1 /*
2 * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/symbolTable.hpp"
27 #include "classfile/systemDictionary.hpp"
28 #include "code/codeCache.hpp"
29 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
33 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
34 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
36 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
37 #include "gc_implementation/parNew/parNewGeneration.hpp"
38 #include "gc_implementation/shared/collectorCounters.hpp"
39 #include "gc_implementation/shared/gcTimer.hpp"
40 #include "gc_implementation/shared/gcTrace.hpp"
41 #include "gc_implementation/shared/gcTraceTime.hpp"
42 #include "gc_implementation/shared/isGCActiveMark.hpp"
43 #include "gc_interface/collectedHeap.inline.hpp"
44 #include "memory/allocation.hpp"
45 #include "memory/cardTableRS.hpp"
46 #include "memory/collectorPolicy.hpp"
47 #include "memory/gcLocker.inline.hpp"
48 #include "memory/genCollectedHeap.hpp"
49 #include "memory/genMarkSweep.hpp"
50 #include "memory/genOopClosures.inline.hpp"
51 #include "memory/iterator.hpp"
52 #include "memory/referencePolicy.hpp"
53 #include "memory/resourceArea.hpp"
54 #include "oops/oop.inline.hpp"
55 #include "prims/jvmtiExport.hpp"
56 #include "runtime/globals_extension.hpp"
57 #include "runtime/handles.inline.hpp"
58 #include "runtime/java.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "services/memoryService.hpp"
61 #include "services/runtimeService.hpp"
62
63 // statics
64 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
65 bool CMSCollector::_full_gc_requested = false;
66 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
67
68 //////////////////////////////////////////////////////////////////
69 // In support of CMS/VM thread synchronization
70 //////////////////////////////////////////////////////////////////
71 // We split use of the CGC_lock into 2 "levels".
72 // The low-level locking is of the usual CGC_lock monitor. We introduce
73 // a higher level "token" (hereafter "CMS token") built on top of the
74 // low level monitor (hereafter "CGC lock").
75 // The token-passing protocol gives priority to the VM thread. The
76 // CMS-lock doesn't provide any fairness guarantees, but clients
77 // should ensure that it is only held for very short, bounded
78 // durations.
79 //
80 // When either of the CMS thread or the VM thread is involved in
81 // collection operations during which it does not want the other
82 // thread to interfere, it obtains the CMS token.
83 //
84 // If either thread tries to get the token while the other has
85 // it, that thread waits. However, if the VM thread and CMS thread
86 // both want the token, then the VM thread gets priority while the
87 // CMS thread waits. This ensures, for instance, that the "concurrent"
88 // phases of the CMS thread's work do not block out the VM thread
89 // for long periods of time as the CMS thread continues to hog
90 // the token. (See bug 4616232).
91 //
92 // The baton-passing functions are, however, controlled by the
93 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
94 // and here the low-level CMS lock, not the high level token,
95 // ensures mutual exclusion.
96 //
97 // Two important conditions that we have to satisfy:
98 // 1. if a thread does a low-level wait on the CMS lock, then it
99 // relinquishes the CMS token if it were holding that token
100 // when it acquired the low-level CMS lock.
101 // 2. any low-level notifications on the low-level lock
102 // should only be sent when a thread has relinquished the token.
103 //
104 // In the absence of either property, we'd have potential deadlock.
105 //
106 // We protect each of the CMS (concurrent and sequential) phases
107 // with the CMS _token_, not the CMS _lock_.
108 //
109 // The only code protected by CMS lock is the token acquisition code
110 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
111 // baton-passing code.
112 //
113 // Unfortunately, i couldn't come up with a good abstraction to factor and
114 // hide the naked CGC_lock manipulation in the baton-passing code
115 // further below. That's something we should try to do. Also, the proof
116 // of correctness of this 2-level locking scheme is far from obvious,
117 // and potentially quite slippery. We have an uneasy supsicion, for instance,
118 // that there may be a theoretical possibility of delay/starvation in the
119 // low-level lock/wait/notify scheme used for the baton-passing because of
120 // potential intereference with the priority scheme embodied in the
121 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
122 // invocation further below and marked with "XXX 20011219YSR".
123 // Indeed, as we note elsewhere, this may become yet more slippery
124 // in the presence of multiple CMS and/or multiple VM threads. XXX
125
126 class CMSTokenSync: public StackObj {
127 private:
128 bool _is_cms_thread;
129 public:
130 CMSTokenSync(bool is_cms_thread):
131 _is_cms_thread(is_cms_thread) {
132 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
133 "Incorrect argument to constructor");
134 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
135 }
136
137 ~CMSTokenSync() {
138 assert(_is_cms_thread ?
139 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
140 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
141 "Incorrect state");
142 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
143 }
144 };
145
146 // Convenience class that does a CMSTokenSync, and then acquires
147 // upto three locks.
148 class CMSTokenSyncWithLocks: public CMSTokenSync {
149 private:
150 // Note: locks are acquired in textual declaration order
151 // and released in the opposite order
152 MutexLockerEx _locker1, _locker2, _locker3;
153 public:
154 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
155 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
156 CMSTokenSync(is_cms_thread),
157 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
158 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
159 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
160 { }
161 };
162
163
164 // Wrapper class to temporarily disable icms during a foreground cms collection.
165 class ICMSDisabler: public StackObj {
166 public:
167 // The ctor disables icms and wakes up the thread so it notices the change;
168 // the dtor re-enables icms. Note that the CMSCollector methods will check
169 // CMSIncrementalMode.
170 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
171 ~ICMSDisabler() { CMSCollector::enable_icms(); }
172 };
173
174 //////////////////////////////////////////////////////////////////
175 // Concurrent Mark-Sweep Generation /////////////////////////////
176 //////////////////////////////////////////////////////////////////
177
178 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
179
180 // This struct contains per-thread things necessary to support parallel
181 // young-gen collection.
182 class CMSParGCThreadState: public CHeapObj<mtGC> {
183 public:
184 CFLS_LAB lab;
185 PromotionInfo promo;
186
187 // Constructor.
188 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
189 promo.setSpace(cfls);
190 }
191 };
192
193 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
194 ReservedSpace rs, size_t initial_byte_size, int level,
195 CardTableRS* ct, bool use_adaptive_freelists,
196 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
197 CardGeneration(rs, initial_byte_size, level, ct),
198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
199 _debug_collection_type(Concurrent_collection_type)
200 {
201 HeapWord* bottom = (HeapWord*) _virtual_space.low();
202 HeapWord* end = (HeapWord*) _virtual_space.high();
203
204 _direct_allocated_words = 0;
205 NOT_PRODUCT(
206 _numObjectsPromoted = 0;
207 _numWordsPromoted = 0;
208 _numObjectsAllocated = 0;
209 _numWordsAllocated = 0;
210 )
211
212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
213 use_adaptive_freelists,
214 dictionaryChoice);
215 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
216 if (_cmsSpace == NULL) {
217 vm_exit_during_initialization(
218 "CompactibleFreeListSpace allocation failure");
219 }
220 _cmsSpace->_gen = this;
221
222 _gc_stats = new CMSGCStats();
223
224 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
225 // offsets match. The ability to tell free chunks from objects
226 // depends on this property.
227 debug_only(
228 FreeChunk* junk = NULL;
229 assert(UseCompressedOops ||
230 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
231 "Offset of FreeChunk::_prev within FreeChunk must match"
232 " that of OopDesc::_klass within OopDesc");
233 )
234 if (CollectedHeap::use_parallel_gc_threads()) {
235 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
236 _par_gc_thread_states =
237 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
238 if (_par_gc_thread_states == NULL) {
239 vm_exit_during_initialization("Could not allocate par gc structs");
240 }
241 for (uint i = 0; i < ParallelGCThreads; i++) {
242 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
243 if (_par_gc_thread_states[i] == NULL) {
244 vm_exit_during_initialization("Could not allocate par gc structs");
245 }
246 }
247 } else {
248 _par_gc_thread_states = NULL;
249 }
250 _incremental_collection_failed = false;
251 // The "dilatation_factor" is the expansion that can occur on
252 // account of the fact that the minimum object size in the CMS
253 // generation may be larger than that in, say, a contiguous young
254 // generation.
255 // Ideally, in the calculation below, we'd compute the dilatation
256 // factor as: MinChunkSize/(promoting_gen's min object size)
257 // Since we do not have such a general query interface for the
258 // promoting generation, we'll instead just use the mimimum
259 // object size (which today is a header's worth of space);
260 // note that all arithmetic is in units of HeapWords.
261 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
262 assert(_dilatation_factor >= 1.0, "from previous assert");
263 }
264
265
266 // The field "_initiating_occupancy" represents the occupancy percentage
267 // at which we trigger a new collection cycle. Unless explicitly specified
268 // via CMSInitiating[Perm]OccupancyFraction (argument "io" below), it
269 // is calculated by:
270 //
271 // Let "f" be MinHeapFreeRatio in
272 //
273 // _intiating_occupancy = 100-f +
274 // f * (CMSTrigger[Perm]Ratio/100)
275 // where CMSTrigger[Perm]Ratio is the argument "tr" below.
276 //
277 // That is, if we assume the heap is at its desired maximum occupancy at the
278 // end of a collection, we let CMSTrigger[Perm]Ratio of the (purported) free
279 // space be allocated before initiating a new collection cycle.
280 //
281 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, intx tr) {
282 assert(io <= 100 && tr >= 0 && tr <= 100, "Check the arguments");
283 if (io >= 0) {
284 _initiating_occupancy = (double)io / 100.0;
285 } else {
286 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
287 (double)(tr * MinHeapFreeRatio) / 100.0)
288 / 100.0;
289 }
290 }
291
292 void ConcurrentMarkSweepGeneration::ref_processor_init() {
293 assert(collector() != NULL, "no collector");
294 collector()->ref_processor_init();
295 }
296
297 void CMSCollector::ref_processor_init() {
298 if (_ref_processor == NULL) {
299 // Allocate and initialize a reference processor
300 _ref_processor =
301 new ReferenceProcessor(_span, // span
302 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
303 (int) ParallelGCThreads, // mt processing degree
304 _cmsGen->refs_discovery_is_mt(), // mt discovery
305 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
306 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
307 &_is_alive_closure, // closure for liveness info
308 false); // next field updates do not need write barrier
309 // Initialize the _ref_processor field of CMSGen
310 _cmsGen->set_ref_processor(_ref_processor);
311
312 // Allocate a dummy ref processor for perm gen.
313 ReferenceProcessor* rp2 = new ReferenceProcessor();
314 if (rp2 == NULL) {
315 vm_exit_during_initialization("Could not allocate ReferenceProcessor object");
316 }
317 _permGen->set_ref_processor(rp2);
318 }
319 }
320
321 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
322 GenCollectedHeap* gch = GenCollectedHeap::heap();
323 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
324 "Wrong type of heap");
325 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
326 gch->gen_policy()->size_policy();
327 assert(sp->is_gc_cms_adaptive_size_policy(),
328 "Wrong type of size policy");
329 return sp;
330 }
331
332 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
333 CMSGCAdaptivePolicyCounters* results =
334 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
335 assert(
336 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
337 "Wrong gc policy counter kind");
338 return results;
339 }
340
341
342 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
343
344 const char* gen_name = "old";
345
346 // Generation Counters - generation 1, 1 subspace
347 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
348
349 _space_counters = new GSpaceCounters(gen_name, 0,
350 _virtual_space.reserved_size(),
351 this, _gen_counters);
352 }
353
354 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
355 _cms_gen(cms_gen)
356 {
357 assert(alpha <= 100, "bad value");
358 _saved_alpha = alpha;
359
360 // Initialize the alphas to the bootstrap value of 100.
361 _gc0_alpha = _cms_alpha = 100;
362
363 _cms_begin_time.update();
364 _cms_end_time.update();
365
366 _gc0_duration = 0.0;
367 _gc0_period = 0.0;
368 _gc0_promoted = 0;
369
370 _cms_duration = 0.0;
371 _cms_period = 0.0;
372 _cms_allocated = 0;
373
374 _cms_used_at_gc0_begin = 0;
375 _cms_used_at_gc0_end = 0;
376 _allow_duty_cycle_reduction = false;
377 _valid_bits = 0;
378 _icms_duty_cycle = CMSIncrementalDutyCycle;
379 }
380
381 double CMSStats::cms_free_adjustment_factor(size_t free) const {
382 // TBD: CR 6909490
383 return 1.0;
384 }
385
386 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
387 }
388
389 // If promotion failure handling is on use
390 // the padded average size of the promotion for each
391 // young generation collection.
392 double CMSStats::time_until_cms_gen_full() const {
393 size_t cms_free = _cms_gen->cmsSpace()->free();
394 GenCollectedHeap* gch = GenCollectedHeap::heap();
395 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
396 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
397 if (cms_free > expected_promotion) {
398 // Start a cms collection if there isn't enough space to promote
399 // for the next minor collection. Use the padded average as
400 // a safety factor.
401 cms_free -= expected_promotion;
402
403 // Adjust by the safety factor.
404 double cms_free_dbl = (double)cms_free;
405 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
406 // Apply a further correction factor which tries to adjust
407 // for recent occurance of concurrent mode failures.
408 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
409 cms_free_dbl = cms_free_dbl * cms_adjustment;
410
411 if (PrintGCDetails && Verbose) {
412 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
413 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
414 cms_free, expected_promotion);
415 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
416 cms_free_dbl, cms_consumption_rate() + 1.0);
417 }
418 // Add 1 in case the consumption rate goes to zero.
419 return cms_free_dbl / (cms_consumption_rate() + 1.0);
420 }
421 return 0.0;
422 }
423
424 // Compare the duration of the cms collection to the
425 // time remaining before the cms generation is empty.
426 // Note that the time from the start of the cms collection
427 // to the start of the cms sweep (less than the total
428 // duration of the cms collection) can be used. This
429 // has been tried and some applications experienced
430 // promotion failures early in execution. This was
431 // possibly because the averages were not accurate
432 // enough at the beginning.
433 double CMSStats::time_until_cms_start() const {
434 // We add "gc0_period" to the "work" calculation
435 // below because this query is done (mostly) at the
436 // end of a scavenge, so we need to conservatively
437 // account for that much possible delay
438 // in the query so as to avoid concurrent mode failures
439 // due to starting the collection just a wee bit too
440 // late.
441 double work = cms_duration() + gc0_period();
442 double deadline = time_until_cms_gen_full();
443 // If a concurrent mode failure occurred recently, we want to be
444 // more conservative and halve our expected time_until_cms_gen_full()
445 if (work > deadline) {
446 if (Verbose && PrintGCDetails) {
447 gclog_or_tty->print(
448 " CMSCollector: collect because of anticipated promotion "
449 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
450 gc0_period(), time_until_cms_gen_full());
451 }
452 return 0.0;
453 }
454 return work - deadline;
455 }
456
457 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
458 // amount of change to prevent wild oscillation.
459 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
460 unsigned int new_duty_cycle) {
461 assert(old_duty_cycle <= 100, "bad input value");
462 assert(new_duty_cycle <= 100, "bad input value");
463
464 // Note: use subtraction with caution since it may underflow (values are
465 // unsigned). Addition is safe since we're in the range 0-100.
466 unsigned int damped_duty_cycle = new_duty_cycle;
467 if (new_duty_cycle < old_duty_cycle) {
468 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
469 if (new_duty_cycle + largest_delta < old_duty_cycle) {
470 damped_duty_cycle = old_duty_cycle - largest_delta;
471 }
472 } else if (new_duty_cycle > old_duty_cycle) {
473 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
474 if (new_duty_cycle > old_duty_cycle + largest_delta) {
475 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
476 }
477 }
478 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
479
480 if (CMSTraceIncrementalPacing) {
481 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
482 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
483 }
484 return damped_duty_cycle;
485 }
486
487 unsigned int CMSStats::icms_update_duty_cycle_impl() {
488 assert(CMSIncrementalPacing && valid(),
489 "should be handled in icms_update_duty_cycle()");
490
491 double cms_time_so_far = cms_timer().seconds();
492 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
493 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
494
495 // Avoid division by 0.
496 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
497 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
498
499 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
500 if (new_duty_cycle > _icms_duty_cycle) {
501 // Avoid very small duty cycles (1 or 2); 0 is allowed.
502 if (new_duty_cycle > 2) {
503 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
504 new_duty_cycle);
505 }
506 } else if (_allow_duty_cycle_reduction) {
507 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
508 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
509 // Respect the minimum duty cycle.
510 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
511 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
512 }
513
514 if (PrintGCDetails || CMSTraceIncrementalPacing) {
515 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
516 }
517
518 _allow_duty_cycle_reduction = false;
519 return _icms_duty_cycle;
520 }
521
522 #ifndef PRODUCT
523 void CMSStats::print_on(outputStream *st) const {
524 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
525 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
526 gc0_duration(), gc0_period(), gc0_promoted());
527 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
528 cms_duration(), cms_duration_per_mb(),
529 cms_period(), cms_allocated());
530 st->print(",cms_since_beg=%g,cms_since_end=%g",
531 cms_time_since_begin(), cms_time_since_end());
532 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
533 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
534 if (CMSIncrementalMode) {
535 st->print(",dc=%d", icms_duty_cycle());
536 }
537
538 if (valid()) {
539 st->print(",promo_rate=%g,cms_alloc_rate=%g",
540 promotion_rate(), cms_allocation_rate());
541 st->print(",cms_consumption_rate=%g,time_until_full=%g",
542 cms_consumption_rate(), time_until_cms_gen_full());
543 }
544 st->print(" ");
545 }
546 #endif // #ifndef PRODUCT
547
548 CMSCollector::CollectorState CMSCollector::_collectorState =
549 CMSCollector::Idling;
550 bool CMSCollector::_foregroundGCIsActive = false;
551 bool CMSCollector::_foregroundGCShouldWait = false;
552
553 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
554 ConcurrentMarkSweepGeneration* permGen,
555 CardTableRS* ct,
556 ConcurrentMarkSweepPolicy* cp):
557 _cmsGen(cmsGen),
558 _permGen(permGen),
559 _ct(ct),
560 _ref_processor(NULL), // will be set later
561 _conc_workers(NULL), // may be set later
562 _abort_preclean(false),
563 _start_sampling(false),
564 _between_prologue_and_epilogue(false),
565 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
566 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"),
567 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
568 -1 /* lock-free */, "No_lock" /* dummy */),
569 _modUnionClosure(&_modUnionTable),
570 _modUnionClosurePar(&_modUnionTable),
571 // Adjust my span to cover old (cms) gen and perm gen
572 _span(cmsGen->reserved()._union(permGen->reserved())),
573 // Construct the is_alive_closure with _span & markBitMap
574 _is_alive_closure(_span, &_markBitMap),
575 _restart_addr(NULL),
576 _overflow_list(NULL),
577 _stats(cmsGen),
578 _eden_chunk_array(NULL), // may be set in ctor body
579 _eden_chunk_capacity(0), // -- ditto --
580 _eden_chunk_index(0), // -- ditto --
581 _survivor_plab_array(NULL), // -- ditto --
582 _survivor_chunk_array(NULL), // -- ditto --
583 _survivor_chunk_capacity(0), // -- ditto --
584 _survivor_chunk_index(0), // -- ditto --
585 _ser_pmc_preclean_ovflw(0),
586 _ser_kac_preclean_ovflw(0),
587 _ser_pmc_remark_ovflw(0),
588 _par_pmc_remark_ovflw(0),
589 _ser_kac_ovflw(0),
590 _par_kac_ovflw(0),
591 #ifndef PRODUCT
592 _num_par_pushes(0),
593 #endif
594 _collection_count_start(0),
595 _verifying(false),
596 _icms_start_limit(NULL),
597 _icms_stop_limit(NULL),
598 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
599 _completed_initialization(false),
600 _collector_policy(cp),
601 _should_unload_classes(false),
602 _concurrent_cycles_since_last_unload(0),
603 _roots_scanning_options(0),
604 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
605 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
606 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
607 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
608 _cms_start_registered(false)
609 {
610 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
611 ExplicitGCInvokesConcurrent = true;
612 }
613 // Now expand the span and allocate the collection support structures
614 // (MUT, marking bit map etc.) to cover both generations subject to
615 // collection.
616
617 // First check that _permGen is adjacent to _cmsGen and above it.
618 assert( _cmsGen->reserved().word_size() > 0
619 && _permGen->reserved().word_size() > 0,
620 "generations should not be of zero size");
621 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(),
622 "_cmsGen and _permGen should not overlap");
623 assert(_cmsGen->reserved().end() == _permGen->reserved().start(),
624 "_cmsGen->end() different from _permGen->start()");
625
626 // For use by dirty card to oop closures.
627 _cmsGen->cmsSpace()->set_collector(this);
628 _permGen->cmsSpace()->set_collector(this);
629
630 // Allocate MUT and marking bit map
631 {
632 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
633 if (!_markBitMap.allocate(_span)) {
634 warning("Failed to allocate CMS Bit Map");
635 return;
636 }
637 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
638 }
639 {
640 _modUnionTable.allocate(_span);
641 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
642 }
643
644 if (!_markStack.allocate(MarkStackSize)) {
645 warning("Failed to allocate CMS Marking Stack");
646 return;
647 }
648 if (!_revisitStack.allocate(CMSRevisitStackSize)) {
649 warning("Failed to allocate CMS Revisit Stack");
650 return;
651 }
652
653 // Support for multi-threaded concurrent phases
654 if (CMSConcurrentMTEnabled) {
655 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
656 // just for now
657 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
658 }
659 if (ConcGCThreads > 1) {
660 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
661 ConcGCThreads, true);
662 if (_conc_workers == NULL) {
663 warning("GC/CMS: _conc_workers allocation failure: "
664 "forcing -CMSConcurrentMTEnabled");
665 CMSConcurrentMTEnabled = false;
666 } else {
667 _conc_workers->initialize_workers();
668 }
669 } else {
670 CMSConcurrentMTEnabled = false;
671 }
672 }
673 if (!CMSConcurrentMTEnabled) {
674 ConcGCThreads = 0;
675 } else {
676 // Turn off CMSCleanOnEnter optimization temporarily for
677 // the MT case where it's not fixed yet; see 6178663.
678 CMSCleanOnEnter = false;
679 }
680 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
681 "Inconsistency");
682
683 // Parallel task queues; these are shared for the
684 // concurrent and stop-world phases of CMS, but
685 // are not shared with parallel scavenge (ParNew).
686 {
687 uint i;
688 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
689
690 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
691 || ParallelRefProcEnabled)
692 && num_queues > 0) {
693 _task_queues = new OopTaskQueueSet(num_queues);
694 if (_task_queues == NULL) {
695 warning("task_queues allocation failure.");
696 return;
697 }
698 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
699 if (_hash_seed == NULL) {
700 warning("_hash_seed array allocation failure");
701 return;
702 }
703
704 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
705 for (i = 0; i < num_queues; i++) {
706 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
707 if (q == NULL) {
708 warning("work_queue allocation failure.");
709 return;
710 }
711 _task_queues->register_queue(i, q);
712 }
713 for (i = 0; i < num_queues; i++) {
714 _task_queues->queue(i)->initialize();
715 _hash_seed[i] = 17; // copied from ParNew
716 }
717 }
718 }
719
720 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
721 _permGen->init_initiating_occupancy(CMSInitiatingPermOccupancyFraction, CMSTriggerPermRatio);
722
723 // Clip CMSBootstrapOccupancy between 0 and 100.
724 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
725 /(double)100;
726
727 _full_gcs_since_conc_gc = 0;
728
729 // Now tell CMS generations the identity of their collector
730 ConcurrentMarkSweepGeneration::set_collector(this);
731
732 // Create & start a CMS thread for this CMS collector
733 _cmsThread = ConcurrentMarkSweepThread::start(this);
734 assert(cmsThread() != NULL, "CMS Thread should have been created");
735 assert(cmsThread()->collector() == this,
736 "CMS Thread should refer to this gen");
737 assert(CGC_lock != NULL, "Where's the CGC_lock?");
738
739 // Support for parallelizing young gen rescan
740 GenCollectedHeap* gch = GenCollectedHeap::heap();
741 _young_gen = gch->prev_gen(_cmsGen);
742 if (gch->supports_inline_contig_alloc()) {
743 _top_addr = gch->top_addr();
744 _end_addr = gch->end_addr();
745 assert(_young_gen != NULL, "no _young_gen");
746 _eden_chunk_index = 0;
747 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
748 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
749 if (_eden_chunk_array == NULL) {
750 _eden_chunk_capacity = 0;
751 warning("GC/CMS: _eden_chunk_array allocation failure");
752 }
753 }
754 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
755
756 // Support for parallelizing survivor space rescan
757 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
758 const size_t max_plab_samples =
759 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
760
761 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
762 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
763 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
764 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
765 || _cursor == NULL) {
766 warning("Failed to allocate survivor plab/chunk array");
767 if (_survivor_plab_array != NULL) {
768 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
769 _survivor_plab_array = NULL;
770 }
771 if (_survivor_chunk_array != NULL) {
772 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
773 _survivor_chunk_array = NULL;
774 }
775 if (_cursor != NULL) {
776 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
777 _cursor = NULL;
778 }
779 } else {
780 _survivor_chunk_capacity = 2*max_plab_samples;
781 for (uint i = 0; i < ParallelGCThreads; i++) {
782 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
783 if (vec == NULL) {
784 warning("Failed to allocate survivor plab array");
785 for (int j = i; j > 0; j--) {
786 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
787 }
788 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
789 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
790 _survivor_plab_array = NULL;
791 _survivor_chunk_array = NULL;
792 _survivor_chunk_capacity = 0;
793 break;
794 } else {
795 ChunkArray* cur =
796 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
797 max_plab_samples);
798 assert(cur->end() == 0, "Should be 0");
799 assert(cur->array() == vec, "Should be vec");
800 assert(cur->capacity() == max_plab_samples, "Error");
801 }
802 }
803 }
804 }
805 assert( ( _survivor_plab_array != NULL
806 && _survivor_chunk_array != NULL)
807 || ( _survivor_chunk_capacity == 0
808 && _survivor_chunk_index == 0),
809 "Error");
810
811 // Choose what strong roots should be scanned depending on verification options
812 // and perm gen collection mode.
813 if (!CMSClassUnloadingEnabled) {
814 // If class unloading is disabled we want to include all classes into the root set.
815 add_root_scanning_option(SharedHeap::SO_AllClasses);
816 } else {
817 add_root_scanning_option(SharedHeap::SO_SystemClasses);
818 }
819
820 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
821 _gc_counters = new CollectorCounters("CMS", 1);
822 _completed_initialization = true;
823 _inter_sweep_timer.start(); // start of time
824 }
825
826 const char* ConcurrentMarkSweepGeneration::name() const {
827 return "concurrent mark-sweep generation";
828 }
829 void ConcurrentMarkSweepGeneration::update_counters() {
830 if (UsePerfData) {
831 _space_counters->update_all();
832 _gen_counters->update_all();
833 }
834 }
835
836 // this is an optimized version of update_counters(). it takes the
837 // used value as a parameter rather than computing it.
838 //
839 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
840 if (UsePerfData) {
841 _space_counters->update_used(used);
842 _space_counters->update_capacity();
843 _gen_counters->update_all();
844 }
845 }
846
847 void ConcurrentMarkSweepGeneration::print() const {
848 Generation::print();
849 cmsSpace()->print();
850 }
851
852 #ifndef PRODUCT
853 void ConcurrentMarkSweepGeneration::print_statistics() {
854 cmsSpace()->printFLCensus(0);
855 }
856 #endif
857
858 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
859 GenCollectedHeap* gch = GenCollectedHeap::heap();
860 if (PrintGCDetails) {
861 if (Verbose) {
862 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
863 level(), short_name(), s, used(), capacity());
864 } else {
865 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
866 level(), short_name(), s, used() / K, capacity() / K);
867 }
868 }
869 if (Verbose) {
870 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
871 gch->used(), gch->capacity());
872 } else {
873 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
874 gch->used() / K, gch->capacity() / K);
875 }
876 }
877
878 size_t
879 ConcurrentMarkSweepGeneration::contiguous_available() const {
880 // dld proposes an improvement in precision here. If the committed
881 // part of the space ends in a free block we should add that to
882 // uncommitted size in the calculation below. Will make this
883 // change later, staying with the approximation below for the
884 // time being. -- ysr.
885 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
886 }
887
888 size_t
889 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
890 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
891 }
892
893 size_t ConcurrentMarkSweepGeneration::max_available() const {
894 return free() + _virtual_space.uncommitted_size();
895 }
896
897 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
898 size_t available = max_available();
899 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
900 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
901 if (Verbose && PrintGCDetails) {
902 gclog_or_tty->print_cr(
903 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
904 "max_promo("SIZE_FORMAT")",
905 res? "":" not", available, res? ">=":"<",
906 av_promo, max_promotion_in_bytes);
907 }
908 return res;
909 }
910
911 // At a promotion failure dump information on block layout in heap
912 // (cms old generation).
913 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
914 if (CMSDumpAtPromotionFailure) {
915 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
916 }
917 }
918
919 CompactibleSpace*
920 ConcurrentMarkSweepGeneration::first_compaction_space() const {
921 return _cmsSpace;
922 }
923
924 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
925 // Clear the promotion information. These pointers can be adjusted
926 // along with all the other pointers into the heap but
927 // compaction is expected to be a rare event with
928 // a heap using cms so don't do it without seeing the need.
929 if (CollectedHeap::use_parallel_gc_threads()) {
930 for (uint i = 0; i < ParallelGCThreads; i++) {
931 _par_gc_thread_states[i]->promo.reset();
932 }
933 }
934 }
935
936 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
937 blk->do_space(_cmsSpace);
938 }
939
940 void ConcurrentMarkSweepGeneration::compute_new_size() {
941 assert_locked_or_safepoint(Heap_lock);
942
943 // If incremental collection failed, we just want to expand
944 // to the limit.
945 if (incremental_collection_failed()) {
946 clear_incremental_collection_failed();
947 grow_to_reserved();
948 return;
949 }
950
951 size_t expand_bytes = 0;
952 double free_percentage = ((double) free()) / capacity();
953 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
954 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
955
956 // compute expansion delta needed for reaching desired free percentage
957 if (free_percentage < desired_free_percentage) {
958 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
959 assert(desired_capacity >= capacity(), "invalid expansion size");
960 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
961 }
962 if (expand_bytes > 0) {
963 if (PrintGCDetails && Verbose) {
964 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
965 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
966 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
967 gclog_or_tty->print_cr(" Desired free fraction %f",
968 desired_free_percentage);
969 gclog_or_tty->print_cr(" Maximum free fraction %f",
970 maximum_free_percentage);
971 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
972 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
973 desired_capacity/1000);
974 int prev_level = level() - 1;
975 if (prev_level >= 0) {
976 size_t prev_size = 0;
977 GenCollectedHeap* gch = GenCollectedHeap::heap();
978 Generation* prev_gen = gch->_gens[prev_level];
979 prev_size = prev_gen->capacity();
980 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
981 prev_size/1000);
982 }
983 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
984 unsafe_max_alloc_nogc()/1000);
985 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
986 contiguous_available()/1000);
987 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
988 expand_bytes);
989 }
990 // safe if expansion fails
991 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
992 if (PrintGCDetails && Verbose) {
993 gclog_or_tty->print_cr(" Expanded free fraction %f",
994 ((double) free()) / capacity());
995 }
996 }
997 }
998
999 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
1000 return cmsSpace()->freelistLock();
1001 }
1002
1003 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
1004 bool tlab) {
1005 CMSSynchronousYieldRequest yr;
1006 MutexLockerEx x(freelistLock(),
1007 Mutex::_no_safepoint_check_flag);
1008 return have_lock_and_allocate(size, tlab);
1009 }
1010
1011 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
1012 bool tlab /* ignored */) {
1013 assert_lock_strong(freelistLock());
1014 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
1015 HeapWord* res = cmsSpace()->allocate(adjustedSize);
1016 // Allocate the object live (grey) if the background collector has
1017 // started marking. This is necessary because the marker may
1018 // have passed this address and consequently this object will
1019 // not otherwise be greyed and would be incorrectly swept up.
1020 // Note that if this object contains references, the writing
1021 // of those references will dirty the card containing this object
1022 // allowing the object to be blackened (and its references scanned)
1023 // either during a preclean phase or at the final checkpoint.
1024 if (res != NULL) {
1025 // We may block here with an uninitialized object with
1026 // its mark-bit or P-bits not yet set. Such objects need
1027 // to be safely navigable by block_start().
1028 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1029 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1030 collector()->direct_allocated(res, adjustedSize);
1031 _direct_allocated_words += adjustedSize;
1032 // allocation counters
1033 NOT_PRODUCT(
1034 _numObjectsAllocated++;
1035 _numWordsAllocated += (int)adjustedSize;
1036 )
1037 }
1038 return res;
1039 }
1040
1041 // In the case of direct allocation by mutators in a generation that
1042 // is being concurrently collected, the object must be allocated
1043 // live (grey) if the background collector has started marking.
1044 // This is necessary because the marker may
1045 // have passed this address and consequently this object will
1046 // not otherwise be greyed and would be incorrectly swept up.
1047 // Note that if this object contains references, the writing
1048 // of those references will dirty the card containing this object
1049 // allowing the object to be blackened (and its references scanned)
1050 // either during a preclean phase or at the final checkpoint.
1051 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1052 assert(_markBitMap.covers(start, size), "Out of bounds");
1053 if (_collectorState >= Marking) {
1054 MutexLockerEx y(_markBitMap.lock(),
1055 Mutex::_no_safepoint_check_flag);
1056 // [see comments preceding SweepClosure::do_blk() below for details]
1057 // 1. need to mark the object as live so it isn't collected
1058 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1059 // 3. need to mark the end of the object so marking, precleaning or sweeping
1060 // can skip over uninitialized or unparsable objects. An allocated
1061 // object is considered uninitialized for our purposes as long as
1062 // its klass word is NULL. (Unparsable objects are those which are
1063 // initialized in the sense just described, but whose sizes can still
1064 // not be correctly determined. Note that the class of unparsable objects
1065 // can only occur in the perm gen. All old gen objects are parsable
1066 // as soon as they are initialized.)
1067 _markBitMap.mark(start); // object is live
1068 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1069 _markBitMap.mark(start + size - 1);
1070 // mark end of object
1071 }
1072 // check that oop looks uninitialized
1073 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1074 }
1075
1076 void CMSCollector::promoted(bool par, HeapWord* start,
1077 bool is_obj_array, size_t obj_size) {
1078 assert(_markBitMap.covers(start), "Out of bounds");
1079 // See comment in direct_allocated() about when objects should
1080 // be allocated live.
1081 if (_collectorState >= Marking) {
1082 // we already hold the marking bit map lock, taken in
1083 // the prologue
1084 if (par) {
1085 _markBitMap.par_mark(start);
1086 } else {
1087 _markBitMap.mark(start);
1088 }
1089 // We don't need to mark the object as uninitialized (as
1090 // in direct_allocated above) because this is being done with the
1091 // world stopped and the object will be initialized by the
1092 // time the marking, precleaning or sweeping get to look at it.
1093 // But see the code for copying objects into the CMS generation,
1094 // where we need to ensure that concurrent readers of the
1095 // block offset table are able to safely navigate a block that
1096 // is in flux from being free to being allocated (and in
1097 // transition while being copied into) and subsequently
1098 // becoming a bona-fide object when the copy/promotion is complete.
1099 assert(SafepointSynchronize::is_at_safepoint(),
1100 "expect promotion only at safepoints");
1101
1102 if (_collectorState < Sweeping) {
1103 // Mark the appropriate cards in the modUnionTable, so that
1104 // this object gets scanned before the sweep. If this is
1105 // not done, CMS generation references in the object might
1106 // not get marked.
1107 // For the case of arrays, which are otherwise precisely
1108 // marked, we need to dirty the entire array, not just its head.
1109 if (is_obj_array) {
1110 // The [par_]mark_range() method expects mr.end() below to
1111 // be aligned to the granularity of a bit's representation
1112 // in the heap. In the case of the MUT below, that's a
1113 // card size.
1114 MemRegion mr(start,
1115 (HeapWord*)round_to((intptr_t)(start + obj_size),
1116 CardTableModRefBS::card_size /* bytes */));
1117 if (par) {
1118 _modUnionTable.par_mark_range(mr);
1119 } else {
1120 _modUnionTable.mark_range(mr);
1121 }
1122 } else { // not an obj array; we can just mark the head
1123 if (par) {
1124 _modUnionTable.par_mark(start);
1125 } else {
1126 _modUnionTable.mark(start);
1127 }
1128 }
1129 }
1130 }
1131 }
1132
1133 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1134 {
1135 size_t delta = pointer_delta(addr, space->bottom());
1136 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1137 }
1138
1139 void CMSCollector::icms_update_allocation_limits()
1140 {
1141 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1142 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1143
1144 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1145 if (CMSTraceIncrementalPacing) {
1146 stats().print();
1147 }
1148
1149 assert(duty_cycle <= 100, "invalid duty cycle");
1150 if (duty_cycle != 0) {
1151 // The duty_cycle is a percentage between 0 and 100; convert to words and
1152 // then compute the offset from the endpoints of the space.
1153 size_t free_words = eden->free() / HeapWordSize;
1154 double free_words_dbl = (double)free_words;
1155 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1156 size_t offset_words = (free_words - duty_cycle_words) / 2;
1157
1158 _icms_start_limit = eden->top() + offset_words;
1159 _icms_stop_limit = eden->end() - offset_words;
1160
1161 // The limits may be adjusted (shifted to the right) by
1162 // CMSIncrementalOffset, to allow the application more mutator time after a
1163 // young gen gc (when all mutators were stopped) and before CMS starts and
1164 // takes away one or more cpus.
1165 if (CMSIncrementalOffset != 0) {
1166 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1167 size_t adjustment = (size_t)adjustment_dbl;
1168 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1169 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1170 _icms_start_limit += adjustment;
1171 _icms_stop_limit = tmp_stop;
1172 }
1173 }
1174 }
1175 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1176 _icms_start_limit = _icms_stop_limit = eden->end();
1177 }
1178
1179 // Install the new start limit.
1180 eden->set_soft_end(_icms_start_limit);
1181
1182 if (CMSTraceIncrementalMode) {
1183 gclog_or_tty->print(" icms alloc limits: "
1184 PTR_FORMAT "," PTR_FORMAT
1185 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1186 _icms_start_limit, _icms_stop_limit,
1187 percent_of_space(eden, _icms_start_limit),
1188 percent_of_space(eden, _icms_stop_limit));
1189 if (Verbose) {
1190 gclog_or_tty->print("eden: ");
1191 eden->print_on(gclog_or_tty);
1192 }
1193 }
1194 }
1195
1196 // Any changes here should try to maintain the invariant
1197 // that if this method is called with _icms_start_limit
1198 // and _icms_stop_limit both NULL, then it should return NULL
1199 // and not notify the icms thread.
1200 HeapWord*
1201 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1202 size_t word_size)
1203 {
1204 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1205 // nop.
1206 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1207 if (top <= _icms_start_limit) {
1208 if (CMSTraceIncrementalMode) {
1209 space->print_on(gclog_or_tty);
1210 gclog_or_tty->stamp();
1211 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1212 ", new limit=" PTR_FORMAT
1213 " (" SIZE_FORMAT "%%)",
1214 top, _icms_stop_limit,
1215 percent_of_space(space, _icms_stop_limit));
1216 }
1217 ConcurrentMarkSweepThread::start_icms();
1218 assert(top < _icms_stop_limit, "Tautology");
1219 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1220 return _icms_stop_limit;
1221 }
1222
1223 // The allocation will cross both the _start and _stop limits, so do the
1224 // stop notification also and return end().
1225 if (CMSTraceIncrementalMode) {
1226 space->print_on(gclog_or_tty);
1227 gclog_or_tty->stamp();
1228 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1229 ", new limit=" PTR_FORMAT
1230 " (" SIZE_FORMAT "%%)",
1231 top, space->end(),
1232 percent_of_space(space, space->end()));
1233 }
1234 ConcurrentMarkSweepThread::stop_icms();
1235 return space->end();
1236 }
1237
1238 if (top <= _icms_stop_limit) {
1239 if (CMSTraceIncrementalMode) {
1240 space->print_on(gclog_or_tty);
1241 gclog_or_tty->stamp();
1242 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT
1243 ", new limit=" PTR_FORMAT
1244 " (" SIZE_FORMAT "%%)",
1245 top, space->end(),
1246 percent_of_space(space, space->end()));
1247 }
1248 ConcurrentMarkSweepThread::stop_icms();
1249 return space->end();
1250 }
1251
1252 if (CMSTraceIncrementalMode) {
1253 space->print_on(gclog_or_tty);
1254 gclog_or_tty->stamp();
1255 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1256 ", new limit=" PTR_FORMAT,
1257 top, NULL);
1258 }
1259 }
1260
1261 return NULL;
1262 }
1263
1264 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1265 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1266 // allocate, copy and if necessary update promoinfo --
1267 // delegate to underlying space.
