1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc/cms/cmsCollectorPolicy.hpp"
31 #include "gc/cms/cmsOopClosures.inline.hpp"
32 #include "gc/cms/compactibleFreeListSpace.hpp"
33 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
34 #include "gc/cms/concurrentMarkSweepThread.hpp"
35 #include "gc/cms/parNewGeneration.hpp"
36 #include "gc/cms/vmCMSOperations.hpp"
37 #include "gc/serial/genMarkSweep.hpp"
38 #include "gc/serial/tenuredGeneration.hpp"
39 #include "gc/shared/adaptiveSizePolicy.hpp"
40 #include "gc/shared/cardGeneration.inline.hpp"
41 #include "gc/shared/cardTableRS.hpp"
42 #include "gc/shared/collectedHeap.inline.hpp"
43 #include "gc/shared/collectorCounters.hpp"
44 #include "gc/shared/collectorPolicy.hpp"
45 #include "gc/shared/gcLocker.inline.hpp"
46 #include "gc/shared/gcPolicyCounters.hpp"
47 #include "gc/shared/gcTimer.hpp"
48 #include "gc/shared/gcTrace.hpp"
49 #include "gc/shared/gcTraceTime.hpp"
50 #include "gc/shared/genCollectedHeap.hpp"
51 #include "gc/shared/genOopClosures.inline.hpp"
52 #include "gc/shared/isGCActiveMark.hpp"
53 #include "gc/shared/referencePolicy.hpp"
54 #include "gc/shared/strongRootsScope.hpp"
55 #include "gc/shared/taskqueue.inline.hpp"
56 #include "memory/allocation.hpp"
57 #include "memory/iterator.inline.hpp"
58 #include "memory/padded.hpp"
59 #include "memory/resourceArea.hpp"
60 #include "oops/oop.inline.hpp"
61 #include "prims/jvmtiExport.hpp"
62 #include "runtime/atomic.inline.hpp"
63 #include "runtime/globals_extension.hpp"
64 #include "runtime/handles.inline.hpp"
65 #include "runtime/java.hpp"
66 #include "runtime/orderAccess.inline.hpp"
67 #include "runtime/vmThread.hpp"
68 #include "services/memoryService.hpp"
69 #include "services/runtimeService.hpp"
70 #include "utilities/stack.inline.hpp"
71
72 // statics
73 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
74 bool CMSCollector::_full_gc_requested = false;
75 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
76
77 //////////////////////////////////////////////////////////////////
78 // In support of CMS/VM thread synchronization
79 //////////////////////////////////////////////////////////////////
80 // We split use of the CGC_lock into 2 "levels".
81 // The low-level locking is of the usual CGC_lock monitor. We introduce
82 // a higher level "token" (hereafter "CMS token") built on top of the
83 // low level monitor (hereafter "CGC lock").
84 // The token-passing protocol gives priority to the VM thread. The
85 // CMS-lock doesn't provide any fairness guarantees, but clients
86 // should ensure that it is only held for very short, bounded
87 // durations.
88 //
89 // When either of the CMS thread or the VM thread is involved in
90 // collection operations during which it does not want the other
91 // thread to interfere, it obtains the CMS token.
92 //
93 // If either thread tries to get the token while the other has
94 // it, that thread waits. However, if the VM thread and CMS thread
95 // both want the token, then the VM thread gets priority while the
96 // CMS thread waits. This ensures, for instance, that the "concurrent"
97 // phases of the CMS thread's work do not block out the VM thread
98 // for long periods of time as the CMS thread continues to hog
99 // the token. (See bug 4616232).
100 //
101 // The baton-passing functions are, however, controlled by the
102 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
103 // and here the low-level CMS lock, not the high level token,
104 // ensures mutual exclusion.
105 //
106 // Two important conditions that we have to satisfy:
107 // 1. if a thread does a low-level wait on the CMS lock, then it
108 // relinquishes the CMS token if it were holding that token
109 // when it acquired the low-level CMS lock.
110 // 2. any low-level notifications on the low-level lock
111 // should only be sent when a thread has relinquished the token.
112 //
113 // In the absence of either property, we'd have potential deadlock.
114 //
115 // We protect each of the CMS (concurrent and sequential) phases
116 // with the CMS _token_, not the CMS _lock_.
117 //
118 // The only code protected by CMS lock is the token acquisition code
119 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
120 // baton-passing code.
121 //
122 // Unfortunately, i couldn't come up with a good abstraction to factor and
123 // hide the naked CGC_lock manipulation in the baton-passing code
124 // further below. That's something we should try to do. Also, the proof
125 // of correctness of this 2-level locking scheme is far from obvious,
126 // and potentially quite slippery. We have an uneasy suspicion, for instance,
127 // that there may be a theoretical possibility of delay/starvation in the
128 // low-level lock/wait/notify scheme used for the baton-passing because of
129 // potential interference with the priority scheme embodied in the
130 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
131 // invocation further below and marked with "XXX 20011219YSR".
132 // Indeed, as we note elsewhere, this may become yet more slippery
133 // in the presence of multiple CMS and/or multiple VM threads. XXX
134
135 class CMSTokenSync: public StackObj {
136 private:
137 bool _is_cms_thread;
138 public:
139 CMSTokenSync(bool is_cms_thread):
140 _is_cms_thread(is_cms_thread) {
141 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
142 "Incorrect argument to constructor");
143 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
144 }
145
146 ~CMSTokenSync() {
147 assert(_is_cms_thread ?
148 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
149 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
150 "Incorrect state");
151 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
152 }
153 };
154
155 // Convenience class that does a CMSTokenSync, and then acquires
156 // upto three locks.
157 class CMSTokenSyncWithLocks: public CMSTokenSync {
158 private:
159 // Note: locks are acquired in textual declaration order
160 // and released in the opposite order
161 MutexLockerEx _locker1, _locker2, _locker3;
162 public:
163 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
164 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
165 CMSTokenSync(is_cms_thread),
166 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
167 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
168 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
169 { }
170 };
171
172
173 //////////////////////////////////////////////////////////////////
174 // Concurrent Mark-Sweep Generation /////////////////////////////
175 //////////////////////////////////////////////////////////////////
176
177 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
178
179 // This struct contains per-thread things necessary to support parallel
180 // young-gen collection.
181 class CMSParGCThreadState: public CHeapObj<mtGC> {
182 public:
183 CFLS_LAB lab;
184 PromotionInfo promo;
185
186 // Constructor.
187 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
188 promo.setSpace(cfls);
189 }
190 };
191
192 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
193 ReservedSpace rs, size_t initial_byte_size,
194 CardTableRS* ct, bool use_adaptive_freelists,
195 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
196 CardGeneration(rs, initial_byte_size, ct),
197 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
198 _did_compact(false)
199 {
200 HeapWord* bottom = (HeapWord*) _virtual_space.low();
201 HeapWord* end = (HeapWord*) _virtual_space.high();
202
203 _direct_allocated_words = 0;
204 NOT_PRODUCT(
205 _numObjectsPromoted = 0;
206 _numWordsPromoted = 0;
207 _numObjectsAllocated = 0;
208 _numWordsAllocated = 0;
209 )
210
211 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
212 use_adaptive_freelists,
213 dictionaryChoice);
214 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
215 _cmsSpace->_old_gen = this;
216
217 _gc_stats = new CMSGCStats();
218
219 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
220 // offsets match. The ability to tell free chunks from objects
221 // depends on this property.
222 debug_only(
223 FreeChunk* junk = NULL;
224 assert(UseCompressedClassPointers ||
225 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
226 "Offset of FreeChunk::_prev within FreeChunk must match"
227 " that of OopDesc::_klass within OopDesc");
228 )
229
230 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
231 for (uint i = 0; i < ParallelGCThreads; i++) {
232 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
233 }
234
235 _incremental_collection_failed = false;
236 // The "dilatation_factor" is the expansion that can occur on
237 // account of the fact that the minimum object size in the CMS
238 // generation may be larger than that in, say, a contiguous young
239 // generation.
240 // Ideally, in the calculation below, we'd compute the dilatation
241 // factor as: MinChunkSize/(promoting_gen's min object size)
242 // Since we do not have such a general query interface for the
243 // promoting generation, we'll instead just use the minimum
244 // object size (which today is a header's worth of space);
245 // note that all arithmetic is in units of HeapWords.
246 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
247 assert(_dilatation_factor >= 1.0, "from previous assert");
248 }
249
250
251 // The field "_initiating_occupancy" represents the occupancy percentage
252 // at which we trigger a new collection cycle. Unless explicitly specified
253 // via CMSInitiatingOccupancyFraction (argument "io" below), it
254 // is calculated by:
255 //
256 // Let "f" be MinHeapFreeRatio in
257 //
258 // _initiating_occupancy = 100-f +
259 // f * (CMSTriggerRatio/100)
260 // where CMSTriggerRatio is the argument "tr" below.
261 //
262 // That is, if we assume the heap is at its desired maximum occupancy at the
263 // end of a collection, we let CMSTriggerRatio of the (purported) free
264 // space be allocated before initiating a new collection cycle.
265 //
266 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
267 assert(io <= 100 && tr <= 100, "Check the arguments");
268 if (io >= 0) {
269 _initiating_occupancy = (double)io / 100.0;
270 } else {
271 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
272 (double)(tr * MinHeapFreeRatio) / 100.0)
273 / 100.0;
274 }
275 }
276
277 void ConcurrentMarkSweepGeneration::ref_processor_init() {
278 assert(collector() != NULL, "no collector");
279 collector()->ref_processor_init();
280 }
281
282 void CMSCollector::ref_processor_init() {
283 if (_ref_processor == NULL) {
284 // Allocate and initialize a reference processor
285 _ref_processor =
286 new ReferenceProcessor(_span, // span
287 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
288 ParallelGCThreads, // mt processing degree
289 _cmsGen->refs_discovery_is_mt(), // mt discovery
290 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
291 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
292 &_is_alive_closure); // closure for liveness info
293 // Initialize the _ref_processor field of CMSGen
294 _cmsGen->set_ref_processor(_ref_processor);
295
296 }
297 }
298
299 AdaptiveSizePolicy* CMSCollector::size_policy() {
300 GenCollectedHeap* gch = GenCollectedHeap::heap();
301 return gch->gen_policy()->size_policy();
302 }
303
304 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
305
306 const char* gen_name = "old";
307 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
308 // Generation Counters - generation 1, 1 subspace
309 _gen_counters = new GenerationCounters(gen_name, 1, 1,
310 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
311
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
316
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
322
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
325
326 _cms_begin_time.update();
327 _cms_end_time.update();
328
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
332
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
336
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 }
342
343 double CMSStats::cms_free_adjustment_factor(size_t free) const {
344 // TBD: CR 6909490
345 return 1.0;
346 }
347
348 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
349 }
350
351 // If promotion failure handling is on use
352 // the padded average size of the promotion for each
353 // young generation collection.
354 double CMSStats::time_until_cms_gen_full() const {
355 size_t cms_free = _cms_gen->cmsSpace()->free();
356 GenCollectedHeap* gch = GenCollectedHeap::heap();
357 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
358 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
359 if (cms_free > expected_promotion) {
360 // Start a cms collection if there isn't enough space to promote
361 // for the next young collection. Use the padded average as
362 // a safety factor.
363 cms_free -= expected_promotion;
364
365 // Adjust by the safety factor.
366 double cms_free_dbl = (double)cms_free;
367 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
368 // Apply a further correction factor which tries to adjust
369 // for recent occurance of concurrent mode failures.
370 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
371 cms_free_dbl = cms_free_dbl * cms_adjustment;
372
373 if (PrintGCDetails && Verbose) {
374 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
375 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
376 cms_free, expected_promotion);
377 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
378 cms_free_dbl, cms_consumption_rate() + 1.0);
379 }
380 // Add 1 in case the consumption rate goes to zero.
381 return cms_free_dbl / (cms_consumption_rate() + 1.0);
382 }
383 return 0.0;
384 }
385
386 // Compare the duration of the cms collection to the
387 // time remaining before the cms generation is empty.
388 // Note that the time from the start of the cms collection
389 // to the start of the cms sweep (less than the total
390 // duration of the cms collection) can be used. This
391 // has been tried and some applications experienced
392 // promotion failures early in execution. This was
393 // possibly because the averages were not accurate
394 // enough at the beginning.
395 double CMSStats::time_until_cms_start() const {
396 // We add "gc0_period" to the "work" calculation
397 // below because this query is done (mostly) at the
398 // end of a scavenge, so we need to conservatively
399 // account for that much possible delay
400 // in the query so as to avoid concurrent mode failures
401 // due to starting the collection just a wee bit too
402 // late.
403 double work = cms_duration() + gc0_period();
404 double deadline = time_until_cms_gen_full();
405 // If a concurrent mode failure occurred recently, we want to be
406 // more conservative and halve our expected time_until_cms_gen_full()
407 if (work > deadline) {
408 if (Verbose && PrintGCDetails) {
409 gclog_or_tty->print(
410 " CMSCollector: collect because of anticipated promotion "
411 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
412 gc0_period(), time_until_cms_gen_full());
413 }
414 return 0.0;
415 }
416 return work - deadline;
417 }
418
419 #ifndef PRODUCT
420 void CMSStats::print_on(outputStream *st) const {
421 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
422 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
423 gc0_duration(), gc0_period(), gc0_promoted());
424 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
425 cms_duration(), cms_period(), cms_allocated());
426 st->print(",cms_since_beg=%g,cms_since_end=%g",
427 cms_time_since_begin(), cms_time_since_end());
428 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
429 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
430
431 if (valid()) {
432 st->print(",promo_rate=%g,cms_alloc_rate=%g",
433 promotion_rate(), cms_allocation_rate());
434 st->print(",cms_consumption_rate=%g,time_until_full=%g",
435 cms_consumption_rate(), time_until_cms_gen_full());
436 }
437 st->print(" ");
438 }
439 #endif // #ifndef PRODUCT
440
441 CMSCollector::CollectorState CMSCollector::_collectorState =
442 CMSCollector::Idling;
443 bool CMSCollector::_foregroundGCIsActive = false;
444 bool CMSCollector::_foregroundGCShouldWait = false;
445
446 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
447 CardTableRS* ct,
448 ConcurrentMarkSweepPolicy* cp):
449 _cmsGen(cmsGen),
450 _ct(ct),
451 _ref_processor(NULL), // will be set later
452 _conc_workers(NULL), // may be set later
453 _abort_preclean(false),
454 _start_sampling(false),
455 _between_prologue_and_epilogue(false),
456 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
457 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
458 -1 /* lock-free */, "No_lock" /* dummy */),
459 _modUnionClosurePar(&_modUnionTable),
460 // Adjust my span to cover old (cms) gen
461 _span(cmsGen->reserved()),
462 // Construct the is_alive_closure with _span & markBitMap
463 _is_alive_closure(_span, &_markBitMap),
464 _restart_addr(NULL),
465 _overflow_list(NULL),
466 _stats(cmsGen),
467 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
468 //verify that this lock should be acquired with safepoint check.
469 Monitor::_safepoint_check_sometimes)),
470 _eden_chunk_array(NULL), // may be set in ctor body
471 _eden_chunk_capacity(0), // -- ditto --
472 _eden_chunk_index(0), // -- ditto --
473 _survivor_plab_array(NULL), // -- ditto --
474 _survivor_chunk_array(NULL), // -- ditto --
475 _survivor_chunk_capacity(0), // -- ditto --
476 _survivor_chunk_index(0), // -- ditto --
477 _ser_pmc_preclean_ovflw(0),
478 _ser_kac_preclean_ovflw(0),
479 _ser_pmc_remark_ovflw(0),
480 _par_pmc_remark_ovflw(0),
481 _ser_kac_ovflw(0),
482 _par_kac_ovflw(0),
483 #ifndef PRODUCT
484 _num_par_pushes(0),
485 #endif
486 _collection_count_start(0),
487 _verifying(false),
488 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
489 _completed_initialization(false),
490 _collector_policy(cp),
491 _should_unload_classes(CMSClassUnloadingEnabled),
492 _concurrent_cycles_since_last_unload(0),
493 _roots_scanning_options(GenCollectedHeap::SO_None),
494 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
495 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
496 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
497 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
498 _cms_start_registered(false)
499 {
500 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
501 ExplicitGCInvokesConcurrent = true;
502 }
503 // Now expand the span and allocate the collection support structures
504 // (MUT, marking bit map etc.) to cover both generations subject to
505 // collection.
506
507 // For use by dirty card to oop closures.
508 _cmsGen->cmsSpace()->set_collector(this);
509
510 // Allocate MUT and marking bit map
511 {
512 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
513 if (!_markBitMap.allocate(_span)) {
514 warning("Failed to allocate CMS Bit Map");
515 return;
516 }
517 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
518 }
519 {
520 _modUnionTable.allocate(_span);
521 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
522 }
523
524 if (!_markStack.allocate(MarkStackSize)) {
525 warning("Failed to allocate CMS Marking Stack");
526 return;
527 }
528
529 // Support for multi-threaded concurrent phases
530 if (CMSConcurrentMTEnabled) {
531 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
532 // just for now
533 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
534 }
535 if (ConcGCThreads > 1) {
536 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
537 ConcGCThreads, true);
538 if (_conc_workers == NULL) {
539 warning("GC/CMS: _conc_workers allocation failure: "
540 "forcing -CMSConcurrentMTEnabled");
541 CMSConcurrentMTEnabled = false;
542 } else {
543 _conc_workers->initialize_workers();
544 }
545 } else {
546 CMSConcurrentMTEnabled = false;
547 }
548 }
549 if (!CMSConcurrentMTEnabled) {
550 ConcGCThreads = 0;
551 } else {
552 // Turn off CMSCleanOnEnter optimization temporarily for
553 // the MT case where it's not fixed yet; see 6178663.
554 CMSCleanOnEnter = false;
555 }
556 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
557 "Inconsistency");
558
559 // Parallel task queues; these are shared for the
560 // concurrent and stop-world phases of CMS, but
561 // are not shared with parallel scavenge (ParNew).
562 {
563 uint i;
564 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
565
566 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
567 || ParallelRefProcEnabled)
568 && num_queues > 0) {
569 _task_queues = new OopTaskQueueSet(num_queues);
570 if (_task_queues == NULL) {
571 warning("task_queues allocation failure.");
572 return;
573 }
574 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
575 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
576 for (i = 0; i < num_queues; i++) {
577 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
578 if (q == NULL) {
579 warning("work_queue allocation failure.");
580 return;
581 }
582 _task_queues->register_queue(i, q);
583 }
584 for (i = 0; i < num_queues; i++) {
585 _task_queues->queue(i)->initialize();
586 _hash_seed[i] = 17; // copied from ParNew
587 }
588 }
589 }
590
591 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
592
593 // Clip CMSBootstrapOccupancy between 0 and 100.
594 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
595
596 // Now tell CMS generations the identity of their collector
597 ConcurrentMarkSweepGeneration::set_collector(this);
598
599 // Create & start a CMS thread for this CMS collector
600 _cmsThread = ConcurrentMarkSweepThread::start(this);
601 assert(cmsThread() != NULL, "CMS Thread should have been created");
602 assert(cmsThread()->collector() == this,
603 "CMS Thread should refer to this gen");
604 assert(CGC_lock != NULL, "Where's the CGC_lock?");
605
606 // Support for parallelizing young gen rescan
607 GenCollectedHeap* gch = GenCollectedHeap::heap();
608 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
609 _young_gen = (ParNewGeneration*)gch->young_gen();
610 if (gch->supports_inline_contig_alloc()) {
611 _top_addr = gch->top_addr();
612 _end_addr = gch->end_addr();
613 assert(_young_gen != NULL, "no _young_gen");
614 _eden_chunk_index = 0;
615 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
616 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
617 }
618
619 // Support for parallelizing survivor space rescan
620 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
621 const size_t max_plab_samples =
622 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
623
624 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
625 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
626 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
627 _survivor_chunk_capacity = max_plab_samples;
628 for (uint i = 0; i < ParallelGCThreads; i++) {
629 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
630 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
631 assert(cur->end() == 0, "Should be 0");
632 assert(cur->array() == vec, "Should be vec");
633 assert(cur->capacity() == max_plab_samples, "Error");
634 }
635 }
636
637 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
638 _gc_counters = new CollectorCounters("CMS", 1);
639 _completed_initialization = true;
640 _inter_sweep_timer.start(); // start of time
641 }
642
643 const char* ConcurrentMarkSweepGeneration::name() const {
644 return "concurrent mark-sweep generation";
645 }
646 void ConcurrentMarkSweepGeneration::update_counters() {
647 if (UsePerfData) {
648 _space_counters->update_all();
649 _gen_counters->update_all();
650 }
651 }
652
653 // this is an optimized version of update_counters(). it takes the
654 // used value as a parameter rather than computing it.
655 //
656 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
657 if (UsePerfData) {
658 _space_counters->update_used(used);
659 _space_counters->update_capacity();
660 _gen_counters->update_all();
661 }
662 }
663
664 void ConcurrentMarkSweepGeneration::print() const {
665 Generation::print();
666 cmsSpace()->print();
667 }
668
669 #ifndef PRODUCT
670 void ConcurrentMarkSweepGeneration::print_statistics() {
671 cmsSpace()->printFLCensus(0);
672 }
673 #endif
674
675 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
676 GenCollectedHeap* gch = GenCollectedHeap::heap();
677 if (PrintGCDetails) {
678 // I didn't want to change the logging when removing the level concept,
679 // but I guess this logging could say "old" or something instead of "1".
680 assert(gch->is_old_gen(this),
681 "The CMS generation should be the old generation");
682 uint level = 1;
683 if (Verbose) {
684 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "(" SIZE_FORMAT ")]",
685 level, short_name(), s, used(), capacity());
686 } else {
687 gclog_or_tty->print("[%u %s-%s: " SIZE_FORMAT "K(" SIZE_FORMAT "K)]",
688 level, short_name(), s, used() / K, capacity() / K);
689 }
690 }
691 if (Verbose) {
692 gclog_or_tty->print(" " SIZE_FORMAT "(" SIZE_FORMAT ")",
693 gch->used(), gch->capacity());
694 } else {
695 gclog_or_tty->print(" " SIZE_FORMAT "K(" SIZE_FORMAT "K)",
696 gch->used() / K, gch->capacity() / K);
697 }
698 }
699
700 size_t
701 ConcurrentMarkSweepGeneration::contiguous_available() const {
702 // dld proposes an improvement in precision here. If the committed
703 // part of the space ends in a free block we should add that to
704 // uncommitted size in the calculation below. Will make this
705 // change later, staying with the approximation below for the
706 // time being. -- ysr.
707 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
708 }
709
710 size_t
711 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
712 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
713 }
714
715 size_t ConcurrentMarkSweepGeneration::max_available() const {
716 return free() + _virtual_space.uncommitted_size();
717 }
718
719 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
720 size_t available = max_available();
721 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
722 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
723 if (Verbose && PrintGCDetails) {
724 gclog_or_tty->print_cr(
725 "CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "),"
726 "max_promo(" SIZE_FORMAT ")",
727 res? "":" not", available, res? ">=":"<",
728 av_promo, max_promotion_in_bytes);
729 }
730 return res;
731 }
732
733 // At a promotion failure dump information on block layout in heap
734 // (cms old generation).
735 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
736 if (CMSDumpAtPromotionFailure) {
737 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
738 }
739 }
740
741 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
742 // Clear the promotion information. These pointers can be adjusted
743 // along with all the other pointers into the heap but
744 // compaction is expected to be a rare event with
745 // a heap using cms so don't do it without seeing the need.
746 for (uint i = 0; i < ParallelGCThreads; i++) {
747 _par_gc_thread_states[i]->promo.reset();
748 }
749 }
750
751 void ConcurrentMarkSweepGeneration::compute_new_size() {
752 assert_locked_or_safepoint(Heap_lock);
753
754 // If incremental collection failed, we just want to expand
755 // to the limit.
756 if (incremental_collection_failed()) {
757 clear_incremental_collection_failed();
758 grow_to_reserved();
759 return;
760 }
761
762 // The heap has been compacted but not reset yet.
763 // Any metric such as free() or used() will be incorrect.
764
765 CardGeneration::compute_new_size();
766
767 // Reset again after a possible resizing
768 if (did_compact()) {
769 cmsSpace()->reset_after_compaction();
770 }
771 }
772
773 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
774 assert_locked_or_safepoint(Heap_lock);
775
776 // If incremental collection failed, we just want to expand
777 // to the limit.
778 if (incremental_collection_failed()) {
779 clear_incremental_collection_failed();
780 grow_to_reserved();
781 return;
782 }
783
784 double free_percentage = ((double) free()) / capacity();
785 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
786 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
787
788 // compute expansion delta needed for reaching desired free percentage
789 if (free_percentage < desired_free_percentage) {
790 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
791 assert(desired_capacity >= capacity(), "invalid expansion size");
792 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
793 if (PrintGCDetails && Verbose) {
794 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
795 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
796 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
797 gclog_or_tty->print_cr(" Desired free fraction %f", desired_free_percentage);
798 gclog_or_tty->print_cr(" Maximum free fraction %f", maximum_free_percentage);
799 gclog_or_tty->print_cr(" Capacity " SIZE_FORMAT, capacity() / 1000);
800 gclog_or_tty->print_cr(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
801 GenCollectedHeap* gch = GenCollectedHeap::heap();
802 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
803 size_t young_size = gch->young_gen()->capacity();
804 gclog_or_tty->print_cr(" Young gen size " SIZE_FORMAT, young_size / 1000);
805 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
806 gclog_or_tty->print_cr(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
807 gclog_or_tty->print_cr(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
808 }
809 // safe if expansion fails
810 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
811 if (PrintGCDetails && Verbose) {
812 gclog_or_tty->print_cr(" Expanded free fraction %f", ((double) free()) / capacity());
813 }
814 } else {
815 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
816 assert(desired_capacity <= capacity(), "invalid expansion size");
817 size_t shrink_bytes = capacity() - desired_capacity;
818 // Don't shrink unless the delta is greater than the minimum shrink we want
819 if (shrink_bytes >= MinHeapDeltaBytes) {
820 shrink_free_list_by(shrink_bytes);
821 }
822 }
823 }
824
825 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
826 return cmsSpace()->freelistLock();
827 }
828
829 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
830 CMSSynchronousYieldRequest yr;
831 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
832 return have_lock_and_allocate(size, tlab);
833 }
834
835 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
836 bool tlab /* ignored */) {
837 assert_lock_strong(freelistLock());
838 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
839 HeapWord* res = cmsSpace()->allocate(adjustedSize);
840 // Allocate the object live (grey) if the background collector has
841 // started marking. This is necessary because the marker may
842 // have passed this address and consequently this object will
843 // not otherwise be greyed and would be incorrectly swept up.
844 // Note that if this object contains references, the writing
845 // of those references will dirty the card containing this object
846 // allowing the object to be blackened (and its references scanned)
847 // either during a preclean phase or at the final checkpoint.
848 if (res != NULL) {
849 // We may block here with an uninitialized object with
850 // its mark-bit or P-bits not yet set. Such objects need
851 // to be safely navigable by block_start().
852 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
853 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
854 collector()->direct_allocated(res, adjustedSize);
855 _direct_allocated_words += adjustedSize;
856 // allocation counters
857 NOT_PRODUCT(
858 _numObjectsAllocated++;
859 _numWordsAllocated += (int)adjustedSize;
860 )
861 }
862 return res;
863 }
864
865 // In the case of direct allocation by mutators in a generation that
866 // is being concurrently collected, the object must be allocated
867 // live (grey) if the background collector has started marking.
868 // This is necessary because the marker may
869 // have passed this address and consequently this object will
870 // not otherwise be greyed and would be incorrectly swept up.
871 // Note that if this object contains references, the writing
872 // of those references will dirty the card containing this object
873 // allowing the object to be blackened (and its references scanned)
874 // either during a preclean phase or at the final checkpoint.
875 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
876 assert(_markBitMap.covers(start, size), "Out of bounds");
877 if (_collectorState >= Marking) {
878 MutexLockerEx y(_markBitMap.lock(),
879 Mutex::_no_safepoint_check_flag);
880 // [see comments preceding SweepClosure::do_blk() below for details]
881 //
882 // Can the P-bits be deleted now? JJJ
883 //
884 // 1. need to mark the object as live so it isn't collected
885 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
886 // 3. need to mark the end of the object so marking, precleaning or sweeping
887 // can skip over uninitialized or unparsable objects. An allocated
888 // object is considered uninitialized for our purposes as long as
889 // its klass word is NULL. All old gen objects are parsable
890 // as soon as they are initialized.)
891 _markBitMap.mark(start); // object is live
892 _markBitMap.mark(start + 1); // object is potentially uninitialized?
893 _markBitMap.mark(start + size - 1);
894 // mark end of object
895 }
896 // check that oop looks uninitialized
897 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
898 }
899
900 void CMSCollector::promoted(bool par, HeapWord* start,
901 bool is_obj_array, size_t obj_size) {
902 assert(_markBitMap.covers(start), "Out of bounds");
903 // See comment in direct_allocated() about when objects should
904 // be allocated live.
905 if (_collectorState >= Marking) {
906 // we already hold the marking bit map lock, taken in
907 // the prologue
908 if (par) {
909 _markBitMap.par_mark(start);
910 } else {
911 _markBitMap.mark(start);
912 }
913 // We don't need to mark the object as uninitialized (as
914 // in direct_allocated above) because this is being done with the
915 // world stopped and the object will be initialized by the
916 // time the marking, precleaning or sweeping get to look at it.
917 // But see the code for copying objects into the CMS generation,
918 // where we need to ensure that concurrent readers of the
919 // block offset table are able to safely navigate a block that
920 // is in flux from being free to being allocated (and in
921 // transition while being copied into) and subsequently
922 // becoming a bona-fide object when the copy/promotion is complete.
923 assert(SafepointSynchronize::is_at_safepoint(),
924 "expect promotion only at safepoints");
925
926 if (_collectorState < Sweeping) {
927 // Mark the appropriate cards in the modUnionTable, so that
928 // this object gets scanned before the sweep. If this is
929 // not done, CMS generation references in the object might
930 // not get marked.
931 // For the case of arrays, which are otherwise precisely
932 // marked, we need to dirty the entire array, not just its head.
933 if (is_obj_array) {
934 // The [par_]mark_range() method expects mr.end() below to
935 // be aligned to the granularity of a bit's representation
936 // in the heap. In the case of the MUT below, that's a
937 // card size.
938 MemRegion mr(start,
939 (HeapWord*)round_to((intptr_t)(start + obj_size),
940 CardTableModRefBS::card_size /* bytes */));
941 if (par) {
942 _modUnionTable.par_mark_range(mr);
943 } else {
944 _modUnionTable.mark_range(mr);
945 }
946 } else { // not an obj array; we can just mark the head
947 if (par) {
948 _modUnionTable.par_mark(start);
949 } else {
950 _modUnionTable.mark(start);
951 }
952 }
953 }
954 }
955 }
956
957 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
958 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
959 // allocate, copy and if necessary update promoinfo --
960 // delegate to underlying space.
961 assert_lock_strong(freelistLock());
962
963 #ifndef PRODUCT
964 if (GenCollectedHeap::heap()->promotion_should_fail()) {
965 return NULL;
966 }
967 #endif // #ifndef PRODUCT
968
969 oop res = _cmsSpace->promote(obj, obj_size);
970 if (res == NULL) {
971 // expand and retry
972 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
973 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
974 // Since this is the old generation, we don't try to promote
975 // into a more senior generation.
976 res = _cmsSpace->promote(obj, obj_size);
977 }
978 if (res != NULL) {
979 // See comment in allocate() about when objects should
980 // be allocated live.
981 assert(obj->is_oop(), "Will dereference klass pointer below");
982 collector()->promoted(false, // Not parallel
983 (HeapWord*)res, obj->is_objArray(), obj_size);
984 // promotion counters
985 NOT_PRODUCT(
986 _numObjectsPromoted++;
987 _numWordsPromoted +=
988 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
989 )
990 }
991 return res;
992 }
993
994
995 // IMPORTANT: Notes on object size recognition in CMS.
996 // ---------------------------------------------------
997 // A block of storage in the CMS generation is always in
998 // one of three states. A free block (FREE), an allocated
999 // object (OBJECT) whose size() method reports the correct size,
1000 // and an intermediate state (TRANSIENT) in which its size cannot
1001 // be accurately determined.
1002 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1003 // -----------------------------------------------------
1004 // FREE: klass_word & 1 == 1; mark_word holds block size
1005 //
1006 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1007 // obj->size() computes correct size
1008 //
1009 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1010 //
1011 // STATE IDENTIFICATION: (64 bit+COOPS)
1012 // ------------------------------------
1013 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1014 //
1015 // OBJECT: klass_word installed; klass_word != 0;
1016 // obj->size() computes correct size
1017 //
1018 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1019 //
1020 //
1021 // STATE TRANSITION DIAGRAM
1022 //
1023 // mut / parnew mut / parnew
1024 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1025 // ^ |
1026 // |------------------------ DEAD <------------------------------------|
1027 // sweep mut
1028 //
1029 // While a block is in TRANSIENT state its size cannot be determined
1030 // so readers will either need to come back later or stall until
1031 // the size can be determined. Note that for the case of direct
1032 // allocation, P-bits, when available, may be used to determine the
1033 // size of an object that may not yet have been initialized.
1034
1035 // Things to support parallel young-gen collection.
1036 oop
1037 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1038 oop old, markOop m,
1039 size_t word_sz) {
1040 #ifndef PRODUCT
1041 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1042 return NULL;
1043 }
1044 #endif // #ifndef PRODUCT
1045
1046 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1047 PromotionInfo* promoInfo = &ps->promo;
1048 // if we are tracking promotions, then first ensure space for
1049 // promotion (including spooling space for saving header if necessary).
1050 // then allocate and copy, then track promoted info if needed.
1051 // When tracking (see PromotionInfo::track()), the mark word may
1052 // be displaced and in this case restoration of the mark word
1053 // occurs in the (oop_since_save_marks_)iterate phase.
1054 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1055 // Out of space for allocating spooling buffers;
1056 // try expanding and allocating spooling buffers.
1057 if (!expand_and_ensure_spooling_space(promoInfo)) {
1058 return NULL;
1059 }
1060 }
1061 assert(promoInfo->has_spooling_space(), "Control point invariant");
1062 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1063 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1064 if (obj_ptr == NULL) {
1065 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1066 if (obj_ptr == NULL) {
1067 return NULL;
1068 }
1069 }
1070 oop obj = oop(obj_ptr);
1071 OrderAccess::storestore();
1072 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1073 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1074 // IMPORTANT: See note on object initialization for CMS above.
1075 // Otherwise, copy the object. Here we must be careful to insert the
1076 // klass pointer last, since this marks the block as an allocated object.
1077 // Except with compressed oops it's the mark word.
1078 HeapWord* old_ptr = (HeapWord*)old;
1079 // Restore the mark word copied above.
1080 obj->set_mark(m);
1081 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1082 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1083 OrderAccess::storestore();
1084
1085 if (UseCompressedClassPointers) {
1086 // Copy gap missed by (aligned) header size calculation below
1087 obj->set_klass_gap(old->klass_gap());
1088 }
1089 if (word_sz > (size_t)oopDesc::header_size()) {
1090 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1091 obj_ptr + oopDesc::header_size(),
1092 word_sz - oopDesc::header_size());
1093 }
1094
1095 // Now we can track the promoted object, if necessary. We take care
1096 // to delay the transition from uninitialized to full object
1097 // (i.e., insertion of klass pointer) until after, so that it
1098 // atomically becomes a promoted object.
1099 if (promoInfo->tracking()) {
1100 promoInfo->track((PromotedObject*)obj, old->klass());
1101 }
1102 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1103 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1104 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1105
1106 // Finally, install the klass pointer (this should be volatile).
1107 OrderAccess::storestore();
1108 obj->set_klass(old->klass());
1109 // We should now be able to calculate the right size for this object
1110 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1111
1112 collector()->promoted(true, // parallel
1113 obj_ptr, old->is_objArray(), word_sz);
1114
1115 NOT_PRODUCT(
1116 Atomic::inc_ptr(&_numObjectsPromoted);
1117 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1118 )
1119
1120 return obj;
1121 }
1122
1123 void
1124 ConcurrentMarkSweepGeneration::
1125 par_promote_alloc_done(int thread_num) {
1126 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1127 ps->lab.retire(thread_num);
1128 }
1129
1130 void
1131 ConcurrentMarkSweepGeneration::
1132 par_oop_since_save_marks_iterate_done(int thread_num) {
1133 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1134 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1135 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1136 }
1137
1138 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1139 size_t size,
1140 bool tlab)
1141 {
1142 // We allow a STW collection only if a full
1143 // collection was requested.
1144 return full || should_allocate(size, tlab); // FIX ME !!!
