1 /*
2 * Copyright (c) 2001, 2018, 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/cmsHeap.hpp"
33 #include "gc/cms/cmsOopClosures.inline.hpp"
34 #include "gc/cms/compactibleFreeListSpace.hpp"
35 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc/cms/concurrentMarkSweepThread.hpp"
37 #include "gc/cms/parNewGeneration.hpp"
38 #include "gc/cms/vmCMSOperations.hpp"
39 #include "gc/serial/genMarkSweep.hpp"
40 #include "gc/serial/tenuredGeneration.hpp"
41 #include "gc/shared/adaptiveSizePolicy.hpp"
42 #include "gc/shared/cardGeneration.inline.hpp"
43 #include "gc/shared/cardTableRS.hpp"
44 #include "gc/shared/collectedHeap.inline.hpp"
45 #include "gc/shared/collectorCounters.hpp"
46 #include "gc/shared/collectorPolicy.hpp"
47 #include "gc/shared/gcLocker.inline.hpp"
48 #include "gc/shared/gcPolicyCounters.hpp"
49 #include "gc/shared/gcTimer.hpp"
50 #include "gc/shared/gcTrace.hpp"
51 #include "gc/shared/gcTraceTime.inline.hpp"
52 #include "gc/shared/genCollectedHeap.hpp"
53 #include "gc/shared/genOopClosures.inline.hpp"
54 #include "gc/shared/isGCActiveMark.hpp"
55 #include "gc/shared/referencePolicy.hpp"
56 #include "gc/shared/strongRootsScope.hpp"
57 #include "gc/shared/taskqueue.inline.hpp"
58 #include "gc/shared/weakProcessor.hpp"
59 #include "logging/log.hpp"
60 #include "logging/logStream.hpp"
61 #include "memory/allocation.hpp"
62 #include "memory/iterator.inline.hpp"
63 #include "memory/padded.hpp"
64 #include "memory/resourceArea.hpp"
65 #include "oops/oop.inline.hpp"
66 #include "prims/jvmtiExport.hpp"
67 #include "runtime/atomic.hpp"
68 #include "runtime/globals_extension.hpp"
69 #include "runtime/handles.inline.hpp"
70 #include "runtime/java.hpp"
71 #include "runtime/orderAccess.inline.hpp"
72 #include "runtime/timer.hpp"
73 #include "runtime/vmThread.hpp"
74 #include "services/memoryService.hpp"
75 #include "services/runtimeService.hpp"
76 #include "utilities/align.hpp"
77 #include "utilities/stack.inline.hpp"
78
79 // statics
80 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
81 bool CMSCollector::_full_gc_requested = false;
82 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
83
84 //////////////////////////////////////////////////////////////////
85 // In support of CMS/VM thread synchronization
86 //////////////////////////////////////////////////////////////////
87 // We split use of the CGC_lock into 2 "levels".
88 // The low-level locking is of the usual CGC_lock monitor. We introduce
89 // a higher level "token" (hereafter "CMS token") built on top of the
90 // low level monitor (hereafter "CGC lock").
91 // The token-passing protocol gives priority to the VM thread. The
92 // CMS-lock doesn't provide any fairness guarantees, but clients
93 // should ensure that it is only held for very short, bounded
94 // durations.
95 //
96 // When either of the CMS thread or the VM thread is involved in
97 // collection operations during which it does not want the other
98 // thread to interfere, it obtains the CMS token.
99 //
100 // If either thread tries to get the token while the other has
101 // it, that thread waits. However, if the VM thread and CMS thread
102 // both want the token, then the VM thread gets priority while the
103 // CMS thread waits. This ensures, for instance, that the "concurrent"
104 // phases of the CMS thread's work do not block out the VM thread
105 // for long periods of time as the CMS thread continues to hog
106 // the token. (See bug 4616232).
107 //
108 // The baton-passing functions are, however, controlled by the
109 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
110 // and here the low-level CMS lock, not the high level token,
111 // ensures mutual exclusion.
112 //
113 // Two important conditions that we have to satisfy:
114 // 1. if a thread does a low-level wait on the CMS lock, then it
115 // relinquishes the CMS token if it were holding that token
116 // when it acquired the low-level CMS lock.
117 // 2. any low-level notifications on the low-level lock
118 // should only be sent when a thread has relinquished the token.
119 //
120 // In the absence of either property, we'd have potential deadlock.
121 //
122 // We protect each of the CMS (concurrent and sequential) phases
123 // with the CMS _token_, not the CMS _lock_.
124 //
125 // The only code protected by CMS lock is the token acquisition code
126 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
127 // baton-passing code.
128 //
129 // Unfortunately, i couldn't come up with a good abstraction to factor and
130 // hide the naked CGC_lock manipulation in the baton-passing code
131 // further below. That's something we should try to do. Also, the proof
132 // of correctness of this 2-level locking scheme is far from obvious,
133 // and potentially quite slippery. We have an uneasy suspicion, for instance,
134 // that there may be a theoretical possibility of delay/starvation in the
135 // low-level lock/wait/notify scheme used for the baton-passing because of
136 // potential interference with the priority scheme embodied in the
137 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
138 // invocation further below and marked with "XXX 20011219YSR".
139 // Indeed, as we note elsewhere, this may become yet more slippery
140 // in the presence of multiple CMS and/or multiple VM threads. XXX
141
142 class CMSTokenSync: public StackObj {
143 private:
144 bool _is_cms_thread;
145 public:
146 CMSTokenSync(bool is_cms_thread):
147 _is_cms_thread(is_cms_thread) {
148 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
149 "Incorrect argument to constructor");
150 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
151 }
152
153 ~CMSTokenSync() {
154 assert(_is_cms_thread ?
155 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
156 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
157 "Incorrect state");
158 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
159 }
160 };
161
162 // Convenience class that does a CMSTokenSync, and then acquires
163 // upto three locks.
164 class CMSTokenSyncWithLocks: public CMSTokenSync {
165 private:
166 // Note: locks are acquired in textual declaration order
167 // and released in the opposite order
168 MutexLockerEx _locker1, _locker2, _locker3;
169 public:
170 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
171 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
172 CMSTokenSync(is_cms_thread),
173 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
174 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
175 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
176 { }
177 };
178
179
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
183
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
185
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CompactibleFreeListSpaceLAB lab;
191 PromotionInfo promo;
192
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
198
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
201 CardGeneration(rs, initial_byte_size, ct),
202 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
203 _did_compact(false)
204 {
205 HeapWord* bottom = (HeapWord*) _virtual_space.low();
206 HeapWord* end = (HeapWord*) _virtual_space.high();
207
208 _direct_allocated_words = 0;
209 NOT_PRODUCT(
210 _numObjectsPromoted = 0;
211 _numWordsPromoted = 0;
212 _numObjectsAllocated = 0;
213 _numWordsAllocated = 0;
214 )
215
216 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
217 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
218 _cmsSpace->_old_gen = this;
219
220 _gc_stats = new CMSGCStats();
221
222 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
223 // offsets match. The ability to tell free chunks from objects
224 // depends on this property.
225 debug_only(
226 FreeChunk* junk = NULL;
227 assert(UseCompressedClassPointers ||
228 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
229 "Offset of FreeChunk::_prev within FreeChunk must match"
230 " that of OopDesc::_klass within OopDesc");
231 )
232
233 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
234 for (uint i = 0; i < ParallelGCThreads; i++) {
235 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
236 }
237
238 _incremental_collection_failed = false;
239 // The "dilatation_factor" is the expansion that can occur on
240 // account of the fact that the minimum object size in the CMS
241 // generation may be larger than that in, say, a contiguous young
242 // generation.
243 // Ideally, in the calculation below, we'd compute the dilatation
244 // factor as: MinChunkSize/(promoting_gen's min object size)
245 // Since we do not have such a general query interface for the
246 // promoting generation, we'll instead just use the minimum
247 // object size (which today is a header's worth of space);
248 // note that all arithmetic is in units of HeapWords.
249 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
250 assert(_dilatation_factor >= 1.0, "from previous assert");
251 }
252
253
254 // The field "_initiating_occupancy" represents the occupancy percentage
255 // at which we trigger a new collection cycle. Unless explicitly specified
256 // via CMSInitiatingOccupancyFraction (argument "io" below), it
257 // is calculated by:
258 //
259 // Let "f" be MinHeapFreeRatio in
260 //
261 // _initiating_occupancy = 100-f +
262 // f * (CMSTriggerRatio/100)
263 // where CMSTriggerRatio is the argument "tr" below.
264 //
265 // That is, if we assume the heap is at its desired maximum occupancy at the
266 // end of a collection, we let CMSTriggerRatio of the (purported) free
267 // space be allocated before initiating a new collection cycle.
268 //
269 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
270 assert(io <= 100 && tr <= 100, "Check the arguments");
271 if (io >= 0) {
272 _initiating_occupancy = (double)io / 100.0;
273 } else {
274 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
275 (double)(tr * MinHeapFreeRatio) / 100.0)
276 / 100.0;
277 }
278 }
279
280 void ConcurrentMarkSweepGeneration::ref_processor_init() {
281 assert(collector() != NULL, "no collector");
282 collector()->ref_processor_init();
283 }
284
285 void CMSCollector::ref_processor_init() {
286 if (_ref_processor == NULL) {
287 // Allocate and initialize a reference processor
288 _ref_processor =
289 new ReferenceProcessor(_span, // span
290 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
291 ParallelGCThreads, // mt processing degree
292 _cmsGen->refs_discovery_is_mt(), // mt discovery
293 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
294 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
295 &_is_alive_closure); // closure for liveness info
296 // Initialize the _ref_processor field of CMSGen
297 _cmsGen->set_ref_processor(_ref_processor);
298
299 }
300 }
301
302 AdaptiveSizePolicy* CMSCollector::size_policy() {
303 return CMSHeap::heap()->size_policy();
304 }
305
306 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
307
308 const char* gen_name = "old";
309 GenCollectorPolicy* gcp = CMSHeap::heap()->gen_policy();
310 // Generation Counters - generation 1, 1 subspace
311 _gen_counters = new GenerationCounters(gen_name, 1, 1,
312 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
313
314 _space_counters = new GSpaceCounters(gen_name, 0,
315 _virtual_space.reserved_size(),
316 this, _gen_counters);
317 }
318
319 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
320 _cms_gen(cms_gen)
321 {
322 assert(alpha <= 100, "bad value");
323 _saved_alpha = alpha;
324
325 // Initialize the alphas to the bootstrap value of 100.
326 _gc0_alpha = _cms_alpha = 100;
327
328 _cms_begin_time.update();
329 _cms_end_time.update();
330
331 _gc0_duration = 0.0;
332 _gc0_period = 0.0;
333 _gc0_promoted = 0;
334
335 _cms_duration = 0.0;
336 _cms_period = 0.0;
337 _cms_allocated = 0;
338
339 _cms_used_at_gc0_begin = 0;
340 _cms_used_at_gc0_end = 0;
341 _allow_duty_cycle_reduction = false;
342 _valid_bits = 0;
343 }
344
345 double CMSStats::cms_free_adjustment_factor(size_t free) const {
346 // TBD: CR 6909490
347 return 1.0;
348 }
349
350 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
351 }
352
353 // If promotion failure handling is on use
354 // the padded average size of the promotion for each
355 // young generation collection.
356 double CMSStats::time_until_cms_gen_full() const {
357 size_t cms_free = _cms_gen->cmsSpace()->free();
358 CMSHeap* heap = CMSHeap::heap();
359 size_t expected_promotion = MIN2(heap->young_gen()->capacity(),
360 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
361 if (cms_free > expected_promotion) {
362 // Start a cms collection if there isn't enough space to promote
363 // for the next young collection. Use the padded average as
364 // a safety factor.
365 cms_free -= expected_promotion;
366
367 // Adjust by the safety factor.
368 double cms_free_dbl = (double)cms_free;
369 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
370 // Apply a further correction factor which tries to adjust
371 // for recent occurance of concurrent mode failures.
372 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
373 cms_free_dbl = cms_free_dbl * cms_adjustment;
374
375 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
376 cms_free, expected_promotion);
377 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
378 // Add 1 in case the consumption rate goes to zero.
379 return cms_free_dbl / (cms_consumption_rate() + 1.0);
380 }
381 return 0.0;
382 }
383
384 // Compare the duration of the cms collection to the
385 // time remaining before the cms generation is empty.
386 // Note that the time from the start of the cms collection
387 // to the start of the cms sweep (less than the total
388 // duration of the cms collection) can be used. This
389 // has been tried and some applications experienced
390 // promotion failures early in execution. This was
391 // possibly because the averages were not accurate
392 // enough at the beginning.
393 double CMSStats::time_until_cms_start() const {
394 // We add "gc0_period" to the "work" calculation
395 // below because this query is done (mostly) at the
396 // end of a scavenge, so we need to conservatively
397 // account for that much possible delay
398 // in the query so as to avoid concurrent mode failures
399 // due to starting the collection just a wee bit too
400 // late.
401 double work = cms_duration() + gc0_period();
402 double deadline = time_until_cms_gen_full();
403 // If a concurrent mode failure occurred recently, we want to be
404 // more conservative and halve our expected time_until_cms_gen_full()
405 if (work > deadline) {
406 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
407 cms_duration(), gc0_period(), time_until_cms_gen_full());
408 return 0.0;
409 }
410 return work - deadline;
411 }
412
413 #ifndef PRODUCT
414 void CMSStats::print_on(outputStream *st) const {
415 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
416 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
417 gc0_duration(), gc0_period(), gc0_promoted());
418 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
419 cms_duration(), cms_period(), cms_allocated());
420 st->print(",cms_since_beg=%g,cms_since_end=%g",
421 cms_time_since_begin(), cms_time_since_end());
422 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
423 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
424
425 if (valid()) {
426 st->print(",promo_rate=%g,cms_alloc_rate=%g",
427 promotion_rate(), cms_allocation_rate());
428 st->print(",cms_consumption_rate=%g,time_until_full=%g",
429 cms_consumption_rate(), time_until_cms_gen_full());
430 }
431 st->cr();
432 }
433 #endif // #ifndef PRODUCT
434
435 CMSCollector::CollectorState CMSCollector::_collectorState =
436 CMSCollector::Idling;
437 bool CMSCollector::_foregroundGCIsActive = false;
438 bool CMSCollector::_foregroundGCShouldWait = false;
439
440 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
441 CardTableRS* ct,
442 ConcurrentMarkSweepPolicy* cp):
443 _cmsGen(cmsGen),
444 _ct(ct),
445 _ref_processor(NULL), // will be set later
446 _conc_workers(NULL), // may be set later
447 _abort_preclean(false),
448 _start_sampling(false),
449 _between_prologue_and_epilogue(false),
450 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
451 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
452 -1 /* lock-free */, "No_lock" /* dummy */),
453 _modUnionClosurePar(&_modUnionTable),
454 // Adjust my span to cover old (cms) gen
455 _span(cmsGen->reserved()),
456 // Construct the is_alive_closure with _span & markBitMap
457 _is_alive_closure(_span, &_markBitMap),
458 _restart_addr(NULL),
459 _overflow_list(NULL),
460 _stats(cmsGen),
461 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
462 //verify that this lock should be acquired with safepoint check.
463 Monitor::_safepoint_check_sometimes)),
464 _eden_chunk_array(NULL), // may be set in ctor body
465 _eden_chunk_capacity(0), // -- ditto --
466 _eden_chunk_index(0), // -- ditto --
467 _survivor_plab_array(NULL), // -- ditto --
468 _survivor_chunk_array(NULL), // -- ditto --
469 _survivor_chunk_capacity(0), // -- ditto --
470 _survivor_chunk_index(0), // -- ditto --
471 _ser_pmc_preclean_ovflw(0),
472 _ser_kac_preclean_ovflw(0),
473 _ser_pmc_remark_ovflw(0),
474 _par_pmc_remark_ovflw(0),
475 _ser_kac_ovflw(0),
476 _par_kac_ovflw(0),
477 #ifndef PRODUCT
478 _num_par_pushes(0),
479 #endif
480 _collection_count_start(0),
481 _verifying(false),
482 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
483 _completed_initialization(false),
484 _collector_policy(cp),
485 _should_unload_classes(CMSClassUnloadingEnabled),
486 _concurrent_cycles_since_last_unload(0),
487 _roots_scanning_options(GenCollectedHeap::SO_None),
488 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
489 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
490 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
491 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
492 _cms_start_registered(false)
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 log_debug(gc)("ConcGCThreads: %u", ConcGCThreads);
549 log_debug(gc)("ParallelGCThreads: %u", ParallelGCThreads);
550
551 // Parallel task queues; these are shared for the
552 // concurrent and stop-world phases of CMS, but
553 // are not shared with parallel scavenge (ParNew).
554 {
555 uint i;
556 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
557
558 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
559 || ParallelRefProcEnabled)
560 && num_queues > 0) {
561 _task_queues = new OopTaskQueueSet(num_queues);
562 if (_task_queues == NULL) {
563 log_warning(gc)("task_queues allocation failure.");
564 return;
565 }
566 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
567 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
568 for (i = 0; i < num_queues; i++) {
569 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
570 if (q == NULL) {
571 log_warning(gc)("work_queue allocation failure.");
572 return;
573 }
574 _task_queues->register_queue(i, q);
575 }
576 for (i = 0; i < num_queues; i++) {
577 _task_queues->queue(i)->initialize();
578 _hash_seed[i] = 17; // copied from ParNew
579 }
580 }
581 }
582
583 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
584
585 // Clip CMSBootstrapOccupancy between 0 and 100.
586 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
587
588 // Now tell CMS generations the identity of their collector
589 ConcurrentMarkSweepGeneration::set_collector(this);
590
591 // Create & start a CMS thread for this CMS collector
592 _cmsThread = ConcurrentMarkSweepThread::start(this);
593 assert(cmsThread() != NULL, "CMS Thread should have been created");
594 assert(cmsThread()->collector() == this,
595 "CMS Thread should refer to this gen");
596 assert(CGC_lock != NULL, "Where's the CGC_lock?");
597
598 // Support for parallelizing young gen rescan
599 CMSHeap* heap = CMSHeap::heap();
600 assert(heap->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
601 _young_gen = (ParNewGeneration*)heap->young_gen();
602 if (heap->supports_inline_contig_alloc()) {
603 _top_addr = heap->top_addr();
604 _end_addr = heap->end_addr();
605 assert(_young_gen != NULL, "no _young_gen");
606 _eden_chunk_index = 0;
607 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
608 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
609 }
610
611 // Support for parallelizing survivor space rescan
612 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
613 const size_t max_plab_samples =
614 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
615
616 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
617 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
618 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
619 _survivor_chunk_capacity = max_plab_samples;
620 for (uint i = 0; i < ParallelGCThreads; i++) {
621 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
622 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
623 assert(cur->end() == 0, "Should be 0");
624 assert(cur->array() == vec, "Should be vec");
625 assert(cur->capacity() == max_plab_samples, "Error");
626 }
627 }
628
629 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
630 _gc_counters = new CollectorCounters("CMS", 1);
631 _completed_initialization = true;
632 _inter_sweep_timer.start(); // start of time
633 }
634
635 const char* ConcurrentMarkSweepGeneration::name() const {
636 return "concurrent mark-sweep generation";
637 }
638 void ConcurrentMarkSweepGeneration::update_counters() {
639 if (UsePerfData) {
640 _space_counters->update_all();
641 _gen_counters->update_all();
642 }
643 }
644
645 // this is an optimized version of update_counters(). it takes the
646 // used value as a parameter rather than computing it.
647 //
648 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
649 if (UsePerfData) {
650 _space_counters->update_used(used);
651 _space_counters->update_capacity();
652 _gen_counters->update_all();
653 }
654 }
655
656 void ConcurrentMarkSweepGeneration::print() const {
657 Generation::print();
658 cmsSpace()->print();
659 }
660
661 #ifndef PRODUCT
662 void ConcurrentMarkSweepGeneration::print_statistics() {
663 cmsSpace()->printFLCensus(0);
664 }
665 #endif
666
667 size_t
668 ConcurrentMarkSweepGeneration::contiguous_available() const {
669 // dld proposes an improvement in precision here. If the committed
670 // part of the space ends in a free block we should add that to
671 // uncommitted size in the calculation below. Will make this
672 // change later, staying with the approximation below for the
673 // time being. -- ysr.
674 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
675 }
676
677 size_t
678 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
679 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
680 }
681
682 size_t ConcurrentMarkSweepGeneration::max_available() const {
683 return free() + _virtual_space.uncommitted_size();
684 }
685
686 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
687 size_t available = max_available();
688 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
689 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
690 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
691 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
692 return res;
693 }
694
695 // At a promotion failure dump information on block layout in heap
696 // (cms old generation).
697 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
698 Log(gc, promotion) log;
699 if (log.is_trace()) {
700 LogStream ls(log.trace());
701 cmsSpace()->dump_at_safepoint_with_locks(collector(), &ls);
702 }
703 }
704
705 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
706 // Clear the promotion information. These pointers can be adjusted
707 // along with all the other pointers into the heap but
708 // compaction is expected to be a rare event with
709 // a heap using cms so don't do it without seeing the need.
710 for (uint i = 0; i < ParallelGCThreads; i++) {
711 _par_gc_thread_states[i]->promo.reset();
712 }
713 }
714
715 void ConcurrentMarkSweepGeneration::compute_new_size() {
716 assert_locked_or_safepoint(Heap_lock);
717
718 // If incremental collection failed, we just want to expand
719 // to the limit.
720 if (incremental_collection_failed()) {
721 clear_incremental_collection_failed();
722 grow_to_reserved();
723 return;
724 }
725
726 // The heap has been compacted but not reset yet.
727 // Any metric such as free() or used() will be incorrect.
728
729 CardGeneration::compute_new_size();
730
731 // Reset again after a possible resizing
732 if (did_compact()) {
733 cmsSpace()->reset_after_compaction();
734 }
735 }
736
737 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
738 assert_locked_or_safepoint(Heap_lock);
739
740 // If incremental collection failed, we just want to expand
741 // to the limit.
742 if (incremental_collection_failed()) {
743 clear_incremental_collection_failed();
744 grow_to_reserved();
745 return;
746 }
747
748 double free_percentage = ((double) free()) / capacity();
749 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
750 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
751
752 // compute expansion delta needed for reaching desired free percentage
753 if (free_percentage < desired_free_percentage) {
754 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
755 assert(desired_capacity >= capacity(), "invalid expansion size");
756 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
757 Log(gc) log;
758 if (log.is_trace()) {
759 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
760 log.trace("From compute_new_size: ");
761 log.trace(" Free fraction %f", free_percentage);
762 log.trace(" Desired free fraction %f", desired_free_percentage);
763 log.trace(" Maximum free fraction %f", maximum_free_percentage);
764 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
765 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
766 CMSHeap* heap = CMSHeap::heap();
767 assert(heap->is_old_gen(this), "The CMS generation should always be the old generation");
768 size_t young_size = heap->young_gen()->capacity();
769 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
770 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
771 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
772 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
773 }
774 // safe if expansion fails
775 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
776 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
777 } else {
778 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
779 assert(desired_capacity <= capacity(), "invalid expansion size");
780 size_t shrink_bytes = capacity() - desired_capacity;
781 // Don't shrink unless the delta is greater than the minimum shrink we want
782 if (shrink_bytes >= MinHeapDeltaBytes) {
783 shrink_free_list_by(shrink_bytes);
784 }
785 }
786 }
787
788 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
789 return cmsSpace()->freelistLock();
790 }
791
792 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
793 CMSSynchronousYieldRequest yr;
794 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
795 return have_lock_and_allocate(size, tlab);
796 }
797
798 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
799 bool tlab /* ignored */) {
800 assert_lock_strong(freelistLock());
801 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
802 HeapWord* res = cmsSpace()->allocate(adjustedSize);
803 // Allocate the object live (grey) if the background collector has
804 // started marking. This is necessary because the marker may
805 // have passed this address and consequently this object will
806 // not otherwise be greyed and would be incorrectly swept up.
807 // Note that if this object contains references, the writing
808 // of those references will dirty the card containing this object
809 // allowing the object to be blackened (and its references scanned)
810 // either during a preclean phase or at the final checkpoint.
811 if (res != NULL) {
812 // We may block here with an uninitialized object with
813 // its mark-bit or P-bits not yet set. Such objects need
814 // to be safely navigable by block_start().
815 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
816 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
817 collector()->direct_allocated(res, adjustedSize);
818 _direct_allocated_words += adjustedSize;
819 // allocation counters
820 NOT_PRODUCT(
821 _numObjectsAllocated++;
822 _numWordsAllocated += (int)adjustedSize;
823 )
824 }
825 return res;
826 }
827
828 // In the case of direct allocation by mutators in a generation that
829 // is being concurrently collected, the object must be allocated
830 // live (grey) if the background collector has started marking.
831 // This is necessary because the marker may
832 // have passed this address and consequently this object will
833 // not otherwise be greyed and would be incorrectly swept up.
834 // Note that if this object contains references, the writing
835 // of those references will dirty the card containing this object
836 // allowing the object to be blackened (and its references scanned)
837 // either during a preclean phase or at the final checkpoint.
838 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
839 assert(_markBitMap.covers(start, size), "Out of bounds");
840 if (_collectorState >= Marking) {
841 MutexLockerEx y(_markBitMap.lock(),
842 Mutex::_no_safepoint_check_flag);
843 // [see comments preceding SweepClosure::do_blk() below for details]
844 //
845 // Can the P-bits be deleted now? JJJ
846 //
847 // 1. need to mark the object as live so it isn't collected
848 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
849 // 3. need to mark the end of the object so marking, precleaning or sweeping
850 // can skip over uninitialized or unparsable objects. An allocated
851 // object is considered uninitialized for our purposes as long as
852 // its klass word is NULL. All old gen objects are parsable
853 // as soon as they are initialized.)
854 _markBitMap.mark(start); // object is live
855 _markBitMap.mark(start + 1); // object is potentially uninitialized?
856 _markBitMap.mark(start + size - 1);
857 // mark end of object
858 }
859 // check that oop looks uninitialized
860 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
861 }
862
863 void CMSCollector::promoted(bool par, HeapWord* start,
864 bool is_obj_array, size_t obj_size) {
865 assert(_markBitMap.covers(start), "Out of bounds");
866 // See comment in direct_allocated() about when objects should
867 // be allocated live.
868 if (_collectorState >= Marking) {
869 // we already hold the marking bit map lock, taken in
870 // the prologue
871 if (par) {
872 _markBitMap.par_mark(start);
873 } else {
874 _markBitMap.mark(start);
875 }
876 // We don't need to mark the object as uninitialized (as
877 // in direct_allocated above) because this is being done with the
878 // world stopped and the object will be initialized by the
879 // time the marking, precleaning or sweeping get to look at it.
880 // But see the code for copying objects into the CMS generation,
881 // where we need to ensure that concurrent readers of the
882 // block offset table are able to safely navigate a block that
883 // is in flux from being free to being allocated (and in
884 // transition while being copied into) and subsequently
885 // becoming a bona-fide object when the copy/promotion is complete.
886 assert(SafepointSynchronize::is_at_safepoint(),
887 "expect promotion only at safepoints");
888
889 if (_collectorState < Sweeping) {
890 // Mark the appropriate cards in the modUnionTable, so that
891 // this object gets scanned before the sweep. If this is
892 // not done, CMS generation references in the object might
893 // not get marked.
894 // For the case of arrays, which are otherwise precisely
895 // marked, we need to dirty the entire array, not just its head.
896 if (is_obj_array) {
897 // The [par_]mark_range() method expects mr.end() below to
898 // be aligned to the granularity of a bit's representation
899 // in the heap. In the case of the MUT below, that's a
900 // card size.
901 MemRegion mr(start,
902 align_up(start + obj_size,
903 CardTableModRefBS::card_size /* bytes */));
904 if (par) {
905 _modUnionTable.par_mark_range(mr);
906 } else {
907 _modUnionTable.mark_range(mr);
908 }
909 } else { // not an obj array; we can just mark the head
910 if (par) {
911 _modUnionTable.par_mark(start);
912 } else {
913 _modUnionTable.mark(start);
914 }
915 }
916 }
917 }
918 }
919
920 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
921 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
922 // allocate, copy and if necessary update promoinfo --
923 // delegate to underlying space.
924 assert_lock_strong(freelistLock());
925
926 #ifndef PRODUCT
927 if (CMSHeap::heap()->promotion_should_fail()) {
928 return NULL;
929 }
930 #endif // #ifndef PRODUCT
931
932 oop res = _cmsSpace->promote(obj, obj_size);
933 if (res == NULL) {
934 // expand and retry
935 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
936 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
937 // Since this is the old generation, we don't try to promote
938 // into a more senior generation.
939 res = _cmsSpace->promote(obj, obj_size);
940 }
941 if (res != NULL) {
942 // See comment in allocate() about when objects should
943 // be allocated live.
944 assert(oopDesc::is_oop(obj), "Will dereference klass pointer below");
945 collector()->promoted(false, // Not parallel
946 (HeapWord*)res, obj->is_objArray(), obj_size);
947 // promotion counters
948 NOT_PRODUCT(
949 _numObjectsPromoted++;
950 _numWordsPromoted +=
951 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
952 )
953 }
954 return res;
955 }
956
957
958 // IMPORTANT: Notes on object size recognition in CMS.
959 // ---------------------------------------------------
960 // A block of storage in the CMS generation is always in
961 // one of three states. A free block (FREE), an allocated
962 // object (OBJECT) whose size() method reports the correct size,
963 // and an intermediate state (TRANSIENT) in which its size cannot
964 // be accurately determined.
965 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
966 // -----------------------------------------------------
967 // FREE: klass_word & 1 == 1; mark_word holds block size
968 //
969 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
970 // obj->size() computes correct size
971 //
972 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
973 //
974 // STATE IDENTIFICATION: (64 bit+COOPS)
975 // ------------------------------------
976 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
977 //
978 // OBJECT: klass_word installed; klass_word != 0;
979 // obj->size() computes correct size
980 //
981 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
982 //
983 //
984 // STATE TRANSITION DIAGRAM
985 //
986 // mut / parnew mut / parnew
987 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
988 // ^ |
989 // |------------------------ DEAD <------------------------------------|
990 // sweep mut
991 //
992 // While a block is in TRANSIENT state its size cannot be determined
993 // so readers will either need to come back later or stall until
994 // the size can be determined. Note that for the case of direct
995 // allocation, P-bits, when available, may be used to determine the
996 // size of an object that may not yet have been initialized.
997
998 // Things to support parallel young-gen collection.
999 oop
1000 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1001 oop old, markOop m,
1002 size_t word_sz) {
1003 #ifndef PRODUCT
1004 if (CMSHeap::heap()->promotion_should_fail()) {
1005 return NULL;
1006 }
1007 #endif // #ifndef PRODUCT
1008
1009 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1010 PromotionInfo* promoInfo = &ps->promo;
1011 // if we are tracking promotions, then first ensure space for
1012 // promotion (including spooling space for saving header if necessary).
1013 // then allocate and copy, then track promoted info if needed.
1014 // When tracking (see PromotionInfo::track()), the mark word may
1015 // be displaced and in this case restoration of the mark word
1016 // occurs in the (oop_since_save_marks_)iterate phase.
1017 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1018 // Out of space for allocating spooling buffers;
1019 // try expanding and allocating spooling buffers.
1020 if (!expand_and_ensure_spooling_space(promoInfo)) {
1021 return NULL;
1022 }
1023 }
1024 assert(!promoInfo->tracking() || promoInfo->has_spooling_space(), "Control point invariant");
1025 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1026 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1027 if (obj_ptr == NULL) {
1028 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1029 if (obj_ptr == NULL) {
1030 return NULL;
1031 }
1032 }
1033 oop obj = oop(obj_ptr);
1034 OrderAccess::storestore();
1035 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1036 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1037 // IMPORTANT: See note on object initialization for CMS above.
1038 // Otherwise, copy the object. Here we must be careful to insert the
1039 // klass pointer last, since this marks the block as an allocated object.
1040 // Except with compressed oops it's the mark word.
1041 HeapWord* old_ptr = (HeapWord*)old;
1042 // Restore the mark word copied above.
1043 obj->set_mark(m);
1044 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1045 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1046 OrderAccess::storestore();
1047
1048 if (UseCompressedClassPointers) {
1049 // Copy gap missed by (aligned) header size calculation below
1050 obj->set_klass_gap(old->klass_gap());
1051 }
1052 if (word_sz > (size_t)oopDesc::header_size()) {
1053 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1054 obj_ptr + oopDesc::header_size(),
1055 word_sz - oopDesc::header_size());
1056 }
1057
1058 // Now we can track the promoted object, if necessary. We take care
1059 // to delay the transition from uninitialized to full object
1060 // (i.e., insertion of klass pointer) until after, so that it
1061 // atomically becomes a promoted object.
1062 if (promoInfo->tracking()) {
1063 promoInfo->track((PromotedObject*)obj, old->klass());
1064 }
1065 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1066 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1067 assert(oopDesc::is_oop(old), "Will use and dereference old klass ptr below");
1068
1069 // Finally, install the klass pointer (this should be volatile).
1070 OrderAccess::storestore();
1071 obj->set_klass(old->klass());
1072 // We should now be able to calculate the right size for this object
1073 assert(oopDesc::is_oop(obj) && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1074
1075 collector()->promoted(true, // parallel
1076 obj_ptr, old->is_objArray(), word_sz);
1077
1078 NOT_PRODUCT(
1079 Atomic::inc(&_numObjectsPromoted);
1080 Atomic::add(alloc_sz, &_numWordsPromoted);
1081 )
1082
1083 return obj;
1084 }
1085
1086 void
1087 ConcurrentMarkSweepGeneration::
1088 par_promote_alloc_done(int thread_num) {
1089 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1090 ps->lab.retire(thread_num);
1091 }
1092
1093 void
1094 ConcurrentMarkSweepGeneration::
1095 par_oop_since_save_marks_iterate_done(int thread_num) {
1096 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1097 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1098 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1099
1100 // Because card-scanning has been completed, subsequent phases
1101 // (e.g., reference processing) will not need to recognize which
1102 // objects have been promoted during this GC. So, we can now disable
1103 // promotion tracking.
1104 ps->promo.stopTrackingPromotions();
1105 }
1106
1107 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1108 size_t size,
1109 bool tlab)
1110 {
1111 // We allow a STW collection only if a full
1112 // collection was requested.
1113 return full || should_allocate(size, tlab); // FIX ME !!!
1114 // This and promotion failure handling are connected at the
1115 // hip and should be fixed by untying them.
1116 }
1117
1118 bool CMSCollector::shouldConcurrentCollect() {
1119 LogTarget(Trace, gc) log;
1120
1121 if (_full_gc_requested) {
1122 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1123 return true;
1124 }
1125
1126 FreelistLocker x(this);
1127 // ------------------------------------------------------------------
1128 // Print out lots of information which affects the initiation of
1129 // a collection.
1130 if (log.is_enabled() && stats().valid()) {
1131 log.print("CMSCollector shouldConcurrentCollect: ");
1132
1133 LogStream out(log);
1134 stats().print_on(&out);
1135
1136 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1137 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1138 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1139 log.print("promotion_rate=%g", stats().promotion_rate());
1140 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1141 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1142 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1143 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1144 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1145 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1146 }
1147 // ------------------------------------------------------------------
1148
1149 // If the estimated time to complete a cms collection (cms_duration())
1150 // is less than the estimated time remaining until the cms generation
1151 // is full, start a collection.
