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