1268 assert_lock_strong(freelistLock());
1269
1270 #ifndef PRODUCT
1271 if (Universe::heap()->promotion_should_fail()) {
1272 return NULL;
1273 }
1274 #endif // #ifndef PRODUCT
1275
1276 oop res = _cmsSpace->promote(obj, obj_size);
1277 if (res == NULL) {
1278 // expand and retry
1279 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1280 expand(s*HeapWordSize, MinHeapDeltaBytes,
1281 CMSExpansionCause::_satisfy_promotion);
1282 // Since there's currently no next generation, we don't try to promote
1283 // into a more senior generation.
1284 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1285 "is made to pass on a possibly failing "
1286 "promotion to next generation");
1287 res = _cmsSpace->promote(obj, obj_size);
1288 }
1289 if (res != NULL) {
1290 // See comment in allocate() about when objects should
1291 // be allocated live.
1292 assert(obj->is_oop(), "Will dereference klass pointer below");
1293 collector()->promoted(false, // Not parallel
1294 (HeapWord*)res, obj->is_objArray(), obj_size);
1295 // promotion counters
1296 NOT_PRODUCT(
1297 _numObjectsPromoted++;
1298 _numWordsPromoted +=
1299 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1300 )
1301 }
1302 return res;
1303 }
1304
1305
1306 HeapWord*
1307 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1308 HeapWord* top,
1309 size_t word_sz)
1310 {
1311 return collector()->allocation_limit_reached(space, top, word_sz);
1312 }
1313
1314 // IMPORTANT: Notes on object size recognition in CMS.
1315 // ---------------------------------------------------
1316 // A block of storage in the CMS generation is always in
1317 // one of three states. A free block (FREE), an allocated
1318 // object (OBJECT) whose size() method reports the correct size,
1319 // and an intermediate state (TRANSIENT) in which its size cannot
1320 // be accurately determined.
1321 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1322 // -----------------------------------------------------
1323 // FREE: klass_word & 1 == 1; mark_word holds block size
1324 //
1325 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1326 // obj->size() computes correct size
1327 // [Perm Gen objects needs to be "parsable" before they can be navigated]
1328 //
1329 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1330 //
1331 // STATE IDENTIFICATION: (64 bit+COOPS)
1332 // ------------------------------------
1333 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1334 //
1335 // OBJECT: klass_word installed; klass_word != 0;
1336 // obj->size() computes correct size
1337 // [Perm Gen comment above continues to hold]
1338 //
1339 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1340 //
1341 //
1342 // STATE TRANSITION DIAGRAM
1343 //
1344 // mut / parnew mut / parnew
1345 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1346 // ^ |
1347 // |------------------------ DEAD <------------------------------------|
1348 // sweep mut
1349 //
1350 // While a block is in TRANSIENT state its size cannot be determined
1351 // so readers will either need to come back later or stall until
1352 // the size can be determined. Note that for the case of direct
1353 // allocation, P-bits, when available, may be used to determine the
1354 // size of an object that may not yet have been initialized.
1355
1356 // Things to support parallel young-gen collection.
1357 oop
1358 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1359 oop old, markOop m,
1360 size_t word_sz) {
1361 #ifndef PRODUCT
1362 if (Universe::heap()->promotion_should_fail()) {
1363 return NULL;
1364 }
1365 #endif // #ifndef PRODUCT
1366
1367 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1368 PromotionInfo* promoInfo = &ps->promo;
1369 // if we are tracking promotions, then first ensure space for
1370 // promotion (including spooling space for saving header if necessary).
1371 // then allocate and copy, then track promoted info if needed.
1372 // When tracking (see PromotionInfo::track()), the mark word may
1373 // be displaced and in this case restoration of the mark word
1374 // occurs in the (oop_since_save_marks_)iterate phase.
1375 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1376 // Out of space for allocating spooling buffers;
1377 // try expanding and allocating spooling buffers.
1378 if (!expand_and_ensure_spooling_space(promoInfo)) {
1379 return NULL;
1380 }
1381 }
1382 assert(promoInfo->has_spooling_space(), "Control point invariant");
1383 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1384 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1385 if (obj_ptr == NULL) {
1386 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1387 if (obj_ptr == NULL) {
1388 return NULL;
1389 }
1390 }
1391 oop obj = oop(obj_ptr);
1392 OrderAccess::storestore();
1393 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1394 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1395 // IMPORTANT: See note on object initialization for CMS above.
1396 // Otherwise, copy the object. Here we must be careful to insert the
1397 // klass pointer last, since this marks the block as an allocated object.
1398 // Except with compressed oops it's the mark word.
1399 HeapWord* old_ptr = (HeapWord*)old;
1400 // Restore the mark word copied above.
1401 obj->set_mark(m);
1402 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1403 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1404 OrderAccess::storestore();
1405
1406 if (UseCompressedOops) {
1407 // Copy gap missed by (aligned) header size calculation below
1408 obj->set_klass_gap(old->klass_gap());
1409 }
1410 if (word_sz > (size_t)oopDesc::header_size()) {
1411 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1412 obj_ptr + oopDesc::header_size(),
1413 word_sz - oopDesc::header_size());
1414 }
1415
1416 // Now we can track the promoted object, if necessary. We take care
1417 // to delay the transition from uninitialized to full object
1418 // (i.e., insertion of klass pointer) until after, so that it
1419 // atomically becomes a promoted object.
1420 if (promoInfo->tracking()) {
1421 promoInfo->track((PromotedObject*)obj, old->klass());
1422 }
1423 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1424 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1425 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1426
1427 // Finally, install the klass pointer (this should be volatile).
1428 OrderAccess::storestore();
1429 obj->set_klass(old->klass());
1430 // We should now be able to calculate the right size for this object
1431 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1432
1433 collector()->promoted(true, // parallel
1434 obj_ptr, old->is_objArray(), word_sz);
1435
1436 NOT_PRODUCT(
1437 Atomic::inc_ptr(&_numObjectsPromoted);
1438 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1439 )
1440
1441 return obj;
1442 }
1443
1444 void
1445 ConcurrentMarkSweepGeneration::
1446 par_promote_alloc_undo(int thread_num,
1447 HeapWord* obj, size_t word_sz) {
1448 // CMS does not support promotion undo.
1449 ShouldNotReachHere();
1450 }
1451
1452 void
1453 ConcurrentMarkSweepGeneration::
1454 par_promote_alloc_done(int thread_num) {
1455 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1456 ps->lab.retire(thread_num);
1457 }
1458
1459 void
1460 ConcurrentMarkSweepGeneration::
1461 par_oop_since_save_marks_iterate_done(int thread_num) {
1462 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1463 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1464 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1465 }
1466
1467 // XXXPERM
1468 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1469 size_t size,
1470 bool tlab)
1471 {
1472 // We allow a STW collection only if a full
1473 // collection was requested.
1474 return full || should_allocate(size, tlab); // FIX ME !!!
1475 // This and promotion failure handling are connected at the
1476 // hip and should be fixed by untying them.
1477 }
1478
1479 bool CMSCollector::shouldConcurrentCollect() {
1480 if (_full_gc_requested) {
1481 if (Verbose && PrintGCDetails) {
1482 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1483 " gc request (or gc_locker)");
1484 }
1485 return true;
1486 }
1487
1488 // For debugging purposes, change the type of collection.
1489 // If the rotation is not on the concurrent collection
1490 // type, don't start a concurrent collection.
1491 NOT_PRODUCT(
1492 if (RotateCMSCollectionTypes &&
1493 (_cmsGen->debug_collection_type() !=
1494 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1495 assert(_cmsGen->debug_collection_type() !=
1496 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1497 "Bad cms collection type");
1498 return false;
1499 }
1500 )
1501
1502 FreelistLocker x(this);
1503 // ------------------------------------------------------------------
1504 // Print out lots of information which affects the initiation of
1505 // a collection.
1506 if (PrintCMSInitiationStatistics && stats().valid()) {
1507 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1508 gclog_or_tty->stamp();
1509 gclog_or_tty->print_cr("");
1510 stats().print_on(gclog_or_tty);
1511 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1512 stats().time_until_cms_gen_full());
1513 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1514 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1515 _cmsGen->contiguous_available());
1516 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1517 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1518 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1519 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1520 gclog_or_tty->print_cr("initiatingPermOccupancy=%3.7f", _permGen->initiating_occupancy());
1521 }
1522 // ------------------------------------------------------------------
1523
1524 // If the estimated time to complete a cms collection (cms_duration())
1525 // is less than the estimated time remaining until the cms generation
1526 // is full, start a collection.
1527 if (!UseCMSInitiatingOccupancyOnly) {
1528 if (stats().valid()) {
1529 if (stats().time_until_cms_start() == 0.0) {
1530 return true;
1531 }
1532 } else {
1533 // We want to conservatively collect somewhat early in order
1534 // to try and "bootstrap" our CMS/promotion statistics;
1535 // this branch will not fire after the first successful CMS
1536 // collection because the stats should then be valid.
1537 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1538 if (Verbose && PrintGCDetails) {
1539 gclog_or_tty->print_cr(
1540 " CMSCollector: collect for bootstrapping statistics:"
1541 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1542 _bootstrap_occupancy);
1543 }
1544 return true;
1545 }
1546 }
1547 }
1548
1549 // Otherwise, we start a collection cycle if either the perm gen or
1550 // old gen want a collection cycle started. Each may use
1551 // an appropriate criterion for making this decision.
1552 // XXX We need to make sure that the gen expansion
1553 // criterion dovetails well with this. XXX NEED TO FIX THIS
1554 if (_cmsGen->should_concurrent_collect()) {
1555 if (Verbose && PrintGCDetails) {
1556 gclog_or_tty->print_cr("CMS old gen initiated");
1557 }
1558 return true;
1559 }
1560
1561 // We start a collection if we believe an incremental collection may fail;
1562 // this is not likely to be productive in practice because it's probably too
1563 // late anyway.
1564 GenCollectedHeap* gch = GenCollectedHeap::heap();
1565 assert(gch->collector_policy()->is_two_generation_policy(),
1566 "You may want to check the correctness of the following");
1567 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1568 if (Verbose && PrintGCDetails) {
1569 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1570 }
1571 return true;
1572 }
1573
1574 if (CMSClassUnloadingEnabled && _permGen->should_concurrent_collect()) {
1575 bool res = update_should_unload_classes();
1576 if (res) {
1577 if (Verbose && PrintGCDetails) {
1578 gclog_or_tty->print_cr("CMS perm gen initiated");
1579 }
1580 return true;
1581 }
1582 }
1583 return false;
1584 }
1585
1586 // Clear _expansion_cause fields of constituent generations
1587 void CMSCollector::clear_expansion_cause() {
1588 _cmsGen->clear_expansion_cause();
1589 _permGen->clear_expansion_cause();
1590 }
1591
1592 // We should be conservative in starting a collection cycle. To
1593 // start too eagerly runs the risk of collecting too often in the
1594 // extreme. To collect too rarely falls back on full collections,
1595 // which works, even if not optimum in terms of concurrent work.
1596 // As a work around for too eagerly collecting, use the flag
1597 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1598 // giving the user an easily understandable way of controlling the
1599 // collections.
1600 // We want to start a new collection cycle if any of the following
1601 // conditions hold:
1602 // . our current occupancy exceeds the configured initiating occupancy
1603 // for this generation, or
1604 // . we recently needed to expand this space and have not, since that
1605 // expansion, done a collection of this generation, or
1606 // . the underlying space believes that it may be a good idea to initiate
1607 // a concurrent collection (this may be based on criteria such as the
1608 // following: the space uses linear allocation and linear allocation is
1609 // going to fail, or there is believed to be excessive fragmentation in
1610 // the generation, etc... or ...
1611 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1612 // the case of the old generation, not the perm generation; see CR 6543076):
1613 // we may be approaching a point at which allocation requests may fail because
1614 // we will be out of sufficient free space given allocation rate estimates.]
1615 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1616
1617 assert_lock_strong(freelistLock());
1618 if (occupancy() > initiating_occupancy()) {
1619 if (PrintGCDetails && Verbose) {
1620 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1621 short_name(), occupancy(), initiating_occupancy());
1622 }
1623 return true;
1624 }
1625 if (UseCMSInitiatingOccupancyOnly) {
1626 return false;
1627 }
1628 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1629 if (PrintGCDetails && Verbose) {
1630 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1631 short_name());
1632 }
1633 return true;
1634 }
1635 if (_cmsSpace->should_concurrent_collect()) {
1636 if (PrintGCDetails && Verbose) {
1637 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1638 short_name());
1639 }
1640 return true;
1641 }
1642 return false;
1643 }
1644
1645 void ConcurrentMarkSweepGeneration::collect(bool full,
1646 bool clear_all_soft_refs,
1647 size_t size,
1648 bool tlab)
1649 {
1650 collector()->collect(full, clear_all_soft_refs, size, tlab);
1651 }
1652
1653 void CMSCollector::collect(bool full,
1654 bool clear_all_soft_refs,
1655 size_t size,
1656 bool tlab)
1657 {
1658 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1659 // For debugging purposes skip the collection if the state
1660 // is not currently idle
1661 if (TraceCMSState) {
1662 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1663 Thread::current(), full, _collectorState);
1664 }
1665 return;
1666 }
1667
1668 // The following "if" branch is present for defensive reasons.
1669 // In the current uses of this interface, it can be replaced with:
1670 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1671 // But I am not placing that assert here to allow future
1672 // generality in invoking this interface.
1673 if (GC_locker::is_active()) {
1674 // A consistency test for GC_locker
1675 assert(GC_locker::needs_gc(), "Should have been set already");
1676 // Skip this foreground collection, instead
1677 // expanding the heap if necessary.
1678 // Need the free list locks for the call to free() in compute_new_size()
1679 compute_new_size();
1680 return;
1681 }
1682 acquire_control_and_collect(full, clear_all_soft_refs);
1683 _full_gcs_since_conc_gc++;
1684
1685 }
1686
1687 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1688 GenCollectedHeap* gch = GenCollectedHeap::heap();
1689 unsigned int gc_count = gch->total_full_collections();
1690 if (gc_count == full_gc_count) {
1691 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1692 _full_gc_requested = true;
1693 _full_gc_cause = cause;
1694 CGC_lock->notify(); // nudge CMS thread
1695 } else {
1696 assert(gc_count > full_gc_count, "Error: causal loop");
1697 }
1698 }
1699
1700 bool CMSCollector::is_external_interruption() {
1701 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1702 return GCCause::is_user_requested_gc(cause) ||
1703 GCCause::is_serviceability_requested_gc(cause);
1704 }
1705
1706 void CMSCollector::report_concurrent_mode_interruption() {
1707 if (is_external_interruption()) {
1708 if (PrintGCDetails) {
1709 gclog_or_tty->print(" (concurrent mode interrupted)");
1710 }
1711 } else {
1712 if (PrintGCDetails) {
1713 gclog_or_tty->print(" (concurrent mode failure)");
1714 }
1715 _gc_tracer_cm->report_concurrent_mode_failure();
1716 }
1717 }
1718
1719 // The foreground and background collectors need to coordinate in order
1720 // to make sure that they do not mutually interfere with CMS collections.
1721 // When a background collection is active,
1722 // the foreground collector may need to take over (preempt) and
1723 // synchronously complete an ongoing collection. Depending on the
1724 // frequency of the background collections and the heap usage
1725 // of the application, this preemption can be seldom or frequent.
1726 // There are only certain
1727 // points in the background collection that the "collection-baton"
1728 // can be passed to the foreground collector.
1729 //
1730 // The foreground collector will wait for the baton before
1731 // starting any part of the collection. The foreground collector
1732 // will only wait at one location.
1733 //
1734 // The background collector will yield the baton before starting a new
1735 // phase of the collection (e.g., before initial marking, marking from roots,
1736 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1737 // of the loop which switches the phases. The background collector does some
1738 // of the phases (initial mark, final re-mark) with the world stopped.
1739 // Because of locking involved in stopping the world,
1740 // the foreground collector should not block waiting for the background
1741 // collector when it is doing a stop-the-world phase. The background
1742 // collector will yield the baton at an additional point just before
1743 // it enters a stop-the-world phase. Once the world is stopped, the
1744 // background collector checks the phase of the collection. If the
1745 // phase has not changed, it proceeds with the collection. If the
1746 // phase has changed, it skips that phase of the collection. See
1747 // the comments on the use of the Heap_lock in collect_in_background().
1748 //
1749 // Variable used in baton passing.
1750 // _foregroundGCIsActive - Set to true by the foreground collector when
1751 // it wants the baton. The foreground clears it when it has finished
1752 // the collection.
1753 // _foregroundGCShouldWait - Set to true by the background collector
1754 // when it is running. The foreground collector waits while
1755 // _foregroundGCShouldWait is true.
1756 // CGC_lock - monitor used to protect access to the above variables
1757 // and to notify the foreground and background collectors.
1758 // _collectorState - current state of the CMS collection.
1759 //
1760 // The foreground collector
1761 // acquires the CGC_lock
1762 // sets _foregroundGCIsActive
1763 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1764 // various locks acquired in preparation for the collection
1765 // are released so as not to block the background collector
1766 // that is in the midst of a collection
1767 // proceeds with the collection
1768 // clears _foregroundGCIsActive
1769 // returns
1770 //
1771 // The background collector in a loop iterating on the phases of the
1772 // collection
1773 // acquires the CGC_lock
1774 // sets _foregroundGCShouldWait
1775 // if _foregroundGCIsActive is set
1776 // clears _foregroundGCShouldWait, notifies _CGC_lock
1777 // waits on _CGC_lock for _foregroundGCIsActive to become false
1778 // and exits the loop.
1779 // otherwise
1780 // proceed with that phase of the collection
1781 // if the phase is a stop-the-world phase,
1782 // yield the baton once more just before enqueueing
1783 // the stop-world CMS operation (executed by the VM thread).
1784 // returns after all phases of the collection are done
1785 //
1786
1787 void CMSCollector::acquire_control_and_collect(bool full,
1788 bool clear_all_soft_refs) {
1789 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1790 assert(!Thread::current()->is_ConcurrentGC_thread(),
1791 "shouldn't try to acquire control from self!");
1792
1793 // Start the protocol for acquiring control of the
1794 // collection from the background collector (aka CMS thread).
1795 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1796 "VM thread should have CMS token");
1797 // Remember the possibly interrupted state of an ongoing
1798 // concurrent collection
1799 CollectorState first_state = _collectorState;
1800
1801 // Signal to a possibly ongoing concurrent collection that
1802 // we want to do a foreground collection.
1803 _foregroundGCIsActive = true;
1804
1805 // Disable incremental mode during a foreground collection.
1806 ICMSDisabler icms_disabler;
1807
1808 // release locks and wait for a notify from the background collector
1809 // releasing the locks in only necessary for phases which
1810 // do yields to improve the granularity of the collection.
1811 assert_lock_strong(bitMapLock());
1812 // We need to lock the Free list lock for the space that we are
1813 // currently collecting.
1814 assert(haveFreelistLocks(), "Must be holding free list locks");
1815 bitMapLock()->unlock();
1816 releaseFreelistLocks();
1817 {
1818 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1819 if (_foregroundGCShouldWait) {
1820 // We are going to be waiting for action for the CMS thread;
1821 // it had better not be gone (for instance at shutdown)!
1822 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1823 "CMS thread must be running");
1824 // Wait here until the background collector gives us the go-ahead
1825 ConcurrentMarkSweepThread::clear_CMS_flag(
1826 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1827 // Get a possibly blocked CMS thread going:
1828 // Note that we set _foregroundGCIsActive true above,
1829 // without protection of the CGC_lock.
1830 CGC_lock->notify();
1831 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1832 "Possible deadlock");
1833 while (_foregroundGCShouldWait) {
1834 // wait for notification
1835 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1836 // Possibility of delay/starvation here, since CMS token does
1837 // not know to give priority to VM thread? Actually, i think
1838 // there wouldn't be any delay/starvation, but the proof of
1839 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1840 }
1841 ConcurrentMarkSweepThread::set_CMS_flag(
1842 ConcurrentMarkSweepThread::CMS_vm_has_token);
1843 }
1844 }
1845 // The CMS_token is already held. Get back the other locks.
1846 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1847 "VM thread should have CMS token");
1848 getFreelistLocks();
1849 bitMapLock()->lock_without_safepoint_check();
1850 if (TraceCMSState) {
1851 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1852 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1853 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1854 }
1855
1856 // Check if we need to do a compaction, or if not, whether
1857 // we need to start the mark-sweep from scratch.
1858 bool should_compact = false;
1859 bool should_start_over = false;
1860 decide_foreground_collection_type(clear_all_soft_refs,
1861 &should_compact, &should_start_over);
1862
1863 NOT_PRODUCT(
1864 if (RotateCMSCollectionTypes) {
1865 if (_cmsGen->debug_collection_type() ==
1866 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1867 should_compact = true;
1868 } else if (_cmsGen->debug_collection_type() ==
1869 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1870 should_compact = false;
1871 }
1872 }
1873 )
1874
1875 if (first_state > Idling) {
1876 report_concurrent_mode_interruption();
1877 }
1878
1879 if (should_compact) {
1880 // If the collection is being acquired from the background
1881 // collector, there may be references on the discovered
1882 // references lists that have NULL referents (being those
1883 // that were concurrently cleared by a mutator) or
1884 // that are no longer active (having been enqueued concurrently
1885 // by the mutator).
1886 // Scrub the list of those references because Mark-Sweep-Compact
1887 // code assumes referents are not NULL and that all discovered
1888 // Reference objects are active.
1889 ref_processor()->clean_up_discovered_references();
1890
1891 do_compaction_work(clear_all_soft_refs);
1892
1893 // Has the GC time limit been exceeded?
1894 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1895 size_t max_eden_size = young_gen->max_capacity() -
1896 young_gen->to()->capacity() -
1897 young_gen->from()->capacity();
1898 GenCollectedHeap* gch = GenCollectedHeap::heap();
1899 GCCause::Cause gc_cause = gch->gc_cause();
1900 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1901 young_gen->eden()->used(),
1902 _cmsGen->max_capacity(),
1903 max_eden_size,
1904 full,
1905 gc_cause,
1906 gch->collector_policy());
1907 } else {
1908 do_mark_sweep_work(clear_all_soft_refs, first_state,
1909 should_start_over);
1910 }
1911 // Reset the expansion cause, now that we just completed
1912 // a collection cycle.
1913 clear_expansion_cause();
1914 _foregroundGCIsActive = false;
1915 return;
1916 }
1917
1918 // Resize the perm generation and the tenured generation
1919 // after obtaining the free list locks for the
1920 // two generations.
1921 void CMSCollector::compute_new_size() {
1922 assert_locked_or_safepoint(Heap_lock);
1923 FreelistLocker z(this);
1924 _permGen->compute_new_size();
1925 _cmsGen->compute_new_size();
1926 }
1927
1928 // A work method used by foreground collection to determine
1929 // what type of collection (compacting or not, continuing or fresh)
1930 // it should do.
1931 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1932 // and CMSCompactWhenClearAllSoftRefs the default in the future
1933 // and do away with the flags after a suitable period.
1934 void CMSCollector::decide_foreground_collection_type(
1935 bool clear_all_soft_refs, bool* should_compact,
1936 bool* should_start_over) {
1937 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1938 // flag is set, and we have either requested a System.gc() or
1939 // the number of full gc's since the last concurrent cycle
1940 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1941 // or if an incremental collection has failed
1942 GenCollectedHeap* gch = GenCollectedHeap::heap();
1943 assert(gch->collector_policy()->is_two_generation_policy(),
1944 "You may want to check the correctness of the following");
1945 // Inform cms gen if this was due to partial collection failing.
1946 // The CMS gen may use this fact to determine its expansion policy.
1947 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1948 assert(!_cmsGen->incremental_collection_failed(),
1949 "Should have been noticed, reacted to and cleared");
1950 _cmsGen->set_incremental_collection_failed();
1951 }
1952 *should_compact =
1953 UseCMSCompactAtFullCollection &&
1954 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1955 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1956 gch->incremental_collection_will_fail(true /* consult_young */));
1957 *should_start_over = false;
1958 if (clear_all_soft_refs && !*should_compact) {
1959 // We are about to do a last ditch collection attempt
1960 // so it would normally make sense to do a compaction
1961 // to reclaim as much space as possible.
1962 if (CMSCompactWhenClearAllSoftRefs) {
1963 // Default: The rationale is that in this case either
1964 // we are past the final marking phase, in which case
1965 // we'd have to start over, or so little has been done
1966 // that there's little point in saving that work. Compaction
1967 // appears to be the sensible choice in either case.
1968 *should_compact = true;
1969 } else {
1970 // We have been asked to clear all soft refs, but not to
1971 // compact. Make sure that we aren't past the final checkpoint
1972 // phase, for that is where we process soft refs. If we are already
1973 // past that phase, we'll need to redo the refs discovery phase and
1974 // if necessary clear soft refs that weren't previously
1975 // cleared. We do so by remembering the phase in which
1976 // we came in, and if we are past the refs processing
1977 // phase, we'll choose to just redo the mark-sweep
1978 // collection from scratch.
1979 if (_collectorState > FinalMarking) {
1980 // We are past the refs processing phase;
1981 // start over and do a fresh synchronous CMS cycle
1982 _collectorState = Resetting; // skip to reset to start new cycle
1983 reset(false /* == !asynch */);
1984 *should_start_over = true;
1985 } // else we can continue a possibly ongoing current cycle
1986 }
1987 }
1988 }
1989
1990 // A work method used by the foreground collector to do
1991 // a mark-sweep-compact.
1992 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1993 GenCollectedHeap* gch = GenCollectedHeap::heap();
1994
1995 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1996 gc_timer->register_gc_start(os::elapsed_counter());
1997
1998 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1999 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2000
2001 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2002 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2003 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2004 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2005 }
2006
2007 // Sample collection interval time and reset for collection pause.
2008 if (UseAdaptiveSizePolicy) {
2009 size_policy()->msc_collection_begin();
2010 }
2011
2012 // Temporarily widen the span of the weak reference processing to
2013 // the entire heap.
2014 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2015 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2016 // Temporarily, clear the "is_alive_non_header" field of the
2017 // reference processor.
2018 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2019 // Temporarily make reference _processing_ single threaded (non-MT).
2020 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2021 // Temporarily make refs discovery atomic
2022 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2023 // Temporarily make reference _discovery_ single threaded (non-MT)
2024 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2025
2026 ref_processor()->set_enqueuing_is_done(false);
2027 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2028 ref_processor()->setup_policy(clear_all_soft_refs);
2029 // If an asynchronous collection finishes, the _modUnionTable is
2030 // all clear. If we are assuming the collection from an asynchronous
2031 // collection, clear the _modUnionTable.
2032 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2033 "_modUnionTable should be clear if the baton was not passed");
2034 _modUnionTable.clear_all();
2035
2036 // We must adjust the allocation statistics being maintained
2037 // in the free list space. We do so by reading and clearing
2038 // the sweep timer and updating the block flux rate estimates below.
2039 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2040 if (_inter_sweep_timer.is_active()) {
2041 _inter_sweep_timer.stop();
2042 // Note that we do not use this sample to update the _inter_sweep_estimate.
2043 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2044 _inter_sweep_estimate.padded_average(),
2045 _intra_sweep_estimate.padded_average());
2046 }
2047
2048 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2049 ref_processor(), clear_all_soft_refs);
2050 #ifdef ASSERT
2051 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2052 size_t free_size = cms_space->free();
2053 assert(free_size ==
2054 pointer_delta(cms_space->end(), cms_space->compaction_top())
2055 * HeapWordSize,
2056 "All the free space should be compacted into one chunk at top");
2057 assert(cms_space->dictionary()->total_chunk_size(
2058 debug_only(cms_space->freelistLock())) == 0 ||
2059 cms_space->totalSizeInIndexedFreeLists() == 0,
2060 "All the free space should be in a single chunk");
2061 size_t num = cms_space->totalCount();
2062 assert((free_size == 0 && num == 0) ||
2063 (free_size > 0 && (num == 1 || num == 2)),
2064 "There should be at most 2 free chunks after compaction");
2065 #endif // ASSERT
2066 _collectorState = Resetting;
2067 assert(_restart_addr == NULL,
2068 "Should have been NULL'd before baton was passed");
2069 reset(false /* == !asynch */);
2070 _cmsGen->reset_after_compaction();
2071 _concurrent_cycles_since_last_unload = 0;
2072
2073 if (verifying() && !should_unload_classes()) {
2074 perm_gen_verify_bit_map()->clear_all();
2075 }
2076
2077 // Clear any data recorded in the PLAB chunk arrays.
2078 if (_survivor_plab_array != NULL) {
2079 reset_survivor_plab_arrays();
2080 }
2081
2082 // Adjust the per-size allocation stats for the next epoch.
2083 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2084 // Restart the "inter sweep timer" for the next epoch.
2085 _inter_sweep_timer.reset();
2086 _inter_sweep_timer.start();
2087
2088 // Sample collection pause time and reset for collection interval.
2089 if (UseAdaptiveSizePolicy) {
2090 size_policy()->msc_collection_end(gch->gc_cause());
2091 }
2092
2093 gc_timer->register_gc_end(os::elapsed_counter());
2094
2095 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2096
2097 // For a mark-sweep-compact, compute_new_size() will be called
2098 // in the heap's do_collection() method.
2099 }
2100
2101 // A work method used by the foreground collector to do
2102 // a mark-sweep, after taking over from a possibly on-going
2103 // concurrent mark-sweep collection.
2104 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2105 CollectorState first_state, bool should_start_over) {
2106 if (PrintGC && Verbose) {
2107 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2108 "collector with count %d",
2109 _full_gcs_since_conc_gc);
2110 }
2111 switch (_collectorState) {
2112 case Idling:
2113 if (first_state == Idling || should_start_over) {
2114 // The background GC was not active, or should
2115 // restarted from scratch; start the cycle.
2116 _collectorState = InitialMarking;
2117 }
2118 // If first_state was not Idling, then a background GC
2119 // was in progress and has now finished. No need to do it
2120 // again. Leave the state as Idling.
2121 break;
2122 case Precleaning:
2123 // In the foreground case don't do the precleaning since
2124 // it is not done concurrently and there is extra work
2125 // required.
2126 _collectorState = FinalMarking;
2127 }
2128 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2129
2130 // For a mark-sweep, compute_new_size() will be called
2131 // in the heap's do_collection() method.
2132 }
2133
2134
2135 void CMSCollector::getFreelistLocks() const {
2136 // Get locks for all free lists in all generations that this
2137 // collector is responsible for
2138 _cmsGen->freelistLock()->lock_without_safepoint_check();
2139 _permGen->freelistLock()->lock_without_safepoint_check();
2140 }
2141
2142 void CMSCollector::releaseFreelistLocks() const {
2143 // Release locks for all free lists in all generations that this
2144 // collector is responsible for
2145 _cmsGen->freelistLock()->unlock();
2146 _permGen->freelistLock()->unlock();
2147 }
2148
2149 bool CMSCollector::haveFreelistLocks() const {
2150 // Check locks for all free lists in all generations that this
2151 // collector is responsible for
2152 assert_lock_strong(_cmsGen->freelistLock());
2153 assert_lock_strong(_permGen->freelistLock());
2154 PRODUCT_ONLY(ShouldNotReachHere());
2155 return true;
2156 }
2157
2158 // A utility class that is used by the CMS collector to
2159 // temporarily "release" the foreground collector from its
2160 // usual obligation to wait for the background collector to
2161 // complete an ongoing phase before proceeding.
2162 class ReleaseForegroundGC: public StackObj {
2163 private:
2164 CMSCollector* _c;
2165 public:
2166 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2167 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2168 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2169 // allow a potentially blocked foreground collector to proceed
2170 _c->_foregroundGCShouldWait = false;
2171 if (_c->_foregroundGCIsActive) {
2172 CGC_lock->notify();
2173 }
2174 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2175 "Possible deadlock");
2176 }
2177
2178 ~ReleaseForegroundGC() {
2179 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2180 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2181 _c->_foregroundGCShouldWait = true;
2182 }
2183 };
2184
2185 // There are separate collect_in_background and collect_in_foreground because of
2186 // the different locking requirements of the background collector and the
2187 // foreground collector. There was originally an attempt to share
2188 // one "collect" method between the background collector and the foreground
2189 // collector but the if-then-else required made it cleaner to have
2190 // separate methods.
2191 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2192 assert(Thread::current()->is_ConcurrentGC_thread(),
2193 "A CMS asynchronous collection is only allowed on a CMS thread.");
2194
2195 GenCollectedHeap* gch = GenCollectedHeap::heap();
2196 {
2197 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2198 MutexLockerEx hl(Heap_lock, safepoint_check);
2199 FreelistLocker fll(this);
2200 MutexLockerEx x(CGC_lock, safepoint_check);
2201 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2202 // The foreground collector is active or we're
2203 // not using asynchronous collections. Skip this
2204 // background collection.
2205 assert(!_foregroundGCShouldWait, "Should be clear");
2206 return;
2207 } else {
2208 assert(_collectorState == Idling, "Should be idling before start.");
2209 _collectorState = InitialMarking;
2210 register_gc_start(cause);
2211 // Reset the expansion cause, now that we are about to begin
2212 // a new cycle.
2213 clear_expansion_cause();
2214 }
2215 // Decide if we want to enable class unloading as part of the
2216 // ensuing concurrent GC cycle.
2217 update_should_unload_classes();
2218 _full_gc_requested = false; // acks all outstanding full gc requests
2219 _full_gc_cause = GCCause::_no_gc;
2220 // Signal that we are about to start a collection
2221 gch->increment_total_full_collections(); // ... starting a collection cycle
2222 _collection_count_start = gch->total_full_collections();
2223 }
2224
2225 // Used for PrintGC
2226 size_t prev_used;
2227 if (PrintGC && Verbose) {
2228 prev_used = _cmsGen->used(); // XXXPERM
2229 }
2230
2231 // The change of the collection state is normally done at this level;
2232 // the exceptions are phases that are executed while the world is
2233 // stopped. For those phases the change of state is done while the
2234 // world is stopped. For baton passing purposes this allows the
2235 // background collector to finish the phase and change state atomically.
2236 // The foreground collector cannot wait on a phase that is done
2237 // while the world is stopped because the foreground collector already
2238 // has the world stopped and would deadlock.
2239 while (_collectorState != Idling) {
2240 if (TraceCMSState) {
2241 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2242 Thread::current(), _collectorState);
2243 }
2244 // The foreground collector
2245 // holds the Heap_lock throughout its collection.
2246 // holds the CMS token (but not the lock)
2247 // except while it is waiting for the background collector to yield.
2248 //
2249 // The foreground collector should be blocked (not for long)
2250 // if the background collector is about to start a phase
2251 // executed with world stopped. If the background
2252 // collector has already started such a phase, the
2253 // foreground collector is blocked waiting for the
2254 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2255 // are executed in the VM thread.
2256 //
2257 // The locking order is
2258 // PendingListLock (PLL) -- if applicable (FinalMarking)
2259 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2260 // CMS token (claimed in
2261 // stop_world_and_do() -->
2262 // safepoint_synchronize() -->
2263 // CMSThread::synchronize())
2264
2265 {
2266 // Check if the FG collector wants us to yield.
2267 CMSTokenSync x(true); // is cms thread
2268 if (waitForForegroundGC()) {
2269 // We yielded to a foreground GC, nothing more to be
2270 // done this round.
2271 assert(_foregroundGCShouldWait == false, "We set it to false in "
2272 "waitForForegroundGC()");
2273 if (TraceCMSState) {
2274 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2275 " exiting collection CMS state %d",
2276 Thread::current(), _collectorState);
2277 }
2278 return;
2279 } else {
2280 // The background collector can run but check to see if the
2281 // foreground collector has done a collection while the
2282 // background collector was waiting to get the CGC_lock
2283 // above. If yes, break so that _foregroundGCShouldWait
2284 // is cleared before returning.
2285 if (_collectorState == Idling) {
2286 break;
2287 }
2288 }
2289 }
2290
2291 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2292 "should be waiting");
2293
2294 switch (_collectorState) {
2295 case InitialMarking:
2296 {
2297 ReleaseForegroundGC x(this);
2298 stats().record_cms_begin();
2299 VM_CMS_Initial_Mark initial_mark_op(this);
2300 VMThread::execute(&initial_mark_op);
2301 }
2302 // The collector state may be any legal state at this point
2303 // since the background collector may have yielded to the
2304 // foreground collector.
2305 break;
2306 case Marking:
2307 // initial marking in checkpointRootsInitialWork has been completed
2308 if (markFromRoots(true)) { // we were successful
2309 assert(_collectorState == Precleaning, "Collector state should "
2310 "have changed");
2311 } else {
2312 assert(_foregroundGCIsActive, "Internal state inconsistency");
2313 }
2314 break;
2315 case Precleaning:
2316 if (UseAdaptiveSizePolicy) {
2317 size_policy()->concurrent_precleaning_begin();
2318 }
2319 // marking from roots in markFromRoots has been completed
2320 preclean();
2321 if (UseAdaptiveSizePolicy) {
2322 size_policy()->concurrent_precleaning_end();
2323 }
2324 assert(_collectorState == AbortablePreclean ||
2325 _collectorState == FinalMarking,
2326 "Collector state should have changed");
2327 break;
2328 case AbortablePreclean:
2329 if (UseAdaptiveSizePolicy) {
2330 size_policy()->concurrent_phases_resume();
2331 }
2332 abortable_preclean();
2333 if (UseAdaptiveSizePolicy) {
2334 size_policy()->concurrent_precleaning_end();
2335 }
2336 assert(_collectorState == FinalMarking, "Collector state should "
2337 "have changed");
2338 break;
2339 case FinalMarking:
2340 {
2341 ReleaseForegroundGC x(this);
2342
2343 VM_CMS_Final_Remark final_remark_op(this);
2344 VMThread::execute(&final_remark_op);
2345 }
2346 assert(_foregroundGCShouldWait, "block post-condition");
2347 break;
2348 case Sweeping:
2349 if (UseAdaptiveSizePolicy) {
2350 size_policy()->concurrent_sweeping_begin();
2351 }
2352 // final marking in checkpointRootsFinal has been completed
2353 sweep(true);
2354 assert(_collectorState == Resizing, "Collector state change "
2355 "to Resizing must be done under the free_list_lock");
2356 _full_gcs_since_conc_gc = 0;
2357
2358 // Stop the timers for adaptive size policy for the concurrent phases
2359 if (UseAdaptiveSizePolicy) {
2360 size_policy()->concurrent_sweeping_end();
2361 size_policy()->concurrent_phases_end(gch->gc_cause(),
2362 gch->prev_gen(_cmsGen)->capacity(),
2363 _cmsGen->free());
2364 }
2365
2366 case Resizing: {
2367 // Sweeping has been completed...
2368 // At this point the background collection has completed.
2369 // Don't move the call to compute_new_size() down
2370 // into code that might be executed if the background
2371 // collection was preempted.
2372 {
2373 ReleaseForegroundGC x(this); // unblock FG collection
2374 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2375 CMSTokenSync z(true); // not strictly needed.
2376 if (_collectorState == Resizing) {
2377 compute_new_size();
2378 save_heap_summary();
2379 _collectorState = Resetting;
2380 } else {
2381 assert(_collectorState == Idling, "The state should only change"
2382 " because the foreground collector has finished the collection");
2383 }
2384 }
2385 break;
2386 }
2387 case Resetting:
2388 // CMS heap resizing has been completed
2389 reset(true);
2390 assert(_collectorState == Idling, "Collector state should "
2391 "have changed");
2392 stats().record_cms_end();
2393 // Don't move the concurrent_phases_end() and compute_new_size()
2394 // calls to here because a preempted background collection
2395 // has it's state set to "Resetting".
2396 break;
2397 case Idling:
2398 default:
2399 ShouldNotReachHere();
2400 break;
2401 }
2402 if (TraceCMSState) {
2403 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2404 Thread::current(), _collectorState);
2405 }
2406 assert(_foregroundGCShouldWait, "block post-condition");
2407 }
2408
2409 // Should this be in gc_epilogue?
2410 collector_policy()->counters()->update_counters();
2411
2412 {
2413 // Clear _foregroundGCShouldWait and, in the event that the
2414 // foreground collector is waiting, notify it, before
2415 // returning.
