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 if (first_state > Idling) {
1892 save_heap_summary();
1893 }
1894
1895 do_compaction_work(clear_all_soft_refs);
1896
1897 // Has the GC time limit been exceeded?
1898 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1899 size_t max_eden_size = young_gen->max_capacity() -
1900 young_gen->to()->capacity() -
1901 young_gen->from()->capacity();
1902 GenCollectedHeap* gch = GenCollectedHeap::heap();
1903 GCCause::Cause gc_cause = gch->gc_cause();
1904 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1905 young_gen->eden()->used(),
1906 _cmsGen->max_capacity(),
1907 max_eden_size,
1908 full,
1909 gc_cause,
1910 gch->collector_policy());
1911 } else {
1912 do_mark_sweep_work(clear_all_soft_refs, first_state,
1913 should_start_over);
1914 }
1915 // Reset the expansion cause, now that we just completed
1916 // a collection cycle.
1917 clear_expansion_cause();
1918 _foregroundGCIsActive = false;
1919 return;
1920 }
1921
1922 // Resize the perm generation and the tenured generation
1923 // after obtaining the free list locks for the
1924 // two generations.
1925 void CMSCollector::compute_new_size() {
1926 assert_locked_or_safepoint(Heap_lock);
1927 FreelistLocker z(this);
1928 _permGen->compute_new_size();
1929 _cmsGen->compute_new_size();
1930 }
1931
1932 // A work method used by foreground collection to determine
1933 // what type of collection (compacting or not, continuing or fresh)
1934 // it should do.
1935 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1936 // and CMSCompactWhenClearAllSoftRefs the default in the future
1937 // and do away with the flags after a suitable period.
1938 void CMSCollector::decide_foreground_collection_type(
1939 bool clear_all_soft_refs, bool* should_compact,
1940 bool* should_start_over) {
1941 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1942 // flag is set, and we have either requested a System.gc() or
1943 // the number of full gc's since the last concurrent cycle
1944 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1945 // or if an incremental collection has failed
1946 GenCollectedHeap* gch = GenCollectedHeap::heap();
1947 assert(gch->collector_policy()->is_two_generation_policy(),
1948 "You may want to check the correctness of the following");
1949 // Inform cms gen if this was due to partial collection failing.
1950 // The CMS gen may use this fact to determine its expansion policy.
1951 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1952 assert(!_cmsGen->incremental_collection_failed(),
1953 "Should have been noticed, reacted to and cleared");
1954 _cmsGen->set_incremental_collection_failed();
1955 }
1956 *should_compact =
1957 UseCMSCompactAtFullCollection &&
1958 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1959 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1960 gch->incremental_collection_will_fail(true /* consult_young */));
1961 *should_start_over = false;
1962 if (clear_all_soft_refs && !*should_compact) {
1963 // We are about to do a last ditch collection attempt
1964 // so it would normally make sense to do a compaction
1965 // to reclaim as much space as possible.
1966 if (CMSCompactWhenClearAllSoftRefs) {
1967 // Default: The rationale is that in this case either
1968 // we are past the final marking phase, in which case
1969 // we'd have to start over, or so little has been done
1970 // that there's little point in saving that work. Compaction
1971 // appears to be the sensible choice in either case.
1972 *should_compact = true;
1973 } else {
1974 // We have been asked to clear all soft refs, but not to
1975 // compact. Make sure that we aren't past the final checkpoint
1976 // phase, for that is where we process soft refs. If we are already
1977 // past that phase, we'll need to redo the refs discovery phase and
1978 // if necessary clear soft refs that weren't previously
1979 // cleared. We do so by remembering the phase in which
1980 // we came in, and if we are past the refs processing
1981 // phase, we'll choose to just redo the mark-sweep
1982 // collection from scratch.
1983 if (_collectorState > FinalMarking) {
1984 // We are past the refs processing phase;
1985 // start over and do a fresh synchronous CMS cycle
1986 _collectorState = Resetting; // skip to reset to start new cycle
1987 reset(false /* == !asynch */);
1988 *should_start_over = true;
1989 } // else we can continue a possibly ongoing current cycle
1990 }
1991 }
1992 }
1993
1994 // A work method used by the foreground collector to do
1995 // a mark-sweep-compact.
1996 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1997 GenCollectedHeap* gch = GenCollectedHeap::heap();
1998
1999 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
2000 gc_timer->register_gc_start(os::elapsed_counter());
2001
2002 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
2003 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
2004
2005 GCTraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, NULL);
2006 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
2007 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
2008 "collections passed to foreground collector", _full_gcs_since_conc_gc);
2009 }
2010
2011 // Sample collection interval time and reset for collection pause.
2012 if (UseAdaptiveSizePolicy) {
2013 size_policy()->msc_collection_begin();
2014 }
2015
2016 // Temporarily widen the span of the weak reference processing to
2017 // the entire heap.
2018 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
2019 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
2020 // Temporarily, clear the "is_alive_non_header" field of the
2021 // reference processor.
2022 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
2023 // Temporarily make reference _processing_ single threaded (non-MT).
2024 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
2025 // Temporarily make refs discovery atomic
2026 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
2027 // Temporarily make reference _discovery_ single threaded (non-MT)
2028 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
2029
2030 ref_processor()->set_enqueuing_is_done(false);
2031 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
2032 ref_processor()->setup_policy(clear_all_soft_refs);
2033 // If an asynchronous collection finishes, the _modUnionTable is
2034 // all clear. If we are assuming the collection from an asynchronous
2035 // collection, clear the _modUnionTable.
2036 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
2037 "_modUnionTable should be clear if the baton was not passed");
2038 _modUnionTable.clear_all();
2039
2040 // We must adjust the allocation statistics being maintained
2041 // in the free list space. We do so by reading and clearing
2042 // the sweep timer and updating the block flux rate estimates below.
2043 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
2044 if (_inter_sweep_timer.is_active()) {
2045 _inter_sweep_timer.stop();
2046 // Note that we do not use this sample to update the _inter_sweep_estimate.
2047 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
2048 _inter_sweep_estimate.padded_average(),
2049 _intra_sweep_estimate.padded_average());
2050 }
2051
2052 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2053 ref_processor(), clear_all_soft_refs);
2054 #ifdef ASSERT
2055 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2056 size_t free_size = cms_space->free();
2057 assert(free_size ==
2058 pointer_delta(cms_space->end(), cms_space->compaction_top())
2059 * HeapWordSize,
2060 "All the free space should be compacted into one chunk at top");
2061 assert(cms_space->dictionary()->total_chunk_size(
2062 debug_only(cms_space->freelistLock())) == 0 ||
2063 cms_space->totalSizeInIndexedFreeLists() == 0,
2064 "All the free space should be in a single chunk");
2065 size_t num = cms_space->totalCount();
2066 assert((free_size == 0 && num == 0) ||
2067 (free_size > 0 && (num == 1 || num == 2)),
2068 "There should be at most 2 free chunks after compaction");
2069 #endif // ASSERT
2070 _collectorState = Resetting;
2071 assert(_restart_addr == NULL,
2072 "Should have been NULL'd before baton was passed");
2073 reset(false /* == !asynch */);
2074 _cmsGen->reset_after_compaction();
2075 _concurrent_cycles_since_last_unload = 0;
2076
2077 if (verifying() && !should_unload_classes()) {
2078 perm_gen_verify_bit_map()->clear_all();
2079 }
2080
2081 // Clear any data recorded in the PLAB chunk arrays.
2082 if (_survivor_plab_array != NULL) {
2083 reset_survivor_plab_arrays();
2084 }
2085
2086 // Adjust the per-size allocation stats for the next epoch.
2087 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2088 // Restart the "inter sweep timer" for the next epoch.
2089 _inter_sweep_timer.reset();
2090 _inter_sweep_timer.start();
2091
2092 // Sample collection pause time and reset for collection interval.
2093 if (UseAdaptiveSizePolicy) {
2094 size_policy()->msc_collection_end(gch->gc_cause());
2095 }
2096
2097 gc_timer->register_gc_end(os::elapsed_counter());
2098
2099 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
2100
2101 // For a mark-sweep-compact, compute_new_size() will be called
2102 // in the heap's do_collection() method.
2103 }
2104
2105 // A work method used by the foreground collector to do
2106 // a mark-sweep, after taking over from a possibly on-going
2107 // concurrent mark-sweep collection.
2108 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2109 CollectorState first_state, bool should_start_over) {
2110 if (PrintGC && Verbose) {
2111 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2112 "collector with count %d",
2113 _full_gcs_since_conc_gc);
2114 }
2115 switch (_collectorState) {
2116 case Idling:
2117 if (first_state == Idling || should_start_over) {
2118 // The background GC was not active, or should
2119 // restarted from scratch; start the cycle.
2120 _collectorState = InitialMarking;
2121 }
2122 // If first_state was not Idling, then a background GC
2123 // was in progress and has now finished. No need to do it
2124 // again. Leave the state as Idling.
2125 break;
2126 case Precleaning:
2127 // In the foreground case don't do the precleaning since
2128 // it is not done concurrently and there is extra work
2129 // required.
2130 _collectorState = FinalMarking;
2131 }
2132 collect_in_foreground(clear_all_soft_refs, GenCollectedHeap::heap()->gc_cause());
2133
2134 // For a mark-sweep, compute_new_size() will be called
2135 // in the heap's do_collection() method.
2136 }
2137
2138
2139 void CMSCollector::getFreelistLocks() const {
2140 // Get locks for all free lists in all generations that this
2141 // collector is responsible for
2142 _cmsGen->freelistLock()->lock_without_safepoint_check();
2143 _permGen->freelistLock()->lock_without_safepoint_check();
2144 }
2145
2146 void CMSCollector::releaseFreelistLocks() const {
2147 // Release locks for all free lists in all generations that this
2148 // collector is responsible for
2149 _cmsGen->freelistLock()->unlock();
2150 _permGen->freelistLock()->unlock();
2151 }
2152
2153 bool CMSCollector::haveFreelistLocks() const {
2154 // Check locks for all free lists in all generations that this
2155 // collector is responsible for
2156 assert_lock_strong(_cmsGen->freelistLock());
2157 assert_lock_strong(_permGen->freelistLock());
2158 PRODUCT_ONLY(ShouldNotReachHere());
2159 return true;
2160 }
2161
2162 // A utility class that is used by the CMS collector to
2163 // temporarily "release" the foreground collector from its
2164 // usual obligation to wait for the background collector to
2165 // complete an ongoing phase before proceeding.
2166 class ReleaseForegroundGC: public StackObj {
2167 private:
2168 CMSCollector* _c;
2169 public:
2170 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2171 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2172 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2173 // allow a potentially blocked foreground collector to proceed
2174 _c->_foregroundGCShouldWait = false;
2175 if (_c->_foregroundGCIsActive) {
2176 CGC_lock->notify();
2177 }
2178 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2179 "Possible deadlock");
2180 }
2181
2182 ~ReleaseForegroundGC() {
2183 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2184 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2185 _c->_foregroundGCShouldWait = true;
2186 }
2187 };
2188
2189 // There are separate collect_in_background and collect_in_foreground because of
2190 // the different locking requirements of the background collector and the
2191 // foreground collector. There was originally an attempt to share
2192 // one "collect" method between the background collector and the foreground
2193 // collector but the if-then-else required made it cleaner to have
2194 // separate methods.
2195 void CMSCollector::collect_in_background(bool clear_all_soft_refs, GCCause::Cause cause) {
2196 assert(Thread::current()->is_ConcurrentGC_thread(),
2197 "A CMS asynchronous collection is only allowed on a CMS thread.");
2198
2199 GenCollectedHeap* gch = GenCollectedHeap::heap();
2200 {
2201 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2202 MutexLockerEx hl(Heap_lock, safepoint_check);
2203 FreelistLocker fll(this);
2204 MutexLockerEx x(CGC_lock, safepoint_check);
2205 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2206 // The foreground collector is active or we're
2207 // not using asynchronous collections. Skip this
2208 // background collection.
2209 assert(!_foregroundGCShouldWait, "Should be clear");
2210 return;
2211 } else {
2212 assert(_collectorState == Idling, "Should be idling before start.");
2213 _collectorState = InitialMarking;
2214 register_gc_start(cause);
2215 // Reset the expansion cause, now that we are about to begin
2216 // a new cycle.
2217 clear_expansion_cause();
2218 }
2219 // Decide if we want to enable class unloading as part of the
2220 // ensuing concurrent GC cycle.
2221 update_should_unload_classes();
2222 _full_gc_requested = false; // acks all outstanding full gc requests
2223 _full_gc_cause = GCCause::_no_gc;
2224 // Signal that we are about to start a collection
2225 gch->increment_total_full_collections(); // ... starting a collection cycle
2226 _collection_count_start = gch->total_full_collections();
2227 }
2228
2229 // Used for PrintGC
2230 size_t prev_used;
2231 if (PrintGC && Verbose) {
2232 prev_used = _cmsGen->used(); // XXXPERM
2233 }
2234
2235 // The change of the collection state is normally done at this level;
2236 // the exceptions are phases that are executed while the world is
2237 // stopped. For those phases the change of state is done while the
2238 // world is stopped. For baton passing purposes this allows the
2239 // background collector to finish the phase and change state atomically.
2240 // The foreground collector cannot wait on a phase that is done
2241 // while the world is stopped because the foreground collector already
2242 // has the world stopped and would deadlock.
2243 while (_collectorState != Idling) {
2244 if (TraceCMSState) {
2245 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2246 Thread::current(), _collectorState);
2247 }
2248 // The foreground collector
2249 // holds the Heap_lock throughout its collection.
2250 // holds the CMS token (but not the lock)
2251 // except while it is waiting for the background collector to yield.
2252 //
2253 // The foreground collector should be blocked (not for long)
2254 // if the background collector is about to start a phase
2255 // executed with world stopped. If the background
2256 // collector has already started such a phase, the
2257 // foreground collector is blocked waiting for the
2258 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2259 // are executed in the VM thread.
2260 //
2261 // The locking order is
2262 // PendingListLock (PLL) -- if applicable (FinalMarking)
2263 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2264 // CMS token (claimed in
2265 // stop_world_and_do() -->
2266 // safepoint_synchronize() -->
2267 // CMSThread::synchronize())
2268
2269 {
2270 // Check if the FG collector wants us to yield.
2271 CMSTokenSync x(true); // is cms thread
2272 if (waitForForegroundGC()) {
2273 // We yielded to a foreground GC, nothing more to be
2274 // done this round.
2275 assert(_foregroundGCShouldWait == false, "We set it to false in "
2276 "waitForForegroundGC()");
2277 if (TraceCMSState) {
2278 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2279 " exiting collection CMS state %d",
2280 Thread::current(), _collectorState);
2281 }
2282 return;
2283 } else {
2284 // The background collector can run but check to see if the
2285 // foreground collector has done a collection while the
2286 // background collector was waiting to get the CGC_lock
2287 // above. If yes, break so that _foregroundGCShouldWait
2288 // is cleared before returning.
2289 if (_collectorState == Idling) {
2290 break;
2291 }
2292 }
2293 }
2294
2295 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2296 "should be waiting");
2297
2298 switch (_collectorState) {
2299 case InitialMarking:
2300 {
2301 ReleaseForegroundGC x(this);
2302 stats().record_cms_begin();
2303 VM_CMS_Initial_Mark initial_mark_op(this);
2304 VMThread::execute(&initial_mark_op);
2305 }
2306 // The collector state may be any legal state at this point
2307 // since the background collector may have yielded to the
2308 // foreground collector.
2309 break;
2310 case Marking:
2311 // initial marking in checkpointRootsInitialWork has been completed
2312 if (markFromRoots(true)) { // we were successful
2313 assert(_collectorState == Precleaning, "Collector state should "
2314 "have changed");
2315 } else {
2316 assert(_foregroundGCIsActive, "Internal state inconsistency");
2317 }
2318 break;
2319 case Precleaning:
2320 if (UseAdaptiveSizePolicy) {
2321 size_policy()->concurrent_precleaning_begin();
2322 }
2323 // marking from roots in markFromRoots has been completed
2324 preclean();
2325 if (UseAdaptiveSizePolicy) {
2326 size_policy()->concurrent_precleaning_end();
2327 }
2328 assert(_collectorState == AbortablePreclean ||
2329 _collectorState == FinalMarking,
2330 "Collector state should have changed");
2331 break;
2332 case AbortablePreclean:
2333 if (UseAdaptiveSizePolicy) {
2334 size_policy()->concurrent_phases_resume();
2335 }
2336 abortable_preclean();
2337 if (UseAdaptiveSizePolicy) {
2338 size_policy()->concurrent_precleaning_end();
2339 }
2340 assert(_collectorState == FinalMarking, "Collector state should "
2341 "have changed");
2342 break;
2343 case FinalMarking:
2344 {
2345 ReleaseForegroundGC x(this);
2346
2347 VM_CMS_Final_Remark final_remark_op(this);
2348 VMThread::execute(&final_remark_op);
2349 }
2350 assert(_foregroundGCShouldWait, "block post-condition");
2351 break;
2352 case Sweeping:
2353 if (UseAdaptiveSizePolicy) {
2354 size_policy()->concurrent_sweeping_begin();
2355 }
2356 // final marking in checkpointRootsFinal has been completed
2357 sweep(true);
2358 assert(_collectorState == Resizing, "Collector state change "
2359 "to Resizing must be done under the free_list_lock");
2360 _full_gcs_since_conc_gc = 0;
2361
2362 // Stop the timers for adaptive size policy for the concurrent phases
2363 if (UseAdaptiveSizePolicy) {
2364 size_policy()->concurrent_sweeping_end();
2365 size_policy()->concurrent_phases_end(gch->gc_cause(),
2366 gch->prev_gen(_cmsGen)->capacity(),
2367 _cmsGen->free());
2368 }
2369
2370 case Resizing: {
2371 // Sweeping has been completed...
2372 // At this point the background collection has completed.
2373 // Don't move the call to compute_new_size() down
2374 // into code that might be executed if the background
2375 // collection was preempted.
2376 {
2377 ReleaseForegroundGC x(this); // unblock FG collection
2378 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2379 CMSTokenSync z(true); // not strictly needed.
2380 if (_collectorState == Resizing) {
2381 compute_new_size();
2382 save_heap_summary();
2383 _collectorState = Resetting;
2384 } else {
2385 assert(_collectorState == Idling, "The state should only change"
2386 " because the foreground collector has finished the collection");
2387 }
2388 }
2389 break;
2390 }
2391 case Resetting:
2392 // CMS heap resizing has been completed
2393 reset(true);
2394 assert(_collectorState == Idling, "Collector state should "
2395 "have changed");
2396 stats().record_cms_end();
2397 // Don't move the concurrent_phases_end() and compute_new_size()
2398 // calls to here because a preempted background collection
2399 // has it's state set to "Resetting".
2400 break;
2401 case Idling:
2402 default:
2403 ShouldNotReachHere();
2404 break;
2405 }
2406 if (TraceCMSState) {
2407 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2408 Thread::current(), _collectorState);
2409 }
2410 assert(_foregroundGCShouldWait, "block post-condition");
2411 }
2412
2413 // Should this be in gc_epilogue?
2414 collector_policy()->counters()->update_counters();
2415
2416 {
2417 // Clear _foregroundGCShouldWait and, in the event that the
2418 // foreground collector is waiting, notify it, before
2419 // returning.
2420 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2421 _foregroundGCShouldWait = false;
2422 if (_foregroundGCIsActive) {
2423 CGC_lock->notify();
2424 }
2425 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2426 "Possible deadlock");
2427 }
2428 if (TraceCMSState) {
2429 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2430 " exiting collection CMS state %d",
2431 Thread::current(), _collectorState);
2432 }
2433 if (PrintGC && Verbose) {
2434 _cmsGen->print_heap_change(prev_used);
2435 }
2436 }
2437
2438 void CMSCollector::register_foreground_gc_start(GCCause::Cause cause) {
2439 if (!_cms_start_registered) {
2440 register_gc_start(cause);
2441 }
2442 }
2443
2444 void CMSCollector::register_gc_start(GCCause::Cause cause) {
2445 _cms_start_registered = true;
2446 _gc_timer_cm->register_gc_start(os::elapsed_counter());
2447 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
2448 }
2449
2450 void CMSCollector::register_gc_end() {
2451 if (_cms_start_registered) {
2452 report_heap_summary(GCWhen::AfterGC);
2453
2454 _gc_timer_cm->register_gc_end(os::elapsed_counter());
2455 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
2456 _cms_start_registered = false;
2457 }
2458 }
2459
2460 void CMSCollector::save_heap_summary() {
2461 GenCollectedHeap* gch = GenCollectedHeap::heap();
2462 _last_heap_summary = gch->create_heap_summary();
2463 _last_perm_gen_summary = gch->create_perm_gen_summary();
2464 }
2465
2466 void CMSCollector::report_heap_summary(GCWhen::Type when) {
2467 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary, _last_perm_gen_summary);
2468 }
2469
2470 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs, GCCause::Cause cause) {
2471 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2472 "Foreground collector should be waiting, not executing");
2473 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2474 "may only be done by the VM Thread with the world stopped");
2475 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2476 "VM thread should have CMS token");
2477
2478 NOT_PRODUCT(GCTraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2479 true, NULL);)
2480 if (UseAdaptiveSizePolicy) {
2481 size_policy()->ms_collection_begin();
2482 }
2483 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2484
2485 HandleMark hm; // Discard invalid handles created during verification
2486
2487 if (VerifyBeforeGC &&
2488 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2489 Universe::verify();
2490 }
2491
2492 // Snapshot the soft reference policy to be used in this collection cycle.
2493 ref_processor()->setup_policy(clear_all_soft_refs);
2494
2495 bool init_mark_was_synchronous = false; // until proven otherwise
2496 while (_collectorState != Idling) {
2497 if (TraceCMSState) {
2498 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2499 Thread::current(), _collectorState);
2500 }
2501 switch (_collectorState) {
2502 case InitialMarking:
2503 register_foreground_gc_start(cause);
2504 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2505 checkpointRootsInitial(false);
2506 assert(_collectorState == Marking, "Collector state should have changed"
2507 " within checkpointRootsInitial()");
2508 break;
2509 case Marking:
2510 // initial marking in checkpointRootsInitialWork has been completed
2511 if (VerifyDuringGC &&
2512 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2513 gclog_or_tty->print("Verify before initial mark: ");
2514 Universe::verify();
2515 }
2516 {
2517 bool res = markFromRoots(false);
2518 assert(res && _collectorState == FinalMarking, "Collector state should "
2519 "have changed");
2520 break;
2521 }
2522 case FinalMarking:
2523 if (VerifyDuringGC &&
2524 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2525 gclog_or_tty->print("Verify before re-mark: ");
2526 Universe::verify();
2527 }
2528 checkpointRootsFinal(false, clear_all_soft_refs,
2529 init_mark_was_synchronous);
2530 assert(_collectorState == Sweeping, "Collector state should not "
2531 "have changed within checkpointRootsFinal()");
2532 break;
2533 case Sweeping:
2534 // final marking in checkpointRootsFinal has been completed
2535 if (VerifyDuringGC &&
2536 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2537 gclog_or_tty->print("Verify before sweep: ");
2538 Universe::verify();
2539 }
2540 sweep(false);
2541 assert(_collectorState == Resizing, "Incorrect state");
2542 break;
2543 case Resizing: {
2544 // Sweeping has been completed; the actual resize in this case
2545 // is done separately; nothing to be done in this state.
2546 _collectorState = Resetting;
2547 break;
2548 }
2549 case Resetting:
2550 // The heap has been resized.
2551 if (VerifyDuringGC &&
2552 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2553 gclog_or_tty->print("Verify before reset: ");
2554 Universe::verify();
2555 }
2556 save_heap_summary();
2557 reset(false);
2558 assert(_collectorState == Idling, "Collector state should "
2559 "have changed");
2560 break;
2561 case Precleaning:
2562 case AbortablePreclean:
2563 // Elide the preclean phase
2564 _collectorState = FinalMarking;
2565 break;
2566 default:
2567 ShouldNotReachHere();
2568 }
2569 if (TraceCMSState) {
2570 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2571 Thread::current(), _collectorState);
2572 }
2573 }
2574
2575 if (UseAdaptiveSizePolicy) {
2576 GenCollectedHeap* gch = GenCollectedHeap::heap();
2577 size_policy()->ms_collection_end(gch->gc_cause());
2578 }
2579
2580 if (VerifyAfterGC &&
2581 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2582 Universe::verify();
2583 }
2584 if (TraceCMSState) {
2585 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2586 " exiting collection CMS state %d",
2587 Thread::current(), _collectorState);
2588 }
2589 }
2590
2591 bool CMSCollector::waitForForegroundGC() {
2592 bool res = false;
2593 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2594 "CMS thread should have CMS token");
2595 // Block the foreground collector until the
2596 // background collectors decides whether to
2597 // yield.
2598 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2599 _foregroundGCShouldWait = true;
2600 if (_foregroundGCIsActive) {
2601 // The background collector yields to the
2602 // foreground collector and returns a value
2603 // indicating that it has yielded. The foreground
2604 // collector can proceed.
2605 res = true;
2606 _foregroundGCShouldWait = false;
2607 ConcurrentMarkSweepThread::clear_CMS_flag(
2608 ConcurrentMarkSweepThread::CMS_cms_has_token);
2609 ConcurrentMarkSweepThread::set_CMS_flag(
2610 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2611 // Get a possibly blocked foreground thread going
2612 CGC_lock->notify();
2613 if (TraceCMSState) {
2614 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2615 Thread::current(), _collectorState);
2616 }
2617 while (_foregroundGCIsActive) {
2618 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2619 }
2620 ConcurrentMarkSweepThread::set_CMS_flag(
2621 ConcurrentMarkSweepThread::CMS_cms_has_token);
2622 ConcurrentMarkSweepThread::clear_CMS_flag(
2623 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2624 }
2625 if (TraceCMSState) {
2626 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2627 Thread::current(), _collectorState);
2628 }
2629 return res;
2630 }
2631
2632 // Because of the need to lock the free lists and other structures in
2633 // the collector, common to all the generations that the collector is
2634 // collecting, we need the gc_prologues of individual CMS generations
2635 // delegate to their collector. It may have been simpler had the
2636 // current infrastructure allowed one to call a prologue on a
2637 // collector. In the absence of that we have the generation's
2638 // prologue delegate to the collector, which delegates back
2639 // some "local" work to a worker method in the individual generations
2640 // that it's responsible for collecting, while itself doing any
2641 // work common to all generations it's responsible for. A similar
2642 // comment applies to the gc_epilogue()'s.
2643 // The role of the varaible _between_prologue_and_epilogue is to
2644 // enforce the invocation protocol.
2645 void CMSCollector::gc_prologue(bool full) {
2646 // Call gc_prologue_work() for each CMSGen and PermGen that
2647 // we are responsible for.
2648
2649 // The following locking discipline assumes that we are only called
2650 // when the world is stopped.
2651 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2652
2653 // The CMSCollector prologue must call the gc_prologues for the
2654 // "generations" (including PermGen if any) that it's responsible
2655 // for.
2656
2657 assert( Thread::current()->is_VM_thread()
2658 || ( CMSScavengeBeforeRemark
2659 && Thread::current()->is_ConcurrentGC_thread()),
2660 "Incorrect thread type for prologue execution");
2661
2662 if (_between_prologue_and_epilogue) {
2663 // We have already been invoked; this is a gc_prologue delegation
2664 // from yet another CMS generation that we are responsible for, just
2665 // ignore it since all relevant work has already been done.
2666 return;
2667 }
2668
2669 // set a bit saying prologue has been called; cleared in epilogue
2670 _between_prologue_and_epilogue = true;
2671 // Claim locks for common data structures, then call gc_prologue_work()
2672 // for each CMSGen and PermGen that we are responsible for.
2673
2674 getFreelistLocks(); // gets free list locks on constituent spaces
2675 bitMapLock()->lock_without_safepoint_check();
2676
2677 // Should call gc_prologue_work() for all cms gens we are responsible for
2678 bool registerClosure = _collectorState >= Marking
2679 && _collectorState < Sweeping;
2680 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2681 &_modUnionClosurePar
2682 : &_modUnionClosure;
2683 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2684 _permGen->gc_prologue_work(full, registerClosure, muc);
2685
2686 if (!full) {
2687 stats().record_gc0_begin();
2688 }
2689 }
2690
2691 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2692 // Delegate to CMScollector which knows how to coordinate between
2693 // this and any other CMS generations that it is responsible for
2694 // collecting.
2695 collector()->gc_prologue(full);
2696 }
2697
2698 // This is a "private" interface for use by this generation's CMSCollector.
2699 // Not to be called directly by any other entity (for instance,
2700 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2701 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2702 bool registerClosure, ModUnionClosure* modUnionClosure) {
2703 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2704 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2705 "Should be NULL");
2706 if (registerClosure) {
2707 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2708 }
2709 cmsSpace()->gc_prologue();
2710 // Clear stat counters
2711 NOT_PRODUCT(
2712 assert(_numObjectsPromoted == 0, "check");
2713 assert(_numWordsPromoted == 0, "check");
2714 if (Verbose && PrintGC) {
2715 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2716 SIZE_FORMAT" bytes concurrently",
2717 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2718 }
2719 _numObjectsAllocated = 0;
2720 _numWordsAllocated = 0;
2721 )
2722 }
2723
2724 void CMSCollector::gc_epilogue(bool full) {
2725 // The following locking discipline assumes that we are only called
2726 // when the world is stopped.
2727 assert(SafepointSynchronize::is_at_safepoint(),
2728 "world is stopped assumption");
2729
2730 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2731 // if linear allocation blocks need to be appropriately marked to allow the
2732 // the blocks to be parsable. We also check here whether we need to nudge the
2733 // CMS collector thread to start a new cycle (if it's not already active).
2734 assert( Thread::current()->is_VM_thread()
2735 || ( CMSScavengeBeforeRemark
2736 && Thread::current()->is_ConcurrentGC_thread()),
2737 "Incorrect thread type for epilogue execution");
2738
2739 if (!_between_prologue_and_epilogue) {
2740 // We have already been invoked; this is a gc_epilogue delegation
2741 // from yet another CMS generation that we are responsible for, just
2742 // ignore it since all relevant work has already been done.
2743 return;
2744 }
2745 assert(haveFreelistLocks(), "must have freelist locks");
2746 assert_lock_strong(bitMapLock());
2747
2748 _cmsGen->gc_epilogue_work(full);
2749 _permGen->gc_epilogue_work(full);
2750
2751 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2752 // in case sampling was not already enabled, enable it
2753 _start_sampling = true;
2754 }
2755 // reset _eden_chunk_array so sampling starts afresh
2756 _eden_chunk_index = 0;
2757
2758 size_t cms_used = _cmsGen->cmsSpace()->used();
2759 size_t perm_used = _permGen->cmsSpace()->used();
2760
2761 // update performance counters - this uses a special version of
2762 // update_counters() that allows the utilization to be passed as a
2763 // parameter, avoiding multiple calls to used().
2764 //
2765 _cmsGen->update_counters(cms_used);
2766 _permGen->update_counters(perm_used);
2767
2768 if (CMSIncrementalMode) {
2769 icms_update_allocation_limits();
2770 }
2771
2772 bitMapLock()->unlock();
2773 releaseFreelistLocks();
2774
2775 if (!CleanChunkPoolAsync) {
2776 Chunk::clean_chunk_pool();
2777 }
2778
2779 _between_prologue_and_epilogue = false; // ready for next cycle
2780 }
2781
2782 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2783 collector()->gc_epilogue(full);
2784
2785 // Also reset promotion tracking in par gc thread states.
2786 if (CollectedHeap::use_parallel_gc_threads()) {
2787 for (uint i = 0; i < ParallelGCThreads; i++) {
2788 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2789 }
2790 }
2791 }
2792
2793 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2794 assert(!incremental_collection_failed(), "Should have been cleared");
2795 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2796 cmsSpace()->gc_epilogue();
2797 // Print stat counters
2798 NOT_PRODUCT(
2799 assert(_numObjectsAllocated == 0, "check");
2800 assert(_numWordsAllocated == 0, "check");
2801 if (Verbose && PrintGC) {
2802 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2803 SIZE_FORMAT" bytes",
2804 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2805 }
2806 _numObjectsPromoted = 0;
2807 _numWordsPromoted = 0;
2808 )
2809
2810 if (PrintGC && Verbose) {
2811 // Call down the chain in contiguous_available needs the freelistLock
2812 // so print this out before releasing the freeListLock.
2813 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2814 contiguous_available());
2815 }
2816 }
2817
2818 #ifndef PRODUCT
2819 bool CMSCollector::have_cms_token() {
2820 Thread* thr = Thread::current();
2821 if (thr->is_VM_thread()) {
2822 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2823 } else if (thr->is_ConcurrentGC_thread()) {
2824 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2825 } else if (thr->is_GC_task_thread()) {
2826 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2827 ParGCRareEvent_lock->owned_by_self();
2828 }
2829 return false;
2830 }
2831 #endif
2832
2833 // Check reachability of the given heap address in CMS generation,
2834 // treating all other generations as roots.
2835 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2836 // We could "guarantee" below, rather than assert, but i'll
2837 // leave these as "asserts" so that an adventurous debugger
2838 // could try this in the product build provided some subset of
2839 // the conditions were met, provided they were intersted in the
2840 // results and knew that the computation below wouldn't interfere
2841 // with other concurrent computations mutating the structures
2842 // being read or written.