1152 if (!UseCMSInitiatingOccupancyOnly) {
1153 if (stats().valid()) {
1154 if (stats().time_until_cms_start() == 0.0) {
1155 return true;
1156 }
1157 } else {
1158 // We want to conservatively collect somewhat early in order
1159 // to try and "bootstrap" our CMS/promotion statistics;
1160 // this branch will not fire after the first successful CMS
1161 // collection because the stats should then be valid.
1162 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1163 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1164 _cmsGen->occupancy(), _bootstrap_occupancy);
1165 return true;
1166 }
1167 }
1168 }
1169
1170 // Otherwise, we start a collection cycle if
1171 // old gen want a collection cycle started. Each may use
1172 // an appropriate criterion for making this decision.
1173 // XXX We need to make sure that the gen expansion
1174 // criterion dovetails well with this. XXX NEED TO FIX THIS
1175 if (_cmsGen->should_concurrent_collect()) {
1176 log.print("CMS old gen initiated");
1177 return true;
1178 }
1179
1180 // We start a collection if we believe an incremental collection may fail;
1181 // this is not likely to be productive in practice because it's probably too
1182 // late anyway.
1183 CMSHeap* heap = CMSHeap::heap();
1184 if (heap->incremental_collection_will_fail(true /* consult_young */)) {
1185 log.print("CMSCollector: collect because incremental collection will fail ");
1186 return true;
1187 }
1188
1189 if (MetaspaceGC::should_concurrent_collect()) {
1190 log.print("CMSCollector: collect for metadata allocation ");
1191 return true;
1192 }
1193
1194 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1195 if (CMSTriggerInterval >= 0) {
1196 if (CMSTriggerInterval == 0) {
1197 // Trigger always
1198 return true;
1199 }
1200
1201 // Check the CMS time since begin (we do not check the stats validity
1202 // as we want to be able to trigger the first CMS cycle as well)
1203 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1204 if (stats().valid()) {
1205 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1206 stats().cms_time_since_begin());
1207 } else {
1208 log.print("CMSCollector: collect because of trigger interval (first collection)");
1209 }
1210 return true;
1211 }
1212 }
1213
1214 return false;
1215 }
1216
1217 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1218
1219 // Clear _expansion_cause fields of constituent generations
1220 void CMSCollector::clear_expansion_cause() {
1221 _cmsGen->clear_expansion_cause();
1222 }
1223
1224 // We should be conservative in starting a collection cycle. To
1225 // start too eagerly runs the risk of collecting too often in the
1226 // extreme. To collect too rarely falls back on full collections,
1227 // which works, even if not optimum in terms of concurrent work.
1228 // As a work around for too eagerly collecting, use the flag
1229 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1230 // giving the user an easily understandable way of controlling the
1231 // collections.
1232 // We want to start a new collection cycle if any of the following
1233 // conditions hold:
1234 // . our current occupancy exceeds the configured initiating occupancy
1235 // for this generation, or
1236 // . we recently needed to expand this space and have not, since that
1237 // expansion, done a collection of this generation, or
1238 // . the underlying space believes that it may be a good idea to initiate
1239 // a concurrent collection (this may be based on criteria such as the
1240 // following: the space uses linear allocation and linear allocation is
1241 // going to fail, or there is believed to be excessive fragmentation in
1242 // the generation, etc... or ...
1243 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1244 // the case of the old generation; see CR 6543076):
1245 // we may be approaching a point at which allocation requests may fail because
1246 // we will be out of sufficient free space given allocation rate estimates.]
1247 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1248
1249 assert_lock_strong(freelistLock());
1250 if (occupancy() > initiating_occupancy()) {
1251 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1252 short_name(), occupancy(), initiating_occupancy());
1253 return true;
1254 }
1255 if (UseCMSInitiatingOccupancyOnly) {
1256 return false;
1257 }
1258 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1259 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1260 return true;
1261 }
1262 return false;
1263 }
1264
1265 void ConcurrentMarkSweepGeneration::collect(bool full,
1266 bool clear_all_soft_refs,
1267 size_t size,
1268 bool tlab)
1269 {
1270 collector()->collect(full, clear_all_soft_refs, size, tlab);
1271 }
1272
1273 void CMSCollector::collect(bool full,
1274 bool clear_all_soft_refs,
1275 size_t size,
1276 bool tlab)
1277 {
1278 // The following "if" branch is present for defensive reasons.
1279 // In the current uses of this interface, it can be replaced with:
1280 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1281 // But I am not placing that assert here to allow future
1282 // generality in invoking this interface.
1283 if (GCLocker::is_active()) {
1284 // A consistency test for GCLocker
1285 assert(GCLocker::needs_gc(), "Should have been set already");
1286 // Skip this foreground collection, instead
1287 // expanding the heap if necessary.
1288 // Need the free list locks for the call to free() in compute_new_size()
1289 compute_new_size();
1290 return;
1291 }
1292 acquire_control_and_collect(full, clear_all_soft_refs);
1293 }
1294
1295 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1296 CMSHeap* heap = CMSHeap::heap();
1297 unsigned int gc_count = heap->total_full_collections();
1298 if (gc_count == full_gc_count) {
1299 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1300 _full_gc_requested = true;
1301 _full_gc_cause = cause;
1302 CGC_lock->notify(); // nudge CMS thread
1303 } else {
1304 assert(gc_count > full_gc_count, "Error: causal loop");
1305 }
1306 }
1307
1308 bool CMSCollector::is_external_interruption() {
1309 GCCause::Cause cause = CMSHeap::heap()->gc_cause();
1310 return GCCause::is_user_requested_gc(cause) ||
1311 GCCause::is_serviceability_requested_gc(cause);
1312 }
1313
1314 void CMSCollector::report_concurrent_mode_interruption() {
1315 if (is_external_interruption()) {
1316 log_debug(gc)("Concurrent mode interrupted");
1317 } else {
1318 log_debug(gc)("Concurrent mode failure");
1319 _gc_tracer_cm->report_concurrent_mode_failure();
1320 }
1321 }
1322
1323
1324 // The foreground and background collectors need to coordinate in order
1325 // to make sure that they do not mutually interfere with CMS collections.
1326 // When a background collection is active,
1327 // the foreground collector may need to take over (preempt) and
1328 // synchronously complete an ongoing collection. Depending on the
1329 // frequency of the background collections and the heap usage
1330 // of the application, this preemption can be seldom or frequent.
1331 // There are only certain
1332 // points in the background collection that the "collection-baton"
1333 // can be passed to the foreground collector.
1334 //
1335 // The foreground collector will wait for the baton before
1336 // starting any part of the collection. The foreground collector
1337 // will only wait at one location.
1338 //
1339 // The background collector will yield the baton before starting a new
1340 // phase of the collection (e.g., before initial marking, marking from roots,
1341 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1342 // of the loop which switches the phases. The background collector does some
1343 // of the phases (initial mark, final re-mark) with the world stopped.
1344 // Because of locking involved in stopping the world,
1345 // the foreground collector should not block waiting for the background
1346 // collector when it is doing a stop-the-world phase. The background
1347 // collector will yield the baton at an additional point just before
1348 // it enters a stop-the-world phase. Once the world is stopped, the
1349 // background collector checks the phase of the collection. If the
1350 // phase has not changed, it proceeds with the collection. If the
1351 // phase has changed, it skips that phase of the collection. See
1352 // the comments on the use of the Heap_lock in collect_in_background().
1353 //
1354 // Variable used in baton passing.
1355 // _foregroundGCIsActive - Set to true by the foreground collector when
1356 // it wants the baton. The foreground clears it when it has finished
1357 // the collection.
1358 // _foregroundGCShouldWait - Set to true by the background collector
1359 // when it is running. The foreground collector waits while
1360 // _foregroundGCShouldWait is true.
1361 // CGC_lock - monitor used to protect access to the above variables
1362 // and to notify the foreground and background collectors.
1363 // _collectorState - current state of the CMS collection.
1364 //
1365 // The foreground collector
1366 // acquires the CGC_lock
1367 // sets _foregroundGCIsActive
1368 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1369 // various locks acquired in preparation for the collection
1370 // are released so as not to block the background collector
1371 // that is in the midst of a collection
1372 // proceeds with the collection
1373 // clears _foregroundGCIsActive
1374 // returns
1375 //
1376 // The background collector in a loop iterating on the phases of the
1377 // collection
1378 // acquires the CGC_lock
1379 // sets _foregroundGCShouldWait
1380 // if _foregroundGCIsActive is set
1381 // clears _foregroundGCShouldWait, notifies _CGC_lock
1382 // waits on _CGC_lock for _foregroundGCIsActive to become false
1383 // and exits the loop.
1384 // otherwise
1385 // proceed with that phase of the collection
1386 // if the phase is a stop-the-world phase,
1387 // yield the baton once more just before enqueueing
1388 // the stop-world CMS operation (executed by the VM thread).
1389 // returns after all phases of the collection are done
1390 //
1391
1392 void CMSCollector::acquire_control_and_collect(bool full,
1393 bool clear_all_soft_refs) {
1394 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1395 assert(!Thread::current()->is_ConcurrentGC_thread(),
1396 "shouldn't try to acquire control from self!");
1397
1398 // Start the protocol for acquiring control of the
1399 // collection from the background collector (aka CMS thread).
1400 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1401 "VM thread should have CMS token");
1402 // Remember the possibly interrupted state of an ongoing
1403 // concurrent collection
1404 CollectorState first_state = _collectorState;
1405
1406 // Signal to a possibly ongoing concurrent collection that
1407 // we want to do a foreground collection.
1408 _foregroundGCIsActive = true;
1409
1410 // release locks and wait for a notify from the background collector
1411 // releasing the locks in only necessary for phases which
1412 // do yields to improve the granularity of the collection.
1413 assert_lock_strong(bitMapLock());
1414 // We need to lock the Free list lock for the space that we are
1415 // currently collecting.
1416 assert(haveFreelistLocks(), "Must be holding free list locks");
1417 bitMapLock()->unlock();
1418 releaseFreelistLocks();
1419 {
1420 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1421 if (_foregroundGCShouldWait) {
1422 // We are going to be waiting for action for the CMS thread;
1423 // it had better not be gone (for instance at shutdown)!
1424 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1425 "CMS thread must be running");
1426 // Wait here until the background collector gives us the go-ahead
1427 ConcurrentMarkSweepThread::clear_CMS_flag(
1428 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1429 // Get a possibly blocked CMS thread going:
1430 // Note that we set _foregroundGCIsActive true above,
1431 // without protection of the CGC_lock.
1432 CGC_lock->notify();
1433 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1434 "Possible deadlock");
1435 while (_foregroundGCShouldWait) {
1436 // wait for notification
1437 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1438 // Possibility of delay/starvation here, since CMS token does
1439 // not know to give priority to VM thread? Actually, i think
1440 // there wouldn't be any delay/starvation, but the proof of
1441 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1442 }
1443 ConcurrentMarkSweepThread::set_CMS_flag(
1444 ConcurrentMarkSweepThread::CMS_vm_has_token);
1445 }
1446 }
1447 // The CMS_token is already held. Get back the other locks.
1448 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1449 "VM thread should have CMS token");
1450 getFreelistLocks();
1451 bitMapLock()->lock_without_safepoint_check();
1452 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1453 p2i(Thread::current()), first_state);
1454 log_debug(gc, state)(" gets control with state %d", _collectorState);
1455
1456 // Inform cms gen if this was due to partial collection failing.
1457 // The CMS gen may use this fact to determine its expansion policy.
1458 CMSHeap* heap = CMSHeap::heap();
1459 if (heap->incremental_collection_will_fail(false /* don't consult_young */)) {
1460 assert(!_cmsGen->incremental_collection_failed(),
1461 "Should have been noticed, reacted to and cleared");
1462 _cmsGen->set_incremental_collection_failed();
1463 }
1464
1465 if (first_state > Idling) {
1466 report_concurrent_mode_interruption();
1467 }
1468
1469 set_did_compact(true);
1470
1471 // If the collection is being acquired from the background
1472 // collector, there may be references on the discovered
1473 // references lists. Abandon those references, since some
1474 // of them may have become unreachable after concurrent
1475 // discovery; the STW compacting collector will redo discovery
1476 // more precisely, without being subject to floating garbage.
1477 // Leaving otherwise unreachable references in the discovered
1478 // lists would require special handling.
1479 ref_processor()->disable_discovery();
1480 ref_processor()->abandon_partial_discovery();
1481 ref_processor()->verify_no_references_recorded();
1482
1483 if (first_state > Idling) {
1484 save_heap_summary();
1485 }
1486
1487 do_compaction_work(clear_all_soft_refs);
1488
1489 // Has the GC time limit been exceeded?
1490 size_t max_eden_size = _young_gen->max_eden_size();
1491 GCCause::Cause gc_cause = heap->gc_cause();
1492 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1493 _young_gen->eden()->used(),
1494 _cmsGen->max_capacity(),
1495 max_eden_size,
1496 full,
1497 gc_cause,
1498 heap->soft_ref_policy());
1499
1500 // Reset the expansion cause, now that we just completed
1501 // a collection cycle.
1502 clear_expansion_cause();
1503 _foregroundGCIsActive = false;
1504 return;
1505 }
1506
1507 // Resize the tenured generation
1508 // after obtaining the free list locks for the
1509 // two generations.
1510 void CMSCollector::compute_new_size() {
1511 assert_locked_or_safepoint(Heap_lock);
1512 FreelistLocker z(this);
1513 MetaspaceGC::compute_new_size();
1514 _cmsGen->compute_new_size_free_list();
1515 }
1516
1517 // A work method used by the foreground collector to do
1518 // a mark-sweep-compact.
1519 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1520 CMSHeap* heap = CMSHeap::heap();
1521
1522 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1523 gc_timer->register_gc_start();
1524
1525 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1526 gc_tracer->report_gc_start(heap->gc_cause(), gc_timer->gc_start());
1527
1528 heap->pre_full_gc_dump(gc_timer);
1529
1530 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1531
1532 // Temporarily widen the span of the weak reference processing to
1533 // the entire heap.
1534 MemRegion new_span(CMSHeap::heap()->reserved_region());
1535 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1536 // Temporarily, clear the "is_alive_non_header" field of the
1537 // reference processor.
1538 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1539 // Temporarily make reference _processing_ single threaded (non-MT).
1540 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1541 // Temporarily make refs discovery atomic
1542 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1543 // Temporarily make reference _discovery_ single threaded (non-MT)
1544 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1545
1546 ref_processor()->set_enqueuing_is_done(false);
1547 ref_processor()->enable_discovery();
1548 ref_processor()->setup_policy(clear_all_soft_refs);
1549 // If an asynchronous collection finishes, the _modUnionTable is
1550 // all clear. If we are assuming the collection from an asynchronous
1551 // collection, clear the _modUnionTable.
1552 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1553 "_modUnionTable should be clear if the baton was not passed");
1554 _modUnionTable.clear_all();
1555 assert(_collectorState != Idling || _ct->cld_rem_set()->mod_union_is_clear(),
1556 "mod union for klasses should be clear if the baton was passed");
1557 _ct->cld_rem_set()->clear_mod_union();
1558
1559
1560 // We must adjust the allocation statistics being maintained
1561 // in the free list space. We do so by reading and clearing
1562 // the sweep timer and updating the block flux rate estimates below.
1563 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1564 if (_inter_sweep_timer.is_active()) {
1565 _inter_sweep_timer.stop();
1566 // Note that we do not use this sample to update the _inter_sweep_estimate.
1567 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1568 _inter_sweep_estimate.padded_average(),
1569 _intra_sweep_estimate.padded_average());
1570 }
1571
1572 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1573 #ifdef ASSERT
1574 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1575 size_t free_size = cms_space->free();
1576 assert(free_size ==
1577 pointer_delta(cms_space->end(), cms_space->compaction_top())
1578 * HeapWordSize,
1579 "All the free space should be compacted into one chunk at top");
1580 assert(cms_space->dictionary()->total_chunk_size(
1581 debug_only(cms_space->freelistLock())) == 0 ||
1582 cms_space->totalSizeInIndexedFreeLists() == 0,
1583 "All the free space should be in a single chunk");
1584 size_t num = cms_space->totalCount();
1585 assert((free_size == 0 && num == 0) ||
1586 (free_size > 0 && (num == 1 || num == 2)),
1587 "There should be at most 2 free chunks after compaction");
1588 #endif // ASSERT
1589 _collectorState = Resetting;
1590 assert(_restart_addr == NULL,
1591 "Should have been NULL'd before baton was passed");
1592 reset_stw();
1593 _cmsGen->reset_after_compaction();
1594 _concurrent_cycles_since_last_unload = 0;
1595
1596 // Clear any data recorded in the PLAB chunk arrays.
1597 if (_survivor_plab_array != NULL) {
1598 reset_survivor_plab_arrays();
1599 }
1600
1601 // Adjust the per-size allocation stats for the next epoch.
1602 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1603 // Restart the "inter sweep timer" for the next epoch.
1604 _inter_sweep_timer.reset();
1605 _inter_sweep_timer.start();
1606
1607 // No longer a need to do a concurrent collection for Metaspace.
1608 MetaspaceGC::set_should_concurrent_collect(false);
1609
1610 heap->post_full_gc_dump(gc_timer);
1611
1612 gc_timer->register_gc_end();
1613
1614 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1615
1616 // For a mark-sweep-compact, compute_new_size() will be called
1617 // in the heap's do_collection() method.
1618 }
1619
1620 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1621 Log(gc, heap) log;
1622 if (!log.is_trace()) {
1623 return;
1624 }
1625
1626 ContiguousSpace* eden_space = _young_gen->eden();
1627 ContiguousSpace* from_space = _young_gen->from();
1628 ContiguousSpace* to_space = _young_gen->to();
1629 // Eden
1630 if (_eden_chunk_array != NULL) {
1631 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1632 p2i(eden_space->bottom()), p2i(eden_space->top()),
1633 p2i(eden_space->end()), eden_space->capacity());
1634 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1635 _eden_chunk_index, _eden_chunk_capacity);
1636 for (size_t i = 0; i < _eden_chunk_index; i++) {
1637 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1638 }
1639 }
1640 // Survivor
1641 if (_survivor_chunk_array != NULL) {
1642 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1643 p2i(from_space->bottom()), p2i(from_space->top()),
1644 p2i(from_space->end()), from_space->capacity());
1645 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1646 _survivor_chunk_index, _survivor_chunk_capacity);
1647 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1648 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1649 }
1650 }
1651 }
1652
1653 void CMSCollector::getFreelistLocks() const {
1654 // Get locks for all free lists in all generations that this
1655 // collector is responsible for
1656 _cmsGen->freelistLock()->lock_without_safepoint_check();
1657 }
1658
1659 void CMSCollector::releaseFreelistLocks() const {
1660 // Release locks for all free lists in all generations that this
1661 // collector is responsible for
1662 _cmsGen->freelistLock()->unlock();
1663 }
1664
1665 bool CMSCollector::haveFreelistLocks() const {
1666 // Check locks for all free lists in all generations that this
1667 // collector is responsible for
1668 assert_lock_strong(_cmsGen->freelistLock());
1669 PRODUCT_ONLY(ShouldNotReachHere());
1670 return true;
1671 }
1672
1673 // A utility class that is used by the CMS collector to
1674 // temporarily "release" the foreground collector from its
1675 // usual obligation to wait for the background collector to
1676 // complete an ongoing phase before proceeding.
1677 class ReleaseForegroundGC: public StackObj {
1678 private:
1679 CMSCollector* _c;
1680 public:
1681 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1682 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1683 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1684 // allow a potentially blocked foreground collector to proceed
1685 _c->_foregroundGCShouldWait = false;
1686 if (_c->_foregroundGCIsActive) {
1687 CGC_lock->notify();
1688 }
1689 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1690 "Possible deadlock");
1691 }
1692
1693 ~ReleaseForegroundGC() {
1694 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1695 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1696 _c->_foregroundGCShouldWait = true;
1697 }
1698 };
1699
1700 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1701 assert(Thread::current()->is_ConcurrentGC_thread(),
1702 "A CMS asynchronous collection is only allowed on a CMS thread.");
1703
1704 CMSHeap* heap = CMSHeap::heap();
1705 {
1706 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1707 MutexLockerEx hl(Heap_lock, safepoint_check);
1708 FreelistLocker fll(this);
1709 MutexLockerEx x(CGC_lock, safepoint_check);
1710 if (_foregroundGCIsActive) {
1711 // The foreground collector is. Skip this
1712 // background collection.
1713 assert(!_foregroundGCShouldWait, "Should be clear");
1714 return;
1715 } else {
1716 assert(_collectorState == Idling, "Should be idling before start.");
1717 _collectorState = InitialMarking;
1718 register_gc_start(cause);
1719 // Reset the expansion cause, now that we are about to begin
1720 // a new cycle.
1721 clear_expansion_cause();
1722
1723 // Clear the MetaspaceGC flag since a concurrent collection
1724 // is starting but also clear it after the collection.
1725 MetaspaceGC::set_should_concurrent_collect(false);
1726 }
1727 // Decide if we want to enable class unloading as part of the
1728 // ensuing concurrent GC cycle.
1729 update_should_unload_classes();
1730 _full_gc_requested = false; // acks all outstanding full gc requests
1731 _full_gc_cause = GCCause::_no_gc;
1732 // Signal that we are about to start a collection
1733 heap->increment_total_full_collections(); // ... starting a collection cycle
1734 _collection_count_start = heap->total_full_collections();
1735 }
1736
1737 size_t prev_used = _cmsGen->used();
1738
1739 // The change of the collection state is normally done at this level;
1740 // the exceptions are phases that are executed while the world is
1741 // stopped. For those phases the change of state is done while the
1742 // world is stopped. For baton passing purposes this allows the
1743 // background collector to finish the phase and change state atomically.
1744 // The foreground collector cannot wait on a phase that is done
1745 // while the world is stopped because the foreground collector already
1746 // has the world stopped and would deadlock.
1747 while (_collectorState != Idling) {
1748 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1749 p2i(Thread::current()), _collectorState);
1750 // The foreground collector
1751 // holds the Heap_lock throughout its collection.
1752 // holds the CMS token (but not the lock)
1753 // except while it is waiting for the background collector to yield.
1754 //
1755 // The foreground collector should be blocked (not for long)
1756 // if the background collector is about to start a phase
1757 // executed with world stopped. If the background
1758 // collector has already started such a phase, the
1759 // foreground collector is blocked waiting for the
1760 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1761 // are executed in the VM thread.
1762 //
1763 // The locking order is
1764 // PendingListLock (PLL) -- if applicable (FinalMarking)
1765 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1766 // CMS token (claimed in
1767 // stop_world_and_do() -->
1768 // safepoint_synchronize() -->
1769 // CMSThread::synchronize())
1770
1771 {
1772 // Check if the FG collector wants us to yield.
1773 CMSTokenSync x(true); // is cms thread
1774 if (waitForForegroundGC()) {
1775 // We yielded to a foreground GC, nothing more to be
1776 // done this round.
1777 assert(_foregroundGCShouldWait == false, "We set it to false in "
1778 "waitForForegroundGC()");
1779 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1780 p2i(Thread::current()), _collectorState);
1781 return;
1782 } else {
1783 // The background collector can run but check to see if the
1784 // foreground collector has done a collection while the
1785 // background collector was waiting to get the CGC_lock
1786 // above. If yes, break so that _foregroundGCShouldWait
1787 // is cleared before returning.
1788 if (_collectorState == Idling) {
1789 break;
1790 }
1791 }
1792 }
1793
1794 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1795 "should be waiting");
1796
1797 switch (_collectorState) {
1798 case InitialMarking:
1799 {
1800 ReleaseForegroundGC x(this);
1801 stats().record_cms_begin();
1802 VM_CMS_Initial_Mark initial_mark_op(this);
1803 VMThread::execute(&initial_mark_op);
1804 }
1805 // The collector state may be any legal state at this point
1806 // since the background collector may have yielded to the
1807 // foreground collector.
1808 break;
1809 case Marking:
1810 // initial marking in checkpointRootsInitialWork has been completed
1811 if (markFromRoots()) { // we were successful
1812 assert(_collectorState == Precleaning, "Collector state should "
1813 "have changed");
1814 } else {
1815 assert(_foregroundGCIsActive, "Internal state inconsistency");
1816 }
1817 break;
1818 case Precleaning:
1819 // marking from roots in markFromRoots has been completed
1820 preclean();
1821 assert(_collectorState == AbortablePreclean ||
1822 _collectorState == FinalMarking,
1823 "Collector state should have changed");
1824 break;
1825 case AbortablePreclean:
1826 abortable_preclean();
1827 assert(_collectorState == FinalMarking, "Collector state should "
1828 "have changed");
1829 break;
1830 case FinalMarking:
1831 {
1832 ReleaseForegroundGC x(this);
1833
1834 VM_CMS_Final_Remark final_remark_op(this);
1835 VMThread::execute(&final_remark_op);
1836 }
1837 assert(_foregroundGCShouldWait, "block post-condition");
1838 break;
1839 case Sweeping:
1840 // final marking in checkpointRootsFinal has been completed
1841 sweep();
1842 assert(_collectorState == Resizing, "Collector state change "
1843 "to Resizing must be done under the free_list_lock");
1844
1845 case Resizing: {
1846 // Sweeping has been completed...
1847 // At this point the background collection has completed.
1848 // Don't move the call to compute_new_size() down
1849 // into code that might be executed if the background
1850 // collection was preempted.
1851 {
1852 ReleaseForegroundGC x(this); // unblock FG collection
1853 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1854 CMSTokenSync z(true); // not strictly needed.
1855 if (_collectorState == Resizing) {
1856 compute_new_size();
1857 save_heap_summary();
1858 _collectorState = Resetting;
1859 } else {
1860 assert(_collectorState == Idling, "The state should only change"
1861 " because the foreground collector has finished the collection");
1862 }
1863 }
1864 break;
1865 }
1866 case Resetting:
1867 // CMS heap resizing has been completed
1868 reset_concurrent();
1869 assert(_collectorState == Idling, "Collector state should "
1870 "have changed");
1871
1872 MetaspaceGC::set_should_concurrent_collect(false);
1873
1874 stats().record_cms_end();
1875 // Don't move the concurrent_phases_end() and compute_new_size()
1876 // calls to here because a preempted background collection
1877 // has it's state set to "Resetting".
1878 break;
1879 case Idling:
1880 default:
1881 ShouldNotReachHere();
1882 break;
1883 }
1884 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1885 p2i(Thread::current()), _collectorState);
1886 assert(_foregroundGCShouldWait, "block post-condition");
1887 }
1888
1889 // Should this be in gc_epilogue?
1890 collector_policy()->counters()->update_counters();
1891
1892 {
1893 // Clear _foregroundGCShouldWait and, in the event that the
1894 // foreground collector is waiting, notify it, before
1895 // returning.
1896 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1897 _foregroundGCShouldWait = false;
1898 if (_foregroundGCIsActive) {
1899 CGC_lock->notify();
1900 }
1901 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1902 "Possible deadlock");
1903 }
1904 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1905 p2i(Thread::current()), _collectorState);
1906 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1907 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1908 }
1909
1910 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1911 _cms_start_registered = true;
1912 _gc_timer_cm->register_gc_start();
1913 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1914 }
1915
1916 void CMSCollector::register_gc_end() {
1917 if (_cms_start_registered) {
1918 report_heap_summary(GCWhen::AfterGC);
1919
1920 _gc_timer_cm->register_gc_end();
1921 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1922 _cms_start_registered = false;
1923 }
1924 }
1925
1926 void CMSCollector::save_heap_summary() {
1927 CMSHeap* heap = CMSHeap::heap();
1928 _last_heap_summary = heap->create_heap_summary();
1929 _last_metaspace_summary = heap->create_metaspace_summary();
1930 }
1931
1932 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1933 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1934 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1935 }
1936
1937 bool CMSCollector::waitForForegroundGC() {
1938 bool res = false;
1939 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1940 "CMS thread should have CMS token");
1941 // Block the foreground collector until the
1942 // background collectors decides whether to
1943 // yield.
1944 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1945 _foregroundGCShouldWait = true;
1946 if (_foregroundGCIsActive) {
1947 // The background collector yields to the
1948 // foreground collector and returns a value
1949 // indicating that it has yielded. The foreground
1950 // collector can proceed.
1951 res = true;
1952 _foregroundGCShouldWait = false;
1953 ConcurrentMarkSweepThread::clear_CMS_flag(
1954 ConcurrentMarkSweepThread::CMS_cms_has_token);
1955 ConcurrentMarkSweepThread::set_CMS_flag(
1956 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1957 // Get a possibly blocked foreground thread going
1958 CGC_lock->notify();
1959 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1960 p2i(Thread::current()), _collectorState);
1961 while (_foregroundGCIsActive) {
1962 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1963 }
1964 ConcurrentMarkSweepThread::set_CMS_flag(
1965 ConcurrentMarkSweepThread::CMS_cms_has_token);
1966 ConcurrentMarkSweepThread::clear_CMS_flag(
1967 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1968 }
1969 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1970 p2i(Thread::current()), _collectorState);
1971 return res;
1972 }
1973
1974 // Because of the need to lock the free lists and other structures in
1975 // the collector, common to all the generations that the collector is
1976 // collecting, we need the gc_prologues of individual CMS generations
1977 // delegate to their collector. It may have been simpler had the
1978 // current infrastructure allowed one to call a prologue on a
1979 // collector. In the absence of that we have the generation's
1980 // prologue delegate to the collector, which delegates back
1981 // some "local" work to a worker method in the individual generations
1982 // that it's responsible for collecting, while itself doing any
1983 // work common to all generations it's responsible for. A similar
1984 // comment applies to the gc_epilogue()'s.
1985 // The role of the variable _between_prologue_and_epilogue is to
1986 // enforce the invocation protocol.
1987 void CMSCollector::gc_prologue(bool full) {
1988 // Call gc_prologue_work() for the CMSGen
1989 // we are responsible for.
1990
1991 // The following locking discipline assumes that we are only called
1992 // when the world is stopped.
1993 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1994
1995 // The CMSCollector prologue must call the gc_prologues for the
1996 // "generations" that it's responsible
1997 // for.
1998
1999 assert( Thread::current()->is_VM_thread()
2000 || ( CMSScavengeBeforeRemark
2001 && Thread::current()->is_ConcurrentGC_thread()),
2002 "Incorrect thread type for prologue execution");
2003
2004 if (_between_prologue_and_epilogue) {
2005 // We have already been invoked; this is a gc_prologue delegation
2006 // from yet another CMS generation that we are responsible for, just
2007 // ignore it since all relevant work has already been done.
2008 return;
2009 }
2010
2011 // set a bit saying prologue has been called; cleared in epilogue
2012 _between_prologue_and_epilogue = true;
2013 // Claim locks for common data structures, then call gc_prologue_work()
2014 // for each CMSGen.
2015
2016 getFreelistLocks(); // gets free list locks on constituent spaces
2017 bitMapLock()->lock_without_safepoint_check();
2018
2019 // Should call gc_prologue_work() for all cms gens we are responsible for
2020 bool duringMarking = _collectorState >= Marking
2021 && _collectorState < Sweeping;
2022
2023 // The young collections clear the modified oops state, which tells if
2024 // there are any modified oops in the class. The remark phase also needs
2025 // that information. Tell the young collection to save the union of all
2026 // modified klasses.
2027 if (duringMarking) {
2028 _ct->cld_rem_set()->set_accumulate_modified_oops(true);
2029 }
2030
2031 bool registerClosure = duringMarking;
2032
2033 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2034
2035 if (!full) {
2036 stats().record_gc0_begin();
2037 }
2038 }
2039
2040 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2041
2042 _capacity_at_prologue = capacity();
2043 _used_at_prologue = used();
2044
2045 // We enable promotion tracking so that card-scanning can recognize
2046 // which objects have been promoted during this GC and skip them.
2047 for (uint i = 0; i < ParallelGCThreads; i++) {
2048 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2049 }
2050
2051 // Delegate to CMScollector which knows how to coordinate between
2052 // this and any other CMS generations that it is responsible for
2053 // collecting.
2054 collector()->gc_prologue(full);
2055 }
2056
2057 // This is a "private" interface for use by this generation's CMSCollector.
2058 // Not to be called directly by any other entity (for instance,
2059 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2060 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2061 bool registerClosure, ModUnionClosure* modUnionClosure) {
2062 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2063 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2064 "Should be NULL");
2065 if (registerClosure) {
2066 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2067 }
2068 cmsSpace()->gc_prologue();
2069 // Clear stat counters
2070 NOT_PRODUCT(
2071 assert(_numObjectsPromoted == 0, "check");
2072 assert(_numWordsPromoted == 0, "check");
2073 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2074 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2075 _numObjectsAllocated = 0;
2076 _numWordsAllocated = 0;
2077 )
2078 }
2079
2080 void CMSCollector::gc_epilogue(bool full) {
2081 // The following locking discipline assumes that we are only called
2082 // when the world is stopped.
2083 assert(SafepointSynchronize::is_at_safepoint(),
2084 "world is stopped assumption");
2085
2086 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2087 // if linear allocation blocks need to be appropriately marked to allow the
2088 // the blocks to be parsable. We also check here whether we need to nudge the
2089 // CMS collector thread to start a new cycle (if it's not already active).
2090 assert( Thread::current()->is_VM_thread()
2091 || ( CMSScavengeBeforeRemark
2092 && Thread::current()->is_ConcurrentGC_thread()),
2093 "Incorrect thread type for epilogue execution");
2094
2095 if (!_between_prologue_and_epilogue) {
2096 // We have already been invoked; this is a gc_epilogue delegation
2097 // from yet another CMS generation that we are responsible for, just
2098 // ignore it since all relevant work has already been done.
2099 return;
2100 }
2101 assert(haveFreelistLocks(), "must have freelist locks");
2102 assert_lock_strong(bitMapLock());
2103
2104 _ct->cld_rem_set()->set_accumulate_modified_oops(false);
2105
2106 _cmsGen->gc_epilogue_work(full);
2107
2108 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2109 // in case sampling was not already enabled, enable it
2110 _start_sampling = true;
2111 }
2112 // reset _eden_chunk_array so sampling starts afresh
2113 _eden_chunk_index = 0;
2114
2115 size_t cms_used = _cmsGen->cmsSpace()->used();
2116
2117 // update performance counters - this uses a special version of
2118 // update_counters() that allows the utilization to be passed as a
2119 // parameter, avoiding multiple calls to used().
2120 //
2121 _cmsGen->update_counters(cms_used);
2122
2123 bitMapLock()->unlock();
2124 releaseFreelistLocks();
2125
2126 if (!CleanChunkPoolAsync) {
2127 Chunk::clean_chunk_pool();
2128 }
2129
2130 set_did_compact(false);
2131 _between_prologue_and_epilogue = false; // ready for next cycle
2132 }
2133
2134 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2135 collector()->gc_epilogue(full);
2136
2137 // When using ParNew, promotion tracking should have already been
2138 // disabled. However, the prologue (which enables promotion
2139 // tracking) and epilogue are called irrespective of the type of
2140 // GC. So they will also be called before and after Full GCs, during
2141 // which promotion tracking will not be explicitly disabled. So,
2142 // it's safer to also disable it here too (to be symmetric with
2143 // enabling it in the prologue).
