Mon, 07 Jul 2014 10:12:40 +0200
8049421: G1 Class Unloading after completing a concurrent mark cycle
Reviewed-by: tschatzl, ehelin, brutisso, coleenp, roland, iveresov
Contributed-by: stefan.karlsson@oracle.com, mikael.gerdin@oracle.com
1 /*
2 * Copyright (c) 2001, 2014, 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.
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23 */
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/gcTimer.hpp"
41 #include "gc_implementation/shared/gcTrace.hpp"
42 #include "gc_implementation/shared/gcTraceTime.hpp"
43 #include "gc_implementation/shared/isGCActiveMark.hpp"
44 #include "gc_interface/collectedHeap.inline.hpp"
45 #include "memory/allocation.hpp"
46 #include "memory/cardTableRS.hpp"
47 #include "memory/collectorPolicy.hpp"
48 #include "memory/gcLocker.inline.hpp"
49 #include "memory/genCollectedHeap.hpp"
50 #include "memory/genMarkSweep.hpp"
51 #include "memory/genOopClosures.inline.hpp"
52 #include "memory/iterator.inline.hpp"
53 #include "memory/padded.hpp"
54 #include "memory/referencePolicy.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/tenuredGeneration.hpp"
57 #include "oops/oop.inline.hpp"
58 #include "prims/jvmtiExport.hpp"
59 #include "runtime/globals_extension.hpp"
60 #include "runtime/handles.inline.hpp"
61 #include "runtime/java.hpp"
62 #include "runtime/orderAccess.inline.hpp"
63 #include "runtime/vmThread.hpp"
64 #include "services/memoryService.hpp"
65 #include "services/runtimeService.hpp"
67 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
69 // statics
70 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
71 bool CMSCollector::_full_gc_requested = false;
72 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
74 //////////////////////////////////////////////////////////////////
75 // In support of CMS/VM thread synchronization
76 //////////////////////////////////////////////////////////////////
77 // We split use of the CGC_lock into 2 "levels".
78 // The low-level locking is of the usual CGC_lock monitor. We introduce
79 // a higher level "token" (hereafter "CMS token") built on top of the
80 // low level monitor (hereafter "CGC lock").
81 // The token-passing protocol gives priority to the VM thread. The
82 // CMS-lock doesn't provide any fairness guarantees, but clients
83 // should ensure that it is only held for very short, bounded
84 // durations.
85 //
86 // When either of the CMS thread or the VM thread is involved in
87 // collection operations during which it does not want the other
88 // thread to interfere, it obtains the CMS token.
89 //
90 // If either thread tries to get the token while the other has
91 // it, that thread waits. However, if the VM thread and CMS thread
92 // both want the token, then the VM thread gets priority while the
93 // CMS thread waits. This ensures, for instance, that the "concurrent"
94 // phases of the CMS thread's work do not block out the VM thread
95 // for long periods of time as the CMS thread continues to hog
96 // the token. (See bug 4616232).
97 //
98 // The baton-passing functions are, however, controlled by the
99 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
100 // and here the low-level CMS lock, not the high level token,
101 // ensures mutual exclusion.
102 //
103 // Two important conditions that we have to satisfy:
104 // 1. if a thread does a low-level wait on the CMS lock, then it
105 // relinquishes the CMS token if it were holding that token
106 // when it acquired the low-level CMS lock.
107 // 2. any low-level notifications on the low-level lock
108 // should only be sent when a thread has relinquished the token.
109 //
110 // In the absence of either property, we'd have potential deadlock.
111 //
112 // We protect each of the CMS (concurrent and sequential) phases
113 // with the CMS _token_, not the CMS _lock_.
114 //
115 // The only code protected by CMS lock is the token acquisition code
116 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
117 // baton-passing code.
118 //
119 // Unfortunately, i couldn't come up with a good abstraction to factor and
120 // hide the naked CGC_lock manipulation in the baton-passing code
121 // further below. That's something we should try to do. Also, the proof
122 // of correctness of this 2-level locking scheme is far from obvious,
123 // and potentially quite slippery. We have an uneasy supsicion, for instance,
124 // that there may be a theoretical possibility of delay/starvation in the
125 // low-level lock/wait/notify scheme used for the baton-passing because of
126 // potential intereference with the priority scheme embodied in the
127 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
128 // invocation further below and marked with "XXX 20011219YSR".
129 // Indeed, as we note elsewhere, this may become yet more slippery
130 // in the presence of multiple CMS and/or multiple VM threads. XXX
132 class CMSTokenSync: public StackObj {
133 private:
134 bool _is_cms_thread;
135 public:
136 CMSTokenSync(bool is_cms_thread):
137 _is_cms_thread(is_cms_thread) {
138 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
139 "Incorrect argument to constructor");
140 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
141 }
143 ~CMSTokenSync() {
144 assert(_is_cms_thread ?
145 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
146 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
147 "Incorrect state");
148 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
149 }
150 };
152 // Convenience class that does a CMSTokenSync, and then acquires
153 // upto three locks.
154 class CMSTokenSyncWithLocks: public CMSTokenSync {
155 private:
156 // Note: locks are acquired in textual declaration order
157 // and released in the opposite order
158 MutexLockerEx _locker1, _locker2, _locker3;
159 public:
160 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
161 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
162 CMSTokenSync(is_cms_thread),
163 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
164 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
165 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
166 { }
167 };
170 // Wrapper class to temporarily disable icms during a foreground cms collection.
171 class ICMSDisabler: public StackObj {
172 public:
173 // The ctor disables icms and wakes up the thread so it notices the change;
174 // the dtor re-enables icms. Note that the CMSCollector methods will check
175 // CMSIncrementalMode.
176 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
177 ~ICMSDisabler() { CMSCollector::enable_icms(); }
178 };
180 //////////////////////////////////////////////////////////////////
181 // Concurrent Mark-Sweep Generation /////////////////////////////
182 //////////////////////////////////////////////////////////////////
184 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
186 // This struct contains per-thread things necessary to support parallel
187 // young-gen collection.
188 class CMSParGCThreadState: public CHeapObj<mtGC> {
189 public:
190 CFLS_LAB lab;
191 PromotionInfo promo;
193 // Constructor.
194 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
195 promo.setSpace(cfls);
196 }
197 };
199 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
200 ReservedSpace rs, size_t initial_byte_size, int level,
201 CardTableRS* ct, bool use_adaptive_freelists,
202 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
203 CardGeneration(rs, initial_byte_size, level, ct),
204 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
205 _debug_collection_type(Concurrent_collection_type),
206 _did_compact(false)
207 {
208 HeapWord* bottom = (HeapWord*) _virtual_space.low();
209 HeapWord* end = (HeapWord*) _virtual_space.high();
211 _direct_allocated_words = 0;
212 NOT_PRODUCT(
213 _numObjectsPromoted = 0;
214 _numWordsPromoted = 0;
215 _numObjectsAllocated = 0;
216 _numWordsAllocated = 0;
217 )
219 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
220 use_adaptive_freelists,
221 dictionaryChoice);
222 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
223 if (_cmsSpace == NULL) {
224 vm_exit_during_initialization(
225 "CompactibleFreeListSpace allocation failure");
226 }
227 _cmsSpace->_gen = this;
229 _gc_stats = new CMSGCStats();
231 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
232 // offsets match. The ability to tell free chunks from objects
233 // depends on this property.
234 debug_only(
235 FreeChunk* junk = NULL;
236 assert(UseCompressedClassPointers ||
237 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
238 "Offset of FreeChunk::_prev within FreeChunk must match"
239 " that of OopDesc::_klass within OopDesc");
240 )
241 if (CollectedHeap::use_parallel_gc_threads()) {
242 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
243 _par_gc_thread_states =
244 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
245 if (_par_gc_thread_states == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 for (uint i = 0; i < ParallelGCThreads; i++) {
249 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
250 if (_par_gc_thread_states[i] == NULL) {
251 vm_exit_during_initialization("Could not allocate par gc structs");
252 }
253 }
254 } else {
255 _par_gc_thread_states = NULL;
256 }
257 _incremental_collection_failed = false;
258 // The "dilatation_factor" is the expansion that can occur on
259 // account of the fact that the minimum object size in the CMS
260 // generation may be larger than that in, say, a contiguous young
261 // generation.
262 // Ideally, in the calculation below, we'd compute the dilatation
263 // factor as: MinChunkSize/(promoting_gen's min object size)
264 // Since we do not have such a general query interface for the
265 // promoting generation, we'll instead just use the mimimum
266 // object size (which today is a header's worth of space);
267 // note that all arithmetic is in units of HeapWords.
268 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
269 assert(_dilatation_factor >= 1.0, "from previous assert");
270 }
273 // The field "_initiating_occupancy" represents the occupancy percentage
274 // at which we trigger a new collection cycle. Unless explicitly specified
275 // via CMSInitiatingOccupancyFraction (argument "io" below), it
276 // is calculated by:
277 //
278 // Let "f" be MinHeapFreeRatio in
279 //
280 // _intiating_occupancy = 100-f +
281 // f * (CMSTriggerRatio/100)
282 // where CMSTriggerRatio is the argument "tr" below.
283 //
284 // That is, if we assume the heap is at its desired maximum occupancy at the
285 // end of a collection, we let CMSTriggerRatio of the (purported) free
286 // space be allocated before initiating a new collection cycle.
287 //
288 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
289 assert(io <= 100 && tr <= 100, "Check the arguments");
290 if (io >= 0) {
291 _initiating_occupancy = (double)io / 100.0;
292 } else {
293 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
294 (double)(tr * MinHeapFreeRatio) / 100.0)
295 / 100.0;
296 }
297 }
299 void ConcurrentMarkSweepGeneration::ref_processor_init() {
300 assert(collector() != NULL, "no collector");
301 collector()->ref_processor_init();
302 }
304 void CMSCollector::ref_processor_init() {
305 if (_ref_processor == NULL) {
306 // Allocate and initialize a reference processor
307 _ref_processor =
308 new ReferenceProcessor(_span, // span
309 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
310 (int) ParallelGCThreads, // mt processing degree
311 _cmsGen->refs_discovery_is_mt(), // mt discovery
312 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
313 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
314 &_is_alive_closure); // closure for liveness info
315 // Initialize the _ref_processor field of CMSGen
316 _cmsGen->set_ref_processor(_ref_processor);
318 }
319 }
321 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
326 gch->gen_policy()->size_policy();
327 assert(sp->is_gc_cms_adaptive_size_policy(),
328 "Wrong type of size policy");
329 return sp;
330 }
332 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
333 CMSGCAdaptivePolicyCounters* results =
334 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
335 assert(
336 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
337 "Wrong gc policy counter kind");
338 return results;
339 }
342 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
344 const char* gen_name = "old";
346 // Generation Counters - generation 1, 1 subspace
347 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
349 _space_counters = new GSpaceCounters(gen_name, 0,
350 _virtual_space.reserved_size(),
351 this, _gen_counters);
352 }
354 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
355 _cms_gen(cms_gen)
356 {
357 assert(alpha <= 100, "bad value");
358 _saved_alpha = alpha;
360 // Initialize the alphas to the bootstrap value of 100.
361 _gc0_alpha = _cms_alpha = 100;
363 _cms_begin_time.update();
364 _cms_end_time.update();
366 _gc0_duration = 0.0;
367 _gc0_period = 0.0;
368 _gc0_promoted = 0;
370 _cms_duration = 0.0;
371 _cms_period = 0.0;
372 _cms_allocated = 0;
374 _cms_used_at_gc0_begin = 0;
375 _cms_used_at_gc0_end = 0;
376 _allow_duty_cycle_reduction = false;
377 _valid_bits = 0;
378 _icms_duty_cycle = CMSIncrementalDutyCycle;
379 }
381 double CMSStats::cms_free_adjustment_factor(size_t free) const {
382 // TBD: CR 6909490
383 return 1.0;
384 }
386 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
387 }
389 // If promotion failure handling is on use
390 // the padded average size of the promotion for each
391 // young generation collection.
392 double CMSStats::time_until_cms_gen_full() const {
393 size_t cms_free = _cms_gen->cmsSpace()->free();
394 GenCollectedHeap* gch = GenCollectedHeap::heap();
395 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
396 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
397 if (cms_free > expected_promotion) {
398 // Start a cms collection if there isn't enough space to promote
399 // for the next minor collection. Use the padded average as
400 // a safety factor.
401 cms_free -= expected_promotion;
403 // Adjust by the safety factor.
404 double cms_free_dbl = (double)cms_free;
405 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
406 // Apply a further correction factor which tries to adjust
407 // for recent occurance of concurrent mode failures.
408 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
409 cms_free_dbl = cms_free_dbl * cms_adjustment;
411 if (PrintGCDetails && Verbose) {
412 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
413 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
414 cms_free, expected_promotion);
415 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
416 cms_free_dbl, cms_consumption_rate() + 1.0);
417 }
418 // Add 1 in case the consumption rate goes to zero.
419 return cms_free_dbl / (cms_consumption_rate() + 1.0);
420 }
421 return 0.0;
422 }
424 // Compare the duration of the cms collection to the
425 // time remaining before the cms generation is empty.
426 // Note that the time from the start of the cms collection
427 // to the start of the cms sweep (less than the total
428 // duration of the cms collection) can be used. This
429 // has been tried and some applications experienced
430 // promotion failures early in execution. This was
431 // possibly because the averages were not accurate
432 // enough at the beginning.
433 double CMSStats::time_until_cms_start() const {
434 // We add "gc0_period" to the "work" calculation
435 // below because this query is done (mostly) at the
436 // end of a scavenge, so we need to conservatively
437 // account for that much possible delay
438 // in the query so as to avoid concurrent mode failures
439 // due to starting the collection just a wee bit too
440 // late.
441 double work = cms_duration() + gc0_period();
442 double deadline = time_until_cms_gen_full();
443 // If a concurrent mode failure occurred recently, we want to be
444 // more conservative and halve our expected time_until_cms_gen_full()
445 if (work > deadline) {
446 if (Verbose && PrintGCDetails) {
447 gclog_or_tty->print(
448 " CMSCollector: collect because of anticipated promotion "
449 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
450 gc0_period(), time_until_cms_gen_full());
451 }
452 return 0.0;
453 }
454 return work - deadline;
455 }
457 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
458 // amount of change to prevent wild oscillation.
459 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
460 unsigned int new_duty_cycle) {
461 assert(old_duty_cycle <= 100, "bad input value");
462 assert(new_duty_cycle <= 100, "bad input value");
464 // Note: use subtraction with caution since it may underflow (values are
465 // unsigned). Addition is safe since we're in the range 0-100.
466 unsigned int damped_duty_cycle = new_duty_cycle;
467 if (new_duty_cycle < old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
469 if (new_duty_cycle + largest_delta < old_duty_cycle) {
470 damped_duty_cycle = old_duty_cycle - largest_delta;
471 }
472 } else if (new_duty_cycle > old_duty_cycle) {
473 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
474 if (new_duty_cycle > old_duty_cycle + largest_delta) {
475 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
476 }
477 }
478 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
480 if (CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
482 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
483 }
484 return damped_duty_cycle;
485 }
487 unsigned int CMSStats::icms_update_duty_cycle_impl() {
488 assert(CMSIncrementalPacing && valid(),
489 "should be handled in icms_update_duty_cycle()");
491 double cms_time_so_far = cms_timer().seconds();
492 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
493 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
495 // Avoid division by 0.
496 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
497 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
499 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
500 if (new_duty_cycle > _icms_duty_cycle) {
501 // Avoid very small duty cycles (1 or 2); 0 is allowed.
502 if (new_duty_cycle > 2) {
503 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
504 new_duty_cycle);
505 }
506 } else if (_allow_duty_cycle_reduction) {
507 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
508 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
509 // Respect the minimum duty cycle.
510 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
511 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
512 }
514 if (PrintGCDetails || CMSTraceIncrementalPacing) {
515 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
516 }
518 _allow_duty_cycle_reduction = false;
519 return _icms_duty_cycle;
520 }
522 #ifndef PRODUCT
523 void CMSStats::print_on(outputStream *st) const {
524 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
525 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
526 gc0_duration(), gc0_period(), gc0_promoted());
527 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
528 cms_duration(), cms_duration_per_mb(),
529 cms_period(), cms_allocated());
530 st->print(",cms_since_beg=%g,cms_since_end=%g",
531 cms_time_since_begin(), cms_time_since_end());
532 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
533 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
534 if (CMSIncrementalMode) {
535 st->print(",dc=%d", icms_duty_cycle());
536 }
538 if (valid()) {
539 st->print(",promo_rate=%g,cms_alloc_rate=%g",
540 promotion_rate(), cms_allocation_rate());
541 st->print(",cms_consumption_rate=%g,time_until_full=%g",
542 cms_consumption_rate(), time_until_cms_gen_full());
543 }
544 st->print(" ");
545 }
546 #endif // #ifndef PRODUCT
548 CMSCollector::CollectorState CMSCollector::_collectorState =
549 CMSCollector::Idling;
550 bool CMSCollector::_foregroundGCIsActive = false;
551 bool CMSCollector::_foregroundGCShouldWait = false;
553 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
554 CardTableRS* ct,
555 ConcurrentMarkSweepPolicy* cp):
556 _cmsGen(cmsGen),
557 _ct(ct),
558 _ref_processor(NULL), // will be set later
559 _conc_workers(NULL), // may be set later
560 _abort_preclean(false),
561 _start_sampling(false),
562 _between_prologue_and_epilogue(false),
563 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
564 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
565 -1 /* lock-free */, "No_lock" /* dummy */),
566 _modUnionClosure(&_modUnionTable),
567 _modUnionClosurePar(&_modUnionTable),
568 // Adjust my span to cover old (cms) gen
569 _span(cmsGen->reserved()),
570 // Construct the is_alive_closure with _span & markBitMap
571 _is_alive_closure(_span, &_markBitMap),
572 _restart_addr(NULL),
573 _overflow_list(NULL),
574 _stats(cmsGen),
575 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true)),
576 _eden_chunk_array(NULL), // may be set in ctor body
577 _eden_chunk_capacity(0), // -- ditto --
578 _eden_chunk_index(0), // -- ditto --
579 _survivor_plab_array(NULL), // -- ditto --
580 _survivor_chunk_array(NULL), // -- ditto --
581 _survivor_chunk_capacity(0), // -- ditto --
582 _survivor_chunk_index(0), // -- ditto --
583 _ser_pmc_preclean_ovflw(0),
584 _ser_kac_preclean_ovflw(0),
585 _ser_pmc_remark_ovflw(0),
586 _par_pmc_remark_ovflw(0),
587 _ser_kac_ovflw(0),
588 _par_kac_ovflw(0),
589 #ifndef PRODUCT
590 _num_par_pushes(0),
591 #endif
592 _collection_count_start(0),
593 _verifying(false),
594 _icms_start_limit(NULL),
595 _icms_stop_limit(NULL),
596 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
597 _completed_initialization(false),
598 _collector_policy(cp),
599 _should_unload_classes(CMSClassUnloadingEnabled),
600 _concurrent_cycles_since_last_unload(0),
601 _roots_scanning_options(SharedHeap::SO_None),
602 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
603 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
604 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
605 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
606 _cms_start_registered(false)
607 {
608 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
609 ExplicitGCInvokesConcurrent = true;
610 }
611 // Now expand the span and allocate the collection support structures
612 // (MUT, marking bit map etc.) to cover both generations subject to
613 // collection.
615 // For use by dirty card to oop closures.
616 _cmsGen->cmsSpace()->set_collector(this);
618 // Allocate MUT and marking bit map
619 {
620 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
621 if (!_markBitMap.allocate(_span)) {
622 warning("Failed to allocate CMS Bit Map");
623 return;
624 }
625 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
626 }
627 {
628 _modUnionTable.allocate(_span);
629 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
630 }
632 if (!_markStack.allocate(MarkStackSize)) {
633 warning("Failed to allocate CMS Marking Stack");
634 return;
635 }
637 // Support for multi-threaded concurrent phases
638 if (CMSConcurrentMTEnabled) {
639 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
640 // just for now
641 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
642 }
643 if (ConcGCThreads > 1) {
644 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
645 ConcGCThreads, true);
646 if (_conc_workers == NULL) {
647 warning("GC/CMS: _conc_workers allocation failure: "
648 "forcing -CMSConcurrentMTEnabled");
649 CMSConcurrentMTEnabled = false;
650 } else {
651 _conc_workers->initialize_workers();
652 }
653 } else {
654 CMSConcurrentMTEnabled = false;
655 }
656 }
657 if (!CMSConcurrentMTEnabled) {
658 ConcGCThreads = 0;
659 } else {
660 // Turn off CMSCleanOnEnter optimization temporarily for
661 // the MT case where it's not fixed yet; see 6178663.
662 CMSCleanOnEnter = false;
663 }
664 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
665 "Inconsistency");
667 // Parallel task queues; these are shared for the
668 // concurrent and stop-world phases of CMS, but
669 // are not shared with parallel scavenge (ParNew).
670 {
671 uint i;
672 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
674 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
675 || ParallelRefProcEnabled)
676 && num_queues > 0) {
677 _task_queues = new OopTaskQueueSet(num_queues);
678 if (_task_queues == NULL) {
679 warning("task_queues allocation failure.");
680 return;
681 }
682 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
683 if (_hash_seed == NULL) {
684 warning("_hash_seed array allocation failure");
685 return;
686 }
688 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
689 for (i = 0; i < num_queues; i++) {
690 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
691 if (q == NULL) {
692 warning("work_queue allocation failure.");
693 return;
694 }
695 _task_queues->register_queue(i, q);
696 }
697 for (i = 0; i < num_queues; i++) {
698 _task_queues->queue(i)->initialize();
699 _hash_seed[i] = 17; // copied from ParNew
700 }
701 }
702 }
704 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
706 // Clip CMSBootstrapOccupancy between 0 and 100.
707 _bootstrap_occupancy = ((double)CMSBootstrapOccupancy)/(double)100;
709 _full_gcs_since_conc_gc = 0;
711 // Now tell CMS generations the identity of their collector
712 ConcurrentMarkSweepGeneration::set_collector(this);
714 // Create & start a CMS thread for this CMS collector
715 _cmsThread = ConcurrentMarkSweepThread::start(this);
716 assert(cmsThread() != NULL, "CMS Thread should have been created");
717 assert(cmsThread()->collector() == this,
718 "CMS Thread should refer to this gen");
719 assert(CGC_lock != NULL, "Where's the CGC_lock?");
721 // Support for parallelizing young gen rescan
722 GenCollectedHeap* gch = GenCollectedHeap::heap();
723 _young_gen = gch->prev_gen(_cmsGen);
724 if (gch->supports_inline_contig_alloc()) {
725 _top_addr = gch->top_addr();
726 _end_addr = gch->end_addr();
727 assert(_young_gen != NULL, "no _young_gen");
728 _eden_chunk_index = 0;
729 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
730 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
731 if (_eden_chunk_array == NULL) {
732 _eden_chunk_capacity = 0;
733 warning("GC/CMS: _eden_chunk_array allocation failure");
734 }
735 }
736 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
738 // Support for parallelizing survivor space rescan
739 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
740 const size_t max_plab_samples =
741 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
743 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
744 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
745 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
746 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
747 || _cursor == NULL) {
748 warning("Failed to allocate survivor plab/chunk array");
749 if (_survivor_plab_array != NULL) {
750 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
751 _survivor_plab_array = NULL;
752 }
753 if (_survivor_chunk_array != NULL) {
754 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
755 _survivor_chunk_array = NULL;
756 }
757 if (_cursor != NULL) {
758 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
759 _cursor = NULL;
760 }
761 } else {
762 _survivor_chunk_capacity = 2*max_plab_samples;
763 for (uint i = 0; i < ParallelGCThreads; i++) {
764 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
765 if (vec == NULL) {
766 warning("Failed to allocate survivor plab array");
767 for (int j = i; j > 0; j--) {
768 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
769 }
770 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
771 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
772 _survivor_plab_array = NULL;
773 _survivor_chunk_array = NULL;
774 _survivor_chunk_capacity = 0;
775 break;
776 } else {
777 ChunkArray* cur =
778 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
779 max_plab_samples);
780 assert(cur->end() == 0, "Should be 0");
781 assert(cur->array() == vec, "Should be vec");
782 assert(cur->capacity() == max_plab_samples, "Error");
783 }
784 }
785 }
786 }
787 assert( ( _survivor_plab_array != NULL
788 && _survivor_chunk_array != NULL)
789 || ( _survivor_chunk_capacity == 0
790 && _survivor_chunk_index == 0),
791 "Error");
793 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
794 _gc_counters = new CollectorCounters("CMS", 1);
795 _completed_initialization = true;
796 _inter_sweep_timer.start(); // start of time
797 }
799 const char* ConcurrentMarkSweepGeneration::name() const {
800 return "concurrent mark-sweep generation";
801 }
802 void ConcurrentMarkSweepGeneration::update_counters() {
803 if (UsePerfData) {
804 _space_counters->update_all();
805 _gen_counters->update_all();
806 }
807 }
809 // this is an optimized version of update_counters(). it takes the
810 // used value as a parameter rather than computing it.
811 //
812 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
813 if (UsePerfData) {
814 _space_counters->update_used(used);
815 _space_counters->update_capacity();
816 _gen_counters->update_all();
817 }
818 }
820 void ConcurrentMarkSweepGeneration::print() const {
821 Generation::print();
822 cmsSpace()->print();
823 }
825 #ifndef PRODUCT
826 void ConcurrentMarkSweepGeneration::print_statistics() {
827 cmsSpace()->printFLCensus(0);
828 }
829 #endif
831 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
832 GenCollectedHeap* gch = GenCollectedHeap::heap();
833 if (PrintGCDetails) {
834 if (Verbose) {
835 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
836 level(), short_name(), s, used(), capacity());
837 } else {
838 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
839 level(), short_name(), s, used() / K, capacity() / K);
840 }
841 }
842 if (Verbose) {
843 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
844 gch->used(), gch->capacity());
845 } else {
846 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
847 gch->used() / K, gch->capacity() / K);
848 }
849 }
851 size_t
852 ConcurrentMarkSweepGeneration::contiguous_available() const {
853 // dld proposes an improvement in precision here. If the committed
854 // part of the space ends in a free block we should add that to
855 // uncommitted size in the calculation below. Will make this
856 // change later, staying with the approximation below for the
857 // time being. -- ysr.
858 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
859 }
861 size_t
862 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
863 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
864 }
866 size_t ConcurrentMarkSweepGeneration::max_available() const {
867 return free() + _virtual_space.uncommitted_size();
868 }
870 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
871 size_t available = max_available();
872 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
873 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
874 if (Verbose && PrintGCDetails) {
875 gclog_or_tty->print_cr(
876 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
877 "max_promo("SIZE_FORMAT")",
878 res? "":" not", available, res? ">=":"<",
879 av_promo, max_promotion_in_bytes);
880 }
881 return res;
882 }
884 // At a promotion failure dump information on block layout in heap
885 // (cms old generation).
886 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
887 if (CMSDumpAtPromotionFailure) {
888 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
889 }
890 }
892 CompactibleSpace*
893 ConcurrentMarkSweepGeneration::first_compaction_space() const {
894 return _cmsSpace;
895 }
897 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
898 // Clear the promotion information. These pointers can be adjusted
899 // along with all the other pointers into the heap but
900 // compaction is expected to be a rare event with
901 // a heap using cms so don't do it without seeing the need.
902 if (CollectedHeap::use_parallel_gc_threads()) {
903 for (uint i = 0; i < ParallelGCThreads; i++) {
904 _par_gc_thread_states[i]->promo.reset();
905 }
906 }
907 }
909 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
910 blk->do_space(_cmsSpace);
911 }
913 void ConcurrentMarkSweepGeneration::compute_new_size() {
914 assert_locked_or_safepoint(Heap_lock);
916 // If incremental collection failed, we just want to expand
917 // to the limit.
918 if (incremental_collection_failed()) {
919 clear_incremental_collection_failed();
920 grow_to_reserved();
921 return;
922 }
924 // The heap has been compacted but not reset yet.
925 // Any metric such as free() or used() will be incorrect.
927 CardGeneration::compute_new_size();
929 // Reset again after a possible resizing
930 if (did_compact()) {
931 cmsSpace()->reset_after_compaction();
932 }
933 }
935 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
936 assert_locked_or_safepoint(Heap_lock);
938 // If incremental collection failed, we just want to expand
939 // to the limit.
940 if (incremental_collection_failed()) {
941 clear_incremental_collection_failed();
942 grow_to_reserved();
943 return;
944 }
946 double free_percentage = ((double) free()) / capacity();
947 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
948 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
950 // compute expansion delta needed for reaching desired free percentage
951 if (free_percentage < desired_free_percentage) {
952 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
953 assert(desired_capacity >= capacity(), "invalid expansion size");
954 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
955 if (PrintGCDetails && Verbose) {
956 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
957 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
958 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
959 gclog_or_tty->print_cr(" Desired free fraction %f",
960 desired_free_percentage);
961 gclog_or_tty->print_cr(" Maximum free fraction %f",
962 maximum_free_percentage);
963 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
964 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
965 desired_capacity/1000);
966 int prev_level = level() - 1;
967 if (prev_level >= 0) {
968 size_t prev_size = 0;
969 GenCollectedHeap* gch = GenCollectedHeap::heap();
970 Generation* prev_gen = gch->_gens[prev_level];
971 prev_size = prev_gen->capacity();
972 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
973 prev_size/1000);
974 }
975 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
976 unsafe_max_alloc_nogc()/1000);
977 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
978 contiguous_available()/1000);
979 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
980 expand_bytes);
981 }
982 // safe if expansion fails
983 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
984 if (PrintGCDetails && Verbose) {
985 gclog_or_tty->print_cr(" Expanded free fraction %f",
986 ((double) free()) / capacity());
987 }
988 } else {
989 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
990 assert(desired_capacity <= capacity(), "invalid expansion size");
991 size_t shrink_bytes = capacity() - desired_capacity;
992 // Don't shrink unless the delta is greater than the minimum shrink we want
993 if (shrink_bytes >= MinHeapDeltaBytes) {
994 shrink_free_list_by(shrink_bytes);
995 }
996 }
997 }
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 //
1058 // Can the P-bits be deleted now? JJJ
1059 //
1060 // 1. need to mark the object as live so it isn't collected
1061 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1062 // 3. need to mark the end of the object so marking, precleaning or sweeping
1063 // can skip over uninitialized or unparsable objects. An allocated
1064 // object is considered uninitialized for our purposes as long as
1065 // its klass word is NULL. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 p2i(_icms_start_limit), p2i(_icms_stop_limit),
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 p2i(top), p2i(_icms_stop_limit),
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 p2i(top), p2i(space->end()),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1261 return NULL;
1262 }
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 //
1328 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1329 //
1330 // STATE IDENTIFICATION: (64 bit+COOPS)
1331 // ------------------------------------
1332 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1333 //
1334 // OBJECT: klass_word installed; klass_word != 0;
1335 // obj->size() computes correct size
1336 //
1337 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1338 //
1339 //
1340 // STATE TRANSITION DIAGRAM
1341 //
1342 // mut / parnew mut / parnew
1343 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1344 // ^ |
1345 // |------------------------ DEAD <------------------------------------|
1346 // sweep mut
1347 //
1348 // While a block is in TRANSIENT state its size cannot be determined
1349 // so readers will either need to come back later or stall until
1350 // the size can be determined. Note that for the case of direct
1351 // allocation, P-bits, when available, may be used to determine the
1352 // size of an object that may not yet have been initialized.
1354 // Things to support parallel young-gen collection.
1355 oop
1356 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1357 oop old, markOop m,
1358 size_t word_sz) {
1359 #ifndef PRODUCT
1360 if (Universe::heap()->promotion_should_fail()) {
1361 return NULL;
1362 }
1363 #endif // #ifndef PRODUCT
1365 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1366 PromotionInfo* promoInfo = &ps->promo;
1367 // if we are tracking promotions, then first ensure space for
1368 // promotion (including spooling space for saving header if necessary).
1369 // then allocate and copy, then track promoted info if needed.
1370 // When tracking (see PromotionInfo::track()), the mark word may
1371 // be displaced and in this case restoration of the mark word
1372 // occurs in the (oop_since_save_marks_)iterate phase.
1373 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1374 // Out of space for allocating spooling buffers;
1375 // try expanding and allocating spooling buffers.
1376 if (!expand_and_ensure_spooling_space(promoInfo)) {
1377 return NULL;
1378 }
1379 }
1380 assert(promoInfo->has_spooling_space(), "Control point invariant");
1381 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1382 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1383 if (obj_ptr == NULL) {
1384 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1385 if (obj_ptr == NULL) {
1386 return NULL;
1387 }
1388 }
1389 oop obj = oop(obj_ptr);
1390 OrderAccess::storestore();
1391 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1392 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1393 // IMPORTANT: See note on object initialization for CMS above.
1394 // Otherwise, copy the object. Here we must be careful to insert the
1395 // klass pointer last, since this marks the block as an allocated object.
1396 // Except with compressed oops it's the mark word.
1397 HeapWord* old_ptr = (HeapWord*)old;
1398 // Restore the mark word copied above.
1399 obj->set_mark(m);
1400 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1401 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1402 OrderAccess::storestore();
1404 if (UseCompressedClassPointers) {
1405 // Copy gap missed by (aligned) header size calculation below
1406 obj->set_klass_gap(old->klass_gap());
1407 }
1408 if (word_sz > (size_t)oopDesc::header_size()) {
1409 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1410 obj_ptr + oopDesc::header_size(),
1411 word_sz - oopDesc::header_size());
1412 }
1414 // Now we can track the promoted object, if necessary. We take care
1415 // to delay the transition from uninitialized to full object
1416 // (i.e., insertion of klass pointer) until after, so that it
1417 // atomically becomes a promoted object.
1418 if (promoInfo->tracking()) {
1419 promoInfo->track((PromotedObject*)obj, old->klass());
1420 }
1421 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1422 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1423 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1425 // Finally, install the klass pointer (this should be volatile).
1426 OrderAccess::storestore();
1427 obj->set_klass(old->klass());
1428 // We should now be able to calculate the right size for this object
1429 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1431 collector()->promoted(true, // parallel
1432 obj_ptr, old->is_objArray(), word_sz);
1434 NOT_PRODUCT(
1435 Atomic::inc_ptr(&_numObjectsPromoted);
1436 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1437 )
1439 return obj;
1440 }
1442 void
1443 ConcurrentMarkSweepGeneration::
1444 par_promote_alloc_undo(int thread_num,
1445 HeapWord* obj, size_t word_sz) {
1446 // CMS does not support promotion undo.
1447 ShouldNotReachHere();
1448 }
1450 void
1451 ConcurrentMarkSweepGeneration::
1452 par_promote_alloc_done(int thread_num) {
1453 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1454 ps->lab.retire(thread_num);
1455 }
1457 void
1458 ConcurrentMarkSweepGeneration::
1459 par_oop_since_save_marks_iterate_done(int thread_num) {
1460 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1461 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1462 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1463 }
1465 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1466 size_t size,
1467 bool tlab)
1468 {
1469 // We allow a STW collection only if a full
1470 // collection was requested.
1471 return full || should_allocate(size, tlab); // FIX ME !!!
1472 // This and promotion failure handling are connected at the
1473 // hip and should be fixed by untying them.
1474 }
1476 bool CMSCollector::shouldConcurrentCollect() {
1477 if (_full_gc_requested) {
1478 if (Verbose && PrintGCDetails) {
1479 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1480 " gc request (or gc_locker)");
1481 }
1482 return true;
1483 }
1485 // For debugging purposes, change the type of collection.
1486 // If the rotation is not on the concurrent collection
1487 // type, don't start a concurrent collection.
1488 NOT_PRODUCT(
1489 if (RotateCMSCollectionTypes &&
1490 (_cmsGen->debug_collection_type() !=
1491 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1492 assert(_cmsGen->debug_collection_type() !=
1493 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1494 "Bad cms collection type");
1495 return false;
1496 }
1497 )
1499 FreelistLocker x(this);
1500 // ------------------------------------------------------------------
1501 // Print out lots of information which affects the initiation of
1502 // a collection.
1503 if (PrintCMSInitiationStatistics && stats().valid()) {
1504 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1505 gclog_or_tty->stamp();
1506 gclog_or_tty->cr();
1507 stats().print_on(gclog_or_tty);
1508 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1509 stats().time_until_cms_gen_full());
1510 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1511 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1512 _cmsGen->contiguous_available());
1513 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1514 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1515 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1516 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1517 gclog_or_tty->print_cr("metadata initialized %d",
1518 MetaspaceGC::should_concurrent_collect());
1519 }
1520 // ------------------------------------------------------------------
1522 // If the estimated time to complete a cms collection (cms_duration())
1523 // is less than the estimated time remaining until the cms generation
1524 // is full, start a collection.
1525 if (!UseCMSInitiatingOccupancyOnly) {
1526 if (stats().valid()) {
1527 if (stats().time_until_cms_start() == 0.0) {
1528 return true;
1529 }
1530 } else {
1531 // We want to conservatively collect somewhat early in order
1532 // to try and "bootstrap" our CMS/promotion statistics;
1533 // this branch will not fire after the first successful CMS
1534 // collection because the stats should then be valid.
1535 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1536 if (Verbose && PrintGCDetails) {
1537 gclog_or_tty->print_cr(
1538 " CMSCollector: collect for bootstrapping statistics:"
1539 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1540 _bootstrap_occupancy);
1541 }
1542 return true;
1543 }
1544 }
1545 }
1547 // Otherwise, we start a collection cycle if
1548 // old gen want a collection cycle started. Each may use
1549 // an appropriate criterion for making this decision.
1550 // XXX We need to make sure that the gen expansion
1551 // criterion dovetails well with this. XXX NEED TO FIX THIS
1552 if (_cmsGen->should_concurrent_collect()) {
1553 if (Verbose && PrintGCDetails) {
1554 gclog_or_tty->print_cr("CMS old gen initiated");
1555 }
1556 return true;
1557 }
1559 // We start a collection if we believe an incremental collection may fail;
1560 // this is not likely to be productive in practice because it's probably too
1561 // late anyway.
1562 GenCollectedHeap* gch = GenCollectedHeap::heap();
1563 assert(gch->collector_policy()->is_two_generation_policy(),
1564 "You may want to check the correctness of the following");
1565 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1566 if (Verbose && PrintGCDetails) {
1567 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1568 }
1569 return true;
1570 }
1572 if (MetaspaceGC::should_concurrent_collect()) {
1573 if (Verbose && PrintGCDetails) {
1574 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1575 }
1576 return true;
1577 }
1579 return false;
1580 }
1582 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1584 // Clear _expansion_cause fields of constituent generations
1585 void CMSCollector::clear_expansion_cause() {
1586 _cmsGen->clear_expansion_cause();
1587 }
1589 // We should be conservative in starting a collection cycle. To
1590 // start too eagerly runs the risk of collecting too often in the
1591 // extreme. To collect too rarely falls back on full collections,
1592 // which works, even if not optimum in terms of concurrent work.
1593 // As a work around for too eagerly collecting, use the flag
1594 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1595 // giving the user an easily understandable way of controlling the
1596 // collections.