1145 // This and promotion failure handling are connected at the
1146 // hip and should be fixed by untying them.
1147 }
1148
1149 bool CMSCollector::shouldConcurrentCollect() {
1150 if (_full_gc_requested) {
1151 if (Verbose && PrintGCDetails) {
1152 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1153 " gc request (or gc_locker)");
1154 }
1155 return true;
1156 }
1157
1158 FreelistLocker x(this);
1159 // ------------------------------------------------------------------
1160 // Print out lots of information which affects the initiation of
1161 // a collection.
1162 if (PrintCMSInitiationStatistics && stats().valid()) {
1163 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1164 gclog_or_tty->stamp();
1165 gclog_or_tty->cr();
1166 stats().print_on(gclog_or_tty);
1167 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1168 stats().time_until_cms_gen_full());
1169 gclog_or_tty->print_cr("free=" SIZE_FORMAT, _cmsGen->free());
1170 gclog_or_tty->print_cr("contiguous_available=" SIZE_FORMAT,
1171 _cmsGen->contiguous_available());
1172 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1173 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1174 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1175 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1176 gclog_or_tty->print_cr("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1177 gclog_or_tty->print_cr("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1178 gclog_or_tty->print_cr("metadata initialized %d",
1179 MetaspaceGC::should_concurrent_collect());
1180 }
1181 // ------------------------------------------------------------------
1182
1183 // If the estimated time to complete a cms collection (cms_duration())
1184 // is less than the estimated time remaining until the cms generation
1185 // is full, start a collection.
1186 if (!UseCMSInitiatingOccupancyOnly) {
1187 if (stats().valid()) {
1188 if (stats().time_until_cms_start() == 0.0) {
1189 return true;
1190 }
1191 } else {
1192 // We want to conservatively collect somewhat early in order
1193 // to try and "bootstrap" our CMS/promotion statistics;
1194 // this branch will not fire after the first successful CMS
1195 // collection because the stats should then be valid.
1196 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1197 if (Verbose && PrintGCDetails) {
1198 gclog_or_tty->print_cr(
1199 " CMSCollector: collect for bootstrapping statistics:"
1200 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1201 _bootstrap_occupancy);
1202 }
1203 return true;
1204 }
1205 }
1206 }
1207
1208 // Otherwise, we start a collection cycle if
1209 // old gen want a collection cycle started. Each may use
1210 // an appropriate criterion for making this decision.
1211 // XXX We need to make sure that the gen expansion
1212 // criterion dovetails well with this. XXX NEED TO FIX THIS
1213 if (_cmsGen->should_concurrent_collect()) {
1214 if (Verbose && PrintGCDetails) {
1215 gclog_or_tty->print_cr("CMS old gen initiated");
1216 }
1217 return true;
1218 }
1219
1220 // We start a collection if we believe an incremental collection may fail;
1221 // this is not likely to be productive in practice because it's probably too
1222 // late anyway.
1223 GenCollectedHeap* gch = GenCollectedHeap::heap();
1224 assert(gch->collector_policy()->is_generation_policy(),
1225 "You may want to check the correctness of the following");
1226 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1227 if (Verbose && PrintGCDetails) {
1228 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1229 }
1230 return true;
1231 }
1232
1233 if (MetaspaceGC::should_concurrent_collect()) {
1234 if (Verbose && PrintGCDetails) {
1235 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1236 }
1237 return true;
1238 }
1239
1240 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1241 if (CMSTriggerInterval >= 0) {
1242 if (CMSTriggerInterval == 0) {
1243 // Trigger always
1244 return true;
1245 }
1246
1247 // Check the CMS time since begin (we do not check the stats validity
1248 // as we want to be able to trigger the first CMS cycle as well)
1249 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1250 if (Verbose && PrintGCDetails) {
1251 if (stats().valid()) {
1252 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1253 stats().cms_time_since_begin());
1254 } else {
1255 gclog_or_tty->print_cr("CMSCollector: collect because of trigger interval (first collection)");
1256 }
1257 }
1258 return true;
1259 }
1260 }
1261
1262 return false;
1263 }
1264
1265 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1266
1267 // Clear _expansion_cause fields of constituent generations
1268 void CMSCollector::clear_expansion_cause() {
1269 _cmsGen->clear_expansion_cause();
1270 }
1271
1272 // We should be conservative in starting a collection cycle. To
1273 // start too eagerly runs the risk of collecting too often in the
1274 // extreme. To collect too rarely falls back on full collections,
1275 // which works, even if not optimum in terms of concurrent work.
1276 // As a work around for too eagerly collecting, use the flag
1277 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1278 // giving the user an easily understandable way of controlling the
1279 // collections.
1280 // We want to start a new collection cycle if any of the following
1281 // conditions hold:
1282 // . our current occupancy exceeds the configured initiating occupancy
1283 // for this generation, or
1284 // . we recently needed to expand this space and have not, since that
1285 // expansion, done a collection of this generation, or
1286 // . the underlying space believes that it may be a good idea to initiate
1287 // a concurrent collection (this may be based on criteria such as the
1288 // following: the space uses linear allocation and linear allocation is
1289 // going to fail, or there is believed to be excessive fragmentation in
1290 // the generation, etc... or ...
1291 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1292 // the case of the old generation; see CR 6543076):
1293 // we may be approaching a point at which allocation requests may fail because
1294 // we will be out of sufficient free space given allocation rate estimates.]
1295 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1296
1297 assert_lock_strong(freelistLock());
1298 if (occupancy() > initiating_occupancy()) {
1299 if (PrintGCDetails && Verbose) {
1300 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1301 short_name(), occupancy(), initiating_occupancy());
1302 }
1303 return true;
1304 }
1305 if (UseCMSInitiatingOccupancyOnly) {
1306 return false;
1307 }
1308 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1309 if (PrintGCDetails && Verbose) {
1310 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1311 short_name());
1312 }
1313 return true;
1314 }
1315 if (_cmsSpace->should_concurrent_collect()) {
1316 if (PrintGCDetails && Verbose) {
1317 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1318 short_name());
1319 }
1320 return true;
1321 }
1322 return false;
1323 }
1324
1325 void ConcurrentMarkSweepGeneration::collect(bool full,
1326 bool clear_all_soft_refs,
1327 size_t size,
1328 bool tlab)
1329 {
1330 collector()->collect(full, clear_all_soft_refs, size, tlab);
1331 }
1332
1333 void CMSCollector::collect(bool full,
1334 bool clear_all_soft_refs,
1335 size_t size,
1336 bool tlab)
1337 {
1338 // The following "if" branch is present for defensive reasons.
1339 // In the current uses of this interface, it can be replaced with:
1340 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1341 // But I am not placing that assert here to allow future
1342 // generality in invoking this interface.
1343 if (GC_locker::is_active()) {
1344 // A consistency test for GC_locker
1345 assert(GC_locker::needs_gc(), "Should have been set already");
1346 // Skip this foreground collection, instead
1347 // expanding the heap if necessary.
1348 // Need the free list locks for the call to free() in compute_new_size()
1349 compute_new_size();
1350 return;
1351 }
1352 acquire_control_and_collect(full, clear_all_soft_refs);
1353 }
1354
1355 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1356 GenCollectedHeap* gch = GenCollectedHeap::heap();
1357 unsigned int gc_count = gch->total_full_collections();
1358 if (gc_count == full_gc_count) {
1359 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1360 _full_gc_requested = true;
1361 _full_gc_cause = cause;
1362 CGC_lock->notify(); // nudge CMS thread
1363 } else {
1364 assert(gc_count > full_gc_count, "Error: causal loop");
1365 }
1366 }
1367
1368 bool CMSCollector::is_external_interruption() {
1369 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1370 return GCCause::is_user_requested_gc(cause) ||
1371 GCCause::is_serviceability_requested_gc(cause);
1372 }
1373
1374 void CMSCollector::report_concurrent_mode_interruption() {
1375 if (is_external_interruption()) {
1376 if (PrintGCDetails) {
1377 gclog_or_tty->print(" (concurrent mode interrupted)");
1378 }
1379 } else {
1380 if (PrintGCDetails) {
1381 gclog_or_tty->print(" (concurrent mode failure)");
1382 }
1383 _gc_tracer_cm->report_concurrent_mode_failure();
1384 }
1385 }
1386
1387
1388 // The foreground and background collectors need to coordinate in order
1389 // to make sure that they do not mutually interfere with CMS collections.
1390 // When a background collection is active,
1391 // the foreground collector may need to take over (preempt) and
1392 // synchronously complete an ongoing collection. Depending on the
1393 // frequency of the background collections and the heap usage
1394 // of the application, this preemption can be seldom or frequent.
1395 // There are only certain
1396 // points in the background collection that the "collection-baton"
1397 // can be passed to the foreground collector.
1398 //
1399 // The foreground collector will wait for the baton before
1400 // starting any part of the collection. The foreground collector
1401 // will only wait at one location.
1402 //
1403 // The background collector will yield the baton before starting a new
1404 // phase of the collection (e.g., before initial marking, marking from roots,
1405 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1406 // of the loop which switches the phases. The background collector does some
1407 // of the phases (initial mark, final re-mark) with the world stopped.
1408 // Because of locking involved in stopping the world,
1409 // the foreground collector should not block waiting for the background
1410 // collector when it is doing a stop-the-world phase. The background
1411 // collector will yield the baton at an additional point just before
1412 // it enters a stop-the-world phase. Once the world is stopped, the
1413 // background collector checks the phase of the collection. If the
1414 // phase has not changed, it proceeds with the collection. If the
1415 // phase has changed, it skips that phase of the collection. See
1416 // the comments on the use of the Heap_lock in collect_in_background().
1417 //
1418 // Variable used in baton passing.
1419 // _foregroundGCIsActive - Set to true by the foreground collector when
1420 // it wants the baton. The foreground clears it when it has finished
1421 // the collection.
1422 // _foregroundGCShouldWait - Set to true by the background collector
1423 // when it is running. The foreground collector waits while
1424 // _foregroundGCShouldWait is true.
1425 // CGC_lock - monitor used to protect access to the above variables
1426 // and to notify the foreground and background collectors.
1427 // _collectorState - current state of the CMS collection.
1428 //
1429 // The foreground collector
1430 // acquires the CGC_lock
1431 // sets _foregroundGCIsActive
1432 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1433 // various locks acquired in preparation for the collection
1434 // are released so as not to block the background collector
1435 // that is in the midst of a collection
1436 // proceeds with the collection
1437 // clears _foregroundGCIsActive
1438 // returns
1439 //
1440 // The background collector in a loop iterating on the phases of the
1441 // collection
1442 // acquires the CGC_lock
1443 // sets _foregroundGCShouldWait
1444 // if _foregroundGCIsActive is set
1445 // clears _foregroundGCShouldWait, notifies _CGC_lock
1446 // waits on _CGC_lock for _foregroundGCIsActive to become false
1447 // and exits the loop.
1448 // otherwise
1449 // proceed with that phase of the collection
1450 // if the phase is a stop-the-world phase,
1451 // yield the baton once more just before enqueueing
1452 // the stop-world CMS operation (executed by the VM thread).
1453 // returns after all phases of the collection are done
1454 //
1455
1456 void CMSCollector::acquire_control_and_collect(bool full,
1457 bool clear_all_soft_refs) {
1458 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1459 assert(!Thread::current()->is_ConcurrentGC_thread(),
1460 "shouldn't try to acquire control from self!");
1461
1462 // Start the protocol for acquiring control of the
1463 // collection from the background collector (aka CMS thread).
1464 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1465 "VM thread should have CMS token");
1466 // Remember the possibly interrupted state of an ongoing
1467 // concurrent collection
1468 CollectorState first_state = _collectorState;
1469
1470 // Signal to a possibly ongoing concurrent collection that
1471 // we want to do a foreground collection.
1472 _foregroundGCIsActive = true;
1473
1474 // release locks and wait for a notify from the background collector
1475 // releasing the locks in only necessary for phases which
1476 // do yields to improve the granularity of the collection.
1477 assert_lock_strong(bitMapLock());
1478 // We need to lock the Free list lock for the space that we are
1479 // currently collecting.
1480 assert(haveFreelistLocks(), "Must be holding free list locks");
1481 bitMapLock()->unlock();
1482 releaseFreelistLocks();
1483 {
1484 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1485 if (_foregroundGCShouldWait) {
1486 // We are going to be waiting for action for the CMS thread;
1487 // it had better not be gone (for instance at shutdown)!
1488 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1489 "CMS thread must be running");
1490 // Wait here until the background collector gives us the go-ahead
1491 ConcurrentMarkSweepThread::clear_CMS_flag(
1492 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1493 // Get a possibly blocked CMS thread going:
1494 // Note that we set _foregroundGCIsActive true above,
1495 // without protection of the CGC_lock.
1496 CGC_lock->notify();
1497 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1498 "Possible deadlock");
1499 while (_foregroundGCShouldWait) {
1500 // wait for notification
1501 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1502 // Possibility of delay/starvation here, since CMS token does
1503 // not know to give priority to VM thread? Actually, i think
1504 // there wouldn't be any delay/starvation, but the proof of
1505 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1506 }
1507 ConcurrentMarkSweepThread::set_CMS_flag(
1508 ConcurrentMarkSweepThread::CMS_vm_has_token);
1509 }
1510 }
1511 // The CMS_token is already held. Get back the other locks.
1512 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1513 "VM thread should have CMS token");
1514 getFreelistLocks();
1515 bitMapLock()->lock_without_safepoint_check();
1516 if (TraceCMSState) {
1517 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1518 INTPTR_FORMAT " with first state %d", p2i(Thread::current()), first_state);
1519 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1520 }
1521
1522 // Inform cms gen if this was due to partial collection failing.
1523 // The CMS gen may use this fact to determine its expansion policy.
1524 GenCollectedHeap* gch = GenCollectedHeap::heap();
1525 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1526 assert(!_cmsGen->incremental_collection_failed(),
1527 "Should have been noticed, reacted to and cleared");
1528 _cmsGen->set_incremental_collection_failed();
1529 }
1530
1531 if (first_state > Idling) {
1532 report_concurrent_mode_interruption();
1533 }
1534
1535 set_did_compact(true);
1536
1537 // If the collection is being acquired from the background
1538 // collector, there may be references on the discovered
1539 // references lists. Abandon those references, since some
1540 // of them may have become unreachable after concurrent
1541 // discovery; the STW compacting collector will redo discovery
1542 // more precisely, without being subject to floating garbage.
1543 // Leaving otherwise unreachable references in the discovered
1544 // lists would require special handling.
1545 ref_processor()->disable_discovery();
1546 ref_processor()->abandon_partial_discovery();
1547 ref_processor()->verify_no_references_recorded();
1548
1549 if (first_state > Idling) {
1550 save_heap_summary();
1551 }
1552
1553 do_compaction_work(clear_all_soft_refs);
1554
1555 // Has the GC time limit been exceeded?
1556 size_t max_eden_size = _young_gen->max_capacity() -
1557 _young_gen->to()->capacity() -
1558 _young_gen->from()->capacity();
1559 GCCause::Cause gc_cause = gch->gc_cause();
1560 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1561 _young_gen->eden()->used(),
1562 _cmsGen->max_capacity(),
1563 max_eden_size,
1564 full,
1565 gc_cause,
1566 gch->collector_policy());
1567
1568 // Reset the expansion cause, now that we just completed
1569 // a collection cycle.
1570 clear_expansion_cause();
1571 _foregroundGCIsActive = false;
1572 return;
1573 }
1574
1575 // Resize the tenured generation
1576 // after obtaining the free list locks for the
1577 // two generations.
1578 void CMSCollector::compute_new_size() {
1579 assert_locked_or_safepoint(Heap_lock);
1580 FreelistLocker z(this);
1581 MetaspaceGC::compute_new_size();
1582 _cmsGen->compute_new_size_free_list();
1583 }
1584
1585 // A work method used by the foreground collector to do
1586 // a mark-sweep-compact.
1587 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1588 GenCollectedHeap* gch = GenCollectedHeap::heap();
1589
1590 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1591 gc_timer->register_gc_start();
1592
1593 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1594 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1595
1596 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
1597
1598 // Temporarily widen the span of the weak reference processing to
1599 // the entire heap.
1600 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1601 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1602 // Temporarily, clear the "is_alive_non_header" field of the
1603 // reference processor.
1604 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1605 // Temporarily make reference _processing_ single threaded (non-MT).
1606 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1607 // Temporarily make refs discovery atomic
1608 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1609 // Temporarily make reference _discovery_ single threaded (non-MT)
1610 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1611
1612 ref_processor()->set_enqueuing_is_done(false);
1613 ref_processor()->enable_discovery();
1614 ref_processor()->setup_policy(clear_all_soft_refs);
1615 // If an asynchronous collection finishes, the _modUnionTable is
1616 // all clear. If we are assuming the collection from an asynchronous
1617 // collection, clear the _modUnionTable.
1618 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1619 "_modUnionTable should be clear if the baton was not passed");
1620 _modUnionTable.clear_all();
1621 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1622 "mod union for klasses should be clear if the baton was passed");
1623 _ct->klass_rem_set()->clear_mod_union();
1624
1625 // We must adjust the allocation statistics being maintained
1626 // in the free list space. We do so by reading and clearing
1627 // the sweep timer and updating the block flux rate estimates below.
1628 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1629 if (_inter_sweep_timer.is_active()) {
1630 _inter_sweep_timer.stop();
1631 // Note that we do not use this sample to update the _inter_sweep_estimate.
1632 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1633 _inter_sweep_estimate.padded_average(),
1634 _intra_sweep_estimate.padded_average());
1635 }
1636
1637 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1638 #ifdef ASSERT
1639 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1640 size_t free_size = cms_space->free();
1641 assert(free_size ==
1642 pointer_delta(cms_space->end(), cms_space->compaction_top())
1643 * HeapWordSize,
1644 "All the free space should be compacted into one chunk at top");
1645 assert(cms_space->dictionary()->total_chunk_size(
1646 debug_only(cms_space->freelistLock())) == 0 ||
1647 cms_space->totalSizeInIndexedFreeLists() == 0,
1648 "All the free space should be in a single chunk");
1649 size_t num = cms_space->totalCount();
1650 assert((free_size == 0 && num == 0) ||
1651 (free_size > 0 && (num == 1 || num == 2)),
1652 "There should be at most 2 free chunks after compaction");
1653 #endif // ASSERT
1654 _collectorState = Resetting;
1655 assert(_restart_addr == NULL,
1656 "Should have been NULL'd before baton was passed");
1657 reset_stw();
1658 _cmsGen->reset_after_compaction();
1659 _concurrent_cycles_since_last_unload = 0;
1660
1661 // Clear any data recorded in the PLAB chunk arrays.
1662 if (_survivor_plab_array != NULL) {
1663 reset_survivor_plab_arrays();
1664 }
1665
1666 // Adjust the per-size allocation stats for the next epoch.
1667 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1668 // Restart the "inter sweep timer" for the next epoch.
1669 _inter_sweep_timer.reset();
1670 _inter_sweep_timer.start();
1671
1672 gc_timer->register_gc_end();
1673
1674 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1675
1676 // For a mark-sweep-compact, compute_new_size() will be called
1677 // in the heap's do_collection() method.
1678 }
1679
1680 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1681 ContiguousSpace* eden_space = _young_gen->eden();
1682 ContiguousSpace* from_space = _young_gen->from();
1683 ContiguousSpace* to_space = _young_gen->to();
1684 // Eden
1685 if (_eden_chunk_array != NULL) {
1686 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1687 p2i(eden_space->bottom()), p2i(eden_space->top()),
1688 p2i(eden_space->end()), eden_space->capacity());
1689 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
1690 "_eden_chunk_capacity=" SIZE_FORMAT,
1691 _eden_chunk_index, _eden_chunk_capacity);
1692 for (size_t i = 0; i < _eden_chunk_index; i++) {
1693 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1694 i, p2i(_eden_chunk_array[i]));
1695 }
1696 }
1697 // Survivor
1698 if (_survivor_chunk_array != NULL) {
1699 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1700 p2i(from_space->bottom()), p2i(from_space->top()),
1701 p2i(from_space->end()), from_space->capacity());
1702 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
1703 "_survivor_chunk_capacity=" SIZE_FORMAT,
1704 _survivor_chunk_index, _survivor_chunk_capacity);
1705 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1706 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
1707 i, p2i(_survivor_chunk_array[i]));
1708 }
1709 }
1710 }
1711
1712 void CMSCollector::getFreelistLocks() const {
1713 // Get locks for all free lists in all generations that this
1714 // collector is responsible for
1715 _cmsGen->freelistLock()->lock_without_safepoint_check();
1716 }
1717
1718 void CMSCollector::releaseFreelistLocks() const {
1719 // Release locks for all free lists in all generations that this
1720 // collector is responsible for
1721 _cmsGen->freelistLock()->unlock();
1722 }
1723
1724 bool CMSCollector::haveFreelistLocks() const {
1725 // Check locks for all free lists in all generations that this
1726 // collector is responsible for
1727 assert_lock_strong(_cmsGen->freelistLock());
1728 PRODUCT_ONLY(ShouldNotReachHere());
1729 return true;
1730 }
1731
1732 // A utility class that is used by the CMS collector to
1733 // temporarily "release" the foreground collector from its
1734 // usual obligation to wait for the background collector to
1735 // complete an ongoing phase before proceeding.
1736 class ReleaseForegroundGC: public StackObj {
1737 private:
1738 CMSCollector* _c;
1739 public:
1740 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1741 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1742 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1743 // allow a potentially blocked foreground collector to proceed
1744 _c->_foregroundGCShouldWait = false;
1745 if (_c->_foregroundGCIsActive) {
1746 CGC_lock->notify();
1747 }
1748 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1749 "Possible deadlock");
1750 }
1751
1752 ~ReleaseForegroundGC() {
1753 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1754 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1755 _c->_foregroundGCShouldWait = true;
1756 }
1757 };
1758
1759 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1760 assert(Thread::current()->is_ConcurrentGC_thread(),
1761 "A CMS asynchronous collection is only allowed on a CMS thread.");
1762
1763 GenCollectedHeap* gch = GenCollectedHeap::heap();
1764 {
1765 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1766 MutexLockerEx hl(Heap_lock, safepoint_check);
1767 FreelistLocker fll(this);
1768 MutexLockerEx x(CGC_lock, safepoint_check);
1769 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
1770 // The foreground collector is active or we're
1771 // not using asynchronous collections. Skip this
1772 // background collection.
1773 assert(!_foregroundGCShouldWait, "Should be clear");
1774 return;
1775 } else {
1776 assert(_collectorState == Idling, "Should be idling before start.");
1777 _collectorState = InitialMarking;
1778 register_gc_start(cause);
1779 // Reset the expansion cause, now that we are about to begin
1780 // a new cycle.
1781 clear_expansion_cause();
1782
1783 // Clear the MetaspaceGC flag since a concurrent collection
1784 // is starting but also clear it after the collection.
1785 MetaspaceGC::set_should_concurrent_collect(false);
1786 }
1787 // Decide if we want to enable class unloading as part of the
1788 // ensuing concurrent GC cycle.
1789 update_should_unload_classes();
1790 _full_gc_requested = false; // acks all outstanding full gc requests
1791 _full_gc_cause = GCCause::_no_gc;
1792 // Signal that we are about to start a collection
1793 gch->increment_total_full_collections(); // ... starting a collection cycle
1794 _collection_count_start = gch->total_full_collections();
1795 }
1796
1797 // Used for PrintGC
1798 size_t prev_used;
1799 if (PrintGC && Verbose) {
1800 prev_used = _cmsGen->used();
1801 }
1802
1803 // The change of the collection state is normally done at this level;
1804 // the exceptions are phases that are executed while the world is
1805 // stopped. For those phases the change of state is done while the
1806 // world is stopped. For baton passing purposes this allows the
1807 // background collector to finish the phase and change state atomically.
1808 // The foreground collector cannot wait on a phase that is done
1809 // while the world is stopped because the foreground collector already
1810 // has the world stopped and would deadlock.
1811 while (_collectorState != Idling) {
1812 if (TraceCMSState) {
1813 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
1814 p2i(Thread::current()), _collectorState);
1815 }
1816 // The foreground collector
1817 // holds the Heap_lock throughout its collection.
1818 // holds the CMS token (but not the lock)
1819 // except while it is waiting for the background collector to yield.
1820 //
1821 // The foreground collector should be blocked (not for long)
1822 // if the background collector is about to start a phase
1823 // executed with world stopped. If the background
1824 // collector has already started such a phase, the
1825 // foreground collector is blocked waiting for the
1826 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1827 // are executed in the VM thread.
1828 //
1829 // The locking order is
1830 // PendingListLock (PLL) -- if applicable (FinalMarking)
1831 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1832 // CMS token (claimed in
1833 // stop_world_and_do() -->
1834 // safepoint_synchronize() -->
1835 // CMSThread::synchronize())
1836
1837 {
1838 // Check if the FG collector wants us to yield.
1839 CMSTokenSync x(true); // is cms thread
1840 if (waitForForegroundGC()) {
1841 // We yielded to a foreground GC, nothing more to be
1842 // done this round.
1843 assert(_foregroundGCShouldWait == false, "We set it to false in "
1844 "waitForForegroundGC()");
1845 if (TraceCMSState) {
1846 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1847 " exiting collection CMS state %d",
1848 p2i(Thread::current()), _collectorState);
1849 }
1850 return;
1851 } else {
1852 // The background collector can run but check to see if the
1853 // foreground collector has done a collection while the
1854 // background collector was waiting to get the CGC_lock
1855 // above. If yes, break so that _foregroundGCShouldWait
1856 // is cleared before returning.
1857 if (_collectorState == Idling) {
1858 break;
1859 }
1860 }
1861 }
1862
1863 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1864 "should be waiting");
1865
1866 switch (_collectorState) {
1867 case InitialMarking:
1868 {
1869 ReleaseForegroundGC x(this);
1870 stats().record_cms_begin();
1871 VM_CMS_Initial_Mark initial_mark_op(this);
1872 VMThread::execute(&initial_mark_op);
1873 }
1874 // The collector state may be any legal state at this point
1875 // since the background collector may have yielded to the
1876 // foreground collector.
1877 break;
1878 case Marking:
1879 // initial marking in checkpointRootsInitialWork has been completed
1880 if (markFromRoots()) { // we were successful
1881 assert(_collectorState == Precleaning, "Collector state should "
1882 "have changed");
1883 } else {
1884 assert(_foregroundGCIsActive, "Internal state inconsistency");
1885 }
1886 break;
1887 case Precleaning:
1888 // marking from roots in markFromRoots has been completed
1889 preclean();
1890 assert(_collectorState == AbortablePreclean ||
1891 _collectorState == FinalMarking,
1892 "Collector state should have changed");
1893 break;
1894 case AbortablePreclean:
1895 abortable_preclean();
1896 assert(_collectorState == FinalMarking, "Collector state should "
1897 "have changed");
1898 break;
1899 case FinalMarking:
1900 {
1901 ReleaseForegroundGC x(this);
1902
1903 VM_CMS_Final_Remark final_remark_op(this);
1904 VMThread::execute(&final_remark_op);
1905 }
1906 assert(_foregroundGCShouldWait, "block post-condition");
1907 break;
1908 case Sweeping:
1909 // final marking in checkpointRootsFinal has been completed
1910 sweep();
1911 assert(_collectorState == Resizing, "Collector state change "
1912 "to Resizing must be done under the free_list_lock");
1913
1914 case Resizing: {
1915 // Sweeping has been completed...
1916 // At this point the background collection has completed.
1917 // Don't move the call to compute_new_size() down
1918 // into code that might be executed if the background
1919 // collection was preempted.
1920 {
1921 ReleaseForegroundGC x(this); // unblock FG collection
1922 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1923 CMSTokenSync z(true); // not strictly needed.
1924 if (_collectorState == Resizing) {
1925 compute_new_size();
1926 save_heap_summary();
1927 _collectorState = Resetting;
1928 } else {
1929 assert(_collectorState == Idling, "The state should only change"
1930 " because the foreground collector has finished the collection");
1931 }
1932 }
1933 break;
1934 }
1935 case Resetting:
1936 // CMS heap resizing has been completed
1937 reset_concurrent();
1938 assert(_collectorState == Idling, "Collector state should "
1939 "have changed");
1940
1941 MetaspaceGC::set_should_concurrent_collect(false);
1942
1943 stats().record_cms_end();
1944 // Don't move the concurrent_phases_end() and compute_new_size()
1945 // calls to here because a preempted background collection
1946 // has it's state set to "Resetting".
1947 break;
1948 case Idling:
1949 default:
1950 ShouldNotReachHere();
1951 break;
1952 }
1953 if (TraceCMSState) {
1954 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1955 p2i(Thread::current()), _collectorState);
1956 }
1957 assert(_foregroundGCShouldWait, "block post-condition");
1958 }
1959
1960 // Should this be in gc_epilogue?
1961 collector_policy()->counters()->update_counters();
1962
1963 {
1964 // Clear _foregroundGCShouldWait and, in the event that the
1965 // foreground collector is waiting, notify it, before
1966 // returning.
1967 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1968 _foregroundGCShouldWait = false;
1969 if (_foregroundGCIsActive) {
1970 CGC_lock->notify();
1971 }
1972 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1973 "Possible deadlock");
1974 }
1975 if (TraceCMSState) {
1976 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
1977 " exiting collection CMS state %d",
1978 p2i(Thread::current()), _collectorState);
1979 }
1980 if (PrintGC && Verbose) {
1981 _cmsGen->print_heap_change(prev_used);
1982 }
1983 }
1984
1985 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1986 _cms_start_registered = true;
1987 _gc_timer_cm->register_gc_start();
1988 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1989 }
1990
1991 void CMSCollector::register_gc_end() {
1992 if (_cms_start_registered) {
1993 report_heap_summary(GCWhen::AfterGC);
1994
1995 _gc_timer_cm->register_gc_end();
1996 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1997 _cms_start_registered = false;
1998 }
1999 }
2000
2001 void CMSCollector::save_heap_summary() {
2002 GenCollectedHeap* gch = GenCollectedHeap::heap();
2003 _last_heap_summary = gch->create_heap_summary();
2004 _last_metaspace_summary = gch->create_metaspace_summary();
2005 }
2006
2007 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2008 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2009 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2010 }
2011
2012 bool CMSCollector::waitForForegroundGC() {
2013 bool res = false;
2014 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2015 "CMS thread should have CMS token");
2016 // Block the foreground collector until the
2017 // background collectors decides whether to
2018 // yield.
2019 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2020 _foregroundGCShouldWait = true;
2021 if (_foregroundGCIsActive) {
2022 // The background collector yields to the
2023 // foreground collector and returns a value
2024 // indicating that it has yielded. The foreground
2025 // collector can proceed.
2026 res = true;
2027 _foregroundGCShouldWait = false;
2028 ConcurrentMarkSweepThread::clear_CMS_flag(
2029 ConcurrentMarkSweepThread::CMS_cms_has_token);
2030 ConcurrentMarkSweepThread::set_CMS_flag(
2031 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2032 // Get a possibly blocked foreground thread going
2033 CGC_lock->notify();
2034 if (TraceCMSState) {
2035 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2036 p2i(Thread::current()), _collectorState);
2037 }
2038 while (_foregroundGCIsActive) {
2039 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2040 }
2041 ConcurrentMarkSweepThread::set_CMS_flag(
2042 ConcurrentMarkSweepThread::CMS_cms_has_token);
2043 ConcurrentMarkSweepThread::clear_CMS_flag(
2044 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2045 }
2046 if (TraceCMSState) {
2047 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2048 p2i(Thread::current()), _collectorState);
2049 }
2050 return res;
2051 }
2052
2053 // Because of the need to lock the free lists and other structures in
2054 // the collector, common to all the generations that the collector is
2055 // collecting, we need the gc_prologues of individual CMS generations
2056 // delegate to their collector. It may have been simpler had the
2057 // current infrastructure allowed one to call a prologue on a
2058 // collector. In the absence of that we have the generation's
2059 // prologue delegate to the collector, which delegates back
2060 // some "local" work to a worker method in the individual generations
2061 // that it's responsible for collecting, while itself doing any
2062 // work common to all generations it's responsible for. A similar
2063 // comment applies to the gc_epilogue()'s.
2064 // The role of the variable _between_prologue_and_epilogue is to
2065 // enforce the invocation protocol.
2066 void CMSCollector::gc_prologue(bool full) {
2067 // Call gc_prologue_work() for the CMSGen
2068 // we are responsible for.
2069
2070 // The following locking discipline assumes that we are only called
2071 // when the world is stopped.
2072 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2073
2074 // The CMSCollector prologue must call the gc_prologues for the
2075 // "generations" that it's responsible
2076 // for.
2077
2078 assert( Thread::current()->is_VM_thread()
2079 || ( CMSScavengeBeforeRemark
2080 && Thread::current()->is_ConcurrentGC_thread()),
2081 "Incorrect thread type for prologue execution");
2082
2083 if (_between_prologue_and_epilogue) {
2084 // We have already been invoked; this is a gc_prologue delegation
2085 // from yet another CMS generation that we are responsible for, just
2086 // ignore it since all relevant work has already been done.
2087 return;
2088 }
2089
2090 // set a bit saying prologue has been called; cleared in epilogue
2091 _between_prologue_and_epilogue = true;
2092 // Claim locks for common data structures, then call gc_prologue_work()
2093 // for each CMSGen.
2094
2095 getFreelistLocks(); // gets free list locks on constituent spaces
2096 bitMapLock()->lock_without_safepoint_check();
2097
2098 // Should call gc_prologue_work() for all cms gens we are responsible for
2099 bool duringMarking = _collectorState >= Marking
2100 && _collectorState < Sweeping;
2101
2102 // The young collections clear the modified oops state, which tells if
2103 // there are any modified oops in the class. The remark phase also needs
2104 // that information. Tell the young collection to save the union of all
2105 // modified klasses.
2106 if (duringMarking) {
2107 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2108 }
2109
2110 bool registerClosure = duringMarking;
2111
2112 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2113
2114 if (!full) {
2115 stats().record_gc0_begin();
2116 }
2117 }
2118
2119 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2120
2121 _capacity_at_prologue = capacity();
2122 _used_at_prologue = used();
2123
2124 // Delegate to CMScollector which knows how to coordinate between
2125 // this and any other CMS generations that it is responsible for
2126 // collecting.
2127 collector()->gc_prologue(full);
2128 }
2129
2130 // This is a "private" interface for use by this generation's CMSCollector.
2131 // Not to be called directly by any other entity (for instance,
2132 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2133 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2134 bool registerClosure, ModUnionClosure* modUnionClosure) {
2135 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2136 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2137 "Should be NULL");
2138 if (registerClosure) {
2139 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2140 }
2141 cmsSpace()->gc_prologue();
2142 // Clear stat counters
2143 NOT_PRODUCT(
2144 assert(_numObjectsPromoted == 0, "check");
2145 assert(_numWordsPromoted == 0, "check");
2146 if (Verbose && PrintGC) {
2147 gclog_or_tty->print("Allocated " SIZE_FORMAT " objects, "
2148 SIZE_FORMAT " bytes concurrently",
2149 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2150 }
2151 _numObjectsAllocated = 0;
2152 _numWordsAllocated = 0;
2153 )
2154 }
2155
2156 void CMSCollector::gc_epilogue(bool full) {
2157 // The following locking discipline assumes that we are only called
2158 // when the world is stopped.
2159 assert(SafepointSynchronize::is_at_safepoint(),
2160 "world is stopped assumption");
2161
2162 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2163 // if linear allocation blocks need to be appropriately marked to allow the
2164 // the blocks to be parsable. We also check here whether we need to nudge the
2165 // CMS collector thread to start a new cycle (if it's not already active).
2166 assert( Thread::current()->is_VM_thread()
2167 || ( CMSScavengeBeforeRemark
2168 && Thread::current()->is_ConcurrentGC_thread()),
2169 "Incorrect thread type for epilogue execution");
2170
2171 if (!_between_prologue_and_epilogue) {
2172 // We have already been invoked; this is a gc_epilogue delegation
2173 // from yet another CMS generation that we are responsible for, just
2174 // ignore it since all relevant work has already been done.
2175 return;
2176 }
2177 assert(haveFreelistLocks(), "must have freelist locks");
2178 assert_lock_strong(bitMapLock());
2179
2180 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2181
2182 _cmsGen->gc_epilogue_work(full);
2183
2184 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2185 // in case sampling was not already enabled, enable it
2186 _start_sampling = true;
2187 }
2188 // reset _eden_chunk_array so sampling starts afresh
2189 _eden_chunk_index = 0;
2190
2191 size_t cms_used = _cmsGen->cmsSpace()->used();
2192
2193 // update performance counters - this uses a special version of
2194 // update_counters() that allows the utilization to be passed as a
2195 // parameter, avoiding multiple calls to used().