2843 assert(SafepointSynchronize::is_at_safepoint(),
2844 "Else mutations in object graph will make answer suspect");
2845 assert(have_cms_token(), "Should hold cms token");
2846 assert(haveFreelistLocks(), "must hold free list locks");
2847 assert_lock_strong(bitMapLock());
2848
2849 // Clear the marking bit map array before starting, but, just
2850 // for kicks, first report if the given address is already marked
2851 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2852 _markBitMap.isMarked(addr) ? "" : " not");
2853
2854 if (verify_after_remark()) {
2855 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2856 bool result = verification_mark_bm()->isMarked(addr);
2857 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2858 result ? "IS" : "is NOT");
2859 return result;
2860 } else {
2861 gclog_or_tty->print_cr("Could not compute result");
2862 return false;
2863 }
2864 }
2865
2866 ////////////////////////////////////////////////////////
2867 // CMS Verification Support
2868 ////////////////////////////////////////////////////////
2869 // Following the remark phase, the following invariant
2870 // should hold -- each object in the CMS heap which is
2871 // marked in markBitMap() should be marked in the verification_mark_bm().
2872
2873 class VerifyMarkedClosure: public BitMapClosure {
2874 CMSBitMap* _marks;
2875 bool _failed;
2876
2877 public:
2878 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2879
2880 bool do_bit(size_t offset) {
2881 HeapWord* addr = _marks->offsetToHeapWord(offset);
2882 if (!_marks->isMarked(addr)) {
2883 oop(addr)->print_on(gclog_or_tty);
2884 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2885 _failed = true;
2886 }
2887 return true;
2888 }
2889
2890 bool failed() { return _failed; }
2891 };
2892
2893 bool CMSCollector::verify_after_remark() {
2894 gclog_or_tty->print(" [Verifying CMS Marking... ");
2895 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2896 static bool init = false;
2897
2898 assert(SafepointSynchronize::is_at_safepoint(),
2899 "Else mutations in object graph will make answer suspect");
2900 assert(have_cms_token(),
2901 "Else there may be mutual interference in use of "
2902 " verification data structures");
2903 assert(_collectorState > Marking && _collectorState <= Sweeping,
2904 "Else marking info checked here may be obsolete");
2905 assert(haveFreelistLocks(), "must hold free list locks");
2906 assert_lock_strong(bitMapLock());
2907
2908
2909 // Allocate marking bit map if not already allocated
2910 if (!init) { // first time
2911 if (!verification_mark_bm()->allocate(_span)) {
2912 return false;
2913 }
2914 init = true;
2915 }
2916
2917 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2918
2919 // Turn off refs discovery -- so we will be tracing through refs.
2920 // This is as intended, because by this time
2921 // GC must already have cleared any refs that need to be cleared,
2922 // and traced those that need to be marked; moreover,
2923 // the marking done here is not going to intefere in any
2924 // way with the marking information used by GC.
2925 NoRefDiscovery no_discovery(ref_processor());
2926
2927 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2928
2929 // Clear any marks from a previous round
2930 verification_mark_bm()->clear_all();
2931 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2932 verify_work_stacks_empty();
2933
2934 GenCollectedHeap* gch = GenCollectedHeap::heap();
2935 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2936 // Update the saved marks which may affect the root scans.
2937 gch->save_marks();
2938
2939 if (CMSRemarkVerifyVariant == 1) {
2940 // In this first variant of verification, we complete
2941 // all marking, then check if the new marks-verctor is
2942 // a subset of the CMS marks-vector.
2943 verify_after_remark_work_1();
2944 } else if (CMSRemarkVerifyVariant == 2) {
2945 // In this second variant of verification, we flag an error
2946 // (i.e. an object reachable in the new marks-vector not reachable
2947 // in the CMS marks-vector) immediately, also indicating the
2948 // identify of an object (A) that references the unmarked object (B) --
2949 // presumably, a mutation to A failed to be picked up by preclean/remark?
2950 verify_after_remark_work_2();
2951 } else {
2952 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2953 CMSRemarkVerifyVariant);
2954 }
2955 gclog_or_tty->print(" done] ");
2956 return true;
2957 }
2958
2959 void CMSCollector::verify_after_remark_work_1() {
2960 ResourceMark rm;
2961 HandleMark hm;
2962 GenCollectedHeap* gch = GenCollectedHeap::heap();
2963
2964 // Mark from roots one level into CMS
2965 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2966 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2967
2968 gch->gen_process_strong_roots(_cmsGen->level(),
2969 true, // younger gens are roots
2970 true, // activate StrongRootsScope
2971 true, // collecting perm gen
2972 SharedHeap::ScanningOption(roots_scanning_options()),
2973 ¬Older,
2974 true, // walk code active on stacks
2975 NULL);
2976
2977 // Now mark from the roots
2978 assert(_revisitStack.isEmpty(), "Should be empty");
2979 MarkFromRootsClosure markFromRootsClosure(this, _span,
2980 verification_mark_bm(), verification_mark_stack(), &_revisitStack,
2981 false /* don't yield */, true /* verifying */);
2982 assert(_restart_addr == NULL, "Expected pre-condition");
2983 verification_mark_bm()->iterate(&markFromRootsClosure);
2984 while (_restart_addr != NULL) {
2985 // Deal with stack overflow: by restarting at the indicated
2986 // address.
2987 HeapWord* ra = _restart_addr;
2988 markFromRootsClosure.reset(ra);
2989 _restart_addr = NULL;
2990 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2991 }
2992 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2993 verify_work_stacks_empty();
2994 // Should reset the revisit stack above, since no class tree
2995 // surgery is forthcoming.
2996 _revisitStack.reset(); // throwing away all contents
2997
2998 // Marking completed -- now verify that each bit marked in
2999 // verification_mark_bm() is also marked in markBitMap(); flag all
3000 // errors by printing corresponding objects.
3001 VerifyMarkedClosure vcl(markBitMap());
3002 verification_mark_bm()->iterate(&vcl);
3003 if (vcl.failed()) {
3004 gclog_or_tty->print("Verification failed");
3005 Universe::heap()->print_on(gclog_or_tty);
3006 fatal("CMS: failed marking verification after remark");
3007 }
3008 }
3009
3010 void CMSCollector::verify_after_remark_work_2() {
3011 ResourceMark rm;
3012 HandleMark hm;
3013 GenCollectedHeap* gch = GenCollectedHeap::heap();
3014
3015 // Mark from roots one level into CMS
3016 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
3017 markBitMap());
3018 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3019 gch->gen_process_strong_roots(_cmsGen->level(),
3020 true, // younger gens are roots
3021 true, // activate StrongRootsScope
3022 true, // collecting perm gen
3023 SharedHeap::ScanningOption(roots_scanning_options()),
3024 ¬Older,
3025 true, // walk code active on stacks
3026 NULL);
3027
3028 // Now mark from the roots
3029 assert(_revisitStack.isEmpty(), "Should be empty");
3030 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
3031 verification_mark_bm(), markBitMap(), verification_mark_stack());
3032 assert(_restart_addr == NULL, "Expected pre-condition");
3033 verification_mark_bm()->iterate(&markFromRootsClosure);
3034 while (_restart_addr != NULL) {
3035 // Deal with stack overflow: by restarting at the indicated
3036 // address.
3037 HeapWord* ra = _restart_addr;
3038 markFromRootsClosure.reset(ra);
3039 _restart_addr = NULL;
3040 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
3041 }
3042 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
3043 verify_work_stacks_empty();
3044 // Should reset the revisit stack above, since no class tree
3045 // surgery is forthcoming.
3046 _revisitStack.reset(); // throwing away all contents
3047
3048 // Marking completed -- now verify that each bit marked in
3049 // verification_mark_bm() is also marked in markBitMap(); flag all
3050 // errors by printing corresponding objects.
3051 VerifyMarkedClosure vcl(markBitMap());
3052 verification_mark_bm()->iterate(&vcl);
3053 assert(!vcl.failed(), "Else verification above should not have succeeded");
3054 }
3055
3056 void ConcurrentMarkSweepGeneration::save_marks() {
3057 // delegate to CMS space
3058 cmsSpace()->save_marks();
3059 for (uint i = 0; i < ParallelGCThreads; i++) {
3060 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3061 }
3062 }
3063
3064 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3065 return cmsSpace()->no_allocs_since_save_marks();
3066 }
3067
3068 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3069 \
3070 void ConcurrentMarkSweepGeneration:: \
3071 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3072 cl->set_generation(this); \
3073 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3074 cl->reset_generation(); \
3075 save_marks(); \
3076 }
3077
3078 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3079
3080 void
3081 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3082 {
3083 // Not currently implemented; need to do the following. -- ysr.
3084 // dld -- I think that is used for some sort of allocation profiler. So it
3085 // really means the objects allocated by the mutator since the last
3086 // GC. We could potentially implement this cheaply by recording only
3087 // the direct allocations in a side data structure.
3088 //
3089 // I think we probably ought not to be required to support these
3090 // iterations at any arbitrary point; I think there ought to be some
3091 // call to enable/disable allocation profiling in a generation/space,
3092 // and the iterator ought to return the objects allocated in the
3093 // gen/space since the enable call, or the last iterator call (which
3094 // will probably be at a GC.) That way, for gens like CM&S that would
3095 // require some extra data structure to support this, we only pay the
3096 // cost when it's in use...
3097 cmsSpace()->object_iterate_since_last_GC(blk);
3098 }
3099
3100 void
3101 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3102 cl->set_generation(this);
3103 younger_refs_in_space_iterate(_cmsSpace, cl);
3104 cl->reset_generation();
3105 }
3106
3107 void
3108 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) {
3109 if (freelistLock()->owned_by_self()) {
3110 Generation::oop_iterate(mr, cl);
3111 } else {
3112 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3113 Generation::oop_iterate(mr, cl);
3114 }
3115 }
3116
3117 void
3118 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) {
3119 if (freelistLock()->owned_by_self()) {
3120 Generation::oop_iterate(cl);
3121 } else {
3122 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3123 Generation::oop_iterate(cl);
3124 }
3125 }
3126
3127 void
3128 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3129 if (freelistLock()->owned_by_self()) {
3130 Generation::object_iterate(cl);
3131 } else {
3132 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3133 Generation::object_iterate(cl);
3134 }
3135 }
3136
3137 void
3138 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3139 if (freelistLock()->owned_by_self()) {
3140 Generation::safe_object_iterate(cl);
3141 } else {
3142 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3143 Generation::safe_object_iterate(cl);
3144 }
3145 }
3146
3147 void
3148 ConcurrentMarkSweepGeneration::pre_adjust_pointers() {
3149 }
3150
3151 void
3152 ConcurrentMarkSweepGeneration::post_compact() {
3153 }
3154
3155 void
3156 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3157 // Fix the linear allocation blocks to look like free blocks.
3158
3159 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3160 // are not called when the heap is verified during universe initialization and
3161 // at vm shutdown.
3162 if (freelistLock()->owned_by_self()) {
3163 cmsSpace()->prepare_for_verify();
3164 } else {
3165 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3166 cmsSpace()->prepare_for_verify();
3167 }
3168 }
3169
3170 void
3171 ConcurrentMarkSweepGeneration::verify() {
3172 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3173 // are not called when the heap is verified during universe initialization and
3174 // at vm shutdown.
3175 if (freelistLock()->owned_by_self()) {
3176 cmsSpace()->verify();
3177 } else {
3178 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3179 cmsSpace()->verify();
3180 }
3181 }
3182
3183 void CMSCollector::verify() {
3184 _cmsGen->verify();
3185 _permGen->verify();
3186 }
3187
3188 #ifndef PRODUCT
3189 bool CMSCollector::overflow_list_is_empty() const {
3190 assert(_num_par_pushes >= 0, "Inconsistency");
3191 if (_overflow_list == NULL) {
3192 assert(_num_par_pushes == 0, "Inconsistency");
3193 }
3194 return _overflow_list == NULL;
3195 }
3196
3197 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3198 // merely consolidate assertion checks that appear to occur together frequently.
3199 void CMSCollector::verify_work_stacks_empty() const {
3200 assert(_markStack.isEmpty(), "Marking stack should be empty");
3201 assert(overflow_list_is_empty(), "Overflow list should be empty");
3202 }
3203
3204 void CMSCollector::verify_overflow_empty() const {
3205 assert(overflow_list_is_empty(), "Overflow list should be empty");
3206 assert(no_preserved_marks(), "No preserved marks");
3207 }
3208 #endif // PRODUCT
3209
3210 // Decide if we want to enable class unloading as part of the
3211 // ensuing concurrent GC cycle. We will collect the perm gen and
3212 // unload classes if it's the case that:
3213 // (1) an explicit gc request has been made and the flag
3214 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3215 // (2) (a) class unloading is enabled at the command line, and
3216 // (b) (i) perm gen threshold has been crossed, or
3217 // (ii) old gen is getting really full, or
3218 // (iii) the previous N CMS collections did not collect the
3219 // perm gen
3220 // NOTE: Provided there is no change in the state of the heap between
3221 // calls to this method, it should have idempotent results. Moreover,
3222 // its results should be monotonically increasing (i.e. going from 0 to 1,
3223 // but not 1 to 0) between successive calls between which the heap was
3224 // not collected. For the implementation below, it must thus rely on
3225 // the property that concurrent_cycles_since_last_unload()
3226 // will not decrease unless a collection cycle happened and that
3227 // _permGen->should_concurrent_collect() and _cmsGen->is_too_full() are
3228 // themselves also monotonic in that sense. See check_monotonicity()
3229 // below.
3230 bool CMSCollector::update_should_unload_classes() {
3231 _should_unload_classes = false;
3232 // Condition 1 above
3233 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3234 _should_unload_classes = true;
3235 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3236 // Disjuncts 2.b.(i,ii,iii) above
3237 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3238 CMSClassUnloadingMaxInterval)
3239 || _permGen->should_concurrent_collect()
3240 || _cmsGen->is_too_full();
3241 }
3242 return _should_unload_classes;
3243 }
3244
3245 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3246 bool res = should_concurrent_collect();
3247 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3248 return res;
3249 }
3250
3251 void CMSCollector::setup_cms_unloading_and_verification_state() {
3252 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3253 || VerifyBeforeExit;
3254 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3255
3256 if (should_unload_classes()) { // Should unload classes this cycle
3257 remove_root_scanning_option(rso); // Shrink the root set appropriately
3258 set_verifying(should_verify); // Set verification state for this cycle
3259 return; // Nothing else needs to be done at this time
3260 }
3261
3262 // Not unloading classes this cycle
3263 assert(!should_unload_classes(), "Inconsitency!");
3264 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3265 // We were not verifying, or we _were_ unloading classes in the last cycle,
3266 // AND some verification options are enabled this cycle; in this case,
3267 // we must make sure that the deadness map is allocated if not already so,
3268 // and cleared (if already allocated previously --
3269 // CMSBitMap::sizeInBits() is used to determine if it's allocated).
3270 if (perm_gen_verify_bit_map()->sizeInBits() == 0) {
3271 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) {
3272 warning("Failed to allocate permanent generation verification CMS Bit Map;\n"
3273 "permanent generation verification disabled");
3274 return; // Note that we leave verification disabled, so we'll retry this
3275 // allocation next cycle. We _could_ remember this failure
3276 // and skip further attempts and permanently disable verification
3277 // attempts if that is considered more desirable.
3278 }
3279 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()),
3280 "_perm_gen_ver_bit_map inconsistency?");
3281 } else {
3282 perm_gen_verify_bit_map()->clear_all();
3283 }
3284 // Include symbols, strings and code cache elements to prevent their resurrection.
3285 add_root_scanning_option(rso);
3286 set_verifying(true);
3287 } else if (verifying() && !should_verify) {
3288 // We were verifying, but some verification flags got disabled.
3289 set_verifying(false);
3290 // Exclude symbols, strings and code cache elements from root scanning to
3291 // reduce IM and RM pauses.
3292 remove_root_scanning_option(rso);
3293 }
3294 }
3295
3296
3297 #ifndef PRODUCT
3298 HeapWord* CMSCollector::block_start(const void* p) const {
3299 const HeapWord* addr = (HeapWord*)p;
3300 if (_span.contains(p)) {
3301 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3302 return _cmsGen->cmsSpace()->block_start(p);
3303 } else {
3304 assert(_permGen->cmsSpace()->is_in_reserved(addr),
3305 "Inconsistent _span?");
3306 return _permGen->cmsSpace()->block_start(p);
3307 }
3308 }
3309 return NULL;
3310 }
3311 #endif
3312
3313 HeapWord*
3314 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3315 bool tlab,
3316 bool parallel) {
3317 CMSSynchronousYieldRequest yr;
3318 assert(!tlab, "Can't deal with TLAB allocation");
3319 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3320 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3321 CMSExpansionCause::_satisfy_allocation);
3322 if (GCExpandToAllocateDelayMillis > 0) {
3323 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3324 }
3325 return have_lock_and_allocate(word_size, tlab);
3326 }
3327
3328 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3329 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3330 // to CardGeneration and share it...
3331 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3332 return CardGeneration::expand(bytes, expand_bytes);
3333 }
3334
3335 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3336 CMSExpansionCause::Cause cause)
3337 {
3338
3339 bool success = expand(bytes, expand_bytes);
3340
3341 // remember why we expanded; this information is used
3342 // by shouldConcurrentCollect() when making decisions on whether to start
3343 // a new CMS cycle.
3344 if (success) {
3345 set_expansion_cause(cause);
3346 if (PrintGCDetails && Verbose) {
3347 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3348 CMSExpansionCause::to_string(cause));
3349 }
3350 }
3351 }
3352
3353 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3354 HeapWord* res = NULL;
3355 MutexLocker x(ParGCRareEvent_lock);
3356 while (true) {
3357 // Expansion by some other thread might make alloc OK now:
3358 res = ps->lab.alloc(word_sz);
3359 if (res != NULL) return res;
3360 // If there's not enough expansion space available, give up.
3361 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3362 return NULL;
3363 }
3364 // Otherwise, we try expansion.
3365 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3366 CMSExpansionCause::_allocate_par_lab);
3367 // Now go around the loop and try alloc again;
3368 // A competing par_promote might beat us to the expansion space,
3369 // so we may go around the loop again if promotion fails agaion.
3370 if (GCExpandToAllocateDelayMillis > 0) {
3371 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3372 }
3373 }
3374 }
3375
3376
3377 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3378 PromotionInfo* promo) {
3379 MutexLocker x(ParGCRareEvent_lock);
3380 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3381 while (true) {
3382 // Expansion by some other thread might make alloc OK now:
3383 if (promo->ensure_spooling_space()) {
3384 assert(promo->has_spooling_space(),
3385 "Post-condition of successful ensure_spooling_space()");
3386 return true;
3387 }
3388 // If there's not enough expansion space available, give up.
3389 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3390 return false;
3391 }
3392 // Otherwise, we try expansion.
3393 expand(refill_size_bytes, MinHeapDeltaBytes,
3394 CMSExpansionCause::_allocate_par_spooling_space);
3395 // Now go around the loop and try alloc again;
3396 // A competing allocation might beat us to the expansion space,
3397 // so we may go around the loop again if allocation fails again.
3398 if (GCExpandToAllocateDelayMillis > 0) {
3399 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3400 }
3401 }
3402 }
3403
3404
3405
3406 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3407 assert_locked_or_safepoint(Heap_lock);
3408 size_t size = ReservedSpace::page_align_size_down(bytes);
3409 if (size > 0) {
3410 shrink_by(size);
3411 }
3412 }
3413
3414 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3415 assert_locked_or_safepoint(Heap_lock);
3416 bool result = _virtual_space.expand_by(bytes);
3417 if (result) {
3418 HeapWord* old_end = _cmsSpace->end();
3419 size_t new_word_size =
3420 heap_word_size(_virtual_space.committed_size());
3421 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3422 _bts->resize(new_word_size); // resize the block offset shared array
3423 Universe::heap()->barrier_set()->resize_covered_region(mr);
3424 // Hmmmm... why doesn't CFLS::set_end verify locking?
3425 // This is quite ugly; FIX ME XXX
3426 _cmsSpace->assert_locked(freelistLock());
3427 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3428
3429 // update the space and generation capacity counters
3430 if (UsePerfData) {
3431 _space_counters->update_capacity();
3432 _gen_counters->update_all();
3433 }
3434
3435 if (Verbose && PrintGC) {
3436 size_t new_mem_size = _virtual_space.committed_size();
3437 size_t old_mem_size = new_mem_size - bytes;
3438 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK",
3439 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3440 }
3441 }
3442 return result;
3443 }
3444
3445 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3446 assert_locked_or_safepoint(Heap_lock);
3447 bool success = true;
3448 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3449 if (remaining_bytes > 0) {
3450 success = grow_by(remaining_bytes);
3451 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3452 }
3453 return success;
3454 }
3455
3456 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3457 assert_locked_or_safepoint(Heap_lock);
3458 assert_lock_strong(freelistLock());
3459 // XXX Fix when compaction is implemented.
3460 warning("Shrinking of CMS not yet implemented");
3461 return;
3462 }
3463
3464
3465 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3466 // phases.
3467 class CMSPhaseAccounting: public StackObj {
3468 public:
3469 CMSPhaseAccounting(CMSCollector *collector,
3470 const char *phase,
3471 bool print_cr = true);
3472 ~CMSPhaseAccounting();
3473
3474 private:
3475 CMSCollector *_collector;
3476 const char *_phase;
3477 elapsedTimer _wallclock;
3478 bool _print_cr;
3479
3480 public:
3481 // Not MT-safe; so do not pass around these StackObj's
3482 // where they may be accessed by other threads.
3483 jlong wallclock_millis() {
3484 assert(_wallclock.is_active(), "Wall clock should not stop");
3485 _wallclock.stop(); // to record time
3486 jlong ret = _wallclock.milliseconds();
3487 _wallclock.start(); // restart
3488 return ret;
3489 }
3490 };
3491
3492 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3493 const char *phase,
3494 bool print_cr) :
3495 _collector(collector), _phase(phase), _print_cr(print_cr) {
3496
3497 if (PrintCMSStatistics != 0) {
3498 _collector->resetYields();
3499 }
3500 if (PrintGCDetails && PrintGCTimeStamps) {
3501 gclog_or_tty->date_stamp(PrintGCDateStamps);
3502 gclog_or_tty->stamp();
3503 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]",
3504 _collector->cmsGen()->short_name(), _phase);
3505 }
3506 _collector->resetTimer();
3507 _wallclock.start();
3508 _collector->startTimer();
3509 }
3510
3511 CMSPhaseAccounting::~CMSPhaseAccounting() {
3512 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3513 _collector->stopTimer();
3514 _wallclock.stop();
3515 if (PrintGCDetails) {
3516 gclog_or_tty->date_stamp(PrintGCDateStamps);
3517 gclog_or_tty->stamp(PrintGCTimeStamps);
3518 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3519 _collector->cmsGen()->short_name(),
3520 _phase, _collector->timerValue(), _wallclock.seconds());
3521 if (_print_cr) {
3522 gclog_or_tty->print_cr("");
3523 }
3524 if (PrintCMSStatistics != 0) {
3525 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3526 _collector->yields());
3527 }
3528 }
3529 }
3530
3531 // CMS work
3532
3533 // Checkpoint the roots into this generation from outside
3534 // this generation. [Note this initial checkpoint need only
3535 // be approximate -- we'll do a catch up phase subsequently.]
3536 void CMSCollector::checkpointRootsInitial(bool asynch) {
3537 assert(_collectorState == InitialMarking, "Wrong collector state");
3538 check_correct_thread_executing();
3539 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3540
3541 save_heap_summary();
3542 report_heap_summary(GCWhen::BeforeGC);
3543
3544 ReferenceProcessor* rp = ref_processor();
3545 SpecializationStats::clear();
3546 assert(_restart_addr == NULL, "Control point invariant");
3547 if (asynch) {
3548 // acquire locks for subsequent manipulations
3549 MutexLockerEx x(bitMapLock(),
3550 Mutex::_no_safepoint_check_flag);
3551 checkpointRootsInitialWork(asynch);
3552 // enable ("weak") refs discovery
3553 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3554 _collectorState = Marking;
3555 } else {
3556 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3557 // which recognizes if we are a CMS generation, and doesn't try to turn on
3558 // discovery; verify that they aren't meddling.
3559 assert(!rp->discovery_is_atomic(),
3560 "incorrect setting of discovery predicate");
3561 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3562 "ref discovery for this generation kind");
3563 // already have locks
3564 checkpointRootsInitialWork(asynch);
3565 // now enable ("weak") refs discovery
3566 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3567 _collectorState = Marking;
3568 }
3569 SpecializationStats::print();
3570 }
3571
3572 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3573 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3574 assert(_collectorState == InitialMarking, "just checking");
3575
3576 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3577 // precede our marking with a collection of all
3578 // younger generations to keep floating garbage to a minimum.
3579 // XXX: we won't do this for now -- it's an optimization to be done later.
3580
3581 // already have locks
3582 assert_lock_strong(bitMapLock());
3583 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3584
3585 // Setup the verification and class unloading state for this
3586 // CMS collection cycle.
3587 setup_cms_unloading_and_verification_state();
3588
3589 NOT_PRODUCT(GCTraceTime t("\ncheckpointRootsInitialWork",
3590 PrintGCDetails && Verbose, true, _gc_timer_cm);)
3591 if (UseAdaptiveSizePolicy) {
3592 size_policy()->checkpoint_roots_initial_begin();
3593 }
3594
3595 // Reset all the PLAB chunk arrays if necessary.
3596 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3597 reset_survivor_plab_arrays();
3598 }
3599
3600 ResourceMark rm;
3601 HandleMark hm;
3602
3603 FalseClosure falseClosure;
3604 // In the case of a synchronous collection, we will elide the
3605 // remark step, so it's important to catch all the nmethod oops
3606 // in this step.
3607 // The final 'true' flag to gen_process_strong_roots will ensure this.
3608 // If 'async' is true, we can relax the nmethod tracing.
3609 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3610 GenCollectedHeap* gch = GenCollectedHeap::heap();
3611
3612 verify_work_stacks_empty();
3613 verify_overflow_empty();
3614
3615 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3616 // Update the saved marks which may affect the root scans.
3617 gch->save_marks();
3618
3619 // weak reference processing has not started yet.
3620 ref_processor()->set_enqueuing_is_done(false);
3621
3622 {
3623 // This is not needed. DEBUG_ONLY(RememberKlassesChecker imx(true);)
3624 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3625 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3626 gch->gen_process_strong_roots(_cmsGen->level(),
3627 true, // younger gens are roots
3628 true, // activate StrongRootsScope
3629 true, // collecting perm gen
3630 SharedHeap::ScanningOption(roots_scanning_options()),
3631 ¬Older,
3632 true, // walk all of code cache if (so & SO_CodeCache)
3633 NULL);
3634 }
3635
3636 // Clear mod-union table; it will be dirtied in the prologue of
3637 // CMS generation per each younger generation collection.
3638
3639 assert(_modUnionTable.isAllClear(),
3640 "Was cleared in most recent final checkpoint phase"
3641 " or no bits are set in the gc_prologue before the start of the next "
3642 "subsequent marking phase.");
3643
3644 // Save the end of the used_region of the constituent generations
3645 // to be used to limit the extent of sweep in each generation.
3646 save_sweep_limits();
3647 if (UseAdaptiveSizePolicy) {
3648 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3649 }
3650 verify_overflow_empty();
3651 }
3652
3653 bool CMSCollector::markFromRoots(bool asynch) {
3654 // we might be tempted to assert that:
3655 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3656 // "inconsistent argument?");
3657 // However that wouldn't be right, because it's possible that
3658 // a safepoint is indeed in progress as a younger generation
3659 // stop-the-world GC happens even as we mark in this generation.
3660 assert(_collectorState == Marking, "inconsistent state?");
3661 check_correct_thread_executing();
3662 verify_overflow_empty();
3663
3664 bool res;
3665 if (asynch) {
3666
3667 // Start the timers for adaptive size policy for the concurrent phases
3668 // Do it here so that the foreground MS can use the concurrent
3669 // timer since a foreground MS might has the sweep done concurrently
3670 // or STW.
3671 if (UseAdaptiveSizePolicy) {
3672 size_policy()->concurrent_marking_begin();
3673 }
3674
3675 // Weak ref discovery note: We may be discovering weak
3676 // refs in this generation concurrent (but interleaved) with
3677 // weak ref discovery by a younger generation collector.
3678
3679 CMSTokenSyncWithLocks ts(true, bitMapLock());
3680 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3681 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3682 res = markFromRootsWork(asynch);
3683 if (res) {
3684 _collectorState = Precleaning;
3685 } else { // We failed and a foreground collection wants to take over
3686 assert(_foregroundGCIsActive, "internal state inconsistency");
3687 assert(_restart_addr == NULL, "foreground will restart from scratch");
3688 if (PrintGCDetails) {
3689 gclog_or_tty->print_cr("bailing out to foreground collection");
3690 }
3691 }
3692 if (UseAdaptiveSizePolicy) {
3693 size_policy()->concurrent_marking_end();
3694 }
3695 } else {
3696 assert(SafepointSynchronize::is_at_safepoint(),
3697 "inconsistent with asynch == false");
3698 if (UseAdaptiveSizePolicy) {
3699 size_policy()->ms_collection_marking_begin();
3700 }
3701 // already have locks
3702 res = markFromRootsWork(asynch);
3703 _collectorState = FinalMarking;
3704 if (UseAdaptiveSizePolicy) {
3705 GenCollectedHeap* gch = GenCollectedHeap::heap();
3706 size_policy()->ms_collection_marking_end(gch->gc_cause());
3707 }
3708 }
3709 verify_overflow_empty();
3710 return res;
3711 }
3712
3713 bool CMSCollector::markFromRootsWork(bool asynch) {
3714 // iterate over marked bits in bit map, doing a full scan and mark
3715 // from these roots using the following algorithm:
3716 // . if oop is to the right of the current scan pointer,
3717 // mark corresponding bit (we'll process it later)
3718 // . else (oop is to left of current scan pointer)
3719 // push oop on marking stack
3720 // . drain the marking stack
3721
3722 // Note that when we do a marking step we need to hold the
3723 // bit map lock -- recall that direct allocation (by mutators)
3724 // and promotion (by younger generation collectors) is also
3725 // marking the bit map. [the so-called allocate live policy.]
3726 // Because the implementation of bit map marking is not
3727 // robust wrt simultaneous marking of bits in the same word,
3728 // we need to make sure that there is no such interference
3729 // between concurrent such updates.
3730
3731 // already have locks
3732 assert_lock_strong(bitMapLock());
3733
3734 // Clear the revisit stack, just in case there are any
3735 // obsolete contents from a short-circuited previous CMS cycle.
3736 _revisitStack.reset();
3737 verify_work_stacks_empty();
3738 verify_overflow_empty();
3739 assert(_revisitStack.isEmpty(), "tabula rasa");
3740 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
3741 bool result = false;
3742 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3743 result = do_marking_mt(asynch);
3744 } else {
3745 result = do_marking_st(asynch);
3746 }
3747 return result;
3748 }
3749
3750 // Forward decl
3751 class CMSConcMarkingTask;
3752
3753 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3754 CMSCollector* _collector;
3755 CMSConcMarkingTask* _task;
3756 public:
3757 virtual void yield();
3758
3759 // "n_threads" is the number of threads to be terminated.
3760 // "queue_set" is a set of work queues of other threads.
3761 // "collector" is the CMS collector associated with this task terminator.
3762 // "yield" indicates whether we need the gang as a whole to yield.
3763 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3764 ParallelTaskTerminator(n_threads, queue_set),
3765 _collector(collector) { }
3766
3767 void set_task(CMSConcMarkingTask* task) {
3768 _task = task;
3769 }
3770 };
3771
3772 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3773 CMSConcMarkingTask* _task;
3774 public:
3775 bool should_exit_termination();
3776 void set_task(CMSConcMarkingTask* task) {
3777 _task = task;
3778 }
3779 };
3780
3781 // MT Concurrent Marking Task
3782 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3783 CMSCollector* _collector;
3784 int _n_workers; // requested/desired # workers
3785 bool _asynch;
3786 bool _result;
3787 CompactibleFreeListSpace* _cms_space;
3788 CompactibleFreeListSpace* _perm_space;
3789 char _pad_front[64]; // padding to ...
3790 HeapWord* _global_finger; // ... avoid sharing cache line
3791 char _pad_back[64];
3792 HeapWord* _restart_addr;
3793
3794 // Exposed here for yielding support
3795 Mutex* const _bit_map_lock;
3796
3797 // The per thread work queues, available here for stealing
3798 OopTaskQueueSet* _task_queues;
3799
3800 // Termination (and yielding) support
3801 CMSConcMarkingTerminator _term;
3802 CMSConcMarkingTerminatorTerminator _term_term;
3803
3804 public:
3805 CMSConcMarkingTask(CMSCollector* collector,
3806 CompactibleFreeListSpace* cms_space,
3807 CompactibleFreeListSpace* perm_space,
3808 bool asynch,
3809 YieldingFlexibleWorkGang* workers,
3810 OopTaskQueueSet* task_queues):
3811 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3812 _collector(collector),
3813 _cms_space(cms_space),
3814 _perm_space(perm_space),
3815 _asynch(asynch), _n_workers(0), _result(true),
3816 _task_queues(task_queues),
3817 _term(_n_workers, task_queues, _collector),
3818 _bit_map_lock(collector->bitMapLock())
3819 {
3820 _requested_size = _n_workers;
3821 _term.set_task(this);
3822 _term_term.set_task(this);
3823 assert(_cms_space->bottom() < _perm_space->bottom(),
3824 "Finger incorrectly initialized below");
3825 _restart_addr = _global_finger = _cms_space->bottom();
3826 }
3827
3828
3829 OopTaskQueueSet* task_queues() { return _task_queues; }
3830
3831 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3832
3833 HeapWord** global_finger_addr() { return &_global_finger; }
3834
3835 CMSConcMarkingTerminator* terminator() { return &_term; }
3836
3837 virtual void set_for_termination(int active_workers) {
3838 terminator()->reset_for_reuse(active_workers);
3839 }
3840
3841 void work(uint worker_id);
3842 bool should_yield() {
3843 return ConcurrentMarkSweepThread::should_yield()
3844 && !_collector->foregroundGCIsActive()
3845 && _asynch;
3846 }
3847
3848 virtual void coordinator_yield(); // stuff done by coordinator
3849 bool result() { return _result; }
3850
3851 void reset(HeapWord* ra) {
3852 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3853 assert(_global_finger >= _perm_space->end(), "Postcondition of ::work(i)");
3854 assert(ra < _perm_space->end(), "ra too large");
3855 _restart_addr = _global_finger = ra;
3856 _term.reset_for_reuse();
3857 }
3858
3859 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3860 OopTaskQueue* work_q);
3861
3862 private:
3863 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3864 void do_work_steal(int i);
3865 void bump_global_finger(HeapWord* f);
3866 };
3867
3868 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3869 assert(_task != NULL, "Error");
3870 return _task->yielding();
3871 // Note that we do not need the disjunct || _task->should_yield() above
3872 // because we want terminating threads to yield only if the task
3873 // is already in the midst of yielding, which happens only after at least one
3874 // thread has yielded.