2416 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2417 _foregroundGCShouldWait = false;
2418 if (_foregroundGCIsActive) {
2419 CGC_lock->notify();
2420 }
2421 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2422 "Possible deadlock");
2423 }
2424 if (TraceCMSState) {
2425 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2426 " exiting collection CMS state %d",
2427 Thread::current(), _collectorState);
2428 }
2429 if (PrintGC && Verbose) {
2430 _cmsGen->print_heap_change(prev_used);
2431 }
2432 }
2433
2434 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2435 if (!_cms_start_registered) {
2436 register_gc_start(cause);
2437 }
2438 }
2439
2440 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2441 _cms_start_registered = true;
2442 _gc_timer_cm->register_gc_start(os::elapsed_counter());
2443 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2444 }
2445
2446 void CMSCollector::register_gc_end() {
2447 if (_cms_start_registered) {
2448 report_heap_summary(GCWhen::AfterGC);
2449
2450 _gc_timer_cm->register_gc_end(os::elapsed_counter());
2451 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2452 _cms_start_registered = false;
2453 }
2454 }
2455
2456 void CMSCollector::save_heap_summary() {
2457 GenCollectedHeap* gch = GenCollectedHeap::heap();
2458 _last_heap_summary = gch->create_heap_summary();
2459 _last_perm_gen_summary = gch->create_perm_gen_summary();
2460 }
2461
2462 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2463 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_perm_gen_summary);
2464 }
2465
2466 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2467 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2468 "Foreground collector should be waiting, not executing");
2469 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2470 "may only be done by the VM Thread with the world stopped");
2471 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2472 "VM thread should have CMS token");
2473
2474 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2475 true, NULL);)
2476 if (UseAdaptiveSizePolicy) {
2477 size_policy()->ms_collection_begin();
2478 }
2479 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2480
2481 HandleMark hm; // Discard invalid handles created during verification
2482
2483 if (VerifyBeforeGC &&
2484 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2485 Universe::verify();
2486 }
2487
2488 // Snapshot the soft reference policy to be used in this collection cycle.
2489 ref_processor()->setup_policy(clear_all_soft_refs);
2490
2491 bool init_mark_was_synchronous = false; // until proven otherwise
2492 while (_collectorState != Idling) {
2493 if (TraceCMSState) {
2494 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2495 Thread::current(), _collectorState);
2496 }
2497 switch (_collectorState) {
2498 case InitialMarking:
2499 register_foreground_gc_start(cause);
2500 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2501 checkpointRootsInitial(false);
2502 assert(_collectorState == Marking, "Collector state should have changed"
2503 " within checkpointRootsInitial()");
2504 break;
2505 case Marking:
2506 // initial marking in checkpointRootsInitialWork has been completed
2507 if (VerifyDuringGC &&
2508 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2509 gclog_or_tty->print("Verify before initial mark: ");
2510 Universe::verify();
2511 }
2512 {
2513 bool res = markFromRoots(false);
2514 assert(res && _collectorState == FinalMarking, "Collector state should "
2515 "have changed");
2516 break;
2517 }
2518 case FinalMarking:
2519 if (VerifyDuringGC &&
2520 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2521 gclog_or_tty->print("Verify before re-mark: ");
2522 Universe::verify();
2523 }
2524 checkpointRootsFinal(false, clear_all_soft_refs,
2525 init_mark_was_synchronous);
2526 assert(_collectorState == Sweeping, "Collector state should not "
2527 "have changed within checkpointRootsFinal()");
2528 break;
2529 case Sweeping:
2530 // final marking in checkpointRootsFinal has been completed
2531 if (VerifyDuringGC &&
2532 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2533 gclog_or_tty->print("Verify before sweep: ");
2534 Universe::verify();
2535 }
2536 sweep(false);
2537 assert(_collectorState == Resizing, "Incorrect state");
2538 break;
2539 case Resizing: {
2540 // Sweeping has been completed; the actual resize in this case
2541 // is done separately; nothing to be done in this state.
2542 _collectorState = Resetting;
2543 break;
2544 }
2545 case Resetting:
2546 // The heap has been resized.
2547 if (VerifyDuringGC &&
2548 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2549 gclog_or_tty->print("Verify before reset: ");
2550 Universe::verify();
2551 }
2552 save_heap_summary();
2553 reset(false);
2554 assert(_collectorState == Idling, "Collector state should "
2555 "have changed");
2556 break;
2557 case Precleaning:
2558 case AbortablePreclean:
2559 // Elide the preclean phase
2560 _collectorState = FinalMarking;
2561 break;
2562 default:
2563 ShouldNotReachHere();
2564 }
2565 if (TraceCMSState) {
2566 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2567 Thread::current(), _collectorState);
2568 }
2569 }
2570
2571 if (UseAdaptiveSizePolicy) {
2572 GenCollectedHeap* gch = GenCollectedHeap::heap();
2573 size_policy()->ms_collection_end(gch->gc_cause());
2574 }
2575
2576 if (VerifyAfterGC &&
2577 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2578 Universe::verify();
2579 }
2580 if (TraceCMSState) {
2581 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2582 " exiting collection CMS state %d",
2583 Thread::current(), _collectorState);
2584 }
2585 }
2586
2587 bool CMSCollector::waitForForegroundGC() {
2588 bool res = false;
2589 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2590 "CMS thread should have CMS token");
2591 // Block the foreground collector until the
2592 // background collectors decides whether to
2593 // yield.
2594 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2595 _foregroundGCShouldWait = true;
2596 if (_foregroundGCIsActive) {
2597 // The background collector yields to the
2598 // foreground collector and returns a value
2599 // indicating that it has yielded. The foreground
2600 // collector can proceed.
2601 res = true;
2602 _foregroundGCShouldWait = false;
2603 ConcurrentMarkSweepThread::clear_CMS_flag(
2604 ConcurrentMarkSweepThread::CMS_cms_has_token);
2605 ConcurrentMarkSweepThread::set_CMS_flag(
2606 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2607 // Get a possibly blocked foreground thread going
2608 CGC_lock->notify();
2609 if (TraceCMSState) {
2610 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2611 Thread::current(), _collectorState);
2612 }
2613 while (_foregroundGCIsActive) {
2614 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2615 }
2616 ConcurrentMarkSweepThread::set_CMS_flag(
2617 ConcurrentMarkSweepThread::CMS_cms_has_token);
2618 ConcurrentMarkSweepThread::clear_CMS_flag(
2619 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2620 }
2621 if (TraceCMSState) {
2622 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2623 Thread::current(), _collectorState);
2624 }
2625 return res;
2626 }
2627
2628 // Because of the need to lock the free lists and other structures in
2629 // the collector, common to all the generations that the collector is
2630 // collecting, we need the gc_prologues of individual CMS generations
2631 // delegate to their collector. It may have been simpler had the
2632 // current infrastructure allowed one to call a prologue on a
2633 // collector. In the absence of that we have the generation's
2634 // prologue delegate to the collector, which delegates back
2635 // some "local" work to a worker method in the individual generations
2636 // that it's responsible for collecting, while itself doing any
2637 // work common to all generations it's responsible for. A similar
2638 // comment applies to the gc_epilogue()'s.
2639 // The role of the varaible _between_prologue_and_epilogue is to
2640 // enforce the invocation protocol.
2641 void CMSCollector::gc_prologue(bool full) {
2642 // Call gc_prologue_work() for each CMSGen and PermGen that
2643 // we are responsible for.
2644
2645 // The following locking discipline assumes that we are only called
2646 // when the world is stopped.
2647 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2648
2649 // The CMSCollector prologue must call the gc_prologues for the
2650 // "generations" (including PermGen if any) that it's responsible
2651 // for.
2652
2653 assert( Thread::current()->is_VM_thread()
2654 || ( CMSScavengeBeforeRemark
2655 && Thread::current()->is_ConcurrentGC_thread()),
2656 "Incorrect thread type for prologue execution");
2657
2658 if (_between_prologue_and_epilogue) {
2659 // We have already been invoked; this is a gc_prologue delegation
2660 // from yet another CMS generation that we are responsible for, just
2661 // ignore it since all relevant work has already been done.
2662 return;
2663 }
2664
2665 // set a bit saying prologue has been called; cleared in epilogue
2666 _between_prologue_and_epilogue = true;
2667 // Claim locks for common data structures, then call gc_prologue_work()
2668 // for each CMSGen and PermGen that we are responsible for.
2669
2670 getFreelistLocks(); // gets free list locks on constituent spaces
2671 bitMapLock()->lock_without_safepoint_check();
2672
2673 // Should call gc_prologue_work() for all cms gens we are responsible for
2674 bool registerClosure = _collectorState >= Marking
2675 && _collectorState < Sweeping;
2676 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2677 &_modUnionClosurePar
2678 : &_modUnionClosure;
2679 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2680 _permGen->gc_prologue_work(full, registerClosure, muc);
2681
2682 if (!full) {
2683 stats().record_gc0_begin();
2684 }
2685 }
2686
2687 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2688 // Delegate to CMScollector which knows how to coordinate between
2689 // this and any other CMS generations that it is responsible for
2690 // collecting.
2691 collector()->gc_prologue(full);
2692 }
2693
2694 // This is a "private" interface for use by this generation's CMSCollector.
2695 // Not to be called directly by any other entity (for instance,
2696 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2697 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2698 bool registerClosure, ModUnionClosure* modUnionClosure) {
2699 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2700 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2701 "Should be NULL");
2702 if (registerClosure) {
2703 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2704 }
2705 cmsSpace()->gc_prologue();
2706 // Clear stat counters
2707 NOT_PRODUCT(
2708 assert(_numObjectsPromoted == 0, "check");
2709 assert(_numWordsPromoted == 0, "check");
2710 if (Verbose && PrintGC) {
2711 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2712 SIZE_FORMAT" bytes concurrently",
2713 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2714 }
2715 _numObjectsAllocated = 0;
2716 _numWordsAllocated = 0;
2717 )
2718 }
2719
2720 void CMSCollector::gc_epilogue(bool full) {
2721 // The following locking discipline assumes that we are only called
2722 // when the world is stopped.
2723 assert(SafepointSynchronize::is_at_safepoint(),
2724 "world is stopped assumption");
2725
2726 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2727 // if linear allocation blocks need to be appropriately marked to allow the
2728 // the blocks to be parsable. We also check here whether we need to nudge the
2729 // CMS collector thread to start a new cycle (if it's not already active).
2730 assert( Thread::current()->is_VM_thread()
2731 || ( CMSScavengeBeforeRemark
2732 && Thread::current()->is_ConcurrentGC_thread()),
2733 "Incorrect thread type for epilogue execution");
2734
2735 if (!_between_prologue_and_epilogue) {
2736 // We have already been invoked; this is a gc_epilogue delegation
2737 // from yet another CMS generation that we are responsible for, just
2738 // ignore it since all relevant work has already been done.
2739 return;
2740 }
2741 assert(haveFreelistLocks(), "must have freelist locks");
2742 assert_lock_strong(bitMapLock());
2743
2744 _cmsGen->gc_epilogue_work(full);
2745 _permGen->gc_epilogue_work(full);
2746
2747 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2748 // in case sampling was not already enabled, enable it
2749 _start_sampling = true;
2750 }
2751 // reset _eden_chunk_array so sampling starts afresh
2752 _eden_chunk_index = 0;
2753
2754 size_t cms_used = _cmsGen->cmsSpace()->used();
2755 size_t perm_used = _permGen->cmsSpace()->used();
2756
2757 // update performance counters - this uses a special version of
2758 // update_counters() that allows the utilization to be passed as a
2759 // parameter, avoiding multiple calls to used().
2760 //
2761 _cmsGen->update_counters(cms_used);
2762 _permGen->update_counters(perm_used);
2763
2764 if (CMSIncrementalMode) {
2765 icms_update_allocation_limits();
2766 }
2767
2768 bitMapLock()->unlock();
2769 releaseFreelistLocks();
2770
2771 if (!CleanChunkPoolAsync) {
2772 Chunk::clean_chunk_pool();
2773 }
2774
2775 _between_prologue_and_epilogue = false; // ready for next cycle
2776 }
2777
2778 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2779 collector()->gc_epilogue(full);
2780
2781 // Also reset promotion tracking in par gc thread states.
2782 if (CollectedHeap::use_parallel_gc_threads()) {
2783 for (uint i = 0; i < ParallelGCThreads; i++) {
2784 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2785 }
2786 }
2787 }
2788
2789 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2790 assert(!incremental_collection_failed(), "Should have been cleared");
2791 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2792 cmsSpace()->gc_epilogue();
2793 // Print stat counters
2794 NOT_PRODUCT(
2795 assert(_numObjectsAllocated == 0, "check");
2796 assert(_numWordsAllocated == 0, "check");
2797 if (Verbose && PrintGC) {
2798 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2799 SIZE_FORMAT" bytes",
2800 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2801 }
2802 _numObjectsPromoted = 0;
2803 _numWordsPromoted = 0;
2804 )
2805
2806 if (PrintGC && Verbose) {
2807 // Call down the chain in contiguous_available needs the freelistLock
2808 // so print this out before releasing the freeListLock.
2809 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2810 contiguous_available());
2811 }
2812 }
2813
2814 #ifndef PRODUCT
2815 bool CMSCollector::have_cms_token() {
2816 Thread* thr = Thread::current();
2817 if (thr->is_VM_thread()) {
2818 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2819 } else if (thr->is_ConcurrentGC_thread()) {
2820 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2821 } else if (thr->is_GC_task_thread()) {
2822 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2823 ParGCRareEvent_lock->owned_by_self();
2824 }
2825 return false;
2826 }
2827 #endif
2828
2829 // Check reachability of the given heap address in CMS generation,
2830 // treating all other generations as roots.
2831 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2832 // We could "guarantee" below, rather than assert, but i'll
2833 // leave these as "asserts" so that an adventurous debugger
2834 // could try this in the product build provided some subset of
2835 // the conditions were met, provided they were intersted in the
2836 // results and knew that the computation below wouldn't interfere
2837 // with other concurrent computations mutating the structures
2838 // being read or written.
2839 assert(SafepointSynchronize::is_at_safepoint(),
2840 "Else mutations in object graph will make answer suspect");
2841 assert(have_cms_token(), "Should hold cms token");
2842 assert(haveFreelistLocks(), "must hold free list locks");
2843 assert_lock_strong(bitMapLock());
2844
2845 // Clear the marking bit map array before starting, but, just
2846 // for kicks, first report if the given address is already marked
2847 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2848 _markBitMap.isMarked(addr) ? "" : " not");
2849
2850 if (verify_after_remark()) {
2851 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2852 bool result = verification_mark_bm()->isMarked(addr);
2853 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2854 result ? "IS" : "is NOT");
2855 return result;
2856 } else {
2857 gclog_or_tty->print_cr("Could not compute result");
2858 return false;
2859 }
2860 }
2861
2862 ////////////////////////////////////////////////////////
2863 // CMS Verification Support
2864 ////////////////////////////////////////////////////////
2865 // Following the remark phase, the following invariant
2866 // should hold -- each object in the CMS heap which is
2867 // marked in markBitMap() should be marked in the verification_mark_bm().
2868
2869 class VerifyMarkedClosure: public BitMapClosure {
2870 CMSBitMap* _marks;
2871 bool _failed;
2872
2873 public:
2874 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2875
2876 bool do_bit(size_t offset) {
2877 HeapWord* addr = _marks->offsetToHeapWord(offset);
2878 if (!_marks->isMarked(addr)) {
2879 oop(addr)->print_on(gclog_or_tty);
2880 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2881 _failed = true;
2882 }
2883 return true;
2884 }
2885
2886 bool failed() { return _failed; }
2887 };
2888
2889 bool CMSCollector::verify_after_remark() {
2890 gclog_or_tty->print(" [Verifying CMS Marking... ");
2891 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2892 static bool init = false;
2893
2894 assert(SafepointSynchronize::is_at_safepoint(),
2895 "Else mutations in object graph will make answer suspect");
2896 assert(have_cms_token(),
2897 "Else there may be mutual interference in use of "
2898 " verification data structures");
2899 assert(_collectorState > Marking && _collectorState <= Sweeping,
2900 "Else marking info checked here may be obsolete");
2901 assert(haveFreelistLocks(), "must hold free list locks");
2902 assert_lock_strong(bitMapLock());
2903
2904
2905 // Allocate marking bit map if not already allocated
2906 if (!init) { // first time
2907 if (!verification_mark_bm()->allocate(_span)) {
2908 return false;
2909 }
2910 init = true;
2911 }
2912
2913 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2914
2915 // Turn off refs discovery -- so we will be tracing through refs.
2916 // This is as intended, because by this time
2917 // GC must already have cleared any refs that need to be cleared,
2918 // and traced those that need to be marked; moreover,
2919 // the marking done here is not going to intefere in any
2920 // way with the marking information used by GC.
2921 NoRefDiscovery no_discovery(ref_processor());
2922
2923 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2924
2925 // Clear any marks from a previous round
2926 verification_mark_bm()->clear_all();
2927 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2928 verify_work_stacks_empty();
2929
2930 GenCollectedHeap* gch = GenCollectedHeap::heap();
2931 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2932 // Update the saved marks which may affect the root scans.
2933 gch->save_marks();
2934
2935 if (CMSRemarkVerifyVariant == 1) {
2936 // In this first variant of verification, we complete
2937 // all marking, then check if the new marks-verctor is
2938 // a subset of the CMS marks-vector.
2939 verify_after_remark_work_1();
2940 } else if (CMSRemarkVerifyVariant == 2) {
2941 // In this second variant of verification, we flag an error
2942 // (i.e. an object reachable in the new marks-vector not reachable
2943 // in the CMS marks-vector) immediately, also indicating the
2944 // identify of an object (A) that references the unmarked object (B) --
2945 // presumably, a mutation to A failed to be picked up by preclean/remark?
2946 verify_after_remark_work_2();
2947 } else {
2948 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2949 CMSRemarkVerifyVariant);
2950 }
2951 gclog_or_tty->print(" done] ");
2952 return true;
2953 }
2954
2955 void CMSCollector::verify_after_remark_work_1() {
2956 ResourceMark rm;
2957 HandleMark hm;
2958 GenCollectedHeap* gch = GenCollectedHeap::heap();
2959
2960 // Mark from roots one level into CMS
2961 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2962 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2963
2964 gch->gen_process_strong_roots(_cmsGen->level(),
2965 true, // younger gens are roots
2966 true, // activate StrongRootsScope
2967 true, // collecting perm gen
2968 SharedHeap::ScanningOption(roots_scanning_options()),
2969 ¬Older,
2970 true, // walk code active on stacks
2971 NULL);
2972
2973 // Now mark from the roots
2974 assert(_revisitStack.isEmpty(), "Should be empty");
2975 MarkFromRootsClosure markFromRootsClosure(this, _span,
2976 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2977 false /* don't yield */, true /* verifying */);
2978 assert(_restart_addr == NULL, "Expected pre-condition");
2979 verification_mark_bm()->iterate(&markFromRootsClosure);
2980 while (_restart_addr != NULL) {
2981 // Deal with stack overflow: by restarting at the indicated
2982 // address.
2983 HeapWord* ra = _restart_addr;
2984 markFromRootsClosure.reset(ra);
2985 _restart_addr = NULL;
2986 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2987 }
2988 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2989 verify_work_stacks_empty();
2990 // Should reset the revisit stack above, since no class tree
2991 // surgery is forthcoming.
2992 _revisitStack.reset(); // throwing away all contents
2993
2994 // Marking completed -- now verify that each bit marked in
2995 // verification_mark_bm() is also marked in markBitMap(); flag all
2996 // errors by printing corresponding objects.
2997 VerifyMarkedClosure vcl(markBitMap());
2998 verification_mark_bm()->iterate(&vcl);
2999 if (vcl.failed()) {
3000 gclog_or_tty->print("Verification failed");
3001 Universe::heap()->print_on(gclog_or_tty);
3002 fatal("CMS: failed marking verification after remark");
3003 }
3004 }
3005
3006 void CMSCollector::verify_after_remark_work_2() {
3007 ResourceMark rm;
3008 HandleMark hm;
3009 GenCollectedHeap* gch = GenCollectedHeap::heap();
3010
3011 // Mark from roots one level into CMS
3012 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3013 markBitMap());
3014 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3015 gch->gen_process_strong_roots(_cmsGen->level(),
3016 true, // younger gens are roots
3017 true, // activate StrongRootsScope
3018 true, // collecting perm gen
3019 SharedHeap::ScanningOption(roots_scanning_options()),
3020 ¬Older,
3021 true, // walk code active on stacks
3022 NULL);
3023
3024 // Now mark from the roots
3025 assert(_revisitStack.isEmpty(), "Should be empty");
3026 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3027 verification_mark_bm(), markBitMap(), verification_mark_stack());
3028 assert(_restart_addr == NULL, "Expected pre-condition");
3029 verification_mark_bm()->iterate(&markFromRootsClosure);
3030 while (_restart_addr != NULL) {
3031 // Deal with stack overflow: by restarting at the indicated
3032 // address.
3033 HeapWord* ra = _restart_addr;
3034 markFromRootsClosure.reset(ra);
3035 _restart_addr = NULL;
3036 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3037 }
3038 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3039 verify_work_stacks_empty();
3040 // Should reset the revisit stack above, since no class tree
3041 // surgery is forthcoming.
3042 _revisitStack.reset(); // throwing away all contents
3043
3044 // Marking completed -- now verify that each bit marked in
3045 // verification_mark_bm() is also marked in markBitMap(); flag all
3046 // errors by printing corresponding objects.
3047 VerifyMarkedClosure vcl(markBitMap());
3048 verification_mark_bm()->iterate(&vcl);
3049 assert(!vcl.failed(), "Else verification above should not have succeeded");
3050 }
3051
3052 void ConcurrentMarkSweepGeneration::save_marks() {
3053 // delegate to CMS space
3054 cmsSpace()->save_marks();
3055 for (uint i = 0; i < ParallelGCThreads; i++) {
3056 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3057 }
3058 }
3059
3060 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3061 return cmsSpace()->no_allocs_since_save_marks();
3062 }
3063
3064 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3065 \
3066 void ConcurrentMarkSweepGeneration:: \
3067 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3068 cl->set_generation(this); \
3069 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3070 cl->reset_generation(); \
3071 save_marks(); \
3072 }
3073
3074 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3075
3076 void
3077 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3078 {
3079 // Not currently implemented; need to do the following. -- ysr.
3080 // dld -- I think that is used for some sort of allocation profiler. So it
3081 // really means the objects allocated by the mutator since the last
3082 // GC. We could potentially implement this cheaply by recording only
3083 // the direct allocations in a side data structure.
3084 //
3085 // I think we probably ought not to be required to support these
3086 // iterations at any arbitrary point; I think there ought to be some
3087 // call to enable/disable allocation profiling in a generation/space,
3088 // and the iterator ought to return the objects allocated in the
3089 // gen/space since the enable call, or the last iterator call (which
3090 // will probably be at a GC.) That way, for gens like CM&S that would
3091 // require some extra data structure to support this, we only pay the
3092 // cost when it's in use...
3093 cmsSpace()->object_iterate_since_last_GC(blk);
3094 }
3095
3096 void
3097 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3098 cl->set_generation(this);
3099 younger_refs_in_space_iterate(_cmsSpace, cl);
3100 cl->reset_generation();
3101 }
3102
3103 void
3104 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3105 if (freelistLock()->owned_by_self()) {
3106 Generation::oop_iterate(mr, cl);
3107 } else {
3108 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3109 Generation::oop_iterate(mr, cl);
3110 }
3111 }
3112
3113 void
3114 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3115 if (freelistLock()->owned_by_self()) {
3116 Generation::oop_iterate(cl);
3117 } else {
3118 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3119 Generation::oop_iterate(cl);
3120 }
3121 }
3122
3123 void
3124 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3125 if (freelistLock()->owned_by_self()) {
3126 Generation::object_iterate(cl);
3127 } else {
3128 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3129 Generation::object_iterate(cl);
3130 }
3131 }
3132
3133 void
3134 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3135 if (freelistLock()->owned_by_self()) {
3136 Generation::safe_object_iterate(cl);
3137 } else {
3138 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3139 Generation::safe_object_iterate(cl);
3140 }
3141 }
3142
3143 void
3144 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3145 }
3146
3147 void
3148 ConcurrentMarkSweepGeneration::post_compact() {
3149 }
3150
3151 void
3152 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3153 // Fix the linear allocation blocks to look like free blocks.
3154
3155 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3156 // are not called when the heap is verified during universe initialization and
3157 // at vm shutdown.
3158 if (freelistLock()->owned_by_self()) {
3159 cmsSpace()->prepare_for_verify();
3160 } else {
3161 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3162 cmsSpace()->prepare_for_verify();
3163 }
3164 }
3165
3166 void
3167 ConcurrentMarkSweepGeneration::verify() {
3168 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3169 // are not called when the heap is verified during universe initialization and
3170 // at vm shutdown.
3171 if (freelistLock()->owned_by_self()) {
3172 cmsSpace()->verify();
3173 } else {
3174 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3175 cmsSpace()->verify();
3176 }
3177 }
3178
3179 void CMSCollector::verify() {
3180 _cmsGen->verify();
3181 _permGen->verify();
3182 }
3183
3184 #ifndef PRODUCT
3185 bool CMSCollector::overflow_list_is_empty() const {
3186 assert(_num_par_pushes >= 0, "Inconsistency");
3187 if (_overflow_list == NULL) {
3188 assert(_num_par_pushes == 0, "Inconsistency");
3189 }
3190 return _overflow_list == NULL;
3191 }
3192
3193 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3194 // merely consolidate assertion checks that appear to occur together frequently.
3195 void CMSCollector::verify_work_stacks_empty() const {
3196 assert(_markStack.isEmpty(), "Marking stack should be empty");
3197 assert(overflow_list_is_empty(), "Overflow list should be empty");
3198 }
3199
3200 void CMSCollector::verify_overflow_empty() const {
3201 assert(overflow_list_is_empty(), "Overflow list should be empty");
3202 assert(no_preserved_marks(), "No preserved marks");
3203 }
3204 #endif // PRODUCT
3205
3206 // Decide if we want to enable class unloading as part of the
3207 // ensuing concurrent GC cycle. We will collect the perm gen and
3208 // unload classes if it's the case that:
3209 // (1) an explicit gc request has been made and the flag
3210 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3211 // (2) (a) class unloading is enabled at the command line, and
3212 // (b) (i) perm gen threshold has been crossed, or
3213 // (ii) old gen is getting really full, or
3214 // (iii) the previous N CMS collections did not collect the
3215 // perm gen
3216 // NOTE: Provided there is no change in the state of the heap between
3217 // calls to this method, it should have idempotent results. Moreover,
3218 // its results should be monotonically increasing (i.e. going from 0 to 1,
3219 // but not 1 to 0) between successive calls between which the heap was
3220 // not collected. For the implementation below, it must thus rely on
3221 // the property that concurrent_cycles_since_last_unload()
3222 // will not decrease unless a collection cycle happened and that
3223 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3224 // themselves also monotonic in that sense. See check_monotonicity()
3225 // below.
3226 bool CMSCollector::update_should_unload_classes() {
3227 _should_unload_classes = false;
3228 // Condition 1 above
3229 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3230 _should_unload_classes = true;
3231 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3232 // Disjuncts 2.b.(i,ii,iii) above
3233 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3234 CMSClassUnloadingMaxInterval)
3235 || _permGen->should_concurrent_collect()
3236 || _cmsGen->is_too_full();
3237 }
3238 return _should_unload_classes;
3239 }
3240
3241 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3242 bool res = should_concurrent_collect();
3243 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3244 return res;
3245 }
3246
3247 void CMSCollector::setup_cms_unloading_and_verification_state() {
3248 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3249 || VerifyBeforeExit;
3250 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3251
3252 if (should_unload_classes()) { // Should unload classes this cycle
3253 remove_root_scanning_option(rso); // Shrink the root set appropriately
3254 set_verifying(should_verify); // Set verification state for this cycle
3255 return; // Nothing else needs to be done at this time
3256 }
3257
3258 // Not unloading classes this cycle
3259 assert(!should_unload_classes(), "Inconsitency!");
3260 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3261 // We were not verifying, or we _were_ unloading classes in the last cycle,
3262 // AND some verification options are enabled this cycle; in this case,
3263 // we must make sure that the deadness map is allocated if not already so,
3264 // and cleared (if already allocated previously --
3265 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3266 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3267 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3268 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3269 "permanent generation verification disabled");
3270 return; // Note that we leave verification disabled, so we'll retry this
3271 // allocation next cycle. We _could_ remember this failure
3272 // and skip further attempts and permanently disable verification
3273 // attempts if that is considered more desirable.
3274 }
3275 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3276 "_perm_gen_ver_bit_map inconsistency?");
3277 } else {
3278 perm_gen_verify_bit_map()->clear_all();
3279 }
3280 // Include symbols, strings and code cache elements to prevent their resurrection.
3281 add_root_scanning_option(rso);
3282 set_verifying(true);
3283 } else if (verifying() && !should_verify) {
3284 // We were verifying, but some verification flags got disabled.
3285 set_verifying(false);
3286 // Exclude symbols, strings and code cache elements from root scanning to
3287 // reduce IM and RM pauses.
3288 remove_root_scanning_option(rso);
3289 }
3290 }
3291
3292
3293 #ifndef PRODUCT
3294 HeapWord* CMSCollector::block_start(const void* p) const {
3295 const HeapWord* addr = (HeapWord*)p;
3296 if (_span.contains(p)) {
3297 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3298 return _cmsGen->cmsSpace()->block_start(p);
3299 } else {
3300 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3301 "Inconsistent _span?");
3302 return _permGen->cmsSpace()->block_start(p);
3303 }
3304 }
3305 return NULL;
3306 }
3307 #endif
3308
3309 HeapWord*
3310 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3311 bool tlab,
3312 bool parallel) {
3313 CMSSynchronousYieldRequest yr;
3314 assert(!tlab, "Can't deal with TLAB allocation");
3315 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3316 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3317 CMSExpansionCause::_satisfy_allocation);
3318 if (GCExpandToAllocateDelayMillis > 0) {
3319 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3320 }
3321 return have_lock_and_allocate(word_size, tlab);
3322 }
3323
3324 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3325 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3326 // to CardGeneration and share it...
3327 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3328 return CardGeneration::expand(bytes, expand_bytes);
3329 }
3330
3331 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3332 CMSExpansionCause::Cause cause)
3333 {
3334
3335 bool success = expand(bytes, expand_bytes);
3336
3337 // remember why we expanded; this information is used
3338 // by shouldConcurrentCollect() when making decisions on whether to start
3339 // a new CMS cycle.
3340 if (success) {
3341 set_expansion_cause(cause);
3342 if (PrintGCDetails && Verbose) {
3343 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3344 CMSExpansionCause::to_string(cause));
3345 }
3346 }
3347 }
3348
3349 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3350 HeapWord* res = NULL;
3351 MutexLocker x(ParGCRareEvent_lock);
3352 while (true) {
3353 // Expansion by some other thread might make alloc OK now:
3354 res = ps->lab.alloc(word_sz);
3355 if (res != NULL) return res;
3356 // If there's not enough expansion space available, give up.
3357 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3358 return NULL;
3359 }
3360 // Otherwise, we try expansion.
3361 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3362 CMSExpansionCause::_allocate_par_lab);
3363 // Now go around the loop and try alloc again;
3364 // A competing par_promote might beat us to the expansion space,
3365 // so we may go around the loop again if promotion fails agaion.
3366 if (GCExpandToAllocateDelayMillis > 0) {
3367 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3368 }
3369 }
3370 }
3371
3372
3373 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3374 PromotionInfo* promo) {
3375 MutexLocker x(ParGCRareEvent_lock);
3376 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3377 while (true) {
3378 // Expansion by some other thread might make alloc OK now:
3379 if (promo->ensure_spooling_space()) {
3380 assert(promo->has_spooling_space(),
3381 "Post-condition of successful ensure_spooling_space()");
3382 return true;
3383 }
3384 // If there's not enough expansion space available, give up.
3385 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3386 return false;
3387 }
3388 // Otherwise, we try expansion.
3389 expand(refill_size_bytes, MinHeapDeltaBytes,
3390 CMSExpansionCause::_allocate_par_spooling_space);
3391 // Now go around the loop and try alloc again;
3392 // A competing allocation might beat us to the expansion space,
3393 // so we may go around the loop again if allocation fails again.
3394 if (GCExpandToAllocateDelayMillis > 0) {
3395 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3396 }
3397 }
3398 }
3399
3400
3401
3402 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3403 assert_locked_or_safepoint(Heap_lock);
3404 size_t size = ReservedSpace::page_align_size_down(bytes);
3405 if (size > 0) {
3406 shrink_by(size);
3407 }
3408 }
3409
3410 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3411 assert_locked_or_safepoint(Heap_lock);
3412 bool result = _virtual_space.expand_by(bytes);
3413 if (result) {
3414 HeapWord* old_end = _cmsSpace->end();
3415 size_t new_word_size =
3416 heap_word_size(_virtual_space.committed_size());
3417 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3418 _bts->resize(new_word_size); // resize the block offset shared array
3419 Universe::heap()->barrier_set()->resize_covered_region(mr);
3420 // Hmmmm... why doesn't CFLS::set_end verify locking?
3421 // This is quite ugly; FIX ME XXX
3422 _cmsSpace->assert_locked(freelistLock());
3423 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3424
3425 // update the space and generation capacity counters
3426 if (UsePerfData) {
3427 _space_counters->update_capacity();
3428 _gen_counters->update_all();
3429 }
3430
3431 if (Verbose && PrintGC) {
3432 size_t new_mem_size = _virtual_space.committed_size();
3433 size_t old_mem_size = new_mem_size - bytes;
3434 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3435 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3436 }
3437 }
3438 return result;
3439 }
3440
3441 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3442 assert_locked_or_safepoint(Heap_lock);
3443 bool success = true;
3444 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3445 if (remaining_bytes > 0) {
3446 success = grow_by(remaining_bytes);
3447 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3448 }
3449 return success;
3450 }
3451
3452 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3453 assert_locked_or_safepoint(Heap_lock);
3454 assert_lock_strong(freelistLock());
3455 // XXX Fix when compaction is implemented.
3456 warning("Shrinking of CMS not yet implemented");
3457 return;
3458 }
3459
3460
3461 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3462 // phases.
3463 class CMSPhaseAccounting: public StackObj {
3464 public:
3465 CMSPhaseAccounting(CMSCollector *collector,
3466 const char *phase,
3467 bool print_cr = true);
3468 ~CMSPhaseAccounting();
3469
3470 private:
3471 CMSCollector *_collector;
3472 const char *_phase;
3473 elapsedTimer _wallclock;
3474 bool _print_cr;
3475
3476 public:
3477 // Not MT-safe; so do not pass around these StackObj's
3478 // where they may be accessed by other threads.
3479 jlong wallclock_millis() {
3480 assert(_wallclock.is_active(), "Wall clock should not stop");
3481 _wallclock.stop(); // to record time
3482 jlong ret = _wallclock.milliseconds();
3483 _wallclock.start(); // restart
3484 return ret;
3485 }
3486 };
3487
3488 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3489 const char *phase,
3490 bool print_cr) :
3491 _collector(collector), _phase(phase), _print_cr(print_cr) {
3492
3493 if (PrintCMSStatistics != 0) {
3494 _collector->resetYields();
3495 }
3496 if (PrintGCDetails && PrintGCTimeStamps) {
3497 gclog_or_tty->date_stamp(PrintGCDateStamps);
3498 gclog_or_tty->stamp();
3499 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3500 _collector->cmsGen()->short_name(), _phase);
3501 }
3502 _collector->resetTimer();
3503 _wallclock.start();
3504 _collector->startTimer();
3505 }
3506
3507 CMSPhaseAccounting::~CMSPhaseAccounting() {
3508 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3509 _collector->stopTimer();
3510 _wallclock.stop();
3511 if (PrintGCDetails) {
3512 gclog_or_tty->date_stamp(PrintGCDateStamps);
3513 gclog_or_tty->stamp(PrintGCTimeStamps);
3514 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3515 _collector->cmsGen()->short_name(),
3516 _phase, _collector->timerValue(), _wallclock.seconds());
3517 if (_print_cr) {
3518 gclog_or_tty->print_cr("");
3519 }
3520 if (PrintCMSStatistics != 0) {
3521 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3522 _collector->yields());
3523 }
3524 }
3525 }
3526
3527 // CMS work
3528
3529 // Checkpoint the roots into this generation from outside
3530 // this generation. [Note this initial checkpoint need only
3531 // be approximate -- we'll do a catch up phase subsequently.]
3532 void CMSCollector::checkpointRootsInitial(bool asynch) {
3533 assert(_collectorState == InitialMarking, "Wrong collector state");
3534 check_correct_thread_executing();
3535 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3536
3537 save_heap_summary();
3538 report_heap_summary(GCWhen::BeforeGC);
3539
3540 ReferenceProcessor* rp = ref_processor();
3541 SpecializationStats::clear();
3542 assert(_restart_addr == NULL, "Control point invariant");
3543 if (asynch) {
3544 // acquire locks for subsequent manipulations
3545 MutexLockerEx x(bitMapLock(),
3546 Mutex::_no_safepoint_check_flag);
3547 checkpointRootsInitialWork(asynch);
3548 // enable ("weak") refs discovery
3549 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3550 _collectorState = Marking;
3551 } else {
3552 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3553 // which recognizes if we are a CMS generation, and doesn't try to turn on
3554 // discovery; verify that they aren't meddling.
3555 assert(!rp->discovery_is_atomic(),
3556 "incorrect setting of discovery predicate");
3557 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3558 "ref discovery for this generation kind");
3559 // already have locks
3560 checkpointRootsInitialWork(asynch);
3561 // now enable ("weak") refs discovery
3562 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3563 _collectorState = Marking;
3564 }
3565 SpecializationStats::print();
3566 }
3567
3568 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3569 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3570 assert(_collectorState == InitialMarking, "just checking");
3571
3572 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3573 // precede our marking with a collection of all
3574 // younger generations to keep floating garbage to a minimum.
3575 // XXX: we won't do this for now -- it's an optimization to be done later.
3576
3577 // already have locks
3578 assert_lock_strong(bitMapLock());
3579 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3580
3581 // Setup the verification and class unloading state for this
3582 // CMS collection cycle.
3583 setup_cms_unloading_and_verification_state();
3584
3585 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3586 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3587 if (UseAdaptiveSizePolicy) {
3588 size_policy()->checkpoint_roots_initial_begin();
3589 }
3590
3591 // Reset all the PLAB chunk arrays if necessary.
3592 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3593 reset_survivor_plab_arrays();
3594 }
3595
3596 ResourceMark rm;
3597 HandleMark hm;
3598
3599 FalseClosure falseClosure;
3600 // In the case of a synchronous collection, we will elide the
3601 // remark step, so it's important to catch all the nmethod oops
3602 // in this step.
3603 // The final 'true' flag to gen_process_strong_roots will ensure this.
3604 // If 'async' is true, we can relax the nmethod tracing.
3605 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3606 GenCollectedHeap* gch = GenCollectedHeap::heap();
3607
3608 verify_work_stacks_empty();
3609 verify_overflow_empty();
3610
3611 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3612 // Update the saved marks which may affect the root scans.
3613 gch->save_marks();
3614
3615 // weak reference processing has not started yet.
3616 ref_processor()->set_enqueuing_is_done(false);
3617
3618 {
3619 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3620 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3621 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3622 gch->gen_process_strong_roots(_cmsGen->level(),
3623 true, // younger gens are roots
3624 true, // activate StrongRootsScope
3625 true, // collecting perm gen
3626 SharedHeap::ScanningOption(roots_scanning_options()),
3627 ¬Older,
3628 true, // walk all of code cache if (so & SO_CodeCache)
3629 NULL);
3630 }
3631
3632 // Clear mod-union table; it will be dirtied in the prologue of
3633 // CMS generation per each younger generation collection.
3634
3635 assert(_modUnionTable.isAllClear(),
3636 "Was cleared in most recent final checkpoint phase"
3637 " or no bits are set in the gc_prologue before the start of the next "
3638 "subsequent marking phase.");
3639
3640 // Save the end of the used_region of the constituent generations
3641 // to be used to limit the extent of sweep in each generation.
3642 save_sweep_limits();
3643 if (UseAdaptiveSizePolicy) {
3644 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3645 }
3646 verify_overflow_empty();
3647 }
3648
3649 bool CMSCollector::markFromRoots(bool asynch) {
3650 // we might be tempted to assert that:
3651 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3652 // "inconsistent argument?");
3653 // However that wouldn't be right, because it's possible that
3654 // a safepoint is indeed in progress as a younger generation
3655 // stop-the-world GC happens even as we mark in this generation.