2196 //
2197 _cmsGen->update_counters(cms_used);
2198
2199 bitMapLock()->unlock();
2200 releaseFreelistLocks();
2201
2202 if (!CleanChunkPoolAsync) {
2203 Chunk::clean_chunk_pool();
2204 }
2205
2206 set_did_compact(false);
2207 _between_prologue_and_epilogue = false; // ready for next cycle
2208 }
2209
2210 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2211 collector()->gc_epilogue(full);
2212
2213 // Also reset promotion tracking in par gc thread states.
2214 for (uint i = 0; i < ParallelGCThreads; i++) {
2215 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2216 }
2217 }
2218
2219 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2220 assert(!incremental_collection_failed(), "Should have been cleared");
2221 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2222 cmsSpace()->gc_epilogue();
2223 // Print stat counters
2224 NOT_PRODUCT(
2225 assert(_numObjectsAllocated == 0, "check");
2226 assert(_numWordsAllocated == 0, "check");
2227 if (Verbose && PrintGC) {
2228 gclog_or_tty->print("Promoted " SIZE_FORMAT " objects, "
2229 SIZE_FORMAT " bytes",
2230 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2231 }
2232 _numObjectsPromoted = 0;
2233 _numWordsPromoted = 0;
2234 )
2235
2236 if (PrintGC && Verbose) {
2237 // Call down the chain in contiguous_available needs the freelistLock
2238 // so print this out before releasing the freeListLock.
2239 gclog_or_tty->print(" Contiguous available " SIZE_FORMAT " bytes ",
2240 contiguous_available());
2241 }
2242 }
2243
2244 #ifndef PRODUCT
2245 bool CMSCollector::have_cms_token() {
2246 Thread* thr = Thread::current();
2247 if (thr->is_VM_thread()) {
2248 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2249 } else if (thr->is_ConcurrentGC_thread()) {
2250 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2251 } else if (thr->is_GC_task_thread()) {
2252 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2253 ParGCRareEvent_lock->owned_by_self();
2254 }
2255 return false;
2256 }
2257 #endif
2258
2259 // Check reachability of the given heap address in CMS generation,
2260 // treating all other generations as roots.
2261 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2262 // We could "guarantee" below, rather than assert, but I'll
2263 // leave these as "asserts" so that an adventurous debugger
2264 // could try this in the product build provided some subset of
2265 // the conditions were met, provided they were interested in the
2266 // results and knew that the computation below wouldn't interfere
2267 // with other concurrent computations mutating the structures
2268 // being read or written.
2269 assert(SafepointSynchronize::is_at_safepoint(),
2270 "Else mutations in object graph will make answer suspect");
2271 assert(have_cms_token(), "Should hold cms token");
2272 assert(haveFreelistLocks(), "must hold free list locks");
2273 assert_lock_strong(bitMapLock());
2274
2275 // Clear the marking bit map array before starting, but, just
2276 // for kicks, first report if the given address is already marked
2277 gclog_or_tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2278 _markBitMap.isMarked(addr) ? "" : " not");
2279
2280 if (verify_after_remark()) {
2281 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2282 bool result = verification_mark_bm()->isMarked(addr);
2283 gclog_or_tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2284 result ? "IS" : "is NOT");
2285 return result;
2286 } else {
2287 gclog_or_tty->print_cr("Could not compute result");
2288 return false;
2289 }
2290 }
2291
2292
2293 void
2294 CMSCollector::print_on_error(outputStream* st) {
2295 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2296 if (collector != NULL) {
2297 CMSBitMap* bitmap = &collector->_markBitMap;
2298 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2299 bitmap->print_on_error(st, " Bits: ");
2300
2301 st->cr();
2302
2303 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2304 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2305 mut_bitmap->print_on_error(st, " Bits: ");
2306 }
2307 }
2308
2309 ////////////////////////////////////////////////////////
2310 // CMS Verification Support
2311 ////////////////////////////////////////////////////////
2312 // Following the remark phase, the following invariant
2313 // should hold -- each object in the CMS heap which is
2314 // marked in markBitMap() should be marked in the verification_mark_bm().
2315
2316 class VerifyMarkedClosure: public BitMapClosure {
2317 CMSBitMap* _marks;
2318 bool _failed;
2319
2320 public:
2321 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2322
2323 bool do_bit(size_t offset) {
2324 HeapWord* addr = _marks->offsetToHeapWord(offset);
2325 if (!_marks->isMarked(addr)) {
2326 oop(addr)->print_on(gclog_or_tty);
2327 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2328 _failed = true;
2329 }
2330 return true;
2331 }
2332
2333 bool failed() { return _failed; }
2334 };
2335
2336 bool CMSCollector::verify_after_remark(bool silent) {
2337 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2338 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2339 static bool init = false;
2340
2341 assert(SafepointSynchronize::is_at_safepoint(),
2342 "Else mutations in object graph will make answer suspect");
2343 assert(have_cms_token(),
2344 "Else there may be mutual interference in use of "
2345 " verification data structures");
2346 assert(_collectorState > Marking && _collectorState <= Sweeping,
2347 "Else marking info checked here may be obsolete");
2348 assert(haveFreelistLocks(), "must hold free list locks");
2349 assert_lock_strong(bitMapLock());
2350
2351
2352 // Allocate marking bit map if not already allocated
2353 if (!init) { // first time
2354 if (!verification_mark_bm()->allocate(_span)) {
2355 return false;
2356 }
2357 init = true;
2358 }
2359
2360 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2361
2362 // Turn off refs discovery -- so we will be tracing through refs.
2363 // This is as intended, because by this time
2364 // GC must already have cleared any refs that need to be cleared,
2365 // and traced those that need to be marked; moreover,
2366 // the marking done here is not going to interfere in any
2367 // way with the marking information used by GC.
2368 NoRefDiscovery no_discovery(ref_processor());
2369
2370 #if defined(COMPILER2) || INCLUDE_JVMCI
2371 DerivedPointerTableDeactivate dpt_deact;
2372 #endif
2373
2374 // Clear any marks from a previous round
2375 verification_mark_bm()->clear_all();
2376 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2377 verify_work_stacks_empty();
2378
2379 GenCollectedHeap* gch = GenCollectedHeap::heap();
2380 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2381 // Update the saved marks which may affect the root scans.
2382 gch->save_marks();
2383
2384 if (CMSRemarkVerifyVariant == 1) {
2385 // In this first variant of verification, we complete
2386 // all marking, then check if the new marks-vector is
2387 // a subset of the CMS marks-vector.
2388 verify_after_remark_work_1();
2389 } else if (CMSRemarkVerifyVariant == 2) {
2390 // In this second variant of verification, we flag an error
2391 // (i.e. an object reachable in the new marks-vector not reachable
2392 // in the CMS marks-vector) immediately, also indicating the
2393 // identify of an object (A) that references the unmarked object (B) --
2394 // presumably, a mutation to A failed to be picked up by preclean/remark?
2395 verify_after_remark_work_2();
2396 } else {
2397 warning("Unrecognized value " UINTX_FORMAT " for CMSRemarkVerifyVariant",
2398 CMSRemarkVerifyVariant);
2399 }
2400 if (!silent) gclog_or_tty->print(" done] ");
2401 return true;
2402 }
2403
2404 void CMSCollector::verify_after_remark_work_1() {
2405 ResourceMark rm;
2406 HandleMark hm;
2407 GenCollectedHeap* gch = GenCollectedHeap::heap();
2408
2409 // Get a clear set of claim bits for the roots processing to work with.
2410 ClassLoaderDataGraph::clear_claimed_marks();
2411
2412 // Mark from roots one level into CMS
2413 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2414 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2415
2416 {
2417 StrongRootsScope srs(1);
2418
2419 gch->gen_process_roots(&srs,
2420 GenCollectedHeap::OldGen,
2421 true, // young gen as roots
2422 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2423 should_unload_classes(),
2424 ¬Older,
2425 NULL,
2426 NULL);
2427 }
2428
2429 // Now mark from the roots
2430 MarkFromRootsClosure markFromRootsClosure(this, _span,
2431 verification_mark_bm(), verification_mark_stack(),
2432 false /* don't yield */, true /* verifying */);
2433 assert(_restart_addr == NULL, "Expected pre-condition");
2434 verification_mark_bm()->iterate(&markFromRootsClosure);
2435 while (_restart_addr != NULL) {
2436 // Deal with stack overflow: by restarting at the indicated
2437 // address.
2438 HeapWord* ra = _restart_addr;
2439 markFromRootsClosure.reset(ra);
2440 _restart_addr = NULL;
2441 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2442 }
2443 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2444 verify_work_stacks_empty();
2445
2446 // Marking completed -- now verify that each bit marked in
2447 // verification_mark_bm() is also marked in markBitMap(); flag all
2448 // errors by printing corresponding objects.
2449 VerifyMarkedClosure vcl(markBitMap());
2450 verification_mark_bm()->iterate(&vcl);
2451 if (vcl.failed()) {
2452 gclog_or_tty->print("Verification failed");
2453 gch->print_on(gclog_or_tty);
2454 fatal("CMS: failed marking verification after remark");
2455 }
2456 }
2457
2458 class VerifyKlassOopsKlassClosure : public KlassClosure {
2459 class VerifyKlassOopsClosure : public OopClosure {
2460 CMSBitMap* _bitmap;
2461 public:
2462 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2463 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2464 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2465 } _oop_closure;
2466 public:
2467 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2468 void do_klass(Klass* k) {
2469 k->oops_do(&_oop_closure);
2470 }
2471 };
2472
2473 void CMSCollector::verify_after_remark_work_2() {
2474 ResourceMark rm;
2475 HandleMark hm;
2476 GenCollectedHeap* gch = GenCollectedHeap::heap();
2477
2478 // Get a clear set of claim bits for the roots processing to work with.
2479 ClassLoaderDataGraph::clear_claimed_marks();
2480
2481 // Mark from roots one level into CMS
2482 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2483 markBitMap());
2484 CLDToOopClosure cld_closure(¬Older, true);
2485
2486 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2487
2488 {
2489 StrongRootsScope srs(1);
2490
2491 gch->gen_process_roots(&srs,
2492 GenCollectedHeap::OldGen,
2493 true, // young gen as roots
2494 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2495 should_unload_classes(),
2496 ¬Older,
2497 NULL,
2498 &cld_closure);
2499 }
2500
2501 // Now mark from the roots
2502 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2503 verification_mark_bm(), markBitMap(), verification_mark_stack());
2504 assert(_restart_addr == NULL, "Expected pre-condition");
2505 verification_mark_bm()->iterate(&markFromRootsClosure);
2506 while (_restart_addr != NULL) {
2507 // Deal with stack overflow: by restarting at the indicated
2508 // address.
2509 HeapWord* ra = _restart_addr;
2510 markFromRootsClosure.reset(ra);
2511 _restart_addr = NULL;
2512 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2513 }
2514 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2515 verify_work_stacks_empty();
2516
2517 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2518 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2519
2520 // Marking completed -- now verify that each bit marked in
2521 // verification_mark_bm() is also marked in markBitMap(); flag all
2522 // errors by printing corresponding objects.
2523 VerifyMarkedClosure vcl(markBitMap());
2524 verification_mark_bm()->iterate(&vcl);
2525 assert(!vcl.failed(), "Else verification above should not have succeeded");
2526 }
2527
2528 void ConcurrentMarkSweepGeneration::save_marks() {
2529 // delegate to CMS space
2530 cmsSpace()->save_marks();
2531 for (uint i = 0; i < ParallelGCThreads; i++) {
2532 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2533 }
2534 }
2535
2536 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2537 return cmsSpace()->no_allocs_since_save_marks();
2538 }
2539
2540 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2541 \
2542 void ConcurrentMarkSweepGeneration:: \
2543 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2544 cl->set_generation(this); \
2545 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2546 cl->reset_generation(); \
2547 save_marks(); \
2548 }
2549
2550 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2551
2552 void
2553 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2554 if (freelistLock()->owned_by_self()) {
2555 Generation::oop_iterate(cl);
2556 } else {
2557 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2558 Generation::oop_iterate(cl);
2559 }
2560 }
2561
2562 void
2563 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2564 if (freelistLock()->owned_by_self()) {
2565 Generation::object_iterate(cl);
2566 } else {
2567 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2568 Generation::object_iterate(cl);
2569 }
2570 }
2571
2572 void
2573 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2574 if (freelistLock()->owned_by_self()) {
2575 Generation::safe_object_iterate(cl);
2576 } else {
2577 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2578 Generation::safe_object_iterate(cl);
2579 }
2580 }
2581
2582 void
2583 ConcurrentMarkSweepGeneration::post_compact() {
2584 }
2585
2586 void
2587 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2588 // Fix the linear allocation blocks to look like free blocks.
2589
2590 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2591 // are not called when the heap is verified during universe initialization and
2592 // at vm shutdown.
2593 if (freelistLock()->owned_by_self()) {
2594 cmsSpace()->prepare_for_verify();
2595 } else {
2596 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2597 cmsSpace()->prepare_for_verify();
2598 }
2599 }
2600
2601 void
2602 ConcurrentMarkSweepGeneration::verify() {
2603 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2604 // are not called when the heap is verified during universe initialization and
2605 // at vm shutdown.
2606 if (freelistLock()->owned_by_self()) {
2607 cmsSpace()->verify();
2608 } else {
2609 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2610 cmsSpace()->verify();
2611 }
2612 }
2613
2614 void CMSCollector::verify() {
2615 _cmsGen->verify();
2616 }
2617
2618 #ifndef PRODUCT
2619 bool CMSCollector::overflow_list_is_empty() const {
2620 assert(_num_par_pushes >= 0, "Inconsistency");
2621 if (_overflow_list == NULL) {
2622 assert(_num_par_pushes == 0, "Inconsistency");
2623 }
2624 return _overflow_list == NULL;
2625 }
2626
2627 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2628 // merely consolidate assertion checks that appear to occur together frequently.
2629 void CMSCollector::verify_work_stacks_empty() const {
2630 assert(_markStack.isEmpty(), "Marking stack should be empty");
2631 assert(overflow_list_is_empty(), "Overflow list should be empty");
2632 }
2633
2634 void CMSCollector::verify_overflow_empty() const {
2635 assert(overflow_list_is_empty(), "Overflow list should be empty");
2636 assert(no_preserved_marks(), "No preserved marks");
2637 }
2638 #endif // PRODUCT
2639
2640 // Decide if we want to enable class unloading as part of the
2641 // ensuing concurrent GC cycle. We will collect and
2642 // unload classes if it's the case that:
2643 // (1) an explicit gc request has been made and the flag
2644 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2645 // (2) (a) class unloading is enabled at the command line, and
2646 // (b) old gen is getting really full
2647 // NOTE: Provided there is no change in the state of the heap between
2648 // calls to this method, it should have idempotent results. Moreover,
2649 // its results should be monotonically increasing (i.e. going from 0 to 1,
2650 // but not 1 to 0) between successive calls between which the heap was
2651 // not collected. For the implementation below, it must thus rely on
2652 // the property that concurrent_cycles_since_last_unload()
2653 // will not decrease unless a collection cycle happened and that
2654 // _cmsGen->is_too_full() are
2655 // themselves also monotonic in that sense. See check_monotonicity()
2656 // below.
2657 void CMSCollector::update_should_unload_classes() {
2658 _should_unload_classes = false;
2659 // Condition 1 above
2660 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2661 _should_unload_classes = true;
2662 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2663 // Disjuncts 2.b.(i,ii,iii) above
2664 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2665 CMSClassUnloadingMaxInterval)
2666 || _cmsGen->is_too_full();
2667 }
2668 }
2669
2670 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2671 bool res = should_concurrent_collect();
2672 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2673 return res;
2674 }
2675
2676 void CMSCollector::setup_cms_unloading_and_verification_state() {
2677 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2678 || VerifyBeforeExit;
2679 const int rso = GenCollectedHeap::SO_AllCodeCache;
2680
2681 // We set the proper root for this CMS cycle here.
2682 if (should_unload_classes()) { // Should unload classes this cycle
2683 remove_root_scanning_option(rso); // Shrink the root set appropriately
2684 set_verifying(should_verify); // Set verification state for this cycle
2685 return; // Nothing else needs to be done at this time
2686 }
2687
2688 // Not unloading classes this cycle
2689 assert(!should_unload_classes(), "Inconsistency!");
2690
2691 // If we are not unloading classes then add SO_AllCodeCache to root
2692 // scanning options.
2693 add_root_scanning_option(rso);
2694
2695 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2696 set_verifying(true);
2697 } else if (verifying() && !should_verify) {
2698 // We were verifying, but some verification flags got disabled.
2699 set_verifying(false);
2700 // Exclude symbols, strings and code cache elements from root scanning to
2701 // reduce IM and RM pauses.
2702 remove_root_scanning_option(rso);
2703 }
2704 }
2705
2706
2707 #ifndef PRODUCT
2708 HeapWord* CMSCollector::block_start(const void* p) const {
2709 const HeapWord* addr = (HeapWord*)p;
2710 if (_span.contains(p)) {
2711 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2712 return _cmsGen->cmsSpace()->block_start(p);
2713 }
2714 }
2715 return NULL;
2716 }
2717 #endif
2718
2719 HeapWord*
2720 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2721 bool tlab,
2722 bool parallel) {
2723 CMSSynchronousYieldRequest yr;
2724 assert(!tlab, "Can't deal with TLAB allocation");
2725 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2726 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2727 if (GCExpandToAllocateDelayMillis > 0) {
2728 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2729 }
2730 return have_lock_and_allocate(word_size, tlab);
2731 }
2732
2733 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2734 size_t bytes,
2735 size_t expand_bytes,
2736 CMSExpansionCause::Cause cause)
2737 {
2738
2739 bool success = expand(bytes, expand_bytes);
2740
2741 // remember why we expanded; this information is used
2742 // by shouldConcurrentCollect() when making decisions on whether to start
2743 // a new CMS cycle.
2744 if (success) {
2745 set_expansion_cause(cause);
2746 if (PrintGCDetails && Verbose) {
2747 gclog_or_tty->print_cr("Expanded CMS gen for %s",
2748 CMSExpansionCause::to_string(cause));
2749 }
2750 }
2751 }
2752
2753 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2754 HeapWord* res = NULL;
2755 MutexLocker x(ParGCRareEvent_lock);
2756 while (true) {
2757 // Expansion by some other thread might make alloc OK now:
2758 res = ps->lab.alloc(word_sz);
2759 if (res != NULL) return res;
2760 // If there's not enough expansion space available, give up.
2761 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2762 return NULL;
2763 }
2764 // Otherwise, we try expansion.
2765 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2766 // Now go around the loop and try alloc again;
2767 // A competing par_promote might beat us to the expansion space,
2768 // so we may go around the loop again if promotion fails again.
2769 if (GCExpandToAllocateDelayMillis > 0) {
2770 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2771 }
2772 }
2773 }
2774
2775
2776 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2777 PromotionInfo* promo) {
2778 MutexLocker x(ParGCRareEvent_lock);
2779 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2780 while (true) {
2781 // Expansion by some other thread might make alloc OK now:
2782 if (promo->ensure_spooling_space()) {
2783 assert(promo->has_spooling_space(),
2784 "Post-condition of successful ensure_spooling_space()");
2785 return true;
2786 }
2787 // If there's not enough expansion space available, give up.
2788 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2789 return false;
2790 }
2791 // Otherwise, we try expansion.
2792 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2793 // Now go around the loop and try alloc again;
2794 // A competing allocation might beat us to the expansion space,
2795 // so we may go around the loop again if allocation fails again.
2796 if (GCExpandToAllocateDelayMillis > 0) {
2797 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2798 }
2799 }
2800 }
2801
2802 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2803 // Only shrink if a compaction was done so that all the free space
2804 // in the generation is in a contiguous block at the end.
2805 if (did_compact()) {
2806 CardGeneration::shrink(bytes);
2807 }
2808 }
2809
2810 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2811 assert_locked_or_safepoint(Heap_lock);
2812 }
2813
2814 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2815 assert_locked_or_safepoint(Heap_lock);
2816 assert_lock_strong(freelistLock());
2817 if (PrintGCDetails && Verbose) {
2818 warning("Shrinking of CMS not yet implemented");
2819 }
2820 return;
2821 }
2822
2823
2824 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2825 // phases.
2826 class CMSPhaseAccounting: public StackObj {
2827 public:
2828 CMSPhaseAccounting(CMSCollector *collector,
2829 const char *phase,
2830 bool print_cr = true);
2831 ~CMSPhaseAccounting();
2832
2833 private:
2834 CMSCollector *_collector;
2835 const char *_phase;
2836 elapsedTimer _wallclock;
2837 bool _print_cr;
2838
2839 public:
2840 // Not MT-safe; so do not pass around these StackObj's
2841 // where they may be accessed by other threads.
2842 jlong wallclock_millis() {
2843 assert(_wallclock.is_active(), "Wall clock should not stop");
2844 _wallclock.stop(); // to record time
2845 jlong ret = _wallclock.milliseconds();
2846 _wallclock.start(); // restart
2847 return ret;
2848 }
2849 };
2850
2851 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2852 const char *phase,
2853 bool print_cr) :
2854 _collector(collector), _phase(phase), _print_cr(print_cr) {
2855
2856 if (PrintCMSStatistics != 0) {
2857 _collector->resetYields();
2858 }
2859 if (PrintGCDetails) {
2860 gclog_or_tty->gclog_stamp();
2861 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
2862 _collector->cmsGen()->short_name(), _phase);
2863 }
2864 _collector->resetTimer();
2865 _wallclock.start();
2866 _collector->startTimer();
2867 }
2868
2869 CMSPhaseAccounting::~CMSPhaseAccounting() {
2870 assert(_wallclock.is_active(), "Wall clock should not have stopped");
2871 _collector->stopTimer();
2872 _wallclock.stop();
2873 if (PrintGCDetails) {
2874 gclog_or_tty->gclog_stamp();
2875 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
2876 _collector->cmsGen()->short_name(),
2877 _phase, _collector->timerValue(), _wallclock.seconds());
2878 if (_print_cr) {
2879 gclog_or_tty->cr();
2880 }
2881 if (PrintCMSStatistics != 0) {
2882 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
2883 _collector->yields());
2884 }
2885 }
2886 }
2887
2888 // CMS work
2889
2890 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2891 class CMSParMarkTask : public AbstractGangTask {
2892 protected:
2893 CMSCollector* _collector;
2894 uint _n_workers;
2895 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2896 AbstractGangTask(name),
2897 _collector(collector),
2898 _n_workers(n_workers) {}
2899 // Work method in support of parallel rescan ... of young gen spaces
2900 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
2901 ContiguousSpace* space,
2902 HeapWord** chunk_array, size_t chunk_top);
2903 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
2904 };
2905
2906 // Parallel initial mark task
2907 class CMSParInitialMarkTask: public CMSParMarkTask {
2908 StrongRootsScope* _strong_roots_scope;
2909 public:
2910 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2911 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2912 _strong_roots_scope(strong_roots_scope) {}
2913 void work(uint worker_id);
2914 };
2915
2916 // Checkpoint the roots into this generation from outside
2917 // this generation. [Note this initial checkpoint need only
2918 // be approximate -- we'll do a catch up phase subsequently.]
2919 void CMSCollector::checkpointRootsInitial() {
2920 assert(_collectorState == InitialMarking, "Wrong collector state");
2921 check_correct_thread_executing();
2922 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2923
2924 save_heap_summary();
2925 report_heap_summary(GCWhen::BeforeGC);
2926
2927 ReferenceProcessor* rp = ref_processor();
2928 assert(_restart_addr == NULL, "Control point invariant");
2929 {
2930 // acquire locks for subsequent manipulations
2931 MutexLockerEx x(bitMapLock(),
2932 Mutex::_no_safepoint_check_flag);
2933 checkpointRootsInitialWork();
2934 // enable ("weak") refs discovery
2935 rp->enable_discovery();
2936 _collectorState = Marking;
2937 }
2938 }
2939
2940 void CMSCollector::checkpointRootsInitialWork() {
2941 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2942 assert(_collectorState == InitialMarking, "just checking");
2943
2944 // Already have locks.
2945 assert_lock_strong(bitMapLock());
2946 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2947
2948 // Setup the verification and class unloading state for this
2949 // CMS collection cycle.
2950 setup_cms_unloading_and_verification_state();
2951
2952 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
2953 PrintGCDetails && Verbose, true, _gc_timer_cm);)
2954
2955 // Reset all the PLAB chunk arrays if necessary.
2956 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2957 reset_survivor_plab_arrays();
2958 }
2959
2960 ResourceMark rm;
2961 HandleMark hm;
2962
2963 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2964 GenCollectedHeap* gch = GenCollectedHeap::heap();
2965
2966 verify_work_stacks_empty();
2967 verify_overflow_empty();
2968
2969 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2970 // Update the saved marks which may affect the root scans.
2971 gch->save_marks();
2972
2973 // weak reference processing has not started yet.
2974 ref_processor()->set_enqueuing_is_done(false);
2975
2976 // Need to remember all newly created CLDs,
2977 // so that we can guarantee that the remark finds them.
2978 ClassLoaderDataGraph::remember_new_clds(true);
2979
2980 // Whenever a CLD is found, it will be claimed before proceeding to mark
2981 // the klasses. The claimed marks need to be cleared before marking starts.
2982 ClassLoaderDataGraph::clear_claimed_marks();
2983
2984 if (CMSPrintEdenSurvivorChunks) {
2985 print_eden_and_survivor_chunk_arrays();
2986 }
2987
2988 {
2989 #if defined(COMPILER2) || INCLUDE_JVMCI
2990 DerivedPointerTableDeactivate dpt_deact;
2991 #endif
2992 if (CMSParallelInitialMarkEnabled) {
2993 // The parallel version.
2994 WorkGang* workers = gch->workers();
2995 assert(workers != NULL, "Need parallel worker threads.");
2996 uint n_workers = workers->active_workers();
2997
2998 StrongRootsScope srs(n_workers);
2999
3000 CMSParInitialMarkTask tsk(this, &srs, n_workers);
3001 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3002 if (n_workers > 1) {
3003 workers->run_task(&tsk);
3004 } else {
3005 tsk.work(0);
3006 }
3007 } else {
3008 // The serial version.
3009 CLDToOopClosure cld_closure(¬Older, true);
3010 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3011
3012 StrongRootsScope srs(1);
3013
3014 gch->gen_process_roots(&srs,
3015 GenCollectedHeap::OldGen,
3016 true, // young gen as roots
3017 GenCollectedHeap::ScanningOption(roots_scanning_options()),
3018 should_unload_classes(),
3019 ¬Older,
3020 NULL,
3021 &cld_closure);
3022 }
3023 }
3024
3025 // Clear mod-union table; it will be dirtied in the prologue of
3026 // CMS generation per each young generation collection.
3027
3028 assert(_modUnionTable.isAllClear(),
3029 "Was cleared in most recent final checkpoint phase"
3030 " or no bits are set in the gc_prologue before the start of the next "
3031 "subsequent marking phase.");
3032
3033 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3034
3035 // Save the end of the used_region of the constituent generations
3036 // to be used to limit the extent of sweep in each generation.
3037 save_sweep_limits();
3038 verify_overflow_empty();
3039 }
3040
3041 bool CMSCollector::markFromRoots() {
3042 // we might be tempted to assert that:
3043 // assert(!SafepointSynchronize::is_at_safepoint(),
3044 // "inconsistent argument?");
3045 // However that wouldn't be right, because it's possible that
3046 // a safepoint is indeed in progress as a young generation
3047 // stop-the-world GC happens even as we mark in this generation.
3048 assert(_collectorState == Marking, "inconsistent state?");
3049 check_correct_thread_executing();
3050 verify_overflow_empty();
3051
3052 // Weak ref discovery note: We may be discovering weak
3053 // refs in this generation concurrent (but interleaved) with
3054 // weak ref discovery by the young generation collector.
3055
3056 CMSTokenSyncWithLocks ts(true, bitMapLock());
3057 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3058 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3059 bool res = markFromRootsWork();
3060 if (res) {
3061 _collectorState = Precleaning;
3062 } else { // We failed and a foreground collection wants to take over
3063 assert(_foregroundGCIsActive, "internal state inconsistency");
3064 assert(_restart_addr == NULL, "foreground will restart from scratch");
3065 if (PrintGCDetails) {
3066 gclog_or_tty->print_cr("bailing out to foreground collection");
3067 }
3068 }
3069 verify_overflow_empty();
3070 return res;
3071 }
3072
3073 bool CMSCollector::markFromRootsWork() {
3074 // iterate over marked bits in bit map, doing a full scan and mark
3075 // from these roots using the following algorithm:
3076 // . if oop is to the right of the current scan pointer,
3077 // mark corresponding bit (we'll process it later)
3078 // . else (oop is to left of current scan pointer)
3079 // push oop on marking stack
3080 // . drain the marking stack
3081
3082 // Note that when we do a marking step we need to hold the
3083 // bit map lock -- recall that direct allocation (by mutators)
3084 // and promotion (by the young generation collector) is also
3085 // marking the bit map. [the so-called allocate live policy.]
3086 // Because the implementation of bit map marking is not
3087 // robust wrt simultaneous marking of bits in the same word,
3088 // we need to make sure that there is no such interference
3089 // between concurrent such updates.
3090
3091 // already have locks
3092 assert_lock_strong(bitMapLock());
3093
3094 verify_work_stacks_empty();
3095 verify_overflow_empty();
3096 bool result = false;
3097 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3098 result = do_marking_mt();
3099 } else {
3100 result = do_marking_st();
3101 }
3102 return result;
3103 }
3104
3105 // Forward decl
3106 class CMSConcMarkingTask;
3107
3108 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3109 CMSCollector* _collector;
3110 CMSConcMarkingTask* _task;
3111 public:
3112 virtual void yield();
3113
3114 // "n_threads" is the number of threads to be terminated.
3115 // "queue_set" is a set of work queues of other threads.
3116 // "collector" is the CMS collector associated with this task terminator.
3117 // "yield" indicates whether we need the gang as a whole to yield.
3118 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3119 ParallelTaskTerminator(n_threads, queue_set),
3120 _collector(collector) { }
3121
3122 void set_task(CMSConcMarkingTask* task) {
3123 _task = task;
3124 }
3125 };
3126
3127 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3128 CMSConcMarkingTask* _task;
3129 public:
3130 bool should_exit_termination();
3131 void set_task(CMSConcMarkingTask* task) {
3132 _task = task;
3133 }
3134 };
3135
3136 // MT Concurrent Marking Task
3137 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3138 CMSCollector* _collector;
3139 uint _n_workers; // requested/desired # workers
3140 bool _result;
3141 CompactibleFreeListSpace* _cms_space;
3142 char _pad_front[64]; // padding to ...
3143 HeapWord* _global_finger; // ... avoid sharing cache line
3144 char _pad_back[64];
3145 HeapWord* _restart_addr;
3146
3147 // Exposed here for yielding support
3148 Mutex* const _bit_map_lock;
3149
3150 // The per thread work queues, available here for stealing
3151 OopTaskQueueSet* _task_queues;
3152
3153 // Termination (and yielding) support
3154 CMSConcMarkingTerminator _term;
3155 CMSConcMarkingTerminatorTerminator _term_term;
3156
3157 public:
3158 CMSConcMarkingTask(CMSCollector* collector,
3159 CompactibleFreeListSpace* cms_space,
3160 YieldingFlexibleWorkGang* workers,
3161 OopTaskQueueSet* task_queues):
3162 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3163 _collector(collector),
3164 _cms_space(cms_space),
3165 _n_workers(0), _result(true),
3166 _task_queues(task_queues),
3167 _term(_n_workers, task_queues, _collector),
3168 _bit_map_lock(collector->bitMapLock())
3169 {
3170 _requested_size = _n_workers;
3171 _term.set_task(this);
3172 _term_term.set_task(this);
3173 _restart_addr = _global_finger = _cms_space->bottom();
3174 }
3175
3176
3177 OopTaskQueueSet* task_queues() { return _task_queues; }
3178
3179 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3180
3181 HeapWord** global_finger_addr() { return &_global_finger; }
3182
3183 CMSConcMarkingTerminator* terminator() { return &_term; }
3184
3185 virtual void set_for_termination(uint active_workers) {
3186 terminator()->reset_for_reuse(active_workers);
3187 }
3188
3189 void work(uint worker_id);
3190 bool should_yield() {
3191 return ConcurrentMarkSweepThread::should_yield()
3192 && !_collector->foregroundGCIsActive();
3193 }
3194
3195 virtual void coordinator_yield(); // stuff done by coordinator
3196 bool result() { return _result; }
3197
3198 void reset(HeapWord* ra) {
3199 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3200 _restart_addr = _global_finger = ra;
3201 _term.reset_for_reuse();
3202 }
3203
3204 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3205 OopTaskQueue* work_q);
3206
3207 private:
3208 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3209 void do_work_steal(int i);
3210 void bump_global_finger(HeapWord* f);
3211 };
3212
3213 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3214 assert(_task != NULL, "Error");
3215 return _task->yielding();
3216 // Note that we do not need the disjunct || _task->should_yield() above
3217 // because we want terminating threads to yield only if the task
3218 // is already in the midst of yielding, which happens only after at least one
3219 // thread has yielded.
3220 }
3221
3222 void CMSConcMarkingTerminator::yield() {
3223 if (_task->should_yield()) {
3224 _task->yield();
3225 } else {
3226 ParallelTaskTerminator::yield();
3227 }
3228 }
3229
3230 ////////////////////////////////////////////////////////////////
3231 // Concurrent Marking Algorithm Sketch
3232 ////////////////////////////////////////////////////////////////
3233 // Until all tasks exhausted (both spaces):
3234 // -- claim next available chunk
3235 // -- bump global finger via CAS
3236 // -- find first object that starts in this chunk
3237 // and start scanning bitmap from that position
3238 // -- scan marked objects for oops
3239 // -- CAS-mark target, and if successful:
3240 // . if target oop is above global finger (volatile read)
3241 // nothing to do
3242 // . if target oop is in chunk and above local finger
3243 // then nothing to do
3244 // . else push on work-queue
3245 // -- Deal with possible overflow issues:
3246 // . local work-queue overflow causes stuff to be pushed on
3247 // global (common) overflow queue
3248 // . always first empty local work queue
3249 // . then get a batch of oops from global work queue if any
3250 // . then do work stealing
3251 // -- When all tasks claimed (both spaces)
3252 // and local work queue empty,
3253 // then in a loop do:
3254 // . check global overflow stack; steal a batch of oops and trace
3255 // . try to steal from other threads oif GOS is empty
3256 // . if neither is available, offer termination
3257 // -- Terminate and return result
3258 //
3259 void CMSConcMarkingTask::work(uint worker_id) {
3260 elapsedTimer _timer;
3261 ResourceMark rm;
3262 HandleMark hm;
3263
3264 DEBUG_ONLY(_collector->verify_overflow_empty();)
3265
3266 // Before we begin work, our work queue should be empty
3267 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3268 // Scan the bitmap covering _cms_space, tracing through grey objects.
3269 _timer.start();
3270 do_scan_and_mark(worker_id, _cms_space);
3271 _timer.stop();
3272 if (PrintCMSStatistics != 0) {
3273 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3274 worker_id, _timer.seconds());
3275 // XXX: need xxx/xxx type of notation, two timers
3276 }
3277
3278 // ... do work stealing
3279 _timer.reset();
3280 _timer.start();
3281 do_work_steal(worker_id);
3282 _timer.stop();
3283 if (PrintCMSStatistics != 0) {
3284 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3285 worker_id, _timer.seconds());
3286 // XXX: need xxx/xxx type of notation, two timers
3287 }
3288 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3289 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3290 // Note that under the current task protocol, the
3291 // following assertion is true even of the spaces
3292 // expanded since the completion of the concurrent
3293 // marking. XXX This will likely change under a strict
3294 // ABORT semantics.
3295 // After perm removal the comparison was changed to
3296 // greater than or equal to from strictly greater than.
3297 // Before perm removal the highest address sweep would
3298 // have been at the end of perm gen but now is at the
3299 // end of the tenured gen.
3300 assert(_global_finger >= _cms_space->end(),
3301 "All tasks have been completed");
3302 DEBUG_ONLY(_collector->verify_overflow_empty();)
3303 }
3304
3305 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3306 HeapWord* read = _global_finger;
3307 HeapWord* cur = read;
3308 while (f > read) {
3309 cur = read;
3310 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3311 if (cur == read) {
3312 // our cas succeeded
3313 assert(_global_finger >= f, "protocol consistency");
3314 break;
3315 }
3316 }
3317 }
3318
3319 // This is really inefficient, and should be redone by
3320 // using (not yet available) block-read and -write interfaces to the
3321 // stack and the work_queue. XXX FIX ME !!!
