1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size, int level,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, level, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 (int) ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = (GenCollectorPolicy*) GenCollectedHeap::heap()->collector_policy();
308
309 // Generation Counters - generation 1, 1 subspace
310 _gen_counters = new GenerationCounters(gen_name, 1, 1,
311 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
312
313 _space_counters = new GSpaceCounters(gen_name, 0,
314 _virtual_space.reserved_size(),
315 this, _gen_counters);
316 }
317
318 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
319 _cms_gen(cms_gen)
320 {
321 assert(alpha <= 100, "bad value");
322 _saved_alpha = alpha;
323
324 // Initialize the alphas to the bootstrap value of 100.
325 _gc0_alpha = _cms_alpha = 100;
326
327 _cms_begin_time.update();
328 _cms_end_time.update();
329
330 _gc0_duration = 0.0;
331 _gc0_period = 0.0;
332 _gc0_promoted = 0;
333
334 _cms_duration = 0.0;
335 _cms_period = 0.0;
336 _cms_allocated = 0;
337
338 _cms_used_at_gc0_begin = 0;
339 _cms_used_at_gc0_end = 0;
340 _allow_duty_cycle_reduction = false;
341 _valid_bits = 0;
342 }
343
344 double CMSStats::cms_free_adjustment_factor(size_t free) const {
345 // TBD: CR 6909490
346 return 1.0;
347 }
348
349 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
350 }
351
352 // If promotion failure handling is on use
353 // the padded average size of the promotion for each
354 // young generation collection.
355 double CMSStats::time_until_cms_gen_full() const {
356 size_t cms_free = _cms_gen->cmsSpace()->free();
357 GenCollectedHeap* gch = GenCollectedHeap::heap();
358 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
359 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
360 if (cms_free > expected_promotion) {
361 // Start a cms collection if there isn't enough space to promote
362 // for the next minor collection. Use the padded average as
363 // a safety factor.
364 cms_free -= expected_promotion;
365
366 // Adjust by the safety factor.
367 double cms_free_dbl = (double)cms_free;
368 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
369 // Apply a further correction factor which tries to adjust
370 // for recent occurance of concurrent mode failures.
371 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
372 cms_free_dbl = cms_free_dbl * cms_adjustment;
373
374 if (PrintGCDetails && Verbose) {
375 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
376 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
377 cms_free, expected_promotion);
378 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
379 cms_free_dbl, cms_consumption_rate() + 1.0);
380 }
381 // Add 1 in case the consumption rate goes to zero.
382 return cms_free_dbl / (cms_consumption_rate() + 1.0);
383 }
384 return 0.0;
385 }
386
387 // Compare the duration of the cms collection to the
388 // time remaining before the cms generation is empty.
389 // Note that the time from the start of the cms collection
390 // to the start of the cms sweep (less than the total
391 // duration of the cms collection) can be used. This
392 // has been tried and some applications experienced
393 // promotion failures early in execution. This was
394 // possibly because the averages were not accurate
395 // enough at the beginning.
396 double CMSStats::time_until_cms_start() const {
397 // We add "gc0_period" to the "work" calculation
398 // below because this query is done (mostly) at the
399 // end of a scavenge, so we need to conservatively
400 // account for that much possible delay
401 // in the query so as to avoid concurrent mode failures
402 // due to starting the collection just a wee bit too
403 // late.
404 double work = cms_duration() + gc0_period();
405 double deadline = time_until_cms_gen_full();
406 // If a concurrent mode failure occurred recently, we want to be
407 // more conservative and halve our expected time_until_cms_gen_full()
408 if (work > deadline) {
409 if (Verbose && PrintGCDetails) {
410 gclog_or_tty->print(
411 " CMSCollector: collect because of anticipated promotion "
412 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
413 gc0_period(), time_until_cms_gen_full());
414 }
415 return 0.0;
416 }
417 return work - deadline;
418 }
419
420 #ifndef PRODUCT
421 void CMSStats::print_on(outputStream *st) const {
422 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
423 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
424 gc0_duration(), gc0_period(), gc0_promoted());
425 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
426 cms_duration(), cms_period(), cms_allocated());
427 st->print(",cms_since_beg=%g,cms_since_end=%g",
428 cms_time_since_begin(), cms_time_since_end());
429 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
430 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
431
432 if (valid()) {
433 st->print(",promo_rate=%g,cms_alloc_rate=%g",
434 promotion_rate(), cms_allocation_rate());
435 st->print(",cms_consumption_rate=%g,time_until_full=%g",
436 cms_consumption_rate(), time_until_cms_gen_full());
437 }
438 st->print(" ");
439 }
440 #endif // #ifndef PRODUCT
441
442 CMSCollector::CollectorState CMSCollector::_collectorState =
443 CMSCollector::Idling;
444 bool CMSCollector::_foregroundGCIsActive = false;
445 bool CMSCollector::_foregroundGCShouldWait = false;
446
447 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
448 CardTableRS* ct,
449 ConcurrentMarkSweepPolicy* cp):
450 _cmsGen(cmsGen),
451 _ct(ct),
452 _ref_processor(NULL), // will be set later
453 _conc_workers(NULL), // may be set later
454 _abort_preclean(false),
455 _start_sampling(false),
456 _between_prologue_and_epilogue(false),
457 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
458 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
459 -1 /* lock-free */, "No_lock" /* dummy */),
460 _modUnionClosurePar(&_modUnionTable),
461 // Adjust my span to cover old (cms) gen
462 _span(cmsGen->reserved()),
463 // Construct the is_alive_closure with _span & markBitMap
464 _is_alive_closure(_span, &_markBitMap),
465 _restart_addr(NULL),
466 _overflow_list(NULL),
467 _stats(cmsGen),
468 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
469 //verify that this lock should be acquired with safepoint check.
470 Monitor::_safepoint_check_sometimes)),
471 _eden_chunk_array(NULL), // may be set in ctor body
472 _eden_chunk_capacity(0), // -- ditto --
473 _eden_chunk_index(0), // -- ditto --
474 _survivor_plab_array(NULL), // -- ditto --
475 _survivor_chunk_array(NULL), // -- ditto --
476 _survivor_chunk_capacity(0), // -- ditto --
477 _survivor_chunk_index(0), // -- ditto --
478 _ser_pmc_preclean_ovflw(0),
479 _ser_kac_preclean_ovflw(0),
480 _ser_pmc_remark_ovflw(0),
481 _par_pmc_remark_ovflw(0),
482 _ser_kac_ovflw(0),
483 _par_kac_ovflw(0),
484 #ifndef PRODUCT
485 _num_par_pushes(0),
486 #endif
487 _collection_count_start(0),
488 _verifying(false),
489 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
490 _completed_initialization(false),
491 _collector_policy(cp),
492 _should_unload_classes(CMSClassUnloadingEnabled),
493 _concurrent_cycles_since_last_unload(0),
494 _roots_scanning_options(GenCollectedHeap::SO_None),
495 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
497 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
498 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
499 _cms_start_registered(false)
500 {
501 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
502 ExplicitGCInvokesConcurrent = true;
503 }
504 // Now expand the span and allocate the collection support structures
505 // (MUT, marking bit map etc.) to cover both generations subject to
506 // collection.
507
508 // For use by dirty card to oop closures.
509 _cmsGen->cmsSpace()->set_collector(this);
510
511 // Allocate MUT and marking bit map
512 {
513 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
514 if (!_markBitMap.allocate(_span)) {
515 warning("Failed to allocate CMS Bit Map");
516 return;
517 }
518 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
519 }
520 {
521 _modUnionTable.allocate(_span);
522 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
523 }
524
525 if (!_markStack.allocate(MarkStackSize)) {
526 warning("Failed to allocate CMS Marking Stack");
527 return;
528 }
529
530 // Support for multi-threaded concurrent phases
531 if (CMSConcurrentMTEnabled) {
532 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
533 // just for now
534 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
535 }
536 if (ConcGCThreads > 1) {
537 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
538 ConcGCThreads, true);
539 if (_conc_workers == NULL) {
540 warning("GC/CMS: _conc_workers allocation failure: "
541 "forcing -CMSConcurrentMTEnabled");
542 CMSConcurrentMTEnabled = false;
543 } else {
544 _conc_workers->initialize_workers();
545 }
546 } else {
547 CMSConcurrentMTEnabled = false;
548 }
549 }
550 if (!CMSConcurrentMTEnabled) {
551 ConcGCThreads = 0;
552 } else {
553 // Turn off CMSCleanOnEnter optimization temporarily for
554 // the MT case where it's not fixed yet; see 6178663.
555 CMSCleanOnEnter = false;
556 }
557 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
558 "Inconsistency");
559
560 // Parallel task queues; these are shared for the
561 // concurrent and stop-world phases of CMS, but
562 // are not shared with parallel scavenge (ParNew).
563 {
564 uint i;
565 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
566
567 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
568 || ParallelRefProcEnabled)
569 && num_queues > 0) {
570 _task_queues = new OopTaskQueueSet(num_queues);
571 if (_task_queues == NULL) {
572 warning("task_queues allocation failure.");
573 return;
574 }
575 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
576 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
577 for (i = 0; i < num_queues; i++) {
578 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
579 if (q == NULL) {
580 warning("work_queue allocation failure.");
581 return;
582 }
583 _task_queues->register_queue(i, q);
584 }
585 for (i = 0; i < num_queues; i++) {
586 _task_queues->queue(i)->initialize();
587 _hash_seed[i] = 17; // copied from ParNew
588 }
589 }
590 }
591
592 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
593
594 // Clip CMSBootstrapOccupancy between 0 and 100.
595 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
596
597 // Now tell CMS generations the identity of their collector
598 ConcurrentMarkSweepGeneration::set_collector(this);
599
600 // Create & start a CMS thread for this CMS collector
601 _cmsThread = ConcurrentMarkSweepThread::start(this);
602 assert(cmsThread() != NULL, "CMS Thread should have been created");
603 assert(cmsThread()->collector() == this,
604 "CMS Thread should refer to this gen");
605 assert(CGC_lock != NULL, "Where's the CGC_lock?");
606
607 // Support for parallelizing young gen rescan
608 GenCollectedHeap* gch = GenCollectedHeap::heap();
609 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
610 _young_gen = (ParNewGeneration*)gch->young_gen();
611 if (gch->supports_inline_contig_alloc()) {
612 _top_addr = gch->top_addr();
613 _end_addr = gch->end_addr();
614 assert(_young_gen != NULL, "no _young_gen");
615 _eden_chunk_index = 0;
616 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
617 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
618 }
619
620 // Support for parallelizing survivor space rescan
621 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
622 const size_t max_plab_samples =
623 ((DefNewGeneration*)_young_gen)->max_survivor_size() / plab_sample_minimum_size();
624
625 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
626 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
627 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
628 _survivor_chunk_capacity = 2*max_plab_samples;
629 for (uint i = 0; i < ParallelGCThreads; i++) {
630 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
631 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
632 assert(cur->end() == 0, "Should be 0");
633 assert(cur->array() == vec, "Should be vec");
634 assert(cur->capacity() == max_plab_samples, "Error");
635 }
636 }
637
638 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
639 _gc_counters = new CollectorCounters("CMS", 1);
640 _completed_initialization = true;
641 _inter_sweep_timer.start(); // start of time
642 }
643
644 size_t CMSCollector::plab_sample_minimum_size() {
645 // The default value of MinTLABSize is 2k, but there is
646 // no way to get the default value if the flag has been overridden.
647 return MAX2(ThreadLocalAllocBuffer::min_size() * HeapWordSize, 2 * K);
648 }
649
650 const char* ConcurrentMarkSweepGeneration::name() const {
651 return "concurrent mark-sweep generation";
652 }
653 void ConcurrentMarkSweepGeneration::update_counters() {
654 if (UsePerfData) {
655 _space_counters->update_all();
656 _gen_counters->update_all();
657 }
658 }
659
660 // this is an optimized version of update_counters(). it takes the
661 // used value as a parameter rather than computing it.
662 //
663 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
664 if (UsePerfData) {
665 _space_counters->update_used(used);
666 _space_counters->update_capacity();
667 _gen_counters->update_all();
668 }
669 }
670
671 void ConcurrentMarkSweepGeneration::print() const {
672 Generation::print();
673 cmsSpace()->print();
674 }
675
676 #ifndef PRODUCT
677 void ConcurrentMarkSweepGeneration::print_statistics() {
678 cmsSpace()->printFLCensus(0);
679 }
680 #endif
681
682 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
683 GenCollectedHeap* gch = GenCollectedHeap::heap();
684 if (PrintGCDetails) {
685 if (Verbose) {
686 gclog_or_tty->print("[%d %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
687 level(), short_name(), s, used(), capacity());
688 } else {
689 gclog_or_tty->print("[%d %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
690 level(), short_name(), s, used() / K, capacity() / K);
691 }
692 }
693 if (Verbose) {
694 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
695 gch->used(), gch->capacity());
696 } else {
697 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
698 gch->used() / K, gch->capacity() / K);
699 }
700 }
701
702 size_t
703 ConcurrentMarkSweepGeneration::contiguous_available() const {
704 // dld proposes an improvement in precision here. If the committed
705 // part of the space ends in a free block we should add that to
706 // uncommitted size in the calculation below. Will make this
707 // change later, staying with the approximation below for the
708 // time being. -- ysr.
709 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
710 }
711
712 size_t
713 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
714 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
715 }
716
717 size_t ConcurrentMarkSweepGeneration::max_available() const {
718 return free() + _virtual_space.uncommitted_size();
719 }
720
721 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
722 size_t available = max_available();
723 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
724 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
725 if (Verbose && PrintGCDetails) {
726 gclog_or_tty->print_cr(
727 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
728 "max_promo(" SIZE_FORMAT ")",
729 res? "":" not", available, res? ">=":"<",
730 av_promo, max_promotion_in_bytes);
731 }
732 return res;
733 }
734
735 // At a promotion failure dump information on block layout in heap
736 // (cms old generation).
737 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
738 if (CMSDumpAtPromotionFailure) {
739 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
740 }
741 }
742
743 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
744 // Clear the promotion information. These pointers can be adjusted
745 // along with all the other pointers into the heap but
746 // compaction is expected to be a rare event with
747 // a heap using cms so don't do it without seeing the need.
748 for (uint i = 0; i < ParallelGCThreads; i++) {
749 _par_gc_thread_states[i]->promo.reset();
750 }
751 }
752
753 void ConcurrentMarkSweepGeneration::compute_new_size() {
754 assert_locked_or_safepoint(Heap_lock);
755
756 // If incremental collection failed, we just want to expand
757 // to the limit.
758 if (incremental_collection_failed()) {
759 clear_incremental_collection_failed();
760 grow_to_reserved();
761 return;
762 }
763
764 // The heap has been compacted but not reset yet.
765 // Any metric such as free() or used() will be incorrect.
766
767 CardGeneration::compute_new_size();
768
769 // Reset again after a possible resizing
770 if (did_compact()) {
771 cmsSpace()->reset_after_compaction();
772 }
773 }
774
775 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
776 assert_locked_or_safepoint(Heap_lock);
777
778 // If incremental collection failed, we just want to expand
779 // to the limit.
780 if (incremental_collection_failed()) {
781 clear_incremental_collection_failed();
782 grow_to_reserved();
783 return;
784 }
785
786 double free_percentage = ((double) free()) / capacity();
787 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
788 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
789
790 // compute expansion delta needed for reaching desired free percentage
791 if (free_percentage < desired_free_percentage) {
792 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
793 assert(desired_capacity >= capacity(), "invalid expansion size");
794 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
795 if (PrintGCDetails && Verbose) {
796 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
797 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
798 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
799 gclog_or_tty->print_cr(" Desired free fraction %f",
800 desired_free_percentage);
801 gclog_or_tty->print_cr(" Maximum free fraction %f",
802 maximum_free_percentage);
803 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity()/1000);
804 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT,
805 desired_capacity/1000);
806 int prev_level = level() - 1;
807 if (prev_level >= 0) {
808 size_t prev_size = 0;
809 GenCollectedHeap* gch = GenCollectedHeap::heap();
810 Generation* prev_gen = gch->young_gen();
811 prev_size = prev_gen->capacity();
812 gclog_or_tty->print_cr(" Younger gen size " SIZE_FORMAT,
813 prev_size/1000);
814 }
815 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT,
816 unsafe_max_alloc_nogc()/1000);
817 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT,
818 contiguous_available()/1000);
819 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)",
820 expand_bytes);
821 }
822 // safe if expansion fails
823 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
824 if (PrintGCDetails && Verbose) {
825 gclog_or_tty->print_cr(" Expanded free fraction %f",
826 ((double) free()) / capacity());
827 }
828 } else {
829 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
830 assert(desired_capacity <= capacity(), "invalid expansion size");
831 size_t shrink_bytes = capacity() - desired_capacity;
832 // Don't shrink unless the delta is greater than the minimum shrink we want
833 if (shrink_bytes >= MinHeapDeltaBytes) {
834 shrink_free_list_by(shrink_bytes);
835 }
836 }
837 }
838
839 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
840 return cmsSpace()->freelistLock();
841 }
842
843 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
844 bool tlab) {
845 CMSSynchronousYieldRequest yr;
846 MutexLockerEx x(freelistLock(),
847 Mutex::_no_safepoint_check_flag);
848 return have_lock_and_allocate(size, tlab);
849 }
850
851 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
852 bool tlab /* ignored */) {
853 assert_lock_strong(freelistLock());
854 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
855 HeapWord* res = cmsSpace()->allocate(adjustedSize);
856 // Allocate the object live (grey) if the background collector has
857 // started marking. This is necessary because the marker may
858 // have passed this address and consequently this object will
859 // not otherwise be greyed and would be incorrectly swept up.
860 // Note that if this object contains references, the writing
861 // of those references will dirty the card containing this object
862 // allowing the object to be blackened (and its references scanned)
863 // either during a preclean phase or at the final checkpoint.
864 if (res != NULL) {
865 // We may block here with an uninitialized object with
866 // its mark-bit or P-bits not yet set. Such objects need
867 // to be safely navigable by block_start().
868 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
869 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
870 collector()->direct_allocated(res, adjustedSize);
871 _direct_allocated_words += adjustedSize;
872 // allocation counters
873 NOT_PRODUCT(
874 _numObjectsAllocated++;
875 _numWordsAllocated += (int)adjustedSize;
876 )
877 }
878 return res;
879 }
880
881 // In the case of direct allocation by mutators in a generation that
882 // is being concurrently collected, the object must be allocated
883 // live (grey) if the background collector has started marking.
884 // This is necessary because the marker may
885 // have passed this address and consequently this object will
886 // not otherwise be greyed and would be incorrectly swept up.
887 // Note that if this object contains references, the writing
888 // of those references will dirty the card containing this object
889 // allowing the object to be blackened (and its references scanned)
890 // either during a preclean phase or at the final checkpoint.
891 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
892 assert(_markBitMap.covers(start, size), "Out of bounds");
893 if (_collectorState >= Marking) {
894 MutexLockerEx y(_markBitMap.lock(),
895 Mutex::_no_safepoint_check_flag);
896 // [see comments preceding SweepClosure::do_blk() below for details]
897 //
898 // Can the P-bits be deleted now? JJJ
899 //
900 // 1. need to mark the object as live so it isn't collected
901 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
902 // 3. need to mark the end of the object so marking, precleaning or sweeping
903 // can skip over uninitialized or unparsable objects. An allocated
904 // object is considered uninitialized for our purposes as long as
905 // its klass word is NULL. All old gen objects are parsable
906 // as soon as they are initialized.)
907 _markBitMap.mark(start); // object is live
908 _markBitMap.mark(start + 1); // object is potentially uninitialized?
909 _markBitMap.mark(start + size - 1);
910 // mark end of object
911 }
912 // check that oop looks uninitialized
913 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
914 }
915
916 void CMSCollector::promoted(bool par, HeapWord* start,
917 bool is_obj_array, size_t obj_size) {
918 assert(_markBitMap.covers(start), "Out of bounds");
919 // See comment in direct_allocated() about when objects should
920 // be allocated live.
921 if (_collectorState >= Marking) {
922 // we already hold the marking bit map lock, taken in
923 // the prologue
924 if (par) {
925 _markBitMap.par_mark(start);
926 } else {
927 _markBitMap.mark(start);
928 }
929 // We don't need to mark the object as uninitialized (as
930 // in direct_allocated above) because this is being done with the
931 // world stopped and the object will be initialized by the
932 // time the marking, precleaning or sweeping get to look at it.
933 // But see the code for copying objects into the CMS generation,
934 // where we need to ensure that concurrent readers of the
935 // block offset table are able to safely navigate a block that
936 // is in flux from being free to being allocated (and in
937 // transition while being copied into) and subsequently
938 // becoming a bona-fide object when the copy/promotion is complete.
939 assert(SafepointSynchronize::is_at_safepoint(),
940 "expect promotion only at safepoints");
941
942 if (_collectorState < Sweeping) {
943 // Mark the appropriate cards in the modUnionTable, so that
944 // this object gets scanned before the sweep. If this is
945 // not done, CMS generation references in the object might
946 // not get marked.
947 // For the case of arrays, which are otherwise precisely
948 // marked, we need to dirty the entire array, not just its head.
949 if (is_obj_array) {
950 // The [par_]mark_range() method expects mr.end() below to
951 // be aligned to the granularity of a bit's representation
952 // in the heap. In the case of the MUT below, that's a
953 // card size.
954 MemRegion mr(start,
955 (HeapWord*)round_to((intptr_t)(start + obj_size),
956 CardTableModRefBS::card_size /* bytes */));
957 if (par) {
958 _modUnionTable.par_mark_range(mr);
959 } else {
960 _modUnionTable.mark_range(mr);
961 }
962 } else { // not an obj array; we can just mark the head
963 if (par) {
964 _modUnionTable.par_mark(start);
965 } else {
966 _modUnionTable.mark(start);
967 }
968 }
969 }
970 }
971 }
972
973 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
974 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
975 // allocate, copy and if necessary update promoinfo --
976 // delegate to underlying space.
977 assert_lock_strong(freelistLock());
978
979 #ifndef PRODUCT
980 if (GenCollectedHeap::heap()->promotion_should_fail()) {
981 return NULL;
982 }
983 #endif // #ifndef PRODUCT
984
985 oop res = _cmsSpace->promote(obj, obj_size);
986 if (res == NULL) {
987 // expand and retry
988 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
989 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
990 // Since this is the old generation, we don't try to promote
991 // into a more senior generation.
992 res = _cmsSpace->promote(obj, obj_size);
993 }
994 if (res != NULL) {
995 // See comment in allocate() about when objects should
996 // be allocated live.
997 assert(obj->is_oop(), "Will dereference klass pointer below");
998 collector()->promoted(false, // Not parallel
999 (HeapWord*)res, obj->is_objArray(), obj_size);
1000 // promotion counters
1001 NOT_PRODUCT(
1002 _numObjectsPromoted++;
1003 _numWordsPromoted +=
1004 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1005 )
1006 }
1007 return res;
1008 }
1009
1010
1011 // IMPORTANT: Notes on object size recognition in CMS.
1012 // ---------------------------------------------------
1013 // A block of storage in the CMS generation is always in
1014 // one of three states. A free block (FREE), an allocated
1015 // object (OBJECT) whose size() method reports the correct size,
1016 // and an intermediate state (TRANSIENT) in which its size cannot
1017 // be accurately determined.
1018 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1019 // -----------------------------------------------------
1020 // FREE: klass_word & 1 == 1; mark_word holds block size
1021 //
1022 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1023 // obj->size() computes correct size
1024 //
1025 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1026 //
1027 // STATE IDENTIFICATION: (64 bit+COOPS)
1028 // ------------------------------------
1029 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1030 //
1031 // OBJECT: klass_word installed; klass_word != 0;
1032 // obj->size() computes correct size
1033 //
1034 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1035 //
1036 //
1037 // STATE TRANSITION DIAGRAM
1038 //
1039 // mut / parnew mut / parnew
1040 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1041 // ^ |
1042 // |------------------------ DEAD <------------------------------------|
1043 // sweep mut
1044 //
1045 // While a block is in TRANSIENT state its size cannot be determined
1046 // so readers will either need to come back later or stall until
1047 // the size can be determined. Note that for the case of direct
1048 // allocation, P-bits, when available, may be used to determine the
1049 // size of an object that may not yet have been initialized.
1050
1051 // Things to support parallel young-gen collection.
1052 oop
1053 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1054 oop old, markOop m,
1055 size_t word_sz) {
1056 #ifndef PRODUCT
1057 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1058 return NULL;
1059 }
1060 #endif // #ifndef PRODUCT
1061
1062 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1063 PromotionInfo* promoInfo = &ps->promo;
1064 // if we are tracking promotions, then first ensure space for
1065 // promotion (including spooling space for saving header if necessary).
1066 // then allocate and copy, then track promoted info if needed.
1067 // When tracking (see PromotionInfo::track()), the mark word may
1068 // be displaced and in this case restoration of the mark word
1069 // occurs in the (oop_since_save_marks_)iterate phase.
1070 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1071 // Out of space for allocating spooling buffers;
1072 // try expanding and allocating spooling buffers.
1073 if (!expand_and_ensure_spooling_space(promoInfo)) {
1074 return NULL;
1075 }
1076 }
1077 assert(promoInfo->has_spooling_space(), "Control point invariant");
1078 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1079 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1080 if (obj_ptr == NULL) {
1081 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1082 if (obj_ptr == NULL) {
1083 return NULL;
1084 }
1085 }
1086 oop obj = oop(obj_ptr);
1087 OrderAccess::storestore();
1088 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1089 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1090 // IMPORTANT: See note on object initialization for CMS above.
1091 // Otherwise, copy the object. Here we must be careful to insert the
1092 // klass pointer last, since this marks the block as an allocated object.
1093 // Except with compressed oops it's the mark word.
1094 HeapWord* old_ptr = (HeapWord*)old;
1095 // Restore the mark word copied above.
1096 obj->set_mark(m);
1097 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1098 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1099 OrderAccess::storestore();
1100
1101 if (UseCompressedClassPointers) {
1102 // Copy gap missed by (aligned) header size calculation below
1103 obj->set_klass_gap(old->klass_gap());
1104 }
1105 if (word_sz > (size_t)oopDesc::header_size()) {
1106 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1107 obj_ptr + oopDesc::header_size(),
1108 word_sz - oopDesc::header_size());
1109 }
1110
1111 // Now we can track the promoted object, if necessary. We take care
1112 // to delay the transition from uninitialized to full object
1113 // (i.e., insertion of klass pointer) until after, so that it
1114 // atomically becomes a promoted object.
1115 if (promoInfo->tracking()) {
1116 promoInfo->track((PromotedObject*)obj, old->klass());
1117 }
1118 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1119 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1120 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1121
1122 // Finally, install the klass pointer (this should be volatile).
1123 OrderAccess::storestore();
1124 obj->set_klass(old->klass());
1125 // We should now be able to calculate the right size for this object
1126 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1127
1128 collector()->promoted(true, // parallel
1129 obj_ptr, old->is_objArray(), word_sz);
1130
1131 NOT_PRODUCT(
1132 Atomic::inc_ptr(&_numObjectsPromoted);
1133 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1134 )
1135
1136 return obj;
1137 }
1138
1139 void
1140 ConcurrentMarkSweepGeneration::
1141 par_promote_alloc_done(int thread_num) {
1142 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1143 ps->lab.retire(thread_num);
1144 }
1145
1146 void
1147 ConcurrentMarkSweepGeneration::
1148 par_oop_since_save_marks_iterate_done(int thread_num) {
1149 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1150 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1151 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1152 }
1153
1154 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1155 size_t size,
1156 bool tlab)
1157 {
1158 // We allow a STW collection only if a full
1159 // collection was requested.
1160 return full || should_allocate(size, tlab); // FIX ME !!!
1161 // This and promotion failure handling are connected at the
1162 // hip and should be fixed by untying them.
1163 }
1164
1165 bool CMSCollector::shouldConcurrentCollect() {
1166 if (_full_gc_requested) {
1167 if (Verbose && PrintGCDetails) {
1168 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1169 " gc request (or gc_locker)");
1170 }
1171 return true;
1172 }
1173
1174 FreelistLocker x(this);
1175 // ------------------------------------------------------------------
1176 // Print out lots of information which affects the initiation of
1177 // a collection.
1178 if (PrintCMSInitiationStatistics && stats().valid()) {
1179 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1180 gclog_or_tty->stamp();
1181 gclog_or_tty->cr();
1182 stats().print_on(gclog_or_tty);
1183 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1184 stats().time_until_cms_gen_full());
1185 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1186 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1187 _cmsGen->contiguous_available());
1188 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1189 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1190 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1191 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1192 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1193 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1194 gclog_or_tty->print_cr("metadata initialized %d",
1195 MetaspaceGC::should_concurrent_collect());
1196 }
1197 // ------------------------------------------------------------------
1198
1199 // If the estimated time to complete a cms collection (cms_duration())
1200 // is less than the estimated time remaining until the cms generation
1201 // is full, start a collection.
1202 if (!UseCMSInitiatingOccupancyOnly) {
1203 if (stats().valid()) {
1204 if (stats().time_until_cms_start() == 0.0) {
1205 return true;
1206 }
1207 } else {
1208 // We want to conservatively collect somewhat early in order
1209 // to try and "bootstrap" our CMS/promotion statistics;
1210 // this branch will not fire after the first successful CMS
1211 // collection because the stats should then be valid.
1212 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1213 if (Verbose && PrintGCDetails) {
1214 gclog_or_tty->print_cr(
1215 " CMSCollector: collect for bootstrapping statistics:"
1216 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1217 _bootstrap_occupancy);
1218 }
1219 return true;
1220 }
1221 }
1222 }
1223
1224 // Otherwise, we start a collection cycle if
1225 // old gen want a collection cycle started. Each may use
1226 // an appropriate criterion for making this decision.
1227 // XXX We need to make sure that the gen expansion
1228 // criterion dovetails well with this. XXX NEED TO FIX THIS
1229 if (_cmsGen->should_concurrent_collect()) {
1230 if (Verbose && PrintGCDetails) {
1231 gclog_or_tty->print_cr("CMS old gen initiated");
1232 }
1233 return true;
1234 }
1235
1236 // We start a collection if we believe an incremental collection may fail;
1237 // this is not likely to be productive in practice because it's probably too
1238 // late anyway.
1239 GenCollectedHeap* gch = GenCollectedHeap::heap();
1240 assert(gch->collector_policy()->is_generation_policy(),
1241 "You may want to check the correctness of the following");
1242 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1243 if (Verbose && PrintGCDetails) {
1244 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1245 }
1246 return true;
1247 }
1248
1249 if (MetaspaceGC::should_concurrent_collect()) {
1250 if (Verbose && PrintGCDetails) {
1251 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1252 }
1253 return true;
1254 }
1255
1256 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1257 if (CMSTriggerInterval >= 0) {
1258 if (CMSTriggerInterval == 0) {
1259 // Trigger always
1260 return true;
1261 }
1262
1263 // Check the CMS time since begin (we do not check the stats validity
1264 // as we want to be able to trigger the first CMS cycle as well)
1265 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1266 if (Verbose && PrintGCDetails) {
1267 if (stats().valid()) {
1268 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1269 stats().cms_time_since_begin());
1270 } else {
1271 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1272 }
1273 }
1274 return true;
1275 }
1276 }
1277
1278 return false;
1279 }
1280
1281 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1282
1283 // Clear _expansion_cause fields of constituent generations
1284 void CMSCollector::clear_expansion_cause() {
1285 _cmsGen->clear_expansion_cause();
1286 }
1287
1288 // We should be conservative in starting a collection cycle. To
1289 // start too eagerly runs the risk of collecting too often in the
1290 // extreme. To collect too rarely falls back on full collections,
1291 // which works, even if not optimum in terms of concurrent work.
1292 // As a work around for too eagerly collecting, use the flag
1293 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1294 // giving the user an easily understandable way of controlling the
1295 // collections.
1296 // We want to start a new collection cycle if any of the following
1297 // conditions hold:
1298 // . our current occupancy exceeds the configured initiating occupancy
1299 // for this generation, or
1300 // . we recently needed to expand this space and have not, since that
1301 // expansion, done a collection of this generation, or
1302 // . the underlying space believes that it may be a good idea to initiate
1303 // a concurrent collection (this may be based on criteria such as the
1304 // following: the space uses linear allocation and linear allocation is
1305 // going to fail, or there is believed to be excessive fragmentation in
1306 // the generation, etc... or ...
1307 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1308 // the case of the old generation; see CR 6543076):
1309 // we may be approaching a point at which allocation requests may fail because
1310 // we will be out of sufficient free space given allocation rate estimates.]
1311 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1312
1313 assert_lock_strong(freelistLock());
1314 if (occupancy() > initiating_occupancy()) {
1315 if (PrintGCDetails && Verbose) {
1316 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1317 short_name(), occupancy(), initiating_occupancy());
1318 }
1319 return true;
1320 }
1321 if (UseCMSInitiatingOccupancyOnly) {
1322 return false;
1323 }
1324 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1325 if (PrintGCDetails && Verbose) {
1326 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1327 short_name());
1328 }
1329 return true;
1330 }
1331 if (_cmsSpace->should_concurrent_collect()) {
1332 if (PrintGCDetails && Verbose) {
1333 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1334 short_name());
1335 }
1336 return true;
1337 }
1338 return false;
1339 }
1340
1341 void ConcurrentMarkSweepGeneration::collect(bool full,
1342 bool clear_all_soft_refs,
1343 size_t size,
1344 bool tlab)
1345 {
1346 collector()->collect(full, clear_all_soft_refs, size, tlab);
1347 }
1348
1349 void CMSCollector::collect(bool full,
1350 bool clear_all_soft_refs,
1351 size_t size,
1352 bool tlab)
1353 {
1354 // The following "if" branch is present for defensive reasons.
1355 // In the current uses of this interface, it can be replaced with:
1356 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1357 // But I am not placing that assert here to allow future
1358 // generality in invoking this interface.
1359 if (GC_locker::is_active()) {
1360 // A consistency test for GC_locker
1361 assert(GC_locker::needs_gc(), "Should have been set already");
1362 // Skip this foreground collection, instead
1363 // expanding the heap if necessary.
1364 // Need the free list locks for the call to free() in compute_new_size()
1365 compute_new_size();
1366 return;
1367 }
1368 acquire_control_and_collect(full, clear_all_soft_refs);
1369 }
1370
1371 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1372 GenCollectedHeap* gch = GenCollectedHeap::heap();
1373 unsigned int gc_count = gch->total_full_collections();
1374 if (gc_count == full_gc_count) {
1375 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1376 _full_gc_requested = true;
1377 _full_gc_cause = cause;
1378 CGC_lock->notify(); // nudge CMS thread
1379 } else {
1380 assert(gc_count > full_gc_count, "Error: causal loop");
1381 }
1382 }
1383
1384 bool CMSCollector::is_external_interruption() {
1385 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1386 return GCCause::is_user_requested_gc(cause) ||
1387 GCCause::is_serviceability_requested_gc(cause);
1388 }
1389
1390 void CMSCollector::report_concurrent_mode_interruption() {
1391 if (is_external_interruption()) {
1392 if (PrintGCDetails) {
1393 gclog_or_tty->print(" (concurrent mode interrupted)");
1394 }
1395 } else {
1396 if (PrintGCDetails) {
1397 gclog_or_tty->print(" (concurrent mode failure)");
1398 }
1399 _gc_tracer_cm->report_concurrent_mode_failure();
1400 }
1401 }
1402
1403
1404 // The foreground and background collectors need to coordinate in order
1405 // to make sure that they do not mutually interfere with CMS collections.