2144 for (uint i = 0; i < ParallelGCThreads; i++) {
2145 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2146 }
2147 }
2148
2149 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2150 assert(!incremental_collection_failed(), "Should have been cleared");
2151 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2152 cmsSpace()->gc_epilogue();
2153 // Print stat counters
2154 NOT_PRODUCT(
2155 assert(_numObjectsAllocated == 0, "check");
2156 assert(_numWordsAllocated == 0, "check");
2157 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2158 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2159 _numObjectsPromoted = 0;
2160 _numWordsPromoted = 0;
2161 )
2162
2163 // Call down the chain in contiguous_available needs the freelistLock
2164 // so print this out before releasing the freeListLock.
2165 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2166 }
2167
2168 #ifndef PRODUCT
2169 bool CMSCollector::have_cms_token() {
2170 Thread* thr = Thread::current();
2171 if (thr->is_VM_thread()) {
2172 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2173 } else if (thr->is_ConcurrentGC_thread()) {
2174 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2175 } else if (thr->is_GC_task_thread()) {
2176 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2177 ParGCRareEvent_lock->owned_by_self();
2178 }
2179 return false;
2180 }
2181
2182 // Check reachability of the given heap address in CMS generation,
2183 // treating all other generations as roots.
2184 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2185 // We could "guarantee" below, rather than assert, but I'll
2186 // leave these as "asserts" so that an adventurous debugger
2187 // could try this in the product build provided some subset of
2188 // the conditions were met, provided they were interested in the
2189 // results and knew that the computation below wouldn't interfere
2190 // with other concurrent computations mutating the structures
2191 // being read or written.
2192 assert(SafepointSynchronize::is_at_safepoint(),
2193 "Else mutations in object graph will make answer suspect");
2194 assert(have_cms_token(), "Should hold cms token");
2195 assert(haveFreelistLocks(), "must hold free list locks");
2196 assert_lock_strong(bitMapLock());
2197
2198 // Clear the marking bit map array before starting, but, just
2199 // for kicks, first report if the given address is already marked
2200 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2201 _markBitMap.isMarked(addr) ? "" : " not");
2202
2203 if (verify_after_remark()) {
2204 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2205 bool result = verification_mark_bm()->isMarked(addr);
2206 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2207 result ? "IS" : "is NOT");
2208 return result;
2209 } else {
2210 tty->print_cr("Could not compute result");
2211 return false;
2212 }
2213 }
2214 #endif
2215
2216 void
2217 CMSCollector::print_on_error(outputStream* st) {
2218 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2219 if (collector != NULL) {
2220 CMSBitMap* bitmap = &collector->_markBitMap;
2221 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2222 bitmap->print_on_error(st, " Bits: ");
2223
2224 st->cr();
2225
2226 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2227 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2228 mut_bitmap->print_on_error(st, " Bits: ");
2229 }
2230 }
2231
2232 ////////////////////////////////////////////////////////
2233 // CMS Verification Support
2234 ////////////////////////////////////////////////////////
2235 // Following the remark phase, the following invariant
2236 // should hold -- each object in the CMS heap which is
2237 // marked in markBitMap() should be marked in the verification_mark_bm().
2238
2239 class VerifyMarkedClosure: public BitMapClosure {
2240 CMSBitMap* _marks;
2241 bool _failed;
2242
2243 public:
2244 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2245
2246 bool do_bit(size_t offset) {
2247 HeapWord* addr = _marks->offsetToHeapWord(offset);
2248 if (!_marks->isMarked(addr)) {
2249 Log(gc, verify) log;
2250 ResourceMark rm;
2251 LogStream ls(log.error());
2252 oop(addr)->print_on(&ls);
2253 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2254 _failed = true;
2255 }
2256 return true;
2257 }
2258
2259 bool failed() { return _failed; }
2260 };
2261
2262 bool CMSCollector::verify_after_remark() {
2263 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2264 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2265 static bool init = false;
2266
2267 assert(SafepointSynchronize::is_at_safepoint(),
2268 "Else mutations in object graph will make answer suspect");
2269 assert(have_cms_token(),
2270 "Else there may be mutual interference in use of "
2271 " verification data structures");
2272 assert(_collectorState > Marking && _collectorState <= Sweeping,
2273 "Else marking info checked here may be obsolete");
2274 assert(haveFreelistLocks(), "must hold free list locks");
2275 assert_lock_strong(bitMapLock());
2276
2277
2278 // Allocate marking bit map if not already allocated
2279 if (!init) { // first time
2280 if (!verification_mark_bm()->allocate(_span)) {
2281 return false;
2282 }
2283 init = true;
2284 }
2285
2286 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2287
2288 // Turn off refs discovery -- so we will be tracing through refs.
2289 // This is as intended, because by this time
2290 // GC must already have cleared any refs that need to be cleared,
2291 // and traced those that need to be marked; moreover,
2292 // the marking done here is not going to interfere in any
2293 // way with the marking information used by GC.
2294 NoRefDiscovery no_discovery(ref_processor());
2295
2296 #if COMPILER2_OR_JVMCI
2297 DerivedPointerTableDeactivate dpt_deact;
2298 #endif
2299
2300 // Clear any marks from a previous round
2301 verification_mark_bm()->clear_all();
2302 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2303 verify_work_stacks_empty();
2304
2305 CMSHeap* heap = CMSHeap::heap();
2306 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2307 // Update the saved marks which may affect the root scans.
2308 heap->save_marks();
2309
2310 if (CMSRemarkVerifyVariant == 1) {
2311 // In this first variant of verification, we complete
2312 // all marking, then check if the new marks-vector is
2313 // a subset of the CMS marks-vector.
2314 verify_after_remark_work_1();
2315 } else {
2316 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2317 // In this second variant of verification, we flag an error
2318 // (i.e. an object reachable in the new marks-vector not reachable
2319 // in the CMS marks-vector) immediately, also indicating the
2320 // identify of an object (A) that references the unmarked object (B) --
2321 // presumably, a mutation to A failed to be picked up by preclean/remark?
2322 verify_after_remark_work_2();
2323 }
2324
2325 return true;
2326 }
2327
2328 void CMSCollector::verify_after_remark_work_1() {
2329 ResourceMark rm;
2330 HandleMark hm;
2331 CMSHeap* heap = CMSHeap::heap();
2332
2333 // Get a clear set of claim bits for the roots processing to work with.
2334 ClassLoaderDataGraph::clear_claimed_marks();
2335
2336 // Mark from roots one level into CMS
2337 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2338 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2339
2340 {
2341 StrongRootsScope srs(1);
2342
2343 heap->cms_process_roots(&srs,
2344 true, // young gen as roots
2345 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2346 should_unload_classes(),
2347 ¬Older,
2348 NULL);
2349 }
2350
2351 // Now mark from the roots
2352 MarkFromRootsClosure markFromRootsClosure(this, _span,
2353 verification_mark_bm(), verification_mark_stack(),
2354 false /* don't yield */, true /* verifying */);
2355 assert(_restart_addr == NULL, "Expected pre-condition");
2356 verification_mark_bm()->iterate(&markFromRootsClosure);
2357 while (_restart_addr != NULL) {
2358 // Deal with stack overflow: by restarting at the indicated
2359 // address.
2360 HeapWord* ra = _restart_addr;
2361 markFromRootsClosure.reset(ra);
2362 _restart_addr = NULL;
2363 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2364 }
2365 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2366 verify_work_stacks_empty();
2367
2368 // Marking completed -- now verify that each bit marked in
2369 // verification_mark_bm() is also marked in markBitMap(); flag all
2370 // errors by printing corresponding objects.
2371 VerifyMarkedClosure vcl(markBitMap());
2372 verification_mark_bm()->iterate(&vcl);
2373 if (vcl.failed()) {
2374 Log(gc, verify) log;
2375 log.error("Failed marking verification after remark");
2376 ResourceMark rm;
2377 LogStream ls(log.error());
2378 heap->print_on(&ls);
2379 fatal("CMS: failed marking verification after remark");
2380 }
2381 }
2382
2383 class VerifyCLDOopsCLDClosure : public CLDClosure {
2384 class VerifyCLDOopsClosure : public OopClosure {
2385 CMSBitMap* _bitmap;
2386 public:
2387 VerifyCLDOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2388 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2389 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2390 } _oop_closure;
2391 public:
2392 VerifyCLDOopsCLDClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2393 void do_cld(ClassLoaderData* cld) {
2394 cld->oops_do(&_oop_closure, false, false);
2395 }
2396 };
2397
2398 void CMSCollector::verify_after_remark_work_2() {
2399 ResourceMark rm;
2400 HandleMark hm;
2401 CMSHeap* heap = CMSHeap::heap();
2402
2403 // Get a clear set of claim bits for the roots processing to work with.
2404 ClassLoaderDataGraph::clear_claimed_marks();
2405
2406 // Mark from roots one level into CMS
2407 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2408 markBitMap());
2409 CLDToOopClosure cld_closure(¬Older, true);
2410
2411 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2412
2413 {
2414 StrongRootsScope srs(1);
2415
2416 heap->cms_process_roots(&srs,
2417 true, // young gen as roots
2418 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2419 should_unload_classes(),
2420 ¬Older,
2421 &cld_closure);
2422 }
2423
2424 // Now mark from the roots
2425 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2426 verification_mark_bm(), markBitMap(), verification_mark_stack());
2427 assert(_restart_addr == NULL, "Expected pre-condition");
2428 verification_mark_bm()->iterate(&markFromRootsClosure);
2429 while (_restart_addr != NULL) {
2430 // Deal with stack overflow: by restarting at the indicated
2431 // address.
2432 HeapWord* ra = _restart_addr;
2433 markFromRootsClosure.reset(ra);
2434 _restart_addr = NULL;
2435 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2436 }
2437 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2438 verify_work_stacks_empty();
2439
2440 VerifyCLDOopsCLDClosure verify_cld_oops(verification_mark_bm());
2441 ClassLoaderDataGraph::cld_do(&verify_cld_oops);
2442
2443 // Marking completed -- now verify that each bit marked in
2444 // verification_mark_bm() is also marked in markBitMap(); flag all
2445 // errors by printing corresponding objects.
2446 VerifyMarkedClosure vcl(markBitMap());
2447 verification_mark_bm()->iterate(&vcl);
2448 assert(!vcl.failed(), "Else verification above should not have succeeded");
2449 }
2450
2451 void ConcurrentMarkSweepGeneration::save_marks() {
2452 // delegate to CMS space
2453 cmsSpace()->save_marks();
2454 }
2455
2456 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2457 return cmsSpace()->no_allocs_since_save_marks();
2458 }
2459
2460 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2461 \
2462 void ConcurrentMarkSweepGeneration:: \
2463 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2464 cl->set_generation(this); \
2465 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2466 cl->reset_generation(); \
2467 save_marks(); \
2468 }
2469
2470 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2471
2472 void
2473 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2474 if (freelistLock()->owned_by_self()) {
2475 Generation::oop_iterate(cl);
2476 } else {
2477 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2478 Generation::oop_iterate(cl);
2479 }
2480 }
2481
2482 void
2483 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2484 if (freelistLock()->owned_by_self()) {
2485 Generation::object_iterate(cl);
2486 } else {
2487 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2488 Generation::object_iterate(cl);
2489 }
2490 }
2491
2492 void
2493 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2494 if (freelistLock()->owned_by_self()) {
2495 Generation::safe_object_iterate(cl);
2496 } else {
2497 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2498 Generation::safe_object_iterate(cl);
2499 }
2500 }
2501
2502 void
2503 ConcurrentMarkSweepGeneration::post_compact() {
2504 }
2505
2506 void
2507 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2508 // Fix the linear allocation blocks to look like free blocks.
2509
2510 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2511 // are not called when the heap is verified during universe initialization and
2512 // at vm shutdown.
2513 if (freelistLock()->owned_by_self()) {
2514 cmsSpace()->prepare_for_verify();
2515 } else {
2516 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2517 cmsSpace()->prepare_for_verify();
2518 }
2519 }
2520
2521 void
2522 ConcurrentMarkSweepGeneration::verify() {
2523 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2524 // are not called when the heap is verified during universe initialization and
2525 // at vm shutdown.
2526 if (freelistLock()->owned_by_self()) {
2527 cmsSpace()->verify();
2528 } else {
2529 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2530 cmsSpace()->verify();
2531 }
2532 }
2533
2534 void CMSCollector::verify() {
2535 _cmsGen->verify();
2536 }
2537
2538 #ifndef PRODUCT
2539 bool CMSCollector::overflow_list_is_empty() const {
2540 assert(_num_par_pushes >= 0, "Inconsistency");
2541 if (_overflow_list == NULL) {
2542 assert(_num_par_pushes == 0, "Inconsistency");
2543 }
2544 return _overflow_list == NULL;
2545 }
2546
2547 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2548 // merely consolidate assertion checks that appear to occur together frequently.
2549 void CMSCollector::verify_work_stacks_empty() const {
2550 assert(_markStack.isEmpty(), "Marking stack should be empty");
2551 assert(overflow_list_is_empty(), "Overflow list should be empty");
2552 }
2553
2554 void CMSCollector::verify_overflow_empty() const {
2555 assert(overflow_list_is_empty(), "Overflow list should be empty");
2556 assert(no_preserved_marks(), "No preserved marks");
2557 }
2558 #endif // PRODUCT
2559
2560 // Decide if we want to enable class unloading as part of the
2561 // ensuing concurrent GC cycle. We will collect and
2562 // unload classes if it's the case that:
2563 // (a) class unloading is enabled at the command line, and
2564 // (b) old gen is getting really full
2565 // NOTE: Provided there is no change in the state of the heap between
2566 // calls to this method, it should have idempotent results. Moreover,
2567 // its results should be monotonically increasing (i.e. going from 0 to 1,
2568 // but not 1 to 0) between successive calls between which the heap was
2569 // not collected. For the implementation below, it must thus rely on
2570 // the property that concurrent_cycles_since_last_unload()
2571 // will not decrease unless a collection cycle happened and that
2572 // _cmsGen->is_too_full() are
2573 // themselves also monotonic in that sense. See check_monotonicity()
2574 // below.
2575 void CMSCollector::update_should_unload_classes() {
2576 _should_unload_classes = false;
2577 if (CMSClassUnloadingEnabled) {
2578 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2579 CMSClassUnloadingMaxInterval)
2580 || _cmsGen->is_too_full();
2581 }
2582 }
2583
2584 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2585 bool res = should_concurrent_collect();
2586 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2587 return res;
2588 }
2589
2590 void CMSCollector::setup_cms_unloading_and_verification_state() {
2591 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2592 || VerifyBeforeExit;
2593 const int rso = GenCollectedHeap::SO_AllCodeCache;
2594
2595 // We set the proper root for this CMS cycle here.
2596 if (should_unload_classes()) { // Should unload classes this cycle
2597 remove_root_scanning_option(rso); // Shrink the root set appropriately
2598 set_verifying(should_verify); // Set verification state for this cycle
2599 return; // Nothing else needs to be done at this time
2600 }
2601
2602 // Not unloading classes this cycle
2603 assert(!should_unload_classes(), "Inconsistency!");
2604
2605 // If we are not unloading classes then add SO_AllCodeCache to root
2606 // scanning options.
2607 add_root_scanning_option(rso);
2608
2609 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2610 set_verifying(true);
2611 } else if (verifying() && !should_verify) {
2612 // We were verifying, but some verification flags got disabled.
2613 set_verifying(false);
2614 // Exclude symbols, strings and code cache elements from root scanning to
2615 // reduce IM and RM pauses.
2616 remove_root_scanning_option(rso);
2617 }
2618 }
2619
2620
2621 #ifndef PRODUCT
2622 HeapWord* CMSCollector::block_start(const void* p) const {
2623 const HeapWord* addr = (HeapWord*)p;
2624 if (_span.contains(p)) {
2625 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2626 return _cmsGen->cmsSpace()->block_start(p);
2627 }
2628 }
2629 return NULL;
2630 }
2631 #endif
2632
2633 HeapWord*
2634 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2635 bool tlab,
2636 bool parallel) {
2637 CMSSynchronousYieldRequest yr;
2638 assert(!tlab, "Can't deal with TLAB allocation");
2639 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2640 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2641 if (GCExpandToAllocateDelayMillis > 0) {
2642 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2643 }
2644 return have_lock_and_allocate(word_size, tlab);
2645 }
2646
2647 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2648 size_t bytes,
2649 size_t expand_bytes,
2650 CMSExpansionCause::Cause cause)
2651 {
2652
2653 bool success = expand(bytes, expand_bytes);
2654
2655 // remember why we expanded; this information is used
2656 // by shouldConcurrentCollect() when making decisions on whether to start
2657 // a new CMS cycle.
2658 if (success) {
2659 set_expansion_cause(cause);
2660 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2661 }
2662 }
2663
2664 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2665 HeapWord* res = NULL;
2666 MutexLocker x(ParGCRareEvent_lock);
2667 while (true) {
2668 // Expansion by some other thread might make alloc OK now:
2669 res = ps->lab.alloc(word_sz);
2670 if (res != NULL) return res;
2671 // If there's not enough expansion space available, give up.
2672 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2673 return NULL;
2674 }
2675 // Otherwise, we try expansion.
2676 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2677 // Now go around the loop and try alloc again;
2678 // A competing par_promote might beat us to the expansion space,
2679 // so we may go around the loop again if promotion fails again.
2680 if (GCExpandToAllocateDelayMillis > 0) {
2681 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2682 }
2683 }
2684 }
2685
2686
2687 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2688 PromotionInfo* promo) {
2689 MutexLocker x(ParGCRareEvent_lock);
2690 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2691 while (true) {
2692 // Expansion by some other thread might make alloc OK now:
2693 if (promo->ensure_spooling_space()) {
2694 assert(promo->has_spooling_space(),
2695 "Post-condition of successful ensure_spooling_space()");
2696 return true;
2697 }
2698 // If there's not enough expansion space available, give up.
2699 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2700 return false;
2701 }
2702 // Otherwise, we try expansion.
2703 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2704 // Now go around the loop and try alloc again;
2705 // A competing allocation might beat us to the expansion space,
2706 // so we may go around the loop again if allocation fails again.
2707 if (GCExpandToAllocateDelayMillis > 0) {
2708 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2709 }
2710 }
2711 }
2712
2713 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2714 // Only shrink if a compaction was done so that all the free space
2715 // in the generation is in a contiguous block at the end.
2716 if (did_compact()) {
2717 CardGeneration::shrink(bytes);
2718 }
2719 }
2720
2721 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2722 assert_locked_or_safepoint(Heap_lock);
2723 }
2724
2725 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2726 assert_locked_or_safepoint(Heap_lock);
2727 assert_lock_strong(freelistLock());
2728 log_trace(gc)("Shrinking of CMS not yet implemented");
2729 return;
2730 }
2731
2732
2733 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2734 // phases.
2735 class CMSPhaseAccounting: public StackObj {
2736 public:
2737 CMSPhaseAccounting(CMSCollector *collector,
2738 const char *title);
2739 ~CMSPhaseAccounting();
2740
2741 private:
2742 CMSCollector *_collector;
2743 const char *_title;
2744 GCTraceConcTime(Info, gc) _trace_time;
2745
2746 public:
2747 // Not MT-safe; so do not pass around these StackObj's
2748 // where they may be accessed by other threads.
2749 double wallclock_millis() {
2750 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2751 }
2752 };
2753
2754 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2755 const char *title) :
2756 _collector(collector), _title(title), _trace_time(title) {
2757
2758 _collector->resetYields();
2759 _collector->resetTimer();
2760 _collector->startTimer();
2761 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2762 }
2763
2764 CMSPhaseAccounting::~CMSPhaseAccounting() {
2765 _collector->gc_timer_cm()->register_gc_concurrent_end();
2766 _collector->stopTimer();
2767 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2768 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2769 }
2770
2771 // CMS work
2772
2773 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2774 class CMSParMarkTask : public AbstractGangTask {
2775 protected:
2776 CMSCollector* _collector;
2777 uint _n_workers;
2778 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2779 AbstractGangTask(name),
2780 _collector(collector),
2781 _n_workers(n_workers) {}
2782 // Work method in support of parallel rescan ... of young gen spaces
2783 void do_young_space_rescan(OopsInGenClosure* cl,
2784 ContiguousSpace* space,
2785 HeapWord** chunk_array, size_t chunk_top);
2786 void work_on_young_gen_roots(OopsInGenClosure* cl);
2787 };
2788
2789 // Parallel initial mark task
2790 class CMSParInitialMarkTask: public CMSParMarkTask {
2791 StrongRootsScope* _strong_roots_scope;
2792 public:
2793 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2794 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2795 _strong_roots_scope(strong_roots_scope) {}
2796 void work(uint worker_id);
2797 };
2798
2799 // Checkpoint the roots into this generation from outside
2800 // this generation. [Note this initial checkpoint need only
2801 // be approximate -- we'll do a catch up phase subsequently.]
2802 void CMSCollector::checkpointRootsInitial() {
2803 assert(_collectorState == InitialMarking, "Wrong collector state");
2804 check_correct_thread_executing();
2805 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
2806
2807 save_heap_summary();
2808 report_heap_summary(GCWhen::BeforeGC);
2809
2810 ReferenceProcessor* rp = ref_processor();
2811 assert(_restart_addr == NULL, "Control point invariant");
2812 {
2813 // acquire locks for subsequent manipulations
2814 MutexLockerEx x(bitMapLock(),
2815 Mutex::_no_safepoint_check_flag);
2816 checkpointRootsInitialWork();
2817 // enable ("weak") refs discovery
2818 rp->enable_discovery();
2819 _collectorState = Marking;
2820 }
2821 }
2822
2823 void CMSCollector::checkpointRootsInitialWork() {
2824 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2825 assert(_collectorState == InitialMarking, "just checking");
2826
2827 // Already have locks.
2828 assert_lock_strong(bitMapLock());
2829 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2830
2831 // Setup the verification and class unloading state for this
2832 // CMS collection cycle.
2833 setup_cms_unloading_and_verification_state();
2834
2835 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2836
2837 // Reset all the PLAB chunk arrays if necessary.
2838 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2839 reset_survivor_plab_arrays();
2840 }
2841
2842 ResourceMark rm;
2843 HandleMark hm;
2844
2845 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2846 CMSHeap* heap = CMSHeap::heap();
2847
2848 verify_work_stacks_empty();
2849 verify_overflow_empty();
2850
2851 heap->ensure_parsability(false); // fill TLABs, but no need to retire them
2852 // Update the saved marks which may affect the root scans.
2853 heap->save_marks();
2854
2855 // weak reference processing has not started yet.
2856 ref_processor()->set_enqueuing_is_done(false);
2857
2858 // Need to remember all newly created CLDs,
2859 // so that we can guarantee that the remark finds them.
2860 ClassLoaderDataGraph::remember_new_clds(true);
2861
2862 // Whenever a CLD is found, it will be claimed before proceeding to mark
2863 // the klasses. The claimed marks need to be cleared before marking starts.
2864 ClassLoaderDataGraph::clear_claimed_marks();
2865
2866 print_eden_and_survivor_chunk_arrays();
2867
2868 {
2869 #if COMPILER2_OR_JVMCI
2870 DerivedPointerTableDeactivate dpt_deact;
2871 #endif
2872 if (CMSParallelInitialMarkEnabled) {
2873 // The parallel version.
2874 WorkGang* workers = heap->workers();
2875 assert(workers != NULL, "Need parallel worker threads.");
2876 uint n_workers = workers->active_workers();
2877
2878 StrongRootsScope srs(n_workers);
2879
2880 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2881 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2882 // If the total workers is greater than 1, then multiple workers
2883 // may be used at some time and the initialization has been set
2884 // such that the single threaded path cannot be used.
2885 if (workers->total_workers() > 1) {
2886 workers->run_task(&tsk);
2887 } else {
2888 tsk.work(0);
2889 }
2890 } else {
2891 // The serial version.
2892 CLDToOopClosure cld_closure(¬Older, true);
2893 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2894
2895 StrongRootsScope srs(1);
2896
2897 heap->cms_process_roots(&srs,
2898 true, // young gen as roots
2899 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2900 should_unload_classes(),
2901 ¬Older,
2902 &cld_closure);
2903 }
2904 }
2905
2906 // Clear mod-union table; it will be dirtied in the prologue of
2907 // CMS generation per each young generation collection.
2908
2909 assert(_modUnionTable.isAllClear(),
2910 "Was cleared in most recent final checkpoint phase"
2911 " or no bits are set in the gc_prologue before the start of the next "
2912 "subsequent marking phase.");
2913
2914 assert(_ct->cld_rem_set()->mod_union_is_clear(), "Must be");
2915
2916 // Save the end of the used_region of the constituent generations
2917 // to be used to limit the extent of sweep in each generation.
2918 save_sweep_limits();
2919 verify_overflow_empty();
2920 }
2921
2922 bool CMSCollector::markFromRoots() {
2923 // we might be tempted to assert that:
2924 // assert(!SafepointSynchronize::is_at_safepoint(),
2925 // "inconsistent argument?");
2926 // However that wouldn't be right, because it's possible that
2927 // a safepoint is indeed in progress as a young generation
2928 // stop-the-world GC happens even as we mark in this generation.
2929 assert(_collectorState == Marking, "inconsistent state?");
2930 check_correct_thread_executing();
2931 verify_overflow_empty();
2932
2933 // Weak ref discovery note: We may be discovering weak
2934 // refs in this generation concurrent (but interleaved) with
2935 // weak ref discovery by the young generation collector.
2936
2937 CMSTokenSyncWithLocks ts(true, bitMapLock());
2938 GCTraceCPUTime tcpu;
2939 CMSPhaseAccounting pa(this, "Concurrent Mark");
2940 bool res = markFromRootsWork();
2941 if (res) {
2942 _collectorState = Precleaning;
2943 } else { // We failed and a foreground collection wants to take over
2944 assert(_foregroundGCIsActive, "internal state inconsistency");
2945 assert(_restart_addr == NULL, "foreground will restart from scratch");
2946 log_debug(gc)("bailing out to foreground collection");
2947 }
2948 verify_overflow_empty();
2949 return res;
2950 }
2951
2952 bool CMSCollector::markFromRootsWork() {
2953 // iterate over marked bits in bit map, doing a full scan and mark
2954 // from these roots using the following algorithm:
2955 // . if oop is to the right of the current scan pointer,
2956 // mark corresponding bit (we'll process it later)
2957 // . else (oop is to left of current scan pointer)
2958 // push oop on marking stack
2959 // . drain the marking stack
2960
2961 // Note that when we do a marking step we need to hold the
2962 // bit map lock -- recall that direct allocation (by mutators)
2963 // and promotion (by the young generation collector) is also
2964 // marking the bit map. [the so-called allocate live policy.]
2965 // Because the implementation of bit map marking is not
2966 // robust wrt simultaneous marking of bits in the same word,
2967 // we need to make sure that there is no such interference
2968 // between concurrent such updates.
2969
2970 // already have locks
2971 assert_lock_strong(bitMapLock());
2972
2973 verify_work_stacks_empty();
2974 verify_overflow_empty();
2975 bool result = false;
2976 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2977 result = do_marking_mt();
2978 } else {
2979 result = do_marking_st();
2980 }
2981 return result;
2982 }
2983
2984 // Forward decl
2985 class CMSConcMarkingTask;
2986
2987 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2988 CMSCollector* _collector;
2989 CMSConcMarkingTask* _task;
2990 public:
2991 virtual void yield();
2992
2993 // "n_threads" is the number of threads to be terminated.
2994 // "queue_set" is a set of work queues of other threads.
2995 // "collector" is the CMS collector associated with this task terminator.
2996 // "yield" indicates whether we need the gang as a whole to yield.
2997 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2998 ParallelTaskTerminator(n_threads, queue_set),
2999 _collector(collector) { }
3000
3001 void set_task(CMSConcMarkingTask* task) {
3002 _task = task;
3003 }
3004 };
3005
3006 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3007 CMSConcMarkingTask* _task;
3008 public:
3009 bool should_exit_termination();
3010 void set_task(CMSConcMarkingTask* task) {
3011 _task = task;
3012 }
3013 };
3014
3015 // MT Concurrent Marking Task
3016 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3017 CMSCollector* _collector;
3018 uint _n_workers; // requested/desired # workers
3019 bool _result;
3020 CompactibleFreeListSpace* _cms_space;
3021 char _pad_front[64]; // padding to ...
3022 HeapWord* volatile _global_finger; // ... avoid sharing cache line
3023 char _pad_back[64];
3024 HeapWord* _restart_addr;
3025
3026 // Exposed here for yielding support
3027 Mutex* const _bit_map_lock;
3028
3029 // The per thread work queues, available here for stealing
3030 OopTaskQueueSet* _task_queues;
3031
3032 // Termination (and yielding) support
3033 CMSConcMarkingTerminator _term;
3034 CMSConcMarkingTerminatorTerminator _term_term;
3035
3036 public:
3037 CMSConcMarkingTask(CMSCollector* collector,
3038 CompactibleFreeListSpace* cms_space,
3039 YieldingFlexibleWorkGang* workers,
3040 OopTaskQueueSet* task_queues):
3041 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3042 _collector(collector),
3043 _cms_space(cms_space),
3044 _n_workers(0), _result(true),
3045 _task_queues(task_queues),
3046 _term(_n_workers, task_queues, _collector),
3047 _bit_map_lock(collector->bitMapLock())
3048 {
3049 _requested_size = _n_workers;
3050 _term.set_task(this);
3051 _term_term.set_task(this);
3052 _restart_addr = _global_finger = _cms_space->bottom();
3053 }
3054
3055
3056 OopTaskQueueSet* task_queues() { return _task_queues; }
3057
3058 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3059
3060 HeapWord* volatile* global_finger_addr() { return &_global_finger; }
3061
3062 CMSConcMarkingTerminator* terminator() { return &_term; }
3063
3064 virtual void set_for_termination(uint active_workers) {
3065 terminator()->reset_for_reuse(active_workers);
3066 }
3067
3068 void work(uint worker_id);
3069 bool should_yield() {
3070 return ConcurrentMarkSweepThread::should_yield()
3071 && !_collector->foregroundGCIsActive();
3072 }
3073
3074 virtual void coordinator_yield(); // stuff done by coordinator
3075 bool result() { return _result; }
3076
3077 void reset(HeapWord* ra) {
3078 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3079 _restart_addr = _global_finger = ra;
3080 _term.reset_for_reuse();
3081 }
3082
3083 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3084 OopTaskQueue* work_q);
3085
3086 private:
3087 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3088 void do_work_steal(int i);
3089 void bump_global_finger(HeapWord* f);
3090 };
3091
3092 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3093 assert(_task != NULL, "Error");
3094 return _task->yielding();
3095 // Note that we do not need the disjunct || _task->should_yield() above
3096 // because we want terminating threads to yield only if the task
3097 // is already in the midst of yielding, which happens only after at least one
3098 // thread has yielded.
3099 }
3100
3101 void CMSConcMarkingTerminator::yield() {
3102 if (_task->should_yield()) {
3103 _task->yield();
3104 } else {
3105 ParallelTaskTerminator::yield();
3106 }
3107 }
3108
3109 ////////////////////////////////////////////////////////////////
3110 // Concurrent Marking Algorithm Sketch
3111 ////////////////////////////////////////////////////////////////
3112 // Until all tasks exhausted (both spaces):
3113 // -- claim next available chunk
3114 // -- bump global finger via CAS
3115 // -- find first object that starts in this chunk
3116 // and start scanning bitmap from that position
3117 // -- scan marked objects for oops
3118 // -- CAS-mark target, and if successful:
3119 // . if target oop is above global finger (volatile read)
3120 // nothing to do
3121 // . if target oop is in chunk and above local finger
3122 // then nothing to do
3123 // . else push on work-queue
3124 // -- Deal with possible overflow issues:
3125 // . local work-queue overflow causes stuff to be pushed on
3126 // global (common) overflow queue
3127 // . always first empty local work queue
3128 // . then get a batch of oops from global work queue if any
3129 // . then do work stealing
3130 // -- When all tasks claimed (both spaces)
3131 // and local work queue empty,
3132 // then in a loop do:
3133 // . check global overflow stack; steal a batch of oops and trace
3134 // . try to steal from other threads oif GOS is empty
3135 // . if neither is available, offer termination
3136 // -- Terminate and return result
3137 //
3138 void CMSConcMarkingTask::work(uint worker_id) {
3139 elapsedTimer _timer;
3140 ResourceMark rm;
3141 HandleMark hm;
3142
3143 DEBUG_ONLY(_collector->verify_overflow_empty();)
3144
3145 // Before we begin work, our work queue should be empty
3146 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3147 // Scan the bitmap covering _cms_space, tracing through grey objects.
3148 _timer.start();
3149 do_scan_and_mark(worker_id, _cms_space);
3150 _timer.stop();
3151 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3152
3153 // ... do work stealing
3154 _timer.reset();
3155 _timer.start();
3156 do_work_steal(worker_id);
3157 _timer.stop();
3158 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3159 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3160 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3161 // Note that under the current task protocol, the
3162 // following assertion is true even of the spaces
3163 // expanded since the completion of the concurrent
3164 // marking. XXX This will likely change under a strict
3165 // ABORT semantics.
3166 // After perm removal the comparison was changed to
3167 // greater than or equal to from strictly greater than.
3168 // Before perm removal the highest address sweep would
3169 // have been at the end of perm gen but now is at the
3170 // end of the tenured gen.
3171 assert(_global_finger >= _cms_space->end(),
3172 "All tasks have been completed");
3173 DEBUG_ONLY(_collector->verify_overflow_empty();)
3174 }
3175
3176 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3177 HeapWord* read = _global_finger;
3178 HeapWord* cur = read;
3179 while (f > read) {
3180 cur = read;
3181 read = Atomic::cmpxchg(f, &_global_finger, cur);
3182 if (cur == read) {
3183 // our cas succeeded
3184 assert(_global_finger >= f, "protocol consistency");
3185 break;
3186 }
3187 }
3188 }
3189
3190 // This is really inefficient, and should be redone by
3191 // using (not yet available) block-read and -write interfaces to the
3192 // stack and the work_queue. XXX FIX ME !!!
3193 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3194 OopTaskQueue* work_q) {
3195 // Fast lock-free check
3196 if (ovflw_stk->length() == 0) {
3197 return false;
3198 }
3199 assert(work_q->size() == 0, "Shouldn't steal");
3200 MutexLockerEx ml(ovflw_stk->par_lock(),
3201 Mutex::_no_safepoint_check_flag);
3202 // Grab up to 1/4 the size of the work queue
3203 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3204 (size_t)ParGCDesiredObjsFromOverflowList);
3205 num = MIN2(num, ovflw_stk->length());
3206 for (int i = (int) num; i > 0; i--) {
3207 oop cur = ovflw_stk->pop();
3208 assert(cur != NULL, "Counted wrong?");
3209 work_q->push(cur);
3210 }
3211 return num > 0;
3212 }
3213
3214 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3215 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3216 int n_tasks = pst->n_tasks();
3217 // We allow that there may be no tasks to do here because
3218 // we are restarting after a stack overflow.
3219 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3220 uint nth_task = 0;
3221
3222 HeapWord* aligned_start = sp->bottom();
3223 if (sp->used_region().contains(_restart_addr)) {
3224 // Align down to a card boundary for the start of 0th task
3225 // for this space.
