Mon, 01 Dec 2008 23:25:24 -0800
6778647: snap(), snap_policy() should be renamed setup(), setup_policy()
Summary: Renamed Reference{Policy,Pocessor} methods from snap{,_policy}() to setup{,_policy}()
Reviewed-by: apetrusenko
1 /*
2 * Copyright 2001-2008 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 # include "incls/_precompiled.incl"
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl"
28 // statics
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
30 bool CMSCollector::_full_gc_requested = false;
32 //////////////////////////////////////////////////////////////////
33 // In support of CMS/VM thread synchronization
34 //////////////////////////////////////////////////////////////////
35 // We split use of the CGC_lock into 2 "levels".
36 // The low-level locking is of the usual CGC_lock monitor. We introduce
37 // a higher level "token" (hereafter "CMS token") built on top of the
38 // low level monitor (hereafter "CGC lock").
39 // The token-passing protocol gives priority to the VM thread. The
40 // CMS-lock doesn't provide any fairness guarantees, but clients
41 // should ensure that it is only held for very short, bounded
42 // durations.
43 //
44 // When either of the CMS thread or the VM thread is involved in
45 // collection operations during which it does not want the other
46 // thread to interfere, it obtains the CMS token.
47 //
48 // If either thread tries to get the token while the other has
49 // it, that thread waits. However, if the VM thread and CMS thread
50 // both want the token, then the VM thread gets priority while the
51 // CMS thread waits. This ensures, for instance, that the "concurrent"
52 // phases of the CMS thread's work do not block out the VM thread
53 // for long periods of time as the CMS thread continues to hog
54 // the token. (See bug 4616232).
55 //
56 // The baton-passing functions are, however, controlled by the
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
58 // and here the low-level CMS lock, not the high level token,
59 // ensures mutual exclusion.
60 //
61 // Two important conditions that we have to satisfy:
62 // 1. if a thread does a low-level wait on the CMS lock, then it
63 // relinquishes the CMS token if it were holding that token
64 // when it acquired the low-level CMS lock.
65 // 2. any low-level notifications on the low-level lock
66 // should only be sent when a thread has relinquished the token.
67 //
68 // In the absence of either property, we'd have potential deadlock.
69 //
70 // We protect each of the CMS (concurrent and sequential) phases
71 // with the CMS _token_, not the CMS _lock_.
72 //
73 // The only code protected by CMS lock is the token acquisition code
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
75 // baton-passing code.
76 //
77 // Unfortunately, i couldn't come up with a good abstraction to factor and
78 // hide the naked CGC_lock manipulation in the baton-passing code
79 // further below. That's something we should try to do. Also, the proof
80 // of correctness of this 2-level locking scheme is far from obvious,
81 // and potentially quite slippery. We have an uneasy supsicion, for instance,
82 // that there may be a theoretical possibility of delay/starvation in the
83 // low-level lock/wait/notify scheme used for the baton-passing because of
84 // potential intereference with the priority scheme embodied in the
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
86 // invocation further below and marked with "XXX 20011219YSR".
87 // Indeed, as we note elsewhere, this may become yet more slippery
88 // in the presence of multiple CMS and/or multiple VM threads. XXX
90 class CMSTokenSync: public StackObj {
91 private:
92 bool _is_cms_thread;
93 public:
94 CMSTokenSync(bool is_cms_thread):
95 _is_cms_thread(is_cms_thread) {
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
97 "Incorrect argument to constructor");
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
99 }
101 ~CMSTokenSync() {
102 assert(_is_cms_thread ?
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
105 "Incorrect state");
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
107 }
108 };
110 // Convenience class that does a CMSTokenSync, and then acquires
111 // upto three locks.
112 class CMSTokenSyncWithLocks: public CMSTokenSync {
113 private:
114 // Note: locks are acquired in textual declaration order
115 // and released in the opposite order
116 MutexLockerEx _locker1, _locker2, _locker3;
117 public:
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
120 CMSTokenSync(is_cms_thread),
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
124 { }
125 };
128 // Wrapper class to temporarily disable icms during a foreground cms collection.
129 class ICMSDisabler: public StackObj {
130 public:
131 // The ctor disables icms and wakes up the thread so it notices the change;
132 // the dtor re-enables icms. Note that the CMSCollector methods will check
133 // CMSIncrementalMode.
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
135 ~ICMSDisabler() { CMSCollector::enable_icms(); }
136 };
138 //////////////////////////////////////////////////////////////////
139 // Concurrent Mark-Sweep Generation /////////////////////////////
140 //////////////////////////////////////////////////////////////////
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
144 // This struct contains per-thread things necessary to support parallel
145 // young-gen collection.
146 class CMSParGCThreadState: public CHeapObj {
147 public:
148 CFLS_LAB lab;
149 PromotionInfo promo;
151 // Constructor.
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
153 promo.setSpace(cfls);
154 }
155 };
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
158 ReservedSpace rs, size_t initial_byte_size, int level,
159 CardTableRS* ct, bool use_adaptive_freelists,
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) :
161 CardGeneration(rs, initial_byte_size, level, ct),
162 _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))),
163 _debug_collection_type(Concurrent_collection_type)
164 {
165 HeapWord* bottom = (HeapWord*) _virtual_space.low();
166 HeapWord* end = (HeapWord*) _virtual_space.high();
168 _direct_allocated_words = 0;
169 NOT_PRODUCT(
170 _numObjectsPromoted = 0;
171 _numWordsPromoted = 0;
172 _numObjectsAllocated = 0;
173 _numWordsAllocated = 0;
174 )
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
177 use_adaptive_freelists,
178 dictionaryChoice);
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
180 if (_cmsSpace == NULL) {
181 vm_exit_during_initialization(
182 "CompactibleFreeListSpace allocation failure");
183 }
184 _cmsSpace->_gen = this;
186 _gc_stats = new CMSGCStats();
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
189 // offsets match. The ability to tell free chunks from objects
190 // depends on this property.
191 debug_only(
192 FreeChunk* junk = NULL;
193 assert(UseCompressedOops ||
194 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
195 "Offset of FreeChunk::_prev within FreeChunk must match"
196 " that of OopDesc::_klass within OopDesc");
197 )
198 if (ParallelGCThreads > 0) {
199 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
200 _par_gc_thread_states =
201 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads);
202 if (_par_gc_thread_states == NULL) {
203 vm_exit_during_initialization("Could not allocate par gc structs");
204 }
205 for (uint i = 0; i < ParallelGCThreads; i++) {
206 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
207 if (_par_gc_thread_states[i] == NULL) {
208 vm_exit_during_initialization("Could not allocate par gc structs");
209 }
210 }
211 } else {
212 _par_gc_thread_states = NULL;
213 }
214 _incremental_collection_failed = false;
215 // The "dilatation_factor" is the expansion that can occur on
216 // account of the fact that the minimum object size in the CMS
217 // generation may be larger than that in, say, a contiguous young
218 // generation.
219 // Ideally, in the calculation below, we'd compute the dilatation
220 // factor as: MinChunkSize/(promoting_gen's min object size)
221 // Since we do not have such a general query interface for the
222 // promoting generation, we'll instead just use the mimimum
223 // object size (which today is a header's worth of space);
224 // note that all arithmetic is in units of HeapWords.
225 assert(MinChunkSize >= oopDesc::header_size(), "just checking");
226 assert(_dilatation_factor >= 1.0, "from previous assert");
227 }
230 // The field "_initiating_occupancy" represents the occupancy percentage
231 // at which we trigger a new collection cycle. Unless explicitly specified
232 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
233 // is calculated by:
234 //
235 // Let "f" be MinHeapFreeRatio in
236 //
237 // _intiating_occupancy = 100-f +
238 // f * (CMSTrigger[Perm]Ratio/100)
239 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
240 //
241 // That is, if we assume the heap is at its desired maximum occupancy at the
242 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
243 // space be allocated before initiating a new collection cycle.
244 //
245 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
246 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
247 if (io >= 0) {
248 _initiating_occupancy = (double)io / 100.0;
249 } else {
250 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
251 (double)(tr * MinHeapFreeRatio) / 100.0)
252 / 100.0;
253 }
254 }
257 void ConcurrentMarkSweepGeneration::ref_processor_init() {
258 assert(collector() != NULL, "no collector");
259 collector()->ref_processor_init();
260 }
262 void CMSCollector::ref_processor_init() {
263 if (_ref_processor == NULL) {
264 // Allocate and initialize a reference processor
265 _ref_processor = ReferenceProcessor::create_ref_processor(
266 _span, // span
267 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery
268 _cmsGen->refs_discovery_is_mt(), // mt_discovery
269 &_is_alive_closure,
270 ParallelGCThreads,
271 ParallelRefProcEnabled);
272 // Initialize the _ref_processor field of CMSGen
273 _cmsGen->set_ref_processor(_ref_processor);
275 // Allocate a dummy ref processor for perm gen.
276 ReferenceProcessor* rp2 = new ReferenceProcessor();
277 if (rp2 == NULL) {
278 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
279 }
280 _permGen->set_ref_processor(rp2);
281 }
282 }
284 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
285 GenCollectedHeap* gch = GenCollectedHeap::heap();
286 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
287 "Wrong type of heap");
288 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
289 gch->gen_policy()->size_policy();
290 assert(sp->is_gc_cms_adaptive_size_policy(),
291 "Wrong type of size policy");
292 return sp;
293 }
295 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
296 CMSGCAdaptivePolicyCounters* results =
297 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
298 assert(
299 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
300 "Wrong gc policy counter kind");
301 return results;
302 }
305 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
307 const char* gen_name = "old";
309 // Generation Counters - generation 1, 1 subspace
310 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
312 _space_counters = new GSpaceCounters(gen_name, 0,
313 _virtual_space.reserved_size(),
314 this, _gen_counters);
315 }
317 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
318 _cms_gen(cms_gen)
319 {
320 assert(alpha <= 100, "bad value");
321 _saved_alpha = alpha;
323 // Initialize the alphas to the bootstrap value of 100.
324 _gc0_alpha = _cms_alpha = 100;
326 _cms_begin_time.update();
327 _cms_end_time.update();
329 _gc0_duration = 0.0;
330 _gc0_period = 0.0;
331 _gc0_promoted = 0;
333 _cms_duration = 0.0;
334 _cms_period = 0.0;
335 _cms_allocated = 0;
337 _cms_used_at_gc0_begin = 0;
338 _cms_used_at_gc0_end = 0;
339 _allow_duty_cycle_reduction = false;
340 _valid_bits = 0;
341 _icms_duty_cycle = CMSIncrementalDutyCycle;
342 }
344 // If promotion failure handling is on use
345 // the padded average size of the promotion for each
346 // young generation collection.
347 double CMSStats::time_until_cms_gen_full() const {
348 size_t cms_free = _cms_gen->cmsSpace()->free();
349 GenCollectedHeap* gch = GenCollectedHeap::heap();
350 size_t expected_promotion = gch->get_gen(0)->capacity();
351 if (HandlePromotionFailure) {
352 expected_promotion = MIN2(
353 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(),
354 expected_promotion);
355 }
356 if (cms_free > expected_promotion) {
357 // Start a cms collection if there isn't enough space to promote
358 // for the next minor collection. Use the padded average as
359 // a safety factor.
360 cms_free -= expected_promotion;
362 // Adjust by the safety factor.
363 double cms_free_dbl = (double)cms_free;
364 cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0;
366 if (PrintGCDetails && Verbose) {
367 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
368 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
369 cms_free, expected_promotion);
370 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
371 cms_free_dbl, cms_consumption_rate() + 1.0);
372 }
373 // Add 1 in case the consumption rate goes to zero.
374 return cms_free_dbl / (cms_consumption_rate() + 1.0);
375 }
376 return 0.0;
377 }
379 // Compare the duration of the cms collection to the
380 // time remaining before the cms generation is empty.
381 // Note that the time from the start of the cms collection
382 // to the start of the cms sweep (less than the total
383 // duration of the cms collection) can be used. This
384 // has been tried and some applications experienced
385 // promotion failures early in execution. This was
386 // possibly because the averages were not accurate
387 // enough at the beginning.
388 double CMSStats::time_until_cms_start() const {
389 // We add "gc0_period" to the "work" calculation
390 // below because this query is done (mostly) at the
391 // end of a scavenge, so we need to conservatively
392 // account for that much possible delay
393 // in the query so as to avoid concurrent mode failures
394 // due to starting the collection just a wee bit too
395 // late.
396 double work = cms_duration() + gc0_period();
397 double deadline = time_until_cms_gen_full();
398 if (work > deadline) {
399 if (Verbose && PrintGCDetails) {
400 gclog_or_tty->print(
401 " CMSCollector: collect because of anticipated promotion "
402 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
403 gc0_period(), time_until_cms_gen_full());
404 }
405 return 0.0;
406 }
407 return work - deadline;
408 }
410 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
411 // amount of change to prevent wild oscillation.
412 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
413 unsigned int new_duty_cycle) {
414 assert(old_duty_cycle <= 100, "bad input value");
415 assert(new_duty_cycle <= 100, "bad input value");
417 // Note: use subtraction with caution since it may underflow (values are
418 // unsigned). Addition is safe since we're in the range 0-100.
419 unsigned int damped_duty_cycle = new_duty_cycle;
420 if (new_duty_cycle < old_duty_cycle) {
421 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
422 if (new_duty_cycle + largest_delta < old_duty_cycle) {
423 damped_duty_cycle = old_duty_cycle - largest_delta;
424 }
425 } else if (new_duty_cycle > old_duty_cycle) {
426 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
427 if (new_duty_cycle > old_duty_cycle + largest_delta) {
428 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
429 }
430 }
431 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
433 if (CMSTraceIncrementalPacing) {
434 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
435 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
436 }
437 return damped_duty_cycle;
438 }
440 unsigned int CMSStats::icms_update_duty_cycle_impl() {
441 assert(CMSIncrementalPacing && valid(),
442 "should be handled in icms_update_duty_cycle()");
444 double cms_time_so_far = cms_timer().seconds();
445 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
446 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
448 // Avoid division by 0.
449 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
450 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
452 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
453 if (new_duty_cycle > _icms_duty_cycle) {
454 // Avoid very small duty cycles (1 or 2); 0 is allowed.
455 if (new_duty_cycle > 2) {
456 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
457 new_duty_cycle);
458 }
459 } else if (_allow_duty_cycle_reduction) {
460 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
461 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
462 // Respect the minimum duty cycle.
463 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
464 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
465 }
467 if (PrintGCDetails || CMSTraceIncrementalPacing) {
468 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
469 }
471 _allow_duty_cycle_reduction = false;
472 return _icms_duty_cycle;
473 }
475 #ifndef PRODUCT
476 void CMSStats::print_on(outputStream *st) const {
477 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
478 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
479 gc0_duration(), gc0_period(), gc0_promoted());
480 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
481 cms_duration(), cms_duration_per_mb(),
482 cms_period(), cms_allocated());
483 st->print(",cms_since_beg=%g,cms_since_end=%g",
484 cms_time_since_begin(), cms_time_since_end());
485 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
486 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
487 if (CMSIncrementalMode) {
488 st->print(",dc=%d", icms_duty_cycle());
489 }
491 if (valid()) {
492 st->print(",promo_rate=%g,cms_alloc_rate=%g",
493 promotion_rate(), cms_allocation_rate());
494 st->print(",cms_consumption_rate=%g,time_until_full=%g",
495 cms_consumption_rate(), time_until_cms_gen_full());
496 }
497 st->print(" ");
498 }
499 #endif // #ifndef PRODUCT
501 CMSCollector::CollectorState CMSCollector::_collectorState =
502 CMSCollector::Idling;
503 bool CMSCollector::_foregroundGCIsActive = false;
504 bool CMSCollector::_foregroundGCShouldWait = false;
506 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
507 ConcurrentMarkSweepGeneration* permGen,
508 CardTableRS* ct,
509 ConcurrentMarkSweepPolicy* cp):
510 _cmsGen(cmsGen),
511 _permGen(permGen),
512 _ct(ct),
513 _ref_processor(NULL), // will be set later
514 _conc_workers(NULL), // may be set later
515 _abort_preclean(false),
516 _start_sampling(false),
517 _between_prologue_and_epilogue(false),
518 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
519 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
520 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
521 -1 /* lock-free */, "No_lock" /* dummy */),
522 _modUnionClosure(&_modUnionTable),
523 _modUnionClosurePar(&_modUnionTable),
524 // Adjust my span to cover old (cms) gen and perm gen
525 _span(cmsGen->reserved()._union(permGen->reserved())),
526 // Construct the is_alive_closure with _span & markBitMap
527 _is_alive_closure(_span, &_markBitMap),
528 _restart_addr(NULL),
529 _overflow_list(NULL),
530 _preserved_oop_stack(NULL),
531 _preserved_mark_stack(NULL),
532 _stats(cmsGen),
533 _eden_chunk_array(NULL), // may be set in ctor body
534 _eden_chunk_capacity(0), // -- ditto --
535 _eden_chunk_index(0), // -- ditto --
536 _survivor_plab_array(NULL), // -- ditto --
537 _survivor_chunk_array(NULL), // -- ditto --
538 _survivor_chunk_capacity(0), // -- ditto --
539 _survivor_chunk_index(0), // -- ditto --
540 _ser_pmc_preclean_ovflw(0),
541 _ser_kac_preclean_ovflw(0),
542 _ser_pmc_remark_ovflw(0),
543 _par_pmc_remark_ovflw(0),
544 _ser_kac_ovflw(0),
545 _par_kac_ovflw(0),
546 #ifndef PRODUCT
547 _num_par_pushes(0),
548 #endif
549 _collection_count_start(0),
550 _verifying(false),
551 _icms_start_limit(NULL),
552 _icms_stop_limit(NULL),
553 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
554 _completed_initialization(false),
555 _collector_policy(cp),
556 _should_unload_classes(false),
557 _concurrent_cycles_since_last_unload(0),
558 _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
559 {
560 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
561 ExplicitGCInvokesConcurrent = true;
562 }
563 // Now expand the span and allocate the collection support structures
564 // (MUT, marking bit map etc.) to cover both generations subject to
565 // collection.
567 // First check that _permGen is adjacent to _cmsGen and above it.
568 assert( _cmsGen->reserved().word_size() > 0
569 && _permGen->reserved().word_size() > 0,
570 "generations should not be of zero size");
571 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
572 "_cmsGen and _permGen should not overlap");
573 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
574 "_cmsGen->end() different from _permGen->start()");
576 // For use by dirty card to oop closures.
577 _cmsGen->cmsSpace()->set_collector(this);
578 _permGen->cmsSpace()->set_collector(this);
580 // Allocate MUT and marking bit map
581 {
582 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
583 if (!_markBitMap.allocate(_span)) {
584 warning("Failed to allocate CMS Bit Map");
585 return;
586 }
587 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
588 }
589 {
590 _modUnionTable.allocate(_span);
591 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
592 }
594 if (!_markStack.allocate(CMSMarkStackSize)) {
595 warning("Failed to allocate CMS Marking Stack");
596 return;
597 }
598 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
599 warning("Failed to allocate CMS Revisit Stack");
600 return;
601 }
603 // Support for multi-threaded concurrent phases
604 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) {
605 if (FLAG_IS_DEFAULT(ParallelCMSThreads)) {
606 // just for now
607 FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4);
608 }
609 if (ParallelCMSThreads > 1) {
610 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
611 ParallelCMSThreads, true);
612 if (_conc_workers == NULL) {
613 warning("GC/CMS: _conc_workers allocation failure: "
614 "forcing -CMSConcurrentMTEnabled");
615 CMSConcurrentMTEnabled = false;
616 }
617 } else {
618 CMSConcurrentMTEnabled = false;
619 }
620 }
621 if (!CMSConcurrentMTEnabled) {
622 ParallelCMSThreads = 0;
623 } else {
624 // Turn off CMSCleanOnEnter optimization temporarily for
625 // the MT case where it's not fixed yet; see 6178663.
626 CMSCleanOnEnter = false;
627 }
628 assert((_conc_workers != NULL) == (ParallelCMSThreads > 1),
629 "Inconsistency");
631 // Parallel task queues; these are shared for the
632 // concurrent and stop-world phases of CMS, but
633 // are not shared with parallel scavenge (ParNew).
634 {
635 uint i;
636 uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads);
638 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
639 || ParallelRefProcEnabled)
640 && num_queues > 0) {
641 _task_queues = new OopTaskQueueSet(num_queues);
642 if (_task_queues == NULL) {
643 warning("task_queues allocation failure.");
644 return;
645 }
646 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues);
647 if (_hash_seed == NULL) {
648 warning("_hash_seed array allocation failure");
649 return;
650 }
652 // XXX use a global constant instead of 64!
653 typedef struct OopTaskQueuePadded {
654 OopTaskQueue work_queue;
655 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing
656 } OopTaskQueuePadded;
658 for (i = 0; i < num_queues; i++) {
659 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded();
660 if (q_padded == NULL) {
661 warning("work_queue allocation failure.");
662 return;
663 }
664 _task_queues->register_queue(i, &q_padded->work_queue);
665 }
666 for (i = 0; i < num_queues; i++) {
667 _task_queues->queue(i)->initialize();
668 _hash_seed[i] = 17; // copied from ParNew
669 }
670 }
671 }
673 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
674 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
676 // Clip CMSBootstrapOccupancy between 0 and 100.
677 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
678 /(double)100;
680 _full_gcs_since_conc_gc = 0;
682 // Now tell CMS generations the identity of their collector
683 ConcurrentMarkSweepGeneration::set_collector(this);
685 // Create & start a CMS thread for this CMS collector
686 _cmsThread = ConcurrentMarkSweepThread::start(this);
687 assert(cmsThread() != NULL, "CMS Thread should have been created");
688 assert(cmsThread()->collector() == this,
689 "CMS Thread should refer to this gen");
690 assert(CGC_lock != NULL, "Where's the CGC_lock?");
692 // Support for parallelizing young gen rescan
693 GenCollectedHeap* gch = GenCollectedHeap::heap();
694 _young_gen = gch->prev_gen(_cmsGen);
695 if (gch->supports_inline_contig_alloc()) {
696 _top_addr = gch->top_addr();
697 _end_addr = gch->end_addr();
698 assert(_young_gen != NULL, "no _young_gen");
699 _eden_chunk_index = 0;
700 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
701 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity);
702 if (_eden_chunk_array == NULL) {
703 _eden_chunk_capacity = 0;
704 warning("GC/CMS: _eden_chunk_array allocation failure");
705 }
706 }
707 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
709 // Support for parallelizing survivor space rescan
710 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
711 size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize);
712 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads);
713 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples);
714 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads);
715 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
716 || _cursor == NULL) {
717 warning("Failed to allocate survivor plab/chunk array");
718 if (_survivor_plab_array != NULL) {
719 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
720 _survivor_plab_array = NULL;
721 }
722 if (_survivor_chunk_array != NULL) {
723 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
724 _survivor_chunk_array = NULL;
725 }
726 if (_cursor != NULL) {
727 FREE_C_HEAP_ARRAY(size_t, _cursor);
728 _cursor = NULL;
729 }
730 } else {
731 _survivor_chunk_capacity = 2*max_plab_samples;
732 for (uint i = 0; i < ParallelGCThreads; i++) {
733 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples);
734 if (vec == NULL) {
735 warning("Failed to allocate survivor plab array");
736 for (int j = i; j > 0; j--) {
737 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array());
738 }
739 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array);
740 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array);
741 _survivor_plab_array = NULL;
742 _survivor_chunk_array = NULL;
743 _survivor_chunk_capacity = 0;
744 break;
745 } else {
746 ChunkArray* cur =
747 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
748 max_plab_samples);
749 assert(cur->end() == 0, "Should be 0");
750 assert(cur->array() == vec, "Should be vec");
751 assert(cur->capacity() == max_plab_samples, "Error");
752 }
753 }
754 }
755 }
756 assert( ( _survivor_plab_array != NULL
757 && _survivor_chunk_array != NULL)
758 || ( _survivor_chunk_capacity == 0
759 && _survivor_chunk_index == 0),
760 "Error");
762 // Choose what strong roots should be scanned depending on verification options
763 // and perm gen collection mode.
764 if (!CMSClassUnloadingEnabled) {
765 // If class unloading is disabled we want to include all classes into the root set.
766 add_root_scanning_option(SharedHeap::SO_AllClasses);
767 } else {
768 add_root_scanning_option(SharedHeap::SO_SystemClasses);
769 }
771 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
772 _gc_counters = new CollectorCounters("CMS", 1);
773 _completed_initialization = true;
774 _sweep_timer.start(); // start of time
775 }
777 const char* ConcurrentMarkSweepGeneration::name() const {
778 return "concurrent mark-sweep generation";
779 }
780 void ConcurrentMarkSweepGeneration::update_counters() {
781 if (UsePerfData) {
782 _space_counters->update_all();
783 _gen_counters->update_all();
784 }
785 }
787 // this is an optimized version of update_counters(). it takes the
788 // used value as a parameter rather than computing it.
789 //
790 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
791 if (UsePerfData) {
792 _space_counters->update_used(used);
793 _space_counters->update_capacity();
794 _gen_counters->update_all();
795 }
796 }
798 void ConcurrentMarkSweepGeneration::print() const {
799 Generation::print();
800 cmsSpace()->print();
801 }
803 #ifndef PRODUCT
804 void ConcurrentMarkSweepGeneration::print_statistics() {
805 cmsSpace()->printFLCensus(0);
806 }
807 #endif
809 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
810 GenCollectedHeap* gch = GenCollectedHeap::heap();
811 if (PrintGCDetails) {
812 if (Verbose) {
813 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
814 level(), short_name(), s, used(), capacity());
815 } else {
816 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
817 level(), short_name(), s, used() / K, capacity() / K);
818 }
819 }
820 if (Verbose) {
821 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
822 gch->used(), gch->capacity());
823 } else {
824 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
825 gch->used() / K, gch->capacity() / K);
826 }
827 }
829 size_t
830 ConcurrentMarkSweepGeneration::contiguous_available() const {
831 // dld proposes an improvement in precision here. If the committed
832 // part of the space ends in a free block we should add that to
833 // uncommitted size in the calculation below. Will make this
834 // change later, staying with the approximation below for the
835 // time being. -- ysr.
836 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
837 }
839 size_t
840 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
841 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
842 }
844 size_t ConcurrentMarkSweepGeneration::max_available() const {
845 return free() + _virtual_space.uncommitted_size();
846 }
848 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(
849 size_t max_promotion_in_bytes,
850 bool younger_handles_promotion_failure) const {
852 // This is the most conservative test. Full promotion is
853 // guaranteed if this is used. The multiplicative factor is to
854 // account for the worst case "dilatation".
855 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes;
856 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t
857 adjusted_max_promo_bytes = (double)max_uintx;
858 }
859 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes);
861 if (younger_handles_promotion_failure && !result) {
862 // Full promotion is not guaranteed because fragmentation
863 // of the cms generation can prevent the full promotion.
864 result = (max_available() >= (size_t)adjusted_max_promo_bytes);
866 if (!result) {
867 // With promotion failure handling the test for the ability
868 // to support the promotion does not have to be guaranteed.
869 // Use an average of the amount promoted.
870 result = max_available() >= (size_t)
871 gc_stats()->avg_promoted()->padded_average();
872 if (PrintGC && Verbose && result) {
873 gclog_or_tty->print_cr(
874 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
875 " max_available: " SIZE_FORMAT
876 " avg_promoted: " SIZE_FORMAT,
877 max_available(), (size_t)
878 gc_stats()->avg_promoted()->padded_average());
879 }
880 } else {
881 if (PrintGC && Verbose) {
882 gclog_or_tty->print_cr(
883 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
884 " max_available: " SIZE_FORMAT
885 " adj_max_promo_bytes: " SIZE_FORMAT,
886 max_available(), (size_t)adjusted_max_promo_bytes);
887 }
888 }
889 } else {
890 if (PrintGC && Verbose) {
891 gclog_or_tty->print_cr(
892 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe"
893 " contiguous_available: " SIZE_FORMAT
894 " adj_max_promo_bytes: " SIZE_FORMAT,
895 max_contiguous_available(), (size_t)adjusted_max_promo_bytes);
896 }
897 }
898 return result;
899 }
901 CompactibleSpace*
902 ConcurrentMarkSweepGeneration::first_compaction_space() const {
903 return _cmsSpace;
904 }
906 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
907 // Clear the promotion information. These pointers can be adjusted
908 // along with all the other pointers into the heap but
909 // compaction is expected to be a rare event with
910 // a heap using cms so don't do it without seeing the need.
911 if (ParallelGCThreads > 0) {
912 for (uint i = 0; i < ParallelGCThreads; i++) {
913 _par_gc_thread_states[i]->promo.reset();
914 }
915 }
916 }
918 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
919 blk->do_space(_cmsSpace);
920 }
922 void ConcurrentMarkSweepGeneration::compute_new_size() {
923 assert_locked_or_safepoint(Heap_lock);
925 // If incremental collection failed, we just want to expand
926 // to the limit.
927 if (incremental_collection_failed()) {
928 clear_incremental_collection_failed();
929 grow_to_reserved();
930 return;
931 }
933 size_t expand_bytes = 0;
934 double free_percentage = ((double) free()) / capacity();
935 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
936 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
938 // compute expansion delta needed for reaching desired free percentage
939 if (free_percentage < desired_free_percentage) {
940 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
941 assert(desired_capacity >= capacity(), "invalid expansion size");
942 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
943 }
944 if (expand_bytes > 0) {
945 if (PrintGCDetails && Verbose) {
946 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
947 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
948 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
949 gclog_or_tty->print_cr(" Desired free fraction %f",
950 desired_free_percentage);
951 gclog_or_tty->print_cr(" Maximum free fraction %f",
952 maximum_free_percentage);
953 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
954 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
955 desired_capacity/1000);
956 int prev_level = level() - 1;
957 if (prev_level >= 0) {
958 size_t prev_size = 0;
959 GenCollectedHeap* gch = GenCollectedHeap::heap();
960 Generation* prev_gen = gch->_gens[prev_level];
961 prev_size = prev_gen->capacity();
962 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
963 prev_size/1000);
964 }
965 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
966 unsafe_max_alloc_nogc()/1000);
967 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
968 contiguous_available()/1000);
969 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
970 expand_bytes);
971 }
972 // safe if expansion fails
973 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
974 if (PrintGCDetails && Verbose) {
975 gclog_or_tty->print_cr(" Expanded free fraction %f",
976 ((double) free()) / capacity());
977 }
978 }
979 }
981 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
982 return cmsSpace()->freelistLock();
983 }
985 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
986 bool tlab) {
987 CMSSynchronousYieldRequest yr;
988 MutexLockerEx x(freelistLock(),
989 Mutex::_no_safepoint_check_flag);
990 return have_lock_and_allocate(size, tlab);
991 }
993 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
994 bool tlab) {
995 assert_lock_strong(freelistLock());
996 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
997 HeapWord* res = cmsSpace()->allocate(adjustedSize);
998 // Allocate the object live (grey) if the background collector has
999 // started marking. This is necessary because the marker may
1000 // have passed this address and consequently this object will
1001 // not otherwise be greyed and would be incorrectly swept up.
1002 // Note that if this object contains references, the writing
1003 // of those references will dirty the card containing this object
1004 // allowing the object to be blackened (and its references scanned)
1005 // either during a preclean phase or at the final checkpoint.
1006 if (res != NULL) {
1007 collector()->direct_allocated(res, adjustedSize);
1008 _direct_allocated_words += adjustedSize;
1009 // allocation counters
1010 NOT_PRODUCT(
1011 _numObjectsAllocated++;
1012 _numWordsAllocated += (int)adjustedSize;
1013 )
1014 }
1015 return res;
1016 }
1018 // In the case of direct allocation by mutators in a generation that
1019 // is being concurrently collected, the object must be allocated
1020 // live (grey) if the background collector has started marking.
1021 // This is necessary because the marker may
1022 // have passed this address and consequently this object will
1023 // not otherwise be greyed and would be incorrectly swept up.
1024 // Note that if this object contains references, the writing
1025 // of those references will dirty the card containing this object
1026 // allowing the object to be blackened (and its references scanned)
1027 // either during a preclean phase or at the final checkpoint.
1028 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1029 assert(_markBitMap.covers(start, size), "Out of bounds");
1030 if (_collectorState >= Marking) {
1031 MutexLockerEx y(_markBitMap.lock(),
1032 Mutex::_no_safepoint_check_flag);
1033 // [see comments preceding SweepClosure::do_blk() below for details]
1034 // 1. need to mark the object as live so it isn't collected
1035 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1036 // 3. need to mark the end of the object so sweeper can skip over it
1037 // if it's uninitialized when the sweeper reaches it.
1038 _markBitMap.mark(start); // object is live
1039 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1040 _markBitMap.mark(start + size - 1);
1041 // mark end of object
1042 }
1043 // check that oop looks uninitialized
1044 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1045 }
1047 void CMSCollector::promoted(bool par, HeapWord* start,
1048 bool is_obj_array, size_t obj_size) {
1049 assert(_markBitMap.covers(start), "Out of bounds");
1050 // See comment in direct_allocated() about when objects should
1051 // be allocated live.
1052 if (_collectorState >= Marking) {
1053 // we already hold the marking bit map lock, taken in
1054 // the prologue
1055 if (par) {
1056 _markBitMap.par_mark(start);
1057 } else {
1058 _markBitMap.mark(start);
1059 }
1060 // We don't need to mark the object as uninitialized (as
1061 // in direct_allocated above) because this is being done with the
1062 // world stopped and the object will be initialized by the
1063 // time the sweeper gets to look at it.
1064 assert(SafepointSynchronize::is_at_safepoint(),
1065 "expect promotion only at safepoints");
1067 if (_collectorState < Sweeping) {
1068 // Mark the appropriate cards in the modUnionTable, so that
1069 // this object gets scanned before the sweep. If this is
1070 // not done, CMS generation references in the object might
1071 // not get marked.
1072 // For the case of arrays, which are otherwise precisely
1073 // marked, we need to dirty the entire array, not just its head.
1074 if (is_obj_array) {
1075 // The [par_]mark_range() method expects mr.end() below to
1076 // be aligned to the granularity of a bit's representation
1077 // in the heap. In the case of the MUT below, that's a
1078 // card size.
1079 MemRegion mr(start,
1080 (HeapWord*)round_to((intptr_t)(start + obj_size),
1081 CardTableModRefBS::card_size /* bytes */));
1082 if (par) {
1083 _modUnionTable.par_mark_range(mr);
1084 } else {
1085 _modUnionTable.mark_range(mr);
1086 }
1087 } else { // not an obj array; we can just mark the head
1088 if (par) {
1089 _modUnionTable.par_mark(start);
1090 } else {
1091 _modUnionTable.mark(start);
1092 }
1093 }
1094 }
1095 }
1096 }
1098 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1099 {
1100 size_t delta = pointer_delta(addr, space->bottom());
1101 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1102 }
1104 void CMSCollector::icms_update_allocation_limits()
1105 {
1106 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1107 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1109 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1110 if (CMSTraceIncrementalPacing) {
1111 stats().print();
1112 }
1114 assert(duty_cycle <= 100, "invalid duty cycle");
1115 if (duty_cycle != 0) {
1116 // The duty_cycle is a percentage between 0 and 100; convert to words and
1117 // then compute the offset from the endpoints of the space.
1118 size_t free_words = eden->free() / HeapWordSize;
1119 double free_words_dbl = (double)free_words;
1120 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1121 size_t offset_words = (free_words - duty_cycle_words) / 2;
1123 _icms_start_limit = eden->top() + offset_words;
1124 _icms_stop_limit = eden->end() - offset_words;
1126 // The limits may be adjusted (shifted to the right) by
1127 // CMSIncrementalOffset, to allow the application more mutator time after a
1128 // young gen gc (when all mutators were stopped) and before CMS starts and
1129 // takes away one or more cpus.
1130 if (CMSIncrementalOffset != 0) {
1131 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1132 size_t adjustment = (size_t)adjustment_dbl;
1133 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1134 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1135 _icms_start_limit += adjustment;
1136 _icms_stop_limit = tmp_stop;
1137 }
1138 }
1139 }
1140 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1141 _icms_start_limit = _icms_stop_limit = eden->end();
1142 }
1144 // Install the new start limit.
1145 eden->set_soft_end(_icms_start_limit);
1147 if (CMSTraceIncrementalMode) {
1148 gclog_or_tty->print(" icms alloc limits: "
1149 PTR_FORMAT "," PTR_FORMAT
1150 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1151 _icms_start_limit, _icms_stop_limit,
1152 percent_of_space(eden, _icms_start_limit),
1153 percent_of_space(eden, _icms_stop_limit));
1154 if (Verbose) {
1155 gclog_or_tty->print("eden: ");
1156 eden->print_on(gclog_or_tty);
1157 }
1158 }
1159 }
1161 // Any changes here should try to maintain the invariant
1162 // that if this method is called with _icms_start_limit
1163 // and _icms_stop_limit both NULL, then it should return NULL
1164 // and not notify the icms thread.
1165 HeapWord*
1166 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1167 size_t word_size)
1168 {
1169 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1170 // nop.
1171 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1172 if (top <= _icms_start_limit) {
1173 if (CMSTraceIncrementalMode) {
1174 space->print_on(gclog_or_tty);
1175 gclog_or_tty->stamp();
1176 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1177 ", new limit=" PTR_FORMAT
1178 " (" SIZE_FORMAT "%%)",
1179 top, _icms_stop_limit,
1180 percent_of_space(space, _icms_stop_limit));
1181 }
1182 ConcurrentMarkSweepThread::start_icms();
1183 assert(top < _icms_stop_limit, "Tautology");
1184 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1185 return _icms_stop_limit;
1186 }
1188 // The allocation will cross both the _start and _stop limits, so do the
1189 // stop notification also and return end().
1190 if (CMSTraceIncrementalMode) {
1191 space->print_on(gclog_or_tty);
1192 gclog_or_tty->stamp();
1193 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1194 ", new limit=" PTR_FORMAT
1195 " (" SIZE_FORMAT "%%)",
1196 top, space->end(),
1197 percent_of_space(space, space->end()));
1198 }
1199 ConcurrentMarkSweepThread::stop_icms();
1200 return space->end();
1201 }
1203 if (top <= _icms_stop_limit) {
1204 if (CMSTraceIncrementalMode) {
1205 space->print_on(gclog_or_tty);
1206 gclog_or_tty->stamp();
1207 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1208 ", new limit=" PTR_FORMAT
1209 " (" SIZE_FORMAT "%%)",
1210 top, space->end(),
1211 percent_of_space(space, space->end()));
1212 }
1213 ConcurrentMarkSweepThread::stop_icms();
1214 return space->end();
1215 }
1217 if (CMSTraceIncrementalMode) {
1218 space->print_on(gclog_or_tty);
1219 gclog_or_tty->stamp();
1220 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1221 ", new limit=" PTR_FORMAT,
1222 top, NULL);
1223 }
1224 }
1226 return NULL;
1227 }
1229 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1230 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1231 // allocate, copy and if necessary update promoinfo --
1232 // delegate to underlying space.