3875 }
3876
3877 void CMSConcMarkingTerminator::yield() {
3878 if (_task->should_yield()) {
3879 _task->yield();
3880 } else {
3881 ParallelTaskTerminator::yield();
3882 }
3883 }
3884
3885 ////////////////////////////////////////////////////////////////
3886 // Concurrent Marking Algorithm Sketch
3887 ////////////////////////////////////////////////////////////////
3888 // Until all tasks exhausted (both spaces):
3889 // -- claim next available chunk
3890 // -- bump global finger via CAS
3891 // -- find first object that starts in this chunk
3892 // and start scanning bitmap from that position
3893 // -- scan marked objects for oops
3894 // -- CAS-mark target, and if successful:
3895 // . if target oop is above global finger (volatile read)
3896 // nothing to do
3897 // . if target oop is in chunk and above local finger
3898 // then nothing to do
3899 // . else push on work-queue
3900 // -- Deal with possible overflow issues:
3901 // . local work-queue overflow causes stuff to be pushed on
3902 // global (common) overflow queue
3903 // . always first empty local work queue
3904 // . then get a batch of oops from global work queue if any
3905 // . then do work stealing
3906 // -- When all tasks claimed (both spaces)
3907 // and local work queue empty,
3908 // then in a loop do:
3909 // . check global overflow stack; steal a batch of oops and trace
3910 // . try to steal from other threads oif GOS is empty
3911 // . if neither is available, offer termination
3912 // -- Terminate and return result
3913 //
3914 void CMSConcMarkingTask::work(uint worker_id) {
3915 elapsedTimer _timer;
3916 ResourceMark rm;
3917 HandleMark hm;
3918
3919 DEBUG_ONLY(_collector->verify_overflow_empty();)
3920
3921 // Before we begin work, our work queue should be empty
3922 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3923 // Scan the bitmap covering _cms_space, tracing through grey objects.
3924 _timer.start();
3925 do_scan_and_mark(worker_id, _cms_space);
3926 _timer.stop();
3927 if (PrintCMSStatistics != 0) {
3928 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3929 worker_id, _timer.seconds());
3930 // XXX: need xxx/xxx type of notation, two timers
3931 }
3932
3933 // ... do the same for the _perm_space
3934 _timer.reset();
3935 _timer.start();
3936 do_scan_and_mark(worker_id, _perm_space);
3937 _timer.stop();
3938 if (PrintCMSStatistics != 0) {
3939 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec",
3940 worker_id, _timer.seconds());
3941 // XXX: need xxx/xxx type of notation, two timers
3942 }
3943
3944 // ... do work stealing
3945 _timer.reset();
3946 _timer.start();
3947 do_work_steal(worker_id);
3948 _timer.stop();
3949 if (PrintCMSStatistics != 0) {
3950 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3951 worker_id, _timer.seconds());
3952 // XXX: need xxx/xxx type of notation, two timers
3953 }
3954 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3955 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3956 // Note that under the current task protocol, the
3957 // following assertion is true even of the spaces
3958 // expanded since the completion of the concurrent
3959 // marking. XXX This will likely change under a strict
3960 // ABORT semantics.
3961 assert(_global_finger > _cms_space->end() &&
3962 _global_finger >= _perm_space->end(),
3963 "All tasks have been completed");
3964 DEBUG_ONLY(_collector->verify_overflow_empty();)
3965 }
3966
3967 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3968 HeapWord* read = _global_finger;
3969 HeapWord* cur = read;
3970 while (f > read) {
3971 cur = read;
3972 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3973 if (cur == read) {
3974 // our cas succeeded
3975 assert(_global_finger >= f, "protocol consistency");
3976 break;
3977 }
3978 }
3979 }
3980
3981 // This is really inefficient, and should be redone by
3982 // using (not yet available) block-read and -write interfaces to the
3983 // stack and the work_queue. XXX FIX ME !!!
3984 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3985 OopTaskQueue* work_q) {
3986 // Fast lock-free check
3987 if (ovflw_stk->length() == 0) {
3988 return false;
3989 }
3990 assert(work_q->size() == 0, "Shouldn't steal");
3991 MutexLockerEx ml(ovflw_stk->par_lock(),
3992 Mutex::_no_safepoint_check_flag);
3993 // Grab up to 1/4 the size of the work queue
3994 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3995 (size_t)ParGCDesiredObjsFromOverflowList);
3996 num = MIN2(num, ovflw_stk->length());
3997 for (int i = (int) num; i > 0; i--) {
3998 oop cur = ovflw_stk->pop();
3999 assert(cur != NULL, "Counted wrong?");
4000 work_q->push(cur);
4001 }
4002 return num > 0;
4003 }
4004
4005 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
4006 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4007 int n_tasks = pst->n_tasks();
4008 // We allow that there may be no tasks to do here because
4009 // we are restarting after a stack overflow.
4010 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
4011 uint nth_task = 0;
4012
4013 HeapWord* aligned_start = sp->bottom();
4014 if (sp->used_region().contains(_restart_addr)) {
4015 // Align down to a card boundary for the start of 0th task
4016 // for this space.
4017 aligned_start =
4018 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
4019 CardTableModRefBS::card_size);
4020 }
4021
4022 size_t chunk_size = sp->marking_task_size();
4023 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4024 // Having claimed the nth task in this space,
4025 // compute the chunk that it corresponds to:
4026 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
4027 aligned_start + (nth_task+1)*chunk_size);
4028 // Try and bump the global finger via a CAS;
4029 // note that we need to do the global finger bump
4030 // _before_ taking the intersection below, because
4031 // the task corresponding to that region will be
4032 // deemed done even if the used_region() expands
4033 // because of allocation -- as it almost certainly will
4034 // during start-up while the threads yield in the
4035 // closure below.
4036 HeapWord* finger = span.end();
4037 bump_global_finger(finger); // atomically
4038 // There are null tasks here corresponding to chunks
4039 // beyond the "top" address of the space.
4040 span = span.intersection(sp->used_region());
4041 if (!span.is_empty()) { // Non-null task
4042 HeapWord* prev_obj;
4043 assert(!span.contains(_restart_addr) || nth_task == 0,
4044 "Inconsistency");
4045 if (nth_task == 0) {
4046 // For the 0th task, we'll not need to compute a block_start.
4047 if (span.contains(_restart_addr)) {
4048 // In the case of a restart because of stack overflow,
4049 // we might additionally skip a chunk prefix.
4050 prev_obj = _restart_addr;
4051 } else {
4052 prev_obj = span.start();
4053 }
4054 } else {
4055 // We want to skip the first object because
4056 // the protocol is to scan any object in its entirety
4057 // that _starts_ in this span; a fortiori, any
4058 // object starting in an earlier span is scanned
4059 // as part of an earlier claimed task.
4060 // Below we use the "careful" version of block_start
4061 // so we do not try to navigate uninitialized objects.
4062 prev_obj = sp->block_start_careful(span.start());
4063 // Below we use a variant of block_size that uses the
4064 // Printezis bits to avoid waiting for allocated
4065 // objects to become initialized/parsable.
4066 while (prev_obj < span.start()) {
4067 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
4068 if (sz > 0) {
4069 prev_obj += sz;
4070 } else {
4071 // In this case we may end up doing a bit of redundant
4072 // scanning, but that appears unavoidable, short of
4073 // locking the free list locks; see bug 6324141.
4074 break;
4075 }
4076 }
4077 }
4078 if (prev_obj < span.end()) {
4079 MemRegion my_span = MemRegion(prev_obj, span.end());
4080 // Do the marking work within a non-empty span --
4081 // the last argument to the constructor indicates whether the
4082 // iteration should be incremental with periodic yields.
4083 Par_MarkFromRootsClosure cl(this, _collector, my_span,
4084 &_collector->_markBitMap,
4085 work_queue(i),
4086 &_collector->_markStack,
4087 &_collector->_revisitStack,
4088 _asynch);
4089 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4090 } // else nothing to do for this task
4091 } // else nothing to do for this task
4092 }
4093 // We'd be tempted to assert here that since there are no
4094 // more tasks left to claim in this space, the global_finger
4095 // must exceed space->top() and a fortiori space->end(). However,
4096 // that would not quite be correct because the bumping of
4097 // global_finger occurs strictly after the claiming of a task,
4098 // so by the time we reach here the global finger may not yet
4099 // have been bumped up by the thread that claimed the last
4100 // task.
4101 pst->all_tasks_completed();
4102 }
4103
4104 class Par_ConcMarkingClosure: public Par_KlassRememberingOopClosure {
4105 private:
4106 CMSConcMarkingTask* _task;
4107 MemRegion _span;
4108 CMSBitMap* _bit_map;
4109 CMSMarkStack* _overflow_stack;
4110 OopTaskQueue* _work_queue;
4111 protected:
4112 DO_OOP_WORK_DEFN
4113 public:
4114 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4115 CMSBitMap* bit_map, CMSMarkStack* overflow_stack,
4116 CMSMarkStack* revisit_stack):
4117 Par_KlassRememberingOopClosure(collector, collector->ref_processor(), revisit_stack),
4118 _task(task),
4119 _span(collector->_span),
4120 _work_queue(work_queue),
4121 _bit_map(bit_map),
4122 _overflow_stack(overflow_stack)
4123 { }
4124 virtual void do_oop(oop* p);
4125 virtual void do_oop(narrowOop* p);
4126 void trim_queue(size_t max);
4127 void handle_stack_overflow(HeapWord* lost);
4128 void do_yield_check() {
4129 if (_task->should_yield()) {
4130 _task->yield();
4131 }
4132 }
4133 };
4134
4135 // Grey object scanning during work stealing phase --
4136 // the salient assumption here is that any references
4137 // that are in these stolen objects being scanned must
4138 // already have been initialized (else they would not have
4139 // been published), so we do not need to check for
4140 // uninitialized objects before pushing here.
4141 void Par_ConcMarkingClosure::do_oop(oop obj) {
4142 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4143 HeapWord* addr = (HeapWord*)obj;
4144 // Check if oop points into the CMS generation
4145 // and is not marked
4146 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4147 // a white object ...
4148 // If we manage to "claim" the object, by being the
4149 // first thread to mark it, then we push it on our
4150 // marking stack
4151 if (_bit_map->par_mark(addr)) { // ... now grey
4152 // push on work queue (grey set)
4153 bool simulate_overflow = false;
4154 NOT_PRODUCT(
4155 if (CMSMarkStackOverflowALot &&
4156 _collector->simulate_overflow()) {
4157 // simulate a stack overflow
4158 simulate_overflow = true;
4159 }
4160 )
4161 if (simulate_overflow ||
4162 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4163 // stack overflow
4164 if (PrintCMSStatistics != 0) {
4165 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4166 SIZE_FORMAT, _overflow_stack->capacity());
4167 }
4168 // We cannot assert that the overflow stack is full because
4169 // it may have been emptied since.
4170 assert(simulate_overflow ||
4171 _work_queue->size() == _work_queue->max_elems(),
4172 "Else push should have succeeded");
4173 handle_stack_overflow(addr);
4174 }
4175 } // Else, some other thread got there first
4176 do_yield_check();
4177 }
4178 }
4179
4180 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4181 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4182
4183 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4184 while (_work_queue->size() > max) {
4185 oop new_oop;
4186 if (_work_queue->pop_local(new_oop)) {
4187 assert(new_oop->is_oop(), "Should be an oop");
4188 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4189 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4190 assert(new_oop->is_parsable(), "Should be parsable");
4191 new_oop->oop_iterate(this); // do_oop() above
4192 do_yield_check();
4193 }
4194 }
4195 }
4196
4197 // Upon stack overflow, we discard (part of) the stack,
4198 // remembering the least address amongst those discarded
4199 // in CMSCollector's _restart_address.
4200 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4201 // We need to do this under a mutex to prevent other
4202 // workers from interfering with the work done below.
4203 MutexLockerEx ml(_overflow_stack->par_lock(),
4204 Mutex::_no_safepoint_check_flag);
4205 // Remember the least grey address discarded
4206 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4207 _collector->lower_restart_addr(ra);
4208 _overflow_stack->reset(); // discard stack contents
4209 _overflow_stack->expand(); // expand the stack if possible
4210 }
4211
4212
4213 void CMSConcMarkingTask::do_work_steal(int i) {
4214 OopTaskQueue* work_q = work_queue(i);
4215 oop obj_to_scan;
4216 CMSBitMap* bm = &(_collector->_markBitMap);
4217 CMSMarkStack* ovflw = &(_collector->_markStack);
4218 CMSMarkStack* revisit = &(_collector->_revisitStack);
4219 int* seed = _collector->hash_seed(i);
4220 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw, revisit);
4221 while (true) {
4222 cl.trim_queue(0);
4223 assert(work_q->size() == 0, "Should have been emptied above");
4224 if (get_work_from_overflow_stack(ovflw, work_q)) {
4225 // Can't assert below because the work obtained from the
4226 // overflow stack may already have been stolen from us.
4227 // assert(work_q->size() > 0, "Work from overflow stack");
4228 continue;
4229 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4230 assert(obj_to_scan->is_oop(), "Should be an oop");
4231 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4232 obj_to_scan->oop_iterate(&cl);
4233 } else if (terminator()->offer_termination(&_term_term)) {
4234 assert(work_q->size() == 0, "Impossible!");
4235 break;
4236 } else if (yielding() || should_yield()) {
4237 yield();
4238 }
4239 }
4240 }
4241
4242 // This is run by the CMS (coordinator) thread.
4243 void CMSConcMarkingTask::coordinator_yield() {
4244 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4245 "CMS thread should hold CMS token");
4246 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4247 // First give up the locks, then yield, then re-lock
4248 // We should probably use a constructor/destructor idiom to
4249 // do this unlock/lock or modify the MutexUnlocker class to
4250 // serve our purpose. XXX
4251 assert_lock_strong(_bit_map_lock);
4252 _bit_map_lock->unlock();
4253 ConcurrentMarkSweepThread::desynchronize(true);
4254 ConcurrentMarkSweepThread::acknowledge_yield_request();
4255 _collector->stopTimer();
4256 if (PrintCMSStatistics != 0) {
4257 _collector->incrementYields();
4258 }
4259 _collector->icms_wait();
4260
4261 // It is possible for whichever thread initiated the yield request
4262 // not to get a chance to wake up and take the bitmap lock between
4263 // this thread releasing it and reacquiring it. So, while the
4264 // should_yield() flag is on, let's sleep for a bit to give the
4265 // other thread a chance to wake up. The limit imposed on the number
4266 // of iterations is defensive, to avoid any unforseen circumstances
4267 // putting us into an infinite loop. Since it's always been this
4268 // (coordinator_yield()) method that was observed to cause the
4269 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4270 // which is by default non-zero. For the other seven methods that
4271 // also perform the yield operation, as are using a different
4272 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4273 // can enable the sleeping for those methods too, if necessary.
4274 // See 6442774.
4275 //
4276 // We really need to reconsider the synchronization between the GC
4277 // thread and the yield-requesting threads in the future and we
4278 // should really use wait/notify, which is the recommended
4279 // way of doing this type of interaction. Additionally, we should
4280 // consolidate the eight methods that do the yield operation and they
4281 // are almost identical into one for better maintenability and
4282 // readability. See 6445193.
4283 //
4284 // Tony 2006.06.29
4285 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4286 ConcurrentMarkSweepThread::should_yield() &&
4287 !CMSCollector::foregroundGCIsActive(); ++i) {
4288 os::sleep(Thread::current(), 1, false);
4289 ConcurrentMarkSweepThread::acknowledge_yield_request();
4290 }
4291
4292 ConcurrentMarkSweepThread::synchronize(true);
4293 _bit_map_lock->lock_without_safepoint_check();
4294 _collector->startTimer();
4295 }
4296
4297 bool CMSCollector::do_marking_mt(bool asynch) {
4298 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4299 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4300 conc_workers()->total_workers(),
4301 conc_workers()->active_workers(),
4302 Threads::number_of_non_daemon_threads());
4303 conc_workers()->set_active_workers(num_workers);
4304
4305 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4306 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
4307
4308 CMSConcMarkingTask tsk(this,
4309 cms_space,
4310 perm_space,
4311 asynch,
4312 conc_workers(),
4313 task_queues());
4314
4315 // Since the actual number of workers we get may be different
4316 // from the number we requested above, do we need to do anything different
4317 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4318 // class?? XXX
4319 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4320 perm_space->initialize_sequential_subtasks_for_marking(num_workers);
4321
4322 // Refs discovery is already non-atomic.
4323 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4324 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4325 DEBUG_ONLY(RememberKlassesChecker cmx(should_unload_classes());)
4326 conc_workers()->start_task(&tsk);
4327 while (tsk.yielded()) {
4328 tsk.coordinator_yield();
4329 conc_workers()->continue_task(&tsk);
4330 }
4331 // If the task was aborted, _restart_addr will be non-NULL
4332 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4333 while (_restart_addr != NULL) {
4334 // XXX For now we do not make use of ABORTED state and have not
4335 // yet implemented the right abort semantics (even in the original
4336 // single-threaded CMS case). That needs some more investigation
4337 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4338 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4339 // If _restart_addr is non-NULL, a marking stack overflow
4340 // occurred; we need to do a fresh marking iteration from the
4341 // indicated restart address.
4342 if (_foregroundGCIsActive && asynch) {
4343 // We may be running into repeated stack overflows, having
4344 // reached the limit of the stack size, while making very
4345 // slow forward progress. It may be best to bail out and
4346 // let the foreground collector do its job.
4347 // Clear _restart_addr, so that foreground GC
4348 // works from scratch. This avoids the headache of
4349 // a "rescan" which would otherwise be needed because
4350 // of the dirty mod union table & card table.
4351 _restart_addr = NULL;
4352 return false;
4353 }
4354 // Adjust the task to restart from _restart_addr
4355 tsk.reset(_restart_addr);
4356 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4357 _restart_addr);
4358 perm_space->initialize_sequential_subtasks_for_marking(num_workers,
4359 _restart_addr);
4360 _restart_addr = NULL;
4361 // Get the workers going again
4362 conc_workers()->start_task(&tsk);
4363 while (tsk.yielded()) {
4364 tsk.coordinator_yield();
4365 conc_workers()->continue_task(&tsk);
4366 }
4367 }
4368 assert(tsk.completed(), "Inconsistency");
4369 assert(tsk.result() == true, "Inconsistency");
4370 return true;
4371 }
4372
4373 bool CMSCollector::do_marking_st(bool asynch) {
4374 ResourceMark rm;
4375 HandleMark hm;
4376
4377 // Temporarily make refs discovery single threaded (non-MT)
4378 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4379 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4380 &_markStack, &_revisitStack, CMSYield && asynch);
4381 // the last argument to iterate indicates whether the iteration
4382 // should be incremental with periodic yields.
4383 _markBitMap.iterate(&markFromRootsClosure);
4384 // If _restart_addr is non-NULL, a marking stack overflow
4385 // occurred; we need to do a fresh iteration from the
4386 // indicated restart address.
4387 while (_restart_addr != NULL) {
4388 if (_foregroundGCIsActive && asynch) {
4389 // We may be running into repeated stack overflows, having
4390 // reached the limit of the stack size, while making very
4391 // slow forward progress. It may be best to bail out and
4392 // let the foreground collector do its job.
4393 // Clear _restart_addr, so that foreground GC
4394 // works from scratch. This avoids the headache of
4395 // a "rescan" which would otherwise be needed because
4396 // of the dirty mod union table & card table.
4397 _restart_addr = NULL;
4398 return false; // indicating failure to complete marking
4399 }
4400 // Deal with stack overflow:
4401 // we restart marking from _restart_addr
4402 HeapWord* ra = _restart_addr;
4403 markFromRootsClosure.reset(ra);
4404 _restart_addr = NULL;
4405 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4406 }
4407 return true;
4408 }
4409
4410 void CMSCollector::preclean() {
4411 check_correct_thread_executing();
4412 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4413 verify_work_stacks_empty();
4414 verify_overflow_empty();
4415 _abort_preclean = false;
4416 if (CMSPrecleaningEnabled) {
4417 _eden_chunk_index = 0;
4418 size_t used = get_eden_used();
4419 size_t capacity = get_eden_capacity();
4420 // Don't start sampling unless we will get sufficiently
4421 // many samples.
4422 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4423 * CMSScheduleRemarkEdenPenetration)) {
4424 _start_sampling = true;
4425 } else {
4426 _start_sampling = false;
4427 }
4428 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4429 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4430 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4431 }
4432 CMSTokenSync x(true); // is cms thread
4433 if (CMSPrecleaningEnabled) {
4434 sample_eden();
4435 _collectorState = AbortablePreclean;
4436 } else {
4437 _collectorState = FinalMarking;
4438 }
4439 verify_work_stacks_empty();
4440 verify_overflow_empty();
4441 }
4442
4443 // Try and schedule the remark such that young gen
4444 // occupancy is CMSScheduleRemarkEdenPenetration %.
4445 void CMSCollector::abortable_preclean() {
4446 check_correct_thread_executing();
4447 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4448 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4449
4450 // If Eden's current occupancy is below this threshold,
4451 // immediately schedule the remark; else preclean
4452 // past the next scavenge in an effort to
4453 // schedule the pause as described avove. By choosing
4454 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4455 // we will never do an actual abortable preclean cycle.
4456 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4457 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4458 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4459 // We need more smarts in the abortable preclean
4460 // loop below to deal with cases where allocation
4461 // in young gen is very very slow, and our precleaning
4462 // is running a losing race against a horde of
4463 // mutators intent on flooding us with CMS updates
4464 // (dirty cards).
4465 // One, admittedly dumb, strategy is to give up
4466 // after a certain number of abortable precleaning loops
4467 // or after a certain maximum time. We want to make
4468 // this smarter in the next iteration.
4469 // XXX FIX ME!!! YSR
4470 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4471 while (!(should_abort_preclean() ||
4472 ConcurrentMarkSweepThread::should_terminate())) {
4473 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4474 cumworkdone += workdone;
4475 loops++;
4476 // Voluntarily terminate abortable preclean phase if we have
4477 // been at it for too long.
4478 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4479 loops >= CMSMaxAbortablePrecleanLoops) {
4480 if (PrintGCDetails) {
4481 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4482 }
4483 break;
4484 }
4485 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4486 if (PrintGCDetails) {
4487 gclog_or_tty->print(" CMS: abort preclean due to time ");
4488 }
4489 break;
4490 }
4491 // If we are doing little work each iteration, we should
4492 // take a short break.
4493 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4494 // Sleep for some time, waiting for work to accumulate
4495 stopTimer();
4496 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4497 startTimer();
4498 waited++;
4499 }
4500 }
4501 if (PrintCMSStatistics > 0) {
4502 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4503 loops, waited, cumworkdone);
4504 }
4505 }
4506 CMSTokenSync x(true); // is cms thread
4507 if (_collectorState != Idling) {
4508 assert(_collectorState == AbortablePreclean,
4509 "Spontaneous state transition?");
4510 _collectorState = FinalMarking;
4511 } // Else, a foreground collection completed this CMS cycle.
4512 return;
4513 }
4514
4515 // Respond to an Eden sampling opportunity
4516 void CMSCollector::sample_eden() {
4517 // Make sure a young gc cannot sneak in between our
4518 // reading and recording of a sample.
4519 assert(Thread::current()->is_ConcurrentGC_thread(),
4520 "Only the cms thread may collect Eden samples");
4521 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4522 "Should collect samples while holding CMS token");
4523 if (!_start_sampling) {
4524 return;
4525 }
4526 if (_eden_chunk_array) {
4527 if (_eden_chunk_index < _eden_chunk_capacity) {
4528 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4529 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4530 "Unexpected state of Eden");
4531 // We'd like to check that what we just sampled is an oop-start address;
4532 // however, we cannot do that here since the object may not yet have been
4533 // initialized. So we'll instead do the check when we _use_ this sample
4534 // later.
4535 if (_eden_chunk_index == 0 ||
4536 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4537 _eden_chunk_array[_eden_chunk_index-1])
4538 >= CMSSamplingGrain)) {
4539 _eden_chunk_index++; // commit sample
4540 }
4541 }
4542 }
4543 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4544 size_t used = get_eden_used();
4545 size_t capacity = get_eden_capacity();
4546 assert(used <= capacity, "Unexpected state of Eden");
4547 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4548 _abort_preclean = true;
4549 }
4550 }
4551 }
4552
4553
4554 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4555 assert(_collectorState == Precleaning ||
4556 _collectorState == AbortablePreclean, "incorrect state");
4557 ResourceMark rm;
4558 HandleMark hm;
4559
4560 // Precleaning is currently not MT but the reference processor
4561 // may be set for MT. Disable it temporarily here.
4562 ReferenceProcessor* rp = ref_processor();
4563 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4564
4565 // Do one pass of scrubbing the discovered reference lists
4566 // to remove any reference objects with strongly-reachable
4567 // referents.
4568 if (clean_refs) {
4569 CMSPrecleanRefsYieldClosure yield_cl(this);
4570 assert(rp->span().equals(_span), "Spans should be equal");
4571 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4572 &_markStack, &_revisitStack,
4573 true /* preclean */);
4574 CMSDrainMarkingStackClosure complete_trace(this,
4575 _span, &_markBitMap, &_markStack,
4576 &keep_alive, true /* preclean */);
4577
4578 // We don't want this step to interfere with a young
4579 // collection because we don't want to take CPU
4580 // or memory bandwidth away from the young GC threads
4581 // (which may be as many as there are CPUs).
4582 // Note that we don't need to protect ourselves from
4583 // interference with mutators because they can't
4584 // manipulate the discovered reference lists nor affect
4585 // the computed reachability of the referents, the
4586 // only properties manipulated by the precleaning
4587 // of these reference lists.
4588 stopTimer();
4589 CMSTokenSyncWithLocks x(true /* is cms thread */,
4590 bitMapLock());
4591 startTimer();
4592 sample_eden();
4593
4594 // The following will yield to allow foreground
4595 // collection to proceed promptly. XXX YSR:
4596 // The code in this method may need further
4597 // tweaking for better performance and some restructuring
4598 // for cleaner interfaces.
4599 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
4600 rp->preclean_discovered_references(
4601 rp->is_alive_non_header(), &keep_alive, &complete_trace,
4602 &yield_cl, should_unload_classes(), gc_timer);
4603 }
4604
4605 if (clean_survivor) { // preclean the active survivor space(s)
4606 assert(_young_gen->kind() == Generation::DefNew ||
4607 _young_gen->kind() == Generation::ParNew ||
4608 _young_gen->kind() == Generation::ASParNew,
4609 "incorrect type for cast");
4610 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4611 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4612 &_markBitMap, &_modUnionTable,
4613 &_markStack, &_revisitStack,
4614 true /* precleaning phase */);
4615 stopTimer();
4616 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4617 bitMapLock());
4618 startTimer();
4619 unsigned int before_count =
4620 GenCollectedHeap::heap()->total_collections();
4621 SurvivorSpacePrecleanClosure
4622 sss_cl(this, _span, &_markBitMap, &_markStack,
4623 &pam_cl, before_count, CMSYield);
4624 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4625 dng->from()->object_iterate_careful(&sss_cl);
4626 dng->to()->object_iterate_careful(&sss_cl);
4627 }
4628 MarkRefsIntoAndScanClosure
4629 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4630 &_markStack, &_revisitStack, this, CMSYield,
4631 true /* precleaning phase */);
4632 // CAUTION: The following closure has persistent state that may need to
4633 // be reset upon a decrease in the sequence of addresses it
4634 // processes.
4635 ScanMarkedObjectsAgainCarefullyClosure
4636 smoac_cl(this, _span,
4637 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield);
4638
4639 // Preclean dirty cards in ModUnionTable and CardTable using
4640 // appropriate convergence criterion;
4641 // repeat CMSPrecleanIter times unless we find that
4642 // we are losing.
4643 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4644 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4645 "Bad convergence multiplier");
4646 assert(CMSPrecleanThreshold >= 100,
4647 "Unreasonably low CMSPrecleanThreshold");
4648
4649 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4650 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4651 numIter < CMSPrecleanIter;
4652 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4653 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4654 if (CMSPermGenPrecleaningEnabled) {
4655 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl);
4656 }
4657 if (Verbose && PrintGCDetails) {
4658 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4659 }
4660 // Either there are very few dirty cards, so re-mark
4661 // pause will be small anyway, or our pre-cleaning isn't
4662 // that much faster than the rate at which cards are being
4663 // dirtied, so we might as well stop and re-mark since
4664 // precleaning won't improve our re-mark time by much.
4665 if (curNumCards <= CMSPrecleanThreshold ||
4666 (numIter > 0 &&
4667 (curNumCards * CMSPrecleanDenominator >
4668 lastNumCards * CMSPrecleanNumerator))) {
4669 numIter++;
4670 cumNumCards += curNumCards;
4671 break;
4672 }
4673 }
4674 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4675 if (CMSPermGenPrecleaningEnabled) {
4676 curNumCards += preclean_card_table(_permGen, &smoac_cl);
4677 }
4678 cumNumCards += curNumCards;
4679 if (PrintGCDetails && PrintCMSStatistics != 0) {
4680 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4681 curNumCards, cumNumCards, numIter);
4682 }
4683 return cumNumCards; // as a measure of useful work done
4684 }
4685
4686 // PRECLEANING NOTES:
4687 // Precleaning involves:
4688 // . reading the bits of the modUnionTable and clearing the set bits.
4689 // . For the cards corresponding to the set bits, we scan the
4690 // objects on those cards. This means we need the free_list_lock
4691 // so that we can safely iterate over the CMS space when scanning
4692 // for oops.
4693 // . When we scan the objects, we'll be both reading and setting
4694 // marks in the marking bit map, so we'll need the marking bit map.
4695 // . For protecting _collector_state transitions, we take the CGC_lock.
4696 // Note that any races in the reading of of card table entries by the
4697 // CMS thread on the one hand and the clearing of those entries by the
4698 // VM thread or the setting of those entries by the mutator threads on the
4699 // other are quite benign. However, for efficiency it makes sense to keep
4700 // the VM thread from racing with the CMS thread while the latter is
4701 // dirty card info to the modUnionTable. We therefore also use the
4702 // CGC_lock to protect the reading of the card table and the mod union
4703 // table by the CM thread.
4704 // . We run concurrently with mutator updates, so scanning
4705 // needs to be done carefully -- we should not try to scan
4706 // potentially uninitialized objects.
4707 //
4708 // Locking strategy: While holding the CGC_lock, we scan over and
4709 // reset a maximal dirty range of the mod union / card tables, then lock
4710 // the free_list_lock and bitmap lock to do a full marking, then
4711 // release these locks; and repeat the cycle. This allows for a
4712 // certain amount of fairness in the sharing of these locks between
4713 // the CMS collector on the one hand, and the VM thread and the
4714 // mutators on the other.
4715
4716 // NOTE: preclean_mod_union_table() and preclean_card_table()
4717 // further below are largely identical; if you need to modify
4718 // one of these methods, please check the other method too.
4719
4720 size_t CMSCollector::preclean_mod_union_table(
4721 ConcurrentMarkSweepGeneration* gen,
4722 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4723 verify_work_stacks_empty();
4724 verify_overflow_empty();
4725
4726 // Turn off checking for this method but turn it back on
4727 // selectively. There are yield points in this method
4728 // but it is difficult to turn the checking off just around
4729 // the yield points. It is simpler to selectively turn
4730 // it on.
4731 DEBUG_ONLY(RememberKlassesChecker mux(false);)
4732
4733 // strategy: starting with the first card, accumulate contiguous
4734 // ranges of dirty cards; clear these cards, then scan the region
4735 // covered by these cards.
4736
4737 // Since all of the MUT is committed ahead, we can just use
4738 // that, in case the generations expand while we are precleaning.
4739 // It might also be fine to just use the committed part of the
4740 // generation, but we might potentially miss cards when the
4741 // generation is rapidly expanding while we are in the midst
4742 // of precleaning.