1406 // When a background collection is active,
1407 // the foreground collector may need to take over (preempt) and
1408 // synchronously complete an ongoing collection. Depending on the
1409 // frequency of the background collections and the heap usage
1410 // of the application, this preemption can be seldom or frequent.
1411 // There are only certain
1412 // points in the background collection that the "collection-baton"
1413 // can be passed to the foreground collector.
1414 //
1415 // The foreground collector will wait for the baton before
1416 // starting any part of the collection. The foreground collector
1417 // will only wait at one location.
1418 //
1419 // The background collector will yield the baton before starting a new
1420 // phase of the collection (e.g., before initial marking, marking from roots,
1421 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1422 // of the loop which switches the phases. The background collector does some
1423 // of the phases (initial mark, final re-mark) with the world stopped.
1424 // Because of locking involved in stopping the world,
1425 // the foreground collector should not block waiting for the background
1426 // collector when it is doing a stop-the-world phase. The background
1427 // collector will yield the baton at an additional point just before
1428 // it enters a stop-the-world phase. Once the world is stopped, the
1429 // background collector checks the phase of the collection. If the
1430 // phase has not changed, it proceeds with the collection. If the
1431 // phase has changed, it skips that phase of the collection. See
1432 // the comments on the use of the Heap_lock in collect_in_background().
1433 //
1434 // Variable used in baton passing.
1435 // _foregroundGCIsActive - Set to true by the foreground collector when
1436 // it wants the baton. The foreground clears it when it has finished
1437 // the collection.
1438 // _foregroundGCShouldWait - Set to true by the background collector
1439 // when it is running. The foreground collector waits while
1440 // _foregroundGCShouldWait is true.
1441 // CGC_lock - monitor used to protect access to the above variables
1442 // and to notify the foreground and background collectors.
1443 // _collectorState - current state of the CMS collection.
1444 //
1445 // The foreground collector
1446 // acquires the CGC_lock
1447 // sets _foregroundGCIsActive
1448 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1449 // various locks acquired in preparation for the collection
1450 // are released so as not to block the background collector
1451 // that is in the midst of a collection
1452 // proceeds with the collection
1453 // clears _foregroundGCIsActive
1454 // returns
1455 //
1456 // The background collector in a loop iterating on the phases of the
1457 // collection
1458 // acquires the CGC_lock
1459 // sets _foregroundGCShouldWait
1460 // if _foregroundGCIsActive is set
1461 // clears _foregroundGCShouldWait, notifies _CGC_lock
1462 // waits on _CGC_lock for _foregroundGCIsActive to become false
1463 // and exits the loop.
1464 // otherwise
1465 // proceed with that phase of the collection
1466 // if the phase is a stop-the-world phase,
1467 // yield the baton once more just before enqueueing
1468 // the stop-world CMS operation (executed by the VM thread).
1469 // returns after all phases of the collection are done
1470 //
1471
1472 void CMSCollector::acquire_control_and_collect(bool full,
1473 bool clear_all_soft_refs) {
1474 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1475 assert(!Thread::current()->is_ConcurrentGC_thread(),
1476 "shouldn't try to acquire control from self!");
1477
1478 // Start the protocol for acquiring control of the
1479 // collection from the background collector (aka CMS thread).
1480 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1481 "VM thread should have CMS token");
1482 // Remember the possibly interrupted state of an ongoing
1483 // concurrent collection
1484 CollectorState first_state = _collectorState;
1485
1486 // Signal to a possibly ongoing concurrent collection that
1487 // we want to do a foreground collection.
1488 _foregroundGCIsActive = true;
1489
1490 // release locks and wait for a notify from the background collector
1491 // releasing the locks in only necessary for phases which
1492 // do yields to improve the granularity of the collection.
1493 assert_lock_strong(bitMapLock());
1494 // We need to lock the Free list lock for the space that we are
1495 // currently collecting.
1496 assert(haveFreelistLocks(), "Must be holding free list locks");
1497 bitMapLock()->unlock();
1498 releaseFreelistLocks();
1499 {
1500 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1501 if (_foregroundGCShouldWait) {
1502 // We are going to be waiting for action for the CMS thread;
1503 // it had better not be gone (for instance at shutdown)!
1504 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1505 "CMS thread must be running");
1506 // Wait here until the background collector gives us the go-ahead
1507 ConcurrentMarkSweepThread::clear_CMS_flag(
1508 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1509 // Get a possibly blocked CMS thread going:
1510 // Note that we set _foregroundGCIsActive true above,
1511 // without protection of the CGC_lock.
1512 CGC_lock->notify();
1513 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1514 "Possible deadlock");
1515 while (_foregroundGCShouldWait) {
1516 // wait for notification
1517 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1518 // Possibility of delay/starvation here, since CMS token does
1519 // not know to give priority to VM thread? Actually, i think
1520 // there wouldn't be any delay/starvation, but the proof of
1521 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1522 }
1523 ConcurrentMarkSweepThread::set_CMS_flag(
1524 ConcurrentMarkSweepThread::CMS_vm_has_token);
1525 }
1526 }
1527 // The CMS_token is already held. Get back the other locks.
1528 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1529 "VM thread should have CMS token");
1530 getFreelistLocks();
1531 bitMapLock()->lock_without_safepoint_check();
1532 if (TraceCMSState) {
1533 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1534 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1535 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1536 }
1537
1538 // Inform cms gen if this was due to partial collection failing.
1539 // The CMS gen may use this fact to determine its expansion policy.
1540 GenCollectedHeap* gch = GenCollectedHeap::heap();
1541 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1542 assert(!_cmsGen->incremental_collection_failed(),
1543 "Should have been noticed, reacted to and cleared");
1544 _cmsGen->set_incremental_collection_failed();
1545 }
1546
1547 if (first_state > Idling) {
1548 report_concurrent_mode_interruption();
1549 }
1550
1551 set_did_compact(true);
1552
1553 // If the collection is being acquired from the background
1554 // collector, there may be references on the discovered
1555 // references lists. Abandon those references, since some
1556 // of them may have become unreachable after concurrent
1557 // discovery; the STW compacting collector will redo discovery
1558 // more precisely, without being subject to floating garbage.
1559 // Leaving otherwise unreachable references in the discovered
1560 // lists would require special handling.
1561 ref_processor()->disable_discovery();
1562 ref_processor()->abandon_partial_discovery();
1563 ref_processor()->verify_no_references_recorded();
1564
1565 if (first_state > Idling) {
1566 save_heap_summary();
1567 }
1568
1569 do_compaction_work(clear_all_soft_refs);
1570
1571 // Has the GC time limit been exceeded?
1572 size_t max_eden_size = _young_gen->max_capacity() -
1573 _young_gen->to()->capacity() -
1574 _young_gen->from()->capacity();
1575 GCCause::Cause gc_cause = gch->gc_cause();
1576 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1577 _young_gen->eden()->used(),
1578 _cmsGen->max_capacity(),
1579 max_eden_size,
1580 full,
1581 gc_cause,
1582 gch->collector_policy());
1583
1584 // Reset the expansion cause, now that we just completed
1585 // a collection cycle.
1586 clear_expansion_cause();
1587 _foregroundGCIsActive = false;
1588 return;
1589 }
1590
1591 // Resize the tenured generation
1592 // after obtaining the free list locks for the
1593 // two generations.
1594 void CMSCollector::compute_new_size() {
1595 assert_locked_or_safepoint(Heap_lock);
1596 FreelistLocker z(this);
1597 MetaspaceGC::compute_new_size();
1598 _cmsGen->compute_new_size_free_list();
1599 }
1600
1601 // A work method used by the foreground collector to do
1602 // a mark-sweep-compact.
1603 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1604 GenCollectedHeap* gch = GenCollectedHeap::heap();
1605
1606 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1607 gc_timer->register_gc_start();
1608
1609 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1610 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1611
1612 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
1613
1614 // Temporarily widen the span of the weak reference processing to
1615 // the entire heap.
1616 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1617 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1618 // Temporarily, clear the "is_alive_non_header" field of the
1619 // reference processor.
1620 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1621 // Temporarily make reference _processing_ single threaded (non-MT).
1622 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1623 // Temporarily make refs discovery atomic
1624 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1625 // Temporarily make reference _discovery_ single threaded (non-MT)
1626 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1627
1628 ref_processor()->set_enqueuing_is_done(false);
1629 ref_processor()->enable_discovery();
1630 ref_processor()->setup_policy(clear_all_soft_refs);
1631 // If an asynchronous collection finishes, the _modUnionTable is
1632 // all clear. If we are assuming the collection from an asynchronous
1633 // collection, clear the _modUnionTable.
1634 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1635 "_modUnionTable should be clear if the baton was not passed");
1636 _modUnionTable.clear_all();
1637 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1638 "mod union for klasses should be clear if the baton was passed");
1639 _ct->klass_rem_set()->clear_mod_union();
1640
1641 // We must adjust the allocation statistics being maintained
1642 // in the free list space. We do so by reading and clearing
1643 // the sweep timer and updating the block flux rate estimates below.
1644 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1645 if (_inter_sweep_timer.is_active()) {
1646 _inter_sweep_timer.stop();
1647 // Note that we do not use this sample to update the _inter_sweep_estimate.
1648 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1649 _inter_sweep_estimate.padded_average(),
1650 _intra_sweep_estimate.padded_average());
1651 }
1652
1653 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1654 ref_processor(), clear_all_soft_refs);
1655 #ifdef ASSERT
1656 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1657 size_t free_size = cms_space->free();
1658 assert(free_size ==
1659 pointer_delta(cms_space->end(), cms_space->compaction_top())
1660 * HeapWordSize,
1661 "All the free space should be compacted into one chunk at top");
1662 assert(cms_space->dictionary()->total_chunk_size(
1663 debug_only(cms_space->freelistLock())) == 0 ||
1664 cms_space->totalSizeInIndexedFreeLists() == 0,
1665 "All the free space should be in a single chunk");
1666 size_t num = cms_space->totalCount();
1667 assert((free_size == 0 && num == 0) ||
1668 (free_size > 0 && (num == 1 || num == 2)),
1669 "There should be at most 2 free chunks after compaction");
1670 #endif // ASSERT
1671 _collectorState = Resetting;
1672 assert(_restart_addr == NULL,
1673 "Should have been NULL'd before baton was passed");
1674 reset(false /* == !concurrent */);
1675 _cmsGen->reset_after_compaction();
1676 _concurrent_cycles_since_last_unload = 0;
1677
1678 // Clear any data recorded in the PLAB chunk arrays.
1679 if (_survivor_plab_array != NULL) {
1680 reset_survivor_plab_arrays();
1681 }
1682
1683 // Adjust the per-size allocation stats for the next epoch.
1684 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1685 // Restart the "inter sweep timer" for the next epoch.
1686 _inter_sweep_timer.reset();
1687 _inter_sweep_timer.start();
1688
1689 gc_timer->register_gc_end();
1690
1691 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1692
1693 // For a mark-sweep-compact, compute_new_size() will be called
1694 // in the heap's do_collection() method.
1695 }
1696
1697 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1698 ContiguousSpace* eden_space = _young_gen->eden();
1699 ContiguousSpace* from_space = _young_gen->from();
1700 ContiguousSpace* to_space = _young_gen->to();
1701 // Eden
1702 if (_eden_chunk_array != NULL) {
1703 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1704 p2i(eden_space->bottom()), p2i(eden_space->top()),
1705 p2i(eden_space->end()), eden_space->capacity());
1706 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1707 "_eden_chunk_capacity=" SIZE_FORMAT,
1708 _eden_chunk_index, _eden_chunk_capacity);
1709 for (size_t i = 0; i < _eden_chunk_index; i++) {
1710 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1711 i, p2i(_eden_chunk_array[i]));
1712 }
1713 }
1714 // Survivor
1715 if (_survivor_chunk_array != NULL) {
1716 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1717 p2i(from_space->bottom()), p2i(from_space->top()),
1718 p2i(from_space->end()), from_space->capacity());
1719 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1720 "_survivor_chunk_capacity=" SIZE_FORMAT,
1721 _survivor_chunk_index, _survivor_chunk_capacity);
1722 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1723 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1724 i, p2i(_survivor_chunk_array[i]));
1725 }
1726 }
1727 }
1728
1729 void CMSCollector::getFreelistLocks() const {
1730 // Get locks for all free lists in all generations that this
1731 // collector is responsible for
1732 _cmsGen->freelistLock()->lock_without_safepoint_check();
1733 }
1734
1735 void CMSCollector::releaseFreelistLocks() const {
1736 // Release locks for all free lists in all generations that this
1737 // collector is responsible for
1738 _cmsGen->freelistLock()->unlock();
1739 }
1740
1741 bool CMSCollector::haveFreelistLocks() const {
1742 // Check locks for all free lists in all generations that this
1743 // collector is responsible for
1744 assert_lock_strong(_cmsGen->freelistLock());
1745 PRODUCT_ONLY(ShouldNotReachHere());
1746 return true;
1747 }
1748
1749 // A utility class that is used by the CMS collector to
1750 // temporarily "release" the foreground collector from its
1751 // usual obligation to wait for the background collector to
1752 // complete an ongoing phase before proceeding.
1753 class ReleaseForegroundGC: public StackObj {
1754 private:
1755 CMSCollector* _c;
1756 public:
1757 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1758 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1759 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1760 // allow a potentially blocked foreground collector to proceed
1761 _c->_foregroundGCShouldWait = false;
1762 if (_c->_foregroundGCIsActive) {
1763 CGC_lock->notify();
1764 }
1765 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1766 "Possible deadlock");
1767 }
1768
1769 ~ReleaseForegroundGC() {
1770 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1771 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1772 _c->_foregroundGCShouldWait = true;
1773 }
1774 };
1775
1776 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1777 assert(Thread::current()->is_ConcurrentGC_thread(),
1778 "A CMS asynchronous collection is only allowed on a CMS thread.");
1779
1780 GenCollectedHeap* gch = GenCollectedHeap::heap();
1781 {
1782 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1783 MutexLockerEx hl(Heap_lock, safepoint_check);
1784 FreelistLocker fll(this);
1785 MutexLockerEx x(CGC_lock, safepoint_check);
1786 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1787 // The foreground collector is active or we're
1788 // not using asynchronous collections. Skip this
1789 // background collection.
1790 assert(!_foregroundGCShouldWait, "Should be clear");
1791 return;
1792 } else {
1793 assert(_collectorState == Idling, "Should be idling before start.");
1794 _collectorState = InitialMarking;
1795 register_gc_start(cause);
1796 // Reset the expansion cause, now that we are about to begin
1797 // a new cycle.
1798 clear_expansion_cause();
1799
1800 // Clear the MetaspaceGC flag since a concurrent collection
1801 // is starting but also clear it after the collection.
1802 MetaspaceGC::set_should_concurrent_collect(false);
1803 }
1804 // Decide if we want to enable class unloading as part of the
1805 // ensuing concurrent GC cycle.
1806 update_should_unload_classes();
1807 _full_gc_requested = false; // acks all outstanding full gc requests
1808 _full_gc_cause = GCCause::_no_gc;
1809 // Signal that we are about to start a collection
1810 gch->increment_total_full_collections(); // ... starting a collection cycle
1811 _collection_count_start = gch->total_full_collections();
1812 }
1813
1814 // Used for PrintGC
1815 size_t prev_used;
1816 if (PrintGC && Verbose) {
1817 prev_used = _cmsGen->used();
1818 }
1819
1820 // The change of the collection state is normally done at this level;
1821 // the exceptions are phases that are executed while the world is
1822 // stopped. For those phases the change of state is done while the
1823 // world is stopped. For baton passing purposes this allows the
1824 // background collector to finish the phase and change state atomically.
1825 // The foreground collector cannot wait on a phase that is done
1826 // while the world is stopped because the foreground collector already
1827 // has the world stopped and would deadlock.
1828 while (_collectorState != Idling) {
1829 if (TraceCMSState) {
1830 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1831 p2i(Thread::current()), _collectorState);
1832 }
1833 // The foreground collector
1834 // holds the Heap_lock throughout its collection.
1835 // holds the CMS token (but not the lock)
1836 // except while it is waiting for the background collector to yield.
1837 //
1838 // The foreground collector should be blocked (not for long)
1839 // if the background collector is about to start a phase
1840 // executed with world stopped. If the background
1841 // collector has already started such a phase, the
1842 // foreground collector is blocked waiting for the
1843 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1844 // are executed in the VM thread.
1845 //
1846 // The locking order is
1847 // PendingListLock (PLL) -- if applicable (FinalMarking)
1848 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1849 // CMS token (claimed in
1850 // stop_world_and_do() -->
1851 // safepoint_synchronize() -->
1852 // CMSThread::synchronize())
1853
1854 {
1855 // Check if the FG collector wants us to yield.
1856 CMSTokenSync x(true); // is cms thread
1857 if (waitForForegroundGC()) {
1858 // We yielded to a foreground GC, nothing more to be
1859 // done this round.
1860 assert(_foregroundGCShouldWait == false, "We set it to false in "
1861 "waitForForegroundGC()");
1862 if (TraceCMSState) {
1863 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1864 " exiting collection CMS state %d",
1865 p2i(Thread::current()), _collectorState);
1866 }
1867 return;
1868 } else {
1869 // The background collector can run but check to see if the
1870 // foreground collector has done a collection while the
1871 // background collector was waiting to get the CGC_lock
1872 // above. If yes, break so that _foregroundGCShouldWait
1873 // is cleared before returning.
1874 if (_collectorState == Idling) {
1875 break;
1876 }
1877 }
1878 }
1879
1880 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1881 "should be waiting");
1882
1883 switch (_collectorState) {
1884 case InitialMarking:
1885 {
1886 ReleaseForegroundGC x(this);
1887 stats().record_cms_begin();
1888 VM_CMS_Initial_Mark initial_mark_op(this);
1889 VMThread::execute(&initial_mark_op);
1890 }
1891 // The collector state may be any legal state at this point
1892 // since the background collector may have yielded to the
1893 // foreground collector.
1894 break;
1895 case Marking:
1896 // initial marking in checkpointRootsInitialWork has been completed
1897 if (markFromRoots()) { // we were successful
1898 assert(_collectorState == Precleaning, "Collector state should "
1899 "have changed");
1900 } else {
1901 assert(_foregroundGCIsActive, "Internal state inconsistency");
1902 }
1903 break;
1904 case Precleaning:
1905 // marking from roots in markFromRoots has been completed
1906 preclean();
1907 assert(_collectorState == AbortablePreclean ||
1908 _collectorState == FinalMarking,
1909 "Collector state should have changed");
1910 break;
1911 case AbortablePreclean:
1912 abortable_preclean();
1913 assert(_collectorState == FinalMarking, "Collector state should "
1914 "have changed");
1915 break;
1916 case FinalMarking:
1917 {
1918 ReleaseForegroundGC x(this);
1919
1920 VM_CMS_Final_Remark final_remark_op(this);
1921 VMThread::execute(&final_remark_op);
1922 }
1923 assert(_foregroundGCShouldWait, "block post-condition");
1924 break;
1925 case Sweeping:
1926 // final marking in checkpointRootsFinal has been completed
1927 sweep();
1928 assert(_collectorState == Resizing, "Collector state change "
1929 "to Resizing must be done under the free_list_lock");
1930
1931 case Resizing: {
1932 // Sweeping has been completed...
1933 // At this point the background collection has completed.
1934 // Don't move the call to compute_new_size() down
1935 // into code that might be executed if the background
1936 // collection was preempted.
1937 {
1938 ReleaseForegroundGC x(this); // unblock FG collection
1939 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1940 CMSTokenSync z(true); // not strictly needed.
1941 if (_collectorState == Resizing) {
1942 compute_new_size();
1943 save_heap_summary();
1944 _collectorState = Resetting;
1945 } else {
1946 assert(_collectorState == Idling, "The state should only change"
1947 " because the foreground collector has finished the collection");
1948 }
1949 }
1950 break;
1951 }
1952 case Resetting:
1953 // CMS heap resizing has been completed
1954 reset(true);
1955 assert(_collectorState == Idling, "Collector state should "
1956 "have changed");
1957
1958 MetaspaceGC::set_should_concurrent_collect(false);
1959
1960 stats().record_cms_end();
1961 // Don't move the concurrent_phases_end() and compute_new_size()
1962 // calls to here because a preempted background collection
1963 // has it's state set to "Resetting".
1964 break;
1965 case Idling:
1966 default:
1967 ShouldNotReachHere();
1968 break;
1969 }
1970 if (TraceCMSState) {
1971 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1972 p2i(Thread::current()), _collectorState);
1973 }
1974 assert(_foregroundGCShouldWait, "block post-condition");
1975 }
1976
1977 // Should this be in gc_epilogue?
1978 collector_policy()->counters()->update_counters();
1979
1980 {
1981 // Clear _foregroundGCShouldWait and, in the event that the
1982 // foreground collector is waiting, notify it, before
1983 // returning.
1984 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1985 _foregroundGCShouldWait = false;
1986 if (_foregroundGCIsActive) {
1987 CGC_lock->notify();
1988 }
1989 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1990 "Possible deadlock");
1991 }
1992 if (TraceCMSState) {
1993 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1994 " exiting collection CMS state %d",
1995 p2i(Thread::current()), _collectorState);
1996 }
1997 if (PrintGC && Verbose) {
1998 _cmsGen->print_heap_change(prev_used);
1999 }
2000 }
2001
2002 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2003 _cms_start_registered = true;
2004 _gc_timer_cm->register_gc_start();
2005 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2006 }
2007
2008 void CMSCollector::register_gc_end() {
2009 if (_cms_start_registered) {
2010 report_heap_summary(GCWhen::AfterGC);
2011
2012 _gc_timer_cm->register_gc_end();
2013 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2014 _cms_start_registered = false;
2015 }
2016 }
2017
2018 void CMSCollector::save_heap_summary() {
2019 GenCollectedHeap* gch = GenCollectedHeap::heap();
2020 _last_heap_summary = gch->create_heap_summary();
2021 _last_metaspace_summary = gch->create_metaspace_summary();
2022 }
2023
2024 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2025 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2026 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2027 }
2028
2029 bool CMSCollector::waitForForegroundGC() {
2030 bool res = false;
2031 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2032 "CMS thread should have CMS token");
2033 // Block the foreground collector until the
2034 // background collectors decides whether to
2035 // yield.
2036 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2037 _foregroundGCShouldWait = true;
2038 if (_foregroundGCIsActive) {
2039 // The background collector yields to the
2040 // foreground collector and returns a value
2041 // indicating that it has yielded. The foreground
2042 // collector can proceed.
2043 res = true;
2044 _foregroundGCShouldWait = false;
2045 ConcurrentMarkSweepThread::clear_CMS_flag(
2046 ConcurrentMarkSweepThread::CMS_cms_has_token);
2047 ConcurrentMarkSweepThread::set_CMS_flag(
2048 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2049 // Get a possibly blocked foreground thread going
2050 CGC_lock->notify();
2051 if (TraceCMSState) {
2052 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2053 p2i(Thread::current()), _collectorState);
2054 }
2055 while (_foregroundGCIsActive) {
2056 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2057 }
2058 ConcurrentMarkSweepThread::set_CMS_flag(
2059 ConcurrentMarkSweepThread::CMS_cms_has_token);
2060 ConcurrentMarkSweepThread::clear_CMS_flag(
2061 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2062 }
2063 if (TraceCMSState) {
2064 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2065 p2i(Thread::current()), _collectorState);
2066 }
2067 return res;
2068 }
2069
2070 // Because of the need to lock the free lists and other structures in
2071 // the collector, common to all the generations that the collector is
2072 // collecting, we need the gc_prologues of individual CMS generations
2073 // delegate to their collector. It may have been simpler had the
2074 // current infrastructure allowed one to call a prologue on a
2075 // collector. In the absence of that we have the generation's
2076 // prologue delegate to the collector, which delegates back
2077 // some "local" work to a worker method in the individual generations
2078 // that it's responsible for collecting, while itself doing any
2079 // work common to all generations it's responsible for. A similar
2080 // comment applies to the gc_epilogue()'s.
2081 // The role of the variable _between_prologue_and_epilogue is to
2082 // enforce the invocation protocol.
2083 void CMSCollector::gc_prologue(bool full) {
2084 // Call gc_prologue_work() for the CMSGen
2085 // we are responsible for.
2086
2087 // The following locking discipline assumes that we are only called
2088 // when the world is stopped.
2089 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2090
2091 // The CMSCollector prologue must call the gc_prologues for the
2092 // "generations" that it's responsible
2093 // for.
2094
2095 assert( Thread::current()->is_VM_thread()
2096 || ( CMSScavengeBeforeRemark
2097 && Thread::current()->is_ConcurrentGC_thread()),
2098 "Incorrect thread type for prologue execution");
2099
2100 if (_between_prologue_and_epilogue) {
2101 // We have already been invoked; this is a gc_prologue delegation
2102 // from yet another CMS generation that we are responsible for, just
2103 // ignore it since all relevant work has already been done.
2104 return;
2105 }
2106
2107 // set a bit saying prologue has been called; cleared in epilogue
2108 _between_prologue_and_epilogue = true;
2109 // Claim locks for common data structures, then call gc_prologue_work()
2110 // for each CMSGen.
2111
2112 getFreelistLocks(); // gets free list locks on constituent spaces
2113 bitMapLock()->lock_without_safepoint_check();
2114
2115 // Should call gc_prologue_work() for all cms gens we are responsible for
2116 bool duringMarking = _collectorState >= Marking
2117 && _collectorState < Sweeping;
2118
2119 // The young collections clear the modified oops state, which tells if
2120 // there are any modified oops in the class. The remark phase also needs
2121 // that information. Tell the young collection to save the union of all
2122 // modified klasses.
2123 if (duringMarking) {
2124 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2125 }
2126
2127 bool registerClosure = duringMarking;
2128
2129 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2130
2131 if (!full) {
2132 stats().record_gc0_begin();
2133 }
2134 }
2135
2136 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2137
2138 _capacity_at_prologue = capacity();
2139 _used_at_prologue = used();
2140
2141 // Delegate to CMScollector which knows how to coordinate between
2142 // this and any other CMS generations that it is responsible for
2143 // collecting.
2144 collector()->gc_prologue(full);
2145 }
2146
2147 // This is a "private" interface for use by this generation's CMSCollector.
2148 // Not to be called directly by any other entity (for instance,
2149 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2150 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2151 bool registerClosure, ModUnionClosure* modUnionClosure) {
2152 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2153 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2154 "Should be NULL");
2155 if (registerClosure) {
2156 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2157 }
2158 cmsSpace()->gc_prologue();
2159 // Clear stat counters
2160 NOT_PRODUCT(
2161 assert(_numObjectsPromoted == 0, "check");
2162 assert(_numWordsPromoted == 0, "check");
2163 if (Verbose && PrintGC) {
2164 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2165 SIZE_FORMAT " bytes concurrently",
2166 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2167 }
2168 _numObjectsAllocated = 0;
2169 _numWordsAllocated = 0;
2170 )
2171 }
2172
2173 void CMSCollector::gc_epilogue(bool full) {
2174 // The following locking discipline assumes that we are only called
2175 // when the world is stopped.
2176 assert(SafepointSynchronize::is_at_safepoint(),
2177 "world is stopped assumption");
2178
2179 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2180 // if linear allocation blocks need to be appropriately marked to allow the
2181 // the blocks to be parsable. We also check here whether we need to nudge the
2182 // CMS collector thread to start a new cycle (if it's not already active).
2183 assert( Thread::current()->is_VM_thread()
2184 || ( CMSScavengeBeforeRemark
2185 && Thread::current()->is_ConcurrentGC_thread()),
2186 "Incorrect thread type for epilogue execution");
2187
2188 if (!_between_prologue_and_epilogue) {
2189 // We have already been invoked; this is a gc_epilogue delegation
2190 // from yet another CMS generation that we are responsible for, just
2191 // ignore it since all relevant work has already been done.
2192 return;
2193 }
2194 assert(haveFreelistLocks(), "must have freelist locks");
2195 assert_lock_strong(bitMapLock());
2196
2197 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2198
2199 _cmsGen->gc_epilogue_work(full);
2200
2201 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2202 // in case sampling was not already enabled, enable it
2203 _start_sampling = true;
2204 }
2205 // reset _eden_chunk_array so sampling starts afresh
2206 _eden_chunk_index = 0;
2207
2208 size_t cms_used = _cmsGen->cmsSpace()->used();
2209
2210 // update performance counters - this uses a special version of
2211 // update_counters() that allows the utilization to be passed as a
2212 // parameter, avoiding multiple calls to used().
2213 //
2214 _cmsGen->update_counters(cms_used);
2215
2216 bitMapLock()->unlock();
2217 releaseFreelistLocks();
2218
2219 if (!CleanChunkPoolAsync) {
2220 Chunk::clean_chunk_pool();
2221 }
2222
2223 set_did_compact(false);
2224 _between_prologue_and_epilogue = false; // ready for next cycle
2225 }
2226
2227 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2228 collector()->gc_epilogue(full);
2229
2230 // Also reset promotion tracking in par gc thread states.
2231 for (uint i = 0; i < ParallelGCThreads; i++) {
2232 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2233 }
2234 }
2235
2236 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2237 assert(!incremental_collection_failed(), "Should have been cleared");
2238 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2239 cmsSpace()->gc_epilogue();
2240 // Print stat counters
2241 NOT_PRODUCT(
2242 assert(_numObjectsAllocated == 0, "check");
2243 assert(_numWordsAllocated == 0, "check");
2244 if (Verbose && PrintGC) {
2245 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2246 SIZE_FORMAT " bytes",
2247 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2248 }
2249 _numObjectsPromoted = 0;
2250 _numWordsPromoted = 0;
2251 )
2252
2253 if (PrintGC && Verbose) {
2254 // Call down the chain in contiguous_available needs the freelistLock
2255 // so print this out before releasing the freeListLock.
2256 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2257 contiguous_available());
2258 }
2259 }
2260
2261 #ifndef PRODUCT
2262 bool CMSCollector::have_cms_token() {
2263 Thread* thr = Thread::current();
2264 if (thr->is_VM_thread()) {
2265 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2266 } else if (thr->is_ConcurrentGC_thread()) {
2267 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2268 } else if (thr->is_GC_task_thread()) {
2269 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2270 ParGCRareEvent_lock->owned_by_self();
2271 }
2272 return false;
2273 }
2274 #endif
2275
2276 // Check reachability of the given heap address in CMS generation,
2277 // treating all other generations as roots.
2278 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2279 // We could "guarantee" below, rather than assert, but I'll
2280 // leave these as "asserts" so that an adventurous debugger
2281 // could try this in the product build provided some subset of
2282 // the conditions were met, provided they were interested in the
2283 // results and knew that the computation below wouldn't interfere
2284 // with other concurrent computations mutating the structures
2285 // being read or written.
2286 assert(SafepointSynchronize::is_at_safepoint(),
2287 "Else mutations in object graph will make answer suspect");
2288 assert(have_cms_token(), "Should hold cms token");
2289 assert(haveFreelistLocks(), "must hold free list locks");
2290 assert_lock_strong(bitMapLock());
2291
2292 // Clear the marking bit map array before starting, but, just
2293 // for kicks, first report if the given address is already marked
2294 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2295 _markBitMap.isMarked(addr) ? "" : " not");
2296
2297 if (verify_after_remark()) {
2298 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2299 bool result = verification_mark_bm()->isMarked(addr);
2300 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2301 result ? "IS" : "is NOT");
2302 return result;
2303 } else {
2304 gclog_or_tty->print_cr("Could not compute result");
2305 return false;
2306 }
2307 }
2308
2309
2310 void
2311 CMSCollector::print_on_error(outputStream* st) {
2312 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2313 if (collector != NULL) {
2314 CMSBitMap* bitmap = &collector->_markBitMap;
2315 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2316 bitmap->print_on_error(st, " Bits: ");
2317
2318 st->cr();
2319
2320 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2321 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2322 mut_bitmap->print_on_error(st, " Bits: ");
2323 }
2324 }
2325
2326 ////////////////////////////////////////////////////////
2327 // CMS Verification Support
2328 ////////////////////////////////////////////////////////
2329 // Following the remark phase, the following invariant
2330 // should hold -- each object in the CMS heap which is
2331 // marked in markBitMap() should be marked in the verification_mark_bm().
2332
2333 class VerifyMarkedClosure: public BitMapClosure {
2334 CMSBitMap* _marks;
2335 bool _failed;
2336
2337 public:
2338 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2339
2340 bool do_bit(size_t offset) {
2341 HeapWord* addr = _marks->offsetToHeapWord(offset);
2342 if (!_marks->isMarked(addr)) {
2343 oop(addr)->print_on(gclog_or_tty);
2344 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2345 _failed = true;
2346 }
2347 return true;
2348 }
2349
2350 bool failed() { return _failed; }
2351 };
2352
2353 bool CMSCollector::verify_after_remark(bool silent) {
2354 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2355 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2356 static bool init = false;
2357
2358 assert(SafepointSynchronize::is_at_safepoint(),
2359 "Else mutations in object graph will make answer suspect");
2360 assert(have_cms_token(),
2361 "Else there may be mutual interference in use of "
2362 " verification data structures");
2363 assert(_collectorState > Marking && _collectorState <= Sweeping,
2364 "Else marking info checked here may be obsolete");
2365 assert(haveFreelistLocks(), "must hold free list locks");
2366 assert_lock_strong(bitMapLock());
2367
2368
2369 // Allocate marking bit map if not already allocated
2370 if (!init) { // first time
2371 if (!verification_mark_bm()->allocate(_span)) {
2372 return false;
2373 }
2374 init = true;
2375 }
2376
2377 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2378
2379 // Turn off refs discovery -- so we will be tracing through refs.
2380 // This is as intended, because by this time
2381 // GC must already have cleared any refs that need to be cleared,
2382 // and traced those that need to be marked; moreover,
2383 // the marking done here is not going to interfere in any
2384 // way with the marking information used by GC.
2385 NoRefDiscovery no_discovery(ref_processor());
2386
2387 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2388
2389 // Clear any marks from a previous round
2390 verification_mark_bm()->clear_all();
2391 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2392 verify_work_stacks_empty();
2393
2394 GenCollectedHeap* gch = GenCollectedHeap::heap();
2395 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2396 // Update the saved marks which may affect the root scans.
2397 gch->save_marks();
2398
2399 if (CMSRemarkVerifyVariant == 1) {
2400 // In this first variant of verification, we complete
2401 // all marking, then check if the new marks-vector is
2402 // a subset of the CMS marks-vector.
2403 verify_after_remark_work_1();
2404 } else if (CMSRemarkVerifyVariant == 2) {
2405 // In this second variant of verification, we flag an error
2406 // (i.e. an object reachable in the new marks-vector not reachable
2407 // in the CMS marks-vector) immediately, also indicating the
2408 // identify of an object (A) that references the unmarked object (B) --
2409 // presumably, a mutation to A failed to be picked up by preclean/remark?