1233 assert_lock_strong(freelistLock());
1235 #ifndef PRODUCT
1236 if (Universe::heap()->promotion_should_fail()) {
1237 return NULL;
1238 }
1239 #endif // #ifndef PRODUCT
1241 oop res = _cmsSpace->promote(obj, obj_size);
1242 if (res == NULL) {
1243 // expand and retry
1244 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1245 expand(s*HeapWordSize, MinHeapDeltaBytes,
1246 CMSExpansionCause::_satisfy_promotion);
1247 // Since there's currently no next generation, we don't try to promote
1248 // into a more senior generation.
1249 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1250 "is made to pass on a possibly failing "
1251 "promotion to next generation");
1252 res = _cmsSpace->promote(obj, obj_size);
1253 }
1254 if (res != NULL) {
1255 // See comment in allocate() about when objects should
1256 // be allocated live.
1257 assert(obj->is_oop(), "Will dereference klass pointer below");
1258 collector()->promoted(false, // Not parallel
1259 (HeapWord*)res, obj->is_objArray(), obj_size);
1260 // promotion counters
1261 NOT_PRODUCT(
1262 _numObjectsPromoted++;
1263 _numWordsPromoted +=
1264 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1265 )
1266 }
1267 return res;
1268 }
1271 HeapWord*
1272 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1273 HeapWord* top,
1274 size_t word_sz)
1275 {
1276 return collector()->allocation_limit_reached(space, top, word_sz);
1277 }
1279 // Things to support parallel young-gen collection.
1280 oop
1281 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1282 oop old, markOop m,
1283 size_t word_sz) {
1284 #ifndef PRODUCT
1285 if (Universe::heap()->promotion_should_fail()) {
1286 return NULL;
1287 }
1288 #endif // #ifndef PRODUCT
1290 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1291 PromotionInfo* promoInfo = &ps->promo;
1292 // if we are tracking promotions, then first ensure space for
1293 // promotion (including spooling space for saving header if necessary).
1294 // then allocate and copy, then track promoted info if needed.
1295 // When tracking (see PromotionInfo::track()), the mark word may
1296 // be displaced and in this case restoration of the mark word
1297 // occurs in the (oop_since_save_marks_)iterate phase.
1298 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1299 // Out of space for allocating spooling buffers;
1300 // try expanding and allocating spooling buffers.
1301 if (!expand_and_ensure_spooling_space(promoInfo)) {
1302 return NULL;
1303 }
1304 }
1305 assert(promoInfo->has_spooling_space(), "Control point invariant");
1306 HeapWord* obj_ptr = ps->lab.alloc(word_sz);
1307 if (obj_ptr == NULL) {
1308 obj_ptr = expand_and_par_lab_allocate(ps, word_sz);
1309 if (obj_ptr == NULL) {
1310 return NULL;
1311 }
1312 }
1313 oop obj = oop(obj_ptr);
1314 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1315 // Otherwise, copy the object. Here we must be careful to insert the
1316 // klass pointer last, since this marks the block as an allocated object.
1317 // Except with compressed oops it's the mark word.
1318 HeapWord* old_ptr = (HeapWord*)old;
1319 if (word_sz > (size_t)oopDesc::header_size()) {
1320 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1321 obj_ptr + oopDesc::header_size(),
1322 word_sz - oopDesc::header_size());
1323 }
1325 if (UseCompressedOops) {
1326 // Copy gap missed by (aligned) header size calculation above
1327 obj->set_klass_gap(old->klass_gap());
1328 }
1330 // Restore the mark word copied above.
1331 obj->set_mark(m);
1333 // Now we can track the promoted object, if necessary. We take care
1334 // To delay the transition from uninitialized to full object
1335 // (i.e., insertion of klass pointer) until after, so that it
1336 // atomically becomes a promoted object.
1337 if (promoInfo->tracking()) {
1338 promoInfo->track((PromotedObject*)obj, old->klass());
1339 }
1341 // Finally, install the klass pointer (this should be volatile).
1342 obj->set_klass(old->klass());
1344 assert(old->is_oop(), "Will dereference klass ptr below");
1345 collector()->promoted(true, // parallel
1346 obj_ptr, old->is_objArray(), word_sz);
1348 NOT_PRODUCT(
1349 Atomic::inc(&_numObjectsPromoted);
1350 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()),
1351 &_numWordsPromoted);
1352 )
1354 return obj;
1355 }
1357 void
1358 ConcurrentMarkSweepGeneration::
1359 par_promote_alloc_undo(int thread_num,
1360 HeapWord* obj, size_t word_sz) {
1361 // CMS does not support promotion undo.
1362 ShouldNotReachHere();
1363 }
1365 void
1366 ConcurrentMarkSweepGeneration::
1367 par_promote_alloc_done(int thread_num) {
1368 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1369 ps->lab.retire();
1370 #if CFLS_LAB_REFILL_STATS
1371 if (thread_num == 0) {
1372 _cmsSpace->print_par_alloc_stats();
1373 }
1374 #endif
1375 }
1377 void
1378 ConcurrentMarkSweepGeneration::
1379 par_oop_since_save_marks_iterate_done(int thread_num) {
1380 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1381 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1382 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1383 }
1385 // XXXPERM
1386 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1387 size_t size,
1388 bool tlab)
1389 {
1390 // We allow a STW collection only if a full
1391 // collection was requested.
1392 return full || should_allocate(size, tlab); // FIX ME !!!
1393 // This and promotion failure handling are connected at the
1394 // hip and should be fixed by untying them.
1395 }
1397 bool CMSCollector::shouldConcurrentCollect() {
1398 if (_full_gc_requested) {
1399 assert(ExplicitGCInvokesConcurrent, "Unexpected state");
1400 if (Verbose && PrintGCDetails) {
1401 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1402 " gc request");
1403 }
1404 return true;
1405 }
1407 // For debugging purposes, change the type of collection.
1408 // If the rotation is not on the concurrent collection
1409 // type, don't start a concurrent collection.
1410 NOT_PRODUCT(
1411 if (RotateCMSCollectionTypes &&
1412 (_cmsGen->debug_collection_type() !=
1413 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1414 assert(_cmsGen->debug_collection_type() !=
1415 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1416 "Bad cms collection type");
1417 return false;
1418 }
1419 )
1421 FreelistLocker x(this);
1422 // ------------------------------------------------------------------
1423 // Print out lots of information which affects the initiation of
1424 // a collection.
1425 if (PrintCMSInitiationStatistics && stats().valid()) {
1426 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1427 gclog_or_tty->stamp();
1428 gclog_or_tty->print_cr("");
1429 stats().print_on(gclog_or_tty);
1430 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1431 stats().time_until_cms_gen_full());
1432 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1433 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1434 _cmsGen->contiguous_available());
1435 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1436 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1437 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1438 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1439 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1440 }
1441 // ------------------------------------------------------------------
1443 // If the estimated time to complete a cms collection (cms_duration())
1444 // is less than the estimated time remaining until the cms generation
1445 // is full, start a collection.
1446 if (!UseCMSInitiatingOccupancyOnly) {
1447 if (stats().valid()) {
1448 if (stats().time_until_cms_start() == 0.0) {
1449 return true;
1450 }
1451 } else {
1452 // We want to conservatively collect somewhat early in order
1453 // to try and "bootstrap" our CMS/promotion statistics;
1454 // this branch will not fire after the first successful CMS
1455 // collection because the stats should then be valid.
1456 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1457 if (Verbose && PrintGCDetails) {
1458 gclog_or_tty->print_cr(
1459 " CMSCollector: collect for bootstrapping statistics:"
1460 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1461 _bootstrap_occupancy);
1462 }
1463 return true;
1464 }
1465 }
1466 }
1468 // Otherwise, we start a collection cycle if either the perm gen or
1469 // old gen want a collection cycle started. Each may use
1470 // an appropriate criterion for making this decision.
1471 // XXX We need to make sure that the gen expansion
1472 // criterion dovetails well with this. XXX NEED TO FIX THIS
1473 if (_cmsGen->should_concurrent_collect()) {
1474 if (Verbose && PrintGCDetails) {
1475 gclog_or_tty->print_cr("CMS old gen initiated");
1476 }
1477 return true;
1478 }
1480 // We start a collection if we believe an incremental collection may fail;
1481 // this is not likely to be productive in practice because it's probably too
1482 // late anyway.
1483 GenCollectedHeap* gch = GenCollectedHeap::heap();
1484 assert(gch->collector_policy()->is_two_generation_policy(),
1485 "You may want to check the correctness of the following");
1486 if (gch->incremental_collection_will_fail()) {
1487 if (PrintGCDetails && Verbose) {
1488 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1489 }
1490 return true;
1491 }
1493 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1494 bool res = update_should_unload_classes();
1495 if (res) {
1496 if (Verbose && PrintGCDetails) {
1497 gclog_or_tty->print_cr("CMS perm gen initiated");
1498 }
1499 return true;
1500 }
1501 }
1502 return false;
1503 }
1505 // Clear _expansion_cause fields of constituent generations
1506 void CMSCollector::clear_expansion_cause() {
1507 _cmsGen->clear_expansion_cause();
1508 _permGen->clear_expansion_cause();
1509 }
1511 // We should be conservative in starting a collection cycle. To
1512 // start too eagerly runs the risk of collecting too often in the
1513 // extreme. To collect too rarely falls back on full collections,
1514 // which works, even if not optimum in terms of concurrent work.
1515 // As a work around for too eagerly collecting, use the flag
1516 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1517 // giving the user an easily understandable way of controlling the
1518 // collections.
1519 // We want to start a new collection cycle if any of the following
1520 // conditions hold:
1521 // . our current occupancy exceeds the configured initiating occupancy
1522 // for this generation, or
1523 // . we recently needed to expand this space and have not, since that
1524 // expansion, done a collection of this generation, or
1525 // . the underlying space believes that it may be a good idea to initiate
1526 // a concurrent collection (this may be based on criteria such as the
1527 // following: the space uses linear allocation and linear allocation is
1528 // going to fail, or there is believed to be excessive fragmentation in
1529 // the generation, etc... or ...
1530 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1531 // the case of the old generation, not the perm generation; see CR 6543076):
1532 // we may be approaching a point at which allocation requests may fail because
1533 // we will be out of sufficient free space given allocation rate estimates.]
1534 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1536 assert_lock_strong(freelistLock());
1537 if (occupancy() > initiating_occupancy()) {
1538 if (PrintGCDetails && Verbose) {
1539 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1540 short_name(), occupancy(), initiating_occupancy());
1541 }
1542 return true;
1543 }
1544 if (UseCMSInitiatingOccupancyOnly) {
1545 return false;
1546 }
1547 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1548 if (PrintGCDetails && Verbose) {
1549 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1550 short_name());
1551 }
1552 return true;
1553 }
1554 if (_cmsSpace->should_concurrent_collect()) {
1555 if (PrintGCDetails && Verbose) {
1556 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1557 short_name());
1558 }
1559 return true;
1560 }
1561 return false;
1562 }
1564 void ConcurrentMarkSweepGeneration::collect(bool full,
1565 bool clear_all_soft_refs,
1566 size_t size,
1567 bool tlab)
1568 {
1569 collector()->collect(full, clear_all_soft_refs, size, tlab);
1570 }
1572 void CMSCollector::collect(bool full,
1573 bool clear_all_soft_refs,
1574 size_t size,
1575 bool tlab)
1576 {
1577 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1578 // For debugging purposes skip the collection if the state
1579 // is not currently idle
1580 if (TraceCMSState) {
1581 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1582 Thread::current(), full, _collectorState);
1583 }
1584 return;
1585 }
1587 // The following "if" branch is present for defensive reasons.
1588 // In the current uses of this interface, it can be replaced with:
1589 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1590 // But I am not placing that assert here to allow future
1591 // generality in invoking this interface.
1592 if (GC_locker::is_active()) {
1593 // A consistency test for GC_locker
1594 assert(GC_locker::needs_gc(), "Should have been set already");
1595 // Skip this foreground collection, instead
1596 // expanding the heap if necessary.
1597 // Need the free list locks for the call to free() in compute_new_size()
1598 compute_new_size();
1599 return;
1600 }
1601 acquire_control_and_collect(full, clear_all_soft_refs);
1602 _full_gcs_since_conc_gc++;
1604 }
1606 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1607 GenCollectedHeap* gch = GenCollectedHeap::heap();
1608 unsigned int gc_count = gch->total_full_collections();
1609 if (gc_count == full_gc_count) {
1610 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1611 _full_gc_requested = true;
1612 CGC_lock->notify(); // nudge CMS thread
1613 }
1614 }
1617 // The foreground and background collectors need to coordinate in order
1618 // to make sure that they do not mutually interfere with CMS collections.
1619 // When a background collection is active,
1620 // the foreground collector may need to take over (preempt) and
1621 // synchronously complete an ongoing collection. Depending on the
1622 // frequency of the background collections and the heap usage
1623 // of the application, this preemption can be seldom or frequent.
1624 // There are only certain
1625 // points in the background collection that the "collection-baton"
1626 // can be passed to the foreground collector.
1627 //
1628 // The foreground collector will wait for the baton before
1629 // starting any part of the collection. The foreground collector
1630 // will only wait at one location.
1631 //
1632 // The background collector will yield the baton before starting a new
1633 // phase of the collection (e.g., before initial marking, marking from roots,
1634 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1635 // of the loop which switches the phases. The background collector does some
1636 // of the phases (initial mark, final re-mark) with the world stopped.
1637 // Because of locking involved in stopping the world,
1638 // the foreground collector should not block waiting for the background
1639 // collector when it is doing a stop-the-world phase. The background
1640 // collector will yield the baton at an additional point just before
1641 // it enters a stop-the-world phase. Once the world is stopped, the
1642 // background collector checks the phase of the collection. If the
1643 // phase has not changed, it proceeds with the collection. If the
1644 // phase has changed, it skips that phase of the collection. See
1645 // the comments on the use of the Heap_lock in collect_in_background().
1646 //
1647 // Variable used in baton passing.
1648 // _foregroundGCIsActive - Set to true by the foreground collector when
1649 // it wants the baton. The foreground clears it when it has finished
1650 // the collection.
1651 // _foregroundGCShouldWait - Set to true by the background collector
1652 // when it is running. The foreground collector waits while
1653 // _foregroundGCShouldWait is true.
1654 // CGC_lock - monitor used to protect access to the above variables
1655 // and to notify the foreground and background collectors.
1656 // _collectorState - current state of the CMS collection.
1657 //
1658 // The foreground collector
1659 // acquires the CGC_lock
1660 // sets _foregroundGCIsActive
1661 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1662 // various locks acquired in preparation for the collection
1663 // are released so as not to block the background collector
1664 // that is in the midst of a collection
1665 // proceeds with the collection
1666 // clears _foregroundGCIsActive
1667 // returns
1668 //
1669 // The background collector in a loop iterating on the phases of the
1670 // collection
1671 // acquires the CGC_lock
1672 // sets _foregroundGCShouldWait
1673 // if _foregroundGCIsActive is set
1674 // clears _foregroundGCShouldWait, notifies _CGC_lock
1675 // waits on _CGC_lock for _foregroundGCIsActive to become false
1676 // and exits the loop.
1677 // otherwise
1678 // proceed with that phase of the collection
1679 // if the phase is a stop-the-world phase,
1680 // yield the baton once more just before enqueueing
1681 // the stop-world CMS operation (executed by the VM thread).
1682 // returns after all phases of the collection are done
1683 //
1685 void CMSCollector::acquire_control_and_collect(bool full,
1686 bool clear_all_soft_refs) {
1687 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1688 assert(!Thread::current()->is_ConcurrentGC_thread(),
1689 "shouldn't try to acquire control from self!");
1691 // Start the protocol for acquiring control of the
1692 // collection from the background collector (aka CMS thread).
1693 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1694 "VM thread should have CMS token");
1695 // Remember the possibly interrupted state of an ongoing
1696 // concurrent collection
1697 CollectorState first_state = _collectorState;
1699 // Signal to a possibly ongoing concurrent collection that
1700 // we want to do a foreground collection.
1701 _foregroundGCIsActive = true;
1703 // Disable incremental mode during a foreground collection.
1704 ICMSDisabler icms_disabler;
1706 // release locks and wait for a notify from the background collector
1707 // releasing the locks in only necessary for phases which
1708 // do yields to improve the granularity of the collection.
1709 assert_lock_strong(bitMapLock());
1710 // We need to lock the Free list lock for the space that we are
1711 // currently collecting.
1712 assert(haveFreelistLocks(), "Must be holding free list locks");
1713 bitMapLock()->unlock();
1714 releaseFreelistLocks();
1715 {
1716 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1717 if (_foregroundGCShouldWait) {
1718 // We are going to be waiting for action for the CMS thread;
1719 // it had better not be gone (for instance at shutdown)!
1720 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1721 "CMS thread must be running");
1722 // Wait here until the background collector gives us the go-ahead
1723 ConcurrentMarkSweepThread::clear_CMS_flag(
1724 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1725 // Get a possibly blocked CMS thread going:
1726 // Note that we set _foregroundGCIsActive true above,
1727 // without protection of the CGC_lock.
1728 CGC_lock->notify();
1729 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1730 "Possible deadlock");
1731 while (_foregroundGCShouldWait) {
1732 // wait for notification
1733 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1734 // Possibility of delay/starvation here, since CMS token does
1735 // not know to give priority to VM thread? Actually, i think
1736 // there wouldn't be any delay/starvation, but the proof of
1737 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1738 }
1739 ConcurrentMarkSweepThread::set_CMS_flag(
1740 ConcurrentMarkSweepThread::CMS_vm_has_token);
1741 }
1742 }
1743 // The CMS_token is already held. Get back the other locks.
1744 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1745 "VM thread should have CMS token");
1746 getFreelistLocks();
1747 bitMapLock()->lock_without_safepoint_check();
1748 if (TraceCMSState) {
1749 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1750 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1751 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1752 }
1754 // Check if we need to do a compaction, or if not, whether
1755 // we need to start the mark-sweep from scratch.
1756 bool should_compact = false;
1757 bool should_start_over = false;
1758 decide_foreground_collection_type(clear_all_soft_refs,
1759 &should_compact, &should_start_over);
1761 NOT_PRODUCT(
1762 if (RotateCMSCollectionTypes) {
1763 if (_cmsGen->debug_collection_type() ==
1764 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1765 should_compact = true;
1766 } else if (_cmsGen->debug_collection_type() ==
1767 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1768 should_compact = false;
1769 }
1770 }
1771 )
1773 if (PrintGCDetails && first_state > Idling) {
1774 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1775 if (GCCause::is_user_requested_gc(cause) ||
1776 GCCause::is_serviceability_requested_gc(cause)) {
1777 gclog_or_tty->print(" (concurrent mode interrupted)");
1778 } else {
1779 gclog_or_tty->print(" (concurrent mode failure)");
1780 }
1781 }
1783 if (should_compact) {
1784 // If the collection is being acquired from the background
1785 // collector, there may be references on the discovered
1786 // references lists that have NULL referents (being those
1787 // that were concurrently cleared by a mutator) or
1788 // that are no longer active (having been enqueued concurrently
1789 // by the mutator).
1790 // Scrub the list of those references because Mark-Sweep-Compact
1791 // code assumes referents are not NULL and that all discovered
1792 // Reference objects are active.
1793 ref_processor()->clean_up_discovered_references();
1795 do_compaction_work(clear_all_soft_refs);
1797 // Has the GC time limit been exceeded?
1798 check_gc_time_limit();
1800 } else {
1801 do_mark_sweep_work(clear_all_soft_refs, first_state,
1802 should_start_over);
1803 }
1804 // Reset the expansion cause, now that we just completed
1805 // a collection cycle.
1806 clear_expansion_cause();
1807 _foregroundGCIsActive = false;
1808 return;
1809 }
1811 void CMSCollector::check_gc_time_limit() {
1813 // Ignore explicit GC's. Exiting here does not set the flag and
1814 // does not reset the count. Updating of the averages for system
1815 // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC.
1816 GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause();
1817 if (GCCause::is_user_requested_gc(gc_cause) ||
1818 GCCause::is_serviceability_requested_gc(gc_cause)) {
1819 return;
1820 }
1822 // Calculate the fraction of the CMS generation was freed during
1823 // the last collection.
1824 // Only consider the STW compacting cost for now.
1825 //
1826 // Note that the gc time limit test only works for the collections
1827 // of the young gen + tenured gen and not for collections of the
1828 // permanent gen. That is because the calculation of the space
1829 // freed by the collection is the free space in the young gen +
1830 // tenured gen.
1832 double fraction_free =
1833 ((double)_cmsGen->free())/((double)_cmsGen->max_capacity());
1834 if ((100.0 * size_policy()->compacting_gc_cost()) >
1835 ((double) GCTimeLimit) &&
1836 ((fraction_free * 100) < GCHeapFreeLimit)) {
1837 size_policy()->inc_gc_time_limit_count();
1838 if (UseGCOverheadLimit &&
1839 (size_policy()->gc_time_limit_count() >
1840 AdaptiveSizePolicyGCTimeLimitThreshold)) {
1841 size_policy()->set_gc_time_limit_exceeded(true);
1842 // Avoid consecutive OOM due to the gc time limit by resetting
1843 // the counter.
1844 size_policy()->reset_gc_time_limit_count();
1845 if (PrintGCDetails) {
1846 gclog_or_tty->print_cr(" GC is exceeding overhead limit "
1847 "of %d%%", GCTimeLimit);
1848 }
1849 } else {
1850 if (PrintGCDetails) {
1851 gclog_or_tty->print_cr(" GC would exceed overhead limit "
1852 "of %d%%", GCTimeLimit);
1853 }
1854 }
1855 } else {
1856 size_policy()->reset_gc_time_limit_count();
1857 }
1858 }
1860 // Resize the perm generation and the tenured generation
1861 // after obtaining the free list locks for the
1862 // two generations.
1863 void CMSCollector::compute_new_size() {
1864 assert_locked_or_safepoint(Heap_lock);
1865 FreelistLocker z(this);
1866 _permGen->compute_new_size();
1867 _cmsGen->compute_new_size();
1868 }
1870 // A work method used by foreground collection to determine
1871 // what type of collection (compacting or not, continuing or fresh)
1872 // it should do.
1873 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1874 // and CMSCompactWhenClearAllSoftRefs the default in the future
1875 // and do away with the flags after a suitable period.
1876 void CMSCollector::decide_foreground_collection_type(
1877 bool clear_all_soft_refs, bool* should_compact,
1878 bool* should_start_over) {
1879 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1880 // flag is set, and we have either requested a System.gc() or
1881 // the number of full gc's since the last concurrent cycle
1882 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1883 // or if an incremental collection has failed
1884 GenCollectedHeap* gch = GenCollectedHeap::heap();
1885 assert(gch->collector_policy()->is_two_generation_policy(),
1886 "You may want to check the correctness of the following");
1887 // Inform cms gen if this was due to partial collection failing.
1888 // The CMS gen may use this fact to determine its expansion policy.
1889 if (gch->incremental_collection_will_fail()) {
1890 assert(!_cmsGen->incremental_collection_failed(),
1891 "Should have been noticed, reacted to and cleared");
1892 _cmsGen->set_incremental_collection_failed();
1893 }
1894 *should_compact =
1895 UseCMSCompactAtFullCollection &&
1896 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1897 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1898 gch->incremental_collection_will_fail());
1899 *should_start_over = false;
1900 if (clear_all_soft_refs && !*should_compact) {
1901 // We are about to do a last ditch collection attempt
1902 // so it would normally make sense to do a compaction
1903 // to reclaim as much space as possible.
1904 if (CMSCompactWhenClearAllSoftRefs) {
1905 // Default: The rationale is that in this case either
1906 // we are past the final marking phase, in which case
1907 // we'd have to start over, or so little has been done
1908 // that there's little point in saving that work. Compaction
1909 // appears to be the sensible choice in either case.
1910 *should_compact = true;
1911 } else {
1912 // We have been asked to clear all soft refs, but not to
1913 // compact. Make sure that we aren't past the final checkpoint
1914 // phase, for that is where we process soft refs. If we are already
1915 // past that phase, we'll need to redo the refs discovery phase and
1916 // if necessary clear soft refs that weren't previously
1917 // cleared. We do so by remembering the phase in which
1918 // we came in, and if we are past the refs processing
1919 // phase, we'll choose to just redo the mark-sweep
1920 // collection from scratch.
1921 if (_collectorState > FinalMarking) {
1922 // We are past the refs processing phase;
1923 // start over and do a fresh synchronous CMS cycle
1924 _collectorState = Resetting; // skip to reset to start new cycle
1925 reset(false /* == !asynch */);
1926 *should_start_over = true;
1927 } // else we can continue a possibly ongoing current cycle
1928 }
1929 }
1930 }
1932 // A work method used by the foreground collector to do
1933 // a mark-sweep-compact.
1934 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1935 GenCollectedHeap* gch = GenCollectedHeap::heap();
1936 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1937 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1938 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1939 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1940 }
1942 // Sample collection interval time and reset for collection pause.
1943 if (UseAdaptiveSizePolicy) {
1944 size_policy()->msc_collection_begin();
1945 }
1947 // Temporarily widen the span of the weak reference processing to
1948 // the entire heap.
1949 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1950 ReferenceProcessorSpanMutator x(ref_processor(), new_span);
1952 // Temporarily, clear the "is_alive_non_header" field of the
1953 // reference processor.
1954 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL);
1956 // Temporarily make reference _processing_ single threaded (non-MT).
1957 ReferenceProcessorMTProcMutator z(ref_processor(), false);
1959 // Temporarily make refs discovery atomic
1960 ReferenceProcessorAtomicMutator w(ref_processor(), true);
1962 ref_processor()->set_enqueuing_is_done(false);
1963 ref_processor()->enable_discovery();
1964 ref_processor()->setup_policy(clear_all_soft_refs);
1965 // If an asynchronous collection finishes, the _modUnionTable is
1966 // all clear. If we are assuming the collection from an asynchronous
1967 // collection, clear the _modUnionTable.
1968 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1969 "_modUnionTable should be clear if the baton was not passed");
1970 _modUnionTable.clear_all();
1972 // We must adjust the allocation statistics being maintained
1973 // in the free list space. We do so by reading and clearing
1974 // the sweep timer and updating the block flux rate estimates below.
1975 assert(_sweep_timer.is_active(), "We should never see the timer inactive");
1976 _sweep_timer.stop();
1977 // Note that we do not use this sample to update the _sweep_estimate.
1978 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
1979 _sweep_estimate.padded_average());
1981 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
1982 ref_processor(), clear_all_soft_refs);
1983 #ifdef ASSERT
1984 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1985 size_t free_size = cms_space->free();
1986 assert(free_size ==
1987 pointer_delta(cms_space->end(), cms_space->compaction_top())
1988 * HeapWordSize,
1989 "All the free space should be compacted into one chunk at top");
1990 assert(cms_space->dictionary()->totalChunkSize(
1991 debug_only(cms_space->freelistLock())) == 0 ||
1992 cms_space->totalSizeInIndexedFreeLists() == 0,
1993 "All the free space should be in a single chunk");
1994 size_t num = cms_space->totalCount();
1995 assert((free_size == 0 && num == 0) ||
1996 (free_size > 0 && (num == 1 || num == 2)),
1997 "There should be at most 2 free chunks after compaction");
1998 #endif // ASSERT
1999 _collectorState = Resetting;
2000 assert(_restart_addr == NULL,
2001 "Should have been NULL'd before baton was passed");
2002 reset(false /* == !asynch */);
2003 _cmsGen->reset_after_compaction();
2004 _concurrent_cycles_since_last_unload = 0;
2006 if (verifying() && !should_unload_classes()) {
2007 perm_gen_verify_bit_map()->clear_all();
2008 }
2010 // Clear any data recorded in the PLAB chunk arrays.
2011 if (_survivor_plab_array != NULL) {
2012 reset_survivor_plab_arrays();
2013 }
2015 // Adjust the per-size allocation stats for the next epoch.
2016 _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */);
2017 // Restart the "sweep timer" for next epoch.
2018 _sweep_timer.reset();
2019 _sweep_timer.start();
2021 // Sample collection pause time and reset for collection interval.
2022 if (UseAdaptiveSizePolicy) {
2023 size_policy()->msc_collection_end(gch->gc_cause());
2024 }
2026 // For a mark-sweep-compact, compute_new_size() will be called
2027 // in the heap's do_collection() method.
2028 }
2030 // A work method used by the foreground collector to do
2031 // a mark-sweep, after taking over from a possibly on-going
2032 // concurrent mark-sweep collection.
2033 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2034 CollectorState first_state, bool should_start_over) {
2035 if (PrintGC && Verbose) {
2036 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2037 "collector with count %d",
2038 _full_gcs_since_conc_gc);
2039 }
2040 switch (_collectorState) {
2041 case Idling:
2042 if (first_state == Idling || should_start_over) {
2043 // The background GC was not active, or should
2044 // restarted from scratch; start the cycle.
2045 _collectorState = InitialMarking;
2046 }
2047 // If first_state was not Idling, then a background GC
2048 // was in progress and has now finished. No need to do it
2049 // again. Leave the state as Idling.
2050 break;
2051 case Precleaning:
2052 // In the foreground case don't do the precleaning since
2053 // it is not done concurrently and there is extra work
2054 // required.
2055 _collectorState = FinalMarking;
2056 }
2057 if (PrintGCDetails &&
2058 (_collectorState > Idling ||
2059 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2060 gclog_or_tty->print(" (concurrent mode failure)");
2061 }
2062 collect_in_foreground(clear_all_soft_refs);
2064 // For a mark-sweep, compute_new_size() will be called
2065 // in the heap's do_collection() method.
2066 }
2069 void CMSCollector::getFreelistLocks() const {
2070 // Get locks for all free lists in all generations that this
2071 // collector is responsible for
2072 _cmsGen->freelistLock()->lock_without_safepoint_check();
2073 _permGen->freelistLock()->lock_without_safepoint_check();
2074 }
2076 void CMSCollector::releaseFreelistLocks() const {
2077 // Release locks for all free lists in all generations that this
2078 // collector is responsible for
2079 _cmsGen->freelistLock()->unlock();
2080 _permGen->freelistLock()->unlock();
2081 }
2083 bool CMSCollector::haveFreelistLocks() const {
2084 // Check locks for all free lists in all generations that this
2085 // collector is responsible for
2086 assert_lock_strong(_cmsGen->freelistLock());
2087 assert_lock_strong(_permGen->freelistLock());
2088 PRODUCT_ONLY(ShouldNotReachHere());
2089 return true;
2090 }
2092 // A utility class that is used by the CMS collector to
2093 // temporarily "release" the foreground collector from its
2094 // usual obligation to wait for the background collector to
2095 // complete an ongoing phase before proceeding.
2096 class ReleaseForegroundGC: public StackObj {
2097 private:
2098 CMSCollector* _c;
2099 public:
2100 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2101 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2102 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2103 // allow a potentially blocked foreground collector to proceed
2104 _c->_foregroundGCShouldWait = false;
2105 if (_c->_foregroundGCIsActive) {
2106 CGC_lock->notify();
2107 }
2108 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2109 "Possible deadlock");
2110 }
2112 ~ReleaseForegroundGC() {
2113 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2114 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2115 _c->_foregroundGCShouldWait = true;
2116 }
2117 };
2119 // There are separate collect_in_background and collect_in_foreground because of
2120 // the different locking requirements of the background collector and the
2121 // foreground collector. There was originally an attempt to share
2122 // one "collect" method between the background collector and the foreground
2123 // collector but the if-then-else required made it cleaner to have
2124 // separate methods.
2125 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2126 assert(Thread::current()->is_ConcurrentGC_thread(),
2127 "A CMS asynchronous collection is only allowed on a CMS thread.");
2129 GenCollectedHeap* gch = GenCollectedHeap::heap();
2130 {
2131 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2132 MutexLockerEx hl(Heap_lock, safepoint_check);
2133 FreelistLocker fll(this);
2134 MutexLockerEx x(CGC_lock, safepoint_check);
2135 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2136 // The foreground collector is active or we're
2137 // not using asynchronous collections. Skip this
2138 // background collection.
2139 assert(!_foregroundGCShouldWait, "Should be clear");
2140 return;
2141 } else {
2142 assert(_collectorState == Idling, "Should be idling before start.");
2143 _collectorState = InitialMarking;
2144 // Reset the expansion cause, now that we are about to begin
2145 // a new cycle.
2146 clear_expansion_cause();
2147 }
2148 // Decide if we want to enable class unloading as part of the
2149 // ensuing concurrent GC cycle.
2150 update_should_unload_classes();
2151 _full_gc_requested = false; // acks all outstanding full gc requests
2152 // Signal that we are about to start a collection
2153 gch->increment_total_full_collections(); // ... starting a collection cycle
2154 _collection_count_start = gch->total_full_collections();
2155 }
2157 // Used for PrintGC
2158 size_t prev_used;
2159 if (PrintGC && Verbose) {
2160 prev_used = _cmsGen->used(); // XXXPERM
2161 }
2163 // The change of the collection state is normally done at this level;
2164 // the exceptions are phases that are executed while the world is
2165 // stopped. For those phases the change of state is done while the
2166 // world is stopped. For baton passing purposes this allows the
2167 // background collector to finish the phase and change state atomically.
2168 // The foreground collector cannot wait on a phase that is done
2169 // while the world is stopped because the foreground collector already
2170 // has the world stopped and would deadlock.
2171 while (_collectorState != Idling) {
2172 if (TraceCMSState) {
2173 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2174 Thread::current(), _collectorState);
2175 }
2176 // The foreground collector
2177 // holds the Heap_lock throughout its collection.
2178 // holds the CMS token (but not the lock)
2179 // except while it is waiting for the background collector to yield.
2180 //
2181 // The foreground collector should be blocked (not for long)
2182 // if the background collector is about to start a phase
2183 // executed with world stopped. If the background
2184 // collector has already started such a phase, the
2185 // foreground collector is blocked waiting for the
2186 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2187 // are executed in the VM thread.
2188 //
2189 // The locking order is
2190 // PendingListLock (PLL) -- if applicable (FinalMarking)
2191 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2192 // CMS token (claimed in
2193 // stop_world_and_do() -->
2194 // safepoint_synchronize() -->
2195 // CMSThread::synchronize())
2197 {
2198 // Check if the FG collector wants us to yield.
2199 CMSTokenSync x(true); // is cms thread
2200 if (waitForForegroundGC()) {
2201 // We yielded to a foreground GC, nothing more to be
2202 // done this round.
2203 assert(_foregroundGCShouldWait == false, "We set it to false in "
2204 "waitForForegroundGC()");
2205 if (TraceCMSState) {
2206 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2207 " exiting collection CMS state %d",
2208 Thread::current(), _collectorState);
2209 }
2210 return;
2211 } else {
2212 // The background collector can run but check to see if the
2213 // foreground collector has done a collection while the
2214 // background collector was waiting to get the CGC_lock
2215 // above. If yes, break so that _foregroundGCShouldWait
2216 // is cleared before returning.
2217 if (_collectorState == Idling) {
2218 break;
2219 }
2220 }
2221 }
2223 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2224 "should be waiting");
2226 switch (_collectorState) {
2227 case InitialMarking:
2228 {
2229 ReleaseForegroundGC x(this);
2230 stats().record_cms_begin();
2232 VM_CMS_Initial_Mark initial_mark_op(this);
2233 VMThread::execute(&initial_mark_op);
2234 }
2235 // The collector state may be any legal state at this point
2236 // since the background collector may have yielded to the
2237 // foreground collector.
2238 break;
2239 case Marking:
2240 // initial marking in checkpointRootsInitialWork has been completed
2241 if (markFromRoots(true)) { // we were successful
2242 assert(_collectorState == Precleaning, "Collector state should "
2243 "have changed");
2244 } else {
2245 assert(_foregroundGCIsActive, "Internal state inconsistency");
2246 }
2247 break;
2248 case Precleaning:
2249 if (UseAdaptiveSizePolicy) {
2250 size_policy()->concurrent_precleaning_begin();
2251 }
2252 // marking from roots in markFromRoots has been completed
2253 preclean();
2254 if (UseAdaptiveSizePolicy) {
2255 size_policy()->concurrent_precleaning_end();
2256 }
2257 assert(_collectorState == AbortablePreclean ||
2258 _collectorState == FinalMarking,
2259 "Collector state should have changed");
2260 break;
2261 case AbortablePreclean:
2262 if (UseAdaptiveSizePolicy) {
2263 size_policy()->concurrent_phases_resume();
2264 }
2265 abortable_preclean();
2266 if (UseAdaptiveSizePolicy) {
2267 size_policy()->concurrent_precleaning_end();
2268 }
2269 assert(_collectorState == FinalMarking, "Collector state should "
2270 "have changed");
2271 break;
2272 case FinalMarking:
2273 {
2274 ReleaseForegroundGC x(this);
2276 VM_CMS_Final_Remark final_remark_op(this);
2277 VMThread::execute(&final_remark_op);
2278 }
2279 assert(_foregroundGCShouldWait, "block post-condition");
2280 break;
2281 case Sweeping:
2282 if (UseAdaptiveSizePolicy) {
2283 size_policy()->concurrent_sweeping_begin();
2284 }
2285 // final marking in checkpointRootsFinal has been completed
2286 sweep(true);
2287 assert(_collectorState == Resizing, "Collector state change "
2288 "to Resizing must be done under the free_list_lock");
2289 _full_gcs_since_conc_gc = 0;
2291 // Stop the timers for adaptive size policy for the concurrent phases
2292 if (UseAdaptiveSizePolicy) {
2293 size_policy()->concurrent_sweeping_end();
2294 size_policy()->concurrent_phases_end(gch->gc_cause(),
2295 gch->prev_gen(_cmsGen)->capacity(),
2296 _cmsGen->free());
2297 }
2299 case Resizing: {
2300 // Sweeping has been completed...
2301 // At this point the background collection has completed.