1597 // We want to start a new collection cycle if any of the following
1598 // conditions hold:
1599 // . our current occupancy exceeds the configured initiating occupancy
1600 // for this generation, or
1601 // . we recently needed to expand this space and have not, since that
1602 // expansion, done a collection of this generation, or
1603 // . the underlying space believes that it may be a good idea to initiate
1604 // a concurrent collection (this may be based on criteria such as the
1605 // following: the space uses linear allocation and linear allocation is
1606 // going to fail, or there is believed to be excessive fragmentation in
1607 // the generation, etc... or ...
1608 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1609 // the case of the old generation; see CR 6543076):
1610 // we may be approaching a point at which allocation requests may fail because
1611 // we will be out of sufficient free space given allocation rate estimates.]
1612 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1614 assert_lock_strong(freelistLock());
1615 if (occupancy() > initiating_occupancy()) {
1616 if (PrintGCDetails && Verbose) {
1617 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1618 short_name(), occupancy(), initiating_occupancy());
1619 }
1620 return true;
1621 }
1622 if (UseCMSInitiatingOccupancyOnly) {
1623 return false;
1624 }
1625 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1626 if (PrintGCDetails && Verbose) {
1627 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1628 short_name());
1629 }
1630 return true;
1631 }
1632 if (_cmsSpace->should_concurrent_collect()) {
1633 if (PrintGCDetails && Verbose) {
1634 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1635 short_name());
1636 }
1637 return true;
1638 }
1639 return false;
1640 }
1642 void ConcurrentMarkSweepGeneration::collect(bool full,
1643 bool clear_all_soft_refs,
1644 size_t size,
1645 bool tlab)
1646 {
1647 collector()->collect(full, clear_all_soft_refs, size, tlab);
1648 }
1650 void CMSCollector::collect(bool full,
1651 bool clear_all_soft_refs,
1652 size_t size,
1653 bool tlab)
1654 {
1655 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1656 // For debugging purposes skip the collection if the state
1657 // is not currently idle
1658 if (TraceCMSState) {
1659 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1660 Thread::current(), full, _collectorState);
1661 }
1662 return;
1663 }
1665 // The following "if" branch is present for defensive reasons.
1666 // In the current uses of this interface, it can be replaced with:
1667 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1668 // But I am not placing that assert here to allow future
1669 // generality in invoking this interface.
1670 if (GC_locker::is_active()) {
1671 // A consistency test for GC_locker
1672 assert(GC_locker::needs_gc(), "Should have been set already");
1673 // Skip this foreground collection, instead
1674 // expanding the heap if necessary.
1675 // Need the free list locks for the call to free() in compute_new_size()
1676 compute_new_size();
1677 return;
1678 }
1679 acquire_control_and_collect(full, clear_all_soft_refs);
1680 _full_gcs_since_conc_gc++;
1681 }
1683 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1684 GenCollectedHeap* gch = GenCollectedHeap::heap();
1685 unsigned int gc_count = gch->total_full_collections();
1686 if (gc_count == full_gc_count) {
1687 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1688 _full_gc_requested = true;
1689 _full_gc_cause = cause;
1690 CGC_lock->notify(); // nudge CMS thread
1691 } else {
1692 assert(gc_count > full_gc_count, "Error: causal loop");
1693 }
1694 }
1696 bool CMSCollector::is_external_interruption() {
1697 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1698 return GCCause::is_user_requested_gc(cause) ||
1699 GCCause::is_serviceability_requested_gc(cause);
1700 }
1702 void CMSCollector::report_concurrent_mode_interruption() {
1703 if (is_external_interruption()) {
1704 if (PrintGCDetails) {
1705 gclog_or_tty->print(" (concurrent mode interrupted)");
1706 }
1707 } else {
1708 if (PrintGCDetails) {
1709 gclog_or_tty->print(" (concurrent mode failure)");
1710 }
1711 _gc_tracer_cm->report_concurrent_mode_failure();
1712 }
1713 }
1716 // The foreground and background collectors need to coordinate in order
1717 // to make sure that they do not mutually interfere with CMS collections.
1718 // When a background collection is active,
1719 // the foreground collector may need to take over (preempt) and
1720 // synchronously complete an ongoing collection. Depending on the
1721 // frequency of the background collections and the heap usage
1722 // of the application, this preemption can be seldom or frequent.
1723 // There are only certain
1724 // points in the background collection that the "collection-baton"
1725 // can be passed to the foreground collector.
1726 //
1727 // The foreground collector will wait for the baton before
1728 // starting any part of the collection. The foreground collector
1729 // will only wait at one location.
1730 //
1731 // The background collector will yield the baton before starting a new
1732 // phase of the collection (e.g., before initial marking, marking from roots,
1733 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1734 // of the loop which switches the phases. The background collector does some
1735 // of the phases (initial mark, final re-mark) with the world stopped.
1736 // Because of locking involved in stopping the world,
1737 // the foreground collector should not block waiting for the background
1738 // collector when it is doing a stop-the-world phase. The background
1739 // collector will yield the baton at an additional point just before
1740 // it enters a stop-the-world phase. Once the world is stopped, the
1741 // background collector checks the phase of the collection. If the
1742 // phase has not changed, it proceeds with the collection. If the
1743 // phase has changed, it skips that phase of the collection. See
1744 // the comments on the use of the Heap_lock in collect_in_background().
1745 //
1746 // Variable used in baton passing.
1747 // _foregroundGCIsActive - Set to true by the foreground collector when
1748 // it wants the baton. The foreground clears it when it has finished
1749 // the collection.
1750 // _foregroundGCShouldWait - Set to true by the background collector
1751 // when it is running. The foreground collector waits while
1752 // _foregroundGCShouldWait is true.
1753 // CGC_lock - monitor used to protect access to the above variables
1754 // and to notify the foreground and background collectors.
1755 // _collectorState - current state of the CMS collection.
1756 //
1757 // The foreground collector
1758 // acquires the CGC_lock
1759 // sets _foregroundGCIsActive
1760 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1761 // various locks acquired in preparation for the collection
1762 // are released so as not to block the background collector
1763 // that is in the midst of a collection
1764 // proceeds with the collection
1765 // clears _foregroundGCIsActive
1766 // returns
1767 //
1768 // The background collector in a loop iterating on the phases of the
1769 // collection
1770 // acquires the CGC_lock
1771 // sets _foregroundGCShouldWait
1772 // if _foregroundGCIsActive is set
1773 // clears _foregroundGCShouldWait, notifies _CGC_lock
1774 // waits on _CGC_lock for _foregroundGCIsActive to become false
1775 // and exits the loop.
1776 // otherwise
1777 // proceed with that phase of the collection
1778 // if the phase is a stop-the-world phase,
1779 // yield the baton once more just before enqueueing
1780 // the stop-world CMS operation (executed by the VM thread).
1781 // returns after all phases of the collection are done
1782 //
1784 void CMSCollector::acquire_control_and_collect(bool full,
1785 bool clear_all_soft_refs) {
1786 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1787 assert(!Thread::current()->is_ConcurrentGC_thread(),
1788 "shouldn't try to acquire control from self!");
1790 // Start the protocol for acquiring control of the
1791 // collection from the background collector (aka CMS thread).
1792 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1793 "VM thread should have CMS token");
1794 // Remember the possibly interrupted state of an ongoing
1795 // concurrent collection
1796 CollectorState first_state = _collectorState;
1798 // Signal to a possibly ongoing concurrent collection that
1799 // we want to do a foreground collection.
1800 _foregroundGCIsActive = true;
1802 // Disable incremental mode during a foreground collection.
1803 ICMSDisabler icms_disabler;
1805 // release locks and wait for a notify from the background collector
1806 // releasing the locks in only necessary for phases which
1807 // do yields to improve the granularity of the collection.
1808 assert_lock_strong(bitMapLock());
1809 // We need to lock the Free list lock for the space that we are
1810 // currently collecting.
1811 assert(haveFreelistLocks(), "Must be holding free list locks");
1812 bitMapLock()->unlock();
1813 releaseFreelistLocks();
1814 {
1815 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1816 if (_foregroundGCShouldWait) {
1817 // We are going to be waiting for action for the CMS thread;
1818 // it had better not be gone (for instance at shutdown)!
1819 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1820 "CMS thread must be running");
1821 // Wait here until the background collector gives us the go-ahead
1822 ConcurrentMarkSweepThread::clear_CMS_flag(
1823 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1824 // Get a possibly blocked CMS thread going:
1825 // Note that we set _foregroundGCIsActive true above,
1826 // without protection of the CGC_lock.
1827 CGC_lock->notify();
1828 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1829 "Possible deadlock");
1830 while (_foregroundGCShouldWait) {
1831 // wait for notification
1832 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1833 // Possibility of delay/starvation here, since CMS token does
1834 // not know to give priority to VM thread? Actually, i think
1835 // there wouldn't be any delay/starvation, but the proof of
1836 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1837 }
1838 ConcurrentMarkSweepThread::set_CMS_flag(
1839 ConcurrentMarkSweepThread::CMS_vm_has_token);
1840 }
1841 }
1842 // The CMS_token is already held. Get back the other locks.
1843 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1844 "VM thread should have CMS token");
1845 getFreelistLocks();
1846 bitMapLock()->lock_without_safepoint_check();
1847 if (TraceCMSState) {
1848 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1849 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1850 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1851 }
1853 // Check if we need to do a compaction, or if not, whether
1854 // we need to start the mark-sweep from scratch.
1855 bool should_compact = false;
1856 bool should_start_over = false;
1857 decide_foreground_collection_type(clear_all_soft_refs,
1858 &should_compact, &should_start_over);
1860 NOT_PRODUCT(
1861 if (RotateCMSCollectionTypes) {
1862 if (_cmsGen->debug_collection_type() ==
1863 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1864 should_compact = true;
1865 } else if (_cmsGen->debug_collection_type() ==
1866 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1867 should_compact = false;
1868 }
1869 }
1870 )
1872 if (first_state > Idling) {
1873 report_concurrent_mode_interruption();
1874 }
1876 set_did_compact(should_compact);
1877 if (should_compact) {
1878 // If the collection is being acquired from the background
1879 // collector, there may be references on the discovered
1880 // references lists that have NULL referents (being those
1881 // that were concurrently cleared by a mutator) or
1882 // that are no longer active (having been enqueued concurrently
1883 // by the mutator).
1884 // Scrub the list of those references because Mark-Sweep-Compact
1885 // code assumes referents are not NULL and that all discovered
1886 // Reference objects are active.
1887 ref_processor()->clean_up_discovered_references();
1889 if (first_state > Idling) {
1890 save_heap_summary();
1891 }
1893 do_compaction_work(clear_all_soft_refs);
1895 // Has the GC time limit been exceeded?
1896 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1897 size_t max_eden_size = young_gen->max_capacity() -
1898 young_gen->to()->capacity() -
1899 young_gen->from()->capacity();
1900 GenCollectedHeap* gch = GenCollectedHeap::heap();
1901 GCCause::Cause gc_cause = gch->gc_cause();
1902 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1903 young_gen->eden()->used(),
1904 _cmsGen->max_capacity(),
1905 max_eden_size,
1906 full,
1907 gc_cause,
1908 gch->collector_policy());
1909 } else {
1910 do_mark_sweep_work(clear_all_soft_refs, first_state,
1911 should_start_over);
1912 }
1913 // Reset the expansion cause, now that we just completed
1914 // a collection cycle.
1915 clear_expansion_cause();
1916 _foregroundGCIsActive = false;
1917 return;
1918 }
1920 // Resize the tenured generation
1921 // after obtaining the free list locks for the
1922 // two generations.
1923 void CMSCollector::compute_new_size() {
1924 assert_locked_or_safepoint(Heap_lock);
1925 FreelistLocker z(this);
1926 MetaspaceGC::compute_new_size();
1927 _cmsGen->compute_new_size_free_list();
1928 }
1930 // A work method used by foreground collection to determine
1931 // what type of collection (compacting or not, continuing or fresh)
1932 // it should do.
1933 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1934 // and CMSCompactWhenClearAllSoftRefs the default in the future
1935 // and do away with the flags after a suitable period.
1936 void CMSCollector::decide_foreground_collection_type(
1937 bool clear_all_soft_refs, bool* should_compact,
1938 bool* should_start_over) {
1939 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1940 // flag is set, and we have either requested a System.gc() or
1941 // the number of full gc's since the last concurrent cycle
1942 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1943 // or if an incremental collection has failed
1944 GenCollectedHeap* gch = GenCollectedHeap::heap();
1945 assert(gch->collector_policy()->is_two_generation_policy(),
1946 "You may want to check the correctness of the following");
1947 // Inform cms gen if this was due to partial collection failing.
1948 // The CMS gen may use this fact to determine its expansion policy.
1949 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1950 assert(!_cmsGen->incremental_collection_failed(),
1951 "Should have been noticed, reacted to and cleared");
1952 _cmsGen->set_incremental_collection_failed();
1953 }
1954 *should_compact =
1955 UseCMSCompactAtFullCollection &&
1956 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1957 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1958 gch->incremental_collection_will_fail(true /* consult_young */));
1959 *should_start_over = false;
1960 if (clear_all_soft_refs && !*should_compact) {
1961 // We are about to do a last ditch collection attempt
1962 // so it would normally make sense to do a compaction
1963 // to reclaim as much space as possible.
1964 if (CMSCompactWhenClearAllSoftRefs) {
1965 // Default: The rationale is that in this case either
1966 // we are past the final marking phase, in which case
1967 // we'd have to start over, or so little has been done
1968 // that there's little point in saving that work. Compaction
1969 // appears to be the sensible choice in either case.
1970 *should_compact = true;
1971 } else {
1972 // We have been asked to clear all soft refs, but not to
1973 // compact. Make sure that we aren't past the final checkpoint
1974 // phase, for that is where we process soft refs. If we are already
1975 // past that phase, we'll need to redo the refs discovery phase and
1976 // if necessary clear soft refs that weren't previously
1977 // cleared. We do so by remembering the phase in which
1978 // we came in, and if we are past the refs processing
1979 // phase, we'll choose to just redo the mark-sweep
1980 // collection from scratch.
1981 if (_collectorState > FinalMarking) {
1982 // We are past the refs processing phase;
1983 // start over and do a fresh synchronous CMS cycle
1984 _collectorState = Resetting; // skip to reset to start new cycle
1985 reset(false /* == !asynch */);
1986 *should_start_over = true;
1987 } // else we can continue a possibly ongoing current cycle
1988 }
1989 }
1990 }
1992 // A work method used by the foreground collector to do
1993 // a mark-sweep-compact.
1994 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1995 GenCollectedHeap* gch = GenCollectedHeap::heap();
1997 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1998 gc_timer->register_gc_start();
2000 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2001 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2003 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL, gc_tracer->gc_id());
2004 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2005 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2006 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2007 }
2009 // Sample collection interval time and reset for collection pause.
2010 if (UseAdaptiveSizePolicy) {
2011 size_policy()->msc_collection_begin();
2012 }
2014 // Temporarily widen the span of the weak reference processing to
2015 // the entire heap.
2016 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2017 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2018 // Temporarily, clear the "is_alive_non_header" field of the
2019 // reference processor.
2020 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2021 // Temporarily make reference _processing_ single threaded (non-MT).
2022 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2023 // Temporarily make refs discovery atomic
2024 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2025 // Temporarily make reference _discovery_ single threaded (non-MT)
2026 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2028 ref_processor()->set_enqueuing_is_done(false);
2029 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2030 ref_processor()->setup_policy(clear_all_soft_refs);
2031 // If an asynchronous collection finishes, the _modUnionTable is
2032 // all clear. If we are assuming the collection from an asynchronous
2033 // collection, clear the _modUnionTable.
2034 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2035 "_modUnionTable should be clear if the baton was not passed");
2036 _modUnionTable.clear_all();
2037 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
2038 "mod union for klasses should be clear if the baton was passed");
2039 _ct->klass_rem_set()->clear_mod_union();
2041 // We must adjust the allocation statistics being maintained
2042 // in the free list space. We do so by reading and clearing
2043 // the sweep timer and updating the block flux rate estimates below.
2044 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2045 if (_inter_sweep_timer.is_active()) {
2046 _inter_sweep_timer.stop();
2047 // Note that we do not use this sample to update the _inter_sweep_estimate.
2048 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2049 _inter_sweep_estimate.padded_average(),
2050 _intra_sweep_estimate.padded_average());
2051 }
2053 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2054 ref_processor(), clear_all_soft_refs);
2055 #ifdef ASSERT
2056 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2057 size_t free_size = cms_space->free();
2058 assert(free_size ==
2059 pointer_delta(cms_space->end(), cms_space->compaction_top())
2060 * HeapWordSize,
2061 "All the free space should be compacted into one chunk at top");
2062 assert(cms_space->dictionary()->total_chunk_size(
2063 debug_only(cms_space->freelistLock())) == 0 ||
2064 cms_space->totalSizeInIndexedFreeLists() == 0,
2065 "All the free space should be in a single chunk");
2066 size_t num = cms_space->totalCount();
2067 assert((free_size == 0 && num == 0) ||
2068 (free_size > 0 && (num == 1 || num == 2)),
2069 "There should be at most 2 free chunks after compaction");
2070 #endif // ASSERT
2071 _collectorState = Resetting;
2072 assert(_restart_addr == NULL,
2073 "Should have been NULL'd before baton was passed");
2074 reset(false /* == !asynch */);
2075 _cmsGen->reset_after_compaction();
2076 _concurrent_cycles_since_last_unload = 0;
2078 // Clear any data recorded in the PLAB chunk arrays.
2079 if (_survivor_plab_array != NULL) {
2080 reset_survivor_plab_arrays();
2081 }
2083 // Adjust the per-size allocation stats for the next epoch.
2084 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2085 // Restart the "inter sweep timer" for the next epoch.
2086 _inter_sweep_timer.reset();
2087 _inter_sweep_timer.start();
2089 // Sample collection pause time and reset for collection interval.
2090 if (UseAdaptiveSizePolicy) {
2091 size_policy()->msc_collection_end(gch->gc_cause());
2092 }
2094 gc_timer->register_gc_end();
2096 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2098 // For a mark-sweep-compact, compute_new_size() will be called
2099 // in the heap's do_collection() method.
2100 }
2102 // A work method used by the foreground collector to do
2103 // a mark-sweep, after taking over from a possibly on-going
2104 // concurrent mark-sweep collection.
2105 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2106 CollectorState first_state, bool should_start_over) {
2107 if (PrintGC && Verbose) {
2108 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2109 "collector with count %d",
2110 _full_gcs_since_conc_gc);
2111 }
2112 switch (_collectorState) {
2113 case Idling:
2114 if (first_state == Idling || should_start_over) {
2115 // The background GC was not active, or should
2116 // restarted from scratch; start the cycle.
2117 _collectorState = InitialMarking;
2118 }
2119 // If first_state was not Idling, then a background GC
2120 // was in progress and has now finished. No need to do it
2121 // again. Leave the state as Idling.
2122 break;
2123 case Precleaning:
2124 // In the foreground case don't do the precleaning since
2125 // it is not done concurrently and there is extra work
2126 // required.
2127 _collectorState = FinalMarking;
2128 }
2129 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2131 // For a mark-sweep, compute_new_size() will be called
2132 // in the heap's do_collection() method.
2133 }
2136 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
2137 DefNewGeneration* dng = _young_gen->as_DefNewGeneration();
2138 EdenSpace* eden_space = dng->eden();
2139 ContiguousSpace* from_space = dng->from();
2140 ContiguousSpace* to_space = dng->to();
2141 // Eden
2142 if (_eden_chunk_array != NULL) {
2143 gclog_or_tty->print_cr("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2144 eden_space->bottom(), eden_space->top(),
2145 eden_space->end(), eden_space->capacity());
2146 gclog_or_tty->print_cr("_eden_chunk_index=" SIZE_FORMAT ", "
2147 "_eden_chunk_capacity=" SIZE_FORMAT,
2148 _eden_chunk_index, _eden_chunk_capacity);
2149 for (size_t i = 0; i < _eden_chunk_index; i++) {
2150 gclog_or_tty->print_cr("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2151 i, _eden_chunk_array[i]);
2152 }
2153 }
2154 // Survivor
2155 if (_survivor_chunk_array != NULL) {
2156 gclog_or_tty->print_cr("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
2157 from_space->bottom(), from_space->top(),
2158 from_space->end(), from_space->capacity());
2159 gclog_or_tty->print_cr("_survivor_chunk_index=" SIZE_FORMAT ", "
2160 "_survivor_chunk_capacity=" SIZE_FORMAT,
2161 _survivor_chunk_index, _survivor_chunk_capacity);
2162 for (size_t i = 0; i < _survivor_chunk_index; i++) {
2163 gclog_or_tty->print_cr("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT,
2164 i, _survivor_chunk_array[i]);
2165 }
2166 }
2167 }
2169 void CMSCollector::getFreelistLocks() const {
2170 // Get locks for all free lists in all generations that this
2171 // collector is responsible for
2172 _cmsGen->freelistLock()->lock_without_safepoint_check();
2173 }
2175 void CMSCollector::releaseFreelistLocks() const {
2176 // Release locks for all free lists in all generations that this
2177 // collector is responsible for
2178 _cmsGen->freelistLock()->unlock();
2179 }
2181 bool CMSCollector::haveFreelistLocks() const {
2182 // Check locks for all free lists in all generations that this
2183 // collector is responsible for
2184 assert_lock_strong(_cmsGen->freelistLock());
2185 PRODUCT_ONLY(ShouldNotReachHere());
2186 return true;
2187 }
2189 // A utility class that is used by the CMS collector to
2190 // temporarily "release" the foreground collector from its
2191 // usual obligation to wait for the background collector to
2192 // complete an ongoing phase before proceeding.
2193 class ReleaseForegroundGC: public StackObj {
2194 private:
2195 CMSCollector* _c;
2196 public:
2197 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2198 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2199 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2200 // allow a potentially blocked foreground collector to proceed
2201 _c->_foregroundGCShouldWait = false;
2202 if (_c->_foregroundGCIsActive) {
2203 CGC_lock->notify();
2204 }
2205 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2206 "Possible deadlock");
2207 }
2209 ~ReleaseForegroundGC() {
2210 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2211 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2212 _c->_foregroundGCShouldWait = true;
2213 }
2214 };
2216 // There are separate collect_in_background and collect_in_foreground because of
2217 // the different locking requirements of the background collector and the
2218 // foreground collector. There was originally an attempt to share
2219 // one "collect" method between the background collector and the foreground
2220 // collector but the if-then-else required made it cleaner to have
2221 // separate methods.
2222 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2223 assert(Thread::current()->is_ConcurrentGC_thread(),
2224 "A CMS asynchronous collection is only allowed on a CMS thread.");
2226 GenCollectedHeap* gch = GenCollectedHeap::heap();
2227 {
2228 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2229 MutexLockerEx hl(Heap_lock, safepoint_check);
2230 FreelistLocker fll(this);
2231 MutexLockerEx x(CGC_lock, safepoint_check);
2232 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2233 // The foreground collector is active or we're
2234 // not using asynchronous collections. Skip this
2235 // background collection.
2236 assert(!_foregroundGCShouldWait, "Should be clear");
2237 return;
2238 } else {
2239 assert(_collectorState == Idling, "Should be idling before start.");
2240 _collectorState = InitialMarking;
2241 register_gc_start(cause);
2242 // Reset the expansion cause, now that we are about to begin
2243 // a new cycle.
2244 clear_expansion_cause();
2246 // Clear the MetaspaceGC flag since a concurrent collection
2247 // is starting but also clear it after the collection.
2248 MetaspaceGC::set_should_concurrent_collect(false);
2249 }
2250 // Decide if we want to enable class unloading as part of the
2251 // ensuing concurrent GC cycle.
2252 update_should_unload_classes();
2253 _full_gc_requested = false; // acks all outstanding full gc requests
2254 _full_gc_cause = GCCause::_no_gc;
2255 // Signal that we are about to start a collection
2256 gch->increment_total_full_collections(); // ... starting a collection cycle
2257 _collection_count_start = gch->total_full_collections();
2258 }
2260 // Used for PrintGC
2261 size_t prev_used;
2262 if (PrintGC && Verbose) {
2263 prev_used = _cmsGen->used(); // XXXPERM
2264 }
2266 // The change of the collection state is normally done at this level;
2267 // the exceptions are phases that are executed while the world is
2268 // stopped. For those phases the change of state is done while the
2269 // world is stopped. For baton passing purposes this allows the
2270 // background collector to finish the phase and change state atomically.
2271 // The foreground collector cannot wait on a phase that is done
2272 // while the world is stopped because the foreground collector already
2273 // has the world stopped and would deadlock.
2274 while (_collectorState != Idling) {
2275 if (TraceCMSState) {
2276 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2277 Thread::current(), _collectorState);
2278 }
2279 // The foreground collector
2280 // holds the Heap_lock throughout its collection.
2281 // holds the CMS token (but not the lock)
2282 // except while it is waiting for the background collector to yield.
2283 //
2284 // The foreground collector should be blocked (not for long)
2285 // if the background collector is about to start a phase
2286 // executed with world stopped. If the background
2287 // collector has already started such a phase, the
2288 // foreground collector is blocked waiting for the
2289 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2290 // are executed in the VM thread.
2291 //
2292 // The locking order is
2293 // PendingListLock (PLL) -- if applicable (FinalMarking)
2294 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2295 // CMS token (claimed in
2296 // stop_world_and_do() -->
2297 // safepoint_synchronize() -->
2298 // CMSThread::synchronize())
2300 {
2301 // Check if the FG collector wants us to yield.
2302 CMSTokenSync x(true); // is cms thread
2303 if (waitForForegroundGC()) {
2304 // We yielded to a foreground GC, nothing more to be
2305 // done this round.
2306 assert(_foregroundGCShouldWait == false, "We set it to false in "
2307 "waitForForegroundGC()");
2308 if (TraceCMSState) {
2309 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2310 " exiting collection CMS state %d",
2311 Thread::current(), _collectorState);
2312 }
2313 return;
2314 } else {
2315 // The background collector can run but check to see if the
2316 // foreground collector has done a collection while the
2317 // background collector was waiting to get the CGC_lock
2318 // above. If yes, break so that _foregroundGCShouldWait
2319 // is cleared before returning.
2320 if (_collectorState == Idling) {
2321 break;
2322 }
2323 }
2324 }
2326 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2327 "should be waiting");
2329 switch (_collectorState) {
2330 case InitialMarking:
2331 {
2332 ReleaseForegroundGC x(this);
2333 stats().record_cms_begin();
2334 VM_CMS_Initial_Mark initial_mark_op(this);
2335 VMThread::execute(&initial_mark_op);
2336 }
2337 // The collector state may be any legal state at this point
2338 // since the background collector may have yielded to the
2339 // foreground collector.
2340 break;
2341 case Marking:
2342 // initial marking in checkpointRootsInitialWork has been completed
2343 if (markFromRoots(true)) { // we were successful
2344 assert(_collectorState == Precleaning, "Collector state should "
2345 "have changed");
2346 } else {
2347 assert(_foregroundGCIsActive, "Internal state inconsistency");
2348 }
2349 break;
2350 case Precleaning:
2351 if (UseAdaptiveSizePolicy) {
2352 size_policy()->concurrent_precleaning_begin();
2353 }
2354 // marking from roots in markFromRoots has been completed
2355 preclean();
2356 if (UseAdaptiveSizePolicy) {
2357 size_policy()->concurrent_precleaning_end();
2358 }
2359 assert(_collectorState == AbortablePreclean ||
2360 _collectorState == FinalMarking,
2361 "Collector state should have changed");
2362 break;
2363 case AbortablePreclean:
2364 if (UseAdaptiveSizePolicy) {
2365 size_policy()->concurrent_phases_resume();
2366 }
2367 abortable_preclean();
2368 if (UseAdaptiveSizePolicy) {
2369 size_policy()->concurrent_precleaning_end();
2370 }
2371 assert(_collectorState == FinalMarking, "Collector state should "
2372 "have changed");
2373 break;
2374 case FinalMarking:
2375 {
2376 ReleaseForegroundGC x(this);
2378 VM_CMS_Final_Remark final_remark_op(this);
2379 VMThread::execute(&final_remark_op);
2380 }
2381 assert(_foregroundGCShouldWait, "block post-condition");
2382 break;
2383 case Sweeping:
2384 if (UseAdaptiveSizePolicy) {
2385 size_policy()->concurrent_sweeping_begin();
2386 }
2387 // final marking in checkpointRootsFinal has been completed
2388 sweep(true);
2389 assert(_collectorState == Resizing, "Collector state change "
2390 "to Resizing must be done under the free_list_lock");
2391 _full_gcs_since_conc_gc = 0;
2393 // Stop the timers for adaptive size policy for the concurrent phases
2394 if (UseAdaptiveSizePolicy) {
2395 size_policy()->concurrent_sweeping_end();
2396 size_policy()->concurrent_phases_end(gch->gc_cause(),
2397 gch->prev_gen(_cmsGen)->capacity(),
2398 _cmsGen->free());
2399 }
2401 case Resizing: {
2402 // Sweeping has been completed...
2403 // At this point the background collection has completed.
2404 // Don't move the call to compute_new_size() down
2405 // into code that might be executed if the background
2406 // collection was preempted.
2407 {
2408 ReleaseForegroundGC x(this); // unblock FG collection
2409 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2410 CMSTokenSync z(true); // not strictly needed.
2411 if (_collectorState == Resizing) {
2412 compute_new_size();
2413 save_heap_summary();
2414 _collectorState = Resetting;
2415 } else {
2416 assert(_collectorState == Idling, "The state should only change"
2417 " because the foreground collector has finished the collection");
2418 }
2419 }
2420 break;
2421 }
2422 case Resetting:
2423 // CMS heap resizing has been completed
2424 reset(true);
2425 assert(_collectorState == Idling, "Collector state should "
2426 "have changed");
2428 MetaspaceGC::set_should_concurrent_collect(false);
2430 stats().record_cms_end();
2431 // Don't move the concurrent_phases_end() and compute_new_size()
2432 // calls to here because a preempted background collection
2433 // has it's state set to "Resetting".
2434 break;
2435 case Idling:
2436 default:
2437 ShouldNotReachHere();
2438 break;
2439 }
2440 if (TraceCMSState) {
2441 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2442 Thread::current(), _collectorState);
2443 }
2444 assert(_foregroundGCShouldWait, "block post-condition");
2445 }
2447 // Should this be in gc_epilogue?
2448 collector_policy()->counters()->update_counters();
2450 {
2451 // Clear _foregroundGCShouldWait and, in the event that the
2452 // foreground collector is waiting, notify it, before
2453 // returning.
2454 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2455 _foregroundGCShouldWait = false;
2456 if (_foregroundGCIsActive) {
2457 CGC_lock->notify();
2458 }
2459 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2460 "Possible deadlock");
2461 }
2462 if (TraceCMSState) {
2463 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2464 " exiting collection CMS state %d",
2465 Thread::current(), _collectorState);
2466 }
2467 if (PrintGC && Verbose) {
2468 _cmsGen->print_heap_change(prev_used);
2469 }
2470 }
2472 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2473 if (!_cms_start_registered) {
2474 register_gc_start(cause);
2475 }
2476 }
2478 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2479 _cms_start_registered = true;
2480 _gc_timer_cm->register_gc_start();
2481 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2482 }
2484 void CMSCollector::register_gc_end() {
2485 if (_cms_start_registered) {
2486 report_heap_summary(GCWhen::AfterGC);
2488 _gc_timer_cm->register_gc_end();
2489 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2490 _cms_start_registered = false;
2491 }
2492 }
2494 void CMSCollector::save_heap_summary() {
2495 GenCollectedHeap* gch = GenCollectedHeap::heap();
2496 _last_heap_summary = gch->create_heap_summary();
2497 _last_metaspace_summary = gch->create_metaspace_summary();
2498 }
2500 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2501 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
2502 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
2503 }
2505 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2506 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2507 "Foreground collector should be waiting, not executing");
2508 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2509 "may only be done by the VM Thread with the world stopped");
2510 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2511 "VM thread should have CMS token");
2513 // The gc id is created in register_foreground_gc_start if this collection is synchronous
2514 const GCId gc_id = _collectorState == InitialMarking ? GCId::peek() : _gc_tracer_cm->gc_id();
2515 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2516 true, NULL, gc_id);)
2517 if (UseAdaptiveSizePolicy) {
2518 size_policy()->ms_collection_begin();
2519 }
2520 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2522 HandleMark hm; // Discard invalid handles created during verification
2524 if (VerifyBeforeGC &&
2525 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2526 Universe::verify();
2527 }
2529 // Snapshot the soft reference policy to be used in this collection cycle.
2530 ref_processor()->setup_policy(clear_all_soft_refs);
2532 // Decide if class unloading should be done
2533 update_should_unload_classes();
2535 bool init_mark_was_synchronous = false; // until proven otherwise
2536 while (_collectorState != Idling) {
2537 if (TraceCMSState) {
2538 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2539 Thread::current(), _collectorState);
2540 }
2541 switch (_collectorState) {
2542 case InitialMarking:
2543 register_foreground_gc_start(cause);
2544 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2545 checkpointRootsInitial(false);
2546 assert(_collectorState == Marking, "Collector state should have changed"
2547 " within checkpointRootsInitial()");
2548 break;
2549 case Marking:
2550 // initial marking in checkpointRootsInitialWork has been completed
2551 if (VerifyDuringGC &&
2552 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2553 Universe::verify("Verify before initial mark: ");
2554 }
2555 {
2556 bool res = markFromRoots(false);
2557 assert(res && _collectorState == FinalMarking, "Collector state should "
2558 "have changed");
2559 break;
2560 }
2561 case FinalMarking:
2562 if (VerifyDuringGC &&
2563 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2564 Universe::verify("Verify before re-mark: ");
2565 }
2566 checkpointRootsFinal(false, clear_all_soft_refs,
2567 init_mark_was_synchronous);
2568 assert(_collectorState == Sweeping, "Collector state should not "
2569 "have changed within checkpointRootsFinal()");
2570 break;
2571 case Sweeping:
2572 // final marking in checkpointRootsFinal has been completed
2573 if (VerifyDuringGC &&
2574 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2575 Universe::verify("Verify before sweep: ");
2576 }
2577 sweep(false);
2578 assert(_collectorState == Resizing, "Incorrect state");
2579 break;
2580 case Resizing: {
2581 // Sweeping has been completed; the actual resize in this case
2582 // is done separately; nothing to be done in this state.
2583 _collectorState = Resetting;
2584 break;
2585 }
2586 case Resetting:
2587 // The heap has been resized.
2588 if (VerifyDuringGC &&
2589 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2590 Universe::verify("Verify before reset: ");
2591 }
2592 save_heap_summary();
2593 reset(false);
2594 assert(_collectorState == Idling, "Collector state should "
2595 "have changed");
2596 break;
2597 case Precleaning:
2598 case AbortablePreclean:
2599 // Elide the preclean phase
2600 _collectorState = FinalMarking;
2601 break;
2602 default:
2603 ShouldNotReachHere();
2604 }
2605 if (TraceCMSState) {
2606 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2607 Thread::current(), _collectorState);
2608 }
2609 }
2611 if (UseAdaptiveSizePolicy) {
2612 GenCollectedHeap* gch = GenCollectedHeap::heap();
2613 size_policy()->ms_collection_end(gch->gc_cause());
2614 }
2616 if (VerifyAfterGC &&
2617 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2618 Universe::verify();
2619 }
2620 if (TraceCMSState) {
2621 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2622 " exiting collection CMS state %d",
2623 Thread::current(), _collectorState);
2624 }
2625 }
2627 bool CMSCollector::waitForForegroundGC() {
2628 bool res = false;
2629 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2630 "CMS thread should have CMS token");
2631 // Block the foreground collector until the
2632 // background collectors decides whether to
2633 // yield.
2634 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2635 _foregroundGCShouldWait = true;
2636 if (_foregroundGCIsActive) {
2637 // The background collector yields to the
2638 // foreground collector and returns a value
2639 // indicating that it has yielded. The foreground
2640 // collector can proceed.
2641 res = true;
2642 _foregroundGCShouldWait = false;
2643 ConcurrentMarkSweepThread::clear_CMS_flag(
2644 ConcurrentMarkSweepThread::CMS_cms_has_token);
2645 ConcurrentMarkSweepThread::set_CMS_flag(
2646 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2647 // Get a possibly blocked foreground thread going
2648 CGC_lock->notify();
2649 if (TraceCMSState) {
2650 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2651 Thread::current(), _collectorState);
2652 }
2653 while (_foregroundGCIsActive) {
2654 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2655 }
2656 ConcurrentMarkSweepThread::set_CMS_flag(
2657 ConcurrentMarkSweepThread::CMS_cms_has_token);
2658 ConcurrentMarkSweepThread::clear_CMS_flag(
2659 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2660 }
2661 if (TraceCMSState) {
2662 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2663 Thread::current(), _collectorState);
2664 }
2665 return res;
2666 }
2668 // Because of the need to lock the free lists and other structures in
2669 // the collector, common to all the generations that the collector is
2670 // collecting, we need the gc_prologues of individual CMS generations
2671 // delegate to their collector. It may have been simpler had the
2672 // current infrastructure allowed one to call a prologue on a
2673 // collector. In the absence of that we have the generation's
2674 // prologue delegate to the collector, which delegates back
2675 // some "local" work to a worker method in the individual generations
2676 // that it's responsible for collecting, while itself doing any
2677 // work common to all generations it's responsible for. A similar
2678 // comment applies to the gc_epilogue()'s.
2679 // The role of the varaible _between_prologue_and_epilogue is to
2680 // enforce the invocation protocol.
2681 void CMSCollector::gc_prologue(bool full) {
2682 // Call gc_prologue_work() for the CMSGen
2683 // we are responsible for.
2685 // The following locking discipline assumes that we are only called
2686 // when the world is stopped.
2687 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2689 // The CMSCollector prologue must call the gc_prologues for the
2690 // "generations" that it's responsible
2691 // for.
2693 assert( Thread::current()->is_VM_thread()
2694 || ( CMSScavengeBeforeRemark
2695 && Thread::current()->is_ConcurrentGC_thread()),
2696 "Incorrect thread type for prologue execution");
2698 if (_between_prologue_and_epilogue) {
2699 // We have already been invoked; this is a gc_prologue delegation
2700 // from yet another CMS generation that we are responsible for, just
2701 // ignore it since all relevant work has already been done.
2702 return;
2703 }
2705 // set a bit saying prologue has been called; cleared in epilogue
2706 _between_prologue_and_epilogue = true;
2707 // Claim locks for common data structures, then call gc_prologue_work()
2708 // for each CMSGen.
2710 getFreelistLocks(); // gets free list locks on constituent spaces
2711 bitMapLock()->lock_without_safepoint_check();
2713 // Should call gc_prologue_work() for all cms gens we are responsible for
2714 bool duringMarking = _collectorState >= Marking
2715 && _collectorState < Sweeping;
2717 // The young collections clear the modified oops state, which tells if
2718 // there are any modified oops in the class. The remark phase also needs
2719 // that information. Tell the young collection to save the union of all
2720 // modified klasses.