3656 assert(_collectorState == Marking, "inconsistent state?");
3657 check_correct_thread_executing();
3658 verify_overflow_empty();
3659
3660 bool res;
3661 if (asynch) {
3662
3663 // Start the timers for adaptive size policy for the concurrent phases
3664 // Do it here so that the foreground MS can use the concurrent
3665 // timer since a foreground MS might has the sweep done concurrently
3666 // or STW.
3667 if (UseAdaptiveSizePolicy) {
3668 size_policy()->concurrent_marking_begin();
3669 }
3670
3671 // Weak ref discovery note: We may be discovering weak
3672 // refs in this generation concurrent (but interleaved) with
3673 // weak ref discovery by a younger generation collector.
3674
3675 CMSTokenSyncWithLocks ts(true, bitMapLock());
3676 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3677 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3678 res = markFromRootsWork(asynch);
3679 if (res) {
3680 _collectorState = Precleaning;
3681 } else { // We failed and a foreground collection wants to take over
3682 assert(_foregroundGCIsActive, "internal state inconsistency");
3683 assert(_restart_addr == NULL, "foreground will restart from scratch");
3684 if (PrintGCDetails) {
3685 gclog_or_tty->print_cr("bailing out to foreground collection");
3686 }
3687 }
3688 if (UseAdaptiveSizePolicy) {
3689 size_policy()->concurrent_marking_end();
3690 }
3691 } else {
3692 assert(SafepointSynchronize::is_at_safepoint(),
3693 "inconsistent with asynch == false");
3694 if (UseAdaptiveSizePolicy) {
3695 size_policy()->ms_collection_marking_begin();
3696 }
3697 // already have locks
3698 res = markFromRootsWork(asynch);
3699 _collectorState = FinalMarking;
3700 if (UseAdaptiveSizePolicy) {
3701 GenCollectedHeap* gch = GenCollectedHeap::heap();
3702 size_policy()->ms_collection_marking_end(gch->gc_cause());
3703 }
3704 }
3705 verify_overflow_empty();
3706 return res;
3707 }
3708
3709 bool CMSCollector::markFromRootsWork(bool asynch) {
3710 // iterate over marked bits in bit map, doing a full scan and mark
3711 // from these roots using the following algorithm:
3712 // . if oop is to the right of the current scan pointer,
3713 // mark corresponding bit (we'll process it later)
3714 // . else (oop is to left of current scan pointer)
3715 // push oop on marking stack
3716 // . drain the marking stack
3717
3718 // Note that when we do a marking step we need to hold the
3719 // bit map lock -- recall that direct allocation (by mutators)
3720 // and promotion (by younger generation collectors) is also
3721 // marking the bit map. [the so-called allocate live policy.]
3722 // Because the implementation of bit map marking is not
3723 // robust wrt simultaneous marking of bits in the same word,
3724 // we need to make sure that there is no such interference
3725 // between concurrent such updates.
3726
3727 // already have locks
3728 assert_lock_strong(bitMapLock());
3729
3730 // Clear the revisit stack, just in case there are any
3731 // obsolete contents from a short-circuited previous CMS cycle.
3732 _revisitStack.reset();
3733 verify_work_stacks_empty();
3734 verify_overflow_empty();
3735 assert(_revisitStack.isEmpty(), "tabula rasa");
3736 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3737 bool result = false;
3738 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3739 result = do_marking_mt(asynch);
3740 } else {
3741 result = do_marking_st(asynch);
3742 }
3743 return result;
3744 }
3745
3746 // Forward decl
3747 class CMSConcMarkingTask;
3748
3749 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3750 CMSCollector* _collector;
3751 CMSConcMarkingTask* _task;
3752 public:
3753 virtual void yield();
3754
3755 // "n_threads" is the number of threads to be terminated.
3756 // "queue_set" is a set of work queues of other threads.
3757 // "collector" is the CMS collector associated with this task terminator.
3758 // "yield" indicates whether we need the gang as a whole to yield.
3759 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3760 ParallelTaskTerminator(n_threads, queue_set),
3761 _collector(collector) { }
3762
3763 void set_task(CMSConcMarkingTask* task) {
3764 _task = task;
3765 }
3766 };
3767
3768 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3769 CMSConcMarkingTask* _task;
3770 public:
3771 bool should_exit_termination();
3772 void set_task(CMSConcMarkingTask* task) {
3773 _task = task;
3774 }
3775 };
3776
3777 // MT Concurrent Marking Task
3778 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3779 CMSCollector* _collector;
3780 int _n_workers; // requested/desired # workers
3781 bool _asynch;
3782 bool _result;
3783 CompactibleFreeListSpace* _cms_space;
3784 CompactibleFreeListSpace* _perm_space;
3785 char _pad_front[64]; // padding to ...
3786 HeapWord* _global_finger; // ... avoid sharing cache line
3787 char _pad_back[64];
3788 HeapWord* _restart_addr;
3789
3790 // Exposed here for yielding support
3791 Mutex* const _bit_map_lock;
3792
3793 // The per thread work queues, available here for stealing
3794 OopTaskQueueSet* _task_queues;
3795
3796 // Termination (and yielding) support
3797 CMSConcMarkingTerminator _term;
3798 CMSConcMarkingTerminatorTerminator _term_term;
3799
3800 public:
3801 CMSConcMarkingTask(CMSCollector* collector,
3802 CompactibleFreeListSpace* cms_space,
3803 CompactibleFreeListSpace* perm_space,
3804 bool asynch,
3805 YieldingFlexibleWorkGang* workers,
3806 OopTaskQueueSet* task_queues):
3807 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3808 _collector(collector),
3809 _cms_space(cms_space),
3810 _perm_space(perm_space),
3811 _asynch(asynch), _n_workers(0), _result(true),
3812 _task_queues(task_queues),
3813 _term(_n_workers, task_queues, _collector),
3814 _bit_map_lock(collector->bitMapLock())
3815 {
3816 _requested_size = _n_workers;
3817 _term.set_task(this);
3818 _term_term.set_task(this);
3819 assert(_cms_space->bottom() < _perm_space->bottom(),
3820 "Finger incorrectly initialized below");
3821 _restart_addr = _global_finger = _cms_space->bottom();
3822 }
3823
3824
3825 OopTaskQueueSet* task_queues() { return _task_queues; }
3826
3827 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3828
3829 HeapWord** global_finger_addr() { return &_global_finger; }
3830
3831 CMSConcMarkingTerminator* terminator() { return &_term; }
3832
3833 virtual void set_for_termination(int active_workers) {
3834 terminator()->reset_for_reuse(active_workers);
3835 }
3836
3837 void work(uint worker_id);
3838 bool should_yield() {
3839 return ConcurrentMarkSweepThread::should_yield()
3840 && !_collector->foregroundGCIsActive()
3841 && _asynch;
3842 }
3843
3844 virtual void coordinator_yield(); // stuff done by coordinator
3845 bool result() { return _result; }
3846
3847 void reset(HeapWord* ra) {
3848 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3849 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3850 assert(ra < _perm_space->end(), "ra too large");
3851 _restart_addr = _global_finger = ra;
3852 _term.reset_for_reuse();
3853 }
3854
3855 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3856 OopTaskQueue* work_q);
3857
3858 private:
3859 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3860 void do_work_steal(int i);
3861 void bump_global_finger(HeapWord* f);
3862 };
3863
3864 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3865 assert(_task != NULL, "Error");
3866 return _task->yielding();
3867 // Note that we do not need the disjunct || _task->should_yield() above
3868 // because we want terminating threads to yield only if the task
3869 // is already in the midst of yielding, which happens only after at least one
3870 // thread has yielded.
3871 }
3872
3873 void CMSConcMarkingTerminator::yield() {
3874 if (_task->should_yield()) {
3875 _task->yield();
3876 } else {
3877 ParallelTaskTerminator::yield();
3878 }
3879 }
3880
3881 ////////////////////////////////////////////////////////////////
3882 // Concurrent Marking Algorithm Sketch
3883 ////////////////////////////////////////////////////////////////
3884 // Until all tasks exhausted (both spaces):
3885 // -- claim next available chunk
3886 // -- bump global finger via CAS
3887 // -- find first object that starts in this chunk
3888 // and start scanning bitmap from that position
3889 // -- scan marked objects for oops
3890 // -- CAS-mark target, and if successful:
3891 // . if target oop is above global finger (volatile read)
3892 // nothing to do
3893 // . if target oop is in chunk and above local finger
3894 // then nothing to do
3895 // . else push on work-queue
3896 // -- Deal with possible overflow issues:
3897 // . local work-queue overflow causes stuff to be pushed on
3898 // global (common) overflow queue
3899 // . always first empty local work queue
3900 // . then get a batch of oops from global work queue if any
3901 // . then do work stealing
3902 // -- When all tasks claimed (both spaces)
3903 // and local work queue empty,
3904 // then in a loop do:
3905 // . check global overflow stack; steal a batch of oops and trace
3906 // . try to steal from other threads oif GOS is empty
3907 // . if neither is available, offer termination
3908 // -- Terminate and return result
3909 //
3910 void CMSConcMarkingTask::work(uint worker_id) {
3911 elapsedTimer _timer;
3912 ResourceMark rm;
3913 HandleMark hm;
3914
3915 DEBUG_ONLY(_collector->verify_overflow_empty();)
3916
3917 // Before we begin work, our work queue should be empty
3918 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3919 // Scan the bitmap covering _cms_space, tracing through grey objects.
3920 _timer.start();
3921 do_scan_and_mark(worker_id, _cms_space);
3922 _timer.stop();
3923 if (PrintCMSStatistics != 0) {
3924 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3925 worker_id, _timer.seconds());
3926 // XXX: need xxx/xxx type of notation, two timers
3927 }
3928
3929 // ... do the same for the _perm_space
3930 _timer.reset();
3931 _timer.start();
3932 do_scan_and_mark(worker_id, _perm_space);
3933 _timer.stop();
3934 if (PrintCMSStatistics != 0) {
3935 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3936 worker_id, _timer.seconds());
3937 // XXX: need xxx/xxx type of notation, two timers
3938 }
3939
3940 // ... do work stealing
3941 _timer.reset();
3942 _timer.start();
3943 do_work_steal(worker_id);
3944 _timer.stop();
3945 if (PrintCMSStatistics != 0) {
3946 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3947 worker_id, _timer.seconds());
3948 // XXX: need xxx/xxx type of notation, two timers
3949 }
3950 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3951 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3952 // Note that under the current task protocol, the
3953 // following assertion is true even of the spaces
3954 // expanded since the completion of the concurrent
3955 // marking. XXX This will likely change under a strict
3956 // ABORT semantics.
3957 assert(_global_finger > _cms_space->end() &&
3958 _global_finger >= _perm_space->end(),
3959 "All tasks have been completed");
3960 DEBUG_ONLY(_collector->verify_overflow_empty();)
3961 }
3962
3963 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3964 HeapWord* read = _global_finger;
3965 HeapWord* cur = read;
3966 while (f > read) {
3967 cur = read;
3968 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3969 if (cur == read) {
3970 // our cas succeeded
3971 assert(_global_finger >= f, "protocol consistency");
3972 break;
3973 }
3974 }
3975 }
3976
3977 // This is really inefficient, and should be redone by
3978 // using (not yet available) block-read and -write interfaces to the
3979 // stack and the work_queue. XXX FIX ME !!!
3980 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3981 OopTaskQueue* work_q) {
3982 // Fast lock-free check
3983 if (ovflw_stk->length() == 0) {
3984 return false;
3985 }
3986 assert(work_q->size() == 0, "Shouldn't steal");
3987 MutexLockerEx ml(ovflw_stk->par_lock(),
3988 Mutex::_no_safepoint_check_flag);
3989 // Grab up to 1/4 the size of the work queue
3990 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3991 (size_t)ParGCDesiredObjsFromOverflowList);
3992 num = MIN2(num, ovflw_stk->length());
3993 for (int i = (int) num; i > 0; i--) {
3994 oop cur = ovflw_stk->pop();
3995 assert(cur != NULL, "Counted wrong?");
3996 work_q->push(cur);
3997 }
3998 return num > 0;
3999 }
4000
4001 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4002 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4003 int n_tasks = pst->n_tasks();
4004 // We allow that there may be no tasks to do here because
4005 // we are restarting after a stack overflow.
4006 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4007 uint nth_task = 0;
4008
4009 HeapWord* aligned_start = sp->bottom();
4010 if (sp->used_region().contains(_restart_addr)) {
4011 // Align down to a card boundary for the start of 0th task
4012 // for this space.
4013 aligned_start =
4014 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4015 CardTableModRefBS::card_size);
4016 }
4017
4018 size_t chunk_size = sp->marking_task_size();
4019 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4020 // Having claimed the nth task in this space,
4021 // compute the chunk that it corresponds to:
4022 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4023 aligned_start + (nth_task+1)*chunk_size);
4024 // Try and bump the global finger via a CAS;
4025 // note that we need to do the global finger bump
4026 // _before_ taking the intersection below, because
4027 // the task corresponding to that region will be
4028 // deemed done even if the used_region() expands
4029 // because of allocation -- as it almost certainly will
4030 // during start-up while the threads yield in the
4031 // closure below.
4032 HeapWord* finger = span.end();
4033 bump_global_finger(finger); // atomically
4034 // There are null tasks here corresponding to chunks
4035 // beyond the "top" address of the space.
4036 span = span.intersection(sp->used_region());
4037 if (!span.is_empty()) { // Non-null task
4038 HeapWord* prev_obj;
4039 assert(!span.contains(_restart_addr) || nth_task == 0,
4040 "Inconsistency");
4041 if (nth_task == 0) {
4042 // For the 0th task, we'll not need to compute a block_start.
4043 if (span.contains(_restart_addr)) {
4044 // In the case of a restart because of stack overflow,
4045 // we might additionally skip a chunk prefix.
4046 prev_obj = _restart_addr;
4047 } else {
4048 prev_obj = span.start();
4049 }
4050 } else {
4051 // We want to skip the first object because
4052 // the protocol is to scan any object in its entirety
4053 // that _starts_ in this span; a fortiori, any
4054 // object starting in an earlier span is scanned
4055 // as part of an earlier claimed task.
4056 // Below we use the "careful" version of block_start
4057 // so we do not try to navigate uninitialized objects.
4058 prev_obj = sp->block_start_careful(span.start());
4059 // Below we use a variant of block_size that uses the
4060 // Printezis bits to avoid waiting for allocated
4061 // objects to become initialized/parsable.
4062 while (prev_obj < span.start()) {
4063 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4064 if (sz > 0) {
4065 prev_obj += sz;
4066 } else {
4067 // In this case we may end up doing a bit of redundant
4068 // scanning, but that appears unavoidable, short of
4069 // locking the free list locks; see bug 6324141.
4070 break;
4071 }
4072 }
4073 }
4074 if (prev_obj < span.end()) {
4075 MemRegion my_span = MemRegion(prev_obj, span.end());
4076 // Do the marking work within a non-empty span --
4077 // the last argument to the constructor indicates whether the
4078 // iteration should be incremental with periodic yields.
4079 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4080 &_collector->_markBitMap,
4081 work_queue(i),
4082 &_collector->_markStack,
4083 &_collector->_revisitStack,
4084 _asynch);
4085 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4086 } // else nothing to do for this task
4087 } // else nothing to do for this task
4088 }
4089 // We'd be tempted to assert here that since there are no
4090 // more tasks left to claim in this space, the global_finger
4091 // must exceed space->top() and a fortiori space->end(). However,
4092 // that would not quite be correct because the bumping of
4093 // global_finger occurs strictly after the claiming of a task,
4094 // so by the time we reach here the global finger may not yet
4095 // have been bumped up by the thread that claimed the last
4096 // task.
4097 pst->all_tasks_completed();
4098 }
4099
4100 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4101 private:
4102 CMSConcMarkingTask* _task;
4103 MemRegion _span;
4104 CMSBitMap* _bit_map;
4105 CMSMarkStack* _overflow_stack;
4106 OopTaskQueue* _work_queue;
4107 protected:
4108 DO_OOP_WORK_DEFN
4109 public:
4110 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4111 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4112 CMSMarkStack* revisit_stack):
4113 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4114 _task(task),
4115 _span(collector->_span),
4116 _work_queue(work_queue),
4117 _bit_map(bit_map),
4118 _overflow_stack(overflow_stack)
4119 { }
4120 virtual void do_oop(oop* p);
4121 virtual void do_oop(narrowOop* p);
4122 void trim_queue(size_t max);
4123 void handle_stack_overflow(HeapWord* lost);
4124 void do_yield_check() {
4125 if (_task->should_yield()) {
4126 _task->yield();
4127 }
4128 }
4129 };
4130
4131 // Grey object scanning during work stealing phase --
4132 // the salient assumption here is that any references
4133 // that are in these stolen objects being scanned must
4134 // already have been initialized (else they would not have
4135 // been published), so we do not need to check for
4136 // uninitialized objects before pushing here.
4137 void Par_ConcMarkingClosure::do_oop(oop obj) {
4138 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4139 HeapWord* addr = (HeapWord*)obj;
4140 // Check if oop points into the CMS generation
4141 // and is not marked
4142 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4143 // a white object ...
4144 // If we manage to "claim" the object, by being the
4145 // first thread to mark it, then we push it on our
4146 // marking stack
4147 if (_bit_map->par_mark(addr)) { // ... now grey
4148 // push on work queue (grey set)
4149 bool simulate_overflow = false;
4150 NOT_PRODUCT(
4151 if (CMSMarkStackOverflowALot &&
4152 _collector->simulate_overflow()) {
4153 // simulate a stack overflow
4154 simulate_overflow = true;
4155 }
4156 )
4157 if (simulate_overflow ||
4158 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4159 // stack overflow
4160 if (PrintCMSStatistics != 0) {
4161 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4162 SIZE_FORMAT, _overflow_stack->capacity());
4163 }
4164 // We cannot assert that the overflow stack is full because
4165 // it may have been emptied since.
4166 assert(simulate_overflow ||
4167 _work_queue->size() == _work_queue->max_elems(),
4168 "Else push should have succeeded");
4169 handle_stack_overflow(addr);
4170 }
4171 } // Else, some other thread got there first
4172 do_yield_check();
4173 }
4174 }
4175
4176 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4177 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4178
4179 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4180 while (_work_queue->size() > max) {
4181 oop new_oop;
4182 if (_work_queue->pop_local(new_oop)) {
4183 assert(new_oop->is_oop(), "Should be an oop");
4184 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4185 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4186 assert(new_oop->is_parsable(), "Should be parsable");
4187 new_oop->oop_iterate(this); // do_oop() above
4188 do_yield_check();
4189 }
4190 }
4191 }
4192
4193 // Upon stack overflow, we discard (part of) the stack,
4194 // remembering the least address amongst those discarded
4195 // in CMSCollector's _restart_address.
4196 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4197 // We need to do this under a mutex to prevent other
4198 // workers from interfering with the work done below.
4199 MutexLockerEx ml(_overflow_stack->par_lock(),
4200 Mutex::_no_safepoint_check_flag);
4201 // Remember the least grey address discarded
4202 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4203 _collector->lower_restart_addr(ra);
4204 _overflow_stack->reset(); // discard stack contents
4205 _overflow_stack->expand(); // expand the stack if possible
4206 }
4207
4208
4209 void CMSConcMarkingTask::do_work_steal(int i) {
4210 OopTaskQueue* work_q = work_queue(i);
4211 oop obj_to_scan;
4212 CMSBitMap* bm = &(_collector->_markBitMap);
4213 CMSMarkStack* ovflw = &(_collector->_markStack);
4214 CMSMarkStack* revisit = &(_collector->_revisitStack);
4215 int* seed = _collector->hash_seed(i);
4216 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4217 while (true) {
4218 cl.trim_queue(0);
4219 assert(work_q->size() == 0, "Should have been emptied above");
4220 if (get_work_from_overflow_stack(ovflw, work_q)) {
4221 // Can't assert below because the work obtained from the
4222 // overflow stack may already have been stolen from us.
4223 // assert(work_q->size() > 0, "Work from overflow stack");
4224 continue;
4225 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4226 assert(obj_to_scan->is_oop(), "Should be an oop");
4227 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4228 obj_to_scan->oop_iterate(&cl);
4229 } else if (terminator()->offer_termination(&_term_term)) {
4230 assert(work_q->size() == 0, "Impossible!");
4231 break;
4232 } else if (yielding() || should_yield()) {
4233 yield();
4234 }
4235 }
4236 }
4237
4238 // This is run by the CMS (coordinator) thread.
4239 void CMSConcMarkingTask::coordinator_yield() {
4240 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4241 "CMS thread should hold CMS token");
4242 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4243 // First give up the locks, then yield, then re-lock
4244 // We should probably use a constructor/destructor idiom to
4245 // do this unlock/lock or modify the MutexUnlocker class to
4246 // serve our purpose. XXX
4247 assert_lock_strong(_bit_map_lock);
4248 _bit_map_lock->unlock();
4249 ConcurrentMarkSweepThread::desynchronize(true);
4250 ConcurrentMarkSweepThread::acknowledge_yield_request();
4251 _collector->stopTimer();
4252 if (PrintCMSStatistics != 0) {
4253 _collector->incrementYields();
4254 }
4255 _collector->icms_wait();
4256
4257 // It is possible for whichever thread initiated the yield request
4258 // not to get a chance to wake up and take the bitmap lock between
4259 // this thread releasing it and reacquiring it. So, while the
4260 // should_yield() flag is on, let's sleep for a bit to give the
4261 // other thread a chance to wake up. The limit imposed on the number
4262 // of iterations is defensive, to avoid any unforseen circumstances
4263 // putting us into an infinite loop. Since it's always been this
4264 // (coordinator_yield()) method that was observed to cause the
4265 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4266 // which is by default non-zero. For the other seven methods that
4267 // also perform the yield operation, as are using a different
4268 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4269 // can enable the sleeping for those methods too, if necessary.
4270 // See 6442774.
4271 //
4272 // We really need to reconsider the synchronization between the GC
4273 // thread and the yield-requesting threads in the future and we
4274 // should really use wait/notify, which is the recommended
4275 // way of doing this type of interaction. Additionally, we should
4276 // consolidate the eight methods that do the yield operation and they
4277 // are almost identical into one for better maintenability and
4278 // readability. See 6445193.
4279 //
4280 // Tony 2006.06.29
4281 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4282 ConcurrentMarkSweepThread::should_yield() &&
4283 !CMSCollector::foregroundGCIsActive(); ++i) {
4284 os::sleep(Thread::current(), 1, false);
4285 ConcurrentMarkSweepThread::acknowledge_yield_request();
4286 }
4287
4288 ConcurrentMarkSweepThread::synchronize(true);
4289 _bit_map_lock->lock_without_safepoint_check();
4290 _collector->startTimer();
4291 }
4292
4293 bool CMSCollector::do_marking_mt(bool asynch) {
4294 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4295 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4296 conc_workers()->total_workers(),
4297 conc_workers()->active_workers(),
4298 Threads::number_of_non_daemon_threads());
4299 conc_workers()->set_active_workers(num_workers);
4300
4301 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4302 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4303
4304 CMSConcMarkingTask tsk(this,
4305 cms_space,
4306 perm_space,
4307 asynch,
4308 conc_workers(),
4309 task_queues());
4310
4311 // Since the actual number of workers we get may be different
4312 // from the number we requested above, do we need to do anything different
4313 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4314 // class?? XXX
4315 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4316 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4317
4318 // Refs discovery is already non-atomic.
4319 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4320 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4321 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4322 conc_workers()->start_task(&tsk);
4323 while (tsk.yielded()) {
4324 tsk.coordinator_yield();
4325 conc_workers()->continue_task(&tsk);
4326 }
4327 // If the task was aborted, _restart_addr will be non-NULL
4328 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4329 while (_restart_addr != NULL) {
4330 // XXX For now we do not make use of ABORTED state and have not
4331 // yet implemented the right abort semantics (even in the original
4332 // single-threaded CMS case). That needs some more investigation
4333 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4334 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4335 // If _restart_addr is non-NULL, a marking stack overflow
4336 // occurred; we need to do a fresh marking iteration from the
4337 // indicated restart address.
4338 if (_foregroundGCIsActive && asynch) {
4339 // We may be running into repeated stack overflows, having
4340 // reached the limit of the stack size, while making very
4341 // slow forward progress. It may be best to bail out and
4342 // let the foreground collector do its job.
4343 // Clear _restart_addr, so that foreground GC
4344 // works from scratch. This avoids the headache of
4345 // a "rescan" which would otherwise be needed because
4346 // of the dirty mod union table & card table.
4347 _restart_addr = NULL;
4348 return false;
4349 }
4350 // Adjust the task to restart from _restart_addr
4351 tsk.reset(_restart_addr);
4352 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4353 _restart_addr);
4354 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4355 _restart_addr);
4356 _restart_addr = NULL;
4357 // Get the workers going again
4358 conc_workers()->start_task(&tsk);
4359 while (tsk.yielded()) {
4360 tsk.coordinator_yield();
4361 conc_workers()->continue_task(&tsk);
4362 }
4363 }
4364 assert(tsk.completed(), "Inconsistency");
4365 assert(tsk.result() == true, "Inconsistency");
4366 return true;
4367 }
4368
4369 bool CMSCollector::do_marking_st(bool asynch) {
4370 ResourceMark rm;
4371 HandleMark hm;
4372
4373 // Temporarily make refs discovery single threaded (non-MT)
4374 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4375 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4376 &_markStack, &_revisitStack, CMSYield && asynch);
4377 // the last argument to iterate indicates whether the iteration
4378 // should be incremental with periodic yields.
4379 _markBitMap.iterate(&markFromRootsClosure);
4380 // If _restart_addr is non-NULL, a marking stack overflow
4381 // occurred; we need to do a fresh iteration from the
4382 // indicated restart address.
4383 while (_restart_addr != NULL) {
4384 if (_foregroundGCIsActive && asynch) {
4385 // We may be running into repeated stack overflows, having
4386 // reached the limit of the stack size, while making very
4387 // slow forward progress. It may be best to bail out and
4388 // let the foreground collector do its job.
4389 // Clear _restart_addr, so that foreground GC
4390 // works from scratch. This avoids the headache of
4391 // a "rescan" which would otherwise be needed because
4392 // of the dirty mod union table & card table.
4393 _restart_addr = NULL;
4394 return false; // indicating failure to complete marking
4395 }
4396 // Deal with stack overflow:
4397 // we restart marking from _restart_addr
4398 HeapWord* ra = _restart_addr;
4399 markFromRootsClosure.reset(ra);
4400 _restart_addr = NULL;
4401 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4402 }
4403 return true;
4404 }
4405
4406 void CMSCollector::preclean() {
4407 check_correct_thread_executing();
4408 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4409 verify_work_stacks_empty();
4410 verify_overflow_empty();
4411 _abort_preclean = false;
4412 if (CMSPrecleaningEnabled) {
4413 _eden_chunk_index = 0;
4414 size_t used = get_eden_used();
4415 size_t capacity = get_eden_capacity();
4416 // Don't start sampling unless we will get sufficiently
4417 // many samples.
4418 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4419 * CMSScheduleRemarkEdenPenetration)) {
4420 _start_sampling = true;
4421 } else {
4422 _start_sampling = false;
4423 }
4424 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4425 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4426 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4427 }
4428 CMSTokenSync x(true); // is cms thread
4429 if (CMSPrecleaningEnabled) {
4430 sample_eden();
4431 _collectorState = AbortablePreclean;
4432 } else {
4433 _collectorState = FinalMarking;
4434 }
4435 verify_work_stacks_empty();
4436 verify_overflow_empty();
4437 }
4438
4439 // Try and schedule the remark such that young gen
4440 // occupancy is CMSScheduleRemarkEdenPenetration %.
4441 void CMSCollector::abortable_preclean() {
4442 check_correct_thread_executing();
4443 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4444 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4445
4446 // If Eden's current occupancy is below this threshold,
4447 // immediately schedule the remark; else preclean
4448 // past the next scavenge in an effort to
4449 // schedule the pause as described avove. By choosing
4450 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4451 // we will never do an actual abortable preclean cycle.
4452 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4453 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4454 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4455 // We need more smarts in the abortable preclean
4456 // loop below to deal with cases where allocation
4457 // in young gen is very very slow, and our precleaning
4458 // is running a losing race against a horde of
4459 // mutators intent on flooding us with CMS updates
4460 // (dirty cards).
4461 // One, admittedly dumb, strategy is to give up
4462 // after a certain number of abortable precleaning loops
4463 // or after a certain maximum time. We want to make
4464 // this smarter in the next iteration.
4465 // XXX FIX ME!!! YSR
4466 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4467 while (!(should_abort_preclean() ||
4468 ConcurrentMarkSweepThread::should_terminate())) {
4469 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4470 cumworkdone += workdone;
4471 loops++;
4472 // Voluntarily terminate abortable preclean phase if we have
4473 // been at it for too long.
4474 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4475 loops >= CMSMaxAbortablePrecleanLoops) {
4476 if (PrintGCDetails) {
4477 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4478 }
4479 break;
4480 }
4481 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4482 if (PrintGCDetails) {
4483 gclog_or_tty->print(" CMS: abort preclean due to time ");
4484 }
4485 break;
4486 }
4487 // If we are doing little work each iteration, we should
4488 // take a short break.
4489 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4490 // Sleep for some time, waiting for work to accumulate
4491 stopTimer();
4492 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4493 startTimer();
4494 waited++;
4495 }
4496 }
4497 if (PrintCMSStatistics > 0) {
4498 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4499 loops, waited, cumworkdone);
4500 }
4501 }
4502 CMSTokenSync x(true); // is cms thread
4503 if (_collectorState != Idling) {
4504 assert(_collectorState == AbortablePreclean,
4505 "Spontaneous state transition?");
4506 _collectorState = FinalMarking;
4507 } // Else, a foreground collection completed this CMS cycle.
4508 return;
4509 }
4510
4511 // Respond to an Eden sampling opportunity
4512 void CMSCollector::sample_eden() {
4513 // Make sure a young gc cannot sneak in between our
4514 // reading and recording of a sample.
4515 assert(Thread::current()->is_ConcurrentGC_thread(),
4516 "Only the cms thread may collect Eden samples");
4517 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4518 "Should collect samples while holding CMS token");
4519 if (!_start_sampling) {
4520 return;
4521 }
4522 if (_eden_chunk_array) {
4523 if (_eden_chunk_index < _eden_chunk_capacity) {
4524 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4525 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4526 "Unexpected state of Eden");
4527 // We'd like to check that what we just sampled is an oop-start address;
4528 // however, we cannot do that here since the object may not yet have been
4529 // initialized. So we'll instead do the check when we _use_ this sample
4530 // later.
4531 if (_eden_chunk_index == 0 ||
4532 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4533 _eden_chunk_array[_eden_chunk_index-1])
4534 >= CMSSamplingGrain)) {
4535 _eden_chunk_index++; // commit sample
4536 }
4537 }
4538 }
4539 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4540 size_t used = get_eden_used();
4541 size_t capacity = get_eden_capacity();
4542 assert(used <= capacity, "Unexpected state of Eden");
4543 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4544 _abort_preclean = true;
4545 }
4546 }
4547 }
4548
4549
4550 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4551 assert(_collectorState == Precleaning ||
4552 _collectorState == AbortablePreclean, "incorrect state");
4553 ResourceMark rm;
4554 HandleMark hm;
4555
4556 // Precleaning is currently not MT but the reference processor
4557 // may be set for MT. Disable it temporarily here.
4558 ReferenceProcessor* rp = ref_processor();
4559 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4560
4561 // Do one pass of scrubbing the discovered reference lists
4562 // to remove any reference objects with strongly-reachable
4563 // referents.
4564 if (clean_refs) {
4565 CMSPrecleanRefsYieldClosure yield_cl(this);
4566 assert(rp->span().equals(_span), "Spans should be equal");
4567 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4568 &_markStack, &_revisitStack,
4569 true /* preclean */);
4570 CMSDrainMarkingStackClosure complete_trace(this,
4571 _span, &_markBitMap, &_markStack,
4572 &keep_alive, true /* preclean */);
4573
4574 // We don't want this step to interfere with a young
4575 // collection because we don't want to take CPU
4576 // or memory bandwidth away from the young GC threads
4577 // (which may be as many as there are CPUs).
4578 // Note that we don't need to protect ourselves from
4579 // interference with mutators because they can't
4580 // manipulate the discovered reference lists nor affect
4581 // the computed reachability of the referents, the
4582 // only properties manipulated by the precleaning
4583 // of these reference lists.
4584 stopTimer();
4585 CMSTokenSyncWithLocks x(true /* is cms thread */,
4586 bitMapLock());
4587 startTimer();
4588 sample_eden();
4589
4590 // The following will yield to allow foreground
4591 // collection to proceed promptly. XXX YSR:
4592 // The code in this method may need further
4593 // tweaking for better performance and some restructuring
4594 // for cleaner interfaces.
4595 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4596 rp->preclean_discovered_references(
4597 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4598 &yield_cl, should_unload_classes(), gc_timer);
4599 }
4600
4601 if (clean_survivor) { // preclean the active survivor space(s)
4602 assert(_young_gen->kind() == Generation::DefNew ||
4603 _young_gen->kind() == Generation::ParNew ||
4604 _young_gen->kind() == Generation::ASParNew,
4605 "incorrect type for cast");
4606 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4607 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4608 &_markBitMap, &_modUnionTable,
4609 &_markStack, &_revisitStack,
4610 true /* precleaning phase */);
4611 stopTimer();
4612 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4613 bitMapLock());
4614 startTimer();
4615 unsigned int before_count =
4616 GenCollectedHeap::heap()->total_collections();
4617 SurvivorSpacePrecleanClosure
4618 sss_cl(this, _span, &_markBitMap, &_markStack,
4619 &pam_cl, before_count, CMSYield);
4620 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4621 dng->from()->object_iterate_careful(&sss_cl);
4622 dng->to()->object_iterate_careful(&sss_cl);
4623 }
4624 MarkRefsIntoAndScanClosure
4625 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4626 &_markStack, &_revisitStack, this, CMSYield,
4627 true /* precleaning phase */);
4628 // CAUTION: The following closure has persistent state that may need to
4629 // be reset upon a decrease in the sequence of addresses it
4630 // processes.
4631 ScanMarkedObjectsAgainCarefullyClosure
4632 smoac_cl(this, _span,
4633 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4634
4635 // Preclean dirty cards in ModUnionTable and CardTable using
4636 // appropriate convergence criterion;
4637 // repeat CMSPrecleanIter times unless we find that
4638 // we are losing.
4639 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4640 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4641 "Bad convergence multiplier");
4642 assert(CMSPrecleanThreshold >= 100,
4643 "Unreasonably low CMSPrecleanThreshold");
4644
4645 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4646 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4647 numIter < CMSPrecleanIter;
4648 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4649 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4650 if (CMSPermGenPrecleaningEnabled) {
4651 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4652 }
4653 if (Verbose && PrintGCDetails) {
4654 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4655 }
4656 // Either there are very few dirty cards, so re-mark
4657 // pause will be small anyway, or our pre-cleaning isn't
4658 // that much faster than the rate at which cards are being
4659 // dirtied, so we might as well stop and re-mark since
4660 // precleaning won't improve our re-mark time by much.
4661 if (curNumCards <= CMSPrecleanThreshold ||
4662 (numIter > 0 &&
4663 (curNumCards * CMSPrecleanDenominator >
4664 lastNumCards * CMSPrecleanNumerator))) {
4665 numIter++;
4666 cumNumCards += curNumCards;
4667 break;
4668 }
4669 }
4670 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4671 if (CMSPermGenPrecleaningEnabled) {
4672 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4673 }
4674 cumNumCards += curNumCards;
4675 if (PrintGCDetails && PrintCMSStatistics != 0) {
4676 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4677 curNumCards, cumNumCards, numIter);
4678 }
4679 return cumNumCards; // as a measure of useful work done
4680 }
4681
4682 // PRECLEANING NOTES:
4683 // Precleaning involves:
4684 // . reading the bits of the modUnionTable and clearing the set bits.
4685 // . For the cards corresponding to the set bits, we scan the
4686 // objects on those cards. This means we need the free_list_lock
4687 // so that we can safely iterate over the CMS space when scanning
4688 // for oops.
4689 // . When we scan the objects, we'll be both reading and setting
4690 // marks in the marking bit map, so we'll need the marking bit map.
4691 // . For protecting _collector_state transitions, we take the CGC_lock.
4692 // Note that any races in the reading of of card table entries by the
4693 // CMS thread on the one hand and the clearing of those entries by the
4694 // VM thread or the setting of those entries by the mutator threads on the
4695 // other are quite benign. However, for efficiency it makes sense to keep
4696 // the VM thread from racing with the CMS thread while the latter is
4697 // dirty card info to the modUnionTable. We therefore also use the
4698 // CGC_lock to protect the reading of the card table and the mod union
4699 // table by the CM thread.
4700 // . We run concurrently with mutator updates, so scanning
4701 // needs to be done carefully -- we should not try to scan
4702 // potentially uninitialized objects.
4703 //
4704 // Locking strategy: While holding the CGC_lock, we scan over and
4705 // reset a maximal dirty range of the mod union / card tables, then lock
4706 // the free_list_lock and bitmap lock to do a full marking, then
4707 // release these locks; and repeat the cycle. This allows for a
4708 // certain amount of fairness in the sharing of these locks between
4709 // the CMS collector on the one hand, and the VM thread and the
4710 // mutators on the other.
4711
4712 // NOTE: preclean_mod_union_table() and preclean_card_table()
4713 // further below are largely identical; if you need to modify
4714 // one of these methods, please check the other method too.
4715
4716 size_t CMSCollector::preclean_mod_union_table(
4717 ConcurrentMarkSweepGeneration* gen,
4718 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4719 verify_work_stacks_empty();
4720 verify_overflow_empty();
4721
4722 // Turn off checking for this method but turn it back on
4723 // selectively. There are yield points in this method
4724 // but it is difficult to turn the checking off just around
4725 // the yield points. It is simpler to selectively turn
4726 // it on.
4727 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4728
4729 // strategy: starting with the first card, accumulate contiguous
4730 // ranges of dirty cards; clear these cards, then scan the region
4731 // covered by these cards.
4732
4733 // Since all of the MUT is committed ahead, we can just use
4734 // that, in case the generations expand while we are precleaning.
4735 // It might also be fine to just use the committed part of the
4736 // generation, but we might potentially miss cards when the
4737 // generation is rapidly expanding while we are in the midst
4738 // of precleaning.
4739 HeapWord* startAddr = gen->reserved().start();
4740 HeapWord* endAddr = gen->reserved().end();
4741
4742 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4743
4744 size_t numDirtyCards, cumNumDirtyCards;
4745 HeapWord *nextAddr, *lastAddr;
4746 for (cumNumDirtyCards = numDirtyCards = 0,
4747 nextAddr = lastAddr = startAddr;
4748 nextAddr < endAddr;
4749 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4750
4751 ResourceMark rm;
4752 HandleMark hm;
4753
4754 MemRegion dirtyRegion;
4755 {
4756 stopTimer();
4757 // Potential yield point
4758 CMSTokenSync ts(true);
4759 startTimer();
4760 sample_eden();
4761 // Get dirty region starting at nextOffset (inclusive),
4762 // simultaneously clearing it.
4763 dirtyRegion =
4764 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4765 assert(dirtyRegion.start() >= nextAddr,
4766 "returned region inconsistent?");
4767 }
4768 // Remember where the next search should begin.
4769 // The returned region (if non-empty) is a right open interval,
4770 // so lastOffset is obtained from the right end of that
4771 // interval.
4772 lastAddr = dirtyRegion.end();
4773 // Should do something more transparent and less hacky XXX
4774 numDirtyCards =
4775 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4776
4777 // We'll scan the cards in the dirty region (with periodic
4778 // yields for foreground GC as needed).
4779 if (!dirtyRegion.is_empty()) {
4780 assert(numDirtyCards > 0, "consistency check");
4781 HeapWord* stop_point = NULL;
4782 stopTimer();
4783 // Potential yield point
4784 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4785 bitMapLock());
4786 startTimer();
4787 {
4788 verify_work_stacks_empty();
4789 verify_overflow_empty();
4790 sample_eden();
4791 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4792 stop_point =
4793 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4794 }
4795 if (stop_point != NULL) {
4796 // The careful iteration stopped early either because it found an
4797 // uninitialized object, or because we were in the midst of an
4798 // "abortable preclean", which should now be aborted. Redirty
4799 // the bits corresponding to the partially-scanned or unscanned
4800 // cards. We'll either restart at the next block boundary or
4801 // abort the preclean.