3226 aligned_start = align_down(_restart_addr, CardTableModRefBS::card_size);
3227 }
3228
3229 size_t chunk_size = sp->marking_task_size();
3230 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3231 // Having claimed the nth task in this space,
3232 // compute the chunk that it corresponds to:
3233 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3234 aligned_start + (nth_task+1)*chunk_size);
3235 // Try and bump the global finger via a CAS;
3236 // note that we need to do the global finger bump
3237 // _before_ taking the intersection below, because
3238 // the task corresponding to that region will be
3239 // deemed done even if the used_region() expands
3240 // because of allocation -- as it almost certainly will
3241 // during start-up while the threads yield in the
3242 // closure below.
3243 HeapWord* finger = span.end();
3244 bump_global_finger(finger); // atomically
3245 // There are null tasks here corresponding to chunks
3246 // beyond the "top" address of the space.
3247 span = span.intersection(sp->used_region());
3248 if (!span.is_empty()) { // Non-null task
3249 HeapWord* prev_obj;
3250 assert(!span.contains(_restart_addr) || nth_task == 0,
3251 "Inconsistency");
3252 if (nth_task == 0) {
3253 // For the 0th task, we'll not need to compute a block_start.
3254 if (span.contains(_restart_addr)) {
3255 // In the case of a restart because of stack overflow,
3256 // we might additionally skip a chunk prefix.
3257 prev_obj = _restart_addr;
3258 } else {
3259 prev_obj = span.start();
3260 }
3261 } else {
3262 // We want to skip the first object because
3263 // the protocol is to scan any object in its entirety
3264 // that _starts_ in this span; a fortiori, any
3265 // object starting in an earlier span is scanned
3266 // as part of an earlier claimed task.
3267 // Below we use the "careful" version of block_start
3268 // so we do not try to navigate uninitialized objects.
3269 prev_obj = sp->block_start_careful(span.start());
3270 // Below we use a variant of block_size that uses the
3271 // Printezis bits to avoid waiting for allocated
3272 // objects to become initialized/parsable.
3273 while (prev_obj < span.start()) {
3274 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3275 if (sz > 0) {
3276 prev_obj += sz;
3277 } else {
3278 // In this case we may end up doing a bit of redundant
3279 // scanning, but that appears unavoidable, short of
3280 // locking the free list locks; see bug 6324141.
3281 break;
3282 }
3283 }
3284 }
3285 if (prev_obj < span.end()) {
3286 MemRegion my_span = MemRegion(prev_obj, span.end());
3287 // Do the marking work within a non-empty span --
3288 // the last argument to the constructor indicates whether the
3289 // iteration should be incremental with periodic yields.
3290 ParMarkFromRootsClosure cl(this, _collector, my_span,
3291 &_collector->_markBitMap,
3292 work_queue(i),
3293 &_collector->_markStack);
3294 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3295 } // else nothing to do for this task
3296 } // else nothing to do for this task
3297 }
3298 // We'd be tempted to assert here that since there are no
3299 // more tasks left to claim in this space, the global_finger
3300 // must exceed space->top() and a fortiori space->end(). However,
3301 // that would not quite be correct because the bumping of
3302 // global_finger occurs strictly after the claiming of a task,
3303 // so by the time we reach here the global finger may not yet
3304 // have been bumped up by the thread that claimed the last
3305 // task.
3306 pst->all_tasks_completed();
3307 }
3308
3309 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3310 private:
3311 CMSCollector* _collector;
3312 CMSConcMarkingTask* _task;
3313 MemRegion _span;
3314 CMSBitMap* _bit_map;
3315 CMSMarkStack* _overflow_stack;
3316 OopTaskQueue* _work_queue;
3317 protected:
3318 DO_OOP_WORK_DEFN
3319 public:
3320 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3321 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3322 MetadataAwareOopClosure(collector->ref_processor()),
3323 _collector(collector),
3324 _task(task),
3325 _span(collector->_span),
3326 _work_queue(work_queue),
3327 _bit_map(bit_map),
3328 _overflow_stack(overflow_stack)
3329 { }
3330 virtual void do_oop(oop* p);
3331 virtual void do_oop(narrowOop* p);
3332
3333 void trim_queue(size_t max);
3334 void handle_stack_overflow(HeapWord* lost);
3335 void do_yield_check() {
3336 if (_task->should_yield()) {
3337 _task->yield();
3338 }
3339 }
3340 };
3341
3342 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3343
3344 // Grey object scanning during work stealing phase --
3345 // the salient assumption here is that any references
3346 // that are in these stolen objects being scanned must
3347 // already have been initialized (else they would not have
3348 // been published), so we do not need to check for
3349 // uninitialized objects before pushing here.
3350 void ParConcMarkingClosure::do_oop(oop obj) {
3351 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3352 HeapWord* addr = (HeapWord*)obj;
3353 // Check if oop points into the CMS generation
3354 // and is not marked
3355 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3356 // a white object ...
3357 // If we manage to "claim" the object, by being the
3358 // first thread to mark it, then we push it on our
3359 // marking stack
3360 if (_bit_map->par_mark(addr)) { // ... now grey
3361 // push on work queue (grey set)
3362 bool simulate_overflow = false;
3363 NOT_PRODUCT(
3364 if (CMSMarkStackOverflowALot &&
3365 _collector->simulate_overflow()) {
3366 // simulate a stack overflow
3367 simulate_overflow = true;
3368 }
3369 )
3370 if (simulate_overflow ||
3371 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3372 // stack overflow
3373 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3374 // We cannot assert that the overflow stack is full because
3375 // it may have been emptied since.
3376 assert(simulate_overflow ||
3377 _work_queue->size() == _work_queue->max_elems(),
3378 "Else push should have succeeded");
3379 handle_stack_overflow(addr);
3380 }
3381 } // Else, some other thread got there first
3382 do_yield_check();
3383 }
3384 }
3385
3386 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3387 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3388
3389 void ParConcMarkingClosure::trim_queue(size_t max) {
3390 while (_work_queue->size() > max) {
3391 oop new_oop;
3392 if (_work_queue->pop_local(new_oop)) {
3393 assert(oopDesc::is_oop(new_oop), "Should be an oop");
3394 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3395 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3396 new_oop->oop_iterate(this); // do_oop() above
3397 do_yield_check();
3398 }
3399 }
3400 }
3401
3402 // Upon stack overflow, we discard (part of) the stack,
3403 // remembering the least address amongst those discarded
3404 // in CMSCollector's _restart_address.
3405 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3406 // We need to do this under a mutex to prevent other
3407 // workers from interfering with the work done below.
3408 MutexLockerEx ml(_overflow_stack->par_lock(),
3409 Mutex::_no_safepoint_check_flag);
3410 // Remember the least grey address discarded
3411 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3412 _collector->lower_restart_addr(ra);
3413 _overflow_stack->reset(); // discard stack contents
3414 _overflow_stack->expand(); // expand the stack if possible
3415 }
3416
3417
3418 void CMSConcMarkingTask::do_work_steal(int i) {
3419 OopTaskQueue* work_q = work_queue(i);
3420 oop obj_to_scan;
3421 CMSBitMap* bm = &(_collector->_markBitMap);
3422 CMSMarkStack* ovflw = &(_collector->_markStack);
3423 int* seed = _collector->hash_seed(i);
3424 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3425 while (true) {
3426 cl.trim_queue(0);
3427 assert(work_q->size() == 0, "Should have been emptied above");
3428 if (get_work_from_overflow_stack(ovflw, work_q)) {
3429 // Can't assert below because the work obtained from the
3430 // overflow stack may already have been stolen from us.
3431 // assert(work_q->size() > 0, "Work from overflow stack");
3432 continue;
3433 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3434 assert(oopDesc::is_oop(obj_to_scan), "Should be an oop");
3435 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3436 obj_to_scan->oop_iterate(&cl);
3437 } else if (terminator()->offer_termination(&_term_term)) {
3438 assert(work_q->size() == 0, "Impossible!");
3439 break;
3440 } else if (yielding() || should_yield()) {
3441 yield();
3442 }
3443 }
3444 }
3445
3446 // This is run by the CMS (coordinator) thread.
3447 void CMSConcMarkingTask::coordinator_yield() {
3448 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3449 "CMS thread should hold CMS token");
3450 // First give up the locks, then yield, then re-lock
3451 // We should probably use a constructor/destructor idiom to
3452 // do this unlock/lock or modify the MutexUnlocker class to
3453 // serve our purpose. XXX
3454 assert_lock_strong(_bit_map_lock);
3455 _bit_map_lock->unlock();
3456 ConcurrentMarkSweepThread::desynchronize(true);
3457 _collector->stopTimer();
3458 _collector->incrementYields();
3459
3460 // It is possible for whichever thread initiated the yield request
3461 // not to get a chance to wake up and take the bitmap lock between
3462 // this thread releasing it and reacquiring it. So, while the
3463 // should_yield() flag is on, let's sleep for a bit to give the
3464 // other thread a chance to wake up. The limit imposed on the number
3465 // of iterations is defensive, to avoid any unforseen circumstances
3466 // putting us into an infinite loop. Since it's always been this
3467 // (coordinator_yield()) method that was observed to cause the
3468 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3469 // which is by default non-zero. For the other seven methods that
3470 // also perform the yield operation, as are using a different
3471 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3472 // can enable the sleeping for those methods too, if necessary.
3473 // See 6442774.
3474 //
3475 // We really need to reconsider the synchronization between the GC
3476 // thread and the yield-requesting threads in the future and we
3477 // should really use wait/notify, which is the recommended
3478 // way of doing this type of interaction. Additionally, we should
3479 // consolidate the eight methods that do the yield operation and they
3480 // are almost identical into one for better maintainability and
3481 // readability. See 6445193.
3482 //
3483 // Tony 2006.06.29
3484 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3485 ConcurrentMarkSweepThread::should_yield() &&
3486 !CMSCollector::foregroundGCIsActive(); ++i) {
3487 os::sleep(Thread::current(), 1, false);
3488 }
3489
3490 ConcurrentMarkSweepThread::synchronize(true);
3491 _bit_map_lock->lock_without_safepoint_check();
3492 _collector->startTimer();
3493 }
3494
3495 bool CMSCollector::do_marking_mt() {
3496 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3497 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3498 conc_workers()->active_workers(),
3499 Threads::number_of_non_daemon_threads());
3500 num_workers = conc_workers()->update_active_workers(num_workers);
3501 log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
3502
3503 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3504
3505 CMSConcMarkingTask tsk(this,
3506 cms_space,
3507 conc_workers(),
3508 task_queues());
3509
3510 // Since the actual number of workers we get may be different
3511 // from the number we requested above, do we need to do anything different
3512 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3513 // class?? XXX
3514 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3515
3516 // Refs discovery is already non-atomic.
3517 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3518 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3519 conc_workers()->start_task(&tsk);
3520 while (tsk.yielded()) {
3521 tsk.coordinator_yield();
3522 conc_workers()->continue_task(&tsk);
3523 }
3524 // If the task was aborted, _restart_addr will be non-NULL
3525 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3526 while (_restart_addr != NULL) {
3527 // XXX For now we do not make use of ABORTED state and have not
3528 // yet implemented the right abort semantics (even in the original
3529 // single-threaded CMS case). That needs some more investigation
3530 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3531 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3532 // If _restart_addr is non-NULL, a marking stack overflow
3533 // occurred; we need to do a fresh marking iteration from the
3534 // indicated restart address.
3535 if (_foregroundGCIsActive) {
3536 // We may be running into repeated stack overflows, having
3537 // reached the limit of the stack size, while making very
3538 // slow forward progress. It may be best to bail out and
3539 // let the foreground collector do its job.
3540 // Clear _restart_addr, so that foreground GC
3541 // works from scratch. This avoids the headache of
3542 // a "rescan" which would otherwise be needed because
3543 // of the dirty mod union table & card table.
3544 _restart_addr = NULL;
3545 return false;
3546 }
3547 // Adjust the task to restart from _restart_addr
3548 tsk.reset(_restart_addr);
3549 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3550 _restart_addr);
3551 _restart_addr = NULL;
3552 // Get the workers going again
3553 conc_workers()->start_task(&tsk);
3554 while (tsk.yielded()) {
3555 tsk.coordinator_yield();
3556 conc_workers()->continue_task(&tsk);
3557 }
3558 }
3559 assert(tsk.completed(), "Inconsistency");
3560 assert(tsk.result() == true, "Inconsistency");
3561 return true;
3562 }
3563
3564 bool CMSCollector::do_marking_st() {
3565 ResourceMark rm;
3566 HandleMark hm;
3567
3568 // Temporarily make refs discovery single threaded (non-MT)
3569 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3570 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3571 &_markStack, CMSYield);
3572 // the last argument to iterate indicates whether the iteration
3573 // should be incremental with periodic yields.
3574 _markBitMap.iterate(&markFromRootsClosure);
3575 // If _restart_addr is non-NULL, a marking stack overflow
3576 // occurred; we need to do a fresh iteration from the
3577 // indicated restart address.
3578 while (_restart_addr != NULL) {
3579 if (_foregroundGCIsActive) {
3580 // We may be running into repeated stack overflows, having
3581 // reached the limit of the stack size, while making very
3582 // slow forward progress. It may be best to bail out and
3583 // let the foreground collector do its job.
3584 // Clear _restart_addr, so that foreground GC
3585 // works from scratch. This avoids the headache of
3586 // a "rescan" which would otherwise be needed because
3587 // of the dirty mod union table & card table.
3588 _restart_addr = NULL;
3589 return false; // indicating failure to complete marking
3590 }
3591 // Deal with stack overflow:
3592 // we restart marking from _restart_addr
3593 HeapWord* ra = _restart_addr;
3594 markFromRootsClosure.reset(ra);
3595 _restart_addr = NULL;
3596 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3597 }
3598 return true;
3599 }
3600
3601 void CMSCollector::preclean() {
3602 check_correct_thread_executing();
3603 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3604 verify_work_stacks_empty();
3605 verify_overflow_empty();
3606 _abort_preclean = false;
3607 if (CMSPrecleaningEnabled) {
3608 if (!CMSEdenChunksRecordAlways) {
3609 _eden_chunk_index = 0;
3610 }
3611 size_t used = get_eden_used();
3612 size_t capacity = get_eden_capacity();
3613 // Don't start sampling unless we will get sufficiently
3614 // many samples.
3615 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3616 * CMSScheduleRemarkEdenPenetration)) {
3617 _start_sampling = true;
3618 } else {
3619 _start_sampling = false;
3620 }
3621 GCTraceCPUTime tcpu;
3622 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3623 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3624 }
3625 CMSTokenSync x(true); // is cms thread
3626 if (CMSPrecleaningEnabled) {
3627 sample_eden();
3628 _collectorState = AbortablePreclean;
3629 } else {
3630 _collectorState = FinalMarking;
3631 }
3632 verify_work_stacks_empty();
3633 verify_overflow_empty();
3634 }
3635
3636 // Try and schedule the remark such that young gen
3637 // occupancy is CMSScheduleRemarkEdenPenetration %.
3638 void CMSCollector::abortable_preclean() {
3639 check_correct_thread_executing();
3640 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3641 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3642
3643 // If Eden's current occupancy is below this threshold,
3644 // immediately schedule the remark; else preclean
3645 // past the next scavenge in an effort to
3646 // schedule the pause as described above. By choosing
3647 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3648 // we will never do an actual abortable preclean cycle.
3649 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3650 GCTraceCPUTime tcpu;
3651 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3652 // We need more smarts in the abortable preclean
3653 // loop below to deal with cases where allocation
3654 // in young gen is very very slow, and our precleaning
3655 // is running a losing race against a horde of
3656 // mutators intent on flooding us with CMS updates
3657 // (dirty cards).
3658 // One, admittedly dumb, strategy is to give up
3659 // after a certain number of abortable precleaning loops
3660 // or after a certain maximum time. We want to make
3661 // this smarter in the next iteration.
3662 // XXX FIX ME!!! YSR
3663 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3664 while (!(should_abort_preclean() ||
3665 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3666 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3667 cumworkdone += workdone;
3668 loops++;
3669 // Voluntarily terminate abortable preclean phase if we have
3670 // been at it for too long.
3671 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3672 loops >= CMSMaxAbortablePrecleanLoops) {
3673 log_debug(gc)(" CMS: abort preclean due to loops ");
3674 break;
3675 }
3676 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3677 log_debug(gc)(" CMS: abort preclean due to time ");
3678 break;
3679 }
3680 // If we are doing little work each iteration, we should
3681 // take a short break.
3682 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3683 // Sleep for some time, waiting for work to accumulate
3684 stopTimer();
3685 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3686 startTimer();
3687 waited++;
3688 }
3689 }
3690 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3691 loops, waited, cumworkdone);
3692 }
3693 CMSTokenSync x(true); // is cms thread
3694 if (_collectorState != Idling) {
3695 assert(_collectorState == AbortablePreclean,
3696 "Spontaneous state transition?");
3697 _collectorState = FinalMarking;
3698 } // Else, a foreground collection completed this CMS cycle.
3699 return;
3700 }
3701
3702 // Respond to an Eden sampling opportunity
3703 void CMSCollector::sample_eden() {
3704 // Make sure a young gc cannot sneak in between our
3705 // reading and recording of a sample.
3706 assert(Thread::current()->is_ConcurrentGC_thread(),
3707 "Only the cms thread may collect Eden samples");
3708 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3709 "Should collect samples while holding CMS token");
3710 if (!_start_sampling) {
3711 return;
3712 }
3713 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3714 // is populated by the young generation.
3715 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3716 if (_eden_chunk_index < _eden_chunk_capacity) {
3717 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3718 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3719 "Unexpected state of Eden");
3720 // We'd like to check that what we just sampled is an oop-start address;
3721 // however, we cannot do that here since the object may not yet have been
3722 // initialized. So we'll instead do the check when we _use_ this sample
3723 // later.
3724 if (_eden_chunk_index == 0 ||
3725 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3726 _eden_chunk_array[_eden_chunk_index-1])
3727 >= CMSSamplingGrain)) {
3728 _eden_chunk_index++; // commit sample
3729 }
3730 }
3731 }
3732 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3733 size_t used = get_eden_used();
3734 size_t capacity = get_eden_capacity();
3735 assert(used <= capacity, "Unexpected state of Eden");
3736 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3737 _abort_preclean = true;
3738 }
3739 }
3740 }
3741
3742
3743 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3744 assert(_collectorState == Precleaning ||
3745 _collectorState == AbortablePreclean, "incorrect state");
3746 ResourceMark rm;
3747 HandleMark hm;
3748
3749 // Precleaning is currently not MT but the reference processor
3750 // may be set for MT. Disable it temporarily here.
3751 ReferenceProcessor* rp = ref_processor();
3752 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3753
3754 // Do one pass of scrubbing the discovered reference lists
3755 // to remove any reference objects with strongly-reachable
3756 // referents.
3757 if (clean_refs) {
3758 CMSPrecleanRefsYieldClosure yield_cl(this);
3759 assert(rp->span().equals(_span), "Spans should be equal");
3760 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3761 &_markStack, true /* preclean */);
3762 CMSDrainMarkingStackClosure complete_trace(this,
3763 _span, &_markBitMap, &_markStack,
3764 &keep_alive, true /* preclean */);
3765
3766 // We don't want this step to interfere with a young
3767 // collection because we don't want to take CPU
3768 // or memory bandwidth away from the young GC threads
3769 // (which may be as many as there are CPUs).
3770 // Note that we don't need to protect ourselves from
3771 // interference with mutators because they can't
3772 // manipulate the discovered reference lists nor affect
3773 // the computed reachability of the referents, the
3774 // only properties manipulated by the precleaning
3775 // of these reference lists.
3776 stopTimer();
3777 CMSTokenSyncWithLocks x(true /* is cms thread */,
3778 bitMapLock());
3779 startTimer();
3780 sample_eden();
3781
3782 // The following will yield to allow foreground
3783 // collection to proceed promptly. XXX YSR:
3784 // The code in this method may need further
3785 // tweaking for better performance and some restructuring
3786 // for cleaner interfaces.
3787 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3788 rp->preclean_discovered_references(
3789 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3790 gc_timer);
3791 }
3792
3793 if (clean_survivor) { // preclean the active survivor space(s)
3794 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3795 &_markBitMap, &_modUnionTable,
3796 &_markStack, true /* precleaning phase */);
3797 stopTimer();
3798 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3799 bitMapLock());
3800 startTimer();
3801 unsigned int before_count =
3802 CMSHeap::heap()->total_collections();
3803 SurvivorSpacePrecleanClosure
3804 sss_cl(this, _span, &_markBitMap, &_markStack,
3805 &pam_cl, before_count, CMSYield);
3806 _young_gen->from()->object_iterate_careful(&sss_cl);
3807 _young_gen->to()->object_iterate_careful(&sss_cl);
3808 }
3809 MarkRefsIntoAndScanClosure
3810 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3811 &_markStack, this, CMSYield,
3812 true /* precleaning phase */);
3813 // CAUTION: The following closure has persistent state that may need to
3814 // be reset upon a decrease in the sequence of addresses it
3815 // processes.
3816 ScanMarkedObjectsAgainCarefullyClosure
3817 smoac_cl(this, _span,
3818 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3819
3820 // Preclean dirty cards in ModUnionTable and CardTable using
3821 // appropriate convergence criterion;
3822 // repeat CMSPrecleanIter times unless we find that
3823 // we are losing.
3824 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3825 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3826 "Bad convergence multiplier");
3827 assert(CMSPrecleanThreshold >= 100,
3828 "Unreasonably low CMSPrecleanThreshold");
3829
3830 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3831 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3832 numIter < CMSPrecleanIter;
3833 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3834 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3835 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3836 // Either there are very few dirty cards, so re-mark
3837 // pause will be small anyway, or our pre-cleaning isn't
3838 // that much faster than the rate at which cards are being
3839 // dirtied, so we might as well stop and re-mark since
3840 // precleaning won't improve our re-mark time by much.
3841 if (curNumCards <= CMSPrecleanThreshold ||
3842 (numIter > 0 &&
3843 (curNumCards * CMSPrecleanDenominator >
3844 lastNumCards * CMSPrecleanNumerator))) {
3845 numIter++;
3846 cumNumCards += curNumCards;
3847 break;
3848 }
3849 }
3850
3851 preclean_cld(&mrias_cl, _cmsGen->freelistLock());
3852
3853 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3854 cumNumCards += curNumCards;
3855 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3856 curNumCards, cumNumCards, numIter);
3857 return cumNumCards; // as a measure of useful work done
3858 }
3859
3860 // PRECLEANING NOTES:
3861 // Precleaning involves:
3862 // . reading the bits of the modUnionTable and clearing the set bits.
3863 // . For the cards corresponding to the set bits, we scan the
3864 // objects on those cards. This means we need the free_list_lock
3865 // so that we can safely iterate over the CMS space when scanning
3866 // for oops.
3867 // . When we scan the objects, we'll be both reading and setting
3868 // marks in the marking bit map, so we'll need the marking bit map.
3869 // . For protecting _collector_state transitions, we take the CGC_lock.
3870 // Note that any races in the reading of of card table entries by the
3871 // CMS thread on the one hand and the clearing of those entries by the
3872 // VM thread or the setting of those entries by the mutator threads on the
3873 // other are quite benign. However, for efficiency it makes sense to keep
3874 // the VM thread from racing with the CMS thread while the latter is
3875 // dirty card info to the modUnionTable. We therefore also use the
3876 // CGC_lock to protect the reading of the card table and the mod union
3877 // table by the CM thread.
3878 // . We run concurrently with mutator updates, so scanning
3879 // needs to be done carefully -- we should not try to scan
3880 // potentially uninitialized objects.
3881 //
3882 // Locking strategy: While holding the CGC_lock, we scan over and
3883 // reset a maximal dirty range of the mod union / card tables, then lock
3884 // the free_list_lock and bitmap lock to do a full marking, then
3885 // release these locks; and repeat the cycle. This allows for a
3886 // certain amount of fairness in the sharing of these locks between
3887 // the CMS collector on the one hand, and the VM thread and the
3888 // mutators on the other.
3889
3890 // NOTE: preclean_mod_union_table() and preclean_card_table()
3891 // further below are largely identical; if you need to modify
3892 // one of these methods, please check the other method too.
3893
3894 size_t CMSCollector::preclean_mod_union_table(
3895 ConcurrentMarkSweepGeneration* old_gen,
3896 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3897 verify_work_stacks_empty();
3898 verify_overflow_empty();
3899
3900 // strategy: starting with the first card, accumulate contiguous
3901 // ranges of dirty cards; clear these cards, then scan the region
3902 // covered by these cards.
3903
3904 // Since all of the MUT is committed ahead, we can just use
3905 // that, in case the generations expand while we are precleaning.
3906 // It might also be fine to just use the committed part of the
3907 // generation, but we might potentially miss cards when the
3908 // generation is rapidly expanding while we are in the midst
3909 // of precleaning.
3910 HeapWord* startAddr = old_gen->reserved().start();
3911 HeapWord* endAddr = old_gen->reserved().end();
3912
3913 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3914
3915 size_t numDirtyCards, cumNumDirtyCards;
3916 HeapWord *nextAddr, *lastAddr;
3917 for (cumNumDirtyCards = numDirtyCards = 0,
3918 nextAddr = lastAddr = startAddr;
3919 nextAddr < endAddr;
3920 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3921
3922 ResourceMark rm;
3923 HandleMark hm;
3924
3925 MemRegion dirtyRegion;
3926 {
3927 stopTimer();
3928 // Potential yield point
3929 CMSTokenSync ts(true);
3930 startTimer();
3931 sample_eden();
3932 // Get dirty region starting at nextOffset (inclusive),
3933 // simultaneously clearing it.
3934 dirtyRegion =
3935 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3936 assert(dirtyRegion.start() >= nextAddr,
3937 "returned region inconsistent?");
3938 }
3939 // Remember where the next search should begin.
3940 // The returned region (if non-empty) is a right open interval,
3941 // so lastOffset is obtained from the right end of that
3942 // interval.
3943 lastAddr = dirtyRegion.end();
3944 // Should do something more transparent and less hacky XXX
3945 numDirtyCards =
3946 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3947
3948 // We'll scan the cards in the dirty region (with periodic
3949 // yields for foreground GC as needed).
3950 if (!dirtyRegion.is_empty()) {
3951 assert(numDirtyCards > 0, "consistency check");
3952 HeapWord* stop_point = NULL;
3953 stopTimer();
3954 // Potential yield point
3955 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3956 bitMapLock());
3957 startTimer();
3958 {
3959 verify_work_stacks_empty();
3960 verify_overflow_empty();
3961 sample_eden();
3962 stop_point =
3963 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3964 }
3965 if (stop_point != NULL) {
3966 // The careful iteration stopped early either because it found an
3967 // uninitialized object, or because we were in the midst of an
3968 // "abortable preclean", which should now be aborted. Redirty
3969 // the bits corresponding to the partially-scanned or unscanned
3970 // cards. We'll either restart at the next block boundary or
3971 // abort the preclean.
3972 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3973 "Should only be AbortablePreclean.");
3974 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3975 if (should_abort_preclean()) {
3976 break; // out of preclean loop
3977 } else {
3978 // Compute the next address at which preclean should pick up;
3979 // might need bitMapLock in order to read P-bits.
3980 lastAddr = next_card_start_after_block(stop_point);
3981 }
3982 }
3983 } else {
3984 assert(lastAddr == endAddr, "consistency check");
3985 assert(numDirtyCards == 0, "consistency check");
3986 break;
3987 }
3988 }
3989 verify_work_stacks_empty();
3990 verify_overflow_empty();
3991 return cumNumDirtyCards;
3992 }
3993
3994 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3995 // below are largely identical; if you need to modify
3996 // one of these methods, please check the other method too.
3997
3998 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3999 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4000 // strategy: it's similar to precleamModUnionTable above, in that
4001 // we accumulate contiguous ranges of dirty cards, mark these cards
4002 // precleaned, then scan the region covered by these cards.
4003 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
4004 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
4005
4006 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
4007
4008 size_t numDirtyCards, cumNumDirtyCards;
4009 HeapWord *lastAddr, *nextAddr;
4010
4011 for (cumNumDirtyCards = numDirtyCards = 0,
4012 nextAddr = lastAddr = startAddr;
4013 nextAddr < endAddr;
4014 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4015
4016 ResourceMark rm;
4017 HandleMark hm;
4018
4019 MemRegion dirtyRegion;
4020 {
4021 // See comments in "Precleaning notes" above on why we
4022 // do this locking. XXX Could the locking overheads be
4023 // too high when dirty cards are sparse? [I don't think so.]
4024 stopTimer();
4025 CMSTokenSync x(true); // is cms thread
4026 startTimer();
4027 sample_eden();
4028 // Get and clear dirty region from card table
4029 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4030 MemRegion(nextAddr, endAddr),
4031 true,
4032 CardTableModRefBS::precleaned_card_val());
4033
4034 assert(dirtyRegion.start() >= nextAddr,
4035 "returned region inconsistent?");
4036 }
4037 lastAddr = dirtyRegion.end();
4038 numDirtyCards =
4039 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4040
4041 if (!dirtyRegion.is_empty()) {
4042 stopTimer();
4043 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4044 startTimer();
4045 sample_eden();
4046 verify_work_stacks_empty();
4047 verify_overflow_empty();
4048 HeapWord* stop_point =
4049 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4050 if (stop_point != NULL) {
4051 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4052 "Should only be AbortablePreclean.");
4053 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4054 if (should_abort_preclean()) {
4055 break; // out of preclean loop
4056 } else {
4057 // Compute the next address at which preclean should pick up.
4058 lastAddr = next_card_start_after_block(stop_point);
4059 }
4060 }
4061 } else {
4062 break;
4063 }
4064 }
4065 verify_work_stacks_empty();
4066 verify_overflow_empty();
4067 return cumNumDirtyCards;
4068 }
4069
4070 class PrecleanCLDClosure : public CLDClosure {
4071 MetadataAwareOopsInGenClosure* _cm_closure;
4072 public:
4073 PrecleanCLDClosure(MetadataAwareOopsInGenClosure* oop_closure) : _cm_closure(oop_closure) {}
4074 void do_cld(ClassLoaderData* cld) {
4075 if (cld->has_accumulated_modified_oops()) {
4076 cld->clear_accumulated_modified_oops();
4077
4078 _cm_closure->do_cld(cld);
4079 }
4080 }
4081 };
4082
4083 // The freelist lock is needed to prevent asserts, is it really needed?
4084 void CMSCollector::preclean_cld(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4085
4086 cl->set_freelistLock(freelistLock);
4087
4088 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4089
4090 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4091 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4092 PrecleanCLDClosure preclean_closure(cl);
4093 ClassLoaderDataGraph::cld_do(&preclean_closure);
4094
4095 verify_work_stacks_empty();
4096 verify_overflow_empty();
4097 }
4098
4099 void CMSCollector::checkpointRootsFinal() {
4100 assert(_collectorState == FinalMarking, "incorrect state transition?");
4101 check_correct_thread_executing();
4102 // world is stopped at this checkpoint
4103 assert(SafepointSynchronize::is_at_safepoint(),
4104 "world should be stopped");
4105 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
4106
4107 verify_work_stacks_empty();
4108 verify_overflow_empty();
4109
4110 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4111 _young_gen->used() / K, _young_gen->capacity() / K);
4112 {
4113 if (CMSScavengeBeforeRemark) {
4114 CMSHeap* heap = CMSHeap::heap();
4115 // Temporarily set flag to false, GCH->do_collection will
4116 // expect it to be false and set to true
4117 FlagSetting fl(heap->_is_gc_active, false);
4118
4119 heap->do_collection(true, // full (i.e. force, see below)
4120 false, // !clear_all_soft_refs
4121 0, // size
4122 false, // is_tlab
4123 GenCollectedHeap::YoungGen // type
4124 );
4125 }
4126 FreelistLocker x(this);
4127 MutexLockerEx y(bitMapLock(),
4128 Mutex::_no_safepoint_check_flag);
4129 checkpointRootsFinalWork();
4130 }
4131 verify_work_stacks_empty();
4132 verify_overflow_empty();
4133 }
4134
4135 void CMSCollector::checkpointRootsFinalWork() {
4136 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4137
4138 assert(haveFreelistLocks(), "must have free list locks");
4139 assert_lock_strong(bitMapLock());
4140
4141 ResourceMark rm;
4142 HandleMark hm;
4143
4144 CMSHeap* heap = CMSHeap::heap();
4145
4146 if (should_unload_classes()) {
4147 CodeCache::gc_prologue();
4148 }
4149 assert(haveFreelistLocks(), "must have free list locks");
4150 assert_lock_strong(bitMapLock());
4151
4152 // We might assume that we need not fill TLAB's when
4153 // CMSScavengeBeforeRemark is set, because we may have just done
4154 // a scavenge which would have filled all TLAB's -- and besides
4155 // Eden would be empty. This however may not always be the case --
4156 // for instance although we asked for a scavenge, it may not have
4157 // happened because of a JNI critical section. We probably need
4158 // a policy for deciding whether we can in that case wait until
4159 // the critical section releases and then do the remark following
4160 // the scavenge, and skip it here. In the absence of that policy,
4161 // or of an indication of whether the scavenge did indeed occur,
4162 // we cannot rely on TLAB's having been filled and must do
4163 // so here just in case a scavenge did not happen.
4164 heap->ensure_parsability(false); // fill TLAB's, but no need to retire them
4165 // Update the saved marks which may affect the root scans.
4166 heap->save_marks();
4167
4168 print_eden_and_survivor_chunk_arrays();
4169
4170 {
4171 #if COMPILER2_OR_JVMCI
4172 DerivedPointerTableDeactivate dpt_deact;
4173 #endif
4174
4175 // Note on the role of the mod union table:
4176 // Since the marker in "markFromRoots" marks concurrently with
4177 // mutators, it is possible for some reachable objects not to have been
4178 // scanned. For instance, an only reference to an object A was
4179 // placed in object B after the marker scanned B. Unless B is rescanned,
4180 // A would be collected. Such updates to references in marked objects
4181 // are detected via the mod union table which is the set of all cards
4182 // dirtied since the first checkpoint in this GC cycle and prior to
4183 // the most recent young generation GC, minus those cleaned up by the
4184 // concurrent precleaning.
4185 if (CMSParallelRemarkEnabled) {
4186 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4187 do_remark_parallel();
4188 } else {
4189 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4190 do_remark_non_parallel();
4191 }
4192 }
4193 verify_work_stacks_empty();
4194 verify_overflow_empty();
4195
4196 {
4197 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4198 refProcessingWork();
4199 }
4200 verify_work_stacks_empty();
4201 verify_overflow_empty();
4202
4203 if (should_unload_classes()) {
4204 CodeCache::gc_epilogue();
4205 }
4206 JvmtiExport::gc_epilogue();
4207
4208 // If we encountered any (marking stack / work queue) overflow
4209 // events during the current CMS cycle, take appropriate
4210 // remedial measures, where possible, so as to try and avoid
4211 // recurrence of that condition.