2721 if (duringMarking) {
2722 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2723 }
2725 bool registerClosure = duringMarking;
2727 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2728 &_modUnionClosurePar
2729 : &_modUnionClosure;
2730 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2732 if (!full) {
2733 stats().record_gc0_begin();
2734 }
2735 }
2737 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2739 _capacity_at_prologue = capacity();
2740 _used_at_prologue = used();
2742 // Delegate to CMScollector which knows how to coordinate between
2743 // this and any other CMS generations that it is responsible for
2744 // collecting.
2745 collector()->gc_prologue(full);
2746 }
2748 // This is a "private" interface for use by this generation's CMSCollector.
2749 // Not to be called directly by any other entity (for instance,
2750 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2751 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2752 bool registerClosure, ModUnionClosure* modUnionClosure) {
2753 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2754 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2755 "Should be NULL");
2756 if (registerClosure) {
2757 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2758 }
2759 cmsSpace()->gc_prologue();
2760 // Clear stat counters
2761 NOT_PRODUCT(
2762 assert(_numObjectsPromoted == 0, "check");
2763 assert(_numWordsPromoted == 0, "check");
2764 if (Verbose && PrintGC) {
2765 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2766 SIZE_FORMAT" bytes concurrently",
2767 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2768 }
2769 _numObjectsAllocated = 0;
2770 _numWordsAllocated = 0;
2771 )
2772 }
2774 void CMSCollector::gc_epilogue(bool full) {
2775 // The following locking discipline assumes that we are only called
2776 // when the world is stopped.
2777 assert(SafepointSynchronize::is_at_safepoint(),
2778 "world is stopped assumption");
2780 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2781 // if linear allocation blocks need to be appropriately marked to allow the
2782 // the blocks to be parsable. We also check here whether we need to nudge the
2783 // CMS collector thread to start a new cycle (if it's not already active).
2784 assert( Thread::current()->is_VM_thread()
2785 || ( CMSScavengeBeforeRemark
2786 && Thread::current()->is_ConcurrentGC_thread()),
2787 "Incorrect thread type for epilogue execution");
2789 if (!_between_prologue_and_epilogue) {
2790 // We have already been invoked; this is a gc_epilogue delegation
2791 // from yet another CMS generation that we are responsible for, just
2792 // ignore it since all relevant work has already been done.
2793 return;
2794 }
2795 assert(haveFreelistLocks(), "must have freelist locks");
2796 assert_lock_strong(bitMapLock());
2798 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2800 _cmsGen->gc_epilogue_work(full);
2802 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2803 // in case sampling was not already enabled, enable it
2804 _start_sampling = true;
2805 }
2806 // reset _eden_chunk_array so sampling starts afresh
2807 _eden_chunk_index = 0;
2809 size_t cms_used = _cmsGen->cmsSpace()->used();
2811 // update performance counters - this uses a special version of
2812 // update_counters() that allows the utilization to be passed as a
2813 // parameter, avoiding multiple calls to used().
2814 //
2815 _cmsGen->update_counters(cms_used);
2817 if (CMSIncrementalMode) {
2818 icms_update_allocation_limits();
2819 }
2821 bitMapLock()->unlock();
2822 releaseFreelistLocks();
2824 if (!CleanChunkPoolAsync) {
2825 Chunk::clean_chunk_pool();
2826 }
2828 set_did_compact(false);
2829 _between_prologue_and_epilogue = false; // ready for next cycle
2830 }
2832 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2833 collector()->gc_epilogue(full);
2835 // Also reset promotion tracking in par gc thread states.
2836 if (CollectedHeap::use_parallel_gc_threads()) {
2837 for (uint i = 0; i < ParallelGCThreads; i++) {
2838 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2839 }
2840 }
2841 }
2843 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2844 assert(!incremental_collection_failed(), "Should have been cleared");
2845 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2846 cmsSpace()->gc_epilogue();
2847 // Print stat counters
2848 NOT_PRODUCT(
2849 assert(_numObjectsAllocated == 0, "check");
2850 assert(_numWordsAllocated == 0, "check");
2851 if (Verbose && PrintGC) {
2852 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2853 SIZE_FORMAT" bytes",
2854 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2855 }
2856 _numObjectsPromoted = 0;
2857 _numWordsPromoted = 0;
2858 )
2860 if (PrintGC && Verbose) {
2861 // Call down the chain in contiguous_available needs the freelistLock
2862 // so print this out before releasing the freeListLock.
2863 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2864 contiguous_available());
2865 }
2866 }
2868 #ifndef PRODUCT
2869 bool CMSCollector::have_cms_token() {
2870 Thread* thr = Thread::current();
2871 if (thr->is_VM_thread()) {
2872 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2873 } else if (thr->is_ConcurrentGC_thread()) {
2874 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2875 } else if (thr->is_GC_task_thread()) {
2876 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2877 ParGCRareEvent_lock->owned_by_self();
2878 }
2879 return false;
2880 }
2881 #endif
2883 // Check reachability of the given heap address in CMS generation,
2884 // treating all other generations as roots.
2885 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2886 // We could "guarantee" below, rather than assert, but i'll
2887 // leave these as "asserts" so that an adventurous debugger
2888 // could try this in the product build provided some subset of
2889 // the conditions were met, provided they were intersted in the
2890 // results and knew that the computation below wouldn't interfere
2891 // with other concurrent computations mutating the structures
2892 // being read or written.
2893 assert(SafepointSynchronize::is_at_safepoint(),
2894 "Else mutations in object graph will make answer suspect");
2895 assert(have_cms_token(), "Should hold cms token");
2896 assert(haveFreelistLocks(), "must hold free list locks");
2897 assert_lock_strong(bitMapLock());
2899 // Clear the marking bit map array before starting, but, just
2900 // for kicks, first report if the given address is already marked
2901 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2902 _markBitMap.isMarked(addr) ? "" : " not");
2904 if (verify_after_remark()) {
2905 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2906 bool result = verification_mark_bm()->isMarked(addr);
2907 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2908 result ? "IS" : "is NOT");
2909 return result;
2910 } else {
2911 gclog_or_tty->print_cr("Could not compute result");
2912 return false;
2913 }
2914 }
2917 void
2918 CMSCollector::print_on_error(outputStream* st) {
2919 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2920 if (collector != NULL) {
2921 CMSBitMap* bitmap = &collector->_markBitMap;
2922 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, bitmap);
2923 bitmap->print_on_error(st, " Bits: ");
2925 st->cr();
2927 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2928 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, mut_bitmap);
2929 mut_bitmap->print_on_error(st, " Bits: ");
2930 }
2931 }
2933 ////////////////////////////////////////////////////////
2934 // CMS Verification Support
2935 ////////////////////////////////////////////////////////
2936 // Following the remark phase, the following invariant
2937 // should hold -- each object in the CMS heap which is
2938 // marked in markBitMap() should be marked in the verification_mark_bm().
2940 class VerifyMarkedClosure: public BitMapClosure {
2941 CMSBitMap* _marks;
2942 bool _failed;
2944 public:
2945 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2947 bool do_bit(size_t offset) {
2948 HeapWord* addr = _marks->offsetToHeapWord(offset);
2949 if (!_marks->isMarked(addr)) {
2950 oop(addr)->print_on(gclog_or_tty);
2951 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2952 _failed = true;
2953 }
2954 return true;
2955 }
2957 bool failed() { return _failed; }
2958 };
2960 bool CMSCollector::verify_after_remark(bool silent) {
2961 if (!silent) gclog_or_tty->print(" [Verifying CMS Marking... ");
2962 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2963 static bool init = false;
2965 assert(SafepointSynchronize::is_at_safepoint(),
2966 "Else mutations in object graph will make answer suspect");
2967 assert(have_cms_token(),
2968 "Else there may be mutual interference in use of "
2969 " verification data structures");
2970 assert(_collectorState > Marking && _collectorState <= Sweeping,
2971 "Else marking info checked here may be obsolete");
2972 assert(haveFreelistLocks(), "must hold free list locks");
2973 assert_lock_strong(bitMapLock());
2976 // Allocate marking bit map if not already allocated
2977 if (!init) { // first time
2978 if (!verification_mark_bm()->allocate(_span)) {
2979 return false;
2980 }
2981 init = true;
2982 }
2984 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2986 // Turn off refs discovery -- so we will be tracing through refs.
2987 // This is as intended, because by this time
2988 // GC must already have cleared any refs that need to be cleared,
2989 // and traced those that need to be marked; moreover,
2990 // the marking done here is not going to intefere in any
2991 // way with the marking information used by GC.
2992 NoRefDiscovery no_discovery(ref_processor());
2994 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2996 // Clear any marks from a previous round
2997 verification_mark_bm()->clear_all();
2998 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2999 verify_work_stacks_empty();
3001 GenCollectedHeap* gch = GenCollectedHeap::heap();
3002 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3003 // Update the saved marks which may affect the root scans.
3004 gch->save_marks();
3006 if (CMSRemarkVerifyVariant == 1) {
3007 // In this first variant of verification, we complete
3008 // all marking, then check if the new marks-verctor is
3009 // a subset of the CMS marks-vector.
3010 verify_after_remark_work_1();
3011 } else if (CMSRemarkVerifyVariant == 2) {
3012 // In this second variant of verification, we flag an error
3013 // (i.e. an object reachable in the new marks-vector not reachable
3014 // in the CMS marks-vector) immediately, also indicating the
3015 // identify of an object (A) that references the unmarked object (B) --
3016 // presumably, a mutation to A failed to be picked up by preclean/remark?
3017 verify_after_remark_work_2();
3018 } else {
3019 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
3020 CMSRemarkVerifyVariant);
3021 }
3022 if (!silent) gclog_or_tty->print(" done] ");
3023 return true;
3024 }
3026 void CMSCollector::verify_after_remark_work_1() {
3027 ResourceMark rm;
3028 HandleMark hm;
3029 GenCollectedHeap* gch = GenCollectedHeap::heap();
3031 // Get a clear set of claim bits for the roots processing to work with.
3032 ClassLoaderDataGraph::clear_claimed_marks();
3034 // Mark from roots one level into CMS
3035 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
3036 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3038 gch->gen_process_roots(_cmsGen->level(),
3039 true, // younger gens are roots
3040 true, // activate StrongRootsScope
3041 SharedHeap::ScanningOption(roots_scanning_options()),
3042 should_unload_classes(),
3043 ¬Older,
3044 NULL,
3045 NULL); // SSS: Provide correct closure
3047 // Now mark from the roots
3048 MarkFromRootsClosure markFromRootsClosure(this, _span,
3049 verification_mark_bm(), verification_mark_stack(),
3050 false /* don't yield */, true /* verifying */);
3051 assert(_restart_addr == NULL, "Expected pre-condition");
3052 verification_mark_bm()->iterate(&markFromRootsClosure);
3053 while (_restart_addr != NULL) {
3054 // Deal with stack overflow: by restarting at the indicated
3055 // address.
3056 HeapWord* ra = _restart_addr;
3057 markFromRootsClosure.reset(ra);
3058 _restart_addr = NULL;
3059 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3060 }
3061 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3062 verify_work_stacks_empty();
3064 // Marking completed -- now verify that each bit marked in
3065 // verification_mark_bm() is also marked in markBitMap(); flag all
3066 // errors by printing corresponding objects.
3067 VerifyMarkedClosure vcl(markBitMap());
3068 verification_mark_bm()->iterate(&vcl);
3069 if (vcl.failed()) {
3070 gclog_or_tty->print("Verification failed");
3071 Universe::heap()->print_on(gclog_or_tty);
3072 fatal("CMS: failed marking verification after remark");
3073 }
3074 }
3076 class VerifyKlassOopsKlassClosure : public KlassClosure {
3077 class VerifyKlassOopsClosure : public OopClosure {
3078 CMSBitMap* _bitmap;
3079 public:
3080 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
3081 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
3082 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
3083 } _oop_closure;
3084 public:
3085 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
3086 void do_klass(Klass* k) {
3087 k->oops_do(&_oop_closure);
3088 }
3089 };
3091 void CMSCollector::verify_after_remark_work_2() {
3092 ResourceMark rm;
3093 HandleMark hm;
3094 GenCollectedHeap* gch = GenCollectedHeap::heap();
3096 // Get a clear set of claim bits for the roots processing to work with.
3097 ClassLoaderDataGraph::clear_claimed_marks();
3099 // Mark from roots one level into CMS
3100 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3101 markBitMap());
3102 CLDToOopClosure cld_closure(¬Older, true);
3104 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3106 gch->gen_process_roots(_cmsGen->level(),
3107 true, // younger gens are roots
3108 true, // activate StrongRootsScope
3109 SharedHeap::ScanningOption(roots_scanning_options()),
3110 should_unload_classes(),
3111 ¬Older,
3112 NULL,
3113 &cld_closure);
3115 // Now mark from the roots
3116 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3117 verification_mark_bm(), markBitMap(), verification_mark_stack());
3118 assert(_restart_addr == NULL, "Expected pre-condition");
3119 verification_mark_bm()->iterate(&markFromRootsClosure);
3120 while (_restart_addr != NULL) {
3121 // Deal with stack overflow: by restarting at the indicated
3122 // address.
3123 HeapWord* ra = _restart_addr;
3124 markFromRootsClosure.reset(ra);
3125 _restart_addr = NULL;
3126 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3127 }
3128 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3129 verify_work_stacks_empty();
3131 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
3132 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
3134 // Marking completed -- now verify that each bit marked in
3135 // verification_mark_bm() is also marked in markBitMap(); flag all
3136 // errors by printing corresponding objects.
3137 VerifyMarkedClosure vcl(markBitMap());
3138 verification_mark_bm()->iterate(&vcl);
3139 assert(!vcl.failed(), "Else verification above should not have succeeded");
3140 }
3142 void ConcurrentMarkSweepGeneration::save_marks() {
3143 // delegate to CMS space
3144 cmsSpace()->save_marks();
3145 for (uint i = 0; i < ParallelGCThreads; i++) {
3146 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3147 }
3148 }
3150 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3151 return cmsSpace()->no_allocs_since_save_marks();
3152 }
3154 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3155 \
3156 void ConcurrentMarkSweepGeneration:: \
3157 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3158 cl->set_generation(this); \
3159 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3160 cl->reset_generation(); \
3161 save_marks(); \
3162 }
3164 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3166 void
3167 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3168 cl->set_generation(this);
3169 younger_refs_in_space_iterate(_cmsSpace, cl);
3170 cl->reset_generation();
3171 }
3173 void
3174 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3175 if (freelistLock()->owned_by_self()) {
3176 Generation::oop_iterate(cl);
3177 } else {
3178 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3179 Generation::oop_iterate(cl);
3180 }
3181 }
3183 void
3184 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3185 if (freelistLock()->owned_by_self()) {
3186 Generation::object_iterate(cl);
3187 } else {
3188 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3189 Generation::object_iterate(cl);
3190 }
3191 }
3193 void
3194 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3195 if (freelistLock()->owned_by_self()) {
3196 Generation::safe_object_iterate(cl);
3197 } else {
3198 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3199 Generation::safe_object_iterate(cl);
3200 }
3201 }
3203 void
3204 ConcurrentMarkSweepGeneration::post_compact() {
3205 }
3207 void
3208 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3209 // Fix the linear allocation blocks to look like free blocks.
3211 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3212 // are not called when the heap is verified during universe initialization and
3213 // at vm shutdown.
3214 if (freelistLock()->owned_by_self()) {
3215 cmsSpace()->prepare_for_verify();
3216 } else {
3217 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3218 cmsSpace()->prepare_for_verify();
3219 }
3220 }
3222 void
3223 ConcurrentMarkSweepGeneration::verify() {
3224 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3225 // are not called when the heap is verified during universe initialization and
3226 // at vm shutdown.
3227 if (freelistLock()->owned_by_self()) {
3228 cmsSpace()->verify();
3229 } else {
3230 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3231 cmsSpace()->verify();
3232 }
3233 }
3235 void CMSCollector::verify() {
3236 _cmsGen->verify();
3237 }
3239 #ifndef PRODUCT
3240 bool CMSCollector::overflow_list_is_empty() const {
3241 assert(_num_par_pushes >= 0, "Inconsistency");
3242 if (_overflow_list == NULL) {
3243 assert(_num_par_pushes == 0, "Inconsistency");
3244 }
3245 return _overflow_list == NULL;
3246 }
3248 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3249 // merely consolidate assertion checks that appear to occur together frequently.
3250 void CMSCollector::verify_work_stacks_empty() const {
3251 assert(_markStack.isEmpty(), "Marking stack should be empty");
3252 assert(overflow_list_is_empty(), "Overflow list should be empty");
3253 }
3255 void CMSCollector::verify_overflow_empty() const {
3256 assert(overflow_list_is_empty(), "Overflow list should be empty");
3257 assert(no_preserved_marks(), "No preserved marks");
3258 }
3259 #endif // PRODUCT
3261 // Decide if we want to enable class unloading as part of the
3262 // ensuing concurrent GC cycle. We will collect and
3263 // unload classes if it's the case that:
3264 // (1) an explicit gc request has been made and the flag
3265 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3266 // (2) (a) class unloading is enabled at the command line, and
3267 // (b) old gen is getting really full
3268 // NOTE: Provided there is no change in the state of the heap between
3269 // calls to this method, it should have idempotent results. Moreover,
3270 // its results should be monotonically increasing (i.e. going from 0 to 1,
3271 // but not 1 to 0) between successive calls between which the heap was
3272 // not collected. For the implementation below, it must thus rely on
3273 // the property that concurrent_cycles_since_last_unload()
3274 // will not decrease unless a collection cycle happened and that
3275 // _cmsGen->is_too_full() are
3276 // themselves also monotonic in that sense. See check_monotonicity()
3277 // below.
3278 void CMSCollector::update_should_unload_classes() {
3279 _should_unload_classes = false;
3280 // Condition 1 above
3281 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3282 _should_unload_classes = true;
3283 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3284 // Disjuncts 2.b.(i,ii,iii) above
3285 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3286 CMSClassUnloadingMaxInterval)
3287 || _cmsGen->is_too_full();
3288 }
3289 }
3291 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3292 bool res = should_concurrent_collect();
3293 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3294 return res;
3295 }
3297 void CMSCollector::setup_cms_unloading_and_verification_state() {
3298 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3299 || VerifyBeforeExit;
3300 const int rso = SharedHeap::SO_AllCodeCache;
3302 // We set the proper root for this CMS cycle here.
3303 if (should_unload_classes()) { // Should unload classes this cycle
3304 remove_root_scanning_option(rso); // Shrink the root set appropriately
3305 set_verifying(should_verify); // Set verification state for this cycle
3306 return; // Nothing else needs to be done at this time
3307 }
3309 // Not unloading classes this cycle
3310 assert(!should_unload_classes(), "Inconsitency!");
3312 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3313 // Include symbols, strings and code cache elements to prevent their resurrection.
3314 add_root_scanning_option(rso);
3315 set_verifying(true);
3316 } else if (verifying() && !should_verify) {
3317 // We were verifying, but some verification flags got disabled.
3318 set_verifying(false);
3319 // Exclude symbols, strings and code cache elements from root scanning to
3320 // reduce IM and RM pauses.
3321 remove_root_scanning_option(rso);
3322 }
3323 }
3326 #ifndef PRODUCT
3327 HeapWord* CMSCollector::block_start(const void* p) const {
3328 const HeapWord* addr = (HeapWord*)p;
3329 if (_span.contains(p)) {
3330 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3331 return _cmsGen->cmsSpace()->block_start(p);
3332 }
3333 }
3334 return NULL;
3335 }
3336 #endif
3338 HeapWord*
3339 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3340 bool tlab,
3341 bool parallel) {
3342 CMSSynchronousYieldRequest yr;
3343 assert(!tlab, "Can't deal with TLAB allocation");
3344 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3345 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3346 CMSExpansionCause::_satisfy_allocation);
3347 if (GCExpandToAllocateDelayMillis > 0) {
3348 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3349 }
3350 return have_lock_and_allocate(word_size, tlab);
3351 }
3353 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3354 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3355 // to CardGeneration and share it...
3356 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3357 return CardGeneration::expand(bytes, expand_bytes);
3358 }
3360 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3361 CMSExpansionCause::Cause cause)
3362 {
3364 bool success = expand(bytes, expand_bytes);
3366 // remember why we expanded; this information is used
3367 // by shouldConcurrentCollect() when making decisions on whether to start
3368 // a new CMS cycle.
3369 if (success) {
3370 set_expansion_cause(cause);
3371 if (PrintGCDetails && Verbose) {
3372 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3373 CMSExpansionCause::to_string(cause));
3374 }
3375 }
3376 }
3378 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3379 HeapWord* res = NULL;
3380 MutexLocker x(ParGCRareEvent_lock);
3381 while (true) {
3382 // Expansion by some other thread might make alloc OK now:
3383 res = ps->lab.alloc(word_sz);
3384 if (res != NULL) return res;
3385 // If there's not enough expansion space available, give up.
3386 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3387 return NULL;
3388 }
3389 // Otherwise, we try expansion.
3390 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3391 CMSExpansionCause::_allocate_par_lab);
3392 // Now go around the loop and try alloc again;
3393 // A competing par_promote might beat us to the expansion space,
3394 // so we may go around the loop again if promotion fails agaion.
3395 if (GCExpandToAllocateDelayMillis > 0) {
3396 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3397 }
3398 }
3399 }
3402 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3403 PromotionInfo* promo) {
3404 MutexLocker x(ParGCRareEvent_lock);
3405 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3406 while (true) {
3407 // Expansion by some other thread might make alloc OK now:
3408 if (promo->ensure_spooling_space()) {
3409 assert(promo->has_spooling_space(),
3410 "Post-condition of successful ensure_spooling_space()");
3411 return true;
3412 }
3413 // If there's not enough expansion space available, give up.
3414 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3415 return false;
3416 }
3417 // Otherwise, we try expansion.
3418 expand(refill_size_bytes, MinHeapDeltaBytes,
3419 CMSExpansionCause::_allocate_par_spooling_space);
3420 // Now go around the loop and try alloc again;
3421 // A competing allocation might beat us to the expansion space,
3422 // so we may go around the loop again if allocation fails again.
3423 if (GCExpandToAllocateDelayMillis > 0) {
3424 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3425 }
3426 }
3427 }
3430 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3431 assert_locked_or_safepoint(ExpandHeap_lock);
3432 // Shrink committed space
3433 _virtual_space.shrink_by(bytes);
3434 // Shrink space; this also shrinks the space's BOT
3435 _cmsSpace->set_end((HeapWord*) _virtual_space.high());
3436 size_t new_word_size = heap_word_size(_cmsSpace->capacity());
3437 // Shrink the shared block offset array
3438 _bts->resize(new_word_size);
3439 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3440 // Shrink the card table
3441 Universe::heap()->barrier_set()->resize_covered_region(mr);
3443 if (Verbose && PrintGC) {
3444 size_t new_mem_size = _virtual_space.committed_size();
3445 size_t old_mem_size = new_mem_size + bytes;
3446 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3447 name(), old_mem_size/K, new_mem_size/K);
3448 }
3449 }
3451 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3452 assert_locked_or_safepoint(Heap_lock);
3453 size_t size = ReservedSpace::page_align_size_down(bytes);
3454 // Only shrink if a compaction was done so that all the free space
3455 // in the generation is in a contiguous block at the end.
3456 if (size > 0 && did_compact()) {
3457 shrink_by(size);
3458 }
3459 }
3461 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3462 assert_locked_or_safepoint(Heap_lock);
3463 bool result = _virtual_space.expand_by(bytes);
3464 if (result) {
3465 size_t new_word_size =
3466 heap_word_size(_virtual_space.committed_size());
3467 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3468 _bts->resize(new_word_size); // resize the block offset shared array
3469 Universe::heap()->barrier_set()->resize_covered_region(mr);
3470 // Hmmmm... why doesn't CFLS::set_end verify locking?
3471 // This is quite ugly; FIX ME XXX
3472 _cmsSpace->assert_locked(freelistLock());
3473 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3475 // update the space and generation capacity counters
3476 if (UsePerfData) {
3477 _space_counters->update_capacity();
3478 _gen_counters->update_all();
3479 }
3481 if (Verbose && PrintGC) {
3482 size_t new_mem_size = _virtual_space.committed_size();
3483 size_t old_mem_size = new_mem_size - bytes;
3484 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3485 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3486 }
3487 }
3488 return result;
3489 }
3491 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3492 assert_locked_or_safepoint(Heap_lock);
3493 bool success = true;
3494 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3495 if (remaining_bytes > 0) {
3496 success = grow_by(remaining_bytes);
3497 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3498 }
3499 return success;
3500 }
3502 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
3503 assert_locked_or_safepoint(Heap_lock);
3504 assert_lock_strong(freelistLock());
3505 if (PrintGCDetails && Verbose) {
3506 warning("Shrinking of CMS not yet implemented");
3507 }
3508 return;
3509 }
3512 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3513 // phases.
3514 class CMSPhaseAccounting: public StackObj {
3515 public:
3516 CMSPhaseAccounting(CMSCollector *collector,
3517 const char *phase,
3518 const GCId gc_id,
3519 bool print_cr = true);
3520 ~CMSPhaseAccounting();
3522 private:
3523 CMSCollector *_collector;
3524 const char *_phase;
3525 elapsedTimer _wallclock;
3526 bool _print_cr;
3527 const GCId _gc_id;
3529 public:
3530 // Not MT-safe; so do not pass around these StackObj's
3531 // where they may be accessed by other threads.
3532 jlong wallclock_millis() {
3533 assert(_wallclock.is_active(), "Wall clock should not stop");
3534 _wallclock.stop(); // to record time
3535 jlong ret = _wallclock.milliseconds();
3536 _wallclock.start(); // restart
3537 return ret;
3538 }
3539 };
3541 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3542 const char *phase,
3543 const GCId gc_id,
3544 bool print_cr) :
3545 _collector(collector), _phase(phase), _print_cr(print_cr), _gc_id(gc_id) {
3547 if (PrintCMSStatistics != 0) {
3548 _collector->resetYields();
3549 }
3550 if (PrintGCDetails) {
3551 gclog_or_tty->gclog_stamp(_gc_id);
3552 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3553 _collector->cmsGen()->short_name(), _phase);
3554 }
3555 _collector->resetTimer();
3556 _wallclock.start();
3557 _collector->startTimer();
3558 }
3560 CMSPhaseAccounting::~CMSPhaseAccounting() {
3561 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3562 _collector->stopTimer();
3563 _wallclock.stop();
3564 if (PrintGCDetails) {
3565 gclog_or_tty->gclog_stamp(_gc_id);
3566 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3567 _collector->cmsGen()->short_name(),
3568 _phase, _collector->timerValue(), _wallclock.seconds());
3569 if (_print_cr) {
3570 gclog_or_tty->cr();
3571 }
3572 if (PrintCMSStatistics != 0) {
3573 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3574 _collector->yields());
3575 }
3576 }
3577 }
3579 // CMS work
3581 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
3582 class CMSParMarkTask : public AbstractGangTask {
3583 protected:
3584 CMSCollector* _collector;
3585 int _n_workers;
3586 CMSParMarkTask(const char* name, CMSCollector* collector, int n_workers) :
3587 AbstractGangTask(name),
3588 _collector(collector),
3589 _n_workers(n_workers) {}
3590 // Work method in support of parallel rescan ... of young gen spaces
3591 void do_young_space_rescan(uint worker_id, OopsInGenClosure* cl,
3592 ContiguousSpace* space,
3593 HeapWord** chunk_array, size_t chunk_top);
3594 void work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl);
3595 };
3597 // Parallel initial mark task
3598 class CMSParInitialMarkTask: public CMSParMarkTask {
3599 public:
3600 CMSParInitialMarkTask(CMSCollector* collector, int n_workers) :
3601 CMSParMarkTask("Scan roots and young gen for initial mark in parallel",
3602 collector, n_workers) {}
3603 void work(uint worker_id);
3604 };
3606 // Checkpoint the roots into this generation from outside
3607 // this generation. [Note this initial checkpoint need only
3608 // be approximate -- we'll do a catch up phase subsequently.]
3609 void CMSCollector::checkpointRootsInitial(bool asynch) {
3610 assert(_collectorState == InitialMarking, "Wrong collector state");
3611 check_correct_thread_executing();
3612 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3614 save_heap_summary();
3615 report_heap_summary(GCWhen::BeforeGC);
3617 ReferenceProcessor* rp = ref_processor();
3618 SpecializationStats::clear();
3619 assert(_restart_addr == NULL, "Control point invariant");
3620 if (asynch) {
3621 // acquire locks for subsequent manipulations
3622 MutexLockerEx x(bitMapLock(),
3623 Mutex::_no_safepoint_check_flag);
3624 checkpointRootsInitialWork(asynch);
3625 // enable ("weak") refs discovery
3626 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3627 _collectorState = Marking;
3628 } else {
3629 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3630 // which recognizes if we are a CMS generation, and doesn't try to turn on
3631 // discovery; verify that they aren't meddling.
3632 assert(!rp->discovery_is_atomic(),
3633 "incorrect setting of discovery predicate");
3634 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3635 "ref discovery for this generation kind");
3636 // already have locks
3637 checkpointRootsInitialWork(asynch);
3638 // now enable ("weak") refs discovery
3639 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3640 _collectorState = Marking;
3641 }
3642 SpecializationStats::print();
3643 }
3645 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3646 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3647 assert(_collectorState == InitialMarking, "just checking");
3649 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3650 // precede our marking with a collection of all
3651 // younger generations to keep floating garbage to a minimum.
3652 // XXX: we won't do this for now -- it's an optimization to be done later.
3654 // already have locks
3655 assert_lock_strong(bitMapLock());
3656 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3658 // Setup the verification and class unloading state for this
3659 // CMS collection cycle.
3660 setup_cms_unloading_and_verification_state();
3662 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3663 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
3664 if (UseAdaptiveSizePolicy) {
3665 size_policy()->checkpoint_roots_initial_begin();
3666 }
3668 // Reset all the PLAB chunk arrays if necessary.
3669 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3670 reset_survivor_plab_arrays();
3671 }
3673 ResourceMark rm;
3674 HandleMark hm;
3676 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3677 GenCollectedHeap* gch = GenCollectedHeap::heap();
3679 verify_work_stacks_empty();
3680 verify_overflow_empty();
3682 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3683 // Update the saved marks which may affect the root scans.
3684 gch->save_marks();
3686 // weak reference processing has not started yet.
3687 ref_processor()->set_enqueuing_is_done(false);
3689 // Need to remember all newly created CLDs,
3690 // so that we can guarantee that the remark finds them.
3691 ClassLoaderDataGraph::remember_new_clds(true);
3693 // Whenever a CLD is found, it will be claimed before proceeding to mark
3694 // the klasses. The claimed marks need to be cleared before marking starts.
3695 ClassLoaderDataGraph::clear_claimed_marks();
3697 if (CMSPrintEdenSurvivorChunks) {
3698 print_eden_and_survivor_chunk_arrays();
3699 }
3701 {
3702 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3703 if (CMSParallelInitialMarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
3704 // The parallel version.
3705 FlexibleWorkGang* workers = gch->workers();
3706 assert(workers != NULL, "Need parallel worker threads.");
3707 int n_workers = workers->active_workers();
3708 CMSParInitialMarkTask tsk(this, n_workers);
3709 gch->set_par_threads(n_workers);
3710 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
3711 if (n_workers > 1) {
3712 GenCollectedHeap::StrongRootsScope srs(gch);
3713 workers->run_task(&tsk);
3714 } else {
3715 GenCollectedHeap::StrongRootsScope srs(gch);
3716 tsk.work(0);
3717 }
3718 gch->set_par_threads(0);
3719 } else {
3720 // The serial version.
3721 CLDToOopClosure cld_closure(¬Older, true);
3722 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3723 gch->gen_process_roots(_cmsGen->level(),
3724 true, // younger gens are roots
3725 true, // activate StrongRootsScope
3726 SharedHeap::ScanningOption(roots_scanning_options()),
3727 should_unload_classes(),
3728 ¬Older,
3729 NULL,
3730 &cld_closure);
3731 }
3732 }
3734 // Clear mod-union table; it will be dirtied in the prologue of
3735 // CMS generation per each younger generation collection.
3737 assert(_modUnionTable.isAllClear(),
3738 "Was cleared in most recent final checkpoint phase"
3739 " or no bits are set in the gc_prologue before the start of the next "
3740 "subsequent marking phase.");
3742 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3744 // Save the end of the used_region of the constituent generations
3745 // to be used to limit the extent of sweep in each generation.
3746 save_sweep_limits();
3747 if (UseAdaptiveSizePolicy) {
3748 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3749 }
3750 verify_overflow_empty();
3751 }
3753 bool CMSCollector::markFromRoots(bool asynch) {
3754 // we might be tempted to assert that:
3755 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3756 // "inconsistent argument?");
3757 // However that wouldn't be right, because it's possible that
3758 // a safepoint is indeed in progress as a younger generation
3759 // stop-the-world GC happens even as we mark in this generation.
3760 assert(_collectorState == Marking, "inconsistent state?");
3761 check_correct_thread_executing();
3762 verify_overflow_empty();
3764 bool res;
3765 if (asynch) {
3767 // Start the timers for adaptive size policy for the concurrent phases
3768 // Do it here so that the foreground MS can use the concurrent
3769 // timer since a foreground MS might has the sweep done concurrently
3770 // or STW.
3771 if (UseAdaptiveSizePolicy) {
3772 size_policy()->concurrent_marking_begin();
3773 }
3775 // Weak ref discovery note: We may be discovering weak
3776 // refs in this generation concurrent (but interleaved) with
3777 // weak ref discovery by a younger generation collector.
3779 CMSTokenSyncWithLocks ts(true, bitMapLock());
3780 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3781 CMSPhaseAccounting pa(this, "mark", _gc_tracer_cm->gc_id(), !PrintGCDetails);
3782 res = markFromRootsWork(asynch);
3783 if (res) {
3784 _collectorState = Precleaning;
3785 } else { // We failed and a foreground collection wants to take over
3786 assert(_foregroundGCIsActive, "internal state inconsistency");
3787 assert(_restart_addr == NULL, "foreground will restart from scratch");
3788 if (PrintGCDetails) {
3789 gclog_or_tty->print_cr("bailing out to foreground collection");
3790 }
3791 }
3792 if (UseAdaptiveSizePolicy) {
3793 size_policy()->concurrent_marking_end();
3794 }
3795 } else {
3796 assert(SafepointSynchronize::is_at_safepoint(),
3797 "inconsistent with asynch == false");
3798 if (UseAdaptiveSizePolicy) {
3799 size_policy()->ms_collection_marking_begin();
3800 }
3801 // already have locks
3802 res = markFromRootsWork(asynch);
3803 _collectorState = FinalMarking;
3804 if (UseAdaptiveSizePolicy) {
3805 GenCollectedHeap* gch = GenCollectedHeap::heap();
3806 size_policy()->ms_collection_marking_end(gch->gc_cause());
3807 }
3808 }
3809 verify_overflow_empty();
3810 return res;
3811 }
3813 bool CMSCollector::markFromRootsWork(bool asynch) {
3814 // iterate over marked bits in bit map, doing a full scan and mark
3815 // from these roots using the following algorithm:
3816 // . if oop is to the right of the current scan pointer,
3817 // mark corresponding bit (we'll process it later)
3818 // . else (oop is to left of current scan pointer)
3819 // push oop on marking stack
3820 // . drain the marking stack
3822 // Note that when we do a marking step we need to hold the
3823 // bit map lock -- recall that direct allocation (by mutators)
3824 // and promotion (by younger generation collectors) is also
3825 // marking the bit map. [the so-called allocate live policy.]
3826 // Because the implementation of bit map marking is not
3827 // robust wrt simultaneous marking of bits in the same word,
3828 // we need to make sure that there is no such interference
3829 // between concurrent such updates.
3831 // already have locks
3832 assert_lock_strong(bitMapLock());
3834 verify_work_stacks_empty();
3835 verify_overflow_empty();
3836 bool result = false;
3837 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3838 result = do_marking_mt(asynch);
3839 } else {
3840 result = do_marking_st(asynch);
3841 }
3842 return result;
3843 }
3845 // Forward decl
3846 class CMSConcMarkingTask;
3848 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3849 CMSCollector* _collector;
3850 CMSConcMarkingTask* _task;
3851 public:
3852 virtual void yield();
3854 // "n_threads" is the number of threads to be terminated.
3855 // "queue_set" is a set of work queues of other threads.
3856 // "collector" is the CMS collector associated with this task terminator.
3857 // "yield" indicates whether we need the gang as a whole to yield.
3858 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3859 ParallelTaskTerminator(n_threads, queue_set),
3860 _collector(collector) { }
3862 void set_task(CMSConcMarkingTask* task) {
3863 _task = task;
3864 }
3865 };
3867 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3868 CMSConcMarkingTask* _task;
3869 public:
3870 bool should_exit_termination();
3871 void set_task(CMSConcMarkingTask* task) {
3872 _task = task;
3873 }
3874 };
3876 // MT Concurrent Marking Task
3877 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3878 CMSCollector* _collector;
3879 int _n_workers; // requested/desired # workers
3880 bool _asynch;
3881 bool _result;
3882 CompactibleFreeListSpace* _cms_space;
3883 char _pad_front[64]; // padding to ...
3884 HeapWord* _global_finger; // ... avoid sharing cache line
3885 char _pad_back[64];
3886 HeapWord* _restart_addr;
3888 // Exposed here for yielding support
3889 Mutex* const _bit_map_lock;
3891 // The per thread work queues, available here for stealing
3892 OopTaskQueueSet* _task_queues;
3894 // Termination (and yielding) support
3895 CMSConcMarkingTerminator _term;
3896 CMSConcMarkingTerminatorTerminator _term_term;
3898 public:
3899 CMSConcMarkingTask(CMSCollector* collector,
3900 CompactibleFreeListSpace* cms_space,
3901 bool asynch,
3902 YieldingFlexibleWorkGang* workers,
3903 OopTaskQueueSet* task_queues):
3904 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3905 _collector(collector),
3906 _cms_space(cms_space),
3907 _asynch(asynch), _n_workers(0), _result(true),
3908 _task_queues(task_queues),
3909 _term(_n_workers, task_queues, _collector),
3910 _bit_map_lock(collector->bitMapLock())
3911 {
3912 _requested_size = _n_workers;
3913 _term.set_task(this);
3914 _term_term.set_task(this);
3915 _restart_addr = _global_finger = _cms_space->bottom();
3916 }
3919 OopTaskQueueSet* task_queues() { return _task_queues; }
3921 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3923 HeapWord** global_finger_addr() { return &_global_finger; }
3925 CMSConcMarkingTerminator* terminator() { return &_term; }
3927 virtual void set_for_termination(int active_workers) {
3928 terminator()->reset_for_reuse(active_workers);
3929 }
3931 void work(uint worker_id);
3932 bool should_yield() {
3933 return ConcurrentMarkSweepThread::should_yield()
3934 && !_collector->foregroundGCIsActive()
3935 && _asynch;
3936 }
3938 virtual void coordinator_yield(); // stuff done by coordinator
3939 bool result() { return _result; }
3941 void reset(HeapWord* ra) {
3942 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3943 _restart_addr = _global_finger = ra;
3944 _term.reset_for_reuse();
3945 }
3947 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3948 OopTaskQueue* work_q);
3950 private:
3951 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3952 void do_work_steal(int i);
3953 void bump_global_finger(HeapWord* f);
3954 };
3956 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3957 assert(_task != NULL, "Error");
3958 return _task->yielding();
3959 // Note that we do not need the disjunct || _task->should_yield() above
3960 // because we want terminating threads to yield only if the task
3961 // is already in the midst of yielding, which happens only after at least one
3962 // thread has yielded.