2410 verify_after_remark_work_2();
2411 } else {
2412 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2413 CMSRemarkVerifyVariant);
2414 }
2415 if (!silent) gclog_or_tty->print(" done] ");
2416 return true;
2417 }
2418
2419 void CMSCollector::verify_after_remark_work_1() {
2420 ResourceMark rm;
2421 HandleMark hm;
2422 GenCollectedHeap* gch = GenCollectedHeap::heap();
2423
2424 // Get a clear set of claim bits for the roots processing to work with.
2425 ClassLoaderDataGraph::clear_claimed_marks();
2426
2427 // Mark from roots one level into CMS
2428 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2429 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2430
2431 gch->gen_process_roots(_cmsGen->level(),
2432 true, // younger gens are roots
2433 true, // activate StrongRootsScope
2434 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2435 should_unload_classes(),
2436 ¬Older,
2437 NULL,
2438 NULL); // SSS: Provide correct closure
2439
2440 // Now mark from the roots
2441 MarkFromRootsClosure markFromRootsClosure(this, _span,
2442 verification_mark_bm(), verification_mark_stack(),
2443 false /* don't yield */, true /* verifying */);
2444 assert(_restart_addr == NULL, "Expected pre-condition");
2445 verification_mark_bm()->iterate(&markFromRootsClosure);
2446 while (_restart_addr != NULL) {
2447 // Deal with stack overflow: by restarting at the indicated
2448 // address.
2449 HeapWord* ra = _restart_addr;
2450 markFromRootsClosure.reset(ra);
2451 _restart_addr = NULL;
2452 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2453 }
2454 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2455 verify_work_stacks_empty();
2456
2457 // Marking completed -- now verify that each bit marked in
2458 // verification_mark_bm() is also marked in markBitMap(); flag all
2459 // errors by printing corresponding objects.
2460 VerifyMarkedClosure vcl(markBitMap());
2461 verification_mark_bm()->iterate(&vcl);
2462 if (vcl.failed()) {
2463 gclog_or_tty->print("Verification failed");
2464 gch->print_on(gclog_or_tty);
2465 fatal("CMS: failed marking verification after remark");
2466 }
2467 }
2468
2469 class VerifyKlassOopsKlassClosure : public KlassClosure {
2470 class VerifyKlassOopsClosure : public OopClosure {
2471 CMSBitMap* _bitmap;
2472 public:
2473 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2474 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2475 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2476 } _oop_closure;
2477 public:
2478 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2479 void do_klass(Klass* k) {
2480 k->oops_do(&_oop_closure);
2481 }
2482 };
2483
2484 void CMSCollector::verify_after_remark_work_2() {
2485 ResourceMark rm;
2486 HandleMark hm;
2487 GenCollectedHeap* gch = GenCollectedHeap::heap();
2488
2489 // Get a clear set of claim bits for the roots processing to work with.
2490 ClassLoaderDataGraph::clear_claimed_marks();
2491
2492 // Mark from roots one level into CMS
2493 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2494 markBitMap());
2495 CLDToOopClosure cld_closure(¬Older, true);
2496
2497 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2498
2499 gch->gen_process_roots(_cmsGen->level(),
2500 true, // younger gens are roots
2501 true, // activate StrongRootsScope
2502 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2503 should_unload_classes(),
2504 ¬Older,
2505 NULL,
2506 &cld_closure);
2507
2508 // Now mark from the roots
2509 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2510 verification_mark_bm(), markBitMap(), verification_mark_stack());
2511 assert(_restart_addr == NULL, "Expected pre-condition");
2512 verification_mark_bm()->iterate(&markFromRootsClosure);
2513 while (_restart_addr != NULL) {
2514 // Deal with stack overflow: by restarting at the indicated
2515 // address.
2516 HeapWord* ra = _restart_addr;
2517 markFromRootsClosure.reset(ra);
2518 _restart_addr = NULL;
2519 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2520 }
2521 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2522 verify_work_stacks_empty();
2523
2524 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2525 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2526
2527 // Marking completed -- now verify that each bit marked in
2528 // verification_mark_bm() is also marked in markBitMap(); flag all
2529 // errors by printing corresponding objects.
2530 VerifyMarkedClosure vcl(markBitMap());
2531 verification_mark_bm()->iterate(&vcl);
2532 assert(!vcl.failed(), "Else verification above should not have succeeded");
2533 }
2534
2535 void ConcurrentMarkSweepGeneration::save_marks() {
2536 // delegate to CMS space
2537 cmsSpace()->save_marks();
2538 for (uint i = 0; i < ParallelGCThreads; i++) {
2539 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2540 }
2541 }
2542
2543 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2544 return cmsSpace()->no_allocs_since_save_marks();
2545 }
2546
2547 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2548 \
2549 void ConcurrentMarkSweepGeneration:: \
2550 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2551 cl->set_generation(this); \
2552 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2553 cl->reset_generation(); \
2554 save_marks(); \
2555 }
2556
2557 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2558
2559 void
2560 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2561 if (freelistLock()->owned_by_self()) {
2562 Generation::oop_iterate(cl);
2563 } else {
2564 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2565 Generation::oop_iterate(cl);
2566 }
2567 }
2568
2569 void
2570 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2571 if (freelistLock()->owned_by_self()) {
2572 Generation::object_iterate(cl);
2573 } else {
2574 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2575 Generation::object_iterate(cl);
2576 }
2577 }
2578
2579 void
2580 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2581 if (freelistLock()->owned_by_self()) {
2582 Generation::safe_object_iterate(cl);
2583 } else {
2584 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2585 Generation::safe_object_iterate(cl);
2586 }
2587 }
2588
2589 void
2590 ConcurrentMarkSweepGeneration::post_compact() {
2591 }
2592
2593 void
2594 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2595 // Fix the linear allocation blocks to look like free blocks.
2596
2597 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2598 // are not called when the heap is verified during universe initialization and
2599 // at vm shutdown.
2600 if (freelistLock()->owned_by_self()) {
2601 cmsSpace()->prepare_for_verify();
2602 } else {
2603 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2604 cmsSpace()->prepare_for_verify();
2605 }
2606 }
2607
2608 void
2609 ConcurrentMarkSweepGeneration::verify() {
2610 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2611 // are not called when the heap is verified during universe initialization and
2612 // at vm shutdown.
2613 if (freelistLock()->owned_by_self()) {
2614 cmsSpace()->verify();
2615 } else {
2616 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2617 cmsSpace()->verify();
2618 }
2619 }
2620
2621 void CMSCollector::verify() {
2622 _cmsGen->verify();
2623 }
2624
2625 #ifndef PRODUCT
2626 bool CMSCollector::overflow_list_is_empty() const {
2627 assert(_num_par_pushes >= 0, "Inconsistency");
2628 if (_overflow_list == NULL) {
2629 assert(_num_par_pushes == 0, "Inconsistency");
2630 }
2631 return _overflow_list == NULL;
2632 }
2633
2634 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2635 // merely consolidate assertion checks that appear to occur together frequently.
2636 void CMSCollector::verify_work_stacks_empty() const {
2637 assert(_markStack.isEmpty(), "Marking stack should be empty");
2638 assert(overflow_list_is_empty(), "Overflow list should be empty");
2639 }
2640
2641 void CMSCollector::verify_overflow_empty() const {
2642 assert(overflow_list_is_empty(), "Overflow list should be empty");
2643 assert(no_preserved_marks(), "No preserved marks");
2644 }
2645 #endif // PRODUCT
2646
2647 // Decide if we want to enable class unloading as part of the
2648 // ensuing concurrent GC cycle. We will collect and
2649 // unload classes if it's the case that:
2650 // (1) an explicit gc request has been made and the flag
2651 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2652 // (2) (a) class unloading is enabled at the command line, and
2653 // (b) old gen is getting really full
2654 // NOTE: Provided there is no change in the state of the heap between
2655 // calls to this method, it should have idempotent results. Moreover,
2656 // its results should be monotonically increasing (i.e. going from 0 to 1,
2657 // but not 1 to 0) between successive calls between which the heap was
2658 // not collected. For the implementation below, it must thus rely on
2659 // the property that concurrent_cycles_since_last_unload()
2660 // will not decrease unless a collection cycle happened and that
2661 // _cmsGen->is_too_full() are
2662 // themselves also monotonic in that sense. See check_monotonicity()
2663 // below.
2664 void CMSCollector::update_should_unload_classes() {
2665 _should_unload_classes = false;
2666 // Condition 1 above
2667 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2668 _should_unload_classes = true;
2669 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2670 // Disjuncts 2.b.(i,ii,iii) above
2671 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2672 CMSClassUnloadingMaxInterval)
2673 || _cmsGen->is_too_full();
2674 }
2675 }
2676
2677 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2678 bool res = should_concurrent_collect();
2679 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2680 return res;
2681 }
2682
2683 void CMSCollector::setup_cms_unloading_and_verification_state() {
2684 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2685 || VerifyBeforeExit;
2686 const int rso = GenCollectedHeap::SO_AllCodeCache;
2687
2688 // We set the proper root for this CMS cycle here.
2689 if (should_unload_classes()) { // Should unload classes this cycle
2690 remove_root_scanning_option(rso); // Shrink the root set appropriately
2691 set_verifying(should_verify); // Set verification state for this cycle
2692 return; // Nothing else needs to be done at this time
2693 }
2694
2695 // Not unloading classes this cycle
2696 assert(!should_unload_classes(), "Inconsistency!");
2697
2698 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2699 // Include symbols, strings and code cache elements to prevent their resurrection.
2700 add_root_scanning_option(rso);
2701 set_verifying(true);
2702 } else if (verifying() && !should_verify) {
2703 // We were verifying, but some verification flags got disabled.
2704 set_verifying(false);
2705 // Exclude symbols, strings and code cache elements from root scanning to
2706 // reduce IM and RM pauses.
2707 remove_root_scanning_option(rso);
2708 }
2709 }
2710
2711
2712 #ifndef PRODUCT
2713 HeapWord* CMSCollector::block_start(const void* p) const {
2714 const HeapWord* addr = (HeapWord*)p;
2715 if (_span.contains(p)) {
2716 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2717 return _cmsGen->cmsSpace()->block_start(p);
2718 }
2719 }
2720 return NULL;
2721 }
2722 #endif
2723
2724 HeapWord*
2725 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2726 bool tlab,
2727 bool parallel) {
2728 CMSSynchronousYieldRequest yr;
2729 assert(!tlab, "Can't deal with TLAB allocation");
2730 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2731 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2732 if (GCExpandToAllocateDelayMillis > 0) {
2733 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2734 }
2735 return have_lock_and_allocate(word_size, tlab);
2736 }
2737
2738 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2739 size_t bytes,
2740 size_t expand_bytes,
2741 CMSExpansionCause::Cause cause)
2742 {
2743
2744 bool success = expand(bytes, expand_bytes);
2745
2746 // remember why we expanded; this information is used
2747 // by shouldConcurrentCollect() when making decisions on whether to start
2748 // a new CMS cycle.
2749 if (success) {
2750 set_expansion_cause(cause);
2751 if (PrintGCDetails && Verbose) {
2752 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2753 CMSExpansionCause::to_string(cause));
2754 }
2755 }
2756 }
2757
2758 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2759 HeapWord* res = NULL;
2760 MutexLocker x(ParGCRareEvent_lock);
2761 while (true) {
2762 // Expansion by some other thread might make alloc OK now:
2763 res = ps->lab.alloc(word_sz);
2764 if (res != NULL) return res;
2765 // If there's not enough expansion space available, give up.
2766 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2767 return NULL;
2768 }
2769 // Otherwise, we try expansion.
2770 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2771 // Now go around the loop and try alloc again;
2772 // A competing par_promote might beat us to the expansion space,
2773 // so we may go around the loop again if promotion fails again.
2774 if (GCExpandToAllocateDelayMillis > 0) {
2775 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2776 }
2777 }
2778 }
2779
2780
2781 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2782 PromotionInfo* promo) {
2783 MutexLocker x(ParGCRareEvent_lock);
2784 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2785 while (true) {
2786 // Expansion by some other thread might make alloc OK now:
2787 if (promo->ensure_spooling_space()) {
2788 assert(promo->has_spooling_space(),
2789 "Post-condition of successful ensure_spooling_space()");
2790 return true;
2791 }
2792 // If there's not enough expansion space available, give up.
2793 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2794 return false;
2795 }
2796 // Otherwise, we try expansion.
2797 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2798 // Now go around the loop and try alloc again;
2799 // A competing allocation might beat us to the expansion space,
2800 // so we may go around the loop again if allocation fails again.
2801 if (GCExpandToAllocateDelayMillis > 0) {
2802 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2803 }
2804 }
2805 }
2806
2807 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2808 // Only shrink if a compaction was done so that all the free space
2809 // in the generation is in a contiguous block at the end.
2810 if (did_compact()) {
2811 CardGeneration::shrink(bytes);
2812 }
2813 }
2814
2815 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2816 assert_locked_or_safepoint(Heap_lock);
2817 }
2818
2819 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2820 assert_locked_or_safepoint(Heap_lock);
2821 assert_lock_strong(freelistLock());
2822 if (PrintGCDetails && Verbose) {
2823 warning("Shrinking of CMS not yet implemented");
2824 }
2825 return;
2826 }
2827
2828
2829 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2830 // phases.
2831 class CMSPhaseAccounting: public StackObj {
2832 public:
2833 CMSPhaseAccounting(CMSCollector *collector,
2834 const char *phase,
2835 const GCId gc_id,
2836 bool print_cr = true);
2837 ~CMSPhaseAccounting();
2838
2839 private:
2840 CMSCollector *_collector;
2841 const char *_phase;
2842 elapsedTimer _wallclock;
2843 bool _print_cr;
2844 const GCId _gc_id;
2845
2846 public:
2847 // Not MT-safe; so do not pass around these StackObj's
2848 // where they may be accessed by other threads.
2849 jlong wallclock_millis() {
2850 assert(_wallclock.is_active(), "Wall clock should not stop");
2851 _wallclock.stop(); // to record time
2852 jlong ret = _wallclock.milliseconds();
2853 _wallclock.start(); // restart
2854 return ret;
2855 }
2856 };
2857
2858 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2859 const char *phase,
2860 const GCId gc_id,
2861 bool print_cr) :
2862 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
2863
2864 if (PrintCMSStatistics != 0) {
2865 _collector->resetYields();
2866 }
2867 if (PrintGCDetails) {
2868 gclog_or_tty->gclog_stamp(_gc_id);
2869 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2870 _collector->cmsGen()->short_name(), _phase);
2871 }
2872 _collector->resetTimer();
2873 _wallclock.start();
2874 _collector->startTimer();
2875 }
2876
2877 CMSPhaseAccounting::~CMSPhaseAccounting() {
2878 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2879 _collector->stopTimer();
2880 _wallclock.stop();
2881 if (PrintGCDetails) {
2882 gclog_or_tty->gclog_stamp(_gc_id);
2883 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2884 _collector->cmsGen()->short_name(),
2885 _phase, _collector->timerValue(), _wallclock.seconds());
2886 if (_print_cr) {
2887 gclog_or_tty->cr();
2888 }
2889 if (PrintCMSStatistics != 0) {
2890 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2891 _collector->yields());
2892 }
2893 }
2894 }
2895
2896 // CMS work
2897
2898 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2899 class CMSParMarkTask : public AbstractGangTask {
2900 protected:
2901 CMSCollector* _collector;
2902 uint _n_workers;
2903 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2904 AbstractGangTask(name),
2905 _collector(collector),
2906 _n_workers(n_workers) {}
2907 // Work method in support of parallel rescan ... of young gen spaces
2908 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2909 ContiguousSpace* space,
2910 HeapWord** chunk_array, size_t chunk_top);
2911 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2912 };
2913
2914 // Parallel initial mark task
2915 class CMSParInitialMarkTask: public CMSParMarkTask {
2916 public:
2917 CMSParInitialMarkTask(CMSCollector* collector, uint n_workers) :
2918 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
2919 collector, n_workers) {}
2920 void work(uint worker_id);
2921 };
2922
2923 // Checkpoint the roots into this generation from outside
2924 // this generation. [Note this initial checkpoint need only
2925 // be approximate -- we'll do a catch up phase subsequently.]
2926 void CMSCollector::checkpointRootsInitial() {
2927 assert(_collectorState == InitialMarking, "Wrong collector state");
2928 check_correct_thread_executing();
2929 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2930
2931 save_heap_summary();
2932 report_heap_summary(GCWhen::BeforeGC);
2933
2934 ReferenceProcessor* rp = ref_processor();
2935 assert(_restart_addr == NULL, "Control point invariant");
2936 {
2937 // acquire locks for subsequent manipulations
2938 MutexLockerEx x(bitMapLock(),
2939 Mutex::_no_safepoint_check_flag);
2940 checkpointRootsInitialWork();
2941 // enable ("weak") refs discovery
2942 rp->enable_discovery();
2943 _collectorState = Marking;
2944 }
2945 }
2946
2947 void CMSCollector::checkpointRootsInitialWork() {
2948 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2949 assert(_collectorState == InitialMarking, "just checking");
2950
2951 // If there has not been a GC[n-1] since last GC[n] cycle completed,
2952 // precede our marking with a collection of all
2953 // younger generations to keep floating garbage to a minimum.
2954 // XXX: we won't do this for now -- it's an optimization to be done later.
2955
2956 // already have locks
2957 assert_lock_strong(bitMapLock());
2958 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2959
2960 // Setup the verification and class unloading state for this
2961 // CMS collection cycle.
2962 setup_cms_unloading_and_verification_state();
2963
2964 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2965 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
2966
2967 // Reset all the PLAB chunk arrays if necessary.
2968 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2969 reset_survivor_plab_arrays();
2970 }
2971
2972 ResourceMark rm;
2973 HandleMark hm;
2974
2975 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2976 GenCollectedHeap* gch = GenCollectedHeap::heap();
2977
2978 verify_work_stacks_empty();
2979 verify_overflow_empty();
2980
2981 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2982 // Update the saved marks which may affect the root scans.
2983 gch->save_marks();
2984
2985 // weak reference processing has not started yet.
2986 ref_processor()->set_enqueuing_is_done(false);
2987
2988 // Need to remember all newly created CLDs,
2989 // so that we can guarantee that the remark finds them.
2990 ClassLoaderDataGraph::remember_new_clds(true);
2991
2992 // Whenever a CLD is found, it will be claimed before proceeding to mark
2993 // the klasses. The claimed marks need to be cleared before marking starts.
2994 ClassLoaderDataGraph::clear_claimed_marks();
2995
2996 if (CMSPrintEdenSurvivorChunks) {
2997 print_eden_and_survivor_chunk_arrays();
2998 }
2999
3000 {
3001 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3002 if (CMSParallelInitialMarkEnabled) {
3003 // The parallel version.
3004 FlexibleWorkGang* workers = gch->workers();
3005 assert(workers != NULL, "Need parallel worker threads.");
3006 uint n_workers = workers->active_workers();
3007 CMSParInitialMarkTask tsk(this, n_workers);
3008 gch->set_par_threads(n_workers);
3009 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3010 if (n_workers > 1) {
3011 StrongRootsScope srs;
3012 workers->run_task(&tsk);
3013 } else {
3014 StrongRootsScope srs;
3015 tsk.work(0);
3016 }
3017 gch->set_par_threads(0);
3018 } else {
3019 // The serial version.
3020 CLDToOopClosure cld_closure(¬Older, true);
3021 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3022 gch->gen_process_roots(_cmsGen->level(),
3023 true, // younger gens are roots
3024 true, // activate StrongRootsScope
3025 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3026 should_unload_classes(),
3027 ¬Older,
3028 NULL,
3029 &cld_closure);
3030 }
3031 }
3032
3033 // Clear mod-union table; it will be dirtied in the prologue of
3034 // CMS generation per each younger generation collection.
3035
3036 assert(_modUnionTable.isAllClear(),
3037 "Was cleared in most recent final checkpoint phase"
3038 " or no bits are set in the gc_prologue before the start of the next "
3039 "subsequent marking phase.");
3040
3041 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3042
3043 // Save the end of the used_region of the constituent generations
3044 // to be used to limit the extent of sweep in each generation.
3045 save_sweep_limits();
3046 verify_overflow_empty();
3047 }
3048
3049 bool CMSCollector::markFromRoots() {
3050 // we might be tempted to assert that:
3051 // assert(!SafepointSynchronize::is_at_safepoint(),
3052 // "inconsistent argument?");
3053 // However that wouldn't be right, because it's possible that
3054 // a safepoint is indeed in progress as a younger generation
3055 // stop-the-world GC happens even as we mark in this generation.
3056 assert(_collectorState == Marking, "inconsistent state?");
3057 check_correct_thread_executing();
3058 verify_overflow_empty();
3059
3060 // Weak ref discovery note: We may be discovering weak
3061 // refs in this generation concurrent (but interleaved) with
3062 // weak ref discovery by a younger generation collector.
3063
3064 CMSTokenSyncWithLocks ts(true, bitMapLock());
3065 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3066 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3067 bool res = markFromRootsWork();
3068 if (res) {
3069 _collectorState = Precleaning;
3070 } else { // We failed and a foreground collection wants to take over
3071 assert(_foregroundGCIsActive, "internal state inconsistency");
3072 assert(_restart_addr == NULL, "foreground will restart from scratch");
3073 if (PrintGCDetails) {
3074 gclog_or_tty->print_cr("bailing out to foreground collection");
3075 }
3076 }
3077 verify_overflow_empty();
3078 return res;
3079 }
3080
3081 bool CMSCollector::markFromRootsWork() {
3082 // iterate over marked bits in bit map, doing a full scan and mark
3083 // from these roots using the following algorithm:
3084 // . if oop is to the right of the current scan pointer,
3085 // mark corresponding bit (we'll process it later)
3086 // . else (oop is to left of current scan pointer)
3087 // push oop on marking stack
3088 // . drain the marking stack
3089
3090 // Note that when we do a marking step we need to hold the
3091 // bit map lock -- recall that direct allocation (by mutators)
3092 // and promotion (by younger generation collectors) is also
3093 // marking the bit map. [the so-called allocate live policy.]
3094 // Because the implementation of bit map marking is not
3095 // robust wrt simultaneous marking of bits in the same word,
3096 // we need to make sure that there is no such interference
3097 // between concurrent such updates.
3098
3099 // already have locks
3100 assert_lock_strong(bitMapLock());
3101
3102 verify_work_stacks_empty();
3103 verify_overflow_empty();
3104 bool result = false;
3105 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3106 result = do_marking_mt();
3107 } else {
3108 result = do_marking_st();
3109 }
3110 return result;
3111 }
3112
3113 // Forward decl
3114 class CMSConcMarkingTask;
3115
3116 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3117 CMSCollector* _collector;
3118 CMSConcMarkingTask* _task;
3119 public:
3120 virtual void yield();
3121
3122 // "n_threads" is the number of threads to be terminated.
3123 // "queue_set" is a set of work queues of other threads.
3124 // "collector" is the CMS collector associated with this task terminator.
3125 // "yield" indicates whether we need the gang as a whole to yield.
3126 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3127 ParallelTaskTerminator(n_threads, queue_set),
3128 _collector(collector) { }
3129
3130 void set_task(CMSConcMarkingTask* task) {
3131 _task = task;
3132 }
3133 };
3134
3135 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3136 CMSConcMarkingTask* _task;
3137 public:
3138 bool should_exit_termination();
3139 void set_task(CMSConcMarkingTask* task) {
3140 _task = task;
3141 }
3142 };
3143
3144 // MT Concurrent Marking Task
3145 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3146 CMSCollector* _collector;
3147 uint _n_workers; // requested/desired # workers
3148 bool _result;
3149 CompactibleFreeListSpace* _cms_space;
3150 char _pad_front[64]; // padding to ...
3151 HeapWord* _global_finger; // ... avoid sharing cache line
3152 char _pad_back[64];
3153 HeapWord* _restart_addr;
3154
3155 // Exposed here for yielding support
3156 Mutex* const _bit_map_lock;
3157
3158 // The per thread work queues, available here for stealing
3159 OopTaskQueueSet* _task_queues;
3160
3161 // Termination (and yielding) support
3162 CMSConcMarkingTerminator _term;
3163 CMSConcMarkingTerminatorTerminator _term_term;
3164
3165 public:
3166 CMSConcMarkingTask(CMSCollector* collector,
3167 CompactibleFreeListSpace* cms_space,
3168 YieldingFlexibleWorkGang* workers,
3169 OopTaskQueueSet* task_queues):
3170 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3171 _collector(collector),
3172 _cms_space(cms_space),
3173 _n_workers(0), _result(true),
3174 _task_queues(task_queues),
3175 _term(_n_workers, task_queues, _collector),
3176 _bit_map_lock(collector->bitMapLock())
3177 {
3178 _requested_size = _n_workers;
3179 _term.set_task(this);
3180 _term_term.set_task(this);
3181 _restart_addr = _global_finger = _cms_space->bottom();
3182 }
3183
3184
3185 OopTaskQueueSet* task_queues() { return _task_queues; }
3186
3187 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3188
3189 HeapWord** global_finger_addr() { return &_global_finger; }
3190
3191 CMSConcMarkingTerminator* terminator() { return &_term; }
3192
3193 virtual void set_for_termination(uint active_workers) {
3194 terminator()->reset_for_reuse(active_workers);
3195 }
3196
3197 void work(uint worker_id);
3198 bool should_yield() {
3199 return ConcurrentMarkSweepThread::should_yield()
3200 && !_collector->foregroundGCIsActive();
3201 }
3202
3203 virtual void coordinator_yield(); // stuff done by coordinator
3204 bool result() { return _result; }
3205
3206 void reset(HeapWord* ra) {
3207 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3208 _restart_addr = _global_finger = ra;
3209 _term.reset_for_reuse();
3210 }
3211
3212 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3213 OopTaskQueue* work_q);
3214
3215 private:
3216 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3217 void do_work_steal(int i);
3218 void bump_global_finger(HeapWord* f);
3219 };
3220
3221 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3222 assert(_task != NULL, "Error");
3223 return _task->yielding();
3224 // Note that we do not need the disjunct || _task->should_yield() above
3225 // because we want terminating threads to yield only if the task
3226 // is already in the midst of yielding, which happens only after at least one
3227 // thread has yielded.
3228 }
3229
3230 void CMSConcMarkingTerminator::yield() {
3231 if (_task->should_yield()) {
3232 _task->yield();
3233 } else {
3234 ParallelTaskTerminator::yield();
3235 }
3236 }
3237
3238 ////////////////////////////////////////////////////////////////
3239 // Concurrent Marking Algorithm Sketch
3240 ////////////////////////////////////////////////////////////////
3241 // Until all tasks exhausted (both spaces):
3242 // -- claim next available chunk
3243 // -- bump global finger via CAS
3244 // -- find first object that starts in this chunk
3245 // and start scanning bitmap from that position
3246 // -- scan marked objects for oops
3247 // -- CAS-mark target, and if successful:
3248 // . if target oop is above global finger (volatile read)
3249 // nothing to do
3250 // . if target oop is in chunk and above local finger
3251 // then nothing to do
3252 // . else push on work-queue
3253 // -- Deal with possible overflow issues:
3254 // . local work-queue overflow causes stuff to be pushed on
3255 // global (common) overflow queue
3256 // . always first empty local work queue
3257 // . then get a batch of oops from global work queue if any
3258 // . then do work stealing
3259 // -- When all tasks claimed (both spaces)
3260 // and local work queue empty,
3261 // then in a loop do:
3262 // . check global overflow stack; steal a batch of oops and trace
3263 // . try to steal from other threads oif GOS is empty
3264 // . if neither is available, offer termination
3265 // -- Terminate and return result
3266 //
3267 void CMSConcMarkingTask::work(uint worker_id) {
3268 elapsedTimer _timer;
3269 ResourceMark rm;
3270 HandleMark hm;
3271
3272 DEBUG_ONLY(_collector->verify_overflow_empty();)
3273
3274 // Before we begin work, our work queue should be empty
3275 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3276 // Scan the bitmap covering _cms_space, tracing through grey objects.
3277 _timer.start();
3278 do_scan_and_mark(worker_id, _cms_space);
3279 _timer.stop();
3280 if (PrintCMSStatistics != 0) {
3281 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3282 worker_id, _timer.seconds());
3283 // XXX: need xxx/xxx type of notation, two timers
3284 }
3285
3286 // ... do work stealing
3287 _timer.reset();
3288 _timer.start();
3289 do_work_steal(worker_id);
3290 _timer.stop();
3291 if (PrintCMSStatistics != 0) {
3292 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3293 worker_id, _timer.seconds());
3294 // XXX: need xxx/xxx type of notation, two timers
3295 }
3296 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3297 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3298 // Note that under the current task protocol, the
3299 // following assertion is true even of the spaces
3300 // expanded since the completion of the concurrent
3301 // marking. XXX This will likely change under a strict
3302 // ABORT semantics.
3303 // After perm removal the comparison was changed to
3304 // greater than or equal to from strictly greater than.
3305 // Before perm removal the highest address sweep would
3306 // have been at the end of perm gen but now is at the
3307 // end of the tenured gen.
3308 assert(_global_finger >= _cms_space->end(),
3309 "All tasks have been completed");
3310 DEBUG_ONLY(_collector->verify_overflow_empty();)
3311 }
3312
3313 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3314 HeapWord* read = _global_finger;
3315 HeapWord* cur = read;
3316 while (f > read) {
3317 cur = read;
3318 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3319 if (cur == read) {
3320 // our cas succeeded
3321 assert(_global_finger >= f, "protocol consistency");
3322 break;
3323 }
3324 }
3325 }
3326
3327 // This is really inefficient, and should be redone by
3328 // using (not yet available) block-read and -write interfaces to the
3329 // stack and the work_queue. XXX FIX ME !!!
3330 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3331 OopTaskQueue* work_q) {
3332 // Fast lock-free check
3333 if (ovflw_stk->length() == 0) {
3334 return false;
3335 }
3336 assert(work_q->size() == 0, "Shouldn't steal");
3337 MutexLockerEx ml(ovflw_stk->par_lock(),
3338 Mutex::_no_safepoint_check_flag);
3339 // Grab up to 1/4 the size of the work queue
3340 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3341 (size_t)ParGCDesiredObjsFromOverflowList);
3342 num = MIN2(num, ovflw_stk->length());
3343 for (int i = (int) num; i > 0; i--) {
3344 oop cur = ovflw_stk->pop();
3345 assert(cur != NULL, "Counted wrong?");
3346 work_q->push(cur);
3347 }
3348 return num > 0;
3349 }
3350
3351 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3352 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3353 int n_tasks = pst->n_tasks();
3354 // We allow that there may be no tasks to do here because
3355 // we are restarting after a stack overflow.
3356 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3357 uint nth_task = 0;
3358
3359 HeapWord* aligned_start = sp->bottom();
3360 if (sp->used_region().contains(_restart_addr)) {
3361 // Align down to a card boundary for the start of 0th task
3362 // for this space.
3363 aligned_start =
3364 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3365 CardTableModRefBS::card_size);
3366 }
3367
3368 size_t chunk_size = sp->marking_task_size();
3369 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3370 // Having claimed the nth task in this space,
3371 // compute the chunk that it corresponds to:
3372 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3373 aligned_start + (nth_task+1)*chunk_size);
3374 // Try and bump the global finger via a CAS;
3375 // note that we need to do the global finger bump
3376 // _before_ taking the intersection below, because
3377 // the task corresponding to that region will be
3378 // deemed done even if the used_region() expands
3379 // because of allocation -- as it almost certainly will
3380 // during start-up while the threads yield in the
3381 // closure below.
3382 HeapWord* finger = span.end();
3383 bump_global_finger(finger); // atomically
3384 // There are null tasks here corresponding to chunks
3385 // beyond the "top" address of the space.
3386 span = span.intersection(sp->used_region());
3387 if (!span.is_empty()) { // Non-null task
3388 HeapWord* prev_obj;
3389 assert(!span.contains(_restart_addr) || nth_task == 0,
3390 "Inconsistency");
3391 if (nth_task == 0) {
3392 // For the 0th task, we'll not need to compute a block_start.
3393 if (span.contains(_restart_addr)) {
3394 // In the case of a restart because of stack overflow,
3395 // we might additionally skip a chunk prefix.
3396 prev_obj = _restart_addr;
3397 } else {
3398 prev_obj = span.start();
3399 }
3400 } else {
3401 // We want to skip the first object because
3402 // the protocol is to scan any object in its entirety
3403 // that _starts_ in this span; a fortiori, any
3404 // object starting in an earlier span is scanned
3405 // as part of an earlier claimed task.
3406 // Below we use the "careful" version of block_start
3407 // so we do not try to navigate uninitialized objects.
3408 prev_obj = sp->block_start_careful(span.start());
3409 // Below we use a variant of block_size that uses the
3410 // Printezis bits to avoid waiting for allocated
3411 // objects to become initialized/parsable.
3412 while (prev_obj < span.start()) {
3413 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3414 if (sz > 0) {
3415 prev_obj += sz;
3416 } else {
3417 // In this case we may end up doing a bit of redundant
3418 // scanning, but that appears unavoidable, short of
3419 // locking the free list locks; see bug 6324141.
3420 break;
3421 }
3422 }
3423 }
3424 if (prev_obj < span.end()) {
3425 MemRegion my_span = MemRegion(prev_obj, span.end());
3426 // Do the marking work within a non-empty span --
3427 // the last argument to the constructor indicates whether the
3428 // iteration should be incremental with periodic yields.
3429 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3430 &_collector->_markBitMap,
3431 work_queue(i),
3432 &_collector->_markStack);
3433 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3434 } // else nothing to do for this task
3435 } // else nothing to do for this task
3436 }
3437 // We'd be tempted to assert here that since there are no
3438 // more tasks left to claim in this space, the global_finger
3439 // must exceed space->top() and a fortiori space->end(). However,
3440 // that would not quite be correct because the bumping of
3441 // global_finger occurs strictly after the claiming of a task,
3442 // so by the time we reach here the global finger may not yet
3443 // have been bumped up by the thread that claimed the last
3444 // task.
3445 pst->all_tasks_completed();
3446 }
3447
3448 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3449 private:
3450 CMSCollector* _collector;
3451 CMSConcMarkingTask* _task;
3452 MemRegion _span;
3453 CMSBitMap* _bit_map;
3454 CMSMarkStack* _overflow_stack;
3455 OopTaskQueue* _work_queue;
3456 protected:
3457 DO_OOP_WORK_DEFN
3458 public:
3459 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3460 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3461 MetadataAwareOopClosure(collector->ref_processor()),
3462 _collector(collector),
3463 _task(task),
3464 _span(collector->_span),
3465 _work_queue(work_queue),
3466 _bit_map(bit_map),
3467 _overflow_stack(overflow_stack)
3468 { }
3469 virtual void do_oop(oop* p);
3470 virtual void do_oop(narrowOop* p);
3471
3472 void trim_queue(size_t max);
3473 void handle_stack_overflow(HeapWord* lost);
3474 void do_yield_check() {
3475 if (_task->should_yield()) {
3476 _task->yield();
3477 }
3478 }
3479 };
3480
3481 // Grey object scanning during work stealing phase --
3482 // the salient assumption here is that any references
3483 // that are in these stolen objects being scanned must
3484 // already have been initialized (else they would not have
3485 // been published), so we do not need to check for
3486 // uninitialized objects before pushing here.
3487 void Par_ConcMarkingClosure::do_oop(oop obj) {
3488 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
3489 HeapWord* addr = (HeapWord*)obj;
3490 // Check if oop points into the CMS generation
3491 // and is not marked
3492 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3493 // a white object ...