4212 assert(_markStack.isEmpty(), "No grey objects");
4213 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4214 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4215 if (ser_ovflw > 0) {
4216 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4217 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4218 _markStack.expand();
4219 _ser_pmc_remark_ovflw = 0;
4220 _ser_pmc_preclean_ovflw = 0;
4221 _ser_kac_preclean_ovflw = 0;
4222 _ser_kac_ovflw = 0;
4223 }
4224 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4225 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4226 _par_pmc_remark_ovflw, _par_kac_ovflw);
4227 _par_pmc_remark_ovflw = 0;
4228 _par_kac_ovflw = 0;
4229 }
4230 if (_markStack._hit_limit > 0) {
4231 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4232 _markStack._hit_limit);
4233 }
4234 if (_markStack._failed_double > 0) {
4235 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4236 _markStack._failed_double, _markStack.capacity());
4237 }
4238 _markStack._hit_limit = 0;
4239 _markStack._failed_double = 0;
4240
4241 if ((VerifyAfterGC || VerifyDuringGC) &&
4242 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4243 verify_after_remark();
4244 }
4245
4246 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4247
4248 // Change under the freelistLocks.
4249 _collectorState = Sweeping;
4250 // Call isAllClear() under bitMapLock
4251 assert(_modUnionTable.isAllClear(),
4252 "Should be clear by end of the final marking");
4253 assert(_ct->cld_rem_set()->mod_union_is_clear(),
4254 "Should be clear by end of the final marking");
4255 }
4256
4257 void CMSParInitialMarkTask::work(uint worker_id) {
4258 elapsedTimer _timer;
4259 ResourceMark rm;
4260 HandleMark hm;
4261
4262 // ---------- scan from roots --------------
4263 _timer.start();
4264 CMSHeap* heap = CMSHeap::heap();
4265 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4266
4267 // ---------- young gen roots --------------
4268 {
4269 work_on_young_gen_roots(&par_mri_cl);
4270 _timer.stop();
4271 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4272 }
4273
4274 // ---------- remaining roots --------------
4275 _timer.reset();
4276 _timer.start();
4277
4278 CLDToOopClosure cld_closure(&par_mri_cl, true);
4279
4280 heap->cms_process_roots(_strong_roots_scope,
4281 false, // yg was scanned above
4282 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4283 _collector->should_unload_classes(),
4284 &par_mri_cl,
4285 &cld_closure);
4286 assert(_collector->should_unload_classes()
4287 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4288 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4289 _timer.stop();
4290 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4291 }
4292
4293 // Parallel remark task
4294 class CMSParRemarkTask: public CMSParMarkTask {
4295 CompactibleFreeListSpace* _cms_space;
4296
4297 // The per-thread work queues, available here for stealing.
4298 OopTaskQueueSet* _task_queues;
4299 ParallelTaskTerminator _term;
4300 StrongRootsScope* _strong_roots_scope;
4301
4302 public:
4303 // A value of 0 passed to n_workers will cause the number of
4304 // workers to be taken from the active workers in the work gang.
4305 CMSParRemarkTask(CMSCollector* collector,
4306 CompactibleFreeListSpace* cms_space,
4307 uint n_workers, WorkGang* workers,
4308 OopTaskQueueSet* task_queues,
4309 StrongRootsScope* strong_roots_scope):
4310 CMSParMarkTask("Rescan roots and grey objects in parallel",
4311 collector, n_workers),
4312 _cms_space(cms_space),
4313 _task_queues(task_queues),
4314 _term(n_workers, task_queues),
4315 _strong_roots_scope(strong_roots_scope) { }
4316
4317 OopTaskQueueSet* task_queues() { return _task_queues; }
4318
4319 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4320
4321 ParallelTaskTerminator* terminator() { return &_term; }
4322 uint n_workers() { return _n_workers; }
4323
4324 void work(uint worker_id);
4325
4326 private:
4327 // ... of dirty cards in old space
4328 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4329 ParMarkRefsIntoAndScanClosure* cl);
4330
4331 // ... work stealing for the above
4332 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4333 };
4334
4335 class RemarkCLDClosure : public CLDClosure {
4336 CLDToOopClosure _cm_closure;
4337 public:
4338 RemarkCLDClosure(OopClosure* oop_closure) : _cm_closure(oop_closure) {}
4339 void do_cld(ClassLoaderData* cld) {
4340 // Check if we have modified any oops in the CLD during the concurrent marking.
4341 if (cld->has_accumulated_modified_oops()) {
4342 cld->clear_accumulated_modified_oops();
4343
4344 // We could have transfered the current modified marks to the accumulated marks,
4345 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4346 } else if (cld->has_modified_oops()) {
4347 // Don't clear anything, this info is needed by the next young collection.
4348 } else {
4349 // No modified oops in the ClassLoaderData.
4350 return;
4351 }
4352
4353 // The klass has modified fields, need to scan the klass.
4354 _cm_closure.do_cld(cld);
4355 }
4356 };
4357
4358 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4359 ParNewGeneration* young_gen = _collector->_young_gen;
4360 ContiguousSpace* eden_space = young_gen->eden();
4361 ContiguousSpace* from_space = young_gen->from();
4362 ContiguousSpace* to_space = young_gen->to();
4363
4364 HeapWord** eca = _collector->_eden_chunk_array;
4365 size_t ect = _collector->_eden_chunk_index;
4366 HeapWord** sca = _collector->_survivor_chunk_array;
4367 size_t sct = _collector->_survivor_chunk_index;
4368
4369 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4370 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4371
4372 do_young_space_rescan(cl, to_space, NULL, 0);
4373 do_young_space_rescan(cl, from_space, sca, sct);
4374 do_young_space_rescan(cl, eden_space, eca, ect);
4375 }
4376
4377 // work_queue(i) is passed to the closure
4378 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4379 // also is passed to do_dirty_card_rescan_tasks() and to
4380 // do_work_steal() to select the i-th task_queue.
4381
4382 void CMSParRemarkTask::work(uint worker_id) {
4383 elapsedTimer _timer;
4384 ResourceMark rm;
4385 HandleMark hm;
4386
4387 // ---------- rescan from roots --------------
4388 _timer.start();
4389 CMSHeap* heap = CMSHeap::heap();
4390 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4391 _collector->_span, _collector->ref_processor(),
4392 &(_collector->_markBitMap),
4393 work_queue(worker_id));
4394
4395 // Rescan young gen roots first since these are likely
4396 // coarsely partitioned and may, on that account, constitute
4397 // the critical path; thus, it's best to start off that
4398 // work first.
4399 // ---------- young gen roots --------------
4400 {
4401 work_on_young_gen_roots(&par_mrias_cl);
4402 _timer.stop();
4403 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4404 }
4405
4406 // ---------- remaining roots --------------
4407 _timer.reset();
4408 _timer.start();
4409 heap->cms_process_roots(_strong_roots_scope,
4410 false, // yg was scanned above
4411 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4412 _collector->should_unload_classes(),
4413 &par_mrias_cl,
4414 NULL); // The dirty klasses will be handled below
4415
4416 assert(_collector->should_unload_classes()
4417 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4418 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4419 _timer.stop();
4420 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4421
4422 // ---------- unhandled CLD scanning ----------
4423 if (worker_id == 0) { // Single threaded at the moment.
4424 _timer.reset();
4425 _timer.start();
4426
4427 // Scan all new class loader data objects and new dependencies that were
4428 // introduced during concurrent marking.
4429 ResourceMark rm;
4430 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4431 for (int i = 0; i < array->length(); i++) {
4432 par_mrias_cl.do_cld_nv(array->at(i));
4433 }
4434
4435 // We don't need to keep track of new CLDs anymore.
4436 ClassLoaderDataGraph::remember_new_clds(false);
4437
4438 _timer.stop();
4439 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4440 }
4441
4442 // We might have added oops to ClassLoaderData::_handles during the
4443 // concurrent marking phase. These oops do not always point to newly allocated objects
4444 // that are guaranteed to be kept alive. Hence,
4445 // we do have to revisit the _handles block during the remark phase.
4446
4447 // ---------- dirty CLD scanning ----------
4448 if (worker_id == 0) { // Single threaded at the moment.
4449 _timer.reset();
4450 _timer.start();
4451
4452 // Scan all classes that was dirtied during the concurrent marking phase.
4453 RemarkCLDClosure remark_closure(&par_mrias_cl);
4454 ClassLoaderDataGraph::cld_do(&remark_closure);
4455
4456 _timer.stop();
4457 log_trace(gc, task)("Finished dirty CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4458 }
4459
4460
4461 // ---------- rescan dirty cards ------------
4462 _timer.reset();
4463 _timer.start();
4464
4465 // Do the rescan tasks for each of the two spaces
4466 // (cms_space) in turn.
4467 // "worker_id" is passed to select the task_queue for "worker_id"
4468 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4469 _timer.stop();
4470 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4471
4472 // ---------- steal work from other threads ...
4473 // ---------- ... and drain overflow list.
4474 _timer.reset();
4475 _timer.start();
4476 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4477 _timer.stop();
4478 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4479 }
4480
4481 void
4482 CMSParMarkTask::do_young_space_rescan(
4483 OopsInGenClosure* cl, ContiguousSpace* space,
4484 HeapWord** chunk_array, size_t chunk_top) {
4485 // Until all tasks completed:
4486 // . claim an unclaimed task
4487 // . compute region boundaries corresponding to task claimed
4488 // using chunk_array
4489 // . par_oop_iterate(cl) over that region
4490
4491 ResourceMark rm;
4492 HandleMark hm;
4493
4494 SequentialSubTasksDone* pst = space->par_seq_tasks();
4495
4496 uint nth_task = 0;
4497 uint n_tasks = pst->n_tasks();
4498
4499 if (n_tasks > 0) {
4500 assert(pst->valid(), "Uninitialized use?");
4501 HeapWord *start, *end;
4502 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4503 // We claimed task # nth_task; compute its boundaries.
4504 if (chunk_top == 0) { // no samples were taken
4505 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4506 start = space->bottom();
4507 end = space->top();
4508 } else if (nth_task == 0) {
4509 start = space->bottom();
4510 end = chunk_array[nth_task];
4511 } else if (nth_task < (uint)chunk_top) {
4512 assert(nth_task >= 1, "Control point invariant");
4513 start = chunk_array[nth_task - 1];
4514 end = chunk_array[nth_task];
4515 } else {
4516 assert(nth_task == (uint)chunk_top, "Control point invariant");
4517 start = chunk_array[chunk_top - 1];
4518 end = space->top();
4519 }
4520 MemRegion mr(start, end);
4521 // Verify that mr is in space
4522 assert(mr.is_empty() || space->used_region().contains(mr),
4523 "Should be in space");
4524 // Verify that "start" is an object boundary
4525 assert(mr.is_empty() || oopDesc::is_oop(oop(mr.start())),
4526 "Should be an oop");
4527 space->par_oop_iterate(mr, cl);
4528 }
4529 pst->all_tasks_completed();
4530 }
4531 }
4532
4533 void
4534 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4535 CompactibleFreeListSpace* sp, int i,
4536 ParMarkRefsIntoAndScanClosure* cl) {
4537 // Until all tasks completed:
4538 // . claim an unclaimed task
4539 // . compute region boundaries corresponding to task claimed
4540 // . transfer dirty bits ct->mut for that region
4541 // . apply rescanclosure to dirty mut bits for that region
4542
4543 ResourceMark rm;
4544 HandleMark hm;
4545
4546 OopTaskQueue* work_q = work_queue(i);
4547 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4548 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4549 // CAUTION: This closure has state that persists across calls to
4550 // the work method dirty_range_iterate_clear() in that it has
4551 // embedded in it a (subtype of) UpwardsObjectClosure. The
4552 // use of that state in the embedded UpwardsObjectClosure instance
4553 // assumes that the cards are always iterated (even if in parallel
4554 // by several threads) in monotonically increasing order per each
4555 // thread. This is true of the implementation below which picks
4556 // card ranges (chunks) in monotonically increasing order globally
4557 // and, a-fortiori, in monotonically increasing order per thread
4558 // (the latter order being a subsequence of the former).
4559 // If the work code below is ever reorganized into a more chaotic
4560 // work-partitioning form than the current "sequential tasks"
4561 // paradigm, the use of that persistent state will have to be
4562 // revisited and modified appropriately. See also related
4563 // bug 4756801 work on which should examine this code to make
4564 // sure that the changes there do not run counter to the
4565 // assumptions made here and necessary for correctness and
4566 // efficiency. Note also that this code might yield inefficient
4567 // behavior in the case of very large objects that span one or
4568 // more work chunks. Such objects would potentially be scanned
4569 // several times redundantly. Work on 4756801 should try and
4570 // address that performance anomaly if at all possible. XXX
4571 MemRegion full_span = _collector->_span;
4572 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4573 MarkFromDirtyCardsClosure
4574 greyRescanClosure(_collector, full_span, // entire span of interest
4575 sp, bm, work_q, cl);
4576
4577 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4578 assert(pst->valid(), "Uninitialized use?");
4579 uint nth_task = 0;
4580 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4581 MemRegion span = sp->used_region();
4582 HeapWord* start_addr = span.start();
4583 HeapWord* end_addr = align_up(span.end(), alignment);
4584 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4585 assert(is_aligned(start_addr, alignment), "Check alignment");
4586 assert(is_aligned(chunk_size, alignment), "Check alignment");
4587
4588 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4589 // Having claimed the nth_task, compute corresponding mem-region,
4590 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4591 // The alignment restriction ensures that we do not need any
4592 // synchronization with other gang-workers while setting or
4593 // clearing bits in thus chunk of the MUT.
4594 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4595 start_addr + (nth_task+1)*chunk_size);
4596 // The last chunk's end might be way beyond end of the
4597 // used region. In that case pull back appropriately.
4598 if (this_span.end() > end_addr) {
4599 this_span.set_end(end_addr);
4600 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4601 }
4602 // Iterate over the dirty cards covering this chunk, marking them
4603 // precleaned, and setting the corresponding bits in the mod union
4604 // table. Since we have been careful to partition at Card and MUT-word
4605 // boundaries no synchronization is needed between parallel threads.
4606 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4607 &modUnionClosure);
4608
4609 // Having transferred these marks into the modUnionTable,
4610 // rescan the marked objects on the dirty cards in the modUnionTable.
4611 // Even if this is at a synchronous collection, the initial marking
4612 // may have been done during an asynchronous collection so there
4613 // may be dirty bits in the mod-union table.
4614 _collector->_modUnionTable.dirty_range_iterate_clear(
4615 this_span, &greyRescanClosure);
4616 _collector->_modUnionTable.verifyNoOneBitsInRange(
4617 this_span.start(),
4618 this_span.end());
4619 }
4620 pst->all_tasks_completed(); // declare that i am done
4621 }
4622
4623 // . see if we can share work_queues with ParNew? XXX
4624 void
4625 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4626 int* seed) {
4627 OopTaskQueue* work_q = work_queue(i);
4628 NOT_PRODUCT(int num_steals = 0;)
4629 oop obj_to_scan;
4630 CMSBitMap* bm = &(_collector->_markBitMap);
4631
4632 while (true) {
4633 // Completely finish any left over work from (an) earlier round(s)
4634 cl->trim_queue(0);
4635 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4636 (size_t)ParGCDesiredObjsFromOverflowList);
4637 // Now check if there's any work in the overflow list
4638 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4639 // only affects the number of attempts made to get work from the
4640 // overflow list and does not affect the number of workers. Just
4641 // pass ParallelGCThreads so this behavior is unchanged.
4642 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4643 work_q,
4644 ParallelGCThreads)) {
4645 // found something in global overflow list;
4646 // not yet ready to go stealing work from others.
4647 // We'd like to assert(work_q->size() != 0, ...)
4648 // because we just took work from the overflow list,
4649 // but of course we can't since all of that could have
4650 // been already stolen from us.
4651 // "He giveth and He taketh away."
4652 continue;
4653 }
4654 // Verify that we have no work before we resort to stealing
4655 assert(work_q->size() == 0, "Have work, shouldn't steal");
4656 // Try to steal from other queues that have work
4657 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4658 NOT_PRODUCT(num_steals++;)
4659 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
4660 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4661 // Do scanning work
4662 obj_to_scan->oop_iterate(cl);
4663 // Loop around, finish this work, and try to steal some more
4664 } else if (terminator()->offer_termination()) {
4665 break; // nirvana from the infinite cycle
4666 }
4667 }
4668 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4669 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4670 "Else our work is not yet done");
4671 }
4672
4673 // Record object boundaries in _eden_chunk_array by sampling the eden
4674 // top in the slow-path eden object allocation code path and record
4675 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4676 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4677 // sampling in sample_eden() that activates during the part of the
4678 // preclean phase.
4679 void CMSCollector::sample_eden_chunk() {
4680 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4681 if (_eden_chunk_lock->try_lock()) {
4682 // Record a sample. This is the critical section. The contents
4683 // of the _eden_chunk_array have to be non-decreasing in the
4684 // address order.
4685 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4686 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4687 "Unexpected state of Eden");
4688 if (_eden_chunk_index == 0 ||
4689 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4690 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4691 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4692 _eden_chunk_index++; // commit sample
4693 }
4694 _eden_chunk_lock->unlock();
4695 }
4696 }
4697 }
4698
4699 // Return a thread-local PLAB recording array, as appropriate.
4700 void* CMSCollector::get_data_recorder(int thr_num) {
4701 if (_survivor_plab_array != NULL &&
4702 (CMSPLABRecordAlways ||
4703 (_collectorState > Marking && _collectorState < FinalMarking))) {
4704 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4705 ChunkArray* ca = &_survivor_plab_array[thr_num];
4706 ca->reset(); // clear it so that fresh data is recorded
4707 return (void*) ca;
4708 } else {
4709 return NULL;
4710 }
4711 }
4712
4713 // Reset all the thread-local PLAB recording arrays
4714 void CMSCollector::reset_survivor_plab_arrays() {
4715 for (uint i = 0; i < ParallelGCThreads; i++) {
4716 _survivor_plab_array[i].reset();
4717 }
4718 }
4719
4720 // Merge the per-thread plab arrays into the global survivor chunk
4721 // array which will provide the partitioning of the survivor space
4722 // for CMS initial scan and rescan.
4723 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4724 int no_of_gc_threads) {
4725 assert(_survivor_plab_array != NULL, "Error");
4726 assert(_survivor_chunk_array != NULL, "Error");
4727 assert(_collectorState == FinalMarking ||
4728 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4729 for (int j = 0; j < no_of_gc_threads; j++) {
4730 _cursor[j] = 0;
4731 }
4732 HeapWord* top = surv->top();
4733 size_t i;
4734 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4735 HeapWord* min_val = top; // Higher than any PLAB address
4736 uint min_tid = 0; // position of min_val this round
4737 for (int j = 0; j < no_of_gc_threads; j++) {
4738 ChunkArray* cur_sca = &_survivor_plab_array[j];
4739 if (_cursor[j] == cur_sca->end()) {
4740 continue;
4741 }
4742 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4743 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4744 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4745 if (cur_val < min_val) {
4746 min_tid = j;
4747 min_val = cur_val;
4748 } else {
4749 assert(cur_val < top, "All recorded addresses should be less");
4750 }
4751 }
4752 // At this point min_val and min_tid are respectively
4753 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4754 // and the thread (j) that witnesses that address.
4755 // We record this address in the _survivor_chunk_array[i]
4756 // and increment _cursor[min_tid] prior to the next round i.
4757 if (min_val == top) {
4758 break;
4759 }
4760 _survivor_chunk_array[i] = min_val;
4761 _cursor[min_tid]++;
4762 }
4763 // We are all done; record the size of the _survivor_chunk_array
4764 _survivor_chunk_index = i; // exclusive: [0, i)
4765 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4766 // Verify that we used up all the recorded entries
4767 #ifdef ASSERT
4768 size_t total = 0;
4769 for (int j = 0; j < no_of_gc_threads; j++) {
4770 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4771 total += _cursor[j];
4772 }
4773 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4774 // Check that the merged array is in sorted order
4775 if (total > 0) {
4776 for (size_t i = 0; i < total - 1; i++) {
4777 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4778 i, p2i(_survivor_chunk_array[i]));
4779 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4780 "Not sorted");
4781 }
4782 }
4783 #endif // ASSERT
4784 }
4785
4786 // Set up the space's par_seq_tasks structure for work claiming
4787 // for parallel initial scan and rescan of young gen.
4788 // See ParRescanTask where this is currently used.
4789 void
4790 CMSCollector::
4791 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4792 assert(n_threads > 0, "Unexpected n_threads argument");
4793
4794 // Eden space
4795 if (!_young_gen->eden()->is_empty()) {
4796 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4797 assert(!pst->valid(), "Clobbering existing data?");
4798 // Each valid entry in [0, _eden_chunk_index) represents a task.
4799 size_t n_tasks = _eden_chunk_index + 1;
4800 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4801 // Sets the condition for completion of the subtask (how many threads
4802 // need to finish in order to be done).
4803 pst->set_n_threads(n_threads);
4804 pst->set_n_tasks((int)n_tasks);
4805 }
4806
4807 // Merge the survivor plab arrays into _survivor_chunk_array
4808 if (_survivor_plab_array != NULL) {
4809 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4810 } else {
4811 assert(_survivor_chunk_index == 0, "Error");
4812 }
4813
4814 // To space
4815 {
4816 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4817 assert(!pst->valid(), "Clobbering existing data?");
4818 // Sets the condition for completion of the subtask (how many threads
4819 // need to finish in order to be done).
4820 pst->set_n_threads(n_threads);
4821 pst->set_n_tasks(1);
4822 assert(pst->valid(), "Error");
4823 }
4824
4825 // From space
4826 {
4827 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4828 assert(!pst->valid(), "Clobbering existing data?");
4829 size_t n_tasks = _survivor_chunk_index + 1;
4830 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4831 // Sets the condition for completion of the subtask (how many threads
4832 // need to finish in order to be done).
4833 pst->set_n_threads(n_threads);
4834 pst->set_n_tasks((int)n_tasks);
4835 assert(pst->valid(), "Error");
4836 }
4837 }
4838
4839 // Parallel version of remark
4840 void CMSCollector::do_remark_parallel() {
4841 CMSHeap* heap = CMSHeap::heap();
4842 WorkGang* workers = heap->workers();
4843 assert(workers != NULL, "Need parallel worker threads.");
4844 // Choose to use the number of GC workers most recently set
4845 // into "active_workers".
4846 uint n_workers = workers->active_workers();
4847
4848 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4849
4850 StrongRootsScope srs(n_workers);
4851
4852 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4853
4854 // We won't be iterating over the cards in the card table updating
4855 // the younger_gen cards, so we shouldn't call the following else
4856 // the verification code as well as subsequent younger_refs_iterate
4857 // code would get confused. XXX
4858 // heap->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4859
4860 // The young gen rescan work will not be done as part of
4861 // process_roots (which currently doesn't know how to
4862 // parallelize such a scan), but rather will be broken up into
4863 // a set of parallel tasks (via the sampling that the [abortable]
4864 // preclean phase did of eden, plus the [two] tasks of
4865 // scanning the [two] survivor spaces. Further fine-grain
4866 // parallelization of the scanning of the survivor spaces
4867 // themselves, and of precleaning of the young gen itself
4868 // is deferred to the future.
4869 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4870
4871 // The dirty card rescan work is broken up into a "sequence"
4872 // of parallel tasks (per constituent space) that are dynamically
4873 // claimed by the parallel threads.
4874 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4875
4876 // It turns out that even when we're using 1 thread, doing the work in a
4877 // separate thread causes wide variance in run times. We can't help this
4878 // in the multi-threaded case, but we special-case n=1 here to get
4879 // repeatable measurements of the 1-thread overhead of the parallel code.
4880 if (n_workers > 1) {
4881 // Make refs discovery MT-safe, if it isn't already: it may not
4882 // necessarily be so, since it's possible that we are doing
4883 // ST marking.
4884 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4885 workers->run_task(&tsk);
4886 } else {
4887 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4888 tsk.work(0);
4889 }
4890
4891 // restore, single-threaded for now, any preserved marks
4892 // as a result of work_q overflow
4893 restore_preserved_marks_if_any();
4894 }
4895
4896 // Non-parallel version of remark
4897 void CMSCollector::do_remark_non_parallel() {
4898 ResourceMark rm;
4899 HandleMark hm;
4900 CMSHeap* heap = CMSHeap::heap();
4901 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4902
4903 MarkRefsIntoAndScanClosure
4904 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4905 &_markStack, this,
4906 false /* should_yield */, false /* not precleaning */);
4907 MarkFromDirtyCardsClosure
4908 markFromDirtyCardsClosure(this, _span,
4909 NULL, // space is set further below
4910 &_markBitMap, &_markStack, &mrias_cl);
4911 {
4912 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4913 // Iterate over the dirty cards, setting the corresponding bits in the
4914 // mod union table.
4915 {
4916 ModUnionClosure modUnionClosure(&_modUnionTable);
4917 _ct->ct_bs()->dirty_card_iterate(
4918 _cmsGen->used_region(),
4919 &modUnionClosure);
4920 }
4921 // Having transferred these marks into the modUnionTable, we just need
4922 // to rescan the marked objects on the dirty cards in the modUnionTable.
4923 // The initial marking may have been done during an asynchronous
4924 // collection so there may be dirty bits in the mod-union table.
4925 const int alignment =
4926 CardTableModRefBS::card_size * BitsPerWord;
4927 {
4928 // ... First handle dirty cards in CMS gen
4929 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4930 MemRegion ur = _cmsGen->used_region();
4931 HeapWord* lb = ur.start();
4932 HeapWord* ub = align_up(ur.end(), alignment);
4933 MemRegion cms_span(lb, ub);
4934 _modUnionTable.dirty_range_iterate_clear(cms_span,
4935 &markFromDirtyCardsClosure);
4936 verify_work_stacks_empty();
4937 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4938 }
4939 }
4940 if (VerifyDuringGC &&
4941 CMSHeap::heap()->total_collections() >= VerifyGCStartAt) {
4942 HandleMark hm; // Discard invalid handles created during verification
4943 Universe::verify();
4944 }
4945 {
4946 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4947
4948 verify_work_stacks_empty();
4949
4950 heap->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4951 StrongRootsScope srs(1);
4952
4953 heap->cms_process_roots(&srs,
4954 true, // young gen as roots
4955 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4956 should_unload_classes(),
4957 &mrias_cl,
4958 NULL); // The dirty klasses will be handled below
4959
4960 assert(should_unload_classes()
4961 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4962 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4963 }
4964
4965 {
4966 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4967
4968 verify_work_stacks_empty();
4969
4970 // Scan all class loader data objects that might have been introduced
4971 // during concurrent marking.
4972 ResourceMark rm;
4973 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4974 for (int i = 0; i < array->length(); i++) {
4975 mrias_cl.do_cld_nv(array->at(i));
4976 }
4977
4978 // We don't need to keep track of new CLDs anymore.
4979 ClassLoaderDataGraph::remember_new_clds(false);
4980
4981 verify_work_stacks_empty();
4982 }
4983
4984 // We might have added oops to ClassLoaderData::_handles during the
4985 // concurrent marking phase. These oops do not point to newly allocated objects
4986 // that are guaranteed to be kept alive. Hence,
4987 // we do have to revisit the _handles block during the remark phase.
4988 {
4989 GCTraceTime(Trace, gc, phases) t("Dirty CLD Scan", _gc_timer_cm);
4990
4991 verify_work_stacks_empty();
4992
4993 RemarkCLDClosure remark_closure(&mrias_cl);
4994 ClassLoaderDataGraph::cld_do(&remark_closure);
4995
4996 verify_work_stacks_empty();
4997 }
4998
4999 verify_work_stacks_empty();
5000 // Restore evacuated mark words, if any, used for overflow list links
5001 restore_preserved_marks_if_any();
5002
5003 verify_overflow_empty();
5004 }
5005
5006 ////////////////////////////////////////////////////////
5007 // Parallel Reference Processing Task Proxy Class
5008 ////////////////////////////////////////////////////////
5009 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5010 OopTaskQueueSet* _queues;
5011 ParallelTaskTerminator _terminator;
5012 public:
5013 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5014 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5015 ParallelTaskTerminator* terminator() { return &_terminator; }
5016 OopTaskQueueSet* queues() { return _queues; }
5017 };
5018
5019 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5020 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5021 CMSCollector* _collector;
5022 CMSBitMap* _mark_bit_map;
5023 const MemRegion _span;
5024 ProcessTask& _task;
5025
5026 public:
5027 CMSRefProcTaskProxy(ProcessTask& task,
5028 CMSCollector* collector,
5029 const MemRegion& span,
5030 CMSBitMap* mark_bit_map,
5031 AbstractWorkGang* workers,
5032 OopTaskQueueSet* task_queues):
5033 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5034 task_queues,
5035 workers->active_workers()),
5036 _task(task),
5037 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5038 {
5039 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5040 "Inconsistency in _span");
5041 }
5042
5043 OopTaskQueueSet* task_queues() { return queues(); }
5044
5045 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5046
5047 void do_work_steal(int i,
5048 CMSParDrainMarkingStackClosure* drain,
5049 CMSParKeepAliveClosure* keep_alive,
5050 int* seed);
5051
5052 virtual void work(uint worker_id);
5053 };
5054
5055 void CMSRefProcTaskProxy::work(uint worker_id) {
5056 ResourceMark rm;
5057 HandleMark hm;
5058 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5059 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5060 _mark_bit_map,
5061 work_queue(worker_id));
5062 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5063 _mark_bit_map,
5064 work_queue(worker_id));
5065 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5066 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5067 if (_task.marks_oops_alive()) {
5068 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5069 _collector->hash_seed(worker_id));
5070 }
5071 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5072 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5073 }
5074
5075 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5076 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5077 EnqueueTask& _task;
5078
5079 public:
5080 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5081 : AbstractGangTask("Enqueue reference objects in parallel"),
5082 _task(task)
5083 { }
5084
5085 virtual void work(uint worker_id)
5086 {
5087 _task.work(worker_id);
5088 }
5089 };
5090
5091 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5092 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5093 _span(span),
5094 _bit_map(bit_map),
5095 _work_queue(work_queue),
5096 _mark_and_push(collector, span, bit_map, work_queue),
5097 _low_water_mark(MIN2((work_queue->max_elems()/4),
5098 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5099 { }
5100
5101 // . see if we can share work_queues with ParNew? XXX
5102 void CMSRefProcTaskProxy::do_work_steal(int i,
5103 CMSParDrainMarkingStackClosure* drain,
5104 CMSParKeepAliveClosure* keep_alive,
5105 int* seed) {
5106 OopTaskQueue* work_q = work_queue(i);
5107 NOT_PRODUCT(int num_steals = 0;)
5108 oop obj_to_scan;
5109
5110 while (true) {
5111 // Completely finish any left over work from (an) earlier round(s)
5112 drain->trim_queue(0);
5113 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5114 (size_t)ParGCDesiredObjsFromOverflowList);
5115 // Now check if there's any work in the overflow list
5116 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5117 // only affects the number of attempts made to get work from the
5118 // overflow list and does not affect the number of workers. Just
5119 // pass ParallelGCThreads so this behavior is unchanged.
5120 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5121 work_q,
5122 ParallelGCThreads)) {
5123 // Found something in global overflow list;
5124 // not yet ready to go stealing work from others.
5125 // We'd like to assert(work_q->size() != 0, ...)
5126 // because we just took work from the overflow list,
5127 // but of course we can't, since all of that might have
5128 // been already stolen from us.
5129 continue;
5130 }
5131 // Verify that we have no work before we resort to stealing
5132 assert(work_q->size() == 0, "Have work, shouldn't steal");
5133 // Try to steal from other queues that have work
5134 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5135 NOT_PRODUCT(num_steals++;)
5136 assert(oopDesc::is_oop(obj_to_scan), "Oops, not an oop!");
5137 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5138 // Do scanning work
5139 obj_to_scan->oop_iterate(keep_alive);
5140 // Loop around, finish this work, and try to steal some more
5141 } else if (terminator()->offer_termination()) {
5142 break; // nirvana from the infinite cycle
5143 }
5144 }
5145 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5146 }
5147
5148 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5149 {
5150 CMSHeap* heap = CMSHeap::heap();
5151 WorkGang* workers = heap->workers();
5152 assert(workers != NULL, "Need parallel worker threads.");
5153 CMSRefProcTaskProxy rp_task(task, &_collector,
5154 _collector.ref_processor()->span(),
5155 _collector.markBitMap(),
5156 workers, _collector.task_queues());
5157 workers->run_task(&rp_task);
5158 }
5159
5160 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5161 {
5162
5163 CMSHeap* heap = CMSHeap::heap();
5164 WorkGang* workers = heap->workers();
5165 assert(workers != NULL, "Need parallel worker threads.");
5166 CMSRefEnqueueTaskProxy enq_task(task);
5167 workers->run_task(&enq_task);
5168 }
5169
5170 void CMSCollector::refProcessingWork() {
5171 ResourceMark rm;
5172 HandleMark hm;
5173
5174 ReferenceProcessor* rp = ref_processor();
5175 assert(rp->span().equals(_span), "Spans should be equal");
5176 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5177 // Process weak references.
5178 rp->setup_policy(false);
5179 verify_work_stacks_empty();
5180
5181 ReferenceProcessorPhaseTimes pt(_gc_timer_cm, rp->num_q());
5182 {
5183 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5184
5185 // Setup keep_alive and complete closures.
5186 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5187 &_markStack, false /* !preclean */);
5188 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5189 _span, &_markBitMap, &_markStack,
5190 &cmsKeepAliveClosure, false /* !preclean */);
5191
5192 ReferenceProcessorStats stats;
5193 if (rp->processing_is_mt()) {
5194 // Set the degree of MT here. If the discovery is done MT, there
5195 // may have been a different number of threads doing the discovery
5196 // and a different number of discovered lists may have Ref objects.
5197 // That is OK as long as the Reference lists are balanced (see
5198 // balance_all_queues() and balance_queues()).
5199 CMSHeap* heap = CMSHeap::heap();
5200 uint active_workers = ParallelGCThreads;
5201 WorkGang* workers = heap->workers();
5202 if (workers != NULL) {
5203 active_workers = workers->active_workers();
5204 // The expectation is that active_workers will have already
5205 // been set to a reasonable value. If it has not been set,
5206 // investigate.
5207 assert(active_workers > 0, "Should have been set during scavenge");
5208 }
5209 rp->set_active_mt_degree(active_workers);
5210 CMSRefProcTaskExecutor task_executor(*this);
5211 stats = rp->process_discovered_references(&_is_alive_closure,
5212 &cmsKeepAliveClosure,
5213 &cmsDrainMarkingStackClosure,
5214 &task_executor,
5215 &pt);
5216 } else {
5217 stats = rp->process_discovered_references(&_is_alive_closure,
5218 &cmsKeepAliveClosure,
5219 &cmsDrainMarkingStackClosure,
5220 NULL,
5221 &pt);
5222 }
5223 _gc_tracer_cm->report_gc_reference_stats(stats);
5224 pt.print_all_references();
5225 }
5226
5227 // This is the point where the entire marking should have completed.
5228 verify_work_stacks_empty();
5229
5230 {
5231 GCTraceTime(Debug, gc, phases) t("Weak Processing", _gc_timer_cm);
5232 WeakProcessor::weak_oops_do(&_is_alive_closure, &do_nothing_cl);
5233 }
5234
5235 if (should_unload_classes()) {
5236 {
5237 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5238
5239 // Unload classes and purge the SystemDictionary.
5240 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure, _gc_timer_cm);
5241
5242 // Unload nmethods.
5243 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5244
5245 // Prune dead klasses from subklass/sibling/implementor lists.
5246 Klass::clean_weak_klass_links(&_is_alive_closure);
5247 }
5248
5249 {
5250 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5251 // Clean up unreferenced symbols in symbol table.