3963 }
3965 void CMSConcMarkingTerminator::yield() {
3966 if (_task->should_yield()) {
3967 _task->yield();
3968 } else {
3969 ParallelTaskTerminator::yield();
3970 }
3971 }
3973 ////////////////////////////////////////////////////////////////
3974 // Concurrent Marking Algorithm Sketch
3975 ////////////////////////////////////////////////////////////////
3976 // Until all tasks exhausted (both spaces):
3977 // -- claim next available chunk
3978 // -- bump global finger via CAS
3979 // -- find first object that starts in this chunk
3980 // and start scanning bitmap from that position
3981 // -- scan marked objects for oops
3982 // -- CAS-mark target, and if successful:
3983 // . if target oop is above global finger (volatile read)
3984 // nothing to do
3985 // . if target oop is in chunk and above local finger
3986 // then nothing to do
3987 // . else push on work-queue
3988 // -- Deal with possible overflow issues:
3989 // . local work-queue overflow causes stuff to be pushed on
3990 // global (common) overflow queue
3991 // . always first empty local work queue
3992 // . then get a batch of oops from global work queue if any
3993 // . then do work stealing
3994 // -- When all tasks claimed (both spaces)
3995 // and local work queue empty,
3996 // then in a loop do:
3997 // . check global overflow stack; steal a batch of oops and trace
3998 // . try to steal from other threads oif GOS is empty
3999 // . if neither is available, offer termination
4000 // -- Terminate and return result
4001 //
4002 void CMSConcMarkingTask::work(uint worker_id) {
4003 elapsedTimer _timer;
4004 ResourceMark rm;
4005 HandleMark hm;
4007 DEBUG_ONLY(_collector->verify_overflow_empty();)
4009 // Before we begin work, our work queue should be empty
4010 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
4011 // Scan the bitmap covering _cms_space, tracing through grey objects.
4012 _timer.start();
4013 do_scan_and_mark(worker_id, _cms_space);
4014 _timer.stop();
4015 if (PrintCMSStatistics != 0) {
4016 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
4017 worker_id, _timer.seconds());
4018 // XXX: need xxx/xxx type of notation, two timers
4019 }
4021 // ... do work stealing
4022 _timer.reset();
4023 _timer.start();
4024 do_work_steal(worker_id);
4025 _timer.stop();
4026 if (PrintCMSStatistics != 0) {
4027 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
4028 worker_id, _timer.seconds());
4029 // XXX: need xxx/xxx type of notation, two timers
4030 }
4031 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
4032 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
4033 // Note that under the current task protocol, the
4034 // following assertion is true even of the spaces
4035 // expanded since the completion of the concurrent
4036 // marking. XXX This will likely change under a strict
4037 // ABORT semantics.
4038 // After perm removal the comparison was changed to
4039 // greater than or equal to from strictly greater than.
4040 // Before perm removal the highest address sweep would
4041 // have been at the end of perm gen but now is at the
4042 // end of the tenured gen.
4043 assert(_global_finger >= _cms_space->end(),
4044 "All tasks have been completed");
4045 DEBUG_ONLY(_collector->verify_overflow_empty();)
4046 }
4048 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
4049 HeapWord* read = _global_finger;
4050 HeapWord* cur = read;
4051 while (f > read) {
4052 cur = read;
4053 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
4054 if (cur == read) {
4055 // our cas succeeded
4056 assert(_global_finger >= f, "protocol consistency");
4057 break;
4058 }
4059 }
4060 }
4062 // This is really inefficient, and should be redone by
4063 // using (not yet available) block-read and -write interfaces to the
4064 // stack and the work_queue. XXX FIX ME !!!
4065 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
4066 OopTaskQueue* work_q) {
4067 // Fast lock-free check
4068 if (ovflw_stk->length() == 0) {
4069 return false;
4070 }
4071 assert(work_q->size() == 0, "Shouldn't steal");
4072 MutexLockerEx ml(ovflw_stk->par_lock(),
4073 Mutex::_no_safepoint_check_flag);
4074 // Grab up to 1/4 the size of the work queue
4075 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4076 (size_t)ParGCDesiredObjsFromOverflowList);
4077 num = MIN2(num, ovflw_stk->length());
4078 for (int i = (int) num; i > 0; i--) {
4079 oop cur = ovflw_stk->pop();
4080 assert(cur != NULL, "Counted wrong?");
4081 work_q->push(cur);
4082 }
4083 return num > 0;
4084 }
4086 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4087 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4088 int n_tasks = pst->n_tasks();
4089 // We allow that there may be no tasks to do here because
4090 // we are restarting after a stack overflow.
4091 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4092 uint nth_task = 0;
4094 HeapWord* aligned_start = sp->bottom();
4095 if (sp->used_region().contains(_restart_addr)) {
4096 // Align down to a card boundary for the start of 0th task
4097 // for this space.
4098 aligned_start =
4099 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4100 CardTableModRefBS::card_size);
4101 }
4103 size_t chunk_size = sp->marking_task_size();
4104 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4105 // Having claimed the nth task in this space,
4106 // compute the chunk that it corresponds to:
4107 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4108 aligned_start + (nth_task+1)*chunk_size);
4109 // Try and bump the global finger via a CAS;
4110 // note that we need to do the global finger bump
4111 // _before_ taking the intersection below, because
4112 // the task corresponding to that region will be
4113 // deemed done even if the used_region() expands
4114 // because of allocation -- as it almost certainly will
4115 // during start-up while the threads yield in the
4116 // closure below.
4117 HeapWord* finger = span.end();
4118 bump_global_finger(finger); // atomically
4119 // There are null tasks here corresponding to chunks
4120 // beyond the "top" address of the space.
4121 span = span.intersection(sp->used_region());
4122 if (!span.is_empty()) { // Non-null task
4123 HeapWord* prev_obj;
4124 assert(!span.contains(_restart_addr) || nth_task == 0,
4125 "Inconsistency");
4126 if (nth_task == 0) {
4127 // For the 0th task, we'll not need to compute a block_start.
4128 if (span.contains(_restart_addr)) {
4129 // In the case of a restart because of stack overflow,
4130 // we might additionally skip a chunk prefix.
4131 prev_obj = _restart_addr;
4132 } else {
4133 prev_obj = span.start();
4134 }
4135 } else {
4136 // We want to skip the first object because
4137 // the protocol is to scan any object in its entirety
4138 // that _starts_ in this span; a fortiori, any
4139 // object starting in an earlier span is scanned
4140 // as part of an earlier claimed task.
4141 // Below we use the "careful" version of block_start
4142 // so we do not try to navigate uninitialized objects.
4143 prev_obj = sp->block_start_careful(span.start());
4144 // Below we use a variant of block_size that uses the
4145 // Printezis bits to avoid waiting for allocated
4146 // objects to become initialized/parsable.
4147 while (prev_obj < span.start()) {
4148 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4149 if (sz > 0) {
4150 prev_obj += sz;
4151 } else {
4152 // In this case we may end up doing a bit of redundant
4153 // scanning, but that appears unavoidable, short of
4154 // locking the free list locks; see bug 6324141.
4155 break;
4156 }
4157 }
4158 }
4159 if (prev_obj < span.end()) {
4160 MemRegion my_span = MemRegion(prev_obj, span.end());
4161 // Do the marking work within a non-empty span --
4162 // the last argument to the constructor indicates whether the
4163 // iteration should be incremental with periodic yields.
4164 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4165 &_collector->_markBitMap,
4166 work_queue(i),
4167 &_collector->_markStack,
4168 _asynch);
4169 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4170 } // else nothing to do for this task
4171 } // else nothing to do for this task
4172 }
4173 // We'd be tempted to assert here that since there are no
4174 // more tasks left to claim in this space, the global_finger
4175 // must exceed space->top() and a fortiori space->end(). However,
4176 // that would not quite be correct because the bumping of
4177 // global_finger occurs strictly after the claiming of a task,
4178 // so by the time we reach here the global finger may not yet
4179 // have been bumped up by the thread that claimed the last
4180 // task.
4181 pst->all_tasks_completed();
4182 }
4184 class Par_ConcMarkingClosure: public MetadataAwareOopClosure {
4185 private:
4186 CMSCollector* _collector;
4187 CMSConcMarkingTask* _task;
4188 MemRegion _span;
4189 CMSBitMap* _bit_map;
4190 CMSMarkStack* _overflow_stack;
4191 OopTaskQueue* _work_queue;
4192 protected:
4193 DO_OOP_WORK_DEFN
4194 public:
4195 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4196 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4197 MetadataAwareOopClosure(collector->ref_processor()),
4198 _collector(collector),
4199 _task(task),
4200 _span(collector->_span),
4201 _work_queue(work_queue),
4202 _bit_map(bit_map),
4203 _overflow_stack(overflow_stack)
4204 { }
4205 virtual void do_oop(oop* p);
4206 virtual void do_oop(narrowOop* p);
4208 void trim_queue(size_t max);
4209 void handle_stack_overflow(HeapWord* lost);
4210 void do_yield_check() {
4211 if (_task->should_yield()) {
4212 _task->yield();
4213 }
4214 }
4215 };
4217 // Grey object scanning during work stealing phase --
4218 // the salient assumption here is that any references
4219 // that are in these stolen objects being scanned must
4220 // already have been initialized (else they would not have
4221 // been published), so we do not need to check for
4222 // uninitialized objects before pushing here.
4223 void Par_ConcMarkingClosure::do_oop(oop obj) {
4224 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4225 HeapWord* addr = (HeapWord*)obj;
4226 // Check if oop points into the CMS generation
4227 // and is not marked
4228 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4229 // a white object ...
4230 // If we manage to "claim" the object, by being the
4231 // first thread to mark it, then we push it on our
4232 // marking stack
4233 if (_bit_map->par_mark(addr)) { // ... now grey
4234 // push on work queue (grey set)
4235 bool simulate_overflow = false;
4236 NOT_PRODUCT(
4237 if (CMSMarkStackOverflowALot &&
4238 _collector->simulate_overflow()) {
4239 // simulate a stack overflow
4240 simulate_overflow = true;
4241 }
4242 )
4243 if (simulate_overflow ||
4244 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4245 // stack overflow
4246 if (PrintCMSStatistics != 0) {
4247 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4248 SIZE_FORMAT, _overflow_stack->capacity());
4249 }
4250 // We cannot assert that the overflow stack is full because
4251 // it may have been emptied since.
4252 assert(simulate_overflow ||
4253 _work_queue->size() == _work_queue->max_elems(),
4254 "Else push should have succeeded");
4255 handle_stack_overflow(addr);
4256 }
4257 } // Else, some other thread got there first
4258 do_yield_check();
4259 }
4260 }
4262 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4263 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4265 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4266 while (_work_queue->size() > max) {
4267 oop new_oop;
4268 if (_work_queue->pop_local(new_oop)) {
4269 assert(new_oop->is_oop(), "Should be an oop");
4270 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4271 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4272 new_oop->oop_iterate(this); // do_oop() above
4273 do_yield_check();
4274 }
4275 }
4276 }
4278 // Upon stack overflow, we discard (part of) the stack,
4279 // remembering the least address amongst those discarded
4280 // in CMSCollector's _restart_address.
4281 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4282 // We need to do this under a mutex to prevent other
4283 // workers from interfering with the work done below.
4284 MutexLockerEx ml(_overflow_stack->par_lock(),
4285 Mutex::_no_safepoint_check_flag);
4286 // Remember the least grey address discarded
4287 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4288 _collector->lower_restart_addr(ra);
4289 _overflow_stack->reset(); // discard stack contents
4290 _overflow_stack->expand(); // expand the stack if possible
4291 }
4294 void CMSConcMarkingTask::do_work_steal(int i) {
4295 OopTaskQueue* work_q = work_queue(i);
4296 oop obj_to_scan;
4297 CMSBitMap* bm = &(_collector->_markBitMap);
4298 CMSMarkStack* ovflw = &(_collector->_markStack);
4299 int* seed = _collector->hash_seed(i);
4300 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4301 while (true) {
4302 cl.trim_queue(0);
4303 assert(work_q->size() == 0, "Should have been emptied above");
4304 if (get_work_from_overflow_stack(ovflw, work_q)) {
4305 // Can't assert below because the work obtained from the
4306 // overflow stack may already have been stolen from us.
4307 // assert(work_q->size() > 0, "Work from overflow stack");
4308 continue;
4309 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4310 assert(obj_to_scan->is_oop(), "Should be an oop");
4311 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4312 obj_to_scan->oop_iterate(&cl);
4313 } else if (terminator()->offer_termination(&_term_term)) {
4314 assert(work_q->size() == 0, "Impossible!");
4315 break;
4316 } else if (yielding() || should_yield()) {
4317 yield();
4318 }
4319 }
4320 }
4322 // This is run by the CMS (coordinator) thread.
4323 void CMSConcMarkingTask::coordinator_yield() {
4324 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4325 "CMS thread should hold CMS token");
4326 // First give up the locks, then yield, then re-lock
4327 // We should probably use a constructor/destructor idiom to
4328 // do this unlock/lock or modify the MutexUnlocker class to
4329 // serve our purpose. XXX
4330 assert_lock_strong(_bit_map_lock);
4331 _bit_map_lock->unlock();
4332 ConcurrentMarkSweepThread::desynchronize(true);
4333 ConcurrentMarkSweepThread::acknowledge_yield_request();
4334 _collector->stopTimer();
4335 if (PrintCMSStatistics != 0) {
4336 _collector->incrementYields();
4337 }
4338 _collector->icms_wait();
4340 // It is possible for whichever thread initiated the yield request
4341 // not to get a chance to wake up and take the bitmap lock between
4342 // this thread releasing it and reacquiring it. So, while the
4343 // should_yield() flag is on, let's sleep for a bit to give the
4344 // other thread a chance to wake up. The limit imposed on the number
4345 // of iterations is defensive, to avoid any unforseen circumstances
4346 // putting us into an infinite loop. Since it's always been this
4347 // (coordinator_yield()) method that was observed to cause the
4348 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4349 // which is by default non-zero. For the other seven methods that
4350 // also perform the yield operation, as are using a different
4351 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4352 // can enable the sleeping for those methods too, if necessary.
4353 // See 6442774.
4354 //
4355 // We really need to reconsider the synchronization between the GC
4356 // thread and the yield-requesting threads in the future and we
4357 // should really use wait/notify, which is the recommended
4358 // way of doing this type of interaction. Additionally, we should
4359 // consolidate the eight methods that do the yield operation and they
4360 // are almost identical into one for better maintenability and
4361 // readability. See 6445193.
4362 //
4363 // Tony 2006.06.29
4364 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4365 ConcurrentMarkSweepThread::should_yield() &&
4366 !CMSCollector::foregroundGCIsActive(); ++i) {
4367 os::sleep(Thread::current(), 1, false);
4368 ConcurrentMarkSweepThread::acknowledge_yield_request();
4369 }
4371 ConcurrentMarkSweepThread::synchronize(true);
4372 _bit_map_lock->lock_without_safepoint_check();
4373 _collector->startTimer();
4374 }
4376 bool CMSCollector::do_marking_mt(bool asynch) {
4377 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4378 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4379 conc_workers()->total_workers(),
4380 conc_workers()->active_workers(),
4381 Threads::number_of_non_daemon_threads());
4382 conc_workers()->set_active_workers(num_workers);
4384 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4386 CMSConcMarkingTask tsk(this,
4387 cms_space,
4388 asynch,
4389 conc_workers(),
4390 task_queues());
4392 // Since the actual number of workers we get may be different
4393 // from the number we requested above, do we need to do anything different
4394 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4395 // class?? XXX
4396 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4398 // Refs discovery is already non-atomic.
4399 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4400 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4401 conc_workers()->start_task(&tsk);
4402 while (tsk.yielded()) {
4403 tsk.coordinator_yield();
4404 conc_workers()->continue_task(&tsk);
4405 }
4406 // If the task was aborted, _restart_addr will be non-NULL
4407 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4408 while (_restart_addr != NULL) {
4409 // XXX For now we do not make use of ABORTED state and have not
4410 // yet implemented the right abort semantics (even in the original
4411 // single-threaded CMS case). That needs some more investigation
4412 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4413 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4414 // If _restart_addr is non-NULL, a marking stack overflow
4415 // occurred; we need to do a fresh marking iteration from the
4416 // indicated restart address.
4417 if (_foregroundGCIsActive && asynch) {
4418 // We may be running into repeated stack overflows, having
4419 // reached the limit of the stack size, while making very
4420 // slow forward progress. It may be best to bail out and
4421 // let the foreground collector do its job.
4422 // Clear _restart_addr, so that foreground GC
4423 // works from scratch. This avoids the headache of
4424 // a "rescan" which would otherwise be needed because
4425 // of the dirty mod union table & card table.
4426 _restart_addr = NULL;
4427 return false;
4428 }
4429 // Adjust the task to restart from _restart_addr
4430 tsk.reset(_restart_addr);
4431 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4432 _restart_addr);
4433 _restart_addr = NULL;
4434 // Get the workers going again
4435 conc_workers()->start_task(&tsk);
4436 while (tsk.yielded()) {
4437 tsk.coordinator_yield();
4438 conc_workers()->continue_task(&tsk);
4439 }
4440 }
4441 assert(tsk.completed(), "Inconsistency");
4442 assert(tsk.result() == true, "Inconsistency");
4443 return true;
4444 }
4446 bool CMSCollector::do_marking_st(bool asynch) {
4447 ResourceMark rm;
4448 HandleMark hm;
4450 // Temporarily make refs discovery single threaded (non-MT)
4451 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4452 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4453 &_markStack, CMSYield && asynch);
4454 // the last argument to iterate indicates whether the iteration
4455 // should be incremental with periodic yields.
4456 _markBitMap.iterate(&markFromRootsClosure);
4457 // If _restart_addr is non-NULL, a marking stack overflow
4458 // occurred; we need to do a fresh iteration from the
4459 // indicated restart address.
4460 while (_restart_addr != NULL) {
4461 if (_foregroundGCIsActive && asynch) {
4462 // We may be running into repeated stack overflows, having
4463 // reached the limit of the stack size, while making very
4464 // slow forward progress. It may be best to bail out and
4465 // let the foreground collector do its job.
4466 // Clear _restart_addr, so that foreground GC
4467 // works from scratch. This avoids the headache of
4468 // a "rescan" which would otherwise be needed because
4469 // of the dirty mod union table & card table.
4470 _restart_addr = NULL;
4471 return false; // indicating failure to complete marking
4472 }
4473 // Deal with stack overflow:
4474 // we restart marking from _restart_addr
4475 HeapWord* ra = _restart_addr;
4476 markFromRootsClosure.reset(ra);
4477 _restart_addr = NULL;
4478 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4479 }
4480 return true;
4481 }
4483 void CMSCollector::preclean() {
4484 check_correct_thread_executing();
4485 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4486 verify_work_stacks_empty();
4487 verify_overflow_empty();
4488 _abort_preclean = false;
4489 if (CMSPrecleaningEnabled) {
4490 if (!CMSEdenChunksRecordAlways) {
4491 _eden_chunk_index = 0;
4492 }
4493 size_t used = get_eden_used();
4494 size_t capacity = get_eden_capacity();
4495 // Don't start sampling unless we will get sufficiently
4496 // many samples.
4497 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4498 * CMSScheduleRemarkEdenPenetration)) {
4499 _start_sampling = true;
4500 } else {
4501 _start_sampling = false;
4502 }
4503 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4504 CMSPhaseAccounting pa(this, "preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4505 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4506 }
4507 CMSTokenSync x(true); // is cms thread
4508 if (CMSPrecleaningEnabled) {
4509 sample_eden();
4510 _collectorState = AbortablePreclean;
4511 } else {
4512 _collectorState = FinalMarking;
4513 }
4514 verify_work_stacks_empty();
4515 verify_overflow_empty();
4516 }
4518 // Try and schedule the remark such that young gen
4519 // occupancy is CMSScheduleRemarkEdenPenetration %.
4520 void CMSCollector::abortable_preclean() {
4521 check_correct_thread_executing();
4522 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4523 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4525 // If Eden's current occupancy is below this threshold,
4526 // immediately schedule the remark; else preclean
4527 // past the next scavenge in an effort to
4528 // schedule the pause as described avove. By choosing
4529 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4530 // we will never do an actual abortable preclean cycle.
4531 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4532 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4533 CMSPhaseAccounting pa(this, "abortable-preclean", _gc_tracer_cm->gc_id(), !PrintGCDetails);
4534 // We need more smarts in the abortable preclean
4535 // loop below to deal with cases where allocation
4536 // in young gen is very very slow, and our precleaning
4537 // is running a losing race against a horde of
4538 // mutators intent on flooding us with CMS updates
4539 // (dirty cards).
4540 // One, admittedly dumb, strategy is to give up
4541 // after a certain number of abortable precleaning loops
4542 // or after a certain maximum time. We want to make
4543 // this smarter in the next iteration.
4544 // XXX FIX ME!!! YSR
4545 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4546 while (!(should_abort_preclean() ||
4547 ConcurrentMarkSweepThread::should_terminate())) {
4548 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4549 cumworkdone += workdone;
4550 loops++;
4551 // Voluntarily terminate abortable preclean phase if we have
4552 // been at it for too long.
4553 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4554 loops >= CMSMaxAbortablePrecleanLoops) {
4555 if (PrintGCDetails) {
4556 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4557 }
4558 break;
4559 }
4560 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4561 if (PrintGCDetails) {
4562 gclog_or_tty->print(" CMS: abort preclean due to time ");
4563 }
4564 break;
4565 }
4566 // If we are doing little work each iteration, we should
4567 // take a short break.
4568 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4569 // Sleep for some time, waiting for work to accumulate
4570 stopTimer();
4571 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4572 startTimer();
4573 waited++;
4574 }
4575 }
4576 if (PrintCMSStatistics > 0) {
4577 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4578 loops, waited, cumworkdone);
4579 }
4580 }
4581 CMSTokenSync x(true); // is cms thread
4582 if (_collectorState != Idling) {
4583 assert(_collectorState == AbortablePreclean,
4584 "Spontaneous state transition?");
4585 _collectorState = FinalMarking;
4586 } // Else, a foreground collection completed this CMS cycle.
4587 return;
4588 }
4590 // Respond to an Eden sampling opportunity
4591 void CMSCollector::sample_eden() {
4592 // Make sure a young gc cannot sneak in between our
4593 // reading and recording of a sample.
4594 assert(Thread::current()->is_ConcurrentGC_thread(),
4595 "Only the cms thread may collect Eden samples");
4596 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4597 "Should collect samples while holding CMS token");
4598 if (!_start_sampling) {
4599 return;
4600 }
4601 // When CMSEdenChunksRecordAlways is true, the eden chunk array
4602 // is populated by the young generation.
4603 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
4604 if (_eden_chunk_index < _eden_chunk_capacity) {
4605 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4606 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4607 "Unexpected state of Eden");
4608 // We'd like to check that what we just sampled is an oop-start address;
4609 // however, we cannot do that here since the object may not yet have been
4610 // initialized. So we'll instead do the check when we _use_ this sample
4611 // later.
4612 if (_eden_chunk_index == 0 ||
4613 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4614 _eden_chunk_array[_eden_chunk_index-1])
4615 >= CMSSamplingGrain)) {
4616 _eden_chunk_index++; // commit sample
4617 }
4618 }
4619 }
4620 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4621 size_t used = get_eden_used();
4622 size_t capacity = get_eden_capacity();
4623 assert(used <= capacity, "Unexpected state of Eden");
4624 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4625 _abort_preclean = true;
4626 }
4627 }
4628 }
4631 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4632 assert(_collectorState == Precleaning ||
4633 _collectorState == AbortablePreclean, "incorrect state");
4634 ResourceMark rm;
4635 HandleMark hm;
4637 // Precleaning is currently not MT but the reference processor
4638 // may be set for MT. Disable it temporarily here.
4639 ReferenceProcessor* rp = ref_processor();
4640 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4642 // Do one pass of scrubbing the discovered reference lists
4643 // to remove any reference objects with strongly-reachable
4644 // referents.
4645 if (clean_refs) {
4646 CMSPrecleanRefsYieldClosure yield_cl(this);
4647 assert(rp->span().equals(_span), "Spans should be equal");
4648 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4649 &_markStack, true /* preclean */);
4650 CMSDrainMarkingStackClosure complete_trace(this,
4651 _span, &_markBitMap, &_markStack,
4652 &keep_alive, true /* preclean */);
4654 // We don't want this step to interfere with a young
4655 // collection because we don't want to take CPU
4656 // or memory bandwidth away from the young GC threads
4657 // (which may be as many as there are CPUs).
4658 // Note that we don't need to protect ourselves from
4659 // interference with mutators because they can't
4660 // manipulate the discovered reference lists nor affect
4661 // the computed reachability of the referents, the
4662 // only properties manipulated by the precleaning
4663 // of these reference lists.
4664 stopTimer();
4665 CMSTokenSyncWithLocks x(true /* is cms thread */,
4666 bitMapLock());
4667 startTimer();
4668 sample_eden();
4670 // The following will yield to allow foreground
4671 // collection to proceed promptly. XXX YSR:
4672 // The code in this method may need further
4673 // tweaking for better performance and some restructuring
4674 // for cleaner interfaces.
4675 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4676 rp->preclean_discovered_references(
4677 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
4678 gc_timer, _gc_tracer_cm->gc_id());
4679 }
4681 if (clean_survivor) { // preclean the active survivor space(s)
4682 assert(_young_gen->kind() == Generation::DefNew ||
4683 _young_gen->kind() == Generation::ParNew ||
4684 _young_gen->kind() == Generation::ASParNew,
4685 "incorrect type for cast");
4686 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4687 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4688 &_markBitMap, &_modUnionTable,
4689 &_markStack, true /* precleaning phase */);
4690 stopTimer();
4691 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4692 bitMapLock());
4693 startTimer();
4694 unsigned int before_count =
4695 GenCollectedHeap::heap()->total_collections();
4696 SurvivorSpacePrecleanClosure
4697 sss_cl(this, _span, &_markBitMap, &_markStack,
4698 &pam_cl, before_count, CMSYield);
4699 dng->from()->object_iterate_careful(&sss_cl);
4700 dng->to()->object_iterate_careful(&sss_cl);
4701 }
4702 MarkRefsIntoAndScanClosure
4703 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4704 &_markStack, this, CMSYield,
4705 true /* precleaning phase */);
4706 // CAUTION: The following closure has persistent state that may need to
4707 // be reset upon a decrease in the sequence of addresses it
4708 // processes.
4709 ScanMarkedObjectsAgainCarefullyClosure
4710 smoac_cl(this, _span,
4711 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4713 // Preclean dirty cards in ModUnionTable and CardTable using
4714 // appropriate convergence criterion;
4715 // repeat CMSPrecleanIter times unless we find that
4716 // we are losing.
4717 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4718 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4719 "Bad convergence multiplier");
4720 assert(CMSPrecleanThreshold >= 100,
4721 "Unreasonably low CMSPrecleanThreshold");
4723 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4724 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4725 numIter < CMSPrecleanIter;
4726 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4727 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4728 if (Verbose && PrintGCDetails) {
4729 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4730 }
4731 // Either there are very few dirty cards, so re-mark
4732 // pause will be small anyway, or our pre-cleaning isn't
4733 // that much faster than the rate at which cards are being
4734 // dirtied, so we might as well stop and re-mark since
4735 // precleaning won't improve our re-mark time by much.
4736 if (curNumCards <= CMSPrecleanThreshold ||
4737 (numIter > 0 &&
4738 (curNumCards * CMSPrecleanDenominator >
4739 lastNumCards * CMSPrecleanNumerator))) {
4740 numIter++;
4741 cumNumCards += curNumCards;
4742 break;
4743 }
4744 }
4746 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4748 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4749 cumNumCards += curNumCards;
4750 if (PrintGCDetails && PrintCMSStatistics != 0) {
4751 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4752 curNumCards, cumNumCards, numIter);
4753 }
4754 return cumNumCards; // as a measure of useful work done
4755 }
4757 // PRECLEANING NOTES:
4758 // Precleaning involves:
4759 // . reading the bits of the modUnionTable and clearing the set bits.
4760 // . For the cards corresponding to the set bits, we scan the
4761 // objects on those cards. This means we need the free_list_lock
4762 // so that we can safely iterate over the CMS space when scanning
4763 // for oops.
4764 // . When we scan the objects, we'll be both reading and setting
4765 // marks in the marking bit map, so we'll need the marking bit map.
4766 // . For protecting _collector_state transitions, we take the CGC_lock.
4767 // Note that any races in the reading of of card table entries by the
4768 // CMS thread on the one hand and the clearing of those entries by the
4769 // VM thread or the setting of those entries by the mutator threads on the
4770 // other are quite benign. However, for efficiency it makes sense to keep
4771 // the VM thread from racing with the CMS thread while the latter is
4772 // dirty card info to the modUnionTable. We therefore also use the
4773 // CGC_lock to protect the reading of the card table and the mod union
4774 // table by the CM thread.
4775 // . We run concurrently with mutator updates, so scanning
4776 // needs to be done carefully -- we should not try to scan
4777 // potentially uninitialized objects.
4778 //
4779 // Locking strategy: While holding the CGC_lock, we scan over and
4780 // reset a maximal dirty range of the mod union / card tables, then lock
4781 // the free_list_lock and bitmap lock to do a full marking, then
4782 // release these locks; and repeat the cycle. This allows for a
4783 // certain amount of fairness in the sharing of these locks between
4784 // the CMS collector on the one hand, and the VM thread and the
4785 // mutators on the other.
4787 // NOTE: preclean_mod_union_table() and preclean_card_table()
4788 // further below are largely identical; if you need to modify
4789 // one of these methods, please check the other method too.
4791 size_t CMSCollector::preclean_mod_union_table(
4792 ConcurrentMarkSweepGeneration* gen,
4793 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4794 verify_work_stacks_empty();
4795 verify_overflow_empty();
4797 // strategy: starting with the first card, accumulate contiguous
4798 // ranges of dirty cards; clear these cards, then scan the region
4799 // covered by these cards.
4801 // Since all of the MUT is committed ahead, we can just use
4802 // that, in case the generations expand while we are precleaning.
4803 // It might also be fine to just use the committed part of the
4804 // generation, but we might potentially miss cards when the
4805 // generation is rapidly expanding while we are in the midst
4806 // of precleaning.
4807 HeapWord* startAddr = gen->reserved().start();
4808 HeapWord* endAddr = gen->reserved().end();
4810 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4812 size_t numDirtyCards, cumNumDirtyCards;
4813 HeapWord *nextAddr, *lastAddr;
4814 for (cumNumDirtyCards = numDirtyCards = 0,
4815 nextAddr = lastAddr = startAddr;
4816 nextAddr < endAddr;
4817 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4819 ResourceMark rm;
4820 HandleMark hm;
4822 MemRegion dirtyRegion;
4823 {
4824 stopTimer();
4825 // Potential yield point
4826 CMSTokenSync ts(true);
4827 startTimer();
4828 sample_eden();
4829 // Get dirty region starting at nextOffset (inclusive),
4830 // simultaneously clearing it.
4831 dirtyRegion =
4832 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4833 assert(dirtyRegion.start() >= nextAddr,
4834 "returned region inconsistent?");
4835 }
4836 // Remember where the next search should begin.
4837 // The returned region (if non-empty) is a right open interval,
4838 // so lastOffset is obtained from the right end of that
4839 // interval.
4840 lastAddr = dirtyRegion.end();
4841 // Should do something more transparent and less hacky XXX
4842 numDirtyCards =
4843 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4845 // We'll scan the cards in the dirty region (with periodic
4846 // yields for foreground GC as needed).
4847 if (!dirtyRegion.is_empty()) {
4848 assert(numDirtyCards > 0, "consistency check");
4849 HeapWord* stop_point = NULL;
4850 stopTimer();
4851 // Potential yield point
4852 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4853 bitMapLock());
4854 startTimer();
4855 {
4856 verify_work_stacks_empty();
4857 verify_overflow_empty();
4858 sample_eden();
4859 stop_point =
4860 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4861 }
4862 if (stop_point != NULL) {
4863 // The careful iteration stopped early either because it found an
4864 // uninitialized object, or because we were in the midst of an
4865 // "abortable preclean", which should now be aborted. Redirty
4866 // the bits corresponding to the partially-scanned or unscanned
4867 // cards. We'll either restart at the next block boundary or
4868 // abort the preclean.
4869 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4870 "Should only be AbortablePreclean.");
4871 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4872 if (should_abort_preclean()) {
4873 break; // out of preclean loop
4874 } else {
4875 // Compute the next address at which preclean should pick up;
4876 // might need bitMapLock in order to read P-bits.
4877 lastAddr = next_card_start_after_block(stop_point);
4878 }
4879 }
4880 } else {
4881 assert(lastAddr == endAddr, "consistency check");
4882 assert(numDirtyCards == 0, "consistency check");
4883 break;
4884 }
4885 }
4886 verify_work_stacks_empty();
4887 verify_overflow_empty();
4888 return cumNumDirtyCards;
4889 }
4891 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4892 // below are largely identical; if you need to modify
4893 // one of these methods, please check the other method too.
4895 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4896 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4897 // strategy: it's similar to precleamModUnionTable above, in that
4898 // we accumulate contiguous ranges of dirty cards, mark these cards
4899 // precleaned, then scan the region covered by these cards.
4900 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4901 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4903 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4905 size_t numDirtyCards, cumNumDirtyCards;
4906 HeapWord *lastAddr, *nextAddr;
4908 for (cumNumDirtyCards = numDirtyCards = 0,
4909 nextAddr = lastAddr = startAddr;
4910 nextAddr < endAddr;
4911 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4913 ResourceMark rm;
4914 HandleMark hm;
4916 MemRegion dirtyRegion;
4917 {
4918 // See comments in "Precleaning notes" above on why we
4919 // do this locking. XXX Could the locking overheads be
4920 // too high when dirty cards are sparse? [I don't think so.]
4921 stopTimer();
4922 CMSTokenSync x(true); // is cms thread
4923 startTimer();
4924 sample_eden();
4925 // Get and clear dirty region from card table
4926 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4927 MemRegion(nextAddr, endAddr),
4928 true,
4929 CardTableModRefBS::precleaned_card_val());
4931 assert(dirtyRegion.start() >= nextAddr,
4932 "returned region inconsistent?");
4933 }
4934 lastAddr = dirtyRegion.end();
4935 numDirtyCards =
4936 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4938 if (!dirtyRegion.is_empty()) {
4939 stopTimer();
4940 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4941 startTimer();
4942 sample_eden();
4943 verify_work_stacks_empty();
4944 verify_overflow_empty();
4945 HeapWord* stop_point =
4946 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4947 if (stop_point != NULL) {
4948 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4949 "Should only be AbortablePreclean.");
4950 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4951 if (should_abort_preclean()) {
4952 break; // out of preclean loop
4953 } else {
4954 // Compute the next address at which preclean should pick up.
4955 lastAddr = next_card_start_after_block(stop_point);
4956 }
4957 }
4958 } else {
4959 break;
4960 }
4961 }
4962 verify_work_stacks_empty();
4963 verify_overflow_empty();
4964 return cumNumDirtyCards;
4965 }
4967 class PrecleanKlassClosure : public KlassClosure {
4968 KlassToOopClosure _cm_klass_closure;
4969 public:
4970 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4971 void do_klass(Klass* k) {
4972 if (k->has_accumulated_modified_oops()) {
4973 k->clear_accumulated_modified_oops();
4975 _cm_klass_closure.do_klass(k);
4976 }
4977 }
4978 };
4980 // The freelist lock is needed to prevent asserts, is it really needed?
4981 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4983 cl->set_freelistLock(freelistLock);
4985 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4987 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4988 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4989 PrecleanKlassClosure preclean_klass_closure(cl);
4990 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4992 verify_work_stacks_empty();
4993 verify_overflow_empty();
4994 }
4996 void CMSCollector::checkpointRootsFinal(bool asynch,
4997 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4998 assert(_collectorState == FinalMarking, "incorrect state transition?");
4999 check_correct_thread_executing();
5000 // world is stopped at this checkpoint
5001 assert(SafepointSynchronize::is_at_safepoint(),
5002 "world should be stopped");
5003 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5005 verify_work_stacks_empty();
5006 verify_overflow_empty();
5008 SpecializationStats::clear();
5009 if (PrintGCDetails) {
5010 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
5011 _young_gen->used() / K,
5012 _young_gen->capacity() / K);
5013 }
5014 if (asynch) {
5015 if (CMSScavengeBeforeRemark) {
5016 GenCollectedHeap* gch = GenCollectedHeap::heap();
5017 // Temporarily set flag to false, GCH->do_collection will
5018 // expect it to be false and set to true
5019 FlagSetting fl(gch->_is_gc_active, false);
5020 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
5021 PrintGCDetails && Verbose, true, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5022 int level = _cmsGen->level() - 1;
5023 if (level >= 0) {
5024 gch->do_collection(true, // full (i.e. force, see below)
5025 false, // !clear_all_soft_refs
5026 0, // size
5027 false, // is_tlab
5028 level // max_level
5029 );
5030 }
5031 }
5032 FreelistLocker x(this);
5033 MutexLockerEx y(bitMapLock(),
5034 Mutex::_no_safepoint_check_flag);
5035 assert(!init_mark_was_synchronous, "but that's impossible!");
5036 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
5037 } else {
5038 // already have all the locks
5039 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
5040 init_mark_was_synchronous);
5041 }
5042 verify_work_stacks_empty();
5043 verify_overflow_empty();
5044 SpecializationStats::print();
5045 }
5047 void CMSCollector::checkpointRootsFinalWork(bool asynch,
5048 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
5050 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5052 assert(haveFreelistLocks(), "must have free list locks");
5053 assert_lock_strong(bitMapLock());
5055 if (UseAdaptiveSizePolicy) {
5056 size_policy()->checkpoint_roots_final_begin();
5057 }
5059 ResourceMark rm;
5060 HandleMark hm;
5062 GenCollectedHeap* gch = GenCollectedHeap::heap();
5064 if (should_unload_classes()) {
5065 CodeCache::gc_prologue();
5066 }
5067 assert(haveFreelistLocks(), "must have free list locks");
5068 assert_lock_strong(bitMapLock());
5070 if (!init_mark_was_synchronous) {
5071 // We might assume that we need not fill TLAB's when
5072 // CMSScavengeBeforeRemark is set, because we may have just done
5073 // a scavenge which would have filled all TLAB's -- and besides
5074 // Eden would be empty. This however may not always be the case --
5075 // for instance although we asked for a scavenge, it may not have
5076 // happened because of a JNI critical section. We probably need
5077 // a policy for deciding whether we can in that case wait until
5078 // the critical section releases and then do the remark following
5079 // the scavenge, and skip it here. In the absence of that policy,
5080 // or of an indication of whether the scavenge did indeed occur,
5081 // we cannot rely on TLAB's having been filled and must do
5082 // so here just in case a scavenge did not happen.