4743 HeapWord* startAddr = gen->reserved().start();
4744 HeapWord* endAddr = gen->reserved().end();
4745
4746 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4747
4748 size_t numDirtyCards, cumNumDirtyCards;
4749 HeapWord *nextAddr, *lastAddr;
4750 for (cumNumDirtyCards = numDirtyCards = 0,
4751 nextAddr = lastAddr = startAddr;
4752 nextAddr < endAddr;
4753 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4754
4755 ResourceMark rm;
4756 HandleMark hm;
4757
4758 MemRegion dirtyRegion;
4759 {
4760 stopTimer();
4761 // Potential yield point
4762 CMSTokenSync ts(true);
4763 startTimer();
4764 sample_eden();
4765 // Get dirty region starting at nextOffset (inclusive),
4766 // simultaneously clearing it.
4767 dirtyRegion =
4768 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4769 assert(dirtyRegion.start() >= nextAddr,
4770 "returned region inconsistent?");
4771 }
4772 // Remember where the next search should begin.
4773 // The returned region (if non-empty) is a right open interval,
4774 // so lastOffset is obtained from the right end of that
4775 // interval.
4776 lastAddr = dirtyRegion.end();
4777 // Should do something more transparent and less hacky XXX
4778 numDirtyCards =
4779 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4780
4781 // We'll scan the cards in the dirty region (with periodic
4782 // yields for foreground GC as needed).
4783 if (!dirtyRegion.is_empty()) {
4784 assert(numDirtyCards > 0, "consistency check");
4785 HeapWord* stop_point = NULL;
4786 stopTimer();
4787 // Potential yield point
4788 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4789 bitMapLock());
4790 startTimer();
4791 {
4792 verify_work_stacks_empty();
4793 verify_overflow_empty();
4794 sample_eden();
4795 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4796 stop_point =
4797 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4798 }
4799 if (stop_point != NULL) {
4800 // The careful iteration stopped early either because it found an
4801 // uninitialized object, or because we were in the midst of an
4802 // "abortable preclean", which should now be aborted. Redirty
4803 // the bits corresponding to the partially-scanned or unscanned
4804 // cards. We'll either restart at the next block boundary or
4805 // abort the preclean.
4806 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) ||
4807 (_collectorState == AbortablePreclean && should_abort_preclean()),
4808 "Unparsable objects should only be in perm gen.");
4809 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4810 if (should_abort_preclean()) {
4811 break; // out of preclean loop
4812 } else {
4813 // Compute the next address at which preclean should pick up;
4814 // might need bitMapLock in order to read P-bits.
4815 lastAddr = next_card_start_after_block(stop_point);
4816 }
4817 }
4818 } else {
4819 assert(lastAddr == endAddr, "consistency check");
4820 assert(numDirtyCards == 0, "consistency check");
4821 break;
4822 }
4823 }
4824 verify_work_stacks_empty();
4825 verify_overflow_empty();
4826 return cumNumDirtyCards;
4827 }
4828
4829 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4830 // below are largely identical; if you need to modify
4831 // one of these methods, please check the other method too.
4832
4833 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4834 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4835 // strategy: it's similar to precleamModUnionTable above, in that
4836 // we accumulate contiguous ranges of dirty cards, mark these cards
4837 // precleaned, then scan the region covered by these cards.
4838 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4839 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4840
4841 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4842
4843 size_t numDirtyCards, cumNumDirtyCards;
4844 HeapWord *lastAddr, *nextAddr;
4845
4846 for (cumNumDirtyCards = numDirtyCards = 0,
4847 nextAddr = lastAddr = startAddr;
4848 nextAddr < endAddr;
4849 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4850
4851 ResourceMark rm;
4852 HandleMark hm;
4853
4854 MemRegion dirtyRegion;
4855 {
4856 // See comments in "Precleaning notes" above on why we
4857 // do this locking. XXX Could the locking overheads be
4858 // too high when dirty cards are sparse? [I don't think so.]
4859 stopTimer();
4860 CMSTokenSync x(true); // is cms thread
4861 startTimer();
4862 sample_eden();
4863 // Get and clear dirty region from card table
4864 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4865 MemRegion(nextAddr, endAddr),
4866 true,
4867 CardTableModRefBS::precleaned_card_val());
4868
4869 assert(dirtyRegion.start() >= nextAddr,
4870 "returned region inconsistent?");
4871 }
4872 lastAddr = dirtyRegion.end();
4873 numDirtyCards =
4874 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4875
4876 if (!dirtyRegion.is_empty()) {
4877 stopTimer();
4878 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4879 startTimer();
4880 sample_eden();
4881 verify_work_stacks_empty();
4882 verify_overflow_empty();
4883 DEBUG_ONLY(RememberKlassesChecker mx(should_unload_classes());)
4884 HeapWord* stop_point =
4885 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4886 if (stop_point != NULL) {
4887 // The careful iteration stopped early because it found an
4888 // uninitialized object. Redirty the bits corresponding to the
4889 // partially-scanned or unscanned cards, and start again at the
4890 // next block boundary.
4891 assert(CMSPermGenPrecleaningEnabled ||
4892 (_collectorState == AbortablePreclean && should_abort_preclean()),
4893 "Unparsable objects should only be in perm gen.");
4894 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4895 if (should_abort_preclean()) {
4896 break; // out of preclean loop
4897 } else {
4898 // Compute the next address at which preclean should pick up.
4899 lastAddr = next_card_start_after_block(stop_point);
4900 }
4901 }
4902 } else {
4903 break;
4904 }
4905 }
4906 verify_work_stacks_empty();
4907 verify_overflow_empty();
4908 return cumNumDirtyCards;
4909 }
4910
4911 void CMSCollector::checkpointRootsFinal(bool asynch,
4912 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4913 assert(_collectorState == FinalMarking, "incorrect state transition?");
4914 check_correct_thread_executing();
4915 // world is stopped at this checkpoint
4916 assert(SafepointSynchronize::is_at_safepoint(),
4917 "world should be stopped");
4918 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4919
4920 verify_work_stacks_empty();
4921 verify_overflow_empty();
4922
4923 SpecializationStats::clear();
4924 if (PrintGCDetails) {
4925 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4926 _young_gen->used() / K,
4927 _young_gen->capacity() / K);
4928 }
4929 if (asynch) {
4930 if (CMSScavengeBeforeRemark) {
4931 GenCollectedHeap* gch = GenCollectedHeap::heap();
4932 // Temporarily set flag to false, GCH->do_collection will
4933 // expect it to be false and set to true
4934 FlagSetting fl(gch->_is_gc_active, false);
4935 NOT_PRODUCT(GCTraceTime t("Scavenge-Before-Remark",
4936 PrintGCDetails && Verbose, true, _gc_timer_cm);)
4937 int level = _cmsGen->level() - 1;
4938 if (level >= 0) {
4939 gch->do_collection(true, // full (i.e. force, see below)
4940 false, // !clear_all_soft_refs
4941 0, // size
4942 false, // is_tlab
4943 level // max_level
4944 );
4945 }
4946 }
4947 FreelistLocker x(this);
4948 MutexLockerEx y(bitMapLock(),
4949 Mutex::_no_safepoint_check_flag);
4950 assert(!init_mark_was_synchronous, "but that's impossible!");
4951 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4952 } else {
4953 // already have all the locks
4954 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4955 init_mark_was_synchronous);
4956 }
4957 verify_work_stacks_empty();
4958 verify_overflow_empty();
4959 SpecializationStats::print();
4960 }
4961
4962 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4963 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4964
4965 NOT_PRODUCT(GCTraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, _gc_timer_cm);)
4966
4967 assert(haveFreelistLocks(), "must have free list locks");
4968 assert_lock_strong(bitMapLock());
4969
4970 if (UseAdaptiveSizePolicy) {
4971 size_policy()->checkpoint_roots_final_begin();
4972 }
4973
4974 ResourceMark rm;
4975 HandleMark hm;
4976
4977 GenCollectedHeap* gch = GenCollectedHeap::heap();
4978
4979 if (should_unload_classes()) {
4980 CodeCache::gc_prologue();
4981 }
4982 assert(haveFreelistLocks(), "must have free list locks");
4983 assert_lock_strong(bitMapLock());
4984
4985 DEBUG_ONLY(RememberKlassesChecker fmx(should_unload_classes());)
4986 if (!init_mark_was_synchronous) {
4987 // We might assume that we need not fill TLAB's when
4988 // CMSScavengeBeforeRemark is set, because we may have just done
4989 // a scavenge which would have filled all TLAB's -- and besides
4990 // Eden would be empty. This however may not always be the case --
4991 // for instance although we asked for a scavenge, it may not have
4992 // happened because of a JNI critical section. We probably need
4993 // a policy for deciding whether we can in that case wait until
4994 // the critical section releases and then do the remark following
4995 // the scavenge, and skip it here. In the absence of that policy,
4996 // or of an indication of whether the scavenge did indeed occur,
4997 // we cannot rely on TLAB's having been filled and must do
4998 // so here just in case a scavenge did not happen.
4999 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
5000 // Update the saved marks which may affect the root scans.
5001 gch->save_marks();
5002
5003 {
5004 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
5005
5006 // Note on the role of the mod union table:
5007 // Since the marker in "markFromRoots" marks concurrently with
5008 // mutators, it is possible for some reachable objects not to have been
5009 // scanned. For instance, an only reference to an object A was
5010 // placed in object B after the marker scanned B. Unless B is rescanned,
5011 // A would be collected. Such updates to references in marked objects
5012 // are detected via the mod union table which is the set of all cards
5013 // dirtied since the first checkpoint in this GC cycle and prior to
5014 // the most recent young generation GC, minus those cleaned up by the
5015 // concurrent precleaning.
5016 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
5017 GCTraceTime t("Rescan (parallel) ", PrintGCDetails, false, _gc_timer_cm);
5018 do_remark_parallel();
5019 } else {
5020 GCTraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
5021 _gc_timer_cm);
5022 do_remark_non_parallel();
5023 }
5024 }
5025 } else {
5026 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
5027 // The initial mark was stop-world, so there's no rescanning to
5028 // do; go straight on to the next step below.
5029 }
5030 verify_work_stacks_empty();
5031 verify_overflow_empty();
5032
5033 {
5034 NOT_PRODUCT(GCTraceTime ts("refProcessingWork", PrintGCDetails, false, _gc_timer_cm);)
5035 refProcessingWork(asynch, clear_all_soft_refs);
5036 }
5037 verify_work_stacks_empty();
5038 verify_overflow_empty();
5039
5040 if (should_unload_classes()) {
5041 CodeCache::gc_epilogue();
5042 }
5043 JvmtiExport::gc_epilogue();
5044
5045 // If we encountered any (marking stack / work queue) overflow
5046 // events during the current CMS cycle, take appropriate
5047 // remedial measures, where possible, so as to try and avoid
5048 // recurrence of that condition.
5049 assert(_markStack.isEmpty(), "No grey objects");
5050 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
5051 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
5052 if (ser_ovflw > 0) {
5053 if (PrintCMSStatistics != 0) {
5054 gclog_or_tty->print_cr("Marking stack overflow (benign) "
5055 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
5056 ", kac_preclean="SIZE_FORMAT")",
5057 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
5058 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
5059 }
5060 _markStack.expand();
5061 _ser_pmc_remark_ovflw = 0;
5062 _ser_pmc_preclean_ovflw = 0;
5063 _ser_kac_preclean_ovflw = 0;
5064 _ser_kac_ovflw = 0;
5065 }
5066 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
5067 if (PrintCMSStatistics != 0) {
5068 gclog_or_tty->print_cr("Work queue overflow (benign) "
5069 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
5070 _par_pmc_remark_ovflw, _par_kac_ovflw);
5071 }
5072 _par_pmc_remark_ovflw = 0;
5073 _par_kac_ovflw = 0;
5074 }
5075 if (PrintCMSStatistics != 0) {
5076 if (_markStack._hit_limit > 0) {
5077 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
5078 _markStack._hit_limit);
5079 }
5080 if (_markStack._failed_double > 0) {
5081 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
5082 " current capacity "SIZE_FORMAT,
5083 _markStack._failed_double,
5084 _markStack.capacity());
5085 }
5086 }
5087 _markStack._hit_limit = 0;
5088 _markStack._failed_double = 0;
5089
5090 // Check that all the klasses have been checked
5091 assert(_revisitStack.isEmpty(), "Not all klasses revisited");
5092
5093 if ((VerifyAfterGC || VerifyDuringGC) &&
5094 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5095 verify_after_remark();
5096 }
5097
5098 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
5099
5100 // Change under the freelistLocks.
5101 _collectorState = Sweeping;
5102 // Call isAllClear() under bitMapLock
5103 assert(_modUnionTable.isAllClear(), "Should be clear by end of the"
5104 " final marking");
5105 if (UseAdaptiveSizePolicy) {
5106 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5107 }
5108 }
5109
5110 // Parallel remark task
5111 class CMSParRemarkTask: public AbstractGangTask {
5112 CMSCollector* _collector;
5113 int _n_workers;
5114 CompactibleFreeListSpace* _cms_space;
5115 CompactibleFreeListSpace* _perm_space;
5116
5117 // The per-thread work queues, available here for stealing.
5118 OopTaskQueueSet* _task_queues;
5119 ParallelTaskTerminator _term;
5120
5121 public:
5122 // A value of 0 passed to n_workers will cause the number of
5123 // workers to be taken from the active workers in the work gang.
5124 CMSParRemarkTask(CMSCollector* collector,
5125 CompactibleFreeListSpace* cms_space,
5126 CompactibleFreeListSpace* perm_space,
5127 int n_workers, FlexibleWorkGang* workers,
5128 OopTaskQueueSet* task_queues):
5129 AbstractGangTask("Rescan roots and grey objects in parallel"),
5130 _collector(collector),
5131 _cms_space(cms_space), _perm_space(perm_space),
5132 _n_workers(n_workers),
5133 _task_queues(task_queues),
5134 _term(n_workers, task_queues) { }
5135
5136 OopTaskQueueSet* task_queues() { return _task_queues; }
5137
5138 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5139
5140 ParallelTaskTerminator* terminator() { return &_term; }
5141 int n_workers() { return _n_workers; }
5142
5143 void work(uint worker_id);
5144
5145 private:
5146 // Work method in support of parallel rescan ... of young gen spaces
5147 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5148 ContiguousSpace* space,
5149 HeapWord** chunk_array, size_t chunk_top);
5150
5151 // ... of dirty cards in old space
5152 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5153 Par_MarkRefsIntoAndScanClosure* cl);
5154
5155 // ... work stealing for the above
5156 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5157 };
5158
5159 // work_queue(i) is passed to the closure
5160 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5161 // also is passed to do_dirty_card_rescan_tasks() and to
5162 // do_work_steal() to select the i-th task_queue.
5163
5164 void CMSParRemarkTask::work(uint worker_id) {
5165 elapsedTimer _timer;
5166 ResourceMark rm;
5167 HandleMark hm;
5168
5169 // ---------- rescan from roots --------------
5170 _timer.start();
5171 GenCollectedHeap* gch = GenCollectedHeap::heap();
5172 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5173 _collector->_span, _collector->ref_processor(),
5174 &(_collector->_markBitMap),
5175 work_queue(worker_id), &(_collector->_revisitStack));
5176
5177 // Rescan young gen roots first since these are likely
5178 // coarsely partitioned and may, on that account, constitute
5179 // the critical path; thus, it's best to start off that
5180 // work first.
5181 // ---------- young gen roots --------------
5182 {
5183 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5184 EdenSpace* eden_space = dng->eden();
5185 ContiguousSpace* from_space = dng->from();
5186 ContiguousSpace* to_space = dng->to();
5187
5188 HeapWord** eca = _collector->_eden_chunk_array;
5189 size_t ect = _collector->_eden_chunk_index;
5190 HeapWord** sca = _collector->_survivor_chunk_array;
5191 size_t sct = _collector->_survivor_chunk_index;
5192
5193 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5194 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5195
5196 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5197 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5198 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5199
5200 _timer.stop();
5201 if (PrintCMSStatistics != 0) {
5202 gclog_or_tty->print_cr(
5203 "Finished young gen rescan work in %dth thread: %3.3f sec",
5204 worker_id, _timer.seconds());
5205 }
5206 }
5207
5208 // ---------- remaining roots --------------
5209 _timer.reset();
5210 _timer.start();
5211 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5212 false, // yg was scanned above
5213 false, // this is parallel code
5214 true, // collecting perm gen
5215 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5216 &par_mrias_cl,
5217 true, // walk all of code cache if (so & SO_CodeCache)
5218 NULL);
5219 assert(_collector->should_unload_classes()
5220 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5221 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5222 _timer.stop();
5223 if (PrintCMSStatistics != 0) {
5224 gclog_or_tty->print_cr(
5225 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5226 worker_id, _timer.seconds());
5227 }
5228
5229 // ---------- rescan dirty cards ------------
5230 _timer.reset();
5231 _timer.start();
5232
5233 // Do the rescan tasks for each of the two spaces
5234 // (cms_space and perm_space) in turn.
5235 // "worker_id" is passed to select the task_queue for "worker_id"
5236 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5237 do_dirty_card_rescan_tasks(_perm_space, worker_id, &par_mrias_cl);
5238 _timer.stop();
5239 if (PrintCMSStatistics != 0) {
5240 gclog_or_tty->print_cr(
5241 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5242 worker_id, _timer.seconds());
5243 }
5244
5245 // ---------- steal work from other threads ...
5246 // ---------- ... and drain overflow list.
5247 _timer.reset();
5248 _timer.start();
5249 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5250 _timer.stop();
5251 if (PrintCMSStatistics != 0) {
5252 gclog_or_tty->print_cr(
5253 "Finished work stealing in %dth thread: %3.3f sec",
5254 worker_id, _timer.seconds());
5255 }
5256 }
5257
5258 // Note that parameter "i" is not used.
5259 void
5260 CMSParRemarkTask::do_young_space_rescan(int i,
5261 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5262 HeapWord** chunk_array, size_t chunk_top) {
5263 // Until all tasks completed:
5264 // . claim an unclaimed task
5265 // . compute region boundaries corresponding to task claimed
5266 // using chunk_array
5267 // . par_oop_iterate(cl) over that region
5268
5269 ResourceMark rm;
5270 HandleMark hm;
5271
5272 SequentialSubTasksDone* pst = space->par_seq_tasks();
5273 assert(pst->valid(), "Uninitialized use?");
5274
5275 uint nth_task = 0;
5276 uint n_tasks = pst->n_tasks();
5277
5278 HeapWord *start, *end;
5279 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5280 // We claimed task # nth_task; compute its boundaries.
5281 if (chunk_top == 0) { // no samples were taken
5282 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5283 start = space->bottom();
5284 end = space->top();
5285 } else if (nth_task == 0) {
5286 start = space->bottom();
5287 end = chunk_array[nth_task];
5288 } else if (nth_task < (uint)chunk_top) {
5289 assert(nth_task >= 1, "Control point invariant");
5290 start = chunk_array[nth_task - 1];
5291 end = chunk_array[nth_task];
5292 } else {
5293 assert(nth_task == (uint)chunk_top, "Control point invariant");
5294 start = chunk_array[chunk_top - 1];
5295 end = space->top();
5296 }
5297 MemRegion mr(start, end);
5298 // Verify that mr is in space
5299 assert(mr.is_empty() || space->used_region().contains(mr),
5300 "Should be in space");
5301 // Verify that "start" is an object boundary
5302 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5303 "Should be an oop");
5304 space->par_oop_iterate(mr, cl);
5305 }
5306 pst->all_tasks_completed();
5307 }
5308
5309 void
5310 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5311 CompactibleFreeListSpace* sp, int i,
5312 Par_MarkRefsIntoAndScanClosure* cl) {
5313 // Until all tasks completed:
5314 // . claim an unclaimed task
5315 // . compute region boundaries corresponding to task claimed
5316 // . transfer dirty bits ct->mut for that region
5317 // . apply rescanclosure to dirty mut bits for that region
5318
5319 ResourceMark rm;
5320 HandleMark hm;
5321
5322 OopTaskQueue* work_q = work_queue(i);
5323 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5324 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5325 // CAUTION: This closure has state that persists across calls to
5326 // the work method dirty_range_iterate_clear() in that it has
5327 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5328 // use of that state in the imbedded UpwardsObjectClosure instance
5329 // assumes that the cards are always iterated (even if in parallel
5330 // by several threads) in monotonically increasing order per each
5331 // thread. This is true of the implementation below which picks
5332 // card ranges (chunks) in monotonically increasing order globally
5333 // and, a-fortiori, in monotonically increasing order per thread
5334 // (the latter order being a subsequence of the former).
5335 // If the work code below is ever reorganized into a more chaotic
5336 // work-partitioning form than the current "sequential tasks"
5337 // paradigm, the use of that persistent state will have to be
5338 // revisited and modified appropriately. See also related
5339 // bug 4756801 work on which should examine this code to make
5340 // sure that the changes there do not run counter to the
5341 // assumptions made here and necessary for correctness and
5342 // efficiency. Note also that this code might yield inefficient
5343 // behaviour in the case of very large objects that span one or
5344 // more work chunks. Such objects would potentially be scanned
5345 // several times redundantly. Work on 4756801 should try and
5346 // address that performance anomaly if at all possible. XXX
5347 MemRegion full_span = _collector->_span;
5348 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5349 CMSMarkStack* rs = &(_collector->_revisitStack); // shared
5350 MarkFromDirtyCardsClosure
5351 greyRescanClosure(_collector, full_span, // entire span of interest
5352 sp, bm, work_q, rs, cl);
5353
5354 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5355 assert(pst->valid(), "Uninitialized use?");
5356 uint nth_task = 0;
5357 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5358 MemRegion span = sp->used_region();
5359 HeapWord* start_addr = span.start();
5360 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5361 alignment);
5362 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5363 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5364 start_addr, "Check alignment");
5365 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5366 chunk_size, "Check alignment");
5367
5368 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5369 // Having claimed the nth_task, compute corresponding mem-region,
5370 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5371 // The alignment restriction ensures that we do not need any
5372 // synchronization with other gang-workers while setting or
5373 // clearing bits in thus chunk of the MUT.
5374 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5375 start_addr + (nth_task+1)*chunk_size);
5376 // The last chunk's end might be way beyond end of the
5377 // used region. In that case pull back appropriately.
5378 if (this_span.end() > end_addr) {
5379 this_span.set_end(end_addr);
5380 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5381 }
5382 // Iterate over the dirty cards covering this chunk, marking them
5383 // precleaned, and setting the corresponding bits in the mod union
5384 // table. Since we have been careful to partition at Card and MUT-word
5385 // boundaries no synchronization is needed between parallel threads.
5386 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5387 &modUnionClosure);
5388
5389 // Having transferred these marks into the modUnionTable,
5390 // rescan the marked objects on the dirty cards in the modUnionTable.
5391 // Even if this is at a synchronous collection, the initial marking
5392 // may have been done during an asynchronous collection so there
5393 // may be dirty bits in the mod-union table.
5394 _collector->_modUnionTable.dirty_range_iterate_clear(
5395 this_span, &greyRescanClosure);
5396 _collector->_modUnionTable.verifyNoOneBitsInRange(
5397 this_span.start(),
5398 this_span.end());
5399 }
5400 pst->all_tasks_completed(); // declare that i am done
5401 }
5402
5403 // . see if we can share work_queues with ParNew? XXX
5404 void
5405 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5406 int* seed) {
5407 OopTaskQueue* work_q = work_queue(i);
5408 NOT_PRODUCT(int num_steals = 0;)
5409 oop obj_to_scan;
5410 CMSBitMap* bm = &(_collector->_markBitMap);
5411
5412 while (true) {
5413 // Completely finish any left over work from (an) earlier round(s)
5414 cl->trim_queue(0);
5415 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5416 (size_t)ParGCDesiredObjsFromOverflowList);
5417 // Now check if there's any work in the overflow list
5418 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5419 // only affects the number of attempts made to get work from the
5420 // overflow list and does not affect the number of workers. Just
5421 // pass ParallelGCThreads so this behavior is unchanged.
5422 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5423 work_q,
5424 ParallelGCThreads)) {
5425 // found something in global overflow list;
5426 // not yet ready to go stealing work from others.
5427 // We'd like to assert(work_q->size() != 0, ...)
5428 // because we just took work from the overflow list,
5429 // but of course we can't since all of that could have
5430 // been already stolen from us.
5431 // "He giveth and He taketh away."
5432 continue;
5433 }
5434 // Verify that we have no work before we resort to stealing
5435 assert(work_q->size() == 0, "Have work, shouldn't steal");
5436 // Try to steal from other queues that have work
5437 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5438 NOT_PRODUCT(num_steals++;)
5439 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5440 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5441 // Do scanning work
5442 obj_to_scan->oop_iterate(cl);
5443 // Loop around, finish this work, and try to steal some more
5444 } else if (terminator()->offer_termination()) {
5445 break; // nirvana from the infinite cycle
5446 }
5447 }
5448 NOT_PRODUCT(
5449 if (PrintCMSStatistics != 0) {
5450 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5451 }
5452 )
5453 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5454 "Else our work is not yet done");
5455 }
5456
5457 // Return a thread-local PLAB recording array, as appropriate.
5458 void* CMSCollector::get_data_recorder(int thr_num) {
5459 if (_survivor_plab_array != NULL &&
5460 (CMSPLABRecordAlways ||
5461 (_collectorState > Marking && _collectorState < FinalMarking))) {
5462 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5463 ChunkArray* ca = &_survivor_plab_array[thr_num];
5464 ca->reset(); // clear it so that fresh data is recorded
5465 return (void*) ca;
5466 } else {
5467 return NULL;
5468 }
5469 }
5470
5471 // Reset all the thread-local PLAB recording arrays
5472 void CMSCollector::reset_survivor_plab_arrays() {
5473 for (uint i = 0; i < ParallelGCThreads; i++) {
5474 _survivor_plab_array[i].reset();
5475 }
5476 }
5477
5478 // Merge the per-thread plab arrays into the global survivor chunk
5479 // array which will provide the partitioning of the survivor space
5480 // for CMS rescan.
5481 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5482 int no_of_gc_threads) {
5483 assert(_survivor_plab_array != NULL, "Error");
5484 assert(_survivor_chunk_array != NULL, "Error");
5485 assert(_collectorState == FinalMarking, "Error");
5486 for (int j = 0; j < no_of_gc_threads; j++) {
5487 _cursor[j] = 0;
5488 }
5489 HeapWord* top = surv->top();
5490 size_t i;
5491 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5492 HeapWord* min_val = top; // Higher than any PLAB address
5493 uint min_tid = 0; // position of min_val this round
5494 for (int j = 0; j < no_of_gc_threads; j++) {
5495 ChunkArray* cur_sca = &_survivor_plab_array[j];
5496 if (_cursor[j] == cur_sca->end()) {
5497 continue;
5498 }
5499 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5500 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5501 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5502 if (cur_val < min_val) {
5503 min_tid = j;
5504 min_val = cur_val;
5505 } else {
5506 assert(cur_val < top, "All recorded addresses should be less");
5507 }
5508 }
5509 // At this point min_val and min_tid are respectively
5510 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5511 // and the thread (j) that witnesses that address.
5512 // We record this address in the _survivor_chunk_array[i]
5513 // and increment _cursor[min_tid] prior to the next round i.
5514 if (min_val == top) {
5515 break;
5516 }
5517 _survivor_chunk_array[i] = min_val;
5518 _cursor[min_tid]++;
5519 }
5520 // We are all done; record the size of the _survivor_chunk_array
5521 _survivor_chunk_index = i; // exclusive: [0, i)
5522 if (PrintCMSStatistics > 0) {
5523 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5524 }
5525 // Verify that we used up all the recorded entries
5526 #ifdef ASSERT
5527 size_t total = 0;
5528 for (int j = 0; j < no_of_gc_threads; j++) {
5529 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5530 total += _cursor[j];
5531 }
5532 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5533 // Check that the merged array is in sorted order
5534 if (total > 0) {
5535 for (size_t i = 0; i < total - 1; i++) {
5536 if (PrintCMSStatistics > 0) {
5537 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5538 i, _survivor_chunk_array[i]);
5539 }
5540 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5541 "Not sorted");
5542 }
5543 }
5544 #endif // ASSERT
5545 }
5546
5547 // Set up the space's par_seq_tasks structure for work claiming
5548 // for parallel rescan of young gen.
5549 // See ParRescanTask where this is currently used.
5550 void
5551 CMSCollector::
5552 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5553 assert(n_threads > 0, "Unexpected n_threads argument");
5554 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5555
5556 // Eden space
5557 {
5558 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5559 assert(!pst->valid(), "Clobbering existing data?");
5560 // Each valid entry in [0, _eden_chunk_index) represents a task.
5561 size_t n_tasks = _eden_chunk_index + 1;
5562 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5563 // Sets the condition for completion of the subtask (how many threads
5564 // need to finish in order to be done).
5565 pst->set_n_threads(n_threads);
5566 pst->set_n_tasks((int)n_tasks);
5567 }
5568
5569 // Merge the survivor plab arrays into _survivor_chunk_array
5570 if (_survivor_plab_array != NULL) {
5571 merge_survivor_plab_arrays(dng->from(), n_threads);
5572 } else {
5573 assert(_survivor_chunk_index == 0, "Error");
5574 }
5575
5576 // To space
5577 {
5578 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5579 assert(!pst->valid(), "Clobbering existing data?");
5580 // Sets the condition for completion of the subtask (how many threads
5581 // need to finish in order to be done).
5582 pst->set_n_threads(n_threads);
5583 pst->set_n_tasks(1);
5584 assert(pst->valid(), "Error");
5585 }
5586
5587 // From space
5588 {
5589 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5590 assert(!pst->valid(), "Clobbering existing data?");
5591 size_t n_tasks = _survivor_chunk_index + 1;
5592 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5593 // Sets the condition for completion of the subtask (how many threads
5594 // need to finish in order to be done).
5595 pst->set_n_threads(n_threads);
5596 pst->set_n_tasks((int)n_tasks);
5597 assert(pst->valid(), "Error");
5598 }
5599 }
5600
5601 // Parallel version of remark
5602 void CMSCollector::do_remark_parallel() {
5603 GenCollectedHeap* gch = GenCollectedHeap::heap();
5604 FlexibleWorkGang* workers = gch->workers();
5605 assert(workers != NULL, "Need parallel worker threads.");
5606 // Choose to use the number of GC workers most recently set
5607 // into "active_workers". If active_workers is not set, set it
5608 // to ParallelGCThreads.
5609 int n_workers = workers->active_workers();
5610 if (n_workers == 0) {
5611 assert(n_workers > 0, "Should have been set during scavenge");
5612 n_workers = ParallelGCThreads;
5613 workers->set_active_workers(n_workers);
5614 }
5615 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5616 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace();
5617
5618 CMSParRemarkTask tsk(this,
5619 cms_space, perm_space,
5620 n_workers, workers, task_queues());
5621
5622 // Set up for parallel process_strong_roots work.
5623 gch->set_par_threads(n_workers);
5624 // We won't be iterating over the cards in the card table updating
5625 // the younger_gen cards, so we shouldn't call the following else
5626 // the verification code as well as subsequent younger_refs_iterate
5627 // code would get confused. XXX
5628 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5629
5630 // The young gen rescan work will not be done as part of
5631 // process_strong_roots (which currently doesn't knw how to
5632 // parallelize such a scan), but rather will be broken up into
5633 // a set of parallel tasks (via the sampling that the [abortable]
5634 // preclean phase did of EdenSpace, plus the [two] tasks of
5635 // scanning the [two] survivor spaces. Further fine-grain
5636 // parallelization of the scanning of the survivor spaces
5637 // themselves, and of precleaning of the younger gen itself
5638 // is deferred to the future.
5639 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5640
5641 // The dirty card rescan work is broken up into a "sequence"
5642 // of parallel tasks (per constituent space) that are dynamically
5643 // claimed by the parallel threads.
5644 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5645 perm_space->initialize_sequential_subtasks_for_rescan(n_workers);
5646
5647 // It turns out that even when we're using 1 thread, doing the work in a
5648 // separate thread causes wide variance in run times. We can't help this
5649 // in the multi-threaded case, but we special-case n=1 here to get
5650 // repeatable measurements of the 1-thread overhead of the parallel code.
5651 if (n_workers > 1) {
5652 // Make refs discovery MT-safe, if it isn't already: it may not
5653 // necessarily be so, since it's possible that we are doing
5654 // ST marking.
5655 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5656 GenCollectedHeap::StrongRootsScope srs(gch);
5657 workers->run_task(&tsk);
5658 } else {
5659 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5660 GenCollectedHeap::StrongRootsScope srs(gch);
5661 tsk.work(0);
5662 }
5663 gch->set_par_threads(0); // 0 ==> non-parallel.
5664 // restore, single-threaded for now, any preserved marks
5665 // as a result of work_q overflow
5666 restore_preserved_marks_if_any();
5667 }
5668
5669 // Non-parallel version of remark
5670 void CMSCollector::do_remark_non_parallel() {
5671 ResourceMark rm;
5672 HandleMark hm;
5673 GenCollectedHeap* gch = GenCollectedHeap::heap();
5674 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5675
5676 MarkRefsIntoAndScanClosure
5677 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
5678 &_markStack, &_revisitStack, this,
5679 false /* should_yield */, false /* not precleaning */);
5680 MarkFromDirtyCardsClosure
5681 markFromDirtyCardsClosure(this, _span,
5682 NULL, // space is set further below
5683 &_markBitMap, &_markStack, &_revisitStack,
5684 &mrias_cl);
5685 {
5686 GCTraceTime t("grey object rescan", PrintGCDetails, false, _gc_timer_cm);
5687 // Iterate over the dirty cards, setting the corresponding bits in the
5688 // mod union table.
