet* _queues;
5226 ParallelTaskTerminator _terminator;
5227 public:
5228 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5229 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5230 ParallelTaskTerminator* terminator() { return &_terminator; }
5231 OopTaskQueueSet* queues() { return _queues; }
5232 };
5233
5234 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5235 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5236 CMSCollector* _collector;
5237 CMSBitMap* _mark_bit_map;
5238 const MemRegion _span;
5239 ProcessTask& _task;
5240
5241 public:
5242 CMSRefProcTaskProxy(ProcessTask& task,
5243 CMSCollector* collector,
5244 const MemRegion& span,
5245 CMSBitMap* mark_bit_map,
5246 AbstractWorkGang* workers,
5247 OopTaskQueueSet* task_queues):
5248 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5249 task_queues,
5250 workers->active_workers()),
5251 _task(task),
5252 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5253 {
5254 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5255 "Inconsistency in _span");
5256 }
5257
5258 OopTaskQueueSet* task_queues() { return queues(); }
5259
5260 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5261
5262 void do_work_steal(int i,
5263 CMSParDrainMarkingStackClosure* drain,
5264 CMSParKeepAliveClosure* keep_alive,
5265 int* seed);
5266
5267 virtual void work(uint worker_id);
5268 };
5269
5270 void CMSRefProcTaskProxy::work(uint worker_id) {
5271 ResourceMark rm;
5272 HandleMark hm;
5273 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5274 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5275 _mark_bit_map,
5276 work_queue(worker_id));
5277 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5278 _mark_bit_map,
5279 work_queue(worker_id));
5280 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5281 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5282 if (_task.marks_oops_alive()) {
5283 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5284 _collector->hash_seed(worker_id));
5285 }
5286 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5287 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5288 }
5289
5290 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5291 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5292 EnqueueTask& _task;
5293
5294 public:
5295 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5296 : AbstractGangTask("Enqueue reference objects in parallel"),
5297 _task(task)
5298 { }
5299
5300 virtual void work(uint worker_id)
5301 {
5302 _task.work(worker_id);
5303 }
5304 };
5305
5306 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5307 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5308 _span(span),
5309 _bit_map(bit_map),
5310 _work_queue(work_queue),
5311 _mark_and_push(collector, span, bit_map, work_queue),
5312 _low_water_mark(MIN2((work_queue->max_elems()/4),
5313 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5314 { }
5315
5316 // . see if we can share work_queues with ParNew? XXX
5317 void CMSRefProcTaskProxy::do_work_steal(int i,
5318 CMSParDrainMarkingStackClosure* drain,
5319 CMSParKeepAliveClosure* keep_alive,
5320 int* seed) {
5321 OopTaskQueue* work_q = work_queue(i);
5322 NOT_PRODUCT(int num_steals = 0;)
5323 oop obj_to_scan;
5324
5325 while (true) {
5326 // Completely finish any left over work from (an) earlier round(s)
5327 drain->trim_queue(0);
5328 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5329 (size_t)ParGCDesiredObjsFromOverflowList);
5330 // Now check if there's any work in the overflow list
5331 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5332 // only affects the number of attempts made to get work from the
5333 // overflow list and does not affect the number of workers. Just
5334 // pass ParallelGCThreads so this behavior is unchanged.
5335 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5336 work_q,
5337 ParallelGCThreads)) {
5338 // Found something in global overflow list;
5339 // not yet ready to go stealing work from others.
5340 // We'd like to assert(work_q->size() != 0, ...)
5341 // because we just took work from the overflow list,
5342 // but of course we can't, since all of that might have
5343 // been already stolen from us.
5344 continue;
5345 }
5346 // Verify that we have no work before we resort to stealing
5347 assert(work_q->size() == 0, "Have work, shouldn't steal");
5348 // Try to steal from other queues that have work
5349 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5350 NOT_PRODUCT(num_steals++;)
5351 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5352 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5353 // Do scanning work
5354 obj_to_scan->oop_iterate(keep_alive);
5355 // Loop around, finish this work, and try to steal some more
5356 } else if (terminator()->offer_termination()) {
5357 break; // nirvana from the infinite cycle
5358 }
5359 }
5360 NOT_PRODUCT(
5361 if (PrintCMSStatistics != 0) {
5362 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5363 }
5364 )
5365 }
5366
5367 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5368 {
5369 GenCollectedHeap* gch = GenCollectedHeap::heap();
5370 WorkGang* workers = gch->workers();
5371 assert(workers != NULL, "Need parallel worker threads.");
5372 CMSRefProcTaskProxy rp_task(task, &_collector,
5373 _collector.ref_processor()->span(),
5374 _collector.markBitMap(),
5375 workers, _collector.task_queues());
5376 workers->run_task(&rp_task);
5377 }
5378
5379 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5380 {
5381
5382 GenCollectedHeap* gch = GenCollectedHeap::heap();
5383 WorkGang* workers = gch->workers();
5384 assert(workers != NULL, "Need parallel worker threads.");
5385 CMSRefEnqueueTaskProxy enq_task(task);
5386 workers->run_task(&enq_task);
5387 }
5388
5389 void CMSCollector::refProcessingWork() {
5390 ResourceMark rm;
5391 HandleMark hm;
5392
5393 ReferenceProcessor* rp = ref_processor();
5394 assert(rp->span().equals(_span), "Spans should be equal");
5395 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5396 // Process weak references.
5397 rp->setup_policy(false);
5398 verify_work_stacks_empty();
5399
5400 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5401 &_markStack, false /* !preclean */);
5402 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5403 _span, &_markBitMap, &_markStack,
5404 &cmsKeepAliveClosure, false /* !preclean */);
5405 {
5406 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5407
5408 ReferenceProcessorStats stats;
5409 if (rp->processing_is_mt()) {
5410 // Set the degree of MT here. If the discovery is done MT, there
5411 // may have been a different number of threads doing the discovery
5412 // and a different number of discovered lists may have Ref objects.
5413 // That is OK as long as the Reference lists are balanced (see
5414 // balance_all_queues() and balance_queues()).
5415 GenCollectedHeap* gch = GenCollectedHeap::heap();
5416 uint active_workers = ParallelGCThreads;
5417 WorkGang* workers = gch->workers();
5418 if (workers != NULL) {
5419 active_workers = workers->active_workers();
5420 // The expectation is that active_workers will have already
5421 // been set to a reasonable value. If it has not been set,
5422 // investigate.
5423 assert(active_workers > 0, "Should have been set during scavenge");
5424 }
5425 rp->set_active_mt_degree(active_workers);
5426 CMSRefProcTaskExecutor task_executor(*this);
5427 stats = rp->process_discovered_references(&_is_alive_closure,
5428 &cmsKeepAliveClosure,
5429 &cmsDrainMarkingStackClosure,
5430 &task_executor,
5431 _gc_timer_cm,
5432 _gc_tracer_cm->gc_id());
5433 } else {
5434 stats = rp->process_discovered_references(&_is_alive_closure,
5435 &cmsKeepAliveClosure,
5436 &cmsDrainMarkingStackClosure,
5437 NULL,
5438 _gc_timer_cm,
5439 _gc_tracer_cm->gc_id());
5440 }
5441 _gc_tracer_cm->report_gc_reference_stats(stats);
5442
5443 }
5444
5445 // This is the point where the entire marking should have completed.
5446 verify_work_stacks_empty();
5447
5448 if (should_unload_classes()) {
5449 {
5450 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5451
5452 // Unload classes and purge the SystemDictionary.
5453 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5454
5455 // Unload nmethods.
5456 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5457
5458 // Prune dead klasses from subklass/sibling/implementor lists.
5459 Klass::clean_weak_klass_links(&_is_alive_closure);
5460 }
5461
5462 {
5463 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5464 // Clean up unreferenced symbols in symbol table.
5465 SymbolTable::unlink();
5466 }
5467
5468 {
5469 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5470 // Delete entries for dead interned strings.
5471 StringTable::unlink(&_is_alive_closure);
5472 }
5473 }
5474
5475
5476 // Restore any preserved marks as a result of mark stack or
5477 // work queue overflow
5478 restore_preserved_marks_if_any(); // done single-threaded for now
5479
5480 rp->set_enqueuing_is_done(true);
5481 if (rp->processing_is_mt()) {
5482 rp->balance_all_queues();
5483 CMSRefProcTaskExecutor task_executor(*this);
5484 rp->enqueue_discovered_references(&task_executor);
5485 } else {
5486 rp->enqueue_discovered_references(NULL);
5487 }
5488 rp->verify_no_references_recorded();
5489 assert(!rp->discovery_enabled(), "should have been disabled");
5490 }
5491
5492 #ifndef PRODUCT
5493 void CMSCollector::check_correct_thread_executing() {
5494 Thread* t = Thread::current();
5495 // Only the VM thread or the CMS thread should be here.
5496 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5497 "Unexpected thread type");
5498 // If this is the vm thread, the foreground process
5499 // should not be waiting. Note that _foregroundGCIsActive is
5500 // true while the foreground collector is waiting.
5501 if (_foregroundGCShouldWait) {
5502 // We cannot be the VM thread
5503 assert(t->is_ConcurrentGC_thread(),
5504 "Should be CMS thread");
5505 } else {
5506 // We can be the CMS thread only if we are in a stop-world
5507 // phase of CMS collection.
5508 if (t->is_ConcurrentGC_thread()) {
5509 assert(_collectorState == InitialMarking ||
5510 _collectorState == FinalMarking,
5511 "Should be a stop-world phase");
5512 // The CMS thread should be holding the CMS_token.
5513 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5514 "Potential interference with concurrently "
5515 "executing VM thread");
5516 }
5517 }
5518 }
5519 #endif
5520
5521 void CMSCollector::sweep() {
5522 assert(_collectorState == Sweeping, "just checking");
5523 check_correct_thread_executing();
5524 verify_work_stacks_empty();
5525 verify_overflow_empty();
5526 increment_sweep_count();
5527 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5528
5529 _inter_sweep_timer.stop();
5530 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5531
5532 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5533 _intra_sweep_timer.reset();
5534 _intra_sweep_timer.start();
5535 {
5536 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5537 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5538 // First sweep the old gen
5539 {
5540 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5541 bitMapLock());
5542 sweepWork(_cmsGen);
5543 }
5544
5545 // Update Universe::_heap_*_at_gc figures.
5546 // We need all the free list locks to make the abstract state
5547 // transition from Sweeping to Resetting. See detailed note
5548 // further below.
5549 {
5550 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5551 // Update heap occupancy information which is used as
5552 // input to soft ref clearing policy at the next gc.
5553 Universe::update_heap_info_at_gc();
5554 _collectorState = Resizing;
5555 }
5556 }
5557 verify_work_stacks_empty();
5558 verify_overflow_empty();
5559
5560 if (should_unload_classes()) {
5561 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5562 // requires that the virtual spaces are stable and not deleted.
5563 ClassLoaderDataGraph::set_should_purge(true);
5564 }
5565
5566 _intra_sweep_timer.stop();
5567 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5568
5569 _inter_sweep_timer.reset();
5570 _inter_sweep_timer.start();
5571
5572 // We need to use a monotonically non-decreasing time in ms
5573 // or we will see time-warp warnings and os::javaTimeMillis()
5574 // does not guarantee monotonicity.
5575 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5576 update_time_of_last_gc(now);
5577
5578 // NOTE on abstract state transitions:
5579 // Mutators allocate-live and/or mark the mod-union table dirty
5580 // based on the state of the collection. The former is done in
5581 // the interval [Marking, Sweeping] and the latter in the interval
5582 // [Marking, Sweeping). Thus the transitions into the Marking state
5583 // and out of the Sweeping state must be synchronously visible
5584 // globally to the mutators.
5585 // The transition into the Marking state happens with the world
5586 // stopped so the mutators will globally see it. Sweeping is
5587 // done asynchronously by the background collector so the transition
5588 // from the Sweeping state to the Resizing state must be done
5589 // under the freelistLock (as is the check for whether to
5590 // allocate-live and whether to dirty the mod-union table).
5591 assert(_collectorState == Resizing, "Change of collector state to"
5592 " Resizing must be done under the freelistLocks (plural)");
5593
5594 // Now that sweeping has been completed, we clear
5595 // the incremental_collection_failed flag,
5596 // thus inviting a younger gen collection to promote into
5597 // this generation. If such a promotion may still fail,
5598 // the flag will be set again when a young collection is
5599 // attempted.
5600 GenCollectedHeap* gch = GenCollectedHeap::heap();
5601 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5602 gch->update_full_collections_completed(_collection_count_start);
5603 }
5604
5605 // FIX ME!!! Looks like this belongs in CFLSpace, with
5606 // CMSGen merely delegating to it.
5607 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5608 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5609 HeapWord* minAddr = _cmsSpace->bottom();
5610 HeapWord* largestAddr =
5611 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5612 if (largestAddr == NULL) {
5613 // The dictionary appears to be empty. In this case
5614 // try to coalesce at the end of the heap.
5615 largestAddr = _cmsSpace->end();
5616 }
5617 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5618 size_t nearLargestOffset =
5619 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5620 if (PrintFLSStatistics != 0) {
5621 gclog_or_tty->print_cr(
5622 "CMS: Large Block: " PTR_FORMAT ";"
5623 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5624 p2i(largestAddr),
5625 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5626 }
5627 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5628 }
5629
5630 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5631 return addr >= _cmsSpace->nearLargestChunk();
5632 }
5633
5634 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5635 return _cmsSpace->find_chunk_at_end();
5636 }
5637
5638 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5639 bool full) {
5640 // If the young generation has been collected, gather any statistics
5641 // that are of interest at this point.
5642 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5643 if (!full && current_is_young) {
5644 // Gather statistics on the young generation collection.
5645 collector()->stats().record_gc0_end(used());
5646 }
5647 }
5648
5649 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5650 // We iterate over the space(s) underlying this generation,
5651 // checking the mark bit map to see if the bits corresponding
5652 // to specific blocks are marked or not. Blocks that are
5653 // marked are live and are not swept up. All remaining blocks
5654 // are swept up, with coalescing on-the-fly as we sweep up
5655 // contiguous free and/or garbage blocks:
5656 // We need to ensure that the sweeper synchronizes with allocators
5657 // and stop-the-world collectors. In particular, the following
5658 // locks are used:
5659 // . CMS token: if this is held, a stop the world collection cannot occur
5660 // . freelistLock: if this is held no allocation can occur from this
5661 // generation by another thread
5662 // . bitMapLock: if this is held, no other thread can access or update
5663 //
5664
5665 // Note that we need to hold the freelistLock if we use
5666 // block iterate below; else the iterator might go awry if
5667 // a mutator (or promotion) causes block contents to change
5668 // (for instance if the allocator divvies up a block).