2302 // Don't move the call to compute_new_size() down
2303 // into code that might be executed if the background
2304 // collection was preempted.
2305 {
2306 ReleaseForegroundGC x(this); // unblock FG collection
2307 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2308 CMSTokenSync z(true); // not strictly needed.
2309 if (_collectorState == Resizing) {
2310 compute_new_size();
2311 _collectorState = Resetting;
2312 } else {
2313 assert(_collectorState == Idling, "The state should only change"
2314 " because the foreground collector has finished the collection");
2315 }
2316 }
2317 break;
2318 }
2319 case Resetting:
2320 // CMS heap resizing has been completed
2321 reset(true);
2322 assert(_collectorState == Idling, "Collector state should "
2323 "have changed");
2324 stats().record_cms_end();
2325 // Don't move the concurrent_phases_end() and compute_new_size()
2326 // calls to here because a preempted background collection
2327 // has it's state set to "Resetting".
2328 break;
2329 case Idling:
2330 default:
2331 ShouldNotReachHere();
2332 break;
2333 }
2334 if (TraceCMSState) {
2335 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2336 Thread::current(), _collectorState);
2337 }
2338 assert(_foregroundGCShouldWait, "block post-condition");
2339 }
2341 // Should this be in gc_epilogue?
2342 collector_policy()->counters()->update_counters();
2344 {
2345 // Clear _foregroundGCShouldWait and, in the event that the
2346 // foreground collector is waiting, notify it, before
2347 // returning.
2348 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2349 _foregroundGCShouldWait = false;
2350 if (_foregroundGCIsActive) {
2351 CGC_lock->notify();
2352 }
2353 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2354 "Possible deadlock");
2355 }
2356 if (TraceCMSState) {
2357 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2358 " exiting collection CMS state %d",
2359 Thread::current(), _collectorState);
2360 }
2361 if (PrintGC && Verbose) {
2362 _cmsGen->print_heap_change(prev_used);
2363 }
2364 }
2366 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2367 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2368 "Foreground collector should be waiting, not executing");
2369 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2370 "may only be done by the VM Thread with the world stopped");
2371 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2372 "VM thread should have CMS token");
2374 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2375 true, gclog_or_tty);)
2376 if (UseAdaptiveSizePolicy) {
2377 size_policy()->ms_collection_begin();
2378 }
2379 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2381 HandleMark hm; // Discard invalid handles created during verification
2383 if (VerifyBeforeGC &&
2384 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2385 Universe::verify(true);
2386 }
2388 // Snapshot the soft reference policy to be used in this collection cycle.
2389 ref_processor()->setup_policy(clear_all_soft_refs);
2391 bool init_mark_was_synchronous = false; // until proven otherwise
2392 while (_collectorState != Idling) {
2393 if (TraceCMSState) {
2394 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2395 Thread::current(), _collectorState);
2396 }
2397 switch (_collectorState) {
2398 case InitialMarking:
2399 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2400 checkpointRootsInitial(false);
2401 assert(_collectorState == Marking, "Collector state should have changed"
2402 " within checkpointRootsInitial()");
2403 break;
2404 case Marking:
2405 // initial marking in checkpointRootsInitialWork has been completed
2406 if (VerifyDuringGC &&
2407 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2408 gclog_or_tty->print("Verify before initial mark: ");
2409 Universe::verify(true);
2410 }
2411 {
2412 bool res = markFromRoots(false);
2413 assert(res && _collectorState == FinalMarking, "Collector state should "
2414 "have changed");
2415 break;
2416 }
2417 case FinalMarking:
2418 if (VerifyDuringGC &&
2419 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2420 gclog_or_tty->print("Verify before re-mark: ");
2421 Universe::verify(true);
2422 }
2423 checkpointRootsFinal(false, clear_all_soft_refs,
2424 init_mark_was_synchronous);
2425 assert(_collectorState == Sweeping, "Collector state should not "
2426 "have changed within checkpointRootsFinal()");
2427 break;
2428 case Sweeping:
2429 // final marking in checkpointRootsFinal has been completed
2430 if (VerifyDuringGC &&
2431 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2432 gclog_or_tty->print("Verify before sweep: ");
2433 Universe::verify(true);
2434 }
2435 sweep(false);
2436 assert(_collectorState == Resizing, "Incorrect state");
2437 break;
2438 case Resizing: {
2439 // Sweeping has been completed; the actual resize in this case
2440 // is done separately; nothing to be done in this state.
2441 _collectorState = Resetting;
2442 break;
2443 }
2444 case Resetting:
2445 // The heap has been resized.
2446 if (VerifyDuringGC &&
2447 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2448 gclog_or_tty->print("Verify before reset: ");
2449 Universe::verify(true);
2450 }
2451 reset(false);
2452 assert(_collectorState == Idling, "Collector state should "
2453 "have changed");
2454 break;
2455 case Precleaning:
2456 case AbortablePreclean:
2457 // Elide the preclean phase
2458 _collectorState = FinalMarking;
2459 break;
2460 default:
2461 ShouldNotReachHere();
2462 }
2463 if (TraceCMSState) {
2464 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2465 Thread::current(), _collectorState);
2466 }
2467 }
2469 if (UseAdaptiveSizePolicy) {
2470 GenCollectedHeap* gch = GenCollectedHeap::heap();
2471 size_policy()->ms_collection_end(gch->gc_cause());
2472 }
2474 if (VerifyAfterGC &&
2475 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2476 Universe::verify(true);
2477 }
2478 if (TraceCMSState) {
2479 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2480 " exiting collection CMS state %d",
2481 Thread::current(), _collectorState);
2482 }
2483 }
2485 bool CMSCollector::waitForForegroundGC() {
2486 bool res = false;
2487 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2488 "CMS thread should have CMS token");
2489 // Block the foreground collector until the
2490 // background collectors decides whether to
2491 // yield.
2492 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2493 _foregroundGCShouldWait = true;
2494 if (_foregroundGCIsActive) {
2495 // The background collector yields to the
2496 // foreground collector and returns a value
2497 // indicating that it has yielded. The foreground
2498 // collector can proceed.
2499 res = true;
2500 _foregroundGCShouldWait = false;
2501 ConcurrentMarkSweepThread::clear_CMS_flag(
2502 ConcurrentMarkSweepThread::CMS_cms_has_token);
2503 ConcurrentMarkSweepThread::set_CMS_flag(
2504 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2505 // Get a possibly blocked foreground thread going
2506 CGC_lock->notify();
2507 if (TraceCMSState) {
2508 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2509 Thread::current(), _collectorState);
2510 }
2511 while (_foregroundGCIsActive) {
2512 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2513 }
2514 ConcurrentMarkSweepThread::set_CMS_flag(
2515 ConcurrentMarkSweepThread::CMS_cms_has_token);
2516 ConcurrentMarkSweepThread::clear_CMS_flag(
2517 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2518 }
2519 if (TraceCMSState) {
2520 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2521 Thread::current(), _collectorState);
2522 }
2523 return res;
2524 }
2526 // Because of the need to lock the free lists and other structures in
2527 // the collector, common to all the generations that the collector is
2528 // collecting, we need the gc_prologues of individual CMS generations
2529 // delegate to their collector. It may have been simpler had the
2530 // current infrastructure allowed one to call a prologue on a
2531 // collector. In the absence of that we have the generation's
2532 // prologue delegate to the collector, which delegates back
2533 // some "local" work to a worker method in the individual generations
2534 // that it's responsible for collecting, while itself doing any
2535 // work common to all generations it's responsible for. A similar
2536 // comment applies to the gc_epilogue()'s.
2537 // The role of the varaible _between_prologue_and_epilogue is to
2538 // enforce the invocation protocol.
2539 void CMSCollector::gc_prologue(bool full) {
2540 // Call gc_prologue_work() for each CMSGen and PermGen that
2541 // we are responsible for.
2543 // The following locking discipline assumes that we are only called
2544 // when the world is stopped.
2545 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2547 // The CMSCollector prologue must call the gc_prologues for the
2548 // "generations" (including PermGen if any) that it's responsible
2549 // for.
2551 assert( Thread::current()->is_VM_thread()
2552 || ( CMSScavengeBeforeRemark
2553 && Thread::current()->is_ConcurrentGC_thread()),
2554 "Incorrect thread type for prologue execution");
2556 if (_between_prologue_and_epilogue) {
2557 // We have already been invoked; this is a gc_prologue delegation
2558 // from yet another CMS generation that we are responsible for, just
2559 // ignore it since all relevant work has already been done.
2560 return;
2561 }
2563 // set a bit saying prologue has been called; cleared in epilogue
2564 _between_prologue_and_epilogue = true;
2565 // Claim locks for common data structures, then call gc_prologue_work()
2566 // for each CMSGen and PermGen that we are responsible for.
2568 getFreelistLocks(); // gets free list locks on constituent spaces
2569 bitMapLock()->lock_without_safepoint_check();
2571 // Should call gc_prologue_work() for all cms gens we are responsible for
2572 bool registerClosure = _collectorState >= Marking
2573 && _collectorState < Sweeping;
2574 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar
2575 : &_modUnionClosure;
2576 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2577 _permGen->gc_prologue_work(full, registerClosure, muc);
2579 if (!full) {
2580 stats().record_gc0_begin();
2581 }
2582 }
2584 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2585 // Delegate to CMScollector which knows how to coordinate between
2586 // this and any other CMS generations that it is responsible for
2587 // collecting.
2588 collector()->gc_prologue(full);
2589 }
2591 // This is a "private" interface for use by this generation's CMSCollector.
2592 // Not to be called directly by any other entity (for instance,
2593 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2594 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2595 bool registerClosure, ModUnionClosure* modUnionClosure) {
2596 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2597 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2598 "Should be NULL");
2599 if (registerClosure) {
2600 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2601 }
2602 cmsSpace()->gc_prologue();
2603 // Clear stat counters
2604 NOT_PRODUCT(
2605 assert(_numObjectsPromoted == 0, "check");
2606 assert(_numWordsPromoted == 0, "check");
2607 if (Verbose && PrintGC) {
2608 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2609 SIZE_FORMAT" bytes concurrently",
2610 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2611 }
2612 _numObjectsAllocated = 0;
2613 _numWordsAllocated = 0;
2614 )
2615 }
2617 void CMSCollector::gc_epilogue(bool full) {
2618 // The following locking discipline assumes that we are only called
2619 // when the world is stopped.
2620 assert(SafepointSynchronize::is_at_safepoint(),
2621 "world is stopped assumption");
2623 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2624 // if linear allocation blocks need to be appropriately marked to allow the
2625 // the blocks to be parsable. We also check here whether we need to nudge the
2626 // CMS collector thread to start a new cycle (if it's not already active).
2627 assert( Thread::current()->is_VM_thread()
2628 || ( CMSScavengeBeforeRemark
2629 && Thread::current()->is_ConcurrentGC_thread()),
2630 "Incorrect thread type for epilogue execution");
2632 if (!_between_prologue_and_epilogue) {
2633 // We have already been invoked; this is a gc_epilogue delegation
2634 // from yet another CMS generation that we are responsible for, just
2635 // ignore it since all relevant work has already been done.
2636 return;
2637 }
2638 assert(haveFreelistLocks(), "must have freelist locks");
2639 assert_lock_strong(bitMapLock());
2641 _cmsGen->gc_epilogue_work(full);
2642 _permGen->gc_epilogue_work(full);
2644 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2645 // in case sampling was not already enabled, enable it
2646 _start_sampling = true;
2647 }
2648 // reset _eden_chunk_array so sampling starts afresh
2649 _eden_chunk_index = 0;
2651 size_t cms_used = _cmsGen->cmsSpace()->used();
2652 size_t perm_used = _permGen->cmsSpace()->used();
2654 // update performance counters - this uses a special version of
2655 // update_counters() that allows the utilization to be passed as a
2656 // parameter, avoiding multiple calls to used().
2657 //
2658 _cmsGen->update_counters(cms_used);
2659 _permGen->update_counters(perm_used);
2661 if (CMSIncrementalMode) {
2662 icms_update_allocation_limits();
2663 }
2665 bitMapLock()->unlock();
2666 releaseFreelistLocks();
2668 _between_prologue_and_epilogue = false; // ready for next cycle
2669 }
2671 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2672 collector()->gc_epilogue(full);
2674 // Also reset promotion tracking in par gc thread states.
2675 if (ParallelGCThreads > 0) {
2676 for (uint i = 0; i < ParallelGCThreads; i++) {
2677 _par_gc_thread_states[i]->promo.stopTrackingPromotions();
2678 }
2679 }
2680 }
2682 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2683 assert(!incremental_collection_failed(), "Should have been cleared");
2684 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2685 cmsSpace()->gc_epilogue();
2686 // Print stat counters
2687 NOT_PRODUCT(
2688 assert(_numObjectsAllocated == 0, "check");
2689 assert(_numWordsAllocated == 0, "check");
2690 if (Verbose && PrintGC) {
2691 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2692 SIZE_FORMAT" bytes",
2693 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2694 }
2695 _numObjectsPromoted = 0;
2696 _numWordsPromoted = 0;
2697 )
2699 if (PrintGC && Verbose) {
2700 // Call down the chain in contiguous_available needs the freelistLock
2701 // so print this out before releasing the freeListLock.
2702 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2703 contiguous_available());
2704 }
2705 }
2707 #ifndef PRODUCT
2708 bool CMSCollector::have_cms_token() {
2709 Thread* thr = Thread::current();
2710 if (thr->is_VM_thread()) {
2711 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2712 } else if (thr->is_ConcurrentGC_thread()) {
2713 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2714 } else if (thr->is_GC_task_thread()) {
2715 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2716 ParGCRareEvent_lock->owned_by_self();
2717 }
2718 return false;
2719 }
2720 #endif
2722 // Check reachability of the given heap address in CMS generation,
2723 // treating all other generations as roots.
2724 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2725 // We could "guarantee" below, rather than assert, but i'll
2726 // leave these as "asserts" so that an adventurous debugger
2727 // could try this in the product build provided some subset of
2728 // the conditions were met, provided they were intersted in the
2729 // results and knew that the computation below wouldn't interfere
2730 // with other concurrent computations mutating the structures
2731 // being read or written.
2732 assert(SafepointSynchronize::is_at_safepoint(),
2733 "Else mutations in object graph will make answer suspect");
2734 assert(have_cms_token(), "Should hold cms token");
2735 assert(haveFreelistLocks(), "must hold free list locks");
2736 assert_lock_strong(bitMapLock());
2738 // Clear the marking bit map array before starting, but, just
2739 // for kicks, first report if the given address is already marked
2740 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2741 _markBitMap.isMarked(addr) ? "" : " not");
2743 if (verify_after_remark()) {
2744 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2745 bool result = verification_mark_bm()->isMarked(addr);
2746 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2747 result ? "IS" : "is NOT");
2748 return result;
2749 } else {
2750 gclog_or_tty->print_cr("Could not compute result");
2751 return false;
2752 }
2753 }
2755 ////////////////////////////////////////////////////////
2756 // CMS Verification Support
2757 ////////////////////////////////////////////////////////
2758 // Following the remark phase, the following invariant
2759 // should hold -- each object in the CMS heap which is
2760 // marked in markBitMap() should be marked in the verification_mark_bm().
2762 class VerifyMarkedClosure: public BitMapClosure {
2763 CMSBitMap* _marks;
2764 bool _failed;
2766 public:
2767 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2769 bool do_bit(size_t offset) {
2770 HeapWord* addr = _marks->offsetToHeapWord(offset);
2771 if (!_marks->isMarked(addr)) {
2772 oop(addr)->print();
2773 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2774 _failed = true;
2775 }
2776 return true;
2777 }
2779 bool failed() { return _failed; }
2780 };
2782 bool CMSCollector::verify_after_remark() {
2783 gclog_or_tty->print(" [Verifying CMS Marking... ");
2784 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2785 static bool init = false;
2787 assert(SafepointSynchronize::is_at_safepoint(),
2788 "Else mutations in object graph will make answer suspect");
2789 assert(have_cms_token(),
2790 "Else there may be mutual interference in use of "
2791 " verification data structures");
2792 assert(_collectorState > Marking && _collectorState <= Sweeping,
2793 "Else marking info checked here may be obsolete");
2794 assert(haveFreelistLocks(), "must hold free list locks");
2795 assert_lock_strong(bitMapLock());
2798 // Allocate marking bit map if not already allocated
2799 if (!init) { // first time
2800 if (!verification_mark_bm()->allocate(_span)) {
2801 return false;
2802 }
2803 init = true;
2804 }
2806 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2808 // Turn off refs discovery -- so we will be tracing through refs.
2809 // This is as intended, because by this time
2810 // GC must already have cleared any refs that need to be cleared,
2811 // and traced those that need to be marked; moreover,
2812 // the marking done here is not going to intefere in any
2813 // way with the marking information used by GC.
2814 NoRefDiscovery no_discovery(ref_processor());
2816 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2818 // Clear any marks from a previous round
2819 verification_mark_bm()->clear_all();
2820 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2821 assert(overflow_list_is_empty(), "overflow list should be empty");
2823 GenCollectedHeap* gch = GenCollectedHeap::heap();
2824 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2825 // Update the saved marks which may affect the root scans.
2826 gch->save_marks();
2828 if (CMSRemarkVerifyVariant == 1) {
2829 // In this first variant of verification, we complete
2830 // all marking, then check if the new marks-verctor is
2831 // a subset of the CMS marks-vector.
2832 verify_after_remark_work_1();
2833 } else if (CMSRemarkVerifyVariant == 2) {
2834 // In this second variant of verification, we flag an error
2835 // (i.e. an object reachable in the new marks-vector not reachable
2836 // in the CMS marks-vector) immediately, also indicating the
2837 // identify of an object (A) that references the unmarked object (B) --
2838 // presumably, a mutation to A failed to be picked up by preclean/remark?
2839 verify_after_remark_work_2();
2840 } else {
2841 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2842 CMSRemarkVerifyVariant);
2843 }
2844 gclog_or_tty->print(" done] ");
2845 return true;
2846 }
2848 void CMSCollector::verify_after_remark_work_1() {
2849 ResourceMark rm;
2850 HandleMark hm;
2851 GenCollectedHeap* gch = GenCollectedHeap::heap();
2853 // Mark from roots one level into CMS
2854 MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */);
2855 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2857 gch->gen_process_strong_roots(_cmsGen->level(),
2858 true, // younger gens are roots
2859 true, // collecting perm gen
2860 SharedHeap::ScanningOption(roots_scanning_options()),
2861 NULL, ¬Older);
2863 // Now mark from the roots
2864 assert(_revisitStack.isEmpty(), "Should be empty");
2865 MarkFromRootsClosure markFromRootsClosure(this, _span,
2866 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2867 false /* don't yield */, true /* verifying */);
2868 assert(_restart_addr == NULL, "Expected pre-condition");
2869 verification_mark_bm()->iterate(&markFromRootsClosure);
2870 while (_restart_addr != NULL) {
2871 // Deal with stack overflow: by restarting at the indicated
2872 // address.
2873 HeapWord* ra = _restart_addr;
2874 markFromRootsClosure.reset(ra);
2875 _restart_addr = NULL;
2876 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2877 }
2878 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2879 verify_work_stacks_empty();
2880 // Should reset the revisit stack above, since no class tree
2881 // surgery is forthcoming.
2882 _revisitStack.reset(); // throwing away all contents
2884 // Marking completed -- now verify that each bit marked in
2885 // verification_mark_bm() is also marked in markBitMap(); flag all
2886 // errors by printing corresponding objects.
2887 VerifyMarkedClosure vcl(markBitMap());
2888 verification_mark_bm()->iterate(&vcl);
2889 if (vcl.failed()) {
2890 gclog_or_tty->print("Verification failed");
2891 Universe::heap()->print();
2892 fatal(" ... aborting");
2893 }
2894 }
2896 void CMSCollector::verify_after_remark_work_2() {
2897 ResourceMark rm;
2898 HandleMark hm;
2899 GenCollectedHeap* gch = GenCollectedHeap::heap();
2901 // Mark from roots one level into CMS
2902 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2903 markBitMap(), true /* nmethods */);
2904 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2905 gch->gen_process_strong_roots(_cmsGen->level(),
2906 true, // younger gens are roots
2907 true, // collecting perm gen
2908 SharedHeap::ScanningOption(roots_scanning_options()),
2909 NULL, ¬Older);
2911 // Now mark from the roots
2912 assert(_revisitStack.isEmpty(), "Should be empty");
2913 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2914 verification_mark_bm(), markBitMap(), verification_mark_stack());
2915 assert(_restart_addr == NULL, "Expected pre-condition");
2916 verification_mark_bm()->iterate(&markFromRootsClosure);
2917 while (_restart_addr != NULL) {
2918 // Deal with stack overflow: by restarting at the indicated
2919 // address.
2920 HeapWord* ra = _restart_addr;
2921 markFromRootsClosure.reset(ra);
2922 _restart_addr = NULL;
2923 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2924 }
2925 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2926 verify_work_stacks_empty();
2927 // Should reset the revisit stack above, since no class tree
2928 // surgery is forthcoming.
2929 _revisitStack.reset(); // throwing away all contents
2931 // Marking completed -- now verify that each bit marked in
2932 // verification_mark_bm() is also marked in markBitMap(); flag all
2933 // errors by printing corresponding objects.
2934 VerifyMarkedClosure vcl(markBitMap());
2935 verification_mark_bm()->iterate(&vcl);
2936 assert(!vcl.failed(), "Else verification above should not have succeeded");
2937 }
2939 void ConcurrentMarkSweepGeneration::save_marks() {
2940 // delegate to CMS space
2941 cmsSpace()->save_marks();
2942 for (uint i = 0; i < ParallelGCThreads; i++) {
2943 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2944 }
2945 }
2947 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2948 return cmsSpace()->no_allocs_since_save_marks();
2949 }
2951 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2952 \
2953 void ConcurrentMarkSweepGeneration:: \
2954 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2955 cl->set_generation(this); \
2956 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2957 cl->reset_generation(); \
2958 save_marks(); \
2959 }
2961 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2963 void
2964 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
2965 {
2966 // Not currently implemented; need to do the following. -- ysr.
2967 // dld -- I think that is used for some sort of allocation profiler. So it
2968 // really means the objects allocated by the mutator since the last
2969 // GC. We could potentially implement this cheaply by recording only
2970 // the direct allocations in a side data structure.
2971 //
2972 // I think we probably ought not to be required to support these
2973 // iterations at any arbitrary point; I think there ought to be some
2974 // call to enable/disable allocation profiling in a generation/space,
2975 // and the iterator ought to return the objects allocated in the
2976 // gen/space since the enable call, or the last iterator call (which
2977 // will probably be at a GC.) That way, for gens like CM&S that would
2978 // require some extra data structure to support this, we only pay the
2979 // cost when it's in use...
2980 cmsSpace()->object_iterate_since_last_GC(blk);
2981 }
2983 void
2984 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
2985 cl->set_generation(this);
2986 younger_refs_in_space_iterate(_cmsSpace, cl);
2987 cl->reset_generation();
2988 }
2990 void
2991 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
2992 if (freelistLock()->owned_by_self()) {
2993 Generation::oop_iterate(mr, cl);
2994 } else {
2995 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2996 Generation::oop_iterate(mr, cl);
2997 }
2998 }
3000 void
3001 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3002 if (freelistLock()->owned_by_self()) {
3003 Generation::oop_iterate(cl);
3004 } else {
3005 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3006 Generation::oop_iterate(cl);
3007 }
3008 }
3010 void
3011 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3012 if (freelistLock()->owned_by_self()) {
3013 Generation::object_iterate(cl);
3014 } else {
3015 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3016 Generation::object_iterate(cl);
3017 }
3018 }
3020 void
3021 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3022 }
3024 void
3025 ConcurrentMarkSweepGeneration::post_compact() {
3026 }
3028 void
3029 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3030 // Fix the linear allocation blocks to look like free blocks.
3032 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3033 // are not called when the heap is verified during universe initialization and
3034 // at vm shutdown.
3035 if (freelistLock()->owned_by_self()) {
3036 cmsSpace()->prepare_for_verify();
3037 } else {
3038 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3039 cmsSpace()->prepare_for_verify();
3040 }
3041 }
3043 void
3044 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) {
3045 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3046 // are not called when the heap is verified during universe initialization and
3047 // at vm shutdown.
3048 if (freelistLock()->owned_by_self()) {
3049 cmsSpace()->verify(false /* ignored */);
3050 } else {
3051 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3052 cmsSpace()->verify(false /* ignored */);
3053 }
3054 }
3056 void CMSCollector::verify(bool allow_dirty /* ignored */) {
3057 _cmsGen->verify(allow_dirty);
3058 _permGen->verify(allow_dirty);
3059 }
3061 #ifndef PRODUCT
3062 bool CMSCollector::overflow_list_is_empty() const {
3063 assert(_num_par_pushes >= 0, "Inconsistency");
3064 if (_overflow_list == NULL) {
3065 assert(_num_par_pushes == 0, "Inconsistency");
3066 }
3067 return _overflow_list == NULL;
3068 }
3070 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3071 // merely consolidate assertion checks that appear to occur together frequently.
3072 void CMSCollector::verify_work_stacks_empty() const {
3073 assert(_markStack.isEmpty(), "Marking stack should be empty");
3074 assert(overflow_list_is_empty(), "Overflow list should be empty");
3075 }
3077 void CMSCollector::verify_overflow_empty() const {
3078 assert(overflow_list_is_empty(), "Overflow list should be empty");
3079 assert(no_preserved_marks(), "No preserved marks");
3080 }
3081 #endif // PRODUCT
3083 // Decide if we want to enable class unloading as part of the
3084 // ensuing concurrent GC cycle. We will collect the perm gen and
3085 // unload classes if it's the case that:
3086 // (1) an explicit gc request has been made and the flag
3087 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3088 // (2) (a) class unloading is enabled at the command line, and
3089 // (b) (i) perm gen threshold has been crossed, or
3090 // (ii) old gen is getting really full, or
3091 // (iii) the previous N CMS collections did not collect the
3092 // perm gen
3093 // NOTE: Provided there is no change in the state of the heap between
3094 // calls to this method, it should have idempotent results. Moreover,
3095 // its results should be monotonically increasing (i.e. going from 0 to 1,
3096 // but not 1 to 0) between successive calls between which the heap was
3097 // not collected. For the implementation below, it must thus rely on
3098 // the property that concurrent_cycles_since_last_unload()
3099 // will not decrease unless a collection cycle happened and that
3100 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3101 // themselves also monotonic in that sense. See check_monotonicity()
3102 // below.
3103 bool CMSCollector::update_should_unload_classes() {
3104 _should_unload_classes = false;
3105 // Condition 1 above
3106 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3107 _should_unload_classes = true;
3108 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3109 // Disjuncts 2.b.(i,ii,iii) above
3110 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3111 CMSClassUnloadingMaxInterval)
3112 || _permGen->should_concurrent_collect()
3113 || _cmsGen->is_too_full();
3114 }
3115 return _should_unload_classes;
3116 }
3118 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3119 bool res = should_concurrent_collect();
3120 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3121 return res;
3122 }
3124 void CMSCollector::setup_cms_unloading_and_verification_state() {
3125 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3126 || VerifyBeforeExit;
3127 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings
3128 | SharedHeap::SO_CodeCache;
3130 if (should_unload_classes()) { // Should unload classes this cycle
3131 remove_root_scanning_option(rso); // Shrink the root set appropriately
3132 set_verifying(should_verify); // Set verification state for this cycle
3133 return; // Nothing else needs to be done at this time
3134 }
3136 // Not unloading classes this cycle
3137 assert(!should_unload_classes(), "Inconsitency!");
3138 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3139 // We were not verifying, or we _were_ unloading classes in the last cycle,
3140 // AND some verification options are enabled this cycle; in this case,
3141 // we must make sure that the deadness map is allocated if not already so,
3142 // and cleared (if already allocated previously --
3143 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3144 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3145 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3146 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3147 "permanent generation verification disabled");
3148 return; // Note that we leave verification disabled, so we'll retry this
3149 // allocation next cycle. We _could_ remember this failure
3150 // and skip further attempts and permanently disable verification
3151 // attempts if that is considered more desirable.
3152 }
3153 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3154 "_perm_gen_ver_bit_map inconsistency?");
3155 } else {
3156 perm_gen_verify_bit_map()->clear_all();
3157 }
3158 // Include symbols, strings and code cache elements to prevent their resurrection.
3159 add_root_scanning_option(rso);
3160 set_verifying(true);
3161 } else if (verifying() && !should_verify) {
3162 // We were verifying, but some verification flags got disabled.
3163 set_verifying(false);
3164 // Exclude symbols, strings and code cache elements from root scanning to
3165 // reduce IM and RM pauses.
3166 remove_root_scanning_option(rso);
3167 }
3168 }
3171 #ifndef PRODUCT
3172 HeapWord* CMSCollector::block_start(const void* p) const {
3173 const HeapWord* addr = (HeapWord*)p;
3174 if (_span.contains(p)) {
3175 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3176 return _cmsGen->cmsSpace()->block_start(p);
3177 } else {
3178 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3179 "Inconsistent _span?");
3180 return _permGen->cmsSpace()->block_start(p);
3181 }
3182 }
3183 return NULL;
3184 }
3185 #endif
3187 HeapWord*
3188 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3189 bool tlab,
3190 bool parallel) {
3191 assert(!tlab, "Can't deal with TLAB allocation");
3192 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3193 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3194 CMSExpansionCause::_satisfy_allocation);
3195 if (GCExpandToAllocateDelayMillis > 0) {
3196 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3197 }
3198 return have_lock_and_allocate(word_size, tlab);
3199 }
3201 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3202 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3203 // to CardGeneration and share it...
3204 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3205 return CardGeneration::expand(bytes, expand_bytes);
3206 }
3208 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3209 CMSExpansionCause::Cause cause)
3210 {
3212 bool success = expand(bytes, expand_bytes);
3214 // remember why we expanded; this information is used
3215 // by shouldConcurrentCollect() when making decisions on whether to start
3216 // a new CMS cycle.
3217 if (success) {
3218 set_expansion_cause(cause);
3219 if (PrintGCDetails && Verbose) {
3220 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3221 CMSExpansionCause::to_string(cause));
3222 }
3223 }
3224 }
3226 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3227 HeapWord* res = NULL;
3228 MutexLocker x(ParGCRareEvent_lock);
3229 while (true) {
3230 // Expansion by some other thread might make alloc OK now:
3231 res = ps->lab.alloc(word_sz);
3232 if (res != NULL) return res;
3233 // If there's not enough expansion space available, give up.
3234 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3235 return NULL;
3236 }
3237 // Otherwise, we try expansion.
3238 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3239 CMSExpansionCause::_allocate_par_lab);
3240 // Now go around the loop and try alloc again;
3241 // A competing par_promote might beat us to the expansion space,
3242 // so we may go around the loop again if promotion fails agaion.
3243 if (GCExpandToAllocateDelayMillis > 0) {
3244 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3245 }
3246 }
3247 }
3250 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3251 PromotionInfo* promo) {
3252 MutexLocker x(ParGCRareEvent_lock);
3253 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3254 while (true) {
3255 // Expansion by some other thread might make alloc OK now:
3256 if (promo->ensure_spooling_space()) {
3257 assert(promo->has_spooling_space(),
3258 "Post-condition of successful ensure_spooling_space()");
3259 return true;
3260 }
3261 // If there's not enough expansion space available, give up.
3262 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3263 return false;
3264 }
3265 // Otherwise, we try expansion.
3266 expand(refill_size_bytes, MinHeapDeltaBytes,
3267 CMSExpansionCause::_allocate_par_spooling_space);
3268 // Now go around the loop and try alloc again;
3269 // A competing allocation might beat us to the expansion space,
3270 // so we may go around the loop again if allocation fails again.
3271 if (GCExpandToAllocateDelayMillis > 0) {
3272 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3273 }
3274 }
3275 }
3279 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3280 assert_locked_or_safepoint(Heap_lock);
3281 size_t size = ReservedSpace::page_align_size_down(bytes);
3282 if (size > 0) {
3283 shrink_by(size);
3284 }
3285 }
3287 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3288 assert_locked_or_safepoint(Heap_lock);
3289 bool result = _virtual_space.expand_by(bytes);
3290 if (result) {
3291 HeapWord* old_end = _cmsSpace->end();
3292 size_t new_word_size =
3293 heap_word_size(_virtual_space.committed_size());
3294 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3295 _bts->resize(new_word_size); // resize the block offset shared array
3296 Universe::heap()->barrier_set()->resize_covered_region(mr);
3297 // Hmmmm... why doesn't CFLS::set_end verify locking?
3298 // This is quite ugly; FIX ME XXX
3299 _cmsSpace->assert_locked();
3300 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3302 // update the space and generation capacity counters
3303 if (UsePerfData) {
3304 _space_counters->update_capacity();
3305 _gen_counters->update_all();
3306 }
3308 if (Verbose && PrintGC) {
3309 size_t new_mem_size = _virtual_space.committed_size();
3310 size_t old_mem_size = new_mem_size - bytes;
3311 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3312 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3313 }
3314 }
3315 return result;
3316 }
3318 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3319 assert_locked_or_safepoint(Heap_lock);
3320 bool success = true;
3321 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3322 if (remaining_bytes > 0) {
3323 success = grow_by(remaining_bytes);
3324 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3325 }
3326 return success;
3327 }
3329 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3330 assert_locked_or_safepoint(Heap_lock);
3331 assert_lock_strong(freelistLock());
3332 // XXX Fix when compaction is implemented.
3333 warning("Shrinking of CMS not yet implemented");
3334 return;
3335 }
3338 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3339 // phases.
3340 class CMSPhaseAccounting: public StackObj {
3341 public:
3342 CMSPhaseAccounting(CMSCollector *collector,
3343 const char *phase,
3344 bool print_cr = true);
3345 ~CMSPhaseAccounting();
3347 private:
3348 CMSCollector *_collector;
3349 const char *_phase;
3350 elapsedTimer _wallclock;
3351 bool _print_cr;
3353 public:
3354 // Not MT-safe; so do not pass around these StackObj's
3355 // where they may be accessed by other threads.
3356 jlong wallclock_millis() {
3357 assert(_wallclock.is_active(), "Wall clock should not stop");
3358 _wallclock.stop(); // to record time
3359 jlong ret = _wallclock.milliseconds();
3360 _wallclock.start(); // restart
3361 return ret;
3362 }
3363 };
3365 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3366 const char *phase,
3367 bool print_cr) :
3368 _collector(collector), _phase(phase), _print_cr(print_cr) {
3370 if (PrintCMSStatistics != 0) {
3371 _collector->resetYields();
3372 }
3373 if (PrintGCDetails && PrintGCTimeStamps) {
3374 gclog_or_tty->date_stamp(PrintGCDateStamps);
3375 gclog_or_tty->stamp();
3376 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3377 _collector->cmsGen()->short_name(), _phase);
3378 }
3379 _collector->resetTimer();
3380 _wallclock.start();
3381 _collector->startTimer();
3382 }
3384 CMSPhaseAccounting::~CMSPhaseAccounting() {
3385 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3386 _collector->stopTimer();
3387 _wallclock.stop();
3388 if (PrintGCDetails) {
3389 gclog_or_tty->date_stamp(PrintGCDateStamps);
3390 if (PrintGCTimeStamps) {
3391 gclog_or_tty->stamp();
3392 gclog_or_tty->print(": ");
3393 }
3394 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3395 _collector->cmsGen()->short_name(),
3396 _phase, _collector->timerValue(), _wallclock.seconds());
3397 if (_print_cr) {
3398 gclog_or_tty->print_cr("");
3399 }
3400 if (PrintCMSStatistics != 0) {
3401 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3402 _collector->yields());
3403 }
3404 }
3405 }
3407 // CMS work
3409 // Checkpoint the roots into this generation from outside
3410 // this generation. [Note this initial checkpoint need only
3411 // be approximate -- we'll do a catch up phase subsequently.]
3412 void CMSCollector::checkpointRootsInitial(bool asynch) {
3413 assert(_collectorState == InitialMarking, "Wrong collector state");
3414 check_correct_thread_executing();
3415 ReferenceProcessor* rp = ref_processor();
3416 SpecializationStats::clear();
3417 assert(_restart_addr == NULL, "Control point invariant");
3418 if (asynch) {
3419 // acquire locks for subsequent manipulations
3420 MutexLockerEx x(bitMapLock(),
3421 Mutex::_no_safepoint_check_flag);
3422 checkpointRootsInitialWork(asynch);
3423 rp->verify_no_references_recorded();
3424 rp->enable_discovery(); // enable ("weak") refs discovery
3425 _collectorState = Marking;
3426 } else {
3427 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3428 // which recognizes if we are a CMS generation, and doesn't try to turn on
3429 // discovery; verify that they aren't meddling.
3430 assert(!rp->discovery_is_atomic(),
3431 "incorrect setting of discovery predicate");
3432 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3433 "ref discovery for this generation kind");
3434 // already have locks
3435 checkpointRootsInitialWork(asynch);
3436 rp->enable_discovery(); // now enable ("weak") refs discovery
3437 _collectorState = Marking;
3438 }
3439 SpecializationStats::print();
3440 }
3442 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3443 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3444 assert(_collectorState == InitialMarking, "just checking");
3446 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3447 // precede our marking with a collection of all
3448 // younger generations to keep floating garbage to a minimum.
3449 // XXX: we won't do this for now -- it's an optimization to be done later.
3451 // already have locks
3452 assert_lock_strong(bitMapLock());
3453 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3455 // Setup the verification and class unloading state for this
3456 // CMS collection cycle.
3457 setup_cms_unloading_and_verification_state();
3459 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3460 PrintGCDetails && Verbose, true, gclog_or_tty);)
3461 if (UseAdaptiveSizePolicy) {
3462 size_policy()->checkpoint_roots_initial_begin();
3463 }
3465 // Reset all the PLAB chunk arrays if necessary.
3466 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3467 reset_survivor_plab_arrays();
3468 }
3470 ResourceMark rm;
3471 HandleMark hm;
3473 FalseClosure falseClosure;
3474 // In the case of a synchronous collection, we will elide the
3475 // remark step, so it's important to catch all the nmethod oops
3476 // in this step; hence the last argument to the constrcutor below.
3477 MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */);
3478 GenCollectedHeap* gch = GenCollectedHeap::heap();
3480 verify_work_stacks_empty();
3481 verify_overflow_empty();
3483 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3484 // Update the saved marks which may affect the root scans.
3485 gch->save_marks();
3487 // weak reference processing has not started yet.