3322 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3323 OopTaskQueue* work_q) {
3324 // Fast lock-free check
3325 if (ovflw_stk->length() == 0) {
3326 return false;
3327 }
3328 assert(work_q->size() == 0, "Shouldn't steal");
3329 MutexLockerEx ml(ovflw_stk->par_lock(),
3330 Mutex::_no_safepoint_check_flag);
3331 // Grab up to 1/4 the size of the work queue
3332 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3333 (size_t)ParGCDesiredObjsFromOverflowList);
3334 num = MIN2(num, ovflw_stk->length());
3335 for (int i = (int) num; i > 0; i--) {
3336 oop cur = ovflw_stk->pop();
3337 assert(cur != NULL, "Counted wrong?");
3338 work_q->push(cur);
3339 }
3340 return num > 0;
3341 }
3342
3343 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3344 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3345 int n_tasks = pst->n_tasks();
3346 // We allow that there may be no tasks to do here because
3347 // we are restarting after a stack overflow.
3348 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3349 uint nth_task = 0;
3350
3351 HeapWord* aligned_start = sp->bottom();
3352 if (sp->used_region().contains(_restart_addr)) {
3353 // Align down to a card boundary for the start of 0th task
3354 // for this space.
3355 aligned_start =
3356 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3357 CardTableModRefBS::card_size);
3358 }
3359
3360 size_t chunk_size = sp->marking_task_size();
3361 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3362 // Having claimed the nth task in this space,
3363 // compute the chunk that it corresponds to:
3364 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3365 aligned_start + (nth_task+1)*chunk_size);
3366 // Try and bump the global finger via a CAS;
3367 // note that we need to do the global finger bump
3368 // _before_ taking the intersection below, because
3369 // the task corresponding to that region will be
3370 // deemed done even if the used_region() expands
3371 // because of allocation -- as it almost certainly will
3372 // during start-up while the threads yield in the
3373 // closure below.
3374 HeapWord* finger = span.end();
3375 bump_global_finger(finger); // atomically
3376 // There are null tasks here corresponding to chunks
3377 // beyond the "top" address of the space.
3378 span = span.intersection(sp->used_region());
3379 if (!span.is_empty()) { // Non-null task
3380 HeapWord* prev_obj;
3381 assert(!span.contains(_restart_addr) || nth_task == 0,
3382 "Inconsistency");
3383 if (nth_task == 0) {
3384 // For the 0th task, we'll not need to compute a block_start.
3385 if (span.contains(_restart_addr)) {
3386 // In the case of a restart because of stack overflow,
3387 // we might additionally skip a chunk prefix.
3388 prev_obj = _restart_addr;
3389 } else {
3390 prev_obj = span.start();
3391 }
3392 } else {
3393 // We want to skip the first object because
3394 // the protocol is to scan any object in its entirety
3395 // that _starts_ in this span; a fortiori, any
3396 // object starting in an earlier span is scanned
3397 // as part of an earlier claimed task.
3398 // Below we use the "careful" version of block_start
3399 // so we do not try to navigate uninitialized objects.
3400 prev_obj = sp->block_start_careful(span.start());
3401 // Below we use a variant of block_size that uses the
3402 // Printezis bits to avoid waiting for allocated
3403 // objects to become initialized/parsable.
3404 while (prev_obj < span.start()) {
3405 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3406 if (sz > 0) {
3407 prev_obj += sz;
3408 } else {
3409 // In this case we may end up doing a bit of redundant
3410 // scanning, but that appears unavoidable, short of
3411 // locking the free list locks; see bug 6324141.
3412 break;
3413 }
3414 }
3415 }
3416 if (prev_obj < span.end()) {
3417 MemRegion my_span = MemRegion(prev_obj, span.end());
3418 // Do the marking work within a non-empty span --
3419 // the last argument to the constructor indicates whether the
3420 // iteration should be incremental with periodic yields.
3421 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3422 &_collector->_markBitMap,
3423 work_queue(i),
3424 &_collector->_markStack);
3425 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3426 } // else nothing to do for this task
3427 } // else nothing to do for this task
3428 }
3429 // We'd be tempted to assert here that since there are no
3430 // more tasks left to claim in this space, the global_finger
3431 // must exceed space->top() and a fortiori space->end(). However,
3432 // that would not quite be correct because the bumping of
3433 // global_finger occurs strictly after the claiming of a task,
3434 // so by the time we reach here the global finger may not yet
3435 // have been bumped up by the thread that claimed the last
3436 // task.
3437 pst->all_tasks_completed();
3438 }
3439
3440 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
3441 private:
3442 CMSCollector* _collector;
3443 CMSConcMarkingTask* _task;
3444 MemRegion _span;
3445 CMSBitMap* _bit_map;
3446 CMSMarkStack* _overflow_stack;
3447 OopTaskQueue* _work_queue;
3448 protected:
3449 DO_OOP_WORK_DEFN
3450 public:
3451 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3452 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3453 MetadataAwareOopClosure(collector->ref_processor()),
3454 _collector(collector),
3455 _task(task),
3456 _span(collector->_span),
3457 _work_queue(work_queue),
3458 _bit_map(bit_map),
3459 _overflow_stack(overflow_stack)
3460 { }
3461 virtual void do_oop(oop* p);
3462 virtual void do_oop(narrowOop* p);
3463
3464 void trim_queue(size_t max);
3465 void handle_stack_overflow(HeapWord* lost);
3466 void do_yield_check() {
3467 if (_task->should_yield()) {
3468 _task->yield();
3469 }
3470 }
3471 };
3472
3473 // Grey object scanning during work stealing phase --
3474 // the salient assumption here is that any references
3475 // that are in these stolen objects being scanned must
3476 // already have been initialized (else they would not have
3477 // been published), so we do not need to check for
3478 // uninitialized objects before pushing here.
3479 void Par_ConcMarkingClosure::do_oop(oop obj) {
3480 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3481 HeapWord* addr = (HeapWord*)obj;
3482 // Check if oop points into the CMS generation
3483 // and is not marked
3484 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3485 // a white object ...
3486 // If we manage to "claim" the object, by being the
3487 // first thread to mark it, then we push it on our
3488 // marking stack
3489 if (_bit_map->par_mark(addr)) { // ... now grey
3490 // push on work queue (grey set)
3491 bool simulate_overflow = false;
3492 NOT_PRODUCT(
3493 if (CMSMarkStackOverflowALot &&
3494 _collector->simulate_overflow()) {
3495 // simulate a stack overflow
3496 simulate_overflow = true;
3497 }
3498 )
3499 if (simulate_overflow ||
3500 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3501 // stack overflow
3502 if (PrintCMSStatistics != 0) {
3503 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
3504 SIZE_FORMAT, _overflow_stack->capacity());
3505 }
3506 // We cannot assert that the overflow stack is full because
3507 // it may have been emptied since.
3508 assert(simulate_overflow ||
3509 _work_queue->size() == _work_queue->max_elems(),
3510 "Else push should have succeeded");
3511 handle_stack_overflow(addr);
3512 }
3513 } // Else, some other thread got there first
3514 do_yield_check();
3515 }
3516 }
3517
3518 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3519 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
3520
3521 void Par_ConcMarkingClosure::trim_queue(size_t max) {
3522 while (_work_queue->size() > max) {
3523 oop new_oop;
3524 if (_work_queue->pop_local(new_oop)) {
3525 assert(new_oop->is_oop(), "Should be an oop");
3526 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3527 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3528 new_oop->oop_iterate(this); // do_oop() above
3529 do_yield_check();
3530 }
3531 }
3532 }
3533
3534 // Upon stack overflow, we discard (part of) the stack,
3535 // remembering the least address amongst those discarded
3536 // in CMSCollector's _restart_address.
3537 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3538 // We need to do this under a mutex to prevent other
3539 // workers from interfering with the work done below.
3540 MutexLockerEx ml(_overflow_stack->par_lock(),
3541 Mutex::_no_safepoint_check_flag);
3542 // Remember the least grey address discarded
3543 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3544 _collector->lower_restart_addr(ra);
3545 _overflow_stack->reset(); // discard stack contents
3546 _overflow_stack->expand(); // expand the stack if possible
3547 }
3548
3549
3550 void CMSConcMarkingTask::do_work_steal(int i) {
3551 OopTaskQueue* work_q = work_queue(i);
3552 oop obj_to_scan;
3553 CMSBitMap* bm = &(_collector->_markBitMap);
3554 CMSMarkStack* ovflw = &(_collector->_markStack);
3555 int* seed = _collector->hash_seed(i);
3556 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3557 while (true) {
3558 cl.trim_queue(0);
3559 assert(work_q->size() == 0, "Should have been emptied above");
3560 if (get_work_from_overflow_stack(ovflw, work_q)) {
3561 // Can't assert below because the work obtained from the
3562 // overflow stack may already have been stolen from us.
3563 // assert(work_q->size() > 0, "Work from overflow stack");
3564 continue;
3565 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3566 assert(obj_to_scan->is_oop(), "Should be an oop");
3567 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3568 obj_to_scan->oop_iterate(&cl);
3569 } else if (terminator()->offer_termination(&_term_term)) {
3570 assert(work_q->size() == 0, "Impossible!");
3571 break;
3572 } else if (yielding() || should_yield()) {
3573 yield();
3574 }
3575 }
3576 }
3577
3578 // This is run by the CMS (coordinator) thread.
3579 void CMSConcMarkingTask::coordinator_yield() {
3580 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3581 "CMS thread should hold CMS token");
3582 // First give up the locks, then yield, then re-lock
3583 // We should probably use a constructor/destructor idiom to
3584 // do this unlock/lock or modify the MutexUnlocker class to
3585 // serve our purpose. XXX
3586 assert_lock_strong(_bit_map_lock);
3587 _bit_map_lock->unlock();
3588 ConcurrentMarkSweepThread::desynchronize(true);
3589 _collector->stopTimer();
3590 if (PrintCMSStatistics != 0) {
3591 _collector->incrementYields();
3592 }
3593
3594 // It is possible for whichever thread initiated the yield request
3595 // not to get a chance to wake up and take the bitmap lock between
3596 // this thread releasing it and reacquiring it. So, while the
3597 // should_yield() flag is on, let's sleep for a bit to give the
3598 // other thread a chance to wake up. The limit imposed on the number
3599 // of iterations is defensive, to avoid any unforseen circumstances
3600 // putting us into an infinite loop. Since it's always been this
3601 // (coordinator_yield()) method that was observed to cause the
3602 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3603 // which is by default non-zero. For the other seven methods that
3604 // also perform the yield operation, as are using a different
3605 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3606 // can enable the sleeping for those methods too, if necessary.
3607 // See 6442774.
3608 //
3609 // We really need to reconsider the synchronization between the GC
3610 // thread and the yield-requesting threads in the future and we
3611 // should really use wait/notify, which is the recommended
3612 // way of doing this type of interaction. Additionally, we should
3613 // consolidate the eight methods that do the yield operation and they
3614 // are almost identical into one for better maintainability and
3615 // readability. See 6445193.
3616 //
3617 // Tony 2006.06.29
3618 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3619 ConcurrentMarkSweepThread::should_yield() &&
3620 !CMSCollector::foregroundGCIsActive(); ++i) {
3621 os::sleep(Thread::current(), 1, false);
3622 }
3623
3624 ConcurrentMarkSweepThread::synchronize(true);
3625 _bit_map_lock->lock_without_safepoint_check();
3626 _collector->startTimer();
3627 }
3628
3629 bool CMSCollector::do_marking_mt() {
3630 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3631 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3632 conc_workers()->active_workers(),
3633 Threads::number_of_non_daemon_threads());
3634 conc_workers()->set_active_workers(num_workers);
3635
3636 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3637
3638 CMSConcMarkingTask tsk(this,
3639 cms_space,
3640 conc_workers(),
3641 task_queues());
3642
3643 // Since the actual number of workers we get may be different
3644 // from the number we requested above, do we need to do anything different
3645 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3646 // class?? XXX
3647 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3648
3649 // Refs discovery is already non-atomic.
3650 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3651 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3652 conc_workers()->start_task(&tsk);
3653 while (tsk.yielded()) {
3654 tsk.coordinator_yield();
3655 conc_workers()->continue_task(&tsk);
3656 }
3657 // If the task was aborted, _restart_addr will be non-NULL
3658 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3659 while (_restart_addr != NULL) {
3660 // XXX For now we do not make use of ABORTED state and have not
3661 // yet implemented the right abort semantics (even in the original
3662 // single-threaded CMS case). That needs some more investigation
3663 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3664 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3665 // If _restart_addr is non-NULL, a marking stack overflow
3666 // occurred; we need to do a fresh marking iteration from the
3667 // indicated restart address.
3668 if (_foregroundGCIsActive) {
3669 // We may be running into repeated stack overflows, having
3670 // reached the limit of the stack size, while making very
3671 // slow forward progress. It may be best to bail out and
3672 // let the foreground collector do its job.
3673 // Clear _restart_addr, so that foreground GC
3674 // works from scratch. This avoids the headache of
3675 // a "rescan" which would otherwise be needed because
3676 // of the dirty mod union table & card table.
3677 _restart_addr = NULL;
3678 return false;
3679 }
3680 // Adjust the task to restart from _restart_addr
3681 tsk.reset(_restart_addr);
3682 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3683 _restart_addr);
3684 _restart_addr = NULL;
3685 // Get the workers going again
3686 conc_workers()->start_task(&tsk);
3687 while (tsk.yielded()) {
3688 tsk.coordinator_yield();
3689 conc_workers()->continue_task(&tsk);
3690 }
3691 }
3692 assert(tsk.completed(), "Inconsistency");
3693 assert(tsk.result() == true, "Inconsistency");
3694 return true;
3695 }
3696
3697 bool CMSCollector::do_marking_st() {
3698 ResourceMark rm;
3699 HandleMark hm;
3700
3701 // Temporarily make refs discovery single threaded (non-MT)
3702 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3703 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3704 &_markStack, CMSYield);
3705 // the last argument to iterate indicates whether the iteration
3706 // should be incremental with periodic yields.
3707 _markBitMap.iterate(&markFromRootsClosure);
3708 // If _restart_addr is non-NULL, a marking stack overflow
3709 // occurred; we need to do a fresh iteration from the
3710 // indicated restart address.
3711 while (_restart_addr != NULL) {
3712 if (_foregroundGCIsActive) {
3713 // We may be running into repeated stack overflows, having
3714 // reached the limit of the stack size, while making very
3715 // slow forward progress. It may be best to bail out and
3716 // let the foreground collector do its job.
3717 // Clear _restart_addr, so that foreground GC
3718 // works from scratch. This avoids the headache of
3719 // a "rescan" which would otherwise be needed because
3720 // of the dirty mod union table & card table.
3721 _restart_addr = NULL;
3722 return false; // indicating failure to complete marking
3723 }
3724 // Deal with stack overflow:
3725 // we restart marking from _restart_addr
3726 HeapWord* ra = _restart_addr;
3727 markFromRootsClosure.reset(ra);
3728 _restart_addr = NULL;
3729 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3730 }
3731 return true;
3732 }
3733
3734 void CMSCollector::preclean() {
3735 check_correct_thread_executing();
3736 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3737 verify_work_stacks_empty();
3738 verify_overflow_empty();
3739 _abort_preclean = false;
3740 if (CMSPrecleaningEnabled) {
3741 if (!CMSEdenChunksRecordAlways) {
3742 _eden_chunk_index = 0;
3743 }
3744 size_t used = get_eden_used();
3745 size_t capacity = get_eden_capacity();
3746 // Don't start sampling unless we will get sufficiently
3747 // many samples.
3748 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
3749 * CMSScheduleRemarkEdenPenetration)) {
3750 _start_sampling = true;
3751 } else {
3752 _start_sampling = false;
3753 }
3754 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3755 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
3756 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3757 }
3758 CMSTokenSync x(true); // is cms thread
3759 if (CMSPrecleaningEnabled) {
3760 sample_eden();
3761 _collectorState = AbortablePreclean;
3762 } else {
3763 _collectorState = FinalMarking;
3764 }
3765 verify_work_stacks_empty();
3766 verify_overflow_empty();
3767 }
3768
3769 // Try and schedule the remark such that young gen
3770 // occupancy is CMSScheduleRemarkEdenPenetration %.
3771 void CMSCollector::abortable_preclean() {
3772 check_correct_thread_executing();
3773 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3774 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3775
3776 // If Eden's current occupancy is below this threshold,
3777 // immediately schedule the remark; else preclean
3778 // past the next scavenge in an effort to
3779 // schedule the pause as described above. By choosing
3780 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3781 // we will never do an actual abortable preclean cycle.
3782 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3783 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3784 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
3785 // We need more smarts in the abortable preclean
3786 // loop below to deal with cases where allocation
3787 // in young gen is very very slow, and our precleaning
3788 // is running a losing race against a horde of
3789 // mutators intent on flooding us with CMS updates
3790 // (dirty cards).
3791 // One, admittedly dumb, strategy is to give up
3792 // after a certain number of abortable precleaning loops
3793 // or after a certain maximum time. We want to make
3794 // this smarter in the next iteration.
3795 // XXX FIX ME!!! YSR
3796 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3797 while (!(should_abort_preclean() ||
3798 ConcurrentMarkSweepThread::should_terminate())) {
3799 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3800 cumworkdone += workdone;
3801 loops++;
3802 // Voluntarily terminate abortable preclean phase if we have
3803 // been at it for too long.
3804 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3805 loops >= CMSMaxAbortablePrecleanLoops) {
3806 if (PrintGCDetails) {
3807 gclog_or_tty->print(" CMS: abort preclean due to loops ");
3808 }
3809 break;
3810 }
3811 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3812 if (PrintGCDetails) {
3813 gclog_or_tty->print(" CMS: abort preclean due to time ");
3814 }
3815 break;
3816 }
3817 // If we are doing little work each iteration, we should
3818 // take a short break.
3819 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3820 // Sleep for some time, waiting for work to accumulate
3821 stopTimer();
3822 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3823 startTimer();
3824 waited++;
3825 }
3826 }
3827 if (PrintCMSStatistics > 0) {
3828 gclog_or_tty->print(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3829 loops, waited, cumworkdone);
3830 }
3831 }
3832 CMSTokenSync x(true); // is cms thread
3833 if (_collectorState != Idling) {
3834 assert(_collectorState == AbortablePreclean,
3835 "Spontaneous state transition?");
3836 _collectorState = FinalMarking;
3837 } // Else, a foreground collection completed this CMS cycle.
3838 return;
3839 }
3840
3841 // Respond to an Eden sampling opportunity
3842 void CMSCollector::sample_eden() {
3843 // Make sure a young gc cannot sneak in between our
3844 // reading and recording of a sample.
3845 assert(Thread::current()->is_ConcurrentGC_thread(),
3846 "Only the cms thread may collect Eden samples");
3847 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3848 "Should collect samples while holding CMS token");
3849 if (!_start_sampling) {
3850 return;
3851 }
3852 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3853 // is populated by the young generation.
3854 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3855 if (_eden_chunk_index < _eden_chunk_capacity) {
3856 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3857 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3858 "Unexpected state of Eden");
3859 // We'd like to check that what we just sampled is an oop-start address;
3860 // however, we cannot do that here since the object may not yet have been
3861 // initialized. So we'll instead do the check when we _use_ this sample
3862 // later.
3863 if (_eden_chunk_index == 0 ||
3864 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3865 _eden_chunk_array[_eden_chunk_index-1])
3866 >= CMSSamplingGrain)) {
3867 _eden_chunk_index++; // commit sample
3868 }
3869 }
3870 }
3871 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3872 size_t used = get_eden_used();
3873 size_t capacity = get_eden_capacity();
3874 assert(used <= capacity, "Unexpected state of Eden");
3875 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3876 _abort_preclean = true;
3877 }
3878 }
3879 }
3880
3881
3882 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3883 assert(_collectorState == Precleaning ||
3884 _collectorState == AbortablePreclean, "incorrect state");
3885 ResourceMark rm;
3886 HandleMark hm;
3887
3888 // Precleaning is currently not MT but the reference processor
3889 // may be set for MT. Disable it temporarily here.
3890 ReferenceProcessor* rp = ref_processor();
3891 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3892
3893 // Do one pass of scrubbing the discovered reference lists
3894 // to remove any reference objects with strongly-reachable
3895 // referents.
3896 if (clean_refs) {
3897 CMSPrecleanRefsYieldClosure yield_cl(this);
3898 assert(rp->span().equals(_span), "Spans should be equal");
3899 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3900 &_markStack, true /* preclean */);
3901 CMSDrainMarkingStackClosure complete_trace(this,
3902 _span, &_markBitMap, &_markStack,
3903 &keep_alive, true /* preclean */);
3904
3905 // We don't want this step to interfere with a young
3906 // collection because we don't want to take CPU
3907 // or memory bandwidth away from the young GC threads
3908 // (which may be as many as there are CPUs).
3909 // Note that we don't need to protect ourselves from
3910 // interference with mutators because they can't
3911 // manipulate the discovered reference lists nor affect
3912 // the computed reachability of the referents, the
3913 // only properties manipulated by the precleaning
3914 // of these reference lists.
3915 stopTimer();
3916 CMSTokenSyncWithLocks x(true /* is cms thread */,
3917 bitMapLock());
3918 startTimer();
3919 sample_eden();
3920
3921 // The following will yield to allow foreground
3922 // collection to proceed promptly. XXX YSR:
3923 // The code in this method may need further
3924 // tweaking for better performance and some restructuring
3925 // for cleaner interfaces.
3926 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3927 rp->preclean_discovered_references(
3928 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3929 gc_timer);
3930 }
3931
3932 if (clean_survivor) { // preclean the active survivor space(s)
3933 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3934 &_markBitMap, &_modUnionTable,
3935 &_markStack, true /* precleaning phase */);
3936 stopTimer();
3937 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3938 bitMapLock());
3939 startTimer();
3940 unsigned int before_count =
3941 GenCollectedHeap::heap()->total_collections();
3942 SurvivorSpacePrecleanClosure
3943 sss_cl(this, _span, &_markBitMap, &_markStack,
3944 &pam_cl, before_count, CMSYield);
3945 _young_gen->from()->object_iterate_careful(&sss_cl);
3946 _young_gen->to()->object_iterate_careful(&sss_cl);
3947 }
3948 MarkRefsIntoAndScanClosure
3949 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3950 &_markStack, this, CMSYield,
3951 true /* precleaning phase */);
3952 // CAUTION: The following closure has persistent state that may need to
3953 // be reset upon a decrease in the sequence of addresses it
3954 // processes.
3955 ScanMarkedObjectsAgainCarefullyClosure
3956 smoac_cl(this, _span,
3957 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3958
3959 // Preclean dirty cards in ModUnionTable and CardTable using
3960 // appropriate convergence criterion;
3961 // repeat CMSPrecleanIter times unless we find that
3962 // we are losing.
3963 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3964 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3965 "Bad convergence multiplier");
3966 assert(CMSPrecleanThreshold >= 100,
3967 "Unreasonably low CMSPrecleanThreshold");
3968
3969 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3970 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3971 numIter < CMSPrecleanIter;
3972 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3973 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3974 if (Verbose && PrintGCDetails) {
3975 gclog_or_tty->print(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3976 }
3977 // Either there are very few dirty cards, so re-mark
3978 // pause will be small anyway, or our pre-cleaning isn't
3979 // that much faster than the rate at which cards are being
3980 // dirtied, so we might as well stop and re-mark since
3981 // precleaning won't improve our re-mark time by much.
3982 if (curNumCards <= CMSPrecleanThreshold ||
3983 (numIter > 0 &&
3984 (curNumCards * CMSPrecleanDenominator >
3985 lastNumCards * CMSPrecleanNumerator))) {
3986 numIter++;
3987 cumNumCards += curNumCards;
3988 break;
3989 }
3990 }
3991
3992 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3993
3994 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3995 cumNumCards += curNumCards;
3996 if (PrintGCDetails && PrintCMSStatistics != 0) {
3997 gclog_or_tty->print_cr(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3998 curNumCards, cumNumCards, numIter);
3999 }
4000 return cumNumCards; // as a measure of useful work done
4001 }
4002
4003 // PRECLEANING NOTES:
4004 // Precleaning involves:
4005 // . reading the bits of the modUnionTable and clearing the set bits.
4006 // . For the cards corresponding to the set bits, we scan the
4007 // objects on those cards. This means we need the free_list_lock
4008 // so that we can safely iterate over the CMS space when scanning
4009 // for oops.
4010 // . When we scan the objects, we'll be both reading and setting
4011 // marks in the marking bit map, so we'll need the marking bit map.
4012 // . For protecting _collector_state transitions, we take the CGC_lock.
4013 // Note that any races in the reading of of card table entries by the
4014 // CMS thread on the one hand and the clearing of those entries by the
4015 // VM thread or the setting of those entries by the mutator threads on the
4016 // other are quite benign. However, for efficiency it makes sense to keep
4017 // the VM thread from racing with the CMS thread while the latter is
4018 // dirty card info to the modUnionTable. We therefore also use the
4019 // CGC_lock to protect the reading of the card table and the mod union
4020 // table by the CM thread.
4021 // . We run concurrently with mutator updates, so scanning
4022 // needs to be done carefully -- we should not try to scan
4023 // potentially uninitialized objects.
4024 //
4025 // Locking strategy: While holding the CGC_lock, we scan over and
4026 // reset a maximal dirty range of the mod union / card tables, then lock
4027 // the free_list_lock and bitmap lock to do a full marking, then
4028 // release these locks; and repeat the cycle. This allows for a
4029 // certain amount of fairness in the sharing of these locks between
4030 // the CMS collector on the one hand, and the VM thread and the
4031 // mutators on the other.
4032
4033 // NOTE: preclean_mod_union_table() and preclean_card_table()
4034 // further below are largely identical; if you need to modify
4035 // one of these methods, please check the other method too.
4036
4037 size_t CMSCollector::preclean_mod_union_table(
4038 ConcurrentMarkSweepGeneration* old_gen,
4039 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4040 verify_work_stacks_empty();
4041 verify_overflow_empty();
4042
4043 // strategy: starting with the first card, accumulate contiguous
4044 // ranges of dirty cards; clear these cards, then scan the region
4045 // covered by these cards.
4046
4047 // Since all of the MUT is committed ahead, we can just use
4048 // that, in case the generations expand while we are precleaning.
4049 // It might also be fine to just use the committed part of the
4050 // generation, but we might potentially miss cards when the
4051 // generation is rapidly expanding while we are in the midst
4052 // of precleaning.
4053 HeapWord* startAddr = old_gen->reserved().start();
4054 HeapWord* endAddr = old_gen->reserved().end();
4055
4056 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4057
4058 size_t numDirtyCards, cumNumDirtyCards;
4059 HeapWord *nextAddr, *lastAddr;
4060 for (cumNumDirtyCards = numDirtyCards = 0,
4061 nextAddr = lastAddr = startAddr;
4062 nextAddr < endAddr;
4063 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4064
4065 ResourceMark rm;
4066 HandleMark hm;
4067
4068 MemRegion dirtyRegion;
4069 {
4070 stopTimer();
4071 // Potential yield point
4072 CMSTokenSync ts(true);
4073 startTimer();
4074 sample_eden();
4075 // Get dirty region starting at nextOffset (inclusive),
4076 // simultaneously clearing it.
4077 dirtyRegion =
4078 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4079 assert(dirtyRegion.start() >= nextAddr,
4080 "returned region inconsistent?");
4081 }
4082 // Remember where the next search should begin.
4083 // The returned region (if non-empty) is a right open interval,
4084 // so lastOffset is obtained from the right end of that
4085 // interval.
4086 lastAddr = dirtyRegion.end();
4087 // Should do something more transparent and less hacky XXX
4088 numDirtyCards =
4089 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4090
4091 // We'll scan the cards in the dirty region (with periodic
4092 // yields for foreground GC as needed).
4093 if (!dirtyRegion.is_empty()) {
4094 assert(numDirtyCards > 0, "consistency check");
4095 HeapWord* stop_point = NULL;
4096 stopTimer();
4097 // Potential yield point
4098 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
4099 bitMapLock());
4100 startTimer();
4101 {
4102 verify_work_stacks_empty();
4103 verify_overflow_empty();
4104 sample_eden();
4105 stop_point =
4106 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4107 }
4108 if (stop_point != NULL) {
4109 // The careful iteration stopped early either because it found an
4110 // uninitialized object, or because we were in the midst of an
4111 // "abortable preclean", which should now be aborted. Redirty
4112 // the bits corresponding to the partially-scanned or unscanned
4113 // cards. We'll either restart at the next block boundary or
4114 // abort the preclean.
4115 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4116 "Should only be AbortablePreclean.");
4117 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4118 if (should_abort_preclean()) {
4119 break; // out of preclean loop
4120 } else {
4121 // Compute the next address at which preclean should pick up;
4122 // might need bitMapLock in order to read P-bits.
4123 lastAddr = next_card_start_after_block(stop_point);
4124 }
4125 }
4126 } else {
4127 assert(lastAddr == endAddr, "consistency check");
4128 assert(numDirtyCards == 0, "consistency check");
4129 break;
4130 }
4131 }
4132 verify_work_stacks_empty();
4133 verify_overflow_empty();
4134 return cumNumDirtyCards;
4135 }
4136
4137 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4138 // below are largely identical; if you need to modify
4139 // one of these methods, please check the other method too.
4140
4141 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
4142 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4143 // strategy: it's similar to precleamModUnionTable above, in that
4144 // we accumulate contiguous ranges of dirty cards, mark these cards
4145 // precleaned, then scan the region covered by these cards.
4146 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4147 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4148
4149 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4150
4151 size_t numDirtyCards, cumNumDirtyCards;
4152 HeapWord *lastAddr, *nextAddr;
4153
4154 for (cumNumDirtyCards = numDirtyCards = 0,
4155 nextAddr = lastAddr = startAddr;
4156 nextAddr < endAddr;
4157 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4158
4159 ResourceMark rm;
4160 HandleMark hm;
4161
4162 MemRegion dirtyRegion;
4163 {
4164 // See comments in "Precleaning notes" above on why we
4165 // do this locking. XXX Could the locking overheads be
4166 // too high when dirty cards are sparse? [I don't think so.]
4167 stopTimer();
4168 CMSTokenSync x(true); // is cms thread
4169 startTimer();
4170 sample_eden();
4171 // Get and clear dirty region from card table
4172 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4173 MemRegion(nextAddr, endAddr),
4174 true,
4175 CardTableModRefBS::precleaned_card_val());
4176
4177 assert(dirtyRegion.start() >= nextAddr,
4178 "returned region inconsistent?");
4179 }
4180 lastAddr = dirtyRegion.end();
4181 numDirtyCards =
4182 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4183
4184 if (!dirtyRegion.is_empty()) {
4185 stopTimer();
4186 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4187 startTimer();
4188 sample_eden();
4189 verify_work_stacks_empty();
4190 verify_overflow_empty();
4191 HeapWord* stop_point =
4192 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4193 if (stop_point != NULL) {
4194 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4195 "Should only be AbortablePreclean.");
4196 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4197 if (should_abort_preclean()) {
4198 break; // out of preclean loop
4199 } else {
4200 // Compute the next address at which preclean should pick up.
4201 lastAddr = next_card_start_after_block(stop_point);
4202 }
4203 }
4204 } else {
4205 break;
4206 }
4207 }
4208 verify_work_stacks_empty();
4209 verify_overflow_empty();
4210 return cumNumDirtyCards;
4211 }
4212
4213 class PrecleanKlassClosure : public KlassClosure {
4214 KlassToOopClosure _cm_klass_closure;
4215 public:
4216 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4217 void do_klass(Klass* k) {
4218 if (k->has_accumulated_modified_oops()) {
4219 k->clear_accumulated_modified_oops();
4220
4221 _cm_klass_closure.do_klass(k);
4222 }
4223 }
4224 };
4225
4226 // The freelist lock is needed to prevent asserts, is it really needed?
4227 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4228
4229 cl->set_freelistLock(freelistLock);
4230
4231 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4232
4233 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4234 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4235 PrecleanKlassClosure preclean_klass_closure(cl);
4236 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4237
4238 verify_work_stacks_empty();
4239 verify_overflow_empty();
4240 }
4241
4242 void CMSCollector::checkpointRootsFinal() {
4243 assert(_collectorState == FinalMarking, "incorrect state transition?");
4244 check_correct_thread_executing();
4245 // world is stopped at this checkpoint
4246 assert(SafepointSynchronize::is_at_safepoint(),
4247 "world should be stopped");
4248 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4249
4250 verify_work_stacks_empty();
4251 verify_overflow_empty();
4252
4253 if (PrintGCDetails) {
4254 gclog_or_tty->print("[YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)]",
4255 _young_gen->used() / K,
4256 _young_gen->capacity() / K);
4257 }
4258 {
4259 if (CMSScavengeBeforeRemark) {
4260 GenCollectedHeap* gch = GenCollectedHeap::heap();
4261 // Temporarily set flag to false, GCH->do_collection will
4262 // expect it to be false and set to true
4263 FlagSetting fl(gch->_is_gc_active, false);
4264 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4265 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4266 gch->do_collection(true, // full (i.e. force, see below)
4267 false, // !clear_all_soft_refs
4268 0, // size
4269 false, // is_tlab
4270 GenCollectedHeap::YoungGen // type
4271 );
4272 }
4273 FreelistLocker x(this);
4274 MutexLockerEx y(bitMapLock(),
4275 Mutex::_no_safepoint_check_flag);
4276 checkpointRootsFinalWork();
4277 }
4278 verify_work_stacks_empty();
4279 verify_overflow_empty();
4280 }
4281
4282 void CMSCollector::checkpointRootsFinalWork() {
4283 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4284
4285 assert(haveFreelistLocks(), "must have free list locks");
4286 assert_lock_strong(bitMapLock());
4287
4288 ResourceMark rm;
4289 HandleMark hm;
4290
4291 GenCollectedHeap* gch = GenCollectedHeap::heap();
4292
4293 if (should_unload_classes()) {
4294 CodeCache::gc_prologue();
4295 }
4296 assert(haveFreelistLocks(), "must have free list locks");
4297 assert_lock_strong(bitMapLock());
4298
4299 // We might assume that we need not fill TLAB's when
4300 // CMSScavengeBeforeRemark is set, because we may have just done
4301 // a scavenge which would have filled all TLAB's -- and besides
4302 // Eden would be empty. This however may not always be the case --
4303 // for instance although we asked for a scavenge, it may not have
4304 // happened because of a JNI critical section. We probably need
4305 // a policy for deciding whether we can in that case wait until
4306 // the critical section releases and then do the remark following
4307 // the scavenge, and skip it here. In the absence of that policy,
4308 // or of an indication of whether the scavenge did indeed occur,
4309 // we cannot rely on TLAB's having been filled and must do
4310 // so here just in case a scavenge did not happen.
4311 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4312 // Update the saved marks which may affect the root scans.
4313 gch->save_marks();
4314
4315 if (CMSPrintEdenSurvivorChunks) {
4316 print_eden_and_survivor_chunk_arrays();
4317 }
4318
4319 {
4320 #if defined(COMPILER2) || INCLUDE_JVMCI
4321 DerivedPointerTableDeactivate dpt_deact;
4322 #endif
4323
4324 // Note on the role of the mod union table:
4325 // Since the marker in "markFromRoots" marks concurrently with
4326 // mutators, it is possible for some reachable objects not to have been
4327 // scanned. For instance, an only reference to an object A was
4328 // placed in object B after the marker scanned B. Unless B is rescanned,
4329 // A would be collected. Such updates to references in marked objects
4330 // are detected via the mod union table which is the set of all cards
4331 // dirtied since the first checkpoint in this GC cycle and prior to
4332 // the most recent young generation GC, minus those cleaned up by the
4333 // concurrent precleaning.
4334 if (CMSParallelRemarkEnabled) {
4335 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
4336 do_remark_parallel();
4337 } else {
4338 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, _gc_timer_cm);
4339 do_remark_non_parallel();
4340 }
4341 }
4342 verify_work_stacks_empty();
4343 verify_overflow_empty();
4344
4345 {
4346 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
4347 refProcessingWork();
4348 }
4349 verify_work_stacks_empty();
4350 verify_overflow_empty();
4351
4352 if (should_unload_classes()) {
4353 CodeCache::gc_epilogue();
4354 }
4355 JvmtiExport::gc_epilogue();
4356
4357 // If we encountered any (marking stack / work queue) overflow
4358 // events during the current CMS cycle, take appropriate
4359 // remedial measures, where possible, so as to try and avoid
4360 // recurrence of that condition.