5083 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5084 // Update the saved marks which may affect the root scans.
5085 gch->save_marks();
5087 if (CMSPrintEdenSurvivorChunks) {
5088 print_eden_and_survivor_chunk_arrays();
5089 }
5091 {
5092 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5094 // Note on the role of the mod union table:
5095 // Since the marker in "markFromRoots" marks concurrently with
5096 // mutators, it is possible for some reachable objects not to have been
5097 // scanned. For instance, an only reference to an object A was
5098 // placed in object B after the marker scanned B. Unless B is rescanned,
5099 // A would be collected. Such updates to references in marked objects
5100 // are detected via the mod union table which is the set of all cards
5101 // dirtied since the first checkpoint in this GC cycle and prior to
5102 // the most recent young generation GC, minus those cleaned up by the
5103 // concurrent precleaning.
5104 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5105 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5106 do_remark_parallel();
5107 } else {
5108 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5109 _gc_timer_cm, _gc_tracer_cm->gc_id());
5110 do_remark_non_parallel();
5111 }
5112 }
5113 } else {
5114 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5115 // The initial mark was stop-world, so there's no rescanning to
5116 // do; go straight on to the next step below.
5117 }
5118 verify_work_stacks_empty();
5119 verify_overflow_empty();
5121 {
5122 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());)
5123 refProcessingWork(asynch, clear_all_soft_refs);
5124 }
5125 verify_work_stacks_empty();
5126 verify_overflow_empty();
5128 if (should_unload_classes()) {
5129 CodeCache::gc_epilogue();
5130 }
5131 JvmtiExport::gc_epilogue();
5133 // If we encountered any (marking stack / work queue) overflow
5134 // events during the current CMS cycle, take appropriate
5135 // remedial measures, where possible, so as to try and avoid
5136 // recurrence of that condition.
5137 assert(_markStack.isEmpty(), "No grey objects");
5138 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5139 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5140 if (ser_ovflw > 0) {
5141 if (PrintCMSStatistics != 0) {
5142 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5143 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5144 ", kac_preclean="SIZE_FORMAT")",
5145 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5146 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5147 }
5148 _markStack.expand();
5149 _ser_pmc_remark_ovflw = 0;
5150 _ser_pmc_preclean_ovflw = 0;
5151 _ser_kac_preclean_ovflw = 0;
5152 _ser_kac_ovflw = 0;
5153 }
5154 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5155 if (PrintCMSStatistics != 0) {
5156 gclog_or_tty->print_cr("Work queue overflow (benign) "
5157 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5158 _par_pmc_remark_ovflw, _par_kac_ovflw);
5159 }
5160 _par_pmc_remark_ovflw = 0;
5161 _par_kac_ovflw = 0;
5162 }
5163 if (PrintCMSStatistics != 0) {
5164 if (_markStack._hit_limit > 0) {
5165 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5166 _markStack._hit_limit);
5167 }
5168 if (_markStack._failed_double > 0) {
5169 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5170 " current capacity "SIZE_FORMAT,
5171 _markStack._failed_double,
5172 _markStack.capacity());
5173 }
5174 }
5175 _markStack._hit_limit = 0;
5176 _markStack._failed_double = 0;
5178 if ((VerifyAfterGC || VerifyDuringGC) &&
5179 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5180 verify_after_remark();
5181 }
5183 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5185 // Change under the freelistLocks.
5186 _collectorState = Sweeping;
5187 // Call isAllClear() under bitMapLock
5188 assert(_modUnionTable.isAllClear(),
5189 "Should be clear by end of the final marking");
5190 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5191 "Should be clear by end of the final marking");
5192 if (UseAdaptiveSizePolicy) {
5193 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5194 }
5195 }
5197 void CMSParInitialMarkTask::work(uint worker_id) {
5198 elapsedTimer _timer;
5199 ResourceMark rm;
5200 HandleMark hm;
5202 // ---------- scan from roots --------------
5203 _timer.start();
5204 GenCollectedHeap* gch = GenCollectedHeap::heap();
5205 Par_MarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
5207 // ---------- young gen roots --------------
5208 {
5209 work_on_young_gen_roots(worker_id, &par_mri_cl);
5210 _timer.stop();
5211 if (PrintCMSStatistics != 0) {
5212 gclog_or_tty->print_cr(
5213 "Finished young gen initial mark scan work in %dth thread: %3.3f sec",
5214 worker_id, _timer.seconds());
5215 }
5216 }
5218 // ---------- remaining roots --------------
5219 _timer.reset();
5220 _timer.start();
5222 CLDToOopClosure cld_closure(&par_mri_cl, true);
5224 gch->gen_process_roots(_collector->_cmsGen->level(),
5225 false, // yg was scanned above
5226 false, // this is parallel code
5227 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5228 _collector->should_unload_classes(),
5229 &par_mri_cl,
5230 NULL,
5231 &cld_closure);
5232 assert(_collector->should_unload_classes()
5233 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5234 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5235 _timer.stop();
5236 if (PrintCMSStatistics != 0) {
5237 gclog_or_tty->print_cr(
5238 "Finished remaining root initial mark scan work in %dth thread: %3.3f sec",
5239 worker_id, _timer.seconds());
5240 }
5241 }
5243 // Parallel remark task
5244 class CMSParRemarkTask: public CMSParMarkTask {
5245 CompactibleFreeListSpace* _cms_space;
5247 // The per-thread work queues, available here for stealing.
5248 OopTaskQueueSet* _task_queues;
5249 ParallelTaskTerminator _term;
5251 public:
5252 // A value of 0 passed to n_workers will cause the number of
5253 // workers to be taken from the active workers in the work gang.
5254 CMSParRemarkTask(CMSCollector* collector,
5255 CompactibleFreeListSpace* cms_space,
5256 int n_workers, FlexibleWorkGang* workers,
5257 OopTaskQueueSet* task_queues):
5258 CMSParMarkTask("Rescan roots and grey objects in parallel",
5259 collector, n_workers),
5260 _cms_space(cms_space),
5261 _task_queues(task_queues),
5262 _term(n_workers, task_queues) { }
5264 OopTaskQueueSet* task_queues() { return _task_queues; }
5266 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5268 ParallelTaskTerminator* terminator() { return &_term; }
5269 int n_workers() { return _n_workers; }
5271 void work(uint worker_id);
5273 private:
5274 // ... of dirty cards in old space
5275 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5276 Par_MarkRefsIntoAndScanClosure* cl);
5278 // ... work stealing for the above
5279 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5280 };
5282 class RemarkKlassClosure : public KlassClosure {
5283 KlassToOopClosure _cm_klass_closure;
5284 public:
5285 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5286 void do_klass(Klass* k) {
5287 // Check if we have modified any oops in the Klass during the concurrent marking.
5288 if (k->has_accumulated_modified_oops()) {
5289 k->clear_accumulated_modified_oops();
5291 // We could have transfered the current modified marks to the accumulated marks,
5292 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5293 } else if (k->has_modified_oops()) {
5294 // Don't clear anything, this info is needed by the next young collection.
5295 } else {
5296 // No modified oops in the Klass.
5297 return;
5298 }
5300 // The klass has modified fields, need to scan the klass.
5301 _cm_klass_closure.do_klass(k);
5302 }
5303 };
5305 void CMSParMarkTask::work_on_young_gen_roots(uint worker_id, OopsInGenClosure* cl) {
5306 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5307 EdenSpace* eden_space = dng->eden();
5308 ContiguousSpace* from_space = dng->from();
5309 ContiguousSpace* to_space = dng->to();
5311 HeapWord** eca = _collector->_eden_chunk_array;
5312 size_t ect = _collector->_eden_chunk_index;
5313 HeapWord** sca = _collector->_survivor_chunk_array;
5314 size_t sct = _collector->_survivor_chunk_index;
5316 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5317 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5319 do_young_space_rescan(worker_id, cl, to_space, NULL, 0);
5320 do_young_space_rescan(worker_id, cl, from_space, sca, sct);
5321 do_young_space_rescan(worker_id, cl, eden_space, eca, ect);
5322 }
5324 // work_queue(i) is passed to the closure
5325 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5326 // also is passed to do_dirty_card_rescan_tasks() and to
5327 // do_work_steal() to select the i-th task_queue.
5329 void CMSParRemarkTask::work(uint worker_id) {
5330 elapsedTimer _timer;
5331 ResourceMark rm;
5332 HandleMark hm;
5334 // ---------- rescan from roots --------------
5335 _timer.start();
5336 GenCollectedHeap* gch = GenCollectedHeap::heap();
5337 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5338 _collector->_span, _collector->ref_processor(),
5339 &(_collector->_markBitMap),
5340 work_queue(worker_id));
5342 // Rescan young gen roots first since these are likely
5343 // coarsely partitioned and may, on that account, constitute
5344 // the critical path; thus, it's best to start off that
5345 // work first.
5346 // ---------- young gen roots --------------
5347 {
5348 work_on_young_gen_roots(worker_id, &par_mrias_cl);
5349 _timer.stop();
5350 if (PrintCMSStatistics != 0) {
5351 gclog_or_tty->print_cr(
5352 "Finished young gen rescan work in %dth thread: %3.3f sec",
5353 worker_id, _timer.seconds());
5354 }
5355 }
5357 // ---------- remaining roots --------------
5358 _timer.reset();
5359 _timer.start();
5360 gch->gen_process_roots(_collector->_cmsGen->level(),
5361 false, // yg was scanned above
5362 false, // this is parallel code
5363 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5364 _collector->should_unload_classes(),
5365 &par_mrias_cl,
5366 NULL,
5367 NULL); // The dirty klasses will be handled below
5369 assert(_collector->should_unload_classes()
5370 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5371 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5372 _timer.stop();
5373 if (PrintCMSStatistics != 0) {
5374 gclog_or_tty->print_cr(
5375 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5376 worker_id, _timer.seconds());
5377 }
5379 // ---------- unhandled CLD scanning ----------
5380 if (worker_id == 0) { // Single threaded at the moment.
5381 _timer.reset();
5382 _timer.start();
5384 // Scan all new class loader data objects and new dependencies that were
5385 // introduced during concurrent marking.
5386 ResourceMark rm;
5387 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5388 for (int i = 0; i < array->length(); i++) {
5389 par_mrias_cl.do_class_loader_data(array->at(i));
5390 }
5392 // We don't need to keep track of new CLDs anymore.
5393 ClassLoaderDataGraph::remember_new_clds(false);
5395 _timer.stop();
5396 if (PrintCMSStatistics != 0) {
5397 gclog_or_tty->print_cr(
5398 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5399 worker_id, _timer.seconds());
5400 }
5401 }
5403 // ---------- dirty klass scanning ----------
5404 if (worker_id == 0) { // Single threaded at the moment.
5405 _timer.reset();
5406 _timer.start();
5408 // Scan all classes that was dirtied during the concurrent marking phase.
5409 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5410 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5412 _timer.stop();
5413 if (PrintCMSStatistics != 0) {
5414 gclog_or_tty->print_cr(
5415 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5416 worker_id, _timer.seconds());
5417 }
5418 }
5420 // We might have added oops to ClassLoaderData::_handles during the
5421 // concurrent marking phase. These oops point to newly allocated objects
5422 // that are guaranteed to be kept alive. Either by the direct allocation
5423 // code, or when the young collector processes the roots. Hence,
5424 // we don't have to revisit the _handles block during the remark phase.
5426 // ---------- rescan dirty cards ------------
5427 _timer.reset();
5428 _timer.start();
5430 // Do the rescan tasks for each of the two spaces
5431 // (cms_space) in turn.
5432 // "worker_id" is passed to select the task_queue for "worker_id"
5433 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5434 _timer.stop();
5435 if (PrintCMSStatistics != 0) {
5436 gclog_or_tty->print_cr(
5437 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5438 worker_id, _timer.seconds());
5439 }
5441 // ---------- steal work from other threads ...
5442 // ---------- ... and drain overflow list.
5443 _timer.reset();
5444 _timer.start();
5445 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5446 _timer.stop();
5447 if (PrintCMSStatistics != 0) {
5448 gclog_or_tty->print_cr(
5449 "Finished work stealing in %dth thread: %3.3f sec",
5450 worker_id, _timer.seconds());
5451 }
5452 }
5454 // Note that parameter "i" is not used.
5455 void
5456 CMSParMarkTask::do_young_space_rescan(uint worker_id,
5457 OopsInGenClosure* cl, ContiguousSpace* space,
5458 HeapWord** chunk_array, size_t chunk_top) {
5459 // Until all tasks completed:
5460 // . claim an unclaimed task
5461 // . compute region boundaries corresponding to task claimed
5462 // using chunk_array
5463 // . par_oop_iterate(cl) over that region
5465 ResourceMark rm;
5466 HandleMark hm;
5468 SequentialSubTasksDone* pst = space->par_seq_tasks();
5470 uint nth_task = 0;
5471 uint n_tasks = pst->n_tasks();
5473 if (n_tasks > 0) {
5474 assert(pst->valid(), "Uninitialized use?");
5475 HeapWord *start, *end;
5476 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5477 // We claimed task # nth_task; compute its boundaries.
5478 if (chunk_top == 0) { // no samples were taken
5479 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5480 start = space->bottom();
5481 end = space->top();
5482 } else if (nth_task == 0) {
5483 start = space->bottom();
5484 end = chunk_array[nth_task];
5485 } else if (nth_task < (uint)chunk_top) {
5486 assert(nth_task >= 1, "Control point invariant");
5487 start = chunk_array[nth_task - 1];
5488 end = chunk_array[nth_task];
5489 } else {
5490 assert(nth_task == (uint)chunk_top, "Control point invariant");
5491 start = chunk_array[chunk_top - 1];
5492 end = space->top();
5493 }
5494 MemRegion mr(start, end);
5495 // Verify that mr is in space
5496 assert(mr.is_empty() || space->used_region().contains(mr),
5497 "Should be in space");
5498 // Verify that "start" is an object boundary
5499 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5500 "Should be an oop");
5501 space->par_oop_iterate(mr, cl);
5502 }
5503 pst->all_tasks_completed();
5504 }
5505 }
5507 void
5508 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5509 CompactibleFreeListSpace* sp, int i,
5510 Par_MarkRefsIntoAndScanClosure* cl) {
5511 // Until all tasks completed:
5512 // . claim an unclaimed task
5513 // . compute region boundaries corresponding to task claimed
5514 // . transfer dirty bits ct->mut for that region
5515 // . apply rescanclosure to dirty mut bits for that region
5517 ResourceMark rm;
5518 HandleMark hm;
5520 OopTaskQueue* work_q = work_queue(i);
5521 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5522 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5523 // CAUTION: This closure has state that persists across calls to
5524 // the work method dirty_range_iterate_clear() in that it has
5525 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5526 // use of that state in the imbedded UpwardsObjectClosure instance
5527 // assumes that the cards are always iterated (even if in parallel
5528 // by several threads) in monotonically increasing order per each
5529 // thread. This is true of the implementation below which picks
5530 // card ranges (chunks) in monotonically increasing order globally
5531 // and, a-fortiori, in monotonically increasing order per thread
5532 // (the latter order being a subsequence of the former).
5533 // If the work code below is ever reorganized into a more chaotic
5534 // work-partitioning form than the current "sequential tasks"
5535 // paradigm, the use of that persistent state will have to be
5536 // revisited and modified appropriately. See also related
5537 // bug 4756801 work on which should examine this code to make
5538 // sure that the changes there do not run counter to the
5539 // assumptions made here and necessary for correctness and
5540 // efficiency. Note also that this code might yield inefficient
5541 // behaviour in the case of very large objects that span one or
5542 // more work chunks. Such objects would potentially be scanned
5543 // several times redundantly. Work on 4756801 should try and
5544 // address that performance anomaly if at all possible. XXX
5545 MemRegion full_span = _collector->_span;
5546 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5547 MarkFromDirtyCardsClosure
5548 greyRescanClosure(_collector, full_span, // entire span of interest
5549 sp, bm, work_q, cl);
5551 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5552 assert(pst->valid(), "Uninitialized use?");
5553 uint nth_task = 0;
5554 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5555 MemRegion span = sp->used_region();
5556 HeapWord* start_addr = span.start();
5557 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5558 alignment);
5559 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5560 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5561 start_addr, "Check alignment");
5562 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5563 chunk_size, "Check alignment");
5565 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5566 // Having claimed the nth_task, compute corresponding mem-region,
5567 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5568 // The alignment restriction ensures that we do not need any
5569 // synchronization with other gang-workers while setting or
5570 // clearing bits in thus chunk of the MUT.
5571 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5572 start_addr + (nth_task+1)*chunk_size);
5573 // The last chunk's end might be way beyond end of the
5574 // used region. In that case pull back appropriately.
5575 if (this_span.end() > end_addr) {
5576 this_span.set_end(end_addr);
5577 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5578 }
5579 // Iterate over the dirty cards covering this chunk, marking them
5580 // precleaned, and setting the corresponding bits in the mod union
5581 // table. Since we have been careful to partition at Card and MUT-word
5582 // boundaries no synchronization is needed between parallel threads.
5583 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5584 &modUnionClosure);
5586 // Having transferred these marks into the modUnionTable,
5587 // rescan the marked objects on the dirty cards in the modUnionTable.
5588 // Even if this is at a synchronous collection, the initial marking
5589 // may have been done during an asynchronous collection so there
5590 // may be dirty bits in the mod-union table.
5591 _collector->_modUnionTable.dirty_range_iterate_clear(
5592 this_span, &greyRescanClosure);
5593 _collector->_modUnionTable.verifyNoOneBitsInRange(
5594 this_span.start(),
5595 this_span.end());
5596 }
5597 pst->all_tasks_completed(); // declare that i am done
5598 }
5600 // . see if we can share work_queues with ParNew? XXX
5601 void
5602 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5603 int* seed) {
5604 OopTaskQueue* work_q = work_queue(i);
5605 NOT_PRODUCT(int num_steals = 0;)
5606 oop obj_to_scan;
5607 CMSBitMap* bm = &(_collector->_markBitMap);
5609 while (true) {
5610 // Completely finish any left over work from (an) earlier round(s)
5611 cl->trim_queue(0);
5612 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5613 (size_t)ParGCDesiredObjsFromOverflowList);
5614 // Now check if there's any work in the overflow list
5615 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5616 // only affects the number of attempts made to get work from the
5617 // overflow list and does not affect the number of workers. Just
5618 // pass ParallelGCThreads so this behavior is unchanged.
5619 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5620 work_q,
5621 ParallelGCThreads)) {
5622 // found something in global overflow list;
5623 // not yet ready to go stealing work from others.
5624 // We'd like to assert(work_q->size() != 0, ...)
5625 // because we just took work from the overflow list,
5626 // but of course we can't since all of that could have
5627 // been already stolen from us.
5628 // "He giveth and He taketh away."
5629 continue;
5630 }
5631 // Verify that we have no work before we resort to stealing
5632 assert(work_q->size() == 0, "Have work, shouldn't steal");
5633 // Try to steal from other queues that have work
5634 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5635 NOT_PRODUCT(num_steals++;)
5636 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5637 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5638 // Do scanning work
5639 obj_to_scan->oop_iterate(cl);
5640 // Loop around, finish this work, and try to steal some more
5641 } else if (terminator()->offer_termination()) {
5642 break; // nirvana from the infinite cycle
5643 }
5644 }
5645 NOT_PRODUCT(
5646 if (PrintCMSStatistics != 0) {
5647 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5648 }
5649 )
5650 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5651 "Else our work is not yet done");
5652 }
5654 // Record object boundaries in _eden_chunk_array by sampling the eden
5655 // top in the slow-path eden object allocation code path and record
5656 // the boundaries, if CMSEdenChunksRecordAlways is true. If
5657 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
5658 // sampling in sample_eden() that activates during the part of the
5659 // preclean phase.
5660 void CMSCollector::sample_eden_chunk() {
5661 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
5662 if (_eden_chunk_lock->try_lock()) {
5663 // Record a sample. This is the critical section. The contents
5664 // of the _eden_chunk_array have to be non-decreasing in the
5665 // address order.
5666 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
5667 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
5668 "Unexpected state of Eden");
5669 if (_eden_chunk_index == 0 ||
5670 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
5671 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
5672 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
5673 _eden_chunk_index++; // commit sample
5674 }
5675 _eden_chunk_lock->unlock();
5676 }
5677 }
5678 }
5680 // Return a thread-local PLAB recording array, as appropriate.
5681 void* CMSCollector::get_data_recorder(int thr_num) {
5682 if (_survivor_plab_array != NULL &&
5683 (CMSPLABRecordAlways ||
5684 (_collectorState > Marking && _collectorState < FinalMarking))) {
5685 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5686 ChunkArray* ca = &_survivor_plab_array[thr_num];
5687 ca->reset(); // clear it so that fresh data is recorded
5688 return (void*) ca;
5689 } else {
5690 return NULL;
5691 }
5692 }
5694 // Reset all the thread-local PLAB recording arrays
5695 void CMSCollector::reset_survivor_plab_arrays() {
5696 for (uint i = 0; i < ParallelGCThreads; i++) {
5697 _survivor_plab_array[i].reset();
5698 }
5699 }
5701 // Merge the per-thread plab arrays into the global survivor chunk
5702 // array which will provide the partitioning of the survivor space
5703 // for CMS initial scan and rescan.
5704 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5705 int no_of_gc_threads) {
5706 assert(_survivor_plab_array != NULL, "Error");
5707 assert(_survivor_chunk_array != NULL, "Error");
5708 assert(_collectorState == FinalMarking ||
5709 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
5710 for (int j = 0; j < no_of_gc_threads; j++) {
5711 _cursor[j] = 0;
5712 }
5713 HeapWord* top = surv->top();
5714 size_t i;
5715 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5716 HeapWord* min_val = top; // Higher than any PLAB address
5717 uint min_tid = 0; // position of min_val this round
5718 for (int j = 0; j < no_of_gc_threads; j++) {
5719 ChunkArray* cur_sca = &_survivor_plab_array[j];
5720 if (_cursor[j] == cur_sca->end()) {
5721 continue;
5722 }
5723 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5724 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5725 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5726 if (cur_val < min_val) {
5727 min_tid = j;
5728 min_val = cur_val;
5729 } else {
5730 assert(cur_val < top, "All recorded addresses should be less");
5731 }
5732 }
5733 // At this point min_val and min_tid are respectively
5734 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5735 // and the thread (j) that witnesses that address.
5736 // We record this address in the _survivor_chunk_array[i]
5737 // and increment _cursor[min_tid] prior to the next round i.
5738 if (min_val == top) {
5739 break;
5740 }
5741 _survivor_chunk_array[i] = min_val;
5742 _cursor[min_tid]++;
5743 }
5744 // We are all done; record the size of the _survivor_chunk_array
5745 _survivor_chunk_index = i; // exclusive: [0, i)
5746 if (PrintCMSStatistics > 0) {
5747 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5748 }
5749 // Verify that we used up all the recorded entries
5750 #ifdef ASSERT
5751 size_t total = 0;
5752 for (int j = 0; j < no_of_gc_threads; j++) {
5753 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5754 total += _cursor[j];
5755 }
5756 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5757 // Check that the merged array is in sorted order
5758 if (total > 0) {
5759 for (size_t i = 0; i < total - 1; i++) {
5760 if (PrintCMSStatistics > 0) {
5761 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5762 i, _survivor_chunk_array[i]);
5763 }
5764 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5765 "Not sorted");
5766 }
5767 }
5768 #endif // ASSERT
5769 }
5771 // Set up the space's par_seq_tasks structure for work claiming
5772 // for parallel initial scan and rescan of young gen.
5773 // See ParRescanTask where this is currently used.
5774 void
5775 CMSCollector::
5776 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5777 assert(n_threads > 0, "Unexpected n_threads argument");
5778 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5780 // Eden space
5781 if (!dng->eden()->is_empty()) {
5782 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5783 assert(!pst->valid(), "Clobbering existing data?");
5784 // Each valid entry in [0, _eden_chunk_index) represents a task.
5785 size_t n_tasks = _eden_chunk_index + 1;
5786 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5787 // Sets the condition for completion of the subtask (how many threads
5788 // need to finish in order to be done).
5789 pst->set_n_threads(n_threads);
5790 pst->set_n_tasks((int)n_tasks);
5791 }
5793 // Merge the survivor plab arrays into _survivor_chunk_array
5794 if (_survivor_plab_array != NULL) {
5795 merge_survivor_plab_arrays(dng->from(), n_threads);
5796 } else {
5797 assert(_survivor_chunk_index == 0, "Error");
5798 }
5800 // To space
5801 {
5802 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5803 assert(!pst->valid(), "Clobbering existing data?");
5804 // Sets the condition for completion of the subtask (how many threads
5805 // need to finish in order to be done).
5806 pst->set_n_threads(n_threads);
5807 pst->set_n_tasks(1);
5808 assert(pst->valid(), "Error");
5809 }
5811 // From space
5812 {
5813 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5814 assert(!pst->valid(), "Clobbering existing data?");
5815 size_t n_tasks = _survivor_chunk_index + 1;
5816 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5817 // Sets the condition for completion of the subtask (how many threads
5818 // need to finish in order to be done).
5819 pst->set_n_threads(n_threads);
5820 pst->set_n_tasks((int)n_tasks);
5821 assert(pst->valid(), "Error");
5822 }
5823 }
5825 // Parallel version of remark
5826 void CMSCollector::do_remark_parallel() {
5827 GenCollectedHeap* gch = GenCollectedHeap::heap();
5828 FlexibleWorkGang* workers = gch->workers();
5829 assert(workers != NULL, "Need parallel worker threads.");
5830 // Choose to use the number of GC workers most recently set
5831 // into "active_workers". If active_workers is not set, set it
5832 // to ParallelGCThreads.
5833 int n_workers = workers->active_workers();
5834 if (n_workers == 0) {
5835 assert(n_workers > 0, "Should have been set during scavenge");
5836 n_workers = ParallelGCThreads;
5837 workers->set_active_workers(n_workers);
5838 }
5839 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5841 CMSParRemarkTask tsk(this,
5842 cms_space,
5843 n_workers, workers, task_queues());
5845 // Set up for parallel process_roots work.
5846 gch->set_par_threads(n_workers);
5847 // We won't be iterating over the cards in the card table updating
5848 // the younger_gen cards, so we shouldn't call the following else
5849 // the verification code as well as subsequent younger_refs_iterate
5850 // code would get confused. XXX
5851 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5853 // The young gen rescan work will not be done as part of
5854 // process_roots (which currently doesn't know how to
5855 // parallelize such a scan), but rather will be broken up into
5856 // a set of parallel tasks (via the sampling that the [abortable]
5857 // preclean phase did of EdenSpace, plus the [two] tasks of
5858 // scanning the [two] survivor spaces. Further fine-grain
5859 // parallelization of the scanning of the survivor spaces
5860 // themselves, and of precleaning of the younger gen itself
5861 // is deferred to the future.
5862 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5864 // The dirty card rescan work is broken up into a "sequence"
5865 // of parallel tasks (per constituent space) that are dynamically
5866 // claimed by the parallel threads.
5867 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5869 // It turns out that even when we're using 1 thread, doing the work in a
5870 // separate thread causes wide variance in run times. We can't help this
5871 // in the multi-threaded case, but we special-case n=1 here to get
5872 // repeatable measurements of the 1-thread overhead of the parallel code.
5873 if (n_workers > 1) {
5874 // Make refs discovery MT-safe, if it isn't already: it may not
5875 // necessarily be so, since it's possible that we are doing
5876 // ST marking.
5877 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5878 GenCollectedHeap::StrongRootsScope srs(gch);
5879 workers->run_task(&tsk);
5880 } else {
5881 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5882 GenCollectedHeap::StrongRootsScope srs(gch);
5883 tsk.work(0);
5884 }
5886 gch->set_par_threads(0); // 0 ==> non-parallel.
5887 // restore, single-threaded for now, any preserved marks
5888 // as a result of work_q overflow
5889 restore_preserved_marks_if_any();
5890 }
5892 // Non-parallel version of remark
5893 void CMSCollector::do_remark_non_parallel() {
5894 ResourceMark rm;
5895 HandleMark hm;
5896 GenCollectedHeap* gch = GenCollectedHeap::heap();
5897 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5899 MarkRefsIntoAndScanClosure
5900 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5901 &_markStack, this,
5902 false /* should_yield */, false /* not precleaning */);
5903 MarkFromDirtyCardsClosure
5904 markFromDirtyCardsClosure(this, _span,
5905 NULL, // space is set further below
5906 &_markBitMap, &_markStack, &mrias_cl);
5907 {
5908 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5909 // Iterate over the dirty cards, setting the corresponding bits in the
5910 // mod union table.
5911 {
5912 ModUnionClosure modUnionClosure(&_modUnionTable);
5913 _ct->ct_bs()->dirty_card_iterate(
5914 _cmsGen->used_region(),
5915 &modUnionClosure);
5916 }
5917 // Having transferred these marks into the modUnionTable, we just need
5918 // to rescan the marked objects on the dirty cards in the modUnionTable.
5919 // The initial marking may have been done during an asynchronous
5920 // collection so there may be dirty bits in the mod-union table.
5921 const int alignment =
5922 CardTableModRefBS::card_size * BitsPerWord;
5923 {
5924 // ... First handle dirty cards in CMS gen
5925 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5926 MemRegion ur = _cmsGen->used_region();
5927 HeapWord* lb = ur.start();
5928 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5929 MemRegion cms_span(lb, ub);
5930 _modUnionTable.dirty_range_iterate_clear(cms_span,
5931 &markFromDirtyCardsClosure);
5932 verify_work_stacks_empty();
5933 if (PrintCMSStatistics != 0) {
5934 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5935 markFromDirtyCardsClosure.num_dirty_cards());
5936 }
5937 }
5938 }
5939 if (VerifyDuringGC &&
5940 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5941 HandleMark hm; // Discard invalid handles created during verification
5942 Universe::verify();
5943 }
5944 {
5945 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5947 verify_work_stacks_empty();
5949 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5950 GenCollectedHeap::StrongRootsScope srs(gch);
5952 gch->gen_process_roots(_cmsGen->level(),
5953 true, // younger gens as roots
5954 false, // use the local StrongRootsScope
5955 SharedHeap::ScanningOption(roots_scanning_options()),
5956 should_unload_classes(),
5957 &mrias_cl,
5958 NULL,
5959 NULL); // The dirty klasses will be handled below
5961 assert(should_unload_classes()
5962 || (roots_scanning_options() & SharedHeap::SO_AllCodeCache),
5963 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5964 }
5966 {
5967 GCTraceTime t("visit unhandled CLDs", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5969 verify_work_stacks_empty();
5971 // Scan all class loader data objects that might have been introduced
5972 // during concurrent marking.
5973 ResourceMark rm;
5974 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5975 for (int i = 0; i < array->length(); i++) {
5976 mrias_cl.do_class_loader_data(array->at(i));
5977 }
5979 // We don't need to keep track of new CLDs anymore.
5980 ClassLoaderDataGraph::remember_new_clds(false);
5982 verify_work_stacks_empty();
5983 }
5985 {
5986 GCTraceTime t("dirty klass scan", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
5988 verify_work_stacks_empty();
5990 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5991 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5993 verify_work_stacks_empty();
5994 }
5996 // We might have added oops to ClassLoaderData::_handles during the
5997 // concurrent marking phase. These oops point to newly allocated objects
5998 // that are guaranteed to be kept alive. Either by the direct allocation
5999 // code, or when the young collector processes the roots. Hence,
6000 // we don't have to revisit the _handles block during the remark phase.
6002 verify_work_stacks_empty();
6003 // Restore evacuated mark words, if any, used for overflow list links
6004 if (!CMSOverflowEarlyRestoration) {
6005 restore_preserved_marks_if_any();
6006 }
6007 verify_overflow_empty();
6008 }
6010 ////////////////////////////////////////////////////////
6011 // Parallel Reference Processing Task Proxy Class
6012 ////////////////////////////////////////////////////////
6013 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
6014 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
6015 CMSCollector* _collector;
6016 CMSBitMap* _mark_bit_map;
6017 const MemRegion _span;
6018 ProcessTask& _task;
6020 public:
6021 CMSRefProcTaskProxy(ProcessTask& task,
6022 CMSCollector* collector,
6023 const MemRegion& span,
6024 CMSBitMap* mark_bit_map,
6025 AbstractWorkGang* workers,
6026 OopTaskQueueSet* task_queues):
6027 // XXX Should superclass AGTWOQ also know about AWG since it knows
6028 // about the task_queues used by the AWG? Then it could initialize
6029 // the terminator() object. See 6984287. The set_for_termination()
6030 // below is a temporary band-aid for the regression in 6984287.
6031 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
6032 task_queues),
6033 _task(task),
6034 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
6035 {
6036 assert(_collector->_span.equals(_span) && !_span.is_empty(),
6037 "Inconsistency in _span");
6038 set_for_termination(workers->active_workers());
6039 }
6041 OopTaskQueueSet* task_queues() { return queues(); }
6043 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
6045 void do_work_steal(int i,
6046 CMSParDrainMarkingStackClosure* drain,
6047 CMSParKeepAliveClosure* keep_alive,
6048 int* seed);
6050 virtual void work(uint worker_id);
6051 };
6053 void CMSRefProcTaskProxy::work(uint worker_id) {
6054 assert(_collector->_span.equals(_span), "Inconsistency in _span");
6055 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
6056 _mark_bit_map,
6057 work_queue(worker_id));
6058 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
6059 _mark_bit_map,
6060 work_queue(worker_id));
6061 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
6062 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
6063 if (_task.marks_oops_alive()) {
6064 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
6065 _collector->hash_seed(worker_id));
6066 }
6067 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
6068 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
6069 }
6071 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
6072 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
6073 EnqueueTask& _task;
6075 public:
6076 CMSRefEnqueueTaskProxy(EnqueueTask& task)
6077 : AbstractGangTask("Enqueue reference objects in parallel"),
6078 _task(task)
6079 { }
6081 virtual void work(uint worker_id)
6082 {
6083 _task.work(worker_id);
6084 }
6085 };
6087 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
6088 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
6089 _span(span),
6090 _bit_map(bit_map),
6091 _work_queue(work_queue),
6092 _mark_and_push(collector, span, bit_map, work_queue),
6093 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6094 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
6095 { }
6097 // . see if we can share work_queues with ParNew? XXX
6098 void CMSRefProcTaskProxy::do_work_steal(int i,
6099 CMSParDrainMarkingStackClosure* drain,
6100 CMSParKeepAliveClosure* keep_alive,
6101 int* seed) {
6102 OopTaskQueue* work_q = work_queue(i);
6103 NOT_PRODUCT(int num_steals = 0;)
6104 oop obj_to_scan;
6106 while (true) {
6107 // Completely finish any left over work from (an) earlier round(s)
6108 drain->trim_queue(0);
6109 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
6110 (size_t)ParGCDesiredObjsFromOverflowList);
6111 // Now check if there's any work in the overflow list
6112 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
6113 // only affects the number of attempts made to get work from the
6114 // overflow list and does not affect the number of workers. Just
6115 // pass ParallelGCThreads so this behavior is unchanged.
6116 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
6117 work_q,
6118 ParallelGCThreads)) {
6119 // Found something in global overflow list;
6120 // not yet ready to go stealing work from others.
6121 // We'd like to assert(work_q->size() != 0, ...)
6122 // because we just took work from the overflow list,
6123 // but of course we can't, since all of that might have
6124 // been already stolen from us.
6125 continue;
6126 }
6127 // Verify that we have no work before we resort to stealing
6128 assert(work_q->size() == 0, "Have work, shouldn't steal");
6129 // Try to steal from other queues that have work
6130 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
6131 NOT_PRODUCT(num_steals++;)
6132 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
6133 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
6134 // Do scanning work
6135 obj_to_scan->oop_iterate(keep_alive);
6136 // Loop around, finish this work, and try to steal some more
6137 } else if (terminator()->offer_termination()) {
6138 break; // nirvana from the infinite cycle
6139 }
6140 }
6141 NOT_PRODUCT(
6142 if (PrintCMSStatistics != 0) {
6143 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
6144 }
6145 )
6146 }
6148 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
6149 {
6150 GenCollectedHeap* gch = GenCollectedHeap::heap();
6151 FlexibleWorkGang* workers = gch->workers();
6152 assert(workers != NULL, "Need parallel worker threads.");
6153 CMSRefProcTaskProxy rp_task(task, &_collector,
6154 _collector.ref_processor()->span(),
6155 _collector.markBitMap(),
6156 workers, _collector.task_queues());
6157 workers->run_task(&rp_task);
6158 }
6160 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
6161 {
6163 GenCollectedHeap* gch = GenCollectedHeap::heap();
6164 FlexibleWorkGang* workers = gch->workers();
6165 assert(workers != NULL, "Need parallel worker threads.");
6166 CMSRefEnqueueTaskProxy enq_task(task);
6167 workers->run_task(&enq_task);
6168 }
6170 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
6172 ResourceMark rm;
6173 HandleMark hm;
6175 ReferenceProcessor* rp = ref_processor();
6176 assert(rp->span().equals(_span), "Spans should be equal");
6177 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
6178 // Process weak references.
6179 rp->setup_policy(clear_all_soft_refs);
6180 verify_work_stacks_empty();
6182 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
6183 &_markStack, false /* !preclean */);
6184 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
6185 _span, &_markBitMap, &_markStack,
6186 &cmsKeepAliveClosure, false /* !preclean */);
6187 {
6188 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6190 ReferenceProcessorStats stats;
6191 if (rp->processing_is_mt()) {
6192 // Set the degree of MT here. If the discovery is done MT, there
6193 // may have been a different number of threads doing the discovery
6194 // and a different number of discovered lists may have Ref objects.
6195 // That is OK as long as the Reference lists are balanced (see
6196 // balance_all_queues() and balance_queues()).
6197 GenCollectedHeap* gch = GenCollectedHeap::heap();
6198 int active_workers = ParallelGCThreads;
6199 FlexibleWorkGang* workers = gch->workers();
6200 if (workers != NULL) {
6201 active_workers = workers->active_workers();
6202 // The expectation is that active_workers will have already
6203 // been set to a reasonable value. If it has not been set,
6204 // investigate.
6205 assert(active_workers > 0, "Should have been set during scavenge");
6206 }
6207 rp->set_active_mt_degree(active_workers);
6208 CMSRefProcTaskExecutor task_executor(*this);
6209 stats = rp->process_discovered_references(&_is_alive_closure,
6210 &cmsKeepAliveClosure,
6211 &cmsDrainMarkingStackClosure,
6212 &task_executor,
6213 _gc_timer_cm,
6214 _gc_tracer_cm->gc_id());
6215 } else {
6216 stats = rp->process_discovered_references(&_is_alive_closure,
6217 &cmsKeepAliveClosure,
6218 &cmsDrainMarkingStackClosure,
6219 NULL,
6220 _gc_timer_cm,
6221 _gc_tracer_cm->gc_id());
6222 }
6223 _gc_tracer_cm->report_gc_reference_stats(stats);
6225 }
6227 // This is the point where the entire marking should have completed.