3488 ref_processor()->set_enqueuing_is_done(false);
3490 {
3491 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3492 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3493 gch->gen_process_strong_roots(_cmsGen->level(),
3494 true, // younger gens are roots
3495 true, // collecting perm gen
3496 SharedHeap::ScanningOption(roots_scanning_options()),
3497 NULL, ¬Older);
3498 }
3500 // Clear mod-union table; it will be dirtied in the prologue of
3501 // CMS generation per each younger generation collection.
3503 assert(_modUnionTable.isAllClear(),
3504 "Was cleared in most recent final checkpoint phase"
3505 " or no bits are set in the gc_prologue before the start of the next "
3506 "subsequent marking phase.");
3508 // Temporarily disabled, since pre/post-consumption closures don't
3509 // care about precleaned cards
3510 #if 0
3511 {
3512 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(),
3513 (HeapWord*)_virtual_space.high());
3514 _ct->ct_bs()->preclean_dirty_cards(mr);
3515 }
3516 #endif
3518 // Save the end of the used_region of the constituent generations
3519 // to be used to limit the extent of sweep in each generation.
3520 save_sweep_limits();
3521 if (UseAdaptiveSizePolicy) {
3522 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3523 }
3524 verify_overflow_empty();
3525 }
3527 bool CMSCollector::markFromRoots(bool asynch) {
3528 // we might be tempted to assert that:
3529 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3530 // "inconsistent argument?");
3531 // However that wouldn't be right, because it's possible that
3532 // a safepoint is indeed in progress as a younger generation
3533 // stop-the-world GC happens even as we mark in this generation.
3534 assert(_collectorState == Marking, "inconsistent state?");
3535 check_correct_thread_executing();
3536 verify_overflow_empty();
3538 bool res;
3539 if (asynch) {
3541 // Start the timers for adaptive size policy for the concurrent phases
3542 // Do it here so that the foreground MS can use the concurrent
3543 // timer since a foreground MS might has the sweep done concurrently
3544 // or STW.
3545 if (UseAdaptiveSizePolicy) {
3546 size_policy()->concurrent_marking_begin();
3547 }
3549 // Weak ref discovery note: We may be discovering weak
3550 // refs in this generation concurrent (but interleaved) with
3551 // weak ref discovery by a younger generation collector.
3553 CMSTokenSyncWithLocks ts(true, bitMapLock());
3554 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3555 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3556 res = markFromRootsWork(asynch);
3557 if (res) {
3558 _collectorState = Precleaning;
3559 } else { // We failed and a foreground collection wants to take over
3560 assert(_foregroundGCIsActive, "internal state inconsistency");
3561 assert(_restart_addr == NULL, "foreground will restart from scratch");
3562 if (PrintGCDetails) {
3563 gclog_or_tty->print_cr("bailing out to foreground collection");
3564 }
3565 }
3566 if (UseAdaptiveSizePolicy) {
3567 size_policy()->concurrent_marking_end();
3568 }
3569 } else {
3570 assert(SafepointSynchronize::is_at_safepoint(),
3571 "inconsistent with asynch == false");
3572 if (UseAdaptiveSizePolicy) {
3573 size_policy()->ms_collection_marking_begin();
3574 }
3575 // already have locks
3576 res = markFromRootsWork(asynch);
3577 _collectorState = FinalMarking;
3578 if (UseAdaptiveSizePolicy) {
3579 GenCollectedHeap* gch = GenCollectedHeap::heap();
3580 size_policy()->ms_collection_marking_end(gch->gc_cause());
3581 }
3582 }
3583 verify_overflow_empty();
3584 return res;
3585 }
3587 bool CMSCollector::markFromRootsWork(bool asynch) {
3588 // iterate over marked bits in bit map, doing a full scan and mark
3589 // from these roots using the following algorithm:
3590 // . if oop is to the right of the current scan pointer,
3591 // mark corresponding bit (we'll process it later)
3592 // . else (oop is to left of current scan pointer)
3593 // push oop on marking stack
3594 // . drain the marking stack
3596 // Note that when we do a marking step we need to hold the
3597 // bit map lock -- recall that direct allocation (by mutators)
3598 // and promotion (by younger generation collectors) is also
3599 // marking the bit map. [the so-called allocate live policy.]
3600 // Because the implementation of bit map marking is not
3601 // robust wrt simultaneous marking of bits in the same word,
3602 // we need to make sure that there is no such interference
3603 // between concurrent such updates.
3605 // already have locks
3606 assert_lock_strong(bitMapLock());
3608 // Clear the revisit stack, just in case there are any
3609 // obsolete contents from a short-circuited previous CMS cycle.
3610 _revisitStack.reset();
3611 verify_work_stacks_empty();
3612 verify_overflow_empty();
3613 assert(_revisitStack.isEmpty(), "tabula rasa");
3615 bool result = false;
3616 if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) {
3617 result = do_marking_mt(asynch);
3618 } else {
3619 result = do_marking_st(asynch);
3620 }
3621 return result;
3622 }
3624 // Forward decl
3625 class CMSConcMarkingTask;
3627 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3628 CMSCollector* _collector;
3629 CMSConcMarkingTask* _task;
3630 bool _yield;
3631 protected:
3632 virtual void yield();
3633 public:
3634 // "n_threads" is the number of threads to be terminated.
3635 // "queue_set" is a set of work queues of other threads.
3636 // "collector" is the CMS collector associated with this task terminator.
3637 // "yield" indicates whether we need the gang as a whole to yield.
3638 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set,
3639 CMSCollector* collector, bool yield) :
3640 ParallelTaskTerminator(n_threads, queue_set),
3641 _collector(collector),
3642 _yield(yield) { }
3644 void set_task(CMSConcMarkingTask* task) {
3645 _task = task;
3646 }
3647 };
3649 // MT Concurrent Marking Task
3650 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3651 CMSCollector* _collector;
3652 YieldingFlexibleWorkGang* _workers; // the whole gang
3653 int _n_workers; // requested/desired # workers
3654 bool _asynch;
3655 bool _result;
3656 CompactibleFreeListSpace* _cms_space;
3657 CompactibleFreeListSpace* _perm_space;
3658 HeapWord* _global_finger;
3659 HeapWord* _restart_addr;
3661 // Exposed here for yielding support
3662 Mutex* const _bit_map_lock;
3664 // The per thread work queues, available here for stealing
3665 OopTaskQueueSet* _task_queues;
3666 CMSConcMarkingTerminator _term;
3668 public:
3669 CMSConcMarkingTask(CMSCollector* collector,
3670 CompactibleFreeListSpace* cms_space,
3671 CompactibleFreeListSpace* perm_space,
3672 bool asynch, int n_workers,
3673 YieldingFlexibleWorkGang* workers,
3674 OopTaskQueueSet* task_queues):
3675 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3676 _collector(collector),
3677 _cms_space(cms_space),
3678 _perm_space(perm_space),
3679 _asynch(asynch), _n_workers(n_workers), _result(true),
3680 _workers(workers), _task_queues(task_queues),
3681 _term(n_workers, task_queues, _collector, asynch),
3682 _bit_map_lock(collector->bitMapLock())
3683 {
3684 assert(n_workers <= workers->total_workers(),
3685 "Else termination won't work correctly today"); // XXX FIX ME!
3686 _requested_size = n_workers;
3687 _term.set_task(this);
3688 assert(_cms_space->bottom() < _perm_space->bottom(),
3689 "Finger incorrectly initialized below");
3690 _restart_addr = _global_finger = _cms_space->bottom();
3691 }
3694 OopTaskQueueSet* task_queues() { return _task_queues; }
3696 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3698 HeapWord** global_finger_addr() { return &_global_finger; }
3700 CMSConcMarkingTerminator* terminator() { return &_term; }
3702 void work(int i);
3704 virtual void coordinator_yield(); // stuff done by coordinator
3705 bool result() { return _result; }
3707 void reset(HeapWord* ra) {
3708 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3709 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3710 assert(ra < _perm_space->end(), "ra too large");
3711 _restart_addr = _global_finger = ra;
3712 _term.reset_for_reuse();
3713 }
3715 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3716 OopTaskQueue* work_q);
3718 private:
3719 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3720 void do_work_steal(int i);
3721 void bump_global_finger(HeapWord* f);
3722 };
3724 void CMSConcMarkingTerminator::yield() {
3725 if (ConcurrentMarkSweepThread::should_yield() &&
3726 !_collector->foregroundGCIsActive() &&
3727 _yield) {
3728 _task->yield();
3729 } else {
3730 ParallelTaskTerminator::yield();
3731 }
3732 }
3734 ////////////////////////////////////////////////////////////////
3735 // Concurrent Marking Algorithm Sketch
3736 ////////////////////////////////////////////////////////////////
3737 // Until all tasks exhausted (both spaces):
3738 // -- claim next available chunk
3739 // -- bump global finger via CAS
3740 // -- find first object that starts in this chunk
3741 // and start scanning bitmap from that position
3742 // -- scan marked objects for oops
3743 // -- CAS-mark target, and if successful:
3744 // . if target oop is above global finger (volatile read)
3745 // nothing to do
3746 // . if target oop is in chunk and above local finger
3747 // then nothing to do
3748 // . else push on work-queue
3749 // -- Deal with possible overflow issues:
3750 // . local work-queue overflow causes stuff to be pushed on
3751 // global (common) overflow queue
3752 // . always first empty local work queue
3753 // . then get a batch of oops from global work queue if any
3754 // . then do work stealing
3755 // -- When all tasks claimed (both spaces)
3756 // and local work queue empty,
3757 // then in a loop do:
3758 // . check global overflow stack; steal a batch of oops and trace
3759 // . try to steal from other threads oif GOS is empty
3760 // . if neither is available, offer termination
3761 // -- Terminate and return result
3762 //
3763 void CMSConcMarkingTask::work(int i) {
3764 elapsedTimer _timer;
3765 ResourceMark rm;
3766 HandleMark hm;
3768 DEBUG_ONLY(_collector->verify_overflow_empty();)
3770 // Before we begin work, our work queue should be empty
3771 assert(work_queue(i)->size() == 0, "Expected to be empty");
3772 // Scan the bitmap covering _cms_space, tracing through grey objects.
3773 _timer.start();
3774 do_scan_and_mark(i, _cms_space);
3775 _timer.stop();
3776 if (PrintCMSStatistics != 0) {
3777 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3778 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3779 }
3781 // ... do the same for the _perm_space
3782 _timer.reset();
3783 _timer.start();
3784 do_scan_and_mark(i, _perm_space);
3785 _timer.stop();
3786 if (PrintCMSStatistics != 0) {
3787 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3788 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3789 }
3791 // ... do work stealing
3792 _timer.reset();
3793 _timer.start();
3794 do_work_steal(i);
3795 _timer.stop();
3796 if (PrintCMSStatistics != 0) {
3797 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3798 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers
3799 }
3800 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3801 assert(work_queue(i)->size() == 0, "Should have been emptied");
3802 // Note that under the current task protocol, the
3803 // following assertion is true even of the spaces
3804 // expanded since the completion of the concurrent
3805 // marking. XXX This will likely change under a strict
3806 // ABORT semantics.
3807 assert(_global_finger > _cms_space->end() &&
3808 _global_finger >= _perm_space->end(),
3809 "All tasks have been completed");
3810 DEBUG_ONLY(_collector->verify_overflow_empty();)
3811 }
3813 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3814 HeapWord* read = _global_finger;
3815 HeapWord* cur = read;
3816 while (f > read) {
3817 cur = read;
3818 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3819 if (cur == read) {
3820 // our cas succeeded
3821 assert(_global_finger >= f, "protocol consistency");
3822 break;
3823 }
3824 }
3825 }
3827 // This is really inefficient, and should be redone by
3828 // using (not yet available) block-read and -write interfaces to the
3829 // stack and the work_queue. XXX FIX ME !!!
3830 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3831 OopTaskQueue* work_q) {
3832 // Fast lock-free check
3833 if (ovflw_stk->length() == 0) {
3834 return false;
3835 }
3836 assert(work_q->size() == 0, "Shouldn't steal");
3837 MutexLockerEx ml(ovflw_stk->par_lock(),
3838 Mutex::_no_safepoint_check_flag);
3839 // Grab up to 1/4 the size of the work queue
3840 size_t num = MIN2((size_t)work_q->max_elems()/4,
3841 (size_t)ParGCDesiredObjsFromOverflowList);
3842 num = MIN2(num, ovflw_stk->length());
3843 for (int i = (int) num; i > 0; i--) {
3844 oop cur = ovflw_stk->pop();
3845 assert(cur != NULL, "Counted wrong?");
3846 work_q->push(cur);
3847 }
3848 return num > 0;
3849 }
3851 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3852 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3853 int n_tasks = pst->n_tasks();
3854 // We allow that there may be no tasks to do here because
3855 // we are restarting after a stack overflow.
3856 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3857 int nth_task = 0;
3859 HeapWord* aligned_start = sp->bottom();
3860 if (sp->used_region().contains(_restart_addr)) {
3861 // Align down to a card boundary for the start of 0th task
3862 // for this space.
3863 aligned_start =
3864 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3865 CardTableModRefBS::card_size);
3866 }
3868 size_t chunk_size = sp->marking_task_size();
3869 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3870 // Having claimed the nth task in this space,
3871 // compute the chunk that it corresponds to:
3872 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3873 aligned_start + (nth_task+1)*chunk_size);
3874 // Try and bump the global finger via a CAS;
3875 // note that we need to do the global finger bump
3876 // _before_ taking the intersection below, because
3877 // the task corresponding to that region will be
3878 // deemed done even if the used_region() expands
3879 // because of allocation -- as it almost certainly will
3880 // during start-up while the threads yield in the
3881 // closure below.
3882 HeapWord* finger = span.end();
3883 bump_global_finger(finger); // atomically
3884 // There are null tasks here corresponding to chunks
3885 // beyond the "top" address of the space.
3886 span = span.intersection(sp->used_region());
3887 if (!span.is_empty()) { // Non-null task
3888 HeapWord* prev_obj;
3889 assert(!span.contains(_restart_addr) || nth_task == 0,
3890 "Inconsistency");
3891 if (nth_task == 0) {
3892 // For the 0th task, we'll not need to compute a block_start.
3893 if (span.contains(_restart_addr)) {
3894 // In the case of a restart because of stack overflow,
3895 // we might additionally skip a chunk prefix.
3896 prev_obj = _restart_addr;
3897 } else {
3898 prev_obj = span.start();
3899 }
3900 } else {
3901 // We want to skip the first object because
3902 // the protocol is to scan any object in its entirety
3903 // that _starts_ in this span; a fortiori, any
3904 // object starting in an earlier span is scanned
3905 // as part of an earlier claimed task.
3906 // Below we use the "careful" version of block_start
3907 // so we do not try to navigate uninitialized objects.
3908 prev_obj = sp->block_start_careful(span.start());
3909 // Below we use a variant of block_size that uses the
3910 // Printezis bits to avoid waiting for allocated
3911 // objects to become initialized/parsable.
3912 while (prev_obj < span.start()) {
3913 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3914 if (sz > 0) {
3915 prev_obj += sz;
3916 } else {
3917 // In this case we may end up doing a bit of redundant
3918 // scanning, but that appears unavoidable, short of
3919 // locking the free list locks; see bug 6324141.
3920 break;
3921 }
3922 }
3923 }
3924 if (prev_obj < span.end()) {
3925 MemRegion my_span = MemRegion(prev_obj, span.end());
3926 // Do the marking work within a non-empty span --
3927 // the last argument to the constructor indicates whether the
3928 // iteration should be incremental with periodic yields.
3929 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3930 &_collector->_markBitMap,
3931 work_queue(i),
3932 &_collector->_markStack,
3933 &_collector->_revisitStack,
3934 _asynch);
3935 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3936 } // else nothing to do for this task
3937 } // else nothing to do for this task
3938 }
3939 // We'd be tempted to assert here that since there are no
3940 // more tasks left to claim in this space, the global_finger
3941 // must exceed space->top() and a fortiori space->end(). However,
3942 // that would not quite be correct because the bumping of
3943 // global_finger occurs strictly after the claiming of a task,
3944 // so by the time we reach here the global finger may not yet
3945 // have been bumped up by the thread that claimed the last
3946 // task.
3947 pst->all_tasks_completed();
3948 }
3950 class Par_ConcMarkingClosure: public OopClosure {
3951 private:
3952 CMSCollector* _collector;
3953 MemRegion _span;
3954 CMSBitMap* _bit_map;
3955 CMSMarkStack* _overflow_stack;
3956 CMSMarkStack* _revisit_stack; // XXXXXX Check proper use
3957 OopTaskQueue* _work_queue;
3958 protected:
3959 DO_OOP_WORK_DEFN
3960 public:
3961 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue,
3962 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3963 _collector(collector),
3964 _span(_collector->_span),
3965 _work_queue(work_queue),
3966 _bit_map(bit_map),
3967 _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc.
3968 virtual void do_oop(oop* p);
3969 virtual void do_oop(narrowOop* p);
3970 void trim_queue(size_t max);
3971 void handle_stack_overflow(HeapWord* lost);
3972 };
3974 // Grey object scanning during work stealing phase --
3975 // the salient assumption here is that any references
3976 // that are in these stolen objects being scanned must
3977 // already have been initialized (else they would not have
3978 // been published), so we do not need to check for
3979 // uninitialized objects before pushing here.
3980 void Par_ConcMarkingClosure::do_oop(oop obj) {
3981 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
3982 HeapWord* addr = (HeapWord*)obj;
3983 // Check if oop points into the CMS generation
3984 // and is not marked
3985 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3986 // a white object ...
3987 // If we manage to "claim" the object, by being the
3988 // first thread to mark it, then we push it on our
3989 // marking stack
3990 if (_bit_map->par_mark(addr)) { // ... now grey
3991 // push on work queue (grey set)
3992 bool simulate_overflow = false;
3993 NOT_PRODUCT(
3994 if (CMSMarkStackOverflowALot &&
3995 _collector->simulate_overflow()) {
3996 // simulate a stack overflow
3997 simulate_overflow = true;
3998 }
3999 )
4000 if (simulate_overflow ||
4001 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4002 // stack overflow
4003 if (PrintCMSStatistics != 0) {
4004 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4005 SIZE_FORMAT, _overflow_stack->capacity());
4006 }
4007 // We cannot assert that the overflow stack is full because
4008 // it may have been emptied since.
4009 assert(simulate_overflow ||
4010 _work_queue->size() == _work_queue->max_elems(),
4011 "Else push should have succeeded");
4012 handle_stack_overflow(addr);
4013 }
4014 } // Else, some other thread got there first
4015 }
4016 }
4018 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4019 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4021 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4022 while (_work_queue->size() > max) {
4023 oop new_oop;
4024 if (_work_queue->pop_local(new_oop)) {
4025 assert(new_oop->is_oop(), "Should be an oop");
4026 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4027 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4028 assert(new_oop->is_parsable(), "Should be parsable");
4029 new_oop->oop_iterate(this); // do_oop() above
4030 }
4031 }
4032 }
4034 // Upon stack overflow, we discard (part of) the stack,
4035 // remembering the least address amongst those discarded
4036 // in CMSCollector's _restart_address.
4037 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4038 // We need to do this under a mutex to prevent other
4039 // workers from interfering with the work done below.
4040 MutexLockerEx ml(_overflow_stack->par_lock(),
4041 Mutex::_no_safepoint_check_flag);
4042 // Remember the least grey address discarded
4043 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4044 _collector->lower_restart_addr(ra);
4045 _overflow_stack->reset(); // discard stack contents
4046 _overflow_stack->expand(); // expand the stack if possible
4047 }
4050 void CMSConcMarkingTask::do_work_steal(int i) {
4051 OopTaskQueue* work_q = work_queue(i);
4052 oop obj_to_scan;
4053 CMSBitMap* bm = &(_collector->_markBitMap);
4054 CMSMarkStack* ovflw = &(_collector->_markStack);
4055 int* seed = _collector->hash_seed(i);
4056 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw);
4057 while (true) {
4058 cl.trim_queue(0);
4059 assert(work_q->size() == 0, "Should have been emptied above");
4060 if (get_work_from_overflow_stack(ovflw, work_q)) {
4061 // Can't assert below because the work obtained from the
4062 // overflow stack may already have been stolen from us.
4063 // assert(work_q->size() > 0, "Work from overflow stack");
4064 continue;
4065 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4066 assert(obj_to_scan->is_oop(), "Should be an oop");
4067 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4068 obj_to_scan->oop_iterate(&cl);
4069 } else if (terminator()->offer_termination()) {
4070 assert(work_q->size() == 0, "Impossible!");
4071 break;
4072 }
4073 }
4074 }
4076 // This is run by the CMS (coordinator) thread.
4077 void CMSConcMarkingTask::coordinator_yield() {
4078 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4079 "CMS thread should hold CMS token");
4081 // First give up the locks, then yield, then re-lock
4082 // We should probably use a constructor/destructor idiom to
4083 // do this unlock/lock or modify the MutexUnlocker class to
4084 // serve our purpose. XXX
4085 assert_lock_strong(_bit_map_lock);
4086 _bit_map_lock->unlock();
4087 ConcurrentMarkSweepThread::desynchronize(true);
4088 ConcurrentMarkSweepThread::acknowledge_yield_request();
4089 _collector->stopTimer();
4090 if (PrintCMSStatistics != 0) {
4091 _collector->incrementYields();
4092 }
4093 _collector->icms_wait();
4095 // It is possible for whichever thread initiated the yield request
4096 // not to get a chance to wake up and take the bitmap lock between
4097 // this thread releasing it and reacquiring it. So, while the
4098 // should_yield() flag is on, let's sleep for a bit to give the
4099 // other thread a chance to wake up. The limit imposed on the number
4100 // of iterations is defensive, to avoid any unforseen circumstances
4101 // putting us into an infinite loop. Since it's always been this
4102 // (coordinator_yield()) method that was observed to cause the
4103 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4104 // which is by default non-zero. For the other seven methods that
4105 // also perform the yield operation, as are using a different
4106 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4107 // can enable the sleeping for those methods too, if necessary.
4108 // See 6442774.
4109 //
4110 // We really need to reconsider the synchronization between the GC
4111 // thread and the yield-requesting threads in the future and we
4112 // should really use wait/notify, which is the recommended
4113 // way of doing this type of interaction. Additionally, we should
4114 // consolidate the eight methods that do the yield operation and they
4115 // are almost identical into one for better maintenability and
4116 // readability. See 6445193.
4117 //
4118 // Tony 2006.06.29
4119 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4120 ConcurrentMarkSweepThread::should_yield() &&
4121 !CMSCollector::foregroundGCIsActive(); ++i) {
4122 os::sleep(Thread::current(), 1, false);
4123 ConcurrentMarkSweepThread::acknowledge_yield_request();
4124 }
4126 ConcurrentMarkSweepThread::synchronize(true);
4127 _bit_map_lock->lock_without_safepoint_check();
4128 _collector->startTimer();
4129 }
4131 bool CMSCollector::do_marking_mt(bool asynch) {
4132 assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition");
4133 // In the future this would be determined ergonomically, based
4134 // on #cpu's, # active mutator threads (and load), and mutation rate.
4135 int num_workers = ParallelCMSThreads;
4137 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4138 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4140 CMSConcMarkingTask tsk(this, cms_space, perm_space,
4141 asynch, num_workers /* number requested XXX */,
4142 conc_workers(), task_queues());
4144 // Since the actual number of workers we get may be different
4145 // from the number we requested above, do we need to do anything different
4146 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4147 // class?? XXX
4148 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4149 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4151 // Refs discovery is already non-atomic.
4152 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4153 // Mutate the Refs discovery so it is MT during the
4154 // multi-threaded marking phase.
4155 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1);
4157 conc_workers()->start_task(&tsk);
4158 while (tsk.yielded()) {
4159 tsk.coordinator_yield();
4160 conc_workers()->continue_task(&tsk);
4161 }
4162 // If the task was aborted, _restart_addr will be non-NULL
4163 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4164 while (_restart_addr != NULL) {
4165 // XXX For now we do not make use of ABORTED state and have not
4166 // yet implemented the right abort semantics (even in the original
4167 // single-threaded CMS case). That needs some more investigation
4168 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4169 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4170 // If _restart_addr is non-NULL, a marking stack overflow
4171 // occured; we need to do a fresh marking iteration from the
4172 // indicated restart address.
4173 if (_foregroundGCIsActive && asynch) {
4174 // We may be running into repeated stack overflows, having
4175 // reached the limit of the stack size, while making very
4176 // slow forward progress. It may be best to bail out and
4177 // let the foreground collector do its job.
4178 // Clear _restart_addr, so that foreground GC
4179 // works from scratch. This avoids the headache of
4180 // a "rescan" which would otherwise be needed because
4181 // of the dirty mod union table & card table.
4182 _restart_addr = NULL;
4183 return false;
4184 }
4185 // Adjust the task to restart from _restart_addr
4186 tsk.reset(_restart_addr);
4187 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4188 _restart_addr);
4189 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4190 _restart_addr);
4191 _restart_addr = NULL;
4192 // Get the workers going again
4193 conc_workers()->start_task(&tsk);
4194 while (tsk.yielded()) {
4195 tsk.coordinator_yield();
4196 conc_workers()->continue_task(&tsk);
4197 }
4198 }
4199 assert(tsk.completed(), "Inconsistency");
4200 assert(tsk.result() == true, "Inconsistency");
4201 return true;
4202 }
4204 bool CMSCollector::do_marking_st(bool asynch) {
4205 ResourceMark rm;
4206 HandleMark hm;
4208 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4209 &_markStack, &_revisitStack, CMSYield && asynch);
4210 // the last argument to iterate indicates whether the iteration
4211 // should be incremental with periodic yields.
4212 _markBitMap.iterate(&markFromRootsClosure);
4213 // If _restart_addr is non-NULL, a marking stack overflow
4214 // occured; we need to do a fresh iteration from the
4215 // indicated restart address.
4216 while (_restart_addr != NULL) {
4217 if (_foregroundGCIsActive && asynch) {
4218 // We may be running into repeated stack overflows, having
4219 // reached the limit of the stack size, while making very
4220 // slow forward progress. It may be best to bail out and
4221 // let the foreground collector do its job.
4222 // Clear _restart_addr, so that foreground GC
4223 // works from scratch. This avoids the headache of
4224 // a "rescan" which would otherwise be needed because
4225 // of the dirty mod union table & card table.
4226 _restart_addr = NULL;
4227 return false; // indicating failure to complete marking
4228 }
4229 // Deal with stack overflow:
4230 // we restart marking from _restart_addr
4231 HeapWord* ra = _restart_addr;
4232 markFromRootsClosure.reset(ra);
4233 _restart_addr = NULL;
4234 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4235 }
4236 return true;
4237 }
4239 void CMSCollector::preclean() {
4240 check_correct_thread_executing();
4241 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4242 verify_work_stacks_empty();
4243 verify_overflow_empty();
4244 _abort_preclean = false;
4245 if (CMSPrecleaningEnabled) {
4246 _eden_chunk_index = 0;
4247 size_t used = get_eden_used();
4248 size_t capacity = get_eden_capacity();
4249 // Don't start sampling unless we will get sufficiently
4250 // many samples.
4251 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4252 * CMSScheduleRemarkEdenPenetration)) {
4253 _start_sampling = true;
4254 } else {
4255 _start_sampling = false;
4256 }
4257 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4258 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4259 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4260 }
4261 CMSTokenSync x(true); // is cms thread
4262 if (CMSPrecleaningEnabled) {
4263 sample_eden();
4264 _collectorState = AbortablePreclean;
4265 } else {
4266 _collectorState = FinalMarking;
4267 }
4268 verify_work_stacks_empty();
4269 verify_overflow_empty();
4270 }
4272 // Try and schedule the remark such that young gen
4273 // occupancy is CMSScheduleRemarkEdenPenetration %.
4274 void CMSCollector::abortable_preclean() {
4275 check_correct_thread_executing();
4276 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4277 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4279 // If Eden's current occupancy is below this threshold,
4280 // immediately schedule the remark; else preclean
4281 // past the next scavenge in an effort to
4282 // schedule the pause as described avove. By choosing
4283 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4284 // we will never do an actual abortable preclean cycle.
4285 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4286 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4287 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4288 // We need more smarts in the abortable preclean
4289 // loop below to deal with cases where allocation
4290 // in young gen is very very slow, and our precleaning
4291 // is running a losing race against a horde of
4292 // mutators intent on flooding us with CMS updates
4293 // (dirty cards).
4294 // One, admittedly dumb, strategy is to give up
4295 // after a certain number of abortable precleaning loops
4296 // or after a certain maximum time. We want to make
4297 // this smarter in the next iteration.
4298 // XXX FIX ME!!! YSR
4299 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4300 while (!(should_abort_preclean() ||
4301 ConcurrentMarkSweepThread::should_terminate())) {
4302 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4303 cumworkdone += workdone;
4304 loops++;
4305 // Voluntarily terminate abortable preclean phase if we have
4306 // been at it for too long.
4307 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4308 loops >= CMSMaxAbortablePrecleanLoops) {
4309 if (PrintGCDetails) {
4310 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4311 }
4312 break;
4313 }
4314 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4315 if (PrintGCDetails) {
4316 gclog_or_tty->print(" CMS: abort preclean due to time ");
4317 }
4318 break;
4319 }
4320 // If we are doing little work each iteration, we should
4321 // take a short break.
4322 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4323 // Sleep for some time, waiting for work to accumulate
4324 stopTimer();
4325 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4326 startTimer();
4327 waited++;
4328 }
4329 }
4330 if (PrintCMSStatistics > 0) {
4331 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4332 loops, waited, cumworkdone);
4333 }
4334 }
4335 CMSTokenSync x(true); // is cms thread
4336 if (_collectorState != Idling) {
4337 assert(_collectorState == AbortablePreclean,
4338 "Spontaneous state transition?");
4339 _collectorState = FinalMarking;
4340 } // Else, a foreground collection completed this CMS cycle.
4341 return;
4342 }
4344 // Respond to an Eden sampling opportunity
4345 void CMSCollector::sample_eden() {
4346 // Make sure a young gc cannot sneak in between our
4347 // reading and recording of a sample.
4348 assert(Thread::current()->is_ConcurrentGC_thread(),
4349 "Only the cms thread may collect Eden samples");
4350 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4351 "Should collect samples while holding CMS token");
4352 if (!_start_sampling) {
4353 return;
4354 }
4355 if (_eden_chunk_array) {
4356 if (_eden_chunk_index < _eden_chunk_capacity) {
4357 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4358 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4359 "Unexpected state of Eden");
4360 // We'd like to check that what we just sampled is an oop-start address;
4361 // however, we cannot do that here since the object may not yet have been
4362 // initialized. So we'll instead do the check when we _use_ this sample
4363 // later.
4364 if (_eden_chunk_index == 0 ||
4365 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4366 _eden_chunk_array[_eden_chunk_index-1])
4367 >= CMSSamplingGrain)) {
4368 _eden_chunk_index++; // commit sample
4369 }
4370 }
4371 }
4372 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4373 size_t used = get_eden_used();
4374 size_t capacity = get_eden_capacity();
4375 assert(used <= capacity, "Unexpected state of Eden");
4376 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4377 _abort_preclean = true;
4378 }
4379 }
4380 }
4383 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4384 assert(_collectorState == Precleaning ||
4385 _collectorState == AbortablePreclean, "incorrect state");
4386 ResourceMark rm;
4387 HandleMark hm;
4388 // Do one pass of scrubbing the discovered reference lists
4389 // to remove any reference objects with strongly-reachable
4390 // referents.
4391 if (clean_refs) {
4392 ReferenceProcessor* rp = ref_processor();
4393 CMSPrecleanRefsYieldClosure yield_cl(this);
4394 assert(rp->span().equals(_span), "Spans should be equal");
4395 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4396 &_markStack, true /* preclean */);
4397 CMSDrainMarkingStackClosure complete_trace(this,
4398 _span, &_markBitMap, &_markStack,
4399 &keep_alive, true /* preclean */);
4401 // We don't want this step to interfere with a young
4402 // collection because we don't want to take CPU
4403 // or memory bandwidth away from the young GC threads
4404 // (which may be as many as there are CPUs).
4405 // Note that we don't need to protect ourselves from
4406 // interference with mutators because they can't
4407 // manipulate the discovered reference lists nor affect
4408 // the computed reachability of the referents, the
4409 // only properties manipulated by the precleaning
4410 // of these reference lists.
4411 stopTimer();
4412 CMSTokenSyncWithLocks x(true /* is cms thread */,
4413 bitMapLock());
4414 startTimer();
4415 sample_eden();
4416 // The following will yield to allow foreground
4417 // collection to proceed promptly. XXX YSR:
4418 // The code in this method may need further
4419 // tweaking for better performance and some restructuring
4420 // for cleaner interfaces.
4421 rp->preclean_discovered_references(
4422 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4423 &yield_cl);
4424 }
4426 if (clean_survivor) { // preclean the active survivor space(s)
4427 assert(_young_gen->kind() == Generation::DefNew ||
4428 _young_gen->kind() == Generation::ParNew ||
4429 _young_gen->kind() == Generation::ASParNew,
4430 "incorrect type for cast");
4431 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4432 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4433 &_markBitMap, &_modUnionTable,
4434 &_markStack, &_revisitStack,
4435 true /* precleaning phase */);
4436 stopTimer();
4437 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4438 bitMapLock());
4439 startTimer();
4440 unsigned int before_count =
4441 GenCollectedHeap::heap()->total_collections();
4442 SurvivorSpacePrecleanClosure
4443 sss_cl(this, _span, &_markBitMap, &_markStack,
4444 &pam_cl, before_count, CMSYield);
4445 dng->from()->object_iterate_careful(&sss_cl);
4446 dng->to()->object_iterate_careful(&sss_cl);
4447 }
4448 MarkRefsIntoAndScanClosure
4449 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4450 &_markStack, &_revisitStack, this, CMSYield,
4451 true /* precleaning phase */);
4452 // CAUTION: The following closure has persistent state that may need to
4453 // be reset upon a decrease in the sequence of addresses it
4454 // processes.
4455 ScanMarkedObjectsAgainCarefullyClosure
4456 smoac_cl(this, _span,
4457 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4459 // Preclean dirty cards in ModUnionTable and CardTable using
4460 // appropriate convergence criterion;
4461 // repeat CMSPrecleanIter times unless we find that
4462 // we are losing.
4463 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4464 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4465 "Bad convergence multiplier");
4466 assert(CMSPrecleanThreshold >= 100,
4467 "Unreasonably low CMSPrecleanThreshold");
4469 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4470 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4471 numIter < CMSPrecleanIter;
4472 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4473 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4474 if (CMSPermGenPrecleaningEnabled) {
4475 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4476 }
4477 if (Verbose && PrintGCDetails) {
4478 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4479 }
4480 // Either there are very few dirty cards, so re-mark
4481 // pause will be small anyway, or our pre-cleaning isn't
4482 // that much faster than the rate at which cards are being
4483 // dirtied, so we might as well stop and re-mark since
4484 // precleaning won't improve our re-mark time by much.
4485 if (curNumCards <= CMSPrecleanThreshold ||
4486 (numIter > 0 &&
4487 (curNumCards * CMSPrecleanDenominator >
4488 lastNumCards * CMSPrecleanNumerator))) {
4489 numIter++;
4490 cumNumCards += curNumCards;
4491 break;
4492 }
4493 }
4494 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4495 if (CMSPermGenPrecleaningEnabled) {
4496 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4497 }
4498 cumNumCards += curNumCards;
4499 if (PrintGCDetails && PrintCMSStatistics != 0) {
4500 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4501 curNumCards, cumNumCards, numIter);
4502 }
4503 return cumNumCards; // as a measure of useful work done
4504 }
4506 // PRECLEANING NOTES:
4507 // Precleaning involves:
4508 // . reading the bits of the modUnionTable and clearing the set bits.
4509 // . For the cards corresponding to the set bits, we scan the
4510 // objects on those cards. This means we need the free_list_lock
4511 // so that we can safely iterate over the CMS space when scanning
4512 // for oops.
4513 // . When we scan the objects, we'll be both reading and setting
4514 // marks in the marking bit map, so we'll need the marking bit map.
4515 // . For protecting _collector_state transitions, we take the CGC_lock.
4516 // Note that any races in the reading of of card table entries by the
4517 // CMS thread on the one hand and the clearing of those entries by the
4518 // VM thread or the setting of those entries by the mutator threads on the
4519 // other are quite benign. However, for efficiency it makes sense to keep
4520 // the VM thread from racing with the CMS thread while the latter is
4521 // dirty card info to the modUnionTable. We therefore also use the
4522 // CGC_lock to protect the reading of the card table and the mod union
4523 // table by the CM thread.
4524 // . We run concurrently with mutator updates, so scanning
4525 // needs to be done carefully -- we should not try to scan
4526 // potentially uninitialized objects.
4527 //
4528 // Locking strategy: While holding the CGC_lock, we scan over and
4529 // reset a maximal dirty range of the mod union / card tables, then lock
4530 // the free_list_lock and bitmap lock to do a full marking, then
4531 // release these locks; and repeat the cycle. This allows for a
4532 // certain amount of fairness in the sharing of these locks between
4533 // the CMS collector on the one hand, and the VM thread and the
4534 // mutators on the other.
4536 // NOTE: preclean_mod_union_table() and preclean_card_table()
4537 // further below are largely identical; if you need to modify
4538 // one of these methods, please check the other method too.
4540 size_t CMSCollector::preclean_mod_union_table(
4541 ConcurrentMarkSweepGeneration* gen,
4542 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4543 verify_work_stacks_empty();
4544 verify_overflow_empty();
4546 // strategy: starting with the first card, accumulate contiguous
4547 // ranges of dirty cards; clear these cards, then scan the region
4548 // covered by these cards.
4550 // Since all of the MUT is committed ahead, we can just use
4551 // that, in case the generations expand while we are precleaning.
4552 // It might also be fine to just use the committed part of the
4553 // generation, but we might potentially miss cards when the
4554 // generation is rapidly expanding while we are in the midst
4555 // of precleaning.
4556 HeapWord* startAddr = gen->reserved().start();
4557 HeapWord* endAddr = gen->reserved().end();
4559 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4561 size_t numDirtyCards, cumNumDirtyCards;
4562 HeapWord *nextAddr, *lastAddr;
4563 for (cumNumDirtyCards = numDirtyCards = 0,
4564 nextAddr = lastAddr = startAddr;
4565 nextAddr < endAddr;
4566 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4568 ResourceMark rm;
4569 HandleMark hm;
4571 MemRegion dirtyRegion;
4572 {
4573 stopTimer();
4574 CMSTokenSync ts(true);
4575 startTimer();
4576 sample_eden();
4577 // Get dirty region starting at nextOffset (inclusive),
4578 // simultaneously clearing it.