4361 assert(_markStack.isEmpty(), "No grey objects");
4362 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4363 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4364 if (ser_ovflw > 0) {
4365 if (PrintCMSStatistics != 0) {
4366 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4367 "(pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT
4368 ", kac_preclean=" SIZE_FORMAT ")",
4369 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4370 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4371 }
4372 _markStack.expand();
4373 _ser_pmc_remark_ovflw = 0;
4374 _ser_pmc_preclean_ovflw = 0;
4375 _ser_kac_preclean_ovflw = 0;
4376 _ser_kac_ovflw = 0;
4377 }
4378 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4379 if (PrintCMSStatistics != 0) {
4380 gclog_or_tty->print_cr("Work queue overflow (benign) "
4381 "(pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4382 _par_pmc_remark_ovflw, _par_kac_ovflw);
4383 }
4384 _par_pmc_remark_ovflw = 0;
4385 _par_kac_ovflw = 0;
4386 }
4387 if (PrintCMSStatistics != 0) {
4388 if (_markStack._hit_limit > 0) {
4389 gclog_or_tty->print_cr(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4390 _markStack._hit_limit);
4391 }
4392 if (_markStack._failed_double > 0) {
4393 gclog_or_tty->print_cr(" (benign) Failed stack doubling (" SIZE_FORMAT "),"
4394 " current capacity " SIZE_FORMAT,
4395 _markStack._failed_double,
4396 _markStack.capacity());
4397 }
4398 }
4399 _markStack._hit_limit = 0;
4400 _markStack._failed_double = 0;
4401
4402 if ((VerifyAfterGC || VerifyDuringGC) &&
4403 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4404 verify_after_remark();
4405 }
4406
4407 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4408
4409 // Change under the freelistLocks.
4410 _collectorState = Sweeping;
4411 // Call isAllClear() under bitMapLock
4412 assert(_modUnionTable.isAllClear(),
4413 "Should be clear by end of the final marking");
4414 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4415 "Should be clear by end of the final marking");
4416 }
4417
4418 void CMSParInitialMarkTask::work(uint worker_id) {
4419 elapsedTimer _timer;
4420 ResourceMark rm;
4421 HandleMark hm;
4422
4423 // ---------- scan from roots --------------
4424 _timer.start();
4425 GenCollectedHeap* gch = GenCollectedHeap::heap();
4426 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4427
4428 // ---------- young gen roots --------------
4429 {
4430 work_on_young_gen_roots(worker_id, &par_mri_cl);
4431 _timer.stop();
4432 if (PrintCMSStatistics != 0) {
4433 gclog_or_tty->print_cr(
4434 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
4435 worker_id, _timer.seconds());
4436 }
4437 }
4438
4439 // ---------- remaining roots --------------
4440 _timer.reset();
4441 _timer.start();
4442
4443 CLDToOopClosure cld_closure(&par_mri_cl, true);
4444
4445 gch->gen_process_roots(_strong_roots_scope,
4446 GenCollectedHeap::OldGen,
4447 false, // yg was scanned above
4448 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4449 _collector->should_unload_classes(),
4450 &par_mri_cl,
4451 NULL,
4452 &cld_closure);
4453 assert(_collector->should_unload_classes()
4454 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4455 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4456 _timer.stop();
4457 if (PrintCMSStatistics != 0) {
4458 gclog_or_tty->print_cr(
4459 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
4460 worker_id, _timer.seconds());
4461 }
4462 }
4463
4464 // Parallel remark task
4465 class CMSParRemarkTask: public CMSParMarkTask {
4466 CompactibleFreeListSpace* _cms_space;
4467
4468 // The per-thread work queues, available here for stealing.
4469 OopTaskQueueSet* _task_queues;
4470 ParallelTaskTerminator _term;
4471 StrongRootsScope* _strong_roots_scope;
4472
4473 public:
4474 // A value of 0 passed to n_workers will cause the number of
4475 // workers to be taken from the active workers in the work gang.
4476 CMSParRemarkTask(CMSCollector* collector,
4477 CompactibleFreeListSpace* cms_space,
4478 uint n_workers, WorkGang* workers,
4479 OopTaskQueueSet* task_queues,
4480 StrongRootsScope* strong_roots_scope):
4481 CMSParMarkTask("Rescan roots and grey objects in parallel",
4482 collector, n_workers),
4483 _cms_space(cms_space),
4484 _task_queues(task_queues),
4485 _term(n_workers, task_queues),
4486 _strong_roots_scope(strong_roots_scope) { }
4487
4488 OopTaskQueueSet* task_queues() { return _task_queues; }
4489
4490 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4491
4492 ParallelTaskTerminator* terminator() { return &_term; }
4493 uint n_workers() { return _n_workers; }
4494
4495 void work(uint worker_id);
4496
4497 private:
4498 // ... of dirty cards in old space
4499 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4500 Par_MarkRefsIntoAndScanClosure* cl);
4501
4502 // ... work stealing for the above
4503 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4504 };
4505
4506 class RemarkKlassClosure : public KlassClosure {
4507 KlassToOopClosure _cm_klass_closure;
4508 public:
4509 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4510 void do_klass(Klass* k) {
4511 // Check if we have modified any oops in the Klass during the concurrent marking.
4512 if (k->has_accumulated_modified_oops()) {
4513 k->clear_accumulated_modified_oops();
4514
4515 // We could have transfered the current modified marks to the accumulated marks,
4516 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4517 } else if (k->has_modified_oops()) {
4518 // Don't clear anything, this info is needed by the next young collection.
4519 } else {
4520 // No modified oops in the Klass.
4521 return;
4522 }
4523
4524 // The klass has modified fields, need to scan the klass.
4525 _cm_klass_closure.do_klass(k);
4526 }
4527 };
4528
4529 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
4530 ParNewGeneration* young_gen = _collector->_young_gen;
4531 ContiguousSpace* eden_space = young_gen->eden();
4532 ContiguousSpace* from_space = young_gen->from();
4533 ContiguousSpace* to_space = young_gen->to();
4534
4535 HeapWord** eca = _collector->_eden_chunk_array;
4536 size_t ect = _collector->_eden_chunk_index;
4537 HeapWord** sca = _collector->_survivor_chunk_array;
4538 size_t sct = _collector->_survivor_chunk_index;
4539
4540 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4541 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4542
4543 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
4544 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
4545 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
4546 }
4547
4548 // work_queue(i) is passed to the closure
4549 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
4550 // also is passed to do_dirty_card_rescan_tasks() and to
4551 // do_work_steal() to select the i-th task_queue.
4552
4553 void CMSParRemarkTask::work(uint worker_id) {
4554 elapsedTimer _timer;
4555 ResourceMark rm;
4556 HandleMark hm;
4557
4558 // ---------- rescan from roots --------------
4559 _timer.start();
4560 GenCollectedHeap* gch = GenCollectedHeap::heap();
4561 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4562 _collector->_span, _collector->ref_processor(),
4563 &(_collector->_markBitMap),
4564 work_queue(worker_id));
4565
4566 // Rescan young gen roots first since these are likely
4567 // coarsely partitioned and may, on that account, constitute
4568 // the critical path; thus, it's best to start off that
4569 // work first.
4570 // ---------- young gen roots --------------
4571 {
4572 work_on_young_gen_roots(worker_id, &par_mrias_cl);
4573 _timer.stop();
4574 if (PrintCMSStatistics != 0) {
4575 gclog_or_tty->print_cr(
4576 "Finished young gen rescan work in %dth thread: %3.3f sec",
4577 worker_id, _timer.seconds());
4578 }
4579 }
4580
4581 // ---------- remaining roots --------------
4582 _timer.reset();
4583 _timer.start();
4584 gch->gen_process_roots(_strong_roots_scope,
4585 GenCollectedHeap::OldGen,
4586 false, // yg was scanned above
4587 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4588 _collector->should_unload_classes(),
4589 &par_mrias_cl,
4590 NULL,
4591 NULL); // The dirty klasses will be handled below
4592
4593 assert(_collector->should_unload_classes()
4594 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4595 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4596 _timer.stop();
4597 if (PrintCMSStatistics != 0) {
4598 gclog_or_tty->print_cr(
4599 "Finished remaining root rescan work in %dth thread: %3.3f sec",
4600 worker_id, _timer.seconds());
4601 }
4602
4603 // ---------- unhandled CLD scanning ----------
4604 if (worker_id == 0) { // Single threaded at the moment.
4605 _timer.reset();
4606 _timer.start();
4607
4608 // Scan all new class loader data objects and new dependencies that were
4609 // introduced during concurrent marking.
4610 ResourceMark rm;
4611 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4612 for (int i = 0; i < array->length(); i++) {
4613 par_mrias_cl.do_cld_nv(array->at(i));
4614 }
4615
4616 // We don't need to keep track of new CLDs anymore.
4617 ClassLoaderDataGraph::remember_new_clds(false);
4618
4619 _timer.stop();
4620 if (PrintCMSStatistics != 0) {
4621 gclog_or_tty->print_cr(
4622 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
4623 worker_id, _timer.seconds());
4624 }
4625 }
4626
4627 // ---------- dirty klass scanning ----------
4628 if (worker_id == 0) { // Single threaded at the moment.
4629 _timer.reset();
4630 _timer.start();
4631
4632 // Scan all classes that was dirtied during the concurrent marking phase.
4633 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4634 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4635
4636 _timer.stop();
4637 if (PrintCMSStatistics != 0) {
4638 gclog_or_tty->print_cr(
4639 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
4640 worker_id, _timer.seconds());
4641 }
4642 }
4643
4644 // We might have added oops to ClassLoaderData::_handles during the
4645 // concurrent marking phase. These oops point to newly allocated objects
4646 // that are guaranteed to be kept alive. Either by the direct allocation
4647 // code, or when the young collector processes the roots. Hence,
4648 // we don't have to revisit the _handles block during the remark phase.
4649
4650 // ---------- rescan dirty cards ------------
4651 _timer.reset();
4652 _timer.start();
4653
4654 // Do the rescan tasks for each of the two spaces
4655 // (cms_space) in turn.
4656 // "worker_id" is passed to select the task_queue for "worker_id"
4657 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4658 _timer.stop();
4659 if (PrintCMSStatistics != 0) {
4660 gclog_or_tty->print_cr(
4661 "Finished dirty card rescan work in %dth thread: %3.3f sec",
4662 worker_id, _timer.seconds());
4663 }
4664
4665 // ---------- steal work from other threads ...
4666 // ---------- ... and drain overflow list.
4667 _timer.reset();
4668 _timer.start();
4669 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4670 _timer.stop();
4671 if (PrintCMSStatistics != 0) {
4672 gclog_or_tty->print_cr(
4673 "Finished work stealing in %dth thread: %3.3f sec",
4674 worker_id, _timer.seconds());
4675 }
4676 }
4677
4678 // Note that parameter "i" is not used.
4679 void
4680 CMSParMarkTask::do_young_space_rescan(uint worker_id,
4681 OopsInGenClosure* cl, ContiguousSpace* space,
4682 HeapWord** chunk_array, size_t chunk_top) {
4683 // Until all tasks completed:
4684 // . claim an unclaimed task
4685 // . compute region boundaries corresponding to task claimed
4686 // using chunk_array
4687 // . par_oop_iterate(cl) over that region
4688
4689 ResourceMark rm;
4690 HandleMark hm;
4691
4692 SequentialSubTasksDone* pst = space->par_seq_tasks();
4693
4694 uint nth_task = 0;
4695 uint n_tasks = pst->n_tasks();
4696
4697 if (n_tasks > 0) {
4698 assert(pst->valid(), "Uninitialized use?");
4699 HeapWord *start, *end;
4700 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4701 // We claimed task # nth_task; compute its boundaries.
4702 if (chunk_top == 0) { // no samples were taken
4703 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4704 start = space->bottom();
4705 end = space->top();
4706 } else if (nth_task == 0) {
4707 start = space->bottom();
4708 end = chunk_array[nth_task];
4709 } else if (nth_task < (uint)chunk_top) {
4710 assert(nth_task >= 1, "Control point invariant");
4711 start = chunk_array[nth_task - 1];
4712 end = chunk_array[nth_task];
4713 } else {
4714 assert(nth_task == (uint)chunk_top, "Control point invariant");
4715 start = chunk_array[chunk_top - 1];
4716 end = space->top();
4717 }
4718 MemRegion mr(start, end);
4719 // Verify that mr is in space
4720 assert(mr.is_empty() || space->used_region().contains(mr),
4721 "Should be in space");
4722 // Verify that "start" is an object boundary
4723 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4724 "Should be an oop");
4725 space->par_oop_iterate(mr, cl);
4726 }
4727 pst->all_tasks_completed();
4728 }
4729 }
4730
4731 void
4732 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4733 CompactibleFreeListSpace* sp, int i,
4734 Par_MarkRefsIntoAndScanClosure* cl) {
4735 // Until all tasks completed:
4736 // . claim an unclaimed task
4737 // . compute region boundaries corresponding to task claimed
4738 // . transfer dirty bits ct->mut for that region
4739 // . apply rescanclosure to dirty mut bits for that region
4740
4741 ResourceMark rm;
4742 HandleMark hm;
4743
4744 OopTaskQueue* work_q = work_queue(i);
4745 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4746 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4747 // CAUTION: This closure has state that persists across calls to
4748 // the work method dirty_range_iterate_clear() in that it has
4749 // embedded in it a (subtype of) UpwardsObjectClosure. The
4750 // use of that state in the embedded UpwardsObjectClosure instance
4751 // assumes that the cards are always iterated (even if in parallel
4752 // by several threads) in monotonically increasing order per each
4753 // thread. This is true of the implementation below which picks
4754 // card ranges (chunks) in monotonically increasing order globally
4755 // and, a-fortiori, in monotonically increasing order per thread
4756 // (the latter order being a subsequence of the former).
4757 // If the work code below is ever reorganized into a more chaotic
4758 // work-partitioning form than the current "sequential tasks"
4759 // paradigm, the use of that persistent state will have to be
4760 // revisited and modified appropriately. See also related
4761 // bug 4756801 work on which should examine this code to make
4762 // sure that the changes there do not run counter to the
4763 // assumptions made here and necessary for correctness and
4764 // efficiency. Note also that this code might yield inefficient
4765 // behavior in the case of very large objects that span one or
4766 // more work chunks. Such objects would potentially be scanned
4767 // several times redundantly. Work on 4756801 should try and
4768 // address that performance anomaly if at all possible. XXX
4769 MemRegion full_span = _collector->_span;
4770 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4771 MarkFromDirtyCardsClosure
4772 greyRescanClosure(_collector, full_span, // entire span of interest
4773 sp, bm, work_q, cl);
4774
4775 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4776 assert(pst->valid(), "Uninitialized use?");
4777 uint nth_task = 0;
4778 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4779 MemRegion span = sp->used_region();
4780 HeapWord* start_addr = span.start();
4781 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4782 alignment);
4783 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4784 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4785 start_addr, "Check alignment");
4786 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4787 chunk_size, "Check alignment");
4788
4789 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4790 // Having claimed the nth_task, compute corresponding mem-region,
4791 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4792 // The alignment restriction ensures that we do not need any
4793 // synchronization with other gang-workers while setting or
4794 // clearing bits in thus chunk of the MUT.
4795 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4796 start_addr + (nth_task+1)*chunk_size);
4797 // The last chunk's end might be way beyond end of the
4798 // used region. In that case pull back appropriately.
4799 if (this_span.end() > end_addr) {
4800 this_span.set_end(end_addr);
4801 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4802 }
4803 // Iterate over the dirty cards covering this chunk, marking them
4804 // precleaned, and setting the corresponding bits in the mod union
4805 // table. Since we have been careful to partition at Card and MUT-word
4806 // boundaries no synchronization is needed between parallel threads.
4807 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4808 &modUnionClosure);
4809
4810 // Having transferred these marks into the modUnionTable,
4811 // rescan the marked objects on the dirty cards in the modUnionTable.
4812 // Even if this is at a synchronous collection, the initial marking
4813 // may have been done during an asynchronous collection so there
4814 // may be dirty bits in the mod-union table.
4815 _collector->_modUnionTable.dirty_range_iterate_clear(
4816 this_span, &greyRescanClosure);
4817 _collector->_modUnionTable.verifyNoOneBitsInRange(
4818 this_span.start(),
4819 this_span.end());
4820 }
4821 pst->all_tasks_completed(); // declare that i am done
4822 }
4823
4824 // . see if we can share work_queues with ParNew? XXX
4825 void
4826 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
4827 int* seed) {
4828 OopTaskQueue* work_q = work_queue(i);
4829 NOT_PRODUCT(int num_steals = 0;)
4830 oop obj_to_scan;
4831 CMSBitMap* bm = &(_collector->_markBitMap);
4832
4833 while (true) {
4834 // Completely finish any left over work from (an) earlier round(s)
4835 cl->trim_queue(0);
4836 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4837 (size_t)ParGCDesiredObjsFromOverflowList);
4838 // Now check if there's any work in the overflow list
4839 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4840 // only affects the number of attempts made to get work from the
4841 // overflow list and does not affect the number of workers. Just
4842 // pass ParallelGCThreads so this behavior is unchanged.
4843 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4844 work_q,
4845 ParallelGCThreads)) {
4846 // found something in global overflow list;
4847 // not yet ready to go stealing work from others.
4848 // We'd like to assert(work_q->size() != 0, ...)
4849 // because we just took work from the overflow list,
4850 // but of course we can't since all of that could have
4851 // been already stolen from us.
4852 // "He giveth and He taketh away."
4853 continue;
4854 }
4855 // Verify that we have no work before we resort to stealing
4856 assert(work_q->size() == 0, "Have work, shouldn't steal");
4857 // Try to steal from other queues that have work
4858 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4859 NOT_PRODUCT(num_steals++;)
4860 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4861 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4862 // Do scanning work
4863 obj_to_scan->oop_iterate(cl);
4864 // Loop around, finish this work, and try to steal some more
4865 } else if (terminator()->offer_termination()) {
4866 break; // nirvana from the infinite cycle
4867 }
4868 }
4869 NOT_PRODUCT(
4870 if (PrintCMSStatistics != 0) {
4871 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
4872 }
4873 )
4874 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4875 "Else our work is not yet done");
4876 }
4877
4878 // Record object boundaries in _eden_chunk_array by sampling the eden
4879 // top in the slow-path eden object allocation code path and record
4880 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4881 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4882 // sampling in sample_eden() that activates during the part of the
4883 // preclean phase.
4884 void CMSCollector::sample_eden_chunk() {
4885 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4886 if (_eden_chunk_lock->try_lock()) {
4887 // Record a sample. This is the critical section. The contents
4888 // of the _eden_chunk_array have to be non-decreasing in the
4889 // address order.
4890 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4891 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4892 "Unexpected state of Eden");
4893 if (_eden_chunk_index == 0 ||
4894 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4895 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4896 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4897 _eden_chunk_index++; // commit sample
4898 }
4899 _eden_chunk_lock->unlock();
4900 }
4901 }
4902 }
4903
4904 // Return a thread-local PLAB recording array, as appropriate.
4905 void* CMSCollector::get_data_recorder(int thr_num) {
4906 if (_survivor_plab_array != NULL &&
4907 (CMSPLABRecordAlways ||
4908 (_collectorState > Marking && _collectorState < FinalMarking))) {
4909 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4910 ChunkArray* ca = &_survivor_plab_array[thr_num];
4911 ca->reset(); // clear it so that fresh data is recorded
4912 return (void*) ca;
4913 } else {
4914 return NULL;
4915 }
4916 }
4917
4918 // Reset all the thread-local PLAB recording arrays
4919 void CMSCollector::reset_survivor_plab_arrays() {
4920 for (uint i = 0; i < ParallelGCThreads; i++) {
4921 _survivor_plab_array[i].reset();
4922 }
4923 }
4924
4925 // Merge the per-thread plab arrays into the global survivor chunk
4926 // array which will provide the partitioning of the survivor space
4927 // for CMS initial scan and rescan.
4928 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4929 int no_of_gc_threads) {
4930 assert(_survivor_plab_array != NULL, "Error");
4931 assert(_survivor_chunk_array != NULL, "Error");
4932 assert(_collectorState == FinalMarking ||
4933 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4934 for (int j = 0; j < no_of_gc_threads; j++) {
4935 _cursor[j] = 0;
4936 }
4937 HeapWord* top = surv->top();
4938 size_t i;
4939 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4940 HeapWord* min_val = top; // Higher than any PLAB address
4941 uint min_tid = 0; // position of min_val this round
4942 for (int j = 0; j < no_of_gc_threads; j++) {
4943 ChunkArray* cur_sca = &_survivor_plab_array[j];
4944 if (_cursor[j] == cur_sca->end()) {
4945 continue;
4946 }
4947 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4948 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4949 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4950 if (cur_val < min_val) {
4951 min_tid = j;
4952 min_val = cur_val;
4953 } else {
4954 assert(cur_val < top, "All recorded addresses should be less");
4955 }
4956 }
4957 // At this point min_val and min_tid are respectively
4958 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4959 // and the thread (j) that witnesses that address.
4960 // We record this address in the _survivor_chunk_array[i]
4961 // and increment _cursor[min_tid] prior to the next round i.
4962 if (min_val == top) {
4963 break;
4964 }
4965 _survivor_chunk_array[i] = min_val;
4966 _cursor[min_tid]++;
4967 }
4968 // We are all done; record the size of the _survivor_chunk_array
4969 _survivor_chunk_index = i; // exclusive: [0, i)
4970 if (PrintCMSStatistics > 0) {
4971 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4972 }
4973 // Verify that we used up all the recorded entries
4974 #ifdef ASSERT
4975 size_t total = 0;
4976 for (int j = 0; j < no_of_gc_threads; j++) {
4977 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4978 total += _cursor[j];
4979 }
4980 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4981 // Check that the merged array is in sorted order
4982 if (total > 0) {
4983 for (size_t i = 0; i < total - 1; i++) {
4984 if (PrintCMSStatistics > 0) {
4985 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4986 i, p2i(_survivor_chunk_array[i]));
4987 }
4988 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4989 "Not sorted");
4990 }
4991 }
4992 #endif // ASSERT
4993 }
4994
4995 // Set up the space's par_seq_tasks structure for work claiming
4996 // for parallel initial scan and rescan of young gen.
4997 // See ParRescanTask where this is currently used.
4998 void
4999 CMSCollector::
5000 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5001 assert(n_threads > 0, "Unexpected n_threads argument");
5002
5003 // Eden space
5004 if (!_young_gen->eden()->is_empty()) {
5005 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
5006 assert(!pst->valid(), "Clobbering existing data?");
5007 // Each valid entry in [0, _eden_chunk_index) represents a task.
5008 size_t n_tasks = _eden_chunk_index + 1;
5009 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5010 // Sets the condition for completion of the subtask (how many threads
5011 // need to finish in order to be done).
5012 pst->set_n_threads(n_threads);
5013 pst->set_n_tasks((int)n_tasks);
5014 }
5015
5016 // Merge the survivor plab arrays into _survivor_chunk_array
5017 if (_survivor_plab_array != NULL) {
5018 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
5019 } else {
5020 assert(_survivor_chunk_index == 0, "Error");
5021 }
5022
5023 // To space
5024 {
5025 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
5026 assert(!pst->valid(), "Clobbering existing data?");
5027 // Sets the condition for completion of the subtask (how many threads
5028 // need to finish in order to be done).
5029 pst->set_n_threads(n_threads);
5030 pst->set_n_tasks(1);
5031 assert(pst->valid(), "Error");
5032 }
5033
5034 // From space
5035 {
5036 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
5037 assert(!pst->valid(), "Clobbering existing data?");
5038 size_t n_tasks = _survivor_chunk_index + 1;
5039 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5040 // Sets the condition for completion of the subtask (how many threads
5041 // need to finish in order to be done).
5042 pst->set_n_threads(n_threads);
5043 pst->set_n_tasks((int)n_tasks);
5044 assert(pst->valid(), "Error");
5045 }
5046 }
5047
5048 // Parallel version of remark
5049 void CMSCollector::do_remark_parallel() {
5050 GenCollectedHeap* gch = GenCollectedHeap::heap();
5051 WorkGang* workers = gch->workers();
5052 assert(workers != NULL, "Need parallel worker threads.");
5053 // Choose to use the number of GC workers most recently set
5054 // into "active_workers".
5055 uint n_workers = workers->active_workers();
5056
5057 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5058
5059 StrongRootsScope srs(n_workers);
5060
5061 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
5062
5063 // We won't be iterating over the cards in the card table updating
5064 // the younger_gen cards, so we shouldn't call the following else
5065 // the verification code as well as subsequent younger_refs_iterate
5066 // code would get confused. XXX
5067 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5068
5069 // The young gen rescan work will not be done as part of
5070 // process_roots (which currently doesn't know how to
5071 // parallelize such a scan), but rather will be broken up into
5072 // a set of parallel tasks (via the sampling that the [abortable]
5073 // preclean phase did of eden, plus the [two] tasks of
5074 // scanning the [two] survivor spaces. Further fine-grain
5075 // parallelization of the scanning of the survivor spaces
5076 // themselves, and of precleaning of the young gen itself
5077 // is deferred to the future.
5078 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5079
5080 // The dirty card rescan work is broken up into a "sequence"
5081 // of parallel tasks (per constituent space) that are dynamically
5082 // claimed by the parallel threads.
5083 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5084
5085 // It turns out that even when we're using 1 thread, doing the work in a
5086 // separate thread causes wide variance in run times. We can't help this
5087 // in the multi-threaded case, but we special-case n=1 here to get
5088 // repeatable measurements of the 1-thread overhead of the parallel code.
5089 if (n_workers > 1) {
5090 // Make refs discovery MT-safe, if it isn't already: it may not
5091 // necessarily be so, since it's possible that we are doing
5092 // ST marking.
5093 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5094 workers->run_task(&tsk);
5095 } else {
5096 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5097 tsk.work(0);
5098 }
5099
5100 // restore, single-threaded for now, any preserved marks
5101 // as a result of work_q overflow
5102 restore_preserved_marks_if_any();
5103 }
5104
5105 // Non-parallel version of remark
5106 void CMSCollector::do_remark_non_parallel() {
5107 ResourceMark rm;
5108 HandleMark hm;
5109 GenCollectedHeap* gch = GenCollectedHeap::heap();
5110 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5111
5112 MarkRefsIntoAndScanClosure
5113 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5114 &_markStack, this,
5115 false /* should_yield */, false /* not precleaning */);
5116 MarkFromDirtyCardsClosure
5117 markFromDirtyCardsClosure(this, _span,
5118 NULL, // space is set further below
5119 &_markBitMap, &_markStack, &mrias_cl);
5120 {
5121 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5122 // Iterate over the dirty cards, setting the corresponding bits in the
5123 // mod union table.
5124 {
5125 ModUnionClosure modUnionClosure(&_modUnionTable);
5126 _ct->ct_bs()->dirty_card_iterate(
5127 _cmsGen->used_region(),
5128 &modUnionClosure);
5129 }
5130 // Having transferred these marks into the modUnionTable, we just need
5131 // to rescan the marked objects on the dirty cards in the modUnionTable.
5132 // The initial marking may have been done during an asynchronous
5133 // collection so there may be dirty bits in the mod-union table.
5134 const int alignment =
5135 CardTableModRefBS::card_size * BitsPerWord;
5136 {
5137 // ... First handle dirty cards in CMS gen
5138 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5139 MemRegion ur = _cmsGen->used_region();
5140 HeapWord* lb = ur.start();
5141 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5142 MemRegion cms_span(lb, ub);
5143 _modUnionTable.dirty_range_iterate_clear(cms_span,
5144 &markFromDirtyCardsClosure);
5145 verify_work_stacks_empty();
5146 if (PrintCMSStatistics != 0) {
5147 gclog_or_tty->print(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ",
5148 markFromDirtyCardsClosure.num_dirty_cards());
5149 }
5150 }
5151 }
5152 if (VerifyDuringGC &&
5153 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5154 HandleMark hm; // Discard invalid handles created during verification
5155 Universe::verify();
5156 }
5157 {
5158 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5159
5160 verify_work_stacks_empty();
5161
5162 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5163 StrongRootsScope srs(1);
5164
5165 gch->gen_process_roots(&srs,
5166 GenCollectedHeap::OldGen,
5167 true, // young gen as roots
5168 GenCollectedHeap::ScanningOption(roots_scanning_options()),
5169 should_unload_classes(),
5170 &mrias_cl,
5171 NULL,
5172 NULL); // The dirty klasses will be handled below
5173
5174 assert(should_unload_classes()
5175 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
5176 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5177 }
5178
5179 {
5180 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm);
5181
5182 verify_work_stacks_empty();
5183
5184 // Scan all class loader data objects that might have been introduced
5185 // during concurrent marking.
5186 ResourceMark rm;
5187 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5188 for (int i = 0; i < array->length(); i++) {
5189 mrias_cl.do_cld_nv(array->at(i));
5190 }
5191
5192 // We don't need to keep track of new CLDs anymore.
5193 ClassLoaderDataGraph::remember_new_clds(false);
5194
5195 verify_work_stacks_empty();
5196 }
5197
5198 {
5199 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm);
5200
5201 verify_work_stacks_empty();
5202
5203 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5204 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5205
5206 verify_work_stacks_empty();
5207 }
5208
5209 // We might have added oops to ClassLoaderData::_handles during the
5210 // concurrent marking phase. These oops point to newly allocated objects
5211 // that are guaranteed to be kept alive. Either by the direct allocation
5212 // code, or when the young collector processes the roots. Hence,
5213 // we don't have to revisit the _handles block during the remark phase.
5214
5215 verify_work_stacks_empty();
5216 // Restore evacuated mark words, if any, used for overflow list links
5217 if (!CMSOverflowEarlyRestoration) {
5218 restore_preserved_marks_if_any();
5219 }
5220 verify_overflow_empty();
5221 }
5222
5223 ////////////////////////////////////////////////////////
5224 // Parallel Reference Processing Task Proxy Class
5225 ////////////////////////////////////////////////////////
5226 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5227 OopTaskQueueSet* _queues;
5228 ParallelTaskTerminator _terminator;
5229 public:
5230 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5231 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5232 ParallelTaskTerminator* terminator() { return &_terminator; }
5233 OopTaskQueueSet* queues() { return _queues; }
5234 };
5235
5236 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5237 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5238 CMSCollector* _collector;
5239 CMSBitMap* _mark_bit_map;
5240 const MemRegion _span;
5241 ProcessTask& _task;
5242
5243 public:
5244 CMSRefProcTaskProxy(ProcessTask& task,
5245 CMSCollector* collector,
5246 const MemRegion& span,
5247 CMSBitMap* mark_bit_map,
5248 AbstractWorkGang* workers,
5249 OopTaskQueueSet* task_queues):
5250 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5251 task_queues,
5252 workers->active_workers()),
5253 _task(task),
5254 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5255 {
5256 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5257 "Inconsistency in _span");
5258 }
5259
5260 OopTaskQueueSet* task_queues() { return queues(); }
5261
5262 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5263
5264 void do_work_steal(int i,
5265 CMSParDrainMarkingStackClosure* drain,
5266 CMSParKeepAliveClosure* keep_alive,
5267 int* seed);
5268
5269 virtual void work(uint worker_id);
5270 };
5271
5272 void CMSRefProcTaskProxy::work(uint worker_id) {
5273 ResourceMark rm;
5274 HandleMark hm;
5275 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5276 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5277 _mark_bit_map,
5278 work_queue(worker_id));
5279 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5280 _mark_bit_map,
5281 work_queue(worker_id));
5282 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5283 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5284 if (_task.marks_oops_alive()) {
5285 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5286 _collector->hash_seed(worker_id));
5287 }
5288 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5289 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5290 }
5291
5292 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5293 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5294 EnqueueTask& _task;
5295
5296 public:
5297 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5298 : AbstractGangTask("Enqueue reference objects in parallel"),
5299 _task(task)
5300 { }
5301
5302 virtual void work(uint worker_id)
5303 {
5304 _task.work(worker_id);
5305 }
5306 };
5307
5308 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5309 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5310 _span(span),
5311 _bit_map(bit_map),
5312 _work_queue(work_queue),
5313 _mark_and_push(collector, span, bit_map, work_queue),
5314 _low_water_mark(MIN2((work_queue->max_elems()/4),
5315 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5316 { }
5317
5318 // . see if we can share work_queues with ParNew? XXX
5319 void CMSRefProcTaskProxy::do_work_steal(int i,
5320 CMSParDrainMarkingStackClosure* drain,
5321 CMSParKeepAliveClosure* keep_alive,
5322 int* seed) {
5323 OopTaskQueue* work_q = work_queue(i);
5324 NOT_PRODUCT(int num_steals = 0;)
5325 oop obj_to_scan;
5326
5327 while (true) {
5328 // Completely finish any left over work from (an) earlier round(s)
5329 drain->trim_queue(0);
5330 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5331 (size_t)ParGCDesiredObjsFromOverflowList);
5332 // Now check if there's any work in the overflow list
5333 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5334 // only affects the number of attempts made to get work from the
5335 // overflow list and does not affect the number of workers. Just
5336 // pass ParallelGCThreads so this behavior is unchanged.
5337 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5338 work_q,
5339 ParallelGCThreads)) {
5340 // Found something in global overflow list;
5341 // not yet ready to go stealing work from others.
5342 // We'd like to assert(work_q->size() != 0, ...)
5343 // because we just took work from the overflow list,
5344 // but of course we can't, since all of that might have
5345 // been already stolen from us.
5346 continue;
5347 }
5348 // Verify that we have no work before we resort to stealing
5349 assert(work_q->size() == 0, "Have work, shouldn't steal");
5350 // Try to steal from other queues that have work
5351 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5352 NOT_PRODUCT(num_steals++;)
5353 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5354 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5355 // Do scanning work
5356 obj_to_scan->oop_iterate(keep_alive);
5357 // Loop around, finish this work, and try to steal some more
5358 } else if (terminator()->offer_termination()) {
5359 break; // nirvana from the infinite cycle
5360 }
5361 }
5362 NOT_PRODUCT(
5363 if (PrintCMSStatistics != 0) {
5364 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5365 }
5366 )
5367 }
5368
5369 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5370 {
5371 GenCollectedHeap* gch = GenCollectedHeap::heap();
5372 WorkGang* workers = gch->workers();
5373 assert(workers != NULL, "Need parallel worker threads.");
5374 CMSRefProcTaskProxy rp_task(task, &_collector,
5375 _collector.ref_processor()->span(),
5376 _collector.markBitMap(),
5377 workers, _collector.task_queues());
5378 workers->run_task(&rp_task);
5379 }
5380
5381 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5382 {
5383
5384 GenCollectedHeap* gch = GenCollectedHeap::heap();
5385 WorkGang* workers = gch->workers();
5386 assert(workers != NULL, "Need parallel worker threads.");
5387 CMSRefEnqueueTaskProxy enq_task(task);
5388 workers->run_task(&enq_task);
5389 }
5390
5391 void CMSCollector::refProcessingWork() {
5392 ResourceMark rm;
5393 HandleMark hm;
5394
5395 ReferenceProcessor* rp = ref_processor();
5396 assert(rp->span().equals(_span), "Spans should be equal");
5397 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5398 // Process weak references.
5399 rp->setup_policy(false);
5400 verify_work_stacks_empty();
5401
5402 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5403 &_markStack, false /* !preclean */);
5404 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5405 _span, &_markBitMap, &_markStack,
5406 &cmsKeepAliveClosure, false /* !preclean */);
5407 {
5408 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5409
5410 ReferenceProcessorStats stats;
5411 if (rp->processing_is_mt()) {
5412 // Set the degree of MT here. If the discovery is done MT, there
5413 // may have been a different number of threads doing the discovery
5414 // and a different number of discovered lists may have Ref objects.
5415 // That is OK as long as the Reference lists are balanced (see
5416 // balance_all_queues() and balance_queues()).
5417 GenCollectedHeap* gch = GenCollectedHeap::heap();
5418 uint active_workers = ParallelGCThreads;
5419 WorkGang* workers = gch->workers();
5420 if (workers != NULL) {
5421 active_workers = workers->active_workers();
5422 // The expectation is that active_workers will have already
5423 // been set to a reasonable value. If it has not been set,
5424 // investigate.
5425 assert(active_workers > 0, "Should have been set during scavenge");
5426 }
5427 rp->set_active_mt_degree(active_workers);
5428 CMSRefProcTaskExecutor task_executor(*this);
5429 stats = rp->process_discovered_references(&_is_alive_closure,
5430 &cmsKeepAliveClosure,
5431 &cmsDrainMarkingStackClosure,
5432 &task_executor,
5433 _gc_timer_cm);
5434 } else {
5435 stats = rp->process_discovered_references(&_is_alive_closure,
5436 &cmsKeepAliveClosure,
5437 &cmsDrainMarkingStackClosure,
5438 NULL,
5439 _gc_timer_cm);
5440 }
5441 _gc_tracer_cm->report_gc_reference_stats(stats);
5442
5443 }
5444
5445 // This is the point where the entire marking should have completed.
5446 verify_work_stacks_empty();
5447
5448 if (should_unload_classes()) {
5449 {
5450 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5451
5452 // Unload classes and purge the SystemDictionary.
5453 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5454
5455 // Unload nmethods.
5456 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5457
5458 // Prune dead klasses from subklass/sibling/implementor lists.