5669 // If we hold the free list lock, for all practical purposes
5670 // young generation GC's can't occur (they'll usually need to
5671 // promote), so we might as well prevent all young generation
5672 // GC's while we do a sweeping step. For the same reason, we might
5673 // as well take the bit map lock for the entire duration
5674
5675 // check that we hold the requisite locks
5676 assert(have_cms_token(), "Should hold cms token");
5677 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5678 assert_lock_strong(old_gen->freelistLock());
5679 assert_lock_strong(bitMapLock());
5680
5681 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5682 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5683 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5684 _inter_sweep_estimate.padded_average(),
5685 _intra_sweep_estimate.padded_average());
5686 old_gen->setNearLargestChunk();
5687
5688 {
5689 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5690 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5691 // We need to free-up/coalesce garbage/blocks from a
5692 // co-terminal free run. This is done in the SweepClosure
5693 // destructor; so, do not remove this scope, else the
5694 // end-of-sweep-census below will be off by a little bit.
5695 }
5696 old_gen->cmsSpace()->sweep_completed();
5697 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5698 if (should_unload_classes()) { // unloaded classes this cycle,
5699 _concurrent_cycles_since_last_unload = 0; // ... reset count
5700 } else { // did not unload classes,
5701 _concurrent_cycles_since_last_unload++; // ... increment count
5702 }
5703 }
5704
5705 // Reset CMS data structures (for now just the marking bit map)
5706 // preparatory for the next cycle.
5707 void CMSCollector::reset(bool concurrent) {
5708 if (concurrent) {
5709 CMSTokenSyncWithLocks ts(true, bitMapLock());
5710
5711 // If the state is not "Resetting", the foreground thread
5712 // has done a collection and the resetting.
5713 if (_collectorState != Resetting) {
5714 assert(_collectorState == Idling, "The state should only change"
5715 " because the foreground collector has finished the collection");
5716 return;
5717 }
5718
5719 // Clear the mark bitmap (no grey objects to start with)
5720 // for the next cycle.
5721 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5722 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5723
5724 HeapWord* curAddr = _markBitMap.startWord();
5725 while (curAddr < _markBitMap.endWord()) {
5726 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5727 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5728 _markBitMap.clear_large_range(chunk);
5729 if (ConcurrentMarkSweepThread::should_yield() &&
5730 !foregroundGCIsActive() &&
5731 CMSYield) {
5732 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5733 "CMS thread should hold CMS token");
5734 assert_lock_strong(bitMapLock());
5735 bitMapLock()->unlock();
5736 ConcurrentMarkSweepThread::desynchronize(true);
5737 stopTimer();
5738 if (PrintCMSStatistics != 0) {
5739 incrementYields();
5740 }
5741
5742 // See the comment in coordinator_yield()
5743 for (unsigned i = 0; i < CMSYieldSleepCount &&
5744 ConcurrentMarkSweepThread::should_yield() &&
5745 !CMSCollector::foregroundGCIsActive(); ++i) {
5746 os::sleep(Thread::current(), 1, false);
5747 }
5748
5749 ConcurrentMarkSweepThread::synchronize(true);
5750 bitMapLock()->lock_without_safepoint_check();
5751 startTimer();
5752 }
5753 curAddr = chunk.end();
5754 }
5755 // A successful mostly concurrent collection has been done.
5756 // Because only the full (i.e., concurrent mode failure) collections
5757 // are being measured for gc overhead limits, clean the "near" flag
5758 // and count.
5759 size_policy()->reset_gc_overhead_limit_count();
5760 _collectorState = Idling;
5761 } else {
5762 // already have the lock
5763 assert(_collectorState == Resetting, "just checking");
5764 assert_lock_strong(bitMapLock());
5765 _markBitMap.clear_all();
5766 _collectorState = Idling;
5767 }
5768
5769 register_gc_end();
5770 }
5771
5772 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5773 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5774 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5775 TraceCollectorStats tcs(counters());
5776
5777 switch (op) {
5778 case CMS_op_checkpointRootsInitial: {
5779 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5780 checkpointRootsInitial();
5781 if (PrintGC) {
5782 _cmsGen->printOccupancy("initial-mark");
5783 }
5784 break;
5785 }
5786 case CMS_op_checkpointRootsFinal: {
5787 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5788 checkpointRootsFinal();
5789 if (PrintGC) {
5790 _cmsGen->printOccupancy("remark");
5791 }
5792 break;
5793 }
5794 default:
5795 fatal("No such CMS_op");
5796 }
5797 }
5798
5799 #ifndef PRODUCT
5800 size_t const CMSCollector::skip_header_HeapWords() {
5801 return FreeChunk::header_size();
5802 }
5803
5804 // Try and collect here conditions that should hold when
5805 // CMS thread is exiting. The idea is that the foreground GC
5806 // thread should not be blocked if it wants to terminate
5807 // the CMS thread and yet continue to run the VM for a while
5808 // after that.
5809 void CMSCollector::verify_ok_to_terminate() const {
5810 assert(Thread::current()->is_ConcurrentGC_thread(),
5811 "should be called by CMS thread");
5812 assert(!_foregroundGCShouldWait, "should be false");
5813 // We could check here that all the various low-level locks
5814 // are not held by the CMS thread, but that is overkill; see
5815 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5816 // is checked.
5817 }
5818 #endif
5819
5820 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5821 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5822 "missing Printezis mark?");
5823 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5824 size_t size = pointer_delta(nextOneAddr + 1, addr);
5825 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5826 "alignment problem");
5827 assert(size >= 3, "Necessary for Printezis marks to work");
5828 return size;
5829 }
5830
5831 // A variant of the above (block_size_using_printezis_bits()) except
5832 // that we return 0 if the P-bits are not yet set.
5833 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5834 if (_markBitMap.isMarked(addr + 1)) {
5835 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5836 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5837 size_t size = pointer_delta(nextOneAddr + 1, addr);
5838 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5839 "alignment problem");
5840 assert(size >= 3, "Necessary for Printezis marks to work");
5841 return size;
5842 }
5843 return 0;
5844 }
5845
5846 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5847 size_t sz = 0;
5848 oop p = (oop)addr;
5849 if (p->klass_or_null() != NULL) {
5850 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5851 } else {
5852 sz = block_size_using_printezis_bits(addr);
5853 }
5854 assert(sz > 0, "size must be nonzero");
5855 HeapWord* next_block = addr + sz;
5856 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5857 CardTableModRefBS::card_size);
5858 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5859 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5860 "must be different cards");
5861 return next_card;
5862 }
5863
5864
5865 // CMS Bit Map Wrapper /////////////////////////////////////////
5866
5867 // Construct a CMS bit map infrastructure, but don't create the
5868 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5869 // further below.
5870 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5871 _bm(),
5872 _shifter(shifter),
5873 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5874 Monitor::_safepoint_check_sometimes) : NULL)
5875 {
5876 _bmStartWord = 0;
5877 _bmWordSize = 0;
5878 }
5879
5880 bool CMSBitMap::allocate(MemRegion mr) {
5881 _bmStartWord = mr.start();
5882 _bmWordSize = mr.word_size();
5883 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5884 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5885 if (!brs.is_reserved()) {
5886 warning("CMS bit map allocation failure");
5887 return false;
5888 }
5889 // For now we'll just commit all of the bit map up front.
5890 // Later on we'll try to be more parsimonious with swap.
5891 if (!_virtual_space.initialize(brs, brs.size())) {
5892 warning("CMS bit map backing store failure");
5893 return false;
5894 }
5895 assert(_virtual_space.committed_size() == brs.size(),
5896 "didn't reserve backing store for all of CMS bit map?");
5897 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5898 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5899 _bmWordSize, "inconsistency in bit map sizing");
5900 _bm.set_size(_bmWordSize >> _shifter);
5901
5902 // bm.clear(); // can we rely on getting zero'd memory? verify below
5903 assert(isAllClear(),
5904 "Expected zero'd memory from ReservedSpace constructor");
5905 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5906 "consistency check");
5907 return true;
5908 }
5909
5910 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5911 HeapWord *next_addr, *end_addr, *last_addr;
5912 assert_locked();
5913 assert(covers(mr), "out-of-range error");
5914 // XXX assert that start and end are appropriately aligned
5915 for (next_addr = mr.start(), end_addr = mr.end();
5916 next_addr < end_addr; next_addr = last_addr) {
5917 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5918 last_addr = dirty_region.end();
5919 if (!dirty_region.is_empty()) {
5920 cl->do_MemRegion(dirty_region);
5921 } else {
5922 assert(last_addr == end_addr, "program logic");
5923 return;
5924 }
5925 }
5926 }
5927
5928 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5929 _bm.print_on_error(st, prefix);
5930 }
5931
5932 #ifndef PRODUCT
5933 void CMSBitMap::assert_locked() const {
5934 CMSLockVerifier::assert_locked(lock());
5935 }
5936
5937 bool CMSBitMap::covers(MemRegion mr) const {
5938 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5939 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5940 "size inconsistency");
5941 return (mr.start() >= _bmStartWord) &&
5942 (mr.end() <= endWord());
5943 }
5944
5945 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5946 return (start >= _bmStartWord && (start + size) <= endWord());
5947 }
5948
5949 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5950 // verify that there are no 1 bits in the interval [left, right)
5951 FalseBitMapClosure falseBitMapClosure;
5952 iterate(&falseBitMapClosure, left, right);
5953 }
5954
5955 void CMSBitMap::region_invariant(MemRegion mr)
5956 {
5957 assert_locked();
5958 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5959 assert(!mr.is_empty(), "unexpected empty region");
5960 assert(covers(mr), "mr should be covered by bit map");
5961 // convert address range into offset range
5962 size_t start_ofs = heapWordToOffset(mr.start());
5963 // Make sure that end() is appropriately aligned
5964 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5965 (1 << (_shifter+LogHeapWordSize))),
5966 "Misaligned mr.end()");
5967 size_t end_ofs = heapWordToOffset(mr.end());
5968 assert(end_ofs > start_ofs, "Should mark at least one bit");
5969 }
5970
5971 #endif
5972
5973 bool CMSMarkStack::allocate(size_t size) {
5974 // allocate a stack of the requisite depth
5975 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5976 size * sizeof(oop)));
5977 if (!rs.is_reserved()) {
5978 warning("CMSMarkStack allocation failure");
5979 return false;
5980 }
5981 if (!_virtual_space.initialize(rs, rs.size())) {
5982 warning("CMSMarkStack backing store failure");
5983 return false;
5984 }
5985 assert(_virtual_space.committed_size() == rs.size(),
5986 "didn't reserve backing store for all of CMS stack?");
5987 _base = (oop*)(_virtual_space.low());
5988 _index = 0;
5989 _capacity = size;
5990 NOT_PRODUCT(_max_depth = 0);
5991 return true;
5992 }
5993
5994 // XXX FIX ME !!! In the MT case we come in here holding a
5995 // leaf lock. For printing we need to take a further lock
5996 // which has lower rank. We need to recalibrate the two
5997 // lock-ranks involved in order to be able to print the
5998 // messages below. (Or defer the printing to the caller.
5999 // For now we take the expedient path of just disabling the
6000 // messages for the problematic case.)
6001 void CMSMarkStack::expand() {
6002 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6003 if (_capacity == MarkStackSizeMax) {
6004 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6005 // We print a warning message only once per CMS cycle.
6006 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6007 }
6008 return;
6009 }
6010 // Double capacity if possible
6011 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6012 // Do not give up existing stack until we have managed to
6013 // get the double capacity that we desired.
6014 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6015 new_capacity * sizeof(oop)));
6016 if (rs.is_reserved()) {
6017 // Release the backing store associated with old stack
6018 _virtual_space.release();
6019 // Reinitialize virtual space for new stack
6020 if (!_virtual_space.initialize(rs, rs.size())) {
6021 fatal("Not enough swap for expanded marking stack");
6022 }
6023 _base = (oop*)(_virtual_space.low());
6024 _index = 0;
6025 _capacity = new_capacity;
6026 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6027 // Failed to double capacity, continue;
6028 // we print a detail message only once per CMS cycle.
6029 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6030 SIZE_FORMAT "K",
6031 _capacity / K, new_capacity / K);
6032 }
6033 }
6034
6035
6036 // Closures
6037 // XXX: there seems to be a lot of code duplication here;
6038 // should refactor and consolidate common code.
6039
6040 // This closure is used to mark refs into the CMS generation in
6041 // the CMS bit map. Called at the first checkpoint. This closure
6042 // assumes that we do not need to re-mark dirty cards; if the CMS
6043 // generation on which this is used is not an oldest
6044 // generation then this will lose younger_gen cards!
6045
6046 MarkRefsIntoClosure::MarkRefsIntoClosure(
6047 MemRegion span, CMSBitMap* bitMap):
6048 _span(span),
6049 _bitMap(bitMap)
6050 {
6051 assert(_ref_processor == NULL, "deliberately left NULL");
6052 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6053 }
6054
6055 void MarkRefsIntoClosure::do_oop(oop obj) {
6056 // if p points into _span, then mark corresponding bit in _markBitMap
6057 assert(obj->is_oop(), "expected an oop");
6058 HeapWord* addr = (HeapWord*)obj;
6059 if (_span.contains(addr)) {
6060 // this should be made more efficient
6061 _bitMap->mark(addr);
6062 }
6063 }
6064
6065 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6066 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6067
6068 Par_MarkRefsIntoClosure::Par_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 Par_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->par_mark(addr);
6084 }
6085 }
6086
6087 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6088 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6089
6090 // A variant of the above, used for CMS marking verification.
6091 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6092 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6093 _span(span),
6094 _verification_bm(verification_bm),
6095 _cms_bm(cms_bm)
6096 {
6097 assert(_ref_processor == NULL, "deliberately left NULL");
6098 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6099 }
6100
6101 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6102 // if p points into _span, then mark corresponding bit in _markBitMap
6103 assert(obj->is_oop(), "expected an oop");
6104 HeapWord* addr = (HeapWord*)obj;
6105 if (_span.contains(addr)) {
6106 _verification_bm->mark(addr);
6107 if (!_cms_bm->isMarked(addr)) {
6108 oop(addr)->print();
6109 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6110 fatal("... aborting");
6111 }
6112 }
6113 }
6114
6115 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6116 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6117
6118 //////////////////////////////////////////////////
6119 // MarkRefsIntoAndScanClosure
6120 //////////////////////////////////////////////////
6121
6122 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6123 ReferenceProcessor* rp,
6124 CMSBitMap* bit_map,
6125 CMSBitMap* mod_union_table,
6126 CMSMarkStack* mark_stack,
6127 CMSCollector* collector,
6128 bool should_yield,
6129 bool concurrent_precleaning):
6130 _collector(collector),
6131 _span(span),
6132 _bit_map(bit_map),
6133 _mark_stack(mark_stack),
6134 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6135 mark_stack, concurrent_precleaning),
6136 _yield(should_yield),
6137 _concurrent_precleaning(concurrent_precleaning),
6138 _freelistLock(NULL)
6139 {
6140 _ref_processor = rp;
6141 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6142 }
6143
6144 // This closure is used to mark refs into the CMS generation at the
6145 // second (final) checkpoint, and to scan and transitively follow
6146 // the unmarked oops. It is also used during the concurrent precleaning
6147 // phase while scanning objects on dirty cards in the CMS generation.