4579 dirtyRegion =
4580 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4581 assert(dirtyRegion.start() >= nextAddr,
4582 "returned region inconsistent?");
4583 }
4584 // Remember where the next search should begin.
4585 // The returned region (if non-empty) is a right open interval,
4586 // so lastOffset is obtained from the right end of that
4587 // interval.
4588 lastAddr = dirtyRegion.end();
4589 // Should do something more transparent and less hacky XXX
4590 numDirtyCards =
4591 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4593 // We'll scan the cards in the dirty region (with periodic
4594 // yields for foreground GC as needed).
4595 if (!dirtyRegion.is_empty()) {
4596 assert(numDirtyCards > 0, "consistency check");
4597 HeapWord* stop_point = NULL;
4598 stopTimer();
4599 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4600 bitMapLock());
4601 startTimer();
4602 {
4603 verify_work_stacks_empty();
4604 verify_overflow_empty();
4605 sample_eden();
4606 stop_point =
4607 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4608 }
4609 if (stop_point != NULL) {
4610 // The careful iteration stopped early either because it found an
4611 // uninitialized object, or because we were in the midst of an
4612 // "abortable preclean", which should now be aborted. Redirty
4613 // the bits corresponding to the partially-scanned or unscanned
4614 // cards. We'll either restart at the next block boundary or
4615 // abort the preclean.
4616 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4617 (_collectorState == AbortablePreclean && should_abort_preclean()),
4618 "Unparsable objects should only be in perm gen.");
4619 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4620 if (should_abort_preclean()) {
4621 break; // out of preclean loop
4622 } else {
4623 // Compute the next address at which preclean should pick up;
4624 // might need bitMapLock in order to read P-bits.
4625 lastAddr = next_card_start_after_block(stop_point);
4626 }
4627 }
4628 } else {
4629 assert(lastAddr == endAddr, "consistency check");
4630 assert(numDirtyCards == 0, "consistency check");
4631 break;
4632 }
4633 }
4634 verify_work_stacks_empty();
4635 verify_overflow_empty();
4636 return cumNumDirtyCards;
4637 }
4639 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4640 // below are largely identical; if you need to modify
4641 // one of these methods, please check the other method too.
4643 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4644 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4645 // strategy: it's similar to precleamModUnionTable above, in that
4646 // we accumulate contiguous ranges of dirty cards, mark these cards
4647 // precleaned, then scan the region covered by these cards.
4648 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4649 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4651 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4653 size_t numDirtyCards, cumNumDirtyCards;
4654 HeapWord *lastAddr, *nextAddr;
4656 for (cumNumDirtyCards = numDirtyCards = 0,
4657 nextAddr = lastAddr = startAddr;
4658 nextAddr < endAddr;
4659 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4661 ResourceMark rm;
4662 HandleMark hm;
4664 MemRegion dirtyRegion;
4665 {
4666 // See comments in "Precleaning notes" above on why we
4667 // do this locking. XXX Could the locking overheads be
4668 // too high when dirty cards are sparse? [I don't think so.]
4669 stopTimer();
4670 CMSTokenSync x(true); // is cms thread
4671 startTimer();
4672 sample_eden();
4673 // Get and clear dirty region from card table
4674 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4675 MemRegion(nextAddr, endAddr),
4676 true,
4677 CardTableModRefBS::precleaned_card_val());
4679 assert(dirtyRegion.start() >= nextAddr,
4680 "returned region inconsistent?");
4681 }
4682 lastAddr = dirtyRegion.end();
4683 numDirtyCards =
4684 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4686 if (!dirtyRegion.is_empty()) {
4687 stopTimer();
4688 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4689 startTimer();
4690 sample_eden();
4691 verify_work_stacks_empty();
4692 verify_overflow_empty();
4693 HeapWord* stop_point =
4694 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4695 if (stop_point != NULL) {
4696 // The careful iteration stopped early because it found an
4697 // uninitialized object. Redirty the bits corresponding to the
4698 // partially-scanned or unscanned cards, and start again at the
4699 // next block boundary.
4700 assert(CMSPermGenPrecleaningEnabled ||
4701 (_collectorState == AbortablePreclean && should_abort_preclean()),
4702 "Unparsable objects should only be in perm gen.");
4703 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4704 if (should_abort_preclean()) {
4705 break; // out of preclean loop
4706 } else {
4707 // Compute the next address at which preclean should pick up.
4708 lastAddr = next_card_start_after_block(stop_point);
4709 }
4710 }
4711 } else {
4712 break;
4713 }
4714 }
4715 verify_work_stacks_empty();
4716 verify_overflow_empty();
4717 return cumNumDirtyCards;
4718 }
4720 void CMSCollector::checkpointRootsFinal(bool asynch,
4721 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4722 assert(_collectorState == FinalMarking, "incorrect state transition?");
4723 check_correct_thread_executing();
4724 // world is stopped at this checkpoint
4725 assert(SafepointSynchronize::is_at_safepoint(),
4726 "world should be stopped");
4727 verify_work_stacks_empty();
4728 verify_overflow_empty();
4730 SpecializationStats::clear();
4731 if (PrintGCDetails) {
4732 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4733 _young_gen->used() / K,
4734 _young_gen->capacity() / K);
4735 }
4736 if (asynch) {
4737 if (CMSScavengeBeforeRemark) {
4738 GenCollectedHeap* gch = GenCollectedHeap::heap();
4739 // Temporarily set flag to false, GCH->do_collection will
4740 // expect it to be false and set to true
4741 FlagSetting fl(gch->_is_gc_active, false);
4742 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4743 PrintGCDetails && Verbose, true, gclog_or_tty);)
4744 int level = _cmsGen->level() - 1;
4745 if (level >= 0) {
4746 gch->do_collection(true, // full (i.e. force, see below)
4747 false, // !clear_all_soft_refs
4748 0, // size
4749 false, // is_tlab
4750 level // max_level
4751 );
4752 }
4753 }
4754 FreelistLocker x(this);
4755 MutexLockerEx y(bitMapLock(),
4756 Mutex::_no_safepoint_check_flag);
4757 assert(!init_mark_was_synchronous, "but that's impossible!");
4758 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4759 } else {
4760 // already have all the locks
4761 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4762 init_mark_was_synchronous);
4763 }
4764 verify_work_stacks_empty();
4765 verify_overflow_empty();
4766 SpecializationStats::print();
4767 }
4769 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4770 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4772 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4774 assert(haveFreelistLocks(), "must have free list locks");
4775 assert_lock_strong(bitMapLock());
4777 if (UseAdaptiveSizePolicy) {
4778 size_policy()->checkpoint_roots_final_begin();
4779 }
4781 ResourceMark rm;
4782 HandleMark hm;
4784 GenCollectedHeap* gch = GenCollectedHeap::heap();
4786 if (should_unload_classes()) {
4787 CodeCache::gc_prologue();
4788 }
4789 assert(haveFreelistLocks(), "must have free list locks");
4790 assert_lock_strong(bitMapLock());
4792 if (!init_mark_was_synchronous) {
4793 // We might assume that we need not fill TLAB's when
4794 // CMSScavengeBeforeRemark is set, because we may have just done
4795 // a scavenge which would have filled all TLAB's -- and besides
4796 // Eden would be empty. This however may not always be the case --
4797 // for instance although we asked for a scavenge, it may not have
4798 // happened because of a JNI critical section. We probably need
4799 // a policy for deciding whether we can in that case wait until
4800 // the critical section releases and then do the remark following
4801 // the scavenge, and skip it here. In the absence of that policy,
4802 // or of an indication of whether the scavenge did indeed occur,
4803 // we cannot rely on TLAB's having been filled and must do
4804 // so here just in case a scavenge did not happen.
4805 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4806 // Update the saved marks which may affect the root scans.
4807 gch->save_marks();
4809 {
4810 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4812 // Note on the role of the mod union table:
4813 // Since the marker in "markFromRoots" marks concurrently with
4814 // mutators, it is possible for some reachable objects not to have been
4815 // scanned. For instance, an only reference to an object A was
4816 // placed in object B after the marker scanned B. Unless B is rescanned,
4817 // A would be collected. Such updates to references in marked objects
4818 // are detected via the mod union table which is the set of all cards
4819 // dirtied since the first checkpoint in this GC cycle and prior to
4820 // the most recent young generation GC, minus those cleaned up by the
4821 // concurrent precleaning.
4822 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) {
4823 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4824 do_remark_parallel();
4825 } else {
4826 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4827 gclog_or_tty);
4828 do_remark_non_parallel();
4829 }
4830 }
4831 } else {
4832 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4833 // The initial mark was stop-world, so there's no rescanning to
4834 // do; go straight on to the next step below.
4835 }
4836 verify_work_stacks_empty();
4837 verify_overflow_empty();
4839 {
4840 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4841 refProcessingWork(asynch, clear_all_soft_refs);
4842 }
4843 verify_work_stacks_empty();
4844 verify_overflow_empty();
4846 if (should_unload_classes()) {
4847 CodeCache::gc_epilogue();
4848 }
4850 // If we encountered any (marking stack / work queue) overflow
4851 // events during the current CMS cycle, take appropriate
4852 // remedial measures, where possible, so as to try and avoid
4853 // recurrence of that condition.
4854 assert(_markStack.isEmpty(), "No grey objects");
4855 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4856 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4857 if (ser_ovflw > 0) {
4858 if (PrintCMSStatistics != 0) {
4859 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4860 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4861 ", kac_preclean="SIZE_FORMAT")",
4862 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4863 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4864 }
4865 _markStack.expand();
4866 _ser_pmc_remark_ovflw = 0;
4867 _ser_pmc_preclean_ovflw = 0;
4868 _ser_kac_preclean_ovflw = 0;
4869 _ser_kac_ovflw = 0;
4870 }
4871 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4872 if (PrintCMSStatistics != 0) {
4873 gclog_or_tty->print_cr("Work queue overflow (benign) "
4874 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4875 _par_pmc_remark_ovflw, _par_kac_ovflw);
4876 }
4877 _par_pmc_remark_ovflw = 0;
4878 _par_kac_ovflw = 0;
4879 }
4880 if (PrintCMSStatistics != 0) {
4881 if (_markStack._hit_limit > 0) {
4882 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4883 _markStack._hit_limit);
4884 }
4885 if (_markStack._failed_double > 0) {
4886 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4887 " current capacity "SIZE_FORMAT,
4888 _markStack._failed_double,
4889 _markStack.capacity());
4890 }
4891 }
4892 _markStack._hit_limit = 0;
4893 _markStack._failed_double = 0;
4895 if ((VerifyAfterGC || VerifyDuringGC) &&
4896 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4897 verify_after_remark();
4898 }
4900 // Change under the freelistLocks.
4901 _collectorState = Sweeping;
4902 // Call isAllClear() under bitMapLock
4903 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
4904 " final marking");
4905 if (UseAdaptiveSizePolicy) {
4906 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
4907 }
4908 }
4910 // Parallel remark task
4911 class CMSParRemarkTask: public AbstractGangTask {
4912 CMSCollector* _collector;
4913 WorkGang* _workers;
4914 int _n_workers;
4915 CompactibleFreeListSpace* _cms_space;
4916 CompactibleFreeListSpace* _perm_space;
4918 // The per-thread work queues, available here for stealing.
4919 OopTaskQueueSet* _task_queues;
4920 ParallelTaskTerminator _term;
4922 public:
4923 CMSParRemarkTask(CMSCollector* collector,
4924 CompactibleFreeListSpace* cms_space,
4925 CompactibleFreeListSpace* perm_space,
4926 int n_workers, WorkGang* workers,
4927 OopTaskQueueSet* task_queues):
4928 AbstractGangTask("Rescan roots and grey objects in parallel"),
4929 _collector(collector),
4930 _cms_space(cms_space), _perm_space(perm_space),
4931 _n_workers(n_workers),
4932 _workers(workers),
4933 _task_queues(task_queues),
4934 _term(workers->total_workers(), task_queues) { }
4936 OopTaskQueueSet* task_queues() { return _task_queues; }
4938 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4940 ParallelTaskTerminator* terminator() { return &_term; }
4942 void work(int i);
4944 private:
4945 // Work method in support of parallel rescan ... of young gen spaces
4946 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
4947 ContiguousSpace* space,
4948 HeapWord** chunk_array, size_t chunk_top);
4950 // ... of dirty cards in old space
4951 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4952 Par_MarkRefsIntoAndScanClosure* cl);
4954 // ... work stealing for the above
4955 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
4956 };
4958 void CMSParRemarkTask::work(int i) {
4959 elapsedTimer _timer;
4960 ResourceMark rm;
4961 HandleMark hm;
4963 // ---------- rescan from roots --------------
4964 _timer.start();
4965 GenCollectedHeap* gch = GenCollectedHeap::heap();
4966 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4967 _collector->_span, _collector->ref_processor(),
4968 &(_collector->_markBitMap),
4969 work_queue(i), &(_collector->_revisitStack));
4971 // Rescan young gen roots first since these are likely
4972 // coarsely partitioned and may, on that account, constitute
4973 // the critical path; thus, it's best to start off that
4974 // work first.
4975 // ---------- young gen roots --------------
4976 {
4977 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
4978 EdenSpace* eden_space = dng->eden();
4979 ContiguousSpace* from_space = dng->from();
4980 ContiguousSpace* to_space = dng->to();
4982 HeapWord** eca = _collector->_eden_chunk_array;
4983 size_t ect = _collector->_eden_chunk_index;
4984 HeapWord** sca = _collector->_survivor_chunk_array;
4985 size_t sct = _collector->_survivor_chunk_index;
4987 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4988 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4990 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0);
4991 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct);
4992 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect);
4994 _timer.stop();
4995 if (PrintCMSStatistics != 0) {
4996 gclog_or_tty->print_cr(
4997 "Finished young gen rescan work in %dth thread: %3.3f sec",
4998 i, _timer.seconds());
4999 }
5000 }
5002 // ---------- remaining roots --------------
5003 _timer.reset();
5004 _timer.start();
5005 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5006 false, // yg was scanned above
5007 true, // collecting perm gen
5008 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5009 NULL, &par_mrias_cl);
5010 _timer.stop();
5011 if (PrintCMSStatistics != 0) {
5012 gclog_or_tty->print_cr(
5013 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5014 i, _timer.seconds());
5015 }
5017 // ---------- rescan dirty cards ------------
5018 _timer.reset();
5019 _timer.start();
5021 // Do the rescan tasks for each of the two spaces
5022 // (cms_space and perm_space) in turn.
5023 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl);
5024 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl);
5025 _timer.stop();
5026 if (PrintCMSStatistics != 0) {
5027 gclog_or_tty->print_cr(
5028 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5029 i, _timer.seconds());
5030 }
5032 // ---------- steal work from other threads ...
5033 // ---------- ... and drain overflow list.
5034 _timer.reset();
5035 _timer.start();
5036 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i));
5037 _timer.stop();
5038 if (PrintCMSStatistics != 0) {
5039 gclog_or_tty->print_cr(
5040 "Finished work stealing in %dth thread: %3.3f sec",
5041 i, _timer.seconds());
5042 }
5043 }
5045 void
5046 CMSParRemarkTask::do_young_space_rescan(int i,
5047 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5048 HeapWord** chunk_array, size_t chunk_top) {
5049 // Until all tasks completed:
5050 // . claim an unclaimed task
5051 // . compute region boundaries corresponding to task claimed
5052 // using chunk_array
5053 // . par_oop_iterate(cl) over that region
5055 ResourceMark rm;
5056 HandleMark hm;
5058 SequentialSubTasksDone* pst = space->par_seq_tasks();
5059 assert(pst->valid(), "Uninitialized use?");
5061 int nth_task = 0;
5062 int n_tasks = pst->n_tasks();
5064 HeapWord *start, *end;
5065 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5066 // We claimed task # nth_task; compute its boundaries.
5067 if (chunk_top == 0) { // no samples were taken
5068 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5069 start = space->bottom();
5070 end = space->top();
5071 } else if (nth_task == 0) {
5072 start = space->bottom();
5073 end = chunk_array[nth_task];
5074 } else if (nth_task < (jint)chunk_top) {
5075 assert(nth_task >= 1, "Control point invariant");
5076 start = chunk_array[nth_task - 1];
5077 end = chunk_array[nth_task];
5078 } else {
5079 assert(nth_task == (jint)chunk_top, "Control point invariant");
5080 start = chunk_array[chunk_top - 1];
5081 end = space->top();
5082 }
5083 MemRegion mr(start, end);
5084 // Verify that mr is in space
5085 assert(mr.is_empty() || space->used_region().contains(mr),
5086 "Should be in space");
5087 // Verify that "start" is an object boundary
5088 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5089 "Should be an oop");
5090 space->par_oop_iterate(mr, cl);
5091 }
5092 pst->all_tasks_completed();
5093 }
5095 void
5096 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5097 CompactibleFreeListSpace* sp, int i,
5098 Par_MarkRefsIntoAndScanClosure* cl) {
5099 // Until all tasks completed:
5100 // . claim an unclaimed task
5101 // . compute region boundaries corresponding to task claimed
5102 // . transfer dirty bits ct->mut for that region
5103 // . apply rescanclosure to dirty mut bits for that region
5105 ResourceMark rm;
5106 HandleMark hm;
5108 OopTaskQueue* work_q = work_queue(i);
5109 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5110 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5111 // CAUTION: This closure has state that persists across calls to
5112 // the work method dirty_range_iterate_clear() in that it has
5113 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5114 // use of that state in the imbedded UpwardsObjectClosure instance
5115 // assumes that the cards are always iterated (even if in parallel
5116 // by several threads) in monotonically increasing order per each
5117 // thread. This is true of the implementation below which picks
5118 // card ranges (chunks) in monotonically increasing order globally
5119 // and, a-fortiori, in monotonically increasing order per thread
5120 // (the latter order being a subsequence of the former).
5121 // If the work code below is ever reorganized into a more chaotic
5122 // work-partitioning form than the current "sequential tasks"
5123 // paradigm, the use of that persistent state will have to be
5124 // revisited and modified appropriately. See also related
5125 // bug 4756801 work on which should examine this code to make
5126 // sure that the changes there do not run counter to the
5127 // assumptions made here and necessary for correctness and
5128 // efficiency. Note also that this code might yield inefficient
5129 // behaviour in the case of very large objects that span one or
5130 // more work chunks. Such objects would potentially be scanned
5131 // several times redundantly. Work on 4756801 should try and
5132 // address that performance anomaly if at all possible. XXX
5133 MemRegion full_span = _collector->_span;
5134 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5135 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5136 MarkFromDirtyCardsClosure
5137 greyRescanClosure(_collector, full_span, // entire span of interest
5138 sp, bm, work_q, rs, cl);
5140 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5141 assert(pst->valid(), "Uninitialized use?");
5142 int nth_task = 0;
5143 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5144 MemRegion span = sp->used_region();
5145 HeapWord* start_addr = span.start();
5146 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5147 alignment);
5148 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5149 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5150 start_addr, "Check alignment");
5151 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5152 chunk_size, "Check alignment");
5154 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5155 // Having claimed the nth_task, compute corresponding mem-region,
5156 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5157 // The alignment restriction ensures that we do not need any
5158 // synchronization with other gang-workers while setting or
5159 // clearing bits in thus chunk of the MUT.
5160 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5161 start_addr + (nth_task+1)*chunk_size);
5162 // The last chunk's end might be way beyond end of the
5163 // used region. In that case pull back appropriately.
5164 if (this_span.end() > end_addr) {
5165 this_span.set_end(end_addr);
5166 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5167 }
5168 // Iterate over the dirty cards covering this chunk, marking them
5169 // precleaned, and setting the corresponding bits in the mod union
5170 // table. Since we have been careful to partition at Card and MUT-word
5171 // boundaries no synchronization is needed between parallel threads.
5172 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5173 &modUnionClosure);
5175 // Having transferred these marks into the modUnionTable,
5176 // rescan the marked objects on the dirty cards in the modUnionTable.
5177 // Even if this is at a synchronous collection, the initial marking
5178 // may have been done during an asynchronous collection so there
5179 // may be dirty bits in the mod-union table.
5180 _collector->_modUnionTable.dirty_range_iterate_clear(
5181 this_span, &greyRescanClosure);
5182 _collector->_modUnionTable.verifyNoOneBitsInRange(
5183 this_span.start(),
5184 this_span.end());
5185 }
5186 pst->all_tasks_completed(); // declare that i am done
5187 }
5189 // . see if we can share work_queues with ParNew? XXX
5190 void
5191 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5192 int* seed) {
5193 OopTaskQueue* work_q = work_queue(i);
5194 NOT_PRODUCT(int num_steals = 0;)
5195 oop obj_to_scan;
5196 CMSBitMap* bm = &(_collector->_markBitMap);
5197 size_t num_from_overflow_list =
5198 MIN2((size_t)work_q->max_elems()/4,
5199 (size_t)ParGCDesiredObjsFromOverflowList);
5201 while (true) {
5202 // Completely finish any left over work from (an) earlier round(s)
5203 cl->trim_queue(0);
5204 // Now check if there's any work in the overflow list
5205 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5206 work_q)) {
5207 // found something in global overflow list;
5208 // not yet ready to go stealing work from others.
5209 // We'd like to assert(work_q->size() != 0, ...)
5210 // because we just took work from the overflow list,
5211 // but of course we can't since all of that could have
5212 // been already stolen from us.
5213 // "He giveth and He taketh away."
5214 continue;
5215 }
5216 // Verify that we have no work before we resort to stealing
5217 assert(work_q->size() == 0, "Have work, shouldn't steal");
5218 // Try to steal from other queues that have work
5219 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5220 NOT_PRODUCT(num_steals++;)
5221 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5222 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5223 // Do scanning work
5224 obj_to_scan->oop_iterate(cl);
5225 // Loop around, finish this work, and try to steal some more
5226 } else if (terminator()->offer_termination()) {
5227 break; // nirvana from the infinite cycle
5228 }
5229 }
5230 NOT_PRODUCT(
5231 if (PrintCMSStatistics != 0) {
5232 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5233 }
5234 )
5235 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5236 "Else our work is not yet done");
5237 }
5239 // Return a thread-local PLAB recording array, as appropriate.
5240 void* CMSCollector::get_data_recorder(int thr_num) {
5241 if (_survivor_plab_array != NULL &&
5242 (CMSPLABRecordAlways ||
5243 (_collectorState > Marking && _collectorState < FinalMarking))) {
5244 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5245 ChunkArray* ca = &_survivor_plab_array[thr_num];
5246 ca->reset(); // clear it so that fresh data is recorded
5247 return (void*) ca;
5248 } else {
5249 return NULL;
5250 }
5251 }
5253 // Reset all the thread-local PLAB recording arrays
5254 void CMSCollector::reset_survivor_plab_arrays() {
5255 for (uint i = 0; i < ParallelGCThreads; i++) {
5256 _survivor_plab_array[i].reset();
5257 }
5258 }
5260 // Merge the per-thread plab arrays into the global survivor chunk
5261 // array which will provide the partitioning of the survivor space
5262 // for CMS rescan.
5263 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) {
5264 assert(_survivor_plab_array != NULL, "Error");
5265 assert(_survivor_chunk_array != NULL, "Error");
5266 assert(_collectorState == FinalMarking, "Error");
5267 for (uint j = 0; j < ParallelGCThreads; j++) {
5268 _cursor[j] = 0;
5269 }
5270 HeapWord* top = surv->top();
5271 size_t i;
5272 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5273 HeapWord* min_val = top; // Higher than any PLAB address
5274 uint min_tid = 0; // position of min_val this round
5275 for (uint j = 0; j < ParallelGCThreads; j++) {
5276 ChunkArray* cur_sca = &_survivor_plab_array[j];
5277 if (_cursor[j] == cur_sca->end()) {
5278 continue;
5279 }
5280 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5281 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5282 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5283 if (cur_val < min_val) {
5284 min_tid = j;
5285 min_val = cur_val;
5286 } else {
5287 assert(cur_val < top, "All recorded addresses should be less");
5288 }
5289 }
5290 // At this point min_val and min_tid are respectively
5291 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5292 // and the thread (j) that witnesses that address.
5293 // We record this address in the _survivor_chunk_array[i]
5294 // and increment _cursor[min_tid] prior to the next round i.
5295 if (min_val == top) {
5296 break;
5297 }
5298 _survivor_chunk_array[i] = min_val;
5299 _cursor[min_tid]++;
5300 }
5301 // We are all done; record the size of the _survivor_chunk_array
5302 _survivor_chunk_index = i; // exclusive: [0, i)
5303 if (PrintCMSStatistics > 0) {
5304 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5305 }
5306 // Verify that we used up all the recorded entries
5307 #ifdef ASSERT
5308 size_t total = 0;
5309 for (uint j = 0; j < ParallelGCThreads; j++) {
5310 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5311 total += _cursor[j];
5312 }
5313 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5314 // Check that the merged array is in sorted order
5315 if (total > 0) {
5316 for (size_t i = 0; i < total - 1; i++) {
5317 if (PrintCMSStatistics > 0) {
5318 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5319 i, _survivor_chunk_array[i]);
5320 }
5321 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5322 "Not sorted");
5323 }
5324 }
5325 #endif // ASSERT
5326 }
5328 // Set up the space's par_seq_tasks structure for work claiming
5329 // for parallel rescan of young gen.
5330 // See ParRescanTask where this is currently used.
5331 void
5332 CMSCollector::
5333 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5334 assert(n_threads > 0, "Unexpected n_threads argument");
5335 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5337 // Eden space
5338 {
5339 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5340 assert(!pst->valid(), "Clobbering existing data?");
5341 // Each valid entry in [0, _eden_chunk_index) represents a task.
5342 size_t n_tasks = _eden_chunk_index + 1;
5343 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5344 pst->set_par_threads(n_threads);
5345 pst->set_n_tasks((int)n_tasks);
5346 }
5348 // Merge the survivor plab arrays into _survivor_chunk_array
5349 if (_survivor_plab_array != NULL) {
5350 merge_survivor_plab_arrays(dng->from());
5351 } else {
5352 assert(_survivor_chunk_index == 0, "Error");
5353 }
5355 // To space
5356 {
5357 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5358 assert(!pst->valid(), "Clobbering existing data?");
5359 pst->set_par_threads(n_threads);
5360 pst->set_n_tasks(1);
5361 assert(pst->valid(), "Error");
5362 }
5364 // From space
5365 {
5366 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5367 assert(!pst->valid(), "Clobbering existing data?");
5368 size_t n_tasks = _survivor_chunk_index + 1;
5369 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5370 pst->set_par_threads(n_threads);
5371 pst->set_n_tasks((int)n_tasks);
5372 assert(pst->valid(), "Error");
5373 }
5374 }
5376 // Parallel version of remark
5377 void CMSCollector::do_remark_parallel() {
5378 GenCollectedHeap* gch = GenCollectedHeap::heap();
5379 WorkGang* workers = gch->workers();
5380 assert(workers != NULL, "Need parallel worker threads.");
5381 int n_workers = workers->total_workers();
5382 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5383 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5385 CMSParRemarkTask tsk(this,
5386 cms_space, perm_space,
5387 n_workers, workers, task_queues());
5389 // Set up for parallel process_strong_roots work.
5390 gch->set_par_threads(n_workers);
5391 gch->change_strong_roots_parity();
5392 // We won't be iterating over the cards in the card table updating
5393 // the younger_gen cards, so we shouldn't call the following else
5394 // the verification code as well as subsequent younger_refs_iterate
5395 // code would get confused. XXX
5396 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5398 // The young gen rescan work will not be done as part of
5399 // process_strong_roots (which currently doesn't knw how to
5400 // parallelize such a scan), but rather will be broken up into
5401 // a set of parallel tasks (via the sampling that the [abortable]
5402 // preclean phase did of EdenSpace, plus the [two] tasks of
5403 // scanning the [two] survivor spaces. Further fine-grain
5404 // parallelization of the scanning of the survivor spaces
5405 // themselves, and of precleaning of the younger gen itself
5406 // is deferred to the future.
5407 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5409 // The dirty card rescan work is broken up into a "sequence"
5410 // of parallel tasks (per constituent space) that are dynamically
5411 // claimed by the parallel threads.
5412 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5413 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5415 // It turns out that even when we're using 1 thread, doing the work in a
5416 // separate thread causes wide variance in run times. We can't help this
5417 // in the multi-threaded case, but we special-case n=1 here to get
5418 // repeatable measurements of the 1-thread overhead of the parallel code.
5419 if (n_workers > 1) {
5420 // Make refs discovery MT-safe
5421 ReferenceProcessorMTMutator mt(ref_processor(), true);
5422 workers->run_task(&tsk);
5423 } else {
5424 tsk.work(0);
5425 }
5426 gch->set_par_threads(0); // 0 ==> non-parallel.
5427 // restore, single-threaded for now, any preserved marks
5428 // as a result of work_q overflow
5429 restore_preserved_marks_if_any();
5430 }
5432 // Non-parallel version of remark
5433 void CMSCollector::do_remark_non_parallel() {
5434 ResourceMark rm;
5435 HandleMark hm;
5436 GenCollectedHeap* gch = GenCollectedHeap::heap();
5437 MarkRefsIntoAndScanClosure
5438 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5439 &_markStack, &_revisitStack, this,
5440 false /* should_yield */, false /* not precleaning */);
5441 MarkFromDirtyCardsClosure
5442 markFromDirtyCardsClosure(this, _span,
5443 NULL, // space is set further below
5444 &_markBitMap, &_markStack, &_revisitStack,
5445 &mrias_cl);
5446 {
5447 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5448 // Iterate over the dirty cards, setting the corresponding bits in the
5449 // mod union table.
5450 {
5451 ModUnionClosure modUnionClosure(&_modUnionTable);
5452 _ct->ct_bs()->dirty_card_iterate(
5453 _cmsGen->used_region(),
5454 &modUnionClosure);
5455 _ct->ct_bs()->dirty_card_iterate(
5456 _permGen->used_region(),
5457 &modUnionClosure);
5458 }
5459 // Having transferred these marks into the modUnionTable, we just need
5460 // to rescan the marked objects on the dirty cards in the modUnionTable.
5461 // The initial marking may have been done during an asynchronous
5462 // collection so there may be dirty bits in the mod-union table.
5463 const int alignment =
5464 CardTableModRefBS::card_size * BitsPerWord;
5465 {
5466 // ... First handle dirty cards in CMS gen
5467 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5468 MemRegion ur = _cmsGen->used_region();
5469 HeapWord* lb = ur.start();
5470 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5471 MemRegion cms_span(lb, ub);
5472 _modUnionTable.dirty_range_iterate_clear(cms_span,
5473 &markFromDirtyCardsClosure);
5474 verify_work_stacks_empty();
5475 if (PrintCMSStatistics != 0) {
5476 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5477 markFromDirtyCardsClosure.num_dirty_cards());
5478 }
5479 }
5480 {
5481 // .. and then repeat for dirty cards in perm gen
5482 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5483 MemRegion ur = _permGen->used_region();
5484 HeapWord* lb = ur.start();
5485 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5486 MemRegion perm_span(lb, ub);
5487 _modUnionTable.dirty_range_iterate_clear(perm_span,
5488 &markFromDirtyCardsClosure);
5489 verify_work_stacks_empty();
5490 if (PrintCMSStatistics != 0) {
5491 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5492 markFromDirtyCardsClosure.num_dirty_cards());
5493 }
5494 }
5495 }
5496 if (VerifyDuringGC &&
5497 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5498 HandleMark hm; // Discard invalid handles created during verification
5499 Universe::verify(true);
5500 }
5501 {
5502 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5504 verify_work_stacks_empty();
5506 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5507 gch->gen_process_strong_roots(_cmsGen->level(),
5508 true, // younger gens as roots
5509 true, // collecting perm gen
5510 SharedHeap::ScanningOption(roots_scanning_options()),
5511 NULL, &mrias_cl);
5512 }
5513 verify_work_stacks_empty();
5514 // Restore evacuated mark words, if any, used for overflow list links
5515 if (!CMSOverflowEarlyRestoration) {
5516 restore_preserved_marks_if_any();
5517 }
5518 verify_overflow_empty();
5519 }
5521 ////////////////////////////////////////////////////////
5522 // Parallel Reference Processing Task Proxy Class
5523 ////////////////////////////////////////////////////////
5524 class CMSRefProcTaskProxy: public AbstractGangTask {
5525 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5526 CMSCollector* _collector;
5527 CMSBitMap* _mark_bit_map;
5528 const MemRegion _span;
5529 OopTaskQueueSet* _task_queues;
5530 ParallelTaskTerminator _term;
5531 ProcessTask& _task;
5533 public:
5534 CMSRefProcTaskProxy(ProcessTask& task,
5535 CMSCollector* collector,
5536 const MemRegion& span,
5537 CMSBitMap* mark_bit_map,
5538 int total_workers,
5539 OopTaskQueueSet* task_queues):
5540 AbstractGangTask("Process referents by policy in parallel"),
5541 _task(task),
5542 _collector(collector), _span(span), _mark_bit_map(mark_bit_map),
5543 _task_queues(task_queues),
5544 _term(total_workers, task_queues)
5545 {
5546 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5547 "Inconsistency in _span");
5548 }
5550 OopTaskQueueSet* task_queues() { return _task_queues; }
5552 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5554 ParallelTaskTerminator* terminator() { return &_term; }
5556 void do_work_steal(int i,
5557 CMSParDrainMarkingStackClosure* drain,
5558 CMSParKeepAliveClosure* keep_alive,
5559 int* seed);
5561 virtual void work(int i);
5562 };
5564 void CMSRefProcTaskProxy::work(int i) {
5565 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5566 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5567 _mark_bit_map, work_queue(i));
5568 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5569 _mark_bit_map, work_queue(i));
5570 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5571 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack);
5572 if (_task.marks_oops_alive()) {
5573 do_work_steal(i, &par_drain_stack, &par_keep_alive,
5574 _collector->hash_seed(i));
5575 }
5576 assert(work_queue(i)->size() == 0, "work_queue should be empty");
5577 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5578 }
5580 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5581 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5582 EnqueueTask& _task;
5584 public:
5585 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5586 : AbstractGangTask("Enqueue reference objects in parallel"),
5587 _task(task)
5588 { }
5590 virtual void work(int i)
5591 {
5592 _task.work(i);
5593 }
5594 };
5596 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5597 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5598 _collector(collector),
5599 _span(span),
5600 _bit_map(bit_map),
5601 _work_queue(work_queue),
5602 _mark_and_push(collector, span, bit_map, work_queue),
5603 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5604 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5605 { }
5607 // . see if we can share work_queues with ParNew? XXX
5608 void CMSRefProcTaskProxy::do_work_steal(int i,
5609 CMSParDrainMarkingStackClosure* drain,
5610 CMSParKeepAliveClosure* keep_alive,
5611 int* seed) {
5612 OopTaskQueue* work_q = work_queue(i);
5613 NOT_PRODUCT(int num_steals = 0;)
5614 oop obj_to_scan;
5615 size_t num_from_overflow_list =
5616 MIN2((size_t)work_q->max_elems()/4,
5617 (size_t)ParGCDesiredObjsFromOverflowList);
5619 while (true) {
5620 // Completely finish any left over work from (an) earlier round(s)
5621 drain->trim_queue(0);
5622 // Now check if there's any work in the overflow list
5623 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5624 work_q)) {
5625 // Found something in global overflow list;
5626 // not yet ready to go stealing work from others.
5627 // We'd like to assert(work_q->size() != 0, ...)
5628 // because we just took work from the overflow list,
5629 // but of course we can't, since all of that might have
5630 // been already stolen from us.
5631 continue;
5632 }
5633 // Verify that we have no work before we resort to stealing
5634 assert(work_q->size() == 0, "Have work, shouldn't steal");
5635 // Try to steal from other queues that have work
5636 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5637 NOT_PRODUCT(num_steals++;)
5638 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5639 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5640 // Do scanning work
5641 obj_to_scan->oop_iterate(keep_alive);
5642 // Loop around, finish this work, and try to steal some more
5643 } else if (terminator()->offer_termination()) {
5644 break; // nirvana from the infinite cycle
5645 }
5646 }
5647 NOT_PRODUCT(
5648 if (PrintCMSStatistics != 0) {
5649 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5650 }
5651 )
5652 }
5654 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5655 {
5656 GenCollectedHeap* gch = GenCollectedHeap::heap();
5657 WorkGang* workers = gch->workers();
5658 assert(workers != NULL, "Need parallel worker threads.");
5659 int n_workers = workers->total_workers();
5660 CMSRefProcTaskProxy rp_task(task, &_collector,
5661 _collector.ref_processor()->span(),
5662 _collector.markBitMap(),
5663 n_workers, _collector.task_queues());
5664 workers->run_task(&rp_task);
5665 }
5667 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5668 {
5670 GenCollectedHeap* gch = GenCollectedHeap::heap();
5671 WorkGang* workers = gch->workers();
5672 assert(workers != NULL, "Need parallel worker threads.");
5673 CMSRefEnqueueTaskProxy enq_task(task);
5674 workers->run_task(&enq_task);
5675 }
5677 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5679 ResourceMark rm;
5680 HandleMark hm;
5682 ReferenceProcessor* rp = ref_processor();
5683 assert(rp->span().equals(_span), "Spans should be equal");
5684 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5685 // Process weak references.