5689 {
5690 ModUnionClosure modUnionClosure(&_modUnionTable);
5691 _ct->ct_bs()->dirty_card_iterate(
5692 _cmsGen->used_region(),
5693 &modUnionClosure);
5694 _ct->ct_bs()->dirty_card_iterate(
5695 _permGen->used_region(),
5696 &modUnionClosure);
5697 }
5698 // Having transferred these marks into the modUnionTable, we just need
5699 // to rescan the marked objects on the dirty cards in the modUnionTable.
5700 // The initial marking may have been done during an asynchronous
5701 // collection so there may be dirty bits in the mod-union table.
5702 const int alignment =
5703 CardTableModRefBS::card_size * BitsPerWord;
5704 {
5705 // ... First handle dirty cards in CMS gen
5706 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5707 MemRegion ur = _cmsGen->used_region();
5708 HeapWord* lb = ur.start();
5709 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5710 MemRegion cms_span(lb, ub);
5711 _modUnionTable.dirty_range_iterate_clear(cms_span,
5712 &markFromDirtyCardsClosure);
5713 verify_work_stacks_empty();
5714 if (PrintCMSStatistics != 0) {
5715 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5716 markFromDirtyCardsClosure.num_dirty_cards());
5717 }
5718 }
5719 {
5720 // .. and then repeat for dirty cards in perm gen
5721 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace());
5722 MemRegion ur = _permGen->used_region();
5723 HeapWord* lb = ur.start();
5724 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5725 MemRegion perm_span(lb, ub);
5726 _modUnionTable.dirty_range_iterate_clear(perm_span,
5727 &markFromDirtyCardsClosure);
5728 verify_work_stacks_empty();
5729 if (PrintCMSStatistics != 0) {
5730 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ",
5731 markFromDirtyCardsClosure.num_dirty_cards());
5732 }
5733 }
5734 }
5735 if (VerifyDuringGC &&
5736 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5737 HandleMark hm; // Discard invalid handles created during verification
5738 Universe::verify();
5739 }
5740 {
5741 GCTraceTime t("root rescan", PrintGCDetails, false, _gc_timer_cm);
5742
5743 verify_work_stacks_empty();
5744
5745 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5746 GenCollectedHeap::StrongRootsScope srs(gch);
5747 gch->gen_process_strong_roots(_cmsGen->level(),
5748 true, // younger gens as roots
5749 false, // use the local StrongRootsScope
5750 true, // collecting perm gen
5751 SharedHeap::ScanningOption(roots_scanning_options()),
5752 &mrias_cl,
5753 true, // walk code active on stacks
5754 NULL);
5755 assert(should_unload_classes()
5756 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5757 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5758 }
5759 verify_work_stacks_empty();
5760 // Restore evacuated mark words, if any, used for overflow list links
5761 if (!CMSOverflowEarlyRestoration) {
5762 restore_preserved_marks_if_any();
5763 }
5764 verify_overflow_empty();
5765 }
5766
5767 ////////////////////////////////////////////////////////
5768 // Parallel Reference Processing Task Proxy Class
5769 ////////////////////////////////////////////////////////
5770 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5771 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5772 CMSCollector* _collector;
5773 CMSBitMap* _mark_bit_map;
5774 const MemRegion _span;
5775 ProcessTask& _task;
5776
5777 public:
5778 CMSRefProcTaskProxy(ProcessTask& task,
5779 CMSCollector* collector,
5780 const MemRegion& span,
5781 CMSBitMap* mark_bit_map,
5782 AbstractWorkGang* workers,
5783 OopTaskQueueSet* task_queues):
5784 // XXX Should superclass AGTWOQ also know about AWG since it knows
5785 // about the task_queues used by the AWG? Then it could initialize
5786 // the terminator() object. See 6984287. The set_for_termination()
5787 // below is a temporary band-aid for the regression in 6984287.
5788 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5789 task_queues),
5790 _task(task),
5791 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5792 {
5793 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5794 "Inconsistency in _span");
5795 set_for_termination(workers->active_workers());
5796 }
5797
5798 OopTaskQueueSet* task_queues() { return queues(); }
5799
5800 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5801
5802 void do_work_steal(int i,
5803 CMSParDrainMarkingStackClosure* drain,
5804 CMSParKeepAliveClosure* keep_alive,
5805 int* seed);
5806
5807 virtual void work(uint worker_id);
5808 };
5809
5810 void CMSRefProcTaskProxy::work(uint worker_id) {
5811 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5812 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5813 _mark_bit_map,
5814 &_collector->_revisitStack,
5815 work_queue(worker_id));
5816 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5817 _mark_bit_map,
5818 &_collector->_revisitStack,
5819 work_queue(worker_id));
5820 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5821 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5822 if (_task.marks_oops_alive()) {
5823 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5824 _collector->hash_seed(worker_id));
5825 }
5826 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5827 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5828 }
5829
5830 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5831 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5832 EnqueueTask& _task;
5833
5834 public:
5835 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5836 : AbstractGangTask("Enqueue reference objects in parallel"),
5837 _task(task)
5838 { }
5839
5840 virtual void work(uint worker_id)
5841 {
5842 _task.work(worker_id);
5843 }
5844 };
5845
5846 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5847 MemRegion span, CMSBitMap* bit_map, CMSMarkStack* revisit_stack,
5848 OopTaskQueue* work_queue):
5849 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
5850 _span(span),
5851 _bit_map(bit_map),
5852 _work_queue(work_queue),
5853 _mark_and_push(collector, span, bit_map, revisit_stack, work_queue),
5854 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5855 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5856 { }
5857
5858 // . see if we can share work_queues with ParNew? XXX
5859 void CMSRefProcTaskProxy::do_work_steal(int i,
5860 CMSParDrainMarkingStackClosure* drain,
5861 CMSParKeepAliveClosure* keep_alive,
5862 int* seed) {
5863 OopTaskQueue* work_q = work_queue(i);
5864 NOT_PRODUCT(int num_steals = 0;)
5865 oop obj_to_scan;
5866
5867 while (true) {
5868 // Completely finish any left over work from (an) earlier round(s)
5869 drain->trim_queue(0);
5870 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5871 (size_t)ParGCDesiredObjsFromOverflowList);
5872 // Now check if there's any work in the overflow list
5873 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5874 // only affects the number of attempts made to get work from the
5875 // overflow list and does not affect the number of workers. Just
5876 // pass ParallelGCThreads so this behavior is unchanged.
5877 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5878 work_q,
5879 ParallelGCThreads)) {
5880 // Found something in global overflow list;
5881 // not yet ready to go stealing work from others.
5882 // We'd like to assert(work_q->size() != 0, ...)
5883 // because we just took work from the overflow list,
5884 // but of course we can't, since all of that might have
5885 // been already stolen from us.
5886 continue;
5887 }
5888 // Verify that we have no work before we resort to stealing
5889 assert(work_q->size() == 0, "Have work, shouldn't steal");
5890 // Try to steal from other queues that have work
5891 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5892 NOT_PRODUCT(num_steals++;)
5893 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5894 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5895 // Do scanning work
5896 obj_to_scan->oop_iterate(keep_alive);
5897 // Loop around, finish this work, and try to steal some more
5898 } else if (terminator()->offer_termination()) {
5899 break; // nirvana from the infinite cycle
5900 }
5901 }
5902 NOT_PRODUCT(
5903 if (PrintCMSStatistics != 0) {
5904 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5905 }
5906 )
5907 }
5908
5909 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5910 {
5911 GenCollectedHeap* gch = GenCollectedHeap::heap();
5912 FlexibleWorkGang* workers = gch->workers();
5913 assert(workers != NULL, "Need parallel worker threads.");
5914 CMSRefProcTaskProxy rp_task(task, &_collector,
5915 _collector.ref_processor()->span(),
5916 _collector.markBitMap(),
5917 workers, _collector.task_queues());
5918 workers->run_task(&rp_task);
5919 }
5920
5921 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5922 {
5923
5924 GenCollectedHeap* gch = GenCollectedHeap::heap();
5925 FlexibleWorkGang* workers = gch->workers();
5926 assert(workers != NULL, "Need parallel worker threads.");
5927 CMSRefEnqueueTaskProxy enq_task(task);
5928 workers->run_task(&enq_task);
5929 }
5930
5931 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5932
5933 ResourceMark rm;
5934 HandleMark hm;
5935
5936 ReferenceProcessor* rp = ref_processor();
5937 assert(rp->span().equals(_span), "Spans should be equal");
5938 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5939 // Process weak references.
5940 rp->setup_policy(clear_all_soft_refs);
5941 verify_work_stacks_empty();
5942
5943 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5944 &_markStack, &_revisitStack,
5945 false /* !preclean */);
5946 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5947 _span, &_markBitMap, &_markStack,
5948 &cmsKeepAliveClosure, false /* !preclean */);
5949 {
5950 GCTraceTime t("weak refs processing", PrintGCDetails, false, _gc_timer_cm);
5951
5952 ReferenceProcessorStats stats;
5953 if (rp->processing_is_mt()) {
5954 // Set the degree of MT here. If the discovery is done MT, there
5955 // may have been a different number of threads doing the discovery
5956 // and a different number of discovered lists may have Ref objects.
5957 // That is OK as long as the Reference lists are balanced (see
5958 // balance_all_queues() and balance_queues()).
5959 GenCollectedHeap* gch = GenCollectedHeap::heap();
5960 int active_workers = ParallelGCThreads;
5961 FlexibleWorkGang* workers = gch->workers();
5962 if (workers != NULL) {
5963 active_workers = workers->active_workers();
5964 // The expectation is that active_workers will have already
5965 // been set to a reasonable value. If it has not been set,
5966 // investigate.
5967 assert(active_workers > 0, "Should have been set during scavenge");
5968 }
5969 rp->set_active_mt_degree(active_workers);
5970 CMSRefProcTaskExecutor task_executor(*this);
5971 stats = rp->process_discovered_references(&_is_alive_closure,
5972 &cmsKeepAliveClosure,
5973 &cmsDrainMarkingStackClosure,
5974 &task_executor,
5975 _gc_timer_cm);
5976 } else {
5977 stats = rp->process_discovered_references(&_is_alive_closure,
5978 &cmsKeepAliveClosure,
5979 &cmsDrainMarkingStackClosure,
5980 NULL,
5981 _gc_timer_cm);
5982 }
5983 _gc_tracer_cm->report_gc_reference_stats(stats);
5984
5985 verify_work_stacks_empty();
5986 }
5987
5988 if (should_unload_classes()) {
5989 {
5990 GCTraceTime t("class unloading", PrintGCDetails, false, _gc_timer_cm);
5991
5992 // Follow SystemDictionary roots and unload classes
5993 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5994
5995 // Follow CodeCache roots and unload any methods marked for unloading
5996 CodeCache::do_unloading(&_is_alive_closure,
5997 &cmsKeepAliveClosure,
5998 purged_class);
5999
6000 cmsDrainMarkingStackClosure.do_void();
6001 verify_work_stacks_empty();
6002
6003 // Update subklass/sibling/implementor links in KlassKlass descendants
6004 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty");
6005 oop k;
6006 while ((k = _revisitStack.pop()) != NULL) {
6007 ((Klass*)(oopDesc*)k)->follow_weak_klass_links(
6008 &_is_alive_closure,
6009 &cmsKeepAliveClosure);
6010 }
6011 assert(!ClassUnloading ||
6012 (_markStack.isEmpty() && overflow_list_is_empty()),
6013 "Should not have found new reachable objects");
6014 assert(_revisitStack.isEmpty(), "revisit stack should have been drained");
6015 cmsDrainMarkingStackClosure.do_void();
6016 verify_work_stacks_empty();
6017 }
6018
6019 {
6020 GCTraceTime t("scrub symbol table", PrintGCDetails, false, _gc_timer_cm);
6021 // Clean up unreferenced symbols in symbol table.
6022 SymbolTable::unlink();
6023 }
6024 }
6025
6026 if (should_unload_classes() || !JavaObjectsInPerm) {
6027 GCTraceTime t("scrub string table", PrintGCDetails, false, _gc_timer_cm);
6028 // Now clean up stale oops in StringTable
6029 StringTable::unlink(&_is_alive_closure);
6030 }
6031
6032 verify_work_stacks_empty();
6033 // Restore any preserved marks as a result of mark stack or
6034 // work queue overflow
6035 restore_preserved_marks_if_any(); // done single-threaded for now
6036
6037 rp->set_enqueuing_is_done(true);
6038 if (rp->processing_is_mt()) {
6039 rp->balance_all_queues();
6040 CMSRefProcTaskExecutor task_executor(*this);
6041 rp->enqueue_discovered_references(&task_executor);
6042 } else {
6043 rp->enqueue_discovered_references(NULL);
6044 }
6045 rp->verify_no_references_recorded();
6046 assert(!rp->discovery_enabled(), "should have been disabled");
6047 }
6048
6049 #ifndef PRODUCT
6050 void CMSCollector::check_correct_thread_executing() {
6051 Thread* t = Thread::current();
6052 // Only the VM thread or the CMS thread should be here.
6053 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6054 "Unexpected thread type");
6055 // If this is the vm thread, the foreground process
6056 // should not be waiting. Note that _foregroundGCIsActive is
6057 // true while the foreground collector is waiting.
6058 if (_foregroundGCShouldWait) {
6059 // We cannot be the VM thread
6060 assert(t->is_ConcurrentGC_thread(),
6061 "Should be CMS thread");
6062 } else {
6063 // We can be the CMS thread only if we are in a stop-world
6064 // phase of CMS collection.
6065 if (t->is_ConcurrentGC_thread()) {
6066 assert(_collectorState == InitialMarking ||
6067 _collectorState == FinalMarking,
6068 "Should be a stop-world phase");
6069 // The CMS thread should be holding the CMS_token.
6070 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6071 "Potential interference with concurrently "
6072 "executing VM thread");
6073 }
6074 }
6075 }
6076 #endif
6077
6078 void CMSCollector::sweep(bool asynch) {
6079 assert(_collectorState == Sweeping, "just checking");
6080 check_correct_thread_executing();
6081 verify_work_stacks_empty();
6082 verify_overflow_empty();
6083 increment_sweep_count();
6084 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6085
6086 _inter_sweep_timer.stop();
6087 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6088 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6089
6090 // PermGen verification support: If perm gen sweeping is disabled in
6091 // this cycle, we preserve the perm gen object "deadness" information
6092 // in the perm_gen_verify_bit_map. In order to do that we traverse
6093 // all blocks in perm gen and mark all dead objects.
6094 if (verifying() && !should_unload_classes()) {
6095 assert(perm_gen_verify_bit_map()->sizeInBits() != 0,
6096 "Should have already been allocated");
6097 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(),
6098 markBitMap(), perm_gen_verify_bit_map());
6099 if (asynch) {
6100 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6101 bitMapLock());
6102 _permGen->cmsSpace()->blk_iterate(&mdo);
6103 } else {
6104 // In the case of synchronous sweep, we already have
6105 // the requisite locks/tokens.
6106 _permGen->cmsSpace()->blk_iterate(&mdo);
6107 }
6108 }
6109
6110 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6111 _intra_sweep_timer.reset();
6112 _intra_sweep_timer.start();
6113 if (asynch) {
6114 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6115 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6116 // First sweep the old gen then the perm gen
6117 {
6118 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6119 bitMapLock());
6120 sweepWork(_cmsGen, asynch);
6121 }
6122
6123 // Now repeat for perm gen
6124 if (should_unload_classes()) {
6125 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(),
6126 bitMapLock());
6127 sweepWork(_permGen, asynch);
6128 }
6129
6130 // Update Universe::_heap_*_at_gc figures.
6131 // We need all the free list locks to make the abstract state
6132 // transition from Sweeping to Resetting. See detailed note
6133 // further below.
6134 {
6135 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6136 _permGen->freelistLock());
6137 // Update heap occupancy information which is used as
6138 // input to soft ref clearing policy at the next gc.
6139 Universe::update_heap_info_at_gc();
6140 _collectorState = Resizing;
6141 }
6142 } else {
6143 // already have needed locks
6144 sweepWork(_cmsGen, asynch);
6145
6146 if (should_unload_classes()) {
6147 sweepWork(_permGen, asynch);
6148 }
6149 // Update heap occupancy information which is used as
6150 // input to soft ref clearing policy at the next gc.
6151 Universe::update_heap_info_at_gc();
6152 _collectorState = Resizing;
6153 }
6154 verify_work_stacks_empty();
6155 verify_overflow_empty();
6156
6157 _intra_sweep_timer.stop();
6158 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6159
6160 _inter_sweep_timer.reset();
6161 _inter_sweep_timer.start();
6162
6163 // We need to use a monotonically non-deccreasing time in ms
6164 // or we will see time-warp warnings and os::javaTimeMillis()
6165 // does not guarantee monotonicity.
6166 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6167 update_time_of_last_gc(now);
6168
6169 // NOTE on abstract state transitions:
6170 // Mutators allocate-live and/or mark the mod-union table dirty
6171 // based on the state of the collection. The former is done in
6172 // the interval [Marking, Sweeping] and the latter in the interval
6173 // [Marking, Sweeping). Thus the transitions into the Marking state
6174 // and out of the Sweeping state must be synchronously visible
6175 // globally to the mutators.
6176 // The transition into the Marking state happens with the world
6177 // stopped so the mutators will globally see it. Sweeping is
6178 // done asynchronously by the background collector so the transition
6179 // from the Sweeping state to the Resizing state must be done
6180 // under the freelistLock (as is the check for whether to
6181 // allocate-live and whether to dirty the mod-union table).
6182 assert(_collectorState == Resizing, "Change of collector state to"
6183 " Resizing must be done under the freelistLocks (plural)");
6184
6185 // Now that sweeping has been completed, we clear
6186 // the incremental_collection_failed flag,
6187 // thus inviting a younger gen collection to promote into
6188 // this generation. If such a promotion may still fail,
6189 // the flag will be set again when a young collection is
6190 // attempted.
6191 GenCollectedHeap* gch = GenCollectedHeap::heap();
6192 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6193 gch->update_full_collections_completed(_collection_count_start);
6194 }
6195
6196 // FIX ME!!! Looks like this belongs in CFLSpace, with
6197 // CMSGen merely delegating to it.
6198 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6199 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6200 HeapWord* minAddr = _cmsSpace->bottom();
6201 HeapWord* largestAddr =
6202 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6203 if (largestAddr == NULL) {
6204 // The dictionary appears to be empty. In this case
6205 // try to coalesce at the end of the heap.
6206 largestAddr = _cmsSpace->end();
6207 }
6208 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6209 size_t nearLargestOffset =
6210 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6211 if (PrintFLSStatistics != 0) {
6212 gclog_or_tty->print_cr(
6213 "CMS: Large Block: " PTR_FORMAT ";"
6214 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6215 largestAddr,
6216 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6217 }
6218 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6219 }
6220
6221 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6222 return addr >= _cmsSpace->nearLargestChunk();
6223 }
6224
6225 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6226 return _cmsSpace->find_chunk_at_end();
6227 }
6228
6229 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6230 bool full) {
6231 // The next lower level has been collected. Gather any statistics
6232 // that are of interest at this point.
6233 if (!full && (current_level + 1) == level()) {
6234 // Gather statistics on the young generation collection.
6235 collector()->stats().record_gc0_end(used());
6236 }
6237 }
6238
6239 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6240 GenCollectedHeap* gch = GenCollectedHeap::heap();
6241 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6242 "Wrong type of heap");
6243 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6244 gch->gen_policy()->size_policy();
6245 assert(sp->is_gc_cms_adaptive_size_policy(),
6246 "Wrong type of size policy");
6247 return sp;
6248 }
6249
6250 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6251 if (PrintGCDetails && Verbose) {
6252 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6253 }
6254 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6255 _debug_collection_type =
6256 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6257 if (PrintGCDetails && Verbose) {
6258 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6259 }
6260 }
6261
6262 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6263 bool asynch) {
6264 // We iterate over the space(s) underlying this generation,
6265 // checking the mark bit map to see if the bits corresponding
6266 // to specific blocks are marked or not. Blocks that are
6267 // marked are live and are not swept up. All remaining blocks
6268 // are swept up, with coalescing on-the-fly as we sweep up
6269 // contiguous free and/or garbage blocks:
6270 // We need to ensure that the sweeper synchronizes with allocators
6271 // and stop-the-world collectors. In particular, the following
6272 // locks are used:
6273 // . CMS token: if this is held, a stop the world collection cannot occur
6274 // . freelistLock: if this is held no allocation can occur from this
6275 // generation by another thread
6276 // . bitMapLock: if this is held, no other thread can access or update
6277 //
6278
6279 // Note that we need to hold the freelistLock if we use
6280 // block iterate below; else the iterator might go awry if
6281 // a mutator (or promotion) causes block contents to change
6282 // (for instance if the allocator divvies up a block).
6283 // If we hold the free list lock, for all practical purposes
6284 // young generation GC's can't occur (they'll usually need to
6285 // promote), so we might as well prevent all young generation
6286 // GC's while we do a sweeping step. For the same reason, we might
6287 // as well take the bit map lock for the entire duration
6288
6289 // check that we hold the requisite locks
6290 assert(have_cms_token(), "Should hold cms token");
6291 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6292 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6293 "Should possess CMS token to sweep");
6294 assert_lock_strong(gen->freelistLock());
6295 assert_lock_strong(bitMapLock());
6296
6297 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6298 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6299 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6300 _inter_sweep_estimate.padded_average(),
6301 _intra_sweep_estimate.padded_average());
6302 gen->setNearLargestChunk();
6303
6304 {
6305 SweepClosure sweepClosure(this, gen, &_markBitMap,
6306 CMSYield && asynch);
6307 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6308 // We need to free-up/coalesce garbage/blocks from a
6309 // co-terminal free run. This is done in the SweepClosure
6310 // destructor; so, do not remove this scope, else the
6311 // end-of-sweep-census below will be off by a little bit.
6312 }
6313 gen->cmsSpace()->sweep_completed();
6314 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6315 if (should_unload_classes()) { // unloaded classes this cycle,
6316 _concurrent_cycles_since_last_unload = 0; // ... reset count
6317 } else { // did not unload classes,
6318 _concurrent_cycles_since_last_unload++; // ... increment count
6319 }
6320 }
6321
6322 // Reset CMS data structures (for now just the marking bit map)
6323 // preparatory for the next cycle.
6324 void CMSCollector::reset(bool asynch) {
6325 GenCollectedHeap* gch = GenCollectedHeap::heap();
6326 CMSAdaptiveSizePolicy* sp = size_policy();
6327 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6328 if (asynch) {
6329 CMSTokenSyncWithLocks ts(true, bitMapLock());
6330
6331 // If the state is not "Resetting", the foreground thread
6332 // has done a collection and the resetting.
6333 if (_collectorState != Resetting) {
6334 assert(_collectorState == Idling, "The state should only change"
6335 " because the foreground collector has finished the collection");
6336 return;
6337 }
6338
6339 // Clear the mark bitmap (no grey objects to start with)
6340 // for the next cycle.
6341 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6342 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6343
6344 HeapWord* curAddr = _markBitMap.startWord();
6345 while (curAddr < _markBitMap.endWord()) {
6346 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6347 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6348 _markBitMap.clear_large_range(chunk);
6349 if (ConcurrentMarkSweepThread::should_yield() &&
6350 !foregroundGCIsActive() &&
6351 CMSYield) {
6352 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6353 "CMS thread should hold CMS token");
6354 assert_lock_strong(bitMapLock());
6355 bitMapLock()->unlock();
6356 ConcurrentMarkSweepThread::desynchronize(true);
6357 ConcurrentMarkSweepThread::acknowledge_yield_request();
6358 stopTimer();
6359 if (PrintCMSStatistics != 0) {
6360 incrementYields();
6361 }
6362 icms_wait();
6363
6364 // See the comment in coordinator_yield()
6365 for (unsigned i = 0; i < CMSYieldSleepCount &&
6366 ConcurrentMarkSweepThread::should_yield() &&
6367 !CMSCollector::foregroundGCIsActive(); ++i) {
6368 os::sleep(Thread::current(), 1, false);
6369 ConcurrentMarkSweepThread::acknowledge_yield_request();
6370 }
6371
6372 ConcurrentMarkSweepThread::synchronize(true);
6373 bitMapLock()->lock_without_safepoint_check();
6374 startTimer();
6375 }
6376 curAddr = chunk.end();
6377 }
6378 // A successful mostly concurrent collection has been done.
6379 // Because only the full (i.e., concurrent mode failure) collections
6380 // are being measured for gc overhead limits, clean the "near" flag
6381 // and count.
6382 sp->reset_gc_overhead_limit_count();
6383 _collectorState = Idling;
6384 } else {
6385 // already have the lock
6386 assert(_collectorState == Resetting, "just checking");
6387 assert_lock_strong(bitMapLock());
6388 _markBitMap.clear_all();
6389 _collectorState = Idling;
6390 }
6391
6392 // Stop incremental mode after a cycle completes, so that any future cycles
6393 // are triggered by allocation.
6394 stop_icms();
6395
6396 NOT_PRODUCT(
6397 if (RotateCMSCollectionTypes) {
6398 _cmsGen->rotate_debug_collection_type();
6399 }
6400 )
6401
6402 register_gc_end();
6403 }
6404
6405 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6406 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6407 GCTraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, NULL);
6408 TraceCollectorStats tcs(counters());
6409
6410 switch (op) {
6411 case CMS_op_checkpointRootsInitial: {
6412 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6413 checkpointRootsInitial(true); // asynch
6414 if (PrintGC) {
6415 _cmsGen->printOccupancy("initial-mark");
6416 }
6417 break;
6418 }
6419 case CMS_op_checkpointRootsFinal: {
6420 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6421 checkpointRootsFinal(true, // asynch
6422 false, // !clear_all_soft_refs
6423 false); // !init_mark_was_synchronous
6424 if (PrintGC) {
6425 _cmsGen->printOccupancy("remark");
6426 }
6427 break;
6428 }
6429 default:
6430 fatal("No such CMS_op");
6431 }
6432 }
6433
6434 #ifndef PRODUCT
6435 size_t const CMSCollector::skip_header_HeapWords() {
6436 return FreeChunk::header_size();
6437 }
6438
6439 // Try and collect here conditions that should hold when
6440 // CMS thread is exiting. The idea is that the foreground GC
6441 // thread should not be blocked if it wants to terminate
6442 // the CMS thread and yet continue to run the VM for a while
6443 // after that.
6444 void CMSCollector::verify_ok_to_terminate() const {
6445 assert(Thread::current()->is_ConcurrentGC_thread(),
6446 "should be called by CMS thread");
6447 assert(!_foregroundGCShouldWait, "should be false");
6448 // We could check here that all the various low-level locks
6449 // are not held by the CMS thread, but that is overkill; see
6450 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6451 // is checked.
6452 }
6453 #endif
6454
6455 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6456 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6457 "missing Printezis mark?");
6458 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6459 size_t size = pointer_delta(nextOneAddr + 1, addr);
6460 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6461 "alignment problem");
6462 assert(size >= 3, "Necessary for Printezis marks to work");
6463 return size;
6464 }
6465
6466 // A variant of the above (block_size_using_printezis_bits()) except
6467 // that we return 0 if the P-bits are not yet set.
6468 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6469 if (_markBitMap.isMarked(addr + 1)) {
6470 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6471 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6472 size_t size = pointer_delta(nextOneAddr + 1, addr);
6473 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6474 "alignment problem");
6475 assert(size >= 3, "Necessary for Printezis marks to work");
6476 return size;
6477 }
6478 return 0;
6479 }
6480
6481 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6482 size_t sz = 0;
6483 oop p = (oop)addr;
6484 if (p->klass_or_null() != NULL && p->is_parsable()) {
6485 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6486 } else {
6487 sz = block_size_using_printezis_bits(addr);
6488 }
6489 assert(sz > 0, "size must be nonzero");
6490 HeapWord* next_block = addr + sz;
6491 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6492 CardTableModRefBS::card_size);
6493 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6494 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6495 "must be different cards");
6496 return next_card;
6497 }
6498
6499
6500 // CMS Bit Map Wrapper /////////////////////////////////////////
6501
6502 // Construct a CMS bit map infrastructure, but don't create the
6503 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6504 // further below.
6505 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6506 _bm(),
6507 _shifter(shifter),
6508 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6509 {
6510 _bmStartWord = 0;
6511 _bmWordSize = 0;
6512 }
6513
6514 bool CMSBitMap::allocate(MemRegion mr) {
6515 _bmStartWord = mr.start();
6516 _bmWordSize = mr.word_size();
6517 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6518 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6519 if (!brs.is_reserved()) {
6520 warning("CMS bit map allocation failure");
6521 return false;
6522 }
6523 // For now we'll just commit all of the bit map up fromt.
6524 // Later on we'll try to be more parsimonious with swap.
6525 if (!_virtual_space.initialize(brs, brs.size())) {
6526 warning("CMS bit map backing store failure");
6527 return false;
6528 }
6529 assert(_virtual_space.committed_size() == brs.size(),
6530 "didn't reserve backing store for all of CMS bit map?");
6531 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6532 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6533 _bmWordSize, "inconsistency in bit map sizing");
6534 _bm.set_size(_bmWordSize >> _shifter);
6535
6536 // bm.clear(); // can we rely on getting zero'd memory? verify below
6537 assert(isAllClear(),
6538 "Expected zero'd memory from ReservedSpace constructor");
6539 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6540 "consistency check");
6541 return true;
6542 }
6543
6544 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6545 HeapWord *next_addr, *end_addr, *last_addr;
6546 assert_locked();
6547 assert(covers(mr), "out-of-range error");
6548 // XXX assert that start and end are appropriately aligned
6549 for (next_addr = mr.start(), end_addr = mr.end();
6550 next_addr < end_addr; next_addr = last_addr) {
6551 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6552 last_addr = dirty_region.end();
6553 if (!dirty_region.is_empty()) {
6554 cl->do_MemRegion(dirty_region);
6555 } else {
6556 assert(last_addr == end_addr, "program logic");
6557 return;
6558 }
6559 }
6560 }
6561
6562 #ifndef PRODUCT
6563 void CMSBitMap::assert_locked() const {
6564 CMSLockVerifier::assert_locked(lock());
6565 }
6566
6567 bool CMSBitMap::covers(MemRegion mr) const {
6568 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6569 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6570 "size inconsistency");
6571 return (mr.start() >= _bmStartWord) &&
6572 (mr.end() <= endWord());
6573 }
6574
6575 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6576 return (start >= _bmStartWord && (start + size) <= endWord());
6577 }
6578
6579 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6580 // verify that there are no 1 bits in the interval [left, right)
6581 FalseBitMapClosure falseBitMapClosure;
6582 iterate(&falseBitMapClosure, left, right);
6583 }
6584
6585 void CMSBitMap::region_invariant(MemRegion mr)
6586 {
6587 assert_locked();
6588 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6589 assert(!mr.is_empty(), "unexpected empty region");
6590 assert(covers(mr), "mr should be covered by bit map");
6591 // convert address range into offset range
6592 size_t start_ofs = heapWordToOffset(mr.start());
6593 // Make sure that end() is appropriately aligned
6594 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6595 (1 << (_shifter+LogHeapWordSize))),
6596 "Misaligned mr.end()");
6597 size_t end_ofs = heapWordToOffset(mr.end());
6598 assert(end_ofs > start_ofs, "Should mark at least one bit");
6599 }
6600
6601 #endif
6602
6603 bool CMSMarkStack::allocate(size_t size) {
6604 // allocate a stack of the requisite depth
6605 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6606 size * sizeof(oop)));
6607 if (!rs.is_reserved()) {
6608 warning("CMSMarkStack allocation failure");
6609 return false;
6610 }
6611 if (!_virtual_space.initialize(rs, rs.size())) {
6612 warning("CMSMarkStack backing store failure");
6613 return false;
6614 }
6615 assert(_virtual_space.committed_size() == rs.size(),
6616 "didn't reserve backing store for all of CMS stack?");
6617 _base = (oop*)(_virtual_space.low());
6618 _index = 0;
6619 _capacity = size;
6620 NOT_PRODUCT(_max_depth = 0);
6621 return true;
6622 }
6623
6624 // XXX FIX ME !!! In the MT case we come in here holding a
6625 // leaf lock. For printing we need to take a further lock
6626 // which has lower rank. We need to recallibrate the two
6627 // lock-ranks involved in order to be able to rpint the
6628 // messages below. (Or defer the printing to the caller.
6629 // For now we take the expedient path of just disabling the
6630 // messages for the problematic case.)
6631 void CMSMarkStack::expand() {
6632 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6633 if (_capacity == MarkStackSizeMax) {
6634 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6635 // We print a warning message only once per CMS cycle.
6636 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6637 }
6638 return;
6639 }
6640 // Double capacity if possible
6641 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6642 // Do not give up existing stack until we have managed to
6643 // get the double capacity that we desired.
6644 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6645 new_capacity * sizeof(oop)));
6646 if (rs.is_reserved()) {
6647 // Release the backing store associated with old stack
6648 _virtual_space.release();
6649 // Reinitialize virtual space for new stack
6650 if (!_virtual_space.initialize(rs, rs.size())) {
6651 fatal("Not enough swap for expanded marking stack");
6652 }
6653 _base = (oop*)(_virtual_space.low());
6654 _index = 0;
6655 _capacity = new_capacity;
6656 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6657 // Failed to double capacity, continue;
6658 // we print a detail message only once per CMS cycle.
6659 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6660 SIZE_FORMAT"K",
6661 _capacity / K, new_capacity / K);
6662 }
6663 }
6664
6665
6666 // Closures
6667 // XXX: there seems to be a lot of code duplication here;
6668 // should refactor and consolidate common code.
6669
6670 // This closure is used to mark refs into the CMS generation in
6671 // the CMS bit map. Called at the first checkpoint. This closure
6672 // assumes that we do not need to re-mark dirty cards; if the CMS
6673 // generation on which this is used is not an oldest (modulo perm gen)
6674 // generation then this will lose younger_gen cards!