6148 // The marks are made in the marking bit map and the marking stack is
6149 // used for keeping the (newly) grey objects during the scan.
6150 // The parallel version (Par_...) appears further below.
6151 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6152 if (obj != NULL) {
6153 assert(obj->is_oop(), "expected an oop");
6154 HeapWord* addr = (HeapWord*)obj;
6155 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6156 assert(_collector->overflow_list_is_empty(),
6157 "overflow list should be empty");
6158 if (_span.contains(addr) &&
6159 !_bit_map->isMarked(addr)) {
6160 // mark bit map (object is now grey)
6161 _bit_map->mark(addr);
6162 // push on marking stack (stack should be empty), and drain the
6163 // stack by applying this closure to the oops in the oops popped
6164 // from the stack (i.e. blacken the grey objects)
6165 bool res = _mark_stack->push(obj);
6166 assert(res, "Should have space to push on empty stack");
6167 do {
6168 oop new_oop = _mark_stack->pop();
6169 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6170 assert(_bit_map->isMarked((HeapWord*)new_oop),
6171 "only grey objects on this stack");
6172 // iterate over the oops in this oop, marking and pushing
6173 // the ones in CMS heap (i.e. in _span).
6174 new_oop->oop_iterate(&_pushAndMarkClosure);
6175 // check if it's time to yield
6176 do_yield_check();
6177 } while (!_mark_stack->isEmpty() ||
6178 (!_concurrent_precleaning && take_from_overflow_list()));
6179 // if marking stack is empty, and we are not doing this
6180 // during precleaning, then check the overflow list
6181 }
6182 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6183 assert(_collector->overflow_list_is_empty(),
6184 "overflow list was drained above");
6185 // We could restore evacuated mark words, if any, used for
6186 // overflow list links here because the overflow list is
6187 // provably empty here. That would reduce the maximum
6188 // size requirements for preserved_{oop,mark}_stack.
6189 // But we'll just postpone it until we are all done
6190 // so we can just stream through.
6191 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6192 _collector->restore_preserved_marks_if_any();
6193 assert(_collector->no_preserved_marks(), "No preserved marks");
6194 }
6195 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6196 "All preserved marks should have been restored above");
6197 }
6198 }
6199
6200 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6201 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6202
6203 void MarkRefsIntoAndScanClosure::do_yield_work() {
6204 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6205 "CMS thread should hold CMS token");
6206 assert_lock_strong(_freelistLock);
6207 assert_lock_strong(_bit_map->lock());
6208 // relinquish the free_list_lock and bitMaplock()
6209 _bit_map->lock()->unlock();
6210 _freelistLock->unlock();
6211 ConcurrentMarkSweepThread::desynchronize(true);
6212 _collector->stopTimer();
6213 if (PrintCMSStatistics != 0) {
6214 _collector->incrementYields();
6215 }
6216
6217 // See the comment in coordinator_yield()
6218 for (unsigned i = 0;
6219 i < CMSYieldSleepCount &&
6220 ConcurrentMarkSweepThread::should_yield() &&
6221 !CMSCollector::foregroundGCIsActive();
6222 ++i) {
6223 os::sleep(Thread::current(), 1, false);
6224 }
6225
6226 ConcurrentMarkSweepThread::synchronize(true);
6227 _freelistLock->lock_without_safepoint_check();
6228 _bit_map->lock()->lock_without_safepoint_check();
6229 _collector->startTimer();
6230 }
6231
6232 ///////////////////////////////////////////////////////////
6233 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6234 // MarkRefsIntoAndScanClosure
6235 ///////////////////////////////////////////////////////////
6236 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6237 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6238 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6239 _span(span),
6240 _bit_map(bit_map),
6241 _work_queue(work_queue),
6242 _low_water_mark(MIN2((work_queue->max_elems()/4),
6243 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6244 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6245 {
6246 _ref_processor = rp;
6247 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6248 }
6249
6250 // This closure is used to mark refs into the CMS generation at the
6251 // second (final) checkpoint, and to scan and transitively follow
6252 // the unmarked oops. The marks are made in the marking bit map and
6253 // the work_queue is used for keeping the (newly) grey objects during
6254 // the scan phase whence they are also available for stealing by parallel
6255 // threads. Since the marking bit map is shared, updates are
6256 // synchronized (via CAS).
6257 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6258 if (obj != NULL) {
6259 // Ignore mark word because this could be an already marked oop
6260 // that may be chained at the end of the overflow list.
6261 assert(obj->is_oop(true), "expected an oop");
6262 HeapWord* addr = (HeapWord*)obj;
6263 if (_span.contains(addr) &&
6264 !_bit_map->isMarked(addr)) {
6265 // mark bit map (object will become grey):
6266 // It is possible for several threads to be
6267 // trying to "claim" this object concurrently;
6268 // the unique thread that succeeds in marking the
6269 // object first will do the subsequent push on
6270 // to the work queue (or overflow list).
6271 if (_bit_map->par_mark(addr)) {
6272 // push on work_queue (which may not be empty), and trim the
6273 // queue to an appropriate length by applying this closure to
6274 // the oops in the oops popped from the stack (i.e. blacken the
6275 // grey objects)
6276 bool res = _work_queue->push(obj);
6277 assert(res, "Low water mark should be less than capacity?");
6278 trim_queue(_low_water_mark);
6279 } // Else, another thread claimed the object
6280 }
6281 }
6282 }
6283
6284 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6285 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6286
6287 // This closure is used to rescan the marked objects on the dirty cards
6288 // in the mod union table and the card table proper.
6289 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6290 oop p, MemRegion mr) {
6291
6292 size_t size = 0;
6293 HeapWord* addr = (HeapWord*)p;
6294 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6295 assert(_span.contains(addr), "we are scanning the CMS generation");
6296 // check if it's time to yield
6297 if (do_yield_check()) {
6298 // We yielded for some foreground stop-world work,
6299 // and we have been asked to abort this ongoing preclean cycle.
6300 return 0;
6301 }
6302 if (_bitMap->isMarked(addr)) {
6303 // it's marked; is it potentially uninitialized?
6304 if (p->klass_or_null() != NULL) {
6305 // an initialized object; ignore mark word in verification below
6306 // since we are running concurrent with mutators
6307 assert(p->is_oop(true), "should be an oop");
6308 if (p->is_objArray()) {
6309 // objArrays are precisely marked; restrict scanning
6310 // to dirty cards only.
6311 size = CompactibleFreeListSpace::adjustObjectSize(
6312 p->oop_iterate_size(_scanningClosure, mr));
6313 } else {
6314 // A non-array may have been imprecisely marked; we need
6315 // to scan object in its entirety.
6316 size = CompactibleFreeListSpace::adjustObjectSize(
6317 p->oop_iterate_size(_scanningClosure));
6318 }
6319 #ifdef ASSERT
6320 size_t direct_size =
6321 CompactibleFreeListSpace::adjustObjectSize(p->size());
6322 assert(size == direct_size, "Inconsistency in size");
6323 assert(size >= 3, "Necessary for Printezis marks to work");
6324 if (!_bitMap->isMarked(addr+1)) {
6325 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6326 } else {
6327 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6328 assert(_bitMap->isMarked(addr+size-1),
6329 "inconsistent Printezis mark");
6330 }
6331 #endif // ASSERT
6332 } else {
6333 // An uninitialized object.
6334 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6335 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6336 size = pointer_delta(nextOneAddr + 1, addr);
6337 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6338 "alignment problem");
6339 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6340 // will dirty the card when the klass pointer is installed in the
6341 // object (signaling the completion of initialization).
6342 }
6343 } else {
6344 // Either a not yet marked object or an uninitialized object
6345 if (p->klass_or_null() == NULL) {
6346 // An uninitialized object, skip to the next card, since
6347 // we may not be able to read its P-bits yet.
6348 assert(size == 0, "Initial value");
6349 } else {
6350 // An object not (yet) reached by marking: we merely need to
6351 // compute its size so as to go look at the next block.
6352 assert(p->is_oop(true), "should be an oop");
6353 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6354 }
6355 }
6356 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6357 return size;
6358 }
6359
6360 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6361 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6362 "CMS thread should hold CMS token");
6363 assert_lock_strong(_freelistLock);
6364 assert_lock_strong(_bitMap->lock());
6365 // relinquish the free_list_lock and bitMaplock()
6366 _bitMap->lock()->unlock();
6367 _freelistLock->unlock();
6368 ConcurrentMarkSweepThread::desynchronize(true);
6369 _collector->stopTimer();
6370 if (PrintCMSStatistics != 0) {
6371 _collector->incrementYields();
6372 }
6373
6374 // See the comment in coordinator_yield()
6375 for (unsigned i = 0; i < CMSYieldSleepCount &&
6376 ConcurrentMarkSweepThread::should_yield() &&
6377 !CMSCollector::foregroundGCIsActive(); ++i) {
6378 os::sleep(Thread::current(), 1, false);
6379 }
6380
6381 ConcurrentMarkSweepThread::synchronize(true);
6382 _freelistLock->lock_without_safepoint_check();
6383 _bitMap->lock()->lock_without_safepoint_check();
6384 _collector->startTimer();
6385 }
6386
6387
6388 //////////////////////////////////////////////////////////////////
6389 // SurvivorSpacePrecleanClosure
6390 //////////////////////////////////////////////////////////////////
6391 // This (single-threaded) closure is used to preclean the oops in
6392 // the survivor spaces.
6393 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6394
6395 HeapWord* addr = (HeapWord*)p;
6396 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6397 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6398 assert(p->klass_or_null() != NULL, "object should be initialized");
6399 // an initialized object; ignore mark word in verification below
6400 // since we are running concurrent with mutators
6401 assert(p->is_oop(true), "should be an oop");
6402 // Note that we do not yield while we iterate over
6403 // the interior oops of p, pushing the relevant ones
6404 // on our marking stack.
6405 size_t size = p->oop_iterate_size(_scanning_closure);
6406 do_yield_check();
6407 // Observe that below, we do not abandon the preclean
6408 // phase as soon as we should; rather we empty the
6409 // marking stack before returning. This is to satisfy
6410 // some existing assertions. In general, it may be a
6411 // good idea to abort immediately and complete the marking
6412 // from the grey objects at a later time.
6413 while (!_mark_stack->isEmpty()) {
6414 oop new_oop = _mark_stack->pop();
6415 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6416 assert(_bit_map->isMarked((HeapWord*)new_oop),
6417 "only grey objects on this stack");
6418 // iterate over the oops in this oop, marking and pushing
6419 // the ones in CMS heap (i.e. in _span).
6420 new_oop->oop_iterate(_scanning_closure);
6421 // check if it's time to yield
6422 do_yield_check();
6423 }
6424 unsigned int after_count =
6425 GenCollectedHeap::heap()->total_collections();
6426 bool abort = (_before_count != after_count) ||
6427 _collector->should_abort_preclean();
6428 return abort ? 0 : size;
6429 }
6430
6431 void SurvivorSpacePrecleanClosure::do_yield_work() {
6432 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6433 "CMS thread should hold CMS token");
6434 assert_lock_strong(_bit_map->lock());
6435 // Relinquish the bit map lock
6436 _bit_map->lock()->unlock();
6437 ConcurrentMarkSweepThread::desynchronize(true);
6438 _collector->stopTimer();
6439 if (PrintCMSStatistics != 0) {
6440 _collector->incrementYields();
6441 }
6442
6443 // See the comment in coordinator_yield()
6444 for (unsigned i = 0; i < CMSYieldSleepCount &&
6445 ConcurrentMarkSweepThread::should_yield() &&
6446 !CMSCollector::foregroundGCIsActive(); ++i) {
6447 os::sleep(Thread::current(), 1, false);
6448 }
6449
6450 ConcurrentMarkSweepThread::synchronize(true);
6451 _bit_map->lock()->lock_without_safepoint_check();
6452 _collector->startTimer();
6453 }
6454
6455 // This closure is used to rescan the marked objects on the dirty cards
6456 // in the mod union table and the card table proper. In the parallel
6457 // case, although the bitMap is shared, we do a single read so the
6458 // isMarked() query is "safe".
6459 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6460 // Ignore mark word because we are running concurrent with mutators
6461 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6462 HeapWord* addr = (HeapWord*)p;
6463 assert(_span.contains(addr), "we are scanning the CMS generation");
6464 bool is_obj_array = false;
6465 #ifdef ASSERT
6466 if (!_parallel) {
6467 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6468 assert(_collector->overflow_list_is_empty(),
6469 "overflow list should be empty");
6470
6471 }
6472 #endif // ASSERT
6473 if (_bit_map->isMarked(addr)) {
6474 // Obj arrays are precisely marked, non-arrays are not;
6475 // so we scan objArrays precisely and non-arrays in their
6476 // entirety.
6477 if (p->is_objArray()) {
6478 is_obj_array = true;
6479 if (_parallel) {
6480 p->oop_iterate(_par_scan_closure, mr);
6481 } else {
6482 p->oop_iterate(_scan_closure, mr);
6483 }
6484 } else {
6485 if (_parallel) {
6486 p->oop_iterate(_par_scan_closure);
6487 } else {
6488 p->oop_iterate(_scan_closure);
6489 }
6490 }
6491 }
6492 #ifdef ASSERT
6493 if (!_parallel) {
6494 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6495 assert(_collector->overflow_list_is_empty(),
6496 "overflow list should be empty");
6497
6498 }
6499 #endif // ASSERT
6500 return is_obj_array;
6501 }
6502
6503 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6504 MemRegion span,
6505 CMSBitMap* bitMap, CMSMarkStack* markStack,
6506 bool should_yield, bool verifying):
6507 _collector(collector),
6508 _span(span),
6509 _bitMap(bitMap),
6510 _mut(&collector->_modUnionTable),
6511 _markStack(markStack),
6512 _yield(should_yield),
6513 _skipBits(0)
6514 {
6515 assert(_markStack->isEmpty(), "stack should be empty");
6516 _finger = _bitMap->startWord();
6517 _threshold = _finger;
6518 assert(_collector->_restart_addr == NULL, "Sanity check");
6519 assert(_span.contains(_finger), "Out of bounds _finger?");
6520 DEBUG_ONLY(_verifying = verifying;)
6521 }
6522
6523 void MarkFromRootsClosure::reset(HeapWord* addr) {
6524 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6525 assert(_span.contains(addr), "Out of bounds _finger?");
6526 _finger = addr;
6527 _threshold = (HeapWord*)round_to(
6528 (intptr_t)_finger, CardTableModRefBS::card_size);
6529 }
6530
6531 // Should revisit to see if this should be restructured for
6532 // greater efficiency.