5686 rp->setup_policy(clear_all_soft_refs);
5687 verify_work_stacks_empty();
5689 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5690 &_markStack, false /* !preclean */);
5691 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5692 _span, &_markBitMap, &_markStack,
5693 &cmsKeepAliveClosure, false /* !preclean */);
5694 {
5695 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5696 if (rp->processing_is_mt()) {
5697 CMSRefProcTaskExecutor task_executor(*this);
5698 rp->process_discovered_references(&_is_alive_closure,
5699 &cmsKeepAliveClosure,
5700 &cmsDrainMarkingStackClosure,
5701 &task_executor);
5702 } else {
5703 rp->process_discovered_references(&_is_alive_closure,
5704 &cmsKeepAliveClosure,
5705 &cmsDrainMarkingStackClosure,
5706 NULL);
5707 }
5708 verify_work_stacks_empty();
5709 }
5711 if (should_unload_classes()) {
5712 {
5713 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5715 // Follow SystemDictionary roots and unload classes
5716 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5718 // Follow CodeCache roots and unload any methods marked for unloading
5719 CodeCache::do_unloading(&_is_alive_closure,
5720 &cmsKeepAliveClosure,
5721 purged_class);
5723 cmsDrainMarkingStackClosure.do_void();
5724 verify_work_stacks_empty();
5726 // Update subklass/sibling/implementor links in KlassKlass descendants
5727 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
5728 oop k;
5729 while ((k = _revisitStack.pop()) != NULL) {
5730 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
5731 &_is_alive_closure,
5732 &cmsKeepAliveClosure);
5733 }
5734 assert(!ClassUnloading ||
5735 (_markStack.isEmpty() && overflow_list_is_empty()),
5736 "Should not have found new reachable objects");
5737 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
5738 cmsDrainMarkingStackClosure.do_void();
5739 verify_work_stacks_empty();
5740 }
5742 {
5743 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty);
5744 // Now clean up stale oops in SymbolTable and StringTable
5745 SymbolTable::unlink(&_is_alive_closure);
5746 StringTable::unlink(&_is_alive_closure);
5747 }
5748 }
5750 verify_work_stacks_empty();
5751 // Restore any preserved marks as a result of mark stack or
5752 // work queue overflow
5753 restore_preserved_marks_if_any(); // done single-threaded for now
5755 rp->set_enqueuing_is_done(true);
5756 if (rp->processing_is_mt()) {
5757 CMSRefProcTaskExecutor task_executor(*this);
5758 rp->enqueue_discovered_references(&task_executor);
5759 } else {
5760 rp->enqueue_discovered_references(NULL);
5761 }
5762 rp->verify_no_references_recorded();
5763 assert(!rp->discovery_enabled(), "should have been disabled");
5765 // JVMTI object tagging is based on JNI weak refs. If any of these
5766 // refs were cleared then JVMTI needs to update its maps and
5767 // maybe post ObjectFrees to agents.
5768 JvmtiExport::cms_ref_processing_epilogue();
5769 }
5771 #ifndef PRODUCT
5772 void CMSCollector::check_correct_thread_executing() {
5773 Thread* t = Thread::current();
5774 // Only the VM thread or the CMS thread should be here.
5775 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5776 "Unexpected thread type");
5777 // If this is the vm thread, the foreground process
5778 // should not be waiting. Note that _foregroundGCIsActive is
5779 // true while the foreground collector is waiting.
5780 if (_foregroundGCShouldWait) {
5781 // We cannot be the VM thread
5782 assert(t->is_ConcurrentGC_thread(),
5783 "Should be CMS thread");
5784 } else {
5785 // We can be the CMS thread only if we are in a stop-world
5786 // phase of CMS collection.
5787 if (t->is_ConcurrentGC_thread()) {
5788 assert(_collectorState == InitialMarking ||
5789 _collectorState == FinalMarking,
5790 "Should be a stop-world phase");
5791 // The CMS thread should be holding the CMS_token.
5792 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5793 "Potential interference with concurrently "
5794 "executing VM thread");
5795 }
5796 }
5797 }
5798 #endif
5800 void CMSCollector::sweep(bool asynch) {
5801 assert(_collectorState == Sweeping, "just checking");
5802 check_correct_thread_executing();
5803 verify_work_stacks_empty();
5804 verify_overflow_empty();
5805 incrementSweepCount();
5806 _sweep_timer.stop();
5807 _sweep_estimate.sample(_sweep_timer.seconds());
5808 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
5810 // PermGen verification support: If perm gen sweeping is disabled in
5811 // this cycle, we preserve the perm gen object "deadness" information
5812 // in the perm_gen_verify_bit_map. In order to do that we traverse
5813 // all blocks in perm gen and mark all dead objects.
5814 if (verifying() && !should_unload_classes()) {
5815 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
5816 "Should have already been allocated");
5817 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
5818 markBitMap(), perm_gen_verify_bit_map());
5819 if (asynch) {
5820 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5821 bitMapLock());
5822 _permGen->cmsSpace()->blk_iterate(&mdo);
5823 } else {
5824 // In the case of synchronous sweep, we already have
5825 // the requisite locks/tokens.
5826 _permGen->cmsSpace()->blk_iterate(&mdo);
5827 }
5828 }
5830 if (asynch) {
5831 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
5832 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
5833 // First sweep the old gen then the perm gen
5834 {
5835 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5836 bitMapLock());
5837 sweepWork(_cmsGen, asynch);
5838 }
5840 // Now repeat for perm gen
5841 if (should_unload_classes()) {
5842 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
5843 bitMapLock());
5844 sweepWork(_permGen, asynch);
5845 }
5847 // Update Universe::_heap_*_at_gc figures.
5848 // We need all the free list locks to make the abstract state
5849 // transition from Sweeping to Resetting. See detailed note
5850 // further below.
5851 {
5852 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5853 _permGen->freelistLock());
5854 // Update heap occupancy information which is used as
5855 // input to soft ref clearing policy at the next gc.
5856 Universe::update_heap_info_at_gc();
5857 _collectorState = Resizing;
5858 }
5859 } else {
5860 // already have needed locks
5861 sweepWork(_cmsGen, asynch);
5863 if (should_unload_classes()) {
5864 sweepWork(_permGen, asynch);
5865 }
5866 // Update heap occupancy information which is used as
5867 // input to soft ref clearing policy at the next gc.
5868 Universe::update_heap_info_at_gc();
5869 _collectorState = Resizing;
5870 }
5871 verify_work_stacks_empty();
5872 verify_overflow_empty();
5874 _sweep_timer.reset();
5875 _sweep_timer.start();
5877 update_time_of_last_gc(os::javaTimeMillis());
5879 // NOTE on abstract state transitions:
5880 // Mutators allocate-live and/or mark the mod-union table dirty
5881 // based on the state of the collection. The former is done in
5882 // the interval [Marking, Sweeping] and the latter in the interval
5883 // [Marking, Sweeping). Thus the transitions into the Marking state
5884 // and out of the Sweeping state must be synchronously visible
5885 // globally to the mutators.
5886 // The transition into the Marking state happens with the world
5887 // stopped so the mutators will globally see it. Sweeping is
5888 // done asynchronously by the background collector so the transition
5889 // from the Sweeping state to the Resizing state must be done
5890 // under the freelistLock (as is the check for whether to
5891 // allocate-live and whether to dirty the mod-union table).
5892 assert(_collectorState == Resizing, "Change of collector state to"
5893 " Resizing must be done under the freelistLocks (plural)");
5895 // Now that sweeping has been completed, if the GCH's
5896 // incremental_collection_will_fail flag is set, clear it,
5897 // thus inviting a younger gen collection to promote into
5898 // this generation. If such a promotion may still fail,
5899 // the flag will be set again when a young collection is
5900 // attempted.
5901 // I think the incremental_collection_will_fail flag's use
5902 // is specific to a 2 generation collection policy, so i'll
5903 // assert that that's the configuration we are operating within.
5904 // The use of the flag can and should be generalized appropriately
5905 // in the future to deal with a general n-generation system.
5907 GenCollectedHeap* gch = GenCollectedHeap::heap();
5908 assert(gch->collector_policy()->is_two_generation_policy(),
5909 "Resetting of incremental_collection_will_fail flag"
5910 " may be incorrect otherwise");
5911 gch->clear_incremental_collection_will_fail();
5912 gch->update_full_collections_completed(_collection_count_start);
5913 }
5915 // FIX ME!!! Looks like this belongs in CFLSpace, with
5916 // CMSGen merely delegating to it.
5917 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5918 double nearLargestPercent = 0.999;
5919 HeapWord* minAddr = _cmsSpace->bottom();
5920 HeapWord* largestAddr =
5921 (HeapWord*) _cmsSpace->dictionary()->findLargestDict();
5922 if (largestAddr == 0) {
5923 // The dictionary appears to be empty. In this case
5924 // try to coalesce at the end of the heap.
5925 largestAddr = _cmsSpace->end();
5926 }
5927 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5928 size_t nearLargestOffset =
5929 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5930 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5931 }
5933 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5934 return addr >= _cmsSpace->nearLargestChunk();
5935 }
5937 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5938 return _cmsSpace->find_chunk_at_end();
5939 }
5941 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
5942 bool full) {
5943 // The next lower level has been collected. Gather any statistics
5944 // that are of interest at this point.
5945 if (!full && (current_level + 1) == level()) {
5946 // Gather statistics on the young generation collection.
5947 collector()->stats().record_gc0_end(used());
5948 }
5949 }
5951 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
5952 GenCollectedHeap* gch = GenCollectedHeap::heap();
5953 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
5954 "Wrong type of heap");
5955 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
5956 gch->gen_policy()->size_policy();
5957 assert(sp->is_gc_cms_adaptive_size_policy(),
5958 "Wrong type of size policy");
5959 return sp;
5960 }
5962 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
5963 if (PrintGCDetails && Verbose) {
5964 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
5965 }
5966 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
5967 _debug_collection_type =
5968 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
5969 if (PrintGCDetails && Verbose) {
5970 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
5971 }
5972 }
5974 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
5975 bool asynch) {
5976 // We iterate over the space(s) underlying this generation,
5977 // checking the mark bit map to see if the bits corresponding
5978 // to specific blocks are marked or not. Blocks that are
5979 // marked are live and are not swept up. All remaining blocks
5980 // are swept up, with coalescing on-the-fly as we sweep up
5981 // contiguous free and/or garbage blocks:
5982 // We need to ensure that the sweeper synchronizes with allocators
5983 // and stop-the-world collectors. In particular, the following
5984 // locks are used:
5985 // . CMS token: if this is held, a stop the world collection cannot occur
5986 // . freelistLock: if this is held no allocation can occur from this
5987 // generation by another thread
5988 // . bitMapLock: if this is held, no other thread can access or update
5989 //
5991 // Note that we need to hold the freelistLock if we use
5992 // block iterate below; else the iterator might go awry if
5993 // a mutator (or promotion) causes block contents to change
5994 // (for instance if the allocator divvies up a block).
5995 // If we hold the free list lock, for all practical purposes
5996 // young generation GC's can't occur (they'll usually need to
5997 // promote), so we might as well prevent all young generation
5998 // GC's while we do a sweeping step. For the same reason, we might
5999 // as well take the bit map lock for the entire duration
6001 // check that we hold the requisite locks
6002 assert(have_cms_token(), "Should hold cms token");
6003 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6004 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6005 "Should possess CMS token to sweep");
6006 assert_lock_strong(gen->freelistLock());
6007 assert_lock_strong(bitMapLock());
6009 assert(!_sweep_timer.is_active(), "Was switched off in an outer context");
6010 gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()),
6011 _sweep_estimate.padded_average());
6012 gen->setNearLargestChunk();
6014 {
6015 SweepClosure sweepClosure(this, gen, &_markBitMap,
6016 CMSYield && asynch);
6017 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6018 // We need to free-up/coalesce garbage/blocks from a
6019 // co-terminal free run. This is done in the SweepClosure
6020 // destructor; so, do not remove this scope, else the
6021 // end-of-sweep-census below will be off by a little bit.
6022 }
6023 gen->cmsSpace()->sweep_completed();
6024 gen->cmsSpace()->endSweepFLCensus(sweepCount());
6025 if (should_unload_classes()) { // unloaded classes this cycle,
6026 _concurrent_cycles_since_last_unload = 0; // ... reset count
6027 } else { // did not unload classes,
6028 _concurrent_cycles_since_last_unload++; // ... increment count
6029 }
6030 }
6032 // Reset CMS data structures (for now just the marking bit map)
6033 // preparatory for the next cycle.
6034 void CMSCollector::reset(bool asynch) {
6035 GenCollectedHeap* gch = GenCollectedHeap::heap();
6036 CMSAdaptiveSizePolicy* sp = size_policy();
6037 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6038 if (asynch) {
6039 CMSTokenSyncWithLocks ts(true, bitMapLock());
6041 // If the state is not "Resetting", the foreground thread
6042 // has done a collection and the resetting.
6043 if (_collectorState != Resetting) {
6044 assert(_collectorState == Idling, "The state should only change"
6045 " because the foreground collector has finished the collection");
6046 return;
6047 }
6049 // Clear the mark bitmap (no grey objects to start with)
6050 // for the next cycle.
6051 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6052 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6054 HeapWord* curAddr = _markBitMap.startWord();
6055 while (curAddr < _markBitMap.endWord()) {
6056 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6057 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6058 _markBitMap.clear_large_range(chunk);
6059 if (ConcurrentMarkSweepThread::should_yield() &&
6060 !foregroundGCIsActive() &&
6061 CMSYield) {
6062 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6063 "CMS thread should hold CMS token");
6064 assert_lock_strong(bitMapLock());
6065 bitMapLock()->unlock();
6066 ConcurrentMarkSweepThread::desynchronize(true);
6067 ConcurrentMarkSweepThread::acknowledge_yield_request();
6068 stopTimer();
6069 if (PrintCMSStatistics != 0) {
6070 incrementYields();
6071 }
6072 icms_wait();
6074 // See the comment in coordinator_yield()
6075 for (unsigned i = 0; i < CMSYieldSleepCount &&
6076 ConcurrentMarkSweepThread::should_yield() &&
6077 !CMSCollector::foregroundGCIsActive(); ++i) {
6078 os::sleep(Thread::current(), 1, false);
6079 ConcurrentMarkSweepThread::acknowledge_yield_request();
6080 }
6082 ConcurrentMarkSweepThread::synchronize(true);
6083 bitMapLock()->lock_without_safepoint_check();
6084 startTimer();
6085 }
6086 curAddr = chunk.end();
6087 }
6088 _collectorState = Idling;
6089 } else {
6090 // already have the lock
6091 assert(_collectorState == Resetting, "just checking");
6092 assert_lock_strong(bitMapLock());
6093 _markBitMap.clear_all();
6094 _collectorState = Idling;
6095 }
6097 // Stop incremental mode after a cycle completes, so that any future cycles
6098 // are triggered by allocation.
6099 stop_icms();
6101 NOT_PRODUCT(
6102 if (RotateCMSCollectionTypes) {
6103 _cmsGen->rotate_debug_collection_type();
6104 }
6105 )
6106 }
6108 void CMSCollector::do_CMS_operation(CMS_op_type op) {
6109 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6110 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6111 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty);
6112 TraceCollectorStats tcs(counters());
6114 switch (op) {
6115 case CMS_op_checkpointRootsInitial: {
6116 checkpointRootsInitial(true); // asynch
6117 if (PrintGC) {
6118 _cmsGen->printOccupancy("initial-mark");
6119 }
6120 break;
6121 }
6122 case CMS_op_checkpointRootsFinal: {
6123 checkpointRootsFinal(true, // asynch
6124 false, // !clear_all_soft_refs
6125 false); // !init_mark_was_synchronous
6126 if (PrintGC) {
6127 _cmsGen->printOccupancy("remark");
6128 }
6129 break;
6130 }
6131 default:
6132 fatal("No such CMS_op");
6133 }
6134 }
6136 #ifndef PRODUCT
6137 size_t const CMSCollector::skip_header_HeapWords() {
6138 return FreeChunk::header_size();
6139 }
6141 // Try and collect here conditions that should hold when
6142 // CMS thread is exiting. The idea is that the foreground GC
6143 // thread should not be blocked if it wants to terminate
6144 // the CMS thread and yet continue to run the VM for a while
6145 // after that.
6146 void CMSCollector::verify_ok_to_terminate() const {
6147 assert(Thread::current()->is_ConcurrentGC_thread(),
6148 "should be called by CMS thread");
6149 assert(!_foregroundGCShouldWait, "should be false");
6150 // We could check here that all the various low-level locks
6151 // are not held by the CMS thread, but that is overkill; see
6152 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6153 // is checked.
6154 }
6155 #endif
6157 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6158 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6159 "missing Printezis mark?");
6160 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6161 size_t size = pointer_delta(nextOneAddr + 1, addr);
6162 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6163 "alignment problem");
6164 assert(size >= 3, "Necessary for Printezis marks to work");
6165 return size;
6166 }
6168 // A variant of the above (block_size_using_printezis_bits()) except
6169 // that we return 0 if the P-bits are not yet set.
6170 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6171 if (_markBitMap.isMarked(addr)) {
6172 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?");
6173 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6174 size_t size = pointer_delta(nextOneAddr + 1, addr);
6175 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6176 "alignment problem");
6177 assert(size >= 3, "Necessary for Printezis marks to work");
6178 return size;
6179 } else {
6180 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?");
6181 return 0;
6182 }
6183 }
6185 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6186 size_t sz = 0;
6187 oop p = (oop)addr;
6188 if (p->klass_or_null() != NULL && p->is_parsable()) {
6189 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6190 } else {
6191 sz = block_size_using_printezis_bits(addr);
6192 }
6193 assert(sz > 0, "size must be nonzero");
6194 HeapWord* next_block = addr + sz;
6195 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6196 CardTableModRefBS::card_size);
6197 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6198 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6199 "must be different cards");
6200 return next_card;
6201 }
6204 // CMS Bit Map Wrapper /////////////////////////////////////////
6206 // Construct a CMS bit map infrastructure, but don't create the
6207 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6208 // further below.
6209 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6210 _bm(),
6211 _shifter(shifter),
6212 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6213 {
6214 _bmStartWord = 0;
6215 _bmWordSize = 0;
6216 }
6218 bool CMSBitMap::allocate(MemRegion mr) {
6219 _bmStartWord = mr.start();
6220 _bmWordSize = mr.word_size();
6221 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6222 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6223 if (!brs.is_reserved()) {
6224 warning("CMS bit map allocation failure");
6225 return false;
6226 }
6227 // For now we'll just commit all of the bit map up fromt.
6228 // Later on we'll try to be more parsimonious with swap.
6229 if (!_virtual_space.initialize(brs, brs.size())) {
6230 warning("CMS bit map backing store failure");
6231 return false;
6232 }
6233 assert(_virtual_space.committed_size() == brs.size(),
6234 "didn't reserve backing store for all of CMS bit map?");
6235 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6236 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6237 _bmWordSize, "inconsistency in bit map sizing");
6238 _bm.set_size(_bmWordSize >> _shifter);
6240 // bm.clear(); // can we rely on getting zero'd memory? verify below
6241 assert(isAllClear(),
6242 "Expected zero'd memory from ReservedSpace constructor");
6243 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6244 "consistency check");
6245 return true;
6246 }
6248 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6249 HeapWord *next_addr, *end_addr, *last_addr;
6250 assert_locked();
6251 assert(covers(mr), "out-of-range error");
6252 // XXX assert that start and end are appropriately aligned
6253 for (next_addr = mr.start(), end_addr = mr.end();
6254 next_addr < end_addr; next_addr = last_addr) {
6255 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6256 last_addr = dirty_region.end();
6257 if (!dirty_region.is_empty()) {
6258 cl->do_MemRegion(dirty_region);
6259 } else {
6260 assert(last_addr == end_addr, "program logic");
6261 return;
6262 }
6263 }
6264 }
6266 #ifndef PRODUCT
6267 void CMSBitMap::assert_locked() const {
6268 CMSLockVerifier::assert_locked(lock());
6269 }
6271 bool CMSBitMap::covers(MemRegion mr) const {
6272 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6273 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6274 "size inconsistency");
6275 return (mr.start() >= _bmStartWord) &&
6276 (mr.end() <= endWord());
6277 }
6279 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6280 return (start >= _bmStartWord && (start + size) <= endWord());
6281 }
6283 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6284 // verify that there are no 1 bits in the interval [left, right)
6285 FalseBitMapClosure falseBitMapClosure;
6286 iterate(&falseBitMapClosure, left, right);
6287 }
6289 void CMSBitMap::region_invariant(MemRegion mr)
6290 {
6291 assert_locked();
6292 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6293 assert(!mr.is_empty(), "unexpected empty region");
6294 assert(covers(mr), "mr should be covered by bit map");
6295 // convert address range into offset range
6296 size_t start_ofs = heapWordToOffset(mr.start());
6297 // Make sure that end() is appropriately aligned
6298 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6299 (1 << (_shifter+LogHeapWordSize))),
6300 "Misaligned mr.end()");
6301 size_t end_ofs = heapWordToOffset(mr.end());
6302 assert(end_ofs > start_ofs, "Should mark at least one bit");
6303 }
6305 #endif
6307 bool CMSMarkStack::allocate(size_t size) {
6308 // allocate a stack of the requisite depth
6309 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6310 size * sizeof(oop)));
6311 if (!rs.is_reserved()) {
6312 warning("CMSMarkStack allocation failure");
6313 return false;
6314 }
6315 if (!_virtual_space.initialize(rs, rs.size())) {
6316 warning("CMSMarkStack backing store failure");
6317 return false;
6318 }
6319 assert(_virtual_space.committed_size() == rs.size(),
6320 "didn't reserve backing store for all of CMS stack?");
6321 _base = (oop*)(_virtual_space.low());
6322 _index = 0;
6323 _capacity = size;
6324 NOT_PRODUCT(_max_depth = 0);
6325 return true;
6326 }
6328 // XXX FIX ME !!! In the MT case we come in here holding a
6329 // leaf lock. For printing we need to take a further lock
6330 // which has lower rank. We need to recallibrate the two
6331 // lock-ranks involved in order to be able to rpint the
6332 // messages below. (Or defer the printing to the caller.
6333 // For now we take the expedient path of just disabling the
6334 // messages for the problematic case.)
6335 void CMSMarkStack::expand() {
6336 assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted");
6337 if (_capacity == CMSMarkStackSizeMax) {
6338 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6339 // We print a warning message only once per CMS cycle.
6340 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6341 }
6342 return;
6343 }
6344 // Double capacity if possible
6345 size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax);
6346 // Do not give up existing stack until we have managed to
6347 // get the double capacity that we desired.
6348 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6349 new_capacity * sizeof(oop)));
6350 if (rs.is_reserved()) {
6351 // Release the backing store associated with old stack
6352 _virtual_space.release();
6353 // Reinitialize virtual space for new stack
6354 if (!_virtual_space.initialize(rs, rs.size())) {
6355 fatal("Not enough swap for expanded marking stack");
6356 }
6357 _base = (oop*)(_virtual_space.low());
6358 _index = 0;
6359 _capacity = new_capacity;
6360 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6361 // Failed to double capacity, continue;
6362 // we print a detail message only once per CMS cycle.
6363 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6364 SIZE_FORMAT"K",
6365 _capacity / K, new_capacity / K);
6366 }
6367 }
6370 // Closures
6371 // XXX: there seems to be a lot of code duplication here;
6372 // should refactor and consolidate common code.
6374 // This closure is used to mark refs into the CMS generation in
6375 // the CMS bit map. Called at the first checkpoint. This closure
6376 // assumes that we do not need to re-mark dirty cards; if the CMS
6377 // generation on which this is used is not an oldest (modulo perm gen)
6378 // generation then this will lose younger_gen cards!
6380 MarkRefsIntoClosure::MarkRefsIntoClosure(
6381 MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods):
6382 _span(span),
6383 _bitMap(bitMap),
6384 _should_do_nmethods(should_do_nmethods)
6385 {
6386 assert(_ref_processor == NULL, "deliberately left NULL");
6387 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6388 }
6390 void MarkRefsIntoClosure::do_oop(oop obj) {
6391 // if p points into _span, then mark corresponding bit in _markBitMap
6392 assert(obj->is_oop(), "expected an oop");
6393 HeapWord* addr = (HeapWord*)obj;
6394 if (_span.contains(addr)) {
6395 // this should be made more efficient
6396 _bitMap->mark(addr);
6397 }
6398 }
6400 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6401 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6403 // A variant of the above, used for CMS marking verification.
6404 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6405 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6406 bool should_do_nmethods):
6407 _span(span),
6408 _verification_bm(verification_bm),
6409 _cms_bm(cms_bm),
6410 _should_do_nmethods(should_do_nmethods) {
6411 assert(_ref_processor == NULL, "deliberately left NULL");
6412 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6413 }
6415 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6416 // if p points into _span, then mark corresponding bit in _markBitMap
6417 assert(obj->is_oop(), "expected an oop");
6418 HeapWord* addr = (HeapWord*)obj;
6419 if (_span.contains(addr)) {
6420 _verification_bm->mark(addr);
6421 if (!_cms_bm->isMarked(addr)) {
6422 oop(addr)->print();
6423 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6424 fatal("... aborting");
6425 }
6426 }
6427 }
6429 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6430 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6432 //////////////////////////////////////////////////
6433 // MarkRefsIntoAndScanClosure
6434 //////////////////////////////////////////////////
6436 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6437 ReferenceProcessor* rp,
6438 CMSBitMap* bit_map,
6439 CMSBitMap* mod_union_table,
6440 CMSMarkStack* mark_stack,
6441 CMSMarkStack* revisit_stack,
6442 CMSCollector* collector,
6443 bool should_yield,
6444 bool concurrent_precleaning):
6445 _collector(collector),
6446 _span(span),
6447 _bit_map(bit_map),
6448 _mark_stack(mark_stack),
6449 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6450 mark_stack, revisit_stack, concurrent_precleaning),
6451 _yield(should_yield),
6452 _concurrent_precleaning(concurrent_precleaning),
6453 _freelistLock(NULL)
6454 {
6455 _ref_processor = rp;
6456 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6457 }
6459 // This closure is used to mark refs into the CMS generation at the
6460 // second (final) checkpoint, and to scan and transitively follow
6461 // the unmarked oops. It is also used during the concurrent precleaning
6462 // phase while scanning objects on dirty cards in the CMS generation.
6463 // The marks are made in the marking bit map and the marking stack is
6464 // used for keeping the (newly) grey objects during the scan.
6465 // The parallel version (Par_...) appears further below.
6466 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6467 if (obj != NULL) {
6468 assert(obj->is_oop(), "expected an oop");
6469 HeapWord* addr = (HeapWord*)obj;
6470 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6471 assert(_collector->overflow_list_is_empty(),
6472 "overflow list should be empty");
6473 if (_span.contains(addr) &&
6474 !_bit_map->isMarked(addr)) {
6475 // mark bit map (object is now grey)
6476 _bit_map->mark(addr);
6477 // push on marking stack (stack should be empty), and drain the
6478 // stack by applying this closure to the oops in the oops popped
6479 // from the stack (i.e. blacken the grey objects)
6480 bool res = _mark_stack->push(obj);
6481 assert(res, "Should have space to push on empty stack");
6482 do {
6483 oop new_oop = _mark_stack->pop();
6484 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6485 assert(new_oop->is_parsable(), "Found unparsable oop");
6486 assert(_bit_map->isMarked((HeapWord*)new_oop),
6487 "only grey objects on this stack");
6488 // iterate over the oops in this oop, marking and pushing
6489 // the ones in CMS heap (i.e. in _span).
6490 new_oop->oop_iterate(&_pushAndMarkClosure);
6491 // check if it's time to yield
6492 do_yield_check();
6493 } while (!_mark_stack->isEmpty() ||
6494 (!_concurrent_precleaning && take_from_overflow_list()));
6495 // if marking stack is empty, and we are not doing this
6496 // during precleaning, then check the overflow list
6497 }
6498 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6499 assert(_collector->overflow_list_is_empty(),
6500 "overflow list was drained above");
6501 // We could restore evacuated mark words, if any, used for
6502 // overflow list links here because the overflow list is
6503 // provably empty here. That would reduce the maximum
6504 // size requirements for preserved_{oop,mark}_stack.
6505 // But we'll just postpone it until we are all done
6506 // so we can just stream through.
6507 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6508 _collector->restore_preserved_marks_if_any();
6509 assert(_collector->no_preserved_marks(), "No preserved marks");
6510 }
6511 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6512 "All preserved marks should have been restored above");
6513 }
6514 }
6516 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6517 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6519 void MarkRefsIntoAndScanClosure::do_yield_work() {
6520 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6521 "CMS thread should hold CMS token");
6522 assert_lock_strong(_freelistLock);
6523 assert_lock_strong(_bit_map->lock());
6524 // relinquish the free_list_lock and bitMaplock()
6525 _bit_map->lock()->unlock();
6526 _freelistLock->unlock();
6527 ConcurrentMarkSweepThread::desynchronize(true);
6528 ConcurrentMarkSweepThread::acknowledge_yield_request();
6529 _collector->stopTimer();
6530 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6531 if (PrintCMSStatistics != 0) {
6532 _collector->incrementYields();
6533 }
6534 _collector->icms_wait();
6536 // See the comment in coordinator_yield()
6537 for (unsigned i = 0;
6538 i < CMSYieldSleepCount &&
6539 ConcurrentMarkSweepThread::should_yield() &&
6540 !CMSCollector::foregroundGCIsActive();
6541 ++i) {
6542 os::sleep(Thread::current(), 1, false);
6543 ConcurrentMarkSweepThread::acknowledge_yield_request();
6544 }
6546 ConcurrentMarkSweepThread::synchronize(true);
6547 _freelistLock->lock_without_safepoint_check();
6548 _bit_map->lock()->lock_without_safepoint_check();
6549 _collector->startTimer();
6550 }
6552 ///////////////////////////////////////////////////////////
6553 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6554 // MarkRefsIntoAndScanClosure
6555 ///////////////////////////////////////////////////////////
6556 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6557 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6558 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6559 _span(span),
6560 _bit_map(bit_map),
6561 _work_queue(work_queue),
6562 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6563 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6564 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6565 revisit_stack)
6566 {
6567 _ref_processor = rp;
6568 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6569 }
6571 // This closure is used to mark refs into the CMS generation at the
6572 // second (final) checkpoint, and to scan and transitively follow
6573 // the unmarked oops. The marks are made in the marking bit map and
6574 // the work_queue is used for keeping the (newly) grey objects during
6575 // the scan phase whence they are also available for stealing by parallel
6576 // threads. Since the marking bit map is shared, updates are
6577 // synchronized (via CAS).
6578 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6579 if (obj != NULL) {
6580 // Ignore mark word because this could be an already marked oop
6581 // that may be chained at the end of the overflow list.
6582 assert(obj->is_oop(true), "expected an oop");
6583 HeapWord* addr = (HeapWord*)obj;
6584 if (_span.contains(addr) &&
6585 !_bit_map->isMarked(addr)) {
6586 // mark bit map (object will become grey):
6587 // It is possible for several threads to be
6588 // trying to "claim" this object concurrently;
6589 // the unique thread that succeeds in marking the
6590 // object first will do the subsequent push on
6591 // to the work queue (or overflow list).
6592 if (_bit_map->par_mark(addr)) {
6593 // push on work_queue (which may not be empty), and trim the
6594 // queue to an appropriate length by applying this closure to
6595 // the oops in the oops popped from the stack (i.e. blacken the
6596 // grey objects)
6597 bool res = _work_queue->push(obj);
6598 assert(res, "Low water mark should be less than capacity?");
6599 trim_queue(_low_water_mark);
6600 } // Else, another thread claimed the object
6601 }
6602 }
6603 }
6605 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6606 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6608 // This closure is used to rescan the marked objects on the dirty cards
6609 // in the mod union table and the card table proper.
6610 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6611 oop p, MemRegion mr) {
6613 size_t size = 0;
6614 HeapWord* addr = (HeapWord*)p;
6615 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6616 assert(_span.contains(addr), "we are scanning the CMS generation");
6617 // check if it's time to yield
6618 if (do_yield_check()) {
6619 // We yielded for some foreground stop-world work,
6620 // and we have been asked to abort this ongoing preclean cycle.
6621 return 0;
6622 }
6623 if (_bitMap->isMarked(addr)) {
6624 // it's marked; is it potentially uninitialized?
6625 if (p->klass_or_null() != NULL) {
6626 if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) {
6627 // Signal precleaning to redirty the card since
6628 // the klass pointer is already installed.
6629 assert(size == 0, "Initial value");
6630 } else {
6631 assert(p->is_parsable(), "must be parsable.");
6632 // an initialized object; ignore mark word in verification below
6633 // since we are running concurrent with mutators
6634 assert(p->is_oop(true), "should be an oop");
6635 if (p->is_objArray()) {
6636 // objArrays are precisely marked; restrict scanning
6637 // to dirty cards only.
6638 size = CompactibleFreeListSpace::adjustObjectSize(
6639 p->oop_iterate(_scanningClosure, mr));
6640 } else {
6641 // A non-array may have been imprecisely marked; we need
6642 // to scan object in its entirety.
6643 size = CompactibleFreeListSpace::adjustObjectSize(
6644 p->oop_iterate(_scanningClosure));
6645 }
6646 #ifdef DEBUG
6647 size_t direct_size =
6648 CompactibleFreeListSpace::adjustObjectSize(p->size());
6649 assert(size == direct_size, "Inconsistency in size");
6650 assert(size >= 3, "Necessary for Printezis marks to work");
6651 if (!_bitMap->isMarked(addr+1)) {
6652 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6653 } else {
6654 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6655 assert(_bitMap->isMarked(addr+size-1),
6656 "inconsistent Printezis mark");
6657 }
6658 #endif // DEBUG
6659 }
6660 } else {
6661 // an unitialized object
6662 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6663 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6664 size = pointer_delta(nextOneAddr + 1, addr);
6665 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6666 "alignment problem");
6667 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6668 // will dirty the card when the klass pointer is installed in the
6669 // object (signalling the completion of initialization).
6670 }
6671 } else {
6672 // Either a not yet marked object or an uninitialized object
6673 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6674 // An uninitialized object, skip to the next card, since
6675 // we may not be able to read its P-bits yet.
6676 assert(size == 0, "Initial value");
6677 } else {
6678 // An object not (yet) reached by marking: we merely need to
6679 // compute its size so as to go look at the next block.
6680 assert(p->is_oop(true), "should be an oop");
6681 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6682 }
6683 }
6684 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6685 return size;
6686 }
6688 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6689 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6690 "CMS thread should hold CMS token");
6691 assert_lock_strong(_freelistLock);
6692 assert_lock_strong(_bitMap->lock());
6693 // relinquish the free_list_lock and bitMaplock()
6694 _bitMap->lock()->unlock();
6695 _freelistLock->unlock();
6696 ConcurrentMarkSweepThread::desynchronize(true);
6697 ConcurrentMarkSweepThread::acknowledge_yield_request();
6698 _collector->stopTimer();
6699 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6700 if (PrintCMSStatistics != 0) {
6701 _collector->incrementYields();
6702 }
6703 _collector->icms_wait();
6705 // See the comment in coordinator_yield()
6706 for (unsigned i = 0; i < CMSYieldSleepCount &&
6707 ConcurrentMarkSweepThread::should_yield() &&
6708 !CMSCollector::foregroundGCIsActive(); ++i) {
6709 os::sleep(Thread::current(), 1, false);
6710 ConcurrentMarkSweepThread::acknowledge_yield_request();
6711 }
6713 ConcurrentMarkSweepThread::synchronize(true);
6714 _freelistLock->lock_without_safepoint_check();
6715 _bitMap->lock()->lock_without_safepoint_check();
6716 _collector->startTimer();
6717 }
6720 //////////////////////////////////////////////////////////////////
6721 // SurvivorSpacePrecleanClosure
6722 //////////////////////////////////////////////////////////////////
6723 // This (single-threaded) closure is used to preclean the oops in
6724 // the survivor spaces.
6725 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6727 HeapWord* addr = (HeapWord*)p;
6728 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6729 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6730 assert(p->klass_or_null() != NULL, "object should be initializd");
6731 assert(p->is_parsable(), "must be parsable.");
6732 // an initialized object; ignore mark word in verification below
6733 // since we are running concurrent with mutators
6734 assert(p->is_oop(true), "should be an oop");
6735 // Note that we do not yield while we iterate over
6736 // the interior oops of p, pushing the relevant ones
6737 // on our marking stack.
6738 size_t size = p->oop_iterate(_scanning_closure);
6739 do_yield_check();
6740 // Observe that below, we do not abandon the preclean
6741 // phase as soon as we should; rather we empty the
6742 // marking stack before returning. This is to satisfy
6743 // some existing assertions. In general, it may be a
6744 // good idea to abort immediately and complete the marking
6745 // from the grey objects at a later time.
6746 while (!_mark_stack->isEmpty()) {
6747 oop new_oop = _mark_stack->pop();
6748 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6749 assert(new_oop->is_parsable(), "Found unparsable oop");
6750 assert(_bit_map->isMarked((HeapWord*)new_oop),
6751 "only grey objects on this stack");
6752 // iterate over the oops in this oop, marking and pushing
6753 // the ones in CMS heap (i.e. in _span).
6754 new_oop->oop_iterate(_scanning_closure);
6755 // check if it's time to yield
6756 do_yield_check();
6757 }
6758 unsigned int after_count =
6759 GenCollectedHeap::heap()->total_collections();
6760 bool abort = (_before_count != after_count) ||
6761 _collector->should_abort_preclean();
6762 return abort ? 0 : size;
6763 }
6765 void SurvivorSpacePrecleanClosure::do_yield_work() {
6766 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6767 "CMS thread should hold CMS token");
6768 assert_lock_strong(_bit_map->lock());
6769 // Relinquish the bit map lock
6770 _bit_map->lock()->unlock();
6771 ConcurrentMarkSweepThread::desynchronize(true);
6772 ConcurrentMarkSweepThread::acknowledge_yield_request();
6773 _collector->stopTimer();
6774 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6775 if (PrintCMSStatistics != 0) {
6776 _collector->incrementYields();
6777 }
6778 _collector->icms_wait();
6780 // See the comment in coordinator_yield()
6781 for (unsigned i = 0; i < CMSYieldSleepCount &&
6782 ConcurrentMarkSweepThread::should_yield() &&
6783 !CMSCollector::foregroundGCIsActive(); ++i) {
6784 os::sleep(Thread::current(), 1, false);
6785 ConcurrentMarkSweepThread::acknowledge_yield_request();
6786 }
6788 ConcurrentMarkSweepThread::synchronize(true);
6789 _bit_map->lock()->lock_without_safepoint_check();
6790 _collector->startTimer();
6791 }
6793 // This closure is used to rescan the marked objects on the dirty cards
6794 // in the mod union table and the card table proper. In the parallel
6795 // case, although the bitMap is shared, we do a single read so the
6796 // isMarked() query is "safe".
6797 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6798 // Ignore mark word because we are running concurrent with mutators
6799 assert(p->is_oop_or_null(true), "expected an oop or null");
6800 HeapWord* addr = (HeapWord*)p;
6801 assert(_span.contains(addr), "we are scanning the CMS generation");
6802 bool is_obj_array = false;
6803 #ifdef DEBUG
6804 if (!_parallel) {
6805 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6806 assert(_collector->overflow_list_is_empty(),
6807 "overflow list should be empty");
6809 }
6810 #endif // DEBUG
6811 if (_bit_map->isMarked(addr)) {
6812 // Obj arrays are precisely marked, non-arrays are not;
6813 // so we scan objArrays precisely and non-arrays in their
6814 // entirety.