6228 verify_work_stacks_empty();
6230 if (should_unload_classes()) {
6231 {
6232 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6234 // Unload classes and purge the SystemDictionary.
6235 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
6237 // Unload nmethods.
6238 CodeCache::do_unloading(&_is_alive_closure, purged_class);
6240 // Prune dead klasses from subklass/sibling/implementor lists.
6241 Klass::clean_weak_klass_links(&_is_alive_closure);
6242 }
6244 {
6245 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6246 // Clean up unreferenced symbols in symbol table.
6247 SymbolTable::unlink();
6248 }
6250 {
6251 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm, _gc_tracer_cm->gc_id());
6252 // Delete entries for dead interned strings.
6253 StringTable::unlink(&_is_alive_closure);
6254 }
6255 }
6258 // Restore any preserved marks as a result of mark stack or
6259 // work queue overflow
6260 restore_preserved_marks_if_any(); // done single-threaded for now
6262 rp->set_enqueuing_is_done(true);
6263 if (rp->processing_is_mt()) {
6264 rp->balance_all_queues();
6265 CMSRefProcTaskExecutor task_executor(*this);
6266 rp->enqueue_discovered_references(&task_executor);
6267 } else {
6268 rp->enqueue_discovered_references(NULL);
6269 }
6270 rp->verify_no_references_recorded();
6271 assert(!rp->discovery_enabled(), "should have been disabled");
6272 }
6274 #ifndef PRODUCT
6275 void CMSCollector::check_correct_thread_executing() {
6276 Thread* t = Thread::current();
6277 // Only the VM thread or the CMS thread should be here.
6278 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6279 "Unexpected thread type");
6280 // If this is the vm thread, the foreground process
6281 // should not be waiting. Note that _foregroundGCIsActive is
6282 // true while the foreground collector is waiting.
6283 if (_foregroundGCShouldWait) {
6284 // We cannot be the VM thread
6285 assert(t->is_ConcurrentGC_thread(),
6286 "Should be CMS thread");
6287 } else {
6288 // We can be the CMS thread only if we are in a stop-world
6289 // phase of CMS collection.
6290 if (t->is_ConcurrentGC_thread()) {
6291 assert(_collectorState == InitialMarking ||
6292 _collectorState == FinalMarking,
6293 "Should be a stop-world phase");
6294 // The CMS thread should be holding the CMS_token.
6295 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6296 "Potential interference with concurrently "
6297 "executing VM thread");
6298 }
6299 }
6300 }
6301 #endif
6303 void CMSCollector::sweep(bool asynch) {
6304 assert(_collectorState == Sweeping, "just checking");
6305 check_correct_thread_executing();
6306 verify_work_stacks_empty();
6307 verify_overflow_empty();
6308 increment_sweep_count();
6309 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6311 _inter_sweep_timer.stop();
6312 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6313 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6315 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6316 _intra_sweep_timer.reset();
6317 _intra_sweep_timer.start();
6318 if (asynch) {
6319 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6320 CMSPhaseAccounting pa(this, "sweep", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6321 // First sweep the old gen
6322 {
6323 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6324 bitMapLock());
6325 sweepWork(_cmsGen, asynch);
6326 }
6328 // Update Universe::_heap_*_at_gc figures.
6329 // We need all the free list locks to make the abstract state
6330 // transition from Sweeping to Resetting. See detailed note
6331 // further below.
6332 {
6333 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6334 // Update heap occupancy information which is used as
6335 // input to soft ref clearing policy at the next gc.
6336 Universe::update_heap_info_at_gc();
6337 _collectorState = Resizing;
6338 }
6339 } else {
6340 // already have needed locks
6341 sweepWork(_cmsGen, asynch);
6342 // Update heap occupancy information which is used as
6343 // input to soft ref clearing policy at the next gc.
6344 Universe::update_heap_info_at_gc();
6345 _collectorState = Resizing;
6346 }
6347 verify_work_stacks_empty();
6348 verify_overflow_empty();
6350 if (should_unload_classes()) {
6351 // Delay purge to the beginning of the next safepoint. Metaspace::contains
6352 // requires that the virtual spaces are stable and not deleted.
6353 ClassLoaderDataGraph::set_should_purge(true);
6354 }
6356 _intra_sweep_timer.stop();
6357 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6359 _inter_sweep_timer.reset();
6360 _inter_sweep_timer.start();
6362 // We need to use a monotonically non-deccreasing time in ms
6363 // or we will see time-warp warnings and os::javaTimeMillis()
6364 // does not guarantee monotonicity.
6365 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6366 update_time_of_last_gc(now);
6368 // NOTE on abstract state transitions:
6369 // Mutators allocate-live and/or mark the mod-union table dirty
6370 // based on the state of the collection. The former is done in
6371 // the interval [Marking, Sweeping] and the latter in the interval
6372 // [Marking, Sweeping). Thus the transitions into the Marking state
6373 // and out of the Sweeping state must be synchronously visible
6374 // globally to the mutators.
6375 // The transition into the Marking state happens with the world
6376 // stopped so the mutators will globally see it. Sweeping is
6377 // done asynchronously by the background collector so the transition
6378 // from the Sweeping state to the Resizing state must be done
6379 // under the freelistLock (as is the check for whether to
6380 // allocate-live and whether to dirty the mod-union table).
6381 assert(_collectorState == Resizing, "Change of collector state to"
6382 " Resizing must be done under the freelistLocks (plural)");
6384 // Now that sweeping has been completed, we clear
6385 // the incremental_collection_failed flag,
6386 // thus inviting a younger gen collection to promote into
6387 // this generation. If such a promotion may still fail,
6388 // the flag will be set again when a young collection is
6389 // attempted.
6390 GenCollectedHeap* gch = GenCollectedHeap::heap();
6391 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6392 gch->update_full_collections_completed(_collection_count_start);
6393 }
6395 // FIX ME!!! Looks like this belongs in CFLSpace, with
6396 // CMSGen merely delegating to it.
6397 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6398 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6399 HeapWord* minAddr = _cmsSpace->bottom();
6400 HeapWord* largestAddr =
6401 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6402 if (largestAddr == NULL) {
6403 // The dictionary appears to be empty. In this case
6404 // try to coalesce at the end of the heap.
6405 largestAddr = _cmsSpace->end();
6406 }
6407 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6408 size_t nearLargestOffset =
6409 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6410 if (PrintFLSStatistics != 0) {
6411 gclog_or_tty->print_cr(
6412 "CMS: Large Block: " PTR_FORMAT ";"
6413 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6414 largestAddr,
6415 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6416 }
6417 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6418 }
6420 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6421 return addr >= _cmsSpace->nearLargestChunk();
6422 }
6424 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6425 return _cmsSpace->find_chunk_at_end();
6426 }
6428 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6429 bool full) {
6430 // The next lower level has been collected. Gather any statistics
6431 // that are of interest at this point.
6432 if (!full && (current_level + 1) == level()) {
6433 // Gather statistics on the young generation collection.
6434 collector()->stats().record_gc0_end(used());
6435 }
6436 }
6438 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6439 GenCollectedHeap* gch = GenCollectedHeap::heap();
6440 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6441 "Wrong type of heap");
6442 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6443 gch->gen_policy()->size_policy();
6444 assert(sp->is_gc_cms_adaptive_size_policy(),
6445 "Wrong type of size policy");
6446 return sp;
6447 }
6449 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6450 if (PrintGCDetails && Verbose) {
6451 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6452 }
6453 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6454 _debug_collection_type =
6455 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6456 if (PrintGCDetails && Verbose) {
6457 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6458 }
6459 }
6461 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6462 bool asynch) {
6463 // We iterate over the space(s) underlying this generation,
6464 // checking the mark bit map to see if the bits corresponding
6465 // to specific blocks are marked or not. Blocks that are
6466 // marked are live and are not swept up. All remaining blocks
6467 // are swept up, with coalescing on-the-fly as we sweep up
6468 // contiguous free and/or garbage blocks:
6469 // We need to ensure that the sweeper synchronizes with allocators
6470 // and stop-the-world collectors. In particular, the following
6471 // locks are used:
6472 // . CMS token: if this is held, a stop the world collection cannot occur
6473 // . freelistLock: if this is held no allocation can occur from this
6474 // generation by another thread
6475 // . bitMapLock: if this is held, no other thread can access or update
6476 //
6478 // Note that we need to hold the freelistLock if we use
6479 // block iterate below; else the iterator might go awry if
6480 // a mutator (or promotion) causes block contents to change
6481 // (for instance if the allocator divvies up a block).
6482 // If we hold the free list lock, for all practical purposes
6483 // young generation GC's can't occur (they'll usually need to
6484 // promote), so we might as well prevent all young generation
6485 // GC's while we do a sweeping step. For the same reason, we might
6486 // as well take the bit map lock for the entire duration
6488 // check that we hold the requisite locks
6489 assert(have_cms_token(), "Should hold cms token");
6490 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6491 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6492 "Should possess CMS token to sweep");
6493 assert_lock_strong(gen->freelistLock());
6494 assert_lock_strong(bitMapLock());
6496 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6497 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6498 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6499 _inter_sweep_estimate.padded_average(),
6500 _intra_sweep_estimate.padded_average());
6501 gen->setNearLargestChunk();
6503 {
6504 SweepClosure sweepClosure(this, gen, &_markBitMap,
6505 CMSYield && asynch);
6506 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6507 // We need to free-up/coalesce garbage/blocks from a
6508 // co-terminal free run. This is done in the SweepClosure
6509 // destructor; so, do not remove this scope, else the
6510 // end-of-sweep-census below will be off by a little bit.
6511 }
6512 gen->cmsSpace()->sweep_completed();
6513 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6514 if (should_unload_classes()) { // unloaded classes this cycle,
6515 _concurrent_cycles_since_last_unload = 0; // ... reset count
6516 } else { // did not unload classes,
6517 _concurrent_cycles_since_last_unload++; // ... increment count
6518 }
6519 }
6521 // Reset CMS data structures (for now just the marking bit map)
6522 // preparatory for the next cycle.
6523 void CMSCollector::reset(bool asynch) {
6524 GenCollectedHeap* gch = GenCollectedHeap::heap();
6525 CMSAdaptiveSizePolicy* sp = size_policy();
6526 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6527 if (asynch) {
6528 CMSTokenSyncWithLocks ts(true, bitMapLock());
6530 // If the state is not "Resetting", the foreground thread
6531 // has done a collection and the resetting.
6532 if (_collectorState != Resetting) {
6533 assert(_collectorState == Idling, "The state should only change"
6534 " because the foreground collector has finished the collection");
6535 return;
6536 }
6538 // Clear the mark bitmap (no grey objects to start with)
6539 // for the next cycle.
6540 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6541 CMSPhaseAccounting cmspa(this, "reset", _gc_tracer_cm->gc_id(), !PrintGCDetails);
6543 HeapWord* curAddr = _markBitMap.startWord();
6544 while (curAddr < _markBitMap.endWord()) {
6545 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6546 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6547 _markBitMap.clear_large_range(chunk);
6548 if (ConcurrentMarkSweepThread::should_yield() &&
6549 !foregroundGCIsActive() &&
6550 CMSYield) {
6551 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6552 "CMS thread should hold CMS token");
6553 assert_lock_strong(bitMapLock());
6554 bitMapLock()->unlock();
6555 ConcurrentMarkSweepThread::desynchronize(true);
6556 ConcurrentMarkSweepThread::acknowledge_yield_request();
6557 stopTimer();
6558 if (PrintCMSStatistics != 0) {
6559 incrementYields();
6560 }
6561 icms_wait();
6563 // See the comment in coordinator_yield()
6564 for (unsigned i = 0; i < CMSYieldSleepCount &&
6565 ConcurrentMarkSweepThread::should_yield() &&
6566 !CMSCollector::foregroundGCIsActive(); ++i) {
6567 os::sleep(Thread::current(), 1, false);
6568 ConcurrentMarkSweepThread::acknowledge_yield_request();
6569 }
6571 ConcurrentMarkSweepThread::synchronize(true);
6572 bitMapLock()->lock_without_safepoint_check();
6573 startTimer();
6574 }
6575 curAddr = chunk.end();
6576 }
6577 // A successful mostly concurrent collection has been done.
6578 // Because only the full (i.e., concurrent mode failure) collections
6579 // are being measured for gc overhead limits, clean the "near" flag
6580 // and count.
6581 sp->reset_gc_overhead_limit_count();
6582 _collectorState = Idling;
6583 } else {
6584 // already have the lock
6585 assert(_collectorState == Resetting, "just checking");
6586 assert_lock_strong(bitMapLock());
6587 _markBitMap.clear_all();
6588 _collectorState = Idling;
6589 }
6591 // Stop incremental mode after a cycle completes, so that any future cycles
6592 // are triggered by allocation.
6593 stop_icms();
6595 NOT_PRODUCT(
6596 if (RotateCMSCollectionTypes) {
6597 _cmsGen->rotate_debug_collection_type();
6598 }
6599 )
6601 register_gc_end();
6602 }
6604 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6605 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6606 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6607 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL, _gc_tracer_cm->gc_id());
6608 TraceCollectorStats tcs(counters());
6610 switch (op) {
6611 case CMS_op_checkpointRootsInitial: {
6612 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6613 checkpointRootsInitial(true); // asynch
6614 if (PrintGC) {
6615 _cmsGen->printOccupancy("initial-mark");
6616 }
6617 break;
6618 }
6619 case CMS_op_checkpointRootsFinal: {
6620 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6621 checkpointRootsFinal(true, // asynch
6622 false, // !clear_all_soft_refs
6623 false); // !init_mark_was_synchronous
6624 if (PrintGC) {
6625 _cmsGen->printOccupancy("remark");
6626 }
6627 break;
6628 }
6629 default:
6630 fatal("No such CMS_op");
6631 }
6632 }
6634 #ifndef PRODUCT
6635 size_t const CMSCollector::skip_header_HeapWords() {
6636 return FreeChunk::header_size();
6637 }
6639 // Try and collect here conditions that should hold when
6640 // CMS thread is exiting. The idea is that the foreground GC
6641 // thread should not be blocked if it wants to terminate
6642 // the CMS thread and yet continue to run the VM for a while
6643 // after that.
6644 void CMSCollector::verify_ok_to_terminate() const {
6645 assert(Thread::current()->is_ConcurrentGC_thread(),
6646 "should be called by CMS thread");
6647 assert(!_foregroundGCShouldWait, "should be false");
6648 // We could check here that all the various low-level locks
6649 // are not held by the CMS thread, but that is overkill; see
6650 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6651 // is checked.
6652 }
6653 #endif
6655 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6656 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6657 "missing Printezis mark?");
6658 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6659 size_t size = pointer_delta(nextOneAddr + 1, addr);
6660 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6661 "alignment problem");
6662 assert(size >= 3, "Necessary for Printezis marks to work");
6663 return size;
6664 }
6666 // A variant of the above (block_size_using_printezis_bits()) except
6667 // that we return 0 if the P-bits are not yet set.
6668 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6669 if (_markBitMap.isMarked(addr + 1)) {
6670 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6671 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6672 size_t size = pointer_delta(nextOneAddr + 1, addr);
6673 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6674 "alignment problem");
6675 assert(size >= 3, "Necessary for Printezis marks to work");
6676 return size;
6677 }
6678 return 0;
6679 }
6681 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6682 size_t sz = 0;
6683 oop p = (oop)addr;
6684 if (p->klass_or_null() != NULL) {
6685 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6686 } else {
6687 sz = block_size_using_printezis_bits(addr);
6688 }
6689 assert(sz > 0, "size must be nonzero");
6690 HeapWord* next_block = addr + sz;
6691 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6692 CardTableModRefBS::card_size);
6693 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6694 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6695 "must be different cards");
6696 return next_card;
6697 }
6700 // CMS Bit Map Wrapper /////////////////////////////////////////
6702 // Construct a CMS bit map infrastructure, but don't create the
6703 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6704 // further below.
6705 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6706 _bm(),
6707 _shifter(shifter),
6708 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6709 {
6710 _bmStartWord = 0;
6711 _bmWordSize = 0;
6712 }
6714 bool CMSBitMap::allocate(MemRegion mr) {
6715 _bmStartWord = mr.start();
6716 _bmWordSize = mr.word_size();
6717 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6718 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6719 if (!brs.is_reserved()) {
6720 warning("CMS bit map allocation failure");
6721 return false;
6722 }
6723 // For now we'll just commit all of the bit map up fromt.
6724 // Later on we'll try to be more parsimonious with swap.
6725 if (!_virtual_space.initialize(brs, brs.size())) {
6726 warning("CMS bit map backing store failure");
6727 return false;
6728 }
6729 assert(_virtual_space.committed_size() == brs.size(),
6730 "didn't reserve backing store for all of CMS bit map?");
6731 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6732 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6733 _bmWordSize, "inconsistency in bit map sizing");
6734 _bm.set_size(_bmWordSize >> _shifter);
6736 // bm.clear(); // can we rely on getting zero'd memory? verify below
6737 assert(isAllClear(),
6738 "Expected zero'd memory from ReservedSpace constructor");
6739 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6740 "consistency check");
6741 return true;
6742 }
6744 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6745 HeapWord *next_addr, *end_addr, *last_addr;
6746 assert_locked();
6747 assert(covers(mr), "out-of-range error");
6748 // XXX assert that start and end are appropriately aligned
6749 for (next_addr = mr.start(), end_addr = mr.end();
6750 next_addr < end_addr; next_addr = last_addr) {
6751 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6752 last_addr = dirty_region.end();
6753 if (!dirty_region.is_empty()) {
6754 cl->do_MemRegion(dirty_region);
6755 } else {
6756 assert(last_addr == end_addr, "program logic");
6757 return;
6758 }
6759 }
6760 }
6762 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
6763 _bm.print_on_error(st, prefix);
6764 }
6766 #ifndef PRODUCT
6767 void CMSBitMap::assert_locked() const {
6768 CMSLockVerifier::assert_locked(lock());
6769 }
6771 bool CMSBitMap::covers(MemRegion mr) const {
6772 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6773 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6774 "size inconsistency");
6775 return (mr.start() >= _bmStartWord) &&
6776 (mr.end() <= endWord());
6777 }
6779 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6780 return (start >= _bmStartWord && (start + size) <= endWord());
6781 }
6783 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6784 // verify that there are no 1 bits in the interval [left, right)
6785 FalseBitMapClosure falseBitMapClosure;
6786 iterate(&falseBitMapClosure, left, right);
6787 }
6789 void CMSBitMap::region_invariant(MemRegion mr)
6790 {
6791 assert_locked();
6792 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6793 assert(!mr.is_empty(), "unexpected empty region");
6794 assert(covers(mr), "mr should be covered by bit map");
6795 // convert address range into offset range
6796 size_t start_ofs = heapWordToOffset(mr.start());
6797 // Make sure that end() is appropriately aligned
6798 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6799 (1 << (_shifter+LogHeapWordSize))),
6800 "Misaligned mr.end()");
6801 size_t end_ofs = heapWordToOffset(mr.end());
6802 assert(end_ofs > start_ofs, "Should mark at least one bit");
6803 }
6805 #endif
6807 bool CMSMarkStack::allocate(size_t size) {
6808 // allocate a stack of the requisite depth
6809 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6810 size * sizeof(oop)));
6811 if (!rs.is_reserved()) {
6812 warning("CMSMarkStack allocation failure");
6813 return false;
6814 }
6815 if (!_virtual_space.initialize(rs, rs.size())) {
6816 warning("CMSMarkStack backing store failure");
6817 return false;
6818 }
6819 assert(_virtual_space.committed_size() == rs.size(),
6820 "didn't reserve backing store for all of CMS stack?");
6821 _base = (oop*)(_virtual_space.low());
6822 _index = 0;
6823 _capacity = size;
6824 NOT_PRODUCT(_max_depth = 0);
6825 return true;
6826 }
6828 // XXX FIX ME !!! In the MT case we come in here holding a
6829 // leaf lock. For printing we need to take a further lock
6830 // which has lower rank. We need to recallibrate the two
6831 // lock-ranks involved in order to be able to rpint the
6832 // messages below. (Or defer the printing to the caller.
6833 // For now we take the expedient path of just disabling the
6834 // messages for the problematic case.)
6835 void CMSMarkStack::expand() {
6836 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6837 if (_capacity == MarkStackSizeMax) {
6838 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6839 // We print a warning message only once per CMS cycle.
6840 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6841 }
6842 return;
6843 }
6844 // Double capacity if possible
6845 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6846 // Do not give up existing stack until we have managed to
6847 // get the double capacity that we desired.
6848 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6849 new_capacity * sizeof(oop)));
6850 if (rs.is_reserved()) {
6851 // Release the backing store associated with old stack
6852 _virtual_space.release();
6853 // Reinitialize virtual space for new stack
6854 if (!_virtual_space.initialize(rs, rs.size())) {
6855 fatal("Not enough swap for expanded marking stack");
6856 }
6857 _base = (oop*)(_virtual_space.low());
6858 _index = 0;
6859 _capacity = new_capacity;
6860 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6861 // Failed to double capacity, continue;
6862 // we print a detail message only once per CMS cycle.
6863 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6864 SIZE_FORMAT"K",
6865 _capacity / K, new_capacity / K);
6866 }
6867 }
6870 // Closures
6871 // XXX: there seems to be a lot of code duplication here;
6872 // should refactor and consolidate common code.
6874 // This closure is used to mark refs into the CMS generation in
6875 // the CMS bit map. Called at the first checkpoint. This closure
6876 // assumes that we do not need to re-mark dirty cards; if the CMS
6877 // generation on which this is used is not an oldest
6878 // generation then this will lose younger_gen cards!
6880 MarkRefsIntoClosure::MarkRefsIntoClosure(
6881 MemRegion span, CMSBitMap* bitMap):
6882 _span(span),
6883 _bitMap(bitMap)
6884 {
6885 assert(_ref_processor == NULL, "deliberately left NULL");
6886 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6887 }
6889 void MarkRefsIntoClosure::do_oop(oop obj) {
6890 // if p points into _span, then mark corresponding bit in _markBitMap
6891 assert(obj->is_oop(), "expected an oop");
6892 HeapWord* addr = (HeapWord*)obj;
6893 if (_span.contains(addr)) {
6894 // this should be made more efficient
6895 _bitMap->mark(addr);
6896 }
6897 }
6899 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6900 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6902 Par_MarkRefsIntoClosure::Par_MarkRefsIntoClosure(
6903 MemRegion span, CMSBitMap* bitMap):
6904 _span(span),
6905 _bitMap(bitMap)
6906 {
6907 assert(_ref_processor == NULL, "deliberately left NULL");
6908 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6909 }
6911 void Par_MarkRefsIntoClosure::do_oop(oop obj) {
6912 // if p points into _span, then mark corresponding bit in _markBitMap
6913 assert(obj->is_oop(), "expected an oop");
6914 HeapWord* addr = (HeapWord*)obj;
6915 if (_span.contains(addr)) {
6916 // this should be made more efficient
6917 _bitMap->par_mark(addr);
6918 }
6919 }
6921 void Par_MarkRefsIntoClosure::do_oop(oop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6922 void Par_MarkRefsIntoClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoClosure::do_oop_work(p); }
6924 // A variant of the above, used for CMS marking verification.
6925 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6926 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6927 _span(span),
6928 _verification_bm(verification_bm),
6929 _cms_bm(cms_bm)
6930 {
6931 assert(_ref_processor == NULL, "deliberately left NULL");
6932 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6933 }
6935 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6936 // if p points into _span, then mark corresponding bit in _markBitMap
6937 assert(obj->is_oop(), "expected an oop");
6938 HeapWord* addr = (HeapWord*)obj;
6939 if (_span.contains(addr)) {
6940 _verification_bm->mark(addr);
6941 if (!_cms_bm->isMarked(addr)) {
6942 oop(addr)->print();
6943 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6944 fatal("... aborting");
6945 }
6946 }
6947 }
6949 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6950 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6952 //////////////////////////////////////////////////
6953 // MarkRefsIntoAndScanClosure
6954 //////////////////////////////////////////////////
6956 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6957 ReferenceProcessor* rp,
6958 CMSBitMap* bit_map,
6959 CMSBitMap* mod_union_table,
6960 CMSMarkStack* mark_stack,
6961 CMSCollector* collector,
6962 bool should_yield,
6963 bool concurrent_precleaning):
6964 _collector(collector),
6965 _span(span),
6966 _bit_map(bit_map),
6967 _mark_stack(mark_stack),
6968 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6969 mark_stack, concurrent_precleaning),
6970 _yield(should_yield),
6971 _concurrent_precleaning(concurrent_precleaning),
6972 _freelistLock(NULL)
6973 {
6974 _ref_processor = rp;
6975 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6976 }
6978 // This closure is used to mark refs into the CMS generation at the
6979 // second (final) checkpoint, and to scan and transitively follow
6980 // the unmarked oops. It is also used during the concurrent precleaning
6981 // phase while scanning objects on dirty cards in the CMS generation.
6982 // The marks are made in the marking bit map and the marking stack is
6983 // used for keeping the (newly) grey objects during the scan.
6984 // The parallel version (Par_...) appears further below.
6985 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6986 if (obj != NULL) {
6987 assert(obj->is_oop(), "expected an oop");
6988 HeapWord* addr = (HeapWord*)obj;
6989 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6990 assert(_collector->overflow_list_is_empty(),
6991 "overflow list should be empty");
6992 if (_span.contains(addr) &&
6993 !_bit_map->isMarked(addr)) {
6994 // mark bit map (object is now grey)
6995 _bit_map->mark(addr);
6996 // push on marking stack (stack should be empty), and drain the
6997 // stack by applying this closure to the oops in the oops popped
6998 // from the stack (i.e. blacken the grey objects)
6999 bool res = _mark_stack->push(obj);
7000 assert(res, "Should have space to push on empty stack");
7001 do {
7002 oop new_oop = _mark_stack->pop();
7003 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7004 assert(_bit_map->isMarked((HeapWord*)new_oop),
7005 "only grey objects on this stack");
7006 // iterate over the oops in this oop, marking and pushing
7007 // the ones in CMS heap (i.e. in _span).
7008 new_oop->oop_iterate(&_pushAndMarkClosure);
7009 // check if it's time to yield
7010 do_yield_check();
7011 } while (!_mark_stack->isEmpty() ||
7012 (!_concurrent_precleaning && take_from_overflow_list()));
7013 // if marking stack is empty, and we are not doing this
7014 // during precleaning, then check the overflow list
7015 }
7016 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7017 assert(_collector->overflow_list_is_empty(),
7018 "overflow list was drained above");
7019 // We could restore evacuated mark words, if any, used for
7020 // overflow list links here because the overflow list is
7021 // provably empty here. That would reduce the maximum
7022 // size requirements for preserved_{oop,mark}_stack.
7023 // But we'll just postpone it until we are all done
7024 // so we can just stream through.
7025 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
7026 _collector->restore_preserved_marks_if_any();
7027 assert(_collector->no_preserved_marks(), "No preserved marks");
7028 }
7029 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
7030 "All preserved marks should have been restored above");
7031 }
7032 }
7034 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7035 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
7037 void MarkRefsIntoAndScanClosure::do_yield_work() {
7038 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7039 "CMS thread should hold CMS token");
7040 assert_lock_strong(_freelistLock);
7041 assert_lock_strong(_bit_map->lock());
7042 // relinquish the free_list_lock and bitMaplock()
7043 _bit_map->lock()->unlock();
7044 _freelistLock->unlock();
7045 ConcurrentMarkSweepThread::desynchronize(true);
7046 ConcurrentMarkSweepThread::acknowledge_yield_request();
7047 _collector->stopTimer();
7048 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7049 if (PrintCMSStatistics != 0) {
7050 _collector->incrementYields();
7051 }
7052 _collector->icms_wait();
7054 // See the comment in coordinator_yield()
7055 for (unsigned i = 0;
7056 i < CMSYieldSleepCount &&
7057 ConcurrentMarkSweepThread::should_yield() &&
7058 !CMSCollector::foregroundGCIsActive();
7059 ++i) {
7060 os::sleep(Thread::current(), 1, false);
7061 ConcurrentMarkSweepThread::acknowledge_yield_request();
7062 }
7064 ConcurrentMarkSweepThread::synchronize(true);
7065 _freelistLock->lock_without_safepoint_check();
7066 _bit_map->lock()->lock_without_safepoint_check();
7067 _collector->startTimer();
7068 }
7070 ///////////////////////////////////////////////////////////
7071 // Par_MarkRefsIntoAndScanClosure: a parallel version of
7072 // MarkRefsIntoAndScanClosure
7073 ///////////////////////////////////////////////////////////
7074 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
7075 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
7076 CMSBitMap* bit_map, OopTaskQueue* work_queue):
7077 _span(span),
7078 _bit_map(bit_map),
7079 _work_queue(work_queue),
7080 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
7081 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
7082 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
7083 {
7084 _ref_processor = rp;
7085 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7086 }
7088 // This closure is used to mark refs into the CMS generation at the
7089 // second (final) checkpoint, and to scan and transitively follow
7090 // the unmarked oops. The marks are made in the marking bit map and
7091 // the work_queue is used for keeping the (newly) grey objects during
7092 // the scan phase whence they are also available for stealing by parallel
7093 // threads. Since the marking bit map is shared, updates are
7094 // synchronized (via CAS).
7095 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
7096 if (obj != NULL) {
7097 // Ignore mark word because this could be an already marked oop
7098 // that may be chained at the end of the overflow list.
7099 assert(obj->is_oop(true), "expected an oop");
7100 HeapWord* addr = (HeapWord*)obj;
7101 if (_span.contains(addr) &&
7102 !_bit_map->isMarked(addr)) {
7103 // mark bit map (object will become grey):
7104 // It is possible for several threads to be
7105 // trying to "claim" this object concurrently;
7106 // the unique thread that succeeds in marking the
7107 // object first will do the subsequent push on
7108 // to the work queue (or overflow list).
7109 if (_bit_map->par_mark(addr)) {
7110 // push on work_queue (which may not be empty), and trim the
7111 // queue to an appropriate length by applying this closure to
7112 // the oops in the oops popped from the stack (i.e. blacken the
7113 // grey objects)
7114 bool res = _work_queue->push(obj);
7115 assert(res, "Low water mark should be less than capacity?");
7116 trim_queue(_low_water_mark);
7117 } // Else, another thread claimed the object
7118 }
7119 }
7120 }
7122 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7123 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
7125 // This closure is used to rescan the marked objects on the dirty cards
7126 // in the mod union table and the card table proper.
7127 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
7128 oop p, MemRegion mr) {
7130 size_t size = 0;
7131 HeapWord* addr = (HeapWord*)p;
7132 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7133 assert(_span.contains(addr), "we are scanning the CMS generation");
7134 // check if it's time to yield
7135 if (do_yield_check()) {
7136 // We yielded for some foreground stop-world work,
7137 // and we have been asked to abort this ongoing preclean cycle.
7138 return 0;
7139 }
7140 if (_bitMap->isMarked(addr)) {
7141 // it's marked; is it potentially uninitialized?
7142 if (p->klass_or_null() != NULL) {
7143 // an initialized object; ignore mark word in verification below
7144 // since we are running concurrent with mutators
7145 assert(p->is_oop(true), "should be an oop");
7146 if (p->is_objArray()) {
7147 // objArrays are precisely marked; restrict scanning
7148 // to dirty cards only.
7149 size = CompactibleFreeListSpace::adjustObjectSize(
7150 p->oop_iterate(_scanningClosure, mr));
7151 } else {
7152 // A non-array may have been imprecisely marked; we need
7153 // to scan object in its entirety.
7154 size = CompactibleFreeListSpace::adjustObjectSize(
7155 p->oop_iterate(_scanningClosure));
7156 }
7157 #ifdef ASSERT
7158 size_t direct_size =
7159 CompactibleFreeListSpace::adjustObjectSize(p->size());
7160 assert(size == direct_size, "Inconsistency in size");
7161 assert(size >= 3, "Necessary for Printezis marks to work");
7162 if (!_bitMap->isMarked(addr+1)) {
7163 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
7164 } else {
7165 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
7166 assert(_bitMap->isMarked(addr+size-1),
7167 "inconsistent Printezis mark");
7168 }
7169 #endif // ASSERT
7170 } else {
7171 // an unitialized object
7172 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
7173 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7174 size = pointer_delta(nextOneAddr + 1, addr);
7175 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7176 "alignment problem");
7177 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
7178 // will dirty the card when the klass pointer is installed in the
7179 // object (signalling the completion of initialization).
7180 }
7181 } else {
7182 // Either a not yet marked object or an uninitialized object
7183 if (p->klass_or_null() == NULL) {
7184 // An uninitialized object, skip to the next card, since
7185 // we may not be able to read its P-bits yet.
7186 assert(size == 0, "Initial value");
7187 } else {
7188 // An object not (yet) reached by marking: we merely need to
7189 // compute its size so as to go look at the next block.
7190 assert(p->is_oop(true), "should be an oop");
7191 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
7192 }
7193 }
7194 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7195 return size;
7196 }
7198 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
7199 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7200 "CMS thread should hold CMS token");
7201 assert_lock_strong(_freelistLock);
7202 assert_lock_strong(_bitMap->lock());
7203 // relinquish the free_list_lock and bitMaplock()
7204 _bitMap->lock()->unlock();
7205 _freelistLock->unlock();
7206 ConcurrentMarkSweepThread::desynchronize(true);
7207 ConcurrentMarkSweepThread::acknowledge_yield_request();
7208 _collector->stopTimer();
7209 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7210 if (PrintCMSStatistics != 0) {
7211 _collector->incrementYields();
7212 }
7213 _collector->icms_wait();
7215 // See the comment in coordinator_yield()
7216 for (unsigned i = 0; i < CMSYieldSleepCount &&
7217 ConcurrentMarkSweepThread::should_yield() &&
7218 !CMSCollector::foregroundGCIsActive(); ++i) {
7219 os::sleep(Thread::current(), 1, false);
7220 ConcurrentMarkSweepThread::acknowledge_yield_request();
7221 }
7223 ConcurrentMarkSweepThread::synchronize(true);
7224 _freelistLock->lock_without_safepoint_check();
7225 _bitMap->lock()->lock_without_safepoint_check();
7226 _collector->startTimer();
7227 }
7230 //////////////////////////////////////////////////////////////////
7231 // SurvivorSpacePrecleanClosure
7232 //////////////////////////////////////////////////////////////////
7233 // This (single-threaded) closure is used to preclean the oops in
7234 // the survivor spaces.
7235 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7237 HeapWord* addr = (HeapWord*)p;
7238 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7239 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7240 assert(p->klass_or_null() != NULL, "object should be initializd");
7241 // an initialized object; ignore mark word in verification below
7242 // since we are running concurrent with mutators
7243 assert(p->is_oop(true), "should be an oop");
7244 // Note that we do not yield while we iterate over
7245 // the interior oops of p, pushing the relevant ones
7246 // on our marking stack.
7247 size_t size = p->oop_iterate(_scanning_closure);
7248 do_yield_check();
7249 // Observe that below, we do not abandon the preclean
7250 // phase as soon as we should; rather we empty the
7251 // marking stack before returning. This is to satisfy
7252 // some existing assertions. In general, it may be a
7253 // good idea to abort immediately and complete the marking
7254 // from the grey objects at a later time.
7255 while (!_mark_stack->isEmpty()) {
7256 oop new_oop = _mark_stack->pop();
7257 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7258 assert(_bit_map->isMarked((HeapWord*)new_oop),
7259 "only grey objects on this stack");
7260 // iterate over the oops in this oop, marking and pushing
7261 // the ones in CMS heap (i.e. in _span).
7262 new_oop->oop_iterate(_scanning_closure);
7263 // check if it's time to yield
7264 do_yield_check();
7265 }
7266 unsigned int after_count =
7267 GenCollectedHeap::heap()->total_collections();
7268 bool abort = (_before_count != after_count) ||
7269 _collector->should_abort_preclean();
7270 return abort ? 0 : size;
7271 }
7273 void SurvivorSpacePrecleanClosure::do_yield_work() {
7274 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7275 "CMS thread should hold CMS token");
7276 assert_lock_strong(_bit_map->lock());
7277 // Relinquish the bit map lock
7278 _bit_map->lock()->unlock();
7279 ConcurrentMarkSweepThread::desynchronize(true);
7280 ConcurrentMarkSweepThread::acknowledge_yield_request();
7281 _collector->stopTimer();
7282 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7283 if (PrintCMSStatistics != 0) {
7284 _collector->incrementYields();
7285 }
7286 _collector->icms_wait();
7288 // See the comment in coordinator_yield()
7289 for (unsigned i = 0; i < CMSYieldSleepCount &&
7290 ConcurrentMarkSweepThread::should_yield() &&
7291 !CMSCollector::foregroundGCIsActive(); ++i) {
7292 os::sleep(Thread::current(), 1, false);
7293 ConcurrentMarkSweepThread::acknowledge_yield_request();
7294 }
7296 ConcurrentMarkSweepThread::synchronize(true);
7297 _bit_map->lock()->lock_without_safepoint_check();
7298 _collector->startTimer();
7299 }
7301 // This closure is used to rescan the marked objects on the dirty cards
7302 // in the mod union table and the card table proper. In the parallel
7303 // case, although the bitMap is shared, we do a single read so the
7304 // isMarked() query is "safe".
7305 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7306 // Ignore mark word because we are running concurrent with mutators
7307 assert(p->is_oop_or_null(true), "expected an oop or null");
7308 HeapWord* addr = (HeapWord*)p;
7309 assert(_span.contains(addr), "we are scanning the CMS generation");
7310 bool is_obj_array = false;
7311 #ifdef ASSERT
7312 if (!_parallel) {
7313 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7314 assert(_collector->overflow_list_is_empty(),
7315 "overflow list should be empty");
7317 }
7318 #endif // ASSERT
7319 if (_bit_map->isMarked(addr)) {
7320 // Obj arrays are precisely marked, non-arrays are not;
7321 // so we scan objArrays precisely and non-arrays in their
7322 // entirety.