4802 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4803 (_collectorState == AbortablePreclean && should_abort_preclean()),
4804 "Unparsable objects should only be in perm gen.");
4805 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4806 if (should_abort_preclean()) {
4807 break; // out of preclean loop
4808 } else {
4809 // Compute the next address at which preclean should pick up;
4810 // might need bitMapLock in order to read P-bits.
4811 lastAddr = next_card_start_after_block(stop_point);
4812 }
4813 }
4814 } else {
4815 assert(lastAddr == endAddr, "consistency check");
4816 assert(numDirtyCards == 0, "consistency check");
4817 break;
4818 }
4819 }
4820 verify_work_stacks_empty();
4821 verify_overflow_empty();
4822 return cumNumDirtyCards;
4823 }
4824
4825 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4826 // below are largely identical; if you need to modify
4827 // one of these methods, please check the other method too.
4828
4829 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4830 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4831 // strategy: it's similar to precleamModUnionTable above, in that
4832 // we accumulate contiguous ranges of dirty cards, mark these cards
4833 // precleaned, then scan the region covered by these cards.
4834 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4835 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4836
4837 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4838
4839 size_t numDirtyCards, cumNumDirtyCards;
4840 HeapWord *lastAddr, *nextAddr;
4841
4842 for (cumNumDirtyCards = numDirtyCards = 0,
4843 nextAddr = lastAddr = startAddr;
4844 nextAddr < endAddr;
4845 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4846
4847 ResourceMark rm;
4848 HandleMark hm;
4849
4850 MemRegion dirtyRegion;
4851 {
4852 // See comments in "Precleaning notes" above on why we
4853 // do this locking. XXX Could the locking overheads be
4854 // too high when dirty cards are sparse? [I don't think so.]
4855 stopTimer();
4856 CMSTokenSync x(true); // is cms thread
4857 startTimer();
4858 sample_eden();
4859 // Get and clear dirty region from card table
4860 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4861 MemRegion(nextAddr, endAddr),
4862 true,
4863 CardTableModRefBS::precleaned_card_val());
4864
4865 assert(dirtyRegion.start() >= nextAddr,
4866 "returned region inconsistent?");
4867 }
4868 lastAddr = dirtyRegion.end();
4869 numDirtyCards =
4870 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4871
4872 if (!dirtyRegion.is_empty()) {
4873 stopTimer();
4874 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4875 startTimer();
4876 sample_eden();
4877 verify_work_stacks_empty();
4878 verify_overflow_empty();
4879 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4880 HeapWord* stop_point =
4881 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4882 if (stop_point != NULL) {
4883 // The careful iteration stopped early because it found an
4884 // uninitialized object. Redirty the bits corresponding to the
4885 // partially-scanned or unscanned cards, and start again at the
4886 // next block boundary.
4887 assert(CMSPermGenPrecleaningEnabled ||
4888 (_collectorState == AbortablePreclean && should_abort_preclean()),
4889 "Unparsable objects should only be in perm gen.");
4890 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4891 if (should_abort_preclean()) {
4892 break; // out of preclean loop
4893 } else {
4894 // Compute the next address at which preclean should pick up.
4895 lastAddr = next_card_start_after_block(stop_point);
4896 }
4897 }
4898 } else {
4899 break;
4900 }
4901 }
4902 verify_work_stacks_empty();
4903 verify_overflow_empty();
4904 return cumNumDirtyCards;
4905 }
4906
4907 void CMSCollector::checkpointRootsFinal(bool asynch,
4908 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4909 assert(_collectorState == FinalMarking, "incorrect state transition?");
4910 check_correct_thread_executing();
4911 // world is stopped at this checkpoint
4912 assert(SafepointSynchronize::is_at_safepoint(),
4913 "world should be stopped");
4914 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4915
4916 verify_work_stacks_empty();
4917 verify_overflow_empty();
4918
4919 SpecializationStats::clear();
4920 if (PrintGCDetails) {
4921 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4922 _young_gen->used() / K,
4923 _young_gen->capacity() / K);
4924 }
4925 if (asynch) {
4926 if (CMSScavengeBeforeRemark) {
4927 GenCollectedHeap* gch = GenCollectedHeap::heap();
4928 // Temporarily set flag to false, GCH->do_collection will
4929 // expect it to be false and set to true
4930 FlagSetting fl(gch->_is_gc_active, false);
4931 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4932 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4933 int level = _cmsGen->level() - 1;
4934 if (level >= 0) {
4935 gch->do_collection(true, // full (i.e. force, see below)
4936 false, // !clear_all_soft_refs
4937 0, // size
4938 false, // is_tlab
4939 level // max_level
4940 );
4941 }
4942 }
4943 FreelistLocker x(this);
4944 MutexLockerEx y(bitMapLock(),
4945 Mutex::_no_safepoint_check_flag);
4946 assert(!init_mark_was_synchronous, "but that's impossible!");
4947 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4948 } else {
4949 // already have all the locks
4950 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4951 init_mark_was_synchronous);
4952 }
4953 verify_work_stacks_empty();
4954 verify_overflow_empty();
4955 SpecializationStats::print();
4956 }
4957
4958 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4959 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4960
4961 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4962
4963 assert(haveFreelistLocks(), "must have free list locks");
4964 assert_lock_strong(bitMapLock());
4965
4966 if (UseAdaptiveSizePolicy) {
4967 size_policy()->checkpoint_roots_final_begin();
4968 }
4969
4970 ResourceMark rm;
4971 HandleMark hm;
4972
4973 GenCollectedHeap* gch = GenCollectedHeap::heap();
4974
4975 if (should_unload_classes()) {
4976 CodeCache::gc_prologue();
4977 }
4978 assert(haveFreelistLocks(), "must have free list locks");
4979 assert_lock_strong(bitMapLock());
4980
4981 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4982 if (!init_mark_was_synchronous) {
4983 // We might assume that we need not fill TLAB's when
4984 // CMSScavengeBeforeRemark is set, because we may have just done
4985 // a scavenge which would have filled all TLAB's -- and besides
4986 // Eden would be empty. This however may not always be the case --
4987 // for instance although we asked for a scavenge, it may not have
4988 // happened because of a JNI critical section. We probably need
4989 // a policy for deciding whether we can in that case wait until
4990 // the critical section releases and then do the remark following
4991 // the scavenge, and skip it here. In the absence of that policy,
4992 // or of an indication of whether the scavenge did indeed occur,
4993 // we cannot rely on TLAB's having been filled and must do
4994 // so here just in case a scavenge did not happen.
4995 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4996 // Update the saved marks which may affect the root scans.
4997 gch->save_marks();
4998
4999 {
5000 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5001
5002 // Note on the role of the mod union table:
5003 // Since the marker in "markFromRoots" marks concurrently with
5004 // mutators, it is possible for some reachable objects not to have been
5005 // scanned. For instance, an only reference to an object A was
5006 // placed in object B after the marker scanned B. Unless B is rescanned,
5007 // A would be collected. Such updates to references in marked objects
5008 // are detected via the mod union table which is the set of all cards
5009 // dirtied since the first checkpoint in this GC cycle and prior to
5010 // the most recent young generation GC, minus those cleaned up by the
5011 // concurrent precleaning.
5012 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5013 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5014 do_remark_parallel();
5015 } else {
5016 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5017 _gc_timer_cm);
5018 do_remark_non_parallel();
5019 }
5020 }
5021 } else {
5022 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5023 // The initial mark was stop-world, so there's no rescanning to
5024 // do; go straight on to the next step below.
5025 }
5026 verify_work_stacks_empty();
5027 verify_overflow_empty();
5028
5029 {
5030 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5031 refProcessingWork(asynch, clear_all_soft_refs);
5032 }
5033 verify_work_stacks_empty();
5034 verify_overflow_empty();
5035
5036 if (should_unload_classes()) {
5037 CodeCache::gc_epilogue();
5038 }
5039 JvmtiExport::gc_epilogue();
5040
5041 // If we encountered any (marking stack / work queue) overflow
5042 // events during the current CMS cycle, take appropriate
5043 // remedial measures, where possible, so as to try and avoid
5044 // recurrence of that condition.
5045 assert(_markStack.isEmpty(), "No grey objects");
5046 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5047 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5048 if (ser_ovflw > 0) {
5049 if (PrintCMSStatistics != 0) {
5050 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5051 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5052 ", kac_preclean="SIZE_FORMAT")",
5053 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5054 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5055 }
5056 _markStack.expand();
5057 _ser_pmc_remark_ovflw = 0;
5058 _ser_pmc_preclean_ovflw = 0;
5059 _ser_kac_preclean_ovflw = 0;
5060 _ser_kac_ovflw = 0;
5061 }
5062 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5063 if (PrintCMSStatistics != 0) {
5064 gclog_or_tty->print_cr("Work queue overflow (benign) "
5065 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5066 _par_pmc_remark_ovflw, _par_kac_ovflw);
5067 }
5068 _par_pmc_remark_ovflw = 0;
5069 _par_kac_ovflw = 0;
5070 }
5071 if (PrintCMSStatistics != 0) {
5072 if (_markStack._hit_limit > 0) {
5073 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5074 _markStack._hit_limit);
5075 }
5076 if (_markStack._failed_double > 0) {
5077 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5078 " current capacity "SIZE_FORMAT,
5079 _markStack._failed_double,
5080 _markStack.capacity());
5081 }
5082 }
5083 _markStack._hit_limit = 0;
5084 _markStack._failed_double = 0;
5085
5086 // Check that all the klasses have been checked
5087 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5088
5089 if ((VerifyAfterGC || VerifyDuringGC) &&
5090 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5091 verify_after_remark();
5092 }
5093
5094 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5095
5096 // Change under the freelistLocks.
5097 _collectorState = Sweeping;
5098 // Call isAllClear() under bitMapLock
5099 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5100 " final marking");
5101 if (UseAdaptiveSizePolicy) {
5102 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5103 }
5104 }
5105
5106 // Parallel remark task
5107 class CMSParRemarkTask: public AbstractGangTask {
5108 CMSCollector* _collector;
5109 int _n_workers;
5110 CompactibleFreeListSpace* _cms_space;
5111 CompactibleFreeListSpace* _perm_space;
5112
5113 // The per-thread work queues, available here for stealing.
5114 OopTaskQueueSet* _task_queues;
5115 ParallelTaskTerminator _term;
5116
5117 public:
5118 // A value of 0 passed to n_workers will cause the number of
5119 // workers to be taken from the active workers in the work gang.
5120 CMSParRemarkTask(CMSCollector* collector,
5121 CompactibleFreeListSpace* cms_space,
5122 CompactibleFreeListSpace* perm_space,
5123 int n_workers, FlexibleWorkGang* workers,
5124 OopTaskQueueSet* task_queues):
5125 AbstractGangTask("Rescan roots and grey objects in parallel"),
5126 _collector(collector),
5127 _cms_space(cms_space), _perm_space(perm_space),
5128 _n_workers(n_workers),
5129 _task_queues(task_queues),
5130 _term(n_workers, task_queues) { }
5131
5132 OopTaskQueueSet* task_queues() { return _task_queues; }
5133
5134 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5135
5136 ParallelTaskTerminator* terminator() { return &_term; }
5137 int n_workers() { return _n_workers; }
5138
5139 void work(uint worker_id);
5140
5141 private:
5142 // Work method in support of parallel rescan ... of young gen spaces
5143 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5144 ContiguousSpace* space,
5145 HeapWord** chunk_array, size_t chunk_top);
5146
5147 // ... of dirty cards in old space
5148 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5149 Par_MarkRefsIntoAndScanClosure* cl);
5150
5151 // ... work stealing for the above
5152 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5153 };
5154
5155 // work_queue(i) is passed to the closure
5156 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5157 // also is passed to do_dirty_card_rescan_tasks() and to
5158 // do_work_steal() to select the i-th task_queue.
5159
5160 void CMSParRemarkTask::work(uint worker_id) {
5161 elapsedTimer _timer;
5162 ResourceMark rm;
5163 HandleMark hm;
5164
5165 // ---------- rescan from roots --------------
5166 _timer.start();
5167 GenCollectedHeap* gch = GenCollectedHeap::heap();
5168 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5169 _collector->_span, _collector->ref_processor(),
5170 &(_collector->_markBitMap),
5171 work_queue(worker_id), &(_collector->_revisitStack));
5172
5173 // Rescan young gen roots first since these are likely
5174 // coarsely partitioned and may, on that account, constitute
5175 // the critical path; thus, it's best to start off that
5176 // work first.
5177 // ---------- young gen roots --------------
5178 {
5179 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5180 EdenSpace* eden_space = dng->eden();
5181 ContiguousSpace* from_space = dng->from();
5182 ContiguousSpace* to_space = dng->to();
5183
5184 HeapWord** eca = _collector->_eden_chunk_array;
5185 size_t ect = _collector->_eden_chunk_index;
5186 HeapWord** sca = _collector->_survivor_chunk_array;
5187 size_t sct = _collector->_survivor_chunk_index;
5188
5189 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5190 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5191
5192 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5193 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5194 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5195
5196 _timer.stop();
5197 if (PrintCMSStatistics != 0) {
5198 gclog_or_tty->print_cr(
5199 "Finished young gen rescan work in %dth thread: %3.3f sec",
5200 worker_id, _timer.seconds());
5201 }
5202 }
5203
5204 // ---------- remaining roots --------------
5205 _timer.reset();
5206 _timer.start();
5207 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5208 false, // yg was scanned above
5209 false, // this is parallel code
5210 true, // collecting perm gen
5211 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5212 &par_mrias_cl,
5213 true, // walk all of code cache if (so & SO_CodeCache)
5214 NULL);
5215 assert(_collector->should_unload_classes()
5216 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5217 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5218 _timer.stop();
5219 if (PrintCMSStatistics != 0) {
5220 gclog_or_tty->print_cr(
5221 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5222 worker_id, _timer.seconds());
5223 }
5224
5225 // ---------- rescan dirty cards ------------
5226 _timer.reset();
5227 _timer.start();
5228
5229 // Do the rescan tasks for each of the two spaces
5230 // (cms_space and perm_space) in turn.
5231 // "worker_id" is passed to select the task_queue for "worker_id"
5232 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5233 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5234 _timer.stop();
5235 if (PrintCMSStatistics != 0) {
5236 gclog_or_tty->print_cr(
5237 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5238 worker_id, _timer.seconds());
5239 }
5240
5241 // ---------- steal work from other threads ...
5242 // ---------- ... and drain overflow list.
5243 _timer.reset();
5244 _timer.start();
5245 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5246 _timer.stop();
5247 if (PrintCMSStatistics != 0) {
5248 gclog_or_tty->print_cr(
5249 "Finished work stealing in %dth thread: %3.3f sec",
5250 worker_id, _timer.seconds());
5251 }
5252 }
5253
5254 // Note that parameter "i" is not used.
5255 void
5256 CMSParRemarkTask::do_young_space_rescan(int i,
5257 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5258 HeapWord** chunk_array, size_t chunk_top) {
5259 // Until all tasks completed:
5260 // . claim an unclaimed task
5261 // . compute region boundaries corresponding to task claimed
5262 // using chunk_array
5263 // . par_oop_iterate(cl) over that region
5264
5265 ResourceMark rm;
5266 HandleMark hm;
5267
5268 SequentialSubTasksDone* pst = space->par_seq_tasks();
5269 assert(pst->valid(), "Uninitialized use?");
5270
5271 uint nth_task = 0;
5272 uint n_tasks = pst->n_tasks();
5273
5274 HeapWord *start, *end;
5275 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5276 // We claimed task # nth_task; compute its boundaries.
5277 if (chunk_top == 0) { // no samples were taken
5278 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5279 start = space->bottom();
5280 end = space->top();
5281 } else if (nth_task == 0) {
5282 start = space->bottom();
5283 end = chunk_array[nth_task];
5284 } else if (nth_task < (uint)chunk_top) {
5285 assert(nth_task >= 1, "Control point invariant");
5286 start = chunk_array[nth_task - 1];
5287 end = chunk_array[nth_task];
5288 } else {
5289 assert(nth_task == (uint)chunk_top, "Control point invariant");
5290 start = chunk_array[chunk_top - 1];
5291 end = space->top();
5292 }
5293 MemRegion mr(start, end);
5294 // Verify that mr is in space
5295 assert(mr.is_empty() || space->used_region().contains(mr),
5296 "Should be in space");
5297 // Verify that "start" is an object boundary
5298 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5299 "Should be an oop");
5300 space->par_oop_iterate(mr, cl);
5301 }
5302 pst->all_tasks_completed();
5303 }
5304
5305 void
5306 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5307 CompactibleFreeListSpace* sp, int i,
5308 Par_MarkRefsIntoAndScanClosure* cl) {
5309 // Until all tasks completed:
5310 // . claim an unclaimed task
5311 // . compute region boundaries corresponding to task claimed
5312 // . transfer dirty bits ct->mut for that region
5313 // . apply rescanclosure to dirty mut bits for that region
5314
5315 ResourceMark rm;
5316 HandleMark hm;
5317
5318 OopTaskQueue* work_q = work_queue(i);
5319 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5320 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5321 // CAUTION: This closure has state that persists across calls to
5322 // the work method dirty_range_iterate_clear() in that it has
5323 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5324 // use of that state in the imbedded UpwardsObjectClosure instance
5325 // assumes that the cards are always iterated (even if in parallel
5326 // by several threads) in monotonically increasing order per each
5327 // thread. This is true of the implementation below which picks
5328 // card ranges (chunks) in monotonically increasing order globally
5329 // and, a-fortiori, in monotonically increasing order per thread
5330 // (the latter order being a subsequence of the former).
5331 // If the work code below is ever reorganized into a more chaotic
5332 // work-partitioning form than the current "sequential tasks"
5333 // paradigm, the use of that persistent state will have to be
5334 // revisited and modified appropriately. See also related
5335 // bug 4756801 work on which should examine this code to make
5336 // sure that the changes there do not run counter to the
5337 // assumptions made here and necessary for correctness and
5338 // efficiency. Note also that this code might yield inefficient
5339 // behaviour in the case of very large objects that span one or
5340 // more work chunks. Such objects would potentially be scanned
5341 // several times redundantly. Work on 4756801 should try and
5342 // address that performance anomaly if at all possible. XXX
5343 MemRegion full_span = _collector->_span;
5344 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5345 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5346 MarkFromDirtyCardsClosure
5347 greyRescanClosure(_collector, full_span, // entire span of interest
5348 sp, bm, work_q, rs, cl);
5349
5350 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5351 assert(pst->valid(), "Uninitialized use?");
5352 uint nth_task = 0;
5353 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5354 MemRegion span = sp->used_region();
5355 HeapWord* start_addr = span.start();
5356 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5357 alignment);
5358 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5359 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5360 start_addr, "Check alignment");
5361 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5362 chunk_size, "Check alignment");
5363
5364 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5365 // Having claimed the nth_task, compute corresponding mem-region,
5366 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5367 // The alignment restriction ensures that we do not need any
5368 // synchronization with other gang-workers while setting or
5369 // clearing bits in thus chunk of the MUT.
5370 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5371 start_addr + (nth_task+1)*chunk_size);
5372 // The last chunk's end might be way beyond end of the
5373 // used region. In that case pull back appropriately.
5374 if (this_span.end() > end_addr) {
5375 this_span.set_end(end_addr);
5376 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5377 }
5378 // Iterate over the dirty cards covering this chunk, marking them
5379 // precleaned, and setting the corresponding bits in the mod union
5380 // table. Since we have been careful to partition at Card and MUT-word
5381 // boundaries no synchronization is needed between parallel threads.
5382 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5383 &modUnionClosure);
5384
5385 // Having transferred these marks into the modUnionTable,
5386 // rescan the marked objects on the dirty cards in the modUnionTable.
5387 // Even if this is at a synchronous collection, the initial marking
5388 // may have been done during an asynchronous collection so there
5389 // may be dirty bits in the mod-union table.
5390 _collector->_modUnionTable.dirty_range_iterate_clear(
5391 this_span, &greyRescanClosure);
5392 _collector->_modUnionTable.verifyNoOneBitsInRange(
5393 this_span.start(),
5394 this_span.end());
5395 }
5396 pst->all_tasks_completed(); // declare that i am done
5397 }
5398
5399 // . see if we can share work_queues with ParNew? XXX
5400 void
5401 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5402 int* seed) {
5403 OopTaskQueue* work_q = work_queue(i);
5404 NOT_PRODUCT(int num_steals = 0;)
5405 oop obj_to_scan;
5406 CMSBitMap* bm = &(_collector->_markBitMap);
5407
5408 while (true) {
5409 // Completely finish any left over work from (an) earlier round(s)
5410 cl->trim_queue(0);
5411 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5412 (size_t)ParGCDesiredObjsFromOverflowList);
5413 // Now check if there's any work in the overflow list
5414 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5415 // only affects the number of attempts made to get work from the
5416 // overflow list and does not affect the number of workers. Just
5417 // pass ParallelGCThreads so this behavior is unchanged.
5418 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5419 work_q,
5420 ParallelGCThreads)) {
5421 // found something in global overflow list;
5422 // not yet ready to go stealing work from others.
5423 // We'd like to assert(work_q->size() != 0, ...)
5424 // because we just took work from the overflow list,
5425 // but of course we can't since all of that could have
5426 // been already stolen from us.
5427 // "He giveth and He taketh away."
5428 continue;
5429 }
5430 // Verify that we have no work before we resort to stealing
5431 assert(work_q->size() == 0, "Have work, shouldn't steal");
5432 // Try to steal from other queues that have work
5433 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5434 NOT_PRODUCT(num_steals++;)
5435 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5436 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5437 // Do scanning work
5438 obj_to_scan->oop_iterate(cl);
5439 // Loop around, finish this work, and try to steal some more
5440 } else if (terminator()->offer_termination()) {
5441 break; // nirvana from the infinite cycle
5442 }
5443 }
5444 NOT_PRODUCT(
5445 if (PrintCMSStatistics != 0) {
5446 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5447 }
5448 )
5449 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5450 "Else our work is not yet done");
5451 }
5452
5453 // Return a thread-local PLAB recording array, as appropriate.
5454 void* CMSCollector::get_data_recorder(int thr_num) {
5455 if (_survivor_plab_array != NULL &&
5456 (CMSPLABRecordAlways ||
5457 (_collectorState > Marking && _collectorState < FinalMarking))) {
5458 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5459 ChunkArray* ca = &_survivor_plab_array[thr_num];
5460 ca->reset(); // clear it so that fresh data is recorded
5461 return (void*) ca;
5462 } else {
5463 return NULL;
5464 }
5465 }
5466
5467 // Reset all the thread-local PLAB recording arrays
5468 void CMSCollector::reset_survivor_plab_arrays() {
5469 for (uint i = 0; i < ParallelGCThreads; i++) {
5470 _survivor_plab_array[i].reset();
5471 }
5472 }
5473
5474 // Merge the per-thread plab arrays into the global survivor chunk
5475 // array which will provide the partitioning of the survivor space
5476 // for CMS rescan.
5477 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5478 int no_of_gc_threads) {
5479 assert(_survivor_plab_array != NULL, "Error");
5480 assert(_survivor_chunk_array != NULL, "Error");
5481 assert(_collectorState == FinalMarking, "Error");
5482 for (int j = 0; j < no_of_gc_threads; j++) {
5483 _cursor[j] = 0;
5484 }
5485 HeapWord* top = surv->top();
5486 size_t i;
5487 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5488 HeapWord* min_val = top; // Higher than any PLAB address
5489 uint min_tid = 0; // position of min_val this round
5490 for (int j = 0; j < no_of_gc_threads; j++) {
5491 ChunkArray* cur_sca = &_survivor_plab_array[j];
5492 if (_cursor[j] == cur_sca->end()) {
5493 continue;
5494 }
5495 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5496 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5497 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5498 if (cur_val < min_val) {
5499 min_tid = j;
5500 min_val = cur_val;
5501 } else {
5502 assert(cur_val < top, "All recorded addresses should be less");
5503 }
5504 }
5505 // At this point min_val and min_tid are respectively
5506 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5507 // and the thread (j) that witnesses that address.
5508 // We record this address in the _survivor_chunk_array[i]
5509 // and increment _cursor[min_tid] prior to the next round i.
5510 if (min_val == top) {
5511 break;
5512 }
5513 _survivor_chunk_array[i] = min_val;
5514 _cursor[min_tid]++;
5515 }
5516 // We are all done; record the size of the _survivor_chunk_array
5517 _survivor_chunk_index = i; // exclusive: [0, i)
5518 if (PrintCMSStatistics > 0) {
5519 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5520 }
5521 // Verify that we used up all the recorded entries
5522 #ifdef ASSERT
5523 size_t total = 0;
5524 for (int j = 0; j < no_of_gc_threads; j++) {
5525 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5526 total += _cursor[j];
5527 }
5528 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5529 // Check that the merged array is in sorted order
5530 if (total > 0) {
5531 for (size_t i = 0; i < total - 1; i++) {
5532 if (PrintCMSStatistics > 0) {
5533 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5534 i, _survivor_chunk_array[i]);
5535 }
5536 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5537 "Not sorted");
5538 }
5539 }
5540 #endif // ASSERT
5541 }
5542
5543 // Set up the space's par_seq_tasks structure for work claiming
5544 // for parallel rescan of young gen.
5545 // See ParRescanTask where this is currently used.
5546 void
5547 CMSCollector::
5548 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5549 assert(n_threads > 0, "Unexpected n_threads argument");
5550 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5551
5552 // Eden space
5553 {
5554 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5555 assert(!pst->valid(), "Clobbering existing data?");
5556 // Each valid entry in [0, _eden_chunk_index) represents a task.
5557 size_t n_tasks = _eden_chunk_index + 1;
5558 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5559 // Sets the condition for completion of the subtask (how many threads
5560 // need to finish in order to be done).
5561 pst->set_n_threads(n_threads);
5562 pst->set_n_tasks((int)n_tasks);
5563 }
5564
5565 // Merge the survivor plab arrays into _survivor_chunk_array
5566 if (_survivor_plab_array != NULL) {
5567 merge_survivor_plab_arrays(dng->from(), n_threads);
5568 } else {
5569 assert(_survivor_chunk_index == 0, "Error");
5570 }
5571
5572 // To space
5573 {
5574 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5575 assert(!pst->valid(), "Clobbering existing data?");
5576 // Sets the condition for completion of the subtask (how many threads
5577 // need to finish in order to be done).
5578 pst->set_n_threads(n_threads);
5579 pst->set_n_tasks(1);
5580 assert(pst->valid(), "Error");
5581 }
5582
5583 // From space
5584 {
5585 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5586 assert(!pst->valid(), "Clobbering existing data?");
5587 size_t n_tasks = _survivor_chunk_index + 1;
5588 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5589 // Sets the condition for completion of the subtask (how many threads
5590 // need to finish in order to be done).
5591 pst->set_n_threads(n_threads);
5592 pst->set_n_tasks((int)n_tasks);
5593 assert(pst->valid(), "Error");
5594 }
5595 }
5596
5597 // Parallel version of remark
5598 void CMSCollector::do_remark_parallel() {
5599 GenCollectedHeap* gch = GenCollectedHeap::heap();
5600 FlexibleWorkGang* workers = gch->workers();
5601 assert(workers != NULL, "Need parallel worker threads.");
5602 // Choose to use the number of GC workers most recently set
5603 // into "active_workers". If active_workers is not set, set it
5604 // to ParallelGCThreads.
5605 int n_workers = workers->active_workers();
5606 if (n_workers == 0) {
5607 assert(n_workers > 0, "Should have been set during scavenge");
5608 n_workers = ParallelGCThreads;
5609 workers->set_active_workers(n_workers);
5610 }
5611 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5612 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5613
5614 CMSParRemarkTask tsk(this,
5615 cms_space, perm_space,
5616 n_workers, workers, task_queues());
5617
5618 // Set up for parallel process_strong_roots work.
5619 gch->set_par_threads(n_workers);
5620 // We won't be iterating over the cards in the card table updating
5621 // the younger_gen cards, so we shouldn't call the following else
5622 // the verification code as well as subsequent younger_refs_iterate
5623 // code would get confused. XXX
5624 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5625
5626 // The young gen rescan work will not be done as part of
5627 // process_strong_roots (which currently doesn't knw how to
5628 // parallelize such a scan), but rather will be broken up into
5629 // a set of parallel tasks (via the sampling that the [abortable]
5630 // preclean phase did of EdenSpace, plus the [two] tasks of
5631 // scanning the [two] survivor spaces. Further fine-grain
5632 // parallelization of the scanning of the survivor spaces
5633 // themselves, and of precleaning of the younger gen itself
5634 // is deferred to the future.
5635 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5636
5637 // The dirty card rescan work is broken up into a "sequence"
5638 // of parallel tasks (per constituent space) that are dynamically
5639 // claimed by the parallel threads.
5640 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5641 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5642
5643 // It turns out that even when we're using 1 thread, doing the work in a
5644 // separate thread causes wide variance in run times. We can't help this
5645 // in the multi-threaded case, but we special-case n=1 here to get
5646 // repeatable measurements of the 1-thread overhead of the parallel code.
5647 if (n_workers > 1) {
5648 // Make refs discovery MT-safe, if it isn't already: it may not
5649 // necessarily be so, since it's possible that we are doing
5650 // ST marking.
5651 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5652 GenCollectedHeap::StrongRootsScope srs(gch);
5653 workers->run_task(&tsk);
5654 } else {
5655 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5656 GenCollectedHeap::StrongRootsScope srs(gch);
5657 tsk.work(0);
5658 }
5659 gch->set_par_threads(0); // 0 ==> non-parallel.
5660 // restore, single-threaded for now, any preserved marks
5661 // as a result of work_q overflow
5662 restore_preserved_marks_if_any();
5663 }
5664
5665 // Non-parallel version of remark
5666 void CMSCollector::do_remark_non_parallel() {
5667 ResourceMark rm;
5668 HandleMark hm;
5669 GenCollectedHeap* gch = GenCollectedHeap::heap();
5670 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5671
5672 MarkRefsIntoAndScanClosure
5673 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5674 &_markStack, &_revisitStack, this,
5675 false /* should_yield */, false /* not precleaning */);
5676 MarkFromDirtyCardsClosure
5677 markFromDirtyCardsClosure(this, _span,
5678 NULL, // space is set further below
5679 &_markBitMap, &_markStack, &_revisitStack,
5680 &mrias_cl);
5681 {
5682 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5683 // Iterate over the dirty cards, setting the corresponding bits in the
5684 // mod union table.
5685 {
5686 ModUnionClosure modUnionClosure(&_modUnionTable);
5687 _ct->ct_bs()->dirty_card_iterate(
5688 _cmsGen->used_region(),
5689 &modUnionClosure);
5690 _ct->ct_bs()->dirty_card_iterate(
5691 _permGen->used_region(),
5692 &modUnionClosure);
5693 }
5694 // Having transferred these marks into the modUnionTable, we just need
5695 // to rescan the marked objects on the dirty cards in the modUnionTable.
5696 // The initial marking may have been done during an asynchronous
5697 // collection so there may be dirty bits in the mod-union table.
5698 const int alignment =
5699 CardTableModRefBS::card_size * BitsPerWord;
5700 {
5701 // ... First handle dirty cards in CMS gen
5702 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5703 MemRegion ur = _cmsGen->used_region();
5704 HeapWord* lb = ur.start();
5705 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5706 MemRegion cms_span(lb, ub);
5707 _modUnionTable.dirty_range_iterate_clear(cms_span,
5708 &markFromDirtyCardsClosure);
5709 verify_work_stacks_empty();
5710 if (PrintCMSStatistics != 0) {
5711 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5712 markFromDirtyCardsClosure.num_dirty_cards());
5713 }
5714 }
5715 {
5716 // .. and then repeat for dirty cards in perm gen
5717 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5718 MemRegion ur = _permGen->used_region();
5719 HeapWord* lb = ur.start();
5720 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5721 MemRegion perm_span(lb, ub);
5722 _modUnionTable.dirty_range_iterate_clear(perm_span,
5723 &markFromDirtyCardsClosure);
5724 verify_work_stacks_empty();
5725 if (PrintCMSStatistics != 0) {
5726 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5727 markFromDirtyCardsClosure.num_dirty_cards());
5728 }
5729 }
5730 }
5731 if (VerifyDuringGC &&
5732 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5733 HandleMark hm; // Discard invalid handles created during verification
5734 Universe::verify();
5735 }
5736 {
5737 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5738
5739 verify_work_stacks_empty();
5740
5741 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5742 GenCollectedHeap::StrongRootsScope srs(gch);
5743 gch->gen_process_strong_roots(_cmsGen->level(),
5744 true, // younger gens as roots
5745 false, // use the local StrongRootsScope
5746 true, // collecting perm gen
5747 SharedHeap::ScanningOption(roots_scanning_options()),
5748 &mrias_cl,
5749 true, // walk code active on stacks
5750 NULL);
5751 assert(should_unload_classes()
5752 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5753 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5754 }
5755 verify_work_stacks_empty();
5756 // Restore evacuated mark words, if any, used for overflow list links
5757 if (!CMSOverflowEarlyRestoration) {
5758 restore_preserved_marks_if_any();
5759 }
5760 verify_overflow_empty();
5761 }
5762
5763 ////////////////////////////////////////////////////////
5764 // Parallel Reference Processing Task Proxy Class
5765 ////////////////////////////////////////////////////////
5766 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5767 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5768 CMSCollector* _collector;
5769 CMSBitMap* _mark_bit_map;
5770 const MemRegion _span;
5771 ProcessTask& _task;
5772
5773 public:
5774 CMSRefProcTaskProxy(ProcessTask& task,
5775 CMSCollector* collector,
5776 const MemRegion& span,
5777 CMSBitMap* mark_bit_map,
5778 AbstractWorkGang* workers,
5779 OopTaskQueueSet* task_queues):
5780 // XXX Should superclass AGTWOQ also know about AWG since it knows
5781 // about the task_queues used by the AWG? Then it could initialize
5782 // the terminator() object. See 6984287. The set_for_termination()
5783 // below is a temporary band-aid for the regression in 6984287.
5784 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5785 task_queues),
5786 _task(task),
5787 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5788 {
5789 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5790 "Inconsistency in _span");
5791 set_for_termination(workers->active_workers());
5792 }
5793
5794 OopTaskQueueSet* task_queues() { return queues(); }
5795
5796 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5797
5798 void do_work_steal(int i,
5799 CMSParDrainMarkingStackClosure* drain,
5800 CMSParKeepAliveClosure* keep_alive,
5801 int* seed);
5802
5803 virtual void work(uint worker_id);
5804 };
5805
5806 void CMSRefProcTaskProxy::work(uint worker_id) {
5807 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5808 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5809 _mark_bit_map,
5810 &_collector->_revisitStack,
5811 work_queue(worker_id));
5812 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5813 _mark_bit_map,
5814 &_collector->_revisitStack,
5815 work_queue(worker_id));
5816 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5817 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5818 if (_task.marks_oops_alive()) {
5819 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5820 _collector->hash_seed(worker_id));
5821 }
5822 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5823 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5824 }
5825
5826 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5827 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5828 EnqueueTask& _task;
5829
5830 public:
5831 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5832 : AbstractGangTask("Enqueue reference objects in parallel"),
5833 _task(task)
5834 { }
5835
5836 virtual void work(uint worker_id)
5837 {
5838 _task.work(worker_id);
5839 }
5840 };
5841
5842 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5843 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5844 OopTaskQueue* work_queue):
5845 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5846 _span(span),
5847 _bit_map(bit_map),
5848 _work_queue(work_queue),
5849 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5850 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5851 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5852 { }
5853
5854 // . see if we can share work_queues with ParNew? XXX
5855 void CMSRefProcTaskProxy::do_work_steal(int i,
5856 CMSParDrainMarkingStackClosure* drain,
5857 CMSParKeepAliveClosure* keep_alive,
5858 int* seed) {
5859 OopTaskQueue* work_q = work_queue(i);
5860 NOT_PRODUCT(int num_steals = 0;)
5861 oop obj_to_scan;
5862
5863 while (true) {
5864 // Completely finish any left over work from (an) earlier round(s)
5865 drain->trim_queue(0);
5866 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5867 (size_t)ParGCDesiredObjsFromOverflowList);
5868 // Now check if there's any work in the overflow list
5869 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5870 // only affects the number of attempts made to get work from the
5871 // overflow list and does not affect the number of workers. Just
5872 // pass ParallelGCThreads so this behavior is unchanged.
5873 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5874 work_q,
5875 ParallelGCThreads)) {
5876 // Found something in global overflow list;
5877 // not yet ready to go stealing work from others.
5878 // We'd like to assert(work_q->size() != 0, ...)
5879 // because we just took work from the overflow list,
5880 // but of course we can't, since all of that might have
5881 // been already stolen from us.
5882 continue;
5883 }
5884 // Verify that we have no work before we resort to stealing
5885 assert(work_q->size() == 0, "Have work, shouldn't steal");
5886 // Try to steal from other queues that have work
5887 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5888 NOT_PRODUCT(num_steals++;)
5889 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5890 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5891 // Do scanning work
5892 obj_to_scan->oop_iterate(keep_alive);
5893 // Loop around, finish this work, and try to steal some more
5894 } else if (terminator()->offer_termination()) {
5895 break; // nirvana from the infinite cycle
5896 }
5897 }
5898 NOT_PRODUCT(
5899 if (PrintCMSStatistics != 0) {
5900 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5901 }
5902 )
5903 }
5904
5905 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5906 {
5907 GenCollectedHeap* gch = GenCollectedHeap::heap();
5908 FlexibleWorkGang* workers = gch->workers();
5909 assert(workers != NULL, "Need parallel worker threads.");
5910 CMSRefProcTaskProxy rp_task(task, &_collector,
5911 _collector.ref_processor()->span(),
5912 _collector.markBitMap(),
5913 workers, _collector.task_queues());
5914 workers->run_task(&rp_task);
5915 }
5916
5917 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5918 {
5919
5920 GenCollectedHeap* gch = GenCollectedHeap::heap();
5921 FlexibleWorkGang* workers = gch->workers();
5922 assert(workers != NULL, "Need parallel worker threads.");
5923 CMSRefEnqueueTaskProxy enq_task(task);
5924 workers->run_task(&enq_task);
5925 }
5926
5927 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5928
5929 ResourceMark rm;
5930 HandleMark hm;
5931
5932 ReferenceProcessor* rp = ref_processor();
5933 assert(rp->span().equals(_span), "Spans should be equal");
5934 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5935 // Process weak references.
5936 rp->setup_policy(clear_all_soft_refs);
5937 verify_work_stacks_empty();
5938
5939 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5940 &_markStack, &_revisitStack,
5941 false /* !preclean */);
5942 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5943 _span, &_markBitMap, &_markStack,
5944 &cmsKeepAliveClosure, false /* !preclean */);
5945 {
5946 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5947
5948 ReferenceProcessorStats stats;
5949 if (rp->processing_is_mt()) {
5950 // Set the degree of MT here. If the discovery is done MT, there
5951 // may have been a different number of threads doing the discovery
5952 // and a different number of discovered lists may have Ref objects.
5953 // That is OK as long as the Reference lists are balanced (see
5954 // balance_all_queues() and balance_queues()).
5955 GenCollectedHeap* gch = GenCollectedHeap::heap();
5956 int active_workers = ParallelGCThreads;
5957 FlexibleWorkGang* workers = gch->workers();
5958 if (workers != NULL) {
5959 active_workers = workers->active_workers();
5960 // The expectation is that active_workers will have already
5961 // been set to a reasonable value. If it has not been set,
5962 // investigate.
5963 assert(active_workers > 0, "Should have been set during scavenge");
5964 }
5965 rp->set_active_mt_degree(active_workers);
5966 CMSRefProcTaskExecutor task_executor(*this);
5967 stats = rp->process_discovered_references(&_is_alive_closure,
5968 &cmsKeepAliveClosure,
5969 &cmsDrainMarkingStackClosure,
5970 &task_executor,
5971 _gc_timer_cm);
5972 } else {
5973 stats = rp->process_discovered_references(&_is_alive_closure,
5974 &cmsKeepAliveClosure,
5975 &cmsDrainMarkingStackClosure,
5976 NULL,
5977 _gc_timer_cm);
5978 }
5979 _gc_tracer_cm->report_gc_reference_stats(stats);
5980
5981 verify_work_stacks_empty();
5982 }
5983
5984 if (should_unload_classes()) {
5985 {
5986 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5987
5988 // Follow SystemDictionary roots and unload classes
5989 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5990
5991 // Follow CodeCache roots and unload any methods marked for unloading
5992 CodeCache::do_unloading(&_is_alive_closure,
5993 &cmsKeepAliveClosure,
5994 purged_class);
5995
5996 cmsDrainMarkingStackClosure.do_void();
5997 verify_work_stacks_empty();
5998
5999 // Update subklass/sibling/implementor links in KlassKlass descendants
6000 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
6001 oop k;
6002 while ((k = _revisitStack.pop()) != NULL) {
6003 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
6004 &_is_alive_closure,
6005 &cmsKeepAliveClosure);
6006 }
6007 assert(!ClassUnloading ||
6008 (_markStack.isEmpty() && overflow_list_is_empty()),
6009 "Should not have found new reachable objects");
6010 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
6011 cmsDrainMarkingStackClosure.do_void();
6012 verify_work_stacks_empty();
6013 }
6014
6015 {
6016 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6017 // Clean up unreferenced symbols in symbol table.