5252 SymbolTable::unlink();
5253 }
5254
5255 {
5256 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5257 // Delete entries for dead interned strings.
5258 StringTable::unlink(&_is_alive_closure);
5259 }
5260 }
5261
5262 // Restore any preserved marks as a result of mark stack or
5263 // work queue overflow
5264 restore_preserved_marks_if_any(); // done single-threaded for now
5265
5266 rp->set_enqueuing_is_done(true);
5267 if (rp->processing_is_mt()) {
5268 rp->balance_all_queues();
5269 CMSRefProcTaskExecutor task_executor(*this);
5270 rp->enqueue_discovered_references(&task_executor, &pt);
5271 } else {
5272 rp->enqueue_discovered_references(NULL, &pt);
5273 }
5274 rp->verify_no_references_recorded();
5275 pt.print_enqueue_phase();
5276 assert(!rp->discovery_enabled(), "should have been disabled");
5277 }
5278
5279 #ifndef PRODUCT
5280 void CMSCollector::check_correct_thread_executing() {
5281 Thread* t = Thread::current();
5282 // Only the VM thread or the CMS thread should be here.
5283 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5284 "Unexpected thread type");
5285 // If this is the vm thread, the foreground process
5286 // should not be waiting. Note that _foregroundGCIsActive is
5287 // true while the foreground collector is waiting.
5288 if (_foregroundGCShouldWait) {
5289 // We cannot be the VM thread
5290 assert(t->is_ConcurrentGC_thread(),
5291 "Should be CMS thread");
5292 } else {
5293 // We can be the CMS thread only if we are in a stop-world
5294 // phase of CMS collection.
5295 if (t->is_ConcurrentGC_thread()) {
5296 assert(_collectorState == InitialMarking ||
5297 _collectorState == FinalMarking,
5298 "Should be a stop-world phase");
5299 // The CMS thread should be holding the CMS_token.
5300 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5301 "Potential interference with concurrently "
5302 "executing VM thread");
5303 }
5304 }
5305 }
5306 #endif
5307
5308 void CMSCollector::sweep() {
5309 assert(_collectorState == Sweeping, "just checking");
5310 check_correct_thread_executing();
5311 verify_work_stacks_empty();
5312 verify_overflow_empty();
5313 increment_sweep_count();
5314 TraceCMSMemoryManagerStats tms(_collectorState, CMSHeap::heap()->gc_cause());
5315
5316 _inter_sweep_timer.stop();
5317 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5318
5319 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5320 _intra_sweep_timer.reset();
5321 _intra_sweep_timer.start();
5322 {
5323 GCTraceCPUTime tcpu;
5324 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5325 // First sweep the old gen
5326 {
5327 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5328 bitMapLock());
5329 sweepWork(_cmsGen);
5330 }
5331
5332 // Update Universe::_heap_*_at_gc figures.
5333 // We need all the free list locks to make the abstract state
5334 // transition from Sweeping to Resetting. See detailed note
5335 // further below.
5336 {
5337 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5338 // Update heap occupancy information which is used as
5339 // input to soft ref clearing policy at the next gc.
5340 Universe::update_heap_info_at_gc();
5341 _collectorState = Resizing;
5342 }
5343 }
5344 verify_work_stacks_empty();
5345 verify_overflow_empty();
5346
5347 if (should_unload_classes()) {
5348 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5349 // requires that the virtual spaces are stable and not deleted.
5350 ClassLoaderDataGraph::set_should_purge(true);
5351 }
5352
5353 _intra_sweep_timer.stop();
5354 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5355
5356 _inter_sweep_timer.reset();
5357 _inter_sweep_timer.start();
5358
5359 // We need to use a monotonically non-decreasing time in ms
5360 // or we will see time-warp warnings and os::javaTimeMillis()
5361 // does not guarantee monotonicity.
5362 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5363 update_time_of_last_gc(now);
5364
5365 // NOTE on abstract state transitions:
5366 // Mutators allocate-live and/or mark the mod-union table dirty
5367 // based on the state of the collection. The former is done in
5368 // the interval [Marking, Sweeping] and the latter in the interval
5369 // [Marking, Sweeping). Thus the transitions into the Marking state
5370 // and out of the Sweeping state must be synchronously visible
5371 // globally to the mutators.
5372 // The transition into the Marking state happens with the world
5373 // stopped so the mutators will globally see it. Sweeping is
5374 // done asynchronously by the background collector so the transition
5375 // from the Sweeping state to the Resizing state must be done
5376 // under the freelistLock (as is the check for whether to
5377 // allocate-live and whether to dirty the mod-union table).
5378 assert(_collectorState == Resizing, "Change of collector state to"
5379 " Resizing must be done under the freelistLocks (plural)");
5380
5381 // Now that sweeping has been completed, we clear
5382 // the incremental_collection_failed flag,
5383 // thus inviting a younger gen collection to promote into
5384 // this generation. If such a promotion may still fail,
5385 // the flag will be set again when a young collection is
5386 // attempted.
5387 CMSHeap* heap = CMSHeap::heap();
5388 heap->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5389 heap->update_full_collections_completed(_collection_count_start);
5390 }
5391
5392 // FIX ME!!! Looks like this belongs in CFLSpace, with
5393 // CMSGen merely delegating to it.
5394 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5395 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5396 HeapWord* minAddr = _cmsSpace->bottom();
5397 HeapWord* largestAddr =
5398 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5399 if (largestAddr == NULL) {
5400 // The dictionary appears to be empty. In this case
5401 // try to coalesce at the end of the heap.
5402 largestAddr = _cmsSpace->end();
5403 }
5404 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5405 size_t nearLargestOffset =
5406 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5407 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5408 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5409 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5410 }
5411
5412 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5413 return addr >= _cmsSpace->nearLargestChunk();
5414 }
5415
5416 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5417 return _cmsSpace->find_chunk_at_end();
5418 }
5419
5420 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5421 bool full) {
5422 // If the young generation has been collected, gather any statistics
5423 // that are of interest at this point.
5424 bool current_is_young = CMSHeap::heap()->is_young_gen(current_generation);
5425 if (!full && current_is_young) {
5426 // Gather statistics on the young generation collection.
5427 collector()->stats().record_gc0_end(used());
5428 }
5429 }
5430
5431 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5432 // We iterate over the space(s) underlying this generation,
5433 // checking the mark bit map to see if the bits corresponding
5434 // to specific blocks are marked or not. Blocks that are
5435 // marked are live and are not swept up. All remaining blocks
5436 // are swept up, with coalescing on-the-fly as we sweep up
5437 // contiguous free and/or garbage blocks:
5438 // We need to ensure that the sweeper synchronizes with allocators
5439 // and stop-the-world collectors. In particular, the following
5440 // locks are used:
5441 // . CMS token: if this is held, a stop the world collection cannot occur
5442 // . freelistLock: if this is held no allocation can occur from this
5443 // generation by another thread
5444 // . bitMapLock: if this is held, no other thread can access or update
5445 //
5446
5447 // Note that we need to hold the freelistLock if we use
5448 // block iterate below; else the iterator might go awry if
5449 // a mutator (or promotion) causes block contents to change
5450 // (for instance if the allocator divvies up a block).
5451 // If we hold the free list lock, for all practical purposes
5452 // young generation GC's can't occur (they'll usually need to
5453 // promote), so we might as well prevent all young generation
5454 // GC's while we do a sweeping step. For the same reason, we might
5455 // as well take the bit map lock for the entire duration
5456
5457 // check that we hold the requisite locks
5458 assert(have_cms_token(), "Should hold cms token");
5459 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5460 assert_lock_strong(old_gen->freelistLock());
5461 assert_lock_strong(bitMapLock());
5462
5463 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5464 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5465 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5466 _inter_sweep_estimate.padded_average(),
5467 _intra_sweep_estimate.padded_average());
5468 old_gen->setNearLargestChunk();
5469
5470 {
5471 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5472 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5473 // We need to free-up/coalesce garbage/blocks from a
5474 // co-terminal free run. This is done in the SweepClosure
5475 // destructor; so, do not remove this scope, else the
5476 // end-of-sweep-census below will be off by a little bit.
5477 }
5478 old_gen->cmsSpace()->sweep_completed();
5479 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5480 if (should_unload_classes()) { // unloaded classes this cycle,
5481 _concurrent_cycles_since_last_unload = 0; // ... reset count
5482 } else { // did not unload classes,
5483 _concurrent_cycles_since_last_unload++; // ... increment count
5484 }
5485 }
5486
5487 // Reset CMS data structures (for now just the marking bit map)
5488 // preparatory for the next cycle.
5489 void CMSCollector::reset_concurrent() {
5490 CMSTokenSyncWithLocks ts(true, bitMapLock());
5491
5492 // If the state is not "Resetting", the foreground thread
5493 // has done a collection and the resetting.
5494 if (_collectorState != Resetting) {
5495 assert(_collectorState == Idling, "The state should only change"
5496 " because the foreground collector has finished the collection");
5497 return;
5498 }
5499
5500 {
5501 // Clear the mark bitmap (no grey objects to start with)
5502 // for the next cycle.
5503 GCTraceCPUTime tcpu;
5504 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5505
5506 HeapWord* curAddr = _markBitMap.startWord();
5507 while (curAddr < _markBitMap.endWord()) {
5508 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5509 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5510 _markBitMap.clear_large_range(chunk);
5511 if (ConcurrentMarkSweepThread::should_yield() &&
5512 !foregroundGCIsActive() &&
5513 CMSYield) {
5514 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5515 "CMS thread should hold CMS token");
5516 assert_lock_strong(bitMapLock());
5517 bitMapLock()->unlock();
5518 ConcurrentMarkSweepThread::desynchronize(true);
5519 stopTimer();
5520 incrementYields();
5521
5522 // See the comment in coordinator_yield()
5523 for (unsigned i = 0; i < CMSYieldSleepCount &&
5524 ConcurrentMarkSweepThread::should_yield() &&
5525 !CMSCollector::foregroundGCIsActive(); ++i) {
5526 os::sleep(Thread::current(), 1, false);
5527 }
5528
5529 ConcurrentMarkSweepThread::synchronize(true);
5530 bitMapLock()->lock_without_safepoint_check();
5531 startTimer();
5532 }
5533 curAddr = chunk.end();
5534 }
5535 // A successful mostly concurrent collection has been done.
5536 // Because only the full (i.e., concurrent mode failure) collections
5537 // are being measured for gc overhead limits, clean the "near" flag
5538 // and count.
5539 size_policy()->reset_gc_overhead_limit_count();
5540 _collectorState = Idling;
5541 }
5542
5543 register_gc_end();
5544 }
5545
5546 // Same as above but for STW paths
5547 void CMSCollector::reset_stw() {
5548 // already have the lock
5549 assert(_collectorState == Resetting, "just checking");
5550 assert_lock_strong(bitMapLock());
5551 GCIdMark gc_id_mark(_cmsThread->gc_id());
5552 _markBitMap.clear_all();
5553 _collectorState = Idling;
5554 register_gc_end();
5555 }
5556
5557 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5558 GCTraceCPUTime tcpu;
5559 TraceCollectorStats tcs(counters());
5560
5561 switch (op) {
5562 case CMS_op_checkpointRootsInitial: {
5563 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5564 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5565 checkpointRootsInitial();
5566 break;
5567 }
5568 case CMS_op_checkpointRootsFinal: {
5569 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5570 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5571 checkpointRootsFinal();
5572 break;
5573 }
5574 default:
5575 fatal("No such CMS_op");
5576 }
5577 }
5578
5579 #ifndef PRODUCT
5580 size_t const CMSCollector::skip_header_HeapWords() {
5581 return FreeChunk::header_size();
5582 }
5583
5584 // Try and collect here conditions that should hold when
5585 // CMS thread is exiting. The idea is that the foreground GC
5586 // thread should not be blocked if it wants to terminate
5587 // the CMS thread and yet continue to run the VM for a while
5588 // after that.
5589 void CMSCollector::verify_ok_to_terminate() const {
5590 assert(Thread::current()->is_ConcurrentGC_thread(),
5591 "should be called by CMS thread");
5592 assert(!_foregroundGCShouldWait, "should be false");
5593 // We could check here that all the various low-level locks
5594 // are not held by the CMS thread, but that is overkill; see
5595 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5596 // is checked.
5597 }
5598 #endif
5599
5600 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5601 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5602 "missing Printezis mark?");
5603 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5604 size_t size = pointer_delta(nextOneAddr + 1, addr);
5605 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5606 "alignment problem");
5607 assert(size >= 3, "Necessary for Printezis marks to work");
5608 return size;
5609 }
5610
5611 // A variant of the above (block_size_using_printezis_bits()) except
5612 // that we return 0 if the P-bits are not yet set.
5613 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5614 if (_markBitMap.isMarked(addr + 1)) {
5615 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5616 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5617 size_t size = pointer_delta(nextOneAddr + 1, addr);
5618 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5619 "alignment problem");
5620 assert(size >= 3, "Necessary for Printezis marks to work");
5621 return size;
5622 }
5623 return 0;
5624 }
5625
5626 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5627 size_t sz = 0;
5628 oop p = (oop)addr;
5629 if (p->klass_or_null_acquire() != NULL) {
5630 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5631 } else {
5632 sz = block_size_using_printezis_bits(addr);
5633 }
5634 assert(sz > 0, "size must be nonzero");
5635 HeapWord* next_block = addr + sz;
5636 HeapWord* next_card = align_up(next_block, CardTableModRefBS::card_size);
5637 assert(align_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5638 align_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5639 "must be different cards");
5640 return next_card;
5641 }
5642
5643
5644 // CMS Bit Map Wrapper /////////////////////////////////////////
5645
5646 // Construct a CMS bit map infrastructure, but don't create the
5647 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5648 // further below.
5649 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5650 _bm(),
5651 _shifter(shifter),
5652 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5653 Monitor::_safepoint_check_sometimes) : NULL)
5654 {
5655 _bmStartWord = 0;
5656 _bmWordSize = 0;
5657 }
5658
5659 bool CMSBitMap::allocate(MemRegion mr) {
5660 _bmStartWord = mr.start();
5661 _bmWordSize = mr.word_size();
5662 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5663 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5664 if (!brs.is_reserved()) {
5665 log_warning(gc)("CMS bit map allocation failure");
5666 return false;
5667 }
5668 // For now we'll just commit all of the bit map up front.
5669 // Later on we'll try to be more parsimonious with swap.
5670 if (!_virtual_space.initialize(brs, brs.size())) {
5671 log_warning(gc)("CMS bit map backing store failure");
5672 return false;
5673 }
5674 assert(_virtual_space.committed_size() == brs.size(),
5675 "didn't reserve backing store for all of CMS bit map?");
5676 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5677 _bmWordSize, "inconsistency in bit map sizing");
5678 _bm = BitMapView((BitMap::bm_word_t*)_virtual_space.low(), _bmWordSize >> _shifter);
5679
5680 // bm.clear(); // can we rely on getting zero'd memory? verify below
5681 assert(isAllClear(),
5682 "Expected zero'd memory from ReservedSpace constructor");
5683 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5684 "consistency check");
5685 return true;
5686 }
5687
5688 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5689 HeapWord *next_addr, *end_addr, *last_addr;
5690 assert_locked();
5691 assert(covers(mr), "out-of-range error");
5692 // XXX assert that start and end are appropriately aligned
5693 for (next_addr = mr.start(), end_addr = mr.end();
5694 next_addr < end_addr; next_addr = last_addr) {
5695 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5696 last_addr = dirty_region.end();
5697 if (!dirty_region.is_empty()) {
5698 cl->do_MemRegion(dirty_region);
5699 } else {
5700 assert(last_addr == end_addr, "program logic");
5701 return;
5702 }
5703 }
5704 }
5705
5706 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5707 _bm.print_on_error(st, prefix);
5708 }
5709
5710 #ifndef PRODUCT
5711 void CMSBitMap::assert_locked() const {
5712 CMSLockVerifier::assert_locked(lock());
5713 }
5714
5715 bool CMSBitMap::covers(MemRegion mr) const {
5716 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5717 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5718 "size inconsistency");
5719 return (mr.start() >= _bmStartWord) &&
5720 (mr.end() <= endWord());
5721 }
5722
5723 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5724 return (start >= _bmStartWord && (start + size) <= endWord());
5725 }
5726
5727 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5728 // verify that there are no 1 bits in the interval [left, right)
5729 FalseBitMapClosure falseBitMapClosure;
5730 iterate(&falseBitMapClosure, left, right);
5731 }
5732
5733 void CMSBitMap::region_invariant(MemRegion mr)
5734 {
5735 assert_locked();
5736 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5737 assert(!mr.is_empty(), "unexpected empty region");
5738 assert(covers(mr), "mr should be covered by bit map");
5739 // convert address range into offset range
5740 size_t start_ofs = heapWordToOffset(mr.start());
5741 // Make sure that end() is appropriately aligned
5742 assert(mr.end() == align_up(mr.end(), (1 << (_shifter+LogHeapWordSize))),
5743 "Misaligned mr.end()");
5744 size_t end_ofs = heapWordToOffset(mr.end());
5745 assert(end_ofs > start_ofs, "Should mark at least one bit");
5746 }
5747
5748 #endif
5749
5750 bool CMSMarkStack::allocate(size_t size) {
5751 // allocate a stack of the requisite depth
5752 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5753 size * sizeof(oop)));
5754 if (!rs.is_reserved()) {
5755 log_warning(gc)("CMSMarkStack allocation failure");
5756 return false;
5757 }
5758 if (!_virtual_space.initialize(rs, rs.size())) {
5759 log_warning(gc)("CMSMarkStack backing store failure");
5760 return false;
5761 }
5762 assert(_virtual_space.committed_size() == rs.size(),
5763 "didn't reserve backing store for all of CMS stack?");
5764 _base = (oop*)(_virtual_space.low());
5765 _index = 0;
5766 _capacity = size;
5767 NOT_PRODUCT(_max_depth = 0);
5768 return true;
5769 }
5770
5771 // XXX FIX ME !!! In the MT case we come in here holding a
5772 // leaf lock. For printing we need to take a further lock
5773 // which has lower rank. We need to recalibrate the two
5774 // lock-ranks involved in order to be able to print the
5775 // messages below. (Or defer the printing to the caller.
5776 // For now we take the expedient path of just disabling the
5777 // messages for the problematic case.)
5778 void CMSMarkStack::expand() {
5779 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5780 if (_capacity == MarkStackSizeMax) {
5781 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5782 // We print a warning message only once per CMS cycle.
5783 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5784 }
5785 return;
5786 }
5787 // Double capacity if possible
5788 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5789 // Do not give up existing stack until we have managed to
5790 // get the double capacity that we desired.
5791 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5792 new_capacity * sizeof(oop)));
5793 if (rs.is_reserved()) {
5794 // Release the backing store associated with old stack
5795 _virtual_space.release();
5796 // Reinitialize virtual space for new stack
5797 if (!_virtual_space.initialize(rs, rs.size())) {
5798 fatal("Not enough swap for expanded marking stack");
5799 }
5800 _base = (oop*)(_virtual_space.low());
5801 _index = 0;
5802 _capacity = new_capacity;
5803 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5804 // Failed to double capacity, continue;
5805 // we print a detail message only once per CMS cycle.
5806 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5807 _capacity / K, new_capacity / K);
5808 }
5809 }
5810
5811
5812 // Closures
5813 // XXX: there seems to be a lot of code duplication here;
5814 // should refactor and consolidate common code.
5815
5816 // This closure is used to mark refs into the CMS generation in
5817 // the CMS bit map. Called at the first checkpoint. This closure
5818 // assumes that we do not need to re-mark dirty cards; if the CMS
5819 // generation on which this is used is not an oldest
5820 // generation then this will lose younger_gen cards!
5821
5822 MarkRefsIntoClosure::MarkRefsIntoClosure(
5823 MemRegion span, CMSBitMap* bitMap):
5824 _span(span),
5825 _bitMap(bitMap)
5826 {
5827 assert(ref_processor() == NULL, "deliberately left NULL");
5828 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5829 }
5830
5831 void MarkRefsIntoClosure::do_oop(oop obj) {
5832 // if p points into _span, then mark corresponding bit in _markBitMap
5833 assert(oopDesc::is_oop(obj), "expected an oop");
5834 HeapWord* addr = (HeapWord*)obj;
5835 if (_span.contains(addr)) {
5836 // this should be made more efficient
5837 _bitMap->mark(addr);
5838 }
5839 }
5840
5841 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5842 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5843
5844 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5845 MemRegion span, CMSBitMap* bitMap):
5846 _span(span),
5847 _bitMap(bitMap)
5848 {
5849 assert(ref_processor() == NULL, "deliberately left NULL");
5850 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5851 }
5852
5853 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5854 // if p points into _span, then mark corresponding bit in _markBitMap
5855 assert(oopDesc::is_oop(obj), "expected an oop");
5856 HeapWord* addr = (HeapWord*)obj;
5857 if (_span.contains(addr)) {
5858 // this should be made more efficient
5859 _bitMap->par_mark(addr);
5860 }
5861 }
5862
5863 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5864 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5865
5866 // A variant of the above, used for CMS marking verification.
5867 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5868 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5869 _span(span),
5870 _verification_bm(verification_bm),
5871 _cms_bm(cms_bm)
5872 {
5873 assert(ref_processor() == NULL, "deliberately left NULL");
5874 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5875 }
5876
5877 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5878 // if p points into _span, then mark corresponding bit in _markBitMap
5879 assert(oopDesc::is_oop(obj), "expected an oop");
5880 HeapWord* addr = (HeapWord*)obj;
5881 if (_span.contains(addr)) {
5882 _verification_bm->mark(addr);
5883 if (!_cms_bm->isMarked(addr)) {
5884 Log(gc, verify) log;
5885 ResourceMark rm;
5886 LogStream ls(log.error());
5887 oop(addr)->print_on(&ls);
5888 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5889 fatal("... aborting");
5890 }
5891 }
5892 }
5893
5894 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5895 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5896
5897 //////////////////////////////////////////////////
5898 // MarkRefsIntoAndScanClosure
5899 //////////////////////////////////////////////////
5900
5901 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5902 ReferenceProcessor* rp,
5903 CMSBitMap* bit_map,
5904 CMSBitMap* mod_union_table,
5905 CMSMarkStack* mark_stack,
5906 CMSCollector* collector,
5907 bool should_yield,
5908 bool concurrent_precleaning):
5909 _collector(collector),
5910 _span(span),
5911 _bit_map(bit_map),
5912 _mark_stack(mark_stack),
5913 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5914 mark_stack, concurrent_precleaning),
5915 _yield(should_yield),
5916 _concurrent_precleaning(concurrent_precleaning),
5917 _freelistLock(NULL)
5918 {
5919 // FIXME: Should initialize in base class constructor.
5920 assert(rp != NULL, "ref_processor shouldn't be NULL");
5921 set_ref_processor_internal(rp);
5922 }
5923
5924 // This closure is used to mark refs into the CMS generation at the
5925 // second (final) checkpoint, and to scan and transitively follow
5926 // the unmarked oops. It is also used during the concurrent precleaning
5927 // phase while scanning objects on dirty cards in the CMS generation.
5928 // The marks are made in the marking bit map and the marking stack is
5929 // used for keeping the (newly) grey objects during the scan.
5930 // The parallel version (Par_...) appears further below.
5931 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5932 if (obj != NULL) {
5933 assert(oopDesc::is_oop(obj), "expected an oop");
5934 HeapWord* addr = (HeapWord*)obj;
5935 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5936 assert(_collector->overflow_list_is_empty(),
5937 "overflow list should be empty");
5938 if (_span.contains(addr) &&
5939 !_bit_map->isMarked(addr)) {
5940 // mark bit map (object is now grey)
5941 _bit_map->mark(addr);
5942 // push on marking stack (stack should be empty), and drain the
5943 // stack by applying this closure to the oops in the oops popped
5944 // from the stack (i.e. blacken the grey objects)
5945 bool res = _mark_stack->push(obj);
5946 assert(res, "Should have space to push on empty stack");
5947 do {
5948 oop new_oop = _mark_stack->pop();
5949 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
5950 assert(_bit_map->isMarked((HeapWord*)new_oop),
5951 "only grey objects on this stack");
5952 // iterate over the oops in this oop, marking and pushing
5953 // the ones in CMS heap (i.e. in _span).
5954 new_oop->oop_iterate(&_pushAndMarkClosure);
5955 // check if it's time to yield
5956 do_yield_check();
5957 } while (!_mark_stack->isEmpty() ||
5958 (!_concurrent_precleaning && take_from_overflow_list()));
5959 // if marking stack is empty, and we are not doing this
5960 // during precleaning, then check the overflow list
5961 }
5962 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5963 assert(_collector->overflow_list_is_empty(),
5964 "overflow list was drained above");
5965
5966 assert(_collector->no_preserved_marks(),
5967 "All preserved marks should have been restored above");
5968 }
5969 }
5970
5971 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5972 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5973
5974 void MarkRefsIntoAndScanClosure::do_yield_work() {
5975 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5976 "CMS thread should hold CMS token");
5977 assert_lock_strong(_freelistLock);
5978 assert_lock_strong(_bit_map->lock());
5979 // relinquish the free_list_lock and bitMaplock()
5980 _bit_map->lock()->unlock();
5981 _freelistLock->unlock();
5982 ConcurrentMarkSweepThread::desynchronize(true);
5983 _collector->stopTimer();
5984 _collector->incrementYields();
5985
5986 // See the comment in coordinator_yield()
5987 for (unsigned i = 0;
5988 i < CMSYieldSleepCount &&
5989 ConcurrentMarkSweepThread::should_yield() &&
5990 !CMSCollector::foregroundGCIsActive();
5991 ++i) {
5992 os::sleep(Thread::current(), 1, false);
5993 }
5994
5995 ConcurrentMarkSweepThread::synchronize(true);
5996 _freelistLock->lock_without_safepoint_check();
5997 _bit_map->lock()->lock_without_safepoint_check();
5998 _collector->startTimer();
5999 }
6000
6001 ///////////////////////////////////////////////////////////
6002 // ParMarkRefsIntoAndScanClosure: a parallel version of
6003 // MarkRefsIntoAndScanClosure
6004 ///////////////////////////////////////////////////////////
6005 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6006 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6007 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6008 _span(span),
6009 _bit_map(bit_map),
6010 _work_queue(work_queue),
6011 _low_water_mark(MIN2((work_queue->max_elems()/4),
6012 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6013 _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6014 {
6015 // FIXME: Should initialize in base class constructor.
6016 assert(rp != NULL, "ref_processor shouldn't be NULL");
6017 set_ref_processor_internal(rp);
6018 }
6019
6020 // This closure is used to mark refs into the CMS generation at the
6021 // second (final) checkpoint, and to scan and transitively follow
6022 // the unmarked oops. The marks are made in the marking bit map and
6023 // the work_queue is used for keeping the (newly) grey objects during
6024 // the scan phase whence they are also available for stealing by parallel
6025 // threads. Since the marking bit map is shared, updates are
6026 // synchronized (via CAS).
6027 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6028 if (obj != NULL) {
6029 // Ignore mark word because this could be an already marked oop
6030 // that may be chained at the end of the overflow list.
6031 assert(oopDesc::is_oop(obj, true), "expected an oop");
6032 HeapWord* addr = (HeapWord*)obj;
6033 if (_span.contains(addr) &&
6034 !_bit_map->isMarked(addr)) {
6035 // mark bit map (object will become grey):
6036 // It is possible for several threads to be
6037 // trying to "claim" this object concurrently;
6038 // the unique thread that succeeds in marking the
6039 // object first will do the subsequent push on
6040 // to the work queue (or overflow list).
6041 if (_bit_map->par_mark(addr)) {
6042 // push on work_queue (which may not be empty), and trim the
6043 // queue to an appropriate length by applying this closure to
6044 // the oops in the oops popped from the stack (i.e. blacken the
6045 // grey objects)
6046 bool res = _work_queue->push(obj);
6047 assert(res, "Low water mark should be less than capacity?");
6048 trim_queue(_low_water_mark);
6049 } // Else, another thread claimed the object
6050 }
6051 }
6052 }
6053
6054 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6055 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6056
6057 // This closure is used to rescan the marked objects on the dirty cards
6058 // in the mod union table and the card table proper.
6059 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6060 oop p, MemRegion mr) {
6061
6062 size_t size = 0;
6063 HeapWord* addr = (HeapWord*)p;
6064 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6065 assert(_span.contains(addr), "we are scanning the CMS generation");
6066 // check if it's time to yield
6067 if (do_yield_check()) {
6068 // We yielded for some foreground stop-world work,
6069 // and we have been asked to abort this ongoing preclean cycle.
6070 return 0;
6071 }
6072 if (_bitMap->isMarked(addr)) {
6073 // it's marked; is it potentially uninitialized?
6074 if (p->klass_or_null_acquire() != NULL) {
6075 // an initialized object; ignore mark word in verification below
6076 // since we are running concurrent with mutators
6077 assert(oopDesc::is_oop(p, true), "should be an oop");
6078 if (p->is_objArray()) {
6079 // objArrays are precisely marked; restrict scanning
6080 // to dirty cards only.
6081 size = CompactibleFreeListSpace::adjustObjectSize(
6082 p->oop_iterate_size(_scanningClosure, mr));
6083 } else {
6084 // A non-array may have been imprecisely marked; we need
6085 // to scan object in its entirety.
6086 size = CompactibleFreeListSpace::adjustObjectSize(
6087 p->oop_iterate_size(_scanningClosure));
6088 }
6089 #ifdef ASSERT
6090 size_t direct_size =
6091 CompactibleFreeListSpace::adjustObjectSize(p->size());
6092 assert(size == direct_size, "Inconsistency in size");
6093 assert(size >= 3, "Necessary for Printezis marks to work");
6094 HeapWord* start_pbit = addr + 1;
6095 HeapWord* end_pbit = addr + size - 1;
6096 assert(_bitMap->isMarked(start_pbit) == _bitMap->isMarked(end_pbit),
6097 "inconsistent Printezis mark");
6098 // Verify inner mark bits (between Printezis bits) are clear,
6099 // but don't repeat if there are multiple dirty regions for
6100 // the same object, to avoid potential O(N^2) performance.
6101 if (addr != _last_scanned_object) {
6102 _bitMap->verifyNoOneBitsInRange(start_pbit + 1, end_pbit);
6103 _last_scanned_object = addr;
6104 }
6105 #endif // ASSERT
6106 } else {
6107 // An uninitialized object.
6108 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6109 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6110 size = pointer_delta(nextOneAddr + 1, addr);
6111 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6112 "alignment problem");
6113 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6114 // will dirty the card when the klass pointer is installed in the
6115 // object (signaling the completion of initialization).
6116 }
6117 } else {
6118 // Either a not yet marked object or an uninitialized object
6119 if (p->klass_or_null_acquire() == NULL) {
6120 // An uninitialized object, skip to the next card, since
6121 // we may not be able to read its P-bits yet.
6122 assert(size == 0, "Initial value");
6123 } else {
6124 // An object not (yet) reached by marking: we merely need to
6125 // compute its size so as to go look at the next block.
6126 assert(oopDesc::is_oop(p, true), "should be an oop");
6127 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6128 }
6129 }
6130 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6131 return size;
6132 }
6133
6134 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6135 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6136 "CMS thread should hold CMS token");
6137 assert_lock_strong(_freelistLock);
6138 assert_lock_strong(_bitMap->lock());
6139 // relinquish the free_list_lock and bitMaplock()
6140 _bitMap->lock()->unlock();
6141 _freelistLock->unlock();
6142 ConcurrentMarkSweepThread::desynchronize(true);
6143 _collector->stopTimer();
6144 _collector->incrementYields();
6145
6146 // See the comment in coordinator_yield()
6147 for (unsigned i = 0; i < CMSYieldSleepCount &&
6148 ConcurrentMarkSweepThread::should_yield() &&
6149 !CMSCollector::foregroundGCIsActive(); ++i) {
6150 os::sleep(Thread::current(), 1, false);
6151 }
6152
6153 ConcurrentMarkSweepThread::synchronize(true);
6154 _freelistLock->lock_without_safepoint_check();
6155 _bitMap->lock()->lock_without_safepoint_check();
6156 _collector->startTimer();
6157 }
6158
6159
6160 //////////////////////////////////////////////////////////////////
6161 // SurvivorSpacePrecleanClosure
6162 //////////////////////////////////////////////////////////////////
6163 // This (single-threaded) closure is used to preclean the oops in
6164 // the survivor spaces.
6165 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6166
6167 HeapWord* addr = (HeapWord*)p;
6168 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6169 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6170 assert(p->klass_or_null() != NULL, "object should be initialized");
6171 // an initialized object; ignore mark word in verification below
6172 // since we are running concurrent with mutators
6173 assert(oopDesc::is_oop(p, true), "should be an oop");
6174 // Note that we do not yield while we iterate over
6175 // the interior oops of p, pushing the relevant ones
6176 // on our marking stack.
6177 size_t size = p->oop_iterate_size(_scanning_closure);
6178 do_yield_check();
6179 // Observe that below, we do not abandon the preclean
6180 // phase as soon as we should; rather we empty the
6181 // marking stack before returning. This is to satisfy
6182 // some existing assertions. In general, it may be a
6183 // good idea to abort immediately and complete the marking
6184 // from the grey objects at a later time.
6185 while (!_mark_stack->isEmpty()) {
6186 oop new_oop = _mark_stack->pop();
6187 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
6188 assert(_bit_map->isMarked((HeapWord*)new_oop),
6189 "only grey objects on this stack");
6190 // iterate over the oops in this oop, marking and pushing
6191 // the ones in CMS heap (i.e. in _span).
6192 new_oop->oop_iterate(_scanning_closure);
6193 // check if it's time to yield
6194 do_yield_check();
6195 }
6196 unsigned int after_count =
6197 CMSHeap::heap()->total_collections();
6198 bool abort = (_before_count != after_count) ||
6199 _collector->should_abort_preclean();
6200 return abort ? 0 : size;
6201 }
6202
6203 void SurvivorSpacePrecleanClosure::do_yield_work() {
6204 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6205 "CMS thread should hold CMS token");
6206 assert_lock_strong(_bit_map->lock());
6207 // Relinquish the bit map lock
6208 _bit_map->lock()->unlock();
6209 ConcurrentMarkSweepThread::desynchronize(true);
6210 _collector->stopTimer();
6211 _collector->incrementYields();
6212
6213 // See the comment in coordinator_yield()
6214 for (unsigned i = 0; i < CMSYieldSleepCount &&
6215 ConcurrentMarkSweepThread::should_yield() &&
6216 !CMSCollector::foregroundGCIsActive(); ++i) {
6217 os::sleep(Thread::current(), 1, false);
6218 }
6219
6220 ConcurrentMarkSweepThread::synchronize(true);
6221 _bit_map->lock()->lock_without_safepoint_check();
6222 _collector->startTimer();
6223 }
6224
6225 // This closure is used to rescan the marked objects on the dirty cards
6226 // in the mod union table and the card table proper. In the parallel
6227 // case, although the bitMap is shared, we do a single read so the
6228 // isMarked() query is "safe".