6533 bool MarkFromRootsClosure::do_bit(size_t offset) {
6534 if (_skipBits > 0) {
6535 _skipBits--;
6536 return true;
6537 }
6538 // convert offset into a HeapWord*
6539 HeapWord* addr = _bitMap->startWord() + offset;
6540 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6541 "address out of range");
6542 assert(_bitMap->isMarked(addr), "tautology");
6543 if (_bitMap->isMarked(addr+1)) {
6544 // this is an allocated but not yet initialized object
6545 assert(_skipBits == 0, "tautology");
6546 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6547 oop p = oop(addr);
6548 if (p->klass_or_null() == NULL) {
6549 DEBUG_ONLY(if (!_verifying) {)
6550 // We re-dirty the cards on which this object lies and increase
6551 // the _threshold so that we'll come back to scan this object
6552 // during the preclean or remark phase. (CMSCleanOnEnter)
6553 if (CMSCleanOnEnter) {
6554 size_t sz = _collector->block_size_using_printezis_bits(addr);
6555 HeapWord* end_card_addr = (HeapWord*)round_to(
6556 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6557 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6558 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6559 // Bump _threshold to end_card_addr; note that
6560 // _threshold cannot possibly exceed end_card_addr, anyhow.
6561 // This prevents future clearing of the card as the scan proceeds
6562 // to the right.
6563 assert(_threshold <= end_card_addr,
6564 "Because we are just scanning into this object");
6565 if (_threshold < end_card_addr) {
6566 _threshold = end_card_addr;
6567 }
6568 if (p->klass_or_null() != NULL) {
6569 // Redirty the range of cards...
6570 _mut->mark_range(redirty_range);
6571 } // ...else the setting of klass will dirty the card anyway.
6572 }
6573 DEBUG_ONLY(})
6574 return true;
6575 }
6576 }
6577 scanOopsInOop(addr);
6578 return true;
6579 }
6580
6581 // We take a break if we've been at this for a while,
6582 // so as to avoid monopolizing the locks involved.
6583 void MarkFromRootsClosure::do_yield_work() {
6584 // First give up the locks, then yield, then re-lock
6585 // We should probably use a constructor/destructor idiom to
6586 // do this unlock/lock or modify the MutexUnlocker class to
6587 // serve our purpose. XXX
6588 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6589 "CMS thread should hold CMS token");
6590 assert_lock_strong(_bitMap->lock());
6591 _bitMap->lock()->unlock();
6592 ConcurrentMarkSweepThread::desynchronize(true);
6593 _collector->stopTimer();
6594 if (PrintCMSStatistics != 0) {
6595 _collector->incrementYields();
6596 }
6597
6598 // See the comment in coordinator_yield()
6599 for (unsigned i = 0; i < CMSYieldSleepCount &&
6600 ConcurrentMarkSweepThread::should_yield() &&
6601 !CMSCollector::foregroundGCIsActive(); ++i) {
6602 os::sleep(Thread::current(), 1, false);
6603 }
6604
6605 ConcurrentMarkSweepThread::synchronize(true);
6606 _bitMap->lock()->lock_without_safepoint_check();
6607 _collector->startTimer();
6608 }
6609
6610 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6611 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6612 assert(_markStack->isEmpty(),
6613 "should drain stack to limit stack usage");
6614 // convert ptr to an oop preparatory to scanning
6615 oop obj = oop(ptr);
6616 // Ignore mark word in verification below, since we
6617 // may be running concurrent with mutators.
6618 assert(obj->is_oop(true), "should be an oop");
6619 assert(_finger <= ptr, "_finger runneth ahead");
6620 // advance the finger to right end of this object
6621 _finger = ptr + obj->size();
6622 assert(_finger > ptr, "we just incremented it above");
6623 // On large heaps, it may take us some time to get through
6624 // the marking phase. During
6625 // this time it's possible that a lot of mutations have
6626 // accumulated in the card table and the mod union table --
6627 // these mutation records are redundant until we have
6628 // actually traced into the corresponding card.
6629 // Here, we check whether advancing the finger would make
6630 // us cross into a new card, and if so clear corresponding
6631 // cards in the MUT (preclean them in the card-table in the
6632 // future).
6633
6634 DEBUG_ONLY(if (!_verifying) {)
6635 // The clean-on-enter optimization is disabled by default,
6636 // until we fix 6178663.
6637 if (CMSCleanOnEnter && (_finger > _threshold)) {
6638 // [_threshold, _finger) represents the interval
6639 // of cards to be cleared in MUT (or precleaned in card table).
6640 // The set of cards to be cleared is all those that overlap
6641 // with the interval [_threshold, _finger); note that
6642 // _threshold is always kept card-aligned but _finger isn't
6643 // always card-aligned.
6644 HeapWord* old_threshold = _threshold;
6645 assert(old_threshold == (HeapWord*)round_to(
6646 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6647 "_threshold should always be card-aligned");
6648 _threshold = (HeapWord*)round_to(
6649 (intptr_t)_finger, CardTableModRefBS::card_size);
6650 MemRegion mr(old_threshold, _threshold);
6651 assert(!mr.is_empty(), "Control point invariant");
6652 assert(_span.contains(mr), "Should clear within span");
6653 _mut->clear_range(mr);
6654 }
6655 DEBUG_ONLY(})
6656 // Note: the finger doesn't advance while we drain
6657 // the stack below.
6658 PushOrMarkClosure pushOrMarkClosure(_collector,
6659 _span, _bitMap, _markStack,
6660 _finger, this);
6661 bool res = _markStack->push(obj);
6662 assert(res, "Empty non-zero size stack should have space for single push");
6663 while (!_markStack->isEmpty()) {
6664 oop new_oop = _markStack->pop();
6665 // Skip verifying header mark word below because we are
6666 // running concurrent with mutators.
6667 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6668 // now scan this oop's oops
6669 new_oop->oop_iterate(&pushOrMarkClosure);
6670 do_yield_check();
6671 }
6672 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6673 }
6674
6675 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6676 CMSCollector* collector, MemRegion span,
6677 CMSBitMap* bit_map,
6678 OopTaskQueue* work_queue,
6679 CMSMarkStack* overflow_stack):
6680 _collector(collector),
6681 _whole_span(collector->_span),
6682 _span(span),
6683 _bit_map(bit_map),
6684 _mut(&collector->_modUnionTable),
6685 _work_queue(work_queue),
6686 _overflow_stack(overflow_stack),
6687 _skip_bits(0),
6688 _task(task)
6689 {
6690 assert(_work_queue->size() == 0, "work_queue should be empty");
6691 _finger = span.start();
6692 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6693 assert(_span.contains(_finger), "Out of bounds _finger?");
6694 }
6695
6696 // Should revisit to see if this should be restructured for
6697 // greater efficiency.
6698 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6699 if (_skip_bits > 0) {
6700 _skip_bits--;
6701 return true;
6702 }
6703 // convert offset into a HeapWord*
6704 HeapWord* addr = _bit_map->startWord() + offset;
6705 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6706 "address out of range");
6707 assert(_bit_map->isMarked(addr), "tautology");
6708 if (_bit_map->isMarked(addr+1)) {
6709 // this is an allocated object that might not yet be initialized
6710 assert(_skip_bits == 0, "tautology");
6711 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6712 oop p = oop(addr);
6713 if (p->klass_or_null() == NULL) {
6714 // in the case of Clean-on-Enter optimization, redirty card
6715 // and avoid clearing card by increasing the threshold.
6716 return true;
6717 }
6718 }
6719 scan_oops_in_oop(addr);
6720 return true;
6721 }
6722
6723 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6724 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6725 // Should we assert that our work queue is empty or
6726 // below some drain limit?
6727 assert(_work_queue->size() == 0,
6728 "should drain stack to limit stack usage");
6729 // convert ptr to an oop preparatory to scanning
6730 oop obj = oop(ptr);
6731 // Ignore mark word in verification below, since we
6732 // may be running concurrent with mutators.
6733 assert(obj->is_oop(true), "should be an oop");
6734 assert(_finger <= ptr, "_finger runneth ahead");
6735 // advance the finger to right end of this object
6736 _finger = ptr + obj->size();
6737 assert(_finger > ptr, "we just incremented it above");
6738 // On large heaps, it may take us some time to get through
6739 // the marking phase. During
6740 // this time it's possible that a lot of mutations have
6741 // accumulated in the card table and the mod union table --
6742 // these mutation records are redundant until we have
6743 // actually traced into the corresponding card.
6744 // Here, we check whether advancing the finger would make
6745 // us cross into a new card, and if so clear corresponding
6746 // cards in the MUT (preclean them in the card-table in the
6747 // future).
6748
6749 // The clean-on-enter optimization is disabled by default,
6750 // until we fix 6178663.
6751 if (CMSCleanOnEnter && (_finger > _threshold)) {
6752 // [_threshold, _finger) represents the interval
6753 // of cards to be cleared in MUT (or precleaned in card table).
6754 // The set of cards to be cleared is all those that overlap
6755 // with the interval [_threshold, _finger); note that
6756 // _threshold is always kept card-aligned but _finger isn't
6757 // always card-aligned.
6758 HeapWord* old_threshold = _threshold;
6759 assert(old_threshold == (HeapWord*)round_to(
6760 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6761 "_threshold should always be card-aligned");
6762 _threshold = (HeapWord*)round_to(
6763 (intptr_t)_finger, CardTableModRefBS::card_size);
6764 MemRegion mr(old_threshold, _threshold);
6765 assert(!mr.is_empty(), "Control point invariant");
6766 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6767 _mut->clear_range(mr);
6768 }
6769
6770 // Note: the local finger doesn't advance while we drain
6771 // the stack below, but the global finger sure can and will.
6772 HeapWord** gfa = _task->global_finger_addr();
6773 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6774 _span, _bit_map,
6775 _work_queue,
6776 _overflow_stack,
6777 _finger,
6778 gfa, this);
6779 bool res = _work_queue->push(obj); // overflow could occur here
6780 assert(res, "Will hold once we use workqueues");
6781 while (true) {
6782 oop new_oop;
6783 if (!_work_queue->pop_local(new_oop)) {
6784 // We emptied our work_queue; check if there's stuff that can
6785 // be gotten from the overflow stack.
6786 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6787 _overflow_stack, _work_queue)) {
6788 do_yield_check();
6789 continue;
6790 } else { // done
6791 break;
6792 }
6793 }
6794 // Skip verifying header mark word below because we are
6795 // running concurrent with mutators.
6796 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6797 // now scan this oop's oops
6798 new_oop->oop_iterate(&pushOrMarkClosure);
6799 do_yield_check();
6800 }
6801 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6802 }
6803
6804 // Yield in response to a request from VM Thread or
6805 // from mutators.
6806 void Par_MarkFromRootsClosure::do_yield_work() {
6807 assert(_task != NULL, "sanity");
6808 _task->yield();
6809 }
6810
6811 // A variant of the above used for verifying CMS marking work.
6812 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6813 MemRegion span,
6814 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6815 CMSMarkStack* mark_stack):
6816 _collector(collector),
6817 _span(span),
6818 _verification_bm(verification_bm),
6819 _cms_bm(cms_bm),
6820 _mark_stack(mark_stack),
6821 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6822 mark_stack)
6823 {
6824 assert(_mark_stack->isEmpty(), "stack should be empty");
6825 _finger = _verification_bm->startWord();
6826 assert(_collector->_restart_addr == NULL, "Sanity check");
6827 assert(_span.contains(_finger), "Out of bounds _finger?");
6828 }
6829
6830 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6831 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6832 assert(_span.contains(addr), "Out of bounds _finger?");
6833 _finger = addr;
6834 }
6835
6836 // Should revisit to see if this should be restructured for
6837 // greater efficiency.
6838 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6839 // convert offset into a HeapWord*
6840 HeapWord* addr = _verification_bm->startWord() + offset;
6841 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6842 "address out of range");
6843 assert(_verification_bm->isMarked(addr), "tautology");
6844 assert(_cms_bm->isMarked(addr), "tautology");
6845
6846 assert(_mark_stack->isEmpty(),
6847 "should drain stack to limit stack usage");
6848 // convert addr to an oop preparatory to scanning
6849 oop obj = oop(addr);
6850 assert(obj->is_oop(), "should be an oop");
6851 assert(_finger <= addr, "_finger runneth ahead");
6852 // advance the finger to right end of this object
6853 _finger = addr + obj->size();
6854 assert(_finger > addr, "we just incremented it above");
6855 // Note: the finger doesn't advance while we drain
6856 // the stack below.
6857 bool res = _mark_stack->push(obj);
6858 assert(res, "Empty non-zero size stack should have space for single push");
6859 while (!_mark_stack->isEmpty()) {
6860 oop new_oop = _mark_stack->pop();
6861 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6862 // now scan this oop's oops
6863 new_oop->oop_iterate(&_pam_verify_closure);
6864 }
6865 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6866 return true;
6867 }
6868
6869 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6870 CMSCollector* collector, MemRegion span,
6871 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6872 CMSMarkStack* mark_stack):
6873 MetadataAwareOopClosure(collector->ref_processor()),
6874 _collector(collector),
6875 _span(span),
6876 _verification_bm(verification_bm),
6877 _cms_bm(cms_bm),
6878 _mark_stack(mark_stack)
6879 { }
6880
6881 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6882 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6883
6884 // Upon stack overflow, we discard (part of) the stack,
6885 // remembering the least address amongst those discarded
6886 // in CMSCollector's _restart_address.