3494 // If we manage to "claim" the object, by being the
3495 // first thread to mark it, then we push it on our
3496 // marking stack
3497 if (_bit_map->par_mark(addr)) { // ... now grey
3498 // push on work queue (grey set)
3499 bool simulate_overflow = false;
3500 NOT_PRODUCT(
3501 if (CMSMarkStackOverflowALot &&
3502 _collector->simulate_overflow()) {
3503 // simulate a stack overflow
3504 simulate_overflow = true;
3505 }
3506 )
3507 if (simulate_overflow ||
3508 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3509 // stack overflow
3510 if (PrintCMSStatistics != 0) {
3511 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3512 SIZE_FORMAT, _overflow_stack->capacity());
3513 }
3514 // We cannot assert that the overflow stack is full because
3515 // it may have been emptied since.
3516 assert(simulate_overflow ||
3517 _work_queue->size() == _work_queue->max_elems(),
3518 "Else push should have succeeded");
3519 handle_stack_overflow(addr);
3520 }
3521 } // Else, some other thread got there first
3522 do_yield_check();
3523 }
3524 }
3525
3526 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3527 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3528
3529 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3530 while (_work_queue->size() > max) {
3531 oop new_oop;
3532 if (_work_queue->pop_local(new_oop)) {
3533 assert(new_oop->is_oop(), "Should be an oop");
3534 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3535 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3536 new_oop->oop_iterate(this); // do_oop() above
3537 do_yield_check();
3538 }
3539 }
3540 }
3541
3542 // Upon stack overflow, we discard (part of) the stack,
3543 // remembering the least address amongst those discarded
3544 // in CMSCollector's _restart_address.
3545 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3546 // We need to do this under a mutex to prevent other
3547 // workers from interfering with the work done below.
3548 MutexLockerEx ml(_overflow_stack->par_lock(),
3549 Mutex::_no_safepoint_check_flag);
3550 // Remember the least grey address discarded
3551 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3552 _collector->lower_restart_addr(ra);
3553 _overflow_stack->reset(); // discard stack contents
3554 _overflow_stack->expand(); // expand the stack if possible
3555 }
3556
3557
3558 void CMSConcMarkingTask::do_work_steal(int i) {
3559 OopTaskQueue* work_q = work_queue(i);
3560 oop obj_to_scan;
3561 CMSBitMap* bm = &(_collector->_markBitMap);
3562 CMSMarkStack* ovflw = &(_collector->_markStack);
3563 int* seed = _collector->hash_seed(i);
3564 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3565 while (true) {
3566 cl.trim_queue(0);
3567 assert(work_q->size() == 0, "Should have been emptied above");
3568 if (get_work_from_overflow_stack(ovflw, work_q)) {
3569 // Can't assert below because the work obtained from the
3570 // overflow stack may already have been stolen from us.
3571 // assert(work_q->size() > 0, "Work from overflow stack");
3572 continue;
3573 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3574 assert(obj_to_scan->is_oop(), "Should be an oop");
3575 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3576 obj_to_scan->oop_iterate(&cl);
3577 } else if (terminator()->offer_termination(&_term_term)) {
3578 assert(work_q->size() == 0, "Impossible!");
3579 break;
3580 } else if (yielding() || should_yield()) {
3581 yield();
3582 }
3583 }
3584 }
3585
3586 // This is run by the CMS (coordinator) thread.
3587 void CMSConcMarkingTask::coordinator_yield() {
3588 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3589 "CMS thread should hold CMS token");
3590 // First give up the locks, then yield, then re-lock
3591 // We should probably use a constructor/destructor idiom to
3592 // do this unlock/lock or modify the MutexUnlocker class to
3593 // serve our purpose. XXX
3594 assert_lock_strong(_bit_map_lock);
3595 _bit_map_lock->unlock();
3596 ConcurrentMarkSweepThread::desynchronize(true);
3597 _collector->stopTimer();
3598 if (PrintCMSStatistics != 0) {
3599 _collector->incrementYields();
3600 }
3601
3602 // It is possible for whichever thread initiated the yield request
3603 // not to get a chance to wake up and take the bitmap lock between
3604 // this thread releasing it and reacquiring it. So, while the
3605 // should_yield() flag is on, let's sleep for a bit to give the
3606 // other thread a chance to wake up. The limit imposed on the number
3607 // of iterations is defensive, to avoid any unforseen circumstances
3608 // putting us into an infinite loop. Since it's always been this
3609 // (coordinator_yield()) method that was observed to cause the
3610 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3611 // which is by default non-zero. For the other seven methods that
3612 // also perform the yield operation, as are using a different
3613 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3614 // can enable the sleeping for those methods too, if necessary.
3615 // See 6442774.
3616 //
3617 // We really need to reconsider the synchronization between the GC
3618 // thread and the yield-requesting threads in the future and we
3619 // should really use wait/notify, which is the recommended
3620 // way of doing this type of interaction. Additionally, we should
3621 // consolidate the eight methods that do the yield operation and they
3622 // are almost identical into one for better maintainability and
3623 // readability. See 6445193.
3624 //
3625 // Tony 2006.06.29
3626 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3627 ConcurrentMarkSweepThread::should_yield() &&
3628 !CMSCollector::foregroundGCIsActive(); ++i) {
3629 os::sleep(Thread::current(), 1, false);
3630 }
3631
3632 ConcurrentMarkSweepThread::synchronize(true);
3633 _bit_map_lock->lock_without_safepoint_check();
3634 _collector->startTimer();
3635 }
3636
3637 bool CMSCollector::do_marking_mt() {
3638 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3639 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3640 conc_workers()->active_workers(),
3641 Threads::number_of_non_daemon_threads());
3642 conc_workers()->set_active_workers(num_workers);
3643
3644 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3645
3646 CMSConcMarkingTask tsk(this,
3647 cms_space,
3648 conc_workers(),
3649 task_queues());
3650
3651 // Since the actual number of workers we get may be different
3652 // from the number we requested above, do we need to do anything different
3653 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3654 // class?? XXX
3655 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3656
3657 // Refs discovery is already non-atomic.
3658 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3659 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3660 conc_workers()->start_task(&tsk);
3661 while (tsk.yielded()) {
3662 tsk.coordinator_yield();
3663 conc_workers()->continue_task(&tsk);
3664 }
3665 // If the task was aborted, _restart_addr will be non-NULL
3666 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3667 while (_restart_addr != NULL) {
3668 // XXX For now we do not make use of ABORTED state and have not
3669 // yet implemented the right abort semantics (even in the original
3670 // single-threaded CMS case). That needs some more investigation
3671 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3672 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3673 // If _restart_addr is non-NULL, a marking stack overflow
3674 // occurred; we need to do a fresh marking iteration from the
3675 // indicated restart address.
3676 if (_foregroundGCIsActive) {
3677 // We may be running into repeated stack overflows, having
3678 // reached the limit of the stack size, while making very
3679 // slow forward progress. It may be best to bail out and
3680 // let the foreground collector do its job.
3681 // Clear _restart_addr, so that foreground GC
3682 // works from scratch. This avoids the headache of
3683 // a "rescan" which would otherwise be needed because
3684 // of the dirty mod union table & card table.
3685 _restart_addr = NULL;
3686 return false;
3687 }
3688 // Adjust the task to restart from _restart_addr
3689 tsk.reset(_restart_addr);
3690 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3691 _restart_addr);
3692 _restart_addr = NULL;
3693 // Get the workers going again
3694 conc_workers()->start_task(&tsk);
3695 while (tsk.yielded()) {
3696 tsk.coordinator_yield();
3697 conc_workers()->continue_task(&tsk);
3698 }
3699 }
3700 assert(tsk.completed(), "Inconsistency");
3701 assert(tsk.result() == true, "Inconsistency");
3702 return true;
3703 }
3704
3705 bool CMSCollector::do_marking_st() {
3706 ResourceMark rm;
3707 HandleMark hm;
3708
3709 // Temporarily make refs discovery single threaded (non-MT)
3710 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3711 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3712 &_markStack, CMSYield);
3713 // the last argument to iterate indicates whether the iteration
3714 // should be incremental with periodic yields.
3715 _markBitMap.iterate(&markFromRootsClosure);
3716 // If _restart_addr is non-NULL, a marking stack overflow
3717 // occurred; we need to do a fresh iteration from the
3718 // indicated restart address.
3719 while (_restart_addr != NULL) {
3720 if (_foregroundGCIsActive) {
3721 // We may be running into repeated stack overflows, having
3722 // reached the limit of the stack size, while making very
3723 // slow forward progress. It may be best to bail out and
3724 // let the foreground collector do its job.
3725 // Clear _restart_addr, so that foreground GC
3726 // works from scratch. This avoids the headache of
3727 // a "rescan" which would otherwise be needed because
3728 // of the dirty mod union table & card table.
3729 _restart_addr = NULL;
3730 return false; // indicating failure to complete marking
3731 }
3732 // Deal with stack overflow:
3733 // we restart marking from _restart_addr
3734 HeapWord* ra = _restart_addr;
3735 markFromRootsClosure.reset(ra);
3736 _restart_addr = NULL;
3737 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3738 }
3739 return true;
3740 }
3741
3742 void CMSCollector::preclean() {
3743 check_correct_thread_executing();
3744 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3745 verify_work_stacks_empty();
3746 verify_overflow_empty();
3747 _abort_preclean = false;
3748 if (CMSPrecleaningEnabled) {
3749 if (!CMSEdenChunksRecordAlways) {
3750 _eden_chunk_index = 0;
3751 }
3752 size_t used = get_eden_used();
3753 size_t capacity = get_eden_capacity();
3754 // Don't start sampling unless we will get sufficiently
3755 // many samples.
3756 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3757 * CMSScheduleRemarkEdenPenetration)) {
3758 _start_sampling = true;
3759 } else {
3760 _start_sampling = false;
3761 }
3762 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3763 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3764 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3765 }
3766 CMSTokenSync x(true); // is cms thread
3767 if (CMSPrecleaningEnabled) {
3768 sample_eden();
3769 _collectorState = AbortablePreclean;
3770 } else {
3771 _collectorState = FinalMarking;
3772 }
3773 verify_work_stacks_empty();
3774 verify_overflow_empty();
3775 }
3776
3777 // Try and schedule the remark such that young gen
3778 // occupancy is CMSScheduleRemarkEdenPenetration %.
3779 void CMSCollector::abortable_preclean() {
3780 check_correct_thread_executing();
3781 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3782 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3783
3784 // If Eden's current occupancy is below this threshold,
3785 // immediately schedule the remark; else preclean
3786 // past the next scavenge in an effort to
3787 // schedule the pause as described above. By choosing
3788 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3789 // we will never do an actual abortable preclean cycle.
3790 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3791 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3792 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3793 // We need more smarts in the abortable preclean
3794 // loop below to deal with cases where allocation
3795 // in young gen is very very slow, and our precleaning
3796 // is running a losing race against a horde of
3797 // mutators intent on flooding us with CMS updates
3798 // (dirty cards).
3799 // One, admittedly dumb, strategy is to give up
3800 // after a certain number of abortable precleaning loops
3801 // or after a certain maximum time. We want to make
3802 // this smarter in the next iteration.
3803 // XXX FIX ME!!! YSR
3804 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3805 while (!(should_abort_preclean() ||
3806 ConcurrentMarkSweepThread::should_terminate())) {
3807 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3808 cumworkdone += workdone;
3809 loops++;
3810 // Voluntarily terminate abortable preclean phase if we have
3811 // been at it for too long.
3812 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3813 loops >= CMSMaxAbortablePrecleanLoops) {
3814 if (PrintGCDetails) {
3815 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3816 }
3817 break;
3818 }
3819 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3820 if (PrintGCDetails) {
3821 gclog_or_tty->print(" CMS: abort preclean due to time ");
3822 }
3823 break;
3824 }
3825 // If we are doing little work each iteration, we should
3826 // take a short break.
3827 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3828 // Sleep for some time, waiting for work to accumulate
3829 stopTimer();
3830 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3831 startTimer();
3832 waited++;
3833 }
3834 }
3835 if (PrintCMSStatistics > 0) {
3836 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3837 loops, waited, cumworkdone);
3838 }
3839 }
3840 CMSTokenSync x(true); // is cms thread
3841 if (_collectorState != Idling) {
3842 assert(_collectorState == AbortablePreclean,
3843 "Spontaneous state transition?");
3844 _collectorState = FinalMarking;
3845 } // Else, a foreground collection completed this CMS cycle.
3846 return;
3847 }
3848
3849 // Respond to an Eden sampling opportunity
3850 void CMSCollector::sample_eden() {
3851 // Make sure a young gc cannot sneak in between our
3852 // reading and recording of a sample.
3853 assert(Thread::current()->is_ConcurrentGC_thread(),
3854 "Only the cms thread may collect Eden samples");
3855 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3856 "Should collect samples while holding CMS token");
3857 if (!_start_sampling) {
3858 return;
3859 }
3860 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3861 // is populated by the young generation.
3862 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3863 if (_eden_chunk_index < _eden_chunk_capacity) {
3864 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3865 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3866 "Unexpected state of Eden");
3867 // We'd like to check that what we just sampled is an oop-start address;
3868 // however, we cannot do that here since the object may not yet have been
3869 // initialized. So we'll instead do the check when we _use_ this sample
3870 // later.
3871 if (_eden_chunk_index == 0 ||
3872 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3873 _eden_chunk_array[_eden_chunk_index-1])
3874 >= CMSSamplingGrain)) {
3875 _eden_chunk_index++; // commit sample
3876 }
3877 }
3878 }
3879 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3880 size_t used = get_eden_used();
3881 size_t capacity = get_eden_capacity();
3882 assert(used <= capacity, "Unexpected state of Eden");
3883 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3884 _abort_preclean = true;
3885 }
3886 }
3887 }
3888
3889
3890 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3891 assert(_collectorState == Precleaning ||
3892 _collectorState == AbortablePreclean, "incorrect state");
3893 ResourceMark rm;
3894 HandleMark hm;
3895
3896 // Precleaning is currently not MT but the reference processor
3897 // may be set for MT. Disable it temporarily here.
3898 ReferenceProcessor* rp = ref_processor();
3899 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3900
3901 // Do one pass of scrubbing the discovered reference lists
3902 // to remove any reference objects with strongly-reachable
3903 // referents.
3904 if (clean_refs) {
3905 CMSPrecleanRefsYieldClosure yield_cl(this);
3906 assert(rp->span().equals(_span), "Spans should be equal");
3907 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3908 &_markStack, true /* preclean */);
3909 CMSDrainMarkingStackClosure complete_trace(this,
3910 _span, &_markBitMap, &_markStack,
3911 &keep_alive, true /* preclean */);
3912
3913 // We don't want this step to interfere with a young
3914 // collection because we don't want to take CPU
3915 // or memory bandwidth away from the young GC threads
3916 // (which may be as many as there are CPUs).
3917 // Note that we don't need to protect ourselves from
3918 // interference with mutators because they can't
3919 // manipulate the discovered reference lists nor affect
3920 // the computed reachability of the referents, the
3921 // only properties manipulated by the precleaning
3922 // of these reference lists.
3923 stopTimer();
3924 CMSTokenSyncWithLocks x(true /* is cms thread */,
3925 bitMapLock());
3926 startTimer();
3927 sample_eden();
3928
3929 // The following will yield to allow foreground
3930 // collection to proceed promptly. XXX YSR:
3931 // The code in this method may need further
3932 // tweaking for better performance and some restructuring
3933 // for cleaner interfaces.
3934 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3935 rp->preclean_discovered_references(
3936 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3937 gc_timer, _gc_tracer_cm->gc_id());
3938 }
3939
3940 if (clean_survivor) { // preclean the active survivor space(s)
3941 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3942 &_markBitMap, &_modUnionTable,
3943 &_markStack, true /* precleaning phase */);
3944 stopTimer();
3945 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3946 bitMapLock());
3947 startTimer();
3948 unsigned int before_count =
3949 GenCollectedHeap::heap()->total_collections();
3950 SurvivorSpacePrecleanClosure
3951 sss_cl(this, _span, &_markBitMap, &_markStack,
3952 &pam_cl, before_count, CMSYield);
3953 _young_gen->from()->object_iterate_careful(&sss_cl);
3954 _young_gen->to()->object_iterate_careful(&sss_cl);
3955 }
3956 MarkRefsIntoAndScanClosure
3957 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3958 &_markStack, this, CMSYield,
3959 true /* precleaning phase */);
3960 // CAUTION: The following closure has persistent state that may need to
3961 // be reset upon a decrease in the sequence of addresses it
3962 // processes.
3963 ScanMarkedObjectsAgainCarefullyClosure
3964 smoac_cl(this, _span,
3965 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3966
3967 // Preclean dirty cards in ModUnionTable and CardTable using
3968 // appropriate convergence criterion;
3969 // repeat CMSPrecleanIter times unless we find that
3970 // we are losing.
3971 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3972 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3973 "Bad convergence multiplier");
3974 assert(CMSPrecleanThreshold >= 100,
3975 "Unreasonably low CMSPrecleanThreshold");
3976
3977 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3978 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3979 numIter < CMSPrecleanIter;
3980 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3981 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3982 if (Verbose && PrintGCDetails) {
3983 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3984 }
3985 // Either there are very few dirty cards, so re-mark
3986 // pause will be small anyway, or our pre-cleaning isn't
3987 // that much faster than the rate at which cards are being
3988 // dirtied, so we might as well stop and re-mark since
3989 // precleaning won't improve our re-mark time by much.
3990 if (curNumCards <= CMSPrecleanThreshold ||
3991 (numIter > 0 &&
3992 (curNumCards * CMSPrecleanDenominator >
3993 lastNumCards * CMSPrecleanNumerator))) {
3994 numIter++;
3995 cumNumCards += curNumCards;
3996 break;
3997 }
3998 }
3999
4000 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4001
4002 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4003 cumNumCards += curNumCards;
4004 if (PrintGCDetails && PrintCMSStatistics != 0) {
4005 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
4006 curNumCards, cumNumCards, numIter);
4007 }
4008 return cumNumCards; // as a measure of useful work done
4009 }
4010
4011 // PRECLEANING NOTES:
4012 // Precleaning involves:
4013 // . reading the bits of the modUnionTable and clearing the set bits.
4014 // . For the cards corresponding to the set bits, we scan the
4015 // objects on those cards. This means we need the free_list_lock
4016 // so that we can safely iterate over the CMS space when scanning
4017 // for oops.
4018 // . When we scan the objects, we'll be both reading and setting
4019 // marks in the marking bit map, so we'll need the marking bit map.
4020 // . For protecting _collector_state transitions, we take the CGC_lock.
4021 // Note that any races in the reading of of card table entries by the
4022 // CMS thread on the one hand and the clearing of those entries by the
4023 // VM thread or the setting of those entries by the mutator threads on the
4024 // other are quite benign. However, for efficiency it makes sense to keep
4025 // the VM thread from racing with the CMS thread while the latter is
4026 // dirty card info to the modUnionTable. We therefore also use the
4027 // CGC_lock to protect the reading of the card table and the mod union
4028 // table by the CM thread.
4029 // . We run concurrently with mutator updates, so scanning
4030 // needs to be done carefully -- we should not try to scan
4031 // potentially uninitialized objects.
4032 //
4033 // Locking strategy: While holding the CGC_lock, we scan over and
4034 // reset a maximal dirty range of the mod union / card tables, then lock
4035 // the free_list_lock and bitmap lock to do a full marking, then
4036 // release these locks; and repeat the cycle. This allows for a
4037 // certain amount of fairness in the sharing of these locks between
4038 // the CMS collector on the one hand, and the VM thread and the
4039 // mutators on the other.
4040
4041 // NOTE: preclean_mod_union_table() and preclean_card_table()
4042 // further below are largely identical; if you need to modify
4043 // one of these methods, please check the other method too.
4044
4045 size_t CMSCollector::preclean_mod_union_table(
4046 ConcurrentMarkSweepGeneration* gen,
4047 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4048 verify_work_stacks_empty();
4049 verify_overflow_empty();
4050
4051 // strategy: starting with the first card, accumulate contiguous
4052 // ranges of dirty cards; clear these cards, then scan the region
4053 // covered by these cards.
4054
4055 // Since all of the MUT is committed ahead, we can just use
4056 // that, in case the generations expand while we are precleaning.
4057 // It might also be fine to just use the committed part of the
4058 // generation, but we might potentially miss cards when the
4059 // generation is rapidly expanding while we are in the midst
4060 // of precleaning.
4061 HeapWord* startAddr = gen->reserved().start();
4062 HeapWord* endAddr = gen->reserved().end();
4063
4064 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4065
4066 size_t numDirtyCards, cumNumDirtyCards;
4067 HeapWord *nextAddr, *lastAddr;
4068 for (cumNumDirtyCards = numDirtyCards = 0,
4069 nextAddr = lastAddr = startAddr;
4070 nextAddr < endAddr;
4071 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4072
4073 ResourceMark rm;
4074 HandleMark hm;
4075
4076 MemRegion dirtyRegion;
4077 {
4078 stopTimer();
4079 // Potential yield point
4080 CMSTokenSync ts(true);
4081 startTimer();
4082 sample_eden();
4083 // Get dirty region starting at nextOffset (inclusive),
4084 // simultaneously clearing it.
4085 dirtyRegion =
4086 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4087 assert(dirtyRegion.start() >= nextAddr,
4088 "returned region inconsistent?");
4089 }
4090 // Remember where the next search should begin.
4091 // The returned region (if non-empty) is a right open interval,
4092 // so lastOffset is obtained from the right end of that
4093 // interval.
4094 lastAddr = dirtyRegion.end();
4095 // Should do something more transparent and less hacky XXX
4096 numDirtyCards =
4097 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4098
4099 // We'll scan the cards in the dirty region (with periodic
4100 // yields for foreground GC as needed).
4101 if (!dirtyRegion.is_empty()) {
4102 assert(numDirtyCards > 0, "consistency check");
4103 HeapWord* stop_point = NULL;
4104 stopTimer();
4105 // Potential yield point
4106 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4107 bitMapLock());
4108 startTimer();
4109 {
4110 verify_work_stacks_empty();
4111 verify_overflow_empty();
4112 sample_eden();
4113 stop_point =
4114 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4115 }
4116 if (stop_point != NULL) {
4117 // The careful iteration stopped early either because it found an
4118 // uninitialized object, or because we were in the midst of an
4119 // "abortable preclean", which should now be aborted. Redirty
4120 // the bits corresponding to the partially-scanned or unscanned
4121 // cards. We'll either restart at the next block boundary or
4122 // abort the preclean.
4123 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4124 "Should only be AbortablePreclean.");
4125 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4126 if (should_abort_preclean()) {
4127 break; // out of preclean loop
4128 } else {
4129 // Compute the next address at which preclean should pick up;
4130 // might need bitMapLock in order to read P-bits.
4131 lastAddr = next_card_start_after_block(stop_point);
4132 }
4133 }
4134 } else {
4135 assert(lastAddr == endAddr, "consistency check");
4136 assert(numDirtyCards == 0, "consistency check");
4137 break;
4138 }
4139 }
4140 verify_work_stacks_empty();
4141 verify_overflow_empty();
4142 return cumNumDirtyCards;
4143 }
4144
4145 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4146 // below are largely identical; if you need to modify
4147 // one of these methods, please check the other method too.
4148
4149 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4150 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4151 // strategy: it's similar to precleamModUnionTable above, in that
4152 // we accumulate contiguous ranges of dirty cards, mark these cards
4153 // precleaned, then scan the region covered by these cards.
4154 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4155 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4156
4157 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4158
4159 size_t numDirtyCards, cumNumDirtyCards;
4160 HeapWord *lastAddr, *nextAddr;
4161
4162 for (cumNumDirtyCards = numDirtyCards = 0,
4163 nextAddr = lastAddr = startAddr;
4164 nextAddr < endAddr;
4165 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4166
4167 ResourceMark rm;
4168 HandleMark hm;
4169
4170 MemRegion dirtyRegion;
4171 {
4172 // See comments in "Precleaning notes" above on why we
4173 // do this locking. XXX Could the locking overheads be
4174 // too high when dirty cards are sparse? [I don't think so.]
4175 stopTimer();
4176 CMSTokenSync x(true); // is cms thread
4177 startTimer();
4178 sample_eden();
4179 // Get and clear dirty region from card table
4180 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4181 MemRegion(nextAddr, endAddr),
4182 true,
4183 CardTableModRefBS::precleaned_card_val());
4184
4185 assert(dirtyRegion.start() >= nextAddr,
4186 "returned region inconsistent?");
4187 }
4188 lastAddr = dirtyRegion.end();
4189 numDirtyCards =
4190 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4191
4192 if (!dirtyRegion.is_empty()) {
4193 stopTimer();
4194 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4195 startTimer();
4196 sample_eden();
4197 verify_work_stacks_empty();
4198 verify_overflow_empty();
4199 HeapWord* stop_point =
4200 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4201 if (stop_point != NULL) {
4202 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4203 "Should only be AbortablePreclean.");
4204 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4205 if (should_abort_preclean()) {
4206 break; // out of preclean loop
4207 } else {
4208 // Compute the next address at which preclean should pick up.
4209 lastAddr = next_card_start_after_block(stop_point);
4210 }
4211 }
4212 } else {
4213 break;
4214 }
4215 }
4216 verify_work_stacks_empty();
4217 verify_overflow_empty();
4218 return cumNumDirtyCards;
4219 }
4220
4221 class PrecleanKlassClosure : public KlassClosure {
4222 KlassToOopClosure _cm_klass_closure;
4223 public:
4224 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4225 void do_klass(Klass* k) {
4226 if (k->has_accumulated_modified_oops()) {
4227 k->clear_accumulated_modified_oops();
4228
4229 _cm_klass_closure.do_klass(k);
4230 }
4231 }
4232 };
4233
4234 // The freelist lock is needed to prevent asserts, is it really needed?
4235 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4236
4237 cl->set_freelistLock(freelistLock);
4238
4239 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4240
4241 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4242 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4243 PrecleanKlassClosure preclean_klass_closure(cl);
4244 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4245
4246 verify_work_stacks_empty();
4247 verify_overflow_empty();
4248 }
4249
4250 void CMSCollector::checkpointRootsFinal() {
4251 assert(_collectorState == FinalMarking, "incorrect state transition?");
4252 check_correct_thread_executing();
4253 // world is stopped at this checkpoint
4254 assert(SafepointSynchronize::is_at_safepoint(),
4255 "world should be stopped");
4256 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4257
4258 verify_work_stacks_empty();
4259 verify_overflow_empty();
4260
4261 if (PrintGCDetails) {
4262 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4263 _young_gen->used() / K,
4264 _young_gen->capacity() / K);
4265 }
4266 {
4267 if (CMSScavengeBeforeRemark) {
4268 GenCollectedHeap* gch = GenCollectedHeap::heap();
4269 // Temporarily set flag to false, GCH->do_collection will
4270 // expect it to be false and set to true
4271 FlagSetting fl(gch->_is_gc_active, false);
4272 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4273 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4274 int level = _cmsGen->level() - 1;
4275 if (level >= 0) {
4276 gch->do_collection(true, // full (i.e. force, see below)
4277 false, // !clear_all_soft_refs
4278 0, // size
4279 false, // is_tlab
4280 level // max_level
4281 );
4282 }
4283 }
4284 FreelistLocker x(this);
4285 MutexLockerEx y(bitMapLock(),
4286 Mutex::_no_safepoint_check_flag);
4287 checkpointRootsFinalWork();
4288 }
4289 verify_work_stacks_empty();
4290 verify_overflow_empty();
4291 }
4292
4293 void CMSCollector::checkpointRootsFinalWork() {
4294 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4295
4296 assert(haveFreelistLocks(), "must have free list locks");
4297 assert_lock_strong(bitMapLock());
4298
4299 ResourceMark rm;
4300 HandleMark hm;
4301
4302 GenCollectedHeap* gch = GenCollectedHeap::heap();
4303
4304 if (should_unload_classes()) {
4305 CodeCache::gc_prologue();
4306 }
4307 assert(haveFreelistLocks(), "must have free list locks");
4308 assert_lock_strong(bitMapLock());
4309
4310 // We might assume that we need not fill TLAB's when
4311 // CMSScavengeBeforeRemark is set, because we may have just done
4312 // a scavenge which would have filled all TLAB's -- and besides
4313 // Eden would be empty. This however may not always be the case --
4314 // for instance although we asked for a scavenge, it may not have
4315 // happened because of a JNI critical section. We probably need
4316 // a policy for deciding whether we can in that case wait until
4317 // the critical section releases and then do the remark following
4318 // the scavenge, and skip it here. In the absence of that policy,
4319 // or of an indication of whether the scavenge did indeed occur,
4320 // we cannot rely on TLAB's having been filled and must do
4321 // so here just in case a scavenge did not happen.
4322 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4323 // Update the saved marks which may affect the root scans.
4324 gch->save_marks();
4325
4326 if (CMSPrintEdenSurvivorChunks) {
4327 print_eden_and_survivor_chunk_arrays();
4328 }
4329
4330 {
4331 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4332
4333 // Note on the role of the mod union table:
4334 // Since the marker in "markFromRoots" marks concurrently with
4335 // mutators, it is possible for some reachable objects not to have been
4336 // scanned. For instance, an only reference to an object A was
4337 // placed in object B after the marker scanned B. Unless B is rescanned,
4338 // A would be collected. Such updates to references in marked objects
4339 // are detected via the mod union table which is the set of all cards
4340 // dirtied since the first checkpoint in this GC cycle and prior to
4341 // the most recent young generation GC, minus those cleaned up by the
4342 // concurrent precleaning.
4343 if (CMSParallelRemarkEnabled) {
4344 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
4345 do_remark_parallel();
4346 } else {
4347 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4348 _gc_timer_cm, _gc_tracer_cm->gc_id());
4349 do_remark_non_parallel();
4350 }
4351 }
4352 verify_work_stacks_empty();
4353 verify_overflow_empty();
4354
4355 {
4356 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
4357 refProcessingWork();
4358 }
4359 verify_work_stacks_empty();
4360 verify_overflow_empty();
4361
4362 if (should_unload_classes()) {
4363 CodeCache::gc_epilogue();
4364 }
4365 JvmtiExport::gc_epilogue();
4366
4367 // If we encountered any (marking stack / work queue) overflow
4368 // events during the current CMS cycle, take appropriate
4369 // remedial measures, where possible, so as to try and avoid
4370 // recurrence of that condition.
4371 assert(_markStack.isEmpty(), "No grey objects");
4372 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4373 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4374 if (ser_ovflw > 0) {
4375 if (PrintCMSStatistics != 0) {
4376 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4377 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4378 ", kac_preclean=" SIZE_FORMAT ")",
4379 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4380 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4381 }
4382 _markStack.expand();
4383 _ser_pmc_remark_ovflw = 0;
4384 _ser_pmc_preclean_ovflw = 0;
4385 _ser_kac_preclean_ovflw = 0;
4386 _ser_kac_ovflw = 0;
4387 }
4388 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4389 if (PrintCMSStatistics != 0) {
4390 gclog_or_tty->print_cr("Work queue overflow (benign) "
4391 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4392 _par_pmc_remark_ovflw, _par_kac_ovflw);
4393 }
4394 _par_pmc_remark_ovflw = 0;
4395 _par_kac_ovflw = 0;
4396 }
4397 if (PrintCMSStatistics != 0) {
4398 if (_markStack._hit_limit > 0) {
4399 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4400 _markStack._hit_limit);
4401 }
4402 if (_markStack._failed_double > 0) {
4403 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4404 " current capacity " SIZE_FORMAT,
4405 _markStack._failed_double,
4406 _markStack.capacity());
4407 }
4408 }
4409 _markStack._hit_limit = 0;
4410 _markStack._failed_double = 0;
4411
4412 if ((VerifyAfterGC || VerifyDuringGC) &&
4413 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4414 verify_after_remark();
4415 }
4416
4417 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4418
4419 // Change under the freelistLocks.
4420 _collectorState = Sweeping;
4421 // Call isAllClear() under bitMapLock
4422 assert(_modUnionTable.isAllClear(),
4423 "Should be clear by end of the final marking");
4424 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4425 "Should be clear by end of the final marking");
4426 }
4427
4428 void CMSParInitialMarkTask::work(uint worker_id) {
4429 elapsedTimer _timer;
4430 ResourceMark rm;
4431 HandleMark hm;
4432
4433 // ---------- scan from roots --------------
4434 _timer.start();
4435 GenCollectedHeap* gch = GenCollectedHeap::heap();
4436 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4437
4438 // ---------- young gen roots --------------
4439 {
4440 work_on_young_gen_roots(worker_id, &par_mri_cl);
4441 _timer.stop();
4442 if (PrintCMSStatistics != 0) {
4443 gclog_or_tty->print_cr(
4444 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4445 worker_id, _timer.seconds());
4446 }
4447 }
4448
4449 // ---------- remaining roots --------------
4450 _timer.reset();
4451 _timer.start();
4452
4453 CLDToOopClosure cld_closure(&par_mri_cl, true);
4454
4455 gch->gen_process_roots(_collector->_cmsGen->level(),
4456 false, // yg was scanned above
4457 false, // this is parallel code
4458 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4459 _collector->should_unload_classes(),
4460 &par_mri_cl,
4461 NULL,
4462 &cld_closure);
4463 assert(_collector->should_unload_classes()
4464 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4465 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4466 _timer.stop();
4467 if (PrintCMSStatistics != 0) {
4468 gclog_or_tty->print_cr(
4469 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4470 worker_id, _timer.seconds());
4471 }
4472 }
4473
4474 // Parallel remark task
4475 class CMSParRemarkTask: public CMSParMarkTask {
4476 CompactibleFreeListSpace* _cms_space;
4477
4478 // The per-thread work queues, available here for stealing.
4479 OopTaskQueueSet* _task_queues;
4480 ParallelTaskTerminator _term;
4481
4482 public:
4483 // A value of 0 passed to n_workers will cause the number of
4484 // workers to be taken from the active workers in the work gang.
4485 CMSParRemarkTask(CMSCollector* collector,
4486 CompactibleFreeListSpace* cms_space,
4487 uint n_workers, FlexibleWorkGang* workers,
4488 OopTaskQueueSet* task_queues):
4489 CMSParMarkTask("Rescan roots and grey objects in parallel",
4490 collector, n_workers),
4491 _cms_space(cms_space),
4492 _task_queues(task_queues),
4493 _term(n_workers, task_queues) { }
4494
4495 OopTaskQueueSet* task_queues() { return _task_queues; }
4496
4497 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4498
4499 ParallelTaskTerminator* terminator() { return &_term; }
4500 uint n_workers() { return _n_workers; }
4501
4502 void work(uint worker_id);
4503
4504 private:
4505 // ... of dirty cards in old space
4506 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4507 Par_MarkRefsIntoAndScanClosure* cl);
4508
4509 // ... work stealing for the above
4510 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4511 };
4512
4513 class RemarkKlassClosure : public KlassClosure {
4514 KlassToOopClosure _cm_klass_closure;
4515 public:
4516 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4517 void do_klass(Klass* k) {
4518 // Check if we have modified any oops in the Klass during the concurrent marking.
4519 if (k->has_accumulated_modified_oops()) {
4520 k->clear_accumulated_modified_oops();
4521
4522 // We could have transfered the current modified marks to the accumulated marks,
4523 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4524 } else if (k->has_modified_oops()) {
4525 // Don't clear anything, this info is needed by the next young collection.
