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