6887 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6888 // Remember the least grey address discarded
6889 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6890 _collector->lower_restart_addr(ra);
6891 _mark_stack->reset(); // discard stack contents
6892 _mark_stack->expand(); // expand the stack if possible
6893 }
6894
6895 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6896 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6897 HeapWord* addr = (HeapWord*)obj;
6898 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6899 // Oop lies in _span and isn't yet grey or black
6900 _verification_bm->mark(addr); // now grey
6901 if (!_cms_bm->isMarked(addr)) {
6902 oop(addr)->print();
6903 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6904 p2i(addr));
6905 fatal("... aborting");
6906 }
6907
6908 if (!_mark_stack->push(obj)) { // stack overflow
6909 if (PrintCMSStatistics != 0) {
6910 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6911 SIZE_FORMAT, _mark_stack->capacity());
6912 }
6913 assert(_mark_stack->isFull(), "Else push should have succeeded");
6914 handle_stack_overflow(addr);
6915 }
6916 // anything including and to the right of _finger
6917 // will be scanned as we iterate over the remainder of the
6918 // bit map
6919 }
6920 }
6921
6922 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6923 MemRegion span,
6924 CMSBitMap* bitMap, CMSMarkStack* markStack,
6925 HeapWord* finger, MarkFromRootsClosure* parent) :
6926 MetadataAwareOopClosure(collector->ref_processor()),
6927 _collector(collector),
6928 _span(span),
6929 _bitMap(bitMap),
6930 _markStack(markStack),
6931 _finger(finger),
6932 _parent(parent)
6933 { }
6934
6935 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6936 MemRegion span,
6937 CMSBitMap* bit_map,
6938 OopTaskQueue* work_queue,
6939 CMSMarkStack* overflow_stack,
6940 HeapWord* finger,
6941 HeapWord** global_finger_addr,
6942 Par_MarkFromRootsClosure* parent) :
6943 MetadataAwareOopClosure(collector->ref_processor()),
6944 _collector(collector),
6945 _whole_span(collector->_span),
6946 _span(span),
6947 _bit_map(bit_map),
6948 _work_queue(work_queue),
6949 _overflow_stack(overflow_stack),
6950 _finger(finger),
6951 _global_finger_addr(global_finger_addr),
6952 _parent(parent)
6953 { }
6954
6955 // Assumes thread-safe access by callers, who are
6956 // responsible for mutual exclusion.
6957 void CMSCollector::lower_restart_addr(HeapWord* low) {
6958 assert(_span.contains(low), "Out of bounds addr");
6959 if (_restart_addr == NULL) {
6960 _restart_addr = low;
6961 } else {
6962 _restart_addr = MIN2(_restart_addr, low);
6963 }
6964 }
6965
6966 // Upon stack overflow, we discard (part of) the stack,
6967 // remembering the least address amongst those discarded
6968 // in CMSCollector's _restart_address.
6969 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6970 // Remember the least grey address discarded
6971 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6972 _collector->lower_restart_addr(ra);
6973 _markStack->reset(); // discard stack contents
6974 _markStack->expand(); // expand the stack if possible
6975 }
6976
6977 // Upon stack overflow, we discard (part of) the stack,
6978 // remembering the least address amongst those discarded
6979 // in CMSCollector's _restart_address.
6980 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6981 // We need to do this under a mutex to prevent other
6982 // workers from interfering with the work done below.
6983 MutexLockerEx ml(_overflow_stack->par_lock(),
6984 Mutex::_no_safepoint_check_flag);
6985 // Remember the least grey address discarded
6986 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6987 _collector->lower_restart_addr(ra);
6988 _overflow_stack->reset(); // discard stack contents
6989 _overflow_stack->expand(); // expand the stack if possible
6990 }
6991
6992 void PushOrMarkClosure::do_oop(oop obj) {
6993 // Ignore mark word because we are running concurrent with mutators.
6994 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6995 HeapWord* addr = (HeapWord*)obj;
6996 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6997 // Oop lies in _span and isn't yet grey or black
6998 _bitMap->mark(addr); // now grey
6999 if (addr < _finger) {
7000 // the bit map iteration has already either passed, or
7001 // sampled, this bit in the bit map; we'll need to
7002 // use the marking stack to scan this oop's oops.
7003 bool simulate_overflow = false;
7004 NOT_PRODUCT(
7005 if (CMSMarkStackOverflowALot &&
7006 _collector->simulate_overflow()) {
7007 // simulate a stack overflow
7008 simulate_overflow = true;
7009 }
7010 )
7011 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7012 if (PrintCMSStatistics != 0) {
7013 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7014 SIZE_FORMAT, _markStack->capacity());
7015 }
7016 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7017 handle_stack_overflow(addr);
7018 }
7019 }
7020 // anything including and to the right of _finger
7021 // will be scanned as we iterate over the remainder of the
7022 // bit map
7023 do_yield_check();
7024 }
7025 }
7026
7027 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7028 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7029
7030 void Par_PushOrMarkClosure::do_oop(oop obj) {
7031 // Ignore mark word because we are running concurrent with mutators.
7032 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7033 HeapWord* addr = (HeapWord*)obj;
7034 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7035 // Oop lies in _span and isn't yet grey or black
7036 // We read the global_finger (volatile read) strictly after marking oop
7037 bool res = _bit_map->par_mark(addr); // now grey
7038 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7039 // Should we push this marked oop on our stack?
7040 // -- if someone else marked it, nothing to do
7041 // -- if target oop is above global finger nothing to do
7042 // -- if target oop is in chunk and above local finger
7043 // then nothing to do
7044 // -- else push on work queue
7045 if ( !res // someone else marked it, they will deal with it
7046 || (addr >= *gfa) // will be scanned in a later task
7047 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7048 return;
7049 }
7050 // the bit map iteration has already either passed, or
7051 // sampled, this bit in the bit map; we'll need to
7052 // use the marking stack to scan this oop's oops.
7053 bool simulate_overflow = false;
7054 NOT_PRODUCT(
7055 if (CMSMarkStackOverflowALot &&
7056 _collector->simulate_overflow()) {
7057 // simulate a stack overflow
7058 simulate_overflow = true;
7059 }
7060 )
7061 if (simulate_overflow ||
7062 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7063 // stack overflow
7064 if (PrintCMSStatistics != 0) {
7065 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7066 SIZE_FORMAT, _overflow_stack->capacity());
7067 }
7068 // We cannot assert that the overflow stack is full because
7069 // it may have been emptied since.
7070 assert(simulate_overflow ||
7071 _work_queue->size() == _work_queue->max_elems(),
7072 "Else push should have succeeded");
7073 handle_stack_overflow(addr);
7074 }
7075 do_yield_check();
7076 }
7077 }
7078
7079 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7080 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7081
7082 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7083 MemRegion span,
7084 ReferenceProcessor* rp,
7085 CMSBitMap* bit_map,
7086 CMSBitMap* mod_union_table,
7087 CMSMarkStack* mark_stack,
7088 bool concurrent_precleaning):
7089 MetadataAwareOopClosure(rp),
7090 _collector(collector),
7091 _span(span),
7092 _bit_map(bit_map),
7093 _mod_union_table(mod_union_table),
7094 _mark_stack(mark_stack),
7095 _concurrent_precleaning(concurrent_precleaning)
7096 {
7097 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7098 }
7099
7100 // Grey object rescan during pre-cleaning and second checkpoint phases --
7101 // the non-parallel version (the parallel version appears further below.)
7102 void PushAndMarkClosure::do_oop(oop obj) {
7103 // Ignore mark word verification. If during concurrent precleaning,
7104 // the object monitor may be locked. If during the checkpoint
7105 // phases, the object may already have been reached by a different
7106 // path and may be at the end of the global overflow list (so
7107 // the mark word may be NULL).
7108 assert(obj->is_oop_or_null(true /* ignore mark word */),
7109 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7110 HeapWord* addr = (HeapWord*)obj;
7111 // Check if oop points into the CMS generation
7112 // and is not marked
7113 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7114 // a white object ...
7115 _bit_map->mark(addr); // ... now grey
7116 // push on the marking stack (grey set)
7117 bool simulate_overflow = false;
7118 NOT_PRODUCT(
7119 if (CMSMarkStackOverflowALot &&
7120 _collector->simulate_overflow()) {
7121 // simulate a stack overflow
7122 simulate_overflow = true;
7123 }
7124 )
7125 if (simulate_overflow || !_mark_stack->push(obj)) {
7126 if (_concurrent_precleaning) {
7127 // During precleaning we can just dirty the appropriate card(s)
7128 // in the mod union table, thus ensuring that the object remains
7129 // in the grey set and continue. In the case of object arrays
7130 // we need to dirty all of the cards that the object spans,
7131 // since the rescan of object arrays will be limited to the
7132 // dirty cards.
7133 // Note that no one can be interfering with us in this action
7134 // of dirtying the mod union table, so no locking or atomics
7135 // are required.
7136 if (obj->is_objArray()) {
7137 size_t sz = obj->size();
7138 HeapWord* end_card_addr = (HeapWord*)round_to(
7139 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7140 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7141 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7142 _mod_union_table->mark_range(redirty_range);
7143 } else {
7144 _mod_union_table->mark(addr);
7145 }
7146 _collector->_ser_pmc_preclean_ovflw++;
7147 } else {
7148 // During the remark phase, we need to remember this oop
7149 // in the overflow list.
7150 _collector->push_on_overflow_list(obj);
7151 _collector->_ser_pmc_remark_ovflw++;
7152 }
7153 }
7154 }
7155 }
7156
7157 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7158 MemRegion span,
7159 ReferenceProcessor* rp,
7160 CMSBitMap* bit_map,
7161 OopTaskQueue* work_queue):
7162 MetadataAwareOopClosure(rp),
7163 _collector(collector),
7164 _span(span),
7165 _bit_map(bit_map),
7166 _work_queue(work_queue)
7167 {
7168 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7169 }
7170
7171 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7172 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7173
7174 // Grey object rescan during second checkpoint phase --
7175 // the parallel version.
7176 void Par_PushAndMarkClosure::do_oop(oop obj) {
7177 // In the assert below, we ignore the mark word because
7178 // this oop may point to an already visited object that is
7179 // on the overflow stack (in which case the mark word has
7180 // been hijacked for chaining into the overflow stack --
7181 // if this is the last object in the overflow stack then
7182 // its mark word will be NULL). Because this object may
7183 // have been subsequently popped off the global overflow
7184 // stack, and the mark word possibly restored to the prototypical
7185 // value, by the time we get to examined this failing assert in
7186 // the debugger, is_oop_or_null(false) may subsequently start
7187 // to hold.
7188 assert(obj->is_oop_or_null(true),
7189 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7190 HeapWord* addr = (HeapWord*)obj;
7191 // Check if oop points into the CMS generation
7192 // and is not marked
7193 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7194 // a white object ...
7195 // If we manage to "claim" the object, by being the
7196 // first thread to mark it, then we push it on our
7197 // marking stack
7198 if (_bit_map->par_mark(addr)) { // ... now grey
7199 // push on work queue (grey set)
7200 bool simulate_overflow = false;
7201 NOT_PRODUCT(
7202 if (CMSMarkStackOverflowALot &&
7203 _collector->par_simulate_overflow()) {
7204 // simulate a stack overflow
7205 simulate_overflow = true;
7206 }
7207 )
7208 if (simulate_overflow || !_work_queue->push(obj)) {
7209 _collector->par_push_on_overflow_list(obj);
7210 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7211 }
7212 } // Else, some other thread got there first
7213 }
7214 }
7215
7216 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7217 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7218
7219 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7220 Mutex* bml = _collector->bitMapLock();
7221 assert_lock_strong(bml);
7222 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7223 "CMS thread should hold CMS token");
7224
7225 bml->unlock();
7226 ConcurrentMarkSweepThread::desynchronize(true);
7227
7228 _collector->stopTimer();
7229 if (PrintCMSStatistics != 0) {
7230 _collector->incrementYields();
7231 }
7232
7233 // See the comment in coordinator_yield()
7234 for (unsigned i = 0; i < CMSYieldSleepCount &&
7235 ConcurrentMarkSweepThread::should_yield() &&
7236 !CMSCollector::foregroundGCIsActive(); ++i) {
7237 os::sleep(Thread::current(), 1, false);
7238 }
7239
7240 ConcurrentMarkSweepThread::synchronize(true);
7241 bml->lock();
7242
7243 _collector->startTimer();
7244 }
7245
7246 bool CMSPrecleanRefsYieldClosure::should_return() {
7247 if (ConcurrentMarkSweepThread::should_yield()) {
7248 do_yield_work();
7249 }
7250 return _collector->foregroundGCIsActive();
7251 }
7252
7253 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7254 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7255 "mr should be aligned to start at a card boundary");
7256 // We'd like to assert:
7257 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7258 // "mr should be a range of cards");
7259 // However, that would be too strong in one case -- the last
7260 // partition ends at _unallocated_block which, in general, can be
7261 // an arbitrary boundary, not necessarily card aligned.
7262 if (PrintCMSStatistics != 0) {
7263 _num_dirty_cards +=
7264 mr.word_size()/CardTableModRefBS::card_size_in_words;
7265 }
7266 _space->object_iterate_mem(mr, &_scan_cl);
7267 }
7268
7269 SweepClosure::SweepClosure(CMSCollector* collector,
7270 ConcurrentMarkSweepGeneration* g,
7271 CMSBitMap* bitMap, bool should_yield) :
7272 _collector(collector),
7273 _g(g),
7274 _sp(g->cmsSpace()),
7275 _limit(_sp->sweep_limit()),
7276 _freelistLock(_sp->freelistLock()),
7277 _bitMap(bitMap),
7278 _yield(should_yield),
7279 _inFreeRange(false), // No free range at beginning of sweep
7280 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7281 _lastFreeRangeCoalesced(false),
7282 _freeFinger(g->used_region().start())
7283 {
7284 NOT_PRODUCT(
7285 _numObjectsFreed = 0;
7286 _numWordsFreed = 0;
7287 _numObjectsLive = 0;
7288 _numWordsLive = 0;
7289 _numObjectsAlreadyFree = 0;
7290 _numWordsAlreadyFree = 0;
7291 _last_fc = NULL;
7292
7293 _sp->initializeIndexedFreeListArrayReturnedBytes();
7294 _sp->dictionary()->initialize_dict_returned_bytes();
7295 )
7296 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7297 "sweep _limit out of bounds");
7298 if (CMSTraceSweeper) {
7299 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7300 p2i(_limit));
7301 }
7302 }
7303
7304 void SweepClosure::print_on(outputStream* st) const {
7305 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7306 p2i(_sp->bottom()), p2i(_sp->end()));
7307 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7308 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7309 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7310 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7311 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7312 }
7313
7314 #ifndef PRODUCT
7315 // Assertion checking only: no useful work in product mode --
7316 // however, if any of the flags below become product flags,
7317 // you may need to review this code to see if it needs to be
7318 // enabled in product mode.