6229 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6230 // Ignore mark word because we are running concurrent with mutators
6231 assert(oopDesc::is_oop_or_null(p, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6232 HeapWord* addr = (HeapWord*)p;
6233 assert(_span.contains(addr), "we are scanning the CMS generation");
6234 bool is_obj_array = false;
6235 #ifdef ASSERT
6236 if (!_parallel) {
6237 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6238 assert(_collector->overflow_list_is_empty(),
6239 "overflow list should be empty");
6240
6241 }
6242 #endif // ASSERT
6243 if (_bit_map->isMarked(addr)) {
6244 // Obj arrays are precisely marked, non-arrays are not;
6245 // so we scan objArrays precisely and non-arrays in their
6246 // entirety.
6247 if (p->is_objArray()) {
6248 is_obj_array = true;
6249 if (_parallel) {
6250 p->oop_iterate(_par_scan_closure, mr);
6251 } else {
6252 p->oop_iterate(_scan_closure, mr);
6253 }
6254 } else {
6255 if (_parallel) {
6256 p->oop_iterate(_par_scan_closure);
6257 } else {
6258 p->oop_iterate(_scan_closure);
6259 }
6260 }
6261 }
6262 #ifdef ASSERT
6263 if (!_parallel) {
6264 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6265 assert(_collector->overflow_list_is_empty(),
6266 "overflow list should be empty");
6267
6268 }
6269 #endif // ASSERT
6270 return is_obj_array;
6271 }
6272
6273 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6274 MemRegion span,
6275 CMSBitMap* bitMap, CMSMarkStack* markStack,
6276 bool should_yield, bool verifying):
6277 _collector(collector),
6278 _span(span),
6279 _bitMap(bitMap),
6280 _mut(&collector->_modUnionTable),
6281 _markStack(markStack),
6282 _yield(should_yield),
6283 _skipBits(0)
6284 {
6285 assert(_markStack->isEmpty(), "stack should be empty");
6286 _finger = _bitMap->startWord();
6287 _threshold = _finger;
6288 assert(_collector->_restart_addr == NULL, "Sanity check");
6289 assert(_span.contains(_finger), "Out of bounds _finger?");
6290 DEBUG_ONLY(_verifying = verifying;)
6291 }
6292
6293 void MarkFromRootsClosure::reset(HeapWord* addr) {
6294 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6295 assert(_span.contains(addr), "Out of bounds _finger?");
6296 _finger = addr;
6297 _threshold = align_up(_finger, CardTableModRefBS::card_size);
6298 }
6299
6300 // Should revisit to see if this should be restructured for
6301 // greater efficiency.
6302 bool MarkFromRootsClosure::do_bit(size_t offset) {
6303 if (_skipBits > 0) {
6304 _skipBits--;
6305 return true;
6306 }
6307 // convert offset into a HeapWord*
6308 HeapWord* addr = _bitMap->startWord() + offset;
6309 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6310 "address out of range");
6311 assert(_bitMap->isMarked(addr), "tautology");
6312 if (_bitMap->isMarked(addr+1)) {
6313 // this is an allocated but not yet initialized object
6314 assert(_skipBits == 0, "tautology");
6315 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6316 oop p = oop(addr);
6317 if (p->klass_or_null_acquire() == NULL) {
6318 DEBUG_ONLY(if (!_verifying) {)
6319 // We re-dirty the cards on which this object lies and increase
6320 // the _threshold so that we'll come back to scan this object
6321 // during the preclean or remark phase. (CMSCleanOnEnter)
6322 if (CMSCleanOnEnter) {
6323 size_t sz = _collector->block_size_using_printezis_bits(addr);
6324 HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
6325 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6326 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6327 // Bump _threshold to end_card_addr; note that
6328 // _threshold cannot possibly exceed end_card_addr, anyhow.
6329 // This prevents future clearing of the card as the scan proceeds
6330 // to the right.
6331 assert(_threshold <= end_card_addr,
6332 "Because we are just scanning into this object");
6333 if (_threshold < end_card_addr) {
6334 _threshold = end_card_addr;
6335 }
6336 if (p->klass_or_null_acquire() != NULL) {
6337 // Redirty the range of cards...
6338 _mut->mark_range(redirty_range);
6339 } // ...else the setting of klass will dirty the card anyway.
6340 }
6341 DEBUG_ONLY(})
6342 return true;
6343 }
6344 }
6345 scanOopsInOop(addr);
6346 return true;
6347 }
6348
6349 // We take a break if we've been at this for a while,
6350 // so as to avoid monopolizing the locks involved.
6351 void MarkFromRootsClosure::do_yield_work() {
6352 // First give up the locks, then yield, then re-lock
6353 // We should probably use a constructor/destructor idiom to
6354 // do this unlock/lock or modify the MutexUnlocker class to
6355 // serve our purpose. XXX
6356 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6357 "CMS thread should hold CMS token");
6358 assert_lock_strong(_bitMap->lock());
6359 _bitMap->lock()->unlock();
6360 ConcurrentMarkSweepThread::desynchronize(true);
6361 _collector->stopTimer();
6362 _collector->incrementYields();
6363
6364 // See the comment in coordinator_yield()
6365 for (unsigned i = 0; i < CMSYieldSleepCount &&
6366 ConcurrentMarkSweepThread::should_yield() &&
6367 !CMSCollector::foregroundGCIsActive(); ++i) {
6368 os::sleep(Thread::current(), 1, false);
6369 }
6370
6371 ConcurrentMarkSweepThread::synchronize(true);
6372 _bitMap->lock()->lock_without_safepoint_check();
6373 _collector->startTimer();
6374 }
6375
6376 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6377 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6378 assert(_markStack->isEmpty(),
6379 "should drain stack to limit stack usage");
6380 // convert ptr to an oop preparatory to scanning
6381 oop obj = oop(ptr);
6382 // Ignore mark word in verification below, since we
6383 // may be running concurrent with mutators.
6384 assert(oopDesc::is_oop(obj, true), "should be an oop");
6385 assert(_finger <= ptr, "_finger runneth ahead");
6386 // advance the finger to right end of this object
6387 _finger = ptr + obj->size();
6388 assert(_finger > ptr, "we just incremented it above");
6389 // On large heaps, it may take us some time to get through
6390 // the marking phase. During
6391 // this time it's possible that a lot of mutations have
6392 // accumulated in the card table and the mod union table --
6393 // these mutation records are redundant until we have
6394 // actually traced into the corresponding card.
6395 // Here, we check whether advancing the finger would make
6396 // us cross into a new card, and if so clear corresponding
6397 // cards in the MUT (preclean them in the card-table in the
6398 // future).
6399
6400 DEBUG_ONLY(if (!_verifying) {)
6401 // The clean-on-enter optimization is disabled by default,
6402 // until we fix 6178663.
6403 if (CMSCleanOnEnter && (_finger > _threshold)) {
6404 // [_threshold, _finger) represents the interval
6405 // of cards to be cleared in MUT (or precleaned in card table).
6406 // The set of cards to be cleared is all those that overlap
6407 // with the interval [_threshold, _finger); note that
6408 // _threshold is always kept card-aligned but _finger isn't
6409 // always card-aligned.
6410 HeapWord* old_threshold = _threshold;
6411 assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6412 "_threshold should always be card-aligned");
6413 _threshold = align_up(_finger, CardTableModRefBS::card_size);
6414 MemRegion mr(old_threshold, _threshold);
6415 assert(!mr.is_empty(), "Control point invariant");
6416 assert(_span.contains(mr), "Should clear within span");
6417 _mut->clear_range(mr);
6418 }
6419 DEBUG_ONLY(})
6420 // Note: the finger doesn't advance while we drain
6421 // the stack below.
6422 PushOrMarkClosure pushOrMarkClosure(_collector,
6423 _span, _bitMap, _markStack,
6424 _finger, this);
6425 bool res = _markStack->push(obj);
6426 assert(res, "Empty non-zero size stack should have space for single push");
6427 while (!_markStack->isEmpty()) {
6428 oop new_oop = _markStack->pop();
6429 // Skip verifying header mark word below because we are
6430 // running concurrent with mutators.
6431 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6432 // now scan this oop's oops
6433 new_oop->oop_iterate(&pushOrMarkClosure);
6434 do_yield_check();
6435 }
6436 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6437 }
6438
6439 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6440 CMSCollector* collector, MemRegion span,
6441 CMSBitMap* bit_map,
6442 OopTaskQueue* work_queue,
6443 CMSMarkStack* overflow_stack):
6444 _collector(collector),
6445 _whole_span(collector->_span),
6446 _span(span),
6447 _bit_map(bit_map),
6448 _mut(&collector->_modUnionTable),
6449 _work_queue(work_queue),
6450 _overflow_stack(overflow_stack),
6451 _skip_bits(0),
6452 _task(task)
6453 {
6454 assert(_work_queue->size() == 0, "work_queue should be empty");
6455 _finger = span.start();
6456 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6457 assert(_span.contains(_finger), "Out of bounds _finger?");
6458 }
6459
6460 // Should revisit to see if this should be restructured for
6461 // greater efficiency.
6462 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6463 if (_skip_bits > 0) {
6464 _skip_bits--;
6465 return true;
6466 }
6467 // convert offset into a HeapWord*
6468 HeapWord* addr = _bit_map->startWord() + offset;
6469 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6470 "address out of range");
6471 assert(_bit_map->isMarked(addr), "tautology");
6472 if (_bit_map->isMarked(addr+1)) {
6473 // this is an allocated object that might not yet be initialized
6474 assert(_skip_bits == 0, "tautology");
6475 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6476 oop p = oop(addr);
6477 if (p->klass_or_null_acquire() == NULL) {
6478 // in the case of Clean-on-Enter optimization, redirty card
6479 // and avoid clearing card by increasing the threshold.
6480 return true;
6481 }
6482 }
6483 scan_oops_in_oop(addr);
6484 return true;
6485 }
6486
6487 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6488 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6489 // Should we assert that our work queue is empty or
6490 // below some drain limit?
6491 assert(_work_queue->size() == 0,
6492 "should drain stack to limit stack usage");
6493 // convert ptr to an oop preparatory to scanning
6494 oop obj = oop(ptr);
6495 // Ignore mark word in verification below, since we
6496 // may be running concurrent with mutators.
6497 assert(oopDesc::is_oop(obj, true), "should be an oop");
6498 assert(_finger <= ptr, "_finger runneth ahead");
6499 // advance the finger to right end of this object
6500 _finger = ptr + obj->size();
6501 assert(_finger > ptr, "we just incremented it above");
6502 // On large heaps, it may take us some time to get through
6503 // the marking phase. During
6504 // this time it's possible that a lot of mutations have
6505 // accumulated in the card table and the mod union table --
6506 // these mutation records are redundant until we have
6507 // actually traced into the corresponding card.
6508 // Here, we check whether advancing the finger would make
6509 // us cross into a new card, and if so clear corresponding
6510 // cards in the MUT (preclean them in the card-table in the
6511 // future).
6512
6513 // The clean-on-enter optimization is disabled by default,
6514 // until we fix 6178663.
6515 if (CMSCleanOnEnter && (_finger > _threshold)) {
6516 // [_threshold, _finger) represents the interval
6517 // of cards to be cleared in MUT (or precleaned in card table).
6518 // The set of cards to be cleared is all those that overlap
6519 // with the interval [_threshold, _finger); note that
6520 // _threshold is always kept card-aligned but _finger isn't
6521 // always card-aligned.
6522 HeapWord* old_threshold = _threshold;
6523 assert(is_aligned(old_threshold, CardTableModRefBS::card_size),
6524 "_threshold should always be card-aligned");
6525 _threshold = align_up(_finger, CardTableModRefBS::card_size);
6526 MemRegion mr(old_threshold, _threshold);
6527 assert(!mr.is_empty(), "Control point invariant");
6528 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6529 _mut->clear_range(mr);
6530 }
6531
6532 // Note: the local finger doesn't advance while we drain
6533 // the stack below, but the global finger sure can and will.
6534 HeapWord* volatile* gfa = _task->global_finger_addr();
6535 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6536 _span, _bit_map,
6537 _work_queue,
6538 _overflow_stack,
6539 _finger,
6540 gfa, this);
6541 bool res = _work_queue->push(obj); // overflow could occur here
6542 assert(res, "Will hold once we use workqueues");
6543 while (true) {
6544 oop new_oop;
6545 if (!_work_queue->pop_local(new_oop)) {
6546 // We emptied our work_queue; check if there's stuff that can
6547 // be gotten from the overflow stack.
6548 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6549 _overflow_stack, _work_queue)) {
6550 do_yield_check();
6551 continue;
6552 } else { // done
6553 break;
6554 }
6555 }
6556 // Skip verifying header mark word below because we are
6557 // running concurrent with mutators.
6558 assert(oopDesc::is_oop(new_oop, true), "Oops! expected to pop an oop");
6559 // now scan this oop's oops
6560 new_oop->oop_iterate(&pushOrMarkClosure);
6561 do_yield_check();
6562 }
6563 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6564 }
6565
6566 // Yield in response to a request from VM Thread or
6567 // from mutators.
6568 void ParMarkFromRootsClosure::do_yield_work() {
6569 assert(_task != NULL, "sanity");
6570 _task->yield();
6571 }
6572
6573 // A variant of the above used for verifying CMS marking work.
6574 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6575 MemRegion span,
6576 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6577 CMSMarkStack* mark_stack):
6578 _collector(collector),
6579 _span(span),
6580 _verification_bm(verification_bm),
6581 _cms_bm(cms_bm),
6582 _mark_stack(mark_stack),
6583 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6584 mark_stack)
6585 {
6586 assert(_mark_stack->isEmpty(), "stack should be empty");
6587 _finger = _verification_bm->startWord();
6588 assert(_collector->_restart_addr == NULL, "Sanity check");
6589 assert(_span.contains(_finger), "Out of bounds _finger?");
6590 }
6591
6592 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6593 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6594 assert(_span.contains(addr), "Out of bounds _finger?");
6595 _finger = addr;
6596 }
6597
6598 // Should revisit to see if this should be restructured for
6599 // greater efficiency.
6600 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6601 // convert offset into a HeapWord*
6602 HeapWord* addr = _verification_bm->startWord() + offset;
6603 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6604 "address out of range");
6605 assert(_verification_bm->isMarked(addr), "tautology");
6606 assert(_cms_bm->isMarked(addr), "tautology");
6607
6608 assert(_mark_stack->isEmpty(),
6609 "should drain stack to limit stack usage");
6610 // convert addr to an oop preparatory to scanning
6611 oop obj = oop(addr);
6612 assert(oopDesc::is_oop(obj), "should be an oop");
6613 assert(_finger <= addr, "_finger runneth ahead");
6614 // advance the finger to right end of this object
6615 _finger = addr + obj->size();
6616 assert(_finger > addr, "we just incremented it above");
6617 // Note: the finger doesn't advance while we drain
6618 // the stack below.
6619 bool res = _mark_stack->push(obj);
6620 assert(res, "Empty non-zero size stack should have space for single push");
6621 while (!_mark_stack->isEmpty()) {
6622 oop new_oop = _mark_stack->pop();
6623 assert(oopDesc::is_oop(new_oop), "Oops! expected to pop an oop");
6624 // now scan this oop's oops
6625 new_oop->oop_iterate(&_pam_verify_closure);
6626 }
6627 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6628 return true;
6629 }
6630
6631 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6632 CMSCollector* collector, MemRegion span,
6633 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6634 CMSMarkStack* mark_stack):
6635 MetadataAwareOopClosure(collector->ref_processor()),
6636 _collector(collector),
6637 _span(span),
6638 _verification_bm(verification_bm),
6639 _cms_bm(cms_bm),
6640 _mark_stack(mark_stack)
6641 { }
6642
6643 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6644 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6645
6646 // Upon stack overflow, we discard (part of) the stack,
6647 // remembering the least address amongst those discarded
6648 // in CMSCollector's _restart_address.
6649 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6650 // Remember the least grey address discarded
6651 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6652 _collector->lower_restart_addr(ra);
6653 _mark_stack->reset(); // discard stack contents
6654 _mark_stack->expand(); // expand the stack if possible
6655 }
6656
6657 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6658 assert(oopDesc::is_oop_or_null(obj), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6659 HeapWord* addr = (HeapWord*)obj;
6660 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6661 // Oop lies in _span and isn't yet grey or black
6662 _verification_bm->mark(addr); // now grey
6663 if (!_cms_bm->isMarked(addr)) {
6664 Log(gc, verify) log;
6665 ResourceMark rm;
6666 LogStream ls(log.error());
6667 oop(addr)->print_on(&ls);
6668 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6669 fatal("... aborting");
6670 }
6671
6672 if (!_mark_stack->push(obj)) { // stack overflow
6673 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6674 assert(_mark_stack->isFull(), "Else push should have succeeded");
6675 handle_stack_overflow(addr);
6676 }
6677 // anything including and to the right of _finger
6678 // will be scanned as we iterate over the remainder of the
6679 // bit map
6680 }
6681 }
6682
6683 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6684 MemRegion span,
6685 CMSBitMap* bitMap, CMSMarkStack* markStack,
6686 HeapWord* finger, MarkFromRootsClosure* parent) :
6687 MetadataAwareOopClosure(collector->ref_processor()),
6688 _collector(collector),
6689 _span(span),
6690 _bitMap(bitMap),
6691 _markStack(markStack),
6692 _finger(finger),
6693 _parent(parent)
6694 { }
6695
6696 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6697 MemRegion span,
6698 CMSBitMap* bit_map,
6699 OopTaskQueue* work_queue,
6700 CMSMarkStack* overflow_stack,
6701 HeapWord* finger,
6702 HeapWord* volatile* global_finger_addr,
6703 ParMarkFromRootsClosure* parent) :
6704 MetadataAwareOopClosure(collector->ref_processor()),
6705 _collector(collector),
6706 _whole_span(collector->_span),
6707 _span(span),
6708 _bit_map(bit_map),
6709 _work_queue(work_queue),
6710 _overflow_stack(overflow_stack),
6711 _finger(finger),
6712 _global_finger_addr(global_finger_addr),
6713 _parent(parent)
6714 { }
6715
6716 // Assumes thread-safe access by callers, who are
6717 // responsible for mutual exclusion.
6718 void CMSCollector::lower_restart_addr(HeapWord* low) {
6719 assert(_span.contains(low), "Out of bounds addr");
6720 if (_restart_addr == NULL) {
6721 _restart_addr = low;
6722 } else {
6723 _restart_addr = MIN2(_restart_addr, low);
6724 }
6725 }
6726
6727 // Upon stack overflow, we discard (part of) the stack,
6728 // remembering the least address amongst those discarded
6729 // in CMSCollector's _restart_address.
6730 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6731 // Remember the least grey address discarded
6732 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6733 _collector->lower_restart_addr(ra);
6734 _markStack->reset(); // discard stack contents
6735 _markStack->expand(); // expand the stack if possible
6736 }
6737
6738 // Upon stack overflow, we discard (part of) the stack,
6739 // remembering the least address amongst those discarded
6740 // in CMSCollector's _restart_address.
6741 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6742 // We need to do this under a mutex to prevent other
6743 // workers from interfering with the work done below.
6744 MutexLockerEx ml(_overflow_stack->par_lock(),
6745 Mutex::_no_safepoint_check_flag);
6746 // Remember the least grey address discarded
6747 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6748 _collector->lower_restart_addr(ra);
6749 _overflow_stack->reset(); // discard stack contents
6750 _overflow_stack->expand(); // expand the stack if possible
6751 }
6752
6753 void PushOrMarkClosure::do_oop(oop obj) {
6754 // Ignore mark word because we are running concurrent with mutators.
6755 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6756 HeapWord* addr = (HeapWord*)obj;
6757 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6758 // Oop lies in _span and isn't yet grey or black
6759 _bitMap->mark(addr); // now grey
6760 if (addr < _finger) {
6761 // the bit map iteration has already either passed, or
6762 // sampled, this bit in the bit map; we'll need to
6763 // use the marking stack to scan this oop's oops.
6764 bool simulate_overflow = false;
6765 NOT_PRODUCT(
6766 if (CMSMarkStackOverflowALot &&
6767 _collector->simulate_overflow()) {
6768 // simulate a stack overflow
6769 simulate_overflow = true;
6770 }
6771 )
6772 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6773 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6774 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6775 handle_stack_overflow(addr);
6776 }
6777 }
6778 // anything including and to the right of _finger
6779 // will be scanned as we iterate over the remainder of the
6780 // bit map
6781 do_yield_check();
6782 }
6783 }
6784
6785 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6786 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6787
6788 void ParPushOrMarkClosure::do_oop(oop obj) {
6789 // Ignore mark word because we are running concurrent with mutators.
6790 assert(oopDesc::is_oop_or_null(obj, true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6791 HeapWord* addr = (HeapWord*)obj;
6792 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6793 // Oop lies in _span and isn't yet grey or black
6794 // We read the global_finger (volatile read) strictly after marking oop
6795 bool res = _bit_map->par_mark(addr); // now grey
6796 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6797 // Should we push this marked oop on our stack?
6798 // -- if someone else marked it, nothing to do
6799 // -- if target oop is above global finger nothing to do
6800 // -- if target oop is in chunk and above local finger
6801 // then nothing to do
6802 // -- else push on work queue
6803 if ( !res // someone else marked it, they will deal with it
6804 || (addr >= *gfa) // will be scanned in a later task
6805 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6806 return;
6807 }
6808 // the bit map iteration has already either passed, or
6809 // sampled, this bit in the bit map; we'll need to
6810 // use the marking stack to scan this oop's oops.
6811 bool simulate_overflow = false;
6812 NOT_PRODUCT(
6813 if (CMSMarkStackOverflowALot &&
6814 _collector->simulate_overflow()) {
6815 // simulate a stack overflow
6816 simulate_overflow = true;
6817 }
6818 )
6819 if (simulate_overflow ||
6820 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6821 // stack overflow
6822 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6823 // We cannot assert that the overflow stack is full because
6824 // it may have been emptied since.
6825 assert(simulate_overflow ||
6826 _work_queue->size() == _work_queue->max_elems(),
6827 "Else push should have succeeded");
6828 handle_stack_overflow(addr);
6829 }
6830 do_yield_check();
6831 }
6832 }
6833
6834 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6835 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6836
6837 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6838 MemRegion span,
6839 ReferenceProcessor* rp,
6840 CMSBitMap* bit_map,
6841 CMSBitMap* mod_union_table,
6842 CMSMarkStack* mark_stack,
6843 bool concurrent_precleaning):
6844 MetadataAwareOopClosure(rp),
6845 _collector(collector),
6846 _span(span),
6847 _bit_map(bit_map),
6848 _mod_union_table(mod_union_table),
6849 _mark_stack(mark_stack),
6850 _concurrent_precleaning(concurrent_precleaning)
6851 {
6852 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6853 }
6854
6855 // Grey object rescan during pre-cleaning and second checkpoint phases --
6856 // the non-parallel version (the parallel version appears further below.)
6857 void PushAndMarkClosure::do_oop(oop obj) {
6858 // Ignore mark word verification. If during concurrent precleaning,
6859 // the object monitor may be locked. If during the checkpoint
6860 // phases, the object may already have been reached by a different
6861 // path and may be at the end of the global overflow list (so
6862 // the mark word may be NULL).
6863 assert(oopDesc::is_oop_or_null(obj, true /* ignore mark word */),
6864 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6865 HeapWord* addr = (HeapWord*)obj;
6866 // Check if oop points into the CMS generation
6867 // and is not marked
6868 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6869 // a white object ...
6870 _bit_map->mark(addr); // ... now grey
6871 // push on the marking stack (grey set)
6872 bool simulate_overflow = false;
6873 NOT_PRODUCT(
6874 if (CMSMarkStackOverflowALot &&
6875 _collector->simulate_overflow()) {
6876 // simulate a stack overflow
6877 simulate_overflow = true;
6878 }
6879 )
6880 if (simulate_overflow || !_mark_stack->push(obj)) {
6881 if (_concurrent_precleaning) {
6882 // During precleaning we can just dirty the appropriate card(s)
6883 // in the mod union table, thus ensuring that the object remains
6884 // in the grey set and continue. In the case of object arrays
6885 // we need to dirty all of the cards that the object spans,
6886 // since the rescan of object arrays will be limited to the
6887 // dirty cards.
6888 // Note that no one can be interfering with us in this action
6889 // of dirtying the mod union table, so no locking or atomics
6890 // are required.
6891 if (obj->is_objArray()) {
6892 size_t sz = obj->size();
6893 HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
6894 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6895 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6896 _mod_union_table->mark_range(redirty_range);
6897 } else {
6898 _mod_union_table->mark(addr);
6899 }
6900 _collector->_ser_pmc_preclean_ovflw++;
6901 } else {
6902 // During the remark phase, we need to remember this oop
6903 // in the overflow list.
6904 _collector->push_on_overflow_list(obj);
6905 _collector->_ser_pmc_remark_ovflw++;
6906 }
6907 }
6908 }
6909 }
6910
6911 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6912 MemRegion span,
6913 ReferenceProcessor* rp,
6914 CMSBitMap* bit_map,
6915 OopTaskQueue* work_queue):
6916 MetadataAwareOopClosure(rp),
6917 _collector(collector),
6918 _span(span),
6919 _bit_map(bit_map),
6920 _work_queue(work_queue)
6921 {
6922 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6923 }
6924
6925 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6926 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6927
6928 // Grey object rescan during second checkpoint phase --
6929 // the parallel version.
6930 void ParPushAndMarkClosure::do_oop(oop obj) {
6931 // In the assert below, we ignore the mark word because
6932 // this oop may point to an already visited object that is
6933 // on the overflow stack (in which case the mark word has
6934 // been hijacked for chaining into the overflow stack --
6935 // if this is the last object in the overflow stack then
6936 // its mark word will be NULL). Because this object may
6937 // have been subsequently popped off the global overflow
6938 // stack, and the mark word possibly restored to the prototypical
6939 // value, by the time we get to examined this failing assert in
6940 // the debugger, is_oop_or_null(false) may subsequently start
6941 // to hold.
6942 assert(oopDesc::is_oop_or_null(obj, true),
6943 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6944 HeapWord* addr = (HeapWord*)obj;
6945 // Check if oop points into the CMS generation
6946 // and is not marked
6947 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6948 // a white object ...
6949 // If we manage to "claim" the object, by being the
6950 // first thread to mark it, then we push it on our
6951 // marking stack
6952 if (_bit_map->par_mark(addr)) { // ... now grey
6953 // push on work queue (grey set)
6954 bool simulate_overflow = false;
6955 NOT_PRODUCT(
6956 if (CMSMarkStackOverflowALot &&
6957 _collector->par_simulate_overflow()) {
6958 // simulate a stack overflow
6959 simulate_overflow = true;
6960 }
6961 )
6962 if (simulate_overflow || !_work_queue->push(obj)) {
6963 _collector->par_push_on_overflow_list(obj);
6964 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6965 }
6966 } // Else, some other thread got there first
6967 }
6968 }
6969
6970 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6971 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6972
6973 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6974 Mutex* bml = _collector->bitMapLock();
6975 assert_lock_strong(bml);
6976 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6977 "CMS thread should hold CMS token");
6978
6979 bml->unlock();
6980 ConcurrentMarkSweepThread::desynchronize(true);
6981
6982 _collector->stopTimer();
6983 _collector->incrementYields();
6984
6985 // See the comment in coordinator_yield()
6986 for (unsigned i = 0; i < CMSYieldSleepCount &&
6987 ConcurrentMarkSweepThread::should_yield() &&
6988 !CMSCollector::foregroundGCIsActive(); ++i) {
6989 os::sleep(Thread::current(), 1, false);
6990 }
6991
6992 ConcurrentMarkSweepThread::synchronize(true);
6993 bml->lock();
6994
6995 _collector->startTimer();
6996 }
6997
6998 bool CMSPrecleanRefsYieldClosure::should_return() {
6999 if (ConcurrentMarkSweepThread::should_yield()) {
7000 do_yield_work();
7001 }
7002 return _collector->foregroundGCIsActive();
7003 }
7004
7005 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7006 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7007 "mr should be aligned to start at a card boundary");
7008 // We'd like to assert:
7009 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7010 // "mr should be a range of cards");
7011 // However, that would be too strong in one case -- the last
7012 // partition ends at _unallocated_block which, in general, can be
7013 // an arbitrary boundary, not necessarily card aligned.
7014 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7015 _space->object_iterate_mem(mr, &_scan_cl);
7016 }
7017
7018 SweepClosure::SweepClosure(CMSCollector* collector,
7019 ConcurrentMarkSweepGeneration* g,
7020 CMSBitMap* bitMap, bool should_yield) :
7021 _collector(collector),
7022 _g(g),
7023 _sp(g->cmsSpace()),
7024 _limit(_sp->sweep_limit()),
7025 _freelistLock(_sp->freelistLock()),
7026 _bitMap(bitMap),
7027 _yield(should_yield),
7028 _inFreeRange(false), // No free range at beginning of sweep
7029 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7030 _lastFreeRangeCoalesced(false),
7031 _freeFinger(g->used_region().start())
7032 {
7033 NOT_PRODUCT(
7034 _numObjectsFreed = 0;
7035 _numWordsFreed = 0;
7036 _numObjectsLive = 0;
7037 _numWordsLive = 0;
7038 _numObjectsAlreadyFree = 0;
7039 _numWordsAlreadyFree = 0;
7040 _last_fc = NULL;
7041
7042 _sp->initializeIndexedFreeListArrayReturnedBytes();
7043 _sp->dictionary()->initialize_dict_returned_bytes();
7044 )
7045 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7046 "sweep _limit out of bounds");
7047 log_develop_trace(gc, sweep)("====================");
7048 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7049 }
7050
7051 void SweepClosure::print_on(outputStream* st) const {
7052 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7053 p2i(_sp->bottom()), p2i(_sp->end()));
7054 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7055 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7056 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7057 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7058 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7059 }
7060
7061 #ifndef PRODUCT
7062 // Assertion checking only: no useful work in product mode --
7063 // however, if any of the flags below become product flags,
7064 // you may need to review this code to see if it needs to be
7065 // enabled in product mode.
7066 SweepClosure::~SweepClosure() {
7067 assert_lock_strong(_freelistLock);
7068 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7069 "sweep _limit out of bounds");
7070 if (inFreeRange()) {
7071 Log(gc, sweep) log;
7072 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7073 ResourceMark rm;
7074 LogStream ls(log.error());
7075 print_on(&ls);
7076 ShouldNotReachHere();
7077 }
7078
7079 if (log_is_enabled(Debug, gc, sweep)) {
7080 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7081 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7082 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7083 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7084 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7085 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7086 }
7087
7088 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7089 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7090 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7091 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7092 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7093 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7094 }
7095 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7096 log_develop_trace(gc, sweep)("================");
7097 }
7098 #endif // PRODUCT
7099
7100 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7101 bool freeRangeInFreeLists) {
7102 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7103 p2i(freeFinger), freeRangeInFreeLists);
7104 assert(!inFreeRange(), "Trampling existing free range");
7105 set_inFreeRange(true);
7106 set_lastFreeRangeCoalesced(false);
7107
7108 set_freeFinger(freeFinger);
7109 set_freeRangeInFreeLists(freeRangeInFreeLists);
7110 if (CMSTestInFreeList) {
7111 if (freeRangeInFreeLists) {
7112 FreeChunk* fc = (FreeChunk*) freeFinger;
7113 assert(fc->is_free(), "A chunk on the free list should be free.");
7114 assert(fc->size() > 0, "Free range should have a size");
7115 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7116 }
7117 }
7118 }
7119
7120 // Note that the sweeper runs concurrently with mutators. Thus,
7121 // it is possible for direct allocation in this generation to happen
7122 // in the middle of the sweep. Note that the sweeper also coalesces
7123 // contiguous free blocks. Thus, unless the sweeper and the allocator
7124 // synchronize appropriately freshly allocated blocks may get swept up.
7125 // This is accomplished by the sweeper locking the free lists while
7126 // it is sweeping. Thus blocks that are determined to be free are
7127 // indeed free. There is however one additional complication:
7128 // blocks that have been allocated since the final checkpoint and
7129 // mark, will not have been marked and so would be treated as
7130 // unreachable and swept up. To prevent this, the allocator marks
7131 // the bit map when allocating during the sweep phase. This leads,
7132 // however, to a further complication -- objects may have been allocated
7133 // but not yet initialized -- in the sense that the header isn't yet
7134 // installed. The sweeper can not then determine the size of the block
7135 // in order to skip over it. To deal with this case, we use a technique
7136 // (due to Printezis) to encode such uninitialized block sizes in the
7137 // bit map. Since the bit map uses a bit per every HeapWord, but the
7138 // CMS generation has a minimum object size of 3 HeapWords, it follows
7139 // that "normal marks" won't be adjacent in the bit map (there will
7140 // always be at least two 0 bits between successive 1 bits). We make use
7141 // of these "unused" bits to represent uninitialized blocks -- the bit
7142 // corresponding to the start of the uninitialized object and the next
7143 // bit are both set. Finally, a 1 bit marks the end of the object that
7144 // started with the two consecutive 1 bits to indicate its potentially
7145 // uninitialized state.
7146
7147 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7148 FreeChunk* fc = (FreeChunk*)addr;
7149 size_t res;
7150
7151 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7152 // than "addr == _limit" because although _limit was a block boundary when
7153 // we started the sweep, it may no longer be one because heap expansion
7154 // may have caused us to coalesce the block ending at the address _limit
7155 // with a newly expanded chunk (this happens when _limit was set to the
7156 // previous _end of the space), so we may have stepped past _limit:
7157 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7158 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7159 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7160 "sweep _limit out of bounds");
7161 assert(addr < _sp->end(), "addr out of bounds");
7162 // Flush any free range we might be holding as a single
7163 // coalesced chunk to the appropriate free list.
7164 if (inFreeRange()) {
7165 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7166 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7167 flush_cur_free_chunk(freeFinger(),
7168 pointer_delta(addr, freeFinger()));
7169 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7170 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7171 lastFreeRangeCoalesced() ? 1 : 0);
7172 }
7173
7174 // help the iterator loop finish
7175 return pointer_delta(_sp->end(), addr);
7176 }
7177
7178 assert(addr < _limit, "sweep invariant");
7179 // check if we should yield
7180 do_yield_check(addr);
7181 if (fc->is_free()) {
7182 // Chunk that is already free
7183 res = fc->size();
7184 do_already_free_chunk(fc);
7185 debug_only(_sp->verifyFreeLists());
7186 // If we flush the chunk at hand in lookahead_and_flush()
7187 // and it's coalesced with a preceding chunk, then the
7188 // process of "mangling" the payload of the coalesced block
7189 // will cause erasure of the size information from the
7190 // (erstwhile) header of all the coalesced blocks but the
7191 // first, so the first disjunct in the assert will not hold
7192 // in that specific case (in which case the second disjunct
7193 // will hold).
7194 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7195 "Otherwise the size info doesn't change at this step");
7196 NOT_PRODUCT(
7197 _numObjectsAlreadyFree++;
7198 _numWordsAlreadyFree += res;
7199 )
7200 NOT_PRODUCT(_last_fc = fc;)
7201 } else if (!_bitMap->isMarked(addr)) {
7202 // Chunk is fresh garbage
7203 res = do_garbage_chunk(fc);
7204 debug_only(_sp->verifyFreeLists());
7205 NOT_PRODUCT(
7206 _numObjectsFreed++;
7207 _numWordsFreed += res;
7208 )
7209 } else {
7210 // Chunk that is alive.