6675
6676 MarkRefsIntoClosure::MarkRefsIntoClosure(
6677 MemRegion span, CMSBitMap* bitMap):
6678 _span(span),
6679 _bitMap(bitMap)
6680 {
6681 assert(_ref_processor == NULL, "deliberately left NULL");
6682 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6683 }
6684
6685 void MarkRefsIntoClosure::do_oop(oop obj) {
6686 // if p points into _span, then mark corresponding bit in _markBitMap
6687 assert(obj->is_oop(), "expected an oop");
6688 HeapWord* addr = (HeapWord*)obj;
6689 if (_span.contains(addr)) {
6690 // this should be made more efficient
6691 _bitMap->mark(addr);
6692 }
6693 }
6694
6695 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6696 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6697
6698 // A variant of the above, used for CMS marking verification.
6699 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6700 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6701 _span(span),
6702 _verification_bm(verification_bm),
6703 _cms_bm(cms_bm)
6704 {
6705 assert(_ref_processor == NULL, "deliberately left NULL");
6706 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6707 }
6708
6709 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6710 // if p points into _span, then mark corresponding bit in _markBitMap
6711 assert(obj->is_oop(), "expected an oop");
6712 HeapWord* addr = (HeapWord*)obj;
6713 if (_span.contains(addr)) {
6714 _verification_bm->mark(addr);
6715 if (!_cms_bm->isMarked(addr)) {
6716 oop(addr)->print();
6717 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6718 fatal("... aborting");
6719 }
6720 }
6721 }
6722
6723 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6724 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6725
6726 //////////////////////////////////////////////////
6727 // MarkRefsIntoAndScanClosure
6728 //////////////////////////////////////////////////
6729
6730 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6731 ReferenceProcessor* rp,
6732 CMSBitMap* bit_map,
6733 CMSBitMap* mod_union_table,
6734 CMSMarkStack* mark_stack,
6735 CMSMarkStack* revisit_stack,
6736 CMSCollector* collector,
6737 bool should_yield,
6738 bool concurrent_precleaning):
6739 _collector(collector),
6740 _span(span),
6741 _bit_map(bit_map),
6742 _mark_stack(mark_stack),
6743 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6744 mark_stack, revisit_stack, concurrent_precleaning),
6745 _yield(should_yield),
6746 _concurrent_precleaning(concurrent_precleaning),
6747 _freelistLock(NULL)
6748 {
6749 _ref_processor = rp;
6750 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6751 }
6752
6753 // This closure is used to mark refs into the CMS generation at the
6754 // second (final) checkpoint, and to scan and transitively follow
6755 // the unmarked oops. It is also used during the concurrent precleaning
6756 // phase while scanning objects on dirty cards in the CMS generation.
6757 // The marks are made in the marking bit map and the marking stack is
6758 // used for keeping the (newly) grey objects during the scan.
6759 // The parallel version (Par_...) appears further below.
6760 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6761 if (obj != NULL) {
6762 assert(obj->is_oop(), "expected an oop");
6763 HeapWord* addr = (HeapWord*)obj;
6764 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6765 assert(_collector->overflow_list_is_empty(),
6766 "overflow list should be empty");
6767 if (_span.contains(addr) &&
6768 !_bit_map->isMarked(addr)) {
6769 // mark bit map (object is now grey)
6770 _bit_map->mark(addr);
6771 // push on marking stack (stack should be empty), and drain the
6772 // stack by applying this closure to the oops in the oops popped
6773 // from the stack (i.e. blacken the grey objects)
6774 bool res = _mark_stack->push(obj);
6775 assert(res, "Should have space to push on empty stack");
6776 do {
6777 oop new_oop = _mark_stack->pop();
6778 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6779 assert(new_oop->is_parsable(), "Found unparsable oop");
6780 assert(_bit_map->isMarked((HeapWord*)new_oop),
6781 "only grey objects on this stack");
6782 // iterate over the oops in this oop, marking and pushing
6783 // the ones in CMS heap (i.e. in _span).
6784 new_oop->oop_iterate(&_pushAndMarkClosure);
6785 // check if it's time to yield
6786 do_yield_check();
6787 } while (!_mark_stack->isEmpty() ||
6788 (!_concurrent_precleaning && take_from_overflow_list()));
6789 // if marking stack is empty, and we are not doing this
6790 // during precleaning, then check the overflow list
6791 }
6792 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6793 assert(_collector->overflow_list_is_empty(),
6794 "overflow list was drained above");
6795 // We could restore evacuated mark words, if any, used for
6796 // overflow list links here because the overflow list is
6797 // provably empty here. That would reduce the maximum
6798 // size requirements for preserved_{oop,mark}_stack.
6799 // But we'll just postpone it until we are all done
6800 // so we can just stream through.
6801 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6802 _collector->restore_preserved_marks_if_any();
6803 assert(_collector->no_preserved_marks(), "No preserved marks");
6804 }
6805 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6806 "All preserved marks should have been restored above");
6807 }
6808 }
6809
6810 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6811 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6812
6813 void MarkRefsIntoAndScanClosure::do_yield_work() {
6814 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6815 "CMS thread should hold CMS token");
6816 assert_lock_strong(_freelistLock);
6817 assert_lock_strong(_bit_map->lock());
6818 // relinquish the free_list_lock and bitMaplock()
6819 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6820 _bit_map->lock()->unlock();
6821 _freelistLock->unlock();
6822 ConcurrentMarkSweepThread::desynchronize(true);
6823 ConcurrentMarkSweepThread::acknowledge_yield_request();
6824 _collector->stopTimer();
6825 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6826 if (PrintCMSStatistics != 0) {
6827 _collector->incrementYields();
6828 }
6829 _collector->icms_wait();
6830
6831 // See the comment in coordinator_yield()
6832 for (unsigned i = 0;
6833 i < CMSYieldSleepCount &&
6834 ConcurrentMarkSweepThread::should_yield() &&
6835 !CMSCollector::foregroundGCIsActive();
6836 ++i) {
6837 os::sleep(Thread::current(), 1, false);
6838 ConcurrentMarkSweepThread::acknowledge_yield_request();
6839 }
6840
6841 ConcurrentMarkSweepThread::synchronize(true);
6842 _freelistLock->lock_without_safepoint_check();
6843 _bit_map->lock()->lock_without_safepoint_check();
6844 _collector->startTimer();
6845 }
6846
6847 ///////////////////////////////////////////////////////////
6848 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6849 // MarkRefsIntoAndScanClosure
6850 ///////////////////////////////////////////////////////////
6851 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6852 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6853 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack):
6854 _span(span),
6855 _bit_map(bit_map),
6856 _work_queue(work_queue),
6857 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6858 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6859 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue,
6860 revisit_stack)
6861 {
6862 _ref_processor = rp;
6863 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6864 }
6865
6866 // This closure is used to mark refs into the CMS generation at the
6867 // second (final) checkpoint, and to scan and transitively follow
6868 // the unmarked oops. The marks are made in the marking bit map and
6869 // the work_queue is used for keeping the (newly) grey objects during
6870 // the scan phase whence they are also available for stealing by parallel
6871 // threads. Since the marking bit map is shared, updates are
6872 // synchronized (via CAS).
6873 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6874 if (obj != NULL) {
6875 // Ignore mark word because this could be an already marked oop
6876 // that may be chained at the end of the overflow list.
6877 assert(obj->is_oop(true), "expected an oop");
6878 HeapWord* addr = (HeapWord*)obj;
6879 if (_span.contains(addr) &&
6880 !_bit_map->isMarked(addr)) {
6881 // mark bit map (object will become grey):
6882 // It is possible for several threads to be
6883 // trying to "claim" this object concurrently;
6884 // the unique thread that succeeds in marking the
6885 // object first will do the subsequent push on
6886 // to the work queue (or overflow list).
6887 if (_bit_map->par_mark(addr)) {
6888 // push on work_queue (which may not be empty), and trim the
6889 // queue to an appropriate length by applying this closure to
6890 // the oops in the oops popped from the stack (i.e. blacken the
6891 // grey objects)
6892 bool res = _work_queue->push(obj);
6893 assert(res, "Low water mark should be less than capacity?");
6894 trim_queue(_low_water_mark);
6895 } // Else, another thread claimed the object
6896 }
6897 }
6898 }
6899
6900 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6901 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6902
6903 // This closure is used to rescan the marked objects on the dirty cards
6904 // in the mod union table and the card table proper.
6905 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6906 oop p, MemRegion mr) {
6907
6908 size_t size = 0;
6909 HeapWord* addr = (HeapWord*)p;
6910 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6911 assert(_span.contains(addr), "we are scanning the CMS generation");
6912 // check if it's time to yield
6913 if (do_yield_check()) {
6914 // We yielded for some foreground stop-world work,
6915 // and we have been asked to abort this ongoing preclean cycle.
6916 return 0;
6917 }
6918 if (_bitMap->isMarked(addr)) {
6919 // it's marked; is it potentially uninitialized?
6920 if (p->klass_or_null() != NULL) {
6921 // If is_conc_safe is false, the object may be undergoing
6922 // change by the VM outside a safepoint. Don't try to
6923 // scan it, but rather leave it for the remark phase.
6924 if (CMSPermGenPrecleaningEnabled &&
6925 (!p->is_conc_safe() || !p->is_parsable())) {
6926 // Signal precleaning to redirty the card since
6927 // the klass pointer is already installed.
6928 assert(size == 0, "Initial value");
6929 } else {
6930 assert(p->is_parsable(), "must be parsable.");
6931 // an initialized object; ignore mark word in verification below
6932 // since we are running concurrent with mutators
6933 assert(p->is_oop(true), "should be an oop");
6934 if (p->is_objArray()) {
6935 // objArrays are precisely marked; restrict scanning
6936 // to dirty cards only.
6937 size = CompactibleFreeListSpace::adjustObjectSize(
6938 p->oop_iterate(_scanningClosure, mr));
6939 } else {
6940 // A non-array may have been imprecisely marked; we need
6941 // to scan object in its entirety.
6942 size = CompactibleFreeListSpace::adjustObjectSize(
6943 p->oop_iterate(_scanningClosure));
6944 }
6945 #ifdef DEBUG
6946 size_t direct_size =
6947 CompactibleFreeListSpace::adjustObjectSize(p->size());
6948 assert(size == direct_size, "Inconsistency in size");
6949 assert(size >= 3, "Necessary for Printezis marks to work");
6950 if (!_bitMap->isMarked(addr+1)) {
6951 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6952 } else {
6953 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6954 assert(_bitMap->isMarked(addr+size-1),
6955 "inconsistent Printezis mark");
6956 }
6957 #endif // DEBUG
6958 }
6959 } else {
6960 // an unitialized object
6961 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6962 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6963 size = pointer_delta(nextOneAddr + 1, addr);
6964 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6965 "alignment problem");
6966 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6967 // will dirty the card when the klass pointer is installed in the
6968 // object (signalling the completion of initialization).
6969 }
6970 } else {
6971 // Either a not yet marked object or an uninitialized object
6972 if (p->klass_or_null() == NULL || !p->is_parsable()) {
6973 // An uninitialized object, skip to the next card, since
6974 // we may not be able to read its P-bits yet.
6975 assert(size == 0, "Initial value");
6976 } else {
6977 // An object not (yet) reached by marking: we merely need to
6978 // compute its size so as to go look at the next block.
6979 assert(p->is_oop(true), "should be an oop");
6980 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6981 }
6982 }
6983 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6984 return size;
6985 }
6986
6987 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6988 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6989 "CMS thread should hold CMS token");
6990 assert_lock_strong(_freelistLock);
6991 assert_lock_strong(_bitMap->lock());
6992 DEBUG_ONLY(RememberKlassesChecker mux(false);)
6993 // relinquish the free_list_lock and bitMaplock()
6994 _bitMap->lock()->unlock();
6995 _freelistLock->unlock();
6996 ConcurrentMarkSweepThread::desynchronize(true);
6997 ConcurrentMarkSweepThread::acknowledge_yield_request();
6998 _collector->stopTimer();
6999 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7000 if (PrintCMSStatistics != 0) {
7001 _collector->incrementYields();
7002 }
7003 _collector->icms_wait();
7004
7005 // See the comment in coordinator_yield()
7006 for (unsigned i = 0; i < CMSYieldSleepCount &&
7007 ConcurrentMarkSweepThread::should_yield() &&
7008 !CMSCollector::foregroundGCIsActive(); ++i) {
7009 os::sleep(Thread::current(), 1, false);
7010 ConcurrentMarkSweepThread::acknowledge_yield_request();
7011 }
7012
7013 ConcurrentMarkSweepThread::synchronize(true);
7014 _freelistLock->lock_without_safepoint_check();
7015 _bitMap->lock()->lock_without_safepoint_check();
7016 _collector->startTimer();
7017 }
7018
7019
7020 //////////////////////////////////////////////////////////////////
7021 // SurvivorSpacePrecleanClosure
7022 //////////////////////////////////////////////////////////////////
7023 // This (single-threaded) closure is used to preclean the oops in
7024 // the survivor spaces.
7025 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
7026
7027 HeapWord* addr = (HeapWord*)p;
7028 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
7029 assert(!_span.contains(addr), "we are scanning the survivor spaces");
7030 assert(p->klass_or_null() != NULL, "object should be initializd");
7031 assert(p->is_parsable(), "must be parsable.");
7032 // an initialized object; ignore mark word in verification below
7033 // since we are running concurrent with mutators
7034 assert(p->is_oop(true), "should be an oop");
7035 // Note that we do not yield while we iterate over
7036 // the interior oops of p, pushing the relevant ones
7037 // on our marking stack.
7038 size_t size = p->oop_iterate(_scanning_closure);
7039 do_yield_check();
7040 // Observe that below, we do not abandon the preclean
7041 // phase as soon as we should; rather we empty the
7042 // marking stack before returning. This is to satisfy
7043 // some existing assertions. In general, it may be a
7044 // good idea to abort immediately and complete the marking
7045 // from the grey objects at a later time.
7046 while (!_mark_stack->isEmpty()) {
7047 oop new_oop = _mark_stack->pop();
7048 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7049 assert(new_oop->is_parsable(), "Found unparsable oop");
7050 assert(_bit_map->isMarked((HeapWord*)new_oop),
7051 "only grey objects on this stack");
7052 // iterate over the oops in this oop, marking and pushing
7053 // the ones in CMS heap (i.e. in _span).
7054 new_oop->oop_iterate(_scanning_closure);
7055 // check if it's time to yield
7056 do_yield_check();
7057 }
7058 unsigned int after_count =
7059 GenCollectedHeap::heap()->total_collections();
7060 bool abort = (_before_count != after_count) ||
7061 _collector->should_abort_preclean();
7062 return abort ? 0 : size;
7063 }
7064
7065 void SurvivorSpacePrecleanClosure::do_yield_work() {
7066 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7067 "CMS thread should hold CMS token");
7068 assert_lock_strong(_bit_map->lock());
7069 DEBUG_ONLY(RememberKlassesChecker smx(false);)
7070 // Relinquish the bit map lock
7071 _bit_map->lock()->unlock();
7072 ConcurrentMarkSweepThread::desynchronize(true);
7073 ConcurrentMarkSweepThread::acknowledge_yield_request();
7074 _collector->stopTimer();
7075 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7076 if (PrintCMSStatistics != 0) {
7077 _collector->incrementYields();
7078 }
7079 _collector->icms_wait();
7080
7081 // See the comment in coordinator_yield()
7082 for (unsigned i = 0; i < CMSYieldSleepCount &&
7083 ConcurrentMarkSweepThread::should_yield() &&
7084 !CMSCollector::foregroundGCIsActive(); ++i) {
7085 os::sleep(Thread::current(), 1, false);
7086 ConcurrentMarkSweepThread::acknowledge_yield_request();
7087 }
7088
7089 ConcurrentMarkSweepThread::synchronize(true);
7090 _bit_map->lock()->lock_without_safepoint_check();
7091 _collector->startTimer();
7092 }
7093
7094 // This closure is used to rescan the marked objects on the dirty cards
7095 // in the mod union table and the card table proper. In the parallel
7096 // case, although the bitMap is shared, we do a single read so the
7097 // isMarked() query is "safe".
7098 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7099 // Ignore mark word because we are running concurrent with mutators
7100 assert(p->is_oop_or_null(true), "expected an oop or null");
7101 HeapWord* addr = (HeapWord*)p;
7102 assert(_span.contains(addr), "we are scanning the CMS generation");
7103 bool is_obj_array = false;
7104 #ifdef DEBUG
7105 if (!_parallel) {
7106 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7107 assert(_collector->overflow_list_is_empty(),
7108 "overflow list should be empty");
7109
7110 }
7111 #endif // DEBUG
7112 if (_bit_map->isMarked(addr)) {
7113 // Obj arrays are precisely marked, non-arrays are not;
7114 // so we scan objArrays precisely and non-arrays in their
7115 // entirety.
7116 if (p->is_objArray()) {
7117 is_obj_array = true;
7118 if (_parallel) {
7119 p->oop_iterate(_par_scan_closure, mr);
7120 } else {
7121 p->oop_iterate(_scan_closure, mr);
7122 }
7123 } else {
7124 if (_parallel) {
7125 p->oop_iterate(_par_scan_closure);
7126 } else {
7127 p->oop_iterate(_scan_closure);
7128 }
7129 }
7130 }
7131 #ifdef DEBUG
7132 if (!_parallel) {
7133 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7134 assert(_collector->overflow_list_is_empty(),
7135 "overflow list should be empty");
7136
7137 }
7138 #endif // DEBUG
7139 return is_obj_array;
7140 }
7141
7142 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7143 MemRegion span,
7144 CMSBitMap* bitMap, CMSMarkStack* markStack,
7145 CMSMarkStack* revisitStack,
7146 bool should_yield, bool verifying):
7147 _collector(collector),
7148 _span(span),
7149 _bitMap(bitMap),
7150 _mut(&collector->_modUnionTable),
7151 _markStack(markStack),
7152 _revisitStack(revisitStack),
7153 _yield(should_yield),
7154 _skipBits(0)
7155 {
7156 assert(_markStack->isEmpty(), "stack should be empty");
7157 _finger = _bitMap->startWord();
7158 _threshold = _finger;
7159 assert(_collector->_restart_addr == NULL, "Sanity check");
7160 assert(_span.contains(_finger), "Out of bounds _finger?");
7161 DEBUG_ONLY(_verifying = verifying;)
7162 }
7163
7164 void MarkFromRootsClosure::reset(HeapWord* addr) {
7165 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7166 assert(_span.contains(addr), "Out of bounds _finger?");
7167 _finger = addr;
7168 _threshold = (HeapWord*)round_to(
7169 (intptr_t)_finger, CardTableModRefBS::card_size);
7170 }
7171
7172 // Should revisit to see if this should be restructured for
7173 // greater efficiency.
7174 bool MarkFromRootsClosure::do_bit(size_t offset) {
7175 if (_skipBits > 0) {
7176 _skipBits--;
7177 return true;
7178 }
7179 // convert offset into a HeapWord*
7180 HeapWord* addr = _bitMap->startWord() + offset;
7181 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7182 "address out of range");
7183 assert(_bitMap->isMarked(addr), "tautology");
7184 if (_bitMap->isMarked(addr+1)) {
7185 // this is an allocated but not yet initialized object
7186 assert(_skipBits == 0, "tautology");
7187 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7188 oop p = oop(addr);
7189 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7190 DEBUG_ONLY(if (!_verifying) {)
7191 // We re-dirty the cards on which this object lies and increase
7192 // the _threshold so that we'll come back to scan this object
7193 // during the preclean or remark phase. (CMSCleanOnEnter)
7194 if (CMSCleanOnEnter) {
7195 size_t sz = _collector->block_size_using_printezis_bits(addr);
7196 HeapWord* end_card_addr = (HeapWord*)round_to(
7197 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7198 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7199 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7200 // Bump _threshold to end_card_addr; note that
7201 // _threshold cannot possibly exceed end_card_addr, anyhow.
7202 // This prevents future clearing of the card as the scan proceeds
7203 // to the right.
7204 assert(_threshold <= end_card_addr,
7205 "Because we are just scanning into this object");
7206 if (_threshold < end_card_addr) {
7207 _threshold = end_card_addr;
7208 }
7209 if (p->klass_or_null() != NULL) {
7210 // Redirty the range of cards...
7211 _mut->mark_range(redirty_range);
7212 } // ...else the setting of klass will dirty the card anyway.
7213 }
7214 DEBUG_ONLY(})
7215 return true;
7216 }
7217 }
7218 scanOopsInOop(addr);
7219 return true;
7220 }
7221
7222 // We take a break if we've been at this for a while,
7223 // so as to avoid monopolizing the locks involved.
7224 void MarkFromRootsClosure::do_yield_work() {
7225 // First give up the locks, then yield, then re-lock
7226 // We should probably use a constructor/destructor idiom to
7227 // do this unlock/lock or modify the MutexUnlocker class to
7228 // serve our purpose. XXX
7229 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7230 "CMS thread should hold CMS token");
7231 assert_lock_strong(_bitMap->lock());
7232 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7233 _bitMap->lock()->unlock();
7234 ConcurrentMarkSweepThread::desynchronize(true);
7235 ConcurrentMarkSweepThread::acknowledge_yield_request();
7236 _collector->stopTimer();
7237 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7238 if (PrintCMSStatistics != 0) {
7239 _collector->incrementYields();
7240 }
7241 _collector->icms_wait();
7242
7243 // See the comment in coordinator_yield()
7244 for (unsigned i = 0; i < CMSYieldSleepCount &&
7245 ConcurrentMarkSweepThread::should_yield() &&
7246 !CMSCollector::foregroundGCIsActive(); ++i) {
7247 os::sleep(Thread::current(), 1, false);
7248 ConcurrentMarkSweepThread::acknowledge_yield_request();
7249 }
7250
7251 ConcurrentMarkSweepThread::synchronize(true);
7252 _bitMap->lock()->lock_without_safepoint_check();
7253 _collector->startTimer();
7254 }
7255
7256 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7257 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7258 assert(_markStack->isEmpty(),
7259 "should drain stack to limit stack usage");
7260 // convert ptr to an oop preparatory to scanning
7261 oop obj = oop(ptr);
7262 // Ignore mark word in verification below, since we
7263 // may be running concurrent with mutators.
7264 assert(obj->is_oop(true), "should be an oop");
7265 assert(_finger <= ptr, "_finger runneth ahead");
7266 // advance the finger to right end of this object
7267 _finger = ptr + obj->size();
7268 assert(_finger > ptr, "we just incremented it above");
7269 // On large heaps, it may take us some time to get through
7270 // the marking phase (especially if running iCMS). During
7271 // this time it's possible that a lot of mutations have
7272 // accumulated in the card table and the mod union table --
7273 // these mutation records are redundant until we have
7274 // actually traced into the corresponding card.
7275 // Here, we check whether advancing the finger would make
7276 // us cross into a new card, and if so clear corresponding
7277 // cards in the MUT (preclean them in the card-table in the
7278 // future).
7279
7280 DEBUG_ONLY(if (!_verifying) {)
7281 // The clean-on-enter optimization is disabled by default,
7282 // until we fix 6178663.
7283 if (CMSCleanOnEnter && (_finger > _threshold)) {
7284 // [_threshold, _finger) represents the interval
7285 // of cards to be cleared in MUT (or precleaned in card table).
7286 // The set of cards to be cleared is all those that overlap
7287 // with the interval [_threshold, _finger); note that
7288 // _threshold is always kept card-aligned but _finger isn't
7289 // always card-aligned.
7290 HeapWord* old_threshold = _threshold;
7291 assert(old_threshold == (HeapWord*)round_to(
7292 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7293 "_threshold should always be card-aligned");
7294 _threshold = (HeapWord*)round_to(
7295 (intptr_t)_finger, CardTableModRefBS::card_size);
7296 MemRegion mr(old_threshold, _threshold);
7297 assert(!mr.is_empty(), "Control point invariant");
7298 assert(_span.contains(mr), "Should clear within span");
7299 // XXX When _finger crosses from old gen into perm gen
7300 // we may be doing unnecessary cleaning; do better in the
7301 // future by detecting that condition and clearing fewer
7302 // MUT/CT entries.
7303 _mut->clear_range(mr);
7304 }
7305 DEBUG_ONLY(})
7306 // Note: the finger doesn't advance while we drain
7307 // the stack below.
7308 PushOrMarkClosure pushOrMarkClosure(_collector,
7309 _span, _bitMap, _markStack,
7310 _revisitStack,
7311 _finger, this);
7312 bool res = _markStack->push(obj);
7313 assert(res, "Empty non-zero size stack should have space for single push");
7314 while (!_markStack->isEmpty()) {
7315 oop new_oop = _markStack->pop();
7316 // Skip verifying header mark word below because we are
7317 // running concurrent with mutators.
7318 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7319 // now scan this oop's oops
7320 new_oop->oop_iterate(&pushOrMarkClosure);
7321 do_yield_check();
7322 }
7323 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7324 }
7325
7326 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7327 CMSCollector* collector, MemRegion span,
7328 CMSBitMap* bit_map,
7329 OopTaskQueue* work_queue,
7330 CMSMarkStack* overflow_stack,
7331 CMSMarkStack* revisit_stack,
7332 bool should_yield):
7333 _collector(collector),
7334 _whole_span(collector->_span),
7335 _span(span),
7336 _bit_map(bit_map),
7337 _mut(&collector->_modUnionTable),
7338 _work_queue(work_queue),
7339 _overflow_stack(overflow_stack),
7340 _revisit_stack(revisit_stack),
7341 _yield(should_yield),
7342 _skip_bits(0),
7343 _task(task)
7344 {
7345 assert(_work_queue->size() == 0, "work_queue should be empty");
7346 _finger = span.start();
7347 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7348 assert(_span.contains(_finger), "Out of bounds _finger?");
7349 }
7350
7351 // Should revisit to see if this should be restructured for
7352 // greater efficiency.
7353 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7354 if (_skip_bits > 0) {
7355 _skip_bits--;
7356 return true;
7357 }
7358 // convert offset into a HeapWord*
7359 HeapWord* addr = _bit_map->startWord() + offset;
7360 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7361 "address out of range");
7362 assert(_bit_map->isMarked(addr), "tautology");
7363 if (_bit_map->isMarked(addr+1)) {
7364 // this is an allocated object that might not yet be initialized
7365 assert(_skip_bits == 0, "tautology");
7366 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7367 oop p = oop(addr);
7368 if (p->klass_or_null() == NULL || !p->is_parsable()) {
7369 // in the case of Clean-on-Enter optimization, redirty card
7370 // and avoid clearing card by increasing the threshold.
7371 return true;
7372 }
7373 }
7374 scan_oops_in_oop(addr);
7375 return true;
7376 }
7377
7378 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7379 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7380 // Should we assert that our work queue is empty or
7381 // below some drain limit?
7382 assert(_work_queue->size() == 0,
7383 "should drain stack to limit stack usage");
7384 // convert ptr to an oop preparatory to scanning
7385 oop obj = oop(ptr);
7386 // Ignore mark word in verification below, since we
7387 // may be running concurrent with mutators.
7388 assert(obj->is_oop(true), "should be an oop");
7389 assert(_finger <= ptr, "_finger runneth ahead");
7390 // advance the finger to right end of this object
7391 _finger = ptr + obj->size();
7392 assert(_finger > ptr, "we just incremented it above");
7393 // On large heaps, it may take us some time to get through
7394 // the marking phase (especially if running iCMS). During
7395 // this time it's possible that a lot of mutations have
7396 // accumulated in the card table and the mod union table --
7397 // these mutation records are redundant until we have
7398 // actually traced into the corresponding card.
7399 // Here, we check whether advancing the finger would make
7400 // us cross into a new card, and if so clear corresponding
7401 // cards in the MUT (preclean them in the card-table in the
7402 // future).
7403
7404 // The clean-on-enter optimization is disabled by default,
7405 // until we fix 6178663.
7406 if (CMSCleanOnEnter && (_finger > _threshold)) {
7407 // [_threshold, _finger) represents the interval
7408 // of cards to be cleared in MUT (or precleaned in card table).
7409 // The set of cards to be cleared is all those that overlap
7410 // with the interval [_threshold, _finger); note that
7411 // _threshold is always kept card-aligned but _finger isn't
7412 // always card-aligned.
7413 HeapWord* old_threshold = _threshold;
7414 assert(old_threshold == (HeapWord*)round_to(
7415 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7416 "_threshold should always be card-aligned");
7417 _threshold = (HeapWord*)round_to(
7418 (intptr_t)_finger, CardTableModRefBS::card_size);
7419 MemRegion mr(old_threshold, _threshold);
7420 assert(!mr.is_empty(), "Control point invariant");
7421 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7422 // XXX When _finger crosses from old gen into perm gen
7423 // we may be doing unnecessary cleaning; do better in the
7424 // future by detecting that condition and clearing fewer
7425 // MUT/CT entries.
7426 _mut->clear_range(mr);
7427 }
7428
7429 // Note: the local finger doesn't advance while we drain
7430 // the stack below, but the global finger sure can and will.
7431 HeapWord** gfa = _task->global_finger_addr();
7432 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7433 _span, _bit_map,
7434 _work_queue,
7435 _overflow_stack,
7436 _revisit_stack,
7437 _finger,
7438 gfa, this);
7439 bool res = _work_queue->push(obj); // overflow could occur here
7440 assert(res, "Will hold once we use workqueues");
7441 while (true) {
7442 oop new_oop;
7443 if (!_work_queue->pop_local(new_oop)) {
7444 // We emptied our work_queue; check if there's stuff that can
7445 // be gotten from the overflow stack.
7446 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7447 _overflow_stack, _work_queue)) {
7448 do_yield_check();
7449 continue;
7450 } else { // done
7451 break;
7452 }
7453 }
7454 // Skip verifying header mark word below because we are
7455 // running concurrent with mutators.
7456 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7457 // now scan this oop's oops
7458 new_oop->oop_iterate(&pushOrMarkClosure);
7459 do_yield_check();
7460 }
7461 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7462 }
7463
7464 // Yield in response to a request from VM Thread or
7465 // from mutators.
7466 void Par_MarkFromRootsClosure::do_yield_work() {
7467 assert(_task != NULL, "sanity");
7468 _task->yield();
7469 }
7470
7471 // A variant of the above used for verifying CMS marking work.
7472 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7473 MemRegion span,
7474 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7475 CMSMarkStack* mark_stack):
7476 _collector(collector),
7477 _span(span),
7478 _verification_bm(verification_bm),
7479 _cms_bm(cms_bm),
7480 _mark_stack(mark_stack),
7481 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7482 mark_stack)
7483 {
7484 assert(_mark_stack->isEmpty(), "stack should be empty");
7485 _finger = _verification_bm->startWord();
7486 assert(_collector->_restart_addr == NULL, "Sanity check");
7487 assert(_span.contains(_finger), "Out of bounds _finger?");
7488 }
7489
7490 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7491 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7492 assert(_span.contains(addr), "Out of bounds _finger?");
7493 _finger = addr;
7494 }
7495
7496 // Should revisit to see if this should be restructured for
7497 // greater efficiency.
7498 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7499 // convert offset into a HeapWord*
7500 HeapWord* addr = _verification_bm->startWord() + offset;
7501 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7502 "address out of range");
7503 assert(_verification_bm->isMarked(addr), "tautology");
7504 assert(_cms_bm->isMarked(addr), "tautology");
7505
7506 assert(_mark_stack->isEmpty(),
7507 "should drain stack to limit stack usage");
7508 // convert addr to an oop preparatory to scanning
7509 oop obj = oop(addr);
7510 assert(obj->is_oop(), "should be an oop");
7511 assert(_finger <= addr, "_finger runneth ahead");
7512 // advance the finger to right end of this object
7513 _finger = addr + obj->size();
7514 assert(_finger > addr, "we just incremented it above");
7515 // Note: the finger doesn't advance while we drain
7516 // the stack below.
7517 bool res = _mark_stack->push(obj);
7518 assert(res, "Empty non-zero size stack should have space for single push");
7519 while (!_mark_stack->isEmpty()) {
7520 oop new_oop = _mark_stack->pop();
7521 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7522 // now scan this oop's oops
7523 new_oop->oop_iterate(&_pam_verify_closure);
7524 }
7525 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7526 return true;
7527 }
7528
7529 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7530 CMSCollector* collector, MemRegion span,
7531 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7532 CMSMarkStack* mark_stack):
7533 OopClosure(collector->ref_processor()),
7534 _collector(collector),
7535 _span(span),
7536 _verification_bm(verification_bm),
7537 _cms_bm(cms_bm),
7538 _mark_stack(mark_stack)
7539 { }
7540
7541 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7542 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7543
7544 // Upon stack overflow, we discard (part of) the stack,
7545 // remembering the least address amongst those discarded
7546 // in CMSCollector's _restart_address.