7319 SweepClosure::~SweepClosure() {
7320 assert_lock_strong(_freelistLock);
7321 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7322 "sweep _limit out of bounds");
7323 if (inFreeRange()) {
7324 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7325 print();
7326 ShouldNotReachHere();
7327 }
7328 if (Verbose && PrintGC) {
7329 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7330 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7331 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7332 SIZE_FORMAT " bytes "
7333 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7334 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7335 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7336 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7337 * sizeof(HeapWord);
7338 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7339
7340 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7341 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7342 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7343 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7344 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7345 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7346 indexListReturnedBytes);
7347 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7348 dict_returned_bytes);
7349 }
7350 }
7351 if (CMSTraceSweeper) {
7352 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7353 p2i(_limit));
7354 }
7355 }
7356 #endif // PRODUCT
7357
7358 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7359 bool freeRangeInFreeLists) {
7360 if (CMSTraceSweeper) {
7361 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7362 p2i(freeFinger), freeRangeInFreeLists);
7363 }
7364 assert(!inFreeRange(), "Trampling existing free range");
7365 set_inFreeRange(true);
7366 set_lastFreeRangeCoalesced(false);
7367
7368 set_freeFinger(freeFinger);
7369 set_freeRangeInFreeLists(freeRangeInFreeLists);
7370 if (CMSTestInFreeList) {
7371 if (freeRangeInFreeLists) {
7372 FreeChunk* fc = (FreeChunk*) freeFinger;
7373 assert(fc->is_free(), "A chunk on the free list should be free.");
7374 assert(fc->size() > 0, "Free range should have a size");
7375 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7376 }
7377 }
7378 }
7379
7380 // Note that the sweeper runs concurrently with mutators. Thus,
7381 // it is possible for direct allocation in this generation to happen
7382 // in the middle of the sweep. Note that the sweeper also coalesces
7383 // contiguous free blocks. Thus, unless the sweeper and the allocator
7384 // synchronize appropriately freshly allocated blocks may get swept up.
7385 // This is accomplished by the sweeper locking the free lists while
7386 // it is sweeping. Thus blocks that are determined to be free are
7387 // indeed free. There is however one additional complication:
7388 // blocks that have been allocated since the final checkpoint and
7389 // mark, will not have been marked and so would be treated as
7390 // unreachable and swept up. To prevent this, the allocator marks
7391 // the bit map when allocating during the sweep phase. This leads,
7392 // however, to a further complication -- objects may have been allocated
7393 // but not yet initialized -- in the sense that the header isn't yet
7394 // installed. The sweeper can not then determine the size of the block
7395 // in order to skip over it. To deal with this case, we use a technique
7396 // (due to Printezis) to encode such uninitialized block sizes in the
7397 // bit map. Since the bit map uses a bit per every HeapWord, but the
7398 // CMS generation has a minimum object size of 3 HeapWords, it follows
7399 // that "normal marks" won't be adjacent in the bit map (there will
7400 // always be at least two 0 bits between successive 1 bits). We make use
7401 // of these "unused" bits to represent uninitialized blocks -- the bit
7402 // corresponding to the start of the uninitialized object and the next
7403 // bit are both set. Finally, a 1 bit marks the end of the object that
7404 // started with the two consecutive 1 bits to indicate its potentially
7405 // uninitialized state.
7406
7407 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7408 FreeChunk* fc = (FreeChunk*)addr;
7409 size_t res;
7410
7411 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7412 // than "addr == _limit" because although _limit was a block boundary when
7413 // we started the sweep, it may no longer be one because heap expansion
7414 // may have caused us to coalesce the block ending at the address _limit
7415 // with a newly expanded chunk (this happens when _limit was set to the
7416 // previous _end of the space), so we may have stepped past _limit:
7417 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7418 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7419 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7420 "sweep _limit out of bounds");
7421 assert(addr < _sp->end(), "addr out of bounds");
7422 // Flush any free range we might be holding as a single
7423 // coalesced chunk to the appropriate free list.
7424 if (inFreeRange()) {
7425 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7426 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7427 flush_cur_free_chunk(freeFinger(),
7428 pointer_delta(addr, freeFinger()));
7429 if (CMSTraceSweeper) {
7430 gclog_or_tty->print("Sweep: last chunk: ");
7431 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7432 "[coalesced:%d]\n",
7433 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7434 lastFreeRangeCoalesced() ? 1 : 0);
7435 }
7436 }
7437
7438 // help the iterator loop finish
7439 return pointer_delta(_sp->end(), addr);
7440 }
7441
7442 assert(addr < _limit, "sweep invariant");
7443 // check if we should yield
7444 do_yield_check(addr);
7445 if (fc->is_free()) {
7446 // Chunk that is already free
7447 res = fc->size();
7448 do_already_free_chunk(fc);
7449 debug_only(_sp->verifyFreeLists());
7450 // If we flush the chunk at hand in lookahead_and_flush()
7451 // and it's coalesced with a preceding chunk, then the
7452 // process of "mangling" the payload of the coalesced block
7453 // will cause erasure of the size information from the
7454 // (erstwhile) header of all the coalesced blocks but the
7455 // first, so the first disjunct in the assert will not hold
7456 // in that specific case (in which case the second disjunct
7457 // will hold).
7458 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7459 "Otherwise the size info doesn't change at this step");
7460 NOT_PRODUCT(
7461 _numObjectsAlreadyFree++;
7462 _numWordsAlreadyFree += res;
7463 )
7464 NOT_PRODUCT(_last_fc = fc;)
7465 } else if (!_bitMap->isMarked(addr)) {
7466 // Chunk is fresh garbage
7467 res = do_garbage_chunk(fc);
7468 debug_only(_sp->verifyFreeLists());
7469 NOT_PRODUCT(
7470 _numObjectsFreed++;
7471 _numWordsFreed += res;
7472 )
7473 } else {
7474 // Chunk that is alive.
7475 res = do_live_chunk(fc);
7476 debug_only(_sp->verifyFreeLists());
7477 NOT_PRODUCT(
7478 _numObjectsLive++;
7479 _numWordsLive += res;
7480 )
7481 }
7482 return res;
7483 }
7484
7485 // For the smart allocation, record following
7486 // split deaths - a free chunk is removed from its free list because
7487 // it is being split into two or more chunks.
7488 // split birth - a free chunk is being added to its free list because
7489 // a larger free chunk has been split and resulted in this free chunk.
7490 // coal death - a free chunk is being removed from its free list because
7491 // it is being coalesced into a large free chunk.
7492 // coal birth - a free chunk is being added to its free list because
7493 // it was created when two or more free chunks where coalesced into
7494 // this free chunk.
7495 //
7496 // These statistics are used to determine the desired number of free
7497 // chunks of a given size. The desired number is chosen to be relative
7498 // to the end of a CMS sweep. The desired number at the end of a sweep
7499 // is the
7500 // count-at-end-of-previous-sweep (an amount that was enough)
7501 // - count-at-beginning-of-current-sweep (the excess)
7502 // + split-births (gains in this size during interval)
7503 // - split-deaths (demands on this size during interval)
7504 // where the interval is from the end of one sweep to the end of the
7505 // next.
7506 //
7507 // When sweeping the sweeper maintains an accumulated chunk which is
7508 // the chunk that is made up of chunks that have been coalesced. That
7509 // will be termed the left-hand chunk. A new chunk of garbage that
7510 // is being considered for coalescing will be referred to as the
7511 // right-hand chunk.
7512 //
7513 // When making a decision on whether to coalesce a right-hand chunk with
7514 // the current left-hand chunk, the current count vs. the desired count
7515 // of the left-hand chunk is considered. Also if the right-hand chunk
7516 // is near the large chunk at the end of the heap (see
7517 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7518 // left-hand chunk is coalesced.
7519 //
7520 // When making a decision about whether to split a chunk, the desired count
7521 // vs. the current count of the candidate to be split is also considered.
7522 // If the candidate is underpopulated (currently fewer chunks than desired)
7523 // a chunk of an overpopulated (currently more chunks than desired) size may
7524 // be chosen. The "hint" associated with a free list, if non-null, points
7525 // to a free list which may be overpopulated.
7526 //
7527
7528 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7529 const size_t size = fc->size();
7530 // Chunks that cannot be coalesced are not in the
7531 // free lists.
7532 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7533 assert(_sp->verify_chunk_in_free_list(fc),
7534 "free chunk should be in free lists");
7535 }
7536 // a chunk that is already free, should not have been
7537 // marked in the bit map
7538 HeapWord* const addr = (HeapWord*) fc;
7539 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7540 // Verify that the bit map has no bits marked between
7541 // addr and purported end of this block.
7542 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7543
7544 // Some chunks cannot be coalesced under any circumstances.
7545 // See the definition of cantCoalesce().
7546 if (!fc->cantCoalesce()) {
7547 // This chunk can potentially be coalesced.
7548 if (_sp->adaptive_freelists()) {
7549 // All the work is done in
7550 do_post_free_or_garbage_chunk(fc, size);
7551 } else { // Not adaptive free lists
7552 // this is a free chunk that can potentially be coalesced by the sweeper;
7553 if (!inFreeRange()) {
7554 // if the next chunk is a free block that can't be coalesced
7555 // it doesn't make sense to remove this chunk from the free lists
7556 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7557 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7558 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7559 nextChunk->is_free() && // ... which is free...
7560 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7561 // nothing to do
7562 } else {
7563 // Potentially the start of a new free range:
7564 // Don't eagerly remove it from the free lists.
7565 // No need to remove it if it will just be put
7566 // back again. (Also from a pragmatic point of view
7567 // if it is a free block in a region that is beyond
7568 // any allocated blocks, an assertion will fail)
7569 // Remember the start of a free run.
7570 initialize_free_range(addr, true);
7571 // end - can coalesce with next chunk
7572 }
7573 } else {
7574 // the midst of a free range, we are coalescing
7575 print_free_block_coalesced(fc);
7576 if (CMSTraceSweeper) {
7577 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7578 }
7579 // remove it from the free lists
7580 _sp->removeFreeChunkFromFreeLists(fc);
7581 set_lastFreeRangeCoalesced(true);
7582 // If the chunk is being coalesced and the current free range is
7583 // in the free lists, remove the current free range so that it
7584 // will be returned to the free lists in its entirety - all
7585 // the coalesced pieces included.
7586 if (freeRangeInFreeLists()) {
7587 FreeChunk* ffc = (FreeChunk*) freeFinger();
7588 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7589 "Size of free range is inconsistent with chunk size.");
7590 if (CMSTestInFreeList) {
7591 assert(_sp->verify_chunk_in_free_list(ffc),
7592 "free range is not in free lists");
7593 }
7594 _sp->removeFreeChunkFromFreeLists(ffc);
7595 set_freeRangeInFreeLists(false);
7596 }
7597 }
7598 }
7599 // Note that if the chunk is not coalescable (the else arm
7600 // below), we unconditionally flush, without needing to do
7601 // a "lookahead," as we do below.
7602 if (inFreeRange()) lookahead_and_flush(fc, size);
7603 } else {
7604 // Code path common to both original and adaptive free lists.
7605
7606 // cant coalesce with previous block; this should be treated
7607 // as the end of a free run if any
7608 if (inFreeRange()) {
7609 // we kicked some butt; time to pick up the garbage
7610 assert(freeFinger() < addr, "freeFinger points too high");
7611 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7612 }
7613 // else, nothing to do, just continue
7614 }
7615 }
7616
7617 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7618 // This is a chunk of garbage. It is not in any free list.
7619 // Add it to a free list or let it possibly be coalesced into
7620 // a larger chunk.
7621 HeapWord* const addr = (HeapWord*) fc;
7622 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7623
7624 if (_sp->adaptive_freelists()) {
7625 // Verify that the bit map has no bits marked between
7626 // addr and purported end of just dead object.
7627 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7628
7629 do_post_free_or_garbage_chunk(fc, size);
7630 } else {
7631 if (!inFreeRange()) {
7632 // start of a new free range
7633 assert(size > 0, "A free range should have a size");
7634 initialize_free_range(addr, false);
7635 } else {
7636 // this will be swept up when we hit the end of the
7637 // free range
7638 if (CMSTraceSweeper) {
7639 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7640 }
7641 // If the chunk is being coalesced and the current free range is
7642 // in the free lists, remove the current free range so that it
7643 // will be returned to the free lists in its entirety - all
7644 // the coalesced pieces included.
7645 if (freeRangeInFreeLists()) {
7646 FreeChunk* ffc = (FreeChunk*)freeFinger();
7647 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7648 "Size of free range is inconsistent with chunk size.");
7649 if (CMSTestInFreeList) {
7650 assert(_sp->verify_chunk_in_free_list(ffc),
7651 "free range is not in free lists");
7652 }
7653 _sp->removeFreeChunkFromFreeLists(ffc);
7654 set_freeRangeInFreeLists(false);
7655 }
7656 set_lastFreeRangeCoalesced(true);
7657 }
7658 // this will be swept up when we hit the end of the free range
7659
7660 // Verify that the bit map has no bits marked between
7661 // addr and purported end of just dead object.
7662 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7663 }
7664 assert(_limit >= addr + size,
7665 "A freshly garbage chunk can't possibly straddle over _limit");
7666 if (inFreeRange()) lookahead_and_flush(fc, size);
7667 return size;
7668 }
7669
7670 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7671 HeapWord* addr = (HeapWord*) fc;
7672 // The sweeper has just found a live object. Return any accumulated
7673 // left hand chunk to the free lists.
7674 if (inFreeRange()) {
7675 assert(freeFinger() < addr, "freeFinger points too high");
7676 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7677 }
7678
7679 // This object is live: we'd normally expect this to be
7680 // an oop, and like to assert the following:
7681 // assert(oop(addr)->is_oop(), "live block should be an oop");
7682 // However, as we commented above, this may be an object whose
7683 // header hasn't yet been initialized.
7684 size_t size;
7685 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7686 if (_bitMap->isMarked(addr + 1)) {
7687 // Determine the size from the bit map, rather than trying to
7688 // compute it from the object header.
7689 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7690 size = pointer_delta(nextOneAddr + 1, addr);
7691 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7692 "alignment problem");
7693
7694 #ifdef ASSERT
7695 if (oop(addr)->klass_or_null() != NULL) {
7696 // Ignore mark word because we are running concurrent with mutators
7697 assert(oop(addr)->is_oop(true), "live block should be an oop");
7698 assert(size ==
7699 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7700 "P-mark and computed size do not agree");
7701 }
7702 #endif
7703
7704 } else {
7705 // This should be an initialized object that's alive.
7706 assert(oop(addr)->klass_or_null() != NULL,
7707 "Should be an initialized object");
7708 // Ignore mark word because we are running concurrent with mutators
7709 assert(oop(addr)->is_oop(true), "live block should be an oop");
7710 // Verify that the bit map has no bits marked between
7711 // addr and purported end of this block.
7712 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7713 assert(size >= 3, "Necessary for Printezis marks to work");
7714 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7715 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7716 }
7717 return size;
7718 }
7719
7720 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7721 size_t chunkSize) {
7722 // do_post_free_or_garbage_chunk() should only be called in the case
7723 // of the adaptive free list allocator.