5459 Klass::clean_weak_klass_links(&_is_alive_closure);
5460 }
5461
5462 {
5463 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
5464 // Clean up unreferenced symbols in symbol table.
5465 SymbolTable::unlink();
5466 }
5467
5468 {
5469 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
5470 // Delete entries for dead interned strings.
5471 StringTable::unlink(&_is_alive_closure);
5472 }
5473 }
5474
5475
5476 // Restore any preserved marks as a result of mark stack or
5477 // work queue overflow
5478 restore_preserved_marks_if_any(); // done single-threaded for now
5479
5480 rp->set_enqueuing_is_done(true);
5481 if (rp->processing_is_mt()) {
5482 rp->balance_all_queues();
5483 CMSRefProcTaskExecutor task_executor(*this);
5484 rp->enqueue_discovered_references(&task_executor);
5485 } else {
5486 rp->enqueue_discovered_references(NULL);
5487 }
5488 rp->verify_no_references_recorded();
5489 assert(!rp->discovery_enabled(), "should have been disabled");
5490 }
5491
5492 #ifndef PRODUCT
5493 void CMSCollector::check_correct_thread_executing() {
5494 Thread* t = Thread::current();
5495 // Only the VM thread or the CMS thread should be here.
5496 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5497 "Unexpected thread type");
5498 // If this is the vm thread, the foreground process
5499 // should not be waiting. Note that _foregroundGCIsActive is
5500 // true while the foreground collector is waiting.
5501 if (_foregroundGCShouldWait) {
5502 // We cannot be the VM thread
5503 assert(t->is_ConcurrentGC_thread(),
5504 "Should be CMS thread");
5505 } else {
5506 // We can be the CMS thread only if we are in a stop-world
5507 // phase of CMS collection.
5508 if (t->is_ConcurrentGC_thread()) {
5509 assert(_collectorState == InitialMarking ||
5510 _collectorState == FinalMarking,
5511 "Should be a stop-world phase");
5512 // The CMS thread should be holding the CMS_token.
5513 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5514 "Potential interference with concurrently "
5515 "executing VM thread");
5516 }
5517 }
5518 }
5519 #endif
5520
5521 void CMSCollector::sweep() {
5522 assert(_collectorState == Sweeping, "just checking");
5523 check_correct_thread_executing();
5524 verify_work_stacks_empty();
5525 verify_overflow_empty();
5526 increment_sweep_count();
5527 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5528
5529 _inter_sweep_timer.stop();
5530 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5531
5532 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5533 _intra_sweep_timer.reset();
5534 _intra_sweep_timer.start();
5535 {
5536 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5537 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5538 // First sweep the old gen
5539 {
5540 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5541 bitMapLock());
5542 sweepWork(_cmsGen);
5543 }
5544
5545 // Update Universe::_heap_*_at_gc figures.
5546 // We need all the free list locks to make the abstract state
5547 // transition from Sweeping to Resetting. See detailed note
5548 // further below.
5549 {
5550 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5551 // Update heap occupancy information which is used as
5552 // input to soft ref clearing policy at the next gc.
5553 Universe::update_heap_info_at_gc();
5554 _collectorState = Resizing;
5555 }
5556 }
5557 verify_work_stacks_empty();
5558 verify_overflow_empty();
5559
5560 if (should_unload_classes()) {
5561 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5562 // requires that the virtual spaces are stable and not deleted.
5563 ClassLoaderDataGraph::set_should_purge(true);
5564 }
5565
5566 _intra_sweep_timer.stop();
5567 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5568
5569 _inter_sweep_timer.reset();
5570 _inter_sweep_timer.start();
5571
5572 // We need to use a monotonically non-decreasing time in ms
5573 // or we will see time-warp warnings and os::javaTimeMillis()
5574 // does not guarantee monotonicity.
5575 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5576 update_time_of_last_gc(now);
5577
5578 // NOTE on abstract state transitions:
5579 // Mutators allocate-live and/or mark the mod-union table dirty
5580 // based on the state of the collection. The former is done in
5581 // the interval [Marking, Sweeping] and the latter in the interval
5582 // [Marking, Sweeping). Thus the transitions into the Marking state
5583 // and out of the Sweeping state must be synchronously visible
5584 // globally to the mutators.
5585 // The transition into the Marking state happens with the world
5586 // stopped so the mutators will globally see it. Sweeping is
5587 // done asynchronously by the background collector so the transition
5588 // from the Sweeping state to the Resizing state must be done
5589 // under the freelistLock (as is the check for whether to
5590 // allocate-live and whether to dirty the mod-union table).
5591 assert(_collectorState == Resizing, "Change of collector state to"
5592 " Resizing must be done under the freelistLocks (plural)");
5593
5594 // Now that sweeping has been completed, we clear
5595 // the incremental_collection_failed flag,
5596 // thus inviting a younger gen collection to promote into
5597 // this generation. If such a promotion may still fail,
5598 // the flag will be set again when a young collection is
5599 // attempted.
5600 GenCollectedHeap* gch = GenCollectedHeap::heap();
5601 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5602 gch->update_full_collections_completed(_collection_count_start);
5603 }
5604
5605 // FIX ME!!! Looks like this belongs in CFLSpace, with
5606 // CMSGen merely delegating to it.
5607 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5608 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5609 HeapWord* minAddr = _cmsSpace->bottom();
5610 HeapWord* largestAddr =
5611 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5612 if (largestAddr == NULL) {
5613 // The dictionary appears to be empty. In this case
5614 // try to coalesce at the end of the heap.
5615 largestAddr = _cmsSpace->end();
5616 }
5617 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5618 size_t nearLargestOffset =
5619 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5620 if (PrintFLSStatistics != 0) {
5621 gclog_or_tty->print_cr(
5622 "CMS: Large Block: " PTR_FORMAT ";"
5623 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5624 p2i(largestAddr),
5625 p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5626 }
5627 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5628 }
5629
5630 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5631 return addr >= _cmsSpace->nearLargestChunk();
5632 }
5633
5634 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5635 return _cmsSpace->find_chunk_at_end();
5636 }
5637
5638 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5639 bool full) {
5640 // If the young generation has been collected, gather any statistics
5641 // that are of interest at this point.
5642 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5643 if (!full && current_is_young) {
5644 // Gather statistics on the young generation collection.
5645 collector()->stats().record_gc0_end(used());
5646 }
5647 }
5648
5649 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5650 // We iterate over the space(s) underlying this generation,
5651 // checking the mark bit map to see if the bits corresponding
5652 // to specific blocks are marked or not. Blocks that are
5653 // marked are live and are not swept up. All remaining blocks
5654 // are swept up, with coalescing on-the-fly as we sweep up
5655 // contiguous free and/or garbage blocks:
5656 // We need to ensure that the sweeper synchronizes with allocators
5657 // and stop-the-world collectors. In particular, the following
5658 // locks are used:
5659 // . CMS token: if this is held, a stop the world collection cannot occur
5660 // . freelistLock: if this is held no allocation can occur from this
5661 // generation by another thread
5662 // . bitMapLock: if this is held, no other thread can access or update
5663 //
5664
5665 // Note that we need to hold the freelistLock if we use
5666 // block iterate below; else the iterator might go awry if
5667 // a mutator (or promotion) causes block contents to change
5668 // (for instance if the allocator divvies up a block).
5669 // If we hold the free list lock, for all practical purposes
5670 // young generation GC's can't occur (they'll usually need to
5671 // promote), so we might as well prevent all young generation
5672 // GC's while we do a sweeping step. For the same reason, we might
5673 // as well take the bit map lock for the entire duration
5674
5675 // check that we hold the requisite locks
5676 assert(have_cms_token(), "Should hold cms token");
5677 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5678 assert_lock_strong(old_gen->freelistLock());
5679 assert_lock_strong(bitMapLock());
5680
5681 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5682 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5683 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5684 _inter_sweep_estimate.padded_average(),
5685 _intra_sweep_estimate.padded_average());
5686 old_gen->setNearLargestChunk();
5687
5688 {
5689 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5690 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5691 // We need to free-up/coalesce garbage/blocks from a
5692 // co-terminal free run. This is done in the SweepClosure
5693 // destructor; so, do not remove this scope, else the
5694 // end-of-sweep-census below will be off by a little bit.
5695 }
5696 old_gen->cmsSpace()->sweep_completed();
5697 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5698 if (should_unload_classes()) { // unloaded classes this cycle,
5699 _concurrent_cycles_since_last_unload = 0; // ... reset count
5700 } else { // did not unload classes,
5701 _concurrent_cycles_since_last_unload++; // ... increment count
5702 }
5703 }
5704
5705 // Reset CMS data structures (for now just the marking bit map)
5706 // preparatory for the next cycle.
5707 void CMSCollector::reset_concurrent() {
5708 CMSTokenSyncWithLocks ts(true, bitMapLock());
5709
5710 // If the state is not "Resetting", the foreground thread
5711 // has done a collection and the resetting.
5712 if (_collectorState != Resetting) {
5713 assert(_collectorState == Idling, "The state should only change"
5714 " because the foreground collector has finished the collection");
5715 return;
5716 }
5717
5718 // Clear the mark bitmap (no grey objects to start with)
5719 // for the next cycle.
5720 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5721 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
5722
5723 HeapWord* curAddr = _markBitMap.startWord();
5724 while (curAddr < _markBitMap.endWord()) {
5725 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5726 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5727 _markBitMap.clear_large_range(chunk);
5728 if (ConcurrentMarkSweepThread::should_yield() &&
5729 !foregroundGCIsActive() &&
5730 CMSYield) {
5731 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5732 "CMS thread should hold CMS token");
5733 assert_lock_strong(bitMapLock());
5734 bitMapLock()->unlock();
5735 ConcurrentMarkSweepThread::desynchronize(true);
5736 stopTimer();
5737 if (PrintCMSStatistics != 0) {
5738 incrementYields();
5739 }
5740
5741 // See the comment in coordinator_yield()
5742 for (unsigned i = 0; i < CMSYieldSleepCount &&
5743 ConcurrentMarkSweepThread::should_yield() &&
5744 !CMSCollector::foregroundGCIsActive(); ++i) {
5745 os::sleep(Thread::current(), 1, false);
5746 }
5747
5748 ConcurrentMarkSweepThread::synchronize(true);
5749 bitMapLock()->lock_without_safepoint_check();
5750 startTimer();
5751 }
5752 curAddr = chunk.end();
5753 }
5754 // A successful mostly concurrent collection has been done.
5755 // Because only the full (i.e., concurrent mode failure) collections
5756 // are being measured for gc overhead limits, clean the "near" flag
5757 // and count.
5758 size_policy()->reset_gc_overhead_limit_count();
5759 _collectorState = Idling;
5760
5761 register_gc_end();
5762 }
5763
5764 // Same as above but for STW paths
5765 void CMSCollector::reset_stw() {
5766 // already have the lock
5767 assert(_collectorState == Resetting, "just checking");
5768 assert_lock_strong(bitMapLock());
5769 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5770 _markBitMap.clear_all();
5771 _collectorState = Idling;
5772 register_gc_end();
5773 }
5774
5775 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5776 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5777 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
5778 TraceCollectorStats tcs(counters());
5779
5780 switch (op) {
5781 case CMS_op_checkpointRootsInitial: {
5782 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5783 checkpointRootsInitial();
5784 if (PrintGC) {
5785 _cmsGen->printOccupancy("initial-mark");
5786 }
5787 break;
5788 }
5789 case CMS_op_checkpointRootsFinal: {
5790 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5791 checkpointRootsFinal();
5792 if (PrintGC) {
5793 _cmsGen->printOccupancy("remark");
5794 }
5795 break;
5796 }
5797 default:
5798 fatal("No such CMS_op");
5799 }
5800 }
5801
5802 #ifndef PRODUCT
5803 size_t const CMSCollector::skip_header_HeapWords() {
5804 return FreeChunk::header_size();
5805 }
5806
5807 // Try and collect here conditions that should hold when
5808 // CMS thread is exiting. The idea is that the foreground GC
5809 // thread should not be blocked if it wants to terminate
5810 // the CMS thread and yet continue to run the VM for a while
5811 // after that.
5812 void CMSCollector::verify_ok_to_terminate() const {
5813 assert(Thread::current()->is_ConcurrentGC_thread(),
5814 "should be called by CMS thread");
5815 assert(!_foregroundGCShouldWait, "should be false");
5816 // We could check here that all the various low-level locks
5817 // are not held by the CMS thread, but that is overkill; see
5818 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5819 // is checked.
5820 }
5821 #endif
5822
5823 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5824 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5825 "missing Printezis mark?");
5826 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5827 size_t size = pointer_delta(nextOneAddr + 1, addr);
5828 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5829 "alignment problem");
5830 assert(size >= 3, "Necessary for Printezis marks to work");
5831 return size;
5832 }
5833
5834 // A variant of the above (block_size_using_printezis_bits()) except
5835 // that we return 0 if the P-bits are not yet set.
5836 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5837 if (_markBitMap.isMarked(addr + 1)) {
5838 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5839 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5840 size_t size = pointer_delta(nextOneAddr + 1, addr);
5841 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5842 "alignment problem");
5843 assert(size >= 3, "Necessary for Printezis marks to work");
5844 return size;
5845 }
5846 return 0;
5847 }
5848
5849 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5850 size_t sz = 0;
5851 oop p = (oop)addr;
5852 if (p->klass_or_null() != NULL) {
5853 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5854 } else {
5855 sz = block_size_using_printezis_bits(addr);
5856 }
5857 assert(sz > 0, "size must be nonzero");
5858 HeapWord* next_block = addr + sz;
5859 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5860 CardTableModRefBS::card_size);
5861 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5862 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5863 "must be different cards");
5864 return next_card;
5865 }
5866
5867
5868 // CMS Bit Map Wrapper /////////////////////////////////////////
5869
5870 // Construct a CMS bit map infrastructure, but don't create the
5871 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5872 // further below.
5873 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5874 _bm(),
5875 _shifter(shifter),
5876 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5877 Monitor::_safepoint_check_sometimes) : NULL)
5878 {
5879 _bmStartWord = 0;
5880 _bmWordSize = 0;
5881 }
5882
5883 bool CMSBitMap::allocate(MemRegion mr) {
5884 _bmStartWord = mr.start();
5885 _bmWordSize = mr.word_size();
5886 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5887 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5888 if (!brs.is_reserved()) {
5889 warning("CMS bit map allocation failure");
5890 return false;
5891 }
5892 // For now we'll just commit all of the bit map up front.
5893 // Later on we'll try to be more parsimonious with swap.
5894 if (!_virtual_space.initialize(brs, brs.size())) {
5895 warning("CMS bit map backing store failure");
5896 return false;
5897 }
5898 assert(_virtual_space.committed_size() == brs.size(),
5899 "didn't reserve backing store for all of CMS bit map?");
5900 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5901 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5902 _bmWordSize, "inconsistency in bit map sizing");
5903 _bm.set_size(_bmWordSize >> _shifter);
5904
5905 // bm.clear(); // can we rely on getting zero'd memory? verify below
5906 assert(isAllClear(),
5907 "Expected zero'd memory from ReservedSpace constructor");
5908 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5909 "consistency check");
5910 return true;
5911 }
5912
5913 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5914 HeapWord *next_addr, *end_addr, *last_addr;
5915 assert_locked();
5916 assert(covers(mr), "out-of-range error");
5917 // XXX assert that start and end are appropriately aligned
5918 for (next_addr = mr.start(), end_addr = mr.end();
5919 next_addr < end_addr; next_addr = last_addr) {
5920 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5921 last_addr = dirty_region.end();
5922 if (!dirty_region.is_empty()) {
5923 cl->do_MemRegion(dirty_region);
5924 } else {
5925 assert(last_addr == end_addr, "program logic");
5926 return;
5927 }
5928 }
5929 }
5930
5931 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5932 _bm.print_on_error(st, prefix);
5933 }
5934
5935 #ifndef PRODUCT
5936 void CMSBitMap::assert_locked() const {
5937 CMSLockVerifier::assert_locked(lock());
5938 }
5939
5940 bool CMSBitMap::covers(MemRegion mr) const {
5941 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5942 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5943 "size inconsistency");
5944 return (mr.start() >= _bmStartWord) &&
5945 (mr.end() <= endWord());
5946 }
5947
5948 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5949 return (start >= _bmStartWord && (start + size) <= endWord());
5950 }
5951
5952 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5953 // verify that there are no 1 bits in the interval [left, right)
5954 FalseBitMapClosure falseBitMapClosure;
5955 iterate(&falseBitMapClosure, left, right);
5956 }
5957
5958 void CMSBitMap::region_invariant(MemRegion mr)
5959 {
5960 assert_locked();
5961 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5962 assert(!mr.is_empty(), "unexpected empty region");
5963 assert(covers(mr), "mr should be covered by bit map");
5964 // convert address range into offset range
5965 size_t start_ofs = heapWordToOffset(mr.start());
5966 // Make sure that end() is appropriately aligned
5967 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5968 (1 << (_shifter+LogHeapWordSize))),
5969 "Misaligned mr.end()");
5970 size_t end_ofs = heapWordToOffset(mr.end());
5971 assert(end_ofs > start_ofs, "Should mark at least one bit");
5972 }
5973
5974 #endif
5975
5976 bool CMSMarkStack::allocate(size_t size) {
5977 // allocate a stack of the requisite depth
5978 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5979 size * sizeof(oop)));
5980 if (!rs.is_reserved()) {
5981 warning("CMSMarkStack allocation failure");
5982 return false;
5983 }
5984 if (!_virtual_space.initialize(rs, rs.size())) {
5985 warning("CMSMarkStack backing store failure");
5986 return false;
5987 }
5988 assert(_virtual_space.committed_size() == rs.size(),
5989 "didn't reserve backing store for all of CMS stack?");
5990 _base = (oop*)(_virtual_space.low());
5991 _index = 0;
5992 _capacity = size;
5993 NOT_PRODUCT(_max_depth = 0);
5994 return true;
5995 }
5996
5997 // XXX FIX ME !!! In the MT case we come in here holding a
5998 // leaf lock. For printing we need to take a further lock
5999 // which has lower rank. We need to recalibrate the two
6000 // lock-ranks involved in order to be able to print the
6001 // messages below. (Or defer the printing to the caller.
6002 // For now we take the expedient path of just disabling the
6003 // messages for the problematic case.)
6004 void CMSMarkStack::expand() {
6005 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6006 if (_capacity == MarkStackSizeMax) {
6007 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6008 // We print a warning message only once per CMS cycle.
6009 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6010 }
6011 return;
6012 }
6013 // Double capacity if possible
6014 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6015 // Do not give up existing stack until we have managed to
6016 // get the double capacity that we desired.
6017 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6018 new_capacity * sizeof(oop)));
6019 if (rs.is_reserved()) {
6020 // Release the backing store associated with old stack
6021 _virtual_space.release();
6022 // Reinitialize virtual space for new stack
6023 if (!_virtual_space.initialize(rs, rs.size())) {
6024 fatal("Not enough swap for expanded marking stack");
6025 }
6026 _base = (oop*)(_virtual_space.low());
6027 _index = 0;
6028 _capacity = new_capacity;
6029 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6030 // Failed to double capacity, continue;
6031 // we print a detail message only once per CMS cycle.
6032 gclog_or_tty->print(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to "
6033 SIZE_FORMAT "K",
6034 _capacity / K, new_capacity / K);
6035 }
6036 }
6037
6038
6039 // Closures
6040 // XXX: there seems to be a lot of code duplication here;
6041 // should refactor and consolidate common code.
6042
6043 // This closure is used to mark refs into the CMS generation in
6044 // the CMS bit map. Called at the first checkpoint. This closure
6045 // assumes that we do not need to re-mark dirty cards; if the CMS
6046 // generation on which this is used is not an oldest
6047 // generation then this will lose younger_gen cards!
6048
6049 MarkRefsIntoClosure::MarkRefsIntoClosure(
6050 MemRegion span, CMSBitMap* bitMap):
6051 _span(span),
6052 _bitMap(bitMap)
6053 {
6054 assert(ref_processor() == NULL, "deliberately left NULL");
6055 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6056 }
6057
6058 void MarkRefsIntoClosure::do_oop(oop obj) {
6059 // if p points into _span, then mark corresponding bit in _markBitMap
6060 assert(obj->is_oop(), "expected an oop");
6061 HeapWord* addr = (HeapWord*)obj;
6062 if (_span.contains(addr)) {
6063 // this should be made more efficient
6064 _bitMap->mark(addr);
6065 }
6066 }
6067
6068 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6069 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6070
6071 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6072 MemRegion span, CMSBitMap* bitMap):
6073 _span(span),
6074 _bitMap(bitMap)
6075 {
6076 assert(ref_processor() == NULL, "deliberately left NULL");
6077 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6078 }
6079
6080 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6081 // if p points into _span, then mark corresponding bit in _markBitMap
6082 assert(obj->is_oop(), "expected an oop");
6083 HeapWord* addr = (HeapWord*)obj;
6084 if (_span.contains(addr)) {
6085 // this should be made more efficient
6086 _bitMap->par_mark(addr);
6087 }
6088 }
6089
6090 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6091 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6092
6093 // A variant of the above, used for CMS marking verification.
6094 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6095 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6096 _span(span),
6097 _verification_bm(verification_bm),
6098 _cms_bm(cms_bm)
6099 {
6100 assert(ref_processor() == NULL, "deliberately left NULL");
6101 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6102 }
6103
6104 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6105 // if p points into _span, then mark corresponding bit in _markBitMap
6106 assert(obj->is_oop(), "expected an oop");
6107 HeapWord* addr = (HeapWord*)obj;
6108 if (_span.contains(addr)) {
6109 _verification_bm->mark(addr);
6110 if (!_cms_bm->isMarked(addr)) {
6111 oop(addr)->print();
6112 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6113 fatal("... aborting");
6114 }
6115 }
6116 }
6117
6118 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6119 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6120
6121 //////////////////////////////////////////////////
6122 // MarkRefsIntoAndScanClosure
6123 //////////////////////////////////////////////////
6124
6125 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6126 ReferenceProcessor* rp,
6127 CMSBitMap* bit_map,
6128 CMSBitMap* mod_union_table,
6129 CMSMarkStack* mark_stack,
6130 CMSCollector* collector,
6131 bool should_yield,
6132 bool concurrent_precleaning):
6133 _collector(collector),
6134 _span(span),
6135 _bit_map(bit_map),
6136 _mark_stack(mark_stack),
6137 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6138 mark_stack, concurrent_precleaning),
6139 _yield(should_yield),
6140 _concurrent_precleaning(concurrent_precleaning),
6141 _freelistLock(NULL)
6142 {
6143 // FIXME: Should initialize in base class constructor.
6144 assert(rp != NULL, "ref_processor shouldn't be NULL");
6145 set_ref_processor_internal(rp);
6146 }
6147
6148 // This closure is used to mark refs into the CMS generation at the
6149 // second (final) checkpoint, and to scan and transitively follow
6150 // the unmarked oops. It is also used during the concurrent precleaning
6151 // phase while scanning objects on dirty cards in the CMS generation.
6152 // The marks are made in the marking bit map and the marking stack is
6153 // used for keeping the (newly) grey objects during the scan.
6154 // The parallel version (Par_...) appears further below.
6155 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6156 if (obj != NULL) {
6157 assert(obj->is_oop(), "expected an oop");
6158 HeapWord* addr = (HeapWord*)obj;
6159 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6160 assert(_collector->overflow_list_is_empty(),
6161 "overflow list should be empty");
6162 if (_span.contains(addr) &&
6163 !_bit_map->isMarked(addr)) {
6164 // mark bit map (object is now grey)
6165 _bit_map->mark(addr);
6166 // push on marking stack (stack should be empty), and drain the
6167 // stack by applying this closure to the oops in the oops popped
6168 // from the stack (i.e. blacken the grey objects)
6169 bool res = _mark_stack->push(obj);
6170 assert(res, "Should have space to push on empty stack");
6171 do {
6172 oop new_oop = _mark_stack->pop();
6173 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6174 assert(_bit_map->isMarked((HeapWord*)new_oop),
6175 "only grey objects on this stack");
6176 // iterate over the oops in this oop, marking and pushing
6177 // the ones in CMS heap (i.e. in _span).
6178 new_oop->oop_iterate(&_pushAndMarkClosure);
6179 // check if it's time to yield
6180 do_yield_check();
6181 } while (!_mark_stack->isEmpty() ||
6182 (!_concurrent_precleaning && take_from_overflow_list()));
6183 // if marking stack is empty, and we are not doing this
6184 // during precleaning, then check the overflow list
6185 }
6186 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6187 assert(_collector->overflow_list_is_empty(),
6188 "overflow list was drained above");
6189 // We could restore evacuated mark words, if any, used for
6190 // overflow list links here because the overflow list is
6191 // provably empty here. That would reduce the maximum
6192 // size requirements for preserved_{oop,mark}_stack.
6193 // But we'll just postpone it until we are all done
6194 // so we can just stream through.
6195 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6196 _collector->restore_preserved_marks_if_any();
6197 assert(_collector->no_preserved_marks(), "No preserved marks");
6198 }
6199 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6200 "All preserved marks should have been restored above");
6201 }
6202 }
6203
6204 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6205 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6206
6207 void MarkRefsIntoAndScanClosure::do_yield_work() {
6208 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6209 "CMS thread should hold CMS token");
6210 assert_lock_strong(_freelistLock);
6211 assert_lock_strong(_bit_map->lock());
6212 // relinquish the free_list_lock and bitMaplock()
6213 _bit_map->lock()->unlock();
6214 _freelistLock->unlock();
6215 ConcurrentMarkSweepThread::desynchronize(true);
6216 _collector->stopTimer();
6217 if (PrintCMSStatistics != 0) {
6218 _collector->incrementYields();
6219 }
6220
6221 // See the comment in coordinator_yield()
6222 for (unsigned i = 0;
6223 i < CMSYieldSleepCount &&
6224 ConcurrentMarkSweepThread::should_yield() &&
6225 !CMSCollector::foregroundGCIsActive();
6226 ++i) {
6227 os::sleep(Thread::current(), 1, false);
6228 }
6229
6230 ConcurrentMarkSweepThread::synchronize(true);
6231 _freelistLock->lock_without_safepoint_check();
6232 _bit_map->lock()->lock_without_safepoint_check();
6233 _collector->startTimer();
6234 }
6235
6236 ///////////////////////////////////////////////////////////
6237 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6238 // MarkRefsIntoAndScanClosure
6239 ///////////////////////////////////////////////////////////
6240 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6241 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6242 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6243 _span(span),
6244 _bit_map(bit_map),
6245 _work_queue(work_queue),
6246 _low_water_mark(MIN2((work_queue->max_elems()/4),
6247 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6248 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6249 {
6250 // FIXME: Should initialize in base class constructor.
6251 assert(rp != NULL, "ref_processor shouldn't be NULL");
6252 set_ref_processor_internal(rp);
6253 }
6254
6255 // This closure is used to mark refs into the CMS generation at the
6256 // second (final) checkpoint, and to scan and transitively follow
6257 // the unmarked oops. The marks are made in the marking bit map and
6258 // the work_queue is used for keeping the (newly) grey objects during
6259 // the scan phase whence they are also available for stealing by parallel
6260 // threads. Since the marking bit map is shared, updates are
6261 // synchronized (via CAS).
6262 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6263 if (obj != NULL) {
6264 // Ignore mark word because this could be an already marked oop
6265 // that may be chained at the end of the overflow list.
6266 assert(obj->is_oop(true), "expected an oop");
6267 HeapWord* addr = (HeapWord*)obj;
6268 if (_span.contains(addr) &&
6269 !_bit_map->isMarked(addr)) {
6270 // mark bit map (object will become grey):
6271 // It is possible for several threads to be
6272 // trying to "claim" this object concurrently;
6273 // the unique thread that succeeds in marking the
6274 // object first will do the subsequent push on
6275 // to the work queue (or overflow list).
6276 if (_bit_map->par_mark(addr)) {
6277 // push on work_queue (which may not be empty), and trim the
6278 // queue to an appropriate length by applying this closure to
6279 // the oops in the oops popped from the stack (i.e. blacken the
6280 // grey objects)
6281 bool res = _work_queue->push(obj);
6282 assert(res, "Low water mark should be less than capacity?");
6283 trim_queue(_low_water_mark);
6284 } // Else, another thread claimed the object
6285 }
6286 }
6287 }
6288
6289 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6290 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6291
6292 // This closure is used to rescan the marked objects on the dirty cards
6293 // in the mod union table and the card table proper.
6294 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6295 oop p, MemRegion mr) {
6296
6297 size_t size = 0;
6298 HeapWord* addr = (HeapWord*)p;
6299 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6300 assert(_span.contains(addr), "we are scanning the CMS generation");
6301 // check if it's time to yield
6302 if (do_yield_check()) {
6303 // We yielded for some foreground stop-world work,
6304 // and we have been asked to abort this ongoing preclean cycle.
6305 return 0;
6306 }
6307 if (_bitMap->isMarked(addr)) {
6308 // it's marked; is it potentially uninitialized?
6309 if (p->klass_or_null() != NULL) {
6310 // an initialized object; ignore mark word in verification below
6311 // since we are running concurrent with mutators
6312 assert(p->is_oop(true), "should be an oop");
6313 if (p->is_objArray()) {
6314 // objArrays are precisely marked; restrict scanning
6315 // to dirty cards only.
6316 size = CompactibleFreeListSpace::adjustObjectSize(
6317 p->oop_iterate_size(_scanningClosure, mr));
6318 } else {
6319 // A non-array may have been imprecisely marked; we need
6320 // to scan object in its entirety.
6321 size = CompactibleFreeListSpace::adjustObjectSize(
6322 p->oop_iterate_size(_scanningClosure));
6323 }
6324 #ifdef ASSERT
6325 size_t direct_size =
6326 CompactibleFreeListSpace::adjustObjectSize(p->size());
6327 assert(size == direct_size, "Inconsistency in size");
6328 assert(size >= 3, "Necessary for Printezis marks to work");
6329 if (!_bitMap->isMarked(addr+1)) {
6330 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6331 } else {
6332 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6333 assert(_bitMap->isMarked(addr+size-1),
6334 "inconsistent Printezis mark");
6335 }
6336 #endif // ASSERT
6337 } else {
6338 // An uninitialized object.
6339 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6340 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6341 size = pointer_delta(nextOneAddr + 1, addr);
6342 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6343 "alignment problem");
6344 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6345 // will dirty the card when the klass pointer is installed in the
6346 // object (signaling the completion of initialization).
6347 }
6348 } else {
6349 // Either a not yet marked object or an uninitialized object
6350 if (p->klass_or_null() == NULL) {
6351 // An uninitialized object, skip to the next card, since
6352 // we may not be able to read its P-bits yet.
6353 assert(size == 0, "Initial value");
6354 } else {
6355 // An object not (yet) reached by marking: we merely need to
6356 // compute its size so as to go look at the next block.
6357 assert(p->is_oop(true), "should be an oop");
6358 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6359 }
6360 }
6361 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6362 return size;
6363 }
6364
6365 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6366 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6367 "CMS thread should hold CMS token");
6368 assert_lock_strong(_freelistLock);
6369 assert_lock_strong(_bitMap->lock());
6370 // relinquish the free_list_lock and bitMaplock()
6371 _bitMap->lock()->unlock();
6372 _freelistLock->unlock();
6373 ConcurrentMarkSweepThread::desynchronize(true);
6374 _collector->stopTimer();
6375 if (PrintCMSStatistics != 0) {
6376 _collector->incrementYields();
6377 }
6378
6379 // See the comment in coordinator_yield()
6380 for (unsigned i = 0; i < CMSYieldSleepCount &&
6381 ConcurrentMarkSweepThread::should_yield() &&
6382 !CMSCollector::foregroundGCIsActive(); ++i) {
6383 os::sleep(Thread::current(), 1, false);
6384 }
6385
6386 ConcurrentMarkSweepThread::synchronize(true);
6387 _freelistLock->lock_without_safepoint_check();
6388 _bitMap->lock()->lock_without_safepoint_check();
6389 _collector->startTimer();
6390 }
6391
6392
6393 //////////////////////////////////////////////////////////////////
6394 // SurvivorSpacePrecleanClosure
6395 //////////////////////////////////////////////////////////////////
6396 // This (single-threaded) closure is used to preclean the oops in
6397 // the survivor spaces.
6398 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6399
6400 HeapWord* addr = (HeapWord*)p;
6401 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6402 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6403 assert(p->klass_or_null() != NULL, "object should be initialized");
6404 // an initialized object; ignore mark word in verification below
6405 // since we are running concurrent with mutators
6406 assert(p->is_oop(true), "should be an oop");
6407 // Note that we do not yield while we iterate over
6408 // the interior oops of p, pushing the relevant ones
6409 // on our marking stack.
6410 size_t size = p->oop_iterate_size(_scanning_closure);
6411 do_yield_check();
6412 // Observe that below, we do not abandon the preclean
6413 // phase as soon as we should; rather we empty the
6414 // marking stack before returning. This is to satisfy
6415 // some existing assertions. In general, it may be a
6416 // good idea to abort immediately and complete the marking
6417 // from the grey objects at a later time.
6418 while (!_mark_stack->isEmpty()) {
6419 oop new_oop = _mark_stack->pop();
6420 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6421 assert(_bit_map->isMarked((HeapWord*)new_oop),
6422 "only grey objects on this stack");
6423 // iterate over the oops in this oop, marking and pushing
6424 // the ones in CMS heap (i.e. in _span).
6425 new_oop->oop_iterate(_scanning_closure);
6426 // check if it's time to yield
6427 do_yield_check();
6428 }
6429 unsigned int after_count =
6430 GenCollectedHeap::heap()->total_collections();
6431 bool abort = (_before_count != after_count) ||
6432 _collector->should_abort_preclean();
6433 return abort ? 0 : size;
6434 }
6435
6436 void SurvivorSpacePrecleanClosure::do_yield_work() {
6437 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6438 "CMS thread should hold CMS token");
6439 assert_lock_strong(_bit_map->lock());
6440 // Relinquish the bit map lock
6441 _bit_map->lock()->unlock();
6442 ConcurrentMarkSweepThread::desynchronize(true);
6443 _collector->stopTimer();
6444 if (PrintCMSStatistics != 0) {
6445 _collector->incrementYields();
6446 }
6447
6448 // See the comment in coordinator_yield()
6449 for (unsigned i = 0; i < CMSYieldSleepCount &&
6450 ConcurrentMarkSweepThread::should_yield() &&
6451 !CMSCollector::foregroundGCIsActive(); ++i) {
6452 os::sleep(Thread::current(), 1, false);
6453 }
6454
6455 ConcurrentMarkSweepThread::synchronize(true);
6456 _bit_map->lock()->lock_without_safepoint_check();
6457 _collector->startTimer();
6458 }
6459
6460 // This closure is used to rescan the marked objects on the dirty cards
6461 // in the mod union table and the card table proper. In the parallel
6462 // case, although the bitMap is shared, we do a single read so the
6463 // isMarked() query is "safe".
6464 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6465 // Ignore mark word because we are running concurrent with mutators
6466 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6467 HeapWord* addr = (HeapWord*)p;
6468 assert(_span.contains(addr), "we are scanning the CMS generation");
6469 bool is_obj_array = false;
6470 #ifdef ASSERT
6471 if (!_parallel) {
6472 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6473 assert(_collector->overflow_list_is_empty(),
6474 "overflow list should be empty");
6475
6476 }
6477 #endif // ASSERT
6478 if (_bit_map->isMarked(addr)) {
6479 // Obj arrays are precisely marked, non-arrays are not;
6480 // so we scan objArrays precisely and non-arrays in their
6481 // entirety.
6482 if (p->is_objArray()) {
6483 is_obj_array = true;
6484 if (_parallel) {
6485 p->oop_iterate(_par_scan_closure, mr);
6486 } else {
6487 p->oop_iterate(_scan_closure, mr);
6488 }
6489 } else {
6490 if (_parallel) {
6491 p->oop_iterate(_par_scan_closure);
6492 } else {
6493 p->oop_iterate(_scan_closure);
6494 }
6495 }
6496 }
6497 #ifdef ASSERT
6498 if (!_parallel) {
6499 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6500 assert(_collector->overflow_list_is_empty(),
6501 "overflow list should be empty");
6502
6503 }
6504 #endif // ASSERT
6505 return is_obj_array;
6506 }
6507
6508 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6509 MemRegion span,
6510 CMSBitMap* bitMap, CMSMarkStack* markStack,
6511 bool should_yield, bool verifying):
6512 _collector(collector),
6513 _span(span),
6514 _bitMap(bitMap),
6515 _mut(&collector->_modUnionTable),
6516 _markStack(markStack),
6517 _yield(should_yield),
6518 _skipBits(0)
6519 {
6520 assert(_markStack->isEmpty(), "stack should be empty");
6521 _finger = _bitMap->startWord();
6522 _threshold = _finger;
6523 assert(_collector->_restart_addr == NULL, "Sanity check");
6524 assert(_span.contains(_finger), "Out of bounds _finger?");
6525 DEBUG_ONLY(_verifying = verifying;)
6526 }
6527
6528 void MarkFromRootsClosure::reset(HeapWord* addr) {
6529 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6530 assert(_span.contains(addr), "Out of bounds _finger?");
6531 _finger = addr;
6532 _threshold = (HeapWord*)round_to(
6533 (intptr_t)_finger, CardTableModRefBS::card_size);
6534 }
6535
6536 // Should revisit to see if this should be restructured for
6537 // greater efficiency.