7323 if (p->is_objArray()) {
7324 is_obj_array = true;
7325 if (_parallel) {
7326 p->oop_iterate(_par_scan_closure, mr);
7327 } else {
7328 p->oop_iterate(_scan_closure, mr);
7329 }
7330 } else {
7331 if (_parallel) {
7332 p->oop_iterate(_par_scan_closure);
7333 } else {
7334 p->oop_iterate(_scan_closure);
7335 }
7336 }
7337 }
7338 #ifdef ASSERT
7339 if (!_parallel) {
7340 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7341 assert(_collector->overflow_list_is_empty(),
7342 "overflow list should be empty");
7344 }
7345 #endif // ASSERT
7346 return is_obj_array;
7347 }
7349 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7350 MemRegion span,
7351 CMSBitMap* bitMap, CMSMarkStack* markStack,
7352 bool should_yield, bool verifying):
7353 _collector(collector),
7354 _span(span),
7355 _bitMap(bitMap),
7356 _mut(&collector->_modUnionTable),
7357 _markStack(markStack),
7358 _yield(should_yield),
7359 _skipBits(0)
7360 {
7361 assert(_markStack->isEmpty(), "stack should be empty");
7362 _finger = _bitMap->startWord();
7363 _threshold = _finger;
7364 assert(_collector->_restart_addr == NULL, "Sanity check");
7365 assert(_span.contains(_finger), "Out of bounds _finger?");
7366 DEBUG_ONLY(_verifying = verifying;)
7367 }
7369 void MarkFromRootsClosure::reset(HeapWord* addr) {
7370 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7371 assert(_span.contains(addr), "Out of bounds _finger?");
7372 _finger = addr;
7373 _threshold = (HeapWord*)round_to(
7374 (intptr_t)_finger, CardTableModRefBS::card_size);
7375 }
7377 // Should revisit to see if this should be restructured for
7378 // greater efficiency.
7379 bool MarkFromRootsClosure::do_bit(size_t offset) {
7380 if (_skipBits > 0) {
7381 _skipBits--;
7382 return true;
7383 }
7384 // convert offset into a HeapWord*
7385 HeapWord* addr = _bitMap->startWord() + offset;
7386 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7387 "address out of range");
7388 assert(_bitMap->isMarked(addr), "tautology");
7389 if (_bitMap->isMarked(addr+1)) {
7390 // this is an allocated but not yet initialized object
7391 assert(_skipBits == 0, "tautology");
7392 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7393 oop p = oop(addr);
7394 if (p->klass_or_null() == NULL) {
7395 DEBUG_ONLY(if (!_verifying) {)
7396 // We re-dirty the cards on which this object lies and increase
7397 // the _threshold so that we'll come back to scan this object
7398 // during the preclean or remark phase. (CMSCleanOnEnter)
7399 if (CMSCleanOnEnter) {
7400 size_t sz = _collector->block_size_using_printezis_bits(addr);
7401 HeapWord* end_card_addr = (HeapWord*)round_to(
7402 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7403 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7404 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7405 // Bump _threshold to end_card_addr; note that
7406 // _threshold cannot possibly exceed end_card_addr, anyhow.
7407 // This prevents future clearing of the card as the scan proceeds
7408 // to the right.
7409 assert(_threshold <= end_card_addr,
7410 "Because we are just scanning into this object");
7411 if (_threshold < end_card_addr) {
7412 _threshold = end_card_addr;
7413 }
7414 if (p->klass_or_null() != NULL) {
7415 // Redirty the range of cards...
7416 _mut->mark_range(redirty_range);
7417 } // ...else the setting of klass will dirty the card anyway.
7418 }
7419 DEBUG_ONLY(})
7420 return true;
7421 }
7422 }
7423 scanOopsInOop(addr);
7424 return true;
7425 }
7427 // We take a break if we've been at this for a while,
7428 // so as to avoid monopolizing the locks involved.
7429 void MarkFromRootsClosure::do_yield_work() {
7430 // First give up the locks, then yield, then re-lock
7431 // We should probably use a constructor/destructor idiom to
7432 // do this unlock/lock or modify the MutexUnlocker class to
7433 // serve our purpose. XXX
7434 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7435 "CMS thread should hold CMS token");
7436 assert_lock_strong(_bitMap->lock());
7437 _bitMap->lock()->unlock();
7438 ConcurrentMarkSweepThread::desynchronize(true);
7439 ConcurrentMarkSweepThread::acknowledge_yield_request();
7440 _collector->stopTimer();
7441 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7442 if (PrintCMSStatistics != 0) {
7443 _collector->incrementYields();
7444 }
7445 _collector->icms_wait();
7447 // See the comment in coordinator_yield()
7448 for (unsigned i = 0; i < CMSYieldSleepCount &&
7449 ConcurrentMarkSweepThread::should_yield() &&
7450 !CMSCollector::foregroundGCIsActive(); ++i) {
7451 os::sleep(Thread::current(), 1, false);
7452 ConcurrentMarkSweepThread::acknowledge_yield_request();
7453 }
7455 ConcurrentMarkSweepThread::synchronize(true);
7456 _bitMap->lock()->lock_without_safepoint_check();
7457 _collector->startTimer();
7458 }
7460 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7461 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7462 assert(_markStack->isEmpty(),
7463 "should drain stack to limit stack usage");
7464 // convert ptr to an oop preparatory to scanning
7465 oop obj = oop(ptr);
7466 // Ignore mark word in verification below, since we
7467 // may be running concurrent with mutators.
7468 assert(obj->is_oop(true), "should be an oop");
7469 assert(_finger <= ptr, "_finger runneth ahead");
7470 // advance the finger to right end of this object
7471 _finger = ptr + obj->size();
7472 assert(_finger > ptr, "we just incremented it above");
7473 // On large heaps, it may take us some time to get through
7474 // the marking phase (especially if running iCMS). During
7475 // this time it's possible that a lot of mutations have
7476 // accumulated in the card table and the mod union table --
7477 // these mutation records are redundant until we have
7478 // actually traced into the corresponding card.
7479 // Here, we check whether advancing the finger would make
7480 // us cross into a new card, and if so clear corresponding
7481 // cards in the MUT (preclean them in the card-table in the
7482 // future).
7484 DEBUG_ONLY(if (!_verifying) {)
7485 // The clean-on-enter optimization is disabled by default,
7486 // until we fix 6178663.
7487 if (CMSCleanOnEnter && (_finger > _threshold)) {
7488 // [_threshold, _finger) represents the interval
7489 // of cards to be cleared in MUT (or precleaned in card table).
7490 // The set of cards to be cleared is all those that overlap
7491 // with the interval [_threshold, _finger); note that
7492 // _threshold is always kept card-aligned but _finger isn't
7493 // always card-aligned.
7494 HeapWord* old_threshold = _threshold;
7495 assert(old_threshold == (HeapWord*)round_to(
7496 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7497 "_threshold should always be card-aligned");
7498 _threshold = (HeapWord*)round_to(
7499 (intptr_t)_finger, CardTableModRefBS::card_size);
7500 MemRegion mr(old_threshold, _threshold);
7501 assert(!mr.is_empty(), "Control point invariant");
7502 assert(_span.contains(mr), "Should clear within span");
7503 _mut->clear_range(mr);
7504 }
7505 DEBUG_ONLY(})
7506 // Note: the finger doesn't advance while we drain
7507 // the stack below.
7508 PushOrMarkClosure pushOrMarkClosure(_collector,
7509 _span, _bitMap, _markStack,
7510 _finger, this);
7511 bool res = _markStack->push(obj);
7512 assert(res, "Empty non-zero size stack should have space for single push");
7513 while (!_markStack->isEmpty()) {
7514 oop new_oop = _markStack->pop();
7515 // Skip verifying header mark word below because we are
7516 // running concurrent with mutators.
7517 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7518 // now scan this oop's oops
7519 new_oop->oop_iterate(&pushOrMarkClosure);
7520 do_yield_check();
7521 }
7522 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7523 }
7525 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7526 CMSCollector* collector, MemRegion span,
7527 CMSBitMap* bit_map,
7528 OopTaskQueue* work_queue,
7529 CMSMarkStack* overflow_stack,
7530 bool should_yield):
7531 _collector(collector),
7532 _whole_span(collector->_span),
7533 _span(span),
7534 _bit_map(bit_map),
7535 _mut(&collector->_modUnionTable),
7536 _work_queue(work_queue),
7537 _overflow_stack(overflow_stack),
7538 _yield(should_yield),
7539 _skip_bits(0),
7540 _task(task)
7541 {
7542 assert(_work_queue->size() == 0, "work_queue should be empty");
7543 _finger = span.start();
7544 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7545 assert(_span.contains(_finger), "Out of bounds _finger?");
7546 }
7548 // Should revisit to see if this should be restructured for
7549 // greater efficiency.
7550 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7551 if (_skip_bits > 0) {
7552 _skip_bits--;
7553 return true;
7554 }
7555 // convert offset into a HeapWord*
7556 HeapWord* addr = _bit_map->startWord() + offset;
7557 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7558 "address out of range");
7559 assert(_bit_map->isMarked(addr), "tautology");
7560 if (_bit_map->isMarked(addr+1)) {
7561 // this is an allocated object that might not yet be initialized
7562 assert(_skip_bits == 0, "tautology");
7563 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7564 oop p = oop(addr);
7565 if (p->klass_or_null() == NULL) {
7566 // in the case of Clean-on-Enter optimization, redirty card
7567 // and avoid clearing card by increasing the threshold.
7568 return true;
7569 }
7570 }
7571 scan_oops_in_oop(addr);
7572 return true;
7573 }
7575 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7576 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7577 // Should we assert that our work queue is empty or
7578 // below some drain limit?
7579 assert(_work_queue->size() == 0,
7580 "should drain stack to limit stack usage");
7581 // convert ptr to an oop preparatory to scanning
7582 oop obj = oop(ptr);
7583 // Ignore mark word in verification below, since we
7584 // may be running concurrent with mutators.
7585 assert(obj->is_oop(true), "should be an oop");
7586 assert(_finger <= ptr, "_finger runneth ahead");
7587 // advance the finger to right end of this object
7588 _finger = ptr + obj->size();
7589 assert(_finger > ptr, "we just incremented it above");
7590 // On large heaps, it may take us some time to get through
7591 // the marking phase (especially if running iCMS). During
7592 // this time it's possible that a lot of mutations have
7593 // accumulated in the card table and the mod union table --
7594 // these mutation records are redundant until we have
7595 // actually traced into the corresponding card.
7596 // Here, we check whether advancing the finger would make
7597 // us cross into a new card, and if so clear corresponding
7598 // cards in the MUT (preclean them in the card-table in the
7599 // future).
7601 // The clean-on-enter optimization is disabled by default,
7602 // until we fix 6178663.
7603 if (CMSCleanOnEnter && (_finger > _threshold)) {
7604 // [_threshold, _finger) represents the interval
7605 // of cards to be cleared in MUT (or precleaned in card table).
7606 // The set of cards to be cleared is all those that overlap
7607 // with the interval [_threshold, _finger); note that
7608 // _threshold is always kept card-aligned but _finger isn't
7609 // always card-aligned.
7610 HeapWord* old_threshold = _threshold;
7611 assert(old_threshold == (HeapWord*)round_to(
7612 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7613 "_threshold should always be card-aligned");
7614 _threshold = (HeapWord*)round_to(
7615 (intptr_t)_finger, CardTableModRefBS::card_size);
7616 MemRegion mr(old_threshold, _threshold);
7617 assert(!mr.is_empty(), "Control point invariant");
7618 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7619 _mut->clear_range(mr);
7620 }
7622 // Note: the local finger doesn't advance while we drain
7623 // the stack below, but the global finger sure can and will.
7624 HeapWord** gfa = _task->global_finger_addr();
7625 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7626 _span, _bit_map,
7627 _work_queue,
7628 _overflow_stack,
7629 _finger,
7630 gfa, this);
7631 bool res = _work_queue->push(obj); // overflow could occur here
7632 assert(res, "Will hold once we use workqueues");
7633 while (true) {
7634 oop new_oop;
7635 if (!_work_queue->pop_local(new_oop)) {
7636 // We emptied our work_queue; check if there's stuff that can
7637 // be gotten from the overflow stack.
7638 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7639 _overflow_stack, _work_queue)) {
7640 do_yield_check();
7641 continue;
7642 } else { // done
7643 break;
7644 }
7645 }
7646 // Skip verifying header mark word below because we are
7647 // running concurrent with mutators.
7648 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7649 // now scan this oop's oops
7650 new_oop->oop_iterate(&pushOrMarkClosure);
7651 do_yield_check();
7652 }
7653 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7654 }
7656 // Yield in response to a request from VM Thread or
7657 // from mutators.
7658 void Par_MarkFromRootsClosure::do_yield_work() {
7659 assert(_task != NULL, "sanity");
7660 _task->yield();
7661 }
7663 // A variant of the above used for verifying CMS marking work.
7664 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7665 MemRegion span,
7666 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7667 CMSMarkStack* mark_stack):
7668 _collector(collector),
7669 _span(span),
7670 _verification_bm(verification_bm),
7671 _cms_bm(cms_bm),
7672 _mark_stack(mark_stack),
7673 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7674 mark_stack)
7675 {
7676 assert(_mark_stack->isEmpty(), "stack should be empty");
7677 _finger = _verification_bm->startWord();
7678 assert(_collector->_restart_addr == NULL, "Sanity check");
7679 assert(_span.contains(_finger), "Out of bounds _finger?");
7680 }
7682 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7683 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7684 assert(_span.contains(addr), "Out of bounds _finger?");
7685 _finger = addr;
7686 }
7688 // Should revisit to see if this should be restructured for
7689 // greater efficiency.
7690 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7691 // convert offset into a HeapWord*
7692 HeapWord* addr = _verification_bm->startWord() + offset;
7693 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7694 "address out of range");
7695 assert(_verification_bm->isMarked(addr), "tautology");
7696 assert(_cms_bm->isMarked(addr), "tautology");
7698 assert(_mark_stack->isEmpty(),
7699 "should drain stack to limit stack usage");
7700 // convert addr to an oop preparatory to scanning
7701 oop obj = oop(addr);
7702 assert(obj->is_oop(), "should be an oop");
7703 assert(_finger <= addr, "_finger runneth ahead");
7704 // advance the finger to right end of this object
7705 _finger = addr + obj->size();
7706 assert(_finger > addr, "we just incremented it above");
7707 // Note: the finger doesn't advance while we drain
7708 // the stack below.
7709 bool res = _mark_stack->push(obj);
7710 assert(res, "Empty non-zero size stack should have space for single push");
7711 while (!_mark_stack->isEmpty()) {
7712 oop new_oop = _mark_stack->pop();
7713 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7714 // now scan this oop's oops
7715 new_oop->oop_iterate(&_pam_verify_closure);
7716 }
7717 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7718 return true;
7719 }
7721 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7722 CMSCollector* collector, MemRegion span,
7723 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7724 CMSMarkStack* mark_stack):
7725 MetadataAwareOopClosure(collector->ref_processor()),
7726 _collector(collector),
7727 _span(span),
7728 _verification_bm(verification_bm),
7729 _cms_bm(cms_bm),
7730 _mark_stack(mark_stack)
7731 { }
7733 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7734 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7736 // Upon stack overflow, we discard (part of) the stack,
7737 // remembering the least address amongst those discarded
7738 // in CMSCollector's _restart_address.
7739 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7740 // Remember the least grey address discarded
7741 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7742 _collector->lower_restart_addr(ra);
7743 _mark_stack->reset(); // discard stack contents
7744 _mark_stack->expand(); // expand the stack if possible
7745 }
7747 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7748 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7749 HeapWord* addr = (HeapWord*)obj;
7750 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7751 // Oop lies in _span and isn't yet grey or black
7752 _verification_bm->mark(addr); // now grey
7753 if (!_cms_bm->isMarked(addr)) {
7754 oop(addr)->print();
7755 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7756 addr);
7757 fatal("... aborting");
7758 }
7760 if (!_mark_stack->push(obj)) { // stack overflow
7761 if (PrintCMSStatistics != 0) {
7762 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7763 SIZE_FORMAT, _mark_stack->capacity());
7764 }
7765 assert(_mark_stack->isFull(), "Else push should have succeeded");
7766 handle_stack_overflow(addr);
7767 }
7768 // anything including and to the right of _finger
7769 // will be scanned as we iterate over the remainder of the
7770 // bit map
7771 }
7772 }
7774 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7775 MemRegion span,
7776 CMSBitMap* bitMap, CMSMarkStack* markStack,
7777 HeapWord* finger, MarkFromRootsClosure* parent) :
7778 MetadataAwareOopClosure(collector->ref_processor()),
7779 _collector(collector),
7780 _span(span),
7781 _bitMap(bitMap),
7782 _markStack(markStack),
7783 _finger(finger),
7784 _parent(parent)
7785 { }
7787 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7788 MemRegion span,
7789 CMSBitMap* bit_map,
7790 OopTaskQueue* work_queue,
7791 CMSMarkStack* overflow_stack,
7792 HeapWord* finger,
7793 HeapWord** global_finger_addr,
7794 Par_MarkFromRootsClosure* parent) :
7795 MetadataAwareOopClosure(collector->ref_processor()),
7796 _collector(collector),
7797 _whole_span(collector->_span),
7798 _span(span),
7799 _bit_map(bit_map),
7800 _work_queue(work_queue),
7801 _overflow_stack(overflow_stack),
7802 _finger(finger),
7803 _global_finger_addr(global_finger_addr),
7804 _parent(parent)
7805 { }
7807 // Assumes thread-safe access by callers, who are
7808 // responsible for mutual exclusion.
7809 void CMSCollector::lower_restart_addr(HeapWord* low) {
7810 assert(_span.contains(low), "Out of bounds addr");
7811 if (_restart_addr == NULL) {
7812 _restart_addr = low;
7813 } else {
7814 _restart_addr = MIN2(_restart_addr, low);
7815 }
7816 }
7818 // Upon stack overflow, we discard (part of) the stack,
7819 // remembering the least address amongst those discarded
7820 // in CMSCollector's _restart_address.
7821 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7822 // Remember the least grey address discarded
7823 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7824 _collector->lower_restart_addr(ra);
7825 _markStack->reset(); // discard stack contents
7826 _markStack->expand(); // expand the stack if possible
7827 }
7829 // Upon stack overflow, we discard (part of) the stack,
7830 // remembering the least address amongst those discarded
7831 // in CMSCollector's _restart_address.
7832 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7833 // We need to do this under a mutex to prevent other
7834 // workers from interfering with the work done below.
7835 MutexLockerEx ml(_overflow_stack->par_lock(),
7836 Mutex::_no_safepoint_check_flag);
7837 // Remember the least grey address discarded
7838 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7839 _collector->lower_restart_addr(ra);
7840 _overflow_stack->reset(); // discard stack contents
7841 _overflow_stack->expand(); // expand the stack if possible
7842 }
7844 void PushOrMarkClosure::do_oop(oop obj) {
7845 // Ignore mark word because we are running concurrent with mutators.
7846 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7847 HeapWord* addr = (HeapWord*)obj;
7848 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7849 // Oop lies in _span and isn't yet grey or black
7850 _bitMap->mark(addr); // now grey
7851 if (addr < _finger) {
7852 // the bit map iteration has already either passed, or
7853 // sampled, this bit in the bit map; we'll need to
7854 // use the marking stack to scan this oop's oops.
7855 bool simulate_overflow = false;
7856 NOT_PRODUCT(
7857 if (CMSMarkStackOverflowALot &&
7858 _collector->simulate_overflow()) {
7859 // simulate a stack overflow
7860 simulate_overflow = true;
7861 }
7862 )
7863 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7864 if (PrintCMSStatistics != 0) {
7865 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7866 SIZE_FORMAT, _markStack->capacity());
7867 }
7868 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7869 handle_stack_overflow(addr);
7870 }
7871 }
7872 // anything including and to the right of _finger
7873 // will be scanned as we iterate over the remainder of the
7874 // bit map
7875 do_yield_check();
7876 }
7877 }
7879 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7880 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7882 void Par_PushOrMarkClosure::do_oop(oop obj) {
7883 // Ignore mark word because we are running concurrent with mutators.
7884 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7885 HeapWord* addr = (HeapWord*)obj;
7886 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7887 // Oop lies in _span and isn't yet grey or black
7888 // We read the global_finger (volatile read) strictly after marking oop
7889 bool res = _bit_map->par_mark(addr); // now grey
7890 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7891 // Should we push this marked oop on our stack?
7892 // -- if someone else marked it, nothing to do
7893 // -- if target oop is above global finger nothing to do
7894 // -- if target oop is in chunk and above local finger
7895 // then nothing to do
7896 // -- else push on work queue
7897 if ( !res // someone else marked it, they will deal with it
7898 || (addr >= *gfa) // will be scanned in a later task
7899 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7900 return;
7901 }
7902 // the bit map iteration has already either passed, or
7903 // sampled, this bit in the bit map; we'll need to
7904 // use the marking stack to scan this oop's oops.
7905 bool simulate_overflow = false;
7906 NOT_PRODUCT(
7907 if (CMSMarkStackOverflowALot &&
7908 _collector->simulate_overflow()) {
7909 // simulate a stack overflow
7910 simulate_overflow = true;
7911 }
7912 )
7913 if (simulate_overflow ||
7914 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7915 // stack overflow
7916 if (PrintCMSStatistics != 0) {
7917 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7918 SIZE_FORMAT, _overflow_stack->capacity());
7919 }
7920 // We cannot assert that the overflow stack is full because
7921 // it may have been emptied since.
7922 assert(simulate_overflow ||
7923 _work_queue->size() == _work_queue->max_elems(),
7924 "Else push should have succeeded");
7925 handle_stack_overflow(addr);
7926 }
7927 do_yield_check();
7928 }
7929 }
7931 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7932 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7934 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7935 MemRegion span,
7936 ReferenceProcessor* rp,
7937 CMSBitMap* bit_map,
7938 CMSBitMap* mod_union_table,
7939 CMSMarkStack* mark_stack,
7940 bool concurrent_precleaning):
7941 MetadataAwareOopClosure(rp),
7942 _collector(collector),
7943 _span(span),
7944 _bit_map(bit_map),
7945 _mod_union_table(mod_union_table),
7946 _mark_stack(mark_stack),
7947 _concurrent_precleaning(concurrent_precleaning)
7948 {
7949 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7950 }
7952 // Grey object rescan during pre-cleaning and second checkpoint phases --
7953 // the non-parallel version (the parallel version appears further below.)
7954 void PushAndMarkClosure::do_oop(oop obj) {
7955 // Ignore mark word verification. If during concurrent precleaning,
7956 // the object monitor may be locked. If during the checkpoint
7957 // phases, the object may already have been reached by a different
7958 // path and may be at the end of the global overflow list (so
7959 // the mark word may be NULL).
7960 assert(obj->is_oop_or_null(true /* ignore mark word */),
7961 "expected an oop or NULL");
7962 HeapWord* addr = (HeapWord*)obj;
7963 // Check if oop points into the CMS generation
7964 // and is not marked
7965 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7966 // a white object ...
7967 _bit_map->mark(addr); // ... now grey
7968 // push on the marking stack (grey set)
7969 bool simulate_overflow = false;
7970 NOT_PRODUCT(
7971 if (CMSMarkStackOverflowALot &&
7972 _collector->simulate_overflow()) {
7973 // simulate a stack overflow
7974 simulate_overflow = true;
7975 }
7976 )
7977 if (simulate_overflow || !_mark_stack->push(obj)) {
7978 if (_concurrent_precleaning) {
7979 // During precleaning we can just dirty the appropriate card(s)
7980 // in the mod union table, thus ensuring that the object remains
7981 // in the grey set and continue. In the case of object arrays
7982 // we need to dirty all of the cards that the object spans,
7983 // since the rescan of object arrays will be limited to the
7984 // dirty cards.
7985 // Note that no one can be intefering with us in this action
7986 // of dirtying the mod union table, so no locking or atomics
7987 // are required.
7988 if (obj->is_objArray()) {
7989 size_t sz = obj->size();
7990 HeapWord* end_card_addr = (HeapWord*)round_to(
7991 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7992 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7993 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7994 _mod_union_table->mark_range(redirty_range);
7995 } else {
7996 _mod_union_table->mark(addr);
7997 }
7998 _collector->_ser_pmc_preclean_ovflw++;
7999 } else {
8000 // During the remark phase, we need to remember this oop
8001 // in the overflow list.
8002 _collector->push_on_overflow_list(obj);
8003 _collector->_ser_pmc_remark_ovflw++;
8004 }
8005 }
8006 }
8007 }
8009 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
8010 MemRegion span,
8011 ReferenceProcessor* rp,
8012 CMSBitMap* bit_map,
8013 OopTaskQueue* work_queue):
8014 MetadataAwareOopClosure(rp),
8015 _collector(collector),
8016 _span(span),
8017 _bit_map(bit_map),
8018 _work_queue(work_queue)
8019 {
8020 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
8021 }
8023 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
8024 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
8026 // Grey object rescan during second checkpoint phase --
8027 // the parallel version.
8028 void Par_PushAndMarkClosure::do_oop(oop obj) {
8029 // In the assert below, we ignore the mark word because
8030 // this oop may point to an already visited object that is
8031 // on the overflow stack (in which case the mark word has
8032 // been hijacked for chaining into the overflow stack --
8033 // if this is the last object in the overflow stack then
8034 // its mark word will be NULL). Because this object may
8035 // have been subsequently popped off the global overflow
8036 // stack, and the mark word possibly restored to the prototypical
8037 // value, by the time we get to examined this failing assert in
8038 // the debugger, is_oop_or_null(false) may subsequently start
8039 // to hold.
8040 assert(obj->is_oop_or_null(true),
8041 "expected an oop or NULL");
8042 HeapWord* addr = (HeapWord*)obj;
8043 // Check if oop points into the CMS generation
8044 // and is not marked
8045 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
8046 // a white object ...
8047 // If we manage to "claim" the object, by being the
8048 // first thread to mark it, then we push it on our
8049 // marking stack
8050 if (_bit_map->par_mark(addr)) { // ... now grey
8051 // push on work queue (grey set)
8052 bool simulate_overflow = false;
8053 NOT_PRODUCT(
8054 if (CMSMarkStackOverflowALot &&
8055 _collector->par_simulate_overflow()) {
8056 // simulate a stack overflow
8057 simulate_overflow = true;
8058 }
8059 )
8060 if (simulate_overflow || !_work_queue->push(obj)) {
8061 _collector->par_push_on_overflow_list(obj);
8062 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
8063 }
8064 } // Else, some other thread got there first
8065 }
8066 }
8068 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8069 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
8071 void CMSPrecleanRefsYieldClosure::do_yield_work() {
8072 Mutex* bml = _collector->bitMapLock();
8073 assert_lock_strong(bml);
8074 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8075 "CMS thread should hold CMS token");
8077 bml->unlock();
8078 ConcurrentMarkSweepThread::desynchronize(true);
8080 ConcurrentMarkSweepThread::acknowledge_yield_request();
8082 _collector->stopTimer();
8083 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8084 if (PrintCMSStatistics != 0) {
8085 _collector->incrementYields();
8086 }
8087 _collector->icms_wait();
8089 // See the comment in coordinator_yield()
8090 for (unsigned i = 0; i < CMSYieldSleepCount &&
8091 ConcurrentMarkSweepThread::should_yield() &&
8092 !CMSCollector::foregroundGCIsActive(); ++i) {
8093 os::sleep(Thread::current(), 1, false);
8094 ConcurrentMarkSweepThread::acknowledge_yield_request();
8095 }
8097 ConcurrentMarkSweepThread::synchronize(true);
8098 bml->lock();
8100 _collector->startTimer();
8101 }
8103 bool CMSPrecleanRefsYieldClosure::should_return() {
8104 if (ConcurrentMarkSweepThread::should_yield()) {
8105 do_yield_work();
8106 }
8107 return _collector->foregroundGCIsActive();
8108 }
8110 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
8111 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
8112 "mr should be aligned to start at a card boundary");
8113 // We'd like to assert:
8114 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
8115 // "mr should be a range of cards");
8116 // However, that would be too strong in one case -- the last
8117 // partition ends at _unallocated_block which, in general, can be
8118 // an arbitrary boundary, not necessarily card aligned.
8119 if (PrintCMSStatistics != 0) {
8120 _num_dirty_cards +=
8121 mr.word_size()/CardTableModRefBS::card_size_in_words;
8122 }
8123 _space->object_iterate_mem(mr, &_scan_cl);
8124 }
8126 SweepClosure::SweepClosure(CMSCollector* collector,
8127 ConcurrentMarkSweepGeneration* g,
8128 CMSBitMap* bitMap, bool should_yield) :
8129 _collector(collector),
8130 _g(g),
8131 _sp(g->cmsSpace()),
8132 _limit(_sp->sweep_limit()),
8133 _freelistLock(_sp->freelistLock()),
8134 _bitMap(bitMap),
8135 _yield(should_yield),
8136 _inFreeRange(false), // No free range at beginning of sweep
8137 _freeRangeInFreeLists(false), // No free range at beginning of sweep
8138 _lastFreeRangeCoalesced(false),
8139 _freeFinger(g->used_region().start())
8140 {
8141 NOT_PRODUCT(
8142 _numObjectsFreed = 0;
8143 _numWordsFreed = 0;
8144 _numObjectsLive = 0;
8145 _numWordsLive = 0;
8146 _numObjectsAlreadyFree = 0;
8147 _numWordsAlreadyFree = 0;
8148 _last_fc = NULL;
8150 _sp->initializeIndexedFreeListArrayReturnedBytes();
8151 _sp->dictionary()->initialize_dict_returned_bytes();
8152 )
8153 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8154 "sweep _limit out of bounds");
8155 if (CMSTraceSweeper) {
8156 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
8157 _limit);
8158 }
8159 }
8161 void SweepClosure::print_on(outputStream* st) const {
8162 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
8163 _sp->bottom(), _sp->end());
8164 tty->print_cr("_limit = " PTR_FORMAT, _limit);
8165 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
8166 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
8167 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
8168 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
8169 }
8171 #ifndef PRODUCT
8172 // Assertion checking only: no useful work in product mode --
8173 // however, if any of the flags below become product flags,
8174 // you may need to review this code to see if it needs to be
8175 // enabled in product mode.
8176 SweepClosure::~SweepClosure() {
8177 assert_lock_strong(_freelistLock);
8178 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8179 "sweep _limit out of bounds");
8180 if (inFreeRange()) {
8181 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8182 print();
8183 ShouldNotReachHere();
8184 }
8185 if (Verbose && PrintGC) {
8186 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8187 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8188 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8189 SIZE_FORMAT" bytes "
8190 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8191 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8192 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8193 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8194 * sizeof(HeapWord);
8195 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8197 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8198 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8199 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8200 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8201 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8202 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8203 indexListReturnedBytes);
8204 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8205 dict_returned_bytes);
8206 }
8207 }
8208 if (CMSTraceSweeper) {
8209 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8210 _limit);
8211 }
8212 }
8213 #endif // PRODUCT
8215 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8216 bool freeRangeInFreeLists) {
8217 if (CMSTraceSweeper) {
8218 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8219 freeFinger, freeRangeInFreeLists);
8220 }
8221 assert(!inFreeRange(), "Trampling existing free range");
8222 set_inFreeRange(true);
8223 set_lastFreeRangeCoalesced(false);
8225 set_freeFinger(freeFinger);
8226 set_freeRangeInFreeLists(freeRangeInFreeLists);
8227 if (CMSTestInFreeList) {
8228 if (freeRangeInFreeLists) {
8229 FreeChunk* fc = (FreeChunk*) freeFinger;
8230 assert(fc->is_free(), "A chunk on the free list should be free.");
8231 assert(fc->size() > 0, "Free range should have a size");
8232 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8233 }
8234 }
8235 }
8237 // Note that the sweeper runs concurrently with mutators. Thus,
8238 // it is possible for direct allocation in this generation to happen
8239 // in the middle of the sweep. Note that the sweeper also coalesces
8240 // contiguous free blocks. Thus, unless the sweeper and the allocator
8241 // synchronize appropriately freshly allocated blocks may get swept up.
8242 // This is accomplished by the sweeper locking the free lists while
8243 // it is sweeping. Thus blocks that are determined to be free are
8244 // indeed free. There is however one additional complication:
8245 // blocks that have been allocated since the final checkpoint and
8246 // mark, will not have been marked and so would be treated as
8247 // unreachable and swept up. To prevent this, the allocator marks
8248 // the bit map when allocating during the sweep phase. This leads,
8249 // however, to a further complication -- objects may have been allocated
8250 // but not yet initialized -- in the sense that the header isn't yet
8251 // installed. The sweeper can not then determine the size of the block
8252 // in order to skip over it. To deal with this case, we use a technique
8253 // (due to Printezis) to encode such uninitialized block sizes in the
8254 // bit map. Since the bit map uses a bit per every HeapWord, but the
8255 // CMS generation has a minimum object size of 3 HeapWords, it follows
8256 // that "normal marks" won't be adjacent in the bit map (there will
8257 // always be at least two 0 bits between successive 1 bits). We make use
8258 // of these "unused" bits to represent uninitialized blocks -- the bit
8259 // corresponding to the start of the uninitialized object and the next
8260 // bit are both set. Finally, a 1 bit marks the end of the object that
8261 // started with the two consecutive 1 bits to indicate its potentially
8262 // uninitialized state.
8264 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8265 FreeChunk* fc = (FreeChunk*)addr;
8266 size_t res;
8268 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8269 // than "addr == _limit" because although _limit was a block boundary when
8270 // we started the sweep, it may no longer be one because heap expansion
8271 // may have caused us to coalesce the block ending at the address _limit
8272 // with a newly expanded chunk (this happens when _limit was set to the
8273 // previous _end of the space), so we may have stepped past _limit:
8274 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8275 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8276 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8277 "sweep _limit out of bounds");
8278 assert(addr < _sp->end(), "addr out of bounds");
8279 // Flush any free range we might be holding as a single
8280 // coalesced chunk to the appropriate free list.
8281 if (inFreeRange()) {
8282 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8283 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8284 flush_cur_free_chunk(freeFinger(),
8285 pointer_delta(addr, freeFinger()));
8286 if (CMSTraceSweeper) {
8287 gclog_or_tty->print("Sweep: last chunk: ");
8288 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8289 "[coalesced:"SIZE_FORMAT"]\n",
8290 freeFinger(), pointer_delta(addr, freeFinger()),
8291 lastFreeRangeCoalesced());
8292 }
8293 }
8295 // help the iterator loop finish
8296 return pointer_delta(_sp->end(), addr);
8297 }
8299 assert(addr < _limit, "sweep invariant");
8300 // check if we should yield
8301 do_yield_check(addr);
8302 if (fc->is_free()) {
8303 // Chunk that is already free
8304 res = fc->size();
8305 do_already_free_chunk(fc);
8306 debug_only(_sp->verifyFreeLists());
8307 // If we flush the chunk at hand in lookahead_and_flush()
8308 // and it's coalesced with a preceding chunk, then the
8309 // process of "mangling" the payload of the coalesced block
8310 // will cause erasure of the size information from the
8311 // (erstwhile) header of all the coalesced blocks but the
8312 // first, so the first disjunct in the assert will not hold
8313 // in that specific case (in which case the second disjunct
8314 // will hold).
8315 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8316 "Otherwise the size info doesn't change at this step");
8317 NOT_PRODUCT(
8318 _numObjectsAlreadyFree++;
8319 _numWordsAlreadyFree += res;
8320 )
8321 NOT_PRODUCT(_last_fc = fc;)
8322 } else if (!_bitMap->isMarked(addr)) {
8323 // Chunk is fresh garbage
8324 res = do_garbage_chunk(fc);
8325 debug_only(_sp->verifyFreeLists());
8326 NOT_PRODUCT(
8327 _numObjectsFreed++;
8328 _numWordsFreed += res;
8329 )
8330 } else {
8331 // Chunk that is alive.
8332 res = do_live_chunk(fc);
8333 debug_only(_sp->verifyFreeLists());
8334 NOT_PRODUCT(
8335 _numObjectsLive++;
8336 _numWordsLive += res;
8337 )
8338 }
8339 return res;
8340 }
8342 // For the smart allocation, record following
8343 // split deaths - a free chunk is removed from its free list because
8344 // it is being split into two or more chunks.
8345 // split birth - a free chunk is being added to its free list because
8346 // a larger free chunk has been split and resulted in this free chunk.
8347 // coal death - a free chunk is being removed from its free list because
8348 // it is being coalesced into a large free chunk.
8349 // coal birth - a free chunk is being added to its free list because
8350 // it was created when two or more free chunks where coalesced into
8351 // this free chunk.
8352 //
8353 // These statistics are used to determine the desired number of free
8354 // chunks of a given size. The desired number is chosen to be relative
8355 // to the end of a CMS sweep. The desired number at the end of a sweep
8356 // is the
8357 // count-at-end-of-previous-sweep (an amount that was enough)
8358 // - count-at-beginning-of-current-sweep (the excess)
8359 // + split-births (gains in this size during interval)
8360 // - split-deaths (demands on this size during interval)
8361 // where the interval is from the end of one sweep to the end of the
8362 // next.
8363 //
8364 // When sweeping the sweeper maintains an accumulated chunk which is
8365 // the chunk that is made up of chunks that have been coalesced. That
8366 // will be termed the left-hand chunk. A new chunk of garbage that
8367 // is being considered for coalescing will be referred to as the
8368 // right-hand chunk.
8369 //
8370 // When making a decision on whether to coalesce a right-hand chunk with
8371 // the current left-hand chunk, the current count vs. the desired count
8372 // of the left-hand chunk is considered. Also if the right-hand chunk
8373 // is near the large chunk at the end of the heap (see
8374 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8375 // left-hand chunk is coalesced.
8376 //
8377 // When making a decision about whether to split a chunk, the desired count
8378 // vs. the current count of the candidate to be split is also considered.
8379 // If the candidate is underpopulated (currently fewer chunks than desired)
8380 // a chunk of an overpopulated (currently more chunks than desired) size may
8381 // be chosen. The "hint" associated with a free list, if non-null, points
8382 // to a free list which may be overpopulated.
8383 //
8385 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8386 const size_t size = fc->size();
8387 // Chunks that cannot be coalesced are not in the
8388 // free lists.
8389 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8390 assert(_sp->verify_chunk_in_free_list(fc),
8391 "free chunk should be in free lists");
8392 }
8393 // a chunk that is already free, should not have been
8394 // marked in the bit map
8395 HeapWord* const addr = (HeapWord*) fc;
8396 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8397 // Verify that the bit map has no bits marked between
8398 // addr and purported end of this block.
8399 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8401 // Some chunks cannot be coalesced under any circumstances.
8402 // See the definition of cantCoalesce().
8403 if (!fc->cantCoalesce()) {
8404 // This chunk can potentially be coalesced.
8405 if (_sp->adaptive_freelists()) {
8406 // All the work is done in
8407 do_post_free_or_garbage_chunk(fc, size);
8408 } else { // Not adaptive free lists
8409 // this is a free chunk that can potentially be coalesced by the sweeper;
8410 if (!inFreeRange()) {
8411 // if the next chunk is a free block that can't be coalesced
8412 // it doesn't make sense to remove this chunk from the free lists
8413 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8414 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8415 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8416 nextChunk->is_free() && // ... which is free...
8417 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8418 // nothing to do
8419 } else {
8420 // Potentially the start of a new free range:
8421 // Don't eagerly remove it from the free lists.
8422 // No need to remove it if it will just be put
8423 // back again. (Also from a pragmatic point of view
8424 // if it is a free block in a region that is beyond
8425 // any allocated blocks, an assertion will fail)
8426 // Remember the start of a free run.