7547 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7548 // Remember the least grey address discarded
7549 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7550 _collector->lower_restart_addr(ra);
7551 _mark_stack->reset(); // discard stack contents
7552 _mark_stack->expand(); // expand the stack if possible
7553 }
7554
7555 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7556 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7557 HeapWord* addr = (HeapWord*)obj;
7558 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7559 // Oop lies in _span and isn't yet grey or black
7560 _verification_bm->mark(addr); // now grey
7561 if (!_cms_bm->isMarked(addr)) {
7562 oop(addr)->print();
7563 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7564 addr);
7565 fatal("... aborting");
7566 }
7567
7568 if (!_mark_stack->push(obj)) { // stack overflow
7569 if (PrintCMSStatistics != 0) {
7570 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7571 SIZE_FORMAT, _mark_stack->capacity());
7572 }
7573 assert(_mark_stack->isFull(), "Else push should have succeeded");
7574 handle_stack_overflow(addr);
7575 }
7576 // anything including and to the right of _finger
7577 // will be scanned as we iterate over the remainder of the
7578 // bit map
7579 }
7580 }
7581
7582 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7583 MemRegion span,
7584 CMSBitMap* bitMap, CMSMarkStack* markStack,
7585 CMSMarkStack* revisitStack,
7586 HeapWord* finger, MarkFromRootsClosure* parent) :
7587 KlassRememberingOopClosure(collector, collector->ref_processor(), revisitStack),
7588 _span(span),
7589 _bitMap(bitMap),
7590 _markStack(markStack),
7591 _finger(finger),
7592 _parent(parent)
7593 { }
7594
7595 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7596 MemRegion span,
7597 CMSBitMap* bit_map,
7598 OopTaskQueue* work_queue,
7599 CMSMarkStack* overflow_stack,
7600 CMSMarkStack* revisit_stack,
7601 HeapWord* finger,
7602 HeapWord** global_finger_addr,
7603 Par_MarkFromRootsClosure* parent) :
7604 Par_KlassRememberingOopClosure(collector,
7605 collector->ref_processor(),
7606 revisit_stack),
7607 _whole_span(collector->_span),
7608 _span(span),
7609 _bit_map(bit_map),
7610 _work_queue(work_queue),
7611 _overflow_stack(overflow_stack),
7612 _finger(finger),
7613 _global_finger_addr(global_finger_addr),
7614 _parent(parent)
7615 { }
7616
7617 // Assumes thread-safe access by callers, who are
7618 // responsible for mutual exclusion.
7619 void CMSCollector::lower_restart_addr(HeapWord* low) {
7620 assert(_span.contains(low), "Out of bounds addr");
7621 if (_restart_addr == NULL) {
7622 _restart_addr = low;
7623 } else {
7624 _restart_addr = MIN2(_restart_addr, low);
7625 }
7626 }
7627
7628 // Upon stack overflow, we discard (part of) the stack,
7629 // remembering the least address amongst those discarded
7630 // in CMSCollector's _restart_address.
7631 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7632 // Remember the least grey address discarded
7633 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7634 _collector->lower_restart_addr(ra);
7635 _markStack->reset(); // discard stack contents
7636 _markStack->expand(); // expand the stack if possible
7637 }
7638
7639 // Upon stack overflow, we discard (part of) the stack,
7640 // remembering the least address amongst those discarded
7641 // in CMSCollector's _restart_address.
7642 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7643 // We need to do this under a mutex to prevent other
7644 // workers from interfering with the work done below.
7645 MutexLockerEx ml(_overflow_stack->par_lock(),
7646 Mutex::_no_safepoint_check_flag);
7647 // Remember the least grey address discarded
7648 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7649 _collector->lower_restart_addr(ra);
7650 _overflow_stack->reset(); // discard stack contents
7651 _overflow_stack->expand(); // expand the stack if possible
7652 }
7653
7654 void PushOrMarkClosure::do_oop(oop obj) {
7655 // Ignore mark word because we are running concurrent with mutators.
7656 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7657 HeapWord* addr = (HeapWord*)obj;
7658 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7659 // Oop lies in _span and isn't yet grey or black
7660 _bitMap->mark(addr); // now grey
7661 if (addr < _finger) {
7662 // the bit map iteration has already either passed, or
7663 // sampled, this bit in the bit map; we'll need to
7664 // use the marking stack to scan this oop's oops.
7665 bool simulate_overflow = false;
7666 NOT_PRODUCT(
7667 if (CMSMarkStackOverflowALot &&
7668 _collector->simulate_overflow()) {
7669 // simulate a stack overflow
7670 simulate_overflow = true;
7671 }
7672 )
7673 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7674 if (PrintCMSStatistics != 0) {
7675 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7676 SIZE_FORMAT, _markStack->capacity());
7677 }
7678 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7679 handle_stack_overflow(addr);
7680 }
7681 }
7682 // anything including and to the right of _finger
7683 // will be scanned as we iterate over the remainder of the
7684 // bit map
7685 do_yield_check();
7686 }
7687 }
7688
7689 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7690 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7691
7692 void Par_PushOrMarkClosure::do_oop(oop obj) {
7693 // Ignore mark word because we are running concurrent with mutators.
7694 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7695 HeapWord* addr = (HeapWord*)obj;
7696 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7697 // Oop lies in _span and isn't yet grey or black
7698 // We read the global_finger (volatile read) strictly after marking oop
7699 bool res = _bit_map->par_mark(addr); // now grey
7700 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7701 // Should we push this marked oop on our stack?
7702 // -- if someone else marked it, nothing to do
7703 // -- if target oop is above global finger nothing to do
7704 // -- if target oop is in chunk and above local finger
7705 // then nothing to do
7706 // -- else push on work queue
7707 if ( !res // someone else marked it, they will deal with it
7708 || (addr >= *gfa) // will be scanned in a later task
7709 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7710 return;
7711 }
7712 // the bit map iteration has already either passed, or
7713 // sampled, this bit in the bit map; we'll need to
7714 // use the marking stack to scan this oop's oops.
7715 bool simulate_overflow = false;
7716 NOT_PRODUCT(
7717 if (CMSMarkStackOverflowALot &&
7718 _collector->simulate_overflow()) {
7719 // simulate a stack overflow
7720 simulate_overflow = true;
7721 }
7722 )
7723 if (simulate_overflow ||
7724 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7725 // stack overflow
7726 if (PrintCMSStatistics != 0) {
7727 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7728 SIZE_FORMAT, _overflow_stack->capacity());
7729 }
7730 // We cannot assert that the overflow stack is full because
7731 // it may have been emptied since.
7732 assert(simulate_overflow ||
7733 _work_queue->size() == _work_queue->max_elems(),
7734 "Else push should have succeeded");
7735 handle_stack_overflow(addr);
7736 }
7737 do_yield_check();
7738 }
7739 }
7740
7741 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7742 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7743
7744 KlassRememberingOopClosure::KlassRememberingOopClosure(CMSCollector* collector,
7745 ReferenceProcessor* rp,
7746 CMSMarkStack* revisit_stack) :
7747 OopClosure(rp),
7748 _collector(collector),
7749 _revisit_stack(revisit_stack),
7750 _should_remember_klasses(collector->should_unload_classes()) {}
7751
7752 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7753 MemRegion span,
7754 ReferenceProcessor* rp,
7755 CMSBitMap* bit_map,
7756 CMSBitMap* mod_union_table,
7757 CMSMarkStack* mark_stack,
7758 CMSMarkStack* revisit_stack,
7759 bool concurrent_precleaning):
7760 KlassRememberingOopClosure(collector, rp, revisit_stack),
7761 _span(span),
7762 _bit_map(bit_map),
7763 _mod_union_table(mod_union_table),
7764 _mark_stack(mark_stack),
7765 _concurrent_precleaning(concurrent_precleaning)
7766 {
7767 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7768 }
7769
7770 // Grey object rescan during pre-cleaning and second checkpoint phases --
7771 // the non-parallel version (the parallel version appears further below.)
7772 void PushAndMarkClosure::do_oop(oop obj) {
7773 // Ignore mark word verification. If during concurrent precleaning,
7774 // the object monitor may be locked. If during the checkpoint
7775 // phases, the object may already have been reached by a different
7776 // path and may be at the end of the global overflow list (so
7777 // the mark word may be NULL).
7778 assert(obj->is_oop_or_null(true /* ignore mark word */),
7779 "expected an oop or NULL");
7780 HeapWord* addr = (HeapWord*)obj;
7781 // Check if oop points into the CMS generation
7782 // and is not marked
7783 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7784 // a white object ...
7785 _bit_map->mark(addr); // ... now grey
7786 // push on the marking stack (grey set)
7787 bool simulate_overflow = false;
7788 NOT_PRODUCT(
7789 if (CMSMarkStackOverflowALot &&
7790 _collector->simulate_overflow()) {
7791 // simulate a stack overflow
7792 simulate_overflow = true;
7793 }
7794 )
7795 if (simulate_overflow || !_mark_stack->push(obj)) {
7796 if (_concurrent_precleaning) {
7797 // During precleaning we can just dirty the appropriate card(s)
7798 // in the mod union table, thus ensuring that the object remains
7799 // in the grey set and continue. In the case of object arrays
7800 // we need to dirty all of the cards that the object spans,
7801 // since the rescan of object arrays will be limited to the
7802 // dirty cards.
7803 // Note that no one can be intefering with us in this action
7804 // of dirtying the mod union table, so no locking or atomics
7805 // are required.
7806 if (obj->is_objArray()) {
7807 size_t sz = obj->size();
7808 HeapWord* end_card_addr = (HeapWord*)round_to(
7809 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7810 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7811 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7812 _mod_union_table->mark_range(redirty_range);
7813 } else {
7814 _mod_union_table->mark(addr);
7815 }
7816 _collector->_ser_pmc_preclean_ovflw++;
7817 } else {
7818 // During the remark phase, we need to remember this oop
7819 // in the overflow list.
7820 _collector->push_on_overflow_list(obj);
7821 _collector->_ser_pmc_remark_ovflw++;
7822 }
7823 }
7824 }
7825 }
7826
7827 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7828 MemRegion span,
7829 ReferenceProcessor* rp,
7830 CMSBitMap* bit_map,
7831 OopTaskQueue* work_queue,
7832 CMSMarkStack* revisit_stack):
7833 Par_KlassRememberingOopClosure(collector, rp, revisit_stack),
7834 _span(span),
7835 _bit_map(bit_map),
7836 _work_queue(work_queue)
7837 {
7838 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7839 }
7840
7841 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7842 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7843
7844 // Grey object rescan during second checkpoint phase --
7845 // the parallel version.
7846 void Par_PushAndMarkClosure::do_oop(oop obj) {
7847 // In the assert below, we ignore the mark word because
7848 // this oop may point to an already visited object that is
7849 // on the overflow stack (in which case the mark word has
7850 // been hijacked for chaining into the overflow stack --
7851 // if this is the last object in the overflow stack then
7852 // its mark word will be NULL). Because this object may
7853 // have been subsequently popped off the global overflow
7854 // stack, and the mark word possibly restored to the prototypical
7855 // value, by the time we get to examined this failing assert in
7856 // the debugger, is_oop_or_null(false) may subsequently start
7857 // to hold.
7858 assert(obj->is_oop_or_null(true),
7859 "expected an oop or NULL");
7860 HeapWord* addr = (HeapWord*)obj;
7861 // Check if oop points into the CMS generation
7862 // and is not marked
7863 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7864 // a white object ...
7865 // If we manage to "claim" the object, by being the
7866 // first thread to mark it, then we push it on our
7867 // marking stack
7868 if (_bit_map->par_mark(addr)) { // ... now grey
7869 // push on work queue (grey set)
7870 bool simulate_overflow = false;
7871 NOT_PRODUCT(
7872 if (CMSMarkStackOverflowALot &&
7873 _collector->par_simulate_overflow()) {
7874 // simulate a stack overflow
7875 simulate_overflow = true;
7876 }
7877 )
7878 if (simulate_overflow || !_work_queue->push(obj)) {
7879 _collector->par_push_on_overflow_list(obj);
7880 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7881 }
7882 } // Else, some other thread got there first
7883 }
7884 }
7885
7886 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7887 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7888
7889 void PushAndMarkClosure::remember_mdo(DataLayout* v) {
7890 // TBD
7891 }
7892
7893 void Par_PushAndMarkClosure::remember_mdo(DataLayout* v) {
7894 // TBD
7895 }
7896
7897 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7898 DEBUG_ONLY(RememberKlassesChecker mux(false);)
7899 Mutex* bml = _collector->bitMapLock();
7900 assert_lock_strong(bml);
7901 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7902 "CMS thread should hold CMS token");
7903
7904 bml->unlock();
7905 ConcurrentMarkSweepThread::desynchronize(true);
7906
7907 ConcurrentMarkSweepThread::acknowledge_yield_request();
7908
7909 _collector->stopTimer();
7910 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7911 if (PrintCMSStatistics != 0) {
7912 _collector->incrementYields();
7913 }
7914 _collector->icms_wait();
7915
7916 // See the comment in coordinator_yield()
7917 for (unsigned i = 0; i < CMSYieldSleepCount &&
7918 ConcurrentMarkSweepThread::should_yield() &&
7919 !CMSCollector::foregroundGCIsActive(); ++i) {
7920 os::sleep(Thread::current(), 1, false);
7921 ConcurrentMarkSweepThread::acknowledge_yield_request();
7922 }
7923
7924 ConcurrentMarkSweepThread::synchronize(true);
7925 bml->lock();
7926
7927 _collector->startTimer();
7928 }
7929
7930 bool CMSPrecleanRefsYieldClosure::should_return() {
7931 if (ConcurrentMarkSweepThread::should_yield()) {
7932 do_yield_work();
7933 }
7934 return _collector->foregroundGCIsActive();
7935 }
7936
7937 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7938 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7939 "mr should be aligned to start at a card boundary");
7940 // We'd like to assert:
7941 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7942 // "mr should be a range of cards");
7943 // However, that would be too strong in one case -- the last
7944 // partition ends at _unallocated_block which, in general, can be
7945 // an arbitrary boundary, not necessarily card aligned.
7946 if (PrintCMSStatistics != 0) {
7947 _num_dirty_cards +=
7948 mr.word_size()/CardTableModRefBS::card_size_in_words;
7949 }
7950 _space->object_iterate_mem(mr, &_scan_cl);
7951 }
7952
7953 SweepClosure::SweepClosure(CMSCollector* collector,
7954 ConcurrentMarkSweepGeneration* g,
7955 CMSBitMap* bitMap, bool should_yield) :
7956 _collector(collector),
7957 _g(g),
7958 _sp(g->cmsSpace()),
7959 _limit(_sp->sweep_limit()),
7960 _freelistLock(_sp->freelistLock()),
7961 _bitMap(bitMap),
7962 _yield(should_yield),
7963 _inFreeRange(false), // No free range at beginning of sweep
7964 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7965 _lastFreeRangeCoalesced(false),
7966 _freeFinger(g->used_region().start())
7967 {
7968 NOT_PRODUCT(
7969 _numObjectsFreed = 0;
7970 _numWordsFreed = 0;
7971 _numObjectsLive = 0;
7972 _numWordsLive = 0;
7973 _numObjectsAlreadyFree = 0;
7974 _numWordsAlreadyFree = 0;
7975 _last_fc = NULL;
7976
7977 _sp->initializeIndexedFreeListArrayReturnedBytes();
7978 _sp->dictionary()->initialize_dict_returned_bytes();
7979 )
7980 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7981 "sweep _limit out of bounds");
7982 if (CMSTraceSweeper) {
7983 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7984 _limit);
7985 }
7986 }
7987
7988 void SweepClosure::print_on(outputStream* st) const {
7989 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7990 _sp->bottom(), _sp->end());
7991 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7992 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7993 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7994 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7995 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7996 }
7997
7998 #ifndef PRODUCT
7999 // Assertion checking only: no useful work in product mode --
8000 // however, if any of the flags below become product flags,
8001 // you may need to review this code to see if it needs to be
8002 // enabled in product mode.
8003 SweepClosure::~SweepClosure() {
8004 assert_lock_strong(_freelistLock);
8005 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8006 "sweep _limit out of bounds");
8007 if (inFreeRange()) {
8008 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
8009 print();
8010 ShouldNotReachHere();
8011 }
8012 if (Verbose && PrintGC) {
8013 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
8014 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
8015 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
8016 SIZE_FORMAT" bytes "
8017 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
8018 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
8019 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
8020 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
8021 * sizeof(HeapWord);
8022 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
8023
8024 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
8025 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
8026 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
8027 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
8028 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
8029 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
8030 indexListReturnedBytes);
8031 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
8032 dict_returned_bytes);
8033 }
8034 }
8035 if (CMSTraceSweeper) {
8036 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
8037 _limit);
8038 }
8039 }
8040 #endif // PRODUCT
8041
8042 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
8043 bool freeRangeInFreeLists) {
8044 if (CMSTraceSweeper) {
8045 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
8046 freeFinger, freeRangeInFreeLists);
8047 }
8048 assert(!inFreeRange(), "Trampling existing free range");
8049 set_inFreeRange(true);
8050 set_lastFreeRangeCoalesced(false);
8051
8052 set_freeFinger(freeFinger);
8053 set_freeRangeInFreeLists(freeRangeInFreeLists);
8054 if (CMSTestInFreeList) {
8055 if (freeRangeInFreeLists) {
8056 FreeChunk* fc = (FreeChunk*) freeFinger;
8057 assert(fc->is_free(), "A chunk on the free list should be free.");
8058 assert(fc->size() > 0, "Free range should have a size");
8059 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
8060 }
8061 }
8062 }
8063
8064 // Note that the sweeper runs concurrently with mutators. Thus,
8065 // it is possible for direct allocation in this generation to happen
8066 // in the middle of the sweep. Note that the sweeper also coalesces
8067 // contiguous free blocks. Thus, unless the sweeper and the allocator
8068 // synchronize appropriately freshly allocated blocks may get swept up.
8069 // This is accomplished by the sweeper locking the free lists while
8070 // it is sweeping. Thus blocks that are determined to be free are
8071 // indeed free. There is however one additional complication:
8072 // blocks that have been allocated since the final checkpoint and
8073 // mark, will not have been marked and so would be treated as
8074 // unreachable and swept up. To prevent this, the allocator marks
8075 // the bit map when allocating during the sweep phase. This leads,
8076 // however, to a further complication -- objects may have been allocated
8077 // but not yet initialized -- in the sense that the header isn't yet
8078 // installed. The sweeper can not then determine the size of the block
8079 // in order to skip over it. To deal with this case, we use a technique
8080 // (due to Printezis) to encode such uninitialized block sizes in the
8081 // bit map. Since the bit map uses a bit per every HeapWord, but the
8082 // CMS generation has a minimum object size of 3 HeapWords, it follows
8083 // that "normal marks" won't be adjacent in the bit map (there will
8084 // always be at least two 0 bits between successive 1 bits). We make use
8085 // of these "unused" bits to represent uninitialized blocks -- the bit
8086 // corresponding to the start of the uninitialized object and the next
8087 // bit are both set. Finally, a 1 bit marks the end of the object that
8088 // started with the two consecutive 1 bits to indicate its potentially
8089 // uninitialized state.
8090
8091 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
8092 FreeChunk* fc = (FreeChunk*)addr;
8093 size_t res;
8094
8095 // Check if we are done sweeping. Below we check "addr >= _limit" rather
8096 // than "addr == _limit" because although _limit was a block boundary when
8097 // we started the sweep, it may no longer be one because heap expansion
8098 // may have caused us to coalesce the block ending at the address _limit
8099 // with a newly expanded chunk (this happens when _limit was set to the
8100 // previous _end of the space), so we may have stepped past _limit:
8101 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
8102 if (addr >= _limit) { // we have swept up to or past the limit: finish up
8103 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8104 "sweep _limit out of bounds");
8105 assert(addr < _sp->end(), "addr out of bounds");
8106 // Flush any free range we might be holding as a single
8107 // coalesced chunk to the appropriate free list.
8108 if (inFreeRange()) {
8109 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8110 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8111 flush_cur_free_chunk(freeFinger(),
8112 pointer_delta(addr, freeFinger()));
8113 if (CMSTraceSweeper) {
8114 gclog_or_tty->print("Sweep: last chunk: ");
8115 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8116 "[coalesced:"SIZE_FORMAT"]\n",
8117 freeFinger(), pointer_delta(addr, freeFinger()),
8118 lastFreeRangeCoalesced());
8119 }
8120 }
8121
8122 // help the iterator loop finish
8123 return pointer_delta(_sp->end(), addr);
8124 }
8125
8126 assert(addr < _limit, "sweep invariant");
8127 // check if we should yield
8128 do_yield_check(addr);
8129 if (fc->is_free()) {
8130 // Chunk that is already free
8131 res = fc->size();
8132 do_already_free_chunk(fc);
8133 debug_only(_sp->verifyFreeLists());
8134 // If we flush the chunk at hand in lookahead_and_flush()
8135 // and it's coalesced with a preceding chunk, then the
8136 // process of "mangling" the payload of the coalesced block
8137 // will cause erasure of the size information from the
8138 // (erstwhile) header of all the coalesced blocks but the
8139 // first, so the first disjunct in the assert will not hold
8140 // in that specific case (in which case the second disjunct
8141 // will hold).
8142 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8143 "Otherwise the size info doesn't change at this step");
8144 NOT_PRODUCT(
8145 _numObjectsAlreadyFree++;
8146 _numWordsAlreadyFree += res;
8147 )
8148 NOT_PRODUCT(_last_fc = fc;)
8149 } else if (!_bitMap->isMarked(addr)) {
8150 // Chunk is fresh garbage
8151 res = do_garbage_chunk(fc);
8152 debug_only(_sp->verifyFreeLists());
8153 NOT_PRODUCT(
8154 _numObjectsFreed++;
8155 _numWordsFreed += res;
8156 )
8157 } else {
8158 // Chunk that is alive.
8159 res = do_live_chunk(fc);
8160 debug_only(_sp->verifyFreeLists());
8161 NOT_PRODUCT(
8162 _numObjectsLive++;
8163 _numWordsLive += res;
8164 )
8165 }
8166 return res;
8167 }
8168
8169 // For the smart allocation, record following
8170 // split deaths - a free chunk is removed from its free list because
8171 // it is being split into two or more chunks.
8172 // split birth - a free chunk is being added to its free list because
8173 // a larger free chunk has been split and resulted in this free chunk.
8174 // coal death - a free chunk is being removed from its free list because
8175 // it is being coalesced into a large free chunk.
8176 // coal birth - a free chunk is being added to its free list because
8177 // it was created when two or more free chunks where coalesced into
8178 // this free chunk.
8179 //
8180 // These statistics are used to determine the desired number of free
8181 // chunks of a given size. The desired number is chosen to be relative
8182 // to the end of a CMS sweep. The desired number at the end of a sweep
8183 // is the
8184 // count-at-end-of-previous-sweep (an amount that was enough)
8185 // - count-at-beginning-of-current-sweep (the excess)
8186 // + split-births (gains in this size during interval)
8187 // - split-deaths (demands on this size during interval)
8188 // where the interval is from the end of one sweep to the end of the
8189 // next.
8190 //
8191 // When sweeping the sweeper maintains an accumulated chunk which is
8192 // the chunk that is made up of chunks that have been coalesced. That
8193 // will be termed the left-hand chunk. A new chunk of garbage that
8194 // is being considered for coalescing will be referred to as the
8195 // right-hand chunk.
8196 //
8197 // When making a decision on whether to coalesce a right-hand chunk with
8198 // the current left-hand chunk, the current count vs. the desired count
8199 // of the left-hand chunk is considered. Also if the right-hand chunk
8200 // is near the large chunk at the end of the heap (see
8201 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8202 // left-hand chunk is coalesced.
8203 //
8204 // When making a decision about whether to split a chunk, the desired count
8205 // vs. the current count of the candidate to be split is also considered.
8206 // If the candidate is underpopulated (currently fewer chunks than desired)
8207 // a chunk of an overpopulated (currently more chunks than desired) size may
8208 // be chosen. The "hint" associated with a free list, if non-null, points
8209 // to a free list which may be overpopulated.
8210 //
8211
8212 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8213 const size_t size = fc->size();
8214 // Chunks that cannot be coalesced are not in the
8215 // free lists.
8216 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8217 assert(_sp->verify_chunk_in_free_list(fc),
8218 "free chunk should be in free lists");
8219 }
8220 // a chunk that is already free, should not have been
8221 // marked in the bit map
8222 HeapWord* const addr = (HeapWord*) fc;
8223 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8224 // Verify that the bit map has no bits marked between
8225 // addr and purported end of this block.
8226 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8227
8228 // Some chunks cannot be coalesced under any circumstances.
8229 // See the definition of cantCoalesce().
8230 if (!fc->cantCoalesce()) {
8231 // This chunk can potentially be coalesced.
8232 if (_sp->adaptive_freelists()) {
8233 // All the work is done in
8234 do_post_free_or_garbage_chunk(fc, size);
8235 } else { // Not adaptive free lists
8236 // this is a free chunk that can potentially be coalesced by the sweeper;
8237 if (!inFreeRange()) {
8238 // if the next chunk is a free block that can't be coalesced
8239 // it doesn't make sense to remove this chunk from the free lists
8240 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8241 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8242 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8243 nextChunk->is_free() && // ... which is free...
8244 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8245 // nothing to do
8246 } else {
8247 // Potentially the start of a new free range:
8248 // Don't eagerly remove it from the free lists.
8249 // No need to remove it if it will just be put
8250 // back again. (Also from a pragmatic point of view
8251 // if it is a free block in a region that is beyond
8252 // any allocated blocks, an assertion will fail)
8253 // Remember the start of a free run.
8254 initialize_free_range(addr, true);
8255 // end - can coalesce with next chunk
8256 }
8257 } else {
8258 // the midst of a free range, we are coalescing
8259 print_free_block_coalesced(fc);
8260 if (CMSTraceSweeper) {
8261 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8262 }
8263 // remove it from the free lists
8264 _sp->removeFreeChunkFromFreeLists(fc);
8265 set_lastFreeRangeCoalesced(true);
8266 // If the chunk is being coalesced and the current free range is
8267 // in the free lists, remove the current free range so that it
8268 // will be returned to the free lists in its entirety - all
8269 // the coalesced pieces included.
8270 if (freeRangeInFreeLists()) {
8271 FreeChunk* ffc = (FreeChunk*) freeFinger();
8272 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8273 "Size of free range is inconsistent with chunk size.");
8274 if (CMSTestInFreeList) {
8275 assert(_sp->verify_chunk_in_free_list(ffc),
8276 "free range is not in free lists");
8277 }
8278 _sp->removeFreeChunkFromFreeLists(ffc);
8279 set_freeRangeInFreeLists(false);
8280 }
8281 }
8282 }
8283 // Note that if the chunk is not coalescable (the else arm
8284 // below), we unconditionally flush, without needing to do
8285 // a "lookahead," as we do below.
8286 if (inFreeRange()) lookahead_and_flush(fc, size);
8287 } else {
8288 // Code path common to both original and adaptive free lists.
8289
8290 // cant coalesce with previous block; this should be treated
8291 // as the end of a free run if any
8292 if (inFreeRange()) {
8293 // we kicked some butt; time to pick up the garbage
8294 assert(freeFinger() < addr, "freeFinger points too high");
8295 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8296 }
8297 // else, nothing to do, just continue
8298 }
8299 }
8300
8301 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8302 // This is a chunk of garbage. It is not in any free list.
8303 // Add it to a free list or let it possibly be coalesced into
8304 // a larger chunk.
8305 HeapWord* const addr = (HeapWord*) fc;
8306 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8307
8308 if (_sp->adaptive_freelists()) {
8309 // Verify that the bit map has no bits marked between
8310 // addr and purported end of just dead object.
8311 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8312
8313 do_post_free_or_garbage_chunk(fc, size);
8314 } else {
8315 if (!inFreeRange()) {
8316 // start of a new free range
8317 assert(size > 0, "A free range should have a size");
8318 initialize_free_range(addr, false);
8319 } else {
8320 // this will be swept up when we hit the end of the
8321 // free range
8322 if (CMSTraceSweeper) {
8323 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8324 }
8325 // If the chunk is being coalesced and the current free range is
8326 // in the free lists, remove the current free range so that it
8327 // will be returned to the free lists in its entirety - all
8328 // the coalesced pieces included.
8329 if (freeRangeInFreeLists()) {
8330 FreeChunk* ffc = (FreeChunk*)freeFinger();
8331 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8332 "Size of free range is inconsistent with chunk size.");
8333 if (CMSTestInFreeList) {
8334 assert(_sp->verify_chunk_in_free_list(ffc),
8335 "free range is not in free lists");
8336 }
8337 _sp->removeFreeChunkFromFreeLists(ffc);
8338 set_freeRangeInFreeLists(false);
8339 }
8340 set_lastFreeRangeCoalesced(true);
8341 }
8342 // this will be swept up when we hit the end of the free range
8343
8344 // Verify that the bit map has no bits marked between
8345 // addr and purported end of just dead object.
8346 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8347 }
8348 assert(_limit >= addr + size,
8349 "A freshly garbage chunk can't possibly straddle over _limit");
8350 if (inFreeRange()) lookahead_and_flush(fc, size);
8351 return size;
8352 }
8353
8354 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8355 HeapWord* addr = (HeapWord*) fc;
8356 // The sweeper has just found a live object. Return any accumulated
8357 // left hand chunk to the free lists.
8358 if (inFreeRange()) {
8359 assert(freeFinger() < addr, "freeFinger points too high");
8360 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8361 }
8362
8363 // This object is live: we'd normally expect this to be
8364 // an oop, and like to assert the following:
8365 // assert(oop(addr)->is_oop(), "live block should be an oop");
8366 // However, as we commented above, this may be an object whose
8367 // header hasn't yet been initialized.
8368 size_t size;
8369 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8370 if (_bitMap->isMarked(addr + 1)) {
8371 // Determine the size from the bit map, rather than trying to
8372 // compute it from the object header.
8373 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8374 size = pointer_delta(nextOneAddr + 1, addr);
8375 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8376 "alignment problem");
8377
8378 #ifdef DEBUG
8379 if (oop(addr)->klass_or_null() != NULL &&
8380 ( !_collector->should_unload_classes()
8381 || (oop(addr)->is_parsable()) &&
8382 oop(addr)->is_conc_safe())) {
8383 // Ignore mark word because we are running concurrent with mutators
8384 assert(oop(addr)->is_oop(true), "live block should be an oop");
8385 // is_conc_safe is checked before performing this assertion
8386 // because an object that is not is_conc_safe may yet have
8387 // the return from size() correct.
8388 assert(size ==
8389 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8390 "P-mark and computed size do not agree");
8391 }
8392 #endif
8393
8394 } else {
8395 // This should be an initialized object that's alive.
8396 assert(oop(addr)->klass_or_null() != NULL &&
8397 (!_collector->should_unload_classes()
8398 || oop(addr)->is_parsable()),
8399 "Should be an initialized object");
8400 // Note that there are objects used during class redefinition,
8401 // e.g. merge_cp in VM_RedefineClasses::merge_cp_and_rewrite(),
8402 // which are discarded with their is_conc_safe state still
8403 // false. These object may be floating garbage so may be
8404 // seen here. If they are floating garbage their size
8405 // should be attainable from their klass. Do not that
8406 // is_conc_safe() is true for oop(addr).
8407 // Ignore mark word because we are running concurrent with mutators
8408 assert(oop(addr)->is_oop(true), "live block should be an oop");
8409 // Verify that the bit map has no bits marked between
8410 // addr and purported end of this block.
8411 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8412 assert(size >= 3, "Necessary for Printezis marks to work");
8413 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8414 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8415 }
8416 return size;
8417 }
8418
8419 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8420 size_t chunkSize) {
8421 // do_post_free_or_garbage_chunk() should only be called in the case
8422 // of the adaptive free list allocator.
8423 const bool fcInFreeLists = fc->is_free();
8424 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8425 assert((HeapWord*)fc <= _limit, "sweep invariant");
8426 if (CMSTestInFreeList && fcInFreeLists) {
8427 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8428 }
8429
8430 if (CMSTraceSweeper) {
8431 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8432 }
8433
8434 HeapWord* const fc_addr = (HeapWord*) fc;
8435
8436 bool coalesce;
8437 const size_t left = pointer_delta(fc_addr, freeFinger());
8438 const size_t right = chunkSize;
8439 switch (FLSCoalescePolicy) {
8440 // numeric value forms a coalition aggressiveness metric
8441 case 0: { // never coalesce
8442 coalesce = false;
8443 break;
8444 }
8445 case 1: { // coalesce if left & right chunks on overpopulated lists
8446 coalesce = _sp->coalOverPopulated(left) &&
8447 _sp->coalOverPopulated(right);
8448 break;
8449 }
8450 case 2: { // coalesce if left chunk on overpopulated list (default)
8451 coalesce = _sp->coalOverPopulated(left);
8452 break;
8453 }
8454 case 3: { // coalesce if left OR right chunk on overpopulated list
8455 coalesce = _sp->coalOverPopulated(left) ||
8456 _sp->coalOverPopulated(right);
8457 break;
8458 }
8459 case 4: { // always coalesce
8460 coalesce = true;
8461 break;
8462 }
8463 default:
8464 ShouldNotReachHere();
8465 }
8466
8467 // Should the current free range be coalesced?
8468 // If the chunk is in a free range and either we decided to coalesce above
8469 // or the chunk is near the large block at the end of the heap
8470 // (isNearLargestChunk() returns true), then coalesce this chunk.
8471 const bool doCoalesce = inFreeRange()
8472 && (coalesce || _g->isNearLargestChunk(fc_addr));
8473 if (doCoalesce) {
8474 // Coalesce the current free range on the left with the new
8475 // chunk on the right. If either is on a free list,
8476 // it must be removed from the list and stashed in the closure.
8477 if (freeRangeInFreeLists()) {
8478 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8479 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8480 "Size of free range is inconsistent with chunk size.");
8481 if (CMSTestInFreeList) {
8482 assert(_sp->verify_chunk_in_free_list(ffc),
8483 "Chunk is not in free lists");
8484 }
8485 _sp->coalDeath(ffc->size());
8486 _sp->removeFreeChunkFromFreeLists(ffc);
8487 set_freeRangeInFreeLists(false);
8488 }
8489 if (fcInFreeLists) {
8490 _sp->coalDeath(chunkSize);
8491 assert(fc->size() == chunkSize,
8492 "The chunk has the wrong size or is not in the free lists");
8493 _sp->removeFreeChunkFromFreeLists(fc);
8494 }
8495 set_lastFreeRangeCoalesced(true);
8496 print_free_block_coalesced(fc);
8497 } else { // not in a free range and/or should not coalesce
8498 // Return the current free range and start a new one.
