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