8427 initialize_free_range(addr, true);
8428 // end - can coalesce with next chunk
8429 }
8430 } else {
8431 // the midst of a free range, we are coalescing
8432 print_free_block_coalesced(fc);
8433 if (CMSTraceSweeper) {
8434 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8435 }
8436 // remove it from the free lists
8437 _sp->removeFreeChunkFromFreeLists(fc);
8438 set_lastFreeRangeCoalesced(true);
8439 // If the chunk is being coalesced and the current free range is
8440 // in the free lists, remove the current free range so that it
8441 // will be returned to the free lists in its entirety - all
8442 // the coalesced pieces included.
8443 if (freeRangeInFreeLists()) {
8444 FreeChunk* ffc = (FreeChunk*) freeFinger();
8445 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8446 "Size of free range is inconsistent with chunk size.");
8447 if (CMSTestInFreeList) {
8448 assert(_sp->verify_chunk_in_free_list(ffc),
8449 "free range is not in free lists");
8450 }
8451 _sp->removeFreeChunkFromFreeLists(ffc);
8452 set_freeRangeInFreeLists(false);
8453 }
8454 }
8455 }
8456 // Note that if the chunk is not coalescable (the else arm
8457 // below), we unconditionally flush, without needing to do
8458 // a "lookahead," as we do below.
8459 if (inFreeRange()) lookahead_and_flush(fc, size);
8460 } else {
8461 // Code path common to both original and adaptive free lists.
8463 // cant coalesce with previous block; this should be treated
8464 // as the end of a free run if any
8465 if (inFreeRange()) {
8466 // we kicked some butt; time to pick up the garbage
8467 assert(freeFinger() < addr, "freeFinger points too high");
8468 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8469 }
8470 // else, nothing to do, just continue
8471 }
8472 }
8474 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8475 // This is a chunk of garbage. It is not in any free list.
8476 // Add it to a free list or let it possibly be coalesced into
8477 // a larger chunk.
8478 HeapWord* const addr = (HeapWord*) fc;
8479 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8481 if (_sp->adaptive_freelists()) {
8482 // Verify that the bit map has no bits marked between
8483 // addr and purported end of just dead object.
8484 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8486 do_post_free_or_garbage_chunk(fc, size);
8487 } else {
8488 if (!inFreeRange()) {
8489 // start of a new free range
8490 assert(size > 0, "A free range should have a size");
8491 initialize_free_range(addr, false);
8492 } else {
8493 // this will be swept up when we hit the end of the
8494 // free range
8495 if (CMSTraceSweeper) {
8496 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8497 }
8498 // If the chunk is being coalesced and the current free range is
8499 // in the free lists, remove the current free range so that it
8500 // will be returned to the free lists in its entirety - all
8501 // the coalesced pieces included.
8502 if (freeRangeInFreeLists()) {
8503 FreeChunk* ffc = (FreeChunk*)freeFinger();
8504 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8505 "Size of free range is inconsistent with chunk size.");
8506 if (CMSTestInFreeList) {
8507 assert(_sp->verify_chunk_in_free_list(ffc),
8508 "free range is not in free lists");
8509 }
8510 _sp->removeFreeChunkFromFreeLists(ffc);
8511 set_freeRangeInFreeLists(false);
8512 }
8513 set_lastFreeRangeCoalesced(true);
8514 }
8515 // this will be swept up when we hit the end of the free range
8517 // Verify that the bit map has no bits marked between
8518 // addr and purported end of just dead object.
8519 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8520 }
8521 assert(_limit >= addr + size,
8522 "A freshly garbage chunk can't possibly straddle over _limit");
8523 if (inFreeRange()) lookahead_and_flush(fc, size);
8524 return size;
8525 }
8527 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8528 HeapWord* addr = (HeapWord*) fc;
8529 // The sweeper has just found a live object. Return any accumulated
8530 // left hand chunk to the free lists.
8531 if (inFreeRange()) {
8532 assert(freeFinger() < addr, "freeFinger points too high");
8533 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8534 }
8536 // This object is live: we'd normally expect this to be
8537 // an oop, and like to assert the following:
8538 // assert(oop(addr)->is_oop(), "live block should be an oop");
8539 // However, as we commented above, this may be an object whose
8540 // header hasn't yet been initialized.
8541 size_t size;
8542 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8543 if (_bitMap->isMarked(addr + 1)) {
8544 // Determine the size from the bit map, rather than trying to
8545 // compute it from the object header.
8546 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8547 size = pointer_delta(nextOneAddr + 1, addr);
8548 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8549 "alignment problem");
8551 #ifdef ASSERT
8552 if (oop(addr)->klass_or_null() != NULL) {
8553 // Ignore mark word because we are running concurrent with mutators
8554 assert(oop(addr)->is_oop(true), "live block should be an oop");
8555 assert(size ==
8556 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8557 "P-mark and computed size do not agree");
8558 }
8559 #endif
8561 } else {
8562 // This should be an initialized object that's alive.
8563 assert(oop(addr)->klass_or_null() != NULL,
8564 "Should be an initialized object");
8565 // Ignore mark word because we are running concurrent with mutators
8566 assert(oop(addr)->is_oop(true), "live block should be an oop");
8567 // Verify that the bit map has no bits marked between
8568 // addr and purported end of this block.
8569 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8570 assert(size >= 3, "Necessary for Printezis marks to work");
8571 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8572 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8573 }
8574 return size;
8575 }
8577 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8578 size_t chunkSize) {
8579 // do_post_free_or_garbage_chunk() should only be called in the case
8580 // of the adaptive free list allocator.
8581 const bool fcInFreeLists = fc->is_free();
8582 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8583 assert((HeapWord*)fc <= _limit, "sweep invariant");
8584 if (CMSTestInFreeList && fcInFreeLists) {
8585 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8586 }
8588 if (CMSTraceSweeper) {
8589 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8590 }
8592 HeapWord* const fc_addr = (HeapWord*) fc;
8594 bool coalesce;
8595 const size_t left = pointer_delta(fc_addr, freeFinger());
8596 const size_t right = chunkSize;
8597 switch (FLSCoalescePolicy) {
8598 // numeric value forms a coalition aggressiveness metric
8599 case 0: { // never coalesce
8600 coalesce = false;
8601 break;
8602 }
8603 case 1: { // coalesce if left & right chunks on overpopulated lists
8604 coalesce = _sp->coalOverPopulated(left) &&
8605 _sp->coalOverPopulated(right);
8606 break;
8607 }
8608 case 2: { // coalesce if left chunk on overpopulated list (default)
8609 coalesce = _sp->coalOverPopulated(left);
8610 break;
8611 }
8612 case 3: { // coalesce if left OR right chunk on overpopulated list
8613 coalesce = _sp->coalOverPopulated(left) ||
8614 _sp->coalOverPopulated(right);
8615 break;
8616 }
8617 case 4: { // always coalesce
8618 coalesce = true;
8619 break;
8620 }
8621 default:
8622 ShouldNotReachHere();
8623 }
8625 // Should the current free range be coalesced?
8626 // If the chunk is in a free range and either we decided to coalesce above
8627 // or the chunk is near the large block at the end of the heap
8628 // (isNearLargestChunk() returns true), then coalesce this chunk.
8629 const bool doCoalesce = inFreeRange()
8630 && (coalesce || _g->isNearLargestChunk(fc_addr));
8631 if (doCoalesce) {
8632 // Coalesce the current free range on the left with the new
8633 // chunk on the right. If either is on a free list,
8634 // it must be removed from the list and stashed in the closure.
8635 if (freeRangeInFreeLists()) {
8636 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8637 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8638 "Size of free range is inconsistent with chunk size.");
8639 if (CMSTestInFreeList) {
8640 assert(_sp->verify_chunk_in_free_list(ffc),
8641 "Chunk is not in free lists");
8642 }
8643 _sp->coalDeath(ffc->size());
8644 _sp->removeFreeChunkFromFreeLists(ffc);
8645 set_freeRangeInFreeLists(false);
8646 }
8647 if (fcInFreeLists) {
8648 _sp->coalDeath(chunkSize);
8649 assert(fc->size() == chunkSize,
8650 "The chunk has the wrong size or is not in the free lists");
8651 _sp->removeFreeChunkFromFreeLists(fc);
8652 }
8653 set_lastFreeRangeCoalesced(true);
8654 print_free_block_coalesced(fc);
8655 } else { // not in a free range and/or should not coalesce
8656 // Return the current free range and start a new one.
8657 if (inFreeRange()) {
8658 // In a free range but cannot coalesce with the right hand chunk.
8659 // Put the current free range into the free lists.
8660 flush_cur_free_chunk(freeFinger(),
8661 pointer_delta(fc_addr, freeFinger()));
8662 }
8663 // Set up for new free range. Pass along whether the right hand
8664 // chunk is in the free lists.
8665 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8666 }
8667 }
8669 // Lookahead flush:
8670 // If we are tracking a free range, and this is the last chunk that
8671 // we'll look at because its end crosses past _limit, we'll preemptively
8672 // flush it along with any free range we may be holding on to. Note that
8673 // this can be the case only for an already free or freshly garbage
8674 // chunk. If this block is an object, it can never straddle
8675 // over _limit. The "straddling" occurs when _limit is set at
8676 // the previous end of the space when this cycle started, and
8677 // a subsequent heap expansion caused the previously co-terminal
8678 // free block to be coalesced with the newly expanded portion,
8679 // thus rendering _limit a non-block-boundary making it dangerous
8680 // for the sweeper to step over and examine.
8681 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8682 assert(inFreeRange(), "Should only be called if currently in a free range.");
8683 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8684 assert(_sp->used_region().contains(eob - 1),
8685 err_msg("eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
8686 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8687 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8688 eob, eob-1, _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8689 if (eob >= _limit) {
8690 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8691 if (CMSTraceSweeper) {
8692 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8693 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8694 "[" PTR_FORMAT "," PTR_FORMAT ")",
8695 _limit, fc, eob, _sp->bottom(), _sp->end());
8696 }
8697 // Return the storage we are tracking back into the free lists.
8698 if (CMSTraceSweeper) {
8699 gclog_or_tty->print_cr("Flushing ... ");
8700 }
8701 assert(freeFinger() < eob, "Error");
8702 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8703 }
8704 }
8706 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8707 assert(inFreeRange(), "Should only be called if currently in a free range.");
8708 assert(size > 0,
8709 "A zero sized chunk cannot be added to the free lists.");
8710 if (!freeRangeInFreeLists()) {
8711 if (CMSTestInFreeList) {
8712 FreeChunk* fc = (FreeChunk*) chunk;
8713 fc->set_size(size);
8714 assert(!_sp->verify_chunk_in_free_list(fc),
8715 "chunk should not be in free lists yet");
8716 }
8717 if (CMSTraceSweeper) {
8718 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8719 chunk, size);
8720 }
8721 // A new free range is going to be starting. The current
8722 // free range has not been added to the free lists yet or
8723 // was removed so add it back.
8724 // If the current free range was coalesced, then the death
8725 // of the free range was recorded. Record a birth now.
8726 if (lastFreeRangeCoalesced()) {
8727 _sp->coalBirth(size);
8728 }
8729 _sp->addChunkAndRepairOffsetTable(chunk, size,
8730 lastFreeRangeCoalesced());
8731 } else if (CMSTraceSweeper) {
8732 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8733 }
8734 set_inFreeRange(false);
8735 set_freeRangeInFreeLists(false);
8736 }
8738 // We take a break if we've been at this for a while,
8739 // so as to avoid monopolizing the locks involved.
8740 void SweepClosure::do_yield_work(HeapWord* addr) {
8741 // Return current free chunk being used for coalescing (if any)
8742 // to the appropriate freelist. After yielding, the next
8743 // free block encountered will start a coalescing range of
8744 // free blocks. If the next free block is adjacent to the
8745 // chunk just flushed, they will need to wait for the next
8746 // sweep to be coalesced.
8747 if (inFreeRange()) {
8748 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8749 }
8751 // First give up the locks, then yield, then re-lock.
8752 // We should probably use a constructor/destructor idiom to
8753 // do this unlock/lock or modify the MutexUnlocker class to
8754 // serve our purpose. XXX
8755 assert_lock_strong(_bitMap->lock());
8756 assert_lock_strong(_freelistLock);
8757 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8758 "CMS thread should hold CMS token");
8759 _bitMap->lock()->unlock();
8760 _freelistLock->unlock();
8761 ConcurrentMarkSweepThread::desynchronize(true);
8762 ConcurrentMarkSweepThread::acknowledge_yield_request();
8763 _collector->stopTimer();
8764 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8765 if (PrintCMSStatistics != 0) {
8766 _collector->incrementYields();
8767 }
8768 _collector->icms_wait();
8770 // See the comment in coordinator_yield()
8771 for (unsigned i = 0; i < CMSYieldSleepCount &&
8772 ConcurrentMarkSweepThread::should_yield() &&
8773 !CMSCollector::foregroundGCIsActive(); ++i) {
8774 os::sleep(Thread::current(), 1, false);
8775 ConcurrentMarkSweepThread::acknowledge_yield_request();
8776 }
8778 ConcurrentMarkSweepThread::synchronize(true);
8779 _freelistLock->lock();
8780 _bitMap->lock()->lock_without_safepoint_check();
8781 _collector->startTimer();
8782 }
8784 #ifndef PRODUCT
8785 // This is actually very useful in a product build if it can
8786 // be called from the debugger. Compile it into the product
8787 // as needed.
8788 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8789 return debug_cms_space->verify_chunk_in_free_list(fc);
8790 }
8791 #endif
8793 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8794 if (CMSTraceSweeper) {
8795 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8796 fc, fc->size());
8797 }
8798 }
8800 // CMSIsAliveClosure
8801 bool CMSIsAliveClosure::do_object_b(oop obj) {
8802 HeapWord* addr = (HeapWord*)obj;
8803 return addr != NULL &&
8804 (!_span.contains(addr) || _bit_map->isMarked(addr));
8805 }
8808 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8809 MemRegion span,
8810 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8811 bool cpc):
8812 _collector(collector),
8813 _span(span),
8814 _bit_map(bit_map),
8815 _mark_stack(mark_stack),
8816 _concurrent_precleaning(cpc) {
8817 assert(!_span.is_empty(), "Empty span could spell trouble");
8818 }
8821 // CMSKeepAliveClosure: the serial version
8822 void CMSKeepAliveClosure::do_oop(oop obj) {
8823 HeapWord* addr = (HeapWord*)obj;
8824 if (_span.contains(addr) &&
8825 !_bit_map->isMarked(addr)) {
8826 _bit_map->mark(addr);
8827 bool simulate_overflow = false;
8828 NOT_PRODUCT(
8829 if (CMSMarkStackOverflowALot &&
8830 _collector->simulate_overflow()) {
8831 // simulate a stack overflow
8832 simulate_overflow = true;
8833 }
8834 )
8835 if (simulate_overflow || !_mark_stack->push(obj)) {
8836 if (_concurrent_precleaning) {
8837 // We dirty the overflown object and let the remark
8838 // phase deal with it.
8839 assert(_collector->overflow_list_is_empty(), "Error");
8840 // In the case of object arrays, we need to dirty all of
8841 // the cards that the object spans. No locking or atomics
8842 // are needed since no one else can be mutating the mod union
8843 // table.
8844 if (obj->is_objArray()) {
8845 size_t sz = obj->size();
8846 HeapWord* end_card_addr =
8847 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8848 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8849 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8850 _collector->_modUnionTable.mark_range(redirty_range);
8851 } else {
8852 _collector->_modUnionTable.mark(addr);
8853 }
8854 _collector->_ser_kac_preclean_ovflw++;
8855 } else {
8856 _collector->push_on_overflow_list(obj);
8857 _collector->_ser_kac_ovflw++;
8858 }
8859 }
8860 }
8861 }
8863 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8864 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8866 // CMSParKeepAliveClosure: a parallel version of the above.
8867 // The work queues are private to each closure (thread),
8868 // but (may be) available for stealing by other threads.
8869 void CMSParKeepAliveClosure::do_oop(oop obj) {
8870 HeapWord* addr = (HeapWord*)obj;
8871 if (_span.contains(addr) &&
8872 !_bit_map->isMarked(addr)) {
8873 // In general, during recursive tracing, several threads
8874 // may be concurrently getting here; the first one to
8875 // "tag" it, claims it.
8876 if (_bit_map->par_mark(addr)) {
8877 bool res = _work_queue->push(obj);
8878 assert(res, "Low water mark should be much less than capacity");
8879 // Do a recursive trim in the hope that this will keep
8880 // stack usage lower, but leave some oops for potential stealers
8881 trim_queue(_low_water_mark);
8882 } // Else, another thread got there first
8883 }
8884 }
8886 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8887 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8889 void CMSParKeepAliveClosure::trim_queue(uint max) {
8890 while (_work_queue->size() > max) {
8891 oop new_oop;
8892 if (_work_queue->pop_local(new_oop)) {
8893 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8894 assert(_bit_map->isMarked((HeapWord*)new_oop),
8895 "no white objects on this stack!");
8896 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8897 // iterate over the oops in this oop, marking and pushing
8898 // the ones in CMS heap (i.e. in _span).
8899 new_oop->oop_iterate(&_mark_and_push);
8900 }
8901 }
8902 }
8904 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8905 CMSCollector* collector,
8906 MemRegion span, CMSBitMap* bit_map,
8907 OopTaskQueue* work_queue):
8908 _collector(collector),
8909 _span(span),
8910 _bit_map(bit_map),
8911 _work_queue(work_queue) { }
8913 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8914 HeapWord* addr = (HeapWord*)obj;
8915 if (_span.contains(addr) &&
8916 !_bit_map->isMarked(addr)) {
8917 if (_bit_map->par_mark(addr)) {
8918 bool simulate_overflow = false;
8919 NOT_PRODUCT(
8920 if (CMSMarkStackOverflowALot &&
8921 _collector->par_simulate_overflow()) {
8922 // simulate a stack overflow
8923 simulate_overflow = true;
8924 }
8925 )
8926 if (simulate_overflow || !_work_queue->push(obj)) {
8927 _collector->par_push_on_overflow_list(obj);
8928 _collector->_par_kac_ovflw++;
8929 }
8930 } // Else another thread got there already
8931 }
8932 }
8934 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8935 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8937 //////////////////////////////////////////////////////////////////
8938 // CMSExpansionCause /////////////////////////////
8939 //////////////////////////////////////////////////////////////////
8940 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8941 switch (cause) {
8942 case _no_expansion:
8943 return "No expansion";
8944 case _satisfy_free_ratio:
8945 return "Free ratio";
8946 case _satisfy_promotion:
8947 return "Satisfy promotion";
8948 case _satisfy_allocation:
8949 return "allocation";
8950 case _allocate_par_lab:
8951 return "Par LAB";
8952 case _allocate_par_spooling_space:
8953 return "Par Spooling Space";
8954 case _adaptive_size_policy:
8955 return "Ergonomics";
8956 default:
8957 return "unknown";
8958 }
8959 }
8961 void CMSDrainMarkingStackClosure::do_void() {
8962 // the max number to take from overflow list at a time
8963 const size_t num = _mark_stack->capacity()/4;
8964 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8965 "Overflow list should be NULL during concurrent phases");
8966 while (!_mark_stack->isEmpty() ||
8967 // if stack is empty, check the overflow list
8968 _collector->take_from_overflow_list(num, _mark_stack)) {
8969 oop obj = _mark_stack->pop();
8970 HeapWord* addr = (HeapWord*)obj;
8971 assert(_span.contains(addr), "Should be within span");
8972 assert(_bit_map->isMarked(addr), "Should be marked");
8973 assert(obj->is_oop(), "Should be an oop");
8974 obj->oop_iterate(_keep_alive);
8975 }
8976 }
8978 void CMSParDrainMarkingStackClosure::do_void() {
8979 // drain queue
8980 trim_queue(0);
8981 }
8983 // Trim our work_queue so its length is below max at return
8984 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8985 while (_work_queue->size() > max) {
8986 oop new_oop;
8987 if (_work_queue->pop_local(new_oop)) {
8988 assert(new_oop->is_oop(), "Expected an oop");
8989 assert(_bit_map->isMarked((HeapWord*)new_oop),
8990 "no white objects on this stack!");
8991 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8992 // iterate over the oops in this oop, marking and pushing
8993 // the ones in CMS heap (i.e. in _span).
8994 new_oop->oop_iterate(&_mark_and_push);
8995 }
8996 }
8997 }
8999 ////////////////////////////////////////////////////////////////////
9000 // Support for Marking Stack Overflow list handling and related code
9001 ////////////////////////////////////////////////////////////////////
9002 // Much of the following code is similar in shape and spirit to the
9003 // code used in ParNewGC. We should try and share that code
9004 // as much as possible in the future.
9006 #ifndef PRODUCT
9007 // Debugging support for CMSStackOverflowALot
9009 // It's OK to call this multi-threaded; the worst thing
9010 // that can happen is that we'll get a bunch of closely
9011 // spaced simulated oveflows, but that's OK, in fact
9012 // probably good as it would exercise the overflow code
9013 // under contention.
9014 bool CMSCollector::simulate_overflow() {
9015 if (_overflow_counter-- <= 0) { // just being defensive
9016 _overflow_counter = CMSMarkStackOverflowInterval;
9017 return true;
9018 } else {
9019 return false;
9020 }
9021 }
9023 bool CMSCollector::par_simulate_overflow() {
9024 return simulate_overflow();
9025 }
9026 #endif
9028 // Single-threaded
9029 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
9030 assert(stack->isEmpty(), "Expected precondition");
9031 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
9032 size_t i = num;
9033 oop cur = _overflow_list;
9034 const markOop proto = markOopDesc::prototype();
9035 NOT_PRODUCT(ssize_t n = 0;)
9036 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
9037 next = oop(cur->mark());
9038 cur->set_mark(proto); // until proven otherwise
9039 assert(cur->is_oop(), "Should be an oop");
9040 bool res = stack->push(cur);
9041 assert(res, "Bit off more than can chew?");
9042 NOT_PRODUCT(n++;)
9043 }
9044 _overflow_list = cur;
9045 #ifndef PRODUCT
9046 assert(_num_par_pushes >= n, "Too many pops?");
9047 _num_par_pushes -=n;
9048 #endif
9049 return !stack->isEmpty();
9050 }
9052 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
9053 // (MT-safe) Get a prefix of at most "num" from the list.
9054 // The overflow list is chained through the mark word of
9055 // each object in the list. We fetch the entire list,
9056 // break off a prefix of the right size and return the
9057 // remainder. If other threads try to take objects from
9058 // the overflow list at that time, they will wait for
9059 // some time to see if data becomes available. If (and
9060 // only if) another thread places one or more object(s)
9061 // on the global list before we have returned the suffix
9062 // to the global list, we will walk down our local list
9063 // to find its end and append the global list to
9064 // our suffix before returning it. This suffix walk can
9065 // prove to be expensive (quadratic in the amount of traffic)
9066 // when there are many objects in the overflow list and
9067 // there is much producer-consumer contention on the list.
9068 // *NOTE*: The overflow list manipulation code here and
9069 // in ParNewGeneration:: are very similar in shape,
9070 // except that in the ParNew case we use the old (from/eden)
9071 // copy of the object to thread the list via its klass word.
9072 // Because of the common code, if you make any changes in
9073 // the code below, please check the ParNew version to see if
9074 // similar changes might be needed.
9075 // CR 6797058 has been filed to consolidate the common code.
9076 bool CMSCollector::par_take_from_overflow_list(size_t num,
9077 OopTaskQueue* work_q,
9078 int no_of_gc_threads) {
9079 assert(work_q->size() == 0, "First empty local work queue");
9080 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
9081 if (_overflow_list == NULL) {
9082 return false;
9083 }
9084 // Grab the entire list; we'll put back a suffix
9085 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9086 Thread* tid = Thread::current();
9087 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
9088 // set to ParallelGCThreads.
9089 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
9090 size_t sleep_time_millis = MAX2((size_t)1, num/100);
9091 // If the list is busy, we spin for a short while,
9092 // sleeping between attempts to get the list.
9093 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
9094 os::sleep(tid, sleep_time_millis, false);
9095 if (_overflow_list == NULL) {
9096 // Nothing left to take
9097 return false;
9098 } else if (_overflow_list != BUSY) {
9099 // Try and grab the prefix
9100 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
9101 }
9102 }
9103 // If the list was found to be empty, or we spun long
9104 // enough, we give up and return empty-handed. If we leave
9105 // the list in the BUSY state below, it must be the case that
9106 // some other thread holds the overflow list and will set it
9107 // to a non-BUSY state in the future.
9108 if (prefix == NULL || prefix == BUSY) {
9109 // Nothing to take or waited long enough
9110 if (prefix == NULL) {
9111 // Write back the NULL in case we overwrote it with BUSY above
9112 // and it is still the same value.
9113 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9114 }
9115 return false;
9116 }
9117 assert(prefix != NULL && prefix != BUSY, "Error");
9118 size_t i = num;
9119 oop cur = prefix;
9120 // Walk down the first "num" objects, unless we reach the end.
9121 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
9122 if (cur->mark() == NULL) {
9123 // We have "num" or fewer elements in the list, so there
9124 // is nothing to return to the global list.
9125 // Write back the NULL in lieu of the BUSY we wrote
9126 // above, if it is still the same value.
9127 if (_overflow_list == BUSY) {
9128 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
9129 }
9130 } else {
9131 // Chop off the suffix and rerturn it to the global list.
9132 assert(cur->mark() != BUSY, "Error");
9133 oop suffix_head = cur->mark(); // suffix will be put back on global list
9134 cur->set_mark(NULL); // break off suffix
9135 // It's possible that the list is still in the empty(busy) state
9136 // we left it in a short while ago; in that case we may be
9137 // able to place back the suffix without incurring the cost
9138 // of a walk down the list.
9139 oop observed_overflow_list = _overflow_list;
9140 oop cur_overflow_list = observed_overflow_list;
9141 bool attached = false;
9142 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
9143 observed_overflow_list =
9144 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9145 if (cur_overflow_list == observed_overflow_list) {
9146 attached = true;
9147 break;
9148 } else cur_overflow_list = observed_overflow_list;
9149 }
9150 if (!attached) {
9151 // Too bad, someone else sneaked in (at least) an element; we'll need
9152 // to do a splice. Find tail of suffix so we can prepend suffix to global
9153 // list.
9154 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
9155 oop suffix_tail = cur;
9156 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
9157 "Tautology");
9158 observed_overflow_list = _overflow_list;
9159 do {
9160 cur_overflow_list = observed_overflow_list;
9161 if (cur_overflow_list != BUSY) {
9162 // Do the splice ...
9163 suffix_tail->set_mark(markOop(cur_overflow_list));
9164 } else { // cur_overflow_list == BUSY
9165 suffix_tail->set_mark(NULL);
9166 }
9167 // ... and try to place spliced list back on overflow_list ...
9168 observed_overflow_list =
9169 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9170 } while (cur_overflow_list != observed_overflow_list);
9171 // ... until we have succeeded in doing so.
9172 }
9173 }
9175 // Push the prefix elements on work_q
9176 assert(prefix != NULL, "control point invariant");
9177 const markOop proto = markOopDesc::prototype();
9178 oop next;
9179 NOT_PRODUCT(ssize_t n = 0;)
9180 for (cur = prefix; cur != NULL; cur = next) {
9181 next = oop(cur->mark());
9182 cur->set_mark(proto); // until proven otherwise
9183 assert(cur->is_oop(), "Should be an oop");
9184 bool res = work_q->push(cur);
9185 assert(res, "Bit off more than we can chew?");
9186 NOT_PRODUCT(n++;)
9187 }
9188 #ifndef PRODUCT
9189 assert(_num_par_pushes >= n, "Too many pops?");
9190 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9191 #endif
9192 return true;
9193 }
9195 // Single-threaded
9196 void CMSCollector::push_on_overflow_list(oop p) {
9197 NOT_PRODUCT(_num_par_pushes++;)
9198 assert(p->is_oop(), "Not an oop");
9199 preserve_mark_if_necessary(p);
9200 p->set_mark((markOop)_overflow_list);
9201 _overflow_list = p;
9202 }
9204 // Multi-threaded; use CAS to prepend to overflow list
9205 void CMSCollector::par_push_on_overflow_list(oop p) {
9206 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9207 assert(p->is_oop(), "Not an oop");
9208 par_preserve_mark_if_necessary(p);
9209 oop observed_overflow_list = _overflow_list;
9210 oop cur_overflow_list;
9211 do {
9212 cur_overflow_list = observed_overflow_list;
9213 if (cur_overflow_list != BUSY) {
9214 p->set_mark(markOop(cur_overflow_list));
9215 } else {
9216 p->set_mark(NULL);
9217 }
9218 observed_overflow_list =
9219 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9220 } while (cur_overflow_list != observed_overflow_list);
9221 }
9222 #undef BUSY
9224 // Single threaded
9225 // General Note on GrowableArray: pushes may silently fail
9226 // because we are (temporarily) out of C-heap for expanding
9227 // the stack. The problem is quite ubiquitous and affects
9228 // a lot of code in the JVM. The prudent thing for GrowableArray
9229 // to do (for now) is to exit with an error. However, that may
9230 // be too draconian in some cases because the caller may be
9231 // able to recover without much harm. For such cases, we
9232 // should probably introduce a "soft_push" method which returns
9233 // an indication of success or failure with the assumption that
9234 // the caller may be able to recover from a failure; code in
9235 // the VM can then be changed, incrementally, to deal with such
9236 // failures where possible, thus, incrementally hardening the VM
9237 // in such low resource situations.
9238 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9239 _preserved_oop_stack.push(p);
9240 _preserved_mark_stack.push(m);
9241 assert(m == p->mark(), "Mark word changed");
9242 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9243 "bijection");
9244 }
9246 // Single threaded
9247 void CMSCollector::preserve_mark_if_necessary(oop p) {
9248 markOop m = p->mark();
9249 if (m->must_be_preserved(p)) {
9250 preserve_mark_work(p, m);
9251 }
9252 }
9254 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9255 markOop m = p->mark();
9256 if (m->must_be_preserved(p)) {
9257 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9258 // Even though we read the mark word without holding
9259 // the lock, we are assured that it will not change
9260 // because we "own" this oop, so no other thread can
9261 // be trying to push it on the overflow list; see
9262 // the assertion in preserve_mark_work() that checks
9263 // that m == p->mark().
9264 preserve_mark_work(p, m);
9265 }
9266 }
9268 // We should be able to do this multi-threaded,
9269 // a chunk of stack being a task (this is
9270 // correct because each oop only ever appears
9271 // once in the overflow list. However, it's
9272 // not very easy to completely overlap this with
9273 // other operations, so will generally not be done
9274 // until all work's been completed. Because we
9275 // expect the preserved oop stack (set) to be small,
9276 // it's probably fine to do this single-threaded.
9277 // We can explore cleverer concurrent/overlapped/parallel
9278 // processing of preserved marks if we feel the
9279 // need for this in the future. Stack overflow should
9280 // be so rare in practice and, when it happens, its
9281 // effect on performance so great that this will
9282 // likely just be in the noise anyway.
9283 void CMSCollector::restore_preserved_marks_if_any() {
9284 assert(SafepointSynchronize::is_at_safepoint(),
9285 "world should be stopped");
9286 assert(Thread::current()->is_ConcurrentGC_thread() ||
9287 Thread::current()->is_VM_thread(),
9288 "should be single-threaded");
9289 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9290 "bijection");
9292 while (!_preserved_oop_stack.is_empty()) {
9293 oop p = _preserved_oop_stack.pop();
9294 assert(p->is_oop(), "Should be an oop");
9295 assert(_span.contains(p), "oop should be in _span");
9296 assert(p->mark() == markOopDesc::prototype(),
9297 "Set when taken from overflow list");
9298 markOop m = _preserved_mark_stack.pop();
9299 p->set_mark(m);
9300 }
9301 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9302 "stacks were cleared above");
9303 }
9305 #ifndef PRODUCT
9306 bool CMSCollector::no_preserved_marks() const {
9307 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9308 }
9309 #endif
9311 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9312 {
9313 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9314 CMSAdaptiveSizePolicy* size_policy =
9315 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9316 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9317 "Wrong type for size policy");
9318 return size_policy;
9319 }
9321 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9322 size_t desired_promo_size) {
9323 if (cur_promo_size < desired_promo_size) {
9324 size_t expand_bytes = desired_promo_size - cur_promo_size;
9325 if (PrintAdaptiveSizePolicy && Verbose) {
9326 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9327 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9328 expand_bytes);
9329 }
9330 expand(expand_bytes,
9331 MinHeapDeltaBytes,
9332 CMSExpansionCause::_adaptive_size_policy);
9333 } else if (desired_promo_size < cur_promo_size) {
9334 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9335 if (PrintAdaptiveSizePolicy && Verbose) {
9336 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9337 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9338 shrink_bytes);
9339 }
9340 shrink(shrink_bytes);
9341 }
9342 }
9344 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9345 GenCollectedHeap* gch = GenCollectedHeap::heap();
9346 CMSGCAdaptivePolicyCounters* counters =
9347 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9348 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9349 "Wrong kind of counters");
9350 return counters;
9351 }
9354 void ASConcurrentMarkSweepGeneration::update_counters() {
9355 if (UsePerfData) {
9356 _space_counters->update_all();
9357 _gen_counters->update_all();
9358 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9359 GenCollectedHeap* gch = GenCollectedHeap::heap();
9360 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9361 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9362 "Wrong gc statistics type");
9363 counters->update_counters(gc_stats_l);
9364 }
9365 }
9367 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9368 if (UsePerfData) {
9369 _space_counters->update_used(used);
9370 _space_counters->update_capacity();
9371 _gen_counters->update_all();
9373 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9374 GenCollectedHeap* gch = GenCollectedHeap::heap();
9375 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9376 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9377 "Wrong gc statistics type");
9378 counters->update_counters(gc_stats_l);
9379 }
9380 }
9382 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9383 assert_locked_or_safepoint(Heap_lock);
9384 assert_lock_strong(freelistLock());
9385 HeapWord* old_end = _cmsSpace->end();
9386 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9387 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9388 FreeChunk* chunk_at_end = find_chunk_at_end();
9389 if (chunk_at_end == NULL) {
9390 // No room to shrink
9391 if (PrintGCDetails && Verbose) {
9392 gclog_or_tty->print_cr("No room to shrink: old_end "
9393 PTR_FORMAT " unallocated_start " PTR_FORMAT
9394 " chunk_at_end " PTR_FORMAT,
9395 old_end, unallocated_start, chunk_at_end);
9396 }
9397 return;
9398 } else {
9400 // Find the chunk at the end of the space and determine
9401 // how much it can be shrunk.
9402 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9403 size_t aligned_shrinkable_size_in_bytes =
9404 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9405 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9406 "Inconsistent chunk at end of space");
9407 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9408 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9410 // Shrink the underlying space
9411 _virtual_space.shrink_by(bytes);
9412 if (PrintGCDetails && Verbose) {
9413 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9414 " desired_bytes " SIZE_FORMAT
9415 " shrinkable_size_in_bytes " SIZE_FORMAT
9416 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9417 " bytes " SIZE_FORMAT,
9418 desired_bytes, shrinkable_size_in_bytes,
9419 aligned_shrinkable_size_in_bytes, bytes);
9420 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9421 " unallocated_start " SIZE_FORMAT,
9422 old_end, unallocated_start);
9423 }
9425 // If the space did shrink (shrinking is not guaranteed),
9426 // shrink the chunk at the end by the appropriate amount.
9427 if (((HeapWord*)_virtual_space.high()) < old_end) {
9428 size_t new_word_size =
9429 heap_word_size(_virtual_space.committed_size());
9431 // Have to remove the chunk from the dictionary because it is changing
9432 // size and might be someplace elsewhere in the dictionary.
9434 // Get the chunk at end, shrink it, and put it
9435 // back.
9436 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9437 size_t word_size_change = word_size_before - new_word_size;
9438 size_t chunk_at_end_old_size = chunk_at_end->size();
9439 assert(chunk_at_end_old_size >= word_size_change,
9440 "Shrink is too large");
9441 chunk_at_end->set_size(chunk_at_end_old_size -
9442 word_size_change);
9443 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9444 word_size_change);
9446 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9448 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9449 _bts->resize(new_word_size); // resize the block offset shared array
9450 Universe::heap()->barrier_set()->resize_covered_region(mr);
9451 _cmsSpace->assert_locked();
9452 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9454 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9456 // update the space and generation capacity counters
9457 if (UsePerfData) {
9458 _space_counters->update_capacity();
9459 _gen_counters->update_all();
9460 }
9462 if (Verbose && PrintGCDetails) {
9463 size_t new_mem_size = _virtual_space.committed_size();
9464 size_t old_mem_size = new_mem_size + bytes;
9465 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9466 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9467 }
9468 }
9470 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9471 "Inconsistency at end of space");
9472 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9473 "Shrinking is inconsistent");
9474 return;
9475 }
9476 }
9477 // Transfer some number of overflown objects to usual marking
9478 // stack. Return true if some objects were transferred.
9479 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9480 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9481 (size_t)ParGCDesiredObjsFromOverflowList);
9483 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9484 assert(_collector->overflow_list_is_empty() || res,
9485 "If list is not empty, we should have taken something");
9486 assert(!res || !_mark_stack->isEmpty(),
9487 "If we took something, it should now be on our stack");
9488 return res;
9489 }
9491 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9492 size_t res = _sp->block_size_no_stall(addr, _collector);
9493 if (_sp->block_is_obj(addr)) {
9494 if (_live_bit_map->isMarked(addr)) {
9495 // It can't have been dead in a previous cycle
9496 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9497 } else {
9498 _dead_bit_map->mark(addr); // mark the dead object
9499 }
9500 }
9501 // Could be 0, if the block size could not be computed without stalling.
9502 return res;
9503 }
9505 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9507 switch (phase) {
9508 case CMSCollector::InitialMarking:
9509 initialize(true /* fullGC */ ,
9510 cause /* cause of the GC */,
9511 true /* recordGCBeginTime */,
9512 true /* recordPreGCUsage */,
9513 false /* recordPeakUsage */,
9514 false /* recordPostGCusage */,
9515 true /* recordAccumulatedGCTime */,
9516 false /* recordGCEndTime */,
9517 false /* countCollection */ );
9518 break;
9520 case CMSCollector::FinalMarking:
9521 initialize(true /* fullGC */ ,
9522 cause /* cause of the GC */,
9523 false /* recordGCBeginTime */,
9524 false /* recordPreGCUsage */,
9525 false /* recordPeakUsage */,
9526 false /* recordPostGCusage */,
9527 true /* recordAccumulatedGCTime */,
9528 false /* recordGCEndTime */,
9529 false /* countCollection */ );
9530 break;
9532 case CMSCollector::Sweeping:
9533 initialize(true /* fullGC */ ,
9534 cause /* cause of the GC */,
9535 false /* recordGCBeginTime */,
9536 false /* recordPreGCUsage */,
9537 true /* recordPeakUsage */,
9538 true /* recordPostGCusage */,
9539 false /* recordAccumulatedGCTime */,
9540 true /* recordGCEndTime */,
9541 true /* countCollection */ );
9542 break;
9544 default:
9545 ShouldNotReachHere();
9546 }
9547 }