6538 bool MarkFromRootsClosure::do_bit(size_t offset) {
6539 if (_skipBits > 0) {
6540 _skipBits--;
6541 return true;
6542 }
6543 // convert offset into a HeapWord*
6544 HeapWord* addr = _bitMap->startWord() + offset;
6545 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6546 "address out of range");
6547 assert(_bitMap->isMarked(addr), "tautology");
6548 if (_bitMap->isMarked(addr+1)) {
6549 // this is an allocated but not yet initialized object
6550 assert(_skipBits == 0, "tautology");
6551 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6552 oop p = oop(addr);
6553 if (p->klass_or_null() == NULL) {
6554 DEBUG_ONLY(if (!_verifying) {)
6555 // We re-dirty the cards on which this object lies and increase
6556 // the _threshold so that we'll come back to scan this object
6557 // during the preclean or remark phase. (CMSCleanOnEnter)
6558 if (CMSCleanOnEnter) {
6559 size_t sz = _collector->block_size_using_printezis_bits(addr);
6560 HeapWord* end_card_addr = (HeapWord*)round_to(
6561 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6562 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6563 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6564 // Bump _threshold to end_card_addr; note that
6565 // _threshold cannot possibly exceed end_card_addr, anyhow.
6566 // This prevents future clearing of the card as the scan proceeds
6567 // to the right.
6568 assert(_threshold <= end_card_addr,
6569 "Because we are just scanning into this object");
6570 if (_threshold < end_card_addr) {
6571 _threshold = end_card_addr;
6572 }
6573 if (p->klass_or_null() != NULL) {
6574 // Redirty the range of cards...
6575 _mut->mark_range(redirty_range);
6576 } // ...else the setting of klass will dirty the card anyway.
6577 }
6578 DEBUG_ONLY(})
6579 return true;
6580 }
6581 }
6582 scanOopsInOop(addr);
6583 return true;
6584 }
6585
6586 // We take a break if we've been at this for a while,
6587 // so as to avoid monopolizing the locks involved.
6588 void MarkFromRootsClosure::do_yield_work() {
6589 // First give up the locks, then yield, then re-lock
6590 // We should probably use a constructor/destructor idiom to
6591 // do this unlock/lock or modify the MutexUnlocker class to
6592 // serve our purpose. XXX
6593 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6594 "CMS thread should hold CMS token");
6595 assert_lock_strong(_bitMap->lock());
6596 _bitMap->lock()->unlock();
6597 ConcurrentMarkSweepThread::desynchronize(true);
6598 _collector->stopTimer();
6599 if (PrintCMSStatistics != 0) {
6600 _collector->incrementYields();
6601 }
6602
6603 // See the comment in coordinator_yield()
6604 for (unsigned i = 0; i < CMSYieldSleepCount &&
6605 ConcurrentMarkSweepThread::should_yield() &&
6606 !CMSCollector::foregroundGCIsActive(); ++i) {
6607 os::sleep(Thread::current(), 1, false);
6608 }
6609
6610 ConcurrentMarkSweepThread::synchronize(true);
6611 _bitMap->lock()->lock_without_safepoint_check();
6612 _collector->startTimer();
6613 }
6614
6615 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6616 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6617 assert(_markStack->isEmpty(),
6618 "should drain stack to limit stack usage");
6619 // convert ptr to an oop preparatory to scanning
6620 oop obj = oop(ptr);
6621 // Ignore mark word in verification below, since we
6622 // may be running concurrent with mutators.
6623 assert(obj->is_oop(true), "should be an oop");
6624 assert(_finger <= ptr, "_finger runneth ahead");
6625 // advance the finger to right end of this object
6626 _finger = ptr + obj->size();
6627 assert(_finger > ptr, "we just incremented it above");
6628 // On large heaps, it may take us some time to get through
6629 // the marking phase. During
6630 // this time it's possible that a lot of mutations have
6631 // accumulated in the card table and the mod union table --
6632 // these mutation records are redundant until we have
6633 // actually traced into the corresponding card.
6634 // Here, we check whether advancing the finger would make
6635 // us cross into a new card, and if so clear corresponding
6636 // cards in the MUT (preclean them in the card-table in the
6637 // future).
6638
6639 DEBUG_ONLY(if (!_verifying) {)
6640 // The clean-on-enter optimization is disabled by default,
6641 // until we fix 6178663.
6642 if (CMSCleanOnEnter && (_finger > _threshold)) {
6643 // [_threshold, _finger) represents the interval
6644 // of cards to be cleared in MUT (or precleaned in card table).
6645 // The set of cards to be cleared is all those that overlap
6646 // with the interval [_threshold, _finger); note that
6647 // _threshold is always kept card-aligned but _finger isn't
6648 // always card-aligned.
6649 HeapWord* old_threshold = _threshold;
6650 assert(old_threshold == (HeapWord*)round_to(
6651 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6652 "_threshold should always be card-aligned");
6653 _threshold = (HeapWord*)round_to(
6654 (intptr_t)_finger, CardTableModRefBS::card_size);
6655 MemRegion mr(old_threshold, _threshold);
6656 assert(!mr.is_empty(), "Control point invariant");
6657 assert(_span.contains(mr), "Should clear within span");
6658 _mut->clear_range(mr);
6659 }
6660 DEBUG_ONLY(})
6661 // Note: the finger doesn't advance while we drain
6662 // the stack below.
6663 PushOrMarkClosure pushOrMarkClosure(_collector,
6664 _span, _bitMap, _markStack,
6665 _finger, this);
6666 bool res = _markStack->push(obj);
6667 assert(res, "Empty non-zero size stack should have space for single push");
6668 while (!_markStack->isEmpty()) {
6669 oop new_oop = _markStack->pop();
6670 // Skip verifying header mark word below because we are
6671 // running concurrent with mutators.
6672 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6673 // now scan this oop's oops
6674 new_oop->oop_iterate(&pushOrMarkClosure);
6675 do_yield_check();
6676 }
6677 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6678 }
6679
6680 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
6681 CMSCollector* collector, MemRegion span,
6682 CMSBitMap* bit_map,
6683 OopTaskQueue* work_queue,
6684 CMSMarkStack* overflow_stack):
6685 _collector(collector),
6686 _whole_span(collector->_span),
6687 _span(span),
6688 _bit_map(bit_map),
6689 _mut(&collector->_modUnionTable),
6690 _work_queue(work_queue),
6691 _overflow_stack(overflow_stack),
6692 _skip_bits(0),
6693 _task(task)
6694 {
6695 assert(_work_queue->size() == 0, "work_queue should be empty");
6696 _finger = span.start();
6697 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6698 assert(_span.contains(_finger), "Out of bounds _finger?");
6699 }
6700
6701 // Should revisit to see if this should be restructured for
6702 // greater efficiency.
6703 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
6704 if (_skip_bits > 0) {
6705 _skip_bits--;
6706 return true;
6707 }
6708 // convert offset into a HeapWord*
6709 HeapWord* addr = _bit_map->startWord() + offset;
6710 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6711 "address out of range");
6712 assert(_bit_map->isMarked(addr), "tautology");
6713 if (_bit_map->isMarked(addr+1)) {
6714 // this is an allocated object that might not yet be initialized
6715 assert(_skip_bits == 0, "tautology");
6716 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6717 oop p = oop(addr);
6718 if (p->klass_or_null() == NULL) {
6719 // in the case of Clean-on-Enter optimization, redirty card
6720 // and avoid clearing card by increasing the threshold.
6721 return true;
6722 }
6723 }
6724 scan_oops_in_oop(addr);
6725 return true;
6726 }
6727
6728 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6729 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6730 // Should we assert that our work queue is empty or
6731 // below some drain limit?
6732 assert(_work_queue->size() == 0,
6733 "should drain stack to limit stack usage");
6734 // convert ptr to an oop preparatory to scanning
6735 oop obj = oop(ptr);
6736 // Ignore mark word in verification below, since we
6737 // may be running concurrent with mutators.
6738 assert(obj->is_oop(true), "should be an oop");
6739 assert(_finger <= ptr, "_finger runneth ahead");
6740 // advance the finger to right end of this object
6741 _finger = ptr + obj->size();
6742 assert(_finger > ptr, "we just incremented it above");
6743 // On large heaps, it may take us some time to get through
6744 // the marking phase. During
6745 // this time it's possible that a lot of mutations have
6746 // accumulated in the card table and the mod union table --
6747 // these mutation records are redundant until we have
6748 // actually traced into the corresponding card.
6749 // Here, we check whether advancing the finger would make
6750 // us cross into a new card, and if so clear corresponding
6751 // cards in the MUT (preclean them in the card-table in the
6752 // future).
6753
6754 // The clean-on-enter optimization is disabled by default,
6755 // until we fix 6178663.
6756 if (CMSCleanOnEnter && (_finger > _threshold)) {
6757 // [_threshold, _finger) represents the interval
6758 // of cards to be cleared in MUT (or precleaned in card table).
6759 // The set of cards to be cleared is all those that overlap
6760 // with the interval [_threshold, _finger); note that
6761 // _threshold is always kept card-aligned but _finger isn't
6762 // always card-aligned.
6763 HeapWord* old_threshold = _threshold;
6764 assert(old_threshold == (HeapWord*)round_to(
6765 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6766 "_threshold should always be card-aligned");
6767 _threshold = (HeapWord*)round_to(
6768 (intptr_t)_finger, CardTableModRefBS::card_size);
6769 MemRegion mr(old_threshold, _threshold);
6770 assert(!mr.is_empty(), "Control point invariant");
6771 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6772 _mut->clear_range(mr);
6773 }
6774
6775 // Note: the local finger doesn't advance while we drain
6776 // the stack below, but the global finger sure can and will.
6777 HeapWord** gfa = _task->global_finger_addr();
6778 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
6779 _span, _bit_map,
6780 _work_queue,
6781 _overflow_stack,
6782 _finger,
6783 gfa, this);
6784 bool res = _work_queue->push(obj); // overflow could occur here
6785 assert(res, "Will hold once we use workqueues");
6786 while (true) {
6787 oop new_oop;
6788 if (!_work_queue->pop_local(new_oop)) {
6789 // We emptied our work_queue; check if there's stuff that can
6790 // be gotten from the overflow stack.
6791 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6792 _overflow_stack, _work_queue)) {
6793 do_yield_check();
6794 continue;
6795 } else { // done
6796 break;
6797 }
6798 }
6799 // Skip verifying header mark word below because we are
6800 // running concurrent with mutators.
6801 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6802 // now scan this oop's oops
6803 new_oop->oop_iterate(&pushOrMarkClosure);
6804 do_yield_check();
6805 }
6806 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6807 }
6808
6809 // Yield in response to a request from VM Thread or
6810 // from mutators.
6811 void Par_MarkFromRootsClosure::do_yield_work() {
6812 assert(_task != NULL, "sanity");
6813 _task->yield();
6814 }
6815
6816 // A variant of the above used for verifying CMS marking work.
6817 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6818 MemRegion span,
6819 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6820 CMSMarkStack* mark_stack):
6821 _collector(collector),
6822 _span(span),
6823 _verification_bm(verification_bm),
6824 _cms_bm(cms_bm),
6825 _mark_stack(mark_stack),
6826 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6827 mark_stack)
6828 {
6829 assert(_mark_stack->isEmpty(), "stack should be empty");
6830 _finger = _verification_bm->startWord();
6831 assert(_collector->_restart_addr == NULL, "Sanity check");
6832 assert(_span.contains(_finger), "Out of bounds _finger?");
6833 }
6834
6835 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6836 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6837 assert(_span.contains(addr), "Out of bounds _finger?");
6838 _finger = addr;
6839 }
6840
6841 // Should revisit to see if this should be restructured for
6842 // greater efficiency.
6843 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6844 // convert offset into a HeapWord*
6845 HeapWord* addr = _verification_bm->startWord() + offset;
6846 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6847 "address out of range");
6848 assert(_verification_bm->isMarked(addr), "tautology");
6849 assert(_cms_bm->isMarked(addr), "tautology");
6850
6851 assert(_mark_stack->isEmpty(),
6852 "should drain stack to limit stack usage");
6853 // convert addr to an oop preparatory to scanning
6854 oop obj = oop(addr);
6855 assert(obj->is_oop(), "should be an oop");
6856 assert(_finger <= addr, "_finger runneth ahead");
6857 // advance the finger to right end of this object
6858 _finger = addr + obj->size();
6859 assert(_finger > addr, "we just incremented it above");
6860 // Note: the finger doesn't advance while we drain
6861 // the stack below.
6862 bool res = _mark_stack->push(obj);
6863 assert(res, "Empty non-zero size stack should have space for single push");
6864 while (!_mark_stack->isEmpty()) {
6865 oop new_oop = _mark_stack->pop();
6866 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6867 // now scan this oop's oops
6868 new_oop->oop_iterate(&_pam_verify_closure);
6869 }
6870 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6871 return true;
6872 }
6873
6874 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6875 CMSCollector* collector, MemRegion span,
6876 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6877 CMSMarkStack* mark_stack):
6878 MetadataAwareOopClosure(collector->ref_processor()),
6879 _collector(collector),
6880 _span(span),
6881 _verification_bm(verification_bm),
6882 _cms_bm(cms_bm),
6883 _mark_stack(mark_stack)
6884 { }
6885
6886 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6887 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6888
6889 // Upon stack overflow, we discard (part of) the stack,
6890 // remembering the least address amongst those discarded
6891 // in CMSCollector's _restart_address.
6892 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6893 // Remember the least grey address discarded
6894 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6895 _collector->lower_restart_addr(ra);
6896 _mark_stack->reset(); // discard stack contents
6897 _mark_stack->expand(); // expand the stack if possible
6898 }
6899
6900 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6901 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6902 HeapWord* addr = (HeapWord*)obj;
6903 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6904 // Oop lies in _span and isn't yet grey or black
6905 _verification_bm->mark(addr); // now grey
6906 if (!_cms_bm->isMarked(addr)) {
6907 oop(addr)->print();
6908 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
6909 p2i(addr));
6910 fatal("... aborting");
6911 }
6912
6913 if (!_mark_stack->push(obj)) { // stack overflow
6914 if (PrintCMSStatistics != 0) {
6915 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
6916 SIZE_FORMAT, _mark_stack->capacity());
6917 }
6918 assert(_mark_stack->isFull(), "Else push should have succeeded");
6919 handle_stack_overflow(addr);
6920 }
6921 // anything including and to the right of _finger
6922 // will be scanned as we iterate over the remainder of the
6923 // bit map
6924 }
6925 }
6926
6927 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6928 MemRegion span,
6929 CMSBitMap* bitMap, CMSMarkStack* markStack,
6930 HeapWord* finger, MarkFromRootsClosure* parent) :
6931 MetadataAwareOopClosure(collector->ref_processor()),
6932 _collector(collector),
6933 _span(span),
6934 _bitMap(bitMap),
6935 _markStack(markStack),
6936 _finger(finger),
6937 _parent(parent)
6938 { }
6939
6940 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
6941 MemRegion span,
6942 CMSBitMap* bit_map,
6943 OopTaskQueue* work_queue,
6944 CMSMarkStack* overflow_stack,
6945 HeapWord* finger,
6946 HeapWord** global_finger_addr,
6947 Par_MarkFromRootsClosure* parent) :
6948 MetadataAwareOopClosure(collector->ref_processor()),
6949 _collector(collector),
6950 _whole_span(collector->_span),
6951 _span(span),
6952 _bit_map(bit_map),
6953 _work_queue(work_queue),
6954 _overflow_stack(overflow_stack),
6955 _finger(finger),
6956 _global_finger_addr(global_finger_addr),
6957 _parent(parent)
6958 { }
6959
6960 // Assumes thread-safe access by callers, who are
6961 // responsible for mutual exclusion.
6962 void CMSCollector::lower_restart_addr(HeapWord* low) {
6963 assert(_span.contains(low), "Out of bounds addr");
6964 if (_restart_addr == NULL) {
6965 _restart_addr = low;
6966 } else {
6967 _restart_addr = MIN2(_restart_addr, low);
6968 }
6969 }
6970
6971 // Upon stack overflow, we discard (part of) the stack,
6972 // remembering the least address amongst those discarded
6973 // in CMSCollector's _restart_address.
6974 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6975 // Remember the least grey address discarded
6976 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6977 _collector->lower_restart_addr(ra);
6978 _markStack->reset(); // discard stack contents
6979 _markStack->expand(); // expand the stack if possible
6980 }
6981
6982 // Upon stack overflow, we discard (part of) the stack,
6983 // remembering the least address amongst those discarded
6984 // in CMSCollector's _restart_address.
6985 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6986 // We need to do this under a mutex to prevent other
6987 // workers from interfering with the work done below.
6988 MutexLockerEx ml(_overflow_stack->par_lock(),
6989 Mutex::_no_safepoint_check_flag);
6990 // Remember the least grey address discarded
6991 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6992 _collector->lower_restart_addr(ra);
6993 _overflow_stack->reset(); // discard stack contents
6994 _overflow_stack->expand(); // expand the stack if possible
6995 }
6996
6997 void PushOrMarkClosure::do_oop(oop obj) {
6998 // Ignore mark word because we are running concurrent with mutators.
6999 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7000 HeapWord* addr = (HeapWord*)obj;
7001 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7002 // Oop lies in _span and isn't yet grey or black
7003 _bitMap->mark(addr); // now grey
7004 if (addr < _finger) {
7005 // the bit map iteration has already either passed, or
7006 // sampled, this bit in the bit map; we'll need to
7007 // use the marking stack to scan this oop's oops.
7008 bool simulate_overflow = false;
7009 NOT_PRODUCT(
7010 if (CMSMarkStackOverflowALot &&
7011 _collector->simulate_overflow()) {
7012 // simulate a stack overflow
7013 simulate_overflow = true;
7014 }
7015 )
7016 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7017 if (PrintCMSStatistics != 0) {
7018 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7019 SIZE_FORMAT, _markStack->capacity());
7020 }
7021 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7022 handle_stack_overflow(addr);
7023 }
7024 }
7025 // anything including and to the right of _finger
7026 // will be scanned as we iterate over the remainder of the
7027 // bit map
7028 do_yield_check();
7029 }
7030 }
7031
7032 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7033 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7034
7035 void Par_PushOrMarkClosure::do_oop(oop obj) {
7036 // Ignore mark word because we are running concurrent with mutators.
7037 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7038 HeapWord* addr = (HeapWord*)obj;
7039 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7040 // Oop lies in _span and isn't yet grey or black
7041 // We read the global_finger (volatile read) strictly after marking oop
7042 bool res = _bit_map->par_mark(addr); // now grey
7043 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7044 // Should we push this marked oop on our stack?
7045 // -- if someone else marked it, nothing to do
7046 // -- if target oop is above global finger nothing to do
7047 // -- if target oop is in chunk and above local finger
7048 // then nothing to do
7049 // -- else push on work queue
7050 if ( !res // someone else marked it, they will deal with it
7051 || (addr >= *gfa) // will be scanned in a later task
7052 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7053 return;
7054 }
7055 // the bit map iteration has already either passed, or
7056 // sampled, this bit in the bit map; we'll need to
7057 // use the marking stack to scan this oop's oops.
7058 bool simulate_overflow = false;
7059 NOT_PRODUCT(
7060 if (CMSMarkStackOverflowALot &&
7061 _collector->simulate_overflow()) {
7062 // simulate a stack overflow
7063 simulate_overflow = true;
7064 }
7065 )
7066 if (simulate_overflow ||
7067 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7068 // stack overflow
7069 if (PrintCMSStatistics != 0) {
7070 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7071 SIZE_FORMAT, _overflow_stack->capacity());
7072 }
7073 // We cannot assert that the overflow stack is full because
7074 // it may have been emptied since.
7075 assert(simulate_overflow ||
7076 _work_queue->size() == _work_queue->max_elems(),
7077 "Else push should have succeeded");
7078 handle_stack_overflow(addr);
7079 }
7080 do_yield_check();
7081 }
7082 }
7083
7084 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7085 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7086
7087 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7088 MemRegion span,
7089 ReferenceProcessor* rp,
7090 CMSBitMap* bit_map,
7091 CMSBitMap* mod_union_table,
7092 CMSMarkStack* mark_stack,
7093 bool concurrent_precleaning):
7094 MetadataAwareOopClosure(rp),
7095 _collector(collector),
7096 _span(span),
7097 _bit_map(bit_map),
7098 _mod_union_table(mod_union_table),
7099 _mark_stack(mark_stack),
7100 _concurrent_precleaning(concurrent_precleaning)
7101 {
7102 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7103 }
7104
7105 // Grey object rescan during pre-cleaning and second checkpoint phases --
7106 // the non-parallel version (the parallel version appears further below.)
7107 void PushAndMarkClosure::do_oop(oop obj) {
7108 // Ignore mark word verification. If during concurrent precleaning,
7109 // the object monitor may be locked. If during the checkpoint
7110 // phases, the object may already have been reached by a different
7111 // path and may be at the end of the global overflow list (so
7112 // the mark word may be NULL).
7113 assert(obj->is_oop_or_null(true /* ignore mark word */),
7114 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7115 HeapWord* addr = (HeapWord*)obj;
7116 // Check if oop points into the CMS generation
7117 // and is not marked
7118 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7119 // a white object ...
7120 _bit_map->mark(addr); // ... now grey
7121 // push on the marking stack (grey set)
7122 bool simulate_overflow = false;
7123 NOT_PRODUCT(
7124 if (CMSMarkStackOverflowALot &&
7125 _collector->simulate_overflow()) {
7126 // simulate a stack overflow
7127 simulate_overflow = true;
7128 }
7129 )
7130 if (simulate_overflow || !_mark_stack->push(obj)) {
7131 if (_concurrent_precleaning) {
7132 // During precleaning we can just dirty the appropriate card(s)
7133 // in the mod union table, thus ensuring that the object remains
7134 // in the grey set and continue. In the case of object arrays
7135 // we need to dirty all of the cards that the object spans,
7136 // since the rescan of object arrays will be limited to the
7137 // dirty cards.
7138 // Note that no one can be interfering with us in this action
7139 // of dirtying the mod union table, so no locking or atomics
7140 // are required.
7141 if (obj->is_objArray()) {
7142 size_t sz = obj->size();
7143 HeapWord* end_card_addr = (HeapWord*)round_to(
7144 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7145 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7146 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7147 _mod_union_table->mark_range(redirty_range);
7148 } else {
7149 _mod_union_table->mark(addr);
7150 }
7151 _collector->_ser_pmc_preclean_ovflw++;
7152 } else {
7153 // During the remark phase, we need to remember this oop
7154 // in the overflow list.
7155 _collector->push_on_overflow_list(obj);
7156 _collector->_ser_pmc_remark_ovflw++;
7157 }
7158 }
7159 }
7160 }
7161
7162 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7163 MemRegion span,
7164 ReferenceProcessor* rp,
7165 CMSBitMap* bit_map,
7166 OopTaskQueue* work_queue):
7167 MetadataAwareOopClosure(rp),
7168 _collector(collector),
7169 _span(span),
7170 _bit_map(bit_map),
7171 _work_queue(work_queue)
7172 {
7173 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
7174 }
7175
7176 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7177 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7178
7179 // Grey object rescan during second checkpoint phase --
7180 // the parallel version.
7181 void Par_PushAndMarkClosure::do_oop(oop obj) {
7182 // In the assert below, we ignore the mark word because
7183 // this oop may point to an already visited object that is
7184 // on the overflow stack (in which case the mark word has
7185 // been hijacked for chaining into the overflow stack --
7186 // if this is the last object in the overflow stack then
7187 // its mark word will be NULL). Because this object may
7188 // have been subsequently popped off the global overflow
7189 // stack, and the mark word possibly restored to the prototypical
7190 // value, by the time we get to examined this failing assert in
7191 // the debugger, is_oop_or_null(false) may subsequently start
7192 // to hold.
7193 assert(obj->is_oop_or_null(true),
7194 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
7195 HeapWord* addr = (HeapWord*)obj;
7196 // Check if oop points into the CMS generation
7197 // and is not marked
7198 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7199 // a white object ...
7200 // If we manage to "claim" the object, by being the
7201 // first thread to mark it, then we push it on our
7202 // marking stack
7203 if (_bit_map->par_mark(addr)) { // ... now grey
7204 // push on work queue (grey set)
7205 bool simulate_overflow = false;
7206 NOT_PRODUCT(
7207 if (CMSMarkStackOverflowALot &&
7208 _collector->par_simulate_overflow()) {
7209 // simulate a stack overflow
7210 simulate_overflow = true;
7211 }
7212 )
7213 if (simulate_overflow || !_work_queue->push(obj)) {
7214 _collector->par_push_on_overflow_list(obj);
7215 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7216 }
7217 } // Else, some other thread got there first
7218 }
7219 }
7220
7221 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7222 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7223
7224 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7225 Mutex* bml = _collector->bitMapLock();
7226 assert_lock_strong(bml);
7227 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7228 "CMS thread should hold CMS token");
7229
7230 bml->unlock();
7231 ConcurrentMarkSweepThread::desynchronize(true);
7232
7233 _collector->stopTimer();
7234 if (PrintCMSStatistics != 0) {
7235 _collector->incrementYields();
7236 }
7237
7238 // See the comment in coordinator_yield()
7239 for (unsigned i = 0; i < CMSYieldSleepCount &&
7240 ConcurrentMarkSweepThread::should_yield() &&
7241 !CMSCollector::foregroundGCIsActive(); ++i) {
7242 os::sleep(Thread::current(), 1, false);
7243 }
7244
7245 ConcurrentMarkSweepThread::synchronize(true);
7246 bml->lock();
7247
7248 _collector->startTimer();
7249 }
7250
7251 bool CMSPrecleanRefsYieldClosure::should_return() {
7252 if (ConcurrentMarkSweepThread::should_yield()) {
7253 do_yield_work();
7254 }
7255 return _collector->foregroundGCIsActive();
7256 }
7257
7258 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7259 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7260 "mr should be aligned to start at a card boundary");
7261 // We'd like to assert:
7262 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7263 // "mr should be a range of cards");
7264 // However, that would be too strong in one case -- the last
7265 // partition ends at _unallocated_block which, in general, can be
7266 // an arbitrary boundary, not necessarily card aligned.
7267 if (PrintCMSStatistics != 0) {
7268 _num_dirty_cards +=
7269 mr.word_size()/CardTableModRefBS::card_size_in_words;
7270 }
7271 _space->object_iterate_mem(mr, &_scan_cl);
7272 }
7273
7274 SweepClosure::SweepClosure(CMSCollector* collector,
7275 ConcurrentMarkSweepGeneration* g,
7276 CMSBitMap* bitMap, bool should_yield) :
7277 _collector(collector),
7278 _g(g),
7279 _sp(g->cmsSpace()),
7280 _limit(_sp->sweep_limit()),
7281 _freelistLock(_sp->freelistLock()),
7282 _bitMap(bitMap),
7283 _yield(should_yield),
7284 _inFreeRange(false), // No free range at beginning of sweep
7285 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7286 _lastFreeRangeCoalesced(false),
7287 _freeFinger(g->used_region().start())
7288 {
7289 NOT_PRODUCT(
7290 _numObjectsFreed = 0;
7291 _numWordsFreed = 0;
7292 _numObjectsLive = 0;
7293 _numWordsLive = 0;
7294 _numObjectsAlreadyFree = 0;
7295 _numWordsAlreadyFree = 0;
7296 _last_fc = NULL;
7297
7298 _sp->initializeIndexedFreeListArrayReturnedBytes();
7299 _sp->dictionary()->initialize_dict_returned_bytes();
7300 )
7301 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7302 "sweep _limit out of bounds");
7303 if (CMSTraceSweeper) {
7304 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7305 p2i(_limit));
7306 }
7307 }
7308
7309 void SweepClosure::print_on(outputStream* st) const {
7310 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7311 p2i(_sp->bottom()), p2i(_sp->end()));
7312 tty->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7313 tty->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7314 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7315 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7316 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7317 }
7318
7319 #ifndef PRODUCT
7320 // Assertion checking only: no useful work in product mode --
7321 // however, if any of the flags below become product flags,
7322 // you may need to review this code to see if it needs to be
7323 // enabled in product mode.
7324 SweepClosure::~SweepClosure() {
7325 assert_lock_strong(_freelistLock);
7326 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7327 "sweep _limit out of bounds");
7328 if (inFreeRange()) {
7329 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7330 print();
7331 ShouldNotReachHere();
7332 }
7333 if (Verbose && PrintGC) {
7334 gclog_or_tty->print("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7335 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7336 gclog_or_tty->print_cr("\nLive " SIZE_FORMAT " objects, "
7337 SIZE_FORMAT " bytes "
7338 "Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7339 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7340 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7341 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7342 * sizeof(HeapWord);
7343 gclog_or_tty->print_cr("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7344
7345 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7346 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7347 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7348 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7349 gclog_or_tty->print("Returned " SIZE_FORMAT " bytes", returned_bytes);
7350 gclog_or_tty->print(" Indexed List Returned " SIZE_FORMAT " bytes",
7351 indexListReturnedBytes);
7352 gclog_or_tty->print_cr(" Dictionary Returned " SIZE_FORMAT " bytes",
7353 dict_returned_bytes);
7354 }
7355 }
7356 if (CMSTraceSweeper) {
7357 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7358 p2i(_limit));
7359 }
7360 }
7361 #endif // PRODUCT
7362
7363 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7364 bool freeRangeInFreeLists) {
7365 if (CMSTraceSweeper) {
7366 gclog_or_tty->print("---- Start free range at " PTR_FORMAT " with free block (%d)\n",
7367 p2i(freeFinger), freeRangeInFreeLists);
7368 }
7369 assert(!inFreeRange(), "Trampling existing free range");
7370 set_inFreeRange(true);
7371 set_lastFreeRangeCoalesced(false);
7372
7373 set_freeFinger(freeFinger);
7374 set_freeRangeInFreeLists(freeRangeInFreeLists);
7375 if (CMSTestInFreeList) {
7376 if (freeRangeInFreeLists) {
7377 FreeChunk* fc = (FreeChunk*) freeFinger;
7378 assert(fc->is_free(), "A chunk on the free list should be free.");
7379 assert(fc->size() > 0, "Free range should have a size");
7380 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7381 }
7382 }
7383 }
7384
7385 // Note that the sweeper runs concurrently with mutators. Thus,
7386 // it is possible for direct allocation in this generation to happen
7387 // in the middle of the sweep. Note that the sweeper also coalesces
7388 // contiguous free blocks. Thus, unless the sweeper and the allocator
7389 // synchronize appropriately freshly allocated blocks may get swept up.
7390 // This is accomplished by the sweeper locking the free lists while
7391 // it is sweeping. Thus blocks that are determined to be free are
7392 // indeed free. There is however one additional complication:
7393 // blocks that have been allocated since the final checkpoint and
7394 // mark, will not have been marked and so would be treated as
7395 // unreachable and swept up. To prevent this, the allocator marks
7396 // the bit map when allocating during the sweep phase. This leads,
7397 // however, to a further complication -- objects may have been allocated
7398 // but not yet initialized -- in the sense that the header isn't yet
7399 // installed. The sweeper can not then determine the size of the block
7400 // in order to skip over it. To deal with this case, we use a technique
7401 // (due to Printezis) to encode such uninitialized block sizes in the
7402 // bit map. Since the bit map uses a bit per every HeapWord, but the
7403 // CMS generation has a minimum object size of 3 HeapWords, it follows
7404 // that "normal marks" won't be adjacent in the bit map (there will
7405 // always be at least two 0 bits between successive 1 bits). We make use
7406 // of these "unused" bits to represent uninitialized blocks -- the bit
7407 // corresponding to the start of the uninitialized object and the next
7408 // bit are both set. Finally, a 1 bit marks the end of the object that
7409 // started with the two consecutive 1 bits to indicate its potentially
7410 // uninitialized state.
7411
7412 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7413 FreeChunk* fc = (FreeChunk*)addr;
7414 size_t res;
7415
7416 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7417 // than "addr == _limit" because although _limit was a block boundary when
7418 // we started the sweep, it may no longer be one because heap expansion
7419 // may have caused us to coalesce the block ending at the address _limit
7420 // with a newly expanded chunk (this happens when _limit was set to the
7421 // previous _end of the space), so we may have stepped past _limit:
7422 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7423 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7424 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7425 "sweep _limit out of bounds");
7426 assert(addr < _sp->end(), "addr out of bounds");
7427 // Flush any free range we might be holding as a single
7428 // coalesced chunk to the appropriate free list.
7429 if (inFreeRange()) {
7430 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7431 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7432 flush_cur_free_chunk(freeFinger(),
7433 pointer_delta(addr, freeFinger()));
7434 if (CMSTraceSweeper) {
7435 gclog_or_tty->print("Sweep: last chunk: ");
7436 gclog_or_tty->print("put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") "
7437 "[coalesced:%d]\n",
7438 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7439 lastFreeRangeCoalesced() ? 1 : 0);
7440 }
7441 }
7442
7443 // help the iterator loop finish
7444 return pointer_delta(_sp->end(), addr);
7445 }
7446
7447 assert(addr < _limit, "sweep invariant");
7448 // check if we should yield
7449 do_yield_check(addr);
7450 if (fc->is_free()) {
7451 // Chunk that is already free
7452 res = fc->size();
7453 do_already_free_chunk(fc);
7454 debug_only(_sp->verifyFreeLists());
7455 // If we flush the chunk at hand in lookahead_and_flush()
7456 // and it's coalesced with a preceding chunk, then the
7457 // process of "mangling" the payload of the coalesced block
7458 // will cause erasure of the size information from the
7459 // (erstwhile) header of all the coalesced blocks but the
7460 // first, so the first disjunct in the assert will not hold
7461 // in that specific case (in which case the second disjunct
7462 // will hold).
7463 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7464 "Otherwise the size info doesn't change at this step");
7465 NOT_PRODUCT(
7466 _numObjectsAlreadyFree++;
7467 _numWordsAlreadyFree += res;
7468 )
7469 NOT_PRODUCT(_last_fc = fc;)
7470 } else if (!_bitMap->isMarked(addr)) {
7471 // Chunk is fresh garbage
7472 res = do_garbage_chunk(fc);
7473 debug_only(_sp->verifyFreeLists());
7474 NOT_PRODUCT(
7475 _numObjectsFreed++;
7476 _numWordsFreed += res;
7477 )
7478 } else {
7479 // Chunk that is alive.
7480 res = do_live_chunk(fc);
7481 debug_only(_sp->verifyFreeLists());
7482 NOT_PRODUCT(
7483 _numObjectsLive++;
7484 _numWordsLive += res;
7485 )
7486 }
7487 return res;
7488 }
7489
7490 // For the smart allocation, record following
7491 // split deaths - a free chunk is removed from its free list because
7492 // it is being split into two or more chunks.
7493 // split birth - a free chunk is being added to its free list because
7494 // a larger free chunk has been split and resulted in this free chunk.
7495 // coal death - a free chunk is being removed from its free list because
7496 // it is being coalesced into a large free chunk.
7497 // coal birth - a free chunk is being added to its free list because
7498 // it was created when two or more free chunks where coalesced into
7499 // this free chunk.
7500 //
7501 // These statistics are used to determine the desired number of free
7502 // chunks of a given size. The desired number is chosen to be relative
7503 // to the end of a CMS sweep. The desired number at the end of a sweep
7504 // is the
7505 // count-at-end-of-previous-sweep (an amount that was enough)
7506 // - count-at-beginning-of-current-sweep (the excess)
7507 // + split-births (gains in this size during interval)
7508 // - split-deaths (demands on this size during interval)
7509 // where the interval is from the end of one sweep to the end of the
7510 // next.
7511 //
7512 // When sweeping the sweeper maintains an accumulated chunk which is
7513 // the chunk that is made up of chunks that have been coalesced. That
7514 // will be termed the left-hand chunk. A new chunk of garbage that
7515 // is being considered for coalescing will be referred to as the
7516 // right-hand chunk.
7517 //
7518 // When making a decision on whether to coalesce a right-hand chunk with
7519 // the current left-hand chunk, the current count vs. the desired count
7520 // of the left-hand chunk is considered. Also if the right-hand chunk
7521 // is near the large chunk at the end of the heap (see
7522 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7523 // left-hand chunk is coalesced.