8499 if (inFreeRange()) {
8500 // In a free range but cannot coalesce with the right hand chunk.
8501 // Put the current free range into the free lists.
8502 flush_cur_free_chunk(freeFinger(),
8503 pointer_delta(fc_addr, freeFinger()));
8504 }
8505 // Set up for new free range. Pass along whether the right hand
8506 // chunk is in the free lists.
8507 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8508 }
8509 }
8510
8511 // Lookahead flush:
8512 // If we are tracking a free range, and this is the last chunk that
8513 // we'll look at because its end crosses past _limit, we'll preemptively
8514 // flush it along with any free range we may be holding on to. Note that
8515 // this can be the case only for an already free or freshly garbage
8516 // chunk. If this block is an object, it can never straddle
8517 // over _limit. The "straddling" occurs when _limit is set at
8518 // the previous end of the space when this cycle started, and
8519 // a subsequent heap expansion caused the previously co-terminal
8520 // free block to be coalesced with the newly expanded portion,
8521 // thus rendering _limit a non-block-boundary making it dangerous
8522 // for the sweeper to step over and examine.
8523 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8524 assert(inFreeRange(), "Should only be called if currently in a free range.");
8525 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8526 assert(_sp->used_region().contains(eob - 1),
8527 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8528 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8529 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8530 if (eob >= _limit) {
8531 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8532 if (CMSTraceSweeper) {
8533 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8534 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8535 "[" PTR_FORMAT "," PTR_FORMAT ")",
8536 _limit, fc, eob, _sp->bottom(), _sp->end());
8537 }
8538 // Return the storage we are tracking back into the free lists.
8539 if (CMSTraceSweeper) {
8540 gclog_or_tty->print_cr("Flushing ... ");
8541 }
8542 assert(freeFinger() < eob, "Error");
8543 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8544 }
8545 }
8546
8547 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8548 assert(inFreeRange(), "Should only be called if currently in a free range.");
8549 assert(size > 0,
8550 "A zero sized chunk cannot be added to the free lists.");
8551 if (!freeRangeInFreeLists()) {
8552 if (CMSTestInFreeList) {
8553 FreeChunk* fc = (FreeChunk*) chunk;
8554 fc->set_size(size);
8555 assert(!_sp->verify_chunk_in_free_list(fc),
8556 "chunk should not be in free lists yet");
8557 }
8558 if (CMSTraceSweeper) {
8559 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8560 chunk, size);
8561 }
8562 // A new free range is going to be starting. The current
8563 // free range has not been added to the free lists yet or
8564 // was removed so add it back.
8565 // If the current free range was coalesced, then the death
8566 // of the free range was recorded. Record a birth now.
8567 if (lastFreeRangeCoalesced()) {
8568 _sp->coalBirth(size);
8569 }
8570 _sp->addChunkAndRepairOffsetTable(chunk, size,
8571 lastFreeRangeCoalesced());
8572 } else if (CMSTraceSweeper) {
8573 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8574 }
8575 set_inFreeRange(false);
8576 set_freeRangeInFreeLists(false);
8577 }
8578
8579 // We take a break if we've been at this for a while,
8580 // so as to avoid monopolizing the locks involved.
8581 void SweepClosure::do_yield_work(HeapWord* addr) {
8582 // Return current free chunk being used for coalescing (if any)
8583 // to the appropriate freelist. After yielding, the next
8584 // free block encountered will start a coalescing range of
8585 // free blocks. If the next free block is adjacent to the
8586 // chunk just flushed, they will need to wait for the next
8587 // sweep to be coalesced.
8588 if (inFreeRange()) {
8589 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8590 }
8591
8592 // First give up the locks, then yield, then re-lock.
8593 // We should probably use a constructor/destructor idiom to
8594 // do this unlock/lock or modify the MutexUnlocker class to
8595 // serve our purpose. XXX
8596 assert_lock_strong(_bitMap->lock());
8597 assert_lock_strong(_freelistLock);
8598 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8599 "CMS thread should hold CMS token");
8600 _bitMap->lock()->unlock();
8601 _freelistLock->unlock();
8602 ConcurrentMarkSweepThread::desynchronize(true);
8603 ConcurrentMarkSweepThread::acknowledge_yield_request();
8604 _collector->stopTimer();
8605 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8606 if (PrintCMSStatistics != 0) {
8607 _collector->incrementYields();
8608 }
8609 _collector->icms_wait();
8610
8611 // See the comment in coordinator_yield()
8612 for (unsigned i = 0; i < CMSYieldSleepCount &&
8613 ConcurrentMarkSweepThread::should_yield() &&
8614 !CMSCollector::foregroundGCIsActive(); ++i) {
8615 os::sleep(Thread::current(), 1, false);
8616 ConcurrentMarkSweepThread::acknowledge_yield_request();
8617 }
8618
8619 ConcurrentMarkSweepThread::synchronize(true);
8620 _freelistLock->lock();
8621 _bitMap->lock()->lock_without_safepoint_check();
8622 _collector->startTimer();
8623 }
8624
8625 #ifndef PRODUCT
8626 // This is actually very useful in a product build if it can
8627 // be called from the debugger. Compile it into the product
8628 // as needed.
8629 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8630 return debug_cms_space->verify_chunk_in_free_list(fc);
8631 }
8632 #endif
8633
8634 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8635 if (CMSTraceSweeper) {
8636 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8637 fc, fc->size());
8638 }
8639 }
8640
8641 // CMSIsAliveClosure
8642 bool CMSIsAliveClosure::do_object_b(oop obj) {
8643 HeapWord* addr = (HeapWord*)obj;
8644 return addr != NULL &&
8645 (!_span.contains(addr) || _bit_map->isMarked(addr));
8646 }
8647
8648 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8649 MemRegion span,
8650 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8651 CMSMarkStack* revisit_stack, bool cpc):
8652 KlassRememberingOopClosure(collector, NULL, revisit_stack),
8653 _span(span),
8654 _bit_map(bit_map),
8655 _mark_stack(mark_stack),
8656 _concurrent_precleaning(cpc) {
8657 assert(!_span.is_empty(), "Empty span could spell trouble");
8658 }
8659
8660
8661 // CMSKeepAliveClosure: the serial version
8662 void CMSKeepAliveClosure::do_oop(oop obj) {
8663 HeapWord* addr = (HeapWord*)obj;
8664 if (_span.contains(addr) &&
8665 !_bit_map->isMarked(addr)) {
8666 _bit_map->mark(addr);
8667 bool simulate_overflow = false;
8668 NOT_PRODUCT(
8669 if (CMSMarkStackOverflowALot &&
8670 _collector->simulate_overflow()) {
8671 // simulate a stack overflow
8672 simulate_overflow = true;
8673 }
8674 )
8675 if (simulate_overflow || !_mark_stack->push(obj)) {
8676 if (_concurrent_precleaning) {
8677 // We dirty the overflown object and let the remark
8678 // phase deal with it.
8679 assert(_collector->overflow_list_is_empty(), "Error");
8680 // In the case of object arrays, we need to dirty all of
8681 // the cards that the object spans. No locking or atomics
8682 // are needed since no one else can be mutating the mod union
8683 // table.
8684 if (obj->is_objArray()) {
8685 size_t sz = obj->size();
8686 HeapWord* end_card_addr =
8687 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8688 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8689 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8690 _collector->_modUnionTable.mark_range(redirty_range);
8691 } else {
8692 _collector->_modUnionTable.mark(addr);
8693 }
8694 _collector->_ser_kac_preclean_ovflw++;
8695 } else {
8696 _collector->push_on_overflow_list(obj);
8697 _collector->_ser_kac_ovflw++;
8698 }
8699 }
8700 }
8701 }
8702
8703 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8704 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8705
8706 // CMSParKeepAliveClosure: a parallel version of the above.
8707 // The work queues are private to each closure (thread),
8708 // but (may be) available for stealing by other threads.
8709 void CMSParKeepAliveClosure::do_oop(oop obj) {
8710 HeapWord* addr = (HeapWord*)obj;
8711 if (_span.contains(addr) &&
8712 !_bit_map->isMarked(addr)) {
8713 // In general, during recursive tracing, several threads
8714 // may be concurrently getting here; the first one to
8715 // "tag" it, claims it.
8716 if (_bit_map->par_mark(addr)) {
8717 bool res = _work_queue->push(obj);
8718 assert(res, "Low water mark should be much less than capacity");
8719 // Do a recursive trim in the hope that this will keep
8720 // stack usage lower, but leave some oops for potential stealers
8721 trim_queue(_low_water_mark);
8722 } // Else, another thread got there first
8723 }
8724 }
8725
8726 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8727 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8728
8729 void CMSParKeepAliveClosure::trim_queue(uint max) {
8730 while (_work_queue->size() > max) {
8731 oop new_oop;
8732 if (_work_queue->pop_local(new_oop)) {
8733 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8734 assert(_bit_map->isMarked((HeapWord*)new_oop),
8735 "no white objects on this stack!");
8736 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8737 // iterate over the oops in this oop, marking and pushing
8738 // the ones in CMS heap (i.e. in _span).
8739 new_oop->oop_iterate(&_mark_and_push);
8740 }
8741 }
8742 }
8743
8744 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8745 CMSCollector* collector,
8746 MemRegion span, CMSBitMap* bit_map,
8747 CMSMarkStack* revisit_stack,
8748 OopTaskQueue* work_queue):
8749 Par_KlassRememberingOopClosure(collector, NULL, revisit_stack),
8750 _span(span),
8751 _bit_map(bit_map),
8752 _work_queue(work_queue) { }
8753
8754 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8755 HeapWord* addr = (HeapWord*)obj;
8756 if (_span.contains(addr) &&
8757 !_bit_map->isMarked(addr)) {
8758 if (_bit_map->par_mark(addr)) {
8759 bool simulate_overflow = false;
8760 NOT_PRODUCT(
8761 if (CMSMarkStackOverflowALot &&
8762 _collector->par_simulate_overflow()) {
8763 // simulate a stack overflow
8764 simulate_overflow = true;
8765 }
8766 )
8767 if (simulate_overflow || !_work_queue->push(obj)) {
8768 _collector->par_push_on_overflow_list(obj);
8769 _collector->_par_kac_ovflw++;
8770 }
8771 } // Else another thread got there already
8772 }
8773 }
8774
8775 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8776 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8777
8778 //////////////////////////////////////////////////////////////////
8779 // CMSExpansionCause /////////////////////////////
8780 //////////////////////////////////////////////////////////////////
8781 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8782 switch (cause) {
8783 case _no_expansion:
8784 return "No expansion";
8785 case _satisfy_free_ratio:
8786 return "Free ratio";
8787 case _satisfy_promotion:
8788 return "Satisfy promotion";
8789 case _satisfy_allocation:
8790 return "allocation";
8791 case _allocate_par_lab:
8792 return "Par LAB";
8793 case _allocate_par_spooling_space:
8794 return "Par Spooling Space";
8795 case _adaptive_size_policy:
8796 return "Ergonomics";
8797 default:
8798 return "unknown";
8799 }
8800 }
8801
8802 void CMSDrainMarkingStackClosure::do_void() {
8803 // the max number to take from overflow list at a time
8804 const size_t num = _mark_stack->capacity()/4;
8805 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8806 "Overflow list should be NULL during concurrent phases");
8807 while (!_mark_stack->isEmpty() ||
8808 // if stack is empty, check the overflow list
8809 _collector->take_from_overflow_list(num, _mark_stack)) {
8810 oop obj = _mark_stack->pop();
8811 HeapWord* addr = (HeapWord*)obj;
8812 assert(_span.contains(addr), "Should be within span");
8813 assert(_bit_map->isMarked(addr), "Should be marked");
8814 assert(obj->is_oop(), "Should be an oop");
8815 obj->oop_iterate(_keep_alive);
8816 }
8817 }
8818
8819 void CMSParDrainMarkingStackClosure::do_void() {
8820 // drain queue
8821 trim_queue(0);
8822 }
8823
8824 // Trim our work_queue so its length is below max at return
8825 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8826 while (_work_queue->size() > max) {
8827 oop new_oop;
8828 if (_work_queue->pop_local(new_oop)) {
8829 assert(new_oop->is_oop(), "Expected an oop");
8830 assert(_bit_map->isMarked((HeapWord*)new_oop),
8831 "no white objects on this stack!");
8832 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8833 // iterate over the oops in this oop, marking and pushing
8834 // the ones in CMS heap (i.e. in _span).
8835 new_oop->oop_iterate(&_mark_and_push);
8836 }
8837 }
8838 }
8839
8840 ////////////////////////////////////////////////////////////////////
8841 // Support for Marking Stack Overflow list handling and related code
8842 ////////////////////////////////////////////////////////////////////
8843 // Much of the following code is similar in shape and spirit to the
8844 // code used in ParNewGC. We should try and share that code
8845 // as much as possible in the future.
8846
8847 #ifndef PRODUCT
8848 // Debugging support for CMSStackOverflowALot
8849
8850 // It's OK to call this multi-threaded; the worst thing
8851 // that can happen is that we'll get a bunch of closely
8852 // spaced simulated oveflows, but that's OK, in fact
8853 // probably good as it would exercise the overflow code
8854 // under contention.
8855 bool CMSCollector::simulate_overflow() {
8856 if (_overflow_counter-- <= 0) { // just being defensive
8857 _overflow_counter = CMSMarkStackOverflowInterval;
8858 return true;
8859 } else {
8860 return false;
8861 }
8862 }
8863
8864 bool CMSCollector::par_simulate_overflow() {
8865 return simulate_overflow();
8866 }
8867 #endif
8868
8869 // Single-threaded
8870 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8871 assert(stack->isEmpty(), "Expected precondition");
8872 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8873 size_t i = num;
8874 oop cur = _overflow_list;
8875 const markOop proto = markOopDesc::prototype();
8876 NOT_PRODUCT(ssize_t n = 0;)
8877 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8878 next = oop(cur->mark());
8879 cur->set_mark(proto); // until proven otherwise
8880 assert(cur->is_oop(), "Should be an oop");
8881 bool res = stack->push(cur);
8882 assert(res, "Bit off more than can chew?");
8883 NOT_PRODUCT(n++;)
8884 }
8885 _overflow_list = cur;
8886 #ifndef PRODUCT
8887 assert(_num_par_pushes >= n, "Too many pops?");
8888 _num_par_pushes -=n;
8889 #endif
8890 return !stack->isEmpty();
8891 }
8892
8893 #define BUSY (oop(0x1aff1aff))
8894 // (MT-safe) Get a prefix of at most "num" from the list.
8895 // The overflow list is chained through the mark word of
8896 // each object in the list. We fetch the entire list,
8897 // break off a prefix of the right size and return the
8898 // remainder. If other threads try to take objects from
8899 // the overflow list at that time, they will wait for
8900 // some time to see if data becomes available. If (and
8901 // only if) another thread places one or more object(s)
8902 // on the global list before we have returned the suffix
8903 // to the global list, we will walk down our local list
8904 // to find its end and append the global list to
8905 // our suffix before returning it. This suffix walk can
8906 // prove to be expensive (quadratic in the amount of traffic)
8907 // when there are many objects in the overflow list and
8908 // there is much producer-consumer contention on the list.
8909 // *NOTE*: The overflow list manipulation code here and
8910 // in ParNewGeneration:: are very similar in shape,
8911 // except that in the ParNew case we use the old (from/eden)
8912 // copy of the object to thread the list via its klass word.
8913 // Because of the common code, if you make any changes in
8914 // the code below, please check the ParNew version to see if
8915 // similar changes might be needed.
8916 // CR 6797058 has been filed to consolidate the common code.
8917 bool CMSCollector::par_take_from_overflow_list(size_t num,
8918 OopTaskQueue* work_q,
8919 int no_of_gc_threads) {
8920 assert(work_q->size() == 0, "First empty local work queue");
8921 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8922 if (_overflow_list == NULL) {
8923 return false;
8924 }
8925 // Grab the entire list; we'll put back a suffix
8926 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8927 Thread* tid = Thread::current();
8928 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8929 // set to ParallelGCThreads.
8930 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8931 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8932 // If the list is busy, we spin for a short while,
8933 // sleeping between attempts to get the list.
8934 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8935 os::sleep(tid, sleep_time_millis, false);
8936 if (_overflow_list == NULL) {
8937 // Nothing left to take
8938 return false;
8939 } else if (_overflow_list != BUSY) {
8940 // Try and grab the prefix
8941 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8942 }
8943 }
8944 // If the list was found to be empty, or we spun long
8945 // enough, we give up and return empty-handed. If we leave
8946 // the list in the BUSY state below, it must be the case that
8947 // some other thread holds the overflow list and will set it
8948 // to a non-BUSY state in the future.
8949 if (prefix == NULL || prefix == BUSY) {
8950 // Nothing to take or waited long enough
8951 if (prefix == NULL) {
8952 // Write back the NULL in case we overwrote it with BUSY above
8953 // and it is still the same value.
8954 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8955 }
8956 return false;
8957 }
8958 assert(prefix != NULL && prefix != BUSY, "Error");
8959 size_t i = num;
8960 oop cur = prefix;
8961 // Walk down the first "num" objects, unless we reach the end.
8962 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8963 if (cur->mark() == NULL) {
8964 // We have "num" or fewer elements in the list, so there
8965 // is nothing to return to the global list.
8966 // Write back the NULL in lieu of the BUSY we wrote
8967 // above, if it is still the same value.
8968 if (_overflow_list == BUSY) {
8969 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8970 }
8971 } else {
8972 // Chop off the suffix and rerturn it to the global list.
8973 assert(cur->mark() != BUSY, "Error");
8974 oop suffix_head = cur->mark(); // suffix will be put back on global list
8975 cur->set_mark(NULL); // break off suffix
8976 // It's possible that the list is still in the empty(busy) state
8977 // we left it in a short while ago; in that case we may be
8978 // able to place back the suffix without incurring the cost
8979 // of a walk down the list.
8980 oop observed_overflow_list = _overflow_list;
8981 oop cur_overflow_list = observed_overflow_list;
8982 bool attached = false;
8983 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8984 observed_overflow_list =
8985 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8986 if (cur_overflow_list == observed_overflow_list) {
8987 attached = true;
8988 break;
8989 } else cur_overflow_list = observed_overflow_list;
8990 }
8991 if (!attached) {
8992 // Too bad, someone else sneaked in (at least) an element; we'll need
8993 // to do a splice. Find tail of suffix so we can prepend suffix to global
8994 // list.
8995 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8996 oop suffix_tail = cur;
8997 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8998 "Tautology");
8999 observed_overflow_list = _overflow_list;
9000 do {
9001 cur_overflow_list = observed_overflow_list;
9002 if (cur_overflow_list != BUSY) {
9003 // Do the splice ...
9004 suffix_tail->set_mark(markOop(cur_overflow_list));
9005 } else { // cur_overflow_list == BUSY
9006 suffix_tail->set_mark(NULL);
9007 }
9008 // ... and try to place spliced list back on overflow_list ...
9009 observed_overflow_list =
9010 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
9011 } while (cur_overflow_list != observed_overflow_list);
9012 // ... until we have succeeded in doing so.
9013 }
9014 }
9015
9016 // Push the prefix elements on work_q
9017 assert(prefix != NULL, "control point invariant");
9018 const markOop proto = markOopDesc::prototype();
9019 oop next;
9020 NOT_PRODUCT(ssize_t n = 0;)
9021 for (cur = prefix; cur != NULL; cur = next) {
9022 next = oop(cur->mark());
9023 cur->set_mark(proto); // until proven otherwise
9024 assert(cur->is_oop(), "Should be an oop");
9025 bool res = work_q->push(cur);
9026 assert(res, "Bit off more than we can chew?");
9027 NOT_PRODUCT(n++;)
9028 }
9029 #ifndef PRODUCT
9030 assert(_num_par_pushes >= n, "Too many pops?");
9031 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
9032 #endif
9033 return true;
9034 }
9035
9036 // Single-threaded
9037 void CMSCollector::push_on_overflow_list(oop p) {
9038 NOT_PRODUCT(_num_par_pushes++;)
9039 assert(p->is_oop(), "Not an oop");
9040 preserve_mark_if_necessary(p);
9041 p->set_mark((markOop)_overflow_list);
9042 _overflow_list = p;
9043 }
9044
9045 // Multi-threaded; use CAS to prepend to overflow list
9046 void CMSCollector::par_push_on_overflow_list(oop p) {
9047 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
9048 assert(p->is_oop(), "Not an oop");
9049 par_preserve_mark_if_necessary(p);
9050 oop observed_overflow_list = _overflow_list;
9051 oop cur_overflow_list;
9052 do {
9053 cur_overflow_list = observed_overflow_list;
9054 if (cur_overflow_list != BUSY) {
9055 p->set_mark(markOop(cur_overflow_list));
9056 } else {
9057 p->set_mark(NULL);
9058 }
9059 observed_overflow_list =
9060 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
9061 } while (cur_overflow_list != observed_overflow_list);
9062 }
9063 #undef BUSY
9064
9065 // Single threaded
9066 // General Note on GrowableArray: pushes may silently fail
9067 // because we are (temporarily) out of C-heap for expanding
9068 // the stack. The problem is quite ubiquitous and affects
9069 // a lot of code in the JVM. The prudent thing for GrowableArray
9070 // to do (for now) is to exit with an error. However, that may
9071 // be too draconian in some cases because the caller may be
9072 // able to recover without much harm. For such cases, we
9073 // should probably introduce a "soft_push" method which returns
9074 // an indication of success or failure with the assumption that
9075 // the caller may be able to recover from a failure; code in
9076 // the VM can then be changed, incrementally, to deal with such
9077 // failures where possible, thus, incrementally hardening the VM
9078 // in such low resource situations.
9079 void CMSCollector::preserve_mark_work(oop p, markOop m) {
9080 _preserved_oop_stack.push(p);
9081 _preserved_mark_stack.push(m);
9082 assert(m == p->mark(), "Mark word changed");
9083 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9084 "bijection");
9085 }
9086
9087 // Single threaded
9088 void CMSCollector::preserve_mark_if_necessary(oop p) {
9089 markOop m = p->mark();
9090 if (m->must_be_preserved(p)) {
9091 preserve_mark_work(p, m);
9092 }
9093 }
9094
9095 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
9096 markOop m = p->mark();
9097 if (m->must_be_preserved(p)) {
9098 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
9099 // Even though we read the mark word without holding
9100 // the lock, we are assured that it will not change
9101 // because we "own" this oop, so no other thread can
9102 // be trying to push it on the overflow list; see
9103 // the assertion in preserve_mark_work() that checks
9104 // that m == p->mark().
9105 preserve_mark_work(p, m);
9106 }
9107 }
9108
9109 // We should be able to do this multi-threaded,
9110 // a chunk of stack being a task (this is
9111 // correct because each oop only ever appears
9112 // once in the overflow list. However, it's
9113 // not very easy to completely overlap this with
9114 // other operations, so will generally not be done
9115 // until all work's been completed. Because we
9116 // expect the preserved oop stack (set) to be small,
9117 // it's probably fine to do this single-threaded.
9118 // We can explore cleverer concurrent/overlapped/parallel
9119 // processing of preserved marks if we feel the
9120 // need for this in the future. Stack overflow should
9121 // be so rare in practice and, when it happens, its
9122 // effect on performance so great that this will
9123 // likely just be in the noise anyway.
9124 void CMSCollector::restore_preserved_marks_if_any() {
9125 assert(SafepointSynchronize::is_at_safepoint(),
9126 "world should be stopped");
9127 assert(Thread::current()->is_ConcurrentGC_thread() ||
9128 Thread::current()->is_VM_thread(),
9129 "should be single-threaded");
9130 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9131 "bijection");
9132
9133 while (!_preserved_oop_stack.is_empty()) {
9134 oop p = _preserved_oop_stack.pop();
9135 assert(p->is_oop(), "Should be an oop");
9136 assert(_span.contains(p), "oop should be in _span");
9137 assert(p->mark() == markOopDesc::prototype(),
9138 "Set when taken from overflow list");
9139 markOop m = _preserved_mark_stack.pop();
9140 p->set_mark(m);
9141 }
9142 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9143 "stacks were cleared above");
9144 }
9145
9146 #ifndef PRODUCT
9147 bool CMSCollector::no_preserved_marks() const {
9148 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9149 }
9150 #endif
9151
9152 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9153 {
9154 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9155 CMSAdaptiveSizePolicy* size_policy =
9156 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9157 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9158 "Wrong type for size policy");
9159 return size_policy;
9160 }
9161
9162 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9163 size_t desired_promo_size) {
9164 if (cur_promo_size < desired_promo_size) {
9165 size_t expand_bytes = desired_promo_size - cur_promo_size;
9166 if (PrintAdaptiveSizePolicy && Verbose) {
9167 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9168 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9169 expand_bytes);
9170 }
9171 expand(expand_bytes,
9172 MinHeapDeltaBytes,
9173 CMSExpansionCause::_adaptive_size_policy);
9174 } else if (desired_promo_size < cur_promo_size) {
9175 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9176 if (PrintAdaptiveSizePolicy && Verbose) {
9177 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9178 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9179 shrink_bytes);
9180 }
9181 shrink(shrink_bytes);
9182 }
9183 }
9184
9185 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9186 GenCollectedHeap* gch = GenCollectedHeap::heap();
9187 CMSGCAdaptivePolicyCounters* counters =
9188 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9189 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9190 "Wrong kind of counters");
9191 return counters;
9192 }
9193
9194
9195 void ASConcurrentMarkSweepGeneration::update_counters() {
9196 if (UsePerfData) {
9197 _space_counters->update_all();
9198 _gen_counters->update_all();
9199 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9200 GenCollectedHeap* gch = GenCollectedHeap::heap();
9201 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9202 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9203 "Wrong gc statistics type");
9204 counters->update_counters(gc_stats_l);
9205 }
9206 }
9207
9208 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9209 if (UsePerfData) {
9210 _space_counters->update_used(used);
9211 _space_counters->update_capacity();
9212 _gen_counters->update_all();
9213
9214 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9215 GenCollectedHeap* gch = GenCollectedHeap::heap();
9216 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9217 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9218 "Wrong gc statistics type");
9219 counters->update_counters(gc_stats_l);
9220 }
9221 }
9222
9223 // The desired expansion delta is computed so that:
9224 // . desired free percentage or greater is used
9225 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9226 assert_locked_or_safepoint(Heap_lock);
9227
9228 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9229
9230 // If incremental collection failed, we just want to expand
9231 // to the limit.
9232 if (incremental_collection_failed()) {
9233 clear_incremental_collection_failed();
9234 grow_to_reserved();
9235 return;
9236 }
9237
9238 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9239
9240 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9241 "Wrong type of heap");
9242 int prev_level = level() - 1;
9243 assert(prev_level >= 0, "The cms generation is the lowest generation");
9244 Generation* prev_gen = gch->get_gen(prev_level);
9245 assert(prev_gen->kind() == Generation::ASParNew,
9246 "Wrong type of young generation");
9247 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9248 size_t cur_eden = younger_gen->eden()->capacity();
9249 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9250 size_t cur_promo = free();
9251 size_policy->compute_tenured_generation_free_space(cur_promo,
9252 max_available(),
9253 cur_eden);
9254 resize(cur_promo, size_policy->promo_size());
9255
9256 // Record the new size of the space in the cms generation
9257 // that is available for promotions. This is temporary.
9258 // It should be the desired promo size.
9259 size_policy->avg_cms_promo()->sample(free());
9260 size_policy->avg_old_live()->sample(used());
9261
9262 if (UsePerfData) {
9263 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9264 counters->update_cms_capacity_counter(capacity());
9265 }
9266 }
9267
9268 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9269 assert_locked_or_safepoint(Heap_lock);
9270 assert_lock_strong(freelistLock());
9271 HeapWord* old_end = _cmsSpace->end();
9272 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9273 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9274 FreeChunk* chunk_at_end = find_chunk_at_end();
9275 if (chunk_at_end == NULL) {
9276 // No room to shrink
9277 if (PrintGCDetails && Verbose) {
9278 gclog_or_tty->print_cr("No room to shrink: old_end "
9279 PTR_FORMAT " unallocated_start " PTR_FORMAT
9280 " chunk_at_end " PTR_FORMAT,
9281 old_end, unallocated_start, chunk_at_end);
9282 }
9283 return;
9284 } else {
9285
9286 // Find the chunk at the end of the space and determine
9287 // how much it can be shrunk.
9288 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9289 size_t aligned_shrinkable_size_in_bytes =
9290 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9291 assert(unallocated_start <= chunk_at_end->end(),
9292 "Inconsistent chunk at end of space");
9293 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9294 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9295
9296 // Shrink the underlying space
9297 _virtual_space.shrink_by(bytes);
9298 if (PrintGCDetails && Verbose) {
9299 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9300 " desired_bytes " SIZE_FORMAT
9301 " shrinkable_size_in_bytes " SIZE_FORMAT
9302 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9303 " bytes " SIZE_FORMAT,
9304 desired_bytes, shrinkable_size_in_bytes,
9305 aligned_shrinkable_size_in_bytes, bytes);
9306 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9307 " unallocated_start " SIZE_FORMAT,
9308 old_end, unallocated_start);
9309 }
9310
9311 // If the space did shrink (shrinking is not guaranteed),
9312 // shrink the chunk at the end by the appropriate amount.
9313 if (((HeapWord*)_virtual_space.high()) < old_end) {
9314 size_t new_word_size =
9315 heap_word_size(_virtual_space.committed_size());
9316
9317 // Have to remove the chunk from the dictionary because it is changing
9318 // size and might be someplace elsewhere in the dictionary.
9319
9320 // Get the chunk at end, shrink it, and put it
9321 // back.
9322 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9323 size_t word_size_change = word_size_before - new_word_size;
9324 size_t chunk_at_end_old_size = chunk_at_end->size();
9325 assert(chunk_at_end_old_size >= word_size_change,
9326 "Shrink is too large");
9327 chunk_at_end->set_size(chunk_at_end_old_size -
9328 word_size_change);
9329 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9330 word_size_change);
9331
9332 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9333
9334 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9335 _bts->resize(new_word_size); // resize the block offset shared array
9336 Universe::heap()->barrier_set()->resize_covered_region(mr);
9337 _cmsSpace->assert_locked();
9338 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9339
9340 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9341
9342 // update the space and generation capacity counters
9343 if (UsePerfData) {
9344 _space_counters->update_capacity();
9345 _gen_counters->update_all();
9346 }
9347
9348 if (Verbose && PrintGCDetails) {
9349 size_t new_mem_size = _virtual_space.committed_size();
9350 size_t old_mem_size = new_mem_size + bytes;
9351 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK",
9352 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9353 }
9354 }
9355
9356 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9357 "Inconsistency at end of space");
9358 assert(chunk_at_end->end() == _cmsSpace->end(),
9359 "Shrinking is inconsistent");
9360 return;
9361 }
9362 }
9363
9364 // Transfer some number of overflown objects to usual marking
9365 // stack. Return true if some objects were transferred.
9366 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9367 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9368 (size_t)ParGCDesiredObjsFromOverflowList);
9369
9370 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9371 assert(_collector->overflow_list_is_empty() || res,
9372 "If list is not empty, we should have taken something");
9373 assert(!res || !_mark_stack->isEmpty(),
9374 "If we took something, it should now be on our stack");
9375 return res;
9376 }
9377
9378 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9379 size_t res = _sp->block_size_no_stall(addr, _collector);
9380 if (_sp->block_is_obj(addr)) {
9381 if (_live_bit_map->isMarked(addr)) {
9382 // It can't have been dead in a previous cycle
9383 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9384 } else {
9385 _dead_bit_map->mark(addr); // mark the dead object
9386 }
9387 }
9388 // Could be 0, if the block size could not be computed without stalling.
9389 return res;
9390 }
9391
9392 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9393
9394 switch (phase) {
9395 case CMSCollector::InitialMarking:
9396 initialize(true /* fullGC */ ,
9397 cause /* cause of the GC */,
9398 true /* recordGCBeginTime */,
9399 true /* recordPreGCUsage */,
9400 false /* recordPeakUsage */,
9401 false /* recordPostGCusage */,
9402 true /* recordAccumulatedGCTime */,
9403 false /* recordGCEndTime */,
9404 false /* countCollection */ );
9405 break;
9406
9407 case CMSCollector::FinalMarking:
9408 initialize(true /* fullGC */ ,
9409 cause /* cause of the GC */,
9410 false /* recordGCBeginTime */,
9411 false /* recordPreGCUsage */,
9412 false /* recordPeakUsage */,
9413 false /* recordPostGCusage */,
9414 true /* recordAccumulatedGCTime */,
9415 false /* recordGCEndTime */,
9416 false /* countCollection */ );
9417 break;
9418
9419 case CMSCollector::Sweeping:
9420 initialize(true /* fullGC */ ,
9421 cause /* cause of the GC */,
9422 false /* recordGCBeginTime */,
9423 false /* recordPreGCUsage */,
9424 true /* recordPeakUsage */,
9425 true /* recordPostGCusage */,
9426 false /* recordAccumulatedGCTime */,
9427 true /* recordGCEndTime */,
9428 true /* countCollection */ );
9429 break;
9430
9431 default:
9432 ShouldNotReachHere();
9433 }
9434 }
9435