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