6815 if (p->is_objArray()) {
6816 is_obj_array = true;
6817 if (_parallel) {
6818 p->oop_iterate(_par_scan_closure, mr);
6819 } else {
6820 p->oop_iterate(_scan_closure, mr);
6821 }
6822 } else {
6823 if (_parallel) {
6824 p->oop_iterate(_par_scan_closure);
6825 } else {
6826 p->oop_iterate(_scan_closure);
6827 }
6828 }
6829 }
6830 #ifdef DEBUG
6831 if (!_parallel) {
6832 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6833 assert(_collector->overflow_list_is_empty(),
6834 "overflow list should be empty");
6836 }
6837 #endif // DEBUG
6838 return is_obj_array;
6839 }
6841 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6842 MemRegion span,
6843 CMSBitMap* bitMap, CMSMarkStack* markStack,
6844 CMSMarkStack* revisitStack,
6845 bool should_yield, bool verifying):
6846 _collector(collector),
6847 _span(span),
6848 _bitMap(bitMap),
6849 _mut(&collector->_modUnionTable),
6850 _markStack(markStack),
6851 _revisitStack(revisitStack),
6852 _yield(should_yield),
6853 _skipBits(0)
6854 {
6855 assert(_markStack->isEmpty(), "stack should be empty");
6856 _finger = _bitMap->startWord();
6857 _threshold = _finger;
6858 assert(_collector->_restart_addr == NULL, "Sanity check");
6859 assert(_span.contains(_finger), "Out of bounds _finger?");
6860 DEBUG_ONLY(_verifying = verifying;)
6861 }
6863 void MarkFromRootsClosure::reset(HeapWord* addr) {
6864 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6865 assert(_span.contains(addr), "Out of bounds _finger?");
6866 _finger = addr;
6867 _threshold = (HeapWord*)round_to(
6868 (intptr_t)_finger, CardTableModRefBS::card_size);
6869 }
6871 // Should revisit to see if this should be restructured for
6872 // greater efficiency.
6873 bool MarkFromRootsClosure::do_bit(size_t offset) {
6874 if (_skipBits > 0) {
6875 _skipBits--;
6876 return true;
6877 }
6878 // convert offset into a HeapWord*
6879 HeapWord* addr = _bitMap->startWord() + offset;
6880 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6881 "address out of range");
6882 assert(_bitMap->isMarked(addr), "tautology");
6883 if (_bitMap->isMarked(addr+1)) {
6884 // this is an allocated but not yet initialized object
6885 assert(_skipBits == 0, "tautology");
6886 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6887 oop p = oop(addr);
6888 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6889 DEBUG_ONLY(if (!_verifying) {)
6890 // We re-dirty the cards on which this object lies and increase
6891 // the _threshold so that we'll come back to scan this object
6892 // during the preclean or remark phase. (CMSCleanOnEnter)
6893 if (CMSCleanOnEnter) {
6894 size_t sz = _collector->block_size_using_printezis_bits(addr);
6895 HeapWord* end_card_addr = (HeapWord*)round_to(
6896 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6897 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6898 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6899 // Bump _threshold to end_card_addr; note that
6900 // _threshold cannot possibly exceed end_card_addr, anyhow.
6901 // This prevents future clearing of the card as the scan proceeds
6902 // to the right.
6903 assert(_threshold <= end_card_addr,
6904 "Because we are just scanning into this object");
6905 if (_threshold < end_card_addr) {
6906 _threshold = end_card_addr;
6907 }
6908 if (p->klass_or_null() != NULL) {
6909 // Redirty the range of cards...
6910 _mut->mark_range(redirty_range);
6911 } // ...else the setting of klass will dirty the card anyway.
6912 }
6913 DEBUG_ONLY(})
6914 return true;
6915 }
6916 }
6917 scanOopsInOop(addr);
6918 return true;
6919 }
6921 // We take a break if we've been at this for a while,
6922 // so as to avoid monopolizing the locks involved.
6923 void MarkFromRootsClosure::do_yield_work() {
6924 // First give up the locks, then yield, then re-lock
6925 // We should probably use a constructor/destructor idiom to
6926 // do this unlock/lock or modify the MutexUnlocker class to
6927 // serve our purpose. XXX
6928 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6929 "CMS thread should hold CMS token");
6930 assert_lock_strong(_bitMap->lock());
6931 _bitMap->lock()->unlock();
6932 ConcurrentMarkSweepThread::desynchronize(true);
6933 ConcurrentMarkSweepThread::acknowledge_yield_request();
6934 _collector->stopTimer();
6935 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6936 if (PrintCMSStatistics != 0) {
6937 _collector->incrementYields();
6938 }
6939 _collector->icms_wait();
6941 // See the comment in coordinator_yield()
6942 for (unsigned i = 0; i < CMSYieldSleepCount &&
6943 ConcurrentMarkSweepThread::should_yield() &&
6944 !CMSCollector::foregroundGCIsActive(); ++i) {
6945 os::sleep(Thread::current(), 1, false);
6946 ConcurrentMarkSweepThread::acknowledge_yield_request();
6947 }
6949 ConcurrentMarkSweepThread::synchronize(true);
6950 _bitMap->lock()->lock_without_safepoint_check();
6951 _collector->startTimer();
6952 }
6954 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6955 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6956 assert(_markStack->isEmpty(),
6957 "should drain stack to limit stack usage");
6958 // convert ptr to an oop preparatory to scanning
6959 oop obj = oop(ptr);
6960 // Ignore mark word in verification below, since we
6961 // may be running concurrent with mutators.
6962 assert(obj->is_oop(true), "should be an oop");
6963 assert(_finger <= ptr, "_finger runneth ahead");
6964 // advance the finger to right end of this object
6965 _finger = ptr + obj->size();
6966 assert(_finger > ptr, "we just incremented it above");
6967 // On large heaps, it may take us some time to get through
6968 // the marking phase (especially if running iCMS). During
6969 // this time it's possible that a lot of mutations have
6970 // accumulated in the card table and the mod union table --
6971 // these mutation records are redundant until we have
6972 // actually traced into the corresponding card.
6973 // Here, we check whether advancing the finger would make
6974 // us cross into a new card, and if so clear corresponding
6975 // cards in the MUT (preclean them in the card-table in the
6976 // future).
6978 DEBUG_ONLY(if (!_verifying) {)
6979 // The clean-on-enter optimization is disabled by default,
6980 // until we fix 6178663.
6981 if (CMSCleanOnEnter && (_finger > _threshold)) {
6982 // [_threshold, _finger) represents the interval
6983 // of cards to be cleared in MUT (or precleaned in card table).
6984 // The set of cards to be cleared is all those that overlap
6985 // with the interval [_threshold, _finger); note that
6986 // _threshold is always kept card-aligned but _finger isn't
6987 // always card-aligned.
6988 HeapWord* old_threshold = _threshold;
6989 assert(old_threshold == (HeapWord*)round_to(
6990 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6991 "_threshold should always be card-aligned");
6992 _threshold = (HeapWord*)round_to(
6993 (intptr_t)_finger, CardTableModRefBS::card_size);
6994 MemRegion mr(old_threshold, _threshold);
6995 assert(!mr.is_empty(), "Control point invariant");
6996 assert(_span.contains(mr), "Should clear within span");
6997 // XXX When _finger crosses from old gen into perm gen
6998 // we may be doing unnecessary cleaning; do better in the
6999 // future by detecting that condition and clearing fewer
7000 // MUT/CT entries.
7001 _mut->clear_range(mr);
7002 }
7003 DEBUG_ONLY(})
7005 // Note: the finger doesn't advance while we drain
7006 // the stack below.
7007 PushOrMarkClosure pushOrMarkClosure(_collector,
7008 _span, _bitMap, _markStack,
7009 _revisitStack,
7010 _finger, this);
7011 bool res = _markStack->push(obj);
7012 assert(res, "Empty non-zero size stack should have space for single push");
7013 while (!_markStack->isEmpty()) {
7014 oop new_oop = _markStack->pop();
7015 // Skip verifying header mark word below because we are
7016 // running concurrent with mutators.
7017 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7018 // now scan this oop's oops
7019 new_oop->oop_iterate(&pushOrMarkClosure);
7020 do_yield_check();
7021 }
7022 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7023 }
7025 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7026 CMSCollector* collector, MemRegion span,
7027 CMSBitMap* bit_map,
7028 OopTaskQueue* work_queue,
7029 CMSMarkStack* overflow_stack,
7030 CMSMarkStack* revisit_stack,
7031 bool should_yield):
7032 _collector(collector),
7033 _whole_span(collector->_span),
7034 _span(span),
7035 _bit_map(bit_map),
7036 _mut(&collector->_modUnionTable),
7037 _work_queue(work_queue),
7038 _overflow_stack(overflow_stack),
7039 _revisit_stack(revisit_stack),
7040 _yield(should_yield),
7041 _skip_bits(0),
7042 _task(task)
7043 {
7044 assert(_work_queue->size() == 0, "work_queue should be empty");
7045 _finger = span.start();
7046 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7047 assert(_span.contains(_finger), "Out of bounds _finger?");
7048 }
7050 // Should revisit to see if this should be restructured for
7051 // greater efficiency.
7052 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7053 if (_skip_bits > 0) {
7054 _skip_bits--;
7055 return true;
7056 }
7057 // convert offset into a HeapWord*
7058 HeapWord* addr = _bit_map->startWord() + offset;
7059 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7060 "address out of range");
7061 assert(_bit_map->isMarked(addr), "tautology");
7062 if (_bit_map->isMarked(addr+1)) {
7063 // this is an allocated object that might not yet be initialized
7064 assert(_skip_bits == 0, "tautology");
7065 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7066 oop p = oop(addr);
7067 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7068 // in the case of Clean-on-Enter optimization, redirty card
7069 // and avoid clearing card by increasing the threshold.
7070 return true;
7071 }
7072 }
7073 scan_oops_in_oop(addr);
7074 return true;
7075 }
7077 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7078 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7079 // Should we assert that our work queue is empty or
7080 // below some drain limit?
7081 assert(_work_queue->size() == 0,
7082 "should drain stack to limit stack usage");
7083 // convert ptr to an oop preparatory to scanning
7084 oop obj = oop(ptr);
7085 // Ignore mark word in verification below, since we
7086 // may be running concurrent with mutators.
7087 assert(obj->is_oop(true), "should be an oop");
7088 assert(_finger <= ptr, "_finger runneth ahead");
7089 // advance the finger to right end of this object
7090 _finger = ptr + obj->size();
7091 assert(_finger > ptr, "we just incremented it above");
7092 // On large heaps, it may take us some time to get through
7093 // the marking phase (especially if running iCMS). During
7094 // this time it's possible that a lot of mutations have
7095 // accumulated in the card table and the mod union table --
7096 // these mutation records are redundant until we have
7097 // actually traced into the corresponding card.
7098 // Here, we check whether advancing the finger would make
7099 // us cross into a new card, and if so clear corresponding
7100 // cards in the MUT (preclean them in the card-table in the
7101 // future).
7103 // The clean-on-enter optimization is disabled by default,
7104 // until we fix 6178663.
7105 if (CMSCleanOnEnter && (_finger > _threshold)) {
7106 // [_threshold, _finger) represents the interval
7107 // of cards to be cleared in MUT (or precleaned in card table).
7108 // The set of cards to be cleared is all those that overlap
7109 // with the interval [_threshold, _finger); note that
7110 // _threshold is always kept card-aligned but _finger isn't
7111 // always card-aligned.
7112 HeapWord* old_threshold = _threshold;
7113 assert(old_threshold == (HeapWord*)round_to(
7114 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7115 "_threshold should always be card-aligned");
7116 _threshold = (HeapWord*)round_to(
7117 (intptr_t)_finger, CardTableModRefBS::card_size);
7118 MemRegion mr(old_threshold, _threshold);
7119 assert(!mr.is_empty(), "Control point invariant");
7120 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7121 // XXX When _finger crosses from old gen into perm gen
7122 // we may be doing unnecessary cleaning; do better in the
7123 // future by detecting that condition and clearing fewer
7124 // MUT/CT entries.
7125 _mut->clear_range(mr);
7126 }
7128 // Note: the local finger doesn't advance while we drain
7129 // the stack below, but the global finger sure can and will.
7130 HeapWord** gfa = _task->global_finger_addr();
7131 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7132 _span, _bit_map,
7133 _work_queue,
7134 _overflow_stack,
7135 _revisit_stack,
7136 _finger,
7137 gfa, this);
7138 bool res = _work_queue->push(obj); // overflow could occur here
7139 assert(res, "Will hold once we use workqueues");
7140 while (true) {
7141 oop new_oop;
7142 if (!_work_queue->pop_local(new_oop)) {
7143 // We emptied our work_queue; check if there's stuff that can
7144 // be gotten from the overflow stack.
7145 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7146 _overflow_stack, _work_queue)) {
7147 do_yield_check();
7148 continue;
7149 } else { // done
7150 break;
7151 }
7152 }
7153 // Skip verifying header mark word below because we are
7154 // running concurrent with mutators.
7155 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7156 // now scan this oop's oops
7157 new_oop->oop_iterate(&pushOrMarkClosure);
7158 do_yield_check();
7159 }
7160 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7161 }
7163 // Yield in response to a request from VM Thread or
7164 // from mutators.
7165 void Par_MarkFromRootsClosure::do_yield_work() {
7166 assert(_task != NULL, "sanity");
7167 _task->yield();
7168 }
7170 // A variant of the above used for verifying CMS marking work.
7171 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7172 MemRegion span,
7173 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7174 CMSMarkStack* mark_stack):
7175 _collector(collector),
7176 _span(span),
7177 _verification_bm(verification_bm),
7178 _cms_bm(cms_bm),
7179 _mark_stack(mark_stack),
7180 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7181 mark_stack)
7182 {
7183 assert(_mark_stack->isEmpty(), "stack should be empty");
7184 _finger = _verification_bm->startWord();
7185 assert(_collector->_restart_addr == NULL, "Sanity check");
7186 assert(_span.contains(_finger), "Out of bounds _finger?");
7187 }
7189 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7190 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7191 assert(_span.contains(addr), "Out of bounds _finger?");
7192 _finger = addr;
7193 }
7195 // Should revisit to see if this should be restructured for
7196 // greater efficiency.
7197 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7198 // convert offset into a HeapWord*
7199 HeapWord* addr = _verification_bm->startWord() + offset;
7200 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7201 "address out of range");
7202 assert(_verification_bm->isMarked(addr), "tautology");
7203 assert(_cms_bm->isMarked(addr), "tautology");
7205 assert(_mark_stack->isEmpty(),
7206 "should drain stack to limit stack usage");
7207 // convert addr to an oop preparatory to scanning
7208 oop obj = oop(addr);
7209 assert(obj->is_oop(), "should be an oop");
7210 assert(_finger <= addr, "_finger runneth ahead");
7211 // advance the finger to right end of this object
7212 _finger = addr + obj->size();
7213 assert(_finger > addr, "we just incremented it above");
7214 // Note: the finger doesn't advance while we drain
7215 // the stack below.
7216 bool res = _mark_stack->push(obj);
7217 assert(res, "Empty non-zero size stack should have space for single push");
7218 while (!_mark_stack->isEmpty()) {
7219 oop new_oop = _mark_stack->pop();
7220 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7221 // now scan this oop's oops
7222 new_oop->oop_iterate(&_pam_verify_closure);
7223 }
7224 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7225 return true;
7226 }
7228 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7229 CMSCollector* collector, MemRegion span,
7230 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7231 CMSMarkStack* mark_stack):
7232 OopClosure(collector->ref_processor()),
7233 _collector(collector),
7234 _span(span),
7235 _verification_bm(verification_bm),
7236 _cms_bm(cms_bm),
7237 _mark_stack(mark_stack)
7238 { }
7240 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7241 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7243 // Upon stack overflow, we discard (part of) the stack,
7244 // remembering the least address amongst those discarded
7245 // in CMSCollector's _restart_address.
7246 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7247 // Remember the least grey address discarded
7248 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7249 _collector->lower_restart_addr(ra);
7250 _mark_stack->reset(); // discard stack contents
7251 _mark_stack->expand(); // expand the stack if possible
7252 }
7254 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7255 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7256 HeapWord* addr = (HeapWord*)obj;
7257 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7258 // Oop lies in _span and isn't yet grey or black
7259 _verification_bm->mark(addr); // now grey
7260 if (!_cms_bm->isMarked(addr)) {
7261 oop(addr)->print();
7262 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7263 addr);
7264 fatal("... aborting");
7265 }
7267 if (!_mark_stack->push(obj)) { // stack overflow
7268 if (PrintCMSStatistics != 0) {
7269 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7270 SIZE_FORMAT, _mark_stack->capacity());
7271 }
7272 assert(_mark_stack->isFull(), "Else push should have succeeded");
7273 handle_stack_overflow(addr);
7274 }
7275 // anything including and to the right of _finger
7276 // will be scanned as we iterate over the remainder of the
7277 // bit map
7278 }
7279 }
7281 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7282 MemRegion span,
7283 CMSBitMap* bitMap, CMSMarkStack* markStack,
7284 CMSMarkStack* revisitStack,
7285 HeapWord* finger, MarkFromRootsClosure* parent) :
7286 OopClosure(collector->ref_processor()),
7287 _collector(collector),
7288 _span(span),
7289 _bitMap(bitMap),
7290 _markStack(markStack),
7291 _revisitStack(revisitStack),
7292 _finger(finger),
7293 _parent(parent),
7294 _should_remember_klasses(collector->should_unload_classes())
7295 { }
7297 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7298 MemRegion span,
7299 CMSBitMap* bit_map,
7300 OopTaskQueue* work_queue,
7301 CMSMarkStack* overflow_stack,
7302 CMSMarkStack* revisit_stack,
7303 HeapWord* finger,
7304 HeapWord** global_finger_addr,
7305 Par_MarkFromRootsClosure* parent) :
7306 OopClosure(collector->ref_processor()),
7307 _collector(collector),
7308 _whole_span(collector->_span),
7309 _span(span),
7310 _bit_map(bit_map),
7311 _work_queue(work_queue),
7312 _overflow_stack(overflow_stack),
7313 _revisit_stack(revisit_stack),
7314 _finger(finger),
7315 _global_finger_addr(global_finger_addr),
7316 _parent(parent),
7317 _should_remember_klasses(collector->should_unload_classes())
7318 { }
7320 // Assumes thread-safe access by callers, who are
7321 // responsible for mutual exclusion.
7322 void CMSCollector::lower_restart_addr(HeapWord* low) {
7323 assert(_span.contains(low), "Out of bounds addr");
7324 if (_restart_addr == NULL) {
7325 _restart_addr = low;
7326 } else {
7327 _restart_addr = MIN2(_restart_addr, low);
7328 }
7329 }
7331 // Upon stack overflow, we discard (part of) the stack,
7332 // remembering the least address amongst those discarded
7333 // in CMSCollector's _restart_address.
7334 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7335 // Remember the least grey address discarded
7336 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7337 _collector->lower_restart_addr(ra);
7338 _markStack->reset(); // discard stack contents
7339 _markStack->expand(); // expand the stack if possible
7340 }
7342 // Upon stack overflow, we discard (part of) the stack,
7343 // remembering the least address amongst those discarded
7344 // in CMSCollector's _restart_address.
7345 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7346 // We need to do this under a mutex to prevent other
7347 // workers from interfering with the work done below.
7348 MutexLockerEx ml(_overflow_stack->par_lock(),
7349 Mutex::_no_safepoint_check_flag);
7350 // Remember the least grey address discarded
7351 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7352 _collector->lower_restart_addr(ra);
7353 _overflow_stack->reset(); // discard stack contents
7354 _overflow_stack->expand(); // expand the stack if possible
7355 }
7357 void PushOrMarkClosure::do_oop(oop obj) {
7358 // Ignore mark word because we are running concurrent with mutators.
7359 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7360 HeapWord* addr = (HeapWord*)obj;
7361 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7362 // Oop lies in _span and isn't yet grey or black
7363 _bitMap->mark(addr); // now grey
7364 if (addr < _finger) {
7365 // the bit map iteration has already either passed, or
7366 // sampled, this bit in the bit map; we'll need to
7367 // use the marking stack to scan this oop's oops.
7368 bool simulate_overflow = false;
7369 NOT_PRODUCT(
7370 if (CMSMarkStackOverflowALot &&
7371 _collector->simulate_overflow()) {
7372 // simulate a stack overflow
7373 simulate_overflow = true;
7374 }
7375 )
7376 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7377 if (PrintCMSStatistics != 0) {
7378 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7379 SIZE_FORMAT, _markStack->capacity());
7380 }
7381 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7382 handle_stack_overflow(addr);
7383 }
7384 }
7385 // anything including and to the right of _finger
7386 // will be scanned as we iterate over the remainder of the
7387 // bit map
7388 do_yield_check();
7389 }
7390 }
7392 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7393 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7395 void Par_PushOrMarkClosure::do_oop(oop obj) {
7396 // Ignore mark word because we are running concurrent with mutators.
7397 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7398 HeapWord* addr = (HeapWord*)obj;
7399 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7400 // Oop lies in _span and isn't yet grey or black
7401 // We read the global_finger (volatile read) strictly after marking oop
7402 bool res = _bit_map->par_mark(addr); // now grey
7403 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7404 // Should we push this marked oop on our stack?
7405 // -- if someone else marked it, nothing to do
7406 // -- if target oop is above global finger nothing to do
7407 // -- if target oop is in chunk and above local finger
7408 // then nothing to do
7409 // -- else push on work queue
7410 if ( !res // someone else marked it, they will deal with it
7411 || (addr >= *gfa) // will be scanned in a later task
7412 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7413 return;
7414 }
7415 // the bit map iteration has already either passed, or
7416 // sampled, this bit in the bit map; we'll need to
7417 // use the marking stack to scan this oop's oops.
7418 bool simulate_overflow = false;
7419 NOT_PRODUCT(
7420 if (CMSMarkStackOverflowALot &&
7421 _collector->simulate_overflow()) {
7422 // simulate a stack overflow
7423 simulate_overflow = true;
7424 }
7425 )
7426 if (simulate_overflow ||
7427 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7428 // stack overflow
7429 if (PrintCMSStatistics != 0) {
7430 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7431 SIZE_FORMAT, _overflow_stack->capacity());
7432 }
7433 // We cannot assert that the overflow stack is full because
7434 // it may have been emptied since.
7435 assert(simulate_overflow ||
7436 _work_queue->size() == _work_queue->max_elems(),
7437 "Else push should have succeeded");
7438 handle_stack_overflow(addr);
7439 }
7440 do_yield_check();
7441 }
7442 }
7444 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7445 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7447 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7448 MemRegion span,
7449 ReferenceProcessor* rp,
7450 CMSBitMap* bit_map,
7451 CMSBitMap* mod_union_table,
7452 CMSMarkStack* mark_stack,
7453 CMSMarkStack* revisit_stack,
7454 bool concurrent_precleaning):
7455 OopClosure(rp),
7456 _collector(collector),
7457 _span(span),
7458 _bit_map(bit_map),
7459 _mod_union_table(mod_union_table),
7460 _mark_stack(mark_stack),
7461 _revisit_stack(revisit_stack),
7462 _concurrent_precleaning(concurrent_precleaning),
7463 _should_remember_klasses(collector->should_unload_classes())
7464 {
7465 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7466 }
7468 // Grey object rescan during pre-cleaning and second checkpoint phases --
7469 // the non-parallel version (the parallel version appears further below.)
7470 void PushAndMarkClosure::do_oop(oop obj) {
7471 // Ignore mark word verification. If during concurrent precleaning,
7472 // the object monitor may be locked. If during the checkpoint
7473 // phases, the object may already have been reached by a different
7474 // path and may be at the end of the global overflow list (so
7475 // the mark word may be NULL).
7476 assert(obj->is_oop_or_null(true /* ignore mark word */),
7477 "expected an oop or NULL");
7478 HeapWord* addr = (HeapWord*)obj;
7479 // Check if oop points into the CMS generation
7480 // and is not marked
7481 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7482 // a white object ...
7483 _bit_map->mark(addr); // ... now grey
7484 // push on the marking stack (grey set)
7485 bool simulate_overflow = false;
7486 NOT_PRODUCT(
7487 if (CMSMarkStackOverflowALot &&
7488 _collector->simulate_overflow()) {
7489 // simulate a stack overflow
7490 simulate_overflow = true;
7491 }
7492 )
7493 if (simulate_overflow || !_mark_stack->push(obj)) {
7494 if (_concurrent_precleaning) {
7495 // During precleaning we can just dirty the appropriate card(s)
7496 // in the mod union table, thus ensuring that the object remains
7497 // in the grey set and continue. In the case of object arrays
7498 // we need to dirty all of the cards that the object spans,
7499 // since the rescan of object arrays will be limited to the
7500 // dirty cards.
7501 // Note that no one can be intefering with us in this action
7502 // of dirtying the mod union table, so no locking or atomics
7503 // are required.
7504 if (obj->is_objArray()) {
7505 size_t sz = obj->size();
7506 HeapWord* end_card_addr = (HeapWord*)round_to(
7507 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7508 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7509 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7510 _mod_union_table->mark_range(redirty_range);
7511 } else {
7512 _mod_union_table->mark(addr);
7513 }
7514 _collector->_ser_pmc_preclean_ovflw++;
7515 } else {
7516 // During the remark phase, we need to remember this oop
7517 // in the overflow list.
7518 _collector->push_on_overflow_list(obj);
7519 _collector->_ser_pmc_remark_ovflw++;
7520 }
7521 }
7522 }
7523 }
7525 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7526 MemRegion span,
7527 ReferenceProcessor* rp,
7528 CMSBitMap* bit_map,
7529 OopTaskQueue* work_queue,
7530 CMSMarkStack* revisit_stack):
7531 OopClosure(rp),
7532 _collector(collector),
7533 _span(span),
7534 _bit_map(bit_map),
7535 _work_queue(work_queue),
7536 _revisit_stack(revisit_stack),
7537 _should_remember_klasses(collector->should_unload_classes())
7538 {
7539 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7540 }
7542 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7543 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7545 // Grey object rescan during second checkpoint phase --
7546 // the parallel version.
7547 void Par_PushAndMarkClosure::do_oop(oop obj) {
7548 // In the assert below, we ignore the mark word because
7549 // this oop may point to an already visited object that is
7550 // on the overflow stack (in which case the mark word has
7551 // been hijacked for chaining into the overflow stack --
7552 // if this is the last object in the overflow stack then
7553 // its mark word will be NULL). Because this object may
7554 // have been subsequently popped off the global overflow
7555 // stack, and the mark word possibly restored to the prototypical
7556 // value, by the time we get to examined this failing assert in
7557 // the debugger, is_oop_or_null(false) may subsequently start
7558 // to hold.
7559 assert(obj->is_oop_or_null(true),
7560 "expected an oop or NULL");
7561 HeapWord* addr = (HeapWord*)obj;
7562 // Check if oop points into the CMS generation
7563 // and is not marked
7564 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7565 // a white object ...
7566 // If we manage to "claim" the object, by being the
7567 // first thread to mark it, then we push it on our
7568 // marking stack
7569 if (_bit_map->par_mark(addr)) { // ... now grey
7570 // push on work queue (grey set)
7571 bool simulate_overflow = false;
7572 NOT_PRODUCT(
7573 if (CMSMarkStackOverflowALot &&
7574 _collector->par_simulate_overflow()) {
7575 // simulate a stack overflow
7576 simulate_overflow = true;
7577 }
7578 )
7579 if (simulate_overflow || !_work_queue->push(obj)) {
7580 _collector->par_push_on_overflow_list(obj);
7581 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7582 }
7583 } // Else, some other thread got there first
7584 }
7585 }
7587 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7588 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7590 void PushAndMarkClosure::remember_klass(Klass* k) {
7591 if (!_revisit_stack->push(oop(k))) {
7592 fatal("Revisit stack overflowed in PushAndMarkClosure");
7593 }
7594 }
7596 void Par_PushAndMarkClosure::remember_klass(Klass* k) {
7597 if (!_revisit_stack->par_push(oop(k))) {
7598 fatal("Revist stack overflowed in Par_PushAndMarkClosure");
7599 }
7600 }
7602 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7603 Mutex* bml = _collector->bitMapLock();
7604 assert_lock_strong(bml);
7605 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7606 "CMS thread should hold CMS token");
7608 bml->unlock();
7609 ConcurrentMarkSweepThread::desynchronize(true);
7611 ConcurrentMarkSweepThread::acknowledge_yield_request();
7613 _collector->stopTimer();
7614 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7615 if (PrintCMSStatistics != 0) {
7616 _collector->incrementYields();
7617 }
7618 _collector->icms_wait();
7620 // See the comment in coordinator_yield()
7621 for (unsigned i = 0; i < CMSYieldSleepCount &&
7622 ConcurrentMarkSweepThread::should_yield() &&
7623 !CMSCollector::foregroundGCIsActive(); ++i) {
7624 os::sleep(Thread::current(), 1, false);
7625 ConcurrentMarkSweepThread::acknowledge_yield_request();
7626 }
7628 ConcurrentMarkSweepThread::synchronize(true);
7629 bml->lock();
7631 _collector->startTimer();
7632 }
7634 bool CMSPrecleanRefsYieldClosure::should_return() {
7635 if (ConcurrentMarkSweepThread::should_yield()) {
7636 do_yield_work();
7637 }
7638 return _collector->foregroundGCIsActive();
7639 }
7641 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7642 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7643 "mr should be aligned to start at a card boundary");
7644 // We'd like to assert:
7645 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7646 // "mr should be a range of cards");
7647 // However, that would be too strong in one case -- the last
7648 // partition ends at _unallocated_block which, in general, can be
7649 // an arbitrary boundary, not necessarily card aligned.
7650 if (PrintCMSStatistics != 0) {
7651 _num_dirty_cards +=
7652 mr.word_size()/CardTableModRefBS::card_size_in_words;
7653 }
7654 _space->object_iterate_mem(mr, &_scan_cl);
7655 }
7657 SweepClosure::SweepClosure(CMSCollector* collector,
7658 ConcurrentMarkSweepGeneration* g,
7659 CMSBitMap* bitMap, bool should_yield) :
7660 _collector(collector),
7661 _g(g),
7662 _sp(g->cmsSpace()),
7663 _limit(_sp->sweep_limit()),
7664 _freelistLock(_sp->freelistLock()),
7665 _bitMap(bitMap),
7666 _yield(should_yield),
7667 _inFreeRange(false), // No free range at beginning of sweep
7668 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7669 _lastFreeRangeCoalesced(false),
7670 _freeFinger(g->used_region().start())
7671 {
7672 NOT_PRODUCT(
7673 _numObjectsFreed = 0;
7674 _numWordsFreed = 0;
7675 _numObjectsLive = 0;
7676 _numWordsLive = 0;
7677 _numObjectsAlreadyFree = 0;
7678 _numWordsAlreadyFree = 0;
7679 _last_fc = NULL;
7681 _sp->initializeIndexedFreeListArrayReturnedBytes();
7682 _sp->dictionary()->initializeDictReturnedBytes();
7683 )
7684 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7685 "sweep _limit out of bounds");
7686 if (CMSTraceSweeper) {
7687 gclog_or_tty->print("\n====================\nStarting new sweep\n");
7688 }
7689 }
7691 // We need this destructor to reclaim any space at the end
7692 // of the space, which do_blk below may not have added back to
7693 // the free lists. [basically dealing with the "fringe effect"]
7694 SweepClosure::~SweepClosure() {
7695 assert_lock_strong(_freelistLock);
7696 // this should be treated as the end of a free run if any
7697 // The current free range should be returned to the free lists
7698 // as one coalesced chunk.
7699 if (inFreeRange()) {
7700 flushCurFreeChunk(freeFinger(),
7701 pointer_delta(_limit, freeFinger()));
7702 assert(freeFinger() < _limit, "the finger pointeth off base");
7703 if (CMSTraceSweeper) {
7704 gclog_or_tty->print("destructor:");
7705 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") "
7706 "[coalesced:"SIZE_FORMAT"]\n",
7707 freeFinger(), pointer_delta(_limit, freeFinger()),
7708 lastFreeRangeCoalesced());
7709 }
7710 }
7711 NOT_PRODUCT(
7712 if (Verbose && PrintGC) {
7713 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, "
7714 SIZE_FORMAT " bytes",
7715 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7716 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7717 SIZE_FORMAT" bytes "
7718 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7719 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7720 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7721 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) *
7722 sizeof(HeapWord);
7723 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7725 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7726 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7727 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes();
7728 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes;
7729 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes);
7730 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7731 indexListReturnedBytes);
7732 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7733 dictReturnedBytes);
7734 }
7735 }
7736 )
7737 // Now, in debug mode, just null out the sweep_limit
7738 NOT_PRODUCT(_sp->clear_sweep_limit();)
7739 if (CMSTraceSweeper) {
7740 gclog_or_tty->print("end of sweep\n================\n");
7741 }
7742 }
7744 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7745 bool freeRangeInFreeLists) {
7746 if (CMSTraceSweeper) {
7747 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n",
7748 freeFinger, _sp->block_size(freeFinger),
7749 freeRangeInFreeLists);
7750 }
7751 assert(!inFreeRange(), "Trampling existing free range");
7752 set_inFreeRange(true);
7753 set_lastFreeRangeCoalesced(false);
7755 set_freeFinger(freeFinger);
7756 set_freeRangeInFreeLists(freeRangeInFreeLists);
7757 if (CMSTestInFreeList) {
7758 if (freeRangeInFreeLists) {
7759 FreeChunk* fc = (FreeChunk*) freeFinger;
7760 assert(fc->isFree(), "A chunk on the free list should be free.");
7761 assert(fc->size() > 0, "Free range should have a size");
7762 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists");
7763 }
7764 }
7765 }
7767 // Note that the sweeper runs concurrently with mutators. Thus,
7768 // it is possible for direct allocation in this generation to happen
7769 // in the middle of the sweep. Note that the sweeper also coalesces
7770 // contiguous free blocks. Thus, unless the sweeper and the allocator
7771 // synchronize appropriately freshly allocated blocks may get swept up.
7772 // This is accomplished by the sweeper locking the free lists while
7773 // it is sweeping. Thus blocks that are determined to be free are
7774 // indeed free. There is however one additional complication:
7775 // blocks that have been allocated since the final checkpoint and
7776 // mark, will not have been marked and so would be treated as
7777 // unreachable and swept up. To prevent this, the allocator marks
7778 // the bit map when allocating during the sweep phase. This leads,
7779 // however, to a further complication -- objects may have been allocated
7780 // but not yet initialized -- in the sense that the header isn't yet
7781 // installed. The sweeper can not then determine the size of the block
7782 // in order to skip over it. To deal with this case, we use a technique
7783 // (due to Printezis) to encode such uninitialized block sizes in the
7784 // bit map. Since the bit map uses a bit per every HeapWord, but the
7785 // CMS generation has a minimum object size of 3 HeapWords, it follows
7786 // that "normal marks" won't be adjacent in the bit map (there will
7787 // always be at least two 0 bits between successive 1 bits). We make use
7788 // of these "unused" bits to represent uninitialized blocks -- the bit
7789 // corresponding to the start of the uninitialized object and the next
7790 // bit are both set. Finally, a 1 bit marks the end of the object that
7791 // started with the two consecutive 1 bits to indicate its potentially
7792 // uninitialized state.
7794 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7795 FreeChunk* fc = (FreeChunk*)addr;
7796 size_t res;
7798 // check if we are done sweepinrg
7799 if (addr == _limit) { // we have swept up to the limit, do nothing more
7800 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7801 "sweep _limit out of bounds");
7802 // help the closure application finish
7803 return pointer_delta(_sp->end(), _limit);
7804 }
7805 assert(addr <= _limit, "sweep invariant");
7807 // check if we should yield
7808 do_yield_check(addr);
7809 if (fc->isFree()) {
7810 // Chunk that is already free
7811 res = fc->size();
7812 doAlreadyFreeChunk(fc);
7813 debug_only(_sp->verifyFreeLists());
7814 assert(res == fc->size(), "Don't expect the size to change");
7815 NOT_PRODUCT(
7816 _numObjectsAlreadyFree++;
7817 _numWordsAlreadyFree += res;
7818 )
7819 NOT_PRODUCT(_last_fc = fc;)
7820 } else if (!_bitMap->isMarked(addr)) {
7821 // Chunk is fresh garbage
7822 res = doGarbageChunk(fc);
7823 debug_only(_sp->verifyFreeLists());
7824 NOT_PRODUCT(
7825 _numObjectsFreed++;
7826 _numWordsFreed += res;
7827 )
7828 } else {
7829 // Chunk that is alive.
7830 res = doLiveChunk(fc);
7831 debug_only(_sp->verifyFreeLists());
7832 NOT_PRODUCT(
7833 _numObjectsLive++;
7834 _numWordsLive += res;
7835 )
7836 }
7837 return res;
7838 }
7840 // For the smart allocation, record following
7841 // split deaths - a free chunk is removed from its free list because
7842 // it is being split into two or more chunks.
7843 // split birth - a free chunk is being added to its free list because
7844 // a larger free chunk has been split and resulted in this free chunk.
7845 // coal death - a free chunk is being removed from its free list because
7846 // it is being coalesced into a large free chunk.
7847 // coal birth - a free chunk is being added to its free list because
7848 // it was created when two or more free chunks where coalesced into
7849 // this free chunk.
7850 //
7851 // These statistics are used to determine the desired number of free
7852 // chunks of a given size. The desired number is chosen to be relative
7853 // to the end of a CMS sweep. The desired number at the end of a sweep
7854 // is the
7855 // count-at-end-of-previous-sweep (an amount that was enough)
7856 // - count-at-beginning-of-current-sweep (the excess)
7857 // + split-births (gains in this size during interval)
7858 // - split-deaths (demands on this size during interval)
7859 // where the interval is from the end of one sweep to the end of the
7860 // next.
7861 //
7862 // When sweeping the sweeper maintains an accumulated chunk which is
7863 // the chunk that is made up of chunks that have been coalesced. That
7864 // will be termed the left-hand chunk. A new chunk of garbage that
7865 // is being considered for coalescing will be referred to as the
7866 // right-hand chunk.