4526 } else {
4527 // No modified oops in the Klass.
4528 return;
4529 }
4530
4531 // The klass has modified fields, need to scan the klass.
4532 _cm_klass_closure.do_klass(k);
4533 }
4534 };
4535
4536 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4537 ParNewGeneration* young_gen = _collector->_young_gen;
4538 ContiguousSpace* eden_space = young_gen->eden();
4539 ContiguousSpace* from_space = young_gen->from();
4540 ContiguousSpace* to_space = young_gen->to();
4541
4542 HeapWord** eca = _collector->_eden_chunk_array;
4543 size_t ect = _collector->_eden_chunk_index;
4544 HeapWord** sca = _collector->_survivor_chunk_array;
4545 size_t sct = _collector->_survivor_chunk_index;
4546
4547 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4548 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4549
4550 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4551 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4552 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4553 }
4554
4555 // work_queue(i) is passed to the closure
4556 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4557 // also is passed to do_dirty_card_rescan_tasks() and to
4558 // do_work_steal() to select the i-th task_queue.
4559
4560 void CMSParRemarkTask::work(uint worker_id) {
4561 elapsedTimer _timer;
4562 ResourceMark rm;
4563 HandleMark hm;
4564
4565 // ---------- rescan from roots --------------
4566 _timer.start();
4567 GenCollectedHeap* gch = GenCollectedHeap::heap();
4568 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4569 _collector->_span, _collector->ref_processor(),
4570 &(_collector->_markBitMap),
4571 work_queue(worker_id));
4572
4573 // Rescan young gen roots first since these are likely
4574 // coarsely partitioned and may, on that account, constitute
4575 // the critical path; thus, it's best to start off that
4576 // work first.
4577 // ---------- young gen roots --------------
4578 {
4579 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4580 _timer.stop();
4581 if (PrintCMSStatistics != 0) {
4582 gclog_or_tty->print_cr(
4583 "Finished young gen rescan work in %dth thread: %3.3f sec",
4584 worker_id, _timer.seconds());
4585 }
4586 }
4587
4588 // ---------- remaining roots --------------
4589 _timer.reset();
4590 _timer.start();
4591 gch->gen_process_roots(_collector->_cmsGen->level(),
4592 false, // yg was scanned above
4593 false, // this is parallel code
4594 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4595 _collector->should_unload_classes(),
4596 &par_mrias_cl,
4597 NULL,
4598 NULL); // The dirty klasses will be handled below
4599
4600 assert(_collector->should_unload_classes()
4601 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4602 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4603 _timer.stop();
4604 if (PrintCMSStatistics != 0) {
4605 gclog_or_tty->print_cr(
4606 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4607 worker_id, _timer.seconds());
4608 }
4609
4610 // ---------- unhandled CLD scanning ----------
4611 if (worker_id == 0) { // Single threaded at the moment.
4612 _timer.reset();
4613 _timer.start();
4614
4615 // Scan all new class loader data objects and new dependencies that were
4616 // introduced during concurrent marking.
4617 ResourceMark rm;
4618 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4619 for (int i = 0; i < array->length(); i++) {
4620 par_mrias_cl.do_class_loader_data(array->at(i));
4621 }
4622
4623 // We don't need to keep track of new CLDs anymore.
4624 ClassLoaderDataGraph::remember_new_clds(false);
4625
4626 _timer.stop();
4627 if (PrintCMSStatistics != 0) {
4628 gclog_or_tty->print_cr(
4629 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4630 worker_id, _timer.seconds());
4631 }
4632 }
4633
4634 // ---------- dirty klass scanning ----------
4635 if (worker_id == 0) { // Single threaded at the moment.
4636 _timer.reset();
4637 _timer.start();
4638
4639 // Scan all classes that was dirtied during the concurrent marking phase.
4640 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4641 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4642
4643 _timer.stop();
4644 if (PrintCMSStatistics != 0) {
4645 gclog_or_tty->print_cr(
4646 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4647 worker_id, _timer.seconds());
4648 }
4649 }
4650
4651 // We might have added oops to ClassLoaderData::_handles during the
4652 // concurrent marking phase. These oops point to newly allocated objects
4653 // that are guaranteed to be kept alive. Either by the direct allocation
4654 // code, or when the young collector processes the roots. Hence,
4655 // we don't have to revisit the _handles block during the remark phase.
4656
4657 // ---------- rescan dirty cards ------------
4658 _timer.reset();
4659 _timer.start();
4660
4661 // Do the rescan tasks for each of the two spaces
4662 // (cms_space) in turn.
4663 // "worker_id" is passed to select the task_queue for "worker_id"
4664 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4665 _timer.stop();
4666 if (PrintCMSStatistics != 0) {
4667 gclog_or_tty->print_cr(
4668 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4669 worker_id, _timer.seconds());
4670 }
4671
4672 // ---------- steal work from other threads ...
4673 // ---------- ... and drain overflow list.
4674 _timer.reset();
4675 _timer.start();
4676 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4677 _timer.stop();
4678 if (PrintCMSStatistics != 0) {
4679 gclog_or_tty->print_cr(
4680 "Finished work stealing in %dth thread: %3.3f sec",
4681 worker_id, _timer.seconds());
4682 }
4683 }
4684
4685 // Note that parameter "i" is not used.
4686 void
4687 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4688 OopsInGenClosure* cl, ContiguousSpace* space,
4689 HeapWord** chunk_array, size_t chunk_top) {
4690 // Until all tasks completed:
4691 // . claim an unclaimed task
4692 // . compute region boundaries corresponding to task claimed
4693 // using chunk_array
4694 // . par_oop_iterate(cl) over that region
4695
4696 ResourceMark rm;
4697 HandleMark hm;
4698
4699 SequentialSubTasksDone* pst = space->par_seq_tasks();
4700
4701 uint nth_task = 0;
4702 uint n_tasks = pst->n_tasks();
4703
4704 if (n_tasks > 0) {
4705 assert(pst->valid(), "Uninitialized use?");
4706 HeapWord *start, *end;
4707 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4708 // We claimed task # nth_task; compute its boundaries.
4709 if (chunk_top == 0) { // no samples were taken
4710 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4711 start = space->bottom();
4712 end = space->top();
4713 } else if (nth_task == 0) {
4714 start = space->bottom();
4715 end = chunk_array[nth_task];
4716 } else if (nth_task < (uint)chunk_top) {
4717 assert(nth_task >= 1, "Control point invariant");
4718 start = chunk_array[nth_task - 1];
4719 end = chunk_array[nth_task];
4720 } else {
4721 assert(nth_task == (uint)chunk_top, "Control point invariant");
4722 start = chunk_array[chunk_top - 1];
4723 end = space->top();
4724 }
4725 MemRegion mr(start, end);
4726 // Verify that mr is in space
4727 assert(mr.is_empty() || space->used_region().contains(mr),
4728 "Should be in space");
4729 // Verify that "start" is an object boundary
4730 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4731 "Should be an oop");
4732 space->par_oop_iterate(mr, cl);
4733 }
4734 pst->all_tasks_completed();
4735 }
4736 }
4737
4738 void
4739 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4740 CompactibleFreeListSpace* sp, int i,
4741 Par_MarkRefsIntoAndScanClosure* cl) {
4742 // Until all tasks completed:
4743 // . claim an unclaimed task
4744 // . compute region boundaries corresponding to task claimed
4745 // . transfer dirty bits ct->mut for that region
4746 // . apply rescanclosure to dirty mut bits for that region
4747
4748 ResourceMark rm;
4749 HandleMark hm;
4750
4751 OopTaskQueue* work_q = work_queue(i);
4752 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4753 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4754 // CAUTION: This closure has state that persists across calls to
4755 // the work method dirty_range_iterate_clear() in that it has
4756 // embedded in it a (subtype of) UpwardsObjectClosure. The
4757 // use of that state in the embedded UpwardsObjectClosure instance
4758 // assumes that the cards are always iterated (even if in parallel
4759 // by several threads) in monotonically increasing order per each
4760 // thread. This is true of the implementation below which picks
4761 // card ranges (chunks) in monotonically increasing order globally
4762 // and, a-fortiori, in monotonically increasing order per thread
4763 // (the latter order being a subsequence of the former).
4764 // If the work code below is ever reorganized into a more chaotic
4765 // work-partitioning form than the current "sequential tasks"
4766 // paradigm, the use of that persistent state will have to be
4767 // revisited and modified appropriately. See also related
4768 // bug 4756801 work on which should examine this code to make
4769 // sure that the changes there do not run counter to the
4770 // assumptions made here and necessary for correctness and
4771 // efficiency. Note also that this code might yield inefficient
4772 // behavior in the case of very large objects that span one or
4773 // more work chunks. Such objects would potentially be scanned
4774 // several times redundantly. Work on 4756801 should try and
4775 // address that performance anomaly if at all possible. XXX
4776 MemRegion full_span = _collector->_span;
4777 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4778 MarkFromDirtyCardsClosure
4779 greyRescanClosure(_collector, full_span, // entire span of interest
4780 sp, bm, work_q, cl);
4781
4782 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4783 assert(pst->valid(), "Uninitialized use?");
4784 uint nth_task = 0;
4785 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4786 MemRegion span = sp->used_region();
4787 HeapWord* start_addr = span.start();
4788 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4789 alignment);
4790 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4791 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4792 start_addr, "Check alignment");
4793 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4794 chunk_size, "Check alignment");
4795
4796 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4797 // Having claimed the nth_task, compute corresponding mem-region,
4798 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4799 // The alignment restriction ensures that we do not need any
4800 // synchronization with other gang-workers while setting or
4801 // clearing bits in thus chunk of the MUT.
4802 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4803 start_addr + (nth_task+1)*chunk_size);
4804 // The last chunk's end might be way beyond end of the
4805 // used region. In that case pull back appropriately.
4806 if (this_span.end() > end_addr) {
4807 this_span.set_end(end_addr);
4808 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4809 }
4810 // Iterate over the dirty cards covering this chunk, marking them
4811 // precleaned, and setting the corresponding bits in the mod union
4812 // table. Since we have been careful to partition at Card and MUT-word
4813 // boundaries no synchronization is needed between parallel threads.
4814 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4815 &modUnionClosure);
4816
4817 // Having transferred these marks into the modUnionTable,
4818 // rescan the marked objects on the dirty cards in the modUnionTable.
4819 // Even if this is at a synchronous collection, the initial marking
4820 // may have been done during an asynchronous collection so there
4821 // may be dirty bits in the mod-union table.
4822 _collector->_modUnionTable.dirty_range_iterate_clear(
4823 this_span, &greyRescanClosure);
4824 _collector->_modUnionTable.verifyNoOneBitsInRange(
4825 this_span.start(),
4826 this_span.end());
4827 }
4828 pst->all_tasks_completed(); // declare that i am done
4829 }
4830
4831 // . see if we can share work_queues with ParNew? XXX
4832 void
4833 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4834 int* seed) {
4835 OopTaskQueue* work_q = work_queue(i);
4836 NOT_PRODUCT(int num_steals = 0;)
4837 oop obj_to_scan;
4838 CMSBitMap* bm = &(_collector->_markBitMap);
4839
4840 while (true) {
4841 // Completely finish any left over work from (an) earlier round(s)
4842 cl->trim_queue(0);
4843 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4844 (size_t)ParGCDesiredObjsFromOverflowList);
4845 // Now check if there's any work in the overflow list
4846 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4847 // only affects the number of attempts made to get work from the
4848 // overflow list and does not affect the number of workers. Just
4849 // pass ParallelGCThreads so this behavior is unchanged.
4850 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4851 work_q,
4852 ParallelGCThreads)) {
4853 // found something in global overflow list;
4854 // not yet ready to go stealing work from others.
4855 // We'd like to assert(work_q->size() != 0, ...)
4856 // because we just took work from the overflow list,
4857 // but of course we can't since all of that could have
4858 // been already stolen from us.
4859 // "He giveth and He taketh away."
4860 continue;
4861 }
4862 // Verify that we have no work before we resort to stealing
4863 assert(work_q->size() == 0, "Have work, shouldn't steal");
4864 // Try to steal from other queues that have work
4865 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4866 NOT_PRODUCT(num_steals++;)
4867 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4868 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4869 // Do scanning work
4870 obj_to_scan->oop_iterate(cl);
4871 // Loop around, finish this work, and try to steal some more
4872 } else if (terminator()->offer_termination()) {
4873 break; // nirvana from the infinite cycle
4874 }
4875 }
4876 NOT_PRODUCT(
4877 if (PrintCMSStatistics != 0) {
4878 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4879 }
4880 )
4881 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4882 "Else our work is not yet done");
4883 }
4884
4885 // Record object boundaries in _eden_chunk_array by sampling the eden
4886 // top in the slow-path eden object allocation code path and record
4887 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4888 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4889 // sampling in sample_eden() that activates during the part of the
4890 // preclean phase.
4891 void CMSCollector::sample_eden_chunk() {
4892 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4893 if (_eden_chunk_lock->try_lock()) {
4894 // Record a sample. This is the critical section. The contents
4895 // of the _eden_chunk_array have to be non-decreasing in the
4896 // address order.
4897 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4898 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4899 "Unexpected state of Eden");
4900 if (_eden_chunk_index == 0 ||
4901 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4902 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4903 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4904 _eden_chunk_index++; // commit sample
4905 }
4906 _eden_chunk_lock->unlock();
4907 }
4908 }
4909 }
4910
4911 // Return a thread-local PLAB recording array, as appropriate.
4912 void* CMSCollector::get_data_recorder(int thr_num) {
4913 if (_survivor_plab_array != NULL &&
4914 (CMSPLABRecordAlways ||
4915 (_collectorState > Marking && _collectorState < FinalMarking))) {
4916 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4917 ChunkArray* ca = &_survivor_plab_array[thr_num];
4918 ca->reset(); // clear it so that fresh data is recorded
4919 return (void*) ca;
4920 } else {
4921 return NULL;
4922 }
4923 }
4924
4925 // Reset all the thread-local PLAB recording arrays
4926 void CMSCollector::reset_survivor_plab_arrays() {
4927 for (uint i = 0; i < ParallelGCThreads; i++) {
4928 _survivor_plab_array[i].reset();
4929 }
4930 }
4931
4932 // Merge the per-thread plab arrays into the global survivor chunk
4933 // array which will provide the partitioning of the survivor space
4934 // for CMS initial scan and rescan.
4935 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4936 int no_of_gc_threads) {
4937 assert(_survivor_plab_array != NULL, "Error");
4938 assert(_survivor_chunk_array != NULL, "Error");
4939 assert(_collectorState == FinalMarking ||
4940 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4941 for (int j = 0; j < no_of_gc_threads; j++) {
4942 _cursor[j] = 0;
4943 }
4944 HeapWord* top = surv->top();
4945 size_t i;
4946 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4947 HeapWord* min_val = top; // Higher than any PLAB address
4948 uint min_tid = 0; // position of min_val this round
4949 for (int j = 0; j < no_of_gc_threads; j++) {
4950 ChunkArray* cur_sca = &_survivor_plab_array[j];
4951 if (_cursor[j] == cur_sca->end()) {
4952 continue;
4953 }
4954 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4955 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4956 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4957 if (cur_val < min_val) {
4958 min_tid = j;
4959 min_val = cur_val;
4960 } else {
4961 assert(cur_val < top, "All recorded addresses should be less");
4962 }
4963 }
4964 // At this point min_val and min_tid are respectively
4965 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4966 // and the thread (j) that witnesses that address.
4967 // We record this address in the _survivor_chunk_array[i]
4968 // and increment _cursor[min_tid] prior to the next round i.
4969 if (min_val == top) {
4970 break;
4971 }
4972 _survivor_chunk_array[i] = min_val;
4973 _cursor[min_tid]++;
4974 }
4975 // We are all done; record the size of the _survivor_chunk_array
4976 _survivor_chunk_index = i; // exclusive: [0, i)
4977 if (PrintCMSStatistics > 0) {
4978 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4979 }
4980 // Verify that we used up all the recorded entries
4981 #ifdef ASSERT
4982 size_t total = 0;
4983 for (int j = 0; j < no_of_gc_threads; j++) {
4984 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4985 total += _cursor[j];
4986 }
4987 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4988 // Check that the merged array is in sorted order
4989 if (total > 0) {
4990 for (size_t i = 0; i < total - 1; i++) {
4991 if (PrintCMSStatistics > 0) {
4992 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4993 i, p2i(_survivor_chunk_array[i]));
4994 }
4995 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4996 "Not sorted");
4997 }
4998 }
4999 #endif // ASSERT
5000 }
5001
5002 // Set up the space's par_seq_tasks structure for work claiming
5003 // for parallel initial scan and rescan of young gen.
5004 // See ParRescanTask where this is currently used.
5005 void
5006 CMSCollector::
5007 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5008 assert(n_threads > 0, "Unexpected n_threads argument");
5009
5010 // Eden space
5011 if (!_young_gen->eden()->is_empty()) {
5012 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5013 assert(!pst->valid(), "Clobbering existing data?");
5014 // Each valid entry in [0, _eden_chunk_index) represents a task.
5015 size_t n_tasks = _eden_chunk_index + 1;
5016 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5017 // Sets the condition for completion of the subtask (how many threads
5018 // need to finish in order to be done).
5019 pst->set_n_threads(n_threads);
5020 pst->set_n_tasks((int)n_tasks);
5021 }
5022
5023 // Merge the survivor plab arrays into _survivor_chunk_array
5024 if (_survivor_plab_array != NULL) {
5025 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5026 } else {
5027 assert(_survivor_chunk_index == 0, "Error");
5028 }
5029
5030 // To space
5031 {
5032 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5033 assert(!pst->valid(), "Clobbering existing data?");
5034 // Sets the condition for completion of the subtask (how many threads
5035 // need to finish in order to be done).
5036 pst->set_n_threads(n_threads);
5037 pst->set_n_tasks(1);
5038 assert(pst->valid(), "Error");
5039 }
5040
5041 // From space
5042 {
5043 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5044 assert(!pst->valid(), "Clobbering existing data?");
5045 size_t n_tasks = _survivor_chunk_index + 1;
5046 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5047 // Sets the condition for completion of the subtask (how many threads
5048 // need to finish in order to be done).
5049 pst->set_n_threads(n_threads);
5050 pst->set_n_tasks((int)n_tasks);
5051 assert(pst->valid(), "Error");
5052 }
5053 }
5054
5055 // Parallel version of remark
5056 void CMSCollector::do_remark_parallel() {
5057 GenCollectedHeap* gch = GenCollectedHeap::heap();
5058 FlexibleWorkGang* workers = gch->workers();
5059 assert(workers != NULL, "Need parallel worker threads.");
5060 // Choose to use the number of GC workers most recently set
5061 // into "active_workers". If active_workers is not set, set it
5062 // to ParallelGCThreads.
5063 uint n_workers = workers->active_workers();
5064 if (n_workers == 0) {
5065 assert(n_workers > 0, "Should have been set during scavenge");
5066 n_workers = ParallelGCThreads;
5067 workers->set_active_workers(n_workers);
5068 }
5069 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5070
5071 CMSParRemarkTask tsk(this,
5072 cms_space,
5073 n_workers, workers, task_queues());
5074
5075 // Set up for parallel process_roots work.
5076 gch->set_par_threads(n_workers);
5077 // We won't be iterating over the cards in the card table updating
5078 // the younger_gen cards, so we shouldn't call the following else
5079 // the verification code as well as subsequent younger_refs_iterate
5080 // code would get confused. XXX
5081 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5082
5083 // The young gen rescan work will not be done as part of
5084 // process_roots (which currently doesn't know how to
5085 // parallelize such a scan), but rather will be broken up into
5086 // a set of parallel tasks (via the sampling that the [abortable]
5087 // preclean phase did of eden, plus the [two] tasks of
5088 // scanning the [two] survivor spaces. Further fine-grain
5089 // parallelization of the scanning of the survivor spaces
5090 // themselves, and of precleaning of the younger gen itself
5091 // is deferred to the future.
5092 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5093
5094 // The dirty card rescan work is broken up into a "sequence"
5095 // of parallel tasks (per constituent space) that are dynamically
5096 // claimed by the parallel threads.
5097 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5098
5099 // It turns out that even when we're using 1 thread, doing the work in a
5100 // separate thread causes wide variance in run times. We can't help this
5101 // in the multi-threaded case, but we special-case n=1 here to get
5102 // repeatable measurements of the 1-thread overhead of the parallel code.
5103 if (n_workers > 1) {
5104 // Make refs discovery MT-safe, if it isn't already: it may not
5105 // necessarily be so, since it's possible that we are doing
5106 // ST marking.
5107 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5108 StrongRootsScope srs;
5109 workers->run_task(&tsk);
5110 } else {
5111 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5112 StrongRootsScope srs;
5113 tsk.work(0);
5114 }
5115
5116 gch->set_par_threads(0); // 0 ==> non-parallel.
5117 // restore, single-threaded for now, any preserved marks
5118 // as a result of work_q overflow
5119 restore_preserved_marks_if_any();
5120 }
5121
5122 // Non-parallel version of remark
5123 void CMSCollector::do_remark_non_parallel() {
5124 ResourceMark rm;
5125 HandleMark hm;
5126 GenCollectedHeap* gch = GenCollectedHeap::heap();
5127 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5128
5129 MarkRefsIntoAndScanClosure
5130 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5131 &_markStack, this,
5132 false /* should_yield */, false /* not precleaning */);
5133 MarkFromDirtyCardsClosure
5134 markFromDirtyCardsClosure(this, _span,
5135 NULL, // space is set further below
5136 &_markBitMap, &_markStack, &mrias_cl);
5137 {
5138 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5139 // Iterate over the dirty cards, setting the corresponding bits in the
5140 // mod union table.
5141 {
5142 ModUnionClosure modUnionClosure(&_modUnionTable);
5143 _ct->ct_bs()->dirty_card_iterate(
5144 _cmsGen->used_region(),
5145 &modUnionClosure);
5146 }
5147 // Having transferred these marks into the modUnionTable, we just need
5148 // to rescan the marked objects on the dirty cards in the modUnionTable.
5149 // The initial marking may have been done during an asynchronous
5150 // collection so there may be dirty bits in the mod-union table.
5151 const int alignment =
5152 CardTableModRefBS::card_size * BitsPerWord;
5153 {
5154 // ... First handle dirty cards in CMS gen
5155 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5156 MemRegion ur = _cmsGen->used_region();
5157 HeapWord* lb = ur.start();
5158 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5159 MemRegion cms_span(lb, ub);
5160 _modUnionTable.dirty_range_iterate_clear(cms_span,
5161 &markFromDirtyCardsClosure);
5162 verify_work_stacks_empty();
5163 if (PrintCMSStatistics != 0) {
5164 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5165 markFromDirtyCardsClosure.num_dirty_cards());
5166 }
5167 }
5168 }
5169 if (VerifyDuringGC &&
5170 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5171 HandleMark hm; // Discard invalid handles created during verification
5172 Universe::verify();
5173 }
5174 {
5175 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5176
5177 verify_work_stacks_empty();
5178
5179 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5180 StrongRootsScope srs;
5181
5182 gch->gen_process_roots(_cmsGen->level(),
5183 true, // younger gens as roots
5184 false, // use the local StrongRootsScope
5185 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5186 should_unload_classes(),
5187 &mrias_cl,
5188 NULL,
5189 NULL); // The dirty klasses will be handled below
5190
5191 assert(should_unload_classes()
5192 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5193 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5194 }
5195
5196 {
5197 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5198
5199 verify_work_stacks_empty();
5200
5201 // Scan all class loader data objects that might have been introduced
5202 // during concurrent marking.
5203 ResourceMark rm;
5204 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5205 for (int i = 0; i < array->length(); i++) {
5206 mrias_cl.do_class_loader_data(array->at(i));
5207 }
5208
5209 // We don't need to keep track of new CLDs anymore.
5210 ClassLoaderDataGraph::remember_new_clds(false);
5211
5212 verify_work_stacks_empty();
5213 }
5214
5215 {
5216 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5217
5218 verify_work_stacks_empty();
5219
5220 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5221 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5222
5223 verify_work_stacks_empty();
5224 }
5225
5226 // We might have added oops to ClassLoaderData::_handles during the
5227 // concurrent marking phase. These oops point to newly allocated objects
5228 // that are guaranteed to be kept alive. Either by the direct allocation
5229 // code, or when the young collector processes the roots. Hence,
5230 // we don't have to revisit the _handles block during the remark phase.
5231
5232 verify_work_stacks_empty();
5233 // Restore evacuated mark words, if any, used for overflow list links
5234 if (!CMSOverflowEarlyRestoration) {
5235 restore_preserved_marks_if_any();
5236 }
5237 verify_overflow_empty();
5238 }
5239
5240 ////////////////////////////////////////////////////////
5241 // Parallel Reference Processing Task Proxy Class
5242 ////////////////////////////////////////////////////////
5243 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5244 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5245 CMSCollector* _collector;
5246 CMSBitMap* _mark_bit_map;
5247 const MemRegion _span;
5248 ProcessTask& _task;
5249
5250 public:
5251 CMSRefProcTaskProxy(ProcessTask& task,
5252 CMSCollector* collector,
5253 const MemRegion& span,
5254 CMSBitMap* mark_bit_map,
5255 AbstractWorkGang* workers,
5256 OopTaskQueueSet* task_queues):
5257 // XXX Should superclass AGTWOQ also know about AWG since it knows
5258 // about the task_queues used by the AWG? Then it could initialize
5259 // the terminator() object. See 6984287. The set_for_termination()
5260 // below is a temporary band-aid for the regression in 6984287.
5261 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5262 task_queues),
5263 _task(task),
5264 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5265 {
5266 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5267 "Inconsistency in _span");
5268 set_for_termination(workers->active_workers());
5269 }
5270
5271 OopTaskQueueSet* task_queues() { return queues(); }
5272
5273 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5274
5275 void do_work_steal(int i,
5276 CMSParDrainMarkingStackClosure* drain,
5277 CMSParKeepAliveClosure* keep_alive,
5278 int* seed);
5279
5280 virtual void work(uint worker_id);
5281 };
5282
5283 void CMSRefProcTaskProxy::work(uint worker_id) {
5284 ResourceMark rm;
5285 HandleMark hm;
5286 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5287 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5288 _mark_bit_map,
5289 work_queue(worker_id));
5290 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5291 _mark_bit_map,
5292 work_queue(worker_id));
5293 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5294 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5295 if (_task.marks_oops_alive()) {
5296 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5297 _collector->hash_seed(worker_id));
5298 }
5299 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5300 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5301 }
5302
5303 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5304 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5305 EnqueueTask& _task;
5306
5307 public:
5308 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5309 : AbstractGangTask("Enqueue reference objects in parallel"),
5310 _task(task)
5311 { }
5312
5313 virtual void work(uint worker_id)
5314 {
5315 _task.work(worker_id);
5316 }
5317 };
5318
5319 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5320 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5321 _span(span),
5322 _bit_map(bit_map),
5323 _work_queue(work_queue),
5324 _mark_and_push(collector, span, bit_map, work_queue),
5325 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5326 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5327 { }
5328
5329 // . see if we can share work_queues with ParNew? XXX
5330 void CMSRefProcTaskProxy::do_work_steal(int i,
5331 CMSParDrainMarkingStackClosure* drain,
5332 CMSParKeepAliveClosure* keep_alive,
5333 int* seed) {
5334 OopTaskQueue* work_q = work_queue(i);
5335 NOT_PRODUCT(int num_steals = 0;)
5336 oop obj_to_scan;
5337
5338 while (true) {
5339 // Completely finish any left over work from (an) earlier round(s)
5340 drain->trim_queue(0);
5341 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5342 (size_t)ParGCDesiredObjsFromOverflowList);
5343 // Now check if there's any work in the overflow list
5344 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5345 // only affects the number of attempts made to get work from the
5346 // overflow list and does not affect the number of workers. Just
5347 // pass ParallelGCThreads so this behavior is unchanged.
5348 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5349 work_q,
5350 ParallelGCThreads)) {
5351 // Found something in global overflow list;
5352 // not yet ready to go stealing work from others.
5353 // We'd like to assert(work_q->size() != 0, ...)
5354 // because we just took work from the overflow list,
5355 // but of course we can't, since all of that might have
5356 // been already stolen from us.
5357 continue;
5358 }
5359 // Verify that we have no work before we resort to stealing
5360 assert(work_q->size() == 0, "Have work, shouldn't steal");
5361 // Try to steal from other queues that have work
5362 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5363 NOT_PRODUCT(num_steals++;)
5364 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5365 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5366 // Do scanning work
5367 obj_to_scan->oop_iterate(keep_alive);
5368 // Loop around, finish this work, and try to steal some more
5369 } else if (terminator()->offer_termination()) {
5370 break; // nirvana from the infinite cycle
5371 }
5372 }
5373 NOT_PRODUCT(
5374 if (PrintCMSStatistics != 0) {
5375 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5376 }
5377 )
5378 }
5379
5380 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5381 {
5382 GenCollectedHeap* gch = GenCollectedHeap::heap();
5383 FlexibleWorkGang* workers = gch->workers();
5384 assert(workers != NULL, "Need parallel worker threads.");
5385 CMSRefProcTaskProxy rp_task(task, &_collector,
5386 _collector.ref_processor()->span(),
5387 _collector.markBitMap(),
5388 workers, _collector.task_queues());
5389 workers->run_task(&rp_task);
5390 }
5391
5392 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5393 {
5394
5395 GenCollectedHeap* gch = GenCollectedHeap::heap();
5396 FlexibleWorkGang* workers = gch->workers();
5397 assert(workers != NULL, "Need parallel worker threads.");
5398 CMSRefEnqueueTaskProxy enq_task(task);
5399 workers->run_task(&enq_task);
5400 }
5401
5402 void CMSCollector::refProcessingWork() {
5403 ResourceMark rm;
5404 HandleMark hm;
5405
5406 ReferenceProcessor* rp = ref_processor();
5407 assert(rp->span().equals(_span), "Spans should be equal");
5408 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5409 // Process weak references.
5410 rp->setup_policy(false);
5411 verify_work_stacks_empty();
5412
5413 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5414 &_markStack, false /* !preclean */);
5415 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5416 _span, &_markBitMap, &_markStack,
5417 &cmsKeepAliveClosure, false /* !preclean */);
5418 {
5419 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5420
5421 ReferenceProcessorStats stats;
5422 if (rp->processing_is_mt()) {
5423 // Set the degree of MT here. If the discovery is done MT, there
5424 // may have been a different number of threads doing the discovery
5425 // and a different number of discovered lists may have Ref objects.
5426 // That is OK as long as the Reference lists are balanced (see
5427 // balance_all_queues() and balance_queues()).
5428 GenCollectedHeap* gch = GenCollectedHeap::heap();
5429 uint active_workers = ParallelGCThreads;
5430 FlexibleWorkGang* workers = gch->workers();
5431 if (workers != NULL) {
5432 active_workers = workers->active_workers();
5433 // The expectation is that active_workers will have already
5434 // been set to a reasonable value. If it has not been set,
5435 // investigate.
5436 assert(active_workers > 0, "Should have been set during scavenge");
5437 }
5438 rp->set_active_mt_degree(active_workers);
5439 CMSRefProcTaskExecutor task_executor(*this);
5440 stats = rp->process_discovered_references(&_is_alive_closure,
5441 &cmsKeepAliveClosure,
5442 &cmsDrainMarkingStackClosure,
5443 &task_executor,
5444 _gc_timer_cm,
5445 _gc_tracer_cm->gc_id());
5446 } else {
5447 stats = rp->process_discovered_references(&_is_alive_closure,
5448 &cmsKeepAliveClosure,
5449 &cmsDrainMarkingStackClosure,
5450 NULL,
5451 _gc_timer_cm,
5452 _gc_tracer_cm->gc_id());
5453 }
5454 _gc_tracer_cm->report_gc_reference_stats(stats);
5455
5456 }
5457
5458 // This is the point where the entire marking should have completed.
5459 verify_work_stacks_empty();
5460
5461 if (should_unload_classes()) {
5462 {
5463 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5464
5465 // Unload classes and purge the SystemDictionary.
5466 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5467
5468 // Unload nmethods.
5469 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5470
5471 // Prune dead klasses from subklass/sibling/implementor lists.
5472 Klass::clean_weak_klass_links(&_is_alive_closure);
5473 }
5474
5475 {
5476 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5477 // Clean up unreferenced symbols in symbol table.
5478 SymbolTable::unlink();
5479 }
5480
5481 {
5482 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5483 // Delete entries for dead interned strings.
5484 StringTable::unlink(&_is_alive_closure);
5485 }
5486 }
5487
5488
5489 // Restore any preserved marks as a result of mark stack or
5490 // work queue overflow
5491 restore_preserved_marks_if_any(); // done single-threaded for now
5492
5493 rp->set_enqueuing_is_done(true);
5494 if (rp->processing_is_mt()) {
5495 rp->balance_all_queues();
5496 CMSRefProcTaskExecutor task_executor(*this);
5497 rp->enqueue_discovered_references(&task_executor);
5498 } else {
5499 rp->enqueue_discovered_references(NULL);
5500 }
5501 rp->verify_no_references_recorded();
5502 assert(!rp->discovery_enabled(), "should have been disabled");
5503 }
5504
5505 #ifndef PRODUCT
5506 void CMSCollector::check_correct_thread_executing() {
5507 Thread* t = Thread::current();
5508 // Only the VM thread or the CMS thread should be here.
5509 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5510 "Unexpected thread type");
5511 // If this is the vm thread, the foreground process
5512 // should not be waiting. Note that _foregroundGCIsActive is
5513 // true while the foreground collector is waiting.
5514 if (_foregroundGCShouldWait) {
5515 // We cannot be the VM thread
5516 assert(t->is_ConcurrentGC_thread(),
5517 "Should be CMS thread");
5518 } else {
5519 // We can be the CMS thread only if we are in a stop-world
5520 // phase of CMS collection.
5521 if (t->is_ConcurrentGC_thread()) {
5522 assert(_collectorState == InitialMarking ||
5523 _collectorState == FinalMarking,
5524 "Should be a stop-world phase");
5525 // The CMS thread should be holding the CMS_token.
5526 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5527 "Potential interference with concurrently "
5528 "executing VM thread");
5529 }
5530 }
5531 }
5532 #endif
5533
5534 void CMSCollector::sweep() {
5535 assert(_collectorState == Sweeping, "just checking");
5536 check_correct_thread_executing();
5537 verify_work_stacks_empty();
5538 verify_overflow_empty();
5539 increment_sweep_count();
5540 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5541
5542 _inter_sweep_timer.stop();
5543 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5544
5545 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5546 _intra_sweep_timer.reset();
5547 _intra_sweep_timer.start();
5548 {
5549 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5550 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5551 // First sweep the old gen
5552 {
5553 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5554 bitMapLock());
5555 sweepWork(_cmsGen);
5556 }
5557
5558 // Update Universe::_heap_*_at_gc figures.
5559 // We need all the free list locks to make the abstract state
5560 // transition from Sweeping to Resetting. See detailed note
5561 // further below.
5562 {
5563 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5564 // Update heap occupancy information which is used as
5565 // input to soft ref clearing policy at the next gc.
5566 Universe::update_heap_info_at_gc();
5567 _collectorState = Resizing;
5568 }
5569 }
5570 verify_work_stacks_empty();
5571 verify_overflow_empty();
5572
5573 if (should_unload_classes()) {
5574 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5575 // requires that the virtual spaces are stable and not deleted.
