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