6018 SymbolTable::unlink();
6019 }
6020 }
6021
6022 if (should_unload_classes() || !JavaObjectsInPerm) {
6023 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6024 // Now clean up stale oops in StringTable
6025 StringTable::unlink(&_is_alive_closure);
6026 }
6027
6028 verify_work_stacks_empty();
6029 // Restore any preserved marks as a result of mark stack or
6030 // work queue overflow
6031 restore_preserved_marks_if_any(); // done single-threaded for now
6032
6033 rp->set_enqueuing_is_done(true);
6034 if (rp->processing_is_mt()) {
6035 rp->balance_all_queues();
6036 CMSRefProcTaskExecutor task_executor(*this);
6037 rp->enqueue_discovered_references(&task_executor);
6038 } else {
6039 rp->enqueue_discovered_references(NULL);
6040 }
6041 rp->verify_no_references_recorded();
6042 assert(!rp->discovery_enabled(), "should have been disabled");
6043 }
6044
6045 #ifndef PRODUCT
6046 void CMSCollector::check_correct_thread_executing() {
6047 Thread* t = Thread::current();
6048 // Only the VM thread or the CMS thread should be here.
6049 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6050 "Unexpected thread type");
6051 // If this is the vm thread, the foreground process
6052 // should not be waiting. Note that _foregroundGCIsActive is
6053 // true while the foreground collector is waiting.
6054 if (_foregroundGCShouldWait) {
6055 // We cannot be the VM thread
6056 assert(t->is_ConcurrentGC_thread(),
6057 "Should be CMS thread");
6058 } else {
6059 // We can be the CMS thread only if we are in a stop-world
6060 // phase of CMS collection.
6061 if (t->is_ConcurrentGC_thread()) {
6062 assert(_collectorState == InitialMarking ||
6063 _collectorState == FinalMarking,
6064 "Should be a stop-world phase");
6065 // The CMS thread should be holding the CMS_token.
6066 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6067 "Potential interference with concurrently "
6068 "executing VM thread");
6069 }
6070 }
6071 }
6072 #endif
6073
6074 void CMSCollector::sweep(bool asynch) {
6075 assert(_collectorState == Sweeping, "just checking");
6076 check_correct_thread_executing();
6077 verify_work_stacks_empty();
6078 verify_overflow_empty();
6079 increment_sweep_count();
6080 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6081
6082 _inter_sweep_timer.stop();
6083 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6084 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6085
6086 // PermGen verification support: If perm gen sweeping is disabled in
6087 // this cycle, we preserve the perm gen object "deadness" information
6088 // in the perm_gen_verify_bit_map. In order to do that we traverse
6089 // all blocks in perm gen and mark all dead objects.
6090 if (verifying() && !should_unload_classes()) {
6091 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6092 "Should have already been allocated");
6093 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6094 markBitMap(), perm_gen_verify_bit_map());
6095 if (asynch) {
6096 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6097 bitMapLock());
6098 _permGen->cmsSpace()->blk_iterate(&mdo);
6099 } else {
6100 // In the case of synchronous sweep, we already have
6101 // the requisite locks/tokens.
6102 _permGen->cmsSpace()->blk_iterate(&mdo);
6103 }
6104 }
6105
6106 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6107 _intra_sweep_timer.reset();
6108 _intra_sweep_timer.start();
6109 if (asynch) {
6110 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6111 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6112 // First sweep the old gen then the perm gen
6113 {
6114 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6115 bitMapLock());
6116 sweepWork(_cmsGen, asynch);
6117 }
6118
6119 // Now repeat for perm gen
6120 if (should_unload_classes()) {
6121 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6122 bitMapLock());
6123 sweepWork(_permGen, asynch);
6124 }
6125
6126 // Update Universe::_heap_*_at_gc figures.
6127 // We need all the free list locks to make the abstract state
6128 // transition from Sweeping to Resetting. See detailed note
6129 // further below.
6130 {
6131 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6132 _permGen->freelistLock());
6133 // Update heap occupancy information which is used as
6134 // input to soft ref clearing policy at the next gc.
6135 Universe::update_heap_info_at_gc();
6136 _collectorState = Resizing;
6137 }
6138 } else {
6139 // already have needed locks
6140 sweepWork(_cmsGen, asynch);
6141
6142 if (should_unload_classes()) {
6143 sweepWork(_permGen, asynch);
6144 }
6145 // Update heap occupancy information which is used as
6146 // input to soft ref clearing policy at the next gc.
6147 Universe::update_heap_info_at_gc();
6148 _collectorState = Resizing;
6149 }
6150 verify_work_stacks_empty();
6151 verify_overflow_empty();
6152
6153 _intra_sweep_timer.stop();
6154 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6155
6156 _inter_sweep_timer.reset();
6157 _inter_sweep_timer.start();
6158
6159 // We need to use a monotonically non-deccreasing time in ms
6160 // or we will see time-warp warnings and os::javaTimeMillis()
6161 // does not guarantee monotonicity.
6162 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6163 update_time_of_last_gc(now);
6164
6165 // NOTE on abstract state transitions:
6166 // Mutators allocate-live and/or mark the mod-union table dirty
6167 // based on the state of the collection. The former is done in
6168 // the interval [Marking, Sweeping] and the latter in the interval
6169 // [Marking, Sweeping). Thus the transitions into the Marking state
6170 // and out of the Sweeping state must be synchronously visible
6171 // globally to the mutators.
6172 // The transition into the Marking state happens with the world
6173 // stopped so the mutators will globally see it. Sweeping is
6174 // done asynchronously by the background collector so the transition
6175 // from the Sweeping state to the Resizing state must be done
6176 // under the freelistLock (as is the check for whether to
6177 // allocate-live and whether to dirty the mod-union table).
6178 assert(_collectorState == Resizing, "Change of collector state to"
6179 " Resizing must be done under the freelistLocks (plural)");
6180
6181 // Now that sweeping has been completed, we clear
6182 // the incremental_collection_failed flag,
6183 // thus inviting a younger gen collection to promote into
6184 // this generation. If such a promotion may still fail,
6185 // the flag will be set again when a young collection is
6186 // attempted.
6187 GenCollectedHeap* gch = GenCollectedHeap::heap();
6188 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6189 gch->update_full_collections_completed(_collection_count_start);
6190 }
6191
6192 // FIX ME!!! Looks like this belongs in CFLSpace, with
6193 // CMSGen merely delegating to it.
6194 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6195 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6196 HeapWord* minAddr = _cmsSpace->bottom();
6197 HeapWord* largestAddr =
6198 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6199 if (largestAddr == NULL) {
6200 // The dictionary appears to be empty. In this case
6201 // try to coalesce at the end of the heap.
6202 largestAddr = _cmsSpace->end();
6203 }
6204 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6205 size_t nearLargestOffset =
6206 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6207 if (PrintFLSStatistics != 0) {
6208 gclog_or_tty->print_cr(
6209 "CMS: Large Block: " PTR_FORMAT ";"
6210 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6211 largestAddr,
6212 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6213 }
6214 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6215 }
6216
6217 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6218 return addr >= _cmsSpace->nearLargestChunk();
6219 }
6220
6221 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6222 return _cmsSpace->find_chunk_at_end();
6223 }
6224
6225 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6226 bool full) {
6227 // The next lower level has been collected. Gather any statistics
6228 // that are of interest at this point.
6229 if (!full && (current_level + 1) == level()) {
6230 // Gather statistics on the young generation collection.
6231 collector()->stats().record_gc0_end(used());
6232 }
6233 }
6234
6235 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6236 GenCollectedHeap* gch = GenCollectedHeap::heap();
6237 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6238 "Wrong type of heap");
6239 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6240 gch->gen_policy()->size_policy();
6241 assert(sp->is_gc_cms_adaptive_size_policy(),
6242 "Wrong type of size policy");
6243 return sp;
6244 }
6245
6246 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6247 if (PrintGCDetails && Verbose) {
6248 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6249 }
6250 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6251 _debug_collection_type =
6252 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6253 if (PrintGCDetails && Verbose) {
6254 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6255 }
6256 }
6257
6258 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6259 bool asynch) {
6260 // We iterate over the space(s) underlying this generation,
6261 // checking the mark bit map to see if the bits corresponding
6262 // to specific blocks are marked or not. Blocks that are
6263 // marked are live and are not swept up. All remaining blocks
6264 // are swept up, with coalescing on-the-fly as we sweep up
6265 // contiguous free and/or garbage blocks:
6266 // We need to ensure that the sweeper synchronizes with allocators
6267 // and stop-the-world collectors. In particular, the following
6268 // locks are used:
6269 // . CMS token: if this is held, a stop the world collection cannot occur
6270 // . freelistLock: if this is held no allocation can occur from this
6271 // generation by another thread
6272 // . bitMapLock: if this is held, no other thread can access or update
6273 //
6274
6275 // Note that we need to hold the freelistLock if we use
6276 // block iterate below; else the iterator might go awry if
6277 // a mutator (or promotion) causes block contents to change
6278 // (for instance if the allocator divvies up a block).
6279 // If we hold the free list lock, for all practical purposes
6280 // young generation GC's can't occur (they'll usually need to
6281 // promote), so we might as well prevent all young generation
6282 // GC's while we do a sweeping step. For the same reason, we might
6283 // as well take the bit map lock for the entire duration
6284
6285 // check that we hold the requisite locks
6286 assert(have_cms_token(), "Should hold cms token");
6287 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6288 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6289 "Should possess CMS token to sweep");
6290 assert_lock_strong(gen->freelistLock());
6291 assert_lock_strong(bitMapLock());
6292
6293 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6294 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6295 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6296 _inter_sweep_estimate.padded_average(),
6297 _intra_sweep_estimate.padded_average());
6298 gen->setNearLargestChunk();
6299
6300 {
6301 SweepClosure sweepClosure(this, gen, &_markBitMap,
6302 CMSYield && asynch);
6303 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6304 // We need to free-up/coalesce garbage/blocks from a
6305 // co-terminal free run. This is done in the SweepClosure
6306 // destructor; so, do not remove this scope, else the
6307 // end-of-sweep-census below will be off by a little bit.
6308 }
6309 gen->cmsSpace()->sweep_completed();
6310 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6311 if (should_unload_classes()) { // unloaded classes this cycle,
6312 _concurrent_cycles_since_last_unload = 0; // ... reset count
6313 } else { // did not unload classes,
6314 _concurrent_cycles_since_last_unload++; // ... increment count
6315 }
6316 }
6317
6318 // Reset CMS data structures (for now just the marking bit map)
6319 // preparatory for the next cycle.
6320 void CMSCollector::reset(bool asynch) {
6321 GenCollectedHeap* gch = GenCollectedHeap::heap();
6322 CMSAdaptiveSizePolicy* sp = size_policy();
6323 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6324 if (asynch) {
6325 CMSTokenSyncWithLocks ts(true, bitMapLock());
6326
6327 // If the state is not "Resetting", the foreground thread
6328 // has done a collection and the resetting.
6329 if (_collectorState != Resetting) {
6330 assert(_collectorState == Idling, "The state should only change"
6331 " because the foreground collector has finished the collection");
6332 return;
6333 }
6334
6335 // Clear the mark bitmap (no grey objects to start with)
6336 // for the next cycle.
6337 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6338 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6339
6340 HeapWord* curAddr = _markBitMap.startWord();
6341 while (curAddr < _markBitMap.endWord()) {
6342 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6343 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6344 _markBitMap.clear_large_range(chunk);
6345 if (ConcurrentMarkSweepThread::should_yield() &&
6346 !foregroundGCIsActive() &&
6347 CMSYield) {
6348 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6349 "CMS thread should hold CMS token");
6350 assert_lock_strong(bitMapLock());
6351 bitMapLock()->unlock();
6352 ConcurrentMarkSweepThread::desynchronize(true);
6353 ConcurrentMarkSweepThread::acknowledge_yield_request();
6354 stopTimer();
6355 if (PrintCMSStatistics != 0) {
6356 incrementYields();
6357 }
6358 icms_wait();
6359
6360 // See the comment in coordinator_yield()
6361 for (unsigned i = 0; i < CMSYieldSleepCount &&
6362 ConcurrentMarkSweepThread::should_yield() &&
6363 !CMSCollector::foregroundGCIsActive(); ++i) {
6364 os::sleep(Thread::current(), 1, false);
6365 ConcurrentMarkSweepThread::acknowledge_yield_request();
6366 }
6367
6368 ConcurrentMarkSweepThread::synchronize(true);
6369 bitMapLock()->lock_without_safepoint_check();
6370 startTimer();
6371 }
6372 curAddr = chunk.end();
6373 }
6374 // A successful mostly concurrent collection has been done.
6375 // Because only the full (i.e., concurrent mode failure) collections
6376 // are being measured for gc overhead limits, clean the "near" flag
6377 // and count.
6378 sp->reset_gc_overhead_limit_count();
6379 _collectorState = Idling;
6380 } else {
6381 // already have the lock
6382 assert(_collectorState == Resetting, "just checking");
6383 assert_lock_strong(bitMapLock());
6384 _markBitMap.clear_all();
6385 _collectorState = Idling;
6386 }
6387
6388 // Stop incremental mode after a cycle completes, so that any future cycles
6389 // are triggered by allocation.
6390 stop_icms();
6391
6392 NOT_PRODUCT(
6393 if (RotateCMSCollectionTypes) {
6394 _cmsGen->rotate_debug_collection_type();
6395 }
6396 )
6397
6398 register_gc_end();
6399 }
6400
6401 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6402 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6403 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6404 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6405 TraceCollectorStats tcs(counters());
6406
6407 switch (op) {
6408 case CMS_op_checkpointRootsInitial: {
6409 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6410 checkpointRootsInitial(true); // asynch
6411 if (PrintGC) {
6412 _cmsGen->printOccupancy("initial-mark");
6413 }
6414 break;
6415 }
6416 case CMS_op_checkpointRootsFinal: {
6417 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6418 checkpointRootsFinal(true, // asynch
6419 false, // !clear_all_soft_refs
6420 false); // !init_mark_was_synchronous
6421 if (PrintGC) {
6422 _cmsGen->printOccupancy("remark");
6423 }
6424 break;
6425 }
6426 default:
6427 fatal("No such CMS_op");
6428 }
6429 }
6430
6431 #ifndef PRODUCT
6432 size_t const CMSCollector::skip_header_HeapWords() {
6433 return FreeChunk::header_size();
6434 }
6435
6436 // Try and collect here conditions that should hold when
6437 // CMS thread is exiting. The idea is that the foreground GC
6438 // thread should not be blocked if it wants to terminate
6439 // the CMS thread and yet continue to run the VM for a while
6440 // after that.
6441 void CMSCollector::verify_ok_to_terminate() const {
6442 assert(Thread::current()->is_ConcurrentGC_thread(),
6443 "should be called by CMS thread");
6444 assert(!_foregroundGCShouldWait, "should be false");
6445 // We could check here that all the various low-level locks
6446 // are not held by the CMS thread, but that is overkill; see
6447 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6448 // is checked.
6449 }
6450 #endif
6451
6452 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6453 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6454 "missing Printezis mark?");
6455 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6456 size_t size = pointer_delta(nextOneAddr + 1, addr);
6457 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6458 "alignment problem");
6459 assert(size >= 3, "Necessary for Printezis marks to work");
6460 return size;
6461 }
6462
6463 // A variant of the above (block_size_using_printezis_bits()) except
6464 // that we return 0 if the P-bits are not yet set.
6465 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6466 if (_markBitMap.isMarked(addr + 1)) {
6467 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6468 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6469 size_t size = pointer_delta(nextOneAddr + 1, addr);
6470 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6471 "alignment problem");
6472 assert(size >= 3, "Necessary for Printezis marks to work");
6473 return size;
6474 }
6475 return 0;
6476 }
6477
6478 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6479 size_t sz = 0;
6480 oop p = (oop)addr;
6481 if (p->klass_or_null() != NULL && p->is_parsable()) {
6482 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6483 } else {
6484 sz = block_size_using_printezis_bits(addr);
6485 }
6486 assert(sz > 0, "size must be nonzero");
6487 HeapWord* next_block = addr + sz;
6488 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6489 CardTableModRefBS::card_size);
6490 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6491 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6492 "must be different cards");
6493 return next_card;
6494 }
6495
6496
6497 // CMS Bit Map Wrapper /////////////////////////////////////////
6498
6499 // Construct a CMS bit map infrastructure, but don't create the
6500 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6501 // further below.
6502 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6503 _bm(),
6504 _shifter(shifter),
6505 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6506 {
6507 _bmStartWord = 0;
6508 _bmWordSize = 0;
6509 }
6510
6511 bool CMSBitMap::allocate(MemRegion mr) {
6512 _bmStartWord = mr.start();
6513 _bmWordSize = mr.word_size();
6514 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6515 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6516 if (!brs.is_reserved()) {
6517 warning("CMS bit map allocation failure");
6518 return false;
6519 }
6520 // For now we'll just commit all of the bit map up fromt.
6521 // Later on we'll try to be more parsimonious with swap.
6522 if (!_virtual_space.initialize(brs, brs.size())) {
6523 warning("CMS bit map backing store failure");
6524 return false;
6525 }
6526 assert(_virtual_space.committed_size() == brs.size(),
6527 "didn't reserve backing store for all of CMS bit map?");
6528 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6529 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6530 _bmWordSize, "inconsistency in bit map sizing");
6531 _bm.set_size(_bmWordSize >> _shifter);
6532
6533 // bm.clear(); // can we rely on getting zero'd memory? verify below
6534 assert(isAllClear(),
6535 "Expected zero'd memory from ReservedSpace constructor");
6536 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6537 "consistency check");
6538 return true;
6539 }
6540
6541 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6542 HeapWord *next_addr, *end_addr, *last_addr;
6543 assert_locked();
6544 assert(covers(mr), "out-of-range error");
6545 // XXX assert that start and end are appropriately aligned
6546 for (next_addr = mr.start(), end_addr = mr.end();
6547 next_addr < end_addr; next_addr = last_addr) {
6548 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6549 last_addr = dirty_region.end();
6550 if (!dirty_region.is_empty()) {
6551 cl->do_MemRegion(dirty_region);
6552 } else {
6553 assert(last_addr == end_addr, "program logic");
6554 return;
6555 }
6556 }
6557 }
6558
6559 #ifndef PRODUCT
6560 void CMSBitMap::assert_locked() const {
6561 CMSLockVerifier::assert_locked(lock());
6562 }
6563
6564 bool CMSBitMap::covers(MemRegion mr) const {
6565 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6566 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6567 "size inconsistency");
6568 return (mr.start() >= _bmStartWord) &&
6569 (mr.end() <= endWord());
6570 }
6571
6572 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6573 return (start >= _bmStartWord && (start + size) <= endWord());
6574 }
6575
6576 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6577 // verify that there are no 1 bits in the interval [left, right)
6578 FalseBitMapClosure falseBitMapClosure;
6579 iterate(&falseBitMapClosure, left, right);
6580 }
6581
6582 void CMSBitMap::region_invariant(MemRegion mr)
6583 {
6584 assert_locked();
6585 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6586 assert(!mr.is_empty(), "unexpected empty region");
6587 assert(covers(mr), "mr should be covered by bit map");
6588 // convert address range into offset range
6589 size_t start_ofs = heapWordToOffset(mr.start());
6590 // Make sure that end() is appropriately aligned
6591 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6592 (1 << (_shifter+LogHeapWordSize))),
6593 "Misaligned mr.end()");
6594 size_t end_ofs = heapWordToOffset(mr.end());
6595 assert(end_ofs > start_ofs, "Should mark at least one bit");
6596 }
6597
6598 #endif
6599
6600 bool CMSMarkStack::allocate(size_t size) {
6601 // allocate a stack of the requisite depth
6602 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6603 size * sizeof(oop)));
6604 if (!rs.is_reserved()) {
6605 warning("CMSMarkStack allocation failure");
6606 return false;
6607 }
6608 if (!_virtual_space.initialize(rs, rs.size())) {
6609 warning("CMSMarkStack backing store failure");
6610 return false;
6611 }
6612 assert(_virtual_space.committed_size() == rs.size(),
6613 "didn't reserve backing store for all of CMS stack?");
6614 _base = (oop*)(_virtual_space.low());
6615 _index = 0;
6616 _capacity = size;
6617 NOT_PRODUCT(_max_depth = 0);
6618 return true;
6619 }
6620
6621 // XXX FIX ME !!! In the MT case we come in here holding a
6622 // leaf lock. For printing we need to take a further lock
6623 // which has lower rank. We need to recallibrate the two
6624 // lock-ranks involved in order to be able to rpint the
6625 // messages below. (Or defer the printing to the caller.
6626 // For now we take the expedient path of just disabling the
6627 // messages for the problematic case.)
6628 void CMSMarkStack::expand() {
6629 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6630 if (_capacity == MarkStackSizeMax) {
6631 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6632 // We print a warning message only once per CMS cycle.
6633 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6634 }
6635 return;
6636 }
6637 // Double capacity if possible
6638 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6639 // Do not give up existing stack until we have managed to
6640 // get the double capacity that we desired.
6641 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6642 new_capacity * sizeof(oop)));
6643 if (rs.is_reserved()) {
6644 // Release the backing store associated with old stack
6645 _virtual_space.release();
6646 // Reinitialize virtual space for new stack
6647 if (!_virtual_space.initialize(rs, rs.size())) {
6648 fatal("Not enough swap for expanded marking stack");
6649 }
6650 _base = (oop*)(_virtual_space.low());
6651 _index = 0;
6652 _capacity = new_capacity;
6653 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6654 // Failed to double capacity, continue;
6655 // we print a detail message only once per CMS cycle.
6656 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6657 SIZE_FORMAT"K",
6658 _capacity / K, new_capacity / K);
6659 }
6660 }
6661
6662
6663 // Closures
6664 // XXX: there seems to be a lot of code duplication here;
6665 // should refactor and consolidate common code.
6666
6667 // This closure is used to mark refs into the CMS generation in
6668 // the CMS bit map. Called at the first checkpoint. This closure
6669 // assumes that we do not need to re-mark dirty cards; if the CMS
6670 // generation on which this is used is not an oldest (modulo perm gen)
6671 // generation then this will lose younger_gen cards!
6672
6673 MarkRefsIntoClosure::MarkRefsIntoClosure(
6674 MemRegion span, CMSBitMap* bitMap):
6675 _span(span),
6676 _bitMap(bitMap)
6677 {
6678 assert(_ref_processor == NULL, "deliberately left NULL");
6679 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6680 }
6681
6682 void MarkRefsIntoClosure::do_oop(oop obj) {
6683 // if p points into _span, then mark corresponding bit in _markBitMap
6684 assert(obj->is_oop(), "expected an oop");
6685 HeapWord* addr = (HeapWord*)obj;
6686 if (_span.contains(addr)) {
6687 // this should be made more efficient
6688 _bitMap->mark(addr);
6689 }
6690 }
6691
6692 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6693 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6694
6695 // A variant of the above, used for CMS marking verification.
6696 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6697 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6698 _span(span),
6699 _verification_bm(verification_bm),
6700 _cms_bm(cms_bm)
6701 {
6702 assert(_ref_processor == NULL, "deliberately left NULL");
6703 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6704 }
6705
6706 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6707 // if p points into _span, then mark corresponding bit in _markBitMap
6708 assert(obj->is_oop(), "expected an oop");
6709 HeapWord* addr = (HeapWord*)obj;
6710 if (_span.contains(addr)) {
6711 _verification_bm->mark(addr);
6712 if (!_cms_bm->isMarked(addr)) {
6713 oop(addr)->print();
6714 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6715 fatal("... aborting");
6716 }
6717 }
6718 }
6719
6720 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6721 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6722
6723 //////////////////////////////////////////////////
6724 // MarkRefsIntoAndScanClosure
6725 //////////////////////////////////////////////////
6726
6727 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6728 ReferenceProcessor* rp,
6729 CMSBitMap* bit_map,
6730 CMSBitMap* mod_union_table,
6731 CMSMarkStack* mark_stack,
6732 CMSMarkStack* revisit_stack,
6733 CMSCollector* collector,
6734 bool should_yield,
6735 bool concurrent_precleaning):
6736 _collector(collector),
6737 _span(span),
6738 _bit_map(bit_map),
6739 _mark_stack(mark_stack),
6740 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6741 mark_stack, revisit_stack, concurrent_precleaning),
6742 _yield(should_yield),
6743 _concurrent_precleaning(concurrent_precleaning),
6744 _freelistLock(NULL)
6745 {
6746 _ref_processor = rp;
6747 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6748 }
6749
6750 // This closure is used to mark refs into the CMS generation at the
6751 // second (final) checkpoint, and to scan and transitively follow
6752 // the unmarked oops. It is also used during the concurrent precleaning
6753 // phase while scanning objects on dirty cards in the CMS generation.
6754 // The marks are made in the marking bit map and the marking stack is
6755 // used for keeping the (newly) grey objects during the scan.
6756 // The parallel version (Par_...) appears further below.
6757 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6758 if (obj != NULL) {
6759 assert(obj->is_oop(), "expected an oop");
6760 HeapWord* addr = (HeapWord*)obj;
6761 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6762 assert(_collector->overflow_list_is_empty(),
6763 "overflow list should be empty");
6764 if (_span.contains(addr) &&
6765 !_bit_map->isMarked(addr)) {
6766 // mark bit map (object is now grey)
6767 _bit_map->mark(addr);
6768 // push on marking stack (stack should be empty), and drain the
6769 // stack by applying this closure to the oops in the oops popped
6770 // from the stack (i.e. blacken the grey objects)
6771 bool res = _mark_stack->push(obj);
6772 assert(res, "Should have space to push on empty stack");
6773 do {
6774 oop new_oop = _mark_stack->pop();
6775 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6776 assert(new_oop->is_parsable(), "Found unparsable oop");
6777 assert(_bit_map->isMarked((HeapWord*)new_oop),
6778 "only grey objects on this stack");
6779 // iterate over the oops in this oop, marking and pushing
6780 // the ones in CMS heap (i.e. in _span).
6781 new_oop->oop_iterate(&_pushAndMarkClosure);
6782 // check if it's time to yield
6783 do_yield_check();
6784 } while (!_mark_stack->isEmpty() ||
6785 (!_concurrent_precleaning && take_from_overflow_list()));
6786 // if marking stack is empty, and we are not doing this
6787 // during precleaning, then check the overflow list
6788 }
6789 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6790 assert(_collector->overflow_list_is_empty(),
6791 "overflow list was drained above");
6792 // We could restore evacuated mark words, if any, used for
6793 // overflow list links here because the overflow list is
6794 // provably empty here. That would reduce the maximum
6795 // size requirements for preserved_{oop,mark}_stack.
6796 // But we'll just postpone it until we are all done
6797 // so we can just stream through.
6798 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6799 _collector->restore_preserved_marks_if_any();
6800 assert(_collector->no_preserved_marks(), "No preserved marks");
6801 }
6802 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6803 "All preserved marks should have been restored above");
6804 }
6805 }
6806
6807 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6808 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6809
6810 void MarkRefsIntoAndScanClosure::do_yield_work() {
6811 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6812 "CMS thread should hold CMS token");
6813 assert_lock_strong(_freelistLock);
6814 assert_lock_strong(_bit_map->lock());
6815 // relinquish the free_list_lock and bitMaplock()
6816 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6817 _bit_map->lock()->unlock();
6818 _freelistLock->unlock();
6819 ConcurrentMarkSweepThread::desynchronize(true);
6820 ConcurrentMarkSweepThread::acknowledge_yield_request();
6821 _collector->stopTimer();
6822 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6823 if (PrintCMSStatistics != 0) {
6824 _collector->incrementYields();
6825 }
6826 _collector->icms_wait();
6827
6828 // See the comment in coordinator_yield()
6829 for (unsigned i = 0;
6830 i < CMSYieldSleepCount &&
6831 ConcurrentMarkSweepThread::should_yield() &&
6832 !CMSCollector::foregroundGCIsActive();
6833 ++i) {
6834 os::sleep(Thread::current(), 1, false);
6835 ConcurrentMarkSweepThread::acknowledge_yield_request();
6836 }
6837
6838 ConcurrentMarkSweepThread::synchronize(true);
6839 _freelistLock->lock_without_safepoint_check();
6840 _bit_map->lock()->lock_without_safepoint_check();
6841 _collector->startTimer();
6842 }
6843
6844 ///////////////////////////////////////////////////////////
6845 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6846 // MarkRefsIntoAndScanClosure
6847 ///////////////////////////////////////////////////////////
6848 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6849 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6850 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6851 _span(span),
6852 _bit_map(bit_map),
6853 _work_queue(work_queue),
6854 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6855 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6856 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6857 revisit_stack)
6858 {
6859 _ref_processor = rp;
6860 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6861 }
6862
6863 // This closure is used to mark refs into the CMS generation at the
6864 // second (final) checkpoint, and to scan and transitively follow
6865 // the unmarked oops. The marks are made in the marking bit map and
6866 // the work_queue is used for keeping the (newly) grey objects during
6867 // the scan phase whence they are also available for stealing by parallel
6868 // threads. Since the marking bit map is shared, updates are
6869 // synchronized (via CAS).
6870 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6871 if (obj != NULL) {
6872 // Ignore mark word because this could be an already marked oop
6873 // that may be chained at the end of the overflow list.
6874 assert(obj->is_oop(true), "expected an oop");
6875 HeapWord* addr = (HeapWord*)obj;
6876 if (_span.contains(addr) &&
6877 !_bit_map->isMarked(addr)) {
6878 // mark bit map (object will become grey):
6879 // It is possible for several threads to be
6880 // trying to "claim" this object concurrently;
6881 // the unique thread that succeeds in marking the
6882 // object first will do the subsequent push on
6883 // to the work queue (or overflow list).
6884 if (_bit_map->par_mark(addr)) {
6885 // push on work_queue (which may not be empty), and trim the
6886 // queue to an appropriate length by applying this closure to
6887 // the oops in the oops popped from the stack (i.e. blacken the
6888 // grey objects)
6889 bool res = _work_queue->push(obj);
6890 assert(res, "Low water mark should be less than capacity?");
6891 trim_queue(_low_water_mark);
6892 } // Else, another thread claimed the object
6893 }
6894 }
6895 }
6896
6897 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6898 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6899
6900 // This closure is used to rescan the marked objects on the dirty cards
6901 // in the mod union table and the card table proper.
6902 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6903 oop p, MemRegion mr) {
6904
6905 size_t size = 0;
6906 HeapWord* addr = (HeapWord*)p;
6907 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6908 assert(_span.contains(addr), "we are scanning the CMS generation");
6909 // check if it's time to yield
6910 if (do_yield_check()) {
6911 // We yielded for some foreground stop-world work,
6912 // and we have been asked to abort this ongoing preclean cycle.
6913 return 0;
6914 }
6915 if (_bitMap->isMarked(addr)) {
6916 // it's marked; is it potentially uninitialized?
6917 if (p->klass_or_null() != NULL) {
6918 // If is_conc_safe is false, the object may be undergoing
6919 // change by the VM outside a safepoint. Don't try to
6920 // scan it, but rather leave it for the remark phase.
6921 if (CMSPermGenPrecleaningEnabled &&
6922 (!p->is_conc_safe() || !p->is_parsable())) {
6923 // Signal precleaning to redirty the card since
6924 // the klass pointer is already installed.
6925 assert(size == 0, "Initial value");
6926 } else {
6927 assert(p->is_parsable(), "must be parsable.");
6928 // an initialized object; ignore mark word in verification below
6929 // since we are running concurrent with mutators
6930 assert(p->is_oop(true), "should be an oop");
6931 if (p->is_objArray()) {
6932 // objArrays are precisely marked; restrict scanning
6933 // to dirty cards only.
6934 size = CompactibleFreeListSpace::adjustObjectSize(
6935 p->oop_iterate(_scanningClosure, mr));
6936 } else {
6937 // A non-array may have been imprecisely marked; we need
6938 // to scan object in its entirety.
6939 size = CompactibleFreeListSpace::adjustObjectSize(
6940 p->oop_iterate(_scanningClosure));
6941 }
6942 #ifdef DEBUG
6943 size_t direct_size =
6944 CompactibleFreeListSpace::adjustObjectSize(p->size());
6945 assert(size == direct_size, "Inconsistency in size");
6946 assert(size >= 3, "Necessary for Printezis marks to work");
6947 if (!_bitMap->isMarked(addr+1)) {
6948 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6949 } else {
6950 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6951 assert(_bitMap->isMarked(addr+size-1),
6952 "inconsistent Printezis mark");
6953 }
6954 #endif // DEBUG
6955 }
6956 } else {
6957 // an unitialized object
6958 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6959 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6960 size = pointer_delta(nextOneAddr + 1, addr);
6961 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6962 "alignment problem");
6963 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6964 // will dirty the card when the klass pointer is installed in the
6965 // object (signalling the completion of initialization).
6966 }
6967 } else {
6968 // Either a not yet marked object or an uninitialized object
6969 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6970 // An uninitialized object, skip to the next card, since
6971 // we may not be able to read its P-bits yet.
6972 assert(size == 0, "Initial value");
6973 } else {
6974 // An object not (yet) reached by marking: we merely need to
6975 // compute its size so as to go look at the next block.
6976 assert(p->is_oop(true), "should be an oop");
6977 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6978 }
6979 }
6980 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6981 return size;
6982 }
6983
6984 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6985 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6986 "CMS thread should hold CMS token");
6987 assert_lock_strong(_freelistLock);
6988 assert_lock_strong(_bitMap->lock());
6989 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6990 // relinquish the free_list_lock and bitMaplock()
6991 _bitMap->lock()->unlock();
6992 _freelistLock->unlock();
6993 ConcurrentMarkSweepThread::desynchronize(true);
6994 ConcurrentMarkSweepThread::acknowledge_yield_request();
6995 _collector->stopTimer();
6996 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6997 if (PrintCMSStatistics != 0) {
6998 _collector->incrementYields();
6999 }
7000 _collector->icms_wait();
7001
7002 // See the comment in coordinator_yield()
7003 for (unsigned i = 0; i < CMSYieldSleepCount &&
7004 ConcurrentMarkSweepThread::should_yield() &&
7005 !CMSCollector::foregroundGCIsActive(); ++i) {
7006 os::sleep(Thread::current(), 1, false);
7007 ConcurrentMarkSweepThread::acknowledge_yield_request();
7008 }
7009
7010 ConcurrentMarkSweepThread::synchronize(true);
7011 _freelistLock->lock_without_safepoint_check();
7012 _bitMap->lock()->lock_without_safepoint_check();
7013 _collector->startTimer();
7014 }
7015
7016
7017 //////////////////////////////////////////////////////////////////
7018 // SurvivorSpacePrecleanClosure
7019 //////////////////////////////////////////////////////////////////
7020 // This (single-threaded) closure is used to preclean the oops in
7021 // the survivor spaces.
7022 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7023
7024 HeapWord* addr = (HeapWord*)p;
7025 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7026 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7027 assert(p->klass_or_null() != NULL, "object should be initializd");
7028 assert(p->is_parsable(), "must be parsable.");
7029 // an initialized object; ignore mark word in verification below
7030 // since we are running concurrent with mutators
7031 assert(p->is_oop(true), "should be an oop");
7032 // Note that we do not yield while we iterate over
7033 // the interior oops of p, pushing the relevant ones
7034 // on our marking stack.
7035 size_t size = p->oop_iterate(_scanning_closure);
7036 do_yield_check();
7037 // Observe that below, we do not abandon the preclean
7038 // phase as soon as we should; rather we empty the
7039 // marking stack before returning. This is to satisfy
7040 // some existing assertions. In general, it may be a
7041 // good idea to abort immediately and complete the marking
7042 // from the grey objects at a later time.
7043 while (!_mark_stack->isEmpty()) {
7044 oop new_oop = _mark_stack->pop();
7045 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7046 assert(new_oop->is_parsable(), "Found unparsable oop");
7047 assert(_bit_map->isMarked((HeapWord*)new_oop),
7048 "only grey objects on this stack");
7049 // iterate over the oops in this oop, marking and pushing
7050 // the ones in CMS heap (i.e. in _span).
7051 new_oop->oop_iterate(_scanning_closure);
7052 // check if it's time to yield
7053 do_yield_check();
7054 }
7055 unsigned int after_count =
7056 GenCollectedHeap::heap()->total_collections();
7057 bool abort = (_before_count != after_count) ||
7058 _collector->should_abort_preclean();
7059 return abort ? 0 : size;
7060 }
7061
7062 void SurvivorSpacePrecleanClosure::do_yield_work() {
7063 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7064 "CMS thread should hold CMS token");
7065 assert_lock_strong(_bit_map->lock());
7066 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7067 // Relinquish the bit map lock
7068 _bit_map->lock()->unlock();
7069 ConcurrentMarkSweepThread::desynchronize(true);
7070 ConcurrentMarkSweepThread::acknowledge_yield_request();
7071 _collector->stopTimer();
7072 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7073 if (PrintCMSStatistics != 0) {
7074 _collector->incrementYields();
7075 }
7076 _collector->icms_wait();
7077
7078 // See the comment in coordinator_yield()
7079 for (unsigned i = 0; i < CMSYieldSleepCount &&
7080 ConcurrentMarkSweepThread::should_yield() &&
7081 !CMSCollector::foregroundGCIsActive(); ++i) {
7082 os::sleep(Thread::current(), 1, false);
7083 ConcurrentMarkSweepThread::acknowledge_yield_request();
7084 }
7085
7086 ConcurrentMarkSweepThread::synchronize(true);
7087 _bit_map->lock()->lock_without_safepoint_check();
7088 _collector->startTimer();
7089 }
7090
7091 // This closure is used to rescan the marked objects on the dirty cards
7092 // in the mod union table and the card table proper. In the parallel
7093 // case, although the bitMap is shared, we do a single read so the
7094 // isMarked() query is "safe".
7095 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7096 // Ignore mark word because we are running concurrent with mutators
7097 assert(p->is_oop_or_null(true), "expected an oop or null");
7098 HeapWord* addr = (HeapWord*)p;
7099 assert(_span.contains(addr), "we are scanning the CMS generation");
7100 bool is_obj_array = false;
7101 #ifdef DEBUG
7102 if (!_parallel) {
7103 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7104 assert(_collector->overflow_list_is_empty(),
7105 "overflow list should be empty");
7106
7107 }
7108 #endif // DEBUG
7109 if (_bit_map->isMarked(addr)) {
7110 // Obj arrays are precisely marked, non-arrays are not;
7111 // so we scan objArrays precisely and non-arrays in their
7112 // entirety.
7113 if (p->is_objArray()) {
7114 is_obj_array = true;
7115 if (_parallel) {
7116 p->oop_iterate(_par_scan_closure, mr);
7117 } else {
7118 p->oop_iterate(_scan_closure, mr);
7119 }
7120 } else {
7121 if (_parallel) {
7122 p->oop_iterate(_par_scan_closure);
7123 } else {
7124 p->oop_iterate(_scan_closure);
7125 }
7126 }
7127 }
7128 #ifdef DEBUG
7129 if (!_parallel) {
7130 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7131 assert(_collector->overflow_list_is_empty(),
7132 "overflow list should be empty");
7133
7134 }
7135 #endif // DEBUG
7136 return is_obj_array;
7137 }
7138
7139 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7140 MemRegion span,
7141 CMSBitMap* bitMap, CMSMarkStack* markStack,
7142 CMSMarkStack* revisitStack,
7143 bool should_yield, bool verifying):
7144 _collector(collector),
7145 _span(span),
7146 _bitMap(bitMap),
7147 _mut(&collector->_modUnionTable),
7148 _markStack(markStack),
7149 _revisitStack(revisitStack),
7150 _yield(should_yield),
7151 _skipBits(0)
7152 {
7153 assert(_markStack->isEmpty(), "stack should be empty");
7154 _finger = _bitMap->startWord();
7155 _threshold = _finger;
7156 assert(_collector->_restart_addr == NULL, "Sanity check");
7157 assert(_span.contains(_finger), "Out of bounds _finger?");
7158 DEBUG_ONLY(_verifying = verifying;)
7159 }
7160
7161 void MarkFromRootsClosure::reset(HeapWord* addr) {
7162 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7163 assert(_span.contains(addr), "Out of bounds _finger?");
7164 _finger = addr;
7165 _threshold = (HeapWord*)round_to(
7166 (intptr_t)_finger, CardTableModRefBS::card_size);
7167 }
7168
7169 // Should revisit to see if this should be restructured for
7170 // greater efficiency.