5576 ClassLoaderDataGraph::set_should_purge(true);
5577 }
5578
5579 _intra_sweep_timer.stop();
5580 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5581
5582 _inter_sweep_timer.reset();
5583 _inter_sweep_timer.start();
5584
5585 // We need to use a monotonically non-decreasing time in ms
5586 // or we will see time-warp warnings and os::javaTimeMillis()
5587 // does not guarantee monotonicity.
5588 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5589 update_time_of_last_gc(now);
5590
5591 // NOTE on abstract state transitions:
5592 // Mutators allocate-live and/or mark the mod-union table dirty
5593 // based on the state of the collection. The former is done in
5594 // the interval [Marking, Sweeping] and the latter in the interval
5595 // [Marking, Sweeping). Thus the transitions into the Marking state
5596 // and out of the Sweeping state must be synchronously visible
5597 // globally to the mutators.
5598 // The transition into the Marking state happens with the world
5599 // stopped so the mutators will globally see it. Sweeping is
5600 // done asynchronously by the background collector so the transition
5601 // from the Sweeping state to the Resizing state must be done
5602 // under the freelistLock (as is the check for whether to
5603 // allocate-live and whether to dirty the mod-union table).
5604 assert(_collectorState == Resizing, "Change of collector state to"
5605 " Resizing must be done under the freelistLocks (plural)");
5606
5607 // Now that sweeping has been completed, we clear
5608 // the incremental_collection_failed flag,
5609 // thus inviting a younger gen collection to promote into
5610 // this generation. If such a promotion may still fail,
5611 // the flag will be set again when a young collection is
5612 // attempted.
5613 GenCollectedHeap* gch = GenCollectedHeap::heap();
5614 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5615 gch->update_full_collections_completed(_collection_count_start);
5616 }
5617
5618 // FIX ME!!! Looks like this belongs in CFLSpace, with
5619 // CMSGen merely delegating to it.
5620 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5621 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5622 HeapWord* minAddr = _cmsSpace->bottom();
5623 HeapWord* largestAddr =
5624 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5625 if (largestAddr == NULL) {
5626 // The dictionary appears to be empty. In this case
5627 // try to coalesce at the end of the heap.
5628 largestAddr = _cmsSpace->end();
5629 }
5630 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5631 size_t nearLargestOffset =
5632 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5633 if (PrintFLSStatistics != 0) {
5634 gclog_or_tty->print_cr(
5635 "CMS: Large Block: " PTR_FORMAT ";"
5636 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5637 p2i(largestAddr),
5638 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5639 }
5640 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5641 }
5642
5643 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5644 return addr >= _cmsSpace->nearLargestChunk();
5645 }
5646
5647 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5648 return _cmsSpace->find_chunk_at_end();
5649 }
5650
5651 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5652 bool full) {
5653 // The next lower level has been collected. Gather any statistics
5654 // that are of interest at this point.
5655 if (!full && (current_level + 1) == level()) {
5656 // Gather statistics on the young generation collection.
5657 collector()->stats().record_gc0_end(used());
5658 }
5659 }
5660
5661 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen) {
5662 // We iterate over the space(s) underlying this generation,
5663 // checking the mark bit map to see if the bits corresponding
5664 // to specific blocks are marked or not. Blocks that are
5665 // marked are live and are not swept up. All remaining blocks
5666 // are swept up, with coalescing on-the-fly as we sweep up
5667 // contiguous free and/or garbage blocks:
5668 // We need to ensure that the sweeper synchronizes with allocators
5669 // and stop-the-world collectors. In particular, the following
5670 // locks are used:
5671 // . CMS token: if this is held, a stop the world collection cannot occur
5672 // . freelistLock: if this is held no allocation can occur from this
5673 // generation by another thread
5674 // . bitMapLock: if this is held, no other thread can access or update
5675 //
5676
5677 // Note that we need to hold the freelistLock if we use
5678 // block iterate below; else the iterator might go awry if
5679 // a mutator (or promotion) causes block contents to change
5680 // (for instance if the allocator divvies up a block).
5681 // If we hold the free list lock, for all practical purposes
5682 // young generation GC's can't occur (they'll usually need to
5683 // promote), so we might as well prevent all young generation
5684 // GC's while we do a sweeping step. For the same reason, we might
5685 // as well take the bit map lock for the entire duration
5686
5687 // check that we hold the requisite locks
5688 assert(have_cms_token(), "Should hold cms token");
5689 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5690 assert_lock_strong(gen->freelistLock());
5691 assert_lock_strong(bitMapLock());
5692
5693 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5694 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5695 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5696 _inter_sweep_estimate.padded_average(),
5697 _intra_sweep_estimate.padded_average());
5698 gen->setNearLargestChunk();
5699
5700 {
5701 SweepClosure sweepClosure(this, gen, &_markBitMap, CMSYield);
5702 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5703 // We need to free-up/coalesce garbage/blocks from a
5704 // co-terminal free run. This is done in the SweepClosure
5705 // destructor; so, do not remove this scope, else the
5706 // end-of-sweep-census below will be off by a little bit.
5707 }
5708 gen->cmsSpace()->sweep_completed();
5709 gen->cmsSpace()->endSweepFLCensus(sweep_count());
5710 if (should_unload_classes()) { // unloaded classes this cycle,
5711 _concurrent_cycles_since_last_unload = 0; // ... reset count
5712 } else { // did not unload classes,
5713 _concurrent_cycles_since_last_unload++; // ... increment count
5714 }
5715 }
5716
5717 // Reset CMS data structures (for now just the marking bit map)
5718 // preparatory for the next cycle.
5719 void CMSCollector::reset(bool concurrent) {
5720 if (concurrent) {
5721 CMSTokenSyncWithLocks ts(true, bitMapLock());
5722
5723 // If the state is not "Resetting", the foreground thread
5724 // has done a collection and the resetting.
5725 if (_collectorState != Resetting) {
5726 assert(_collectorState == Idling, "The state should only change"
5727 " because the foreground collector has finished the collection");
5728 return;
5729 }
5730
5731 // Clear the mark bitmap (no grey objects to start with)
5732 // for the next cycle.
5733 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5734 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
5735
5736 HeapWord* curAddr = _markBitMap.startWord();
5737 while (curAddr < _markBitMap.endWord()) {
5738 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5739 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5740 _markBitMap.clear_large_range(chunk);
5741 if (ConcurrentMarkSweepThread::should_yield() &&
5742 !foregroundGCIsActive() &&
5743 CMSYield) {
5744 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5745 "CMS thread should hold CMS token");
5746 assert_lock_strong(bitMapLock());
5747 bitMapLock()->unlock();
5748 ConcurrentMarkSweepThread::desynchronize(true);
5749 stopTimer();
5750 if (PrintCMSStatistics != 0) {
5751 incrementYields();
5752 }
5753
5754 // See the comment in coordinator_yield()
5755 for (unsigned i = 0; i < CMSYieldSleepCount &&
5756 ConcurrentMarkSweepThread::should_yield() &&
5757 !CMSCollector::foregroundGCIsActive(); ++i) {
5758 os::sleep(Thread::current(), 1, false);
5759 }
5760
5761 ConcurrentMarkSweepThread::synchronize(true);
5762 bitMapLock()->lock_without_safepoint_check();
5763 startTimer();
5764 }
5765 curAddr = chunk.end();
5766 }
5767 // A successful mostly concurrent collection has been done.
5768 // Because only the full (i.e., concurrent mode failure) collections
5769 // are being measured for gc overhead limits, clean the "near" flag
5770 // and count.
5771 size_policy()->reset_gc_overhead_limit_count();
5772 _collectorState = Idling;
5773 } else {
5774 // already have the lock
5775 assert(_collectorState == Resetting, "just checking");
5776 assert_lock_strong(bitMapLock());
5777 _markBitMap.clear_all();
5778 _collectorState = Idling;
5779 }
5780
5781 register_gc_end();
5782 }
5783
5784 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5785 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5786 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
5787 TraceCollectorStats tcs(counters());
5788
5789 switch (op) {
5790 case CMS_op_checkpointRootsInitial: {
5791 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5792 checkpointRootsInitial();
5793 if (PrintGC) {
5794 _cmsGen->printOccupancy("initial-mark");
5795 }
5796 break;
5797 }
5798 case CMS_op_checkpointRootsFinal: {
5799 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5800 checkpointRootsFinal();
5801 if (PrintGC) {
5802 _cmsGen->printOccupancy("remark");
5803 }
5804 break;
5805 }
5806 default:
5807 fatal("No such CMS_op");
5808 }
5809 }
5810
5811 #ifndef PRODUCT
5812 size_t const CMSCollector::skip_header_HeapWords() {
5813 return FreeChunk::header_size();
5814 }
5815
5816 // Try and collect here conditions that should hold when
5817 // CMS thread is exiting. The idea is that the foreground GC
5818 // thread should not be blocked if it wants to terminate
5819 // the CMS thread and yet continue to run the VM for a while
5820 // after that.
5821 void CMSCollector::verify_ok_to_terminate() const {
5822 assert(Thread::current()->is_ConcurrentGC_thread(),
5823 "should be called by CMS thread");
5824 assert(!_foregroundGCShouldWait, "should be false");
5825 // We could check here that all the various low-level locks
5826 // are not held by the CMS thread, but that is overkill; see
5827 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5828 // is checked.
5829 }
5830 #endif
5831
5832 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5833 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5834 "missing Printezis mark?");
5835 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5836 size_t size = pointer_delta(nextOneAddr + 1, addr);
5837 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5838 "alignment problem");
5839 assert(size >= 3, "Necessary for Printezis marks to work");
5840 return size;
5841 }
5842
5843 // A variant of the above (block_size_using_printezis_bits()) except
5844 // that we return 0 if the P-bits are not yet set.
5845 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5846 if (_markBitMap.isMarked(addr + 1)) {
5847 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5848 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5849 size_t size = pointer_delta(nextOneAddr + 1, addr);
5850 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5851 "alignment problem");
5852 assert(size >= 3, "Necessary for Printezis marks to work");
5853 return size;
5854 }
5855 return 0;
5856 }
5857
5858 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5859 size_t sz = 0;
5860 oop p = (oop)addr;
5861 if (p->klass_or_null() != NULL) {
5862 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5863 } else {
5864 sz = block_size_using_printezis_bits(addr);
5865 }
5866 assert(sz > 0, "size must be nonzero");
5867 HeapWord* next_block = addr + sz;
5868 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5869 CardTableModRefBS::card_size);
5870 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5871 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5872 "must be different cards");
5873 return next_card;
5874 }
5875
5876
5877 // CMS Bit Map Wrapper /////////////////////////////////////////
5878
5879 // Construct a CMS bit map infrastructure, but don't create the
5880 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5881 // further below.
5882 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5883 _bm(),
5884 _shifter(shifter),
5885 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5886 Monitor::_safepoint_check_sometimes) : NULL)
5887 {
5888 _bmStartWord = 0;
5889 _bmWordSize = 0;
5890 }
5891
5892 bool CMSBitMap::allocate(MemRegion mr) {
5893 _bmStartWord = mr.start();
5894 _bmWordSize = mr.word_size();
5895 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5896 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5897 if (!brs.is_reserved()) {
5898 warning("CMS bit map allocation failure");
5899 return false;
5900 }
5901 // For now we'll just commit all of the bit map up front.
5902 // Later on we'll try to be more parsimonious with swap.
5903 if (!_virtual_space.initialize(brs, brs.size())) {
5904 warning("CMS bit map backing store failure");
5905 return false;
5906 }
5907 assert(_virtual_space.committed_size() == brs.size(),
5908 "didn't reserve backing store for all of CMS bit map?");
5909 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5910 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5911 _bmWordSize, "inconsistency in bit map sizing");
5912 _bm.set_size(_bmWordSize >> _shifter);
5913
5914 // bm.clear(); // can we rely on getting zero'd memory? verify below
5915 assert(isAllClear(),
5916 "Expected zero'd memory from ReservedSpace constructor");
5917 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5918 "consistency check");
5919 return true;
5920 }
5921
5922 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5923 HeapWord *next_addr, *end_addr, *last_addr;
5924 assert_locked();
5925 assert(covers(mr), "out-of-range error");
5926 // XXX assert that start and end are appropriately aligned
5927 for (next_addr = mr.start(), end_addr = mr.end();
5928 next_addr < end_addr; next_addr = last_addr) {
5929 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5930 last_addr = dirty_region.end();
5931 if (!dirty_region.is_empty()) {
5932 cl->do_MemRegion(dirty_region);
5933 } else {
5934 assert(last_addr == end_addr, "program logic");
5935 return;
5936 }
5937 }
5938 }
5939
5940 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5941 _bm.print_on_error(st, prefix);
5942 }
5943
5944 #ifndef PRODUCT
5945 void CMSBitMap::assert_locked() const {
5946 CMSLockVerifier::assert_locked(lock());
5947 }
5948
5949 bool CMSBitMap::covers(MemRegion mr) const {
5950 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5951 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5952 "size inconsistency");
5953 return (mr.start() >= _bmStartWord) &&
5954 (mr.end() <= endWord());
5955 }
5956
5957 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5958 return (start >= _bmStartWord && (start + size) <= endWord());
5959 }
5960
5961 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5962 // verify that there are no 1 bits in the interval [left, right)
5963 FalseBitMapClosure falseBitMapClosure;
5964 iterate(&falseBitMapClosure, left, right);
5965 }
5966
5967 void CMSBitMap::region_invariant(MemRegion mr)
5968 {
5969 assert_locked();
5970 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5971 assert(!mr.is_empty(), "unexpected empty region");
5972 assert(covers(mr), "mr should be covered by bit map");
5973 // convert address range into offset range
5974 size_t start_ofs = heapWordToOffset(mr.start());
5975 // Make sure that end() is appropriately aligned
5976 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5977 (1 << (_shifter+LogHeapWordSize))),
5978 "Misaligned mr.end()");
5979 size_t end_ofs = heapWordToOffset(mr.end());
5980 assert(end_ofs > start_ofs, "Should mark at least one bit");
5981 }
5982
5983 #endif
5984
5985 bool CMSMarkStack::allocate(size_t size) {
5986 // allocate a stack of the requisite depth
5987 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5988 size * sizeof(oop)));
5989 if (!rs.is_reserved()) {
5990 warning("CMSMarkStack allocation failure");
5991 return false;
5992 }
5993 if (!_virtual_space.initialize(rs, rs.size())) {
5994 warning("CMSMarkStack backing store failure");
5995 return false;
5996 }
5997 assert(_virtual_space.committed_size() == rs.size(),
5998 "didn't reserve backing store for all of CMS stack?");
5999 _base = (oop*)(_virtual_space.low());
6000 _index = 0;
6001 _capacity = size;
6002 NOT_PRODUCT(_max_depth = 0);
6003 return true;
6004 }
6005
6006 // XXX FIX ME !!! In the MT case we come in here holding a
6007 // leaf lock. For printing we need to take a further lock
6008 // which has lower rank. We need to recalibrate the two
6009 // lock-ranks involved in order to be able to print the
6010 // messages below. (Or defer the printing to the caller.
6011 // For now we take the expedient path of just disabling the
6012 // messages for the problematic case.)
6013 void CMSMarkStack::expand() {
6014 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6015 if (_capacity == MarkStackSizeMax) {
6016 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6017 // We print a warning message only once per CMS cycle.
6018 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6019 }
6020 return;
6021 }
6022 // Double capacity if possible
6023 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6024 // Do not give up existing stack until we have managed to
6025 // get the double capacity that we desired.
6026 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6027 new_capacity * sizeof(oop)));
6028 if (rs.is_reserved()) {
6029 // Release the backing store associated with old stack
6030 _virtual_space.release();
6031 // Reinitialize virtual space for new stack
6032 if (!_virtual_space.initialize(rs, rs.size())) {
6033 fatal("Not enough swap for expanded marking stack");
6034 }
6035 _base = (oop*)(_virtual_space.low());
6036 _index = 0;
6037 _capacity = new_capacity;
6038 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6039 // Failed to double capacity, continue;
6040 // we print a detail message only once per CMS cycle.
6041 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6042 SIZE_FORMAT "K",
6043 _capacity / K, new_capacity / K);
6044 }
6045 }
6046
6047
6048 // Closures
6049 // XXX: there seems to be a lot of code duplication here;
6050 // should refactor and consolidate common code.
6051
6052 // This closure is used to mark refs into the CMS generation in
6053 // the CMS bit map. Called at the first checkpoint. This closure
6054 // assumes that we do not need to re-mark dirty cards; if the CMS
6055 // generation on which this is used is not an oldest
6056 // generation then this will lose younger_gen cards!
6057
6058 MarkRefsIntoClosure::MarkRefsIntoClosure(
6059 MemRegion span, CMSBitMap* bitMap):
6060 _span(span),
6061 _bitMap(bitMap)
6062 {
6063 assert(_ref_processor == NULL, "deliberately left NULL");
6064 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6065 }
6066
6067 void MarkRefsIntoClosure::do_oop(oop obj) {
6068 // if p points into _span, then mark corresponding bit in _markBitMap
6069 assert(obj->is_oop(), "expected an oop");
6070 HeapWord* addr = (HeapWord*)obj;
6071 if (_span.contains(addr)) {
6072 // this should be made more efficient
6073 _bitMap->mark(addr);
6074 }
6075 }
6076
6077 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6078 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6079
6080 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6081 MemRegion span, CMSBitMap* bitMap):
6082 _span(span),
6083 _bitMap(bitMap)
6084 {
6085 assert(_ref_processor == NULL, "deliberately left NULL");
6086 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6087 }
6088
6089 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6090 // if p points into _span, then mark corresponding bit in _markBitMap
6091 assert(obj->is_oop(), "expected an oop");
6092 HeapWord* addr = (HeapWord*)obj;
6093 if (_span.contains(addr)) {
6094 // this should be made more efficient
6095 _bitMap->par_mark(addr);
6096 }
6097 }
6098
6099 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6100 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6101
6102 // A variant of the above, used for CMS marking verification.
6103 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6104 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6105 _span(span),
6106 _verification_bm(verification_bm),
6107 _cms_bm(cms_bm)
6108 {
6109 assert(_ref_processor == NULL, "deliberately left NULL");
6110 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6111 }
6112
6113 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6114 // if p points into _span, then mark corresponding bit in _markBitMap
6115 assert(obj->is_oop(), "expected an oop");
6116 HeapWord* addr = (HeapWord*)obj;
6117 if (_span.contains(addr)) {
6118 _verification_bm->mark(addr);
6119 if (!_cms_bm->isMarked(addr)) {
6120 oop(addr)->print();
6121 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6122 fatal("... aborting");
6123 }
6124 }
6125 }
6126
6127 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6128 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6129
6130 //////////////////////////////////////////////////
6131 // MarkRefsIntoAndScanClosure
6132 //////////////////////////////////////////////////
6133
6134 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6135 ReferenceProcessor* rp,
6136 CMSBitMap* bit_map,
6137 CMSBitMap* mod_union_table,
6138 CMSMarkStack* mark_stack,
6139 CMSCollector* collector,
6140 bool should_yield,
6141 bool concurrent_precleaning):
6142 _collector(collector),
6143 _span(span),
6144 _bit_map(bit_map),
6145 _mark_stack(mark_stack),
6146 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6147 mark_stack, concurrent_precleaning),
6148 _yield(should_yield),
6149 _concurrent_precleaning(concurrent_precleaning),
6150 _freelistLock(NULL)
6151 {
6152 _ref_processor = rp;
6153 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6154 }
6155
6156 // This closure is used to mark refs into the CMS generation at the
6157 // second (final) checkpoint, and to scan and transitively follow
6158 // the unmarked oops. It is also used during the concurrent precleaning
6159 // phase while scanning objects on dirty cards in the CMS generation.
6160 // The marks are made in the marking bit map and the marking stack is
6161 // used for keeping the (newly) grey objects during the scan.
6162 // The parallel version (Par_...) appears further below.
6163 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6164 if (obj != NULL) {
6165 assert(obj->is_oop(), "expected an oop");
6166 HeapWord* addr = (HeapWord*)obj;
6167 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6168 assert(_collector->overflow_list_is_empty(),
6169 "overflow list should be empty");
6170 if (_span.contains(addr) &&
6171 !_bit_map->isMarked(addr)) {
6172 // mark bit map (object is now grey)
6173 _bit_map->mark(addr);
6174 // push on marking stack (stack should be empty), and drain the
6175 // stack by applying this closure to the oops in the oops popped
6176 // from the stack (i.e. blacken the grey objects)
6177 bool res = _mark_stack->push(obj);
6178 assert(res, "Should have space to push on empty stack");
6179 do {
6180 oop new_oop = _mark_stack->pop();
6181 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6182 assert(_bit_map->isMarked((HeapWord*)new_oop),
6183 "only grey objects on this stack");
6184 // iterate over the oops in this oop, marking and pushing
6185 // the ones in CMS heap (i.e. in _span).
6186 new_oop->oop_iterate(&_pushAndMarkClosure);
6187 // check if it's time to yield
6188 do_yield_check();
6189 } while (!_mark_stack->isEmpty() ||
6190 (!_concurrent_precleaning && take_from_overflow_list()));
6191 // if marking stack is empty, and we are not doing this
6192 // during precleaning, then check the overflow list
6193 }
6194 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6195 assert(_collector->overflow_list_is_empty(),
6196 "overflow list was drained above");
6197 // We could restore evacuated mark words, if any, used for
6198 // overflow list links here because the overflow list is
6199 // provably empty here. That would reduce the maximum
6200 // size requirements for preserved_{oop,mark}_stack.
6201 // But we'll just postpone it until we are all done
6202 // so we can just stream through.
6203 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6204 _collector->restore_preserved_marks_if_any();
6205 assert(_collector->no_preserved_marks(), "No preserved marks");
6206 }
6207 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6208 "All preserved marks should have been restored above");
6209 }
6210 }
6211
6212 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6213 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6214
6215 void MarkRefsIntoAndScanClosure::do_yield_work() {
6216 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6217 "CMS thread should hold CMS token");
6218 assert_lock_strong(_freelistLock);
6219 assert_lock_strong(_bit_map->lock());
6220 // relinquish the free_list_lock and bitMaplock()
6221 _bit_map->lock()->unlock();
6222 _freelistLock->unlock();
6223 ConcurrentMarkSweepThread::desynchronize(true);
6224 _collector->stopTimer();
6225 if (PrintCMSStatistics != 0) {
6226 _collector->incrementYields();
6227 }
6228
6229 // See the comment in coordinator_yield()
6230 for (unsigned i = 0;
6231 i < CMSYieldSleepCount &&
6232 ConcurrentMarkSweepThread::should_yield() &&
6233 !CMSCollector::foregroundGCIsActive();
6234 ++i) {
6235 os::sleep(Thread::current(), 1, false);
6236 }
6237
6238 ConcurrentMarkSweepThread::synchronize(true);
6239 _freelistLock->lock_without_safepoint_check();
6240 _bit_map->lock()->lock_without_safepoint_check();
6241 _collector->startTimer();
6242 }
6243
6244 ///////////////////////////////////////////////////////////
6245 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6246 // MarkRefsIntoAndScanClosure
6247 ///////////////////////////////////////////////////////////
6248 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6249 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6250 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6251 _span(span),
6252 _bit_map(bit_map),
6253 _work_queue(work_queue),
6254 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6255 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6256 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6257 {
6258 _ref_processor = rp;
6259 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6260 }
6261
6262 // This closure is used to mark refs into the CMS generation at the
6263 // second (final) checkpoint, and to scan and transitively follow
6264 // the unmarked oops. The marks are made in the marking bit map and
6265 // the work_queue is used for keeping the (newly) grey objects during
6266 // the scan phase whence they are also available for stealing by parallel
6267 // threads. Since the marking bit map is shared, updates are
6268 // synchronized (via CAS).
6269 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6270 if (obj != NULL) {
6271 // Ignore mark word because this could be an already marked oop
6272 // that may be chained at the end of the overflow list.
6273 assert(obj->is_oop(true), "expected an oop");
6274 HeapWord* addr = (HeapWord*)obj;
6275 if (_span.contains(addr) &&
6276 !_bit_map->isMarked(addr)) {
6277 // mark bit map (object will become grey):
6278 // It is possible for several threads to be
6279 // trying to "claim" this object concurrently;
6280 // the unique thread that succeeds in marking the
6281 // object first will do the subsequent push on
6282 // to the work queue (or overflow list).
6283 if (_bit_map->par_mark(addr)) {
6284 // push on work_queue (which may not be empty), and trim the
6285 // queue to an appropriate length by applying this closure to
6286 // the oops in the oops popped from the stack (i.e. blacken the
6287 // grey objects)
6288 bool res = _work_queue->push(obj);
6289 assert(res, "Low water mark should be less than capacity?");
6290 trim_queue(_low_water_mark);
6291 } // Else, another thread claimed the object
6292 }
6293 }
6294 }
6295
6296 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6297 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6298
6299 // This closure is used to rescan the marked objects on the dirty cards
6300 // in the mod union table and the card table proper.
6301 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6302 oop p, MemRegion mr) {
6303
6304 size_t size = 0;
6305 HeapWord* addr = (HeapWord*)p;
6306 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6307 assert(_span.contains(addr), "we are scanning the CMS generation");
6308 // check if it's time to yield
6309 if (do_yield_check()) {
6310 // We yielded for some foreground stop-world work,
6311 // and we have been asked to abort this ongoing preclean cycle.
6312 return 0;
6313 }
6314 if (_bitMap->isMarked(addr)) {
6315 // it's marked; is it potentially uninitialized?
6316 if (p->klass_or_null() != NULL) {
6317 // an initialized object; ignore mark word in verification below
6318 // since we are running concurrent with mutators
6319 assert(p->is_oop(true), "should be an oop");
6320 if (p->is_objArray()) {
6321 // objArrays are precisely marked; restrict scanning
6322 // to dirty cards only.
6323 size = CompactibleFreeListSpace::adjustObjectSize(
6324 p->oop_iterate(_scanningClosure, mr));
6325 } else {
6326 // A non-array may have been imprecisely marked; we need
6327 // to scan object in its entirety.
6328 size = CompactibleFreeListSpace::adjustObjectSize(
6329 p->oop_iterate(_scanningClosure));
6330 }
6331 #ifdef ASSERT
6332 size_t direct_size =
6333 CompactibleFreeListSpace::adjustObjectSize(p->size());
6334 assert(size == direct_size, "Inconsistency in size");
6335 assert(size >= 3, "Necessary for Printezis marks to work");
6336 if (!_bitMap->isMarked(addr+1)) {
6337 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6338 } else {
6339 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6340 assert(_bitMap->isMarked(addr+size-1),
6341 "inconsistent Printezis mark");
6342 }
6343 #endif // ASSERT
6344 } else {
6345 // An uninitialized object.
6346 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6347 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6348 size = pointer_delta(nextOneAddr + 1, addr);
6349 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6350 "alignment problem");
6351 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6352 // will dirty the card when the klass pointer is installed in the
6353 // object (signaling the completion of initialization).
6354 }
6355 } else {
6356 // Either a not yet marked object or an uninitialized object
6357 if (p->klass_or_null() == NULL) {
6358 // An uninitialized object, skip to the next card, since
6359 // we may not be able to read its P-bits yet.
6360 assert(size == 0, "Initial value");
6361 } else {
6362 // An object not (yet) reached by marking: we merely need to
6363 // compute its size so as to go look at the next block.
6364 assert(p->is_oop(true), "should be an oop");
6365 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6366 }
6367 }
6368 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6369 return size;
6370 }
6371
6372 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6373 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6374 "CMS thread should hold CMS token");
6375 assert_lock_strong(_freelistLock);
6376 assert_lock_strong(_bitMap->lock());
6377 // relinquish the free_list_lock and bitMaplock()
6378 _bitMap->lock()->unlock();
6379 _freelistLock->unlock();
6380 ConcurrentMarkSweepThread::desynchronize(true);
6381 _collector->stopTimer();
6382 if (PrintCMSStatistics != 0) {
6383 _collector->incrementYields();
6384 }
6385
6386 // See the comment in coordinator_yield()
6387 for (unsigned i = 0; i < CMSYieldSleepCount &&
6388 ConcurrentMarkSweepThread::should_yield() &&
6389 !CMSCollector::foregroundGCIsActive(); ++i) {
6390 os::sleep(Thread::current(), 1, false);
6391 }
6392
6393 ConcurrentMarkSweepThread::synchronize(true);
6394 _freelistLock->lock_without_safepoint_check();
6395 _bitMap->lock()->lock_without_safepoint_check();
6396 _collector->startTimer();
6397 }
6398
6399
6400 //////////////////////////////////////////////////////////////////
6401 // SurvivorSpacePrecleanClosure
6402 //////////////////////////////////////////////////////////////////
6403 // This (single-threaded) closure is used to preclean the oops in
6404 // the survivor spaces.
6405 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6406
6407 HeapWord* addr = (HeapWord*)p;
6408 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6409 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6410 assert(p->klass_or_null() != NULL, "object should be initialized");
6411 // an initialized object; ignore mark word in verification below
6412 // since we are running concurrent with mutators
6413 assert(p->is_oop(true), "should be an oop");
6414 // Note that we do not yield while we iterate over
6415 // the interior oops of p, pushing the relevant ones
6416 // on our marking stack.
6417 size_t size = p->oop_iterate(_scanning_closure);
6418 do_yield_check();
6419 // Observe that below, we do not abandon the preclean
6420 // phase as soon as we should; rather we empty the
6421 // marking stack before returning. This is to satisfy
6422 // some existing assertions. In general, it may be a
6423 // good idea to abort immediately and complete the marking
6424 // from the grey objects at a later time.
6425 while (!_mark_stack->isEmpty()) {
6426 oop new_oop = _mark_stack->pop();
6427 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6428 assert(_bit_map->isMarked((HeapWord*)new_oop),
6429 "only grey objects on this stack");
6430 // iterate over the oops in this oop, marking and pushing
6431 // the ones in CMS heap (i.e. in _span).
6432 new_oop->oop_iterate(_scanning_closure);
6433 // check if it's time to yield
6434 do_yield_check();
6435 }
6436 unsigned int after_count =
6437 GenCollectedHeap::heap()->total_collections();
6438 bool abort = (_before_count != after_count) ||
6439 _collector->should_abort_preclean();
6440 return abort ? 0 : size;
6441 }
6442
6443 void SurvivorSpacePrecleanClosure::do_yield_work() {
6444 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6445 "CMS thread should hold CMS token");
6446 assert_lock_strong(_bit_map->lock());
6447 // Relinquish the bit map lock
6448 _bit_map->lock()->unlock();
6449 ConcurrentMarkSweepThread::desynchronize(true);
6450 _collector->stopTimer();
6451 if (PrintCMSStatistics != 0) {
6452 _collector->incrementYields();
6453 }
6454
6455 // See the comment in coordinator_yield()
6456 for (unsigned i = 0; i < CMSYieldSleepCount &&
6457 ConcurrentMarkSweepThread::should_yield() &&
6458 !CMSCollector::foregroundGCIsActive(); ++i) {
6459 os::sleep(Thread::current(), 1, false);
6460 }
6461
6462 ConcurrentMarkSweepThread::synchronize(true);
6463 _bit_map->lock()->lock_without_safepoint_check();
6464 _collector->startTimer();
6465 }
6466
6467 // This closure is used to rescan the marked objects on the dirty cards
6468 // in the mod union table and the card table proper. In the parallel
6469 // case, although the bitMap is shared, we do a single read so the
6470 // isMarked() query is "safe".
6471 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6472 // Ignore mark word because we are running concurrent with mutators
6473 assert(p->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(p)));
6474 HeapWord* addr = (HeapWord*)p;
6475 assert(_span.contains(addr), "we are scanning the CMS generation");
6476 bool is_obj_array = false;
6477 #ifdef ASSERT
6478 if (!_parallel) {
6479 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6480 assert(_collector->overflow_list_is_empty(),
6481 "overflow list should be empty");
6482
6483 }
6484 #endif // ASSERT
6485 if (_bit_map->isMarked(addr)) {
6486 // Obj arrays are precisely marked, non-arrays are not;
6487 // so we scan objArrays precisely and non-arrays in their
6488 // entirety.
6489 if (p->is_objArray()) {
6490 is_obj_array = true;
6491 if (_parallel) {
6492 p->oop_iterate(_par_scan_closure, mr);
6493 } else {
6494 p->oop_iterate(_scan_closure, mr);
6495 }
6496 } else {
6497 if (_parallel) {
6498 p->oop_iterate(_par_scan_closure);
6499 } else {
6500 p->oop_iterate(_scan_closure);
6501 }
6502 }
6503 }
6504 #ifdef ASSERT
6505 if (!_parallel) {
6506 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6507 assert(_collector->overflow_list_is_empty(),
6508 "overflow list should be empty");
6509
6510 }
6511 #endif // ASSERT
6512 return is_obj_array;
6513 }
6514
6515 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6516 MemRegion span,
6517 CMSBitMap* bitMap, CMSMarkStack* markStack,
6518 bool should_yield, bool verifying):
6519 _collector(collector),
6520 _span(span),
6521 _bitMap(bitMap),
6522 _mut(&collector->_modUnionTable),
6523 _markStack(markStack),
6524 _yield(should_yield),
6525 _skipBits(0)
6526 {
6527 assert(_markStack->isEmpty(), "stack should be empty");
6528 _finger = _bitMap->startWord();
6529 _threshold = _finger;
6530 assert(_collector->_restart_addr == NULL, "Sanity check");
6531 assert(_span.contains(_finger), "Out of bounds _finger?");
6532 DEBUG_ONLY(_verifying = verifying;)
6533 }
6534
6535 void MarkFromRootsClosure::reset(HeapWord* addr) {
6536 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6537 assert(_span.contains(addr), "Out of bounds _finger?");
6538 _finger = addr;
6539 _threshold = (HeapWord*)round_to(
6540 (intptr_t)_finger, CardTableModRefBS::card_size);
6541 }
6542
6543 // Should revisit to see if this should be restructured for
6544 // greater efficiency.
6545 bool MarkFromRootsClosure::do_bit(size_t offset) {
6546 if (_skipBits > 0) {
6547 _skipBits--;
6548 return true;
6549 }
6550 // convert offset into a HeapWord*
6551 HeapWord* addr = _bitMap->startWord() + offset;
6552 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6553 "address out of range");
6554 assert(_bitMap->isMarked(addr), "tautology");
6555 if (_bitMap->isMarked(addr+1)) {
6556 // this is an allocated but not yet initialized object
6557 assert(_skipBits == 0, "tautology");
6558 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6559 oop p = oop(addr);
6560 if (p->klass_or_null() == NULL) {
6561 DEBUG_ONLY(if (!_verifying) {)
6562 // We re-dirty the cards on which this object lies and increase
6563 // the _threshold so that we'll come back to scan this object
6564 // during the preclean or remark phase. (CMSCleanOnEnter)
6565 if (CMSCleanOnEnter) {
6566 size_t sz = _collector->block_size_using_printezis_bits(addr);
6567 HeapWord* end_card_addr = (HeapWord*)round_to(
6568 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6569 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6570 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6571 // Bump _threshold to end_card_addr; note that
6572 // _threshold cannot possibly exceed end_card_addr, anyhow.
6573 // This prevents future clearing of the card as the scan proceeds
6574 // to the right.