7724 const bool fcInFreeLists = fc->is_free();
7725 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7726 assert((HeapWord*)fc <= _limit, "sweep invariant");
7727 if (CMSTestInFreeList && fcInFreeLists) {
7728 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7729 }
7730
7731 if (CMSTraceSweeper) {
7732 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7733 }
7734
7735 HeapWord* const fc_addr = (HeapWord*) fc;
7736
7737 bool coalesce;
7738 const size_t left = pointer_delta(fc_addr, freeFinger());
7739 const size_t right = chunkSize;
7740 switch (FLSCoalescePolicy) {
7741 // numeric value forms a coalition aggressiveness metric
7742 case 0: { // never coalesce
7743 coalesce = false;
7744 break;
7745 }
7746 case 1: { // coalesce if left & right chunks on overpopulated lists
7747 coalesce = _sp->coalOverPopulated(left) &&
7748 _sp->coalOverPopulated(right);
7749 break;
7750 }
7751 case 2: { // coalesce if left chunk on overpopulated list (default)
7752 coalesce = _sp->coalOverPopulated(left);
7753 break;
7754 }
7755 case 3: { // coalesce if left OR right chunk on overpopulated list
7756 coalesce = _sp->coalOverPopulated(left) ||
7757 _sp->coalOverPopulated(right);
7758 break;
7759 }
7760 case 4: { // always coalesce
7761 coalesce = true;
7762 break;
7763 }
7764 default:
7765 ShouldNotReachHere();
7766 }
7767
7768 // Should the current free range be coalesced?
7769 // If the chunk is in a free range and either we decided to coalesce above
7770 // or the chunk is near the large block at the end of the heap
7771 // (isNearLargestChunk() returns true), then coalesce this chunk.
7772 const bool doCoalesce = inFreeRange()
7773 && (coalesce || _g->isNearLargestChunk(fc_addr));
7774 if (doCoalesce) {
7775 // Coalesce the current free range on the left with the new
7776 // chunk on the right. If either is on a free list,
7777 // it must be removed from the list and stashed in the closure.
7778 if (freeRangeInFreeLists()) {
7779 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7780 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7781 "Size of free range is inconsistent with chunk size.");
7782 if (CMSTestInFreeList) {
7783 assert(_sp->verify_chunk_in_free_list(ffc),
7784 "Chunk is not in free lists");
7785 }
7786 _sp->coalDeath(ffc->size());
7787 _sp->removeFreeChunkFromFreeLists(ffc);
7788 set_freeRangeInFreeLists(false);
7789 }
7790 if (fcInFreeLists) {
7791 _sp->coalDeath(chunkSize);
7792 assert(fc->size() == chunkSize,
7793 "The chunk has the wrong size or is not in the free lists");
7794 _sp->removeFreeChunkFromFreeLists(fc);
7795 }
7796 set_lastFreeRangeCoalesced(true);
7797 print_free_block_coalesced(fc);
7798 } else { // not in a free range and/or should not coalesce
7799 // Return the current free range and start a new one.
7800 if (inFreeRange()) {
7801 // In a free range but cannot coalesce with the right hand chunk.
7802 // Put the current free range into the free lists.
7803 flush_cur_free_chunk(freeFinger(),
7804 pointer_delta(fc_addr, freeFinger()));
7805 }
7806 // Set up for new free range. Pass along whether the right hand
7807 // chunk is in the free lists.
7808 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7809 }
7810 }
7811
7812 // Lookahead flush:
7813 // If we are tracking a free range, and this is the last chunk that
7814 // we'll look at because its end crosses past _limit, we'll preemptively
7815 // flush it along with any free range we may be holding on to. Note that
7816 // this can be the case only for an already free or freshly garbage
7817 // chunk. If this block is an object, it can never straddle
7818 // over _limit. The "straddling" occurs when _limit is set at
7819 // the previous end of the space when this cycle started, and
7820 // a subsequent heap expansion caused the previously co-terminal
7821 // free block to be coalesced with the newly expanded portion,
7822 // thus rendering _limit a non-block-boundary making it dangerous
7823 // for the sweeper to step over and examine.
7824 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7825 assert(inFreeRange(), "Should only be called if currently in a free range.");
7826 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7827 assert(_sp->used_region().contains(eob - 1),
7828 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7829 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7830 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7831 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7832 if (eob >= _limit) {
7833 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7834 if (CMSTraceSweeper) {
7835 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7836 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7837 "[" PTR_FORMAT "," PTR_FORMAT ")",
7838 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7839 }
7840 // Return the storage we are tracking back into the free lists.
7841 if (CMSTraceSweeper) {
7842 gclog_or_tty->print_cr("Flushing ... ");
7843 }
7844 assert(freeFinger() < eob, "Error");
7845 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7846 }
7847 }
7848
7849 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7850 assert(inFreeRange(), "Should only be called if currently in a free range.");
7851 assert(size > 0,
7852 "A zero sized chunk cannot be added to the free lists.");
7853 if (!freeRangeInFreeLists()) {
7854 if (CMSTestInFreeList) {
7855 FreeChunk* fc = (FreeChunk*) chunk;
7856 fc->set_size(size);
7857 assert(!_sp->verify_chunk_in_free_list(fc),
7858 "chunk should not be in free lists yet");
7859 }
7860 if (CMSTraceSweeper) {
7861 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7862 p2i(chunk), size);
7863 }
7864 // A new free range is going to be starting. The current
7865 // free range has not been added to the free lists yet or
7866 // was removed so add it back.
7867 // If the current free range was coalesced, then the death
7868 // of the free range was recorded. Record a birth now.
7869 if (lastFreeRangeCoalesced()) {
7870 _sp->coalBirth(size);
7871 }
7872 _sp->addChunkAndRepairOffsetTable(chunk, size,
7873 lastFreeRangeCoalesced());
7874 } else if (CMSTraceSweeper) {
7875 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7876 }
7877 set_inFreeRange(false);
7878 set_freeRangeInFreeLists(false);
7879 }
7880
7881 // We take a break if we've been at this for a while,
7882 // so as to avoid monopolizing the locks involved.
7883 void SweepClosure::do_yield_work(HeapWord* addr) {
7884 // Return current free chunk being used for coalescing (if any)
7885 // to the appropriate freelist. After yielding, the next
7886 // free block encountered will start a coalescing range of
7887 // free blocks. If the next free block is adjacent to the
7888 // chunk just flushed, they will need to wait for the next
7889 // sweep to be coalesced.
7890 if (inFreeRange()) {
7891 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7892 }
7893
7894 // First give up the locks, then yield, then re-lock.
7895 // We should probably use a constructor/destructor idiom to
7896 // do this unlock/lock or modify the MutexUnlocker class to
7897 // serve our purpose. XXX
7898 assert_lock_strong(_bitMap->lock());
7899 assert_lock_strong(_freelistLock);
7900 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7901 "CMS thread should hold CMS token");
7902 _bitMap->lock()->unlock();
7903 _freelistLock->unlock();
7904 ConcurrentMarkSweepThread::desynchronize(true);
7905 _collector->stopTimer();
7906 if (PrintCMSStatistics != 0) {
7907 _collector->incrementYields();
7908 }
7909
7910 // See the comment in coordinator_yield()
7911 for (unsigned i = 0; i < CMSYieldSleepCount &&
7912 ConcurrentMarkSweepThread::should_yield() &&
7913 !CMSCollector::foregroundGCIsActive(); ++i) {
7914 os::sleep(Thread::current(), 1, false);
7915 }
7916
7917 ConcurrentMarkSweepThread::synchronize(true);
7918 _freelistLock->lock();
7919 _bitMap->lock()->lock_without_safepoint_check();
7920 _collector->startTimer();
7921 }
7922
7923 #ifndef PRODUCT
7924 // This is actually very useful in a product build if it can
7925 // be called from the debugger. Compile it into the product
7926 // as needed.
7927 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7928 return debug_cms_space->verify_chunk_in_free_list(fc);
7929 }
7930 #endif
7931
7932 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7933 if (CMSTraceSweeper) {
7934 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7935 p2i(fc), fc->size());
7936 }
7937 }
7938
7939 // CMSIsAliveClosure
7940 bool CMSIsAliveClosure::do_object_b(oop obj) {
7941 HeapWord* addr = (HeapWord*)obj;
7942 return addr != NULL &&
7943 (!_span.contains(addr) || _bit_map->isMarked(addr));
7944 }
7945
7946
7947 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7948 MemRegion span,
7949 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7950 bool cpc):
7951 _collector(collector),
7952 _span(span),
7953 _bit_map(bit_map),
7954 _mark_stack(mark_stack),
7955 _concurrent_precleaning(cpc) {
7956 assert(!_span.is_empty(), "Empty span could spell trouble");
7957 }
7958
7959
7960 // CMSKeepAliveClosure: the serial version
7961 void CMSKeepAliveClosure::do_oop(oop obj) {
7962 HeapWord* addr = (HeapWord*)obj;
7963 if (_span.contains(addr) &&
7964 !_bit_map->isMarked(addr)) {
7965 _bit_map->mark(addr);
7966 bool simulate_overflow = false;
7967 NOT_PRODUCT(
7968 if (CMSMarkStackOverflowALot &&
7969 _collector->simulate_overflow()) {
7970 // simulate a stack overflow
7971 simulate_overflow = true;
7972 }
7973 )
7974 if (simulate_overflow || !_mark_stack->push(obj)) {
7975 if (_concurrent_precleaning) {
7976 // We dirty the overflown object and let the remark
7977 // phase deal with it.
7978 assert(_collector->overflow_list_is_empty(), "Error");
7979 // In the case of object arrays, we need to dirty all of
7980 // the cards that the object spans. No locking or atomics
7981 // are needed since no one else can be mutating the mod union
7982 // table.
7983 if (obj->is_objArray()) {
7984 size_t sz = obj->size();
7985 HeapWord* end_card_addr =
7986 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7987 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7988 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7989 _collector->_modUnionTable.mark_range(redirty_range);
7990 } else {
7991 _collector->_modUnionTable.mark(addr);
7992 }
7993 _collector->_ser_kac_preclean_ovflw++;
7994 } else {
7995 _collector->push_on_overflow_list(obj);
7996 _collector->_ser_kac_ovflw++;
7997 }
7998 }
7999 }
8000 }
8001
8002 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8003 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8004
8005 // CMSParKeepAliveClosure: a parallel version of the above.
8006 // The work queues are private to each closure (thread),
8007 // but (may be) available for stealing by other threads.
8008 void CMSParKeepAliveClosure::do_oop(oop obj) {
8009 HeapWord* addr = (HeapWord*)obj;
8010 if (_span.contains(addr) &&
8011 !_bit_map->isMarked(addr)) {
8012 // In general, during recursive tracing, several threads
8013 // may be concurrently getting here; the first one to
8014 // "tag" it, claims it.
8015 if (_bit_map->par_mark(addr)) {
8016 bool res = _work_queue->push(obj);
8017 assert(res, "Low water mark should be much less than capacity");
8018 // Do a recursive trim in the hope that this will keep
8019 // stack usage lower, but leave some oops for potential stealers
8020 trim_queue(_low_water_mark);
8021 } // Else, another thread got there first
8022 }
8023 }
8024
8025 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8026 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8027
8028 void CMSParKeepAliveClosure::trim_queue(uint max) {
8029 while (_work_queue->size() > max) {
8030 oop new_oop;
8031 if (_work_queue->pop_local(new_oop)) {
8032 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8033 assert(_bit_map->isMarked((HeapWord*)new_oop),
8034 "no white objects on this stack!");
8035 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8036 // iterate over the oops in this oop, marking and pushing
8037 // the ones in CMS heap (i.e. in _span).
8038 new_oop->oop_iterate(&_mark_and_push);
8039 }
8040 }
8041 }
8042
8043 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8044 CMSCollector* collector,
8045 MemRegion span, CMSBitMap* bit_map,
8046 OopTaskQueue* work_queue):
8047 _collector(collector),
8048 _span(span),
8049 _bit_map(bit_map),
8050 _work_queue(work_queue) { }
8051
8052 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8053 HeapWord* addr = (HeapWord*)obj;
8054 if (_span.contains(addr) &&
8055 !_bit_map->isMarked(addr)) {
8056 if (_bit_map->par_mark(addr)) {
8057 bool simulate_overflow = false;
8058 NOT_PRODUCT(
8059 if (CMSMarkStackOverflowALot &&
8060 _collector->par_simulate_overflow()) {
8061 // simulate a stack overflow
8062 simulate_overflow = true;
8063 }
8064 )
8065 if (simulate_overflow || !_work_queue->push(obj)) {
8066 _collector->par_push_on_overflow_list(obj);
8067 _collector->_par_kac_ovflw++;
8068 }
8069 } // Else another thread got there already
8070 }
8071 }
8072
8073 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8074 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8075
8076 //////////////////////////////////////////////////////////////////
8077 // CMSExpansionCause /////////////////////////////
8078 //////////////////////////////////////////////////////////////////
8079 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8080 switch (cause) {
8081 case _no_expansion:
8082 return "No expansion";
8083 case _satisfy_free_ratio:
8084 return "Free ratio";
8085 case _satisfy_promotion:
8086 return "Satisfy promotion";
8087 case _satisfy_allocation:
8088 return "allocation";
8089 case _allocate_par_lab:
8090 return "Par LAB";
8091 case _allocate_par_spooling_space:
8092 return "Par Spooling Space";
8093 case _adaptive_size_policy:
8094 return "Ergonomics";
8095 default:
8096 return "unknown";
8097 }
8098 }
8099
8100 void CMSDrainMarkingStackClosure::do_void() {
8101 // the max number to take from overflow list at a time
8102 const size_t num = _mark_stack->capacity()/4;
8103 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8104 "Overflow list should be NULL during concurrent phases");
8105 while (!_mark_stack->isEmpty() ||
8106 // if stack is empty, check the overflow list
8107 _collector->take_from_overflow_list(num, _mark_stack)) {
8108 oop obj = _mark_stack->pop();
8109 HeapWord* addr = (HeapWord*)obj;
8110 assert(_span.contains(addr), "Should be within span");
8111 assert(_bit_map->isMarked(addr), "Should be marked");
8112 assert(obj->is_oop(), "Should be an oop");
8113 obj->oop_iterate(_keep_alive);
8114 }
8115 }
8116
8117 void CMSParDrainMarkingStackClosure::do_void() {
8118 // drain queue
8119 trim_queue(0);
8120 }
8121
8122 // Trim our work_queue so its length is below max at return
8123 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8124 while (_work_queue->size() > max) {
8125 oop new_oop;
8126 if (_work_queue->pop_local(new_oop)) {
8127 assert(new_oop->is_oop(), "Expected an oop");
8128 assert(_bit_map->isMarked((HeapWord*)new_oop),
8129 "no white objects on this stack!");
8130 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8131 // iterate over the oops in this oop, marking and pushing
8132 // the ones in CMS heap (i.e. in _span).