7171 bool MarkFromRootsClosure::do_bit(size_t offset) {
7172 if (_skipBits > 0) {
7173 _skipBits--;
7174 return true;
7175 }
7176 // convert offset into a HeapWord*
7177 HeapWord* addr = _bitMap->startWord() + offset;
7178 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7179 "address out of range");
7180 assert(_bitMap->isMarked(addr), "tautology");
7181 if (_bitMap->isMarked(addr+1)) {
7182 // this is an allocated but not yet initialized object
7183 assert(_skipBits == 0, "tautology");
7184 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7185 oop p = oop(addr);
7186 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7187 DEBUG_ONLY(if (!_verifying) {)
7188 // We re-dirty the cards on which this object lies and increase
7189 // the _threshold so that we'll come back to scan this object
7190 // during the preclean or remark phase. (CMSCleanOnEnter)
7191 if (CMSCleanOnEnter) {
7192 size_t sz = _collector->block_size_using_printezis_bits(addr);
7193 HeapWord* end_card_addr = (HeapWord*)round_to(
7194 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7195 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7196 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7197 // Bump _threshold to end_card_addr; note that
7198 // _threshold cannot possibly exceed end_card_addr, anyhow.
7199 // This prevents future clearing of the card as the scan proceeds
7200 // to the right.
7201 assert(_threshold <= end_card_addr,
7202 "Because we are just scanning into this object");
7203 if (_threshold < end_card_addr) {
7204 _threshold = end_card_addr;
7205 }
7206 if (p->klass_or_null() != NULL) {
7207 // Redirty the range of cards...
7208 _mut->mark_range(redirty_range);
7209 } // ...else the setting of klass will dirty the card anyway.
7210 }
7211 DEBUG_ONLY(})
7212 return true;
7213 }
7214 }
7215 scanOopsInOop(addr);
7216 return true;
7217 }
7218
7219 // We take a break if we've been at this for a while,
7220 // so as to avoid monopolizing the locks involved.
7221 void MarkFromRootsClosure::do_yield_work() {
7222 // First give up the locks, then yield, then re-lock
7223 // We should probably use a constructor/destructor idiom to
7224 // do this unlock/lock or modify the MutexUnlocker class to
7225 // serve our purpose. XXX
7226 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7227 "CMS thread should hold CMS token");
7228 assert_lock_strong(_bitMap->lock());
7229 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7230 _bitMap->lock()->unlock();
7231 ConcurrentMarkSweepThread::desynchronize(true);
7232 ConcurrentMarkSweepThread::acknowledge_yield_request();
7233 _collector->stopTimer();
7234 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7235 if (PrintCMSStatistics != 0) {
7236 _collector->incrementYields();
7237 }
7238 _collector->icms_wait();
7239
7240 // See the comment in coordinator_yield()
7241 for (unsigned i = 0; i < CMSYieldSleepCount &&
7242 ConcurrentMarkSweepThread::should_yield() &&
7243 !CMSCollector::foregroundGCIsActive(); ++i) {
7244 os::sleep(Thread::current(), 1, false);
7245 ConcurrentMarkSweepThread::acknowledge_yield_request();
7246 }
7247
7248 ConcurrentMarkSweepThread::synchronize(true);
7249 _bitMap->lock()->lock_without_safepoint_check();
7250 _collector->startTimer();
7251 }
7252
7253 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7254 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7255 assert(_markStack->isEmpty(),
7256 "should drain stack to limit stack usage");
7257 // convert ptr to an oop preparatory to scanning
7258 oop obj = oop(ptr);
7259 // Ignore mark word in verification below, since we
7260 // may be running concurrent with mutators.
7261 assert(obj->is_oop(true), "should be an oop");
7262 assert(_finger <= ptr, "_finger runneth ahead");
7263 // advance the finger to right end of this object
7264 _finger = ptr + obj->size();
7265 assert(_finger > ptr, "we just incremented it above");
7266 // On large heaps, it may take us some time to get through
7267 // the marking phase (especially if running iCMS). During
7268 // this time it's possible that a lot of mutations have
7269 // accumulated in the card table and the mod union table --
7270 // these mutation records are redundant until we have
7271 // actually traced into the corresponding card.
7272 // Here, we check whether advancing the finger would make
7273 // us cross into a new card, and if so clear corresponding
7274 // cards in the MUT (preclean them in the card-table in the
7275 // future).
7276
7277 DEBUG_ONLY(if (!_verifying) {)
7278 // The clean-on-enter optimization is disabled by default,
7279 // until we fix 6178663.
7280 if (CMSCleanOnEnter && (_finger > _threshold)) {
7281 // [_threshold, _finger) represents the interval
7282 // of cards to be cleared in MUT (or precleaned in card table).
7283 // The set of cards to be cleared is all those that overlap
7284 // with the interval [_threshold, _finger); note that
7285 // _threshold is always kept card-aligned but _finger isn't
7286 // always card-aligned.
7287 HeapWord* old_threshold = _threshold;
7288 assert(old_threshold == (HeapWord*)round_to(
7289 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7290 "_threshold should always be card-aligned");
7291 _threshold = (HeapWord*)round_to(
7292 (intptr_t)_finger, CardTableModRefBS::card_size);
7293 MemRegion mr(old_threshold, _threshold);
7294 assert(!mr.is_empty(), "Control point invariant");
7295 assert(_span.contains(mr), "Should clear within span");
7296 // XXX When _finger crosses from old gen into perm gen
7297 // we may be doing unnecessary cleaning; do better in the
7298 // future by detecting that condition and clearing fewer
7299 // MUT/CT entries.
7300 _mut->clear_range(mr);
7301 }
7302 DEBUG_ONLY(})
7303 // Note: the finger doesn't advance while we drain
7304 // the stack below.
7305 PushOrMarkClosure pushOrMarkClosure(_collector,
7306 _span, _bitMap, _markStack,
7307 _revisitStack,
7308 _finger, this);
7309 bool res = _markStack->push(obj);
7310 assert(res, "Empty non-zero size stack should have space for single push");
7311 while (!_markStack->isEmpty()) {
7312 oop new_oop = _markStack->pop();
7313 // Skip verifying header mark word below because we are
7314 // running concurrent with mutators.
7315 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7316 // now scan this oop's oops
7317 new_oop->oop_iterate(&pushOrMarkClosure);
7318 do_yield_check();
7319 }
7320 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7321 }
7322
7323 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7324 CMSCollector* collector, MemRegion span,
7325 CMSBitMap* bit_map,
7326 OopTaskQueue* work_queue,
7327 CMSMarkStack* overflow_stack,
7328 CMSMarkStack* revisit_stack,
7329 bool should_yield):
7330 _collector(collector),
7331 _whole_span(collector->_span),
7332 _span(span),
7333 _bit_map(bit_map),
7334 _mut(&collector->_modUnionTable),
7335 _work_queue(work_queue),
7336 _overflow_stack(overflow_stack),
7337 _revisit_stack(revisit_stack),
7338 _yield(should_yield),
7339 _skip_bits(0),
7340 _task(task)
7341 {
7342 assert(_work_queue->size() == 0, "work_queue should be empty");
7343 _finger = span.start();
7344 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7345 assert(_span.contains(_finger), "Out of bounds _finger?");
7346 }
7347
7348 // Should revisit to see if this should be restructured for
7349 // greater efficiency.
7350 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7351 if (_skip_bits > 0) {
7352 _skip_bits--;
7353 return true;
7354 }
7355 // convert offset into a HeapWord*
7356 HeapWord* addr = _bit_map->startWord() + offset;
7357 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7358 "address out of range");
7359 assert(_bit_map->isMarked(addr), "tautology");
7360 if (_bit_map->isMarked(addr+1)) {
7361 // this is an allocated object that might not yet be initialized
7362 assert(_skip_bits == 0, "tautology");
7363 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7364 oop p = oop(addr);
7365 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7366 // in the case of Clean-on-Enter optimization, redirty card
7367 // and avoid clearing card by increasing the threshold.
7368 return true;
7369 }
7370 }
7371 scan_oops_in_oop(addr);
7372 return true;
7373 }
7374
7375 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7376 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7377 // Should we assert that our work queue is empty or
7378 // below some drain limit?
7379 assert(_work_queue->size() == 0,
7380 "should drain stack to limit stack usage");
7381 // convert ptr to an oop preparatory to scanning
7382 oop obj = oop(ptr);
7383 // Ignore mark word in verification below, since we
7384 // may be running concurrent with mutators.
7385 assert(obj->is_oop(true), "should be an oop");
7386 assert(_finger <= ptr, "_finger runneth ahead");
7387 // advance the finger to right end of this object
7388 _finger = ptr + obj->size();
7389 assert(_finger > ptr, "we just incremented it above");
7390 // On large heaps, it may take us some time to get through
7391 // the marking phase (especially if running iCMS). During
7392 // this time it's possible that a lot of mutations have
7393 // accumulated in the card table and the mod union table --
7394 // these mutation records are redundant until we have
7395 // actually traced into the corresponding card.
7396 // Here, we check whether advancing the finger would make
7397 // us cross into a new card, and if so clear corresponding
7398 // cards in the MUT (preclean them in the card-table in the
7399 // future).
7400
7401 // The clean-on-enter optimization is disabled by default,
7402 // until we fix 6178663.
7403 if (CMSCleanOnEnter && (_finger > _threshold)) {
7404 // [_threshold, _finger) represents the interval
7405 // of cards to be cleared in MUT (or precleaned in card table).
7406 // The set of cards to be cleared is all those that overlap
7407 // with the interval [_threshold, _finger); note that
7408 // _threshold is always kept card-aligned but _finger isn't
7409 // always card-aligned.
7410 HeapWord* old_threshold = _threshold;
7411 assert(old_threshold == (HeapWord*)round_to(
7412 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7413 "_threshold should always be card-aligned");
7414 _threshold = (HeapWord*)round_to(
7415 (intptr_t)_finger, CardTableModRefBS::card_size);
7416 MemRegion mr(old_threshold, _threshold);
7417 assert(!mr.is_empty(), "Control point invariant");
7418 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7419 // XXX When _finger crosses from old gen into perm gen
7420 // we may be doing unnecessary cleaning; do better in the
7421 // future by detecting that condition and clearing fewer
7422 // MUT/CT entries.
7423 _mut->clear_range(mr);
7424 }
7425
7426 // Note: the local finger doesn't advance while we drain
7427 // the stack below, but the global finger sure can and will.
7428 HeapWord** gfa = _task->global_finger_addr();
7429 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7430 _span, _bit_map,
7431 _work_queue,
7432 _overflow_stack,
7433 _revisit_stack,
7434 _finger,
7435 gfa, this);
7436 bool res = _work_queue->push(obj); // overflow could occur here
7437 assert(res, "Will hold once we use workqueues");
7438 while (true) {
7439 oop new_oop;
7440 if (!_work_queue->pop_local(new_oop)) {
7441 // We emptied our work_queue; check if there's stuff that can
7442 // be gotten from the overflow stack.
7443 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7444 _overflow_stack, _work_queue)) {
7445 do_yield_check();
7446 continue;
7447 } else { // done
7448 break;
7449 }
7450 }
7451 // Skip verifying header mark word below because we are
7452 // running concurrent with mutators.
7453 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7454 // now scan this oop's oops
7455 new_oop->oop_iterate(&pushOrMarkClosure);
7456 do_yield_check();
7457 }
7458 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7459 }
7460
7461 // Yield in response to a request from VM Thread or
7462 // from mutators.
7463 void Par_MarkFromRootsClosure::do_yield_work() {
7464 assert(_task != NULL, "sanity");
7465 _task->yield();
7466 }
7467
7468 // A variant of the above used for verifying CMS marking work.
7469 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7470 MemRegion span,
7471 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7472 CMSMarkStack* mark_stack):
7473 _collector(collector),
7474 _span(span),
7475 _verification_bm(verification_bm),
7476 _cms_bm(cms_bm),
7477 _mark_stack(mark_stack),
7478 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7479 mark_stack)
7480 {
7481 assert(_mark_stack->isEmpty(), "stack should be empty");
7482 _finger = _verification_bm->startWord();
7483 assert(_collector->_restart_addr == NULL, "Sanity check");
7484 assert(_span.contains(_finger), "Out of bounds _finger?");
7485 }
7486
7487 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7488 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7489 assert(_span.contains(addr), "Out of bounds _finger?");
7490 _finger = addr;
7491 }
7492
7493 // Should revisit to see if this should be restructured for
7494 // greater efficiency.
7495 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7496 // convert offset into a HeapWord*
7497 HeapWord* addr = _verification_bm->startWord() + offset;
7498 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7499 "address out of range");
7500 assert(_verification_bm->isMarked(addr), "tautology");
7501 assert(_cms_bm->isMarked(addr), "tautology");
7502
7503 assert(_mark_stack->isEmpty(),
7504 "should drain stack to limit stack usage");
7505 // convert addr to an oop preparatory to scanning
7506 oop obj = oop(addr);
7507 assert(obj->is_oop(), "should be an oop");
7508 assert(_finger <= addr, "_finger runneth ahead");
7509 // advance the finger to right end of this object
7510 _finger = addr + obj->size();
7511 assert(_finger > addr, "we just incremented it above");
7512 // Note: the finger doesn't advance while we drain
7513 // the stack below.
7514 bool res = _mark_stack->push(obj);
7515 assert(res, "Empty non-zero size stack should have space for single push");
7516 while (!_mark_stack->isEmpty()) {
7517 oop new_oop = _mark_stack->pop();
7518 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7519 // now scan this oop's oops
7520 new_oop->oop_iterate(&_pam_verify_closure);
7521 }
7522 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7523 return true;
7524 }
7525
7526 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7527 CMSCollector* collector, MemRegion span,
7528 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7529 CMSMarkStack* mark_stack):
7530 OopClosure(collector->ref_processor()),
7531 _collector(collector),
7532 _span(span),
7533 _verification_bm(verification_bm),
7534 _cms_bm(cms_bm),
7535 _mark_stack(mark_stack)
7536 { }
7537
7538 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7539 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7540
7541 // Upon stack overflow, we discard (part of) the stack,
7542 // remembering the least address amongst those discarded
7543 // in CMSCollector's _restart_address.
7544 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7545 // Remember the least grey address discarded
7546 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7547 _collector->lower_restart_addr(ra);
7548 _mark_stack->reset(); // discard stack contents
7549 _mark_stack->expand(); // expand the stack if possible
7550 }
7551
7552 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7553 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7554 HeapWord* addr = (HeapWord*)obj;
7555 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7556 // Oop lies in _span and isn't yet grey or black
7557 _verification_bm->mark(addr); // now grey
7558 if (!_cms_bm->isMarked(addr)) {
7559 oop(addr)->print();
7560 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7561 addr);
7562 fatal("... aborting");
7563 }
7564
7565 if (!_mark_stack->push(obj)) { // stack overflow
7566 if (PrintCMSStatistics != 0) {
7567 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7568 SIZE_FORMAT, _mark_stack->capacity());
7569 }
7570 assert(_mark_stack->isFull(), "Else push should have succeeded");
7571 handle_stack_overflow(addr);
7572 }
7573 // anything including and to the right of _finger
7574 // will be scanned as we iterate over the remainder of the
7575 // bit map
7576 }
7577 }
7578
7579 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7580 MemRegion span,
7581 CMSBitMap* bitMap, CMSMarkStack* markStack,
7582 CMSMarkStack* revisitStack,
7583 HeapWord* finger, MarkFromRootsClosure* parent) :
7584 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7585 _span(span),
7586 _bitMap(bitMap),
7587 _markStack(markStack),
7588 _finger(finger),
7589 _parent(parent)
7590 { }
7591
7592 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7593 MemRegion span,
7594 CMSBitMap* bit_map,
7595 OopTaskQueue* work_queue,
7596 CMSMarkStack* overflow_stack,
7597 CMSMarkStack* revisit_stack,
7598 HeapWord* finger,
7599 HeapWord** global_finger_addr,
7600 Par_MarkFromRootsClosure* parent) :
7601 Par_KlassRememberingOopClosure(collector,
7602 collector->ref_processor(),
7603 revisit_stack),
7604 _whole_span(collector->_span),
7605 _span(span),
7606 _bit_map(bit_map),
7607 _work_queue(work_queue),
7608 _overflow_stack(overflow_stack),
7609 _finger(finger),
7610 _global_finger_addr(global_finger_addr),
7611 _parent(parent)
7612 { }
7613
7614 // Assumes thread-safe access by callers, who are
7615 // responsible for mutual exclusion.
7616 void CMSCollector::lower_restart_addr(HeapWord* low) {
7617 assert(_span.contains(low), "Out of bounds addr");
7618 if (_restart_addr == NULL) {
7619 _restart_addr = low;
7620 } else {
7621 _restart_addr = MIN2(_restart_addr, low);
7622 }
7623 }
7624
7625 // Upon stack overflow, we discard (part of) the stack,
7626 // remembering the least address amongst those discarded
7627 // in CMSCollector's _restart_address.
7628 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7629 // Remember the least grey address discarded
7630 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7631 _collector->lower_restart_addr(ra);
7632 _markStack->reset(); // discard stack contents
7633 _markStack->expand(); // expand the stack if possible
7634 }
7635
7636 // Upon stack overflow, we discard (part of) the stack,
7637 // remembering the least address amongst those discarded
7638 // in CMSCollector's _restart_address.
7639 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7640 // We need to do this under a mutex to prevent other
7641 // workers from interfering with the work done below.
7642 MutexLockerEx ml(_overflow_stack->par_lock(),
7643 Mutex::_no_safepoint_check_flag);
7644 // Remember the least grey address discarded
7645 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7646 _collector->lower_restart_addr(ra);
7647 _overflow_stack->reset(); // discard stack contents
7648 _overflow_stack->expand(); // expand the stack if possible
7649 }
7650
7651 void PushOrMarkClosure::do_oop(oop obj) {
7652 // Ignore mark word because we are running concurrent with mutators.
7653 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7654 HeapWord* addr = (HeapWord*)obj;
7655 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7656 // Oop lies in _span and isn't yet grey or black
7657 _bitMap->mark(addr); // now grey
7658 if (addr < _finger) {
7659 // the bit map iteration has already either passed, or
7660 // sampled, this bit in the bit map; we'll need to
7661 // use the marking stack to scan this oop's oops.
7662 bool simulate_overflow = false;
7663 NOT_PRODUCT(
7664 if (CMSMarkStackOverflowALot &&
7665 _collector->simulate_overflow()) {
7666 // simulate a stack overflow
7667 simulate_overflow = true;
7668 }
7669 )
7670 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7671 if (PrintCMSStatistics != 0) {
7672 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7673 SIZE_FORMAT, _markStack->capacity());
7674 }
7675 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7676 handle_stack_overflow(addr);
7677 }
7678 }
7679 // anything including and to the right of _finger
7680 // will be scanned as we iterate over the remainder of the
7681 // bit map
7682 do_yield_check();
7683 }
7684 }
7685
7686 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7687 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7688
7689 void Par_PushOrMarkClosure::do_oop(oop obj) {
7690 // Ignore mark word because we are running concurrent with mutators.
7691 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7692 HeapWord* addr = (HeapWord*)obj;
7693 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7694 // Oop lies in _span and isn't yet grey or black
7695 // We read the global_finger (volatile read) strictly after marking oop
7696 bool res = _bit_map->par_mark(addr); // now grey
7697 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7698 // Should we push this marked oop on our stack?
7699 // -- if someone else marked it, nothing to do
7700 // -- if target oop is above global finger nothing to do
7701 // -- if target oop is in chunk and above local finger
7702 // then nothing to do
7703 // -- else push on work queue
7704 if ( !res // someone else marked it, they will deal with it
7705 || (addr >= *gfa) // will be scanned in a later task
7706 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7707 return;
7708 }
7709 // the bit map iteration has already either passed, or
7710 // sampled, this bit in the bit map; we'll need to
7711 // use the marking stack to scan this oop's oops.
7712 bool simulate_overflow = false;
7713 NOT_PRODUCT(
7714 if (CMSMarkStackOverflowALot &&
7715 _collector->simulate_overflow()) {
7716 // simulate a stack overflow
7717 simulate_overflow = true;
7718 }
7719 )
7720 if (simulate_overflow ||
7721 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7722 // stack overflow
7723 if (PrintCMSStatistics != 0) {
7724 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7725 SIZE_FORMAT, _overflow_stack->capacity());
7726 }
7727 // We cannot assert that the overflow stack is full because
7728 // it may have been emptied since.
7729 assert(simulate_overflow ||
7730 _work_queue->size() == _work_queue->max_elems(),
7731 "Else push should have succeeded");
7732 handle_stack_overflow(addr);
7733 }
7734 do_yield_check();
7735 }
7736 }
7737
7738 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7739 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7740
7741 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7742 ReferenceProcessor* rp,
7743 CMSMarkStack* revisit_stack) :
7744 OopClosure(rp),
7745 _collector(collector),
7746 _revisit_stack(revisit_stack),
7747 _should_remember_klasses(collector->should_unload_classes()) {}
7748
7749 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7750 MemRegion span,
7751 ReferenceProcessor* rp,
7752 CMSBitMap* bit_map,
7753 CMSBitMap* mod_union_table,
7754 CMSMarkStack* mark_stack,
7755 CMSMarkStack* revisit_stack,
7756 bool concurrent_precleaning):
7757 KlassRememberingOopClosure(collector, rp, revisit_stack),
7758 _span(span),
7759 _bit_map(bit_map),
7760 _mod_union_table(mod_union_table),
7761 _mark_stack(mark_stack),
7762 _concurrent_precleaning(concurrent_precleaning)
7763 {
7764 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7765 }
7766
7767 // Grey object rescan during pre-cleaning and second checkpoint phases --
7768 // the non-parallel version (the parallel version appears further below.)
7769 void PushAndMarkClosure::do_oop(oop obj) {
7770 // Ignore mark word verification. If during concurrent precleaning,
7771 // the object monitor may be locked. If during the checkpoint
7772 // phases, the object may already have been reached by a different
7773 // path and may be at the end of the global overflow list (so
7774 // the mark word may be NULL).
7775 assert(obj->is_oop_or_null(true /* ignore mark word */),
7776 "expected an oop or NULL");
7777 HeapWord* addr = (HeapWord*)obj;
7778 // Check if oop points into the CMS generation
7779 // and is not marked
7780 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7781 // a white object ...
7782 _bit_map->mark(addr); // ... now grey
7783 // push on the marking stack (grey set)
7784 bool simulate_overflow = false;
7785 NOT_PRODUCT(
7786 if (CMSMarkStackOverflowALot &&
7787 _collector->simulate_overflow()) {
7788 // simulate a stack overflow
7789 simulate_overflow = true;
7790 }
7791 )
7792 if (simulate_overflow || !_mark_stack->push(obj)) {
7793 if (_concurrent_precleaning) {
7794 // During precleaning we can just dirty the appropriate card(s)
7795 // in the mod union table, thus ensuring that the object remains
7796 // in the grey set and continue. In the case of object arrays
7797 // we need to dirty all of the cards that the object spans,
7798 // since the rescan of object arrays will be limited to the
7799 // dirty cards.
7800 // Note that no one can be intefering with us in this action
7801 // of dirtying the mod union table, so no locking or atomics
7802 // are required.
7803 if (obj->is_objArray()) {
7804 size_t sz = obj->size();
7805 HeapWord* end_card_addr = (HeapWord*)round_to(
7806 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7807 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7808 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7809 _mod_union_table->mark_range(redirty_range);
7810 } else {
7811 _mod_union_table->mark(addr);
7812 }
7813 _collector->_ser_pmc_preclean_ovflw++;
7814 } else {
7815 // During the remark phase, we need to remember this oop
7816 // in the overflow list.
7817 _collector->push_on_overflow_list(obj);
7818 _collector->_ser_pmc_remark_ovflw++;
7819 }
7820 }
7821 }
7822 }
7823
7824 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7825 MemRegion span,
7826 ReferenceProcessor* rp,
7827 CMSBitMap* bit_map,
7828 OopTaskQueue* work_queue,
7829 CMSMarkStack* revisit_stack):
7830 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7831 _span(span),
7832 _bit_map(bit_map),
7833 _work_queue(work_queue)
7834 {
7835 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7836 }
7837
7838 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7839 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7840
7841 // Grey object rescan during second checkpoint phase --
7842 // the parallel version.
7843 void Par_PushAndMarkClosure::do_oop(oop obj) {
7844 // In the assert below, we ignore the mark word because
7845 // this oop may point to an already visited object that is
7846 // on the overflow stack (in which case the mark word has
7847 // been hijacked for chaining into the overflow stack --
7848 // if this is the last object in the overflow stack then
7849 // its mark word will be NULL). Because this object may
7850 // have been subsequently popped off the global overflow
7851 // stack, and the mark word possibly restored to the prototypical
7852 // value, by the time we get to examined this failing assert in
7853 // the debugger, is_oop_or_null(false) may subsequently start
7854 // to hold.
7855 assert(obj->is_oop_or_null(true),
7856 "expected an oop or NULL");
7857 HeapWord* addr = (HeapWord*)obj;
7858 // Check if oop points into the CMS generation
7859 // and is not marked
7860 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7861 // a white object ...
7862 // If we manage to "claim" the object, by being the
7863 // first thread to mark it, then we push it on our
7864 // marking stack
7865 if (_bit_map->par_mark(addr)) { // ... now grey
7866 // push on work queue (grey set)
7867 bool simulate_overflow = false;
7868 NOT_PRODUCT(
7869 if (CMSMarkStackOverflowALot &&
7870 _collector->par_simulate_overflow()) {
7871 // simulate a stack overflow
7872 simulate_overflow = true;
7873 }
7874 )
7875 if (simulate_overflow || !_work_queue->push(obj)) {
7876 _collector->par_push_on_overflow_list(obj);
7877 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7878 }
7879 } // Else, some other thread got there first
7880 }
7881 }
7882
7883 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7884 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7885
7886 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7887 // TBD
7888 }
7889
7890 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7891 // TBD
7892 }
7893
7894 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7895 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7896 Mutex* bml = _collector->bitMapLock();
7897 assert_lock_strong(bml);
7898 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7899 "CMS thread should hold CMS token");
7900
7901 bml->unlock();
7902 ConcurrentMarkSweepThread::desynchronize(true);
7903
7904 ConcurrentMarkSweepThread::acknowledge_yield_request();
7905
7906 _collector->stopTimer();
7907 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7908 if (PrintCMSStatistics != 0) {
7909 _collector->incrementYields();
7910 }
7911 _collector->icms_wait();
7912
7913 // See the comment in coordinator_yield()
7914 for (unsigned i = 0; i < CMSYieldSleepCount &&
7915 ConcurrentMarkSweepThread::should_yield() &&
7916 !CMSCollector::foregroundGCIsActive(); ++i) {
7917 os::sleep(Thread::current(), 1, false);
7918 ConcurrentMarkSweepThread::acknowledge_yield_request();
7919 }
7920
7921 ConcurrentMarkSweepThread::synchronize(true);
7922 bml->lock();
7923
7924 _collector->startTimer();
7925 }
7926
7927 bool CMSPrecleanRefsYieldClosure::should_return() {
7928 if (ConcurrentMarkSweepThread::should_yield()) {
7929 do_yield_work();
7930 }
7931 return _collector->foregroundGCIsActive();
7932 }
7933
7934 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7935 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7936 "mr should be aligned to start at a card boundary");
7937 // We'd like to assert:
7938 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7939 // "mr should be a range of cards");
7940 // However, that would be too strong in one case -- the last
7941 // partition ends at _unallocated_block which, in general, can be
7942 // an arbitrary boundary, not necessarily card aligned.
7943 if (PrintCMSStatistics != 0) {
7944 _num_dirty_cards +=
7945 mr.word_size()/CardTableModRefBS::card_size_in_words;
7946 }
7947 _space->object_iterate_mem(mr, &_scan_cl);
7948 }
7949
7950 SweepClosure::SweepClosure(CMSCollector* collector,
7951 ConcurrentMarkSweepGeneration* g,
7952 CMSBitMap* bitMap, bool should_yield) :
7953 _collector(collector),
7954 _g(g),
7955 _sp(g->cmsSpace()),
7956 _limit(_sp->sweep_limit()),
7957 _freelistLock(_sp->freelistLock()),
7958 _bitMap(bitMap),
7959 _yield(should_yield),
7960 _inFreeRange(false), // No free range at beginning of sweep
7961 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7962 _lastFreeRangeCoalesced(false),
7963 _freeFinger(g->used_region().start())
7964 {
7965 NOT_PRODUCT(
7966 _numObjectsFreed = 0;
7967 _numWordsFreed = 0;
7968 _numObjectsLive = 0;
7969 _numWordsLive = 0;
7970 _numObjectsAlreadyFree = 0;
7971 _numWordsAlreadyFree = 0;
7972 _last_fc = NULL;
7973
7974 _sp->initializeIndexedFreeListArrayReturnedBytes();
7975 _sp->dictionary()->initialize_dict_returned_bytes();
7976 )
7977 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7978 "sweep _limit out of bounds");
7979 if (CMSTraceSweeper) {
7980 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7981 _limit);
7982 }
7983 }
7984
7985 void SweepClosure::print_on(outputStream* st) const {
7986 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7987 _sp->bottom(), _sp->end());
7988 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7989 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7990 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7991 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7992 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7993 }
7994
7995 #ifndef PRODUCT
7996 // Assertion checking only: no useful work in product mode --
7997 // however, if any of the flags below become product flags,
7998 // you may need to review this code to see if it needs to be
7999 // enabled in product mode.
8000 SweepClosure::~SweepClosure() {
8001 assert_lock_strong(_freelistLock);
8002 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8003 "sweep _limit out of bounds");
8004 if (inFreeRange()) {
8005 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8006 print();
8007 ShouldNotReachHere();
8008 }
8009 if (Verbose && PrintGC) {
8010 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8011 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8012 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8013 SIZE_FORMAT" bytes "
8014 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8015 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8016 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8017 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8018 * sizeof(HeapWord);
8019 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8020
8021 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8022 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8023 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8024 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8025 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8026 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8027 indexListReturnedBytes);
8028 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8029 dict_returned_bytes);
8030 }
8031 }
8032 if (CMSTraceSweeper) {
8033 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8034 _limit);
8035 }
8036 }
8037 #endif // PRODUCT
8038
8039 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8040 bool freeRangeInFreeLists) {
8041 if (CMSTraceSweeper) {
8042 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8043 freeFinger, freeRangeInFreeLists);
8044 }
8045 assert(!inFreeRange(), "Trampling existing free range");
8046 set_inFreeRange(true);
8047 set_lastFreeRangeCoalesced(false);
8048
8049 set_freeFinger(freeFinger);
8050 set_freeRangeInFreeLists(freeRangeInFreeLists);
8051 if (CMSTestInFreeList) {
8052 if (freeRangeInFreeLists) {
8053 FreeChunk* fc = (FreeChunk*) freeFinger;
8054 assert(fc->is_free(), "A chunk on the free list should be free.");
8055 assert(fc->size() > 0, "Free range should have a size");
8056 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8057 }
8058 }
8059 }
8060
8061 // Note that the sweeper runs concurrently with mutators. Thus,
8062 // it is possible for direct allocation in this generation to happen
8063 // in the middle of the sweep. Note that the sweeper also coalesces
8064 // contiguous free blocks. Thus, unless the sweeper and the allocator
8065 // synchronize appropriately freshly allocated blocks may get swept up.
8066 // This is accomplished by the sweeper locking the free lists while
8067 // it is sweeping. Thus blocks that are determined to be free are
8068 // indeed free. There is however one additional complication:
8069 // blocks that have been allocated since the final checkpoint and
8070 // mark, will not have been marked and so would be treated as
8071 // unreachable and swept up. To prevent this, the allocator marks
8072 // the bit map when allocating during the sweep phase. This leads,
8073 // however, to a further complication -- objects may have been allocated
8074 // but not yet initialized -- in the sense that the header isn't yet
8075 // installed. The sweeper can not then determine the size of the block
8076 // in order to skip over it. To deal with this case, we use a technique
8077 // (due to Printezis) to encode such uninitialized block sizes in the
8078 // bit map. Since the bit map uses a bit per every HeapWord, but the
8079 // CMS generation has a minimum object size of 3 HeapWords, it follows
8080 // that "normal marks" won't be adjacent in the bit map (there will
8081 // always be at least two 0 bits between successive 1 bits). We make use
8082 // of these "unused" bits to represent uninitialized blocks -- the bit
8083 // corresponding to the start of the uninitialized object and the next
8084 // bit are both set. Finally, a 1 bit marks the end of the object that
8085 // started with the two consecutive 1 bits to indicate its potentially
8086 // uninitialized state.
8087
8088 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8089 FreeChunk* fc = (FreeChunk*)addr;
8090 size_t res;
8091
8092 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8093 // than "addr == _limit" because although _limit was a block boundary when
8094 // we started the sweep, it may no longer be one because heap expansion
8095 // may have caused us to coalesce the block ending at the address _limit
8096 // with a newly expanded chunk (this happens when _limit was set to the
8097 // previous _end of the space), so we may have stepped past _limit:
8098 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8099 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8100 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8101 "sweep _limit out of bounds");
8102 assert(addr < _sp->end(), "addr out of bounds");
8103 // Flush any free range we might be holding as a single
8104 // coalesced chunk to the appropriate free list.
8105 if (inFreeRange()) {
8106 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8107 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8108 flush_cur_free_chunk(freeFinger(),
8109 pointer_delta(addr, freeFinger()));
8110 if (CMSTraceSweeper) {
8111 gclog_or_tty->print("Sweep: last chunk: ");
8112 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8113 "[coalesced:"SIZE_FORMAT"]\n",
8114 freeFinger(), pointer_delta(addr, freeFinger()),
8115 lastFreeRangeCoalesced());
8116 }
8117 }
8118
8119 // help the iterator loop finish
8120 return pointer_delta(_sp->end(), addr);
8121 }
8122
8123 assert(addr < _limit, "sweep invariant");
8124 // check if we should yield
8125 do_yield_check(addr);
8126 if (fc->is_free()) {
8127 // Chunk that is already free
8128 res = fc->size();
8129 do_already_free_chunk(fc);
8130 debug_only(_sp->verifyFreeLists());
8131 // If we flush the chunk at hand in lookahead_and_flush()
8132 // and it's coalesced with a preceding chunk, then the
8133 // process of "mangling" the payload of the coalesced block
8134 // will cause erasure of the size information from the
8135 // (erstwhile) header of all the coalesced blocks but the
8136 // first, so the first disjunct in the assert will not hold
8137 // in that specific case (in which case the second disjunct
8138 // will hold).
8139 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8140 "Otherwise the size info doesn't change at this step");
8141 NOT_PRODUCT(
8142 _numObjectsAlreadyFree++;
8143 _numWordsAlreadyFree += res;
8144 )
8145 NOT_PRODUCT(_last_fc = fc;)
8146 } else if (!_bitMap->isMarked(addr)) {
8147 // Chunk is fresh garbage
8148 res = do_garbage_chunk(fc);
8149 debug_only(_sp->verifyFreeLists());
8150 NOT_PRODUCT(
8151 _numObjectsFreed++;
8152 _numWordsFreed += res;
8153 )
8154 } else {
8155 // Chunk that is alive.
8156 res = do_live_chunk(fc);
8157 debug_only(_sp->verifyFreeLists());
8158 NOT_PRODUCT(
8159 _numObjectsLive++;
8160 _numWordsLive += res;
8161 )
8162 }
8163 return res;
8164 }
8165
8166 // For the smart allocation, record following
8167 // split deaths - a free chunk is removed from its free list because
8168 // it is being split into two or more chunks.
8169 // split birth - a free chunk is being added to its free list because
8170 // a larger free chunk has been split and resulted in this free chunk.
8171 // coal death - a free chunk is being removed from its free list because
8172 // it is being coalesced into a large free chunk.
8173 // coal birth - a free chunk is being added to its free list because
8174 // it was created when two or more free chunks where coalesced into
8175 // this free chunk.
8176 //
8177 // These statistics are used to determine the desired number of free
8178 // chunks of a given size. The desired number is chosen to be relative
8179 // to the end of a CMS sweep. The desired number at the end of a sweep
8180 // is the
8181 // count-at-end-of-previous-sweep (an amount that was enough)
8182 // - count-at-beginning-of-current-sweep (the excess)
8183 // + split-births (gains in this size during interval)
8184 // - split-deaths (demands on this size during interval)
8185 // where the interval is from the end of one sweep to the end of the
8186 // next.
8187 //
8188 // When sweeping the sweeper maintains an accumulated chunk which is
8189 // the chunk that is made up of chunks that have been coalesced. That
8190 // will be termed the left-hand chunk. A new chunk of garbage that
8191 // is being considered for coalescing will be referred to as the
8192 // right-hand chunk.
8193 //
8194 // When making a decision on whether to coalesce a right-hand chunk with
8195 // the current left-hand chunk, the current count vs. the desired count
8196 // of the left-hand chunk is considered. Also if the right-hand chunk
8197 // is near the large chunk at the end of the heap (see
8198 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8199 // left-hand chunk is coalesced.
8200 //
8201 // When making a decision about whether to split a chunk, the desired count
8202 // vs. the current count of the candidate to be split is also considered.
8203 // If the candidate is underpopulated (currently fewer chunks than desired)
8204 // a chunk of an overpopulated (currently more chunks than desired) size may
8205 // be chosen. The "hint" associated with a free list, if non-null, points
8206 // to a free list which may be overpopulated.
8207 //
8208
8209 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8210 const size_t size = fc->size();
8211 // Chunks that cannot be coalesced are not in the
8212 // free lists.
8213 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8214 assert(_sp->verify_chunk_in_free_list(fc),
8215 "free chunk should be in free lists");
8216 }
8217 // a chunk that is already free, should not have been
8218 // marked in the bit map
8219 HeapWord* const addr = (HeapWord*) fc;
8220 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8221 // Verify that the bit map has no bits marked between
8222 // addr and purported end of this block.
8223 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8224
8225 // Some chunks cannot be coalesced under any circumstances.
8226 // See the definition of cantCoalesce().
8227 if (!fc->cantCoalesce()) {
8228 // This chunk can potentially be coalesced.
8229 if (_sp->adaptive_freelists()) {
8230 // All the work is done in
8231 do_post_free_or_garbage_chunk(fc, size);
8232 } else { // Not adaptive free lists
8233 // this is a free chunk that can potentially be coalesced by the sweeper;
8234 if (!inFreeRange()) {
8235 // if the next chunk is a free block that can't be coalesced
8236 // it doesn't make sense to remove this chunk from the free lists
8237 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8238 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8239 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8240 nextChunk->is_free() && // ... which is free...
8241 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8242 // nothing to do
8243 } else {
8244 // Potentially the start of a new free range:
8245 // Don't eagerly remove it from the free lists.
8246 // No need to remove it if it will just be put
8247 // back again. (Also from a pragmatic point of view
8248 // if it is a free block in a region that is beyond
8249 // any allocated blocks, an assertion will fail)
8250 // Remember the start of a free run.
8251 initialize_free_range(addr, true);
8252 // end - can coalesce with next chunk
8253 }
8254 } else {
8255 // the midst of a free range, we are coalescing
8256 print_free_block_coalesced(fc);
8257 if (CMSTraceSweeper) {
8258 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8259 }
8260 // remove it from the free lists
8261 _sp->removeFreeChunkFromFreeLists(fc);
8262 set_lastFreeRangeCoalesced(true);
8263 // If the chunk is being coalesced and the current free range is
8264 // in the free lists, remove the current free range so that it
8265 // will be returned to the free lists in its entirety - all
8266 // the coalesced pieces included.
8267 if (freeRangeInFreeLists()) {
8268 FreeChunk* ffc = (FreeChunk*) freeFinger();
8269 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8270 "Size of free range is inconsistent with chunk size.");
8271 if (CMSTestInFreeList) {
8272 assert(_sp->verify_chunk_in_free_list(ffc),
8273 "free range is not in free lists");
8274 }
8275 _sp->removeFreeChunkFromFreeLists(ffc);
8276 set_freeRangeInFreeLists(false);
8277 }
8278 }
8279 }
8280 // Note that if the chunk is not coalescable (the else arm
8281 // below), we unconditionally flush, without needing to do
8282 // a "lookahead," as we do below.