6575 assert(_threshold <= end_card_addr,
6576 "Because we are just scanning into this object");
6577 if (_threshold < end_card_addr) {
6578 _threshold = end_card_addr;
6579 }
6580 if (p->klass_or_null() != NULL) {
6581 // Redirty the range of cards...
6582 _mut->mark_range(redirty_range);
6583 } // ...else the setting of klass will dirty the card anyway.
6584 }
6585 DEBUG_ONLY(})
6586 return true;
6587 }
6588 }
6589 scanOopsInOop(addr);
6590 return true;
6591 }
6592
6593 // We take a break if we've been at this for a while,
6594 // so as to avoid monopolizing the locks involved.
6595 void MarkFromRootsClosure::do_yield_work() {
6596 // First give up the locks, then yield, then re-lock
6597 // We should probably use a constructor/destructor idiom to
6598 // do this unlock/lock or modify the MutexUnlocker class to
6599 // serve our purpose. XXX
6600 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6601 "CMS thread should hold CMS token");
6602 assert_lock_strong(_bitMap->lock());
6603 _bitMap->lock()->unlock();
6604 ConcurrentMarkSweepThread::desynchronize(true);
6605 _collector->stopTimer();
6606 if (PrintCMSStatistics != 0) {
6607 _collector->incrementYields();
6608 }
6609
6610 // See the comment in coordinator_yield()
6611 for (unsigned i = 0; i < CMSYieldSleepCount &&
6612 ConcurrentMarkSweepThread::should_yield() &&
6613 !CMSCollector::foregroundGCIsActive(); ++i) {
6614 os::sleep(Thread::current(), 1, false);
6615 }
6616
6617 ConcurrentMarkSweepThread::synchronize(true);
6618 _bitMap->lock()->lock_without_safepoint_check();
6619 _collector->startTimer();
6620 }
6621
6622 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6623 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6624 assert(_markStack->isEmpty(),
6625 "should drain stack to limit stack usage");
6626 // convert ptr to an oop preparatory to scanning
6627 oop obj = oop(ptr);
6628 // Ignore mark word in verification below, since we
6629 // may be running concurrent with mutators.
6630 assert(obj->is_oop(true), "should be an oop");
6631 assert(_finger <= ptr, "_finger runneth ahead");
6632 // advance the finger to right end of this object
6633 _finger = ptr + obj->size();
6634 assert(_finger > ptr, "we just incremented it above");
6635 // On large heaps, it may take us some time to get through
6636 // the marking phase. During
6637 // this time it's possible that a lot of mutations have
6638 // accumulated in the card table and the mod union table --
6639 // these mutation records are redundant until we have
6640 // actually traced into the corresponding card.
6641 // Here, we check whether advancing the finger would make
6642 // us cross into a new card, and if so clear corresponding
6643 // cards in the MUT (preclean them in the card-table in the
6644 // future).
6645
6646 DEBUG_ONLY(if (!_verifying) {)
6647 // The clean-on-enter optimization is disabled by default,
6648 // until we fix 6178663.
6649 if (CMSCleanOnEnter && (_finger > _threshold)) {
6650 // [_threshold, _finger) represents the interval
6651 // of cards to be cleared in MUT (or precleaned in card table).
6652 // The set of cards to be cleared is all those that overlap
6653 // with the interval [_threshold, _finger); note that
6654 // _threshold is always kept card-aligned but _finger isn't
6655 // always card-aligned.
6656 HeapWord* old_threshold = _threshold;
6657 assert(old_threshold == (HeapWord*)round_to(
6658 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6659 "_threshold should always be card-aligned");
6660 _threshold = (HeapWord*)round_to(
6661 (intptr_t)_finger, CardTableModRefBS::card_size);
6662 MemRegion mr(old_threshold, _threshold);
6663 assert(!mr.is_empty(), "Control point invariant");
6664 assert(_span.contains(mr), "Should clear within span");
6665 _mut->clear_range(mr);
6666 }
6667 DEBUG_ONLY(})
6668 // Note: the finger doesn't advance while we drain
6669 // the stack below.
6670 PushOrMarkClosure pushOrMarkClosure(_collector,
6671 _span, _bitMap, _markStack,
6672 _finger, this);
6673 bool res = _markStack->push(obj);
6674 assert(res, "Empty non-zero size stack should have space for single push");
6675 while (!_markStack->isEmpty()) {
6676 oop new_oop = _markStack->pop();
6677 // Skip verifying header mark word below because we are
6678 // running concurrent with mutators.
6679 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6680 // now scan this oop's oops
6681 new_oop->oop_iterate(&pushOrMarkClosure);
6682 do_yield_check();
6683 }
6684 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6685 }
6686
6687 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6688 CMSCollector* collector, MemRegion span,
6689 CMSBitMap* bit_map,
6690 OopTaskQueue* work_queue,
6691 CMSMarkStack* overflow_stack):
6692 _collector(collector),
6693 _whole_span(collector->_span),
6694 _span(span),
6695 _bit_map(bit_map),
6696 _mut(&collector->_modUnionTable),
6697 _work_queue(work_queue),
6698 _overflow_stack(overflow_stack),
6699 _skip_bits(0),
6700 _task(task)
6701 {
6702 assert(_work_queue->size() == 0, "work_queue should be empty");
6703 _finger = span.start();
6704 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6705 assert(_span.contains(_finger), "Out of bounds _finger?");
6706 }
6707
6708 // Should revisit to see if this should be restructured for
6709 // greater efficiency.
6710 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6711 if (_skip_bits > 0) {
6712 _skip_bits--;
6713 return true;
6714 }
6715 // convert offset into a HeapWord*
6716 HeapWord* addr = _bit_map->startWord() + offset;
6717 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6718 "address out of range");
6719 assert(_bit_map->isMarked(addr), "tautology");
6720 if (_bit_map->isMarked(addr+1)) {
6721 // this is an allocated object that might not yet be initialized
6722 assert(_skip_bits == 0, "tautology");
6723 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6724 oop p = oop(addr);
6725 if (p->klass_or_null() == NULL) {
6726 // in the case of Clean-on-Enter optimization, redirty card
6727 // and avoid clearing card by increasing the threshold.
6728 return true;
6729 }
6730 }
6731 scan_oops_in_oop(addr);
6732 return true;
6733 }
6734
6735 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6736 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6737 // Should we assert that our work queue is empty or
6738 // below some drain limit?
6739 assert(_work_queue->size() == 0,
6740 "should drain stack to limit stack usage");
6741 // convert ptr to an oop preparatory to scanning
6742 oop obj = oop(ptr);
6743 // Ignore mark word in verification below, since we
6744 // may be running concurrent with mutators.
6745 assert(obj->is_oop(true), "should be an oop");
6746 assert(_finger <= ptr, "_finger runneth ahead");
6747 // advance the finger to right end of this object
6748 _finger = ptr + obj->size();
6749 assert(_finger > ptr, "we just incremented it above");
6750 // On large heaps, it may take us some time to get through
6751 // the marking phase. During
6752 // this time it's possible that a lot of mutations have
6753 // accumulated in the card table and the mod union table --
6754 // these mutation records are redundant until we have
6755 // actually traced into the corresponding card.
6756 // Here, we check whether advancing the finger would make
6757 // us cross into a new card, and if so clear corresponding
6758 // cards in the MUT (preclean them in the card-table in the
6759 // future).
6760
6761 // The clean-on-enter optimization is disabled by default,
6762 // until we fix 6178663.
6763 if (CMSCleanOnEnter && (_finger > _threshold)) {
6764 // [_threshold, _finger) represents the interval
6765 // of cards to be cleared in MUT (or precleaned in card table).
6766 // The set of cards to be cleared is all those that overlap
6767 // with the interval [_threshold, _finger); note that
6768 // _threshold is always kept card-aligned but _finger isn't
6769 // always card-aligned.
6770 HeapWord* old_threshold = _threshold;
6771 assert(old_threshold == (HeapWord*)round_to(
6772 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6773 "_threshold should always be card-aligned");
6774 _threshold = (HeapWord*)round_to(
6775 (intptr_t)_finger, CardTableModRefBS::card_size);
6776 MemRegion mr(old_threshold, _threshold);
6777 assert(!mr.is_empty(), "Control point invariant");
6778 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6779 _mut->clear_range(mr);
6780 }
6781
6782 // Note: the local finger doesn't advance while we drain
6783 // the stack below, but the global finger sure can and will.
6784 HeapWord** gfa = _task->global_finger_addr();
6785 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6786 _span, _bit_map,
6787 _work_queue,
6788 _overflow_stack,
6789 _finger,
6790 gfa, this);
6791 bool res = _work_queue->push(obj); // overflow could occur here
6792 assert(res, "Will hold once we use workqueues");
6793 while (true) {
6794 oop new_oop;
6795 if (!_work_queue->pop_local(new_oop)) {
6796 // We emptied our work_queue; check if there's stuff that can
6797 // be gotten from the overflow stack.
6798 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6799 _overflow_stack, _work_queue)) {
6800 do_yield_check();
6801 continue;
6802 } else { // done
6803 break;
6804 }
6805 }
6806 // Skip verifying header mark word below because we are
6807 // running concurrent with mutators.
6808 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6809 // now scan this oop's oops
6810 new_oop->oop_iterate(&pushOrMarkClosure);
6811 do_yield_check();
6812 }
6813 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6814 }
6815
6816 // Yield in response to a request from VM Thread or
6817 // from mutators.
6818 void Par_MarkFromRootsClosure::do_yield_work() {
6819 assert(_task != NULL, "sanity");
6820 _task->yield();
6821 }
6822
6823 // A variant of the above used for verifying CMS marking work.
6824 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6825 MemRegion span,
6826 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6827 CMSMarkStack* mark_stack):
6828 _collector(collector),
6829 _span(span),
6830 _verification_bm(verification_bm),
6831 _cms_bm(cms_bm),
6832 _mark_stack(mark_stack),
6833 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6834 mark_stack)
6835 {
6836 assert(_mark_stack->isEmpty(), "stack should be empty");
6837 _finger = _verification_bm->startWord();
6838 assert(_collector->_restart_addr == NULL, "Sanity check");
6839 assert(_span.contains(_finger), "Out of bounds _finger?");
6840 }
6841
6842 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6843 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6844 assert(_span.contains(addr), "Out of bounds _finger?");
6845 _finger = addr;
6846 }
6847
6848 // Should revisit to see if this should be restructured for
6849 // greater efficiency.
6850 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6851 // convert offset into a HeapWord*
6852 HeapWord* addr = _verification_bm->startWord() + offset;
6853 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6854 "address out of range");
6855 assert(_verification_bm->isMarked(addr), "tautology");
6856 assert(_cms_bm->isMarked(addr), "tautology");
6857
6858 assert(_mark_stack->isEmpty(),
6859 "should drain stack to limit stack usage");
6860 // convert addr to an oop preparatory to scanning
6861 oop obj = oop(addr);
6862 assert(obj->is_oop(), "should be an oop");
6863 assert(_finger <= addr, "_finger runneth ahead");
6864 // advance the finger to right end of this object
6865 _finger = addr + obj->size();
6866 assert(_finger > addr, "we just incremented it above");
6867 // Note: the finger doesn't advance while we drain
6868 // the stack below.
6869 bool res = _mark_stack->push(obj);
6870 assert(res, "Empty non-zero size stack should have space for single push");
6871 while (!_mark_stack->isEmpty()) {
6872 oop new_oop = _mark_stack->pop();
6873 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6874 // now scan this oop's oops
6875 new_oop->oop_iterate(&_pam_verify_closure);
6876 }
6877 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6878 return true;
6879 }
6880
6881 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6882 CMSCollector* collector, MemRegion span,
6883 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6884 CMSMarkStack* mark_stack):
6885 MetadataAwareOopClosure(collector->ref_processor()),
6886 _collector(collector),
6887 _span(span),
6888 _verification_bm(verification_bm),
6889 _cms_bm(cms_bm),
6890 _mark_stack(mark_stack)
6891 { }
6892
6893 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6894 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6895
6896 // Upon stack overflow, we discard (part of) the stack,
6897 // remembering the least address amongst those discarded
6898 // in CMSCollector's _restart_address.
6899 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6900 // Remember the least grey address discarded
6901 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6902 _collector->lower_restart_addr(ra);
6903 _mark_stack->reset(); // discard stack contents
6904 _mark_stack->expand(); // expand the stack if possible
6905 }
6906
6907 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6908 assert(obj->is_oop_or_null(), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
6909 HeapWord* addr = (HeapWord*)obj;
6910 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6911 // Oop lies in _span and isn't yet grey or black
6912 _verification_bm->mark(addr); // now grey
6913 if (!_cms_bm->isMarked(addr)) {
6914 oop(addr)->print();
6915 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6916 p2i(addr));
6917 fatal("... aborting");
6918 }
6919
6920 if (!_mark_stack->push(obj)) { // stack overflow
6921 if (PrintCMSStatistics != 0) {
6922 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6923 SIZE_FORMAT, _mark_stack->capacity());
6924 }
6925 assert(_mark_stack->isFull(), "Else push should have succeeded");
6926 handle_stack_overflow(addr);
6927 }
6928 // anything including and to the right of _finger
6929 // will be scanned as we iterate over the remainder of the
6930 // bit map
6931 }
6932 }
6933
6934 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6935 MemRegion span,
6936 CMSBitMap* bitMap, CMSMarkStack* markStack,
6937 HeapWord* finger, MarkFromRootsClosure* parent) :
6938 MetadataAwareOopClosure(collector->ref_processor()),
6939 _collector(collector),
6940 _span(span),
6941 _bitMap(bitMap),
6942 _markStack(markStack),
6943 _finger(finger),
6944 _parent(parent)
6945 { }
6946
6947 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6948 MemRegion span,
6949 CMSBitMap* bit_map,
6950 OopTaskQueue* work_queue,
6951 CMSMarkStack* overflow_stack,
6952 HeapWord* finger,
6953 HeapWord** global_finger_addr,
6954 Par_MarkFromRootsClosure* parent) :
6955 MetadataAwareOopClosure(collector->ref_processor()),
6956 _collector(collector),
6957 _whole_span(collector->_span),
6958 _span(span),
6959 _bit_map(bit_map),
6960 _work_queue(work_queue),
6961 _overflow_stack(overflow_stack),
6962 _finger(finger),
6963 _global_finger_addr(global_finger_addr),
6964 _parent(parent)
6965 { }
6966
6967 // Assumes thread-safe access by callers, who are
6968 // responsible for mutual exclusion.
6969 void CMSCollector::lower_restart_addr(HeapWord* low) {
6970 assert(_span.contains(low), "Out of bounds addr");
6971 if (_restart_addr == NULL) {
6972 _restart_addr = low;
6973 } else {
6974 _restart_addr = MIN2(_restart_addr, low);
6975 }
6976 }
6977
6978 // Upon stack overflow, we discard (part of) the stack,
6979 // remembering the least address amongst those discarded
6980 // in CMSCollector's _restart_address.
6981 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6982 // Remember the least grey address discarded
6983 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6984 _collector->lower_restart_addr(ra);
6985 _markStack->reset(); // discard stack contents
6986 _markStack->expand(); // expand the stack if possible
6987 }
6988
6989 // Upon stack overflow, we discard (part of) the stack,
6990 // remembering the least address amongst those discarded
6991 // in CMSCollector's _restart_address.
6992 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6993 // We need to do this under a mutex to prevent other
6994 // workers from interfering with the work done below.
6995 MutexLockerEx ml(_overflow_stack->par_lock(),
6996 Mutex::_no_safepoint_check_flag);
6997 // Remember the least grey address discarded
6998 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6999 _collector->lower_restart_addr(ra);
7000 _overflow_stack->reset(); // discard stack contents
7001 _overflow_stack->expand(); // expand the stack if possible
7002 }
7003
7004 void PushOrMarkClosure::do_oop(oop obj) {
7005 // Ignore mark word because we are running concurrent with mutators.
7006 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7007 HeapWord* addr = (HeapWord*)obj;
7008 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7009 // Oop lies in _span and isn't yet grey or black
7010 _bitMap->mark(addr); // now grey
7011 if (addr < _finger) {
7012 // the bit map iteration has already either passed, or
7013 // sampled, this bit in the bit map; we'll need to
7014 // use the marking stack to scan this oop's oops.
7015 bool simulate_overflow = false;
7016 NOT_PRODUCT(
7017 if (CMSMarkStackOverflowALot &&
7018 _collector->simulate_overflow()) {
7019 // simulate a stack overflow
7020 simulate_overflow = true;
7021 }
7022 )
7023 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7024 if (PrintCMSStatistics != 0) {
7025 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7026 SIZE_FORMAT, _markStack->capacity());
7027 }
7028 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7029 handle_stack_overflow(addr);
7030 }
7031 }
7032 // anything including and to the right of _finger
7033 // will be scanned as we iterate over the remainder of the
7034 // bit map
7035 do_yield_check();
7036 }
7037 }
7038
7039 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7040 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7041
7042 void Par_PushOrMarkClosure::do_oop(oop obj) {
7043 // Ignore mark word because we are running concurrent with mutators.
7044 assert(obj->is_oop_or_null(true), err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7045 HeapWord* addr = (HeapWord*)obj;
7046 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7047 // Oop lies in _span and isn't yet grey or black
7048 // We read the global_finger (volatile read) strictly after marking oop
7049 bool res = _bit_map->par_mark(addr); // now grey
7050 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7051 // Should we push this marked oop on our stack?
7052 // -- if someone else marked it, nothing to do
7053 // -- if target oop is above global finger nothing to do
7054 // -- if target oop is in chunk and above local finger
7055 // then nothing to do
7056 // -- else push on work queue
7057 if ( !res // someone else marked it, they will deal with it
7058 || (addr >= *gfa) // will be scanned in a later task
7059 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7060 return;
7061 }
7062 // the bit map iteration has already either passed, or
7063 // sampled, this bit in the bit map; we'll need to
7064 // use the marking stack to scan this oop's oops.
7065 bool simulate_overflow = false;
7066 NOT_PRODUCT(
7067 if (CMSMarkStackOverflowALot &&
7068 _collector->simulate_overflow()) {
7069 // simulate a stack overflow
7070 simulate_overflow = true;
7071 }
7072 )
7073 if (simulate_overflow ||
7074 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7075 // stack overflow
7076 if (PrintCMSStatistics != 0) {
7077 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7078 SIZE_FORMAT, _overflow_stack->capacity());
7079 }
7080 // We cannot assert that the overflow stack is full because
7081 // it may have been emptied since.
7082 assert(simulate_overflow ||
7083 _work_queue->size() == _work_queue->max_elems(),
7084 "Else push should have succeeded");
7085 handle_stack_overflow(addr);
7086 }
7087 do_yield_check();
7088 }
7089 }
7090
7091 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7092 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7093
7094 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7095 MemRegion span,
7096 ReferenceProcessor* rp,
7097 CMSBitMap* bit_map,
7098 CMSBitMap* mod_union_table,
7099 CMSMarkStack* mark_stack,
7100 bool concurrent_precleaning):
7101 MetadataAwareOopClosure(rp),
7102 _collector(collector),
7103 _span(span),
7104 _bit_map(bit_map),
7105 _mod_union_table(mod_union_table),
7106 _mark_stack(mark_stack),
7107 _concurrent_precleaning(concurrent_precleaning)
7108 {
7109 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7110 }
7111
7112 // Grey object rescan during pre-cleaning and second checkpoint phases --
7113 // the non-parallel version (the parallel version appears further below.)
7114 void PushAndMarkClosure::do_oop(oop obj) {
7115 // Ignore mark word verification. If during concurrent precleaning,
7116 // the object monitor may be locked. If during the checkpoint
7117 // phases, the object may already have been reached by a different
7118 // path and may be at the end of the global overflow list (so
7119 // the mark word may be NULL).
7120 assert(obj->is_oop_or_null(true /* ignore mark word */),
7121 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7122 HeapWord* addr = (HeapWord*)obj;
7123 // Check if oop points into the CMS generation
7124 // and is not marked
7125 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7126 // a white object ...
7127 _bit_map->mark(addr); // ... now grey
7128 // push on the marking stack (grey set)
7129 bool simulate_overflow = false;
7130 NOT_PRODUCT(
7131 if (CMSMarkStackOverflowALot &&
7132 _collector->simulate_overflow()) {
7133 // simulate a stack overflow
7134 simulate_overflow = true;
7135 }
7136 )
7137 if (simulate_overflow || !_mark_stack->push(obj)) {
7138 if (_concurrent_precleaning) {
7139 // During precleaning we can just dirty the appropriate card(s)
7140 // in the mod union table, thus ensuring that the object remains
7141 // in the grey set and continue. In the case of object arrays
7142 // we need to dirty all of the cards that the object spans,
7143 // since the rescan of object arrays will be limited to the
7144 // dirty cards.
7145 // Note that no one can be interfering with us in this action
7146 // of dirtying the mod union table, so no locking or atomics
7147 // are required.
7148 if (obj->is_objArray()) {
7149 size_t sz = obj->size();
7150 HeapWord* end_card_addr = (HeapWord*)round_to(
7151 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7152 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7153 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7154 _mod_union_table->mark_range(redirty_range);
7155 } else {
7156 _mod_union_table->mark(addr);
7157 }
7158 _collector->_ser_pmc_preclean_ovflw++;
7159 } else {
7160 // During the remark phase, we need to remember this oop
7161 // in the overflow list.
7162 _collector->push_on_overflow_list(obj);
7163 _collector->_ser_pmc_remark_ovflw++;
7164 }
7165 }
7166 }
7167 }
7168
7169 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7170 MemRegion span,
7171 ReferenceProcessor* rp,
7172 CMSBitMap* bit_map,
7173 OopTaskQueue* work_queue):
7174 MetadataAwareOopClosure(rp),
7175 _collector(collector),
7176 _span(span),
7177 _bit_map(bit_map),
7178 _work_queue(work_queue)
7179 {
7180 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7181 }
7182
7183 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7184 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7185
7186 // Grey object rescan during second checkpoint phase --
7187 // the parallel version.
7188 void Par_PushAndMarkClosure::do_oop(oop obj) {
7189 // In the assert below, we ignore the mark word because
7190 // this oop may point to an already visited object that is
7191 // on the overflow stack (in which case the mark word has
7192 // been hijacked for chaining into the overflow stack --
7193 // if this is the last object in the overflow stack then
7194 // its mark word will be NULL). Because this object may
7195 // have been subsequently popped off the global overflow
7196 // stack, and the mark word possibly restored to the prototypical
7197 // value, by the time we get to examined this failing assert in
7198 // the debugger, is_oop_or_null(false) may subsequently start
7199 // to hold.
7200 assert(obj->is_oop_or_null(true),
7201 err_msg("Expected an oop or NULL at " PTR_FORMAT, p2i(obj)));
7202 HeapWord* addr = (HeapWord*)obj;
7203 // Check if oop points into the CMS generation
7204 // and is not marked
7205 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7206 // a white object ...
7207 // If we manage to "claim" the object, by being the
7208 // first thread to mark it, then we push it on our
7209 // marking stack
7210 if (_bit_map->par_mark(addr)) { // ... now grey
7211 // push on work queue (grey set)
7212 bool simulate_overflow = false;
7213 NOT_PRODUCT(
7214 if (CMSMarkStackOverflowALot &&
7215 _collector->par_simulate_overflow()) {
7216 // simulate a stack overflow
7217 simulate_overflow = true;
7218 }
7219 )
7220 if (simulate_overflow || !_work_queue->push(obj)) {
7221 _collector->par_push_on_overflow_list(obj);
7222 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7223 }
7224 } // Else, some other thread got there first
7225 }
7226 }
7227
7228 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7229 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7230
7231 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7232 Mutex* bml = _collector->bitMapLock();
7233 assert_lock_strong(bml);
7234 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7235 "CMS thread should hold CMS token");
7236
7237 bml->unlock();
7238 ConcurrentMarkSweepThread::desynchronize(true);
7239
7240 _collector->stopTimer();
7241 if (PrintCMSStatistics != 0) {
7242 _collector->incrementYields();
7243 }
7244
7245 // See the comment in coordinator_yield()
7246 for (unsigned i = 0; i < CMSYieldSleepCount &&
7247 ConcurrentMarkSweepThread::should_yield() &&
7248 !CMSCollector::foregroundGCIsActive(); ++i) {
7249 os::sleep(Thread::current(), 1, false);
7250 }
7251
7252 ConcurrentMarkSweepThread::synchronize(true);
7253 bml->lock();
7254
7255 _collector->startTimer();
7256 }
7257
7258 bool CMSPrecleanRefsYieldClosure::should_return() {
7259 if (ConcurrentMarkSweepThread::should_yield()) {
7260 do_yield_work();
7261 }
7262 return _collector->foregroundGCIsActive();
7263 }
7264
7265 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7266 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7267 "mr should be aligned to start at a card boundary");
7268 // We'd like to assert:
7269 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7270 // "mr should be a range of cards");
7271 // However, that would be too strong in one case -- the last
7272 // partition ends at _unallocated_block which, in general, can be
7273 // an arbitrary boundary, not necessarily card aligned.
7274 if (PrintCMSStatistics != 0) {
7275 _num_dirty_cards +=
7276 mr.word_size()/CardTableModRefBS::card_size_in_words;
7277 }
7278 _space->object_iterate_mem(mr, &_scan_cl);
7279 }
7280
7281 SweepClosure::SweepClosure(CMSCollector* collector,
7282 ConcurrentMarkSweepGeneration* g,
7283 CMSBitMap* bitMap, bool should_yield) :
7284 _collector(collector),
7285 _g(g),
7286 _sp(g->cmsSpace()),
7287 _limit(_sp->sweep_limit()),
7288 _freelistLock(_sp->freelistLock()),
7289 _bitMap(bitMap),
7290 _yield(should_yield),
7291 _inFreeRange(false), // No free range at beginning of sweep
7292 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7293 _lastFreeRangeCoalesced(false),
7294 _freeFinger(g->used_region().start())
7295 {
7296 NOT_PRODUCT(
7297 _numObjectsFreed = 0;
7298 _numWordsFreed = 0;
7299 _numObjectsLive = 0;
7300 _numWordsLive = 0;
7301 _numObjectsAlreadyFree = 0;
7302 _numWordsAlreadyFree = 0;
7303 _last_fc = NULL;
7304
7305 _sp->initializeIndexedFreeListArrayReturnedBytes();
7306 _sp->dictionary()->initialize_dict_returned_bytes();
7307 )
7308 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7309 "sweep _limit out of bounds");
7310 if (CMSTraceSweeper) {
7311 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7312 p2i(_limit));
7313 }
7314 }
7315
7316 void SweepClosure::print_on(outputStream* st) const {
7317 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7318 p2i(_sp->bottom()), p2i(_sp->end()));
7319 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7320 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7321 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7322 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7323 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7324 }
7325
7326 #ifndef PRODUCT
7327 // Assertion checking only: no useful work in product mode --
7328 // however, if any of the flags below become product flags,
7329 // you may need to review this code to see if it needs to be
7330 // enabled in product mode.
7331 SweepClosure::~SweepClosure() {
7332 assert_lock_strong(_freelistLock);
7333 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7334 "sweep _limit out of bounds");
7335 if (inFreeRange()) {
7336 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7337 print();
7338 ShouldNotReachHere();
7339 }
7340 if (Verbose && PrintGC) {
7341 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7342 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7343 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7344 SIZE_FORMAT " bytes "
7345 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7346 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7347 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7348 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7349 * sizeof(HeapWord);
7350 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7351
7352 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7353 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7354 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7355 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7356 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7357 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7358 indexListReturnedBytes);
7359 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7360 dict_returned_bytes);
7361 }
7362 }
7363 if (CMSTraceSweeper) {
7364 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7365 p2i(_limit));
7366 }
7367 }
7368 #endif // PRODUCT
7369
7370 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7371 bool freeRangeInFreeLists) {
7372 if (CMSTraceSweeper) {
7373 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7374 p2i(freeFinger), freeRangeInFreeLists);
7375 }
7376 assert(!inFreeRange(), "Trampling existing free range");
7377 set_inFreeRange(true);
7378 set_lastFreeRangeCoalesced(false);
7379
7380 set_freeFinger(freeFinger);
7381 set_freeRangeInFreeLists(freeRangeInFreeLists);
7382 if (CMSTestInFreeList) {
7383 if (freeRangeInFreeLists) {
7384 FreeChunk* fc = (FreeChunk*) freeFinger;
7385 assert(fc->is_free(), "A chunk on the free list should be free.");
7386 assert(fc->size() > 0, "Free range should have a size");
7387 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7388 }
7389 }
7390 }
7391
7392 // Note that the sweeper runs concurrently with mutators. Thus,
7393 // it is possible for direct allocation in this generation to happen
7394 // in the middle of the sweep. Note that the sweeper also coalesces
7395 // contiguous free blocks. Thus, unless the sweeper and the allocator
7396 // synchronize appropriately freshly allocated blocks may get swept up.
7397 // This is accomplished by the sweeper locking the free lists while
7398 // it is sweeping. Thus blocks that are determined to be free are
7399 // indeed free. There is however one additional complication:
7400 // blocks that have been allocated since the final checkpoint and
7401 // mark, will not have been marked and so would be treated as
7402 // unreachable and swept up. To prevent this, the allocator marks
7403 // the bit map when allocating during the sweep phase. This leads,
7404 // however, to a further complication -- objects may have been allocated
7405 // but not yet initialized -- in the sense that the header isn't yet
7406 // installed. The sweeper can not then determine the size of the block
7407 // in order to skip over it. To deal with this case, we use a technique
7408 // (due to Printezis) to encode such uninitialized block sizes in the
7409 // bit map. Since the bit map uses a bit per every HeapWord, but the
7410 // CMS generation has a minimum object size of 3 HeapWords, it follows
7411 // that "normal marks" won't be adjacent in the bit map (there will
7412 // always be at least two 0 bits between successive 1 bits). We make use
7413 // of these "unused" bits to represent uninitialized blocks -- the bit
7414 // corresponding to the start of the uninitialized object and the next
7415 // bit are both set. Finally, a 1 bit marks the end of the object that
7416 // started with the two consecutive 1 bits to indicate its potentially
7417 // uninitialized state.
7418
7419 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7420 FreeChunk* fc = (FreeChunk*)addr;
7421 size_t res;
7422
7423 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7424 // than "addr == _limit" because although _limit was a block boundary when
7425 // we started the sweep, it may no longer be one because heap expansion
7426 // may have caused us to coalesce the block ending at the address _limit
7427 // with a newly expanded chunk (this happens when _limit was set to the
7428 // previous _end of the space), so we may have stepped past _limit:
7429 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7430 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7431 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7432 "sweep _limit out of bounds");
7433 assert(addr < _sp->end(), "addr out of bounds");
7434 // Flush any free range we might be holding as a single
7435 // coalesced chunk to the appropriate free list.
7436 if (inFreeRange()) {
7437 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7438 err_msg("freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger())));
7439 flush_cur_free_chunk(freeFinger(),
7440 pointer_delta(addr, freeFinger()));
7441 if (CMSTraceSweeper) {
7442 gclog_or_tty->print("Sweep: last chunk: ");
7443 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7444 "[coalesced:%d]\n",
7445 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7446 lastFreeRangeCoalesced() ? 1 : 0);
7447 }
7448 }
7449
7450 // help the iterator loop finish
7451 return pointer_delta(_sp->end(), addr);
7452 }
7453
7454 assert(addr < _limit, "sweep invariant");
7455 // check if we should yield
7456 do_yield_check(addr);
7457 if (fc->is_free()) {
7458 // Chunk that is already free
7459 res = fc->size();
7460 do_already_free_chunk(fc);
7461 debug_only(_sp->verifyFreeLists());
7462 // If we flush the chunk at hand in lookahead_and_flush()
7463 // and it's coalesced with a preceding chunk, then the
7464 // process of "mangling" the payload of the coalesced block
7465 // will cause erasure of the size information from the
7466 // (erstwhile) header of all the coalesced blocks but the
7467 // first, so the first disjunct in the assert will not hold
7468 // in that specific case (in which case the second disjunct
7469 // will hold).
7470 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7471 "Otherwise the size info doesn't change at this step");
7472 NOT_PRODUCT(
7473 _numObjectsAlreadyFree++;
7474 _numWordsAlreadyFree += res;
7475 )
7476 NOT_PRODUCT(_last_fc = fc;)
7477 } else if (!_bitMap->isMarked(addr)) {
7478 // Chunk is fresh garbage
7479 res = do_garbage_chunk(fc);
7480 debug_only(_sp->verifyFreeLists());
7481 NOT_PRODUCT(
7482 _numObjectsFreed++;
7483 _numWordsFreed += res;
7484 )
7485 } else {
7486 // Chunk that is alive.
7487 res = do_live_chunk(fc);
7488 debug_only(_sp->verifyFreeLists());
7489 NOT_PRODUCT(
7490 _numObjectsLive++;
7491 _numWordsLive += res;
7492 )
7493 }
7494 return res;
7495 }
7496
7497 // For the smart allocation, record following
7498 // split deaths - a free chunk is removed from its free list because
7499 // it is being split into two or more chunks.
7500 // split birth - a free chunk is being added to its free list because
7501 // a larger free chunk has been split and resulted in this free chunk.
7502 // coal death - a free chunk is being removed from its free list because
7503 // it is being coalesced into a large free chunk.
7504 // coal birth - a free chunk is being added to its free list because
7505 // it was created when two or more free chunks where coalesced into
7506 // this free chunk.
7507 //
7508 // These statistics are used to determine the desired number of free
7509 // chunks of a given size. The desired number is chosen to be relative
7510 // to the end of a CMS sweep. The desired number at the end of a sweep
7511 // is the
7512 // count-at-end-of-previous-sweep (an amount that was enough)
7513 // - count-at-beginning-of-current-sweep (the excess)
7514 // + split-births (gains in this size during interval)
7515 // - split-deaths (demands on this size during interval)
7516 // where the interval is from the end of one sweep to the end of the
7517 // next.
7518 //
7519 // When sweeping the sweeper maintains an accumulated chunk which is
7520 // the chunk that is made up of chunks that have been coalesced. That
7521 // will be termed the left-hand chunk. A new chunk of garbage that
7522 // is being considered for coalescing will be referred to as the
7523 // right-hand chunk.
7524 //
7525 // When making a decision on whether to coalesce a right-hand chunk with
7526 // the current left-hand chunk, the current count vs. the desired count
7527 // of the left-hand chunk is considered. Also if the right-hand chunk
7528 // is near the large chunk at the end of the heap (see
7529 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7530 // left-hand chunk is coalesced.
7531 //
7532 // When making a decision about whether to split a chunk, the desired count
7533 // vs. the current count of the candidate to be split is also considered.
7534 // If the candidate is underpopulated (currently fewer chunks than desired)
7535 // a chunk of an overpopulated (currently more chunks than desired) size may
7536 // be chosen. The "hint" associated with a free list, if non-null, points
7537 // to a free list which may be overpopulated.
7538 //
7539
7540 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7541 const size_t size = fc->size();
7542 // Chunks that cannot be coalesced are not in the
7543 // free lists.
7544 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7545 assert(_sp->verify_chunk_in_free_list(fc),
7546 "free chunk should be in free lists");
7547 }
7548 // a chunk that is already free, should not have been
7549 // marked in the bit map
7550 HeapWord* const addr = (HeapWord*) fc;
7551 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7552 // Verify that the bit map has no bits marked between
7553 // addr and purported end of this block.