8133 new_oop->oop_iterate(&_mark_and_push);
8134 }
8135 }
8136 }
8137
8138 ////////////////////////////////////////////////////////////////////
8139 // Support for Marking Stack Overflow list handling and related code
8140 ////////////////////////////////////////////////////////////////////
8141 // Much of the following code is similar in shape and spirit to the
8142 // code used in ParNewGC. We should try and share that code
8143 // as much as possible in the future.
8144
8145 #ifndef PRODUCT
8146 // Debugging support for CMSStackOverflowALot
8147
8148 // It's OK to call this multi-threaded; the worst thing
8149 // that can happen is that we'll get a bunch of closely
8150 // spaced simulated overflows, but that's OK, in fact
8151 // probably good as it would exercise the overflow code
8152 // under contention.
8153 bool CMSCollector::simulate_overflow() {
8154 if (_overflow_counter-- <= 0) { // just being defensive
8155 _overflow_counter = CMSMarkStackOverflowInterval;
8156 return true;
8157 } else {
8158 return false;
8159 }
8160 }
8161
8162 bool CMSCollector::par_simulate_overflow() {
8163 return simulate_overflow();
8164 }
8165 #endif
8166
8167 // Single-threaded
8168 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8169 assert(stack->isEmpty(), "Expected precondition");
8170 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8171 size_t i = num;
8172 oop cur = _overflow_list;
8173 const markOop proto = markOopDesc::prototype();
8174 NOT_PRODUCT(ssize_t n = 0;)
8175 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8176 next = oop(cur->mark());
8177 cur->set_mark(proto); // until proven otherwise
8178 assert(cur->is_oop(), "Should be an oop");
8179 bool res = stack->push(cur);
8180 assert(res, "Bit off more than can chew?");
8181 NOT_PRODUCT(n++;)
8182 }
8183 _overflow_list = cur;
8184 #ifndef PRODUCT
8185 assert(_num_par_pushes >= n, "Too many pops?");
8186 _num_par_pushes -=n;
8187 #endif
8188 return !stack->isEmpty();
8189 }
8190
8191 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8192 // (MT-safe) Get a prefix of at most "num" from the list.
8193 // The overflow list is chained through the mark word of
8194 // each object in the list. We fetch the entire list,
8195 // break off a prefix of the right size and return the
8196 // remainder. If other threads try to take objects from
8197 // the overflow list at that time, they will wait for
8198 // some time to see if data becomes available. If (and
8199 // only if) another thread places one or more object(s)
8200 // on the global list before we have returned the suffix
8201 // to the global list, we will walk down our local list
8202 // to find its end and append the global list to
8203 // our suffix before returning it. This suffix walk can
8204 // prove to be expensive (quadratic in the amount of traffic)
8205 // when there are many objects in the overflow list and
8206 // there is much producer-consumer contention on the list.
8207 // *NOTE*: The overflow list manipulation code here and
8208 // in ParNewGeneration:: are very similar in shape,
8209 // except that in the ParNew case we use the old (from/eden)
8210 // copy of the object to thread the list via its klass word.
8211 // Because of the common code, if you make any changes in
8212 // the code below, please check the ParNew version to see if
8213 // similar changes might be needed.
8214 // CR 6797058 has been filed to consolidate the common code.
8215 bool CMSCollector::par_take_from_overflow_list(size_t num,
8216 OopTaskQueue* work_q,
8217 int no_of_gc_threads) {
8218 assert(work_q->size() == 0, "First empty local work queue");
8219 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8220 if (_overflow_list == NULL) {
8221 return false;
8222 }
8223 // Grab the entire list; we'll put back a suffix
8224 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8225 Thread* tid = Thread::current();
8226 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8227 // set to ParallelGCThreads.
8228 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8229 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8230 // If the list is busy, we spin for a short while,
8231 // sleeping between attempts to get the list.
8232 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8233 os::sleep(tid, sleep_time_millis, false);
8234 if (_overflow_list == NULL) {
8235 // Nothing left to take
8236 return false;
8237 } else if (_overflow_list != BUSY) {
8238 // Try and grab the prefix
8239 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8240 }
8241 }
8242 // If the list was found to be empty, or we spun long
8243 // enough, we give up and return empty-handed. If we leave
8244 // the list in the BUSY state below, it must be the case that
8245 // some other thread holds the overflow list and will set it
8246 // to a non-BUSY state in the future.
8247 if (prefix == NULL || prefix == BUSY) {
8248 // Nothing to take or waited long enough
8249 if (prefix == NULL) {
8250 // Write back the NULL in case we overwrote it with BUSY above
8251 // and it is still the same value.
8252 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8253 }
8254 return false;
8255 }
8256 assert(prefix != NULL && prefix != BUSY, "Error");
8257 size_t i = num;
8258 oop cur = prefix;
8259 // Walk down the first "num" objects, unless we reach the end.
8260 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8261 if (cur->mark() == NULL) {
8262 // We have "num" or fewer elements in the list, so there
8263 // is nothing to return to the global list.
8264 // Write back the NULL in lieu of the BUSY we wrote
8265 // above, if it is still the same value.
8266 if (_overflow_list == BUSY) {
8267 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8268 }
8269 } else {
8270 // Chop off the suffix and return it to the global list.
8271 assert(cur->mark() != BUSY, "Error");
8272 oop suffix_head = cur->mark(); // suffix will be put back on global list
8273 cur->set_mark(NULL); // break off suffix
8274 // It's possible that the list is still in the empty(busy) state
8275 // we left it in a short while ago; in that case we may be
8276 // able to place back the suffix without incurring the cost
8277 // of a walk down the list.
8278 oop observed_overflow_list = _overflow_list;
8279 oop cur_overflow_list = observed_overflow_list;
8280 bool attached = false;
8281 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8282 observed_overflow_list =
8283 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8284 if (cur_overflow_list == observed_overflow_list) {
8285 attached = true;
8286 break;
8287 } else cur_overflow_list = observed_overflow_list;
8288 }
8289 if (!attached) {
8290 // Too bad, someone else sneaked in (at least) an element; we'll need
8291 // to do a splice. Find tail of suffix so we can prepend suffix to global
8292 // list.
8293 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8294 oop suffix_tail = cur;
8295 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8296 "Tautology");
8297 observed_overflow_list = _overflow_list;
8298 do {
8299 cur_overflow_list = observed_overflow_list;
8300 if (cur_overflow_list != BUSY) {
8301 // Do the splice ...
8302 suffix_tail->set_mark(markOop(cur_overflow_list));
8303 } else { // cur_overflow_list == BUSY
8304 suffix_tail->set_mark(NULL);
8305 }
8306 // ... and try to place spliced list back on overflow_list ...
8307 observed_overflow_list =
8308 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8309 } while (cur_overflow_list != observed_overflow_list);
8310 // ... until we have succeeded in doing so.
8311 }
8312 }
8313
8314 // Push the prefix elements on work_q
8315 assert(prefix != NULL, "control point invariant");
8316 const markOop proto = markOopDesc::prototype();
8317 oop next;
8318 NOT_PRODUCT(ssize_t n = 0;)
8319 for (cur = prefix; cur != NULL; cur = next) {
8320 next = oop(cur->mark());
8321 cur->set_mark(proto); // until proven otherwise
8322 assert(cur->is_oop(), "Should be an oop");
8323 bool res = work_q->push(cur);
8324 assert(res, "Bit off more than we can chew?");
8325 NOT_PRODUCT(n++;)
8326 }
8327 #ifndef PRODUCT
8328 assert(_num_par_pushes >= n, "Too many pops?");
8329 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8330 #endif
8331 return true;
8332 }
8333
8334 // Single-threaded
8335 void CMSCollector::push_on_overflow_list(oop p) {
8336 NOT_PRODUCT(_num_par_pushes++;)
8337 assert(p->is_oop(), "Not an oop");
8338 preserve_mark_if_necessary(p);
8339 p->set_mark((markOop)_overflow_list);
8340 _overflow_list = p;
8341 }
8342
8343 // Multi-threaded; use CAS to prepend to overflow list
8344 void CMSCollector::par_push_on_overflow_list(oop p) {
8345 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8346 assert(p->is_oop(), "Not an oop");
8347 par_preserve_mark_if_necessary(p);
8348 oop observed_overflow_list = _overflow_list;
8349 oop cur_overflow_list;
8350 do {
8351 cur_overflow_list = observed_overflow_list;
8352 if (cur_overflow_list != BUSY) {
8353 p->set_mark(markOop(cur_overflow_list));
8354 } else {
8355 p->set_mark(NULL);
8356 }
8357 observed_overflow_list =
8358 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8359 } while (cur_overflow_list != observed_overflow_list);
8360 }
8361 #undef BUSY
8362
8363 // Single threaded
8364 // General Note on GrowableArray: pushes may silently fail
8365 // because we are (temporarily) out of C-heap for expanding
8366 // the stack. The problem is quite ubiquitous and affects
8367 // a lot of code in the JVM. The prudent thing for GrowableArray
8368 // to do (for now) is to exit with an error. However, that may
8369 // be too draconian in some cases because the caller may be
8370 // able to recover without much harm. For such cases, we
8371 // should probably introduce a "soft_push" method which returns
8372 // an indication of success or failure with the assumption that
8373 // the caller may be able to recover from a failure; code in
8374 // the VM can then be changed, incrementally, to deal with such
8375 // failures where possible, thus, incrementally hardening the VM
8376 // in such low resource situations.
8377 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8378 _preserved_oop_stack.push(p);
8379 _preserved_mark_stack.push(m);
8380 assert(m == p->mark(), "Mark word changed");
8381 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8382 "bijection");
8383 }
8384
8385 // Single threaded
8386 void CMSCollector::preserve_mark_if_necessary(oop p) {
8387 markOop m = p->mark();
8388 if (m->must_be_preserved(p)) {
8389 preserve_mark_work(p, m);
8390 }
8391 }
8392
8393 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8394 markOop m = p->mark();
8395 if (m->must_be_preserved(p)) {
8396 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8397 // Even though we read the mark word without holding
8398 // the lock, we are assured that it will not change
8399 // because we "own" this oop, so no other thread can
8400 // be trying to push it on the overflow list; see
8401 // the assertion in preserve_mark_work() that checks
8402 // that m == p->mark().
8403 preserve_mark_work(p, m);
8404 }
8405 }
8406
8407 // We should be able to do this multi-threaded,
8408 // a chunk of stack being a task (this is
8409 // correct because each oop only ever appears
8410 // once in the overflow list. However, it's
8411 // not very easy to completely overlap this with
8412 // other operations, so will generally not be done
8413 // until all work's been completed. Because we
8414 // expect the preserved oop stack (set) to be small,
8415 // it's probably fine to do this single-threaded.
8416 // We can explore cleverer concurrent/overlapped/parallel
8417 // processing of preserved marks if we feel the
8418 // need for this in the future. Stack overflow should
8419 // be so rare in practice and, when it happens, its
8420 // effect on performance so great that this will
8421 // likely just be in the noise anyway.
8422 void CMSCollector::restore_preserved_marks_if_any() {
8423 assert(SafepointSynchronize::is_at_safepoint(),
8424 "world should be stopped");
8425 assert(Thread::current()->is_ConcurrentGC_thread() ||
8426 Thread::current()->is_VM_thread(),
8427 "should be single-threaded");
8428 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8429 "bijection");
8430
8431 while (!_preserved_oop_stack.is_empty()) {
8432 oop p = _preserved_oop_stack.pop();
8433 assert(p->is_oop(), "Should be an oop");
8434 assert(_span.contains(p), "oop should be in _span");
8435 assert(p->mark() == markOopDesc::prototype(),
8436 "Set when taken from overflow list");
8437 markOop m = _preserved_mark_stack.pop();
8438 p->set_mark(m);
8439 }
8440 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8441 "stacks were cleared above");
8442 }
8443
8444 #ifndef PRODUCT
8445 bool CMSCollector::no_preserved_marks() const {
8446 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8447 }
8448 #endif
8449
8450 // Transfer some number of overflown objects to usual marking
8451 // stack. Return true if some objects were transferred.
8452 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8453 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8454 (size_t)ParGCDesiredObjsFromOverflowList);
8455
8456 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8457 assert(_collector->overflow_list_is_empty() || res,
8458 "If list is not empty, we should have taken something");
8459 assert(!res || !_mark_stack->isEmpty(),
8460 "If we took something, it should now be on our stack");
8461 return res;
8462 }
8463
8464 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8465 size_t res = _sp->block_size_no_stall(addr, _collector);
8466 if (_sp->block_is_obj(addr)) {
8467 if (_live_bit_map->isMarked(addr)) {
8468 // It can't have been dead in a previous cycle
8469 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8470 } else {
8471 _dead_bit_map->mark(addr); // mark the dead object
8472 }
8473 }
8474 // Could be 0, if the block size could not be computed without stalling.
8475 return res;
8476 }
8477
8478 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8479
8480 switch (phase) {
8481 case CMSCollector::InitialMarking:
8482 initialize(true /* fullGC */ ,
8483 cause /* cause of the GC */,
8484 true /* recordGCBeginTime */,
8485 true /* recordPreGCUsage */,
8486 false /* recordPeakUsage */,
8487 false /* recordPostGCusage */,
8488 true /* recordAccumulatedGCTime */,
8489 false /* recordGCEndTime */,
8490 false /* countCollection */ );
8491 break;
8492
8493 case CMSCollector::FinalMarking:
8494 initialize(true /* fullGC */ ,
8495 cause /* cause of the GC */,
8496 false /* recordGCBeginTime */,
8497 false /* recordPreGCUsage */,
8498 false /* recordPeakUsage */,
8499 false /* recordPostGCusage */,
8500 true /* recordAccumulatedGCTime */,
8501 false /* recordGCEndTime */,
8502 false /* countCollection */ );
8503 break;
8504
8505 case CMSCollector::Sweeping:
8506 initialize(true /* fullGC */ ,
8507 cause /* cause of the GC */,
8508 false /* recordGCBeginTime */,
8509 false /* recordPreGCUsage */,
8510 true /* recordPeakUsage */,
8511 true /* recordPostGCusage */,
8512 false /* recordAccumulatedGCTime */,
8513 true /* recordGCEndTime */,
8514 true /* countCollection */ );
8515 break;
8516
8517 default:
8518 ShouldNotReachHere();
8519 }
8520 }