8283 if (inFreeRange()) lookahead_and_flush(fc, size);
8284 } else {
8285 // Code path common to both original and adaptive free lists.
8286
8287 // cant coalesce with previous block; this should be treated
8288 // as the end of a free run if any
8289 if (inFreeRange()) {
8290 // we kicked some butt; time to pick up the garbage
8291 assert(freeFinger() < addr, "freeFinger points too high");
8292 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8293 }
8294 // else, nothing to do, just continue
8295 }
8296 }
8297
8298 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8299 // This is a chunk of garbage. It is not in any free list.
8300 // Add it to a free list or let it possibly be coalesced into
8301 // a larger chunk.
8302 HeapWord* const addr = (HeapWord*) fc;
8303 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8304
8305 if (_sp->adaptive_freelists()) {
8306 // Verify that the bit map has no bits marked between
8307 // addr and purported end of just dead object.
8308 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8309
8310 do_post_free_or_garbage_chunk(fc, size);
8311 } else {
8312 if (!inFreeRange()) {
8313 // start of a new free range
8314 assert(size > 0, "A free range should have a size");
8315 initialize_free_range(addr, false);
8316 } else {
8317 // this will be swept up when we hit the end of the
8318 // free range
8319 if (CMSTraceSweeper) {
8320 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8321 }
8322 // If the chunk is being coalesced and the current free range is
8323 // in the free lists, remove the current free range so that it
8324 // will be returned to the free lists in its entirety - all
8325 // the coalesced pieces included.
8326 if (freeRangeInFreeLists()) {
8327 FreeChunk* ffc = (FreeChunk*)freeFinger();
8328 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8329 "Size of free range is inconsistent with chunk size.");
8330 if (CMSTestInFreeList) {
8331 assert(_sp->verify_chunk_in_free_list(ffc),
8332 "free range is not in free lists");
8333 }
8334 _sp->removeFreeChunkFromFreeLists(ffc);
8335 set_freeRangeInFreeLists(false);
8336 }
8337 set_lastFreeRangeCoalesced(true);
8338 }
8339 // this will be swept up when we hit the end of the free range
8340
8341 // Verify that the bit map has no bits marked between
8342 // addr and purported end of just dead object.
8343 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8344 }
8345 assert(_limit >= addr + size,
8346 "A freshly garbage chunk can't possibly straddle over _limit");
8347 if (inFreeRange()) lookahead_and_flush(fc, size);
8348 return size;
8349 }
8350
8351 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8352 HeapWord* addr = (HeapWord*) fc;
8353 // The sweeper has just found a live object. Return any accumulated
8354 // left hand chunk to the free lists.
8355 if (inFreeRange()) {
8356 assert(freeFinger() < addr, "freeFinger points too high");
8357 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8358 }
8359
8360 // This object is live: we'd normally expect this to be
8361 // an oop, and like to assert the following:
8362 // assert(oop(addr)->is_oop(), "live block should be an oop");
8363 // However, as we commented above, this may be an object whose
8364 // header hasn't yet been initialized.
8365 size_t size;
8366 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8367 if (_bitMap->isMarked(addr + 1)) {
8368 // Determine the size from the bit map, rather than trying to
8369 // compute it from the object header.
8370 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8371 size = pointer_delta(nextOneAddr + 1, addr);
8372 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8373 "alignment problem");
8374
8375 #ifdef DEBUG
8376 if (oop(addr)->klass_or_null() != NULL &&
8377 ( !_collector->should_unload_classes()
8378 || (oop(addr)->is_parsable()) &&
8379 oop(addr)->is_conc_safe())) {
8380 // Ignore mark word because we are running concurrent with mutators
8381 assert(oop(addr)->is_oop(true), "live block should be an oop");
8382 // is_conc_safe is checked before performing this assertion
8383 // because an object that is not is_conc_safe may yet have
8384 // the return from size() correct.
8385 assert(size ==
8386 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8387 "P-mark and computed size do not agree");
8388 }
8389 #endif
8390
8391 } else {
8392 // This should be an initialized object that's alive.
8393 assert(oop(addr)->klass_or_null() != NULL &&
8394 (!_collector->should_unload_classes()
8395 || oop(addr)->is_parsable()),
8396 "Should be an initialized object");
8397 // Note that there are objects used during class redefinition,
8398 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8399 // which are discarded with their is_conc_safe state still
8400 // false. These object may be floating garbage so may be
8401 // seen here. If they are floating garbage their size
8402 // should be attainable from their klass. Do not that
8403 // is_conc_safe() is true for oop(addr).
8404 // Ignore mark word because we are running concurrent with mutators
8405 assert(oop(addr)->is_oop(true), "live block should be an oop");
8406 // Verify that the bit map has no bits marked between
8407 // addr and purported end of this block.
8408 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8409 assert(size >= 3, "Necessary for Printezis marks to work");
8410 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8411 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8412 }
8413 return size;
8414 }
8415
8416 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8417 size_t chunkSize) {
8418 // do_post_free_or_garbage_chunk() should only be called in the case
8419 // of the adaptive free list allocator.
8420 const bool fcInFreeLists = fc->is_free();
8421 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8422 assert((HeapWord*)fc <= _limit, "sweep invariant");
8423 if (CMSTestInFreeList && fcInFreeLists) {
8424 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8425 }
8426
8427 if (CMSTraceSweeper) {
8428 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8429 }
8430
8431 HeapWord* const fc_addr = (HeapWord*) fc;
8432
8433 bool coalesce;
8434 const size_t left = pointer_delta(fc_addr, freeFinger());
8435 const size_t right = chunkSize;
8436 switch (FLSCoalescePolicy) {
8437 // numeric value forms a coalition aggressiveness metric
8438 case 0: { // never coalesce
8439 coalesce = false;
8440 break;
8441 }
8442 case 1: { // coalesce if left & right chunks on overpopulated lists
8443 coalesce = _sp->coalOverPopulated(left) &&
8444 _sp->coalOverPopulated(right);
8445 break;
8446 }
8447 case 2: { // coalesce if left chunk on overpopulated list (default)
8448 coalesce = _sp->coalOverPopulated(left);
8449 break;
8450 }
8451 case 3: { // coalesce if left OR right chunk on overpopulated list
8452 coalesce = _sp->coalOverPopulated(left) ||
8453 _sp->coalOverPopulated(right);
8454 break;
8455 }
8456 case 4: { // always coalesce
8457 coalesce = true;
8458 break;
8459 }
8460 default:
8461 ShouldNotReachHere();
8462 }
8463
8464 // Should the current free range be coalesced?
8465 // If the chunk is in a free range and either we decided to coalesce above
8466 // or the chunk is near the large block at the end of the heap
8467 // (isNearLargestChunk() returns true), then coalesce this chunk.
8468 const bool doCoalesce = inFreeRange()
8469 && (coalesce || _g->isNearLargestChunk(fc_addr));
8470 if (doCoalesce) {
8471 // Coalesce the current free range on the left with the new
8472 // chunk on the right. If either is on a free list,
8473 // it must be removed from the list and stashed in the closure.
8474 if (freeRangeInFreeLists()) {
8475 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8476 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8477 "Size of free range is inconsistent with chunk size.");
8478 if (CMSTestInFreeList) {
8479 assert(_sp->verify_chunk_in_free_list(ffc),
8480 "Chunk is not in free lists");
8481 }
8482 _sp->coalDeath(ffc->size());
8483 _sp->removeFreeChunkFromFreeLists(ffc);
8484 set_freeRangeInFreeLists(false);
8485 }
8486 if (fcInFreeLists) {
8487 _sp->coalDeath(chunkSize);
8488 assert(fc->size() == chunkSize,
8489 "The chunk has the wrong size or is not in the free lists");
8490 _sp->removeFreeChunkFromFreeLists(fc);
8491 }
8492 set_lastFreeRangeCoalesced(true);
8493 print_free_block_coalesced(fc);
8494 } else { // not in a free range and/or should not coalesce
8495 // Return the current free range and start a new one.
8496 if (inFreeRange()) {
8497 // In a free range but cannot coalesce with the right hand chunk.
8498 // Put the current free range into the free lists.
8499 flush_cur_free_chunk(freeFinger(),
8500 pointer_delta(fc_addr, freeFinger()));
8501 }
8502 // Set up for new free range. Pass along whether the right hand
8503 // chunk is in the free lists.
8504 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8505 }
8506 }
8507
8508 // Lookahead flush:
8509 // If we are tracking a free range, and this is the last chunk that
8510 // we'll look at because its end crosses past _limit, we'll preemptively
8511 // flush it along with any free range we may be holding on to. Note that
8512 // this can be the case only for an already free or freshly garbage
8513 // chunk. If this block is an object, it can never straddle
8514 // over _limit. The "straddling" occurs when _limit is set at
8515 // the previous end of the space when this cycle started, and
8516 // a subsequent heap expansion caused the previously co-terminal
8517 // free block to be coalesced with the newly expanded portion,
8518 // thus rendering _limit a non-block-boundary making it dangerous
8519 // for the sweeper to step over and examine.
8520 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8521 assert(inFreeRange(), "Should only be called if currently in a free range.");
8522 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8523 assert(_sp->used_region().contains(eob - 1),
8524 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8525 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8526 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8527 if (eob >= _limit) {
8528 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8529 if (CMSTraceSweeper) {
8530 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8531 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8532 "[" PTR_FORMAT "," PTR_FORMAT ")",
8533 _limit, fc, eob, _sp->bottom(), _sp->end());
8534 }
8535 // Return the storage we are tracking back into the free lists.
8536 if (CMSTraceSweeper) {
8537 gclog_or_tty->print_cr("Flushing ... ");
8538 }
8539 assert(freeFinger() < eob, "Error");
8540 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8541 }
8542 }
8543
8544 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8545 assert(inFreeRange(), "Should only be called if currently in a free range.");
8546 assert(size > 0,
8547 "A zero sized chunk cannot be added to the free lists.");
8548 if (!freeRangeInFreeLists()) {
8549 if (CMSTestInFreeList) {
8550 FreeChunk* fc = (FreeChunk*) chunk;
8551 fc->set_size(size);
8552 assert(!_sp->verify_chunk_in_free_list(fc),
8553 "chunk should not be in free lists yet");
8554 }
8555 if (CMSTraceSweeper) {
8556 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8557 chunk, size);
8558 }
8559 // A new free range is going to be starting. The current
8560 // free range has not been added to the free lists yet or
8561 // was removed so add it back.
8562 // If the current free range was coalesced, then the death
8563 // of the free range was recorded. Record a birth now.
8564 if (lastFreeRangeCoalesced()) {
8565 _sp->coalBirth(size);
8566 }
8567 _sp->addChunkAndRepairOffsetTable(chunk, size,
8568 lastFreeRangeCoalesced());
8569 } else if (CMSTraceSweeper) {
8570 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8571 }
8572 set_inFreeRange(false);
8573 set_freeRangeInFreeLists(false);
8574 }
8575
8576 // We take a break if we've been at this for a while,
8577 // so as to avoid monopolizing the locks involved.
8578 void SweepClosure::do_yield_work(HeapWord* addr) {
8579 // Return current free chunk being used for coalescing (if any)
8580 // to the appropriate freelist. After yielding, the next
8581 // free block encountered will start a coalescing range of
8582 // free blocks. If the next free block is adjacent to the
8583 // chunk just flushed, they will need to wait for the next
8584 // sweep to be coalesced.
8585 if (inFreeRange()) {
8586 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8587 }
8588
8589 // First give up the locks, then yield, then re-lock.
8590 // We should probably use a constructor/destructor idiom to
8591 // do this unlock/lock or modify the MutexUnlocker class to
8592 // serve our purpose. XXX
8593 assert_lock_strong(_bitMap->lock());
8594 assert_lock_strong(_freelistLock);
8595 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8596 "CMS thread should hold CMS token");
8597 _bitMap->lock()->unlock();
8598 _freelistLock->unlock();
8599 ConcurrentMarkSweepThread::desynchronize(true);
8600 ConcurrentMarkSweepThread::acknowledge_yield_request();
8601 _collector->stopTimer();
8602 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8603 if (PrintCMSStatistics != 0) {
8604 _collector->incrementYields();
8605 }
8606 _collector->icms_wait();
8607
8608 // See the comment in coordinator_yield()
8609 for (unsigned i = 0; i < CMSYieldSleepCount &&
8610 ConcurrentMarkSweepThread::should_yield() &&
8611 !CMSCollector::foregroundGCIsActive(); ++i) {
8612 os::sleep(Thread::current(), 1, false);
8613 ConcurrentMarkSweepThread::acknowledge_yield_request();
8614 }
8615
8616 ConcurrentMarkSweepThread::synchronize(true);
8617 _freelistLock->lock();
8618 _bitMap->lock()->lock_without_safepoint_check();
8619 _collector->startTimer();
8620 }
8621
8622 #ifndef PRODUCT
8623 // This is actually very useful in a product build if it can
8624 // be called from the debugger. Compile it into the product
8625 // as needed.
8626 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8627 return debug_cms_space->verify_chunk_in_free_list(fc);
8628 }
8629 #endif
8630
8631 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8632 if (CMSTraceSweeper) {
8633 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8634 fc, fc->size());
8635 }
8636 }
8637
8638 // CMSIsAliveClosure
8639 bool CMSIsAliveClosure::do_object_b(oop obj) {
8640 HeapWord* addr = (HeapWord*)obj;
8641 return addr != NULL &&
8642 (!_span.contains(addr) || _bit_map->isMarked(addr));
8643 }
8644
8645 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8646 MemRegion span,
8647 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8648 CMSMarkStack* revisit_stack, bool cpc):
8649 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8650 _span(span),
8651 _bit_map(bit_map),
8652 _mark_stack(mark_stack),
8653 _concurrent_precleaning(cpc) {
8654 assert(!_span.is_empty(), "Empty span could spell trouble");
8655 }
8656
8657
8658 // CMSKeepAliveClosure: the serial version
8659 void CMSKeepAliveClosure::do_oop(oop obj) {
8660 HeapWord* addr = (HeapWord*)obj;
8661 if (_span.contains(addr) &&
8662 !_bit_map->isMarked(addr)) {
8663 _bit_map->mark(addr);
8664 bool simulate_overflow = false;
8665 NOT_PRODUCT(
8666 if (CMSMarkStackOverflowALot &&
8667 _collector->simulate_overflow()) {
8668 // simulate a stack overflow
8669 simulate_overflow = true;
8670 }
8671 )
8672 if (simulate_overflow || !_mark_stack->push(obj)) {
8673 if (_concurrent_precleaning) {
8674 // We dirty the overflown object and let the remark
8675 // phase deal with it.
8676 assert(_collector->overflow_list_is_empty(), "Error");
8677 // In the case of object arrays, we need to dirty all of
8678 // the cards that the object spans. No locking or atomics
8679 // are needed since no one else can be mutating the mod union
8680 // table.
8681 if (obj->is_objArray()) {
8682 size_t sz = obj->size();
8683 HeapWord* end_card_addr =
8684 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8685 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8686 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8687 _collector->_modUnionTable.mark_range(redirty_range);
8688 } else {
8689 _collector->_modUnionTable.mark(addr);
8690 }
8691 _collector->_ser_kac_preclean_ovflw++;
8692 } else {
8693 _collector->push_on_overflow_list(obj);
8694 _collector->_ser_kac_ovflw++;
8695 }
8696 }
8697 }
8698 }
8699
8700 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8701 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8702
8703 // CMSParKeepAliveClosure: a parallel version of the above.
8704 // The work queues are private to each closure (thread),
8705 // but (may be) available for stealing by other threads.
8706 void CMSParKeepAliveClosure::do_oop(oop obj) {
8707 HeapWord* addr = (HeapWord*)obj;
8708 if (_span.contains(addr) &&
8709 !_bit_map->isMarked(addr)) {
8710 // In general, during recursive tracing, several threads
8711 // may be concurrently getting here; the first one to
8712 // "tag" it, claims it.
8713 if (_bit_map->par_mark(addr)) {
8714 bool res = _work_queue->push(obj);
8715 assert(res, "Low water mark should be much less than capacity");
8716 // Do a recursive trim in the hope that this will keep
8717 // stack usage lower, but leave some oops for potential stealers
8718 trim_queue(_low_water_mark);
8719 } // Else, another thread got there first
8720 }
8721 }
8722
8723 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8724 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8725
8726 void CMSParKeepAliveClosure::trim_queue(uint max) {
8727 while (_work_queue->size() > max) {
8728 oop new_oop;
8729 if (_work_queue->pop_local(new_oop)) {
8730 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8731 assert(_bit_map->isMarked((HeapWord*)new_oop),
8732 "no white objects on this stack!");
8733 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8734 // iterate over the oops in this oop, marking and pushing
8735 // the ones in CMS heap (i.e. in _span).
8736 new_oop->oop_iterate(&_mark_and_push);
8737 }
8738 }
8739 }
8740
8741 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8742 CMSCollector* collector,
8743 MemRegion span, CMSBitMap* bit_map,
8744 CMSMarkStack* revisit_stack,
8745 OopTaskQueue* work_queue):
8746 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8747 _span(span),
8748 _bit_map(bit_map),
8749 _work_queue(work_queue) { }
8750
8751 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8752 HeapWord* addr = (HeapWord*)obj;
8753 if (_span.contains(addr) &&
8754 !_bit_map->isMarked(addr)) {
8755 if (_bit_map->par_mark(addr)) {
8756 bool simulate_overflow = false;
8757 NOT_PRODUCT(
8758 if (CMSMarkStackOverflowALot &&
8759 _collector->par_simulate_overflow()) {
8760 // simulate a stack overflow
8761 simulate_overflow = true;
8762 }
8763 )
8764 if (simulate_overflow || !_work_queue->push(obj)) {
8765 _collector->par_push_on_overflow_list(obj);
8766 _collector->_par_kac_ovflw++;
8767 }
8768 } // Else another thread got there already
8769 }
8770 }
8771
8772 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8773 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8774
8775 //////////////////////////////////////////////////////////////////
8776 // CMSExpansionCause /////////////////////////////
8777 //////////////////////////////////////////////////////////////////
8778 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8779 switch (cause) {
8780 case _no_expansion:
8781 return "No expansion";
8782 case _satisfy_free_ratio:
8783 return "Free ratio";
8784 case _satisfy_promotion:
8785 return "Satisfy promotion";
8786 case _satisfy_allocation:
8787 return "allocation";
8788 case _allocate_par_lab:
8789 return "Par LAB";
8790 case _allocate_par_spooling_space:
8791 return "Par Spooling Space";
8792 case _adaptive_size_policy:
8793 return "Ergonomics";
8794 default:
8795 return "unknown";
8796 }
8797 }
8798
8799 void CMSDrainMarkingStackClosure::do_void() {
8800 // the max number to take from overflow list at a time
8801 const size_t num = _mark_stack->capacity()/4;
8802 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8803 "Overflow list should be NULL during concurrent phases");
8804 while (!_mark_stack->isEmpty() ||
8805 // if stack is empty, check the overflow list
8806 _collector->take_from_overflow_list(num, _mark_stack)) {
8807 oop obj = _mark_stack->pop();
8808 HeapWord* addr = (HeapWord*)obj;
8809 assert(_span.contains(addr), "Should be within span");
8810 assert(_bit_map->isMarked(addr), "Should be marked");
8811 assert(obj->is_oop(), "Should be an oop");
8812 obj->oop_iterate(_keep_alive);
8813 }
8814 }
8815
8816 void CMSParDrainMarkingStackClosure::do_void() {
8817 // drain queue
8818 trim_queue(0);
8819 }
8820
8821 // Trim our work_queue so its length is below max at return
8822 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8823 while (_work_queue->size() > max) {
8824 oop new_oop;
8825 if (_work_queue->pop_local(new_oop)) {
8826 assert(new_oop->is_oop(), "Expected an oop");
8827 assert(_bit_map->isMarked((HeapWord*)new_oop),
8828 "no white objects on this stack!");
8829 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8830 // iterate over the oops in this oop, marking and pushing
8831 // the ones in CMS heap (i.e. in _span).
8832 new_oop->oop_iterate(&_mark_and_push);
8833 }
8834 }
8835 }
8836
8837 ////////////////////////////////////////////////////////////////////
8838 // Support for Marking Stack Overflow list handling and related code
8839 ////////////////////////////////////////////////////////////////////
8840 // Much of the following code is similar in shape and spirit to the
8841 // code used in ParNewGC. We should try and share that code
8842 // as much as possible in the future.
8843
8844 #ifndef PRODUCT
8845 // Debugging support for CMSStackOverflowALot
8846
8847 // It's OK to call this multi-threaded; the worst thing
8848 // that can happen is that we'll get a bunch of closely
8849 // spaced simulated oveflows, but that's OK, in fact
8850 // probably good as it would exercise the overflow code
8851 // under contention.
8852 bool CMSCollector::simulate_overflow() {
8853 if (_overflow_counter-- <= 0) { // just being defensive
8854 _overflow_counter = CMSMarkStackOverflowInterval;
8855 return true;
8856 } else {
8857 return false;
8858 }
8859 }
8860
8861 bool CMSCollector::par_simulate_overflow() {
8862 return simulate_overflow();
8863 }
8864 #endif
8865
8866 // Single-threaded
8867 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8868 assert(stack->isEmpty(), "Expected precondition");
8869 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8870 size_t i = num;
8871 oop cur = _overflow_list;
8872 const markOop proto = markOopDesc::prototype();
8873 NOT_PRODUCT(ssize_t n = 0;)
8874 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8875 next = oop(cur->mark());
8876 cur->set_mark(proto); // until proven otherwise
8877 assert(cur->is_oop(), "Should be an oop");
8878 bool res = stack->push(cur);
8879 assert(res, "Bit off more than can chew?");
8880 NOT_PRODUCT(n++;)
8881 }
8882 _overflow_list = cur;
8883 #ifndef PRODUCT
8884 assert(_num_par_pushes >= n, "Too many pops?");
8885 _num_par_pushes -=n;
8886 #endif
8887 return !stack->isEmpty();
8888 }
8889
8890 #define BUSY (oop(0x1aff1aff))
8891 // (MT-safe) Get a prefix of at most "num" from the list.
8892 // The overflow list is chained through the mark word of
8893 // each object in the list. We fetch the entire list,
8894 // break off a prefix of the right size and return the
8895 // remainder. If other threads try to take objects from
8896 // the overflow list at that time, they will wait for
8897 // some time to see if data becomes available. If (and
8898 // only if) another thread places one or more object(s)
8899 // on the global list before we have returned the suffix
8900 // to the global list, we will walk down our local list
8901 // to find its end and append the global list to
8902 // our suffix before returning it. This suffix walk can
8903 // prove to be expensive (quadratic in the amount of traffic)
8904 // when there are many objects in the overflow list and
8905 // there is much producer-consumer contention on the list.
8906 // *NOTE*: The overflow list manipulation code here and
8907 // in ParNewGeneration:: are very similar in shape,
8908 // except that in the ParNew case we use the old (from/eden)
8909 // copy of the object to thread the list via its klass word.
8910 // Because of the common code, if you make any changes in
8911 // the code below, please check the ParNew version to see if
8912 // similar changes might be needed.
8913 // CR 6797058 has been filed to consolidate the common code.
8914 bool CMSCollector::par_take_from_overflow_list(size_t num,
8915 OopTaskQueue* work_q,
8916 int no_of_gc_threads) {
8917 assert(work_q->size() == 0, "First empty local work queue");
8918 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8919 if (_overflow_list == NULL) {
8920 return false;
8921 }
8922 // Grab the entire list; we'll put back a suffix
8923 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8924 Thread* tid = Thread::current();
8925 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8926 // set to ParallelGCThreads.
8927 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8928 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8929 // If the list is busy, we spin for a short while,
8930 // sleeping between attempts to get the list.
8931 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8932 os::sleep(tid, sleep_time_millis, false);
8933 if (_overflow_list == NULL) {
8934 // Nothing left to take
8935 return false;
8936 } else if (_overflow_list != BUSY) {
8937 // Try and grab the prefix
8938 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8939 }
8940 }
8941 // If the list was found to be empty, or we spun long
8942 // enough, we give up and return empty-handed. If we leave
8943 // the list in the BUSY state below, it must be the case that
8944 // some other thread holds the overflow list and will set it
8945 // to a non-BUSY state in the future.
8946 if (prefix == NULL || prefix == BUSY) {
8947 // Nothing to take or waited long enough
8948 if (prefix == NULL) {
8949 // Write back the NULL in case we overwrote it with BUSY above
8950 // and it is still the same value.
8951 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8952 }
8953 return false;
8954 }
8955 assert(prefix != NULL && prefix != BUSY, "Error");
8956 size_t i = num;
8957 oop cur = prefix;
8958 // Walk down the first "num" objects, unless we reach the end.
8959 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8960 if (cur->mark() == NULL) {
8961 // We have "num" or fewer elements in the list, so there
8962 // is nothing to return to the global list.
8963 // Write back the NULL in lieu of the BUSY we wrote
8964 // above, if it is still the same value.
8965 if (_overflow_list == BUSY) {
8966 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8967 }
8968 } else {
8969 // Chop off the suffix and rerturn it to the global list.
8970 assert(cur->mark() != BUSY, "Error");
8971 oop suffix_head = cur->mark(); // suffix will be put back on global list
8972 cur->set_mark(NULL); // break off suffix
8973 // It's possible that the list is still in the empty(busy) state
8974 // we left it in a short while ago; in that case we may be
8975 // able to place back the suffix without incurring the cost
8976 // of a walk down the list.
8977 oop observed_overflow_list = _overflow_list;
8978 oop cur_overflow_list = observed_overflow_list;
8979 bool attached = false;
8980 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8981 observed_overflow_list =
8982 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8983 if (cur_overflow_list == observed_overflow_list) {
8984 attached = true;
8985 break;
8986 } else cur_overflow_list = observed_overflow_list;
8987 }
8988 if (!attached) {
8989 // Too bad, someone else sneaked in (at least) an element; we'll need
8990 // to do a splice. Find tail of suffix so we can prepend suffix to global
8991 // list.
8992 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8993 oop suffix_tail = cur;
8994 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8995 "Tautology");
8996 observed_overflow_list = _overflow_list;
8997 do {
8998 cur_overflow_list = observed_overflow_list;
8999 if (cur_overflow_list != BUSY) {
9000 // Do the splice ...
9001 suffix_tail->set_mark(markOop(cur_overflow_list));
9002 } else { // cur_overflow_list == BUSY
9003 suffix_tail->set_mark(NULL);
9004 }
9005 // ... and try to place spliced list back on overflow_list ...
9006 observed_overflow_list =
9007 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9008 } while (cur_overflow_list != observed_overflow_list);
9009 // ... until we have succeeded in doing so.
9010 }
9011 }
9012
9013 // Push the prefix elements on work_q
9014 assert(prefix != NULL, "control point invariant");
9015 const markOop proto = markOopDesc::prototype();
9016 oop next;
9017 NOT_PRODUCT(ssize_t n = 0;)
9018 for (cur = prefix; cur != NULL; cur = next) {
9019 next = oop(cur->mark());
9020 cur->set_mark(proto); // until proven otherwise
9021 assert(cur->is_oop(), "Should be an oop");
9022 bool res = work_q->push(cur);
9023 assert(res, "Bit off more than we can chew?");
9024 NOT_PRODUCT(n++;)
9025 }
9026 #ifndef PRODUCT
9027 assert(_num_par_pushes >= n, "Too many pops?");
9028 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9029 #endif
9030 return true;
9031 }
9032
9033 // Single-threaded
9034 void CMSCollector::push_on_overflow_list(oop p) {
9035 NOT_PRODUCT(_num_par_pushes++;)
9036 assert(p->is_oop(), "Not an oop");
9037 preserve_mark_if_necessary(p);
9038 p->set_mark((markOop)_overflow_list);
9039 _overflow_list = p;
9040 }
9041
9042 // Multi-threaded; use CAS to prepend to overflow list
9043 void CMSCollector::par_push_on_overflow_list(oop p) {
9044 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9045 assert(p->is_oop(), "Not an oop");
9046 par_preserve_mark_if_necessary(p);
9047 oop observed_overflow_list = _overflow_list;
9048 oop cur_overflow_list;
9049 do {
9050 cur_overflow_list = observed_overflow_list;
9051 if (cur_overflow_list != BUSY) {
9052 p->set_mark(markOop(cur_overflow_list));
9053 } else {
9054 p->set_mark(NULL);
9055 }
9056 observed_overflow_list =
9057 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9058 } while (cur_overflow_list != observed_overflow_list);
9059 }
9060 #undef BUSY
9061
9062 // Single threaded
9063 // General Note on GrowableArray: pushes may silently fail
9064 // because we are (temporarily) out of C-heap for expanding
9065 // the stack. The problem is quite ubiquitous and affects
9066 // a lot of code in the JVM. The prudent thing for GrowableArray
9067 // to do (for now) is to exit with an error. However, that may
9068 // be too draconian in some cases because the caller may be
9069 // able to recover without much harm. For such cases, we
9070 // should probably introduce a "soft_push" method which returns
9071 // an indication of success or failure with the assumption that
9072 // the caller may be able to recover from a failure; code in
9073 // the VM can then be changed, incrementally, to deal with such
9074 // failures where possible, thus, incrementally hardening the VM
9075 // in such low resource situations.
9076 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9077 _preserved_oop_stack.push(p);
9078 _preserved_mark_stack.push(m);
9079 assert(m == p->mark(), "Mark word changed");
9080 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9081 "bijection");
9082 }
9083
9084 // Single threaded
9085 void CMSCollector::preserve_mark_if_necessary(oop p) {
9086 markOop m = p->mark();
9087 if (m->must_be_preserved(p)) {
9088 preserve_mark_work(p, m);
9089 }
9090 }
9091
9092 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9093 markOop m = p->mark();
9094 if (m->must_be_preserved(p)) {
9095 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9096 // Even though we read the mark word without holding
9097 // the lock, we are assured that it will not change
9098 // because we "own" this oop, so no other thread can
9099 // be trying to push it on the overflow list; see
9100 // the assertion in preserve_mark_work() that checks
9101 // that m == p->mark().
9102 preserve_mark_work(p, m);
9103 }
9104 }
9105
9106 // We should be able to do this multi-threaded,
9107 // a chunk of stack being a task (this is
9108 // correct because each oop only ever appears
9109 // once in the overflow list. However, it's
9110 // not very easy to completely overlap this with
9111 // other operations, so will generally not be done
9112 // until all work's been completed. Because we
9113 // expect the preserved oop stack (set) to be small,
9114 // it's probably fine to do this single-threaded.
9115 // We can explore cleverer concurrent/overlapped/parallel
9116 // processing of preserved marks if we feel the
9117 // need for this in the future. Stack overflow should
9118 // be so rare in practice and, when it happens, its
9119 // effect on performance so great that this will
9120 // likely just be in the noise anyway.
9121 void CMSCollector::restore_preserved_marks_if_any() {
9122 assert(SafepointSynchronize::is_at_safepoint(),
9123 "world should be stopped");
9124 assert(Thread::current()->is_ConcurrentGC_thread() ||
9125 Thread::current()->is_VM_thread(),
9126 "should be single-threaded");
9127 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9128 "bijection");
9129
9130 while (!_preserved_oop_stack.is_empty()) {
9131 oop p = _preserved_oop_stack.pop();
9132 assert(p->is_oop(), "Should be an oop");
9133 assert(_span.contains(p), "oop should be in _span");
9134 assert(p->mark() == markOopDesc::prototype(),
9135 "Set when taken from overflow list");
9136 markOop m = _preserved_mark_stack.pop();
9137 p->set_mark(m);
9138 }
9139 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9140 "stacks were cleared above");
9141 }
9142
9143 #ifndef PRODUCT
9144 bool CMSCollector::no_preserved_marks() const {
9145 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9146 }
9147 #endif
9148
9149 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9150 {
9151 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9152 CMSAdaptiveSizePolicy* size_policy =
9153 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9154 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9155 "Wrong type for size policy");
9156 return size_policy;
9157 }
9158
9159 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9160 size_t desired_promo_size) {
9161 if (cur_promo_size < desired_promo_size) {
9162 size_t expand_bytes = desired_promo_size - cur_promo_size;
9163 if (PrintAdaptiveSizePolicy && Verbose) {
9164 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9165 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9166 expand_bytes);
9167 }
9168 expand(expand_bytes,
9169 MinHeapDeltaBytes,
9170 CMSExpansionCause::_adaptive_size_policy);
9171 } else if (desired_promo_size < cur_promo_size) {
9172 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9173 if (PrintAdaptiveSizePolicy && Verbose) {
9174 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9175 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9176 shrink_bytes);
9177 }
9178 shrink(shrink_bytes);
9179 }
9180 }
9181
9182 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9183 GenCollectedHeap* gch = GenCollectedHeap::heap();
9184 CMSGCAdaptivePolicyCounters* counters =
9185 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9186 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9187 "Wrong kind of counters");
9188 return counters;
9189 }
9190
9191
9192 void ASConcurrentMarkSweepGeneration::update_counters() {
9193 if (UsePerfData) {
9194 _space_counters->update_all();
9195 _gen_counters->update_all();
9196 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9197 GenCollectedHeap* gch = GenCollectedHeap::heap();
9198 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9199 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9200 "Wrong gc statistics type");
9201 counters->update_counters(gc_stats_l);
9202 }
9203 }
9204
9205 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9206 if (UsePerfData) {
9207 _space_counters->update_used(used);
9208 _space_counters->update_capacity();
9209 _gen_counters->update_all();
9210
9211 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9212 GenCollectedHeap* gch = GenCollectedHeap::heap();
9213 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9214 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9215 "Wrong gc statistics type");
9216 counters->update_counters(gc_stats_l);
9217 }
9218 }
9219
9220 // The desired expansion delta is computed so that:
9221 // . desired free percentage or greater is used
9222 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9223 assert_locked_or_safepoint(Heap_lock);
9224
9225 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9226
9227 // If incremental collection failed, we just want to expand
9228 // to the limit.
9229 if (incremental_collection_failed()) {
9230 clear_incremental_collection_failed();
9231 grow_to_reserved();
9232 return;
9233 }
9234
9235 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9236
9237 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9238 "Wrong type of heap");
9239 int prev_level = level() - 1;
9240 assert(prev_level >= 0, "The cms generation is the lowest generation");
9241 Generation* prev_gen = gch->get_gen(prev_level);
9242 assert(prev_gen->kind() == Generation::ASParNew,
9243 "Wrong type of young generation");
9244 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9245 size_t cur_eden = younger_gen->eden()->capacity();
9246 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9247 size_t cur_promo = free();
9248 size_policy->compute_tenured_generation_free_space(cur_promo,
9249 max_available(),
9250 cur_eden);
9251 resize(cur_promo, size_policy->promo_size());
9252
9253 // Record the new size of the space in the cms generation
9254 // that is available for promotions. This is temporary.
9255 // It should be the desired promo size.
9256 size_policy->avg_cms_promo()->sample(free());
9257 size_policy->avg_old_live()->sample(used());
9258
9259 if (UsePerfData) {
9260 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9261 counters->update_cms_capacity_counter(capacity());
9262 }
9263 }
9264
9265 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9266 assert_locked_or_safepoint(Heap_lock);
9267 assert_lock_strong(freelistLock());
9268 HeapWord* old_end = _cmsSpace->end();
9269 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9270 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9271 FreeChunk* chunk_at_end = find_chunk_at_end();
9272 if (chunk_at_end == NULL) {
9273 // No room to shrink
9274 if (PrintGCDetails && Verbose) {
9275 gclog_or_tty->print_cr("No room to shrink: old_end "
9276 PTR_FORMAT " unallocated_start " PTR_FORMAT
9277 " chunk_at_end " PTR_FORMAT,
9278 old_end, unallocated_start, chunk_at_end);
9279 }
9280 return;
9281 } else {
9282
9283 // Find the chunk at the end of the space and determine
9284 // how much it can be shrunk.
9285 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9286 size_t aligned_shrinkable_size_in_bytes =
9287 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9288 assert(unallocated_start <= chunk_at_end->end(),
9289 "Inconsistent chunk at end of space");
9290 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9291 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9292
9293 // Shrink the underlying space
9294 _virtual_space.shrink_by(bytes);
9295 if (PrintGCDetails && Verbose) {
9296 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9297 " desired_bytes " SIZE_FORMAT
9298 " shrinkable_size_in_bytes " SIZE_FORMAT
9299 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9300 " bytes " SIZE_FORMAT,
9301 desired_bytes, shrinkable_size_in_bytes,
9302 aligned_shrinkable_size_in_bytes, bytes);
9303 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9304 " unallocated_start " SIZE_FORMAT,
9305 old_end, unallocated_start);
9306 }
9307
9308 // If the space did shrink (shrinking is not guaranteed),
9309 // shrink the chunk at the end by the appropriate amount.
9310 if (((HeapWord*)_virtual_space.high()) < old_end) {
9311 size_t new_word_size =
9312 heap_word_size(_virtual_space.committed_size());
9313
9314 // Have to remove the chunk from the dictionary because it is changing
9315 // size and might be someplace elsewhere in the dictionary.
9316
9317 // Get the chunk at end, shrink it, and put it
9318 // back.
9319 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9320 size_t word_size_change = word_size_before - new_word_size;
9321 size_t chunk_at_end_old_size = chunk_at_end->size();
9322 assert(chunk_at_end_old_size >= word_size_change,
9323 "Shrink is too large");
9324 chunk_at_end->set_size(chunk_at_end_old_size -
9325 word_size_change);
9326 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9327 word_size_change);
9328
9329 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9330
9331 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9332 _bts->resize(new_word_size); // resize the block offset shared array
9333 Universe::heap()->barrier_set()->resize_covered_region(mr);
9334 _cmsSpace->assert_locked();
9335 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9336
9337 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9338
9339 // update the space and generation capacity counters
9340 if (UsePerfData) {
9341 _space_counters->update_capacity();
9342 _gen_counters->update_all();
9343 }
9344
9345 if (Verbose && PrintGCDetails) {
9346 size_t new_mem_size = _virtual_space.committed_size();
9347 size_t old_mem_size = new_mem_size + bytes;
9348 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9349 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9350 }
9351 }
9352
9353 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9354 "Inconsistency at end of space");
9355 assert(chunk_at_end->end() == _cmsSpace->end(),
9356 "Shrinking is inconsistent");
9357 return;
9358 }
9359 }
9360
9361 // Transfer some number of overflown objects to usual marking
9362 // stack. Return true if some objects were transferred.
9363 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9364 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9365 (size_t)ParGCDesiredObjsFromOverflowList);
9366
9367 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9368 assert(_collector->overflow_list_is_empty() || res,
9369 "If list is not empty, we should have taken something");
9370 assert(!res || !_mark_stack->isEmpty(),
9371 "If we took something, it should now be on our stack");
9372 return res;
9373 }
9374
9375 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9376 size_t res = _sp->block_size_no_stall(addr, _collector);
9377 if (_sp->block_is_obj(addr)) {
9378 if (_live_bit_map->isMarked(addr)) {
9379 // It can't have been dead in a previous cycle
9380 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9381 } else {
9382 _dead_bit_map->mark(addr); // mark the dead object
9383 }
9384 }
9385 // Could be 0, if the block size could not be computed without stalling.
9386 return res;
9387 }
9388
9389 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9390
9391 switch (phase) {
9392 case CMSCollector::InitialMarking:
9393 initialize(true /* fullGC */ ,
9394 cause /* cause of the GC */,
9395 true /* recordGCBeginTime */,
9396 true /* recordPreGCUsage */,
9397 false /* recordPeakUsage */,
9398 false /* recordPostGCusage */,
9399 true /* recordAccumulatedGCTime */,
9400 false /* recordGCEndTime */,
9401 false /* countCollection */ );
9402 break;
9403
9404 case CMSCollector::FinalMarking:
9405 initialize(true /* fullGC */ ,
9406 cause /* cause of the GC */,
9407 false /* recordGCBeginTime */,
9408 false /* recordPreGCUsage */,
9409 false /* recordPeakUsage */,
9410 false /* recordPostGCusage */,
9411 true /* recordAccumulatedGCTime */,
9412 false /* recordGCEndTime */,
9413 false /* countCollection */ );
9414 break;
9415
9416 case CMSCollector::Sweeping:
9417 initialize(true /* fullGC */ ,
9418 cause /* cause of the GC */,
9419 false /* recordGCBeginTime */,
9420 false /* recordPreGCUsage */,
9421 true /* recordPeakUsage */,
9422 true /* recordPostGCusage */,
9423 false /* recordAccumulatedGCTime */,
9424 true /* recordGCEndTime */,
9425 true /* countCollection */ );
9426 break;
9427
9428 default:
9429 ShouldNotReachHere();
9430 }
9431 }
9432