7554 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7555
7556 // Some chunks cannot be coalesced under any circumstances.
7557 // See the definition of cantCoalesce().
7558 if (!fc->cantCoalesce()) {
7559 // This chunk can potentially be coalesced.
7560 if (_sp->adaptive_freelists()) {
7561 // All the work is done in
7562 do_post_free_or_garbage_chunk(fc, size);
7563 } else { // Not adaptive free lists
7564 // this is a free chunk that can potentially be coalesced by the sweeper;
7565 if (!inFreeRange()) {
7566 // if the next chunk is a free block that can't be coalesced
7567 // it doesn't make sense to remove this chunk from the free lists
7568 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7569 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7570 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7571 nextChunk->is_free() && // ... which is free...
7572 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7573 // nothing to do
7574 } else {
7575 // Potentially the start of a new free range:
7576 // Don't eagerly remove it from the free lists.
7577 // No need to remove it if it will just be put
7578 // back again. (Also from a pragmatic point of view
7579 // if it is a free block in a region that is beyond
7580 // any allocated blocks, an assertion will fail)
7581 // Remember the start of a free run.
7582 initialize_free_range(addr, true);
7583 // end - can coalesce with next chunk
7584 }
7585 } else {
7586 // the midst of a free range, we are coalescing
7587 print_free_block_coalesced(fc);
7588 if (CMSTraceSweeper) {
7589 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7590 }
7591 // remove it from the free lists
7592 _sp->removeFreeChunkFromFreeLists(fc);
7593 set_lastFreeRangeCoalesced(true);
7594 // If the chunk is being coalesced and the current free range is
7595 // in the free lists, remove the current free range so that it
7596 // will be returned to the free lists in its entirety - all
7597 // the coalesced pieces included.
7598 if (freeRangeInFreeLists()) {
7599 FreeChunk* ffc = (FreeChunk*) freeFinger();
7600 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7601 "Size of free range is inconsistent with chunk size.");
7602 if (CMSTestInFreeList) {
7603 assert(_sp->verify_chunk_in_free_list(ffc),
7604 "free range is not in free lists");
7605 }
7606 _sp->removeFreeChunkFromFreeLists(ffc);
7607 set_freeRangeInFreeLists(false);
7608 }
7609 }
7610 }
7611 // Note that if the chunk is not coalescable (the else arm
7612 // below), we unconditionally flush, without needing to do
7613 // a "lookahead," as we do below.
7614 if (inFreeRange()) lookahead_and_flush(fc, size);
7615 } else {
7616 // Code path common to both original and adaptive free lists.
7617
7618 // cant coalesce with previous block; this should be treated
7619 // as the end of a free run if any
7620 if (inFreeRange()) {
7621 // we kicked some butt; time to pick up the garbage
7622 assert(freeFinger() < addr, "freeFinger points too high");
7623 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7624 }
7625 // else, nothing to do, just continue
7626 }
7627 }
7628
7629 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7630 // This is a chunk of garbage. It is not in any free list.
7631 // Add it to a free list or let it possibly be coalesced into
7632 // a larger chunk.
7633 HeapWord* const addr = (HeapWord*) fc;
7634 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7635
7636 if (_sp->adaptive_freelists()) {
7637 // Verify that the bit map has no bits marked between
7638 // addr and purported end of just dead object.
7639 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7640
7641 do_post_free_or_garbage_chunk(fc, size);
7642 } else {
7643 if (!inFreeRange()) {
7644 // start of a new free range
7645 assert(size > 0, "A free range should have a size");
7646 initialize_free_range(addr, false);
7647 } else {
7648 // this will be swept up when we hit the end of the
7649 // free range
7650 if (CMSTraceSweeper) {
7651 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7652 }
7653 // If the chunk is being coalesced and the current free range is
7654 // in the free lists, remove the current free range so that it
7655 // will be returned to the free lists in its entirety - all
7656 // the coalesced pieces included.
7657 if (freeRangeInFreeLists()) {
7658 FreeChunk* ffc = (FreeChunk*)freeFinger();
7659 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7660 "Size of free range is inconsistent with chunk size.");
7661 if (CMSTestInFreeList) {
7662 assert(_sp->verify_chunk_in_free_list(ffc),
7663 "free range is not in free lists");
7664 }
7665 _sp->removeFreeChunkFromFreeLists(ffc);
7666 set_freeRangeInFreeLists(false);
7667 }
7668 set_lastFreeRangeCoalesced(true);
7669 }
7670 // this will be swept up when we hit the end of the free range
7671
7672 // Verify that the bit map has no bits marked between
7673 // addr and purported end of just dead object.
7674 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7675 }
7676 assert(_limit >= addr + size,
7677 "A freshly garbage chunk can't possibly straddle over _limit");
7678 if (inFreeRange()) lookahead_and_flush(fc, size);
7679 return size;
7680 }
7681
7682 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7683 HeapWord* addr = (HeapWord*) fc;
7684 // The sweeper has just found a live object. Return any accumulated
7685 // left hand chunk to the free lists.
7686 if (inFreeRange()) {
7687 assert(freeFinger() < addr, "freeFinger points too high");
7688 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7689 }
7690
7691 // This object is live: we'd normally expect this to be
7692 // an oop, and like to assert the following:
7693 // assert(oop(addr)->is_oop(), "live block should be an oop");
7694 // However, as we commented above, this may be an object whose
7695 // header hasn't yet been initialized.
7696 size_t size;
7697 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7698 if (_bitMap->isMarked(addr + 1)) {
7699 // Determine the size from the bit map, rather than trying to
7700 // compute it from the object header.
7701 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7702 size = pointer_delta(nextOneAddr + 1, addr);
7703 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7704 "alignment problem");
7705
7706 #ifdef ASSERT
7707 if (oop(addr)->klass_or_null() != NULL) {
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 assert(size ==
7711 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7712 "P-mark and computed size do not agree");
7713 }
7714 #endif
7715
7716 } else {
7717 // This should be an initialized object that's alive.
7718 assert(oop(addr)->klass_or_null() != NULL,
7719 "Should be an initialized object");
7720 // Ignore mark word because we are running concurrent with mutators
7721 assert(oop(addr)->is_oop(true), "live block should be an oop");
7722 // Verify that the bit map has no bits marked between
7723 // addr and purported end of this block.
7724 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7725 assert(size >= 3, "Necessary for Printezis marks to work");
7726 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7727 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7728 }
7729 return size;
7730 }
7731
7732 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7733 size_t chunkSize) {
7734 // do_post_free_or_garbage_chunk() should only be called in the case
7735 // of the adaptive free list allocator.
7736 const bool fcInFreeLists = fc->is_free();
7737 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7738 assert((HeapWord*)fc <= _limit, "sweep invariant");
7739 if (CMSTestInFreeList && fcInFreeLists) {
7740 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7741 }
7742
7743 if (CMSTraceSweeper) {
7744 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7745 }
7746
7747 HeapWord* const fc_addr = (HeapWord*) fc;
7748
7749 bool coalesce;
7750 const size_t left = pointer_delta(fc_addr, freeFinger());
7751 const size_t right = chunkSize;
7752 switch (FLSCoalescePolicy) {
7753 // numeric value forms a coalition aggressiveness metric
7754 case 0: { // never coalesce
7755 coalesce = false;
7756 break;
7757 }
7758 case 1: { // coalesce if left & right chunks on overpopulated lists
7759 coalesce = _sp->coalOverPopulated(left) &&
7760 _sp->coalOverPopulated(right);
7761 break;
7762 }
7763 case 2: { // coalesce if left chunk on overpopulated list (default)
7764 coalesce = _sp->coalOverPopulated(left);
7765 break;
7766 }
7767 case 3: { // coalesce if left OR right chunk on overpopulated list
7768 coalesce = _sp->coalOverPopulated(left) ||
7769 _sp->coalOverPopulated(right);
7770 break;
7771 }
7772 case 4: { // always coalesce
7773 coalesce = true;
7774 break;
7775 }
7776 default:
7777 ShouldNotReachHere();
7778 }
7779
7780 // Should the current free range be coalesced?
7781 // If the chunk is in a free range and either we decided to coalesce above
7782 // or the chunk is near the large block at the end of the heap
7783 // (isNearLargestChunk() returns true), then coalesce this chunk.
7784 const bool doCoalesce = inFreeRange()
7785 && (coalesce || _g->isNearLargestChunk(fc_addr));
7786 if (doCoalesce) {
7787 // Coalesce the current free range on the left with the new
7788 // chunk on the right. If either is on a free list,
7789 // it must be removed from the list and stashed in the closure.
7790 if (freeRangeInFreeLists()) {
7791 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7792 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7793 "Size of free range is inconsistent with chunk size.");
7794 if (CMSTestInFreeList) {
7795 assert(_sp->verify_chunk_in_free_list(ffc),
7796 "Chunk is not in free lists");
7797 }
7798 _sp->coalDeath(ffc->size());
7799 _sp->removeFreeChunkFromFreeLists(ffc);
7800 set_freeRangeInFreeLists(false);
7801 }
7802 if (fcInFreeLists) {
7803 _sp->coalDeath(chunkSize);
7804 assert(fc->size() == chunkSize,
7805 "The chunk has the wrong size or is not in the free lists");
7806 _sp->removeFreeChunkFromFreeLists(fc);
7807 }
7808 set_lastFreeRangeCoalesced(true);
7809 print_free_block_coalesced(fc);
7810 } else { // not in a free range and/or should not coalesce
7811 // Return the current free range and start a new one.
7812 if (inFreeRange()) {
7813 // In a free range but cannot coalesce with the right hand chunk.
7814 // Put the current free range into the free lists.
7815 flush_cur_free_chunk(freeFinger(),
7816 pointer_delta(fc_addr, freeFinger()));
7817 }
7818 // Set up for new free range. Pass along whether the right hand
7819 // chunk is in the free lists.
7820 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7821 }
7822 }
7823
7824 // Lookahead flush:
7825 // If we are tracking a free range, and this is the last chunk that
7826 // we'll look at because its end crosses past _limit, we'll preemptively
7827 // flush it along with any free range we may be holding on to. Note that
7828 // this can be the case only for an already free or freshly garbage
7829 // chunk. If this block is an object, it can never straddle
7830 // over _limit. The "straddling" occurs when _limit is set at
7831 // the previous end of the space when this cycle started, and
7832 // a subsequent heap expansion caused the previously co-terminal
7833 // free block to be coalesced with the newly expanded portion,
7834 // thus rendering _limit a non-block-boundary making it dangerous
7835 // for the sweeper to step over and examine.
7836 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7837 assert(inFreeRange(), "Should only be called if currently in a free range.");
7838 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7839 assert(_sp->used_region().contains(eob - 1),
7840 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7841 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7842 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7843 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size));
7844 if (eob >= _limit) {
7845 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7846 if (CMSTraceSweeper) {
7847 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7848 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7849 "[" PTR_FORMAT "," PTR_FORMAT ")",
7850 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7851 }
7852 // Return the storage we are tracking back into the free lists.
7853 if (CMSTraceSweeper) {
7854 gclog_or_tty->print_cr("Flushing ... ");
7855 }
7856 assert(freeFinger() < eob, "Error");
7857 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7858 }
7859 }
7860
7861 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7862 assert(inFreeRange(), "Should only be called if currently in a free range.");
7863 assert(size > 0,
7864 "A zero sized chunk cannot be added to the free lists.");
7865 if (!freeRangeInFreeLists()) {
7866 if (CMSTestInFreeList) {
7867 FreeChunk* fc = (FreeChunk*) chunk;
7868 fc->set_size(size);
7869 assert(!_sp->verify_chunk_in_free_list(fc),
7870 "chunk should not be in free lists yet");
7871 }
7872 if (CMSTraceSweeper) {
7873 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7874 p2i(chunk), size);
7875 }
7876 // A new free range is going to be starting. The current
7877 // free range has not been added to the free lists yet or
7878 // was removed so add it back.
7879 // If the current free range was coalesced, then the death
7880 // of the free range was recorded. Record a birth now.
7881 if (lastFreeRangeCoalesced()) {
7882 _sp->coalBirth(size);
7883 }
7884 _sp->addChunkAndRepairOffsetTable(chunk, size,
7885 lastFreeRangeCoalesced());
7886 } else if (CMSTraceSweeper) {
7887 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7888 }
7889 set_inFreeRange(false);
7890 set_freeRangeInFreeLists(false);
7891 }
7892
7893 // We take a break if we've been at this for a while,
7894 // so as to avoid monopolizing the locks involved.
7895 void SweepClosure::do_yield_work(HeapWord* addr) {
7896 // Return current free chunk being used for coalescing (if any)
7897 // to the appropriate freelist. After yielding, the next
7898 // free block encountered will start a coalescing range of
7899 // free blocks. If the next free block is adjacent to the
7900 // chunk just flushed, they will need to wait for the next
7901 // sweep to be coalesced.
7902 if (inFreeRange()) {
7903 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7904 }
7905
7906 // First give up the locks, then yield, then re-lock.
7907 // We should probably use a constructor/destructor idiom to
7908 // do this unlock/lock or modify the MutexUnlocker class to
7909 // serve our purpose. XXX
7910 assert_lock_strong(_bitMap->lock());
7911 assert_lock_strong(_freelistLock);
7912 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7913 "CMS thread should hold CMS token");
7914 _bitMap->lock()->unlock();
7915 _freelistLock->unlock();
7916 ConcurrentMarkSweepThread::desynchronize(true);
7917 _collector->stopTimer();
7918 if (PrintCMSStatistics != 0) {
7919 _collector->incrementYields();
7920 }
7921
7922 // See the comment in coordinator_yield()
7923 for (unsigned i = 0; i < CMSYieldSleepCount &&
7924 ConcurrentMarkSweepThread::should_yield() &&
7925 !CMSCollector::foregroundGCIsActive(); ++i) {
7926 os::sleep(Thread::current(), 1, false);
7927 }
7928
7929 ConcurrentMarkSweepThread::synchronize(true);
7930 _freelistLock->lock();
7931 _bitMap->lock()->lock_without_safepoint_check();
7932 _collector->startTimer();
7933 }
7934
7935 #ifndef PRODUCT
7936 // This is actually very useful in a product build if it can
7937 // be called from the debugger. Compile it into the product
7938 // as needed.
7939 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7940 return debug_cms_space->verify_chunk_in_free_list(fc);
7941 }
7942 #endif
7943
7944 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7945 if (CMSTraceSweeper) {
7946 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7947 p2i(fc), fc->size());
7948 }
7949 }
7950
7951 // CMSIsAliveClosure
7952 bool CMSIsAliveClosure::do_object_b(oop obj) {
7953 HeapWord* addr = (HeapWord*)obj;
7954 return addr != NULL &&
7955 (!_span.contains(addr) || _bit_map->isMarked(addr));
7956 }
7957
7958
7959 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7960 MemRegion span,
7961 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7962 bool cpc):
7963 _collector(collector),
7964 _span(span),
7965 _bit_map(bit_map),
7966 _mark_stack(mark_stack),
7967 _concurrent_precleaning(cpc) {
7968 assert(!_span.is_empty(), "Empty span could spell trouble");
7969 }
7970
7971
7972 // CMSKeepAliveClosure: the serial version
7973 void CMSKeepAliveClosure::do_oop(oop obj) {
7974 HeapWord* addr = (HeapWord*)obj;
7975 if (_span.contains(addr) &&
7976 !_bit_map->isMarked(addr)) {
7977 _bit_map->mark(addr);
7978 bool simulate_overflow = false;
7979 NOT_PRODUCT(
7980 if (CMSMarkStackOverflowALot &&
7981 _collector->simulate_overflow()) {
7982 // simulate a stack overflow
7983 simulate_overflow = true;
7984 }
7985 )
7986 if (simulate_overflow || !_mark_stack->push(obj)) {
7987 if (_concurrent_precleaning) {
7988 // We dirty the overflown object and let the remark
7989 // phase deal with it.
7990 assert(_collector->overflow_list_is_empty(), "Error");
7991 // In the case of object arrays, we need to dirty all of
7992 // the cards that the object spans. No locking or atomics
7993 // are needed since no one else can be mutating the mod union
7994 // table.
7995 if (obj->is_objArray()) {
7996 size_t sz = obj->size();
7997 HeapWord* end_card_addr =
7998 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7999 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8000 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8001 _collector->_modUnionTable.mark_range(redirty_range);
8002 } else {
8003 _collector->_modUnionTable.mark(addr);
8004 }
8005 _collector->_ser_kac_preclean_ovflw++;
8006 } else {
8007 _collector->push_on_overflow_list(obj);
8008 _collector->_ser_kac_ovflw++;
8009 }
8010 }
8011 }
8012 }
8013
8014 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8015 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8016
8017 // CMSParKeepAliveClosure: a parallel version of the above.
8018 // The work queues are private to each closure (thread),
8019 // but (may be) available for stealing by other threads.
8020 void CMSParKeepAliveClosure::do_oop(oop obj) {
8021 HeapWord* addr = (HeapWord*)obj;
8022 if (_span.contains(addr) &&
8023 !_bit_map->isMarked(addr)) {
8024 // In general, during recursive tracing, several threads
8025 // may be concurrently getting here; the first one to
8026 // "tag" it, claims it.
8027 if (_bit_map->par_mark(addr)) {
8028 bool res = _work_queue->push(obj);
8029 assert(res, "Low water mark should be much less than capacity");
8030 // Do a recursive trim in the hope that this will keep
8031 // stack usage lower, but leave some oops for potential stealers
8032 trim_queue(_low_water_mark);
8033 } // Else, another thread got there first
8034 }
8035 }
8036
8037 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8038 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8039
8040 void CMSParKeepAliveClosure::trim_queue(uint max) {
8041 while (_work_queue->size() > max) {
8042 oop new_oop;
8043 if (_work_queue->pop_local(new_oop)) {
8044 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8045 assert(_bit_map->isMarked((HeapWord*)new_oop),
8046 "no white objects on this stack!");
8047 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8048 // iterate over the oops in this oop, marking and pushing
8049 // the ones in CMS heap (i.e. in _span).
8050 new_oop->oop_iterate(&_mark_and_push);
8051 }
8052 }
8053 }
8054
8055 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8056 CMSCollector* collector,
8057 MemRegion span, CMSBitMap* bit_map,
8058 OopTaskQueue* work_queue):
8059 _collector(collector),
8060 _span(span),
8061 _bit_map(bit_map),
8062 _work_queue(work_queue) { }
8063
8064 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8065 HeapWord* addr = (HeapWord*)obj;
8066 if (_span.contains(addr) &&
8067 !_bit_map->isMarked(addr)) {
8068 if (_bit_map->par_mark(addr)) {
8069 bool simulate_overflow = false;
8070 NOT_PRODUCT(
8071 if (CMSMarkStackOverflowALot &&
8072 _collector->par_simulate_overflow()) {
8073 // simulate a stack overflow
8074 simulate_overflow = true;
8075 }
8076 )
8077 if (simulate_overflow || !_work_queue->push(obj)) {
8078 _collector->par_push_on_overflow_list(obj);
8079 _collector->_par_kac_ovflw++;
8080 }
8081 } // Else another thread got there already
8082 }
8083 }
8084
8085 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8086 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8087
8088 //////////////////////////////////////////////////////////////////
8089 // CMSExpansionCause /////////////////////////////
8090 //////////////////////////////////////////////////////////////////
8091 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8092 switch (cause) {
8093 case _no_expansion:
8094 return "No expansion";
8095 case _satisfy_free_ratio:
8096 return "Free ratio";
8097 case _satisfy_promotion:
8098 return "Satisfy promotion";
8099 case _satisfy_allocation:
8100 return "allocation";
8101 case _allocate_par_lab:
8102 return "Par LAB";
8103 case _allocate_par_spooling_space:
8104 return "Par Spooling Space";
8105 case _adaptive_size_policy:
8106 return "Ergonomics";
8107 default:
8108 return "unknown";
8109 }
8110 }
8111
8112 void CMSDrainMarkingStackClosure::do_void() {
8113 // the max number to take from overflow list at a time
8114 const size_t num = _mark_stack->capacity()/4;
8115 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8116 "Overflow list should be NULL during concurrent phases");
8117 while (!_mark_stack->isEmpty() ||
8118 // if stack is empty, check the overflow list
8119 _collector->take_from_overflow_list(num, _mark_stack)) {
8120 oop obj = _mark_stack->pop();
8121 HeapWord* addr = (HeapWord*)obj;
8122 assert(_span.contains(addr), "Should be within span");
8123 assert(_bit_map->isMarked(addr), "Should be marked");
8124 assert(obj->is_oop(), "Should be an oop");
8125 obj->oop_iterate(_keep_alive);
8126 }
8127 }
8128
8129 void CMSParDrainMarkingStackClosure::do_void() {
8130 // drain queue
8131 trim_queue(0);
8132 }
8133
8134 // Trim our work_queue so its length is below max at return
8135 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8136 while (_work_queue->size() > max) {
8137 oop new_oop;
8138 if (_work_queue->pop_local(new_oop)) {
8139 assert(new_oop->is_oop(), "Expected an oop");
8140 assert(_bit_map->isMarked((HeapWord*)new_oop),
8141 "no white objects on this stack!");
8142 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8143 // iterate over the oops in this oop, marking and pushing
8144 // the ones in CMS heap (i.e. in _span).
8145 new_oop->oop_iterate(&_mark_and_push);
8146 }
8147 }
8148 }
8149
8150 ////////////////////////////////////////////////////////////////////
8151 // Support for Marking Stack Overflow list handling and related code
8152 ////////////////////////////////////////////////////////////////////
8153 // Much of the following code is similar in shape and spirit to the
8154 // code used in ParNewGC. We should try and share that code
8155 // as much as possible in the future.
8156
8157 #ifndef PRODUCT
8158 // Debugging support for CMSStackOverflowALot
8159
8160 // It's OK to call this multi-threaded; the worst thing
8161 // that can happen is that we'll get a bunch of closely
8162 // spaced simulated overflows, but that's OK, in fact
8163 // probably good as it would exercise the overflow code
8164 // under contention.
8165 bool CMSCollector::simulate_overflow() {
8166 if (_overflow_counter-- <= 0) { // just being defensive
8167 _overflow_counter = CMSMarkStackOverflowInterval;
8168 return true;
8169 } else {
8170 return false;
8171 }
8172 }
8173
8174 bool CMSCollector::par_simulate_overflow() {
8175 return simulate_overflow();
8176 }
8177 #endif
8178
8179 // Single-threaded
8180 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8181 assert(stack->isEmpty(), "Expected precondition");
8182 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8183 size_t i = num;
8184 oop cur = _overflow_list;
8185 const markOop proto = markOopDesc::prototype();
8186 NOT_PRODUCT(ssize_t n = 0;)
8187 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8188 next = oop(cur->mark());
8189 cur->set_mark(proto); // until proven otherwise
8190 assert(cur->is_oop(), "Should be an oop");
8191 bool res = stack->push(cur);
8192 assert(res, "Bit off more than can chew?");
8193 NOT_PRODUCT(n++;)
8194 }
8195 _overflow_list = cur;
8196 #ifndef PRODUCT
8197 assert(_num_par_pushes >= n, "Too many pops?");
8198 _num_par_pushes -=n;
8199 #endif
8200 return !stack->isEmpty();
8201 }
8202
8203 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8204 // (MT-safe) Get a prefix of at most "num" from the list.
8205 // The overflow list is chained through the mark word of
8206 // each object in the list. We fetch the entire list,
8207 // break off a prefix of the right size and return the
8208 // remainder. If other threads try to take objects from
8209 // the overflow list at that time, they will wait for
8210 // some time to see if data becomes available. If (and
8211 // only if) another thread places one or more object(s)
8212 // on the global list before we have returned the suffix
8213 // to the global list, we will walk down our local list
8214 // to find its end and append the global list to
8215 // our suffix before returning it. This suffix walk can
8216 // prove to be expensive (quadratic in the amount of traffic)
8217 // when there are many objects in the overflow list and
8218 // there is much producer-consumer contention on the list.
8219 // *NOTE*: The overflow list manipulation code here and
8220 // in ParNewGeneration:: are very similar in shape,
8221 // except that in the ParNew case we use the old (from/eden)
8222 // copy of the object to thread the list via its klass word.
8223 // Because of the common code, if you make any changes in
8224 // the code below, please check the ParNew version to see if
8225 // similar changes might be needed.
8226 // CR 6797058 has been filed to consolidate the common code.
8227 bool CMSCollector::par_take_from_overflow_list(size_t num,
8228 OopTaskQueue* work_q,
8229 int no_of_gc_threads) {
8230 assert(work_q->size() == 0, "First empty local work queue");
8231 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8232 if (_overflow_list == NULL) {
8233 return false;
8234 }
8235 // Grab the entire list; we'll put back a suffix
8236 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8237 Thread* tid = Thread::current();
8238 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8239 // set to ParallelGCThreads.
8240 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8241 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8242 // If the list is busy, we spin for a short while,
8243 // sleeping between attempts to get the list.
8244 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8245 os::sleep(tid, sleep_time_millis, false);
8246 if (_overflow_list == NULL) {
8247 // Nothing left to take
8248 return false;
8249 } else if (_overflow_list != BUSY) {
8250 // Try and grab the prefix
8251 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8252 }
8253 }
8254 // If the list was found to be empty, or we spun long
8255 // enough, we give up and return empty-handed. If we leave
8256 // the list in the BUSY state below, it must be the case that
8257 // some other thread holds the overflow list and will set it
8258 // to a non-BUSY state in the future.
8259 if (prefix == NULL || prefix == BUSY) {
8260 // Nothing to take or waited long enough
8261 if (prefix == NULL) {
8262 // Write back the NULL in case we overwrote it with BUSY above
8263 // and it is still the same value.
8264 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8265 }
8266 return false;
8267 }
8268 assert(prefix != NULL && prefix != BUSY, "Error");
8269 size_t i = num;
8270 oop cur = prefix;
8271 // Walk down the first "num" objects, unless we reach the end.
8272 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8273 if (cur->mark() == NULL) {
8274 // We have "num" or fewer elements in the list, so there
8275 // is nothing to return to the global list.
8276 // Write back the NULL in lieu of the BUSY we wrote
8277 // above, if it is still the same value.
8278 if (_overflow_list == BUSY) {
8279 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8280 }
8281 } else {
8282 // Chop off the suffix and return it to the global list.
8283 assert(cur->mark() != BUSY, "Error");
8284 oop suffix_head = cur->mark(); // suffix will be put back on global list
8285 cur->set_mark(NULL); // break off suffix
8286 // It's possible that the list is still in the empty(busy) state
8287 // we left it in a short while ago; in that case we may be
8288 // able to place back the suffix without incurring the cost
8289 // of a walk down the list.
8290 oop observed_overflow_list = _overflow_list;
8291 oop cur_overflow_list = observed_overflow_list;
8292 bool attached = false;
8293 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8294 observed_overflow_list =
8295 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8296 if (cur_overflow_list == observed_overflow_list) {
8297 attached = true;
8298 break;
8299 } else cur_overflow_list = observed_overflow_list;
8300 }
8301 if (!attached) {
8302 // Too bad, someone else sneaked in (at least) an element; we'll need
8303 // to do a splice. Find tail of suffix so we can prepend suffix to global
8304 // list.
8305 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8306 oop suffix_tail = cur;
8307 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8308 "Tautology");
8309 observed_overflow_list = _overflow_list;
8310 do {
8311 cur_overflow_list = observed_overflow_list;
8312 if (cur_overflow_list != BUSY) {
8313 // Do the splice ...
8314 suffix_tail->set_mark(markOop(cur_overflow_list));
8315 } else { // cur_overflow_list == BUSY
8316 suffix_tail->set_mark(NULL);
8317 }
8318 // ... and try to place spliced list back on overflow_list ...
8319 observed_overflow_list =
8320 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8321 } while (cur_overflow_list != observed_overflow_list);
8322 // ... until we have succeeded in doing so.
8323 }
8324 }
8325
8326 // Push the prefix elements on work_q
8327 assert(prefix != NULL, "control point invariant");
8328 const markOop proto = markOopDesc::prototype();
8329 oop next;
8330 NOT_PRODUCT(ssize_t n = 0;)
8331 for (cur = prefix; cur != NULL; cur = next) {
8332 next = oop(cur->mark());
8333 cur->set_mark(proto); // until proven otherwise
8334 assert(cur->is_oop(), "Should be an oop");
8335 bool res = work_q->push(cur);
8336 assert(res, "Bit off more than we can chew?");
8337 NOT_PRODUCT(n++;)
8338 }
8339 #ifndef PRODUCT
8340 assert(_num_par_pushes >= n, "Too many pops?");
8341 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8342 #endif
8343 return true;
8344 }
8345
8346 // Single-threaded
8347 void CMSCollector::push_on_overflow_list(oop p) {
8348 NOT_PRODUCT(_num_par_pushes++;)
8349 assert(p->is_oop(), "Not an oop");
8350 preserve_mark_if_necessary(p);
8351 p->set_mark((markOop)_overflow_list);
8352 _overflow_list = p;
8353 }
8354
8355 // Multi-threaded; use CAS to prepend to overflow list
8356 void CMSCollector::par_push_on_overflow_list(oop p) {
8357 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8358 assert(p->is_oop(), "Not an oop");
8359 par_preserve_mark_if_necessary(p);
8360 oop observed_overflow_list = _overflow_list;
8361 oop cur_overflow_list;
8362 do {
8363 cur_overflow_list = observed_overflow_list;
8364 if (cur_overflow_list != BUSY) {
8365 p->set_mark(markOop(cur_overflow_list));
8366 } else {
8367 p->set_mark(NULL);
8368 }
8369 observed_overflow_list =
8370 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8371 } while (cur_overflow_list != observed_overflow_list);
8372 }
8373 #undef BUSY
8374
8375 // Single threaded
8376 // General Note on GrowableArray: pushes may silently fail
8377 // because we are (temporarily) out of C-heap for expanding
8378 // the stack. The problem is quite ubiquitous and affects
8379 // a lot of code in the JVM. The prudent thing for GrowableArray
8380 // to do (for now) is to exit with an error. However, that may
8381 // be too draconian in some cases because the caller may be
8382 // able to recover without much harm. For such cases, we
8383 // should probably introduce a "soft_push" method which returns
8384 // an indication of success or failure with the assumption that
8385 // the caller may be able to recover from a failure; code in
8386 // the VM can then be changed, incrementally, to deal with such
8387 // failures where possible, thus, incrementally hardening the VM
8388 // in such low resource situations.
8389 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8390 _preserved_oop_stack.push(p);
8391 _preserved_mark_stack.push(m);
8392 assert(m == p->mark(), "Mark word changed");
8393 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8394 "bijection");
8395 }
8396
8397 // Single threaded
8398 void CMSCollector::preserve_mark_if_necessary(oop p) {
8399 markOop m = p->mark();
8400 if (m->must_be_preserved(p)) {
8401 preserve_mark_work(p, m);
8402 }
8403 }
8404
8405 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8406 markOop m = p->mark();
8407 if (m->must_be_preserved(p)) {
8408 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8409 // Even though we read the mark word without holding
8410 // the lock, we are assured that it will not change
8411 // because we "own" this oop, so no other thread can
8412 // be trying to push it on the overflow list; see
8413 // the assertion in preserve_mark_work() that checks
8414 // that m == p->mark().
8415 preserve_mark_work(p, m);
8416 }
8417 }
8418
8419 // We should be able to do this multi-threaded,
8420 // a chunk of stack being a task (this is
8421 // correct because each oop only ever appears
8422 // once in the overflow list. However, it's
8423 // not very easy to completely overlap this with
8424 // other operations, so will generally not be done
8425 // until all work's been completed. Because we
8426 // expect the preserved oop stack (set) to be small,
8427 // it's probably fine to do this single-threaded.
8428 // We can explore cleverer concurrent/overlapped/parallel
8429 // processing of preserved marks if we feel the
8430 // need for this in the future. Stack overflow should
8431 // be so rare in practice and, when it happens, its
8432 // effect on performance so great that this will
8433 // likely just be in the noise anyway.
8434 void CMSCollector::restore_preserved_marks_if_any() {
8435 assert(SafepointSynchronize::is_at_safepoint(),
8436 "world should be stopped");
8437 assert(Thread::current()->is_ConcurrentGC_thread() ||
8438 Thread::current()->is_VM_thread(),
8439 "should be single-threaded");
8440 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8441 "bijection");
8442
8443 while (!_preserved_oop_stack.is_empty()) {
8444 oop p = _preserved_oop_stack.pop();
8445 assert(p->is_oop(), "Should be an oop");
8446 assert(_span.contains(p), "oop should be in _span");
8447 assert(p->mark() == markOopDesc::prototype(),
8448 "Set when taken from overflow list");
8449 markOop m = _preserved_mark_stack.pop();
8450 p->set_mark(m);
8451 }
8452 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8453 "stacks were cleared above");
8454 }
8455
8456 #ifndef PRODUCT
8457 bool CMSCollector::no_preserved_marks() const {
8458 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8459 }
8460 #endif
8461
8462 // Transfer some number of overflown objects to usual marking
8463 // stack. Return true if some objects were transferred.
8464 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8465 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8466 (size_t)ParGCDesiredObjsFromOverflowList);
8467
8468 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8469 assert(_collector->overflow_list_is_empty() || res,
8470 "If list is not empty, we should have taken something");
8471 assert(!res || !_mark_stack->isEmpty(),
8472 "If we took something, it should now be on our stack");
8473 return res;
8474 }
8475
8476 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8477 size_t res = _sp->block_size_no_stall(addr, _collector);
8478 if (_sp->block_is_obj(addr)) {
8479 if (_live_bit_map->isMarked(addr)) {
8480 // It can't have been dead in a previous cycle
8481 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8482 } else {
8483 _dead_bit_map->mark(addr); // mark the dead object
8484 }
8485 }
8486 // Could be 0, if the block size could not be computed without stalling.
8487 return res;
8488 }
8489
8490 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8491
8492 switch (phase) {
8493 case CMSCollector::InitialMarking:
8494 initialize(true /* fullGC */ ,
8495 cause /* cause of the GC */,
8496 true /* recordGCBeginTime */,
8497 true /* recordPreGCUsage */,
8498 false /* recordPeakUsage */,
8499 false /* recordPostGCusage */,
8500 true /* recordAccumulatedGCTime */,
8501 false /* recordGCEndTime */,
8502 false /* countCollection */ );
8503 break;
8504
8505 case CMSCollector::FinalMarking:
8506 initialize(true /* fullGC */ ,
8507 cause /* cause of the GC */,
8508 false /* recordGCBeginTime */,
8509 false /* recordPreGCUsage */,
8510 false /* recordPeakUsage */,
8511 false /* recordPostGCusage */,
8512 true /* recordAccumulatedGCTime */,
8513 false /* recordGCEndTime */,
8514 false /* countCollection */ );
8515 break;
8516
8517 case CMSCollector::Sweeping:
8518 initialize(true /* fullGC */ ,
8519 cause /* cause of the GC */,
8520 false /* recordGCBeginTime */,
8521 false /* recordPreGCUsage */,
8522 true /* recordPeakUsage */,
8523 true /* recordPostGCusage */,
8524 false /* recordAccumulatedGCTime */,
8525 true /* recordGCEndTime */,
8526 true /* countCollection */ );
8527 break;
8528
8529 default:
8530 ShouldNotReachHere();
8531 }
8532 }