7211 res = do_live_chunk(fc);
7212 debug_only(_sp->verifyFreeLists());
7213 NOT_PRODUCT(
7214 _numObjectsLive++;
7215 _numWordsLive += res;
7216 )
7217 }
7218 return res;
7219 }
7220
7221 // For the smart allocation, record following
7222 // split deaths - a free chunk is removed from its free list because
7223 // it is being split into two or more chunks.
7224 // split birth - a free chunk is being added to its free list because
7225 // a larger free chunk has been split and resulted in this free chunk.
7226 // coal death - a free chunk is being removed from its free list because
7227 // it is being coalesced into a large free chunk.
7228 // coal birth - a free chunk is being added to its free list because
7229 // it was created when two or more free chunks where coalesced into
7230 // this free chunk.
7231 //
7232 // These statistics are used to determine the desired number of free
7233 // chunks of a given size. The desired number is chosen to be relative
7234 // to the end of a CMS sweep. The desired number at the end of a sweep
7235 // is the
7236 // count-at-end-of-previous-sweep (an amount that was enough)
7237 // - count-at-beginning-of-current-sweep (the excess)
7238 // + split-births (gains in this size during interval)
7239 // - split-deaths (demands on this size during interval)
7240 // where the interval is from the end of one sweep to the end of the
7241 // next.
7242 //
7243 // When sweeping the sweeper maintains an accumulated chunk which is
7244 // the chunk that is made up of chunks that have been coalesced. That
7245 // will be termed the left-hand chunk. A new chunk of garbage that
7246 // is being considered for coalescing will be referred to as the
7247 // right-hand chunk.
7248 //
7249 // When making a decision on whether to coalesce a right-hand chunk with
7250 // the current left-hand chunk, the current count vs. the desired count
7251 // of the left-hand chunk is considered. Also if the right-hand chunk
7252 // is near the large chunk at the end of the heap (see
7253 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7254 // left-hand chunk is coalesced.
7255 //
7256 // When making a decision about whether to split a chunk, the desired count
7257 // vs. the current count of the candidate to be split is also considered.
7258 // If the candidate is underpopulated (currently fewer chunks than desired)
7259 // a chunk of an overpopulated (currently more chunks than desired) size may
7260 // be chosen. The "hint" associated with a free list, if non-null, points
7261 // to a free list which may be overpopulated.
7262 //
7263
7264 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7265 const size_t size = fc->size();
7266 // Chunks that cannot be coalesced are not in the
7267 // free lists.
7268 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7269 assert(_sp->verify_chunk_in_free_list(fc),
7270 "free chunk should be in free lists");
7271 }
7272 // a chunk that is already free, should not have been
7273 // marked in the bit map
7274 HeapWord* const addr = (HeapWord*) fc;
7275 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7276 // Verify that the bit map has no bits marked between
7277 // addr and purported end of this block.
7278 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7279
7280 // Some chunks cannot be coalesced under any circumstances.
7281 // See the definition of cantCoalesce().
7282 if (!fc->cantCoalesce()) {
7283 // This chunk can potentially be coalesced.
7284 // All the work is done in
7285 do_post_free_or_garbage_chunk(fc, size);
7286 // Note that if the chunk is not coalescable (the else arm
7287 // below), we unconditionally flush, without needing to do
7288 // a "lookahead," as we do below.
7289 if (inFreeRange()) lookahead_and_flush(fc, size);
7290 } else {
7291 // Code path common to both original and adaptive free lists.
7292
7293 // cant coalesce with previous block; this should be treated
7294 // as the end of a free run if any
7295 if (inFreeRange()) {
7296 // we kicked some butt; time to pick up the garbage
7297 assert(freeFinger() < addr, "freeFinger points too high");
7298 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7299 }
7300 // else, nothing to do, just continue
7301 }
7302 }
7303
7304 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7305 // This is a chunk of garbage. It is not in any free list.
7306 // Add it to a free list or let it possibly be coalesced into
7307 // a larger chunk.
7308 HeapWord* const addr = (HeapWord*) fc;
7309 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7310
7311 // Verify that the bit map has no bits marked between
7312 // addr and purported end of just dead object.
7313 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7314 do_post_free_or_garbage_chunk(fc, size);
7315
7316 assert(_limit >= addr + size,
7317 "A freshly garbage chunk can't possibly straddle over _limit");
7318 if (inFreeRange()) lookahead_and_flush(fc, size);
7319 return size;
7320 }
7321
7322 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7323 HeapWord* addr = (HeapWord*) fc;
7324 // The sweeper has just found a live object. Return any accumulated
7325 // left hand chunk to the free lists.
7326 if (inFreeRange()) {
7327 assert(freeFinger() < addr, "freeFinger points too high");
7328 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7329 }
7330
7331 // This object is live: we'd normally expect this to be
7332 // an oop, and like to assert the following:
7333 // assert(oopDesc::is_oop(oop(addr)), "live block should be an oop");
7334 // However, as we commented above, this may be an object whose
7335 // header hasn't yet been initialized.
7336 size_t size;
7337 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7338 if (_bitMap->isMarked(addr + 1)) {
7339 // Determine the size from the bit map, rather than trying to
7340 // compute it from the object header.
7341 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7342 size = pointer_delta(nextOneAddr + 1, addr);
7343 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7344 "alignment problem");
7345
7346 #ifdef ASSERT
7347 if (oop(addr)->klass_or_null_acquire() != NULL) {
7348 // Ignore mark word because we are running concurrent with mutators
7349 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7350 assert(size ==
7351 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7352 "P-mark and computed size do not agree");
7353 }
7354 #endif
7355
7356 } else {
7357 // This should be an initialized object that's alive.
7358 assert(oop(addr)->klass_or_null_acquire() != NULL,
7359 "Should be an initialized object");
7360 // Ignore mark word because we are running concurrent with mutators
7361 assert(oopDesc::is_oop(oop(addr), true), "live block should be an oop");
7362 // Verify that the bit map has no bits marked between
7363 // addr and purported end of this block.
7364 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7365 assert(size >= 3, "Necessary for Printezis marks to work");
7366 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7367 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7368 }
7369 return size;
7370 }
7371
7372 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7373 size_t chunkSize) {
7374 // do_post_free_or_garbage_chunk() should only be called in the case
7375 // of the adaptive free list allocator.
7376 const bool fcInFreeLists = fc->is_free();
7377 assert((HeapWord*)fc <= _limit, "sweep invariant");
7378 if (CMSTestInFreeList && fcInFreeLists) {
7379 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7380 }
7381
7382 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7383
7384 HeapWord* const fc_addr = (HeapWord*) fc;
7385
7386 bool coalesce = false;
7387 const size_t left = pointer_delta(fc_addr, freeFinger());
7388 const size_t right = chunkSize;
7389 switch (FLSCoalescePolicy) {
7390 // numeric value forms a coalition aggressiveness metric
7391 case 0: { // never coalesce
7392 coalesce = false;
7393 break;
7394 }
7395 case 1: { // coalesce if left & right chunks on overpopulated lists
7396 coalesce = _sp->coalOverPopulated(left) &&
7397 _sp->coalOverPopulated(right);
7398 break;
7399 }
7400 case 2: { // coalesce if left chunk on overpopulated list (default)
7401 coalesce = _sp->coalOverPopulated(left);
7402 break;
7403 }
7404 case 3: { // coalesce if left OR right chunk on overpopulated list
7405 coalesce = _sp->coalOverPopulated(left) ||
7406 _sp->coalOverPopulated(right);
7407 break;
7408 }
7409 case 4: { // always coalesce
7410 coalesce = true;
7411 break;
7412 }
7413 default:
7414 ShouldNotReachHere();
7415 }
7416
7417 // Should the current free range be coalesced?
7418 // If the chunk is in a free range and either we decided to coalesce above
7419 // or the chunk is near the large block at the end of the heap
7420 // (isNearLargestChunk() returns true), then coalesce this chunk.
7421 const bool doCoalesce = inFreeRange()
7422 && (coalesce || _g->isNearLargestChunk(fc_addr));
7423 if (doCoalesce) {
7424 // Coalesce the current free range on the left with the new
7425 // chunk on the right. If either is on a free list,
7426 // it must be removed from the list and stashed in the closure.
7427 if (freeRangeInFreeLists()) {
7428 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7429 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7430 "Size of free range is inconsistent with chunk size.");
7431 if (CMSTestInFreeList) {
7432 assert(_sp->verify_chunk_in_free_list(ffc),
7433 "Chunk is not in free lists");
7434 }
7435 _sp->coalDeath(ffc->size());
7436 _sp->removeFreeChunkFromFreeLists(ffc);
7437 set_freeRangeInFreeLists(false);
7438 }
7439 if (fcInFreeLists) {
7440 _sp->coalDeath(chunkSize);
7441 assert(fc->size() == chunkSize,
7442 "The chunk has the wrong size or is not in the free lists");
7443 _sp->removeFreeChunkFromFreeLists(fc);
7444 }
7445 set_lastFreeRangeCoalesced(true);
7446 print_free_block_coalesced(fc);
7447 } else { // not in a free range and/or should not coalesce
7448 // Return the current free range and start a new one.
7449 if (inFreeRange()) {
7450 // In a free range but cannot coalesce with the right hand chunk.
7451 // Put the current free range into the free lists.
7452 flush_cur_free_chunk(freeFinger(),
7453 pointer_delta(fc_addr, freeFinger()));
7454 }
7455 // Set up for new free range. Pass along whether the right hand
7456 // chunk is in the free lists.
7457 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7458 }
7459 }
7460
7461 // Lookahead flush:
7462 // If we are tracking a free range, and this is the last chunk that
7463 // we'll look at because its end crosses past _limit, we'll preemptively
7464 // flush it along with any free range we may be holding on to. Note that
7465 // this can be the case only for an already free or freshly garbage
7466 // chunk. If this block is an object, it can never straddle
7467 // over _limit. The "straddling" occurs when _limit is set at
7468 // the previous end of the space when this cycle started, and
7469 // a subsequent heap expansion caused the previously co-terminal
7470 // free block to be coalesced with the newly expanded portion,
7471 // thus rendering _limit a non-block-boundary making it dangerous
7472 // for the sweeper to step over and examine.
7473 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7474 assert(inFreeRange(), "Should only be called if currently in a free range.");
7475 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7476 assert(_sp->used_region().contains(eob - 1),
7477 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7478 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7479 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7480 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7481 if (eob >= _limit) {
7482 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7483 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7484 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7485 "[" PTR_FORMAT "," PTR_FORMAT ")",
7486 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7487 // Return the storage we are tracking back into the free lists.
7488 log_develop_trace(gc, sweep)("Flushing ... ");
7489 assert(freeFinger() < eob, "Error");
7490 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7491 }
7492 }
7493
7494 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7495 assert(inFreeRange(), "Should only be called if currently in a free range.");
7496 assert(size > 0,
7497 "A zero sized chunk cannot be added to the free lists.");
7498 if (!freeRangeInFreeLists()) {
7499 if (CMSTestInFreeList) {
7500 FreeChunk* fc = (FreeChunk*) chunk;
7501 fc->set_size(size);
7502 assert(!_sp->verify_chunk_in_free_list(fc),
7503 "chunk should not be in free lists yet");
7504 }
7505 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7506 // A new free range is going to be starting. The current
7507 // free range has not been added to the free lists yet or
7508 // was removed so add it back.
7509 // If the current free range was coalesced, then the death
7510 // of the free range was recorded. Record a birth now.
7511 if (lastFreeRangeCoalesced()) {
7512 _sp->coalBirth(size);
7513 }
7514 _sp->addChunkAndRepairOffsetTable(chunk, size,
7515 lastFreeRangeCoalesced());
7516 } else {
7517 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7518 }
7519 set_inFreeRange(false);
7520 set_freeRangeInFreeLists(false);
7521 }
7522
7523 // We take a break if we've been at this for a while,
7524 // so as to avoid monopolizing the locks involved.
7525 void SweepClosure::do_yield_work(HeapWord* addr) {
7526 // Return current free chunk being used for coalescing (if any)
7527 // to the appropriate freelist. After yielding, the next
7528 // free block encountered will start a coalescing range of
7529 // free blocks. If the next free block is adjacent to the
7530 // chunk just flushed, they will need to wait for the next
7531 // sweep to be coalesced.
7532 if (inFreeRange()) {
7533 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7534 }
7535
7536 // First give up the locks, then yield, then re-lock.
7537 // We should probably use a constructor/destructor idiom to
7538 // do this unlock/lock or modify the MutexUnlocker class to
7539 // serve our purpose. XXX
7540 assert_lock_strong(_bitMap->lock());
7541 assert_lock_strong(_freelistLock);
7542 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7543 "CMS thread should hold CMS token");
7544 _bitMap->lock()->unlock();
7545 _freelistLock->unlock();
7546 ConcurrentMarkSweepThread::desynchronize(true);
7547 _collector->stopTimer();
7548 _collector->incrementYields();
7549
7550 // See the comment in coordinator_yield()
7551 for (unsigned i = 0; i < CMSYieldSleepCount &&
7552 ConcurrentMarkSweepThread::should_yield() &&
7553 !CMSCollector::foregroundGCIsActive(); ++i) {
7554 os::sleep(Thread::current(), 1, false);
7555 }
7556
7557 ConcurrentMarkSweepThread::synchronize(true);
7558 _freelistLock->lock();
7559 _bitMap->lock()->lock_without_safepoint_check();
7560 _collector->startTimer();
7561 }
7562
7563 #ifndef PRODUCT
7564 // This is actually very useful in a product build if it can
7565 // be called from the debugger. Compile it into the product
7566 // as needed.
7567 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7568 return debug_cms_space->verify_chunk_in_free_list(fc);
7569 }
7570 #endif
7571
7572 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7573 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7574 p2i(fc), fc->size());
7575 }
7576
7577 // CMSIsAliveClosure
7578 bool CMSIsAliveClosure::do_object_b(oop obj) {
7579 HeapWord* addr = (HeapWord*)obj;
7580 return addr != NULL &&
7581 (!_span.contains(addr) || _bit_map->isMarked(addr));
7582 }
7583
7584
7585 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7586 MemRegion span,
7587 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7588 bool cpc):
7589 _collector(collector),
7590 _span(span),
7591 _bit_map(bit_map),
7592 _mark_stack(mark_stack),
7593 _concurrent_precleaning(cpc) {
7594 assert(!_span.is_empty(), "Empty span could spell trouble");
7595 }
7596
7597
7598 // CMSKeepAliveClosure: the serial version
7599 void CMSKeepAliveClosure::do_oop(oop obj) {
7600 HeapWord* addr = (HeapWord*)obj;
7601 if (_span.contains(addr) &&
7602 !_bit_map->isMarked(addr)) {
7603 _bit_map->mark(addr);
7604 bool simulate_overflow = false;
7605 NOT_PRODUCT(
7606 if (CMSMarkStackOverflowALot &&
7607 _collector->simulate_overflow()) {
7608 // simulate a stack overflow
7609 simulate_overflow = true;
7610 }
7611 )
7612 if (simulate_overflow || !_mark_stack->push(obj)) {
7613 if (_concurrent_precleaning) {
7614 // We dirty the overflown object and let the remark
7615 // phase deal with it.
7616 assert(_collector->overflow_list_is_empty(), "Error");
7617 // In the case of object arrays, we need to dirty all of
7618 // the cards that the object spans. No locking or atomics
7619 // are needed since no one else can be mutating the mod union
7620 // table.
7621 if (obj->is_objArray()) {
7622 size_t sz = obj->size();
7623 HeapWord* end_card_addr = align_up(addr + sz, CardTableModRefBS::card_size);
7624 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7625 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7626 _collector->_modUnionTable.mark_range(redirty_range);
7627 } else {
7628 _collector->_modUnionTable.mark(addr);
7629 }
7630 _collector->_ser_kac_preclean_ovflw++;
7631 } else {
7632 _collector->push_on_overflow_list(obj);
7633 _collector->_ser_kac_ovflw++;
7634 }
7635 }
7636 }
7637 }
7638
7639 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7640 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7641
7642 // CMSParKeepAliveClosure: a parallel version of the above.
7643 // The work queues are private to each closure (thread),
7644 // but (may be) available for stealing by other threads.
7645 void CMSParKeepAliveClosure::do_oop(oop obj) {
7646 HeapWord* addr = (HeapWord*)obj;
7647 if (_span.contains(addr) &&
7648 !_bit_map->isMarked(addr)) {
7649 // In general, during recursive tracing, several threads
7650 // may be concurrently getting here; the first one to
7651 // "tag" it, claims it.
7652 if (_bit_map->par_mark(addr)) {
7653 bool res = _work_queue->push(obj);
7654 assert(res, "Low water mark should be much less than capacity");
7655 // Do a recursive trim in the hope that this will keep
7656 // stack usage lower, but leave some oops for potential stealers
7657 trim_queue(_low_water_mark);
7658 } // Else, another thread got there first
7659 }
7660 }
7661
7662 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7663 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7664
7665 void CMSParKeepAliveClosure::trim_queue(uint max) {
7666 while (_work_queue->size() > max) {
7667 oop new_oop;
7668 if (_work_queue->pop_local(new_oop)) {
7669 assert(new_oop != NULL && oopDesc::is_oop(new_oop), "Expected an oop");
7670 assert(_bit_map->isMarked((HeapWord*)new_oop),
7671 "no white objects on this stack!");
7672 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7673 // iterate over the oops in this oop, marking and pushing
7674 // the ones in CMS heap (i.e. in _span).
7675 new_oop->oop_iterate(&_mark_and_push);
7676 }
7677 }
7678 }
7679
7680 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7681 CMSCollector* collector,
7682 MemRegion span, CMSBitMap* bit_map,
7683 OopTaskQueue* work_queue):
7684 _collector(collector),
7685 _span(span),
7686 _bit_map(bit_map),
7687 _work_queue(work_queue) { }
7688
7689 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7690 HeapWord* addr = (HeapWord*)obj;
7691 if (_span.contains(addr) &&
7692 !_bit_map->isMarked(addr)) {
7693 if (_bit_map->par_mark(addr)) {
7694 bool simulate_overflow = false;
7695 NOT_PRODUCT(
7696 if (CMSMarkStackOverflowALot &&
7697 _collector->par_simulate_overflow()) {
7698 // simulate a stack overflow
7699 simulate_overflow = true;
7700 }
7701 )
7702 if (simulate_overflow || !_work_queue->push(obj)) {
7703 _collector->par_push_on_overflow_list(obj);
7704 _collector->_par_kac_ovflw++;
7705 }
7706 } // Else another thread got there already
7707 }
7708 }
7709
7710 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7711 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7712
7713 //////////////////////////////////////////////////////////////////
7714 // CMSExpansionCause /////////////////////////////
7715 //////////////////////////////////////////////////////////////////
7716 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7717 switch (cause) {
7718 case _no_expansion:
7719 return "No expansion";
7720 case _satisfy_free_ratio:
7721 return "Free ratio";
7722 case _satisfy_promotion:
7723 return "Satisfy promotion";
7724 case _satisfy_allocation:
7725 return "allocation";
7726 case _allocate_par_lab:
7727 return "Par LAB";
7728 case _allocate_par_spooling_space:
7729 return "Par Spooling Space";
7730 case _adaptive_size_policy:
7731 return "Ergonomics";
7732 default:
7733 return "unknown";
7734 }
7735 }
7736
7737 void CMSDrainMarkingStackClosure::do_void() {
7738 // the max number to take from overflow list at a time
7739 const size_t num = _mark_stack->capacity()/4;
7740 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7741 "Overflow list should be NULL during concurrent phases");
7742 while (!_mark_stack->isEmpty() ||
7743 // if stack is empty, check the overflow list
7744 _collector->take_from_overflow_list(num, _mark_stack)) {
7745 oop obj = _mark_stack->pop();
7746 HeapWord* addr = (HeapWord*)obj;
7747 assert(_span.contains(addr), "Should be within span");
7748 assert(_bit_map->isMarked(addr), "Should be marked");
7749 assert(oopDesc::is_oop(obj), "Should be an oop");
7750 obj->oop_iterate(_keep_alive);
7751 }
7752 }
7753
7754 void CMSParDrainMarkingStackClosure::do_void() {
7755 // drain queue
7756 trim_queue(0);
7757 }
7758
7759 // Trim our work_queue so its length is below max at return
7760 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7761 while (_work_queue->size() > max) {
7762 oop new_oop;
7763 if (_work_queue->pop_local(new_oop)) {
7764 assert(oopDesc::is_oop(new_oop), "Expected an oop");
7765 assert(_bit_map->isMarked((HeapWord*)new_oop),
7766 "no white objects on this stack!");
7767 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7768 // iterate over the oops in this oop, marking and pushing
7769 // the ones in CMS heap (i.e. in _span).
7770 new_oop->oop_iterate(&_mark_and_push);
7771 }
7772 }
7773 }
7774
7775 ////////////////////////////////////////////////////////////////////
7776 // Support for Marking Stack Overflow list handling and related code
7777 ////////////////////////////////////////////////////////////////////
7778 // Much of the following code is similar in shape and spirit to the
7779 // code used in ParNewGC. We should try and share that code
7780 // as much as possible in the future.
7781
7782 #ifndef PRODUCT
7783 // Debugging support for CMSStackOverflowALot
7784
7785 // It's OK to call this multi-threaded; the worst thing
7786 // that can happen is that we'll get a bunch of closely
7787 // spaced simulated overflows, but that's OK, in fact
7788 // probably good as it would exercise the overflow code
7789 // under contention.
7790 bool CMSCollector::simulate_overflow() {
7791 if (_overflow_counter-- <= 0) { // just being defensive
7792 _overflow_counter = CMSMarkStackOverflowInterval;
7793 return true;
7794 } else {
7795 return false;
7796 }
7797 }
7798
7799 bool CMSCollector::par_simulate_overflow() {
7800 return simulate_overflow();
7801 }
7802 #endif
7803
7804 // Single-threaded
7805 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7806 assert(stack->isEmpty(), "Expected precondition");
7807 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7808 size_t i = num;
7809 oop cur = _overflow_list;
7810 const markOop proto = markOopDesc::prototype();
7811 NOT_PRODUCT(ssize_t n = 0;)
7812 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7813 next = oop(cur->mark());
7814 cur->set_mark(proto); // until proven otherwise
7815 assert(oopDesc::is_oop(cur), "Should be an oop");
7816 bool res = stack->push(cur);
7817 assert(res, "Bit off more than can chew?");
7818 NOT_PRODUCT(n++;)
7819 }
7820 _overflow_list = cur;
7821 #ifndef PRODUCT
7822 assert(_num_par_pushes >= n, "Too many pops?");
7823 _num_par_pushes -=n;
7824 #endif
7825 return !stack->isEmpty();
7826 }
7827
7828 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7829 // (MT-safe) Get a prefix of at most "num" from the list.
7830 // The overflow list is chained through the mark word of
7831 // each object in the list. We fetch the entire list,
7832 // break off a prefix of the right size and return the
7833 // remainder. If other threads try to take objects from
7834 // the overflow list at that time, they will wait for
7835 // some time to see if data becomes available. If (and
7836 // only if) another thread places one or more object(s)
7837 // on the global list before we have returned the suffix
7838 // to the global list, we will walk down our local list
7839 // to find its end and append the global list to
7840 // our suffix before returning it. This suffix walk can
7841 // prove to be expensive (quadratic in the amount of traffic)
7842 // when there are many objects in the overflow list and
7843 // there is much producer-consumer contention on the list.
7844 // *NOTE*: The overflow list manipulation code here and
7845 // in ParNewGeneration:: are very similar in shape,
7846 // except that in the ParNew case we use the old (from/eden)
7847 // copy of the object to thread the list via its klass word.
7848 // Because of the common code, if you make any changes in
7849 // the code below, please check the ParNew version to see if
7850 // similar changes might be needed.
7851 // CR 6797058 has been filed to consolidate the common code.
7852 bool CMSCollector::par_take_from_overflow_list(size_t num,
7853 OopTaskQueue* work_q,
7854 int no_of_gc_threads) {
7855 assert(work_q->size() == 0, "First empty local work queue");
7856 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7857 if (_overflow_list == NULL) {
7858 return false;
7859 }
7860 // Grab the entire list; we'll put back a suffix
7861 oop prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7862 Thread* tid = Thread::current();
7863 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7864 // set to ParallelGCThreads.
7865 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7866 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7867 // If the list is busy, we spin for a short while,
7868 // sleeping between attempts to get the list.
7869 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7870 os::sleep(tid, sleep_time_millis, false);
7871 if (_overflow_list == NULL) {
7872 // Nothing left to take
7873 return false;
7874 } else if (_overflow_list != BUSY) {
7875 // Try and grab the prefix
7876 prefix = cast_to_oop(Atomic::xchg((oopDesc*)BUSY, &_overflow_list));
7877 }
7878 }
7879 // If the list was found to be empty, or we spun long
7880 // enough, we give up and return empty-handed. If we leave
7881 // the list in the BUSY state below, it must be the case that
7882 // some other thread holds the overflow list and will set it
7883 // to a non-BUSY state in the future.
7884 if (prefix == NULL || prefix == BUSY) {
7885 // Nothing to take or waited long enough
7886 if (prefix == NULL) {
7887 // Write back the NULL in case we overwrote it with BUSY above
7888 // and it is still the same value.
7889 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7890 }
7891 return false;
7892 }
7893 assert(prefix != NULL && prefix != BUSY, "Error");
7894 size_t i = num;
7895 oop cur = prefix;
7896 // Walk down the first "num" objects, unless we reach the end.
7897 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7898 if (cur->mark() == NULL) {
7899 // We have "num" or fewer elements in the list, so there
7900 // is nothing to return to the global list.
7901 // Write back the NULL in lieu of the BUSY we wrote
7902 // above, if it is still the same value.
7903 if (_overflow_list == BUSY) {
7904 Atomic::cmpxchg((oopDesc*)NULL, &_overflow_list, (oopDesc*)BUSY);
7905 }
7906 } else {
7907 // Chop off the suffix and return it to the global list.
7908 assert(cur->mark() != BUSY, "Error");
7909 oop suffix_head = cur->mark(); // suffix will be put back on global list
7910 cur->set_mark(NULL); // break off suffix
7911 // It's possible that the list is still in the empty(busy) state
7912 // we left it in a short while ago; in that case we may be
7913 // able to place back the suffix without incurring the cost
7914 // of a walk down the list.
7915 oop observed_overflow_list = _overflow_list;
7916 oop cur_overflow_list = observed_overflow_list;
7917 bool attached = false;
7918 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7919 observed_overflow_list =
7920 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7921 if (cur_overflow_list == observed_overflow_list) {
7922 attached = true;
7923 break;
7924 } else cur_overflow_list = observed_overflow_list;
7925 }
7926 if (!attached) {
7927 // Too bad, someone else sneaked in (at least) an element; we'll need
7928 // to do a splice. Find tail of suffix so we can prepend suffix to global
7929 // list.
7930 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7931 oop suffix_tail = cur;
7932 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7933 "Tautology");
7934 observed_overflow_list = _overflow_list;
7935 do {
7936 cur_overflow_list = observed_overflow_list;
7937 if (cur_overflow_list != BUSY) {
7938 // Do the splice ...
7939 suffix_tail->set_mark(markOop(cur_overflow_list));
7940 } else { // cur_overflow_list == BUSY
7941 suffix_tail->set_mark(NULL);
7942 }
7943 // ... and try to place spliced list back on overflow_list ...
7944 observed_overflow_list =
7945 Atomic::cmpxchg((oopDesc*)suffix_head, &_overflow_list, (oopDesc*)cur_overflow_list);
7946 } while (cur_overflow_list != observed_overflow_list);
7947 // ... until we have succeeded in doing so.
7948 }
7949 }
7950
7951 // Push the prefix elements on work_q
7952 assert(prefix != NULL, "control point invariant");
7953 const markOop proto = markOopDesc::prototype();
7954 oop next;
7955 NOT_PRODUCT(ssize_t n = 0;)
7956 for (cur = prefix; cur != NULL; cur = next) {
7957 next = oop(cur->mark());
7958 cur->set_mark(proto); // until proven otherwise
7959 assert(oopDesc::is_oop(cur), "Should be an oop");
7960 bool res = work_q->push(cur);
7961 assert(res, "Bit off more than we can chew?");
7962 NOT_PRODUCT(n++;)
7963 }
7964 #ifndef PRODUCT
7965 assert(_num_par_pushes >= n, "Too many pops?");
7966 Atomic::sub(n, &_num_par_pushes);
7967 #endif
7968 return true;
7969 }
7970
7971 // Single-threaded
7972 void CMSCollector::push_on_overflow_list(oop p) {
7973 NOT_PRODUCT(_num_par_pushes++;)
7974 assert(oopDesc::is_oop(p), "Not an oop");
7975 preserve_mark_if_necessary(p);
7976 p->set_mark((markOop)_overflow_list);
7977 _overflow_list = p;
7978 }
7979
7980 // Multi-threaded; use CAS to prepend to overflow list
7981 void CMSCollector::par_push_on_overflow_list(oop p) {
7982 NOT_PRODUCT(Atomic::inc(&_num_par_pushes);)
7983 assert(oopDesc::is_oop(p), "Not an oop");
7984 par_preserve_mark_if_necessary(p);
7985 oop observed_overflow_list = _overflow_list;
7986 oop cur_overflow_list;
7987 do {
7988 cur_overflow_list = observed_overflow_list;
7989 if (cur_overflow_list != BUSY) {
7990 p->set_mark(markOop(cur_overflow_list));
7991 } else {
7992 p->set_mark(NULL);
7993 }
7994 observed_overflow_list =
7995 Atomic::cmpxchg((oopDesc*)p, &_overflow_list, (oopDesc*)cur_overflow_list);
7996 } while (cur_overflow_list != observed_overflow_list);
7997 }
7998 #undef BUSY
7999
8000 // Single threaded
8001 // General Note on GrowableArray: pushes may silently fail
8002 // because we are (temporarily) out of C-heap for expanding
8003 // the stack. The problem is quite ubiquitous and affects
8004 // a lot of code in the JVM. The prudent thing for GrowableArray
8005 // to do (for now) is to exit with an error. However, that may
8006 // be too draconian in some cases because the caller may be
8007 // able to recover without much harm. For such cases, we
8008 // should probably introduce a "soft_push" method which returns
8009 // an indication of success or failure with the assumption that
8010 // the caller may be able to recover from a failure; code in
8011 // the VM can then be changed, incrementally, to deal with such
8012 // failures where possible, thus, incrementally hardening the VM
8013 // in such low resource situations.
8014 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8015 _preserved_oop_stack.push(p);
8016 _preserved_mark_stack.push(m);
8017 assert(m == p->mark(), "Mark word changed");
8018 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8019 "bijection");
8020 }
8021
8022 // Single threaded
8023 void CMSCollector::preserve_mark_if_necessary(oop p) {
8024 markOop m = p->mark();
8025 if (m->must_be_preserved(p)) {
8026 preserve_mark_work(p, m);
8027 }
8028 }
8029
8030 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8031 markOop m = p->mark();
8032 if (m->must_be_preserved(p)) {
8033 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8034 // Even though we read the mark word without holding
8035 // the lock, we are assured that it will not change
8036 // because we "own" this oop, so no other thread can
8037 // be trying to push it on the overflow list; see
8038 // the assertion in preserve_mark_work() that checks
8039 // that m == p->mark().
8040 preserve_mark_work(p, m);
8041 }
8042 }
8043
8044 // We should be able to do this multi-threaded,
8045 // a chunk of stack being a task (this is
8046 // correct because each oop only ever appears
8047 // once in the overflow list. However, it's
8048 // not very easy to completely overlap this with
8049 // other operations, so will generally not be done
8050 // until all work's been completed. Because we
8051 // expect the preserved oop stack (set) to be small,
8052 // it's probably fine to do this single-threaded.
8053 // We can explore cleverer concurrent/overlapped/parallel
8054 // processing of preserved marks if we feel the
8055 // need for this in the future. Stack overflow should
8056 // be so rare in practice and, when it happens, its
8057 // effect on performance so great that this will
8058 // likely just be in the noise anyway.
8059 void CMSCollector::restore_preserved_marks_if_any() {
8060 assert(SafepointSynchronize::is_at_safepoint(),
8061 "world should be stopped");
8062 assert(Thread::current()->is_ConcurrentGC_thread() ||
8063 Thread::current()->is_VM_thread(),
8064 "should be single-threaded");
8065 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8066 "bijection");
8067
8068 while (!_preserved_oop_stack.is_empty()) {
8069 oop p = _preserved_oop_stack.pop();
8070 assert(oopDesc::is_oop(p), "Should be an oop");
8071 assert(_span.contains(p), "oop should be in _span");
8072 assert(p->mark() == markOopDesc::prototype(),
8073 "Set when taken from overflow list");
8074 markOop m = _preserved_mark_stack.pop();
8075 p->set_mark(m);
8076 }
8077 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8078 "stacks were cleared above");
8079 }
8080
8081 #ifndef PRODUCT
8082 bool CMSCollector::no_preserved_marks() const {
8083 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8084 }
8085 #endif
8086
8087 // Transfer some number of overflown objects to usual marking
8088 // stack. Return true if some objects were transferred.
8089 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8090 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8091 (size_t)ParGCDesiredObjsFromOverflowList);
8092
8093 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8094 assert(_collector->overflow_list_is_empty() || res,
8095 "If list is not empty, we should have taken something");
8096 assert(!res || !_mark_stack->isEmpty(),
8097 "If we took something, it should now be on our stack");
8098 return res;
8099 }
8100
8101 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8102 size_t res = _sp->block_size_no_stall(addr, _collector);
8103 if (_sp->block_is_obj(addr)) {
8104 if (_live_bit_map->isMarked(addr)) {
8105 // It can't have been dead in a previous cycle
8106 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8107 } else {
8108 _dead_bit_map->mark(addr); // mark the dead object
8109 }
8110 }
8111 // Could be 0, if the block size could not be computed without stalling.
8112 return res;
8113 }
8114
8115 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8116 GCMemoryManager* manager = CMSHeap::heap()->old_manager();
8117 switch (phase) {
8118 case CMSCollector::InitialMarking:
8119 initialize(manager /* GC manager */ ,
8120 cause /* cause of the GC */,
8121 true /* recordGCBeginTime */,
8122 true /* recordPreGCUsage */,
8123 false /* recordPeakUsage */,
8124 false /* recordPostGCusage */,
8125 true /* recordAccumulatedGCTime */,
8126 false /* recordGCEndTime */,
8127 false /* countCollection */ );
8128 break;
8129
8130 case CMSCollector::FinalMarking:
8131 initialize(manager /* GC manager */ ,
8132 cause /* cause of the GC */,
8133 false /* recordGCBeginTime */,
8134 false /* recordPreGCUsage */,
8135 false /* recordPeakUsage */,
8136 false /* recordPostGCusage */,
8137 true /* recordAccumulatedGCTime */,
8138 false /* recordGCEndTime */,
8139 false /* countCollection */ );
8140 break;
8141
8142 case CMSCollector::Sweeping:
8143 initialize(manager /* GC manager */ ,
8144 cause /* cause of the GC */,
8145 false /* recordGCBeginTime */,
8146 false /* recordPreGCUsage */,
8147 true /* recordPeakUsage */,
8148 true /* recordPostGCusage */,
8149 false /* recordAccumulatedGCTime */,
8150 true /* recordGCEndTime */,
8151 true /* countCollection */ );
8152 break;
8153
8154 default:
8155 ShouldNotReachHere();
8156 }
8157 }