7524 //
7525 // When making a decision about whether to split a chunk, the desired count
7526 // vs. the current count of the candidate to be split is also considered.
7527 // If the candidate is underpopulated (currently fewer chunks than desired)
7528 // a chunk of an overpopulated (currently more chunks than desired) size may
7529 // be chosen. The "hint" associated with a free list, if non-null, points
7530 // to a free list which may be overpopulated.
7531 //
7532
7533 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7534 const size_t size = fc->size();
7535 // Chunks that cannot be coalesced are not in the
7536 // free lists.
7537 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7538 assert(_sp->verify_chunk_in_free_list(fc),
7539 "free chunk should be in free lists");
7540 }
7541 // a chunk that is already free, should not have been
7542 // marked in the bit map
7543 HeapWord* const addr = (HeapWord*) fc;
7544 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7545 // Verify that the bit map has no bits marked between
7546 // addr and purported end of this block.
7547 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7548
7549 // Some chunks cannot be coalesced under any circumstances.
7550 // See the definition of cantCoalesce().
7551 if (!fc->cantCoalesce()) {
7552 // This chunk can potentially be coalesced.
7553 if (_sp->adaptive_freelists()) {
7554 // All the work is done in
7555 do_post_free_or_garbage_chunk(fc, size);
7556 } else { // Not adaptive free lists
7557 // this is a free chunk that can potentially be coalesced by the sweeper;
7558 if (!inFreeRange()) {
7559 // if the next chunk is a free block that can't be coalesced
7560 // it doesn't make sense to remove this chunk from the free lists
7561 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7562 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
7563 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
7564 nextChunk->is_free() && // ... which is free...
7565 nextChunk->cantCoalesce()) { // ... but can't be coalesced
7566 // nothing to do
7567 } else {
7568 // Potentially the start of a new free range:
7569 // Don't eagerly remove it from the free lists.
7570 // No need to remove it if it will just be put
7571 // back again. (Also from a pragmatic point of view
7572 // if it is a free block in a region that is beyond
7573 // any allocated blocks, an assertion will fail)
7574 // Remember the start of a free run.
7575 initialize_free_range(addr, true);
7576 // end - can coalesce with next chunk
7577 }
7578 } else {
7579 // the midst of a free range, we are coalescing
7580 print_free_block_coalesced(fc);
7581 if (CMSTraceSweeper) {
7582 gclog_or_tty->print(" -- pick up free block " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7583 }
7584 // remove it from the free lists
7585 _sp->removeFreeChunkFromFreeLists(fc);
7586 set_lastFreeRangeCoalesced(true);
7587 // If the chunk is being coalesced and the current free range is
7588 // in the free lists, remove the current free range so that it
7589 // will be returned to the free lists in its entirety - all
7590 // the coalesced pieces included.
7591 if (freeRangeInFreeLists()) {
7592 FreeChunk* ffc = (FreeChunk*) freeFinger();
7593 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7594 "Size of free range is inconsistent with chunk size.");
7595 if (CMSTestInFreeList) {
7596 assert(_sp->verify_chunk_in_free_list(ffc),
7597 "free range is not in free lists");
7598 }
7599 _sp->removeFreeChunkFromFreeLists(ffc);
7600 set_freeRangeInFreeLists(false);
7601 }
7602 }
7603 }
7604 // Note that if the chunk is not coalescable (the else arm
7605 // below), we unconditionally flush, without needing to do
7606 // a "lookahead," as we do below.
7607 if (inFreeRange()) lookahead_and_flush(fc, size);
7608 } else {
7609 // Code path common to both original and adaptive free lists.
7610
7611 // cant coalesce with previous block; this should be treated
7612 // as the end of a free run if any
7613 if (inFreeRange()) {
7614 // we kicked some butt; time to pick up the garbage
7615 assert(freeFinger() < addr, "freeFinger points too high");
7616 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7617 }
7618 // else, nothing to do, just continue
7619 }
7620 }
7621
7622 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7623 // This is a chunk of garbage. It is not in any free list.
7624 // Add it to a free list or let it possibly be coalesced into
7625 // a larger chunk.
7626 HeapWord* const addr = (HeapWord*) fc;
7627 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7628
7629 if (_sp->adaptive_freelists()) {
7630 // Verify that the bit map has no bits marked between
7631 // addr and purported end of just dead object.
7632 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7633
7634 do_post_free_or_garbage_chunk(fc, size);
7635 } else {
7636 if (!inFreeRange()) {
7637 // start of a new free range
7638 assert(size > 0, "A free range should have a size");
7639 initialize_free_range(addr, false);
7640 } else {
7641 // this will be swept up when we hit the end of the
7642 // free range
7643 if (CMSTraceSweeper) {
7644 gclog_or_tty->print(" -- pick up garbage " PTR_FORMAT " (" SIZE_FORMAT ")\n", p2i(fc), size);
7645 }
7646 // If the chunk is being coalesced and the current free range is
7647 // in the free lists, remove the current free range so that it
7648 // will be returned to the free lists in its entirety - all
7649 // the coalesced pieces included.
7650 if (freeRangeInFreeLists()) {
7651 FreeChunk* ffc = (FreeChunk*)freeFinger();
7652 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7653 "Size of free range is inconsistent with chunk size.");
7654 if (CMSTestInFreeList) {
7655 assert(_sp->verify_chunk_in_free_list(ffc),
7656 "free range is not in free lists");
7657 }
7658 _sp->removeFreeChunkFromFreeLists(ffc);
7659 set_freeRangeInFreeLists(false);
7660 }
7661 set_lastFreeRangeCoalesced(true);
7662 }
7663 // this will be swept up when we hit the end of the free range
7664
7665 // Verify that the bit map has no bits marked between
7666 // addr and purported end of just dead object.
7667 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7668 }
7669 assert(_limit >= addr + size,
7670 "A freshly garbage chunk can't possibly straddle over _limit");
7671 if (inFreeRange()) lookahead_and_flush(fc, size);
7672 return size;
7673 }
7674
7675 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7676 HeapWord* addr = (HeapWord*) fc;
7677 // The sweeper has just found a live object. Return any accumulated
7678 // left hand chunk to the free lists.
7679 if (inFreeRange()) {
7680 assert(freeFinger() < addr, "freeFinger points too high");
7681 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7682 }
7683
7684 // This object is live: we'd normally expect this to be
7685 // an oop, and like to assert the following:
7686 // assert(oop(addr)->is_oop(), "live block should be an oop");
7687 // However, as we commented above, this may be an object whose
7688 // header hasn't yet been initialized.
7689 size_t size;
7690 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7691 if (_bitMap->isMarked(addr + 1)) {
7692 // Determine the size from the bit map, rather than trying to
7693 // compute it from the object header.
7694 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7695 size = pointer_delta(nextOneAddr + 1, addr);
7696 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7697 "alignment problem");
7698
7699 #ifdef ASSERT
7700 if (oop(addr)->klass_or_null() != NULL) {
7701 // Ignore mark word because we are running concurrent with mutators
7702 assert(oop(addr)->is_oop(true), "live block should be an oop");
7703 assert(size ==
7704 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7705 "P-mark and computed size do not agree");
7706 }
7707 #endif
7708
7709 } else {
7710 // This should be an initialized object that's alive.
7711 assert(oop(addr)->klass_or_null() != NULL,
7712 "Should be an initialized object");
7713 // Ignore mark word because we are running concurrent with mutators
7714 assert(oop(addr)->is_oop(true), "live block should be an oop");
7715 // Verify that the bit map has no bits marked between
7716 // addr and purported end of this block.
7717 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7718 assert(size >= 3, "Necessary for Printezis marks to work");
7719 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7720 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7721 }
7722 return size;
7723 }
7724
7725 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7726 size_t chunkSize) {
7727 // do_post_free_or_garbage_chunk() should only be called in the case
7728 // of the adaptive free list allocator.
7729 const bool fcInFreeLists = fc->is_free();
7730 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
7731 assert((HeapWord*)fc <= _limit, "sweep invariant");
7732 if (CMSTestInFreeList && fcInFreeLists) {
7733 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7734 }
7735
7736 if (CMSTraceSweeper) {
7737 gclog_or_tty->print_cr(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7738 }
7739
7740 HeapWord* const fc_addr = (HeapWord*) fc;
7741
7742 bool coalesce;
7743 const size_t left = pointer_delta(fc_addr, freeFinger());
7744 const size_t right = chunkSize;
7745 switch (FLSCoalescePolicy) {
7746 // numeric value forms a coalition aggressiveness metric
7747 case 0: { // never coalesce
7748 coalesce = false;
7749 break;
7750 }
7751 case 1: { // coalesce if left & right chunks on overpopulated lists
7752 coalesce = _sp->coalOverPopulated(left) &&
7753 _sp->coalOverPopulated(right);
7754 break;
7755 }
7756 case 2: { // coalesce if left chunk on overpopulated list (default)
7757 coalesce = _sp->coalOverPopulated(left);
7758 break;
7759 }
7760 case 3: { // coalesce if left OR right chunk on overpopulated list
7761 coalesce = _sp->coalOverPopulated(left) ||
7762 _sp->coalOverPopulated(right);
7763 break;
7764 }
7765 case 4: { // always coalesce
7766 coalesce = true;
7767 break;
7768 }
7769 default:
7770 ShouldNotReachHere();
7771 }
7772
7773 // Should the current free range be coalesced?
7774 // If the chunk is in a free range and either we decided to coalesce above
7775 // or the chunk is near the large block at the end of the heap
7776 // (isNearLargestChunk() returns true), then coalesce this chunk.
7777 const bool doCoalesce = inFreeRange()
7778 && (coalesce || _g->isNearLargestChunk(fc_addr));
7779 if (doCoalesce) {
7780 // Coalesce the current free range on the left with the new
7781 // chunk on the right. If either is on a free list,
7782 // it must be removed from the list and stashed in the closure.
7783 if (freeRangeInFreeLists()) {
7784 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7785 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7786 "Size of free range is inconsistent with chunk size.");
7787 if (CMSTestInFreeList) {
7788 assert(_sp->verify_chunk_in_free_list(ffc),
7789 "Chunk is not in free lists");
7790 }
7791 _sp->coalDeath(ffc->size());
7792 _sp->removeFreeChunkFromFreeLists(ffc);
7793 set_freeRangeInFreeLists(false);
7794 }
7795 if (fcInFreeLists) {
7796 _sp->coalDeath(chunkSize);
7797 assert(fc->size() == chunkSize,
7798 "The chunk has the wrong size or is not in the free lists");
7799 _sp->removeFreeChunkFromFreeLists(fc);
7800 }
7801 set_lastFreeRangeCoalesced(true);
7802 print_free_block_coalesced(fc);
7803 } else { // not in a free range and/or should not coalesce
7804 // Return the current free range and start a new one.
7805 if (inFreeRange()) {
7806 // In a free range but cannot coalesce with the right hand chunk.
7807 // Put the current free range into the free lists.
7808 flush_cur_free_chunk(freeFinger(),
7809 pointer_delta(fc_addr, freeFinger()));
7810 }
7811 // Set up for new free range. Pass along whether the right hand
7812 // chunk is in the free lists.
7813 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7814 }
7815 }
7816
7817 // Lookahead flush:
7818 // If we are tracking a free range, and this is the last chunk that
7819 // we'll look at because its end crosses past _limit, we'll preemptively
7820 // flush it along with any free range we may be holding on to. Note that
7821 // this can be the case only for an already free or freshly garbage
7822 // chunk. If this block is an object, it can never straddle
7823 // over _limit. The "straddling" occurs when _limit is set at
7824 // the previous end of the space when this cycle started, and
7825 // a subsequent heap expansion caused the previously co-terminal
7826 // free block to be coalesced with the newly expanded portion,
7827 // thus rendering _limit a non-block-boundary making it dangerous
7828 // for the sweeper to step over and examine.
7829 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7830 assert(inFreeRange(), "Should only be called if currently in a free range.");
7831 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7832 assert(_sp->used_region().contains(eob - 1),
7833 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7834 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7835 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7836 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7837 if (eob >= _limit) {
7838 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7839 if (CMSTraceSweeper) {
7840 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
7841 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7842 "[" PTR_FORMAT "," PTR_FORMAT ")",
7843 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7844 }
7845 // Return the storage we are tracking back into the free lists.
7846 if (CMSTraceSweeper) {
7847 gclog_or_tty->print_cr("Flushing ... ");
7848 }
7849 assert(freeFinger() < eob, "Error");
7850 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7851 }
7852 }
7853
7854 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7855 assert(inFreeRange(), "Should only be called if currently in a free range.");
7856 assert(size > 0,
7857 "A zero sized chunk cannot be added to the free lists.");
7858 if (!freeRangeInFreeLists()) {
7859 if (CMSTestInFreeList) {
7860 FreeChunk* fc = (FreeChunk*) chunk;
7861 fc->set_size(size);
7862 assert(!_sp->verify_chunk_in_free_list(fc),
7863 "chunk should not be in free lists yet");
7864 }
7865 if (CMSTraceSweeper) {
7866 gclog_or_tty->print_cr(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists",
7867 p2i(chunk), size);
7868 }
7869 // A new free range is going to be starting. The current
7870 // free range has not been added to the free lists yet or
7871 // was removed so add it back.
7872 // If the current free range was coalesced, then the death
7873 // of the free range was recorded. Record a birth now.
7874 if (lastFreeRangeCoalesced()) {
7875 _sp->coalBirth(size);
7876 }
7877 _sp->addChunkAndRepairOffsetTable(chunk, size,
7878 lastFreeRangeCoalesced());
7879 } else if (CMSTraceSweeper) {
7880 gclog_or_tty->print_cr("Already in free list: nothing to flush");
7881 }
7882 set_inFreeRange(false);
7883 set_freeRangeInFreeLists(false);
7884 }
7885
7886 // We take a break if we've been at this for a while,
7887 // so as to avoid monopolizing the locks involved.
7888 void SweepClosure::do_yield_work(HeapWord* addr) {
7889 // Return current free chunk being used for coalescing (if any)
7890 // to the appropriate freelist. After yielding, the next
7891 // free block encountered will start a coalescing range of
7892 // free blocks. If the next free block is adjacent to the
7893 // chunk just flushed, they will need to wait for the next
7894 // sweep to be coalesced.
7895 if (inFreeRange()) {
7896 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7897 }
7898
7899 // First give up the locks, then yield, then re-lock.
7900 // We should probably use a constructor/destructor idiom to
7901 // do this unlock/lock or modify the MutexUnlocker class to
7902 // serve our purpose. XXX
7903 assert_lock_strong(_bitMap->lock());
7904 assert_lock_strong(_freelistLock);
7905 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7906 "CMS thread should hold CMS token");
7907 _bitMap->lock()->unlock();
7908 _freelistLock->unlock();
7909 ConcurrentMarkSweepThread::desynchronize(true);
7910 _collector->stopTimer();
7911 if (PrintCMSStatistics != 0) {
7912 _collector->incrementYields();
7913 }
7914
7915 // See the comment in coordinator_yield()
7916 for (unsigned i = 0; i < CMSYieldSleepCount &&
7917 ConcurrentMarkSweepThread::should_yield() &&
7918 !CMSCollector::foregroundGCIsActive(); ++i) {
7919 os::sleep(Thread::current(), 1, false);
7920 }
7921
7922 ConcurrentMarkSweepThread::synchronize(true);
7923 _freelistLock->lock();
7924 _bitMap->lock()->lock_without_safepoint_check();
7925 _collector->startTimer();
7926 }
7927
7928 #ifndef PRODUCT
7929 // This is actually very useful in a product build if it can
7930 // be called from the debugger. Compile it into the product
7931 // as needed.
7932 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7933 return debug_cms_space->verify_chunk_in_free_list(fc);
7934 }
7935 #endif
7936
7937 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7938 if (CMSTraceSweeper) {
7939 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7940 p2i(fc), fc->size());
7941 }
7942 }
7943
7944 // CMSIsAliveClosure
7945 bool CMSIsAliveClosure::do_object_b(oop obj) {
7946 HeapWord* addr = (HeapWord*)obj;
7947 return addr != NULL &&
7948 (!_span.contains(addr) || _bit_map->isMarked(addr));
7949 }
7950
7951
7952 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7953 MemRegion span,
7954 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7955 bool cpc):
7956 _collector(collector),
7957 _span(span),
7958 _bit_map(bit_map),
7959 _mark_stack(mark_stack),
7960 _concurrent_precleaning(cpc) {
7961 assert(!_span.is_empty(), "Empty span could spell trouble");
7962 }
7963
7964
7965 // CMSKeepAliveClosure: the serial version
7966 void CMSKeepAliveClosure::do_oop(oop obj) {
7967 HeapWord* addr = (HeapWord*)obj;
7968 if (_span.contains(addr) &&
7969 !_bit_map->isMarked(addr)) {
7970 _bit_map->mark(addr);
7971 bool simulate_overflow = false;
7972 NOT_PRODUCT(
7973 if (CMSMarkStackOverflowALot &&
7974 _collector->simulate_overflow()) {
7975 // simulate a stack overflow
7976 simulate_overflow = true;
7977 }
7978 )
7979 if (simulate_overflow || !_mark_stack->push(obj)) {
7980 if (_concurrent_precleaning) {
7981 // We dirty the overflown object and let the remark
7982 // phase deal with it.
7983 assert(_collector->overflow_list_is_empty(), "Error");
7984 // In the case of object arrays, we need to dirty all of
7985 // the cards that the object spans. No locking or atomics
7986 // are needed since no one else can be mutating the mod union
7987 // table.
7988 if (obj->is_objArray()) {
7989 size_t sz = obj->size();
7990 HeapWord* end_card_addr =
7991 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7992 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7993 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7994 _collector->_modUnionTable.mark_range(redirty_range);
7995 } else {
7996 _collector->_modUnionTable.mark(addr);
7997 }
7998 _collector->_ser_kac_preclean_ovflw++;
7999 } else {
8000 _collector->push_on_overflow_list(obj);
8001 _collector->_ser_kac_ovflw++;
8002 }
8003 }
8004 }
8005 }
8006
8007 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8008 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8009
8010 // CMSParKeepAliveClosure: a parallel version of the above.
8011 // The work queues are private to each closure (thread),
8012 // but (may be) available for stealing by other threads.
8013 void CMSParKeepAliveClosure::do_oop(oop obj) {
8014 HeapWord* addr = (HeapWord*)obj;
8015 if (_span.contains(addr) &&
8016 !_bit_map->isMarked(addr)) {
8017 // In general, during recursive tracing, several threads
8018 // may be concurrently getting here; the first one to
8019 // "tag" it, claims it.
8020 if (_bit_map->par_mark(addr)) {
8021 bool res = _work_queue->push(obj);
8022 assert(res, "Low water mark should be much less than capacity");
8023 // Do a recursive trim in the hope that this will keep
8024 // stack usage lower, but leave some oops for potential stealers
8025 trim_queue(_low_water_mark);
8026 } // Else, another thread got there first
8027 }
8028 }
8029
8030 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8031 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8032
8033 void CMSParKeepAliveClosure::trim_queue(uint max) {
8034 while (_work_queue->size() > max) {
8035 oop new_oop;
8036 if (_work_queue->pop_local(new_oop)) {
8037 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8038 assert(_bit_map->isMarked((HeapWord*)new_oop),
8039 "no white objects on this stack!");
8040 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8041 // iterate over the oops in this oop, marking and pushing
8042 // the ones in CMS heap (i.e. in _span).
8043 new_oop->oop_iterate(&_mark_and_push);
8044 }
8045 }
8046 }
8047
8048 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8049 CMSCollector* collector,
8050 MemRegion span, CMSBitMap* bit_map,
8051 OopTaskQueue* work_queue):
8052 _collector(collector),
8053 _span(span),
8054 _bit_map(bit_map),
8055 _work_queue(work_queue) { }
8056
8057 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8058 HeapWord* addr = (HeapWord*)obj;
8059 if (_span.contains(addr) &&
8060 !_bit_map->isMarked(addr)) {
8061 if (_bit_map->par_mark(addr)) {
8062 bool simulate_overflow = false;
8063 NOT_PRODUCT(
8064 if (CMSMarkStackOverflowALot &&
8065 _collector->par_simulate_overflow()) {
8066 // simulate a stack overflow
8067 simulate_overflow = true;
8068 }
8069 )
8070 if (simulate_overflow || !_work_queue->push(obj)) {
8071 _collector->par_push_on_overflow_list(obj);
8072 _collector->_par_kac_ovflw++;
8073 }
8074 } // Else another thread got there already
8075 }
8076 }
8077
8078 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8079 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8080
8081 //////////////////////////////////////////////////////////////////
8082 // CMSExpansionCause /////////////////////////////
8083 //////////////////////////////////////////////////////////////////
8084 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8085 switch (cause) {
8086 case _no_expansion:
8087 return "No expansion";
8088 case _satisfy_free_ratio:
8089 return "Free ratio";
8090 case _satisfy_promotion:
8091 return "Satisfy promotion";
8092 case _satisfy_allocation:
8093 return "allocation";
8094 case _allocate_par_lab:
8095 return "Par LAB";
8096 case _allocate_par_spooling_space:
8097 return "Par Spooling Space";
8098 case _adaptive_size_policy:
8099 return "Ergonomics";
8100 default:
8101 return "unknown";
8102 }
8103 }
8104
8105 void CMSDrainMarkingStackClosure::do_void() {
8106 // the max number to take from overflow list at a time
8107 const size_t num = _mark_stack->capacity()/4;
8108 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8109 "Overflow list should be NULL during concurrent phases");
8110 while (!_mark_stack->isEmpty() ||
8111 // if stack is empty, check the overflow list
8112 _collector->take_from_overflow_list(num, _mark_stack)) {
8113 oop obj = _mark_stack->pop();
8114 HeapWord* addr = (HeapWord*)obj;
8115 assert(_span.contains(addr), "Should be within span");
8116 assert(_bit_map->isMarked(addr), "Should be marked");
8117 assert(obj->is_oop(), "Should be an oop");
8118 obj->oop_iterate(_keep_alive);
8119 }
8120 }
8121
8122 void CMSParDrainMarkingStackClosure::do_void() {
8123 // drain queue
8124 trim_queue(0);
8125 }
8126
8127 // Trim our work_queue so its length is below max at return
8128 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8129 while (_work_queue->size() > max) {
8130 oop new_oop;
8131 if (_work_queue->pop_local(new_oop)) {
8132 assert(new_oop->is_oop(), "Expected an oop");
8133 assert(_bit_map->isMarked((HeapWord*)new_oop),
8134 "no white objects on this stack!");
8135 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8136 // iterate over the oops in this oop, marking and pushing
8137 // the ones in CMS heap (i.e. in _span).
8138 new_oop->oop_iterate(&_mark_and_push);
8139 }
8140 }
8141 }
8142
8143 ////////////////////////////////////////////////////////////////////
8144 // Support for Marking Stack Overflow list handling and related code
8145 ////////////////////////////////////////////////////////////////////
8146 // Much of the following code is similar in shape and spirit to the
8147 // code used in ParNewGC. We should try and share that code
8148 // as much as possible in the future.
8149
8150 #ifndef PRODUCT
8151 // Debugging support for CMSStackOverflowALot
8152
8153 // It's OK to call this multi-threaded; the worst thing
8154 // that can happen is that we'll get a bunch of closely
8155 // spaced simulated overflows, but that's OK, in fact
8156 // probably good as it would exercise the overflow code
8157 // under contention.
8158 bool CMSCollector::simulate_overflow() {
8159 if (_overflow_counter-- <= 0) { // just being defensive
8160 _overflow_counter = CMSMarkStackOverflowInterval;
8161 return true;
8162 } else {
8163 return false;
8164 }
8165 }
8166
8167 bool CMSCollector::par_simulate_overflow() {
8168 return simulate_overflow();
8169 }
8170 #endif
8171
8172 // Single-threaded
8173 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8174 assert(stack->isEmpty(), "Expected precondition");
8175 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8176 size_t i = num;
8177 oop cur = _overflow_list;
8178 const markOop proto = markOopDesc::prototype();
8179 NOT_PRODUCT(ssize_t n = 0;)
8180 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8181 next = oop(cur->mark());
8182 cur->set_mark(proto); // until proven otherwise
8183 assert(cur->is_oop(), "Should be an oop");
8184 bool res = stack->push(cur);
8185 assert(res, "Bit off more than can chew?");
8186 NOT_PRODUCT(n++;)
8187 }
8188 _overflow_list = cur;
8189 #ifndef PRODUCT
8190 assert(_num_par_pushes >= n, "Too many pops?");
8191 _num_par_pushes -=n;
8192 #endif
8193 return !stack->isEmpty();
8194 }
8195
8196 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
8197 // (MT-safe) Get a prefix of at most "num" from the list.
8198 // The overflow list is chained through the mark word of
8199 // each object in the list. We fetch the entire list,
8200 // break off a prefix of the right size and return the
8201 // remainder. If other threads try to take objects from
8202 // the overflow list at that time, they will wait for
8203 // some time to see if data becomes available. If (and
8204 // only if) another thread places one or more object(s)
8205 // on the global list before we have returned the suffix
8206 // to the global list, we will walk down our local list
8207 // to find its end and append the global list to
8208 // our suffix before returning it. This suffix walk can
8209 // prove to be expensive (quadratic in the amount of traffic)
8210 // when there are many objects in the overflow list and
8211 // there is much producer-consumer contention on the list.
8212 // *NOTE*: The overflow list manipulation code here and
8213 // in ParNewGeneration:: are very similar in shape,
8214 // except that in the ParNew case we use the old (from/eden)
8215 // copy of the object to thread the list via its klass word.
8216 // Because of the common code, if you make any changes in
8217 // the code below, please check the ParNew version to see if
8218 // similar changes might be needed.
8219 // CR 6797058 has been filed to consolidate the common code.
8220 bool CMSCollector::par_take_from_overflow_list(size_t num,
8221 OopTaskQueue* work_q,
8222 int no_of_gc_threads) {
8223 assert(work_q->size() == 0, "First empty local work queue");
8224 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8225 if (_overflow_list == NULL) {
8226 return false;
8227 }
8228 // Grab the entire list; we'll put back a suffix
8229 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8230 Thread* tid = Thread::current();
8231 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8232 // set to ParallelGCThreads.
8233 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8234 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8235 // If the list is busy, we spin for a short while,
8236 // sleeping between attempts to get the list.
8237 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8238 os::sleep(tid, sleep_time_millis, false);
8239 if (_overflow_list == NULL) {
8240 // Nothing left to take
8241 return false;
8242 } else if (_overflow_list != BUSY) {
8243 // Try and grab the prefix
8244 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
8245 }
8246 }
8247 // If the list was found to be empty, or we spun long
8248 // enough, we give up and return empty-handed. If we leave
8249 // the list in the BUSY state below, it must be the case that
8250 // some other thread holds the overflow list and will set it
8251 // to a non-BUSY state in the future.
8252 if (prefix == NULL || prefix == BUSY) {
8253 // Nothing to take or waited long enough
8254 if (prefix == NULL) {
8255 // Write back the NULL in case we overwrote it with BUSY above
8256 // and it is still the same value.
8257 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8258 }
8259 return false;
8260 }
8261 assert(prefix != NULL && prefix != BUSY, "Error");
8262 size_t i = num;
8263 oop cur = prefix;
8264 // Walk down the first "num" objects, unless we reach the end.
8265 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8266 if (cur->mark() == NULL) {
8267 // We have "num" or fewer elements in the list, so there
8268 // is nothing to return to the global list.
8269 // Write back the NULL in lieu of the BUSY we wrote
8270 // above, if it is still the same value.
8271 if (_overflow_list == BUSY) {
8272 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8273 }
8274 } else {
8275 // Chop off the suffix and return it to the global list.
8276 assert(cur->mark() != BUSY, "Error");
8277 oop suffix_head = cur->mark(); // suffix will be put back on global list
8278 cur->set_mark(NULL); // break off suffix
8279 // It's possible that the list is still in the empty(busy) state
8280 // we left it in a short while ago; in that case we may be
8281 // able to place back the suffix without incurring the cost
8282 // of a walk down the list.
8283 oop observed_overflow_list = _overflow_list;
8284 oop cur_overflow_list = observed_overflow_list;
8285 bool attached = false;
8286 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8287 observed_overflow_list =
8288 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8289 if (cur_overflow_list == observed_overflow_list) {
8290 attached = true;
8291 break;
8292 } else cur_overflow_list = observed_overflow_list;
8293 }
8294 if (!attached) {
8295 // Too bad, someone else sneaked in (at least) an element; we'll need
8296 // to do a splice. Find tail of suffix so we can prepend suffix to global
8297 // list.
8298 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8299 oop suffix_tail = cur;
8300 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8301 "Tautology");
8302 observed_overflow_list = _overflow_list;
8303 do {
8304 cur_overflow_list = observed_overflow_list;
8305 if (cur_overflow_list != BUSY) {
8306 // Do the splice ...
8307 suffix_tail->set_mark(markOop(cur_overflow_list));
8308 } else { // cur_overflow_list == BUSY
8309 suffix_tail->set_mark(NULL);
8310 }
8311 // ... and try to place spliced list back on overflow_list ...
8312 observed_overflow_list =
8313 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8314 } while (cur_overflow_list != observed_overflow_list);
8315 // ... until we have succeeded in doing so.
8316 }
8317 }
8318
8319 // Push the prefix elements on work_q
8320 assert(prefix != NULL, "control point invariant");
8321 const markOop proto = markOopDesc::prototype();
8322 oop next;
8323 NOT_PRODUCT(ssize_t n = 0;)
8324 for (cur = prefix; cur != NULL; cur = next) {
8325 next = oop(cur->mark());
8326 cur->set_mark(proto); // until proven otherwise
8327 assert(cur->is_oop(), "Should be an oop");
8328 bool res = work_q->push(cur);
8329 assert(res, "Bit off more than we can chew?");
8330 NOT_PRODUCT(n++;)
8331 }
8332 #ifndef PRODUCT
8333 assert(_num_par_pushes >= n, "Too many pops?");
8334 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8335 #endif
8336 return true;
8337 }
8338
8339 // Single-threaded
8340 void CMSCollector::push_on_overflow_list(oop p) {
8341 NOT_PRODUCT(_num_par_pushes++;)
8342 assert(p->is_oop(), "Not an oop");
8343 preserve_mark_if_necessary(p);
8344 p->set_mark((markOop)_overflow_list);
8345 _overflow_list = p;
8346 }
8347
8348 // Multi-threaded; use CAS to prepend to overflow list
8349 void CMSCollector::par_push_on_overflow_list(oop p) {
8350 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8351 assert(p->is_oop(), "Not an oop");
8352 par_preserve_mark_if_necessary(p);
8353 oop observed_overflow_list = _overflow_list;
8354 oop cur_overflow_list;
8355 do {
8356 cur_overflow_list = observed_overflow_list;
8357 if (cur_overflow_list != BUSY) {
8358 p->set_mark(markOop(cur_overflow_list));
8359 } else {
8360 p->set_mark(NULL);
8361 }
8362 observed_overflow_list =
8363 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8364 } while (cur_overflow_list != observed_overflow_list);
8365 }
8366 #undef BUSY
8367
8368 // Single threaded
8369 // General Note on GrowableArray: pushes may silently fail
8370 // because we are (temporarily) out of C-heap for expanding
8371 // the stack. The problem is quite ubiquitous and affects
8372 // a lot of code in the JVM. The prudent thing for GrowableArray
8373 // to do (for now) is to exit with an error. However, that may
8374 // be too draconian in some cases because the caller may be
8375 // able to recover without much harm. For such cases, we
8376 // should probably introduce a "soft_push" method which returns
8377 // an indication of success or failure with the assumption that
8378 // the caller may be able to recover from a failure; code in
8379 // the VM can then be changed, incrementally, to deal with such
8380 // failures where possible, thus, incrementally hardening the VM
8381 // in such low resource situations.
8382 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8383 _preserved_oop_stack.push(p);
8384 _preserved_mark_stack.push(m);
8385 assert(m == p->mark(), "Mark word changed");
8386 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8387 "bijection");
8388 }
8389
8390 // Single threaded
8391 void CMSCollector::preserve_mark_if_necessary(oop p) {
8392 markOop m = p->mark();
8393 if (m->must_be_preserved(p)) {
8394 preserve_mark_work(p, m);
8395 }
8396 }
8397
8398 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8399 markOop m = p->mark();
8400 if (m->must_be_preserved(p)) {
8401 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8402 // Even though we read the mark word without holding
8403 // the lock, we are assured that it will not change
8404 // because we "own" this oop, so no other thread can
8405 // be trying to push it on the overflow list; see
8406 // the assertion in preserve_mark_work() that checks
8407 // that m == p->mark().
8408 preserve_mark_work(p, m);
8409 }
8410 }
8411
8412 // We should be able to do this multi-threaded,
8413 // a chunk of stack being a task (this is
8414 // correct because each oop only ever appears
8415 // once in the overflow list. However, it's
8416 // not very easy to completely overlap this with
8417 // other operations, so will generally not be done
8418 // until all work's been completed. Because we
8419 // expect the preserved oop stack (set) to be small,
8420 // it's probably fine to do this single-threaded.
8421 // We can explore cleverer concurrent/overlapped/parallel
8422 // processing of preserved marks if we feel the
8423 // need for this in the future. Stack overflow should
8424 // be so rare in practice and, when it happens, its
8425 // effect on performance so great that this will
8426 // likely just be in the noise anyway.
8427 void CMSCollector::restore_preserved_marks_if_any() {
8428 assert(SafepointSynchronize::is_at_safepoint(),
8429 "world should be stopped");
8430 assert(Thread::current()->is_ConcurrentGC_thread() ||
8431 Thread::current()->is_VM_thread(),
8432 "should be single-threaded");
8433 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8434 "bijection");
8435
8436 while (!_preserved_oop_stack.is_empty()) {
8437 oop p = _preserved_oop_stack.pop();
8438 assert(p->is_oop(), "Should be an oop");
8439 assert(_span.contains(p), "oop should be in _span");
8440 assert(p->mark() == markOopDesc::prototype(),
8441 "Set when taken from overflow list");
8442 markOop m = _preserved_mark_stack.pop();
8443 p->set_mark(m);
8444 }
8445 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8446 "stacks were cleared above");
8447 }
8448
8449 #ifndef PRODUCT
8450 bool CMSCollector::no_preserved_marks() const {
8451 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8452 }
8453 #endif
8454
8455 // Transfer some number of overflown objects to usual marking
8456 // stack. Return true if some objects were transferred.
8457 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8458 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8459 (size_t)ParGCDesiredObjsFromOverflowList);
8460
8461 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8462 assert(_collector->overflow_list_is_empty() || res,
8463 "If list is not empty, we should have taken something");
8464 assert(!res || !_mark_stack->isEmpty(),
8465 "If we took something, it should now be on our stack");
8466 return res;
8467 }
8468
8469 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8470 size_t res = _sp->block_size_no_stall(addr, _collector);
8471 if (_sp->block_is_obj(addr)) {
8472 if (_live_bit_map->isMarked(addr)) {
8473 // It can't have been dead in a previous cycle
8474 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8475 } else {
8476 _dead_bit_map->mark(addr); // mark the dead object
8477 }
8478 }
8479 // Could be 0, if the block size could not be computed without stalling.
8480 return res;
8481 }
8482
8483 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8484
8485 switch (phase) {
8486 case CMSCollector::InitialMarking:
8487 initialize(true /* fullGC */ ,
8488 cause /* cause of the GC */,
8489 true /* recordGCBeginTime */,
8490 true /* recordPreGCUsage */,
8491 false /* recordPeakUsage */,
8492 false /* recordPostGCusage */,
8493 true /* recordAccumulatedGCTime */,
8494 false /* recordGCEndTime */,
8495 false /* countCollection */ );
8496 break;
8497
8498 case CMSCollector::FinalMarking:
8499 initialize(true /* fullGC */ ,
8500 cause /* cause of the GC */,
8501 false /* recordGCBeginTime */,
8502 false /* recordPreGCUsage */,
8503 false /* recordPeakUsage */,
8504 false /* recordPostGCusage */,
8505 true /* recordAccumulatedGCTime */,
8506 false /* recordGCEndTime */,
8507 false /* countCollection */ );
8508 break;
8509
8510 case CMSCollector::Sweeping:
8511 initialize(true /* fullGC */ ,
8512 cause /* cause of the GC */,
8513 false /* recordGCBeginTime */,
8514 false /* recordPreGCUsage */,
8515 true /* recordPeakUsage */,
8516 true /* recordPostGCusage */,
8517 false /* recordAccumulatedGCTime */,
8518 true /* recordGCEndTime */,
8519 true /* countCollection */ );
8520 break;
8521
8522 default:
8523 ShouldNotReachHere();
8524 }
8525 }