7867 //
7868 // When making a decision on whether to coalesce a right-hand chunk with
7869 // the current left-hand chunk, the current count vs. the desired count
7870 // of the left-hand chunk is considered. Also if the right-hand chunk
7871 // is near the large chunk at the end of the heap (see
7872 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7873 // left-hand chunk is coalesced.
7874 //
7875 // When making a decision about whether to split a chunk, the desired count
7876 // vs. the current count of the candidate to be split is also considered.
7877 // If the candidate is underpopulated (currently fewer chunks than desired)
7878 // a chunk of an overpopulated (currently more chunks than desired) size may
7879 // be chosen. The "hint" associated with a free list, if non-null, points
7880 // to a free list which may be overpopulated.
7881 //
7883 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) {
7884 size_t size = fc->size();
7885 // Chunks that cannot be coalesced are not in the
7886 // free lists.
7887 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7888 assert(_sp->verifyChunkInFreeLists(fc),
7889 "free chunk should be in free lists");
7890 }
7891 // a chunk that is already free, should not have been
7892 // marked in the bit map
7893 HeapWord* addr = (HeapWord*) fc;
7894 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7895 // Verify that the bit map has no bits marked between
7896 // addr and purported end of this block.
7897 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7899 // Some chunks cannot be coalesced in under any circumstances.
7900 // See the definition of cantCoalesce().
7901 if (!fc->cantCoalesce()) {
7902 // This chunk can potentially be coalesced.
7903 if (_sp->adaptive_freelists()) {
7904 // All the work is done in
7905 doPostIsFreeOrGarbageChunk(fc, size);
7906 } else { // Not adaptive free lists
7907 // this is a free chunk that can potentially be coalesced by the sweeper;
7908 if (!inFreeRange()) {
7909 // if the next chunk is a free block that can't be coalesced
7910 // it doesn't make sense to remove this chunk from the free lists
7911 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
7912 assert((HeapWord*)nextChunk <= _limit, "sweep invariant");
7913 if ((HeapWord*)nextChunk < _limit && // there's a next chunk...
7914 nextChunk->isFree() && // which is free...
7915 nextChunk->cantCoalesce()) { // ... but cant be coalesced
7916 // nothing to do
7917 } else {
7918 // Potentially the start of a new free range:
7919 // Don't eagerly remove it from the free lists.
7920 // No need to remove it if it will just be put
7921 // back again. (Also from a pragmatic point of view
7922 // if it is a free block in a region that is beyond
7923 // any allocated blocks, an assertion will fail)
7924 // Remember the start of a free run.
7925 initialize_free_range(addr, true);
7926 // end - can coalesce with next chunk
7927 }
7928 } else {
7929 // the midst of a free range, we are coalescing
7930 debug_only(record_free_block_coalesced(fc);)
7931 if (CMSTraceSweeper) {
7932 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
7933 }
7934 // remove it from the free lists
7935 _sp->removeFreeChunkFromFreeLists(fc);
7936 set_lastFreeRangeCoalesced(true);
7937 // If the chunk is being coalesced and the current free range is
7938 // in the free lists, remove the current free range so that it
7939 // will be returned to the free lists in its entirety - all
7940 // the coalesced pieces included.
7941 if (freeRangeInFreeLists()) {
7942 FreeChunk* ffc = (FreeChunk*) freeFinger();
7943 assert(ffc->size() == pointer_delta(addr, freeFinger()),
7944 "Size of free range is inconsistent with chunk size.");
7945 if (CMSTestInFreeList) {
7946 assert(_sp->verifyChunkInFreeLists(ffc),
7947 "free range is not in free lists");
7948 }
7949 _sp->removeFreeChunkFromFreeLists(ffc);
7950 set_freeRangeInFreeLists(false);
7951 }
7952 }
7953 }
7954 } else {
7955 // Code path common to both original and adaptive free lists.
7957 // cant coalesce with previous block; this should be treated
7958 // as the end of a free run if any
7959 if (inFreeRange()) {
7960 // we kicked some butt; time to pick up the garbage
7961 assert(freeFinger() < addr, "the finger pointeth off base");
7962 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
7963 }
7964 // else, nothing to do, just continue
7965 }
7966 }
7968 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) {
7969 // This is a chunk of garbage. It is not in any free list.
7970 // Add it to a free list or let it possibly be coalesced into
7971 // a larger chunk.
7972 HeapWord* addr = (HeapWord*) fc;
7973 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7975 if (_sp->adaptive_freelists()) {
7976 // Verify that the bit map has no bits marked between
7977 // addr and purported end of just dead object.
7978 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7980 doPostIsFreeOrGarbageChunk(fc, size);
7981 } else {
7982 if (!inFreeRange()) {
7983 // start of a new free range
7984 assert(size > 0, "A free range should have a size");
7985 initialize_free_range(addr, false);
7987 } else {
7988 // this will be swept up when we hit the end of the
7989 // free range
7990 if (CMSTraceSweeper) {
7991 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
7992 }
7993 // If the chunk is being coalesced and the current free range is
7994 // in the free lists, remove the current free range so that it
7995 // will be returned to the free lists in its entirety - all
7996 // the coalesced pieces included.
7997 if (freeRangeInFreeLists()) {
7998 FreeChunk* ffc = (FreeChunk*)freeFinger();
7999 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8000 "Size of free range is inconsistent with chunk size.");
8001 if (CMSTestInFreeList) {
8002 assert(_sp->verifyChunkInFreeLists(ffc),
8003 "free range is not in free lists");
8004 }
8005 _sp->removeFreeChunkFromFreeLists(ffc);
8006 set_freeRangeInFreeLists(false);
8007 }
8008 set_lastFreeRangeCoalesced(true);
8009 }
8010 // this will be swept up when we hit the end of the free range
8012 // Verify that the bit map has no bits marked between
8013 // addr and purported end of just dead object.
8014 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8015 }
8016 return size;
8017 }
8019 size_t SweepClosure::doLiveChunk(FreeChunk* fc) {
8020 HeapWord* addr = (HeapWord*) fc;
8021 // The sweeper has just found a live object. Return any accumulated
8022 // left hand chunk to the free lists.
8023 if (inFreeRange()) {
8024 if (_sp->adaptive_freelists()) {
8025 flushCurFreeChunk(freeFinger(),
8026 pointer_delta(addr, freeFinger()));
8027 } else { // not adaptive freelists
8028 set_inFreeRange(false);
8029 // Add the free range back to the free list if it is not already
8030 // there.
8031 if (!freeRangeInFreeLists()) {
8032 assert(freeFinger() < addr, "the finger pointeth off base");
8033 if (CMSTraceSweeper) {
8034 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) "
8035 "[coalesced:%d]\n",
8036 freeFinger(), pointer_delta(addr, freeFinger()),
8037 lastFreeRangeCoalesced());
8038 }
8039 _sp->addChunkAndRepairOffsetTable(freeFinger(),
8040 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced());
8041 }
8042 }
8043 }
8045 // Common code path for original and adaptive free lists.
8047 // this object is live: we'd normally expect this to be
8048 // an oop, and like to assert the following:
8049 // assert(oop(addr)->is_oop(), "live block should be an oop");
8050 // However, as we commented above, this may be an object whose
8051 // header hasn't yet been initialized.
8052 size_t size;
8053 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8054 if (_bitMap->isMarked(addr + 1)) {
8055 // Determine the size from the bit map, rather than trying to
8056 // compute it from the object header.
8057 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8058 size = pointer_delta(nextOneAddr + 1, addr);
8059 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8060 "alignment problem");
8062 #ifdef DEBUG
8063 if (oop(addr)->klass_or_null() != NULL &&
8064 ( !_collector->should_unload_classes()
8065 || oop(addr)->is_parsable())) {
8066 // Ignore mark word because we are running concurrent with mutators
8067 assert(oop(addr)->is_oop(true), "live block should be an oop");
8068 assert(size ==
8069 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8070 "P-mark and computed size do not agree");
8071 }
8072 #endif
8074 } else {
8075 // This should be an initialized object that's alive.
8076 assert(oop(addr)->klass_or_null() != NULL &&
8077 (!_collector->should_unload_classes()
8078 || oop(addr)->is_parsable()),
8079 "Should be an initialized object");
8080 // Ignore mark word because we are running concurrent with mutators
8081 assert(oop(addr)->is_oop(true), "live block should be an oop");
8082 // Verify that the bit map has no bits marked between
8083 // addr and purported end of this block.
8084 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8085 assert(size >= 3, "Necessary for Printezis marks to work");
8086 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8087 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8088 }
8089 return size;
8090 }
8092 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc,
8093 size_t chunkSize) {
8094 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation
8095 // scheme.
8096 bool fcInFreeLists = fc->isFree();
8097 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8098 assert((HeapWord*)fc <= _limit, "sweep invariant");
8099 if (CMSTestInFreeList && fcInFreeLists) {
8100 assert(_sp->verifyChunkInFreeLists(fc),
8101 "free chunk is not in free lists");
8102 }
8105 if (CMSTraceSweeper) {
8106 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8107 }
8109 HeapWord* addr = (HeapWord*) fc;
8111 bool coalesce;
8112 size_t left = pointer_delta(addr, freeFinger());
8113 size_t right = chunkSize;
8114 switch (FLSCoalescePolicy) {
8115 // numeric value forms a coalition aggressiveness metric
8116 case 0: { // never coalesce
8117 coalesce = false;
8118 break;
8119 }
8120 case 1: { // coalesce if left & right chunks on overpopulated lists
8121 coalesce = _sp->coalOverPopulated(left) &&
8122 _sp->coalOverPopulated(right);
8123 break;
8124 }
8125 case 2: { // coalesce if left chunk on overpopulated list (default)
8126 coalesce = _sp->coalOverPopulated(left);
8127 break;
8128 }
8129 case 3: { // coalesce if left OR right chunk on overpopulated list
8130 coalesce = _sp->coalOverPopulated(left) ||
8131 _sp->coalOverPopulated(right);
8132 break;
8133 }
8134 case 4: { // always coalesce
8135 coalesce = true;
8136 break;
8137 }
8138 default:
8139 ShouldNotReachHere();
8140 }
8142 // Should the current free range be coalesced?
8143 // If the chunk is in a free range and either we decided to coalesce above
8144 // or the chunk is near the large block at the end of the heap
8145 // (isNearLargestChunk() returns true), then coalesce this chunk.
8146 bool doCoalesce = inFreeRange() &&
8147 (coalesce || _g->isNearLargestChunk((HeapWord*)fc));
8148 if (doCoalesce) {
8149 // Coalesce the current free range on the left with the new
8150 // chunk on the right. If either is on a free list,
8151 // it must be removed from the list and stashed in the closure.
8152 if (freeRangeInFreeLists()) {
8153 FreeChunk* ffc = (FreeChunk*)freeFinger();
8154 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8155 "Size of free range is inconsistent with chunk size.");
8156 if (CMSTestInFreeList) {
8157 assert(_sp->verifyChunkInFreeLists(ffc),
8158 "Chunk is not in free lists");
8159 }
8160 _sp->coalDeath(ffc->size());
8161 _sp->removeFreeChunkFromFreeLists(ffc);
8162 set_freeRangeInFreeLists(false);
8163 }
8164 if (fcInFreeLists) {
8165 _sp->coalDeath(chunkSize);
8166 assert(fc->size() == chunkSize,
8167 "The chunk has the wrong size or is not in the free lists");
8168 _sp->removeFreeChunkFromFreeLists(fc);
8169 }
8170 set_lastFreeRangeCoalesced(true);
8171 } else { // not in a free range and/or should not coalesce
8172 // Return the current free range and start a new one.
8173 if (inFreeRange()) {
8174 // In a free range but cannot coalesce with the right hand chunk.
8175 // Put the current free range into the free lists.
8176 flushCurFreeChunk(freeFinger(),
8177 pointer_delta(addr, freeFinger()));
8178 }
8179 // Set up for new free range. Pass along whether the right hand
8180 // chunk is in the free lists.
8181 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8182 }
8183 }
8184 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) {
8185 assert(inFreeRange(), "Should only be called if currently in a free range.");
8186 assert(size > 0,
8187 "A zero sized chunk cannot be added to the free lists.");
8188 if (!freeRangeInFreeLists()) {
8189 if(CMSTestInFreeList) {
8190 FreeChunk* fc = (FreeChunk*) chunk;
8191 fc->setSize(size);
8192 assert(!_sp->verifyChunkInFreeLists(fc),
8193 "chunk should not be in free lists yet");
8194 }
8195 if (CMSTraceSweeper) {
8196 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8197 chunk, size);
8198 }
8199 // A new free range is going to be starting. The current
8200 // free range has not been added to the free lists yet or
8201 // was removed so add it back.
8202 // If the current free range was coalesced, then the death
8203 // of the free range was recorded. Record a birth now.
8204 if (lastFreeRangeCoalesced()) {
8205 _sp->coalBirth(size);
8206 }
8207 _sp->addChunkAndRepairOffsetTable(chunk, size,
8208 lastFreeRangeCoalesced());
8209 }
8210 set_inFreeRange(false);
8211 set_freeRangeInFreeLists(false);
8212 }
8214 // We take a break if we've been at this for a while,
8215 // so as to avoid monopolizing the locks involved.
8216 void SweepClosure::do_yield_work(HeapWord* addr) {
8217 // Return current free chunk being used for coalescing (if any)
8218 // to the appropriate freelist. After yielding, the next
8219 // free block encountered will start a coalescing range of
8220 // free blocks. If the next free block is adjacent to the
8221 // chunk just flushed, they will need to wait for the next
8222 // sweep to be coalesced.
8223 if (inFreeRange()) {
8224 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger()));
8225 }
8227 // First give up the locks, then yield, then re-lock.
8228 // We should probably use a constructor/destructor idiom to
8229 // do this unlock/lock or modify the MutexUnlocker class to
8230 // serve our purpose. XXX
8231 assert_lock_strong(_bitMap->lock());
8232 assert_lock_strong(_freelistLock);
8233 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8234 "CMS thread should hold CMS token");
8235 _bitMap->lock()->unlock();
8236 _freelistLock->unlock();
8237 ConcurrentMarkSweepThread::desynchronize(true);
8238 ConcurrentMarkSweepThread::acknowledge_yield_request();
8239 _collector->stopTimer();
8240 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8241 if (PrintCMSStatistics != 0) {
8242 _collector->incrementYields();
8243 }
8244 _collector->icms_wait();
8246 // See the comment in coordinator_yield()
8247 for (unsigned i = 0; i < CMSYieldSleepCount &&
8248 ConcurrentMarkSweepThread::should_yield() &&
8249 !CMSCollector::foregroundGCIsActive(); ++i) {
8250 os::sleep(Thread::current(), 1, false);
8251 ConcurrentMarkSweepThread::acknowledge_yield_request();
8252 }
8254 ConcurrentMarkSweepThread::synchronize(true);
8255 _freelistLock->lock();
8256 _bitMap->lock()->lock_without_safepoint_check();
8257 _collector->startTimer();
8258 }
8260 #ifndef PRODUCT
8261 // This is actually very useful in a product build if it can
8262 // be called from the debugger. Compile it into the product
8263 // as needed.
8264 bool debug_verifyChunkInFreeLists(FreeChunk* fc) {
8265 return debug_cms_space->verifyChunkInFreeLists(fc);
8266 }
8268 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const {
8269 if (CMSTraceSweeper) {
8270 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size());
8271 }
8272 }
8273 #endif
8275 // CMSIsAliveClosure
8276 bool CMSIsAliveClosure::do_object_b(oop obj) {
8277 HeapWord* addr = (HeapWord*)obj;
8278 return addr != NULL &&
8279 (!_span.contains(addr) || _bit_map->isMarked(addr));
8280 }
8282 // CMSKeepAliveClosure: the serial version
8283 void CMSKeepAliveClosure::do_oop(oop obj) {
8284 HeapWord* addr = (HeapWord*)obj;
8285 if (_span.contains(addr) &&
8286 !_bit_map->isMarked(addr)) {
8287 _bit_map->mark(addr);
8288 bool simulate_overflow = false;
8289 NOT_PRODUCT(
8290 if (CMSMarkStackOverflowALot &&
8291 _collector->simulate_overflow()) {
8292 // simulate a stack overflow
8293 simulate_overflow = true;
8294 }
8295 )
8296 if (simulate_overflow || !_mark_stack->push(obj)) {
8297 if (_concurrent_precleaning) {
8298 // We dirty the overflown object and let the remark
8299 // phase deal with it.
8300 assert(_collector->overflow_list_is_empty(), "Error");
8301 // In the case of object arrays, we need to dirty all of
8302 // the cards that the object spans. No locking or atomics
8303 // are needed since no one else can be mutating the mod union
8304 // table.
8305 if (obj->is_objArray()) {
8306 size_t sz = obj->size();
8307 HeapWord* end_card_addr =
8308 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8309 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8310 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8311 _collector->_modUnionTable.mark_range(redirty_range);
8312 } else {
8313 _collector->_modUnionTable.mark(addr);
8314 }
8315 _collector->_ser_kac_preclean_ovflw++;
8316 } else {
8317 _collector->push_on_overflow_list(obj);
8318 _collector->_ser_kac_ovflw++;
8319 }
8320 }
8321 }
8322 }
8324 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8325 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8327 // CMSParKeepAliveClosure: a parallel version of the above.
8328 // The work queues are private to each closure (thread),
8329 // but (may be) available for stealing by other threads.
8330 void CMSParKeepAliveClosure::do_oop(oop obj) {
8331 HeapWord* addr = (HeapWord*)obj;
8332 if (_span.contains(addr) &&
8333 !_bit_map->isMarked(addr)) {
8334 // In general, during recursive tracing, several threads
8335 // may be concurrently getting here; the first one to
8336 // "tag" it, claims it.
8337 if (_bit_map->par_mark(addr)) {
8338 bool res = _work_queue->push(obj);
8339 assert(res, "Low water mark should be much less than capacity");
8340 // Do a recursive trim in the hope that this will keep
8341 // stack usage lower, but leave some oops for potential stealers
8342 trim_queue(_low_water_mark);
8343 } // Else, another thread got there first
8344 }
8345 }
8347 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8348 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8350 void CMSParKeepAliveClosure::trim_queue(uint max) {
8351 while (_work_queue->size() > max) {
8352 oop new_oop;
8353 if (_work_queue->pop_local(new_oop)) {
8354 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8355 assert(_bit_map->isMarked((HeapWord*)new_oop),
8356 "no white objects on this stack!");
8357 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8358 // iterate over the oops in this oop, marking and pushing
8359 // the ones in CMS heap (i.e. in _span).
8360 new_oop->oop_iterate(&_mark_and_push);
8361 }
8362 }
8363 }
8365 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8366 HeapWord* addr = (HeapWord*)obj;
8367 if (_span.contains(addr) &&
8368 !_bit_map->isMarked(addr)) {
8369 if (_bit_map->par_mark(addr)) {
8370 bool simulate_overflow = false;
8371 NOT_PRODUCT(
8372 if (CMSMarkStackOverflowALot &&
8373 _collector->par_simulate_overflow()) {
8374 // simulate a stack overflow
8375 simulate_overflow = true;
8376 }
8377 )
8378 if (simulate_overflow || !_work_queue->push(obj)) {
8379 _collector->par_push_on_overflow_list(obj);
8380 _collector->_par_kac_ovflw++;
8381 }
8382 } // Else another thread got there already
8383 }
8384 }
8386 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8387 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8389 //////////////////////////////////////////////////////////////////
8390 // CMSExpansionCause /////////////////////////////
8391 //////////////////////////////////////////////////////////////////
8392 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8393 switch (cause) {
8394 case _no_expansion:
8395 return "No expansion";
8396 case _satisfy_free_ratio:
8397 return "Free ratio";
8398 case _satisfy_promotion:
8399 return "Satisfy promotion";
8400 case _satisfy_allocation:
8401 return "allocation";
8402 case _allocate_par_lab:
8403 return "Par LAB";
8404 case _allocate_par_spooling_space:
8405 return "Par Spooling Space";
8406 case _adaptive_size_policy:
8407 return "Ergonomics";
8408 default:
8409 return "unknown";
8410 }
8411 }
8413 void CMSDrainMarkingStackClosure::do_void() {
8414 // the max number to take from overflow list at a time
8415 const size_t num = _mark_stack->capacity()/4;
8416 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8417 "Overflow list should be NULL during concurrent phases");
8418 while (!_mark_stack->isEmpty() ||
8419 // if stack is empty, check the overflow list
8420 _collector->take_from_overflow_list(num, _mark_stack)) {
8421 oop obj = _mark_stack->pop();
8422 HeapWord* addr = (HeapWord*)obj;
8423 assert(_span.contains(addr), "Should be within span");
8424 assert(_bit_map->isMarked(addr), "Should be marked");
8425 assert(obj->is_oop(), "Should be an oop");
8426 obj->oop_iterate(_keep_alive);
8427 }
8428 }
8430 void CMSParDrainMarkingStackClosure::do_void() {
8431 // drain queue
8432 trim_queue(0);
8433 }
8435 // Trim our work_queue so its length is below max at return
8436 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8437 while (_work_queue->size() > max) {
8438 oop new_oop;
8439 if (_work_queue->pop_local(new_oop)) {
8440 assert(new_oop->is_oop(), "Expected an oop");
8441 assert(_bit_map->isMarked((HeapWord*)new_oop),
8442 "no white objects on this stack!");
8443 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8444 // iterate over the oops in this oop, marking and pushing
8445 // the ones in CMS heap (i.e. in _span).
8446 new_oop->oop_iterate(&_mark_and_push);
8447 }
8448 }
8449 }
8451 ////////////////////////////////////////////////////////////////////
8452 // Support for Marking Stack Overflow list handling and related code
8453 ////////////////////////////////////////////////////////////////////
8454 // Much of the following code is similar in shape and spirit to the
8455 // code used in ParNewGC. We should try and share that code
8456 // as much as possible in the future.
8458 #ifndef PRODUCT
8459 // Debugging support for CMSStackOverflowALot
8461 // It's OK to call this multi-threaded; the worst thing
8462 // that can happen is that we'll get a bunch of closely
8463 // spaced simulated oveflows, but that's OK, in fact
8464 // probably good as it would exercise the overflow code
8465 // under contention.
8466 bool CMSCollector::simulate_overflow() {
8467 if (_overflow_counter-- <= 0) { // just being defensive
8468 _overflow_counter = CMSMarkStackOverflowInterval;
8469 return true;
8470 } else {
8471 return false;
8472 }
8473 }
8475 bool CMSCollector::par_simulate_overflow() {
8476 return simulate_overflow();
8477 }
8478 #endif
8480 // Single-threaded
8481 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8482 assert(stack->isEmpty(), "Expected precondition");
8483 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8484 size_t i = num;
8485 oop cur = _overflow_list;
8486 const markOop proto = markOopDesc::prototype();
8487 NOT_PRODUCT(size_t n = 0;)
8488 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8489 next = oop(cur->mark());
8490 cur->set_mark(proto); // until proven otherwise
8491 assert(cur->is_oop(), "Should be an oop");
8492 bool res = stack->push(cur);
8493 assert(res, "Bit off more than can chew?");
8494 NOT_PRODUCT(n++;)
8495 }
8496 _overflow_list = cur;
8497 #ifndef PRODUCT
8498 assert(_num_par_pushes >= n, "Too many pops?");
8499 _num_par_pushes -=n;
8500 #endif
8501 return !stack->isEmpty();
8502 }
8504 // Multi-threaded; use CAS to break off a prefix
8505 bool CMSCollector::par_take_from_overflow_list(size_t num,
8506 OopTaskQueue* work_q) {
8507 assert(work_q->size() == 0, "That's the current policy");
8508 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8509 if (_overflow_list == NULL) {
8510 return false;
8511 }
8512 // Grab the entire list; we'll put back a suffix
8513 oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list);
8514 if (prefix == NULL) { // someone grabbed it before we did ...
8515 // ... we could spin for a short while, but for now we don't
8516 return false;
8517 }
8518 size_t i = num;
8519 oop cur = prefix;
8520 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8521 if (cur->mark() != NULL) {
8522 oop suffix_head = cur->mark(); // suffix will be put back on global list
8523 cur->set_mark(NULL); // break off suffix
8524 // Find tail of suffix so we can prepend suffix to global list
8525 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8526 oop suffix_tail = cur;
8527 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8528 "Tautology");
8529 oop observed_overflow_list = _overflow_list;
8530 do {
8531 cur = observed_overflow_list;
8532 suffix_tail->set_mark(markOop(cur));
8533 observed_overflow_list =
8534 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur);
8535 } while (cur != observed_overflow_list);
8536 }
8538 // Push the prefix elements on work_q
8539 assert(prefix != NULL, "control point invariant");
8540 const markOop proto = markOopDesc::prototype();
8541 oop next;
8542 NOT_PRODUCT(size_t n = 0;)
8543 for (cur = prefix; cur != NULL; cur = next) {
8544 next = oop(cur->mark());
8545 cur->set_mark(proto); // until proven otherwise
8546 assert(cur->is_oop(), "Should be an oop");
8547 bool res = work_q->push(cur);
8548 assert(res, "Bit off more than we can chew?");
8549 NOT_PRODUCT(n++;)
8550 }
8551 #ifndef PRODUCT
8552 assert(_num_par_pushes >= n, "Too many pops?");
8553 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8554 #endif
8555 return true;
8556 }
8558 // Single-threaded
8559 void CMSCollector::push_on_overflow_list(oop p) {
8560 NOT_PRODUCT(_num_par_pushes++;)
8561 assert(p->is_oop(), "Not an oop");
8562 preserve_mark_if_necessary(p);
8563 p->set_mark((markOop)_overflow_list);
8564 _overflow_list = p;
8565 }
8567 // Multi-threaded; use CAS to prepend to overflow list
8568 void CMSCollector::par_push_on_overflow_list(oop p) {
8569 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8570 assert(p->is_oop(), "Not an oop");
8571 par_preserve_mark_if_necessary(p);
8572 oop observed_overflow_list = _overflow_list;
8573 oop cur_overflow_list;
8574 do {
8575 cur_overflow_list = observed_overflow_list;
8576 p->set_mark(markOop(cur_overflow_list));
8577 observed_overflow_list =
8578 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8579 } while (cur_overflow_list != observed_overflow_list);
8580 }
8582 // Single threaded
8583 // General Note on GrowableArray: pushes may silently fail
8584 // because we are (temporarily) out of C-heap for expanding
8585 // the stack. The problem is quite ubiquitous and affects
8586 // a lot of code in the JVM. The prudent thing for GrowableArray
8587 // to do (for now) is to exit with an error. However, that may
8588 // be too draconian in some cases because the caller may be
8589 // able to recover without much harm. For suych cases, we
8590 // should probably introduce a "soft_push" method which returns
8591 // an indication of success or failure with the assumption that
8592 // the caller may be able to recover from a failure; code in
8593 // the VM can then be changed, incrementally, to deal with such
8594 // failures where possible, thus, incrementally hardening the VM
8595 // in such low resource situations.
8596 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8597 int PreserveMarkStackSize = 128;
8599 if (_preserved_oop_stack == NULL) {
8600 assert(_preserved_mark_stack == NULL,
8601 "bijection with preserved_oop_stack");
8602 // Allocate the stacks
8603 _preserved_oop_stack = new (ResourceObj::C_HEAP)
8604 GrowableArray<oop>(PreserveMarkStackSize, true);
8605 _preserved_mark_stack = new (ResourceObj::C_HEAP)
8606 GrowableArray<markOop>(PreserveMarkStackSize, true);
8607 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) {
8608 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */,
8609 "Preserved Mark/Oop Stack for CMS (C-heap)");
8610 }
8611 }
8612 _preserved_oop_stack->push(p);
8613 _preserved_mark_stack->push(m);
8614 assert(m == p->mark(), "Mark word changed");
8615 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(),
8616 "bijection");
8617 }
8619 // Single threaded
8620 void CMSCollector::preserve_mark_if_necessary(oop p) {
8621 markOop m = p->mark();
8622 if (m->must_be_preserved(p)) {
8623 preserve_mark_work(p, m);
8624 }
8625 }
8627 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8628 markOop m = p->mark();
8629 if (m->must_be_preserved(p)) {
8630 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8631 // Even though we read the mark word without holding
8632 // the lock, we are assured that it will not change
8633 // because we "own" this oop, so no other thread can
8634 // be trying to push it on the overflow list; see
8635 // the assertion in preserve_mark_work() that checks
8636 // that m == p->mark().
8637 preserve_mark_work(p, m);
8638 }
8639 }
8641 // We should be able to do this multi-threaded,
8642 // a chunk of stack being a task (this is
8643 // correct because each oop only ever appears
8644 // once in the overflow list. However, it's
8645 // not very easy to completely overlap this with
8646 // other operations, so will generally not be done
8647 // until all work's been completed. Because we
8648 // expect the preserved oop stack (set) to be small,
8649 // it's probably fine to do this single-threaded.
8650 // We can explore cleverer concurrent/overlapped/parallel
8651 // processing of preserved marks if we feel the
8652 // need for this in the future. Stack overflow should
8653 // be so rare in practice and, when it happens, its
8654 // effect on performance so great that this will
8655 // likely just be in the noise anyway.
8656 void CMSCollector::restore_preserved_marks_if_any() {
8657 if (_preserved_oop_stack == NULL) {
8658 assert(_preserved_mark_stack == NULL,
8659 "bijection with preserved_oop_stack");
8660 return;
8661 }
8663 assert(SafepointSynchronize::is_at_safepoint(),
8664 "world should be stopped");
8665 assert(Thread::current()->is_ConcurrentGC_thread() ||
8666 Thread::current()->is_VM_thread(),
8667 "should be single-threaded");
8669 int length = _preserved_oop_stack->length();
8670 assert(_preserved_mark_stack->length() == length, "bijection");
8671 for (int i = 0; i < length; i++) {
8672 oop p = _preserved_oop_stack->at(i);
8673 assert(p->is_oop(), "Should be an oop");
8674 assert(_span.contains(p), "oop should be in _span");
8675 assert(p->mark() == markOopDesc::prototype(),
8676 "Set when taken from overflow list");
8677 markOop m = _preserved_mark_stack->at(i);
8678 p->set_mark(m);
8679 }
8680 _preserved_mark_stack->clear();
8681 _preserved_oop_stack->clear();
8682 assert(_preserved_mark_stack->is_empty() &&
8683 _preserved_oop_stack->is_empty(),
8684 "stacks were cleared above");
8685 }
8687 #ifndef PRODUCT
8688 bool CMSCollector::no_preserved_marks() const {
8689 return ( ( _preserved_mark_stack == NULL
8690 && _preserved_oop_stack == NULL)
8691 || ( _preserved_mark_stack->is_empty()
8692 && _preserved_oop_stack->is_empty()));
8693 }
8694 #endif
8696 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
8697 {
8698 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8699 CMSAdaptiveSizePolicy* size_policy =
8700 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
8701 assert(size_policy->is_gc_cms_adaptive_size_policy(),
8702 "Wrong type for size policy");
8703 return size_policy;
8704 }
8706 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
8707 size_t desired_promo_size) {
8708 if (cur_promo_size < desired_promo_size) {
8709 size_t expand_bytes = desired_promo_size - cur_promo_size;
8710 if (PrintAdaptiveSizePolicy && Verbose) {
8711 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8712 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
8713 expand_bytes);
8714 }
8715 expand(expand_bytes,
8716 MinHeapDeltaBytes,
8717 CMSExpansionCause::_adaptive_size_policy);
8718 } else if (desired_promo_size < cur_promo_size) {
8719 size_t shrink_bytes = cur_promo_size - desired_promo_size;
8720 if (PrintAdaptiveSizePolicy && Verbose) {
8721 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
8722 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
8723 shrink_bytes);
8724 }
8725 shrink(shrink_bytes);
8726 }
8727 }
8729 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
8730 GenCollectedHeap* gch = GenCollectedHeap::heap();
8731 CMSGCAdaptivePolicyCounters* counters =
8732 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
8733 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
8734 "Wrong kind of counters");
8735 return counters;
8736 }
8739 void ASConcurrentMarkSweepGeneration::update_counters() {
8740 if (UsePerfData) {
8741 _space_counters->update_all();
8742 _gen_counters->update_all();
8743 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8744 GenCollectedHeap* gch = GenCollectedHeap::heap();
8745 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8746 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8747 "Wrong gc statistics type");
8748 counters->update_counters(gc_stats_l);
8749 }
8750 }
8752 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
8753 if (UsePerfData) {
8754 _space_counters->update_used(used);
8755 _space_counters->update_capacity();
8756 _gen_counters->update_all();
8758 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8759 GenCollectedHeap* gch = GenCollectedHeap::heap();
8760 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
8761 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
8762 "Wrong gc statistics type");
8763 counters->update_counters(gc_stats_l);
8764 }
8765 }
8767 // The desired expansion delta is computed so that:
8768 // . desired free percentage or greater is used
8769 void ASConcurrentMarkSweepGeneration::compute_new_size() {
8770 assert_locked_or_safepoint(Heap_lock);
8772 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
8774 // If incremental collection failed, we just want to expand
8775 // to the limit.
8776 if (incremental_collection_failed()) {
8777 clear_incremental_collection_failed();
8778 grow_to_reserved();
8779 return;
8780 }
8782 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
8784 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
8785 "Wrong type of heap");
8786 int prev_level = level() - 1;
8787 assert(prev_level >= 0, "The cms generation is the lowest generation");
8788 Generation* prev_gen = gch->get_gen(prev_level);
8789 assert(prev_gen->kind() == Generation::ASParNew,
8790 "Wrong type of young generation");
8791 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
8792 size_t cur_eden = younger_gen->eden()->capacity();
8793 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
8794 size_t cur_promo = free();
8795 size_policy->compute_tenured_generation_free_space(cur_promo,
8796 max_available(),
8797 cur_eden);
8798 resize(cur_promo, size_policy->promo_size());
8800 // Record the new size of the space in the cms generation
8801 // that is available for promotions. This is temporary.
8802 // It should be the desired promo size.
8803 size_policy->avg_cms_promo()->sample(free());
8804 size_policy->avg_old_live()->sample(used());
8806 if (UsePerfData) {
8807 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
8808 counters->update_cms_capacity_counter(capacity());
8809 }
8810 }
8812 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
8813 assert_locked_or_safepoint(Heap_lock);
8814 assert_lock_strong(freelistLock());
8815 HeapWord* old_end = _cmsSpace->end();
8816 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
8817 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
8818 FreeChunk* chunk_at_end = find_chunk_at_end();
8819 if (chunk_at_end == NULL) {
8820 // No room to shrink
8821 if (PrintGCDetails && Verbose) {
8822 gclog_or_tty->print_cr("No room to shrink: old_end "
8823 PTR_FORMAT " unallocated_start " PTR_FORMAT
8824 " chunk_at_end " PTR_FORMAT,
8825 old_end, unallocated_start, chunk_at_end);
8826 }
8827 return;
8828 } else {
8830 // Find the chunk at the end of the space and determine
8831 // how much it can be shrunk.
8832 size_t shrinkable_size_in_bytes = chunk_at_end->size();
8833 size_t aligned_shrinkable_size_in_bytes =
8834 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
8835 assert(unallocated_start <= chunk_at_end->end(),
8836 "Inconsistent chunk at end of space");
8837 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
8838 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
8840 // Shrink the underlying space
8841 _virtual_space.shrink_by(bytes);
8842 if (PrintGCDetails && Verbose) {
8843 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
8844 " desired_bytes " SIZE_FORMAT
8845 " shrinkable_size_in_bytes " SIZE_FORMAT
8846 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
8847 " bytes " SIZE_FORMAT,
8848 desired_bytes, shrinkable_size_in_bytes,
8849 aligned_shrinkable_size_in_bytes, bytes);
8850 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
8851 " unallocated_start " SIZE_FORMAT,
8852 old_end, unallocated_start);
8853 }
8855 // If the space did shrink (shrinking is not guaranteed),
8856 // shrink the chunk at the end by the appropriate amount.
8857 if (((HeapWord*)_virtual_space.high()) < old_end) {
8858 size_t new_word_size =
8859 heap_word_size(_virtual_space.committed_size());
8861 // Have to remove the chunk from the dictionary because it is changing
8862 // size and might be someplace elsewhere in the dictionary.
8864 // Get the chunk at end, shrink it, and put it
8865 // back.
8866 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
8867 size_t word_size_change = word_size_before - new_word_size;
8868 size_t chunk_at_end_old_size = chunk_at_end->size();
8869 assert(chunk_at_end_old_size >= word_size_change,
8870 "Shrink is too large");
8871 chunk_at_end->setSize(chunk_at_end_old_size -
8872 word_size_change);
8873 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
8874 word_size_change);
8876 _cmsSpace->returnChunkToDictionary(chunk_at_end);
8878 MemRegion mr(_cmsSpace->bottom(), new_word_size);
8879 _bts->resize(new_word_size); // resize the block offset shared array
8880 Universe::heap()->barrier_set()->resize_covered_region(mr);
8881 _cmsSpace->assert_locked();
8882 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
8884 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
8886 // update the space and generation capacity counters
8887 if (UsePerfData) {
8888 _space_counters->update_capacity();
8889 _gen_counters->update_all();
8890 }
8892 if (Verbose && PrintGCDetails) {
8893 size_t new_mem_size = _virtual_space.committed_size();
8894 size_t old_mem_size = new_mem_size + bytes;
8895 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
8896 name(), old_mem_size/K, bytes/K, new_mem_size/K);
8897 }
8898 }
8900 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
8901 "Inconsistency at end of space");
8902 assert(chunk_at_end->end() == _cmsSpace->end(),
8903 "Shrinking is inconsistent");
8904 return;
8905 }
8906 }
8908 // Transfer some number of overflown objects to usual marking
8909 // stack. Return true if some objects were transferred.
8910 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8911 size_t num = MIN2((size_t)_mark_stack->capacity()/4,
8912 (size_t)ParGCDesiredObjsFromOverflowList);
8914 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8915 assert(_collector->overflow_list_is_empty() || res,
8916 "If list is not empty, we should have taken something");
8917 assert(!res || !_mark_stack->isEmpty(),
8918 "If we took something, it should now be on our stack");
8919 return res;
8920 }
8922 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8923 size_t res = _sp->block_size_no_stall(addr, _collector);
8924 assert(res != 0, "Should always be able to compute a size");
8925 if (_sp->block_is_obj(addr)) {
8926 if (_live_bit_map->isMarked(addr)) {
8927 // It can't have been dead in a previous cycle
8928 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8929 } else {
8930 _dead_bit_map->mark(addr); // mark the dead object
8931 }
8932 }
8933 return res;
8934 }